Thin film deposition process based on vertical LPCVD (Low Pressure Chemical Vapor Deposition) equipment

Abstract

The invention discloses a thin film deposition process based on vertical LPCVD (Low Pressure Chemical Vapor Deposition) equipment, which comprises the following steps of: checking whether gas leakage is qualified or not, introducing nitrogen for purging, introducing a reaction gas source, carrying out first thin film deposition on the surface of a wafer, introducing nitrogen for purging, increasing the temperature of a process pipe, introducing the reaction gas source, and carrying out second thin film deposition on the surface of the wafer, and nitrogen is introduced for purging, the pressure is increased to normal pressure, and the boat is discharged. According to the thin film deposition process, the process pipe is purged, and the temperature and the pressure intensity of the process pipe are optimized, so that the wafer boat sticking problem of the vertical LPCVD equipment can be effectively improved, the productivity of the vertical LPCVD equipment can be improved, the pollution risk can be reduced, and particularly, the deposition requirement of an amorphous silicon thin film with the thickness larger than or equal to 1000 nm is met. The method can solve the problem of adhesion by running a process once, has the advantages of simplicity in operation, wide application range and the like, and is high in use value and good in application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor device manufacturing, and relates to a thin film deposition process based on a vertical LPCVD device. BACKGROUND

[0002] In the process of semiconductor device manufacturing, thin film deposition process is an essential key process. Taking amorphous silicon thin film as an example, it plays multiple roles in the process of semiconductor device manufacturing, such as serving as a shielding layer, a mask layer, etc. Compared with PECVD thin film deposition method, LPCVD method has the advantages of good step coverage, high density, small surface damage and low batch production cost, and becomes the first choice in power device manufacturing.

[0003] In the batch production process, due to the large difference in the thermal expansion coefficient of amorphous silicon and silicon dioxide, the bearing material is usually made of silicon carbide. Although silicon carbide has the advantages of small thermal expansion coefficient, small deformation and long service life, it has high requirements for the purity of the material due to high process temperature, and high-purity silicon carbide boats are heavily dependent on imports, with a delivery cycle of more than 15 months, which makes it difficult to meet the actual production needs. To solve this technical bottleneck, high-purity quartz boats are generally used in existing vertical LPCVD devices instead of silicon carbide boats. At the same time, in the production process of vertical LPCVD equipment based on quartz boats, when depositing amorphous / polycrystalline silicon thin films with high thickness, the wafer is easily stuck to the quartz boat, and the quartz boat is also easily stuck to the quartz base. To solve this material bottleneck, the existing technology usually performs two repeated deposition processes, that is, after the first deposition process is completed, the wafer is taken off the boat, and then the wafer transfer and deposition process are repeated. This method separates the wafer from the boat by mechanical transmission, although there is no sticking problem in the second deposition, but it greatly reduces the effective productivity of the machine and increases the possibility of particle contamination, especially when the film thickness is high, the mechanical transmission method is also easy to damage the wafer, which is not conducive to improving the yield of the wafer.

[0004] Therefore, it is of great significance to obtain a simple and widely applicable thin film deposition process based on a vertical LPCVD device to improve the wafer sticking problem of the vertical LPCVD device and promote the wide application of the vertical LPCVD device in the process of semiconductor device manufacturing. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a simple and widely applicable thin film deposition process based on a vertical LPCVD device.

[0006] To solve the above technical problems, the present application adopts the following technical solutions: A thin film deposition process based on a vertical LPCVD equipment includes the following steps: S1. Check if the process pipes of the vertical LPCVD equipment are leaking air; S2. After the leakage rate of the process pipe passes the test, nitrogen is introduced to purge the gas pipeline. S3. Introduce the reaction gas source to perform the first thin film deposition on the wafer surface; S4. After the first thin film deposition is completed, nitrogen gas is introduced to purge the process tube, the boat, and the wafer; S5. Increase the temperature of the process tube and introduce a reactive gas source to perform a second thin film deposition on the wafer surface; the pressure of the process tube during the second thin film deposition process is greater than that during the first thin film deposition. S6. After the second thin film deposition is completed, nitrogen gas is introduced to purge the process tube, the crystal boat and the wafer, the pressure is increased to atmospheric pressure and the wafer is unloaded from the boat.

[0007] In a further improvement to the above-mentioned thin film deposition process, in step S5, the temperature of the process tube during the second thin film deposition process is 10°C to 20°C higher than that during the first thin film deposition; after the process tube reaches the target temperature, the holding time is ≥10 min.

[0008] In a further improvement to the above-mentioned thin film deposition process, in step S5, the pressure in the process tube during the second thin film deposition process is 5 Pa to 15 Pa higher than that during the first thin film deposition.

[0009] In a further improvement to the above-mentioned thin film deposition process, in step S5, the reaction gas source is SiH4; the flow rate of the reaction gas source is 500 sccm to 600 sccm; the process parameters in the second thin film deposition process are: temperature 555℃ to 565℃, pressure 45 Pa to 50 Pa; and the thickness of the thin film is controlled to be 300 nm to 600 nm in the second thin film deposition process.

[0010] In a further improvement to the above-mentioned thin film deposition process, in step S2, if the vacuum leakage rate of the process tube is ≤1.0 Pa / min, it indicates that the leakage rate of the process tube is qualified.

[0011] In a further improvement to the above-mentioned thin film deposition process, in step S2, the flow rate of nitrogen is 2 slm to 5 slm; the process temperature during the purging process is 540℃ to 550℃; and the purging time is 20 min to 30 min.

[0012] In a further improvement to the above-mentioned thin film deposition process, in step S3, the reaction gas source is SiH4; the flow rate of the reaction gas source is 500 sccm to 600 sccm; the process parameters during the first thin film deposition process are: temperature 540℃ to 550℃, pressure 35 Pa to 45 Pa; and the thickness of the thin film is controlled to be 500 nm to 800 nm during the first thin film deposition process.

[0013] In a further improvement to the above-mentioned thin film deposition process, in step S4, the flow rate of nitrogen is 10 slm to 20 slm; and the purging time is ≥20 min.

[0014] In a further improvement to the above-mentioned thin film deposition process, in step S6, the flow rate of nitrogen is 2 slm to 5 slm, and the purging time is 20 min to 40 min.

[0015] Compared with the prior art, the advantages of the present invention are as follows: In view of the shortcomings of existing thin film deposition processes, such as low throughput, high pollution risk, low yield, and difficulty in improving wafer sticking to the boat, this invention creatively provides a thin film deposition process based on a vertical LPCVD equipment. By purging the process tube and optimizing the temperature and pressure of the process tube, the following unexpected technical effects can be achieved: (1) After completing the first thin film deposition process, the temperature is kept constant, and the process tube, the boat, and the wafer are purged with a large flow of nitrogen. By changing the airflow field, the wafer is slightly moved on the boat, which helps to reduce the adhesion of the wafer to the boat. At the same time, the surface deposited film at the contact position between the wafer and the boat is made unique by isothermal recrystallization. (1) Self-crystallization and re-shrinkage effectively reduce adhesion; (2) Before the second thin film deposition process, the process tube temperature is increased. During the heating process, the surface deposited film at the contact position between the wafer and the boat achieves second-stage crystallization and re-shrinkage; (3) During the second thin film deposition process, by increasing the process pressure, the deposition rate of the film will be increased, which not only increases the roughness of the amorphous film, but also changes the interface state characteristics of the film surface, thereby changing the surface properties of the two deposited films; (4) During the second thin film deposition process, by increasing the process temperature, the volume ratio of amorphous and microcrystalline states in the amorphous silicon film will be changed, and the surface properties of the two deposited films will also be further changed. Under the combined effect of the above aspects, the adhesion between the wafer and the boat can be effectively reduced, thereby effectively solving the problem of wafer sticking to the boat. In particular, in the process method of the present invention, there is no need to separate the wafer from the boat through mechanical transfer, which can not only effectively prevent wafer damage, but also effectively increase the film deposition rate, and ultimately improve the yield of the wafer while increasing the production capacity. Compared with conventional thin film deposition processes, this invention, based on a vertical LPCVD equipment, effectively improves the wafer boat adhesion problem in vertical LPCVD equipment by purging the process tube and optimizing its temperature and pressure. It also increases the equipment's throughput. Taking a 1000nm thickness as an example, the hourly throughput (WPH) of the equipment using this method can be increased to approximately 1.8 times that of the original two-stage repetitive deposition method. Simultaneously, it reduces contamination risks. In particular, for amorphous silicon thin film deposition requirements of thickness ≥1000nm, the adhesion problem can be solved with a single process run. It boasts advantages such as simple operation, wide applicability, high practical value, and promising application prospects. Attached Figure Description

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the thin film deposition process based on a vertical LPCVD equipment in Embodiment 1 of the present invention. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 A thin film deposition process based on a vertical LPCVD equipment, specifically, using a vertical LPCVD equipment to prepare amorphous silicon thin films, such as... Figure 1 As shown, it includes the following steps: S1. Check if the process pipe of the vertical LPCVD equipment is leaking. Specifically, heat the temperature to 540℃, close all valves in the air inlet circuit, and evacuate to the lowest possible pressure. If the pressure value is ≤5Pa, close the angle valve in the exhaust pipe. If the vacuum leakage rate of the process pipe is ≤1.0Pa / min after 3 minutes, it means that the leakage rate of the process pipe is qualified.

[0020] S2. After the leakage rate of the process pipe passes the test, nitrogen gas is introduced at a flow rate of 4 slm to purge the gas pipeline for 25 minutes.

[0021] In step S2, in other embodiments, the flow rate of nitrogen gas can also be 2 slm, 3 slm, or 5 slm, and the purging time can also be 20 min, 23 min, 26 min, 28 min, or 30 min.

[0022] S3. Heat to 545℃, set the pressure of the process tube to 35Pa, and introduce a reaction gas source, which is SiH4 with a flow rate of 600sccm. Perform the first thin film deposition on the wafer surface to obtain a first amorphous silicon thin film with a thickness of 600 nm.

[0023] S4. After the first thin film deposition is completed, nitrogen gas is introduced at a flow rate of 15 slm to purge the process tube, the boat, and the wafer for 25 minutes.

[0024] S5. Increase the process tube temperature to 560℃. After the temperature stabilizes, introduce nitrogen gas at a flow rate of 15 slm and continue to purge the process tube, the boat, and the wafer for 10 minutes. Set the pressure of the process tube to 45 Pa. Introduce a reaction gas source, which is SiH4, at a flow rate of 600 sccm. Perform a second thin film deposition on the wafer surface to obtain a second amorphous silicon thin film with a thickness of 400 nm.

[0025] The pressure in the process tube during the second film deposition process is greater than that during the first film deposition process.

[0026] S6. After the second thin film deposition is completed, nitrogen gas is introduced at a flow rate of 5 slm to purge the process tube, the boat, and the wafer for 25 minutes. The pressure is then increased to atmospheric pressure, and the wafer is removed from the boat.

[0027] In this embodiment, the two-step deposition process flow is shown in Table 1 below.

[0028] Table 1. Process parameters used in each step of Example 1

[0029] In Example 1, after multiple reproducible process verifications, no adhesion between the wafer and the quartz boat was observed during wafer removal. This demonstrates that the adhesion problem can be solved by running the process only once in this invention. Furthermore, compared to conventional thin film deposition processes, Example 1 increases the hourly throughput (WPH) by 1.8 times.

[0030] Comparative Example 1 A thin film deposition process based on a vertical LPCVD equipment is basically the same as that in Example 1, except that in Comparative Example 1, the pressure of the process tube during the second thin film deposition process is the same as that during the first thin film deposition, which is 45 Pa.

[0031] In Comparative Example 1, after the process was verified to be reproducible in multiple batches, it was found that some wafers were still stuck to the quartz boat when the wafers were removed.

[0032] Comparative Example 2 A thin film deposition process based on a vertical LPCVD equipment is basically the same as that in Example 1, except that in Comparative Example 2, the process tube is not heated before the second thin film deposition, so that the process temperature of the second thin film deposition is the same as that of the first thin film deposition.

[0033] In Comparative Example 2, after the process was verified to be reproducible in multiple batches, it was found that some wafers were still stuck to the quartz boat when the wafers were removed.

[0034] The results above show that, compared with conventional thin film deposition processes, the thin film deposition process based on vertical LPCVD equipment of this invention, by purging the process tube and optimizing the temperature and pressure of the process tube, can not only effectively improve the wafer boat sticking problem of vertical LPCVD equipment, but also increase the production capacity of vertical LPCVD equipment. Taking the deposition of 1000nm thickness as an example, the hourly production capacity (WPH) of the equipment using the method of this invention can be increased to about 1.8 times that of the original two-stage repetitive deposition method, while reducing the risk of contamination. In particular, for the deposition requirements of amorphous silicon thin films with a thickness ≥1000nm, the sticking problem can be solved by running the process once. It has the advantages of simple operation, wide applicability, high application value, and good application prospects.

[0035] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A thin film deposition process based on a vertical LPCVD equipment, characterized in that, Includes the following steps: S1. Check if the process pipes of the vertical LPCVD equipment are leaking air; S2. After the leakage rate of the process pipe passes the test, nitrogen is introduced to purge the gas pipeline. S3. Introduce the reaction gas source to perform the first thin film deposition on the wafer surface; S4. After the first thin film deposition is completed, nitrogen gas is introduced to purge the process tube, the boat, and the wafer; S5. Increase the temperature of the process tube and introduce a reactive gas source to perform a second thin film deposition on the wafer surface; the pressure of the process tube during the second thin film deposition process is greater than that during the first thin film deposition. S6. After the second thin film deposition is completed, nitrogen gas is introduced to purge the process tube, the crystal boat and the wafer, the pressure is increased to atmospheric pressure and the wafer is unloaded from the boat.

2. The thin film deposition process according to claim 1, characterized in that, In step S5, the temperature of the process tube during the second film deposition process is 10°C to 20°C higher than that during the first film deposition; after the process tube reaches the target temperature, it is held for ≥10 minutes.

3. The thin film deposition process according to claim 2, characterized in that, In step S5, the pressure in the process tube during the second film deposition process is 5 Pa to 15 Pa higher than that during the first film deposition.

4. The thin film deposition process according to claim 3, characterized in that, In step S5, the reaction gas source is SiH4; the flow rate of the reaction gas source is 500 sccm to 600 sccm; the process parameters during the second thin film deposition process are: temperature 555℃ to 565℃, pressure 45 Pa to 50 Pa; and the thickness of the thin film is controlled to be 300 nm to 600 nm during the second thin film deposition process.

5. The thin film deposition process according to any one of claims 1 to 4, characterized in that, In step S2, if the vacuum leakage rate of the process tube is ≤1.0 Pa / min, it indicates that the leakage rate of the process tube is qualified.

6. The thin film deposition process according to any one of claims 1 to 4, characterized in that, In step S2, the flow rate of nitrogen is 2 slm to 5 slm; the process temperature during the purging process is 540℃ to 550℃; and the purging time is 20 min to 30 min.

7. The thin film deposition process according to any one of claims 1 to 4, characterized in that, In step S3, the reaction gas source is SiH4; the flow rate of the reaction gas source is 500 sccm to 600 sccm; the process parameters during the first thin film deposition process are: temperature 540℃ to 550℃, pressure 35 Pa to 45 Pa; and the thickness of the thin film during the first thin film deposition process is controlled to be 500 nm to 800 nm.

8. The thin film deposition process according to any one of claims 1 to 4, characterized in that, In step S4, the flow rate of nitrogen is 10 slm to 20 slm; the purging time is ≥20 min.

9. The thin film deposition process according to any one of claims 1 to 4, characterized in that, In step S6, the flow rate of nitrogen is 2 slm to 5 slm; the purging time is 20 min to 40 min.

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