CN105810563A - Method of washing solar cell silicon wafers - Google Patents

Abstract

The invention discloses a method for cleaning silicon wafers of solar cells, which comprises the steps of: using ozone aqueous solution to soak and clean the silicon wafers to produce an oxide layer on the surface of the silicon wafers; using hydrofluoric acid solution to perform surface corrosion treatment on the silicon wafers; The slices are rinsed. The cleaning method of the present invention first soaks and cleans the silicon chip with an ozone aqueous solution, which can effectively oxidize the organic matter stained on the surface of the silicon chip and form an oxide film on the surface of the silicon chip; then, the silicon chip is corroded and cleaned by a hydrofluoric acid solution , remove the metal dirt on the surface, and corrode the oxide film on the surface, and remove the surface dirt while corroding the surface oxide film, so as to realize the cleaning of the silicon wafer surface. The cleaning method of the present invention adopts an aqueous ozone solution, which reacts with surface organic matter to produce CO ₂ and H ₂ O, which is harmless to the human body, and the waste liquid produced by the aqueous ozone solution has little environmental pollution and does not require special treatment.

Description

A method for cleaning silicon wafers of solar cells

technical field

The invention relates to the technical field of semiconductor manufacturing technology, in particular to a method for cleaning silicon wafers of solar cells.

Background technique

In the solar cell manufacturing process, silicon wafers are the core components of solar cells, and their performance parameters directly affect the power generation efficiency of solar cells. The nature and state of the surface of the silicon wafer before the junction directly affects the junction characteristics, thereby affecting the performance of the finished solar cell. The silicon wafer of the cell achieves a good cleaning effect, which helps to improve the power generation efficiency of the finished solar cell.

In the process of cutting and preparing silicon wafers, as well as during storage and transportation, the surface of silicon wafers will be contaminated with impurities, mainly including: (1) organic substances such as oil, rosin, wax; (2) metal ions and various inorganic compounds; ( 3) Dust and other soluble substances. Silicon wafers are usually cleaned by chemical cleaning. In the prior art, a mixture of nitric acid and hydrofluoric acid is used to clean silicon wafers. The function of nitric acid is to oxidize elemental silicon into silicon dioxide and oxidize the surface of silicon wafers. Finally, a dense silicon dioxide film is formed; due to the presence of hydrofluoric acid in the etching solution, the silicon dioxide is dissolved, and the resulting complex silicon hexafluoride is dissolved in water, so that the surface of the silicon is corroded to achieve the purpose of cleaning the surface.

However, this existing cleaning method has the following disadvantages: nitric acid is used in the mixed solution to oxidize the surface of the silicon wafer, and the reaction will produce nitrogen oxides, which are harmful to the human body and have the risk of endangering the health of operators.

Contents of the invention

In view of this, the present invention provides a method for cleaning silicon wafers of solar cells, which overcomes the problem that harmful substances are produced and endanger human health in existing cleaning methods.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A method for cleaning a silicon wafer of a solar cell, comprising the steps of:

S1: Soak and clean the silicon wafer with ozone aqueous solution to form an oxide layer on the surface of the silicon wafer;

S2: using hydrofluoric acid solution to corrode the surface of the silicon wafer;

S3: rinsing the silicon wafer.

Optionally, the step S1 specifically includes: placing the silicon wafer in water, and continuously bubbling ozone gas into the water at a preset flow rate for a preset time.

Optionally, the preset flow rate ranges from 2 to 10 standard liters/minute, including endpoint values.

Optionally, the preset time ranges from 1 to 5 minutes, including endpoint values.

Optionally, the step S2 specifically includes: placing the silicon wafer in a hydrofluoric acid solution to stand still, and the hydrofluoric acid solution has a first concentration.

Optionally, the range of the first concentration is 5-15%, including endpoint values.

Optionally, the step S3 includes:

S30: Put the silicon chip in the alkaline solution to stand still, take it out and rinse it with water.

Optionally, the alkaline solution is a potassium hydroxide solution having a second concentration, and the second concentration is in a range of 2-8%, inclusive.

Optionally, after the step S30, it also includes:

S31: Put the silicon wafer in the mixed solution of hydrofluoric acid and hydrochloric acid to stand still, take it out and rinse it with water.

Optionally, the concentration range of the hydrofluoric acid is 5-15%, inclusive; the concentration range of the hydrochloric acid is 5-15%, inclusive.

As can be seen from the above technical solutions, the method for cleaning silicon wafers of solar cells provided by the present invention comprises the steps of: S1 adopting an aqueous ozone solution to soak and clean the silicon wafers to produce an oxide layer on the surface of the silicon wafers; S2 adopting hydrofluoric acid solution to clean the silicon wafers. Performing surface etching treatment on the silicon wafer; S3: rinsing the silicon wafer.

In the cleaning method of the present invention, the silicon chip is first soaked and cleaned with an ozone aqueous solution. The ozone aqueous solution has a higher oxidation-reduction potential, which can effectively oxidize organic pollutants on the surface of the silicon chip, and form an oxide film on the surface of the silicon chip; then The silicon wafer is corroded and cleaned by hydrofluoric acid solution, which can remove the metal dirt on the surface and corrode the oxide film on the surface, and remove the surface dirt while corroding the surface oxide film, thereby realizing the cleaning of the silicon wafer surface .

The cleaning method of the present invention adopts ozone aqueous solution, which reacts with surface organic matter to produce _CO2 and _H2O , which is harmless to human body, and the waste liquid produced by the ozone aqueous solution has little environmental pollution and does not need to be treated. Therefore, compared with the existing method, the solar cell silicon wafer cleaning method of the present invention overcomes the problem that harmful substances will be produced in the existing cleaning method, which is harmful to human health.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the flowchart of the cleaning method of a kind of solar cell silicon wafer that the embodiment of the present invention provides;

FIG. 2 is a flow chart of a method for cleaning silicon wafers of solar cells according to another embodiment of the present invention.

detailed description

In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

Please refer to FIG. 1 , which is a flow chart of a cleaning method for a solar cell silicon wafer provided by an embodiment of the present invention. The cleaning method includes steps:

S1: Soak and clean the silicon wafer with ozone aqueous solution to form an oxide layer on the surface of the silicon wafer;

S2: using hydrofluoric acid solution to corrode the surface of the silicon wafer;

S3: rinsing the silicon wafer.

It can be seen from the above technical scheme that the method for cleaning silicon wafers of solar cells provided in this embodiment first soaks and cleans the silicon wafers with an aqueous ozone solution. The aqueous ozone solution has a relatively high oxidation-reduction potential. The organic dirt attached to the surface is oxidized, and an oxide film is formed on the surface of the silicon wafer; then the silicon wafer is corroded and cleaned by hydrofluoric acid solution, which can remove the metal dirt on the surface and corrode the oxide film formed on the surface. While corroding the surface oxide film, the surface dirt is removed, thereby realizing the cleaning of the silicon wafer surface.

The cleaning method in this embodiment uses ozone aqueous solution, which reacts with surface organic pollutants to produce _CO2 and _H2O , which is not harmful to human body, and the waste liquid produced by ozone aqueous solution has little environmental pollution and does not need special treatment. Therefore, compared with the existing method, the cleaning method of the silicon wafer of the solar cell in this embodiment overcomes the problem that the existing cleaning method will produce harmful substances and endanger human health.

The method for cleaning solar cell silicon wafers of the present invention will be described in detail below in conjunction with the specific implementation of each step. The cleaning method of a kind of solar battery silicon chip provided by the present invention specifically comprises the steps:

S1: The silicon wafer is soaked and cleaned with ozone aqueous solution to form an oxide layer on the surface of the silicon wafer. Specifically, it includes: placing the silicon wafer in water, and continuously blowing ozone gas into the water at a preset flow rate for a preset time.

In this embodiment, the silicon wafer to be cleaned is placed in water, and ozone gas is continuously blown into the water, and the ozone gas is dissolved in water to form an ozone aqueous solution, so as to soak and clean the silicon wafer. Ozone aqueous solution is highly corrosive and oxidizing. When silicon wafers come into contact with ozone-dissolved aqueous solutions, the organic pollutants on the surface will react quickly and be oxidized to generate CO ₂ and H ₂ O, and the surface of silicon wafers will also It is quickly oxidized to form an oxide film, that is, a silicon dioxide layer.

In this embodiment, the silicon wafer is chosen to be placed in an aqueous solution, and ozone gas is continuously bubbled into the water to carry out the reaction process. During this reaction process, the reaction speed of the silicon wafer in the ozone aqueous solution is relatively fast. This is because in the process of dissolving the ozone gas in the water, the ozone dissolves in the water and rapidly decomposes to produce peroxide ions and free radicals, which will rapidly react with the silicon wafer. Reaction, the organic dirt on the surface of the silicon wafer is oxidized, and an oxide film is formed on the surface of the silicon wafer. Therefore, in this embodiment, the method of continuously bubbling ozone gas into the aqueous solution is adopted to ensure the reactivity, to have a faster reaction process and higher reaction efficiency.

In the actual cleaning operation, the flow rate and duration of ozone gas blown into the aqueous solution can be adjusted according to the volume of the cleaning tank and water. The oxide layer formed on the surface of the silicon wafer increases with the increase of the ozone concentration in the aqueous solution. In a specific embodiment, the range of the preset flow rate may be 2-10 standard liters/minute, including the endpoint value; the range of the preset time may be 1-5 minutes, including the endpoint value.

In actual operation, a number of silicon wafers to be cleaned can be placed in a flower basket, and the flower basket where the silicon wafers are placed is placed in the water of the cleaning tank, and then ozone gas is continuously introduced into the water. Among them, deionized water is preferably used as water.

S2: Corroding the surface of the silicon wafer by using a hydrofluoric acid solution. After the silicon chip to be cleaned is taken out from the ozone solution, it is placed in a hydrofluoric acid solution having a first concentration and left to stand for a period of time.

Put the silicon chip cleaned by ozone aqueous solution into the hydrofluoric acid solution, the hydrofluoric acid solution can remove the metal contamination on the surface of the silicon chip, and corrode the oxide film (SiO ₂ layer) formed on the surface of the silicon chip, and after corroding the surface At the same time, the oxide film removes the dirt and particles attached to the surface, so as to achieve the cleaning effect.

In a specific embodiment of the present invention, the range of the first concentration is 5-15%, including the endpoint value. The standing time can be controlled and adjusted according to the concentration of the hydrofluoric acid solution and the actual situation of the silicon wafer.

After the silicon wafer is cleaned in the hydrofluoric acid solution, the silicon wafer is taken out from the cleaning tank and rinsed in deionized water.

S3: rinsing the silicon wafer. After the previous two steps of cleaning, the silicon wafer is further rinsed, including:

S30: Put the silicon chip in the alkaline solution to stand still, take it out and rinse it with water.

After the silicon wafers treated in the previous step are taken out and rinsed with deionized water, the silicon wafers are placed in an alkaline solution and left to stand for a period of time. By standing in the alkaline solution, the dirt, particles and oxides attached to the surface of the silicon wafer can be further dissolved. After the silicon wafer is taken out from the alkaline solution, it is rinsed in deionized water.

In a specific embodiment of the present invention, the alkaline solution may be a potassium hydroxide solution having a second concentration, and the second concentration ranges from 2% to 8%, inclusive. It can be understood that in other embodiments of the present invention, other types of alkaline solutions can also be used, and the concentration thereof can be adjusted according to actual conditions, which is not limited here.

S31: Put the silicon wafer in the mixed solution of hydrofluoric acid and hydrochloric acid to stand still, take it out and rinse it with water. By standing and cleaning in the mixed solution of hydrofluoric acid and hydrochloric acid, the oxide and metal contamination on the surface of the silicon wafer can be effectively removed again.

In a specific embodiment, the concentration range of the hydrofluoric acid is 5-15%, the endpoint value is included; the concentration range of the hydrochloric acid is 5-15%, the endpoint value is included. It can be understood that, in actual operation, the concentrations of hydrofluoric acid and hydrochloric acid can be adjusted according to actual conditions.

The silicon chip after cleaning with the mixed solution is taken out, rinsed in deionized water, and then dried. Then the cleaning of the cell silicon wafer is completed.

In addition, the cleaning method described in this embodiment is carried out at room temperature, and a general cleaning tank or pool can be used without replacing existing equipment, and the operation is simple and convenient.

To sum up, the method for cleaning silicon wafers of solar cells provided in this embodiment adopts the method of continuously blowing ozone gas into the aqueous solution to form an aqueous ozone solution to react with silicon wafers. The oxidation-reduction potential of ozone is relatively high, and it is soluble in water It can react quickly with silicon wafers, quickly oxidize organic pollutants attached to the surface of silicon wafers, and form an oxide film layer on the surface of silicon wafers. Compared with the existing method using a mixture of nitric acid and hydrofluoric acid, the oxidation reaction of this method produces CO ₂ and H ₂ O, and the produced substances are non-polluting and harmless, and the waste liquid does not need special treatment, which greatly reduces the pollution of the environment. Moreover, the existing method for preparing the mixed solution consumes a large amount of nitric acid, and takes a long time when changing the solution for preparation, but this method can overcome these shortcomings.

It has been verified by many tests that with this cleaning method, the surface of the oxide film formed on the surface of the silicon wafer is flatter than the original silicon surface, and after the oxide film is removed with hydrofluoric acid, the micro-roughness of the silicon wafer surface is still not deteriorated signs. In a relatively short period of time, both the cleaning effect and the surface state have met the more stringent requirements for the cleanliness of the silicon wafer surface and the requirements of the large-diameter silicon wafer process.

The method for cleaning silicon wafers of solar cells provided by the present invention has been introduced in detail above. In this paper, specific examples are used to illustrate the principle and implementation of the present invention, and the descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

1. A cleaning method for a solar cell silicon wafer, characterized in that, comprising the steps: S1: Soak and clean the silicon wafer with ozone aqueous solution to form an oxide layer on the surface of the silicon wafer; S2: using hydrofluoric acid solution to corrode the surface of the silicon wafer; S3: rinsing the silicon wafer. 2 . The cleaning method according to claim 1 , wherein the step S1 specifically comprises: placing the silicon wafer in water, and continuously blowing ozone gas into the water at a preset flow rate for a preset time. 3 . 3. The cleaning method according to claim 2, characterized in that, the preset flow rate ranges from 2 to 10 standard liters/minute, inclusive. 4. The cleaning method according to claim 3, characterized in that, the range of the preset time is 1-5 minutes, inclusive. 5 . The cleaning method according to claim 1 , wherein the step S2 specifically comprises: placing the silicon wafer in a hydrofluoric acid solution to stand still, and the hydrofluoric acid solution has a first concentration. 6. The cleaning method according to claim 5, wherein the range of the first concentration is 5-15%, inclusive. 7. cleaning method as claimed in claim 1 is characterized in that, described step S3 comprises: S30: Put the silicon chip in the alkaline solution to stand still, take it out and rinse it with water. 8. The cleaning method according to claim 7, wherein the alkaline solution is a potassium hydroxide solution having a second concentration, and the second concentration ranges from 2% to 8%, inclusive. 9. cleaning method as claimed in claim 7 is characterized in that, also comprises after described step S30: S31: Put the silicon wafer in the mixed solution of hydrofluoric acid and hydrochloric acid to stand still, take it out and rinse it with water. 10. The cleaning method according to claim 9, characterized in that, the concentration range of the hydrofluoric acid is 5-15%, inclusive; the concentration range of the hydrochloric acid is 5-15%, inclusive.