Methods for depositing thin films using low-pressure chemical vapor deposition
By first forming a thin intrinsic material film in a low-pressure chemical vapor deposition process, and then forming a doped material film on it, combined with cycle processing and purging operations, the problem of reduced film quality caused by reduced tank spacing was solved, and high-quality thin film deposition was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUA HONG SEMICON WUXI LTD
- Filing Date
- 2023-11-06
- Publication Date
- 2026-05-26
AI Technical Summary
In the process of improving equipment utilization efficiency, the existing low-pressure chemical vapor deposition process has reduced the spacing between the slots, resulting in poor gas flow on the wafer surface, which leads to a decrease in film quality and the appearance of bulges and buried layer granular defects.
The method involves first forming a thin intrinsic material film, and then forming a doped material film on top of it. Through cyclic processing and purging operations, gas flow is ensured, and the intrinsic material film is used as a seed layer to prevent defect proliferation.
It improves the quality of the film, inhibits the adsorption and aggregation of reactants on the wafer surface, reduces the generation of defects, and enhances the uniformity and quality of film formation.
Smart Images
Figure CN117488276B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor manufacturing, and in particular to a method for depositing thin films using a low-pressure chemical vapor deposition process. Background Technology
[0002] In semiconductor manufacturing processes, low-pressure chemical vapor deposition (LPCVD) is widely used to prepare various thin films. LPCVD equipment is categorized into vertical and horizontal types based on the orientation of the furnace. Vertical furnace tube equipment is one of the important process equipment in the front-end processes of semiconductor production lines, used for diffusion, oxidation, annealing, and alloying processes in industries such as large-scale integrated circuits, discrete devices, power electronics, optoelectronic devices, and optical fibers.
[0003] Due to the limited height of cleanrooms and the limited height of vertical furnaces, in order to more effectively improve the utilization efficiency of the equipment, a crystal boat with more slots and smaller slot spacing can be used to load a larger number of wafers. This means that the spacing between wafers on the crystal boat is smaller, which brings about various process problems.
[0004] Therefore, existing LPCVD processes for depositing thin films need further improvement. Summary of the Invention
[0005] The technical problem solved by this invention is to provide a method for depositing thin films using a low-pressure chemical vapor deposition process, so as to improve the quality of the thin films.
[0006] To solve the above-mentioned technical problems, the present invention provides a method for depositing thin films using a low-pressure chemical vapor deposition process, comprising: moving a boat loaded with a plurality of wafers into a reaction chamber; preparing the reaction chamber to a preset process temperature and a preset vacuum level through a preparation process; after the preparation process, performing several cycles of processing until an intrinsic material film with a first thickness is formed on the surface of each wafer, each cycle of processing comprising: an intrinsic film formation process and a cleaning process following the intrinsic film formation process, the intrinsic film formation process comprising introducing a first intrinsic reactive gas into the reaction chamber, the cleaning process comprising, after stopping the introduction of the first intrinsic reactive gas, introducing a protective gas into the reaction chamber to purge the surface of each wafer; after forming the intrinsic material film, forming a doped material film on the intrinsic material film, the method for forming the doped material film comprising: simultaneously introducing a second intrinsic reactive gas and a dopant source gas into the reaction chamber until the total thickness of the doped material film and the intrinsic material film is a second thickness, wherein the first thickness is less than or equal to 10% of the second thickness.
[0007] Optionally, the first intrinsic reactant gas includes silane gas; the second intrinsic reactant gas includes silane gas; the dopant source gas includes a mixture of a main reactant gas and an auxiliary gas, wherein the main reactant gas includes phosphine gas or arsine gas, and the auxiliary gas includes one or both of nitrogen and helium, wherein the mass percentage of the main reactant gas in the dopant source gas ranges from 0.5% wt to 5.0% wt.
[0008] Optionally, in each cycle of processing, the process parameters of the intrinsic film-forming process include: a time range of 5s to 20s; the first intrinsic reactive gas having a first flow rate, the first flow rate range of 0.8slm to 2.0slm; and the reaction chamber having a first pressure.
[0009] Optionally, the formation process parameters of the doped material film include: a time range of 0.33h to 9h; the second intrinsic reactant gas having a second flow rate, the second flow rate being greater than or equal to the first flow rate; the second flow rate ranging from 0.8slm to 2.0slm; the flow rate of the doping source gas ranging from 50sccm to 150sccm; the reaction chamber having a second pressure, the second pressure being greater than or equal to the first pressure; the second pressure ranging from 0.2torr to 0.8torr.
[0010] Optionally, in each cycle of processing, the process parameters of the purging operation include: a time range of 8s to 30s; and a flow rate range of 1.2slm to 3.0slm for the protective gas.
[0011] Optionally, the purging operation further includes using a vacuum pump to extract the gas in the reaction chamber; in each cycle, the process parameters of the purging operation further include a pressure range of 0.01 torr to 0.18 torr.
[0012] Optionally, the number of cycles can range from 1 to 10.
[0013] Optionally, the slot spacing of the crystal boat ranges from 4.8 mm to 5.8 mm.
[0014] Optionally, the range of the first thickness is: to The range of the second thickness is to
[0015] Optionally, the preset vacuum level range is 2 mtorr to 5 mtorr; the preset process temperature range is 525°C to 585°C.
[0016] Optionally, the protective gas includes one or a mixture of nitrogen, argon, and rare gases.
[0017] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects:
[0018] The method for depositing thin films using low-pressure chemical vapor deposition (LPCVD) provided by this invention, on one hand, involves first forming an intrinsic material film of a first thickness, and then forming a doped material film of a second thickness on the intrinsic material film. The first thickness is set to be less than or equal to 10% of the second thickness. Because the intrinsic material film is relatively thin, the dopant in the doped material film can diffuse into the intrinsic material film, resulting in a more uniformly doped film. Furthermore, the formation process of the intrinsic material film is unaffected by the dopant source gas, which is beneficial for forming a high-quality intrinsic material film. On the other hand, the intrinsic... The material film is obtained through several cycles of processing. In each cycle, an intrinsic material film is first formed on the wafer surface, followed by a purging operation on each wafer surface. This increases the flowability of gas on the wafer surface, which can suppress the adsorption and aggregation of reactants on the wafer surface even when the trench spacing is small. This reduces the probability of bulging, buried layer particulate defects, etc., and further improves the quality of the intrinsic material film. In addition, the intrinsic material film can act as a "seed layer". A high-quality intrinsic material film can prevent the continuous proliferation of defects during the film formation process, which is beneficial to improving the quality of the final film. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of an LPCVD furnace tube;
[0020] Figure 2 These are microscope images of two typical defects in an LPCVD furnace tube process.
[0021] Figure 3 This is a flowchart of the method steps for depositing thin films using low-pressure chemical vapor deposition in an embodiment of the present invention. Detailed Implementation
[0022] As described in the background section, existing methods for depositing thin films using LPCVD processes need further improvement, which will now be illustrated in conjunction with the structure of an LPCVD furnace tube.
[0023] Figure 1 This is a schematic diagram of the cross-sectional structure of an LPCVD furnace tube.
[0024] Please refer to Figure 1The LPCVD furnace tube includes a cavity 101, a reaction chamber 102 located within the cavity 101, a crystal boat 103 placed within the reaction chamber 102, and several inlet pipes (not shown in the figure) and outlet pipes (not shown in the figure) located on the cavity 101, connecting the reaction chamber 102 to the outside. The inlet pipes are used to introduce reaction gases, and the outlet pipes are used to discharge waste gases. Figure 1 Only the approximate flow direction of the reactive gas Gas is shown.
[0025] In the process of in-situ doping of polycrystalline silicon, several wafers 104 are placed in the slots of the boat 103 of the aforementioned LPCVD furnace tube. In conventional LPCVD processes, silane is used as the gas for silicon growth, and phosphine is used as the dopant source gas. After the temperature and pressure stabilize to meet the process requirements, silane and phosphine gases are simultaneously introduced into the furnace to obtain phosphorus-doped polycrystalline silicon. During film formation, because phosphine molecules have an isolated electron pair and exhibit strong polarity, the adsorption of phosphine on the wafer surface is much higher than that of silane, resulting in a film quality far lower than that of intrinsic polycrystalline silicon films.
[0026] To improve equipment utilization efficiency, the number of slots is increased without increasing the height of the wafer boat. This results in a corresponding decrease in the slot spacing (d). The reduced slot spacing affects gas flow, leading to stronger adsorption of phosphine on the wafer surface. This can cause abnormalities in the film formation process and result in defects. Please refer to [reference needed]. Figure 2 .
[0027] Figure 2 These are microscope images of two typical defects in an LPCVD furnace tube process.
[0028] Please refer to Figure 2 When the spacing between the slots is reduced from 6.5 mm to 5.32 mm and the number of slots is increased from 143 to 170, more serious defects such as bulge def1 or buried layer granular defects def2 will appear. The size of these defects is about 0.2 μm to 2.0 μm, which seriously affects the quality of the formed film.
[0029] To address the aforementioned problems, this invention provides a method for depositing thin films using a low-pressure chemical vapor deposition process. On one hand, by first forming an intrinsic material film of a first thickness, and then forming a doped material film of a second thickness on the intrinsic material film, the first thickness is set to be less than or equal to 10% of the second thickness. Because the intrinsic material film is relatively thin, the dopant in the doped material film can diffuse into the intrinsic material film, resulting in a more uniformly doped film. Furthermore, the formation process of the intrinsic material film is unaffected by the dopant source gas, which is beneficial for forming a high-quality intrinsic material film. On the other hand, the... The intrinsic material film is obtained through several cycles of processing. In each cycle, the intrinsic material film is first formed on the wafer surface, and then the wafer surface is purged. This increases the flowability of gas on the wafer surface, which can suppress the adsorption and aggregation of reactants on the wafer surface even when the trench spacing is small. This reduces the probability of bulging, buried layer particulate defects, etc., and further improves the quality of the intrinsic material film. In addition, the intrinsic material film can act as a "seed layer". A high-quality intrinsic material film can prevent the continuous proliferation of defects during the film formation process, which is beneficial to improving the quality of the final film.
[0030] To make the above-mentioned objectives, features and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0031] Figure 3 This is a schematic flowchart of the steps in the low-pressure chemical vapor deposition method for depositing thin films according to an embodiment of the present invention.
[0032] In this embodiment, the method for depositing thin films using low-pressure chemical vapor deposition includes the following steps:
[0033] Step 201: The crystal boat containing several wafers is moved into the reaction chamber;
[0034] Step 202: Prepare the reaction chamber to reach the preset process temperature and preset vacuum level through the preparation process;
[0035] Step 203: After the preparation process, the process is repeated several times until an intrinsic material film with a first thickness is formed on the surface of each wafer. Each cycle includes an intrinsic film formation process and a cleaning process after the intrinsic film formation process. The intrinsic film formation process includes introducing a first intrinsic reactive gas into the reaction chamber. The cleaning process includes introducing a protective gas into the reaction chamber after stopping the introduction of the first intrinsic reactive gas and performing a purging operation on the surface of each wafer.
[0036] Step 204: After forming the intrinsic material film, a doped material film is formed on the intrinsic material film. The method for forming the doped material film includes: simultaneously introducing a second intrinsic reaction gas and a dopant source gas into the reaction chamber until the total thickness of the doped material film and the intrinsic material film is a second thickness, wherein the first thickness is less than or equal to 10% of the second thickness.
[0037] The following will provide a detailed explanation.
[0038] Step 201 involves moving a crystal boat containing several wafers into the reaction chamber.
[0039] In this embodiment, the slot spacing of the crystal boat ranges from 4.8 mm to 5.8 mm. A smaller slot spacing is more conducive to loading more wafers and increasing the number of wafers processed in a single operation; however, a smaller slot spacing is less conducive to gas flow.
[0040] Step 202 is executed to bring the reaction chamber to a preset process temperature and preset vacuum level through a preparation process.
[0041] In this embodiment, the preset process temperature range is 525°C to 585°C.
[0042] In this embodiment, the preset vacuum level range is 2 mtor to 5 mtorr.
[0043] Step 203 is performed after the preparation process, through several cycles of processing until an intrinsic material film with a first thickness is formed on the surface of each wafer. Each cycle of processing includes an intrinsic film formation process and a cleaning process after the intrinsic film formation process. The intrinsic film formation process includes introducing a first intrinsic reactive gas into the reaction chamber. The cleaning process includes introducing a protective gas into the reaction chamber after stopping the introduction of the first intrinsic reactive gas and performing a purging operation on the surface of each wafer.
[0044] In this embodiment, the first intrinsic reactive gas includes silane gas. The silane gas is used to form an intrinsic material film, and the material of the intrinsic material film is polycrystalline silicon.
[0045] In this embodiment, the process parameters of the intrinsic film-forming process in each cycle include: a time range of 5s to 20s; the first intrinsic reactive gas having a first flow rate, the first flow rate range being 0.8slm to 2.0slm; and the reaction chamber having a first pressure.
[0046] In this embodiment, the first pressure range is less than or equal to 0.18 torr.
[0047] In this embodiment, the process parameters of the purging operation in each cycle include: a time range of 8s to 30s; and a flow rate range of 1.2slm to 3.0slm for the protective gas.
[0048] In this embodiment, the purging operation further includes using a vacuum pump to extract gas from the reaction chamber. The cleaning process employs a protective gas to purge the surface of each wafer, increasing gas flow on the wafer surface. Even with small trench spacing, this can suppress the adsorption and aggregation of reactants on the wafer surface, thereby reducing the probability of bulging, buried layer particulate defects, etc., and further improving the quality of the intrinsic material film. Specifically, in this embodiment, it is used to suppress the adsorption and aggregation of phosphine on the wafer surface; in another embodiment, it can also be used to suppress the adsorption and aggregation of arsine on the wafer surface.
[0049] In this embodiment, the process parameters for the purging operation in each cycle also include a pressure range of 0.01 torr to 0.18 torr. Increasing the pumping speed of the vacuum pump and the flow rate of the protective gas helps to reduce the uneven nucleation of residual reaction gas or impurities on the wafer surface, further improving the quality of the intrinsic material film.
[0050] The protective gas includes one or a mixture of nitrogen, argon, and rare gases. In this embodiment, the protective gas is nitrogen.
[0051] In this embodiment, the number of cycles ranges from 1 to 10. This range is chosen to avoid too few cycles being ineffective, while also avoiding too many cycles, which could result in a thin film that cannot be formed in a single cycle, thus causing problems with the uniformity of the final film thickness.
[0052] Step 204 involves forming a doped material film on the intrinsic material film after the intrinsic material film is formed. The method for forming the doped material film includes simultaneously introducing a second intrinsic reaction gas and a dopant source gas into the reaction chamber until the total thickness of the doped material film and the intrinsic material film is a second thickness, wherein the first thickness is less than or equal to 10% of the second thickness.
[0053] Here, the first thickness is set to be less than or equal to 10% of the second thickness. Because the intrinsic material film is relatively thin, the dopant in the doped material film can diffuse into the intrinsic material film, resulting in a more uniformly doped film. Furthermore, the formation process of the intrinsic material film is unaffected by the dopant source gas, which is beneficial for forming a high-quality intrinsic material film. In addition, the intrinsic material film can act as a "seed layer," and a high-quality intrinsic material film can prevent the continuous proliferation of defects during the film formation process, thus improving the final film quality.
[0054] The second intrinsic reactant gas includes silane gas; the dopant source gas includes a mixture of a main reactant gas and an auxiliary gas, wherein the main reactant gas includes phosphine gas or arsine gas, and the auxiliary gas includes one or both of nitrogen and helium, wherein the mass percentage of the main reactant gas in the dopant source gas ranges from 0.5% wt to 5.0% wt. The silane gas and the dopant source gas are used to form a doped material film. In this embodiment, the main reactant gas of the dopant source gas is phosphine gas, i.e., used to form phosphorus-doped polycrystalline silicon.
[0055] In this embodiment, the formation process parameters of the doped material film include: a time range of 0.33h to 9h; the second intrinsic reactant gas having a second flow rate, the second flow rate being greater than or equal to the first flow rate; the second flow rate ranging from 0.8slm to 2.0slm; the flow rate of the doping source gas ranging from 50sccm to 150sccm; the reaction chamber having a second pressure, the second pressure being greater than or equal to the first pressure; the second pressure ranging from 0.2torr to 0.8torr.
[0056] In this embodiment, the range of the first thickness is: to The range of the second thickness is to
[0057] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A method for depositing a thin film by a low-pressure chemical vapor deposition process, characterized in that, Including: Moving a boat loaded with a plurality of wafers into a reaction chamber; Making the reaction chamber reach a preset process temperature and a preset vacuum degree through a preparation process; After the preparation process, through several cycles of treatment until an intrinsic material film with a first thickness is formed on the surface of each wafer, the material of the intrinsic material film is polysilicon, and each cycle of treatment includes: An intrinsic film formation process and a cleaning process after the intrinsic film formation process, the intrinsic film formation process includes introducing a first intrinsic reaction gas into the reaction chamber, the first intrinsic reaction gas includes silane gas, the cleaning process includes, after stopping introducing the first intrinsic reaction gas, introducing a protective gas into the reaction chamber to perform a purging operation on the surface of each wafer, the purging operation further includes using a vacuum pump device to extract the gas in the reaction chamber, and the process parameters of the purging operation include: the time range is 8s to 30s, the flow rate range of the protective gas is 1.2slm to 3.0slm, and the pressure range is 0.01torr to 0.18torr; After forming the intrinsic material film, a doped material film is formed on the intrinsic material film, the doped material film is a polysilicon thin film doped with phosphorus or arsenic elements, and the formation method of the doped material film includes: Simultaneously introducing a second intrinsic reaction gas and a doping source gas into the reaction chamber until the total thickness of the doped material film and the intrinsic material film is a second thickness, the first thickness is less than or equal to 10% of the second thickness, the second intrinsic reaction gas includes silane gas, and the doping source gas includes a main reaction gas, and the main reaction gas includes phosphine gas or arsine gas.
2. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, characterized in that, The doping source gas includes a mixed gas of the main reaction gas and an auxiliary gas, the auxiliary gas includes one or both of nitrogen and helium, and the mass percentage range of the main reaction gas in the doping source gas is 0.5%wt to 5.0%wt.
3. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein In each cycle of treatment, the process parameters of the intrinsic film formation process include: the time range is 5s to 20s; the first intrinsic reaction gas has a first flow rate, and the first flow rate range is 0.8slm to 2.0slm; the reaction chamber has a first pressure.
4. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 3, characterized in that, The formation process parameters of the doped material film include: the time range is 0.33h to 9h; the second intrinsic reaction gas has a second flow rate, and the second flow rate is greater than or equal to the first flow rate; the second flow rate range is 0.8slm to 2.0slm; the flow rate range of the doping source gas is 50sccm to 150sccm; the reaction chamber has a second pressure, and the second pressure is greater than or equal to the first pressure; the second pressure range is 0.2torr to 0.8torr.
5. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein The number of cycles of treatment ranges from 1 to 10 times.
6. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein The groove pitch range of the boat is 4.8mm to 5.8mm.
7. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein The range of the first thickness is 20Å to 300Å; the range of the second thickness is 100Å to 13000Å.
8. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein, The preset vacuum degree range is from 2 mtorr to 5 mtorr; the preset process temperature range is from 525 °C to 585 °C.
9. The method for depositing a thin film by the low-pressure chemical vapor deposition process according to claim 1, wherein The protective gas includes a mixture of one or more of nitrogen and noble gases.