Method for preparing polycrystalline silicon thin film through furnace tube
By alternately passing the first and second process gases into the furnace tube reaction chamber to form Si-Si bonds, the problems of surface roughness and unevenness of polycrystalline silicon thin films in the LPCVD process are solved, and high density and uniformity are achieved Polycrystalline silicon thin film improves the electrical performance of integrated circuits.
Patent Information
- Application Number
- CN202411120458.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-15
- Publication Date
- 2024-12-27
AI Technical Summary
When the existing low-voltage chemical vapor deposition (LPCVD) process prepares polysilicon thin films, the film surface roughness is poor and the unevenness is insufficient, resulting in poor electrical performance, limiting the application of polysilicon in integrated circuits.
By alternately passing the first process gas and the second process gas into the furnace tube reaction chamber, the surface of the silicon-containing substrate is activated and Si-Si bonds are formed, and the polycrystalline silicon thin film is deposited in situ, and multiple cycles are performed to improve the density of the film and Uniformity and can be combined with the LPCVD method to take into account the generation efficiency.
The surface roughness and uniformity of the polycrystalline silicon film are significantly improved, its electrical and overall performance are improved, and its application range in integrated circuits is extended.
Smart Images
Figure CN119194608A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of integrated circuit manufacturing, relates to a high-efficiency and low-cost process for preparing polysilicon, and specifically relates to a method for preparing polysilicon thin film by using a furnace tube. Background Art
[0002] Polysilicon (Poly-Si) plays an important role in the manufacture of integrated circuits (ICs) due to its excellent electrical properties and processability. Polysilicon can be used as electrode layers, mask layers, conductive layers, and resistor layers, and is used in logic devices (Logic) and various memory devices (such as DRAM, NAND FLASH, NOR FLASH). By precisely controlling the doping concentration, polysilicon with different resistivities can be prepared to meet the performance requirements of different devices.
[0003] Currently, the main method for preparing polysilicon in integrated circuits is the low-pressure chemical vapor deposition (LPCVD) process, which is favored for its simplicity, high throughput (100 to 150 wafers can be processed at a time), and low cost.
[0004] However, despite the dominance of the LPCVD process in polysilicon preparation, it still has some limitations in the thin film deposition process. For example, when depositing thin films using LPCVD technology, especially when the film is thin, poor surface roughness and pinhole problems may occur, which will affect the electrical properties of the film and the overall performance of the device. Moreover, as the size of the LPCVD reactor increases, the axial uniformity of the polysilicon film may decrease.
[0005] The above defects, such as pinholes, surface roughness, unevenness, etc., may cause electrical discontinuity of polysilicon, thereby limiting its application in integrated circuits. Summary of the invention
[0006] The purpose of the present invention is to improve the quality and uniformity of polysilicon thin films, reduce defects, and thus expand the application range of polysilicon in integrated circuits.
[0007] In order to achieve the above object, the present invention provides a method for preparing a polycrystalline silicon thin film using a furnace tube, comprising:
[0008] Step S1, placing a silicon-containing substrate in a furnace tube reaction chamber;
[0009] Step S2, introducing a first process gas into the furnace tube reaction chamber to activate the surface of the silicon-containing substrate;
[0010] Step S3, introducing a second process gas into the furnace tube reaction chamber, wherein the second process gas reacts with the activated surface of the silicon-containing substrate to in-situ deposit a polysilicon thin film;
[0011] Step S4, performing steps S2 and S3 in a cycle for N times until the thickness of the polysilicon film reaches a first set thickness, wherein N is an integer greater than 0.
[0012] Optionally, the first process gas contains at least one of SiH2Cl2 and SiHCl3.
[0013] Optionally, the second process gas comprises: Si x H y Gas, where x>0, y>0.
[0014] Optionally, the Si x H y The gas contains: SiH4 and / or Si2H6.
[0015] Optionally, the first set thickness is less than or equal to 30 atomic angstroms.
[0016] Optionally, the process conditions of step S2 are: the first process gas flow rate is 1slm~2slm, the ventilation time is 5s~15s, and the temperature in the furnace tube reaction chamber is 550℃~650℃; the process conditions of step S3 are: the second process gas flow rate is 2slm~5slm, the ventilation time is 5s~15s, and the temperature in the furnace tube reaction chamber is 550℃~650℃.
[0017] Optionally, after step S4, the method further comprises step S5: introducing a third process gas to continue depositing the polysilicon film until the total thickness of the polysilicon film reaches a second set thickness.
[0018] Optionally, the second set thickness is greater than 100 atomic angstroms.
[0019] Optionally, the third process gas contains: SiH4 and / or Si2H6.
[0020] Optionally, the silicon-containing substrate comprises a silicon substrate or a silicon oxide substrate.
[0021] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:
[0022] The present invention alternately cyclically introduces a first process gas and a second process gas into the furnace tube reaction chamber, wherein the first process gas activates the surface of the silicon-containing substrate, destroys the Si-O bond on the surface of the silicon-containing substrate, and forms an active dangling bond Si-, which is easily bonded with the second process gas to form a Si-Si bond, thereby depositing a polycrystalline silicon film in situ. Steps S2 and S3 are repeated multiple times until the polycrystalline silicon film reaches a set thickness, and the formed polycrystalline silicon film has high density, good uniformity, and good surface roughness, thereby significantly improving the electrical properties of the film and the overall performance of the device.
[0023] When the polysilicon film to be deposited is thicker, for example, the second set thickness is greater than In the present invention, after depositing a polysilicon film of a first set thickness by repeatedly cycling step S2 and step S3, the third process gas may be switched to deposit the polysilicon film to a second set thickness by using the LPCVD method. In this way, not only the uniformity and surface roughness of the polysilicon film are better, but also the generation efficiency can be taken into consideration. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1a Schematic diagram of the polysilicon deposition process in LPCVD technology, where a represents the first stage, b represents the second stage, and c represents the third stage.
[0025] Figure 1b Schematic diagram of the polysilicon deposition principle in LPCVD technology, where a represents the first stage, b represents the second stage, and c represents the third stage.
[0026] Figure 2 Atomic force microscope (AFM) images of polysilicon deposited with a thickness of 5 nm and 50 nm are shown, wherein a represents an AFM image of polysilicon deposited with a thickness of 5 nm, and b represents an AFM image of polysilicon deposited with a thickness of 50 nm.
[0027] Figure 3 This is a simplified process diagram for LPCVD deposition of polysilicon.
[0028] Figure 4 The schematic diagram is a principle diagram of a method for preparing a polysilicon thin film using a furnace tube according to the present invention, wherein a represents the first stage, b represents the second stage, and c represents the third stage.
[0029] Figure 5 The present invention is a flow chart of a method for preparing polysilicon thin film using a furnace tube.
[0030] Figure 6It is a schematic diagram of the reaction state of the method of the present invention, wherein a represents the bonding reaction state when the first process gas is introduced, b represents the bonding reaction state when the second process gas is introduced, c represents the bonding reaction state when the first process gas is introduced again, and d represents a schematic diagram of the microscopic arrangement of the deposited polysilicon film.
[0031] Figure 7 The present invention is a flow chart of a method for preparing polysilicon thin film using a furnace tube. DETAILED DESCRIPTION
[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0033] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.
[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0035] The "set thickness" described herein refers to the thickness of polysilicon that needs to be deposited in the process. The "first set thickness" refers to a thinner set thickness (e.g., The "second set thickness" refers to a thicker set thickness (e.g.,
[0036] The LPCVD deposition of polysilicon is usually carried out in a temperature range of 530 degrees Celsius (°C) to 630 degrees Celsius, and the pressure is maintained between 0.2 and 2 Torr. The reaction equation is:
[0037] SiH4→Si+H2
[0038] like Figure 1a , 1b As shown, the above polysilicon deposition process can be divided into three stages: the first stage, surface diffusion and nucleation ( Figure 1a , 1b a); in the second stage, the nucleus grows into an island ( Figure 1a , 1b b); In the third stage, the islands grow and contact to form a continuous film ( Figure 1a , 1b c). When the deposited film thickness is thin, the island growth in the third stage is insufficient and it is difficult to fully contact and form a continuous film, which easily leads to pin holes or grain boundary discontinuity, and the surface roughness is poor. Figure 2 As shown in the figure, a represents the atomic force microscope image of polysilicon deposited with a thickness of 5nm, and b represents the atomic force microscope image of polysilicon deposited with a thickness of 50nm. The AFM (atomic force microscope) image shows that when the film thickness is thin (such as 5nm, Figure 2 a), the surface roughness is poor, which is easy to produce pinholes and grain boundary discontinuities; when the film thickness is thick (such as 50nm, Figure 2 b), the surface roughness is good and the pinhole defects are not obvious.
[0039] For the furnace tube process, Figure 3 As shown, SiH4 gas is introduced from the bottom of the chamber, and the gas concentration gradually decreases from the bottom to the top. In order to compensate for this concentration gradient, it is usually necessary to adjust the temperature, for example, so that the temperature gradually increases from the bottom to the top of the furnace tube reaction chamber to ensure that the thickness of the film deposited at different positions is uniform. However, this control process requires high precision, high equipment cost, and great difficulty in operation.
[0040] Compared with the LPCVD process, the principle of forming polysilicon thin film in the present invention is as follows: Figure 4 As shown, in the first stage ( Figure 4 a), the first process gas forms surface adsorption on the surface of the silicon-containing substrate, and the Si-O bond on the surface of the silicon-containing substrate is broken to form a hanging bond Si-; in the second stage ( Figure 4 b), the second process gas bonds with the dangling bond Si- to form a Si-Si bond; in the third stage ( Figure 4 c) in the figure, after multiple cycles of the first stage and the second stage, a polycrystalline silicon film is obtained.
[0041] The present invention activates the surface of the silicon-containing substrate by the first process gas, destroys the Si-O bond on the substrate surface, and forms an active dangling bond Si-. The dangling bond Si- and the second process gas (Si x H y) is easy to bond to form Si-Si bonds, and then polysilicon is deposited in situ. The polysilicon formed by the present invention is formed by in-situ bonding, has good uniformity, is not affected by concentration, and can be repeated for multiple cycles to avoid defects such as pinholes; and the polysilicon layer formed by chemical bonding is more tightly bonded. Furthermore, by repeatedly alternately introducing the first process gas and the second process gas, a dense polysilicon layer can be formed on the surface of the substrate. The following is a detailed description with reference to the accompanying drawings.
[0042] like Figure 5 As shown, a method for preparing a polycrystalline silicon thin film through a furnace tube of the present invention comprises:
[0043] Step S1, placing a silicon-containing substrate in a furnace tube reaction chamber.
[0044] The silicon-containing substrate may be a silicon substrate or a silicon oxide substrate. In this example, the silicon-containing substrate comprises a silicon substrate, and a silicon oxide layer is formed by natural oxidation on the surface of the silicon substrate. That is, from a microscopic level, there are a number of Si-O bonds on the surface of the substrate.
[0045] Step S2, introducing a first process gas into the furnace tube reaction chamber to activate the surface of the silicon-containing substrate.
[0046] The first process gas contains at least one of SiH2Cl2 and SiHCl3. The first process gas has a high reaction temperature, and it is not easy to cause a continuous reaction (for example, a chemical vapor deposition reaction) on the surface of the silicon-containing substrate, but mainly activates the surface of the silicon-containing substrate. Under the action of the first process gas, the Si-O bonds on the surface of the silicon-containing substrate are broken to form active dangling bonds Si-.
[0047] As an example, Figure 6 As shown in a, the first process gas is adsorbed on the surface. Under the action of the first process gas SiH2Cl2, the Si-O bond on the surface of the silicon substrate is easily broken, and the Si-O bond loses O to form an active dangling bond Si-; the H particles (H ions or H radicals) in SiH2Cl2 combine with O to form water and are discharged.
[0048] The process conditions of step S2 are as follows: the flow rate of the first process gas is 1slm to 2slm, the ventilation time is 5s to 15s, the temperature in the furnace tube reaction chamber is 550°C to 650°C; the pressure is relatively low, and the exhaust valve of the furnace tube is fully opened or opened to 95%, which is conducive to timely discharge of the generated H2O or HCl.
[0049] Step S3, introducing a second process gas into the furnace tube reaction chamber, wherein the second process gas reacts with the activated surface of the silicon-containing substrate to in-situ deposit a polysilicon film.
[0050] The second process gas combines with the dangling bond Si- on the surface of the silicon-containing substrate to form Si-Si bonds, thereby achieving in-situ deposition of polysilicon. On the one hand, the dangling bond Si- plays a positioning role, allowing the polysilicon to be deposited uniformly; on the other hand, the deposited polysilicon forms chemical adsorption with the surface of the silicon-containing substrate, with strong adsorption strength and tight bonding.
[0051] The second process gas contains Si x H y Gas, wherein x and y represent the number of atoms or atomic ratios, and are both greater than 0. In some embodiments, the second process gas is Si2H6, and in other embodiments, the second process gas is SiH4.
[0052] like Figure 6 As shown in b, the Si in the second process gas easily combines with the dangling bond Si- to form a Si-Si covalent bond, thereby in-situ depositing Si.
[0053] The process conditions of step S3 are as follows: the flow rate of the second process gas is 2slm-5slm, the ventilation time is 5s-15s, the temperature in the furnace tube reaction chamber is 550°C-650°C; the pressure is relatively low, and the exhaust valve of the furnace tube is fully opened or opened to 95%, which is conducive to timely discharge of the generated H2O or HCl.
[0054] Step S4, performing steps S2 and S3 in a cycle for N times until the thickness of the polysilicon film reaches a first set thickness, wherein N is an integer greater than 0.
[0055] like Figure 6 The first process gas is introduced again in a cycle, and SiH2Cl2 continues to act under high temperature and low pressure, so that the Si-O bond of the substrate is broken and a hanging bond Si- is formed. The microscopic schematic diagram of the polysilicon film formed by multiple cycles of step S2 and step S3 is shown in FIG. Figure 6 As shown in d.
[0056] The number of cycles N can be determined according to the polysilicon thickness required by the process (i.e., the first set thickness). By extending the time of step S2, step S3 or the total process time, the density of the polysilicon film can be increased and the physical properties of the polysilicon film can be improved.
[0057] In some embodiments, in order to form a polysilicon layer with a smaller thickness, such as When the method of the present invention is used, the first process gas and the second process gas are alternately introduced to quickly obtain a polysilicon layer with uniform thickness and compactness.
[0058] like Figure 7As shown, in some embodiments, in order to obtain a thicker polysilicon layer, after step S4, the process further includes: step S5, introducing a third process gas to continue depositing a polysilicon film until the total thickness of the polysilicon film reaches a second set thickness. In the above case, the polysilicon film is deposited in situ only by alternately introducing the first process gas and the second process gas, and the deposition rate is slow and the generation cycle is long. To this end, the present invention can also switch to continuously introducing the third process gas after cyclically performing steps S2 and S3 to form the polysilicon film of the first set thickness, and use the LPCVD method to quickly continue to deposit the polysilicon film until the thickness reaches the second set thickness. Since the polysilicon film of the first set thickness has high density and good surface roughness (surface flatness), the polysilicon film formed thereon by LPCVD has good uniformity and good roughness. The two methods are used in combination to take into account both film quality and production efficiency.
[0059] The third process gas includes: SiH4 or Si2H6.
[0060] Comparative Example 1
[0061] A furnace tube deposition device is provided, and a silicon oxide substrate is placed on a wafer boat and then placed in a furnace tube reaction chamber of the furnace tube deposition device.
[0062] Using the conventional LPCVD technology, SiH4 was introduced into the furnace tube reaction chamber at a flow rate of 5slm, a reaction chamber temperature of 550°C, and a pressure of 0.5torr. SiH4 decomposed and reacted to deposit a polycrystalline silicon film on the surface of the silicon oxide substrate until the thickness reached 5nm. The process time was 5min. After testing, the surface roughness of the polycrystalline silicon film was Ra=0.632nm.
[0063] Example 1
[0064] Step 1, providing a furnace tube deposition device, placing a silicon oxide substrate on a wafer boat, and then placing the substrate in a furnace tube reaction chamber of the furnace tube deposition device.
[0065] Step 2, introducing the first process gas SiH2Cl2 into the furnace tube reaction chamber, the flow rate is 1slm, the continuous introduction time is 15s, the reaction chamber temperature is 550℃~650℃, and the pressure is set to 95% opening of the exhaust valve. SiH2Cl2 breaks the Si-O bond on the surface of the silicon oxide substrate to form an active Si-dangling bond, and the byproduct H2O or HCl formed is discharged.
[0066] Step 3, stop introducing the first process gas, introduce the second process gas Si2H6 into the furnace tube reaction chamber, the flow rate is 5slm, the continuous introduction time is 15s, the reaction chamber temperature is 550℃~650℃, and the pressure is set to 95% opening of the exhaust valve. Si2H6 chemically bonds with the Si-dangling bond to form a Si-Si bond, and a polysilicon film is deposited in situ on the silicon oxide substrate, and the by-product H2O or HCl is discharged.
[0067] Step 4, alternately cycle step 2 and step 3 until the thickness of the polysilicon film reaches 5 nm (the first set thickness), and the process time is 18 minutes. According to the test, the surface roughness of the polysilicon film Ra=0.227 nm.
[0068] Comparing the comparative example with the embodiment, it can be seen that the surface roughness of the polysilicon film prepared by the method of the embodiment is significantly improved.
[0069] In summary, the present invention activates the surface of the silicon-containing substrate by introducing the first process gas to the surface of the silicon-containing substrate, breaks the stable Si-O to form active Si-dangling bonds, and then introduces the second process gas, which is easy to form stable Si-Si covalent bonds with the Si-dangling bonds, and then deposits the polysilicon film in situ. Due to the positioning of the Si-dangling bonds, the film formed by this method has good uniformity and is insensitive to stable changes, and the chemical bonding effect makes the formed polysilicon film tightly bonded to the silicon-containing substrate. By alternately introducing the first process gas and the second process gas for multiple cycles, the polysilicon film can be made denser and the number of cycles can be determined according to the required thickness.
[0070] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.
Claims
1. A method for preparing polycrystalline silicon thin film using a furnace tube, characterized in that: Include: Step S1, placing a silicon-containing substrate in a furnace tube reaction chamber; Step S2, introducing a first process gas into the furnace tube reaction chamber to activate the surface of the silicon-containing substrate; Step S3, introducing a second process gas into the furnace tube reaction chamber, wherein the second process gas reacts with the activated surface of the silicon-containing substrate to in-situ deposit a polysilicon thin film; Step S4, performing steps S2 and S3 in a cycle for N times until the thickness of the polysilicon film reaches a first set thickness, wherein N is an integer greater than 0.
2. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: The first process gas includes at least one of SiH2Cl2 and SiHCl3.
3. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: The second process gas comprises: Si x H y Gas, where x>0, y>0.
4. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 3, characterized in that: The Si x H y The gas includes at least one of SiH4 and Si2H6.
5. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: The first set thickness is less than or equal to 30 atomic angstroms.
6. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: The process conditions of step S2 are: the first process gas flow rate is 1slm~2slm, the ventilation time is 5s~15s, and the temperature in the furnace tube reaction chamber is 550℃~650℃; the process conditions of step S3 are: the second process gas flow rate is 2slm~5slm, the ventilation time is 5s~15s, and the temperature in the furnace tube reaction chamber is 550℃~650℃.
7. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: After step S4, the method further includes step S5: introducing a third process gas to continue depositing the polysilicon film until the total thickness of the polysilicon film reaches a second set thickness.
8. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 7, characterized in that: The second predetermined thickness is greater than 100 atomic angstroms.
9. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 7, characterized in that: The third process gas includes at least one of SiH4 and Si2H6.
10. The method for preparing polycrystalline silicon thin film by furnace tube according to claim 1, characterized in that: The silicon-containing substrate includes a silicon substrate or a silicon oxide substrate.