Patent Application
20080241385
The present invention relates to a method of forming a thin film, a thin film forming apparatus, a program and a computer-readable information recording medium; and, more particularly, to a method of forming a thin film and a thin film forming apparatus for performing a film formation by alternately providing source gases, a program for making a computer perform the method, and a computer-readable information recording medium for storing the program.
Recently, as semiconductor integrated circuits are getting smaller and more highly integrated, metal wiring films and insulation films formed on a substrate (e.g., a semiconductor substrate) need to be thinner, of high-quality without impurities, uniform macroscopically through the entire wafer, and smooth microscopically in the nanometer range. However, conventional chemical vapor deposition methods cannot fulfill one or more of the needs described above. There is presented a film forming method fulfilling these needs by alternately providing plural kinds of source gases, forming a film in a size of an atomic or molecular level through adsorbing source gases onto a substrate surface, and repeatedly carrying out these processes to obtain a thin film with a predetermined thickness.
More specifically, a first source gas is provided onto a substrate to form thereon an adsorbed layer. Thereafter, a second source gas is provided onto the substrate to make it react with the adsorbed layer. In this method, the first source gas is first adsorbed onto the substrate and then reacts with the second gas, thereby making it possible to lower a film-forming temperature. In addition, in case of forming a film in a hole, the deterioration in the coverage property in the conventional CVD methods caused by the fact that the source gas is consumed in an upper portion of the hole can be avoided.
Further, the thickness of the adsorbed layer, which usually corresponds to a single layer of atoms or molecules or two or three layers thereof at most, is determined by the temperature and pressure thereof. Therefore, if the source gas is provided excessively, the excessive gas other than the molecules adsorbed onto the substrate is discharged due to the self limitation of the adsorption, thereby making it easier to control a thickness of an extremely thin film. Besides, since the formation of the film is performed only once in an atomic or molecular level, the reaction is likely to be completed and impurities seldom remain in the film, which is preferable.
Let us see a case where a TiN film is formed by the above-described method. In the case of forming a TiN film, titanium tetrachloride (TiCl4) and ammonia (NH3) are used as source gases.
A TiN film can be formed on a substrate by processing TiCl4 and NH3, for example, at a substrate temperature of 250-550° C. and a total pressure of 15-400 Pa.
However, since TiCl4 is a thermally stable material, it is difficult to make it be adsorbed onto the substrate. When a thermally stable source gas, which is hard to be decomposed, is employed, an adsorbed amount of the gas onto the substrate surface is reduced so that the film-forming rate becomes unfavorably decreased.
The present invention is developed to overcome the aforementioned problems by providing a method for forming a film and a film forming apparatus capable of rapidly forming a high-quality thin film.
In overcoming the aforementioned problems, the present invention is characterized by providing the following process or method.
Specifically, the invention described in claim 1 provides a method of forming a thin film, comprising:
a first step of providing a source gas including an element serving as a source material of the thin film to be formed into a processing chamber to make the source gas be adsorbed onto a substrate or onto molecules of the source gas adsorbed on the substrate; and
a second step of providing the processing chamber with one or more kinds of reactive gases for reacting with the source gas to form the thin film and making the source gas react with the reactive gases to form a thin film layer,
wherein the thin film is formed by repeatedly performing the first step and the second step, and the method of forming the thin film further comprises:
a third step of changing the source gas into a state easy to be adsorbed onto the substrate before the source gas is adsorbed onto the substrate.
The invention described in claim 2 provides the method of claim 1, wherein, at the third step, the source gas is changed into the state easy to be adsorbed onto the substrate by activating the source gas.
The invention described in claim 3 provides the method of claim 1, wherein, at the third step, the source gas is reduced by means of a reduction gas.
The invention described in claim 4 provides the method of one of claims 1 to 3, wherein the source gas is made of metal halide or metal alkoxide.
The invention described in claim 5 provides the method of claim 3 or 4, wherein the source gas is made of titanium tetrachloride, the reactive gas is made of ammonia, and the reduction gas is made of hydrogen.
The invention described in claim 6 provides a thin film forming apparatus, comprising:
a first providing device for providing a source gas including an element serving as a source material of the thin film to be formed into a processing chamber; and
a second providing device for providing one or more kinds of reactive gases for reacting with the source gas to form the thin film into the processing chamber,
wherein the thin film is formed by repeatedly performing the step of providing the source gas by means of the first providing device and the step of providing the reactive gases by means of the second providing device, and the thin film forming apparatus further comprises:
a third providing device for providing a reduction gas into the processing chamber, wherein the reduction gas is provided into the processing chamber before or while the source gas is provided into the processing chamber.
The invention described in claim 7 provides the apparatus of claim 6, wherein the source gas is metal halide or metal alkoxide.
The invention described in claim 8 provides the apparatus of claim 6 or 7, wherein the source gas is titanium tetrachloride, the reactive gas is ammonia, and the reduction gas is hydrogen.
In accordance with the present invention, a source gas is rendered easy to be adsorbed onto a substrate before being adsorbed thereon, so that the rate at which the source gas is adsorbed onto the substrate is enhanced, and an adsorption density of the source gas increases to make it possible to form a uniform film.
Other features and effects of the present invention will become apparent from the following description of preferred embodiments, given in conjunction with the accompanying drawings.
Hereinafter, an embodiment of the present invention will be described together with the drawings.
The gas supply sources 10A-10E provide source gases described later and the like into the processing chamber 30 via gas passages 11-15. That is, the gas supply sources 10A-10E respectively provide a semiconductor wafer W in the processing chamber 30 with gases for performing a predetermined film forming process.
The thin film forming apparatus in accordance with the embodiment forms a titan nitride (TiN) film by using a chemical vapor deposition method. To be more specific, in this embodiment, a TiN film is formed by a reaction between a titanium tetrachloride (TiCl4) gas serving as a source gas and an ammonia (NH3) gas serving as a reactive gas. Further, as will be described later, in this embodiment, it is configured such that a hydrogen (H2) gas is also provided into the processing chamber 30 as a reduction gas.
The gas supply source 10A provides the TiCl4 gas into the processing chamber 30 via the gas passage 11. In the gas passage 11 is installed a valve V1, and thus the flow of the TiCl4 gas can be controlled by opening/closing of the valve V1. In addition, the temperature in the gas passage 11 can be controlled such that it can be heated to be kept at a predetermined temperature, for example, 120° C. Furthermore, the operation of the valve V1 is controlled by the controller 60 described later.
The gas supply source 10B provides the NH3 gas into the processing chamber 30 via the gas passage 12. In the gas passage 12 is installed a valve V2, and thus the flow of the NH3 gas can be controlled by opening/closing of the valve V2. In addition, the operation of the valve V2 can be also controlled by the controller 60 described later.
Further, the gas supply source 10C provides the H2 gas serving as a reducer into the processing chamber 30 via the gas passage 13. A valve V3 is installed in the gas passage 13 in such a way that it communicates with the gas passage 11 connected to the gas supply source 10A. The flow of the H2 gas can be controlled by opening/closing of the valve V3. In addition, the operation of the valve V3 can be also controlled by the controller 60 described later.
The gas supply sources 10E and 10D provide a helium (He) gas, which is an inert gas, as a carrier gas. The gas supply source 10E is connected to the gas passage 11 via the gas passage 15.
In the gas passage 15 is installed a valve V5 controlled by the controller 60. Further, the gas supply source 10D is connected to the gas passage 12 via the gas passage 14. In the gas passage 14 is installed a valve V4 controlled by the controller 60.
The processing chamber 30 is formed of metal such as aluminum (Al) or stainless steel, and, in case of using Al, a surface treatment such as an alumite treatment is performed. The processing chamber 30 includes a susceptor 33 which supports the wafer W that is an object to be processed, wherein the susceptor 33 is made of ceramic material such as AlN or Al2O3 and has a heater 33A buried therein. The susceptor 33 is fixed on a bottom portion of the processing chamber 30 by susceptor supporting components 31 and 32.
On the bottom portion of the processing chamber 30 is installed a gas exhaust port 34 connected to a gas exhaust line 35. In addition, to the gas exhaust line 35 is connected a turbo molecular pump 37 serving as an exhausting device which is configured such that the inside of the processing chamber can be vacuum pumped. Furthermore, in the gas exhaust line 35 is installed an APC (auto pressure control unit) 36 for controlling pressure in the processing chamber 30 by changing a conductance thereof.
Besides, on a side portion of the processing chamber 30 is installed a pressure gauge 38 for measuring pressure in the processing chamber. It is configured such that the pressure measurement obtained by the pressure gauge 38 is sent to the controller 60. In other words, it is configured such that, by feedbacking the pressure measurement obtained by the pressure gauge 38 to the controller 60, the controller 60 can adjust the conductance of the APC 36 to control the pressure in the processing chamber 30 to be kept at a desired value.
Further, on an upper portion of the processing chamber 30 is installed a shower head 40 having a diffusion area 40A. To the diffusion area 40A is connected the gas passages 11 and 12.
The controller 60, which includes a computer, is connected to the respective valves V1 to V5. The controller 60 controls the opening/closing of the respective valves V12-V5 in accordance with a film-forming process program described later, thereby making it possible to fabricate a high-quality TiN film.
Furthermore, besides the valves V1-V5, the controller 60 also controls devices included in the thin film forming apparatus (e.g., the valve 36 and the vacuum pump 37). However, in the following, the description will be given mainly about the valves V1-V5, which are main parts of this embodiment.
In the following, a method of forming a TiN film, which is performed by using the thin film forming apparatus shown in
For forming a TiN film, firstly at step 10 (“step” is abbreviated as “S” in the drawings), the wafer W is mounted on the susceptor 33. The susceptor 33 is heated by the heater 35 to thereby heat the wafer W mounted thereon. In this embodiment, the wafer W can be heated to be kept at a temperature in the range of 250-550° C. (step 12).
Thereafter, the controller 60 opens the valve V4 and V5 (at a timing t1 in
It is configured such that the temperature of the susceptor 33 and the pressure in the processing chamber 30 are detected by respective sensors, which are not shown, and then the measurement results are sent to the controller 60. In addition, if it is judged that the temperature of the wafer W and the pressure in the processing chamber 30 have been reached predetermined levels, the controller 60 opens the valve V1 and the valve V3 at step 16 (at a timing t2).
Thus, the TiCl4 gas, together with the He gas serving as the carrier gas, is provided from the gas supply source 10A to the processing chamber 30 via the gas passage 11. Further, since the valve V3 is opened together with the valve V1 as described above, the H2 gas serving as a reduction gas is provided from the gas supply source 10C to the processing chamber 30 together with the TiCl4 gas serving as a source gas.
The TiCl4 gas and the H2 gas are provided to the processing chamber 30 during a predetermined period of time (a period of time designated by an arrow T1 in
However, since the TiCl4 gas is a thermally stable material as described above, it is difficult to decompose it by only applying a thermal process. Because of this, as described above, in case where only the TiCl4 gas in a stable state is provided into the processing chamber 30, the adsorbed amount on the wafer W is small, and thus the film-forming rate of the TiN film is low.
In contrast, in this embodiment, the TiCl4 gas serving as a source gas is provided to the processing chamber 30 together with the H2 gas serving as the reduction gas. As a result, TiCl4 reacts with H2 so that, by a reduction of the TiCl4, state transitions are taken place as described by Eqs. 1 and 2.
2TiCl4+H2→(TiCl3)++2HCl Eq. (1)
TiCl4+H2→(TiCl2)+++2HCl Eq. (2)
As seen above, by the reduction of TiCl4, a monovalent ion (TiCl3)+ or a bivalent ion (TiCl2)++ is formed. Since (TiCl3)+ and (TiCl2)++ are activated by ionization, an adsorptive force onto the wafer W is higher compared to the case of using TiCl4.
Here, let us observe the composition ratio of each of TiCl4, (TiCl3)+ and (TiCl2)++.
In the conventional method of forming a thin film where the reducer (H2 gas) is not used, the most abundant is TiCl4, which has a high thermal stability so that it cannot be easily adsorbed onto the wafer W. On the other hand, the composition ratios of (TiCl3)+ and (TiCl2)++, which can be easily adsorbed to the wafer W, are low. To be more specific, the respective composition ratios of TiCl4, (TiCl3)+ and (TiCl2)++ are such that [TiCl4]>[(TiCl3)+]>[(TiCl2)++].
On the contrary, in this embodiment, the TiCl4 gas is provided into the processing chamber 30 together with the H2 gas serving as the reducer, thereby resulting in the reduction reactions described in Eqs. (1) and (2) to generate in a large amount (TiCl3)+ and (TiCl2)++ having a strong adsorptive force onto the wafer W compared to TiCl4. To be more specific, the respective composition ratios of TiCl4, (TiCl3)+ and (TiCl2)++ are such that [(TiCl3)+]>[(TiCl2)++]>[TiCl4].
As described above, in this embodiment, the TiCl4 gas, which is the source gas, is provided to the processing chamber 30 together with the H2 gas, which is the reduction gas, so that the processing chamber contains a large amount of (TiCl3)+ and (TiCl2)++, each having a strong adsorptive force onto the wafer W. Therefore, (TiCl3)+ and (TiCl2)++ become adsorbed onto the entire surface of the wafer W in a short time.
Further here, let us observe the respective volumes per molecule of TiCl4, (TiCl3)+ and (TiCl2)++. TiCl4 has a structure where four Cl atoms are attached to a single Ti atom, (TiCl3)+ has a structure where a single chlorine atom is detached from TiCl4, and (TiCl2)++ has a structure where two chlorine atoms are detached from TiCl4. As a result, TiCl4 occupies the greatest volume and the volume of each molecule is in the order of TiCl4, (TiCl3)+ and (TiCl2)++.
In the conventional method, materials adsorbed onto the wafer W were mostly TiCl4 which occupies a large volume so that the number of TiCl4 adsorbed onto the wafer (i.e., the number of Ti atoms) tended to be small. On the contrary, in this embodiment, (TiCl3)+ and (TiCl2)++ which have smaller volumes compared with TiCl4, become adsorbed onto the wafer W so that adsorption density of the molecules gets high, thereby increasing the number of (TiCl3)+ and (TiCl2)++ adsorbed onto the wafer (i.e., the number of Ti atoms) compared to the conventional case.
As shown therein, it can be seen that the range where the adsorbed amount is a in this embodiment (the range designated by an arrow A in the drawing) is wider than the range where the adsorbed amount is a in the conventional method (the range designated by an arrow B in the drawing), i.e., A>B. This is because, in this embodiment, (TiCl3)+ and (TiCl2)++ respectively having stronger adsorptive forces than TiCl4 are adsorbed onto the wafer W in a large amount so that, even if the pressure in the processing chamber 30 changes, the adsorptions of preferable quantity can take place over a wide range of pressure.
As described above, since the adsorption of good quantity can be performed over a wide range of pressure in this embodiment, it is possible to carry out a process of forming a uniform film. In the following, the reason thereof will be explained.
As shown in
If the range B where adsorption of good quantity can be performed is narrow as in the conventional case (see
On the contrary, in this embodiment, the range A where the adsorption of good quantity can be performed is wide such that the resulting differences in the adsorbed amount can be curbed even when there may be some differences in the pressure on the wafer W.
Back to
Thereby, the H2 gas serving as the reducer and the unadsorbed part of the TiCl4 gas remaining in the processing chamber are exhausted from the processing chamber 30 (step 20). This exhausting process is carried out, e.g., for two seconds (the period of time Tp1 designated by arrows). After this period of time has elapsed, the controller 60 reverses the opening of the valve 36 to its original position.
After the exhausting process of step 20 has been completed, the controller 60 opens the valve V2 (at a timing t4). Accordingly, the NH3 gas is provided into the processing chamber 30 from the gas supply source 10B via the gas passage 12 (step 22).
At this time, the materials to be adsorbed (mainly (TiCl3)+ and (TiCl2)++) are uniformly adsorbed onto the wafer W through the processes of step 16 and step 18. Further, there is no residue of TiCl4 left in the processing chamber 30 after performing the process of step 20. Because of this, the adsorbed materials (mainly (TiCl3)+ and (TiCl2)++) adsorbed onto the wafer W rapidly reacts with the NH3 gas (nitridation).
The supply of the NH3 gas into the processing chamber 30 is carried out for a predetermined period of time (the period of time designated by an arrow T2 in
During this period of time, the adsorbed materials (mainly (TiCl3)+ and (TiCl2)++) adsorbed onto the wafer W react with the supplied NH3 gas to form a TiN film. Herein, since thus formed thin TiN film is formed by the nitridation of the adsorbed materials adsorbed during step 16 and step 18 (mainly (TiCl3)+ and (TiCl2)++), it is a thin film of thickness in a molecular/atomic level.
Thereafter, the controller 60 opens the valve in the APC 36 further to increase the pumping force of the vacuum pump 42 again. Thus, the unreacted part of the NH3 gas remaining in the processing chamber 30 is exhausted from the processing chamber 30 (step 26). This exhausting process is carried out, for example, for two seconds (the period of time Tp2 designated by arrows in
Afterwards, the controller 60 performs step 28 to reverse the process back to step 16, and then the processes from step 16 to step 26 are carried out repeatedly for a predetermined number of times (e.g., 200 times). In the second or subsequent turn of step 16 and step 18, the materials to be adsorbed (mainly (TiCl3)+ and (TiCl2)++) are adsorbed onto the TiN film, which is formed as a lower layer.
Also in the second or subsequent turn of step 16 and step 18, TiCl4, which is the source gas, is provided into the processing chamber 30 together with H2 serving as the reducer so that, even in the second or subsequent process for adsorption, the materials mainly adsorbed are (TiCl3)+ and (TiCl2)++, which have respectively stronger adsorptive forces and smaller volumes than TiCl4.
Therefore, the adsorption density and adsorption rate of the adsorbed materials (mainly (TiCl3)+ and (TiCl2)++) are higher than those of TiCl4. As a result, even in the second or subsequent turn, the adsorbed materials (mainly (TiCl3)+ and (TiCl2)++) are adsorbed onto the wafer W (more particularly, on the TiN film which forms the lower layer) rapidly and uniformly.
After the TiN film of a desired thickness has been formed by performing the processes from step 16 to step 26 repeatedly for a predetermined number of times, the process moves on to step 30. The controller 60, at step 30, closes the valves V4 and V5 to stop the He gas (carrier gas) being supplied from the gas supply sources 10D and 10E into the processing chamber 30.
Subsequently, the wafer having a TiN film formed thereon is taken out. By performing the series of the processes as described above, a preferable TiN film can be formed on the wafer W rapidly.
Further, the film thickness uniformity of the TiN film is represented by a standard deviation (the unit is per cent). To be more specific, it is obtained by measuring the film thickness of the TiN film formed on the wafer W, whose diameter is 200 mm, at a number of points, computing the square values of the deviations from the mean film thickness at the measured points, dividing the added amount of these square values at all the points by the number of measurements, and then calculating the square root thereof. Therefore, a smaller value of the film thickness uniformity 1σ represents a more uniform state.
Furthermore, as comparative examples,
Observing the growth rate of the TiN film, we can see that it is the highest (0.060 nm/cycle) in case where the reducer (H2 gas) for this embodiment is provided into the processing chamber 30 together with TiCl4. Further, observing the film thickness uniformity 1σ in the TiN film, we can see that it is the lowest (4.9%) and therefore the TiN film has the most uniform thickness in case where the reducer (H2 gas) for this embodiment is provided into the processing chamber 30 together with TiCl4. The results shown in
In the above embodiment, it has been described as to the case where the present invention is applied to the method of forming a TiN film by causing a reaction between TiCl4 (the source gas) and NH3 (the reactive gas). However, the present invention is not limited thereto but applicable to various kinds of film-formings. Further, although He has been used as the carrier gas in this embodiment, Ar or N2 can be used in lieu of this. Still further, the exhausting process of step 20 and step 26 in this embodiment shown in
Furthermore, the controller shown in
Besides, various kinds of embodiments can be implemented within the scope disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-057665 | Mar 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/02243 | 2/26/2004 | WO | 00 | 5/7/2007 |
