Preparation method of semiconductor substrate and solar cell

Abstract

The invention provides a preparation method of a semiconductor substrate and a solar cell, and the preparation method comprises the following steps: 1), carrying out the metal chemical etching treatment and metal particle cleaning treatment of a pretreated silicon wafer, and obtaining a semi-finished silicon wafer; 2) carrying out primary surface modification treatment on the semi-finished silicon wafer by adopting primary surface modification liquid to obtain a primary silicon wafer; and 3) carrying out secondary surface modification treatment on the primary silicon wafer by using a secondary surface modification liquid to obtain the semiconductor silicon substrate, wherein the primary surface modification liquid comprises hydrofluoric acid and / or a strong oxidant; the secondary surface modification liquid comprises an alkali solution. By using the preparation method, the line mark difference on the surface of the silicon wafer can be reduced, the prepared semiconductor silicon substrate has relatively high surface reflectivity, and when the semiconductor silicon substrate is applied to a solar cell, the efficiency of the cell can be improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a semiconductor substrate and a solar cell, belonging to the technical field of crystalline silicon processing. Background Art

[0002] In the semiconductor industry and solar photovoltaic industry, cutting silicon rods into silicon wafers is a very important process. The quality of silicon wafers is directly related to the manufacturing and processing of subsequent processes. The line marks on the surface of silicon wafers after the silicon rods are cut are one of the problems that affect the surface quality of silicon wafers. Even after the deposition process such as the transparent conductive film layer is completed, the step height difference of the line marks will still affect the grid line printing quality of the battery, causing the problem of broken grids, and the line marks will also affect the passivation performance and increase the battery recombination. In addition, the back of the solar cell generally uses a polished surface to improve the absorption of long waves. The flatness of the polished surface affects the reflection of light, and the presence of line marks also affects the reflectivity of the back polished surface, thereby affecting the conversion efficiency of the battery.

[0003] At present, the semiconductor industry has relatively high requirements for the surface quality of silicon wafers, and mainly removes line marks through chemical grinding and polishing, but this method requires the use of professional equipment and polishing liquid, which is costly. The silicon wafers in the photovoltaic industry are very thin, and the use of chemical grinding and polishing will cause excessive loss of the originally thin silicon wafers, resulting in defects. At present, the photovoltaic industry generally uses concentrated alkali to roughly polish silicon wafers to improve the surface quality of silicon wafers, but this method cannot completely eliminate line marks. Silicon wafers treated with this method will still have a step height difference of 2 to 4 microns.

[0004] Therefore, how to prepare a semiconductor substrate with high surface flatness is a problem that needs to be solved urgently. Summary of the invention

[0005] In view of the above-mentioned defects, the present invention provides a method for preparing a semiconductor substrate and a solar cell. After the cut silicon wafer is processed by this method, the silicon wafer does not lose weight significantly, and the step height difference at the line marks on the surface of the silicon wafer does not exceed 0.15μm. The line marks on the silicon wafer are significantly eliminated, and the preparation process of this method is simple and easy to achieve mass production.

[0006] The present invention provides a semiconductor silicon substrate, which is prepared by the above-mentioned method for preparing a semiconductor substrate. The surface flatness of the semiconductor silicon substrate is relatively high, and can meet the needs of the photovoltaic industry that has relatively high requirements for the flatness of silicon wafers.

[0007] The present invention provides a solar cell, which includes the semiconductor silicon substrate as described above as a back reflective layer or uses the semiconductor silicon substrate as described above for texturing, and the back reflective layer of the silicon wafer of the cell has a high reflectivity to light, and can reflect unabsorbed light back to the active layer to improve the light absorption efficiency, thereby improving the performance of the cell. Using the semiconductor silicon substrate as described above for texturing can provide a more uniform velvet surface, thereby improving the efficiency of the cell.

[0008] One aspect of the present invention provides a method for preparing a semiconductor silicon substrate, the method comprising the following steps:

[0009] Step 1) performing metal chemical etching and metal particle cleaning on the pretreated silicon wafer to obtain a semi-finished silicon wafer;

[0010] Step 2) using a primary surface modification liquid to perform a primary surface modification treatment on the semi-finished silicon wafer to obtain a primary silicon wafer; the primary surface modification liquid comprises hydrofluoric acid and a strong oxidant;

[0011] Step 3) performing secondary surface modification treatment on the primary silicon wafer using a secondary surface modification solution to obtain the semiconductor silicon substrate;

[0012] The secondary surface modification solution includes an alkaline solution; the step height difference at the line marks on the surface of the semiconductor silicon substrate does not exceed 0.15 μm.

[0013] In the preparation method as described above, the metal chemical etching process comprises:

[0014] The pretreated silicon wafer is immersed in a metal chemical etching solution including a metal salt, an oxidant and hydrofluoric acid at 25 to 50° C. for 20 to 240 seconds to obtain an intermediate silicon wafer.

[0015] The preparation method as described above, wherein the metal salt is a salt containing at least one metal ion of Pt, Au, Ag, Cu and Ni, and the molar concentration of the metal salt is 0.5 to 10 M; and / or,

[0016] The oxidant is H 2 O 2 , HNO 3 、KMnO 4 At least one of the above, wherein the molar concentration of the oxidant is 5 to 20 M; and / or,

[0017] The concentration of the hydrofluoric acid is 1-10M.

[0018] In the preparation method as described above, the metal chemical etching process comprises:

[0019] Performing metal deposition treatment on the pretreated silicon wafer to obtain a metal-attached silicon wafer, wherein the thickness of the attached metal layer is 1 to 10 nm;

[0020] The metal-attached silicon wafer is immersed in a metal chemical etching solution including hydrofluoric acid and an oxidant at 25 to 50° C. for 20 to 240 seconds to obtain an intermediate silicon wafer.

[0021] The preparation method as described above, wherein the additional metal layer is an additional metal layer obtained by metal deposition treatment of at least one metal selected from Pt, Au, Ag, Cu and Ni; and / or,

[0022] The hydrofluoric acid concentration is 1 to 10 M; and / or,

[0023] The oxidant is H 2 O 2 , HNO 3 、KMnO 4 At least one of the above, the molar concentration of the oxidant is 5 to 20M.

[0024] In the preparation method as described above, the metal particle cleaning treatment comprises: soaking the intermediate silicon wafer in a metal cleaning agent at 20 to 25° C. for 3 to 10 minutes to obtain the semi-finished silicon wafer;

[0025] in,

[0026] The metal cleaning agent includes HCl, H 2 O 2 , H 2 O mixed solution, the HCl, H 2 O 2 , H 2 The molar concentration ratio of the mixed solution of O is (1-3):(1-3):(3-8); or,

[0027] The metal cleaning agent comprises nitric acid, and the mass fraction of the nitric acid is 30-50wt%; or,

[0028] The metal cleaning agent includes aqua regia; or,

[0029] The metal cleaning agent comprises ammonia water, and the mass fraction of the ammonia water is 5-25wt%.

[0030] The preparation method as described above, wherein the molar concentration of the hydrofluoric acid in the primary surface modification solution is 0.1 to 5 M; and / or,

[0031] The strong oxidant in the primary surface modification solution is at least one of nitric acid, concentrated sulfuric acid and KMnO4, and the concentration of the strong oxidant is 0.1 to 5M; and / or,

[0032] The treatment temperature of the primary surface modification treatment is 25° C., and the treatment time is 30 to 120 seconds.

[0033] The preparation method as described above, wherein the alkali in the alkali solution in the secondary surface modification solution comprises at least one of KOH, NaOH, and TMAH, and the mass fraction of the alkali solution is 5 to 30 wt%; and / or,

[0034] The treatment temperature of the secondary surface modification treatment is 45-60° C., and the treatment time is 10-60 seconds.

[0035] The preparation method as described above, wherein after step 3), further comprises: cleaning the semiconductor silicon substrate, wherein the cleaning comprises cleaning with a mixed solution of alkali and hydrogen peroxide, cleaning with a mixed solution of hydrochloric acid and hydrogen peroxide, or cleaning with hydrofluoric acid;

[0036] or,

[0037] After step 3), the semiconductor silicon substrate is further subjected to texturing treatment.

[0038] The present invention also provides a solar cell, which comprises the semiconductor silicon substrate as described above or the semiconductor silicon substrate prepared by the preparation method as described above, wherein one side of the substrate is provided with a velvet surface and the other side is a polished surface, and one side of the polished surface is suitable for being used as a backlight surface;

[0039] An intrinsic passivation layer, a doping layer, a transparent conductive layer and a metal electrode are sequentially deposited on both sides of the substrate.

[0040] The method for preparing a semiconductor substrate provided by the present invention etches the rough surface of a silicon wafer based on a metal chemical catalytic reaction, and polishes the silicon wafer with a rough surface in combination with acid etching and alkaline etching processes. When the method is used to treat a silicon wafer with a rough surface, the metal chemical etching solution can react quickly with the damaged part of the silicon wafer, accelerate the etching rate of the silicon wafer, and thus the line marks can be quickly removed. Because the silicon wafer is immersed in the metal chemical etching solution for a short time, it is possible to reduce the step height difference without etching the rest of the silicon wafer so that the silicon wafer does not lose weight significantly, and the step height difference at the line marks on the surface of the silicon wafer does not exceed 0.15 μm, and the line marks on the silicon wafer are significantly eliminated, which can meet the damage removal needs of thinner silicon wafers in the solar photovoltaic industry. The reflectivity of the surface of the semiconductor silicon substrate prepared by the method for preparing a semiconductor substrate provided by the present invention is greatly improved, and the method has a simple preparation process and is easy to achieve mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a process flow chart of an embodiment of the present invention;

[0042] Figure 2 The morphology of the semiconductor silicon substrate provided by the embodiment of the present invention;

[0043] Figure 3 This is the morphology of the silicon wafer after rough polishing by the BL process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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.

[0045] A first aspect of the present invention provides a method for preparing a semiconductor substrate, comprising the following steps:

[0046] 1) performing metal chemical etching and metal particle cleaning on the pretreated silicon wafer to obtain a semi-finished silicon wafer;

[0047] 2) performing a surface modification treatment on the semi-finished silicon wafer using a primary surface modification liquid to obtain a primary silicon wafer; the primary surface modification liquid comprises hydrofluoric acid and a strong oxidant;

[0048] 3) performing secondary surface modification treatment on the primary silicon wafer using a secondary surface modification liquid to obtain the semiconductor silicon substrate;

[0049] The secondary surface modification solution includes an alkaline solution; the step height difference at the line marks on the surface of the semiconductor silicon substrate does not exceed 0.15 μm.

[0050] In step 1), the present invention does not limit the pretreatment method, as long as the impurities on the surface of the silicon wafer can be removed. For example, a mixed solution of alkali and hydrogen peroxide can be used for cleaning. The alkali can be potassium hydroxide, sodium hydroxide, or potassium hydroxide and sodium hydroxide. The mass fraction of the alkali can be 1 to 10wt%, and the mass fraction of the hydrogen peroxide can be 0.5 to 10wt%.

[0051] The pretreatment temperature can be 50-80°C, and the pretreatment time can be 2-4 minutes. By pretreating the silicon wafer, impurities such as oil stains on the surface of the silicon wafer can be removed, which is beneficial to the contact reaction between the reagent and the silicon wafer in the subsequent metal chemical etching process, thereby improving the reaction efficiency of the subsequent metal chemical etching process.

[0052] The metal chemical etching process in the present invention utilizes metal chemical catalytic reaction to etch the surface of the silicon wafer. Metal chemical catalytic reaction refers to the process of accelerating chemical reactions by using metals or metal compounds as catalysts. The surface of the metal catalyst has multiple active sites, and the reactant molecules can be adsorbed on these sites and undergo chemical changes; the metal catalyst can also significantly increase the reaction rate by reducing the activation energy required for the reaction.

[0053] The present invention uses a metal chemical catalytic reaction to etch a silicon wafer in a metal chemical etching process, which can provide more active sites between reactants in the metal chemical etching process, accelerate the etching of the silicon wafer surface, and facilitate the rapid removal of line marks. The step height difference at the line marks on the surface of the obtained semiconductor silicon substrate does not exceed 0.15 μm, and the use of metal chemical etching greatly reduces the time consumed by the etching reaction. Because the silicon wafer is immersed in the metal chemical etching solution for a short time, it can be based on significantly reducing the step height difference without etching the rest of the silicon wafer too much, so that the silicon wafer will not produce a significant weight loss. Therefore, the preparation method of the semiconductor substrate using the present invention is conducive to the efficient polishing of silicon wafers, is suitable for the processing of thinner silicon wafers, and can be applied to large-scale industrial preparation and reduce industrial costs.

[0054] In addition, by performing a metal particle cleaning process, the remaining metal particles can be removed without covering the surface of the silicon wafer that needs to undergo a subsequent surface modification process, which is beneficial for improving the reaction rate of the subsequent surface modification process.

[0055] In step 2), the primary surface modification solution is a mixed solution of hydrofluoric acid and a strong oxidant.

[0056] When a strong oxidant is included in the primary surface modification solution, it can convert the silicon in the silicon wafer into oxides, which are easier to remove in the subsequent process. In addition, the use of a strong oxidant can also speed up the etching rate and further flatten the surface of the silicon wafer.

[0057] When the primary surface modification liquid contains hydrofluoric acid, the hydrofluoric acid can remove unnecessary oxide layers or expose a clean silicon surface, which is beneficial to the contact between the primary surface modification liquid and the silicon substrate, further improving the efficiency of the primary surface modification treatment. By using the primary surface modification liquid to perform a primary surface modification treatment on the semi-finished silicon wafer, the step difference of the line mark can be further reduced.

[0058] In step 3), the secondary surface modification solution is an alkaline solution. The present invention uses an alkaline solution to perform secondary surface modification on the primary silicon wafer, thereby further polishing the primary silicon wafer to obtain a semiconductor silicon substrate with higher reflectivity.

[0059] In a specific implementation method, the metal chemical etching process includes:

[0060] At 25 to 50° C., the pretreated silicon wafer is immersed in a metal chemical etching solution including a metal salt, an oxidant and hydrofluoric acid, and after 20 to 240 seconds, an intermediate silicon wafer is obtained. At 25 to 50° C., including but not limited to 25° C., 30° C., 35° C., 40° C., 45° C., 50° C. or any two thereof. The immersion treatment time is 20 to 240 seconds, for example, including but not limited to 20 seconds, 80 seconds, 120 seconds, 160 seconds, 200 seconds, 240 seconds or any two thereof.

[0061] The present invention etches the silicon wafer with a metal chemical etching solution including a metal salt, an oxidant and hydrofluoric acid, so that the metal salt can be used as a catalyst to effectively promote the etching rate of the silicon wafer surface, which is beneficial to the flattening of the silicon wafer surface; by controlling the time and temperature of the silicon wafer immersion treatment within the above range, it is beneficial to control the degree of silicon wafer etching and reduce the step height difference at the line mark on the silicon wafer surface.

[0062] In a specific implementation method, the metal salt in the metal chemical etching process is a salt containing at least one metal ion of Pt, Au, Ag, Cu and Ni, and the molar concentration of the metal salt is 0.5 to 10 M. For example, the metal salt may contain only one metal ion as described above, or may contain two or more metal ions as described above; the molar concentration of the metal salt includes but is not limited to 0.5 M, 1 M, 3 M, 5 M, 7 M, 9 M, 10 M or a range consisting of any two of them.

[0063] The present invention does not limit the type of acid ions in the metal salt. For example, the acid ions of the metal salt may be at least one of chloride ions, sulfate ions, nitrate ions, and carbonate ions.

[0064] The present invention can effectively catalyze the etching reaction of the silicon wafer by using the above metal salt; in addition, the use of the above metal salt does not damage the silicon wafer, and the metal particles can be removed in the subsequent steps without causing new pollution on the silicon wafer. By controlling the concentration of the metal salt within the above range, the reaction speed of the metal chemical etching process can be effectively increased, which is conducive to quickly reducing the step height difference at the line mark on the surface of the silicon wafer.

[0065] In another embodiment, the oxidant in the metal chemical etching process is H 2 O 2 , HNO 3 、KMnO 4At least one of the above, the molar concentration of the oxidant is 5 to 20 M. For example, the molar concentration of the oxidant includes but is not limited to 5 M, 10 M, 15 M, 20 M or any two thereof. The present invention is beneficial to converting silicon in a silicon wafer into oxides during metal chemical etching, thereby accelerating the etching rate by using the above oxidant and controlling the concentration of the oxidant within the above range.

[0066] In another embodiment, the concentration of hydrofluoric acid in the metal chemical etching process is 1 to 10 M. For example, the molar concentration of hydrofluoric acid includes but is not limited to 1 M, 3 M, 5 M, 7 M, 9 M, 10 M or a range consisting of any two of them. The present invention uses hydrofluoric acid and controls the concentration of hydrofluoric acid within the above range, which is beneficial to removing unnecessary oxide layers or exposing clean silicon surfaces in the metal chemical etching process, thereby making the surface of the silicon wafer flatter.

[0067] In a specific embodiment, the metal chemical etching process includes:

[0068] Performing metal deposition treatment on the pretreated silicon wafer to obtain a metal-attached silicon wafer, wherein the thickness of the attached metal layer is 1 to 10 nm;

[0069] The metal-attached silicon wafer is immersed in a metal chemical etching solution including hydrofluoric acid and an oxidant at 25 to 50° C. for 20 to 240 seconds to obtain an intermediate silicon wafer.

[0070] The present invention does not limit the method of metal deposition processing, as long as a metal layer with a thickness of 1 to 10 nm can be obtained. For example, the metal layer can be prepared by physical methods, such as sputtering deposition, evaporation deposition, etc., or by chemical methods.

[0071] The thickness of the attached metal layer is 1 to 10 nm. For example, the thickness of the attached metal layer includes but is not limited to 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 10 nm or any two thereof. By preparing the attached metal layer within the above thickness range, it is beneficial for the metal chemical etching solution including hydrofluoric acid and oxidant to catalytically etch the pretreated silicon wafer with the metal layer as the medium, thereby achieving a better polishing effect. At the same time, setting the metal layer within the above range is also beneficial to further control industrial costs.

[0072] The temperature of the metal chemical etching treatment is 25 to 50° C., for example, including but not limited to 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., or any two thereof. The time for soaking the metal-attached silicon wafer in a metal chemical etching solution including hydrofluoric acid and an oxidant is 20 to 240 seconds, for example, including but not limited to 20 seconds, 80 seconds, 120 seconds, 160 seconds, 200 seconds, 240 seconds, or any two thereof.

[0073] The present invention controls the temperature and time of the metal chemical etching process within the above range, which is beneficial to controlling the etching degree of the silicon wafer, and further beneficial to obtaining a silicon wafer with a smooth surface.

[0074] In a specific embodiment, the additional metal layer is an additional metal layer obtained by metal deposition of at least one metal selected from Pt, Au, Ag, Cu and Ni. For example, one of the metals described above may be used for metal deposition, or two or more of the metals described above may be used for metal deposition.

[0075] The attached metal layer can be prepared using a physical method. When prepared using the physical method, the prepared metal layer has a denser structure and better uniformity. The corresponding physical deposition method can be selected according to needs to deposit the above one or more metals.

[0076] The attached metal layer can also be prepared by chemical methods. When using the chemical method, a mixed solution of a salt of at least one metal including Pt, Au, Ag, Cu and Ni with a molar concentration of 0.5 to 10 M and HF with a molar concentration of 1 to 10 M can be reacted at room temperature for 20 to 120 seconds to perform metal deposition treatment to obtain the attached metal layer.

[0077] In another embodiment, the concentration of hydrofluoric acid in the metal deposition process is 1-10 M. For example, the molar concentration of hydrofluoric acid includes but is not limited to 1 M, 3 M, 5 M, 7 M, 9 M, 10 M or a range consisting of any two of them.

[0078] In another embodiment, the oxidant in the metal deposition process is H 2 O 2 , HNO 3 、KMnO 4 At least one of the above, the molar concentration of the oxidant is 5 to 20 M. For example, the oxidant can be H 2 O 2 , HNO 3 、KMnO 4Any one of the above oxidants can also be used to perform metal chemical etching using a mixed solution of two or more of the above oxidants. The molar concentration of the oxidant is 5 to 20 M. For example, the molar concentration of the oxidant includes but is not limited to 5 M, 10 M, 15 M, 20 M or any two of them.

[0079] In a specific embodiment, the metal particle cleaning process includes: soaking the intermediate silicon wafer with a metal cleaning agent at 20-25°C for 3-10 minutes to obtain a semi-finished silicon wafer. For example, the treatment temperature of the metal particle cleaning process includes but is not limited to 20°C, 23°C, 25°C or any two thereof; the treatment time of the metal particle cleaning process includes but is not limited to 3 minutes, 5 minutes, 7 minutes, 9 minutes, 10 minutes or any two thereof.

[0080] Exemplary metal cleaning agents include HCl, H 2 O 2 , H 2 A mixed solution of O, HCl, H 2 O 2 , H 2 The molar concentration ratio of the mixed solution of O is (1-3):(1-3):(3-8). For example, the molar concentration ratio of the mixed solution includes but is not limited to 1:1:3, 2:2:5, 3:3:7, 3:3:8 or a range consisting of any two of them.

[0081] Exemplarily, the metal cleaning agent includes nitric acid, and the mass concentration of the nitric acid is 30-50wt%. For example, the mass concentration of the nitric acid includes but is not limited to 30wt%, 35wt%, 40wt%, 45wt%, 50wt% or a range consisting of any two thereof.

[0082] Exemplarily, the metal cleaning agent includes aqua regia.

[0083] Exemplarily, the metal cleaning agent includes ammonia water, and the mass concentration of the ammonia water is 5-25wt%. For example, the mass concentration of the ammonia water includes but is not limited to 5wt%, 10wt%, 15wt%, 20wt%, 25%wt or a range consisting of any two thereof.

[0084] The present invention can effectively remove the metal particles remaining on the surface of the silicon wafer without damaging the silicon wafer by using the above-mentioned metal cleaning agent to perform metal particle cleaning treatment and by controlling the temperature and time of the metal particle cleaning treatment within the above-mentioned range, thereby facilitating good contact between the reagent and the silicon wafer in subsequent steps, and further facilitating the flattening of the silicon wafer.

[0085] In a specific embodiment, the molar concentration of the hydrofluoric acid in the primary surface modification solution is 0.1 to 5 M. For example, the molar concentration of the hydrofluoric acid includes but is not limited to 0.1 M, 1 M, 2 M, 3 M, 4 M, 5 M or a range consisting of any two of them. When the primary surface modification solution includes hydrofluoric acid, it is beneficial to further remove impurities on the surface of the silicon wafer and obtain a silicon wafer with a smoother surface.

[0086] In another embodiment, the strong oxidant in the primary surface modification solution is at least one of nitric acid, concentrated sulfuric acid, and KMnO4, and the molar concentration of the strong oxidant is 0.1 to 5 M. For example, the strong oxidant can be one of nitric acid, concentrated sulfuric acid, and KMnO4, or two or more of nitric acid, concentrated sulfuric acid, and KMnO4; the molar concentration of the strong oxidant includes but is not limited to 0.1 M, 1 M, 2 M, 3 M, 4 M, 5 M, or a range consisting of any two of them. When the primary surface modification solution includes a strong oxidant, the uneven area of ​​the silicon wafer can be further modified to make the surface of the silicon wafer smoother.

[0087] In another embodiment, the treatment temperature of a surface modification treatment is 25° C., and the treatment time is 30 to 120 s. For example, the treatment time includes but is not limited to 30 s, 50 s, 80 s, 120 s or a range consisting of any two of them.

[0088] In another embodiment, the alkali in the alkaline solution in the secondary surface modification liquid includes at least one of KOH, NaOH, and TMAH, and the mass fraction of the alkaline solution is 5 to 30wt%. For example, the alkaline solution can be prepared using one alkali as described above, or two or more alkaline solutions as described above can be prepared. The mass fraction of the alkaline solution is 5 to 30wt%, for example, the mass fraction of the alkaline solution includes but is not limited to 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt% or the range of any two of them. By using the alkaline solution of the above concentration as the secondary surface modification liquid, the uneven parts of the surface can be removed by selective etching, thereby making the surface flatter.

[0089] In another embodiment, the treatment temperature of the secondary surface modification treatment is 45-60°C, and the treatment time is 10-60s. For example, the secondary surface modification treatment temperature includes but is not limited to 45°C, 50°C, 55°C, 60°C or a range consisting of any two thereof; the secondary surface modification treatment time includes but is not limited to 10s, 20s, 30s, 40s, 50s, 60s or a range consisting of any two thereof.

[0090] By performing a primary surface modification treatment and a secondary surface modification treatment on the semi-finished silicon wafer and controlling the treatment time and the treatment temperature, the surface of the semi-finished silicon wafer can be further flattened to obtain a semiconductor substrate with high surface flatness.

[0091] In a specific embodiment, after step 3), the method further includes: cleaning the semiconductor silicon substrate, wherein the cleaning process includes sequentially using a mixed solution of alkali and hydrogen peroxide, a mixed solution of hydrochloric acid and hydrogen peroxide, and a hydrofluoric acid solution for cleaning.

[0092] The present invention does not limit the cleaning process, and can be a standard RCA cleaning procedure or other cleaning processes, as long as the impurities on the surface of the semiconductor silicon substrate can be removed. For example, a mixed solution of 1-15wt% alkali and 1-15wt% hydrogen peroxide can be used for cleaning at 50-80°C for 2-4 minutes; then a mixed solution of 1-15wt% hydrochloric acid and 1-15wt% hydrogen peroxide can be used for cleaning at 50-80°C for 2-4 minutes; finally, a hydrofluoric acid with a mass fraction of 8-15wt% can be used for soaking at 25°C for 2-4 minutes to remove the oxide layer on the surface of the silicon wafer to obtain a clean semiconductor silicon substrate.

[0093] In another embodiment, after step 3), the semiconductor silicon substrate is further subjected to texturing treatment.

[0094] The present invention does not impose any special limitation on the texturing process, and the texturing method can be selected according to actual needs.

[0095] The present invention also provides a solar photovoltaic cell, comprising a semiconductor silicon substrate prepared by the above preparation method, one side of the substrate is provided with a velvet surface, and the other side is a polished surface, and one side of the polished surface is suitable for being used as a backlight surface;

[0096] An intrinsic passivation layer, a doping layer, a transparent conductive layer and a metal electrode (optional) are sequentially deposited on both sides of the substrate.

[0097] Among them, the preparation of the intrinsic passivation layer can be prepared by chemical vapor deposition or physical deposition using at least one compound selected from amorphous silicon, silicon nitride, silicon dioxide, and aluminum oxide; the preparation of the doping layer can use at least one compound selected from phosphorus-doped polycrystalline silicon and boron-doped polycrystalline silicon through chemical vapor deposition or physical deposition; the preparation of the transparent conductive layer can use at least one compound selected from indium tin oxide, fluorine-doped tin oxide, aluminum-doped zinc oxide, and gallium-doped zinc oxide through chemical vapor deposition or physical deposition; the preparation of the metal electrode can use at least one substance selected from silver, copper, aluminum, nickel, and gold through processes such as screen printing and electroplating.

[0098] In one embodiment, two sides of the substrate are n-type doped and p-type doped respectively, wherein the n-type doped side serves as the front side of the solar photovoltaic cell; and the p-type doped side serves as the back side of the solar photovoltaic cell.

[0099] The back reflective layer of the solar photovoltaic cell provided by the present invention has a high reflectivity to light and can reflect unabsorbed light back to the front active layer, thereby improving the light absorption efficiency and further improving the working efficiency of the cell.

[0100] Hereinafter, the present invention will be further described in detail through specific examples.

[0101] Example 1

[0102] The method for preparing a semiconductor substrate provided in this embodiment comprises the following steps:

[0103] 1) The pretreated silicon wafer is subjected to metal chemical etching treatment and metal particle cleaning treatment to obtain a semi-finished silicon wafer.

[0104] The metal chemical etching treatment is to immerse the pretreated silicon wafer in a metal chemical etching solution including a metal salt, an oxidant and hydrofluoric acid to obtain an intermediate silicon wafer; in the metal chemical etching solution, the metal salt is silver nitrate, and the metal salt concentration is 0.5M; the oxidant is hydrogen peroxide, and the oxidant concentration is 5M; the hydrofluoric acid concentration is 5M;

[0105] The reaction temperature of the metal chemical etching treatment is 30°C and the reaction time is 60s;

[0106] The intermediate silicon wafer is subjected to a metal particle cleaning treatment to obtain a semi-finished silicon wafer. The metal particle cleaning treatment is performed using a nitric acid reagent as a metal cleaner. The mass fraction of the nitric acid is 30%, the treatment temperature is 25° C., and the treatment time is 3 minutes.

[0107] 2) Using a primary surface modification liquid to perform a primary surface modification treatment on the semi-finished silicon wafer to obtain a primary silicon wafer.

[0108] The primary surface modification solution is a mixture of hydrofluoric acid and nitric acid, with the concentrations of each component being 1 M and 1 M;

[0109] The temperature of the first surface modification treatment was 25°C and the treatment time was 30s.

[0110] 3) Using a secondary surface modification liquid to perform secondary surface modification on the primary silicon wafer to obtain a semiconductor silicon substrate.

[0111] The alkaline solution used in the secondary surface modification solution is a potassium hydroxide solution, and the mass fraction of potassium hydroxide is 30%;

[0112] The temperature of the secondary surface modification treatment is 50°C and the treatment time is 20s.

[0113] The semiconductor substrate surface provided in this embodiment is as follows Figure 2 As shown by Figure 2 It can be seen that the surface of the semiconductor silicon substrate is relatively flat.

[0114] Example 2

[0115] The method for preparing a semiconductor substrate provided in this embodiment is basically the same as that in Embodiment 1, the difference is that the molar concentration of the metal salt in the metal chemical etching solution used in the metal chemical etching treatment in step 1) is 1M;

[0116] The reaction temperature of the metal chemical etching treatment is 30° C., and the reaction time is 50 s.

[0117] Example 3

[0118] The method for preparing a semiconductor substrate provided in this embodiment is basically the same as that in Embodiment 1, the difference is that the molar concentration of the metal salt in the metal chemical etching solution used in the metal chemical etching treatment in step 1) is 2M.

[0119] Example 4

[0120] The method for preparing a semiconductor substrate provided in this embodiment is basically the same as that in Embodiment 1, except that the metal chemical etching process in step 1) includes:

[0121] The pretreated silicon wafer is subjected to metal deposition treatment, specifically, a metal layer is prepared by magnetron sputtering (PVD), wherein the metal is silver, and a metal-attached silicon wafer is obtained, wherein the thickness of the metal layer is 5 nm;

[0122] At 40° C., the metal-attached silicon wafer is immersed in a metal chemical etching solution including hydrofluoric acid and an oxidant for 120 seconds to obtain an intermediate silicon wafer;

[0123] The concentration of hydrofluoric acid is 3M;

[0124] The oxidant is hydrogen peroxide, and the molar concentration of the oxidant is 3M.

[0125] The subsequent processing of the above-mentioned intermediate silicon wafer is the same as that in Example 1.

[0126] Example 5

[0127] The method for preparing the semiconductor substrate provided in this embodiment is basically the same as that in Embodiment 4, except that the thickness of the additional metal layer in the metal chemical etching process in step 1) is 30 nm.

[0128] Example 6

[0129] The method for preparing a semiconductor substrate provided in this embodiment is basically the same as that in Embodiment 1, except that the metal cleaning agent used in step 1) includes ammonia water with a concentration of 20%.

[0130] Comparative Example 1

[0131] The method for preparing the semiconductor substrate provided in this comparative example is basically the same as that in Example 1, except that the metal chemical etching treatment and metal particle cleaning treatment in step 1) are not performed.

[0132] Comparative Example 2

[0133] The method for preparing the semiconductor substrate provided in this comparative example is basically the same as that in Example 1, except that the primary surface modification treatment in step 2) is not performed.

[0134] Comparative example 3.

[0135] The method for preparing the semiconductor substrate provided in this comparative example is basically the same as that in Example 1, except that the secondary surface modification treatment in step 3) is not performed.

[0136] Comparative Example 4

[0137] This comparative example adopts the BL process to prepare the silicon substrate, mainly using an alkali solution with a mass fraction of 2% to immerse the silicon wafer, the immersion temperature is 80° C., and the immersion time is 120 seconds; wherein the alkali is potassium hydroxide or sodium hydroxide.

[0138] The surface of the semiconductor substrate provided in this comparative example is as follows Figure 3 As shown, there are obvious lines on the surface of the semiconductor silicon substrate.

[0139] Test example

[0140] The surface reflectivity of the semiconductor silicon substrates in Examples 1-6 and Comparative Examples 1-4 was tested by a standard 8 degree (D8) reflectivity testing device. The test results are shown in Table 1.

[0141] The step height differences at the line marks of the semiconductor silicon substrates in Examples 1-6 and Comparative Examples 1-4 were detected by 3D microscope equipment. The test results are shown in Table 1.

[0142] The test results are shown in Table 1 by weighing the semiconductor silicon substrates in Examples 1-6 and Comparative Examples 1-4 before and after preparation and calculating the weight loss values.

[0143] Table 1

[0144] Surface reflectivity / % Step height difference at line mark / μm Weight loss value / g Example 1 38.23％ 0.15 0.2 Example 2 39％ 0.1 0.23 Example 3 38.34％ 0.13 0.21 Example 4 39％ 0.14 0.18 Example 5 38％ 0.15 0.34 Example 6 38.24％ 0.15 0.21 Comparative Example 1 34.50％ 3.4 0.08 Comparative Example 2 37.88％ 0.2 0.18 Comparative Example 3 38％ 0.18 0.12 Comparative Example 4 35.62％ 3.2 0.46

[0145] According to the results in the above table, it can be seen that the semiconductor silicon substrates prepared in Examples 1-6 have higher surface reflectivity and step height difference at the line marks than those prepared in Comparative Examples 1-4; in addition, the weight loss value of the semiconductor silicon substrates prepared in Examples 1-6 is significantly reduced compared to the semiconductor silicon substrate prepared in Comparative Example 4, which reduces the mass loss of silicon wafers during the polishing process.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a semiconductor substrate, characterized in that: The following steps are involved: Step 1) performing metal chemical etching and metal particle cleaning on the pretreated silicon wafer to obtain a semi-finished silicon wafer; Step 2) using a primary surface modification liquid to perform a primary surface modification treatment on the semi-finished silicon wafer to obtain a primary silicon wafer; the primary surface modification liquid comprises hydrofluoric acid and a strong oxidant; Step 3) using a secondary surface modification liquid to perform secondary surface modification on the primary silicon wafer to obtain the semiconductor silicon substrate; the secondary surface modification liquid includes an alkaline solution; the step height difference at the line marks on the surface of the semiconductor silicon substrate does not exceed 0.15 μm.

2. The preparation method according to claim 1, characterized in that: The metal chemical etching process comprises: The pretreated silicon wafer is immersed in a metal chemical etching solution including a metal salt, an oxidant and hydrofluoric acid at 25 to 50° C. for 20 to 240 seconds to obtain an intermediate silicon wafer.

3. The preparation method according to claim 2, characterized in that: The metal salt is a salt containing at least one metal ion of Pt, Au, Ag, Cu and Ni, and the molar concentration of the metal salt is 0.5 to 10 M; and / or, The oxidant is at least one of H2O2, HNO3, and KMnO4, and the molar concentration of the oxidant is 5 to 20 M; and / or, The molar concentration of the hydrofluoric acid is 1-10M.

4. The preparation method according to claim 1, characterized in that: The metal chemical etching process comprises: Performing metal deposition treatment on the pretreated silicon wafer to obtain a metal-attached silicon wafer, wherein the thickness of the metal layer attached in the metal-attached silicon wafer is 1 to 10 nm; The metal-attached silicon wafer is immersed in a metal chemical etching solution including hydrofluoric acid and an oxidant at 25 to 50° C. for 20 to 240 seconds to obtain an intermediate silicon wafer.

5. The preparation method according to claim 4, characterized in that: The additional metal layer is obtained by metal deposition treatment of at least one metal selected from Pt, Au, Ag, Cu and Ni; and / or, The hydrofluoric acid concentration is 1 to 10 M; and / or, The oxidant is at least one of H2O2, HNO3, and KMnO4, and the molar concentration of the oxidant is 5 to 20M.

6. The preparation method according to any one of claims 2 to 5, characterized in that: The metal particle cleaning process comprises: soaking the intermediate silicon wafer with a metal cleaning agent at 20 to 25° C. for 3 to 10 minutes to obtain the semi-finished silicon wafer; in, The metal cleaning agent comprises a mixed solution of HCl, H2O2, and H2O, wherein the molar concentration ratio of the mixed solution of HCl, H2O2, and H2O is (1-3):(1-3):(3-8); or, The metal cleaning agent comprises nitric acid, and the mass fraction of the nitric acid is 30-50wt%; or, The metal cleaning agent includes aqua regia; or, The metal cleaning agent comprises ammonia water, and the mass fraction of the ammonia water is 5-25wt%.

7. The preparation method according to claim 6, characterized in that: The molar concentration of the hydrofluoric acid in the primary surface modification solution is 0.1 to 5 M; and / or, The strong oxidant in the primary surface modification solution is at least one of nitric acid, concentrated sulfuric acid and KMnO4, and the molar concentration of the strong oxidant is 0.1 to 5M; and / or, The treatment temperature of the primary surface modification treatment is 25° C., and the treatment time is 30 to 120 seconds.

8. The preparation method according to any one of claims 1 to 5, characterized in that: The alkali in the alkali solution in the secondary surface modification solution comprises at least one of KOH, NaOH and TMAH, and the mass fraction of the alkali solution is 5 to 30 wt %; and / or, The treatment temperature of the secondary surface modification treatment is 45-60° C., and the treatment time is 10-60 seconds.

9. The preparation method according to any one of claims 1 to 5, characterized in that: After step 3), the method further includes: cleaning the semiconductor silicon substrate, wherein the cleaning process includes sequentially using a mixed solution of alkali and hydrogen peroxide, a mixed solution of hydrochloric acid and hydrogen peroxide, and a hydrofluoric acid solution for cleaning; or, After step 3), the semiconductor silicon substrate is further subjected to texturing treatment.

10. A solar cell, comprising a semiconductor silicon substrate prepared by the preparation method according to claim 9, wherein one side of the semiconductor silicon substrate is provided with a velvet surface, and the other side is a polished surface, and one side of the polished surface is suitable for being used as a backlight surface; An intrinsic passivation layer, a doping layer, a transparent conductive layer and a metal electrode are deposited in sequence on both sides of the semiconductor silicon substrate.

Images