Apparatus for producing thin films by low temperature plasma-enhanced chemical vapor deposition

FIELD OF THE INVENTION

This invention relates generally to plasma-enhanced chemical vapor deposition (PECVD) for applying a film coating to a substrate, and more specifically to PECVD conducted at a low effective deposition temperature at the substrate surface. Even more specifically, the invention relates to deposition of titanium-containing films using low temperature CVD.

BACKGROUND OF THE INVENTION

In the formation of integrated circuits (IC's), thin films containing metal and metalloid elements are often deposited upon the surface of a substrate, such as a semiconductor wafer. Thin films are deposited to provide conductive and ohmic contacts in the circuits and between the various devices of an IC. For example, a desired thin film might be applied to the exposed surface of a contact or via hole on a semiconductor wafer, with the film passing through the insulative layers on the wafer to provide plugs of conductive material for the purpose of making interconnections across the insulating layers.

One well known process for depositing thin metal films is chemical vapor deposition (CVD) in which a thin film is deposited using chemical reactions between various deposition or reactant gases at the surface of the substrate. In CVD, reactant gases are pumped into proximity to a substrate inside a reaction chamber, and the gases subsequently react at the substrate surface resulting in one or more reaction by-products which form a film on the substrate surface. Any by-products remaining after the deposition are removed from the chamber. While CVD is a useful technique for depositing films, many of the traditional CVD processes are basically thermal processes and require temperatures in excess of 1000° C. in order to obtain the necessary reactions. Such a deposition temperature is often far too high to be practically useful in IC fabrication due to the effects that high temperatures have on various other aspects and layers of the electrical devices making up the IC.

Particularly, certain aspects of IC components are degraded by exposure to the high temperatures normally related to traditional thermal CVD processes. For example, at the device level of an IC, there are shallow diffusions of semiconductor dopants which form the junctions of the electrical devices within the IC. The dopants are often initially diffused using heat during a diffusion step, and therefore, the dopants will continue to diffuse when the IC is subjected to a high temperature during CVD. Such further diffusion is undesirable because it causes the junction of the device to shift, and thus alters the resulting electrical characteristics of the IC. Therefore, for certain IC devices, exposing the substrate to processing temperatures of above 800° C. is avoided, and the upper temperature limit may be as low as 650° C. for other more temperature sensitive devices.

Furthermore, such temperature limitations may become even more severe if thermal CVD is performed after metal interconnection or wiring has been applied to the IC. For example, many IC's utilize aluminum as an interconnection metal. However, various undesirable voids and extrusions occur in aluminum when it is subjected to high processing temperatures. Therefore, once interconnecting aluminum has been deposited onto an IC, the maximum temperature to which it can be exposed is approximately 500° C., and the preferred upper temperature limit is 400° C. Therefore, as may be appreciated, it is desirable during CVD processes to maintain low deposition temperatures whenever possible.

Consequently, the upper temperature limit to which a substrate must be exposed precludes the use of some traditional thermal CVD processes which might otherwise be very useful in fabricating IC's. A good example of one such useful process is the chemical vapor deposition of titanium. Titanium is typically used to provide ohmic contact between the silicon contacts of an IC device and a metal interconnection. Titanium may be deposited from TiBr

4

, TiCl

4

or Til

4

by using CVD methods such as unimolecular pyrolysis or hydrogen reduction. However, the temperatures necessary for these thermal processes are in excess of 1000° C., and such a deposition temperature is much too high to be practically useful in IC fabrication. Therefore, the deposition of titanium and titanium-containing films presents a problem in formation of integrated circuits.

There are low temperature physical techniques available for depositing titanium on temperature sensitive substrates. Sputtering is one such technique involving the use of a target of layer material and an ionized plasma. To sputter deposit a film, the target is electrically biased and ions from the plasma are attracted to the target to bombard the target and dislodge target material particles. The particles then deposit themselves cumulatively as a film upon the substrate. Titanium may be sputtered, for example, over a silicon substrate after various contacts or via openings are cut into a level of the substrate. The substrate might then be heated to about 800° C. to allow the silicon and titanium to alloy and form a layer of titanium silicide (TiSi

2

). After the deposition of the titanium layer, the excess titanium is etched away from the top surface of the substrate leaving TiSi

2

at the bottom of each contact or via. A metal interconnection is then deposited directly over the TiSi

2

.

While physical sputtering provides deposition of a titanium film at a lower temperature, sputtering processes have various drawbacks. Sputtering normally yields very poor step coverage. Step coverage is defined as the ratio of film thickness on the bottom of a contact on a substrate wafer to the film thickness on the sides of the contact or the top surface of the substrate. Consequently, to sputter deposit a predetermined amount of titanium at the bottom of a contact or via, a larger amount of the sputtered titanium must be deposited on the top surface of the substrate or the sides of the contact. For example, in order to deposit a 200 Å film at the bottom of a contact using sputtering, a 600 Å to 1000 Å film layer may have to be deposited onto the top surface of the substrate or the sides of the contact. Since the excess titanium has to be etched away, sputtering is wasteful and costly when depositing layers containing titanium.

Furthermore, the step coverage of the contact with sputtering techniques decreases as the aspect ratio of the contact or via increases. The aspect ratio of a contact is defined as the ratio of contact depth to the width of the contact. Therefore, a thicker sputtered film must be deposited on the top or sides of a contact that is narrow and deep (high aspect ratio) in order to obtain a particular film thickness at the bottom of the contact than would be necessary with a shallow and wide contact (low aspect ratio). In other words, for smaller device dimensions in an IC, corresponding to high aspect ratio contacts and vias, sputtering is even more inefficient and wasteful. The decreased step coverage during sputter deposition over smaller devices results in an increased amount of titanium that must be deposited, thus increasing the amount of titanium applied and etched away, increasing the titanium deposition time, and increasing the etching time that is necessary to remove excess titanium. Accordingly, as IC device geometries continue to shrink and aspect ratios increase, deposition of titanium-containing layers by sputtering becomes very costly.

On the other hand, using a CVD process for depositing a titanium-containing film layer may be accomplished with nearly 100% step coverage. That is, the film thickness at the bottom of the contact would approximately equal the thickness on the top surface almost regardless of the aspect ratio of the contact or via being filled. However, as discussed above, the temperatures necessary for such CVD processes are too high and would degrade other aspects of the IC. Consequently, it would be desirable to achieve titanium CVD at a temperature less than 800° C., and preferably less than 650° C. Further, it is generally desirable to reduce the deposition temperature for any CVD process which is utilized to deposit a film in IC fabrication.

One approach which has been utilized in CVD processes to lower the reaction temperature is to ionize one or more of the reactant gases. Such a technique is generally referred to as plasma enhanced chemical vapor deposition (PECVD). While it has been possible with such an approach to somewhat lower the deposition temperatures, the high sticking coefficient of the ionized plasma particles degrades the step coverage of the film. That is, ions of the reactant gases are highly reactive and have a tendency to contact and stick to the walls of the vias or contacts in the substrate. The ion particles do not migrate downwardly to the bottom surface of the contact where the coating is desired but rather non-conformally coat the sides of the contact. This results in increased material usage, deposition times and etch times. Therefore, PECVD using ionized reactant gases has not been a completely adequate solution to lowering traditional high CVD temperatures and achieving good step coverage and film conformality.

Additionally, when using a CVD process to apply a film, it is desirable to uniformly deposit the film. To do so, such as to apply a uniform film of tungsten (W), for example, a uniform supply of reactant gases must be supplied across the surface of the substrate and the spent gases and reaction by-products should be removed from the surface being coated. In this respect, prior art CVD processes have again performed with limited success. Specifically, in known CVD processes, turbulence in the flow of reaction gases inhibits the efficiency and uniformity of the coating process and aggravates the deposition and migration of contaminants within the reaction chamber. In tungsten CVD processes, tungsten hexafluoride (WF

6

) is employed as a reactant gas. Tungsten hexafluoride is very costly and thus, when reactant gas utilization efficiency is low, as it is in prior art CVD processes, the overall process costs are significantly increased. Accordingly, there is a need for CVD processes which have improved gas flow and reduced gas flow turbulence to more efficiently and more uniformly supply reaction gases to and remove reaction by-products from the surfaces of the substrate being coated.

Therefore, CVD processes which may be accomplished at lower effective temperatures are desired. It is further desirable to have a low temperature deposition which provides good step coverage. It is still further desirable to have a PECVD process which produces uniform film thickness and effective utilization of reactant gases. Accordingly, the present invention addresses these objectives and the shortcomings of the various CVD and PECVD processes currently available. Further, the present invention, particularly addresses the difficulties associated with depositing titanium and titanium-containing films using CVD.

SUMMARY OF THE INVENTION

The CVD apparatuses and methods of the present invention overcome or obviate the high temperature and gas flow drawbacks associated with many of the currently available thermal CVD and PECVD apparatuses and processes. Specifically, the present invention achieves deposition of a titanium-containing film at a substantially lower temperature as compared to traditional thermal CVD processes. Further, in doing so, the invention does not compromise the conformality of the resulting film layer, and makes efficient use of the activated and reactant gases while reducing gas turbulence at the substrate surface.

The low temperature deposition of the present invention is accomplished in two alternative methods. The first method utilizes the upstream, remote generation of a plasma. The plasma is pumped down to a substrate by a rotating susceptor and is extinguished as it travels to the substrate, so that predominantly activated gas radicals are present. The gas radicals combine with unexcited reactant gases to deposit a film layer on the substrate by CVD techniques. The pumping of the rotating susceptor minimizes gas particle recirculations and collisions to yield a useful percentage of radicals.

The second method utilizes an RF showerhead design which yields a concentrated plasma very close to the substrate surface. All of the gases, both plasma and reactant gases, are passed through the RF showerhead electrode and are excited. Since the susceptor acts as another electrode, the RF showerhead and the susceptor form a parallel plate electrode configuration. With the RF electrode method, the plasma gases utilized in the chemical vapor deposition at the substrate contains a mixture of both ions and radicals which contribute energy to the surface reaction.

More specifically, one CVD process of the present invention utilizes a plasma source to generate, upstream of a substrate wafer, a gas plasma containing various excited particles of the gas, including charged ions and excited, charge-neutral radicals, as well as free electrons. The excited particles of the plasma gas, and predominantly the excited radical particles are brought to the surface before they have had a chance to combine to form neutral molecules. The excited radicals chemically react with one or more reactant gases to form a thin film on a substrate. The excited radicals supply energy to the surface reaction such that CVD may be used in accordance with the principles of the present invention at temperatures substantially lower than those required with traditional CVD methods.

To prevent the particle sticking and the reduced layer conformality associated with traditional PECVD using ionized particles, the upstream method of the present invention utilizes predominantly charge-neutral, activated radicals at the substrate surface which yield conformal, uniform films. However, the lifetime of such activated gas radicals is short as they seek to recombine into a low energy, stable molecular structure. As mentioned above, the present invention provides efficient use of the activated gas radicals by bringing the radicals to the substrate surface before a significant number of them are able to recombine to form the original, stable gas molecules. For efficient delivery of the radicals, the present invention utilizes a rotating susceptor which supports and rotates the substrate and creates a downward pumping action in the direction of the substrate. The rotating susceptor pumps the radicals to the substrate surface.

A reactant gas or gases are introduced into the deposition region above the substrate surface to mix with the activated gas radicals. The downward pumping action of the rotating susceptor simultaneously draws the mixture of radicals and reactant gases toward the substrate surface. At the substrate surface, the mixture of radicals and reactant gases flows radially outward from the center of the substrate in a substantially uniform laminar flow pattern and the excited radicals react with the reactant gas particles in a surface reaction which results in a film layer being deposited upon the substrate surface.

The activated radicals supply energy to the surface reaction and thereby reduce the required energy, such as thermal energy, that is necessary for the chemical reaction to take place at the substrate surface. Therefore, the deposition takes place at a substantially lower temperature than the temperature required by traditional CVD processes. For example, the deposition of a titanium-containing layer using the present invention may be accomplished at 600° C. or below versus 1000° C. for some traditional thermal CVD processes.

The unique pumping action and laminar flow of gases created by the rotating susceptor ensures a useful density of radicals at the substrate surface. For example, by using a gas flow of between 500 to 50,000 sccm (standard cubic centimeters per minute), a susceptor rotation-rate of 0 to 1,000 rpm, a reaction chamber pressure between 0.5 and 10 Torr, and a reactant gas flow rate between 1 to 20 sccm, the present invention has yielded thin films from CVD techniques at temperatures below 650° C. The upstream plasma may be excited using either an RF signal or a microwave signal. Accordingly, the invention has been found to yield desirable results when the plasma is excited at frequencies as high as 2.54 GHz and as low as 13.56 kHz.

The laminar pattern created by the rotating susceptor minimizes gas particle recirculations and subsequent radical recombinations at the substrate surface, and therefore, there are more activated radicals available at the substrate surface for the low temperature CVD process. Additionally, in the method of the present invention, increasing the rotation rate of the susceptor increases the deposition rate at the substrate surface. Due to the unique combination of activated radicals and the laminar flow produced by the pumping action of the rotating susceptor, the deposition rate of the present invention increases beyond what might be achieved solely due to the increase in molecular reactants at the substrate surface resulting from an increased pumping action. That is, increasing the rotation rate of the susceptor accomplishes more than merely drawing reactant gases toward the substrate at a higher rate; it further minimizes recombination of radicals thus providing more available radicals at the substrate surface. This enhancement in the delivery of radicals to the substrate surface is an important advancement in PECVD processes. It allows the majority of the radicals formed upstream or remotely from the substrate to be carried to the substrate surface so that they take place in the surface deposition reaction without a large amount of radical recombination loss. This enhancement and the subsequent increased energy at the surface reaction, in turn, allows the reaction to take place at even lower deposition temperatures.

For the RF electrode plasma generation method of the present invention, the plasma gas is delivered proximate the surface of the substrate utilizing a gas-dispersing showerhead which is biased with RF energy to act as an electrode. A susceptor supporting a substrate acts as another parallel electrode. The RF showerhead/electrode generates a concentrated plasma very close to the surface of the substrate while a gas delivery cylinder attached to the showerhead ensures uniform gas flow to the plasma. The proximity of the plasma to the substrate ensures an ample density of activated radicals and ions for the surface reaction. That is, a combination of both gas radicals and gas ions is utilized in the RF showerhead/electrode method. Utilizing the showerhead/electrode, a spacing of less than 1″ between the generated plasma and the substrate is possible yielding desirable CVD films. Furthermore, the RF showerhead/electrode method keeps the plasma concentrated below the showerhead and close to the substrate for efficient deposition. The RF showerhead has been utilized at RF frequencies from 13.56 MHZ to as low as 450 KHz.

While the present invention may be utilized with a number of different plasma gases and reactant gases, the invention has been found to be particularly useful for depositing titanium-containing films, such as pure titanium (Ti), titanium nitride (TiN) and/or titanium silicide (TiSi

2

) films onto a substrate utilizing plasma containing radicals and ions of hydrogen and nitrogen and/or disassociated titanium tetrachloride (TiCl

4

) and ammonia (NH

3

). A diluent such as argon might be mixed with the plasma gas. Further, different plasma gases besides H

2

, N

2

and NH

3

might be used in accordance with the principles of the present invention to supply radicals and ions to the surface reaction according to the present invention.

In a specific embodiment, the invention has been found useful for depositing titanium films over aluminum layers on a substrate. Deposition temperatures in accordance with the invention are low enough that the aluminum layer is not damaged by reflow during the deposition.

In another specific embodiment, the invention has been found useful for producing selective deposition of titanium over a substrate having a field oxide (silicon oxide) layer patterned with vias into a lower silicon layer. Under certain conditions, it has been found that titanium deposits only on the silicon layers in the vias without significant deposition on the field oxide.

In accordance with various hardware embodiments of the invention, the plasma may be created using energy from various energy sources including microwave and radio frequency (RF) sources. One hardware embodiment utilizes a showerhead/electrode which is biased with RF energy to create a plasma. One possible upstream plasma embodiment utilizes a commercially available plasma source with an RF coil surrounding a plasma region. Still another embodiment utilizes an upstream microwave plasma source which remotely excites a plasma with microwave energy. The remote plasma is then pumped along a tube whereby activated radicals are formed. After exiting the tube and entering the deposition chamber, the radicals are mixed with reactant gases and drawn to the substrate surface by the rotating susceptor.

The invention and the particular advantages and features of the present invention will now be described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a side view and partial cross-section of one embodiment of an upstream plasma-enhanced deposition chamber used to practice the methods of the present invention using microwave energy.

FIG. 1A

is a view of an alternative embodiment of an upstream plasma-enhanced deposition chamber using microwave energy.

FIG. 2

is a side view and partial cross-section of one embodiment of a deposition chamber used to practice the methods of the present invention using an RF showerhead/electrode.

FIG. 2A

is a more detailed view of the configuration of FIG.

2

.

FIG. 2B

is an alternative embodiment of the configuration of FIG.

2

.

FIG. 3

is a side view and partial cross-section of a second embodiment of an upstream plasma-enhanced deposition chamber using RF energy.

FIGS. 4A and 4B

are Arrhenius function graphs of the necessary activation energy for deposition with and without the upstream activated radicals of the present invention, respectively.

FIG. 5

are graphs of deposition rate increase as a function of rotation rate increase with and without the upstream activated radicals, respectively.

FIG. 6

is a photomicrograph showing selective deposition of titanium films onto vias patterned in a silicon oxide layer overlying a silicon substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes both methods and apparatuses for accomplishing low temperature CVD utilizing activated gas radicals and/or activated gas radicals and ions. Proper use of the activated ions and radicals, and a resultant low temperature CVD method, requires a useful density of radicals and/or ions at the substrate surface. A rotating susceptor is used in accordance with the present invention which rotates a substrate inside of a deposition chamber and draws activated gas radicals down to the surface of the substrate. The radicals and reactant gases take part in a surface reaction on the substrate to deposit a film. The activated, charge-neutral radicals and charged ions contribute energy to the surface reaction such that the film is deposited upon the substrate surface in a chemical vapor technique at substantially lower temperatures than are possible with thermal CVD techniques. Also, because the ions and radicals are activated by the plasma, less thermal energy is required to complete the surface reaction.

Preferably, in the upstream plasma generation, predominantly radicals are present at the substrate surface to participate in the low temperature surface reaction. The laminar gas flow created by the susceptor reduces collisions and the subsequent recombinations of the activated radicals into stable molecules so that a useful density of the radicals are delivered to the substrate surface to take place in the surface reaction and subsequent film formation. With the RF showerhead/electrode method, the plasma may be generated very close to the substrate, as discussed further hereinbelow, thus enhancing the efficient use of the activated ions and radicals. The present invention yields a CVD technique that may be accomplished at very low temperatures compared with the traditional thermal CVD techniques thus making it practical for integrated circuit fabrication requiring low deposition temperatures. Furthermore, the inventive method achieves improved step coverage and film conformality over sputter deposition techniques and other CVD techniques. The invention may be utilized to deposit various different films by a low temperature CVD; however, it is particularly useful in depositing titanium-containing films such as titanium nitride (TiN) at low temperatures and especially pure titanium metal.

FIG. 1

shows one embodiment of an upstream plasma source with a rotating susceptor for practicing the upstream plasma-enhanced CVD of the present invention. The embodiment of

FIG. 1

utilizes a microwave plasma source for generating an upstream reactant gas plasma from which the necessary activated radicals are drawn. A reactor

5

includes a chamber housing

10

enclosing a reaction space

12

. The housing

10

may be controllably vacuumed to a desired internal deposition pressure for practicing the invention. Plasma gases to be excited, such as, for example, hydrogen gas (H

2

), nitrogen gas (N

2

), and/or ammonia (NH

3

) are introduced into space

12

through a quartz tube

14

. Plasma tube

14

is L-shaped and has a long portion

16

which extends generally horizontally until it reaches a 90° bend

15

. After the 90° bend

15

, a small straight section

18

extends vertically downward and has an outlet end

19

which opens into space

12

. Housing

10

also contains a rotating susceptor

20

which rotates on a shaft

21

coupled to a motor (not shown), such that the speed of the rotation may be adjusted. Susceptor

20

supports a substrate

22

in the reaction space

10

. A temperature control device (not shown) is coupled to susceptor

20

which is used to heat substrate

22

to the desired temperature. An example of a suitable reactor, including a rotating susceptor, for practicing the methods of the invention is the Rotating Disk Reactor available from Materials Research Corporation (MRC) of Phoenix, Ariz.

A microwave energy source

24

is coupled to plasma tube

14

through a microwave waveguide

26

. The waveguide

26

propagates microwave energy

27

from source

24

to tube

14

to define an excitation region

28

within the tube

14

. Plasma gases are introduced into tube

14

at end

13

and travel along the length of the tube

14

passing through region

28

, wherein the microwave energy

22

is absorbed by the gases to excite the gases to form a plasma. The plasma generated in tube

14

contains various activated particles including ions and activated, charge-neutral radicals. For example, if hydrogen gas (H

2

) is introduced into tube

14

, a hydrogen plasma containing free electrons (e

−

), hydrogen ions (H

+

) and charge-neutral, activated hydrogen radicals (H

*

) is produced, while nitrogen gas (N

2

) yields electrons, nitrogen ions (N

−

) and activated radicals (N

*

). Ammonia gas (NH

3

) might also be utilized to produce radicals of hydrogen H

*

and nitrogen N

*

. However, as discussed in greater detail below, NH

3

reacts with some reactant gases, such as (TiCl

4

), to form an undesired adduct. Therefore, preferably pure H

2

and/or N

2

are excited and utilized to achieve low temperature CVD.

Utilizing hydrogen (H

2

) as the plasma gas, generation of the plasma results in generation of radicals H

*

as well as ionization as follows:

H

2

→2

H

+

+2

e

−

(ionization) (EQ1)

As the excited gas plasma travels along the horizontal section of tube

34

, recombination occurs according to equation 2 below as the plasma is extinguished, and additional hydrogen radicals H

*

are created through a combination of hydrogen ions and free electrons.

H

+

+e

−

→H

*

(recombination) (EQ2)

As time progresses, a second recombination may occur according to equation 3. The second recombination yields inactive, stable hydrogen gas molecules which will not contribute reaction energy to the surface reaction. Therefore, it is important to deliver the activated radicals to a surface

23

of substrate

22

before they recombine.

H

*

+H

*

→H

2

(EQ3)

The hydrogen radicals H

*

and any other remaining gas particles of the plasma travel around the 90° bend

15

of the tube

14

and are drawn downwardly along vertical section

18

and out into the reaction space

12

through outlet

19

by the rotation of susceptor

20

. Rotating susceptor

20

generates a downward pumping action in the direction of substrate

22

. The pumping action creates a laminar flow of gases over the wafer surface

23

as illustrated by arrows

29

.

Preferably, susceptor

20

is operated to achieve matched gas flow conditions. In a matched gas flow, the rate of gas flow in a downward direction indicated by Q−1 equals the rate of gas flow in a horizontal direction designated by Q−2. When these two gas flow rates are equal, matched flow occurs. An additional discussion of matched flow is disclosed in the pending application entitled “A Method For Chemical Vapor Deposition Of Titanium-Nitride Films At Low Temperatures”, Ser. No. 08/131,900, filed Oct. 5, 1993, which application is incorporated herein by reference.

For an efficient CVD reaction according to the principles of the presents invention, it is desirable that the plasma gas reaching the substrate

22

contain a large percentage of radicals, and preferably 80% or more activated radicals by composition. Such a high radical composition requires drawing the plasma gas down to the substrate

22

with minimal recombinations. Maximum utilization of radicals is accomplished by the laminar flow created by the rotating susceptor

20

. It has been determined through experimentation that the laminar flow pattern of the susceptor

20

minimizes the recirculations of the gas reactants and particularly minimizes recirculation of the activated gas radicals at the substrate surface

23

. The minimized recirculation, in turn, minimizes gas phase collisions of the activated radicals, and hence, reduces the rate at which the radicals recombine to form stable molecules. That is, the amount of recombination of H

*

into H

2

according to equation 3 above is reduced. As a result, there is a greater density of useful activated radicals available at the substrate surface

23

to supply energy to the chemical surface reaction and to reduce the thermal energy required in the chemical vapor deposition of the film. Thereby, the present invention effectively reduces the deposition temperature.

When gas radicals are introduced into space

12

, the reactant gases are introduced such as through a vertically adjustable showerhead

30

shown in FIG.

1

. For example, to deposit a titanium containing film, a titanium tetrahalide gas such a titanium tetrachloride (TiCl

4

), titanium tetrabromide (TiBr

4

), or titanium tetraiodide (Til

4

), and preferably TiCl

4

, is introduced. For a pure titanium layer, H

2

might be excited into a plasma and TiCl

4

might be introduced into the reaction space

12

. A mixture of H

*

and TiCl

4

might then occur in space

12

generally above susceptor

20

and substrate

22

. The pumping action of susceptor

20

would draw the mixture down to substrate surface

23

in a laminar flow and the activated H

*

and TiCl

4

should react at surface

23

to deposit a thin film on the substrate

22

. Hydrogen radicals H

*

should supply energy to the surface reaction according to equation 4.

4

H

*

+TiCl

4

→Ti+

4

HCl

(EQ4)

The reaction should yield a film of titanium (Ti) upon the substrate surface

23

and hydrochloric acid (HCl) which might be removed through the appropriate exhaust port

32

. The energy contributed to the reaction of equation 4 by the activated radicals should achieve a CVD film at reduced deposition temperatures.

While the example of the invention described hereinabove might yield a layer of pure titanium upon the substrate

22

, various other material layers might also be deposited according to the principles of the present invention containing titanium or containing other desirable elements. For example, titanium nitride (TiN) might be deposited by introducing hydrogen (H

2

) and nitrogen (N

2

) into the plasma-generating tube

14

to yield H

*

and N

*

radicals. Further, ammonia gas (NH

3

) may be excited and disassociated into a plasma containing H

*

and N

*

radicals. Similar to the recombination of the hydrogen gas plasma particles, the N

*

radicals will eventually combine into nitrogen molecules (N

2

) unless quickly drawn down to the surface of the substrate

23

. As a further example, titanium silicide (TiSi

2

) might also be deposited according to the principles of the present invention. In such a case, silane gas (SiH

4

) might be introduced with the titanium-containing gas (e.g. TiCl

4

) into the reaction space

12

. Additionally, tungsten (W) may be deposited using the apparatus of FIG.

1

and the method described. Examples of chemical reactions for producing titanium nitride and titanium silicide are given below in equations 5 and 6, respectively.

TiCl

4

+N

*

+4

H

*

→TiN+

4

HCl

(EQ5)

TiCl

4

+2

SiH

4

+4

H

*

→TiSi

2

+4

HCl+

4

H

2

(EQ6)

The microwave plasma deposition apparatus of

FIG. 1

was used to deposit a layer of tungsten and several tests were made to determine the viability of the method. Hydrogen was passed through quartz tube

14

. An excited plasma was ignited in the vicinity of region

28

and traveled downstream through tube

14

into reaction space

12

. As the plasma traveled along quartz tube

14

, it was extinguished downstream of the microwave excitation region

28

indicating that recombination of the excited plasma particles had occurred, such as according to equation 2 above to yield additional hydrogen radicals. The hydrogen radicals were subsequently drawn down to substrate surface

23

by rotating susceptor

20

. Simultaneously, tungsten hexafluoride (WF

6

) was introduced through a gas port

29

. A deposition reaction occurred according to Equation 7, below, to deposit a layer of tungsten onto substrate

22

.

WF

6

+6

H

*

→W+

6

HF

(EQ7)

To verify that hydrogen radicals were actually reaching the substrate surface

23

and contributing to the CVD process, an activation energy comparison was made. Specifically, the tungsten deposition rate was measured as a function of substrate temperature. The measurements were made both with the microwave power turned off and no plasma and with the microwave power turned on to create a plasma and hydrogen radicals. The data measured is shown plotted in

FIGS. 4A and 4B

as a logarithmic Arrhenius function, i.e., plotted as ln (k) versus 1/T, where k is the reaction rate constant and T is absolute temperature. The process and deposition parameters for both the non-plasma and plasma depositions illustrated by

FIGS. 4A and 4B

, respectively, were as follows:

H

2

rate=2,000 sccm

WF

6

rate=225 sccm

Pressure=4 Torr

Rotation rate of susceptor=30 RPM

A Microwave Power=900 Watts

From the experiments, and the resulting Arrhenius functions, the activation energy, E

a

, was calculated. For the thermal process, that is, with the microwave power turned off, E

a

=67.1 kJ/mole-degree K. However, when the microwave power was turned on to create a plasma, the activation energy necessary for the deposition process was only E

a

=63.2 kJ/mole-degree K. The decrease in activation energy E

a

between the plasma and non-plasma deposition processes, indicates that activated hydrogen radicals are reaching the substrate surface and participating in the surface reaction according to the principles of the present invention. The decreased activation energy necessary when utilizing the activated radicals results in a decrease in the deposition temperature necessary for the CVD process. As discussed above, a lower deposition temperature is desirable for integrated circuit fabrication of temperature-sensitive circuits requiring deposition temperatures below 650° C.

The deposition rate of tungsten was also plotted as a function of the susceptor rotation rate or substrate rotation rate.

FIG. 5

illustrates that the deposition rate for the thermal process increased with increasing rotation rate as expected. This is due to the fact that the molecular reactants are being pumped to the rotating substrate surface at a higher rate- However, for the upstream radical-assisted process of the present invention, the deposition rate increased much more dramatically as the rotation rate increased. That is, there is an effect beyond the basic pumping of reactants caused by the rotating substrate which produces the increased deposition rate. With the upstream plasma method of the present invention, it was determined that the laminar gas flow pattern provided by the rotating susceptor minimizes the gas phase collisions, and thus reduces the rate at which the necessary activated hydrogen radicals H

*

recombine to form hydrogen molecules H

2

. The efficient delivery of radicals to the substrate surface in the upstream method of the present invention is an important advancement in plasma-enhanced CVD. A majority of the activated radicals are carried to the substrate surface to take place in the surface deposition reaction. Therefore, not only do the activated radicals contribute energy and lower the deposition temperature, but also the high density of radicals delivered to the substrate by the laminar gas flow of susceptor

20

further reduces the deposition temperature below the impractically high temperatures of thermal CVD techniques.

FIG. 1A

shows an alternative CVD configuration which utilizes an upstream microwave source to generate activated gas radicals. A reactor

100

includes a chamber housing

102

enclosing reaction space

104

. Like reactor

5

of

FIG. 1

, the housing may be controllably vacuumed to a desired internal deposition pressure. Plasma gases are introduced into a vertical quartz tube

106

. A microwave wave guide structure

108

is coupled to quartz tube

106

. Wave guide structure

108

includes a horizontal section

110

which includes a microwave source

112

. An angled waveguide section

114

connects horizontal section

110

to a vertical waveguide section

116

. Quartz tube

106

extends through an opening (not shown) in the angled section

114

and extends through section

114

and vertical section

116

whereupon it extends through a top cover plate

15

of housing

102

. Quartz tube

106

extends through plate

118

and terminates at an outlet end

120

above a gas dispersing showerhead

122

. Showerhead

122

is attached to a quartz insulator ring

124

which connects the showerhead

122

to the cover

115

of reactor housing

102

. Also disposed above showerhead

122

and adjacent the outlet end

120

of quartz tube

106

is a reactant gas halo or dispersion ring

128

which has a plurality of openings for dispersing reactant gas. A source line

130

is connected to ring

128

for delivering a reactant gas such as TiCl

4

to the ring

128

.

The microwave source

112

within wave guide section

110

may be a magnetron or any other suitable source which generates energy at microwave frequencies. For example, a coaxial waveguide adapter (not shown) might be attached onto one end of horizontal waveguide section

110

to generate the necessary microwave energy.

The upstream microwave plasma source and reactor

100

of

FIG. 1A

operates somewhat similarly to reactor

5

in FIG.

1

. That is, a plasma gas such as hydrogen, nitrogen and/or ammonia is introduced into quartz tube

106

and travels along the quartz tube

106

and through the microwave waveguide structure

108

such that the gases are excited into a plasma within a section or area of tube

106

. A rotating susceptor

132

supports a substrate

134

below showerhead

122

and halo

128

. Similar to the rotating susceptor of

FIG. 1

, susceptor

132

is coupled to a temperature control device (not shown) which heats substrate

134

to a desired temperature. Furthermore, susceptor

132

is coupled by shaft

134

to a motor (not shown) such that the rotation of susceptor

132

may be set as desired. The rotating susceptor pumps the activated radicals from end

120

of quartz tube

106

and from reactant gas from ring

128

through showerhead

122

to react and deposit a film layer onto substrate

134

. Preferably, the majority of activated plasma particles reaching substrate

134

are activated radicals which contribute energy to the surface reaction to achieve low temperature CVD. The remaining non-utilized gases are exhausted through an exhaust port

138

.

While the laminar gas flow of a rotating susceptor in combination with an upstream plasma source yields desirable radical densities, a method of low temperature CVD of titanium has also been achieved using a gas dispersing showerhead biased as an RF electrode in order to generate a plasma of ions and radicals close to the substrate such that both ions and radicals contribute to the low temperature surface reactions. Accordingly,

FIG. 2

shows a preferred embodiment of a CVD reactor for achieving low temperature deposition using activated radicals and ions in accordance with the principles of the present invention. Referring to

FIG. 2

, the reactor

40

includes a deposition chamber housing

42

and housing cover

43

which defines a reaction space

44

. Housing

42

also encloses a rotating susceptor

46

which supports a substrate

48

in space

44

. Similar to the reactor of

FIG. 1

, reactor

40

may be selectively evacuated to various different internal pressures, while susceptor

46

is coupled to adjustable heat and rotational controls for heating and rotating substrate

48

at various temperatures and speeds, respectively.

Extending downwardly from the top of housing

42

is a cylinder assembly

50

which is attached to a showerhead

52

. Showerhead

52

is suspended above substrate

48

. The gases to be excited into a plasma are introduced through a gas injection ring

54

into cylinder assembly

50

through a plurality of ring holes

56

. Ring

54

is connected to a plasma gas supply by line

55

. Showerhead

52

is coupled to an RF power source

57

by feedline assembly

58

which extends through cylinder assembly

50

to showerhead

52

. Cylinder assembly includes a cylinder

51

, and insulator ring

60

which separates cylinder

51

and showerhead

52

for reasons discussed hereinbelow. In one embodiment of the reactor

40

, cylinder

51

is electrically grounded. The RF energy biases showerhead/electrode

52

so that it acts as an electrode and has an associated RF field. Showerhead/electrode

52

is preferably approximately 0.25 inches thick and contains approximately 300-600 dispersion holes

62

. The gases introduced through plasma gas injection ring

54

flow downwardly in cylinder

51

. The RF field created by the biased showerhead/electrode

52

excites the gases so that a plasma is created below the lower surface

53

of showerhead/electrode

52

. Preferably, the showerhead dispersion holes

62

are dimensioned somewhat smaller than the gas dispersion holes of traditional gas showerheads to prevent creation of a plasma in the holes

62

which results in deposition in the holes and subsequent bombardment of the substrate

48

. Furthermore, the smaller holes

62

of the showerhead

52

prevent formation of a plasma above showerhead

52

inside of cylinder

51

thus concentrating the plasma below showerhead/electrode

52

and close to substrate

48

. The showerhead holes

62

, in a preferred embodiment, are dimensioned to be approximately {fraction (1/32)} of an inch wide. Cylinder

51

preferably has the same diameter as showerhead/electrode

52

to spread the plasma and reactant gases over the entire showerhead

52

.

The reactant gases, such as TICl

4

are introduced through a ring

66

which is generally concentric with ring

54

and is connected to a reactant gas source by line

64

. The gas flow from injector rings

54

and

66

develops within the length of the cylinder

51

as the gases travel to the showerhead/electrode

52

. Utilizing the rotating susceptor

46

, the cylinder

51

, and showerhead/electrode

52

, it is preferable for the velocity profile of the incoming plasma gases passing through showerhead

52

to be fully developed before it reaches the rotating substrate

48

. The showerhead/electrode

52

is spaced between 0.25 to 4 inches from the substrate

48

to ensure that the plasma is close to the substrate

48

. Preferably, the spacing is under 1 inch and in a preferred embodiment is approximately 20 millimeters. As the gases pass through the showerhead/electrode

52

, the pressure drop across the showerhead/electrode

52

flattens out the velocity profile of the gases. That is, the gas tends to have the same velocity at the center of the showerhead/electrode

52

as around the periphery. This is desirable for uniform deposition of a film on substrate surface

49

. The plasma gases pass through showerhead/electrode

52

and are excited into a plasma proximate the bottom side

53

of showerhead/electrode

52

. As mentioned above, it has been found that an RF plasma may be excited with RF energy as low as 450 KHz and as high as 13.56 MHZ and the invention does not seem to be particularly frequency sensitive.

If susceptor

46

is rotated with the deposition configuration of

FIG. 2

, the pumping effect of the rotating susceptor

46

takes place below the showerhead/electrode

52

. In the embodiment of the present invention as shown in

FIG. 2

, the unique use of showerhead/electrode

52

in very close proximity to substrate

48

produces a concentrated plasma with a large density of useful gas radicals and ions proximate the substrate surface

49

. With the RF showerhead/electrode configuration of

FIG. 2

, it has been discovered that there does not seem to be a noticeable enhancement gained in rotating the susceptor

46

faster than approximately 100 rpm. It was also found, however, that a rotation rate of 0 rpm, although not drastically affecting the deposition rate, lowers the uniformity of the reactant and plasma gas flow and the subsequent deposition. Generally, a substrate rotation rate between 0 and 2,000 rpm might be utilized with the deposition configuration utilizing an RF showerhead/electrode.

As illustrated further hereinbelow, a susceptor rotation rate of approximately 100 rpm has proven to be sufficient for deposition. While it is preferable to utilize only radicals in the upstream plasma generation methods, both radicals and ions are present during the deposition using RF showerhead/electrode

52

. That is, both ions and radicals supply energy to the surface reaction. While it is generally not desirable to use only ions due to their tendency to stick to contact and via surfaces and produce non-conformal films, some ion bombardment of the substrate

48

is beneficial because it supplies additional energy to the growing film layer on the surface

49

of the substrate

48

. However, too much ion bombardment of substrate

48

may damage the integrated circuit devices of the substrate

48

and may lead to poor film conformality. Therefore, the deposition parameters and showerhead spacing are chosen as illustrated herein to achieve a useful mixture of radicals and ions. As discussed above, for the configuration of

FIG. 2

, the spacing is under 1 inch and preferably approximately 20 mm.

The reactant gases, such as TICl

4

, are introduced into cylinder

51

through another gas ring

66

. The reactant gases travel down the length of cylinder

51

and are also excited by the RF field created by showerhead/electrode

52

, as they pass through the openings

62

of showerhead

52

. The reactant gas travels to the surface of substrate

48

along with the radicals and ions of the excited plasma. The radicals, ions and excited reactant gas particles react at the surface of substrate

48

to deposit a film such as a titanium-containing film, upon substrate

48

.

Because of the close spacing of the showerhead/electrode

52

from substrate

48

in combination with cylinder

51

, the gas mixture streamlines

65

emanating from showerhead

52

are close to the substrate

48

to provide efficient deposition and reduce the amount of gas mixture which bypasses the substrate

48

. That is, the boundary layer of gas, which is defined as the volume or space below the gas streamlines

65

which is stagnant or non-moving with respect to the susceptor

46

, is very small. Therefore, a large percentage of the radicals, ions and reactant gas particles are being utilized in the surface reaction, and accordingly, the efficiency of the CVD process and the deposition rate are increased.

With the showerhead/electrode

52

acting as an RF electrode, a more uniform plasma is generated at substrate

48

, therefore enhancing the uniformity of radical and ion density at the substrate

48

and the uniformity of the deposited film. In the RF showerhead/electrode configurations of

FIGS. 2

,

2

A and

2

B the deposition rate reaches a maximum when the rotation rate is matched to the incoming plasma and reactant gas flow, i.e., matched gas flow. Accordingly, it is desirable to achieve matched flow when susceptor

46

rotates.

FIG. 2A

discloses an RF showerhead/electrode configuration similar to the configuration of

FIG. 2

except in greater detail. Wherever possible similar reference numerals will be utilized between

FIGS. 2 and 2A

. The configuration of

FIG. 2A

is similar to a structure disclosed within pending U.S. patent application Ser. No. 08/166,745 the disclosure of which is fully incorporated herein by reference.

In

FIG. 2A

, there is shown in break-away a portion of CVD deposition chamber housing

42

, to which is mounted the RF showerhead/electrode apparatus

142

used to practice the low temperature deposition of the present invention. It will be appreciated by persons skilled in the art that certain features to be described may pertain to one or more, but less than all, embodiments of the invention. In

FIG. 2A

, the showerhead/electrode

52

includes an RF line stem

144

mounted thereto. As will be discussed in further detail, the RF line stem

144

is one of several components making up the RF feedline assembly

58

. The RF feedline assembly

58

also acts as a heat pipe to conduct heat away from showerhead/electrode

52

as is also discussed further hereinbelow. Preferably, line stem

144

is machined concentrically into and is integral with upper surface

146

of showerhead/electrode

52

to increase the RF signal conduction and heat conduction efficiency. RF line

148

comprises line stem

144

and an additional length of tubing

150

welded thereto to achieve the desired overall length of the RF line

148

. The weld is represented at

149

. Preferably, showerhead/electrode

52

and integral line stem

144

are made of Nickel-200, while RF line tubing

150

is made of a highly conductive material such as 6061-T6 aluminum. However, it will be appreciated by persons skilled in the art that other materials can be used for the RF line

150

, such as nickel

200

. In one embodiment, the RF line

148

is made of aluminum coated with nickel to prevent an RF plasma from forming within said cylinder

51

of the cylinder assembly

50

during the plasma-enhanced CVD reactions of the present invention. Preferably, the showerhead/electrode is approximately 0.25 inches thick.

Showerhead/electrode

52

is perforated with a pattern of gas dispersion holes

62

to distribute the reactant and plasma gases evenly during CVD processing. As shown in

FIG. 2A

, upstanding RF line stem

144

is provided with a circumferential shoulder flange

152

adjacent and parallel to showerhead/electrode

52

. The flange

152

is spaced above showerhead/electrode upper surface

146

and permits the gas dispersion hole pattern to extend beneath the shoulder flange

152

, thereby minimizing gas flow disturbances. Furthermore, the flange

152

aids in the conduction of the RF energy along line

148

to showerhead/electrode

52

, assists in cooling showerhead/electrode

52

, and provides mechanical support for ceramic isolator tubes

154

,

156

. An alternative embodiment of the showerhead electrode configuration eliminates the flange

152

as shown in FIG.

2

B.

The RF showerhead/electrode apparatus

142

of

FIG. 2A

further includes first and second ceramic isolator tubes

154

,

156

, respectively, which are concentric with and surround at least a portion of RF line

148

. As shown, ceramic isolator tubes

154

,

156

are supported by circumferential shoulder flange

152

. Tubes

154

,

156

are preferably formed of alumina (99.7% Al

2

O

3

) which is readily commercially available such as from Coors Ceramics of Golden, Colo. One function of these isolator tubes

154

,

156

is to prevent RF plasma from forming around the RF line

148

during CVD processing by isolating the RF line

148

from the plasma and reactant gases in the cylinder assembly

50

. As may be appreciated, it is desirable to prevent the formation of any plasma within the cylinder assembly

50

in order to concentrate the plasma below showerhead/electrode

52

. Therefore, the isolator tubes

154

,

156

operate to prevent the formation of such a plasma inside of the cylinder assembly

50

. Additionally, and as described more fully below, the isolator tubes

154

,

156

aid in preventing electrical shorting between gas distributor cover

158

(which is at ground potential) and RF line

148

at the location where RF line

148

passes through gas distributor cover 158. Gas distributor cover

158

is mounted to housing

42

by means of a plurality of screws

150

. As shown in the

FIG. 2A

, gas injection rings or halos such as rings

54

,

66

(shown in phantom) are located slightly below gas distributor cover

158

and supply the CVD reaction and plasma gases to the inside of cylinder assembly

50

. Gas injection rings

54

,

66

may be two of a plurality of concentric rings for introducing numerous reactant gases.

A seal prevents vacuum leaks at the location where RF line

148

passes through gas distributor cover

158

. This is accomplished by means of a shaft seal and a flange seal. As shown in the

FIG. 2A

, a ceramic seal plate

160

is pressed downwardly by two stainless steel clamps

162

. Clamps

162

are biased against distributor cover

158

by spring washer/screw assemblies

164

to obtain a predetermined downward force on the seal components to insure proper sealing, to accommodate tolerance stacks in the seal components, and to take up dimensional changes due to thermal expansion which may occur during CVD processing. Seal plate

160

presses downwardly on a stainless steel ferrule

166

which in turn presses down on an O-ring

168

seated in ceramic seal body

170

. The downward force exerted by clamps

162

on seal plate

160

also forces seal body

170

downwardly against gas distributor cover

158

, which compresses the O-ring

172

located between seal body

170

and gas distributor cover

158

. It should be noted that seal body

170

has a downwardly extending annular flange

174

which surrounds RF line

148

over the entire length of it which passes through gas distributor cover

158

. The lower end

176

of annular flange

174

extends downwardly to a point where it meets ceramic isolator tube

154

. As shown, the outer ceramic isolator tube

156

extends further upward than isolator tube

154

, such that there is no direct line between gas distributor cover

158

and RF line

148

. This prevents arcing when the RF line

148

is used to power showerhead/electrode

52

.

The RF line

148

also functions as a heat pipe structure. With respect to heat pipe structures, such devices are known per se, and in the present invention, the heat pipe structure is used to carry off heat from the showerhead/electrode

52

generated by radiant energy from the heated susceptor

46

, as well as by the RF energy applied to the showerhead/electrode. The center space

178

of RF line

148

is provided with a felt or other suitable capillary wicking material liner (not shown). Space

178

is sealed with a liquid (e.g., acetone) therein under its own vapor pressure that enters the pores of the capillary material wetting all internal surfaces of RF line

148

. By applying heat at any point along the length of the RF line, the liquid at that point boils and enters a vapor state. When that happens, the liquid in the wicking material picks up the latent heat of vaporization and the vapor, which then is at a higher pressure, moves inside the sealed pipe to a cooler location where it condenses and re-enters the liner. Thus, the vapor gives up its latent heat of vaporization and moves heat from the “input” to the “output” end of the heat pipe structure. As a general frame of reference, heat may be moved along a heat pipe at a rate of approximately 500 mph.

With reference to the specific configuration utilized in

FIG. 2A

, the “input” end of the heat pipe structure is the end which is affixed to showerhead/electrode

52

. The “output” end is the upper end shown in the

FIG. 2A

which has a liquid-cooling jacket

180

sealed around it. The seal is effected by O-ring shaft seals

182

and

183

. Cooling jacket

180

is preferably a polymeric material and is provided with TEFLON compression fittings

184

and

185

which connect TEFLON tubing

186

to cooling jacket

180

. A suitable cooling liquid, such as water, flows through tubing

186

and cooling jacket

180

to carry heat away from RF line

148

. This permits direct contact of the cooling liquid with the RF line

148

for efficient conduction of heat from the line

148

. Additionally, with this configuration, at no time is the CVD reactor chamber exposed to the possibility of an internal coolant leak, nor is there any corrosive effect on metal tubing by RF carrying liquid. As stated, the fluid which passes through TEFLON tubing

186

and carries the heat away from the RF line

148

may be water, although a variety of fluids can be used depending on the heat to be conducted away from the line

148

. RF line

148

also includes a cap

188

which is welded in place and has a fill tube

190

for filling the internal space

178

with the desired fluid. A suitable commercially available heat pipe may be obtained from Thermocore Inc., of Lancaster, Pa.

As shown in

FIG. 2A

, an aluminum cylinder

51

is utilized to vary the showerhead/electrode substrate spacing(s). Showerhead/electrode

52

is fastened to cylinder

51

by means of screws

192

, which are preferably made of a material that does not corrode in the presence of an RF plasma. One such material is Hastelloy C-22, which is a trade name of Hanes International, of Kokomo, Ind. Suitable screws made of this material are available from Pinnacle Mfg. of Tempe, Ariz. Quartz ring

60

electrically isolates showerhead/electrode

52

from aluminum cylinder

51

. A suitable quality quartz for ring

60

is Quartz T08-E available from Hereaus Amersil in Tempe, Ariz. Screws

192

, which are at ground potential, are isolated from the showerhead/electrode

52

by two interlocking ceramic isolator sleeves

194

and

196

. Quartz is used for isolator ring

60

because of its significant resistance to thermal shock. This can be important since the RF showerhead/electrode

52

below quartz ring

60

becomes heated to a higher temperature, and more rapidly than aluminum cylinder

51

above quartz ring

60

, thus inducing thermal shock and stress in ring

60

. Screws

198

, which may be made of the same material as screws

192

, are utilized to affix aluminum cylinder

51

to housing

42

. As discussed above, various length cylinders

51

might be utilized to vary the showerhead/electrode-to-substrate spacing. It is preferable that the length of cylinder

51

be chosen to position showerhead/electrode

52

within 1 inch of susceptor

46

.

RF energy is conducted to showerhead/electrode

52

by RF feedline assembly

58

comprising stem

144

and tube

150

. Isolator tubes

154

,

156

are needed to electrically isolate and prevent arcing between tubing

150

and any parts of the metal housing

42

, including distributor cover

158

. Furthermore, the apparatus includes a seal around tubing

150

at the location where it passes through distributor cover

158

, as described hereinabove and shown in FIG.

2

A.

RF energy is supplied through a shielded RF supplying cable

200

which is connected to an RF power source

57

(not shown in

FIG. 2A

) and has a UHF connector

202

at one end. Connector

202

mates with another UHF connector

204

, which in turn is coupled via a length of 12 gauge wire

206

to a stainless steel shaft collar

208

mounted at the upper end of RF line

148

. With this arrangement there is minimal resistance to the flow of RF current. The segment of RF line

148

which is exposed above shaft collar

208

is isolated from the grounded metal shielding

210

by a polymer cap

212

. The apparatus is believed to be capable of delivering 250-300 watts of RF power at 450 KHz to 13.56 MHZ.

FIG. 2B

shows an alternative embodiment of the RF showerhead/electrode configuration utilized to practice the present invention. The CVD apparatus

220

of

FIG. 2B

operates similarly to the apparatuses shown in

FIGS. 2 and 2A

. That is, an RF showerhead/electrode

222

is biased by an RF feedline assembly

224

while plasma and reactant gases are pumped through a cylinder assembly

226

to a substrate

228

on susceptor

230

. However, the embodiment of

FIG. 2B

eliminates the metal cylinder

51

and insulator ring

60

of

FIGS. 2 and 2A

while preventing electrical arcing inside of the cylinder assembly

226

proximate the RF line and preventing the undesired formation of plasma within the cylinder assembly

226

when the showerhead

222

is biased as an electrode. The embodiment of

FIG. 2B

utilizes a housing, such as one similar to housing

42

of

FIG. 2

, which includes a housing cover

232

and includes an RF supply assembly

234

, a heat pipe assembly

236

with cooling jacket

237

and associated fluid supply lines and a gas distributor cover

239

with a sealing assembly

241

all generally similar to the respective components of FIG.

2

. However, the cylinder assembly

226

does not include a metal cylinder

51

and insulator ring

60

as shown in FIG.

2

. Rather, a cylinder

238

made of an insulating material such as quartz surrounds the RF feed line assembly

224

.

Cylinder

238

is preferably formulated out of a high quality quartz such as Quartz T08-E available from Hereaus Amersil, as mentioned above. Quartz cylinder

238

is supported by a nickel showerhead/electrode

222

, made of a conductive metal such as Nickel-200, without the use of screws or other fasteners that are utilized within the embodiments of

FIGS. 2 and 2A

. Specifically, a stepped bore

240

is formed within housing cover

232

to receive an upper end

242

of cylinder

238

. O-rings

243

,

244

are placed at the interface between stepped bore

240

and cylinder

238

to form a seal at the interface. At the lower end

246

of cylinder

238

, an annular notch

248

is formed in cylinder

238

to receive a peripheral edge

250

of the showerhead/electrode

222

. The notch

248

of cylinder

238

rests upon the peripheral edge

250

of showerhead/electrode

222

. Showerhead/electrode

222

includes a stem

252

which is attached to RF line tubing

254

, such as by a weld at

255

, to form a unitary RF line

256

. RF line

256

is frictionally held and supported at its top end by collar

258

similar to collar

208

of FIG.

2

A. The RF line, in turn, supports showerhead/electrode

222

above susceptor

230

. Showerhead/electrode

222

, in turn, supports the cylinder

238

within the cylinder assembly

226

by abutting against cylinder

238

at notch

248

and holding it in bore

240

. The interface between showerhead/electrode peripheral edge

250

and cylinder notch

248

is sealed by a compressed O-ring

258

which is compressed between shelf

248

and a similar corresponding annular notch

260

formed in peripheral edge

250

of the showerhead/electrode

222

. Similar to the embodiments of

FIGS. 2 and 2A

, a plurality of gas halos or rings

262

,

264

introduce the necessary plasma and reactant gases into cylinder

238

.

The embodiment of

FIG. 2B

eliminates the need for metal screws to attach the cylinder

238

to the housing cover

232

and the showerhead/electrode

222

to the cylinder

238

. This further reduces the possibility of arcing inside of cylinder

238

because of the reduced metal proximate the biased RF showerhead/electrode

222

. Furthermore, it is not necessary to utilize ceramic isolator sleeves at the showerhead peripheral edge

250

.

Accordingly, the RF showerhead/electrode

222

has also been modified. Showerhead/electrode

222

includes a stem

252

without a flange. Instead, a slight ridge

266

is formed around stem

252

, and as shown in

FIG. 2A

, ridge

266

supports a generally circular ceramic tray

268

which is formed from a ceramic material, such as alumina (99.7% Al

2

O

3

), similar to the ceramic isolator sleeves

154

,

156

shown in FIG.

2

A. Ceramic tray

268

is supported by ridge

266

, and in turn, supports isolator sleeves

270

,

271

. Isolator sleeves

270

,

271

are also preferably made of a ceramic insulator material similar to that used for sleeves

154

,

156

of FIG.

2

A. As with the embodiments used to practice the present invention which are discussed above, preferably the holes of showerhead/electrode

222

are approximately {fraction (1/32)} (0.0313) inches in diameter to prevent the formation of a plasma inside cylinder

238

and to confine the plasma generally below the showerhead/electrode

222

and above the susceptor

230

. The embodiment of

FIG. 2B

utilizes quartz cylinder

238

and eliminates the metal attachment screws proximate showerhead/electrode

222

which helps to prevent the formation of a plasma within cylinder

238

and to prevent arcing between the RF line

256

and showerhead/electrode

222

and any of the surrounding metal. A layer of insulation

272

may be placed atop gas distributor cover

239

to prevent contact by an operator, because the gas distributor cover

239

becomes very hot during operation.

Numerous deposition runs have been made utilizing the RF electrode/showerhead configuration of

FIGS. 2 and 2A

to illustrate the viability of the present invention. Specifically, a layer of titanium nitride was deposited upon a substrate wafer at approximately a temperature of 400° C. This is substantially lower than the substrate temperature which is ordinarily required for thermal CVD processes to take place, which may be well over 1,000° C. For example, a layer of titanium nitride was deposited using ammonia gas (NH

3

) and nitrogen gas (N

2

) with the parameters listed below and the results shown in Table 1. The configuration of the present invention utilizes plasma gas flows between 500 and 5,000 sccm (50 to 500 sccm for NH

3

) while a reactant gas flow, such as TiCl

4

, between 0.5 and 10 sccm is desired. The reaction space

44

should be evacuated between 0.5 to 10 Torr.

TABLE NO. 1

Deposition Parameters for Table No. 1

TICl

4

(sccm)

10

NH

3

(sccm)

500

N

2

(sccm)

500

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

1

Susceptor Rotation Rate (rpm)

100

Substrate Temp. (° C.)

400

Results and Additional

WAFER NO.

Deposition Parameters

1

2

3

4

5

6

TiN layer thickness (Å)

800

698

608

545

723

910

Deposition Rate (Å/min)

400

348

304

272

241

303

Layer Resistivity (μ′Ω-

1519

1194

970

940

1021

1284

cm)

Deposition Time (sec)

120

120

120

120

180

180

Susceptor Temp (° C.)

414

471

457

461

462

475

Wafers

1

-

3

were silicon, while wafers

4

-

6

were thermal oxide wafers having a thin layer of silicon dioxide on the surface. This was done to ensure that the process of the present invention may be utilized in a broad range of CVD applications for both silicon wafers and oxide wafers. Each of the substrate wafers of Table 1 were also given an RF plasma ammonia (NH

3

) anneal in the apparatus of

FIG. 2

at 250 Watts for approximately 120 seconds with a gas concentration of 5,000 sccm of NH

3

at a pressure of 5 Torr. The rotation rate of the susceptor during the anneal was approximately 100 rpm. The NH

3

RF plasma improves the film quality of the deposited TiN film as discussed further hereinbelow.

The RF plasma electrode/showerhead configuration, in accordance with the principles of the present invention, may be utilized to deposit a titanium nitride (TiN) layer on a substrate utilizing both nitrogen gas (N

2

) and hydrogen gas (H

2

) instead of ammonia gas (NH

3

). The various film results and deposition parameters for the H

2

and N

2

low temperature deposition of TiN are given below in Table Nos. 2, 3, 4 and 5, at increasing deposition temperatures for increasing table numbers.

TABLE NO. 2

Deposition Parameters for Table No. 2

TiCl

4

(sccm)

10

H

2

(sccm)

500

N

2

(sccm)

500

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

1

Susceptor Rotation Rate (rpm)

100

Substrate Temp. (C. °)

400

Deposition Time (seconds)

180

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

9

10

TiN layer

825

1023

1221

1262

1227

1224

1141

1348

1400

1106

thickness (Å)

Deposition

275

341

407

421

409

408

380

449

487

389

Rate (Å/min)

Layer

1530

26864

4118

3108

855

4478

3982

4658

3449

4501

Resistivity

(μΩ-cm)

Susceptor

470

480

488

470

470

460

460

460

460

460

Temp (° C.)

Wafers 1 and 2 of Table No. 2 were silicon, while the remaining wafers

3

-

10

were thermal oxide. Wafers

6

-

10

received a 250 Watt RF plasma anneal for 120 seconds at an NH

3

gas rate of 5,000 sccm, at an internal pressure of 3 Torr (wafer

6

was done at 5 Torr), and a susceptor rotation rate of 100 rpm.

Table No. 3 illustrates the results of deposition runs utilizing a substrate temperature of 450° C., but maintaining the same gas and deposition parameters as were used in the deposition runs of Table No. 2. Wafer

1

and

2

were silicon while wafers

3

-

8

were thermal oxide. The results are as follows with wafers

6

-

8

of Table No. 3 receiving a 120 second RF plasma ammonia anneal at 5000 sccm, 5 Torr and a 100 rpm rotation rate with a power level of 250 Watts.

TABLE NO. 3

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

TiN layer

996

1009

1064

1488

1562

1444

1381

1306

thickness (Å)

Deposition

332

336

355

496

521

481

454

435

Rate (Å/min)

Layer

640

607

666

815

821

7121

5812

6363

Resistivity

(μΩ-cm)

Susceptor

518

519

521

524

521

522

524

523

Temp (° C.)

The low temperature TIN deposition was repeated with the substrate temperature at 500° C. and the results are tabulated according to Table No. 4 below. Wafer

1

was silicon and wafers

2

-

7

were thermal oxide.

TABLE NO. 4

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

TiN layer

990

1088

1034

1092

1004

1001

1004

thickness (Å)

Deposition Rate

330

362

345

364

335

334

335

(Å/min)

Layer Resistivity

578

687

700

786

1892

1840

1886

(μΩ-cm)

Susceptor Temp

579

590

597

595

591

593

594

(° C.)

Wafers

1

-

4

in Table No. 4 were not annealed, while wafers

5

-

7

were annealed using a similar RF plasma NH

3

anneal process and the parameters used for the deposition runs referenced in Table No. 3.

Similarly with a substrate temperature of 600° C., the CVD process of the present invention was used to deposit TiN with the results shown in Table No. 5 below, with wafers

1

and

2

being silicon and wafers

3

-

8

being thermal oxide.

TABLE NO. 5

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

TiN layer

657

822

740

768

767

765

773

910

thickness (Å)

Deposition

219

274

247

263

256

255

258

303

Rate (Å/min)

Layer

391

254

432

543

471

949

973

2710

Resistivity

(μΩ-cm)

Susceptor

650

650

650

650

650

650

650

650

Temp (° C.)

Again, an RF plasma NH

3

anneal was performed on substrate wafers

6

-

8

of Table No. 5 similar to the anneal step of tables 3 and 4 except at a pressure of 1 Torr instead of 5 Torr. Therefore, the deposition of TiN using the low temperature CVD process of the present invention may be accomplished at various temperatures lower than the temperatures necessary for traditional thermal CVD.

While titanium nitride may be deposited with the present invention, it may also be desirable to deposit simply a layer of pure titanium. For example, a titanium layer might be deposited upon a silicon wafer which then reacts with the titanium to form a film of titanium silicide (TiSi

2

). To this end, the present invention may also be used to deposit a layer of titanium.

Table No. 6 below sets forth the results and parameters of a deposition run which resulted in a deposited film of approximately 84% titanium on a thermal oxide wafer at 650° C. This was an excellent result for such low temperature chemical vapor deposition. The deposition run of Table 6 was performed according to the following deposition parameters, with the RF showerhead/electrode configuration of FIG.

2

.

TABLE 6

Deposition Parameters for Table No. 6

TiCl

4

(sccm) 10

H

2

(sccm) 500

RF Power (watts) 250 @ 450 KHZ

Reaction Chamber Pressure (Torr) 1

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 2700

Substrate Temperature (° C.) 565

WAFER NO.

Results and

1

Additional

Parameters

Ti layer

1983

thickness (Å)

Deposition

44

Rate (Å/min)

Layer

929

Resistivity

(μΩ -cm)

Susceptor

651

Temp (° C.)

The substrate wafer of Table No. 6 was not annealed.

Additional Ti-layer deposition runs were made according to the Table No. 7 parameters below with the following results shown in Table No. 7:

TABLE NO. 7

Deposition Parameters for Table No. 7

TiCl

4

(sccm)

10

H

2

(sccm)

500

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

.85

Susceptor Rotation Rate (rpm)

100

Deposition time (sec)

120 (wafer 7 for 180 sec)

Substrate Temperature (° C.)

565

Susceptor Temperature (° C.)

650

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

9

10

11

12

Ti layer

134.8

466.2

209.2

100.8

194.04

154.98

115.92

114.7

152.5

39.06

41.6

50.4

thickness

(Å)

Deposition

67.4

233.1

104.6

50.4

97.0

77.5

38.6

57.3

76.2

19.5

20.6

25.2

Rate

(Å/min)

Layer

2116.1

1767.8

761.8

—

—

—

1001.4

371.6

321.6

—

—

—

Resistivity

(μΩ-cm)

Wafers

1

-

3

and

7

-

9

of Table 7 were silicon while the remaining wafers were thermal oxide. None of the wafers of Table No. 7 received an RF plasma anneal of NH

3

.

Since a benefit of chemical vapor deposition of titanium-containing films is improved step coverage and film conformality over the physical deposition techniques, several of the film layers deposited according to the present invention were tested to measure conformality and step coverage. The layers tested for conformality and step coverage were deposited according to the parameters of Table No. 8 with the results shown in Table No. 8 below. The film conformality and step coverage of the film layers deposited according to the parameters below were very good.

TABLE 8

Deposition Parameters for Conformality and

Step Coverage Deposition Runs of Table 8

TiCl (sccm) 10

H

2

(sccm) 500

N

2

(sccm) 500

RF Power (watts) 250 @ 450 KHz

Reactor Chamber Pressure (Torr) 1

Susceptor Rotation rate (rpm) 100

Substrate Temperature (° C.) 450

Susceptor Temperature (° C.) 520

WAFER NO.

Results and

1

2

Additional

Parameters

TiN layer

586

2423

thickness (Å)

Deposition Rate

362

304

(Å/min)

Layer Resistivity

—

—

(μΩ-cm)

Susceptor Temp

520

520

(° C.)

None of the wafers used in Table 8 and tested for step coverage were annealed with an RF plasma of NH

3

.

As illustrated above a layer of titanium nitride (TiN) may be deposited in accordance with the principles of the present invention without utilizing ammonia gas (NH

3

). Instead, a mixture of H

2

and N

2

gases is used. Low temperature deposition of titanium nitride using TiCl

4

, N

2

and H

2

is desirable because it reduces contaminants within the reaction chamber that are formed by the chemical reactions of TiCl

4

and NH

3

. More specifically, TiCl

4

reacts with NH

3

at temperatures below 120° C. to form a yellow powdery adduct, and to prevent the adduct from forming it was necessary in the past to heat the reaction chamber walls to at least 150° C. Since it is now possible to deposit a layer of titanium nitride at low temperatures using TiCl

4

, N

2

, and H

2

chemistry instead of NH

3

, it is no longer necessary to remove a deposited adduct or to heat the reaction chamber walls, thus greatly reducing the cost of CVD systems.

According to the deposition parameters of Table No. 9, a layer of titanium nitride was deposited upon several thermal oxide substrates using a reaction chamber with unheated walls and a gas mixture of H

2

/N

2

. After the deposition of the films, the reaction chamber was inspected and there was no evidence of a yellow adduct found. None of the wafers of Table No. 9 were annealed with an RF NH

3

anneal.

TABLE NO. 9

Parameters for Adduct Test of Table No. 9

TICl

4

(sccm)

10

N

2

(sccm)

500

H

2

(sccm)

500

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

1

Susceptor Rotation rate (rpm)

100

Substrate Temp. (° C.)

450

Deposition time (sec)

95

Susceptor Temperature (° C.)

approximately 520

Results

and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

9

10

TiN layer

94

132

127

143

143

160

162

162

195

204

thickness

(Å)

Deposition

58

83

80

90

90

101

102

102

123

129

Rate

(Å/min)

Layer

2164

2218

1377

660

764

905

738

830

689

702

Resistivity

(μΩ-cm)

Susceptor

525

523

520

520

520

523

521

520

519

523

Temp (° C.)

Further deposition runs were made utilizing the configuration of

FIG. 2

wherein the plasma and reactant gas flows were adjusted, as well as the internal deposition pressure of the reaction space

44

. For example, the deposition runs shown in

FIG. 10

utilized a higher flow rate of H

2

and an increased deposition pressure from 1 Torr to 5 Torr. Further, Argon was mixed with the H

2

for some of the deposition runs.

TABLE 10

Parameters for Table 10

TiCl

4

(sccm)

10

H

2

(sccm)

5,000 (wafers 1-4); 3,750 (wafers 5-9)

Argon (slm)

0.5 (wafers 5-9)

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

5

Susceptor Rotation rate (rpm)

100

Deposition time (sec)

300 (600 for wafer 9)

Substrate Temp. (° C.)

565

Susceptor Temperature (° C.)

approximately 650

Results and

WAFER NO.

Additional Parameters

1

2

3

4

5

6

7

8

9

TiN layer thickness

798

1076

43.4

89.5

912.2

1082

656.5

577.1

1302

(Å)

Deposition Rate

159.0

215.0

9.1

17.9

182.5

216.5

131.3

115.4

130.2

(Å/min)

Layer Resistivity

53.84

32.66

216.1

377.1

89.23

25.7

212.7

211.3

170.1

(μΩ-cm)

In Table 10, the flow of H

2

was increased to 5,000 sccm for wafers

1

-

4

and to 3,750 sccm for wafers

5

-

9

. The deposition pressure was increased 5 Torr. For wafers

5

-

9

, a flow of 0.5 standard liters per minute (slm) of Argon was utilized with the H

2

as a diluent. In Table 10, wafers

1

-

2

and

5

-

6

were silicon, while wafers

3

-

4

and

7

-

9

were thermal oxide.

Table 11 shows additional runs made with the increased H

2

flow and increased deposition pressure.

TABLE 11

Deposition Parameters for Table No. 11

TiCl

4

(sccm)

10

H

2

(sccm)

3,750

Argon (slm)

0.5

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

5

Susceptor Rotation Rate (rpm)

100

Deposition time (sec)

300 (wafers 9-12 600 seconds)

Substrate Temperature (° C.)

565

Susceptor Temperature (° C.)

650

Results and

Additional

WAFER NO.

Parameters

1

2

3

4

5

6

7

8

9

10

11

12

TiN layer

889.6

3994

510.3

458.6

466.2

385.6

347.8

263.3

792.5

948.8

749.7

714.4

thickness

(Å)

Deposition

177.9

79.9

102.1

91.7

93.2

77.1

69.6

52.7

79.3

94.9

75.0

71.4

Rate

(Å/min)

Layer

54.03

35.71

233.4

274.1

281.0

280.1

545.1

489.1

314.1

203.5

—

—

Resistivity

(μΩ-cm)

The change in deposition pressure from 1 Torr to 5 Torr produced a more stable and symmetric plasma. Additionally, the increased hydrogen flow with the addition of a small flow of argon increased the stability of the plasma flow as well as the plasma intensity. An argon flow of 0-10 slm is preferable. Wafers

1

-

2

were silicon, while wafers

3

-

10

were thermal oxide. Wafers

11

and

12

were borophosphosilicate glass, available from Thin Films, Inc. of Freemont, Calif. None of the wafers of either Table

10

or

11

were annealed with a NH

3

plasma anneal.

Wafers

11

and

12

had field oxide (silicon oxide) top layers, patterned with silicon contacts (i.e., vias through the field oxide to a lower silicon layer). Selective deposition was observed in wafer number

11

after processing in the manner described above.

FIG. 6

shows deposition at the bottoms of silicon contacts (vias), but no deposition onto the oxide field. Selective deposition has been repeated and independently verified using the identified parameters. A selective deposition process can be used in place of multiple process steps to form vias. Selective deposition may be a result of different nucleation times for silicon and silicon oxide—nucleation occurs rapidly on silicon, but only after approximately 30 seconds on silicon oxide. Although the process applied to wafer

11

ran for longer than the normal 30 second nucleation time of silicon oxide, nucleation apparently did not occur over silicon oxide, possibly due to an instability in the plasma. High process pressures appear to be important for producing the selective effect.

Table 12 shows additional deposition runs at a susceptor temperature of 450° C.

TABLE NO. 12

Deposition Parameters for Table No. 12

TiCl

4

(sccm)

5

H

2

(sccm)

3,750

Argon (slm)

0.3

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

5

Susceptor Rotation Rate (rpm)

100

Deposition time (sec)

180

Substrate Temperature (° C.)

approximately 400 ° C.

Susceptor Temperature (° C.)

450

Results and

WAFER NO.

Additional Parameters

1

2

3

4

5

6

7

TiN layer thickness

242

222

210

241

168

136

150

(Å)

Deposition Rate

80.7

74.0

70.0

80.3

56.0

45.3

50.0

(Å/min)

Layer Resistivity

66.0

554.0

494.0

714.0

484.0

0.1

0.1

(μΩ-cm)

Wafers

1

-

4

were silicon, wafer

5

was thermal oxide while wafers

6

and

7

were an aluminum alloy containing aluminum silicon and copper. Runs

6

and

7

of Table 12 illustrate the viability of depositing a titanium-containing film on aluminum using the present invention. The deposition runs of Table 12 utilized a lower flow of reactant gas than the runs of Table 11, i.e., 5 sccm of TiCl

4

.

Good adhesion between the aluminum and titanium layers was obtained by minimizing the corrosion of the aluminum layer. Corrosion is largely a result of exposure of the aluminum layer to chlorine ions (Cl

−

) released from titanium tetrachloride (TiCl

4

) during deposition. By reducing the flow rate of titanium tetrachloride, the corrosion of the aluminum layer is reduced and adhesion is improved. Reduced titanium tetrachloride flow also reduces the deposition rate, allowing dissociated titanium atoms additional time to locate stable sites in the underlying aluminum layer. This additional time is particularly needed due to the low thermal energy and reduced thermal motion of the titanium atoms at reduced process temperatures.

The deposition runs of Table 13 were made at further reduced TiCl

4

flow rates. All of the wafers of Table 13 were thermal oxide. None of the wafers of Table 12 or 13 were annealed with an NH

3

RF anneal.

TABLE NO. 13

Deposition Parameters for Table No. 13

TiCl

4

(sccm)

wafers 1-2, 4 sccm; 3-4, 3 sccm;

5-6, 2 sccm; and wafer 7 at 1 sccm

H

2

(sccm)

3,750

RF Power (watts)

250 @ 450 KHz

Reaction Chamber Pressure (Torr)

5

Susceptor Rotation Rate (rpm)

100

Deposition time (sec)

300 (wafers 1 and 2 at 180 and 240,

respectively)

Substrate Temperature (° C.)

approximately 400 ° C.

Susceptor Temperature (° C.)

450

Results and

WAFER NO.

Additional Parameters

1

2

3

4

5

6

7

TiN layer thickness

89

132

158

149

158

166

107

(Å)

Deposition Rate

30

33

32

32

32

33

21

(Å/min)

Layer Resistivity

259

239

199

199

190

208

482

(μΩ-cm)

Discussion of Results from Deposition Runs

Titanium films have been deposited utilizing the parameters and apparatuses discussed above at rates ranging from 30 Å/min. measured by mass gain and by wave dispersive X-ray fluorescence (WDXRF). It has been found that the deposition rate is directly proportional to the deposition temperature and to the TiCl

4

partial pressure. Film resistivity increases from 120 to 150 μΩ-cm as the deposition temperature is decreased from 550° C. to 450° C. Titanium films deposited at 550° C. onto thermally grown oxide were analyzed by Rutherford Back Scatter Spectroscopy (RBS) and found to be elemental titanium. The only impurity that is detectable by RBS is oxygen. Auger Electron Spectroscopy (AES) depth profiling was performed to identify low level contamination. The AES profiles indicate a bulk chloride content of 0.1%. Chloride was also measured by WDXRF, which indicated a bulk concentration of 0.45%.

Films were also deposited at 550° C. onto non-deglazed silicon substrates. These films were analyzed by RBS and found to have formed a silicide during the deposition process. No post deposition anneal had been performed. The stoichiometry of the in-situ silicided titanium is TiSi

2

but 0.5% chloride was detected. AES depth profiling confirmed the stoichiometry of the in-situ silicide, as well as the bulk chlorine content of 0.5%. The AES profiles indicate a low level of oxygen in the silicide, but there is no evidence of an oxygen peak at the silicon TiSi

2

interface. This indicates that the native oxide has been removed by the CVD-Ti process.

Titanium films were deposited at 550° C. onto patterned borophospho-silicate glass (BPSG) in order to observe film conformality. All contacts were 1 μm to 0.35 μm (aspect ratios varied from 1.0 to 2.9). The titanium films were found to be conformal for all aspect ratios. Film thicknesses of up to 1500 Å were deposited and cross sections were observed by a scanning electron microscope (SEM). There was no evidence of overhang formation at the contact openings. Overhang formation is a fundamental problem with line of sight deposition processes such as sputtering. This problem has been well documented for both conventional and collimated sputtering, and the conformal nature of the CVD-Ti process represents a significant advantage over sputtering technology.

A comparison of the electrical properties obtained with CVD-Ti and sputtered-Ti was made using the electrical test structures described above. Contact resistance measurements were made using Kelvin structures with contact sizes which varied from 0.35 μm to 0.60 μm. In order to deposit 100 Å of titanium at the bottoms of the 0.35 μm contacts, 900 Å of sputtered-Ti was deposited compared to 200 Å of CVD-Ti. The CVD-Ti and sputtered-Ti films provided equivalent contact resistance for all contact sizes. However, the smaller contacts had a much higher probe yield with the CVD-Ti contact layer. For 0.35 μm contacts the yield for the CVD-TI contact layer was double that of the sputtered-Ti layer. The improvement in yield indicates that the CVD-Ti process provides more uniform and repeatable results over the surface of the wafer, and suggests that the process may overcome minor contact to contact variations that are created by the contact etch and contact cleaning processes. This assertion is supported by the AES results reported above which showed that no residual native oxide was detected at the silicon/TiSi

2

interface after CVD-Ti and in-situ silicidation.

A more severe comparison of the two contact layers was made using chains of 10,000 contacts. Again the results were similar for the larger contacts. However at 0.35 μm The CVD contact layer produced superior results. The CVD-Ti contact layer provides contact chain resistance values that are two orders of magnitude lower than those obtained with the sputtered-Ti layer. Furthermore, the probe yield for the CVD-TI layer was five times higher than that for the sputtered layer.

Leakage current measurements for CVD-Ti and sputtered-Ti were similar. This indicates that the in-situ silicidation provided by the CVD-Ti process does not cause junction damage. This is confirmed by SEM cross sections which were performed on the samples after completing the electrical measurements. The cross sections confirm that the silicide formed during the CVD-Ti process at the bottoms of the contacts is uniform.

In conclusion, titanium films have been deposited by chemical vapor deposition at temperatures of 450° C. to 550° C. The titanium is fully converted to TiSi

2

during the deposition process for depositions onto silicon surfaces. Depositions were conformal with no evidence of titanium overhangs at contact openings. Contact resistance and junction leakage measurements indicate that the CVD-Ti process provides equivalent electrical performance to sputtered-Ti for low aspect ratio features. For higher aspect ratio features the CVD-Ti process provides superior contact resistance and yield. The improvement in electrical performance is due to the conformal nature of the CVD-Ti, the removal of the residual native oxide from the contact bottom, and formation of a uniform TiSi

2

layer at the contact bottom.

FIG. 3

shows another embodiment of a deposition chamber with an upstream RF plasma source which might be utilized to generate the necessary radicals for an upstream plasma low temperature PECVD process utilizing a rotating susceptor as discussed and disclosed hereinabove with respect to the upstream plasma generation utilized by the configuration of FIG.

1

. Specifically, a deposition chamber

280

is attached to an RF plasma source

282

. A suitable source is a commercially available RF source available from Prototech Research, Inc., of Tempe, Ariz. RF plasma source

282

includes a housing

284

which forms a plasma generating region

286

therein. The plasma gases to be excited, such as H

2

, N

2

, and/or NH

3

are introduced through gas input lines

287

,

288

and gas rings

289

,

290

, respectively. Within region

286

, the plasma gases are excited by an RF field generated by RF coil

292

which is connected to an RF source

294

. RF energy of, for example, approximately 13.56 MHZ is delivered to the gases within region

286

to create a gas plasma containing free electrons, ions and radicals of the plasma gas. As the excited gases are drawn down the length of plasma-generating region

286

, gas particles combine until preferably an abundance of radicals remain. The radicals are drawn down through a deposition region

296

. The reactant gases, such as TiCl

4

, are introduced into the deposition region

296

by a vertically adjustable gas showerhead

298

, and the reactant gases and activated radicals are drawn down to substrate

300

by rotating susceptor

302

and combine to form a film layer on substrate

300

. The substrate

300

heated as discussed above and similar pressures, susceptor rotation rates and gas flow rates for the examples discussed above might be utilized with the RF plasma source of FIG.

3

. Accordingly, a film, such as a titanium-containing film, may be deposited at substantially lower temperatures than achieved with traditional thermal CVD processes.

While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, the low temperature CVD technique of the present invention may be utilized to deposit other films besides the titanium-containing films discussed in extensive detail herein. Furthermore, activated radicals of gases other than H

2

, N

2

and/or NH

3

might also be utilized to lower the deposition temperature. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicants' general inventive concept.

Number	Name	Date
4138306	Niwa	Feb 1979
4151325	Welch	Apr 1979
4178877	Kudo	Dec 1979
4282267	Kuyel	Aug 1981
4352834	Taketoshi et al.	Oct 1982
4365587	Hirose et al.	Dec 1982
4366208	Akai et al.	Dec 1982
4410758	Grolitzer	Oct 1983
4504518	Ovshinsky et al.	Mar 1985
4532199	Ueno et al.	Jul 1985
4535000	Gordon	Aug 1985
4557943	Rosler et al.	Dec 1985
4618542	Morita et al.	Oct 1986
4657774	Satou et al.	Apr 1987
4678679	Ovshinsky	Jul 1987
4689093	Ishihara et al.	Aug 1987
4702934	Ishihara et al.	Oct 1987
4716048	Ishihara et al.	Dec 1987
4717584	Aoki et al.	Jan 1988
4717585	Ishihara et al.	Jan 1988
4717586	Ishihara et al.	Jan 1988
4718976	Fujimura	Jan 1988
4726963	Ishihara et al.	Feb 1988
4728528	Ishihara et al.	Mar 1988
4759947	Ishihara et al.	Jul 1988
4772486	Ishihara et al.	Sep 1988
4774195	Beneking	Sep 1988
4778692	Ishihara et al.	Oct 1988
4784874	Ishihara et al.	Nov 1988
4792378	Rose et al.	Dec 1988
4798165	deBoer et al.	Jan 1989
4801468	Ishihara et al.	Jan 1989
4803093	Ishihara et al.	Feb 1989
4818560	Ishihara et al.	Apr 1989
4818563	Ishihara et al.	Apr 1989
4835005	Hirooka et al.	May 1989
4844950	Saitoh et al.	Jul 1989
4851302	Nakagawa et al.	Jul 1989
4853251	Ishihara et al.	Aug 1989
4854263	Chang et al.	Aug 1989
4869923	Yamazaki	Sep 1989
4869924	Ito	Sep 1989
4870030	Markunas et al.	Sep 1989
4876983	Fukuda et al.	Oct 1989
4885067	Doty	Dec 1989
4886683	Hoke et al.	Dec 1989
4888062	Nakagawa et al.	Dec 1989
4888088	Slomowitz	Dec 1989
4897709	Yokoyama et al.	Jan 1990
4898118	Murakami et al.	Feb 1990
4900694	Nakagawa	Feb 1990
4908329	Kanai et al.	Mar 1990
4908330	Arai et al.	Mar 1990
4913929	Moslehi et al.	Apr 1990
4914052	Kanai	Apr 1990
4926229	Nakagawa et al.	May 1990
4927786	Nishida	May 1990
4937094	Doehler et al.	Jun 1990
4946514	Nakagawa et al.	Aug 1990
4951602	Kanai	Aug 1990
4954397	Amada et al.	Sep 1990
4957772	Saitoh et al.	Sep 1990
4959106	Nakagawa et al.	Sep 1990
4971832	Arai et al.	Nov 1990
4977106	Smith	Dec 1990
4987856	Hey et al.	Jan 1991
4992305	Erbil	Feb 1991
4992839	Shirai	Feb 1991
4998503	Murakami et al.	Mar 1991
5000113	Wang et al.	Mar 1991
5002617	Kanai et al.	Mar 1991
5002618	Kanai et al.	Mar 1991
5002793	Arai	Mar 1991
5002796	Nishida	Mar 1991
5006180	Kanai et al.	Apr 1991
5007971	Kanai et al.	Apr 1991
5008726	Nakagawa et al.	Apr 1991
5010842	Oda et al.	Apr 1991
5017403	Pang et al.	May 1991
5018479	Markunas et al.	May 1991
5024706	Kanai et al.	Jun 1991
5028488	Nakagawa et al.	Jul 1991
5030475	Ackermann et al.	Jul 1991
5037666	Mori	Aug 1991
5039354	Nakagawa	Aug 1991
5052339	Vakerlis et al.	Oct 1991
5061511	Saitoh et al.	Oct 1991
5073232	Ohmi et al.	Dec 1991
5085885	Foley et al.	Feb 1992
5087542	Yamasaki et al.	Feb 1992
5093149	Doehler et al.	Mar 1992
5093150	Someno et al.	Mar 1992
5099790	Kawakami	Mar 1992
5100495	Ohmi et al.	Mar 1992
5122431	Kodama et al.	Jun 1992
5126169	Ishihara et al.	Jun 1992
5130170	Kanai et al.	Jul 1992
5139825	Gordon et al.	Aug 1992
5151296	Tokunaga	Sep 1992
5154135	Ishihara	Oct 1992
5173327	Sandhu et al.	Dec 1992
5175017	Kobayashi et al.	Dec 1992
5178904	Ishihara et al.	Jan 1993
5178905	Kanai et al.	Jan 1993
5180435	Markunas et al.	Jan 1993
5192370	Oda et al.	Mar 1993
5213997	Ishihara et al.	May 1993
5220181	Kanai et al.	Jun 1993
5246881	Sandhu et al.	Sep 1993
5252134	Stauffer	Oct 1993
5256455	Numasawa	Oct 1993
5260236	Petro et al.	Nov 1993
5268034	Vukelic	Dec 1993
5273588	Foster et al.	Dec 1993
5279857	Eichman et al.	Jan 1994
5296404	Akahori et al.	Mar 1994
5306699	Eddy	Apr 1994
5308655	Eichman et al.	May 1994
5318654	Maruyama et al.	Jun 1994
5342471	Fukasawa et al.	Aug 1994
5342652	Foster et al.	Aug 1994
5356476	Foster et al.	Oct 1994
5370739	Foster et al.	Dec 1994
5378501	Foster et al.	Jan 1995
5416045	Kauffman et al.	May 1995
5433787	Suzuki et al.	Jul 1995
5434110	Foster et al.	Jul 1995
5443647	Aucoin et al.	Aug 1995
5453124	Moslehi et al.	Sep 1995
5567243	Foster et al.	Oct 1996
5595606	Fujikawa et al.	Jan 1997
5610106	Foster et al.	Mar 1997
5628829	Foster et al.	May 1997
5647911	Vanell et al.	Jul 1997
5665640	Foster et al.	Sep 1997
5716870	Foster et al.	Feb 1998

Number	Date	Country
4016765	Nov 1991	DE
0254654	Jan 1988	EP
0359264	Mar 1990	EP
0545460 A2	Nov 1992	EP
2 181 458	Apr 1987	GB
2 192 196	Jan 1988	GB
2 245 600	Jan 1992	GB
53-91664	Aug 1978	JP
53-91663	Aug 1978	JP
60-116126	Jun 1985	JP
60-98629	Jun 1985	JP
60-204880	Oct 1985	JP
61-41763	Feb 1986	JP
63-187619	Aug 1988	JP
2085368	Mar 1990	JP
63-175003	Apr 1990	JP
2217475	Aug 1990	JP
3080537	Apr 1991	JP
61-58320	Jun 1994	JP
9004044	Apr 1990	WO
5-25722	Dec 1993	WO

Apparatus for producing thin films by low temperature plasma-enhanced chemical vapor deposition

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US Referenced Citations (136)

Foreign Referenced Citations (21)

Non-Patent Literature Citations (3)

Entry
M. R. Hilton et al., Composition, Morphology and Mechanical Properties of Plasma-Assisted Chemically Vapor-Deposited TiN Films on M2 Tool Steel, Thin Solid Fils, 139 (1986) 247-260.
Die-chi Sun et al., Formation of TiN on Si and SiO2 by Rapid Processing Using a Large Area Electron Beam, J. of Vacuum Science & Technology, 5 (1987) Sep./Oct., No. 5, 2nd Series, Woodbury, NY.
Nobumasa Suzuki et al., Planarized Deposition of High-Quality Silicon Dioxide Film by Photoassisted Plasma CVD, Jap. J. of Appl. Physics, 29 (1990) Dec., No. 12, Part 2, Tokyo, Japan.