Preparation method of silicon substrate and silicon substrate
Through a combination of wet cleaning and plasma activation, the substrate sheet and diffusion sheet of the silicon substrate are subjected to hydrophilic activation, which solves the problem of insufficient bonding strength of traditional silicon substrates and achieves higher bonding strength and performance improvements.
Patent Information
- Application Number
- CN202411985161.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2025-04-15
AI Technical Summary
In the traditional silicon substrate preparation method, the bonding strength between the substrate sheet and the diffusion sheet is insufficient, resulting in the bonding area being easily broken.
The substrate sheet and diffusion sheet were subjected to hydrophilic activation treatment by combining wet cleaning and plasma activation, increasing the concentration of -OH groups and activation energy of the surface suspended surface, and then vacuum bonding was performed in a vacuum environment.
The bonding strength between the substrate sheet and the diffusion sheet is significantly improved, the fracture and damage problems of the bonding area are improved, and the performance of the silicon substrate is improved.
Smart Images
Figure CN119833395A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the field of chips, and in particular to a method for preparing a silicon substrate and a silicon substrate. Background Art
[0002] Traditionally, in the process of preparing silicon substrates, heavily doped N++ single crystal substrates are often selected as silicon substrate support sheets. Before low-temperature bonding of the single crystal diffusion sheet and the single crystal substrate sheet, the natural oxide layer on the surface needs to be removed to achieve hydrophobic wet activation treatment, followed by low-temperature pre-bonding in the hope of forming -H covalent bonds on the bonding surface of the wafer.
[0003] However, the bonding strength after low-temperature pre-bonding is often insufficient, and the bonded sheets are generally broken in the bonding area after tensile testing.
[0004] Therefore, how to improve the bonding strength between the substrate and the diffusion sheet during the silicon substrate preparation process has become an urgent problem to be solved in this field. Summary of the invention
[0005] The present application discloses a method for preparing a silicon substrate and a silicon substrate, the purpose of which is to improve the bonding strength between a substrate sheet and a diffusion sheet during the preparation process of the silicon substrate.
[0006] The embodiment of the present application discloses a method for preparing a silicon substrate, comprising the steps of: taking a diffusion sheet and a substrate sheet, and cleaning the diffusion sheet and the substrate sheet; spinning the cleaned diffusion sheet and the substrate sheet to remove surface water residue; wet activating the diffusion sheet and the substrate sheet; after the wet activation, plasma activating the diffusion sheet and the substrate sheet; vacuum bonding the diffusion sheet and the substrate sheet at a preset temperature; thinning the bonded diffusion sheet and the substrate sheet, and polishing to obtain a silicon substrate.
[0007] Optionally, the step of cleaning the diffusion sheet and the substrate sheet includes: soaking in a first solution at a first preset temperature for a first preset time to remove impurities on the surface of the diffusion sheet and the substrate sheet; rinsing with hot deionized water for a first preset time; rinsing with cold deionized water for a first preset time; soaking in a second solution for a second preset time to remove the surface oxide layer; rinsing with cold deionized water for a first preset time; soaking in a third solution at a second preset temperature for a first preset time to remove metal ions on the surface of the silicon wafer; rinsing with hot deionized water for a first preset time; rinsing with cold deionized water for a first preset time.
[0008] Optionally, the first solution includes a mixed solution of sulfuric acid and hydrogen peroxide, and the mixing ratio of the sulfuric acid and the hydrogen peroxide is 4:1; the second solution includes a mixed solution of hydrofluoric acid and water, and the mixing ratio of the hydrogen fluoride and water is 1:10; the third solution includes a mixed solution of hydrochloric acid, hydrogen peroxide and water, and the mixing ratio of the hydrochloric acid, the hydrogen peroxide and water is 1:1:5.
[0009] Optionally, the step of wet activating the diffusion sheet and the substrate sheet includes: rinsing the diffusion sheet and the substrate sheet with cold deionized water for a first preset time; soaking them in a fourth solution at a third preset temperature for a first preset time; rinsing them with hot deionized water for a first preset time, and then rinsing them with cold deionized water for a first preset time.
[0010] Optionally, the fourth solution includes a mixed solution of ammonia water, hydrogen peroxide and water, and the mixing ratio of the ammonia water, the hydrogen peroxide and the water is 1:1:5.
[0011] Optionally, the step of plasma activating the diffusion sheet and the substrate sheet includes: placing the wet-activated diffusion sheet and the substrate sheet in a chamber of a plasma dry stripping device; setting the chamber to a first preset condition to form a vacuum environment and a radio frequency electric field; activating the surfaces of the diffusion sheet and the substrate sheet under the action of a radio frequency electric field in the chamber; wherein the first preset condition in the chamber includes: setting the vacuum pressure between 400 mTorr and 600 mTorr, and setting the flow rate between 300 sccm and 400 sccm; and the radio frequency electric field power formed in the chamber is 500 W.
[0012] Optionally, the step of forming a radio frequency electric field in the chamber and activating the surfaces of the diffusion sheet and the substrate sheet under the action of the radio frequency electric field further includes: the time range for activating the diffusion sheet and the substrate sheet is between 70 seconds and 110 seconds.
[0013] Optionally, the step of plasma activating the diffusion sheet and the substrate sheet further includes: after respectively laminating the front sides of the diffusion sheet and the substrate sheet with an activation time within a range of 70 seconds to 110 seconds, annealing under a second preset condition.
[0014] Optionally, the polished surfaces of the plasma-activated diffusion sheet and the substrate sheet are bonded together; the bonded diffusion sheet and the substrate sheet are placed in a first bonding container and bonded at a preset temperature; wherein the preset temperature is 400 degrees Celsius and the first bonding container is a vacuum environment.
[0015] The embodiment of the present application further discloses a silicon substrate, which is manufactured by the above-mentioned method for manufacturing a silicon substrate. The silicon substrate comprises a substrate sheet and a diffusion sheet, and the substrate sheet is bonded to the diffusion sheet.
[0016] The present application makes improvements to the preparation method of silicon substrates, by first wet-cleaning the diffusion sheet and the substrate sheet to remove surface impurities, and then using a combination of wet activation and plasma activation to replace the wet hydrophobic activation method used in the prior art, to perform hydrophilic activation treatment on the surfaces of the substrate sheet and the diffusion sheet, thereby increasing the concentration of -OH groups suspended on the surfaces of the substrate sheet and the diffusion sheet, as well as the surface activation energy of the substrate sheet and the diffusion sheet; and then bonding the substrate sheet and the diffusion sheet in a vacuum environment at a preset temperature, replacing the low-temperature bonding combined with high-temperature annealing method in the prior art, so that the substrate sheet and the diffusion sheet are easier to bond in a vacuum environment, which not only improves the bonding strength between the substrate sheet and the diffusion sheet, but also improves the problems of fracture and breakage in the bonding area. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation methods of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:
[0018] Figure 1 This is a step diagram of a first embodiment of a method for preparing a silicon substrate of the present application;
[0019] Figure 2 This is a diagram showing the steps of cleaning the diffusion sheet and the substrate sheet in the first embodiment of the method for preparing the silicon substrate of the present application;
[0020] Figure 3 This is a diagram showing the steps of wet activating a diffusion sheet and a substrate sheet in an embodiment of a method for preparing a silicon substrate of the present application;
[0021] Figure 4 This is a diagram of the steps of plasma activation of a diffusion sheet and a substrate sheet in an embodiment of a method for preparing a silicon substrate of the present application;
[0022] Figure 5 This is a step diagram of forming a radio frequency electric field in a chamber to activate the surfaces of a diffusion sheet and a substrate sheet under the action of the radio frequency electric field in an embodiment of a method for preparing a silicon substrate of the present application;
[0023] Figure 6A diagram showing the steps of vacuum bonding a diffusion sheet and a substrate sheet at a preset temperature in one embodiment of a method for preparing a silicon substrate of the present application;
[0024] Figure 7 A schematic diagram of a first bonding container in one embodiment of a method for preparing a silicon substrate of the present application;
[0025] Figure 8 This is a diagram showing the steps of thinning and polishing the diffusion sheet and the substrate sheet after bonding in an embodiment of the method for preparing a silicon substrate of the present application;
[0026] Fig. 9 It is a schematic diagram of an embodiment of a silicon substrate of the present application.
[0027] Among them, 10, silicon substrate; 100, substrate sheet; 200, diffusion sheet; 300, first bonding container; 310, base; 320, barrel body. DETAILED DESCRIPTION
[0028] The present application is described in detail below with reference to the accompanying drawings and optional embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.
[0029] Figure 1 This is a step diagram of the first embodiment of the method for preparing a silicon substrate of the present application; the embodiment of the present application discloses a method for preparing a silicon substrate, comprising the steps of:
[0030] S1: taking a diffusion sheet and a substrate sheet, and cleaning the diffusion sheet and the substrate sheet;
[0031] S2: The cleaned diffusion sheet and substrate sheet are spun dry to remove residual water on the surface;
[0032] S3: wet activation of the diffusion sheet and the substrate sheet;
[0033] S4: After wet activation, plasma activation is performed on the diffusion sheet and the substrate sheet;
[0034] S5: vacuum bonding the diffusion sheet and the substrate sheet at a preset temperature;
[0035] S6: Thinning and polishing the bonded diffusion sheet and substrate sheet to obtain a silicon substrate.
[0036] The present application makes improvements to the preparation method of silicon substrates, by first wet-cleaning the diffusion sheet and the substrate sheet to remove surface impurities, and then using a combination of wet activation and plasma activation to replace the wet hydrophobic activation method used in the prior art, to perform hydrophilic activation treatment on the surfaces of the substrate sheet and the diffusion sheet, thereby increasing the concentration of -OH groups suspended on the surfaces of the substrate sheet and the diffusion sheet, as well as the surface activation energy of the substrate sheet and the diffusion sheet; and then bonding the substrate sheet and the diffusion sheet in a vacuum environment at a preset temperature, replacing the low-temperature bonding combined with high-temperature annealing method in the prior art, so that the substrate sheet and the diffusion sheet are easier to bond in a vacuum environment, which not only improves the bonding strength between the substrate sheet and the diffusion sheet, but also improves the problems of fracture and breakage in the bonding area.
[0037] It should be noted that traditional silicon substrate materials are mainly divided into three categories: substrate wafers, epitaxial wafers and SOI (Silicon-On-Insulator) silicon wafers. Substrate wafers provide the basic structure and crystal structure of silicon materials, and their usage accounts for about 70% of the total silicon wafer usage. Epitaxial wafers and SOI silicon wafers are both processed based on substrate wafers.
[0038] The present application prepares a multi-layer concentration silicon substrate by bonding a diffusion sheet and a substrate sheet. Its cost is effectively lower than that of an epitaxial wafer, which greatly reduces the production cost and is particularly suitable for replacing traditional thick epitaxial wafers grown by vapor deposition with a long processing cycle.
[0039] In this application, the diffusion sheet and substrate sheet after surface bonding can be understood as a wafer, and the diffusion sheet and substrate sheet after bonding can be understood as a preliminarily formed silicon substrate.
[0040] In the process of preparing silicon substrates, first select the prepared substrate and diffuser, and clean the substrate and diffuser to remove surface impurities in preparation for subsequent processes. The steps for cleaning the substrate and diffuser are as follows:
[0041] Figure 2 FIG. 1 is a diagram showing the steps of cleaning the diffusion sheet and the substrate sheet in an embodiment of the method for preparing a silicon substrate of the present application, as shown in FIG. Figure 2 As shown, step S1 of cleaning the diffusion sheet and the substrate sheet includes:
[0042] S11: Soaking the diffusion sheet and the substrate sheet in a first solution at a first preset temperature for a first preset time to remove impurities on the surfaces of the diffusion sheet and the substrate sheet;
[0043] S12: Rinse with hot deionized water for a first preset time:
[0044] S13: Rinse with cold deionized water for a first preset time;
[0045] S14: Soaking in the second solution for a second preset time to remove the oxide layer on the surface; rinsing with cold deionized water for a first preset time;
[0046] S15: Soaking the silicon wafer in a third solution at a second preset temperature for a first preset time to remove metal ions on the surface of the silicon wafer;
[0047] S16: Rinse with hot deionized water for a first preset time;
[0048] S17: Rinse with cold deionized water for a first preset time.
[0049] Among them, the first preset time is 10 minutes, the second preset time is 30 seconds, the first preset temperature is 110 degrees Celsius, and the second preset temperature is 80 degrees Celsius.
[0050] In this embodiment, the prepared N- single crystal diffusion sheet and N++ single crystal substrate sheet can be wet cleaned. The specific cleaning steps are as follows:
[0051] Soak in the first solution at 110 degrees Celsius for 10 minutes, wherein the first solution includes a mixed solution of sulfuric acid and hydrogen peroxide, and the mixing ratio of sulfuric acid and hydrogen peroxide is 4:1. Soaking in the first solution with this mixing ratio can effectively remove impurity particles and organic impurities on the surface of the silicon wafer.
[0052] The surface of the wafer soaked in the first solution is hydrophilic, and is rinsed with a large amount of hot deionized water for 10 minutes, and then rinsed with cold deionized water for 10 minutes to further remove surface particles and metal ions.
[0053] Since soaking in the first solution will cause an oxide layer to grow on the surface of the diffusion sheet and the substrate sheet, they need to be soaked in the second solution for 30 seconds, wherein the second solution includes a mixed solution of hydrofluoric acid and water, and the mixing ratio of hydrogen fluoride to water is 1:10; soaking in the second solution with this mixing ratio can effectively remove the surface oxide layer, and then rinse again with cold deionized water for 10 minutes to further remove surface particles and metal ions.
[0054] Then soak it in a third solution at 80°C for 10 minutes, wherein the third solution includes a mixed solution of hydrochloric acid, hydrogen peroxide and water, and the mixing ratio of hydrochloric acid, hydrogen peroxide and water is 1:1:5. Soaking in the third solution with this mixing ratio can effectively remove metal ions on the surface of the silicon wafer. Rinse with a large amount of hot deionized water for 10 minutes, and then rinse with cold deionized water for 10 minutes.
[0055] Finally, a drying step is performed to dehydrate or centrifuge the cleaned diffusion sheet and substrate sheet to remove residual water on the surface, thereby obtaining the diffusion sheet and substrate sheet to be bonded for the next process.
[0056] After the diffuser and the substrate are wet cleaned, they need to be bonded. Before bonding, the surface activity of the diffuser and the substrate needs to be treated to improve the bonding strength between the diffuser and the substrate. The diffuser and the substrate in this application are first activated by wet activation. The specific method is as follows:
[0057] Figure 3 FIG. 1 is a diagram showing the steps of wet activating the diffusion sheet and the substrate sheet in an embodiment of the method for preparing the silicon substrate of the present application, as shown in FIG. Figure 3 As shown, step S3 of wet activating the diffusion sheet and the substrate sheet comprises:
[0058] S31: Rinse the diffusion sheet and the substrate sheet with cold deionized water for a first preset time;
[0059] S32: Soaking in a fourth solution at a third preset temperature for a first preset time;
[0060] S33: Rinse with hot deionized water for a first preset time, and then rinse with cold deionized water for a first preset time.
[0061] Among them, the first preset time is 10 minutes, and the third preset temperature is 80°C.
[0062] First, the diffusion sheet and the substrate sheet were rinsed with a large amount of hot deionized water for 10 minutes, and then rinsed with cold deionized water for 10 minutes, so as to further remove the microparticles and a part of the metal ions on the surface of the diffusion sheet and the substrate sheet.
[0063] Then, the diffuser and the substrate are immersed in a fourth solution at 80°C for 10 minutes, wherein the fourth solution includes a mixed solution of ammonia water, hydrogen peroxide and water, and the mixing ratio of ammonia water, hydrogen peroxide and water is 1:1:5. Immersing in the fourth solution at this mixing ratio can increase the adsorption capacity between the diffuser and the substrate, wherein the weak alkalinity of ammonia water can activate the surface layer of silicon, making the wafer surface hydrophilic, and a certain number of -OH groups are suspended on the surface of the diffuser and the substrate after wet activation treatment, which is conducive to improving the adsorption force between the diffuser and the substrate; finally, the cleaned diffuser and the substrate are dehydrated or centrifuged to remove the surface water residue to prepare for the subsequent process steps.
[0064] Since the amount of -OH on the wafer surface after wet activation treatment is not large, its bonding ability is low. Low-temperature bonding cannot achieve the required bonding strength, and high-temperature annealing must be performed to strengthen the bonding, but this will introduce damage to the bonding interface.
[0065] Based on the above reasons, after the diffusion sheet and the substrate sheet are wet activated, a second activation, namely plasma activation, is required. Specifically, the steps for plasma activation of the diffusion sheet and the substrate sheet are as follows:
[0066] Figure 4 FIG. 1 is a diagram showing the steps of plasma activation of the diffusion sheet and the substrate sheet in an embodiment of the method for preparing the silicon substrate of the present application, as shown in FIG. Figure 4 As shown, step S4 of plasma activation of the diffusion sheet and the substrate sheet includes:
[0067] S41: placing the wet activated diffusion sheet and substrate sheet in a chamber of a plasma dry degumming device;
[0068] S42: The chamber is set to a first preset condition to form a vacuum environment and a radio frequency electric field;
[0069] S43: activating the surfaces of the diffusion sheet and the substrate sheet in the chamber under the action of a radio frequency electric field;
[0070] The first preset conditions in the chamber include: setting the vacuum pressure between 400 mTorr and 600 mTorr, setting the flow rate between 300 sccm and 400 sccm; and the radio frequency electric field power formed in the chamber is 500W.
[0071] In the present application, the wafer after wet activation is placed in a plasma dry degumming device, the chamber is set to a vacuum pressure of 400-600 mtorr, and the oxygen flow rate is set to 300-400 sccm. Under this condition, a stable vacuum environment can be formed.
[0072] The RF power is set to 500W, and ionization occurs under the action of the RF electric field to form plasma, and the plasma is used to activate the wafer surface.
[0073] Plasma activation uses oxygen as the plasma gas source to remove hydrocarbons and other contaminants on the wafer surface through the bombardment of plasma.
[0074] At the same time, since the oxygen plasma activation process will grow an extremely thin oxide layer on the surface of the wafer, this oxide layer has good hydrophilicity, which is beneficial to the subsequent bonding effect in a low-temperature environment. After the wafer has been treated with plasma activation, the number of -OH groups hanging on the surface has increased significantly.
[0075] It should be noted that the plasma activation time needs to be strictly controlled, because as the plasma activation time increases, the roughness of the wafer surface will increase significantly, resulting in excessive differences in the surface morphology of the wafers to be bonded, increasing the difficulty of subsequent bonding; if the plasma activation time is too short, the number of -OH groups on the wafer surface is insufficient, the surface activation energy is insufficient, and it is not conducive to good bonding of the wafer.
[0076] Based on the above problems, the activation time needs to be controlled. The specific activation time is as follows:
[0077] The activation time for the diffuser sheet and the substrate sheet ranges from 70 seconds to 110 seconds.
[0078] In order to determine an optimal plasma activation time, the surface roughness of wafers was tested at different activation times within 100 seconds. It was found that when the plasma activation time exceeded 90 seconds, the surface roughness of the wafer increased significantly.
[0079] The bonding sheet was then subjected to a tensile strength test. When the activation treatment time ranged from 70 seconds to 110 seconds, specifically, when the activation time was less than 80 seconds, the bonding rate continued to increase with the increase in plasma activation time; when the activation time exceeded 90 seconds, the bonding rate showed a downward trend due to the increase in the roughness of the wafer surface; therefore, the bonding rate was highest when the activation time was between 80 seconds and 90 seconds, so the optimal plasma activation time was determined to be between 80 seconds and 90 seconds.
[0080] Furthermore, during the plasma activation process, certain process conditions are required. In order to ensure the effect of plasma activation, the present application has also made improvements, as follows:
[0081] Figure 5 This is a step diagram of forming a radio frequency electric field in a chamber to activate the surfaces of the diffusion sheet and the substrate sheet under the action of the radio frequency electric field in an embodiment of the method for preparing a silicon substrate of the present application, as shown in FIG. Figure 5 As shown, the step S43 of forming a radio frequency electric field in the chamber and performing activation treatment on the surfaces of the diffusion sheet and the substrate sheet under the action of the radio frequency electric field further includes:
[0082] S431: After the front sides of the diffusion sheet and the substrate sheet with activation time within 70 seconds to 110 seconds are respectively bonded together, annealing is performed under the second preset conditions.
[0083] After the front sides of the wafer samples with activation time between 70 seconds and 110 seconds are bonded, annealing treatment is performed under the second preset condition, wherein the second preset condition is nitrogen annealing treatment for 2 hours in a heating environment of 400 degrees Celsius, thereby effectively improving the bonding ability of the wafer.
[0084] This application uses a combination of wet activation and plasma activation to activate the hydrophilicity of the wafer surface, replacing the wet hydrophobic activation treatment in the prior art, significantly increasing the concentration of -OH groups suspended on the wafer surface and the activation energy of the wafer surface, laying the foundation for subsequent tight bonding in a low-temperature environment.
[0085] The present application uses a treatment method combining plasma activation with wet activation to further increase the -OH concentration on the wafer surface through plasma activation, but without causing too much -OH, because too much -OH will cause a large number of byproducts to be generated at the bonding interface during subsequent low-temperature annealing, resulting in a large number of voids. By combining wet activation with plasma activation, the required bonding strength can be obtained, while avoiding the generation of a large number of voids during low-temperature annealing.
[0086] After the plasma activation is completed, the diffusion sheet and the substrate sheet need to be bonded to initially form a silicon substrate. The specific bonding steps are as follows:
[0087] Figure 6 A diagram showing the steps of vacuum bonding a diffusion sheet and a substrate sheet at a preset temperature in one embodiment of a method for preparing a silicon substrate of the present application; Figure 7 FIG. 1 is a schematic diagram of a first bonding container in an embodiment of a method for preparing a silicon substrate of the present application; Figure 6 and Figure 7 As shown, step S5 of vacuum bonding the diffusion sheet and the substrate sheet at a preset temperature includes:
[0088] S51: Laminating the plasma activated diffusion sheet and the polished surface of the substrate sheet;
[0089] S52: placing the bonded diffusion sheet and substrate sheet into a first bonding container and bonding them at a preset temperature;
[0090] The preset temperature is 400 degrees Celsius, the first bonding container is in a vacuum environment, and the first bonding container can be made of quartz material.
[0091] The first bonding container includes a base and a barrel body, the barrel body is arranged on the base, and the barrel body and the base can be made of quartz material, which is conducive to forming an integrated design of the barrel body and the base, and ensuring the structural stability of the first bonding container.
[0092] The cross-section of the barrel is circular, and the diameter of the barrel is larger than the diameter of the diffusion sheet and substrate sheet to be bonded. The front end of the barrel is slotted to facilitate placement of the wafer inside.
[0093] A number of circular guide holes are arranged on the base to facilitate the circulation of process gases; a circular hole is designed at the front end of the base, and the first bonding container can be manually pushed and pulled in the furnace tube by inserting a quartz hook used for pushing and pulling into the circular hole.
[0094] In addition, a quartz cover with a circular flow guide hole is also designed on the top of the barrel to facilitate the stable flow of gas during the process.
[0095] The present application performs low-temperature vacuum bonding by laminating the polished surfaces of the diffusion sheet and the substrate sheet after plasma activation, placing them in a first bonding container made of quartz, and performing low-temperature vacuum bonding in a vacuum environment at 400°C; the bonded diffusion sheet and the substrate sheet are subjected to a tensile test, and the bonding strength can reach 3MPa to 4MPa. In the tensile test, the final fracture surfaces after the diffusion sheet and the substrate sheet are bonded did not occur at the bonding point, thus meeting the requirements for subsequent device processing.
[0096] For ease of understanding, the diffusion sheet and substrate sheet that are activated after bonding are referred to as wafers in this application.
[0097] The specific process method is as follows: use a vacuum suction pen to pick up a wafer to be bonded, with the polished surface facing up, and place the wafer on the base through the groove at the front end of the barrel. Then pick up another wafer to be bonded, and place it on the bottom wafer with the polished surface facing down. Since the backs of the wafers to be bonded are all frosted surfaces and have not been subjected to chemical mechanical polishing, the large roughness makes it difficult to bond the two adjacent wafers on the back, while the polished surfaces facing each other on the front are conducive to bonding due to the smaller surface roughness; therefore, the polished surfaces of the two wafers to be bonded are facing each other, and the two wafers are naturally pressed together due to gravity. Finally, the angle of the positioning edge is adjusted to make them completely fit; then the next wafers to be bonded are placed in sequence according to the above method.
[0098] Use a quartz hook to push the first bonding container with the wafer loaded into the furnace tube, and start the vacuum operation after the furnace door flange is closed; and set the process conditions as follows: process temperature 350℃ to 400℃, vacuum pressure 270 to 300mtorr, nitrogen flow rate 300-400sccm, and low-temperature bonding in a vacuum environment for 60 minutes.
[0099] The vacuum environment will form a microscopic vacuum state at the defects of the wafer bonding interface. After the vacuum bonding is completed, 5 liters of nitrogen are introduced into the cavity to return the pressure to normal pressure, and nitrogen annealing is continued for 30 minutes at 350℃-400℃. At this time, due to the pressure difference between the bonding interface and the external atmospheric pressure, the pressure difference can offset the thermal expansion effect at the defects of the bonded wafer interface during conventional thermal annealing, thereby further increasing the bonding strength.
[0100] The present application adopts a low-temperature bonding method of vacuum bonding combined with annealing to replace the low-temperature bonding combined with high-temperature annealing method in the prior art, which not only ensures the required bonding strength, but also avoids the bonding interface damage and void problems introduced by the high-temperature annealing process.
[0101] When the silicon substrate formed by the preparation method of the present application is used for semiconductor device manufacturing, the device IR reverse leakage level is basically consistent with the epitaxial wafer. The leakage level is greatly improved compared with the bonded silicon wafer in the prior art, thereby improving the device product performance.
[0102] Furthermore, the first bonding container of the present application can realize low-temperature vacuum bonding of wafers in batches at one time, thereby improving production efficiency.
[0103] Figure 8 FIG. 1 is a diagram showing the steps of thinning and polishing the diffusion sheet and the substrate sheet after bonding in an embodiment of the method for preparing a silicon substrate of the present application; Figure 8 As shown, step S6 of thinning and polishing the bonded diffusion sheet and substrate sheet to obtain a silicon substrate includes:
[0104] S61: performing a thinning process on the N-layer of the bonded diffusion sheet and the substrate sheet;
[0105] S62: performing chamfering treatment on the surfaces of the diffusion sheet and the substrate sheet;
[0106] S63: polishing the surfaces of the diffusion sheet and the substrate sheet;
[0107] S64: Cleaning the surfaces of the diffusion sheet and the substrate sheet.
[0108] In the present application, the bonded diffusion sheet and substrate sheet can be understood as the initially formed silicon substrate. After the diffusion sheet and the substrate sheet are bonded in a vacuum environment, the silicon substrate can be thinned according to the actual device performance required, and the N-layer can be thinned according to the N-layer thickness required for device manufacturing, thereby obtaining a multi-layer concentration silicon substrate of N-, N+, and N++.
[0109] Then, the edge of the silicon substrate is chamfered to make the edge of the thinned silicon substrate smoother and enhance the reliability and stability of the silicon substrate. The method of chamfering the silicon substrate is the same as the existing method of chamfering, so it will not be repeated.
[0110] The N-layer surface of the silicon substrate after thinning and chamfering is then polished to repair the surface damage layer of the silicon substrate to achieve a super mirror state.
[0111] Finally, after polishing, the bonded silicon wafer is routinely cleaned to completely remove surface particles and metal ions, thereby finally obtaining the desired silicon substrate. The performance of the silicon substrate is further improved by polishing and thinning the silicon substrate in this application.
[0112] Fig. 9 is a schematic diagram of an embodiment of the silicon substrate of the present application, such as Fig. 9 As shown, the embodiment of the present application also discloses a silicon substrate, which is made by the above-mentioned method for making a silicon substrate, and the silicon substrate includes a substrate and a diffusion sheet, and the substrate and the diffusion sheet are bonded. The performance, reliability and integration of the device can be significantly improved by bonding the substrate and the diffusion sheet.
[0113] In traditional silicon substrates, the bonding strength between the substrate and the diffusion sheet is low, and the substrate and the diffusion sheet are prone to fracture and breakage in the bonding area, which directly affects the performance of the silicon substrate.
[0114] Based on the above problems, the present application has made improvements to the preparation method of silicon substrates, by first wet cleaning the diffusion sheet and the substrate sheet to remove surface impurities, and then using a combination of wet activation and plasma activation to replace the wet hydrophobic activation method used in the prior art, to perform hydrophilic activation treatment on the surfaces of the substrate sheet and the diffusion sheet, thereby increasing the concentration of -OH groups suspended on the surfaces of the substrate sheet and the diffusion sheet, as well as the surface activation energy of the substrate sheet and the diffusion sheet; and then bonding the substrate sheet and the diffusion sheet in a vacuum environment at a preset temperature, replacing the low-temperature bonding combined with high-temperature annealing method in the prior art, so that the substrate sheet and the diffusion sheet are easier to bond in a vacuum environment, which not only improves the bonding strength between the substrate sheet and the diffusion sheet, but also improves the problems of fracture and damage in the bonding area, further improving the performance of the silicon substrate.
[0115] It should be noted that the inventive concept of the present application can form a large number of embodiments, but the length of the application document is limited and it is impossible to list them one by one. Therefore, under the premise of no conflict, the embodiments or technical features described above can be arbitrarily combined to form new embodiments. After the embodiments or technical features are combined, the original technical effects will be enhanced.
[0116] The above content is a further detailed description of the present application in combination with specific optional implementation methods, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, several simple deductions or substitutions can be made without departing from the concept of the present application, which should be deemed to fall within the scope of protection of the present application.
Claims
1. A method for preparing a silicon substrate, characterized in that: Includes steps: Taking a diffusion sheet and a substrate sheet, and cleaning the diffusion sheet and the substrate sheet; The cleaned diffusion sheet and the substrate sheet are spun dry to remove residual water on the surface; Performing wet activation on the diffusion sheet and the substrate sheet; After wet activation, plasma activation is performed on the diffusion sheet and the substrate sheet; Vacuum bonding the diffusion sheet and the substrate sheet at a preset temperature; The bonded diffusion sheet and substrate sheet are thinned and polished to obtain a silicon substrate.
2. The method for preparing a silicon substrate according to claim 1, wherein: The step of cleaning the diffusion sheet and the substrate sheet comprises: Soaking the diffuser sheet and the substrate sheet in a first solution at a first preset temperature for a first preset time to remove impurities on the surfaces of the diffuser sheet and the substrate sheet; Rinse with hot deionized water for the first preset time: flushing with cold deionized water for a first preset time; Soak in the second solution for a second preset time to remove the surface oxide layer: flushing with cold deionized water for a first preset time; Soaking the silicon wafer in a third solution at a second preset temperature for a first preset time to remove metal ions on the surface of the silicon wafer; flushing with hot deionized water for a first preset time; Rinse with cold deionized water for the first preset time.
3. The method for preparing a silicon substrate according to claim 2, wherein: The first solution includes a mixed solution of sulfuric acid and hydrogen peroxide, and the mixing ratio of the sulfuric acid to the hydrogen peroxide is 4:1; The second solution includes a mixed solution of hydrofluoric acid and water, and the mixing ratio of hydrogen fluoride to water is 1:10; The third solution includes a mixed solution of hydrochloric acid, hydrogen peroxide and water, and the mixing ratio of the hydrochloric acid, the hydrogen peroxide and the water is 1:1:
5.
4. The method for preparing a silicon substrate according to claim 2, wherein: The step of wet activating the diffuser and the substrate comprises: Rinse the diffusion sheet and the substrate sheet with cold deionized water for a first preset time; Soaking in a fourth solution at a third preset temperature for a first preset time; Rinse with hot deionized water for a first preset time, and then rinse with cold deionized water for a first preset time.
5. The method for preparing a silicon substrate according to claim 4, wherein: The fourth solution includes a mixed solution of ammonia water, hydrogen peroxide and water, and the mixing ratio of the ammonia water, the hydrogen peroxide and the water is 1:1:
5.
6. The method for preparing a silicon substrate according to claim 2, wherein: The step of plasma activating the diffusion sheet and the substrate sheet comprises: Placing the wet activated diffusion sheet and the substrate sheet in a chamber of a plasma dry degumming device; The chamber is set to a first preset condition to form a vacuum environment and a radio frequency electric field; Performing activation treatment on the surfaces of the diffusion sheet and the substrate sheet in the chamber under the action of a radio frequency electric field; The first preset conditions in the chamber include: setting the vacuum pressure between 400 mTorr and 600 mTorr, setting the flow rate between 300 sccm and 400 sccm; and the radio frequency electric field power formed in the chamber is 500W.
7. The method for preparing a silicon substrate according to claim 6, wherein: The step of forming a radio frequency electric field in the chamber and activating the surfaces of the diffusion sheet and the substrate sheet under the action of the radio frequency electric field also includes: The activation treatment time for the diffusion sheet and the substrate sheet is in a range of 70 seconds to 110 seconds.
8. The method for preparing a silicon substrate according to claim 7, wherein: The step of plasma activating the diffusion sheet and the substrate sheet further comprises: After the diffusion sheet and the substrate sheet with an activation time of 70 seconds to 110 seconds are respectively laminated on their front sides, annealing is performed under a second preset condition.
9. The method for preparing a silicon substrate according to claim 1, wherein: The step of vacuum bonding the diffusion sheet and the substrate sheet at a preset temperature comprises: Laminating the plasma activated diffusion sheet and the polished surface of the substrate sheet; The bonded diffusion sheet and the substrate sheet are placed in a first bonding container and bonded at a preset temperature; wherein the preset temperature is 400 degrees Celsius, and the first bonding container is in a vacuum environment.
10. A silicon substrate, characterized in that: The silicon substrate is manufactured by the method for manufacturing a silicon substrate according to any one of claims 1 to 9, and the silicon substrate comprises a substrate sheet and a diffusion sheet, and the substrate sheet is bonded to the diffusion sheet.