CN115207167A - A kind of cleaning method of silicon polishing surface - Google Patents

Abstract

The invention relates to the technical field of solar cells, and particularly discloses a method for cleaning a polished silicon surface. The cleaning method comprises the following steps: cleaning the silicon wafer by sequentially adopting mixed acid liquid and pure water respectively to obtain a primary processing wafer, wherein the mixed acid liquid is an aqueous solution containing phosphoric acid, fluoboric acid and nitric acid; sequentially adopting alkaline mixed liquor and pure water to respectively clean the primary treatment piece to obtain a secondary treatment piece, wherein the alkaline mixed liquor is an aqueous solution containing strong base and ethanol; and respectively cleaning and drying the secondary processing piece by sequentially adopting oxidizing liquid and pure water to obtain the polished silicon wafer, wherein the oxidizing liquid is an aqueous solution comprising hydrofluoric acid and hydrogen peroxide. The cleaning method provided by the invention can effectively remove the residual tiny particles in the polishing process, reduce the surface roughness and improve the surface morphology; and residual organic matters and metal ions on the surface can be removed, so that the subsequent passivation process is facilitated, and the photoelectric conversion efficiency can be improved.

Description

A kind of cleaning method of silicon polishing surface

technical field

The invention relates to the technical field of solar cells, in particular to a cleaning method for a silicon polishing surface.

Background technique

In the production process of solar cells, whether P-type cells or N-type cells are usually treated with backside polishing to reduce the recombination area of the backside surface, improve the backside reflectivity, and thus improve the cell performance. The back polishing is single-sided polishing, that is, the back is polished and the front remains suede. The process steps of single-side polishing are as follows: one side is protected by a mask, and the other side is etched on one side at a high temperature with a high-concentration polishing liquid, so as to realize the polishing and corrosion effect on the side without a mask. During the polishing and etching process, with the progress of the reaction, due to the deviation of the concentration of the polishing solution, the increase of by-products, and the uniformity of the previous process, it will lead to the existence of fine particles or tiny protrusions on the surface of the polished silicon wafer. It affects the overall flatness, increases the specific surface area, affects the subsequent passivation effect, and is not conducive to further improvement of cell efficiency and yield.

At present, the existing surface defects are usually used as the initial reaction point, and relatively uniform surface defects are used to achieve isotropic corrosion effect. However, for the polished surface, the surface roughness will increase, and the flatness of the polished surface Still can not meet the requirements of use. Therefore, there is an urgent need to develop a cleaning method for silicon wafers after polishing, which is of great significance to effectively remove the tiny particles left by the polishing process, improve the surface morphology, and remove the residual organic matter on the surface.

SUMMARY OF THE INVENTION

Aiming at the problems of high roughness and low flatness on the polishing surface of the existing polished silicon wafer, the present invention provides a cleaning method for the silicon polishing surface, which can effectively remove the tiny particles remaining in the polishing process, reduce the surface roughness, and improve the surface It can also remove residual organic substances and metal ions on the surface, which is beneficial to the subsequent passivation process and can improve the photoelectric conversion efficiency.

In order to achieve the above-mentioned purpose of the invention, the embodiment of the present invention adopts the following technical scheme:

A cleaning method for a silicon polishing surface, the cleaning method comprises the following steps

Step 1, sequentially using mixed acid solution and pure water to respectively clean the silicon wafer to obtain a first-level treatment wafer, wherein the mixed acid solution is an aqueous solution comprising phosphoric acid, fluoroboric acid and nitric acid;

Step 2, successively using alkaline mixed solution and pure water to clean the primary treatment sheet respectively to obtain a secondary treatment sheet, wherein the alkaline mixed solution is an aqueous solution comprising strong alkali and ethanol;

Step 3, sequentially using an oxidizing solution and pure water to clean and dry the secondary treatment wafer respectively to obtain a polished silicon wafer, wherein the oxidizing solution is an aqueous solution comprising hydrofluoric acid and hydrogen peroxide.

Compared with the prior art, the cleaning method of the silicon polishing surface provided by the present application has the following advantages:

In this application, firstly, the mixed acid solution including fluoroboric acid, nitric acid and phosphoric acid is used for cleaning, and nitric acid is used to oxidize the silicon surface, and at the same time, the metal and organic substances that may remain are oxidized; the surface oxide is slowly etched using fluoroboric acid and phosphoric acid. Etching, using temperature to adjust the activity of fluoroboric acid and the overall reaction rate, to achieve surface flatness trimming, reduce surface roughness; then use strong alkali and ethanol to remove possible residual reaction by-products on the surface to ensure surface cleanliness; finally The metal ions are removed by hydrofluoric acid, and then the surface is covered with a thin silicon oxide layer by hydrogen peroxide to protect the surface of the silicon wafer and ensure that the cleaned and polished silicon wafer is not polluted by the environment during the subsequent process.

The cleaning method provided in the present application is mainly used for the cleaning of silicon wafers after polishing, which can effectively remove the tiny particles remaining in the polishing process, reduce the surface roughness, and improve the surface morphology; it can also remove the residual organic substances and metal ions on the surface, which is beneficial to the follow-up Passivation process, significantly improve the photoelectric conversion efficiency.

Optionally, the mixed acid solution includes the following components by volume: phosphoric acid aqueous solution: 50%-60%, fluoroboric acid aqueous solution: 5%-10%, nitric acid aqueous solution: 2%-5%, and the balance is water .

Optionally, the concentration of the phosphoric acid aqueous solution is 80wt%~90wt%.

Further optionally, the concentration of the phosphoric acid aqueous solution is 85wt%.

Optionally, the concentration of the fluoroboric acid aqueous solution is 45wt% to 52wt%.

Further optionally, the concentration of the fluoroboric acid aqueous solution is 49wt%.

Optionally, the concentration of the nitric acid aqueous solution is 60wt%˜68wt%.

Further optionally, the concentration of the nitric acid aqueous solution is 63wt%.

Through the optimal proportion of each component in the mixed acid solution, it is ensured that the fine particles on the polished surface of the silicon wafer can be effectively removed during the cleaning process, the surface flatness is improved, and subsequent passivation is facilitated.

Optionally, the alkaline mixed solution includes the following components by volume percentage: strong alkali aqueous solution: 1% to 5%, ethanol aqueous solution: 5% to 10%, and the balance is water.

Optionally, the concentration of the strong alkali aqueous solution is 45wt% to 55wt%.

Further optionally, the concentration of the strong alkali aqueous solution is 50wt%.

Optionally, the strong base is sodium hydroxide or potassium hydroxide.

Optionally, the concentration of the ethanol aqueous solution is 90wt%~95wt%.

Further optionally, the concentration of the ethanol aqueous solution is 95wt%.

The by-products and organic substances that may remain during the cleaning process of the mixed acid solution can be effectively removed through the optimal proportion of each component in the alkaline mixed solution, so as to ensure the surface cleanliness.

Optionally, the oxidizing solution includes the following components by volume: aqueous hydrofluoric acid: 3% to 10%, aqueous hydrogen peroxide: 2% to 10%, and the balance is water.

Optionally, the concentration of the hydrofluoric acid aqueous solution is 40wt% to 50wt%.

Further optionally, the concentration of the hydrofluoric acid aqueous solution is 49%.

Optionally, the concentration of the hydrogen peroxide aqueous solution is 28wt%˜30wt%.

Further optionally, the concentration of the hydrogen peroxide aqueous solution is 30wt%.

Through the optimal ratio of each component in the oxidizing solution, the residual organic matter and metal ions on the surface of the silicon wafer can be effectively removed, and an extremely thin silicon oxide film can be formed on the surface of the silicon wafer, which can effectively prevent drying or microparticles in the air. contamination of surfaces.

Optionally, in step 1, the conditions for cleaning the mixed acid solution are: the temperature is 10°C to 50°C, and the time is 1 min to 10 min.

Optionally, in step 2, the cleaning time of the alkaline mixed solution is 1 min to 5 min.

Optionally, in step 3, the cleaning time of the oxidizing solution is 2 min to 6 min.

Through the optimal cleaning conditions, the flatness of the polished surface can be effectively improved, the surface morphology can be improved, and the residual organic substances, by-products and metal ions on the surface can be effectively removed, which is beneficial to the subsequent passivation process, thereby improving the photoelectric conversion efficiency of the battery.

Optionally, in step 1, step 2 and step 3, the cleaning conditions of the pure water are as follows: the temperature is 20°C-50°C, and the time is 2min-8min.

Through the preferred cleaning conditions of pure water, it is ensured that there is no residue of mixed acid solution, alkaline mixed solution and oxidizing solution on the surface of the silicon wafer.

Optionally, the drying conditions are: the temperature is 60°C to 100°C, and the time is 5 min to 20 min.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

An embodiment of the present invention provides a process for preparing an N-type solar cell, comprising the following steps:

S1. Texture the N-type single crystal silicon wafer with a resistivity of 1Ω·cm and a reflectivity of 10%;

S2. Boron diffusion doping is performed on the N-type silicon wafer after texturing, and the sheet resistance is 120Ω;

S3. Perform single-side etching and single-side polishing on the N-type silicon wafer after boron diffusion, and the back reflectivity is 36%;

The polished silicon wafers are cleaned by the following cleaning methods:

The silicon wafers were cleaned at 40°C for 5 min with a mixed acid solution, wherein the mixed acid solution included the following components by volume: phosphoric acid aqueous solution with a concentration of 85wt%: 50%, fluoroboric acid aqueous solution with a concentration of 49wt%: 7 %, the concentration is 63wt% nitric acid aqueous solution: 2%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 40°C for 5 minutes with pure water to obtain primary treated wafers;

The above-mentioned primary treatment sheet is cleaned for 3min under normal temperature conditions by using an alkaline mixed solution; the above-mentioned alkaline mixed solution includes each component in the following volume percentage: potassium hydroxide aqueous solution with a concentration of 50wt%: 2.5% with a concentration of 95wt% Aqueous ethanol solution: 6%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 20°C for 8 minutes with pure water to obtain secondary treated wafers;

The secondary treatment sheet is cleaned for 5min under normal temperature conditions by using an oxidizing solution, and the above-mentioned oxidizing solution includes the following components by volume: the concentration of 49wt% hydrofluoric acid aqueous solution: 4%, the concentration of 30wt% hydrogen peroxide solution: 6%, the balance is water;

Use pure water to clean the above-mentioned cleaned silicon wafers at 30°C for 5 minutes, and then dry them at 60°C for 10 minutes to obtain cleaned and polished silicon wafers;

S4, perform polysilicon deposition on the cleaned N-type silicon wafer, with a thickness of 120 nm;

S5, de-plating and cleaning the N-type silicon wafer after depositing polysilicon;

S6. Use ALD to deposit 4nm-thick aluminum oxide on the silicon wafer after de-winding plating and cleaning;

S7. For the silicon wafer after deposition of aluminum oxide, use PECVD to deposit 80nm silicon nitride;

S8. For the silicon wafer after deposition of silicon nitride, use screen printing technology to form electrodes on the front and back of the battery, and sinter at high temperature to form a good contact between the metal and the polysilicon;

S9, conducting electrical performance testing and sorting on the sintered cells.

Example 2

This embodiment provides a preparation process for an N-type solar cell, which is different from Embodiment 1 in that: in step S3, the polished silicon wafer is cleaned by the following cleaning method:

The silicon wafers were cleaned at 50°C for 1 min with a mixed acid solution, wherein the mixed acid solution included the following components in volume percentage: phosphoric acid aqueous solution with a concentration of 90wt%: 55%, fluoroboric acid aqueous solution with a concentration of 52wt%: 5 %, the concentration is 68wt% nitric acid aqueous solution: 5%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 50°C for 2 min with pure water to obtain primary treated wafers;

The above-mentioned primary treatment sheet is cleaned for 1 min under normal temperature conditions by using an alkaline mixed solution; the above-mentioned alkaline mixed solution includes each component of the following volume percentage: a potassium hydroxide aqueous solution with a concentration of 55wt%: 5%, a concentration of 93wt% Ethanol aqueous solution: 10%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 35°C for 5 min with pure water to obtain secondary treated wafers;

The secondary treatment sheet is cleaned for 2 min under normal temperature conditions by using an oxidizing solution, and the above-mentioned oxidizing solution includes the following components by volume: the aqueous solution of hydrofluoric acid with a concentration of 45wt%: 10%, and the aqueous hydrogen peroxide solution with a concentration of 28wt%: 2%, the balance is water;

The above-mentioned cleaned silicon wafers are cleaned at 25° C. for 6 minutes with pure water, and then dried at 100° C. for 5 minutes to obtain cleaned and polished silicon wafers.

Example 3

This embodiment provides a preparation process for an N-type solar cell, which is different from Embodiment 1 in that: in step S3, the polished silicon wafer is cleaned by the following cleaning method:

The silicon wafers were cleaned at 10°C for 10 min with a mixed acid solution, wherein the mixed acid solution included the following components by volume: phosphoric acid aqueous solution with a concentration of 80wt%: 60%, fluoroboric acid aqueous solution with a concentration of 45wt%: 10 %, the concentration is 60wt% nitric acid aqueous solution: 3%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 20°C for 6 minutes with pure water to obtain primary treated wafers;

The above-mentioned primary treatment sheet is cleaned for 5min under normal temperature conditions by using an alkaline mixed solution; the above-mentioned alkaline mixed solution includes each component in the following volume percentage: a potassium hydroxide aqueous solution with a concentration of 45wt%: 1% with a concentration of 90wt% Aqueous ethanol solution: 5%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 20°C for 8 minutes with pure water to obtain secondary treated wafers;

The secondary treatment sheet is cleaned for 6 min under normal temperature conditions by using an oxidizing liquid, and the above-mentioned oxidizing liquid includes each component in the following volume percentages: a 40wt% hydrofluoric acid aqueous solution: 3%, and a 29wt% hydrogen peroxide aqueous solution: 10%, the balance is water;

The above-mentioned cleaned silicon wafers are cleaned at 32° C. for 4.5 minutes with pure water, and then dried at 85° C. for 20 minutes to obtain cleaned and polished silicon wafers.

In order to better illustrate the technical solutions of the present invention, further comparisons are made below with the examples of the present invention through comparative examples.

Comparative Example 1

This comparative example provides a preparation process of an N-type solar cell, which is different from Example 1 in that: in the cleaning step S3, the phosphoric acid aqueous solution with a concentration of 85wt% in the mixed acid solution is replaced with hydrofluoric acid with a concentration of 49wt%.

Comparative Example 2

This comparative example provides a preparation process for an N-type solar cell, which is different from Example 1 in that: in the cleaning step S3, the nitric acid aqueous solution with a concentration of 63wt% in the mixed acid solution is replaced with a hydrogen peroxide solution with a concentration of 30wt%.

Comparative Example 3

This comparative example provides a preparation process of an N-type solar cell, which is different from Example 1 in that: in the cleaning step S3, the potassium hydroxide aqueous solution with a concentration of 50wt% in the alkaline mixed solution is replaced with ammonia with a concentration of 28wt% aqueous solution.

Comparative Example 4

This comparative example provides a preparation process of an N-type solar cell, which is different from Example 1 in that: in the cleaning step S3, the polished silicon wafer is cleaned by the following cleaning method, and the cleaning sequence of the mixed acid solution and the oxidizing solution is Make the exchange as follows:

The silicon wafers were cleaned at 40°C for 5 min with an oxidizing solution, wherein the oxidizing solution included the following components by volume: 49wt% hydrofluoric acid aqueous solution: 4%, 30wt% hydrogen peroxide aqueous solution: 6% , the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 40°C for 5 minutes with pure water to obtain primary treated wafers;

The above-mentioned primary treatment sheet is cleaned for 3min under normal temperature conditions by using an alkaline mixed solution; the above-mentioned alkaline mixed solution includes each component in the following volume percentage: potassium hydroxide aqueous solution with a concentration of 50wt%: 2.5% with a concentration of 95wt% Aqueous ethanol solution: 6%, the balance is water;

The above-mentioned cleaned silicon wafers were cleaned at 20°C for 8 minutes with pure water to obtain secondary treated wafers;

The secondary treatment sheet is cleaned for 5 minutes at room temperature by using a mixed acid solution. The mixed acid solution includes the following components by volume: phosphoric acid aqueous solution with a concentration of 85% by weight: 50% with a concentration of 49% by weight. The fluoroboric acid aqueous solution : 7%, the concentration of nitric acid aqueous solution of 63wt%: 2%, the balance is water;

The above-mentioned cleaned silicon wafer is cleaned at 30° C. for 5 minutes by using pure water, and then dried at 60° C. for 10 minutes to obtain the cleaned and polished silicon wafer.

In order to better illustrate the characteristics of the N-type solar cells provided by the embodiments of the present invention, the performance tests of the N-type solar cells prepared in Examples 1 to 3 and Comparative Examples 1 to 4 are performed below, and the results are shown in Table 1 below.

Table 1

The above Voc is the open circuit voltage, the unit is mV;

The above Jsc is the current density, and the unit is mA/cm ² ;

The above FF is the fill factor, and the unit is %;

The above Eta is the conversion efficiency, and the unit is %.

As can be seen from Table 1, using the cleaning method provided by the present application, the N-type solar cell provided by the present application has a higher conversion efficiency through the characteristic components and specific cleaning sequence. The cleaning method in a specific order can effectively remove the tiny particles remaining in the polishing process, reduce the surface roughness, and improve the surface morphology; it can also remove the residual organic matter and metal ions on the surface, which is beneficial to the subsequent passivation process and can improve the photoelectric conversion efficiency.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (6)

1. a cleaning method of silicon polishing surface, is characterized in that: described cleaning method comprises the following steps: Step 1. Use mixed acid solution and pure water to clean the silicon wafer respectively to obtain a first-stage treatment wafer, wherein, the mixed acid solution is an aqueous solution including phosphoric acid, fluoroboric acid and nitric acid, and the mixed acid solution includes the following volume Percentage of each component: phosphoric acid aqueous solution: 50%~60%, fluoroboric acid aqueous solution: 5%~10%, nitric acid aqueous solution: 2%~5%, and the balance is water; the concentration of the phosphoric acid aqueous solution is 80wt%~90wt% %; the concentration of the fluoroboric acid aqueous solution is 45wt%～52wt%; the concentration of the nitric acid aqueous solution is 60wt%～68wt%; Step 2, successively using alkaline mixed solution and pure water to clean the primary treatment sheet respectively to obtain a secondary treatment sheet, wherein the alkaline mixed solution is an aqueous solution comprising strong alkali and ethanol; Step 3, sequentially using an oxidizing solution and pure water to wash and dry the secondary treatment wafer respectively to obtain a polished silicon wafer, wherein the oxidizing solution is an aqueous solution comprising hydrofluoric acid and hydrogen peroxide. 2. The method for cleaning a silicon polishing surface as claimed in claim 1, wherein the alkaline mixed solution comprises the following components by volume: strong alkaline aqueous solution: 1% to 5%, ethanol aqueous solution: 5% ~10%, the balance is water; the concentration of the strong alkali aqueous solution is 45wt% ~ 55wt%; the strong alkali is sodium hydroxide or potassium hydroxide; the concentration of the ethanol aqueous solution is 90wt% ~ 95wt%. 3. The method for cleaning a silicon polished surface as claimed in claim 1, wherein the oxidizing solution comprises the following components by volume: aqueous hydrofluoric acid: 3%～10%, aqueous hydrogen peroxide: 2%～10% 10%, the balance is water; the concentration of the hydrofluoric acid aqueous solution is 40wt%~50wt%; the concentration of the hydrogen peroxide aqueous solution is 28wt%~30wt%. 4. The method for cleaning a silicon polishing surface as claimed in claim 1, wherein in step 1, the conditions for cleaning with the mixed acid solution are: the temperature is 10°C to 50°C, and the time is 1min to 10min; and/ or In step 2, the cleaning time of described alkaline mixed solution is 1min～5min; And/or In step 3, the cleaning time of described oxidation solution is 2min～6min. 5. The cleaning method of silicon polishing surface as claimed in claim 1, wherein in step 1, step 2 and step 3, the cleaning conditions of described pure water are: temperature is 20 ℃～50 ℃, time is 2min ~8min. 6 . The method for cleaning a silicon polished surface according to claim 1 , wherein the drying conditions are as follows: the temperature is 60° C. to 100° C. and the time is 5 min to 20 min. 7 .