Patent Application
20210054501
Tis application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-149953, filed on Aug. 19, 2019, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a film forming method and a film forming apparatus.
In a semiconductor manufacturing process, a film forming process of forming a silicon nitride (SiN) film on a semiconductor wafer (hereinafter referred to as a “wafer”) as a substrate may be performed. There may be a case where films having different incubation times, which will be described later, are exposed on the surface of the wafer. Even in that case, it is required to form the SiN film to have a highly uniform film thickness in each in-plane portion of the wafer. Patent Document 1 discloses supplying and adsorbing ammonia (NH3) onto a wafer having a silicon (Si) film and a silicon oxide (SiO2) film exposed on the surface thereof, and then nitriding the films by exposing the wafer to plasma of an argon (Ar) gas. Patent Document 1 further discloses that, after nitriding the films, a silicon-containing source gas and a plasmarized NH3 gas are alternately supplied to the wafer to form a silicon nitride (SiN) film.
Patent Document 1: Japanese laid-open publication No. 2017-175106
A film forming method according to the present disclosure is a method of forming a silicon nitride film on a substrate including a first film and a second film formed on a surface of the substrate, wherein the first film and the second film have different required incubation times until growth of the silicon nitride film starts when a source gas containing silicon and a first nitriding gas for nitriding the silicon are supplied. The method includes: supplying a plasmarized hydrogen gas to the substrate; supplying a processing gas formed of silicon halide to the substrate; forming a thin layer of silicon covering the first film and the second film by alternately and repeatedly performing the supplying the plasmarized hydrogen gas and the supplying the processing gas; forming a thin layer of silicon nitride by supplying a second nitriding gas for nitriding the thin layer of silicon to the substrate; and forming the silicon nitride film on the thin layer of the silicon nitride by supplying the source gas and the first nitriding gas to the substrate.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.
Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments.
An outline of a film forming method according to an embodiment of the present disclosure will be described first. In this embodiment, a process of forming a SiN film is performed on a wafer B having a silicon (Si) film, a silicon oxide (SiO2) film, and a tungsten (W) film as a metal film, exposed on the surface thereof. Since tungsten (W) is easily oxidized, the process is performed in a state in which oxygen atoms are present on the surface of the W film.
Here, an incubation time of a SiN film will be described. The incubation time of the SiN film is a time required, when forming a SiN film by supplying a silicon-containing source gas and a nitriding gas for nitriding silicon, until formation of the SiN film starts after starting the supply of one of the above-mentioned gases. More specifically, by supplying the source gas and the nitriding gas, a plurality of island-shaped SiN nuclei are formed in a base film of the SiN film. As the nuclei of SiN spread and grow along the surface of the base film, the nuclei of SiN come into contact with one another to form a thin layer. Then, the thin layer grows as the SiN film (a film thickness increases). Accordingly, a timing at which the growth of the film is started is the timing at which the SiN thin layer is formed. The time required for the formation and growth of the nuclei varies depending on a type of a film, which serves as the base film of the SiN film and is in contact with the SiN film.
The expression “respective films have different SiN film incubation times” means that, in forming SiN films in contact with the respective films by supplying a source gas and a nitriding gas to the respective films under the same condition, times from the start of supplying the gases to the formation of the above-mentioned thin layer differ from one another. Additionally, it means that as a result of comparison without performing processes other than adsorbing the source gas and nitriding silicon in the source gas by using the nitriding gas, the times until the thin layers are formed differ from one another. That is to say, the comparison is performed without performing a reduction process or a modification process using hydrogen plasma, which are processes performed in the present embodiment. In addition, the nitriding gas referred to herein also includes a plasmarized nitriding gas in addition to a non-plasmarized nitriding gas.
When the source gas and the nitriding gas are supplied to respective base films having different incubation times as described above, due to the difference in the incubation times, variations may occur in the thicknesses of SiN films formed to be in contact with the respective base films. A W film, a SiO2 film, and a Si film formed on the wafer B of the present embodiment have different SiN film incubation times. Specifically, when the W film and the SiO2 film are referred to as a first film and the Si film is referred to as a second film, the incubation time of the first film is longer than the incubation time of the second film.
Therefore, in the present embodiment, a preprocessing is performed to suppress influence of the difference in the incubation times and to make the thicknesses of the SiN films uniform. As the preprocessing, first, a hexachlorodisilane (Si2Cl6) gas and a plasmarized hydrogen (H2) gas are alternately and repeatedly supplied to the wafer B to form a thin Si layer covering the above-mentioned films, and the thin Si layer is nitrided to form a thin SiN layer. For reasons to be described later, the nitriding process is performed by supplying a plasmarized NH3 gas (second nitriding gas) to the wafer B.
In addition, after performing the preprocessing, an atomic layer deposition (ALD) process using a Si2Clf gas and a plasmarized NH3 gas (first nitriding gas) is performed to form a SiN film on the thin SiN layer. Hereinafter, hexachlorodisilane (Si2Cl6) may also be referred to as HCD. As described above, the HCD gas is a processing gas for performing the preprocessing, and is also a source gas for forming the SiN film. Further, in the present specification, silicon nitride is referred to as SiN regardless of a stoichiometric ratio thereof. Accordingly, the expression “SiN” includes, for example, Si:N4. Furthermore, the base film includes the wafer B itself, in addition to the film formed on the wafer B. Accordingly, for example, the above-mentioned Si film may be a film formed on a silicon wafer or the silicon wafer itself.
Hereinafter, a film forming apparatus 1, which is an embodiment of an apparatus for carrying out the above-described film forming method, will be described with reference to the vertical cross-sectional view of
Six circular recesses 14 are formed in a top surface of the rotary table 12 along the circumferential direction (rotation direction) of the rotary table 12, and the wafer B is accommodated in each recess 14. That is to say, each wafer B is mounted on the rotary table 12 so as to rotate by the rotation of the rotary table 12. In addition, reference numeral 15 in
Above the rotary table 12, a shower head 2, a plasma forming unit 3A, a plasma forming unit 3B, and a plasma forming unit 3C are provided in this order along the rotation direction of the rotary table 12 towards a downstream side in the rotation direction. The shower head 2, which is a first gas supplier, supplies an HCD gas used for the SiN film formation and the preprocessing to the wafer B. The plasma forming units 3A to 3C, which are a second gas supplier, are units for plasmarizing a plasma forming gas supplied onto the rotary table 12 to perform a plasma processing on the wafers B. Each of the plasma forming units 3A to 3C is configured to independently form plasma of a H2 gas alone and plasma of a NH3 gas and a H2 gas. In addition, below the outside of the rotary table 12 in the vacuum container 11 and outside the second plasma forming unit 3B, an exhaust port 51 for exhausting plasma forming gases supplied by the plasma forming units 3A to 3C is opened. A vacuum exhaust mechanism 50 is connected to the exhaust port 51.
The shower head 2, which is a processing gas supplier and a source gas supplier, will be described with reference to a vertical cross-sectional view of
The fan-shaped region 24 is divided into three zones 24A, 24B, and 24C from the center side of the rotary table 12 towards the peripheral side of the rotary table 12. The shower head 2 is provided with gas flow paths 25A, 25B, and 25C partitioned from one another such that the HCD gas can be independently supplied to the gas ejection ports 21 provided in respective zones 24A, 24B, and 24C. The upstream side of each of the gas flow paths 25A, 25B, 25C is connected to an HCD gas source 26 via a pipe, and a gas supply device 27 including a valve and amass flow controller is provided in each pipe. By the gas supply device 27, supply and cutoff of the HCD to the downstream side of the pipe and flow rate adjustment of the HCD are performed. In addition, each gas supply device (described later) other than the gas supply device 27 is also configured in the same manner as the gas supply device 27, and performs supply and cut off of a gas to the downstream side and flow rate adjustment of the gas.
The exhaust port 22 and the purge gas ejection port 23 are annularly opened in the peripheral edge portion of the bottom surface of the shower head 2 so as to face the top surface of the rotary table 12 while surrounding the fan-shaped region 24. The purge gas ejection port 23 is located outward of the purge gas ejection port so as to surround the exhaust port 22. A region inward of the exhaust port 22 on the rotary table 12 forms an adsorption region R0 in which HCD is adsorbed to the wafer B. The purge gas ejection port 23 ejects, for example, an Ar (argon) gas as a purge gas onto the rotary table 12.
During the ejection of the HCD gas from the gas ejection ports 21, exhaust from the exhaust port 22 and ejection of the purge gas from the purge gas ejection port 23 are both performed. Thus, as illustrated by arrows in
Next, the plasma forming unit 3B will be described with reference to
The dielectric plate 32 is formed in a substantially fan shape that is widened from the center side of rotary table 12 towards the peripheral side in a plan view. The ceiling plate 11B of the vacuum container 11 has a substantially fan-shaped through hole corresponding to the shape of the dielectric plate 32, and the inner peripheral surface of a lower end portion of the through hole slightly protrudes towards the center of the through hole to form a support 34. The dielectric plate 32 closes the fan-shaped through-hole from above and faces the rotary table 12, and a peripheral edge portion of the dielectric plate 32 is supported on the support 34.
The waveguide 33 is provided on the dielectric plate 32, and includes an inner space 35 extending above the ceiling plate 11B. In the drawings, reference numeral 36 denotes a slot plate constituting a bottom side of the waveguide 33. The slot plate 36 has a plurality of slot holes 36A formed therein and is provided to be in contact with the dielectric plate 32. An end portion of the waveguide 33 on the center side of the rotary table 12 is closed, and a microwave generator 37 configured to supply microwaves of, for example, about 2.35 GHz to the waveguide 33 is connected to an end portion of the waveguide 33 on the peripheral side of the rotary table 12. The microwaves pass through the slot holes 36A in the slot plate 36, reach the dielectric plate 32, and are supplied to the plasma forming gas supplied below the dielectric plate 32. Thus, plasma is formed below the dielectric plate 32 in a restricted manner, and the wafer B is processed. As described above, a region below the dielectric plate 32 is configured as a plasma forming region, and is indicated as R2.
Further, the plasma forming unit 3B includes a gas ejection hole 41 and a gas ejection hole 42, which are formed in the support 34. The gas ejection hole 41 ejects the plasma forming gas from the center side of the rotary table 12 towards the outer peripheral side thereof, and the gas ejection hole 42 ejects the plasma forming gas from the outer peripheral side of the rotary table 12 towards the center side thereof. Each of the gas ejection hole 41 and the gas ejection hole 42 is connected to a H2 gas source 43 and a NH3 gas source 44 via a piping system including gas supply devices 45. In addition, the plasma forming units 3A and 3C are configured similarly to the plasma forming unit 3B, and regions corresponding to the plasma forming region R2 in the plasma forming units 3A and 3C are indicated as plasma forming regions R1 and R3, respectively. The plasma forming regions R1 to R3 area second region, and the plasma forming units 3A to 3C form a hydrogen gas supplier and a nitriding gas supplier.
As illustrated in
Hereinafter, the preprocessing and the SiN film forming process performed by the film forming apparatus 1 will be described with reference to
Six wafers B illustrated in
By the plasma forming units 3A to 3C, the H2 gas and the microwaves are supplied to the plasma forming regions R1 to R3 respectively, and plasma of the H2 gas is formed in each of the plasma forming regions R1 to R3. Meanwhile, in the shower head 2, the HCD gas is ejected from the gas ejection ports 21 and the Ar gas is ejected from the purge gas ejection port 23, and exhaust is performed from the exhaust port 22 (step S1 in
Subsequently, the wafer B is located in the adsorption region R0, and the HCD molecules 73 are supplied to the reduced surface of the SiO2 film 64 (see
Although the changes in the surface of the SiO2 film 64 has been described, similarly to the SiO2 film 64, O atoms 72 on the surface of the SiO2 film 62 are also removed and Si atoms 71 are adsorbed to the surface of the SiO2 film 62. In addition, since the surface of the Si film 61 is composed of Si atoms 71, the HCD molecules 73 are easily adsorbed thereto. Thus, similarly to the SiO2 films 62 and 64, Si atoms 71 contained in the HCD molecules 73 are adsorbed to the Si film 61. Similar to the SiO2 films 62 and 64, the W film 63 is presumed to have a relatively large amount of HCD molecules 73 adsorbed to the surface of the W film 63 by the reduction and activation of the surface of the W film 63 by H radicals. That is to say, the Si atoms 71 are efficiently adsorbed on the surface of each of the Si film 61, the SiO2 films 62 and 64, and the W film 63. When the wafer B continues to rotate and the wafer B repeatedly moves between the adsorption region R0 and the plasma forming regions R1 to R3, the adsorption of the Si atoms 71 progresses, and thus a thin layer 66 of Si is formed to cover the entire surface of the wafer B (see
After the supply of the HCD gas from the shower head 2 and the formation of the H2 plasma by the plasma forming units 3A to 3C are started, when the rotary table 12 is rotated a preset number of times, for example, 30 times, the supply of the HCD gas from the shower head 2 is stopped. While the supply of the HCD gas is stopped as described above, the H2 gas and the NH3 gas are supplied to the plasma forming regions R1 to R3, and plasma of these gases is formed (step S2 in
When the rotary table 12 is rotated a preset number of times from the start of the plasma formation of the H2 gas and the NH3 gas, the supply of the HCD gas from the shower head 2 to the adsorption region R0 restarts. Further, in the plasma forming regions R1 and R2, while the supply of the NH3 gas is stopped, the H2 gas is continuously supplied and the plasma of the H2 gas is formed. In the plasma forming region R3, the H2 gas and the NH3 gas are continuously supplied, and the plasma of these gases is formed (step S3 in
Then, the wafer B continues to rotate, and the supply of the HCD gas in the adsorption region R0, the supply of the plasmarized H2 gas in the plasma forming regions R1 and R2, and the supply of the plasmarized H2 gas and NH3 gas in the plasma forming region R3 are sequentially repeated. The Si in the HCD gas adsorbed on the wafer B in the adsorption region R0 is nitrided in the plasma forming region R3 to form SiN. Then, in the plasma forming regions R1 and R2, the deposited SiN is modified by the plasma of the H2 gas. Specifically, H is bonded to dangling bonds in SiN and Cl is removed from the deposited SiN. Thus, the SiN becomes dense and has a low content of impurities.
The formation and growth of SiN nuclei occur as described above, and since the base is the thin layer 67 formed of SiN, which is the same material as that of the nuclei, the nuclei are formed and grown relatively quickly. In addition, the thin layer 67 of SiN is formed commonly on the Si film 61, the SiO2 films 62 and 64, and the W film 63, and the surface conditions of these films are made uniform. Therefore, the formation and growth of the nuclei occur similarly on the Si film 61, the SiO2 films 62 and 64, and the W film 63, and a thin layer of SiN (a SiN film 68) is formed. That is, the SiN film 68 is formed on the Si film 61, the SiO2 films 62 and 64, and the W film 63, as if the incubation times of the Si film 61, the SiO2 films 62 and 64, and the W film 63 are uniform (see
As the rotation of the wafer B continues, the thickness of the SiN film 68 increases, and modification of the SiN film 68 proceeds. Since the SiN film 68 starts to be formed on the Si film 61, the SiO2 films 62 and 64, and the W film 63 at the same timing as described above, the SiN film 68 grows with a highly uniform thickness among these films. After the supply of the HCD gas and the plasma formation of the gases in the plasma forming regions R1 to R3 in step S3 are started, when the rotary table 12 is rotated a preset number of times to form the SiN film 68 having a desired thickness, a process of forming the SiN film 68 is completed (see
As described above, according to the process using the film forming apparatus 1, the influence of the difference in the incubation times of the SiN film 68 among the Si film 61, the SiO2 films 62 and 64, and the W film 63 is suppressed. Thus, it is possible to make the timing at which film formation is started uniform. As a result, it is possible to form the SiN film 68 so as to have a highly uniform thickness on each of the films.
In addition, since the thin layer 67 of SiN generated from the thin layer 66 of Si and the SiN film 68 are formed by different methods, the thin layer 67 of SiN and the SiN film 68 may be different from each other in terms of film quality. Thus, when the thickness of the thin layer 66 of Si becomes too large, the characteristics of a product manufactured from the wafer B may be affected. Therefore, in some embodiments, a thickness H1 of the thin layer 66 of Si (see
The nitridation of the thin layer 66 of Si formed in step S1 described above may be performed using plasma of a N2 gas. However, in order to make the film quality of the thin layer 67 of SiN generated from the thin layer 66 equal to the film quality of the SiN film 68, the thin layer 66 of Si may be nitrided using plasma of a NH3 gas as described above. In addition, the thin layer 66 of Si may be nitrided by supplying a non-plasmarized N2 gas or NH3 gas. As described above, the nitridation of the thin layer 66 of Si is not limited to using plasma of a NH3 gas.
Further, the formation of the SiN film 68 after the formation of the thin layer 67 of SiN is not limited to being performed using an ALD method, and may be performed using a chemical vapor deposition (CVD) method. In forming the SiN film 68, it is sufficient to nitride silicon in the source gas. Thus, the formation of the SiN film 68 is not limited to using the plasmarized NH3 gas, and, for example, a non-plasmarized NH3 gas may be used.
In addition, the formation of the thin layer 66 of Si is not limited to using an HCD gas, and a gas composed of silicon chloride such as a dichlorosilane (DCS) gas may be used. Alternatively, the thin layer 66 of Si may be formed using a silicon halide gas composed of halogen other than chlorine, such as iodine. However, as described above, an HCD gas may be used in some embodiments, because a large amount of Si is contained in one molecule and thus a large amount of Si can be efficiently adsorbed to the wafer B. Further, in the exemplary process described above, the same HCD gas is used as the processing gas for forming the thin layer 66 of Si and as the silicon-containing source gas for forming the SiN film 68. However, the processing gas and the source gas may be different from each other. For example, an HCD gas may be used as the processing gas and a DCS gas may be used as the source gas.
In the exemplary process described above, a SiN film is formed on the W film 63 as a metal film. However, the metal film is not limited to the W film 63, and the present disclosure is effective even when forming the SiN film 68 on a metal film formed of, for example, titanium (Ti) or nickel (Ni). That is, the metal film serving as the base of the SiN film is not limited to the W film. It should be understood that the embodiments disclosed herein are examples in all respects and are not restrictive. The above-described embodiments may be omitted, replaced, or modified in various forms without departing from the scope and spirit of the appended claims.
Hereinafter, evaluation tests performed in relation to the present technology will be described.
As Evaluation Test 1, plural sheets of wafers, each of which is formed of Si and has a bare surface (hereinafter, referred to as bare wafers), and plural sheets of wafers, each of which is formed of Si and has a SiO2 film formed on the surface thereof (hereinafter, referred to as SiO2 wafers) were prepared. Then, a series of processes (the preprocessing and the process of forming the SiN film 68) including steps S1 to S3 described in the embodiments described above were performed on each of the bare wafers and the SiO2 wafers. A processing time for forming the SiN film 68 in step S3 in the series of processes was set to 180 seconds or 360 seconds. After completion of the series of processes, thicknesses of the formed SiN films 68 were measured.
In addition, as Comparative Test 1, instead of performing the process of step S1 described above, a process of nitriding the surfaces of the bare wafers and the SiO2 wafers was performed by supplying a N2 gas to the plasma forming regions R1 to R3 and plasmarizing the N2 gas. After the nitriding process, the above-described step S2 and step S3 were performed on each of the wafers. However, instead of an HCD gas, a DCS gas was used as the source gas in step S3. Except for the above-described differences, the processes of Comparative Test 1 were the same as those of Evaluation Test 1.
The graph of
In Evaluation Test 1, in both cases of setting the film forming time of the SiN film 68 to 180 seconds and 360 seconds, almost no difference was observed in the thicknesses of the SiN film 68 between the SiO2 wafers and the bare wafers. Further, the incubation time with respect to the SiO2 wafers was 9.8 seconds, and the incubation time with respect to the bare wafers was also about 9.8 seconds. In addition, when the film forming time was 9.8 seconds, a difference in the film thickness (a thickness of the SiN film 68 formed on the bare wafers—a thickness of the SiN film 68 formed on the SiO2 wafers) was −0.6 angstrom, i.e., approximately 0 angstrom. That is, it was confirmed that, in both cases of the SiO2 wafers or the bare wafers, the formation of the SiN film 68 started when about 9.8 seconds elapsed after the start of step S3.
In contrast, in Comparative Test 1, in both cases of setting the film forming time of the SiN film 68 to 180 seconds and 360 seconds, a relatively large difference in the thicknesses of the SiN film 68 was observed between the SiO2 wafers and the bare wafers. In addition, the incubation time with respect to the SiO2 wafers was about 0 seconds, but with respect to the bare wafers, the thickness of the SiN film 68 was 13.2 angstrom when the film forming time was 0 seconds. The reason that the SiN film 68 was already formed at the film forming time of 0 seconds can be considered to be that the surfaces of the bare wafers were nitrided to form SiN by being exposed to the plasma of the N2 gas. From the results of Evaluation Test 1 and Comparative Test 1 as described above, it was confirmed that it is possible to make the film thickness uniform between the Si film and the SiO2 film according to the method described in the above-described embodiments.
As Evaluation Test 2, the processes including the above-described steps S1 to S3 were performed on the bare wafers and the SiO2 wafers as in Evaluation Test 1, and the thicknesses of the SiN films 68 were obtained. Then, as described with reference to
As Comparative Test 2-1, the bare wafers and the SiO2 wafers were processed by performing only step S3 without performing the preprocessing of steps S1 and S2. As Comparative Test 2-2, without performing steps S1 and S2, step S3 was performed after supplying an HCD gas from the shower head 2 to the rotating bare wafers and SiO2 wafers. As Comparative Test 2-3, without performing steps S1 and S2, plasma of a H2 gas was formed in the plasma forming regions R1 to R3 to expose the rotating bare wafers and SiO2 wafers to the plasma of the H2 gas, and then step S3 was performed. Except for the above-described differences, the same processes in Evaluation Test 2 were performed in Comparative Tests 2-1 to 2-3. As in Evaluation Test 2, the incubation time was obtained and the difference in film thickness was calculated with respect to the wafers processed in the Comparative Tests 2-1 to 2-3.
The graph of
As shown in the graph, in Comparative Tests 2-1 to 2-3, the difference in incubation time and the difference in film thickness between the Si wafers and the SiO2 wafers were larger than those in Evaluation Test 2. Therefore, it is considered that the processes described in the above embodiments are effective for reducing the difference in incubation time and the difference in film thickness. In addition, from the results of Evaluation Test 2 and Comparative Tests 2-2 and 2-3, it is considered that a sufficient effect cannot be obtained when only one of supplying an HCD and supplying plasma of a H2 gas is performed, and that it is necessary to perform both of these processes as in step S1 of the embodiments in order to obtain a sufficient effect.
According to the present disclosure, in forming a silicon nitride film on a substrate having a first film and a second film exposed on the surface thereof, it is possible to make a film thickness of the silicon nitride film formed on the first film and the second film uniform.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-149953 | Aug 2019 | JP | national |
