Patent Application
20050109276
1. Field of the Invention
Embodiments of the present invention generally relate to substrate processing. More particularly, the invention relates to chemical vapor deposition chambers and processes.
2. Background of the Invention
Thermal chemical vapor deposited (CVD) films are used to form layers of materials within integrated circuits. Thermal CVD films are used as insulators, diffusion sources, diffusion and implantation masks, spacers, and final passivation layers. The films are often deposited in chambers that are designed with specific heat and mass transfer properties to optimize the deposition of a physically and chemically uniform film across the surface of a multiple circuit carrier such as a substrate. The chambers are often part of a larger integrated tool to manufacture multiple components on the substrate surface. The chambers are designed to process one substrate at a time or to process multiple substrates.
As device geometries shrink to enable faster integrated circuits, it is desirable to reduce thermal budgets of deposited films while satisfying increasing demands for high productivity, novel film properties, and low foreign matter. Historically, thermal CVD was performed at temperatures of 700° C. or higher in a batch furnace where deposition occurs in low pressure conditions over a period of a few hours. Lower thermal budget can be achieved by lowering deposition temperature that requires the use of low temperature precursors or reducing deposition time. Thermal CVD processes are sensitive to temperature variations if operating under reaction rate control or to flow non-uniformities if operating under mass transport control, or both if operating under a mix of reaction rate and mass transfer control. Effective chamber designs require precise control of temperature variations and adequately distributed flow to encourage deposition of uniform films on the substrate. Processing chamber and exhaust hardware design are inspected based on properties of precursors and reaction by-products.
The present invention is a CVD chamber that provides uniform heat distribution, uniform distribution of process chemicals, efficient precursor delivery, and efficient residue and exhaust management by changing the mechanical design of a single wafer thermal CVD chamber. The improvements include a processing chamber comprising a chamber body and a chamber lid defining a processing region, a substrate support disposed in the processing region, a gas delivery system mounted on a chamber lid comprising an adapter ring and two blocker plates that define a gas mixing region, and a face plate fastened to the adapter ring, a heating element positioned to heat the adapter ring to a desired temperature, and a temperature controlled exhaust system.
The improvements also include a method for depositing a silicon nitride layer or a carbon doped or carbon containing silicon nitride layer on a substrate, comprising vaporizing bistertiarybutylamino silane (BTBAS) or other silicon precursors, flowing the bistertiarybutylamino silane into a processing chamber, flowing ammonia and/or another nitrogen precursor into a processing chamber, combining the two reactants in a mixer in the chamber lid, having an additional mixing region defined by an adapter ring and at least two blocker plates, heating the adapter ring, and flowing the bistertiarybutylamino silane through a gas distribution plate into a processing region above a substrate. The improvements reduce defects across the surface of the substrate and improve product yield.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Embodiments of the invention provide an apparatus for depositing a layer on a substrate and a method for depositing the layer on a substrate. The hardware discussion including illustrative figures of an embodiment is presented first. An explanation of process modifications and test results follows the hardware discussion.
A substrate support 111 supports the substrate and may provide heat to the chamber. In addition to the substrate support, the base of the chamber may contain a substrate support assembly, a reflector plate or other mechanism tailored to facilitate heat transfer, probes to measure chamber conditions, an exhaust assembly, and other equipment to support the substrate and to control the chamber environment.
Feed gas may enter the chamber through a gas delivery system after passing through a mixer 113 in the lid 110 and holes (not shown) in a first blocker plate 104. The feed gas is gaseous which may include vapors of liquids and gases. The gas then travels through a mixing region 102 created between a first blocker plate 104 and a second blocker plate 105. The second blocker plate 105 is structurally supported by an adapter ring 103. After the gas passes through holes (not shown) in the second blocker plate 105, the gas flows through a face plate 108 and then enters the main processing region defined by the chamber walls 106, the face plate 108, and the substrate support 111. The gas then exits the chamber through the exhaust plate 109. The lid 110 may further include gas feed inlets, a gas mixer, a plasma source, and one or more gas distribution assemblies. Optionally, the chamber may include an insert piece 101 between the chamber walls 106 and the lid 110 that is heated to provide heat to the adaptor ring 103 to heat the mixing region 102 and the face plate 108. Another hardware option illustrated by
The lid assembly includes an initial gas inlet 213 to premix the feed gases and parts to form a space 202 defined by the lid 209, the thermal break elements 212, the heater jacket 203, and the blocker plates 204 and 205. The space 202 provides increased residence time for the reactant gases to mix before entering the substrate processing portion of the chamber. Heat that may be applied by the heater 210 to the surfaces that define the space 202 helps prevent the buildup of raw materials, condensates, and by-products along the surfaces of the space. The heated surfaces also preheat the reactant gases to facilitate better heat and mass transfer once the gases exit the face plate 208 and enter the substrate processing portion of the chamber.
Within the processing portion of the chamber below the face plate 108, 208, heat distribution is controlled by supplying heat to surfaces such as the face plate, the walls of the chamber, the exhaust plate, and the substrate support. Heat distribution is also controlled by the design of the exhaust plate, the optional insertion of an exhaust plate cover, and the optional insertion of a slit valve liner. Chemical distribution within the processing portion of the chamber is influenced by the design of the face plate and the exhaust plate and the optional exhaust plate cover. Plasma cleaning is also improved when there is a substantial space between the gas inlet in the lid and the face plate and when the face plate is heated.
The second blocker plate 105 and the face plate 108 are heated to prevent chemical deposition on the surface of the blocker plate, preheat the gases in the chamber, and reduce heat loss to the lid. The adaptor ring 103 that attaches the second blocker plate and the face plate to the lid helps thermally isolate the second blocker plate and the face plate from the lid. For example, the lid may be maintained at a temperature of about 30-70° C., while the second blocker plate and the face plate may be maintained at a temperature of about 100-350° C. The adapter ring may be designed with uneven thickness to restrict heat loss to the lid, acting like a thermal choke. The thermal separation of the second blocker plate and the face plate from the lid protects the second blocker plate and the face plate from the temperature variations that may be present across the surface of the lid. Thus, the second blocker plate and the face plate are less likely to heat the lid than conventional chambers and can be maintained at a higher temperature than blocker plates and face plates of conventional chambers. The more uniform gas heating provided by the second blocker plate and the face plate results in a more uniform film deposition on a substrate in the chamber. Typically, the second blocker plate and the face plate are heated to a temperature of about 100 to 350° C. or greater, such as between about 150 to 300° C. One observed advantage of a higher temperature second blocker plate and face plate is a higher film deposition rate in the chamber. It is believed that a higher temperature for the second blocker plate and face plate may enhance deposition rates by accelerating the dissociation of the precursors in the chamber. Another advantage of a higher second blocker plate and face plate temperature is a reduction of deposition of CVD reaction byproducts on the second blocker plate and face plate.
The exhaust system also contributes to heat and chemical distribution in the chamber. The pumping plate 109 may be configured with unevenly distributed openings to compensate for heat distribution problems created by the slit valve. The pumping plate may be made of a material that retains heat provided to the processing portion of the chamber by the substrate support assembly to prevent exhaust chemical and by-product deposition on the surface of the plate. The pumping plate features multiple slits placed strategically to also compensate for the slit valve emissivity distortion. The exhaust system helps maintain a pressure of 10 to 350 Torr in the chamber. The exhaust system controls the pressure using throttle valves and isolation valves. These valves may be heated to a desired temperature to prevent by-product and unused gas and vapor residue formation.
The substrate support assembly 111 has several design mechanisms to enable uniform film distribution. The support surface that contacts the substrate may feature multiple zones for heat transfer to distribute variable heat across the radius of the substrate. For example, the substrate support assembly may include a dual zone ceramic heater that may be maintained at a process temperature of 500-800° C., for example 600-700° C. The substrate temperature is typically about 20-30° C. cooler than the measured heater temperature. The support may be rotated to compensate for heat and chemical variability across the interior of the processing portion of the chamber. The support may feature horizontal, vertical, or rotational motion within the chamber to manually or mechanically center the substrate within the chamber.
The surfaces of the processing chamber and its components may be made of anodized aluminum. The anodized aluminum discourages condensation and solid material deposition. The anodized aluminum is better at retaining heat than many substances, so the surface of the material remains warm and thus discourages condensation or product deposition. The material is also less likely to encourage chemical reactions that would result in solid deposition than many conventional chamber surfaces. The lid, walls, spacer pieces, blocker plates, face plate, substrate support assembly, slit valve, slit valve liner, and exhaust assembly may all be coated with or formed of solid anodized aluminum.
Diluent or carrier gas provides another mechanism for tailoring film properties. Nitrogen or helium is used individually or in combination. Hydrogen or argon may also be used. Heavier gas helps distribute heat in the chamber. Lighter gas helps vaporize the precursor liquids before they are added to the chamber. Sufficient dilution of the process gases also helps prevent condensation or solid deposition on the chamber surfaces and in the exhaust system surfaces.
A repeatability test was performed. The film layer thickness for a film deposited in a conventional chamber and a modified chamber that features the additional and/or modified components described above were compared. Significant improvements in wafer uniformity were observed with the modified chamber.
Examples of films that may be deposited in the CVD chambers described herein are provided below. The overall flow rate of gas into the chambers may be 200 to 20,000 sccm and typical processes may have a flow rate of 4,000 sccm. The film composition, specifically the ratio of nitrogen to silicon content, refractive index, wet etch rate, hydrogen content, and stress of any of the films presented herein may be modified by adjusting several parameters. These parameters include the total flow rates, spacing within the chamber, and heating time. The pressure of the system may be adjusted from 10 to 350 Torr and the concentration ratio of NH3 to BTBAS may be adjusted from 0 to 100.
Silicon Nitride Films
Silicon nitride films may be chemical vapor deposited in the chambers described herein by reaction of a silicon precursor with a nitrogen precursor. Silicon precursors that may be used include dichlorosilane (DCS), hexachlorodisilane (HCD), bistertiary butylaminosilane (BTBAS), silane (SiH4), disilane (Si2H6), and many others. Nitrogen precursors that may be used include ammonia (NH3), hydrazine (N2H4), and others. For example, SiH4 and NH3 chemistry may be used.
In the CVD processing chamber, SiH4 dissociates into SiH3, SiH2 primarily, and possibly SiH. NH3 dissociates into NH2, NH, and H2. These intermediates react to form SiH2NH2 or SiH3NH2 or similar amino-silane precursors that diffuse through the gas boundary layer and react at or very near the substrate surface to form a silicon nitride film. It is believed that the warmer chamber surfaces provide heat to the chamber that increases NH2 reactivity. The increased volume of the space between the gas inlet in the lid of the chamber and the second blocker plate increases the feed gas residence time and increases the probability of forming desired amino-silane precursors. The increased amount of the formed precursors reduces the probability of pattern micro-loading, i.e. the depletion of the precursors in densely patterned areas of the substrate.
It was also found that increasing the NH3 flow rate relative to the flow rate of the other precursors enhanced the deposition of films. For example, conventional systems may operate with flow rates of NH3 to SiH4 in a ratio of 60 to 1. Test results indicate a conventional ratio of 60 to 1 to 1000 to 1 provides a uniform film when spacing between the lid and the second blocker plate is increased. It was further found that using a spacing of 750-850 mils between the face plate and the substrate enhanced the film uniformity compared to films deposited at 650 mils.
Carbon Doped Silicon Nitride Films
In one embodiment, BTBAS may be used as a silicon containing precursor for deposition of carbon doped silicon nitride films in the chambers described herein. The following is one mechanism that it may follow to produce a carbon doped silicon nitride film with t-butylamine by-products. The BTBAS may then react with the t-butylamine to form isobutylene.
3C8H22N2Si+NH3=>Si3N4+NH2C4H9
Four example conditions are elucidated. Pressure, temperature, spacing, flow rate, and other conditions are shown in Table 1. Column 1 shows a set of operating conditions at lower BTBAS concentration than the other examples. Column 2 shows operation at low temperature and wet etch ratio. Column 5 shows the lowest wet etch ratio and temperature and column 6 shows operating parameters for the combination of highest deposition rate and the lowest pattern loading effect of the four examples. In the examples, the wafer heater temperature was 675 to 700° C. and the pressure of the chamber was 50 to 275 Torr.
The BTBAS reaction to form the carbon doped silicon nitride film may be reaction rate limited, not mass transfer limited. Films formed on a patterned substrate may uniformly coat the exposed surfaces of the patterned substrate. BTBAS may have less pattern loading effect (PLE) than the conventional silicon precursors, for example SiH4. Table 1 shows the sidewall PLE for BTBAS and NH3 chemistry is less than 5%, compared to more than 15% for a SiH4 and NH3 process in the same chamber. It is believed that the pattern loading effect experienced with some silicon containing precursors is due to the mass transfer limitations of the reactions between those precursors, for example SiH4 with NH3.
Using BTBAS as a reactant gas also allows carbon content tuning. That is, by selecting operating parameters such as pressure and nitrogen containing precursor gas concentration, the carbon content of the resulting film may be modified to produce a film with the desired carbon content and more uniform carbon concentration across the diameter of a substrate. BTBAS may be added to the system at a rate of 0.05 to 2.0 g/min and typical systems may use 0.3-0.6 g/min. Table 2 provides flow rates, concentration, and resulting film properties for three configurations.
The C 5-6% and C 12-13% configurations based on designed experiment data analysis are predicted values. The C 10.5% value is an experimental result. VR indicates the voltage ratio of the outer to inner zones of the dual zone ceramic heater used as the heat source susceptor for the silicon substrate. RI indicates the refractive index. WERR is the wet etch rate ratio of the nitride film relative to that of a thermally grown silicon oxide film used as reference.
Table 3 gives an element by element composition of samples taken from various points across a substrate for different process conditions. The element composition of the samples was measured by nuclear reaction analysis and Rutherford backscattering spectroscopy.
Table 3 illustrates that the variation in carbon content across the surface of the substrate was 0.895%. It was found that carbon doped silicon nitride films having from 2 to 18 atomic percentage carbon were deposited at enhanced rates in the chambers described herein.
Using BTBAS as the silicon containing precursor offers several resulting film property advantages. Increasing the carbon content of the film can improve the dopant retention and junction profile, resulting in improved performance in the positive channel metal oxide semiconductor (PMOS) part of the device. The process parameters may also be tailored when combined with the use of BTBAS to facilitate improved stress profile. Enhanced film stress improves the device performance for the negative channel metal oxide semiconductor (NMOS) part to of the device. Film stress properties are influenced by tailoring the chamber pressure, total feed gas flow, the NH3 and BTBAS feed gas ratio, and the volume fraction of BTBAS.
Additional experimental results indicate that at 675° C. the standard deviation for film non-uniformity was less than 1.5 percent. The standard deviation of the composition of the film non-uniformity over a temperature range of 645 to 675° C. was less than 1.5 percent as well. The particle contamination was less than 30 particles at greater than or equal to 0.12 μm.
The wet etch ratio is lower when low concentration NH3 and low pressure are selected. The pressure range tested was 50 to 275 Torr. The wet etch ratio was measured as less than 0.3. The wet etch ratio of the film was calculated by comparing the film etch to a thermal oxide with 100:1 HF. RMS roughness at 400 Å was measured to be 0.25 nm.
The film deposition rate over 625 to 675° C. was 125 to 425 Å. The deposition rate was higher when higher concentration of BTBAS, lower NH3 concentration, and higher pressure and temperature were selected.
The hydrogen concentration of the film was less than 15 atomic percent. It is estimated that the hydrogen is mostly bonded within the film as N—H. The carbon content of the film was 2 to 18 atomic percent.
The observed stress was 1 E9 to 2 E10 dynes/cm2 (0.1 to 2 GPa) for an enhanced NMOS I-drive. The stress was higher with high concentrations of NH3, low concentration of BTBAS, and low pressure.
The measured refractive index over the same temperature range was 1.75 to 1.95. The refractive index was higher when the system was operated at lower pressure and lower BTBAS concentration.
Also, the observed or estimated carbon concentration ranged from 2 to 18 percent. It was highest when the NH3 concentration was low and the concentration of BTBAS was high.
Table 1 results may be compared to conventional and similar systems. The wet etch rate ratio test results in Table 1 may be compared to silicon nitride films deposited in conventional furnace systems which have a one minute dip in 100:1 HF. The stress test results of Table 3 are similar to other test results for similar operating conditions that have results of 0.1 to 2.0 GPa.
Typically, nitrogen is used as both the carrier gas from the gas source for BTBAS as well as the diluent gas for the thermal CVD reaction. Using hydrogen as the diluent gas results in increasing the deposition rate of the BTBAS and NH3 thermal CVD reaction by up to 30%. Using germane doped in hydrogen as the diluent gas may also increase the deposition rate even further.
While a precursor like BTBAS acts as a source of both silicon and carbon, it is possible to combine a silicon precursor such as silane, disilane, hexachlorodisilane, and dichlorosilane with a carbon precursor such as ethylene, butylenes, and other alkenes or other carbon sources and react the two precursors with NH3 in a single wafer thermal CVD chamber to form a carbon doped silicon nitride film.
Carbon Doped Silicon Oxide Films
BTBAS also offers some process chemistry flexibility. For BTBAS based oxide processes, NH3 can be substituted by an oxidizer such as N2O. Thermal CVD in the hardware described in this invention can be used to deposit oxide films.
While a precursor like BTBAS acts as a source of both silicon and carbon, it is possible to combine a silicon precursor such as silane, disilane, hexachlorodisilane, and dichlorosilane with a carbon precursor such as ethylene, butylenes, and other alkenes or other carbon sources and react the two precursors with N2O in a single wafer thermal CVD chamber to form a carbon doped silicon oxide film.
Carbon Doped Silicon Oxide Nitride Films
In general, carbon doped or carbon containing silicon oxide nitride films can be deposited using a combination of silicon containing precursors, carbon containing precursors, oxygen containing precursors, and nitrogen containing precursors. These films have potential use in future generation devices to enable dielectric constant control in addition to carbon content control. Such low-k thermally deposited CVD films can be of potential benefit in devices.
To manufacture a carbon doped or carbon containing silicon oxide-nitride film, BTBAS may be used with NH3 and an oxidizer such as N2O. Thermal CVD in the hardware described in this invention can be used to deposit oxide nitride films.
While a precursor like BTBAS acts as a source of both silicon and carbon, it is possible to combine a silicon precursor such as silane, disilane, hexachlorodisilane, and dichlorosilane with a carbon precursor such as ethylene, butylenes, and other alkenes or other carbon sources and react the two precursors with both NH3 and N2O in a single wafer thermal CVD chamber to form a carbon doped silicon oxide nitride film.
Many commonly used low-k precursors such as trimethylsilane and tetramethyl silane contain silicon, oxygen, and carbon. These precursors can be reacted with a nitrogen source such as NH3 to form carbon doped silicon oxide nitride films in a single wafer thermal CVD chamber.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 60/525,241, filed Nov. 25, 2003, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60525241 | Nov 2003 | US |
