CN103236406A - Method for detecting polycrystalline silicon wafer dislocation density - Google Patents

Abstract

The invention relates to a method for detecting the dislocation density of a polycrystalline silicon wafer, comprising the following steps: ① dislocation corrosion; ② observing the corrosion result, and calculating the dislocation density, wherein the dislocation etching is to soak the polycrystalline silicon wafer from which the mechanical damage layer has been removed in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching. In the present invention, by adding K ₂ Cr ₂ O ₇ , the corrosion reaction speed is slow, and thinner polycrystalline silicon chips can be corroded, and the surface oxidation of the polycrystalline silicon chips will not occur after corrosion, which is beneficial to the display and analysis of dislocations.

Description

A method for detecting dislocation density of polycrystalline silicon wafer

technical field

The invention relates to a method for detecting the dislocation density of polycrystalline silicon wafers, in particular to a method for detecting the dislocation density of polycrystalline silicon wafers by corrosion metallography, and belongs to the field of dislocation detection of polycrystalline silicon wafers.

Background technique

As one of the most potential forms of renewable resource utilization, solar photovoltaic power generation has achieved rapid development in recent years, and the preparation of cells with high photoelectric conversion efficiency will become the future development direction. However, in the process of polycrystalline ingot casting, due to various reasons, especially the internal stress in the silicon crystal at high temperature, slippage occurs between atomic planes, plastic deformation occurs locally on the crystal plane, and lattice defects are formed in the crystal. wrong.

The dislocation in the silicon crystal will become the intrinsic gathering center of metal impurities and the recombination center of holes and electrons, which will cause a significant decrease in the minority carrier lifetime (average survival time of the minority carrier), resulting in a decrease in the photoelectric conversion efficiency of the cell. The minority carriers are minority carriers, which is a concept of semiconductor physics.

Therefore, it is particularly important to display the dislocation of the silicon wafer, which is beneficial to the analysis of the conversion efficiency of the cell. At present, dislocation display methods include X-ray method, electron microscope method, copper embellishment infrared transmission method and corrosion metallographic method, etc., and the simplest and most commonly used method is corrosion metallographic method.

The test principle of the corrosion metallographic method is: in silicon crystals, where there are dislocations, the arrangement of atoms loses its regularity and the structure is relatively loose. The atoms here have higher energy and are subject to greater tension. The intersection of the line and the surface is easily corroded to form a concave pit, the so-called corrosion pit. The corrosion metallographic method uses this characteristic to display dislocations and stacking faults, and then observes through a metallographic microscope, and through the corrosion pit in the field of view Density calculates the dislocation density.

In the corrosion metallographic method, the traditional etching solution is HNO ₃ -HF mixed acid, that is, HNO ₃ -HF mixed acid polycrystalline silicon wafer dislocation etching method, the reaction speed is fast, which is not conducive to the corrosion of thinner silicon wafers, and after etching, the silicon The surface of the sheet is prone to oxidation, resulting in a black oxide layer, which is not conducive to the display and analysis of dislocations.

Therefore, there is a need in the art to develop a corrosion metallographic method that has a slow corrosion reaction, is convenient for controlling the thickness of the silicon wafer after etching, and does not oxidize the silicon wafer after etching. The method should also meet the requirement that microstructures such as crystal grains, grain boundaries and twins on the surface of the silicon wafer can be clearly seen after the polycrystalline silicon wafer is etched, so as to facilitate dislocation distribution analysis.

Contents of the invention

The invention provides a method for detecting the dislocation density of a polycrystalline silicon wafer, which is used to solve the existing problems of high dislocation corrosion speed, difficulty in control, easy oxidation after corrosion, difficult observation, and inapplicability to thin polycrystalline silicon wafers.

The present invention is achieved through the following technical solutions:

A method for detecting the dislocation density of a polysilicon wafer, comprising the steps of: 1. dislocation corrosion; 2. observing the corrosion result, and calculating the dislocation density; wherein, the dislocation corrosion is to immerse the polysilicon wafer with the mechanically damaged layer removed in K ₂ Dislocation etching was carried out in Cr ₂ O ₇ -HF mixed solution.

The present invention adopts K ₂ Cr ₂ O ₇ -HF mixed solution to carry out dislocation etching on polycrystalline silicon wafers, the reaction speed is relatively slow, it is convenient to etch thin polycrystalline silicon wafers, and the silicon wafers will not be oxidized after etching; meanwhile, After the polycrystalline silicon wafer is etched with the mixed solution, the microstructures such as crystal grains, grain boundaries and twins on the surface of the silicon wafer can be clearly seen, which facilitates the distribution analysis of dislocations. The present invention adds K ₂ Cr ₂ O ₇ substances with weak oxidizing properties, which reduces the speed of corrosion reaction and achieves the purpose of corroding thinner polycrystalline silicon wafers.

In the K ₂ Cr ₂ O ₇ -HF mixed solution of the present invention, the mass ratio of K ₂ Cr ₂ O ₇ to HF acid is 1:1 to 1:4.5, such as 1:1.1, 1:1.3, 1:1.5, 1:1.9, 1:2.4, 1:2.8, 1:3.2, 1:3.5, 1:3.7, 1:3.9, 1:4.3, etc. When the mass ratio is greater than 1:1, the amount of HF acid added is small, the dislocation corrosion is not complete, and the dislocation density cannot be effectively reflected; the mass ratio is less than 1:4.5, the amount of K ₂ Cr ₂ O ₇ added is small, and the corrosion reaction speed is faster , is not conducive to the etching of thinner polysilicon wafers.

As a preferred technical solution, the K ₂ Cr ₂ O ₇ -HF mixed solution of the present invention is formed by mixing K ₂ Cr ₂ O ₇ solution and HF solution with a volume ratio of 1:1 to 1:4, and the volume ratio can be 1 :1.1, 1:1.3, 1:1.5, 1:1.9, 1:2.4, 1:2.8, 1:3.2, 1:3.5, 1:3.7, 1:3.9, etc.;

The K ₂ Cr ₂ O ₇ solution is an aqueous K ₂ Cr ₂ O ₇ solution, and the concentration of the K ₂ Cr ₂ O ₇ solution is 0.1-0.2 mol/L, such as 0.11 mol/L, 0.13 mol/L, 0.14 mol/L, 0.16mol/L, 0.18mol/L, 0.19mol/L, etc., preferably 0.15mol/L;

The HF acid solution is an aqueous solution of HF acid, and the concentration of the HF acid solution is 45-55wt%, such as 45.2wt%, 45.8wt%, 43wt%, 43.5wt%, 44.1wt%, 44.6wt%, 45.6wt% , 46.3wt%, 48wt%, 49.3wt%, 50.5wt%, 52wt%, 53.6wt%, 54.1wt%, 54.8wt%, etc., preferably 49wt%.

Preferably, the immersion time of the polycrystalline silicon wafer in the present invention in the K ₂ Cr ₂ O ₇ -HF mixed solution is 7-10 min, such as 7.1 min, 7.6 min, 8 min, 8.4 min, 8.9 min, 9.3 min, 9.6 min, etc. .

As a preferred technical solution, the dislocation corrosion described in the present invention comprises the following steps:

(1) Cleaning polysilicon wafers;

(2) Soak in H ₂ CrO ₄ -HF mixed acid to remove the mechanical damage layer;

(3) Remove the residual acid on the surface of the polysilicon wafer;

(4) Soak the polysilicon wafer in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching;

(5) Remove the residual solution on the surface of the polysilicon wafer and dry it.

The invention removes the mechanically damaged layer on the surface of the silicon chip through the reaction in H ₂ CrO ₄ -HF mixed acid, so that the microstructures such as crystal grains, grain boundaries and twin crystals on the surface of the silicon chip can be clearly seen by naked eyes.

Preferably, in the H ₂ Cr ₂ O ₇ -HF mixed acid described in the present invention, the mass ratio of H ₂ Cr ₂ O ₇ acid to HF acid is 1:1 to 1:4.5, such as 1:1.1, 1:1.3, 1:1.5, 1:1.9, 1:2.4, 1:2.8, 1:3.2, 1:3.5, 1:3.7, 1:3.9, 1:4.3, etc., preferably 1:1.3～1:4.2.

As a preferred technical solution, the H ₂ Cr ₂ O ₇ -HF mixed acid of the present invention is formed by mixing H ₂ Cr ₂ O ₇ acid solution and HF acid solution with a volume ratio of 1:1 to 3:1, and the volume ratio can be It is 1:1, 1.1:1, 1.3:1, 1.9:1, 2.2:1, 2.5:1, 2.8:1, etc.;

The H ₂ Cr ₂ O ₇ acid solution is prepared from CrO ₃ powder and water, and the concentration of the H ₂ Cr ₂ O ₇ acid solution is 0.8-1.2 mol/L, such as 0.81 mol/L, 0.83 mol/L , 0.94mol/L, 0.96mol/L, 1.04mol/L, 1.09mol/L, 1.13mol/L, 1.17mol/L, etc., preferably 1mol/L;

The HF acid solution is an aqueous solution of HF acid, and the concentration of the HF acid solution is 45-55wt%, such as 45.2wt%, 45.8wt%, 43wt%, 43.5wt%, 44.1wt%, 44.6wt%, 45.6wt% , 46.3wt%, 48wt%, 49.3wt%, 50.5wt%, 52wt%, 53.6wt%, 54.1wt%, 54.8wt%, etc., preferably 49wt%.

Preferably, the immersion time of the polycrystalline silicon wafer in the H ₂ Cr ₂ O ₇ -HF mixed acid is 40-80s, such as 41s, 43s, 47s, 52s, 56s, 62s, 68s, 71s, 79s and so on.

As the most preferred technical solution, the dislocation corrosion described in the present invention comprises the following steps:

(1) Clean the cut polysilicon wafer;

(2) The cleaned polycrystalline silicon wafer is reacted in H ₂ CrO ₄ -HF mixed acid to remove the mechanical damage layer on the surface of the silicon wafer;

Among them, H ₂ CrO ₄ acid is made of analytically pure CrO ₃ powder and pure water to make a solution with a concentration of 1mol/L, and the concentration of HF acid is 49%; the volume ratio of the two acids is H ₂ CrO ₄ :HF=1: 1～3:1, response time 40～80s;

(3) Soak the polysilicon wafer reacted with H ₂ CrO ₄ -HF mixed acid in deionized water, and rinse off the residual acid on the surface of the polysilicon wafer;

(4) Soak the rinsed polysilicon wafer in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching;

Among them, the K ₂ Cr ₂ O ₇ solution is prepared from analytically pure K ₂ Cr ₂ O ₇ powder and pure water to a solution with a concentration of 0.15mol/L, and the concentration of HF is 49%; the volume ratio of the two solutions is K ₂ Cr ₂ O ₇ :HF=1:1～1:4, the reaction time is 7～10min;

(5) The polysilicon wafer etched with the K ₂ Cr ₂ O ₇ -HF mixed solution is soaked in deionized water, and the residual solution on the surface of the polysilicon wafer is rinsed, and then placed in an oven for drying.

The present invention carries out the dislocation observation of the metallographic microscope after the dislocation corrosion, and calculates the dislocation density. The dislocation observation and calculation are conventional techniques in the art, and will not be repeated here, typical but non-limiting The calculation formula of dislocation density (unit: number/cm ² ) is:

N _D =n/s

Among them, _ND is the dislocation density; n is the number of corrosion pits on the observed surface; s is the area of the observed surface.

Because the defects of polysilicon have different shapes, polysilicon defects include dislocations and stacking faults, dislocations are line defects in crystals, and stacking faults are plane defects. Therefore, those skilled in the art should understand that the detection method of the present invention is based on The corrosion of polysilicon dislocation (or stacking fault) defects is detected, and the corrosion principle is the same, so the detection of both dislocation and stacking fault defects can use the method provided by the present invention.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention adjusts the material of the silicon chip corrosion acid solution system and optimizes the acid ratio, especially the addition of K ₂ Cr ₂ O ₇ , a substance with weak oxidizing properties, so that the corrosion reaction speed is slow and the thickness can be reduced. For example, the present invention can process polycrystalline silicon wafers with a thickness greater than 50 μm, for example, polycrystalline silicon wafers with a thickness of 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm, and 230 μm can be processed;

(2) The present invention firstly treats the mechanically damaged layer on the surface of the polycrystalline silicon wafer, so that the microstructures such as grains, grain boundaries and twins on the surface of the silicon wafer are clearly visible to the naked eye, facilitating the distribution of dislocations;

(3) The present invention uses K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching, the reaction speed is slow, and it is convenient to etch thin polycrystalline silicon wafers, and the surface oxidation of silicon wafers will not occur after etching, which is beneficial to Display and analysis of dislocations.

Description of drawings

Fig. 1 is the surface photograph of the polysilicon chip that removes surface mechanical damage layer;

Fig. 2 is a photo of the surface of a polysilicon wafer after dislocation etching.

Detailed ways

In order to facilitate understanding of the present invention, the present invention enumerates the following examples. It should be clear to those skilled in the art that the embodiments are only for helping to understand the present invention, and should not be regarded as specific limitations on the present invention.

Example 1

A method for detecting the dislocation density of a polysilicon wafer, comprising the steps of ① dislocation etching; ② observing the corrosion results, and calculating the dislocation density; wherein, the dislocation etching includes the following steps:

(1) Clean the cut polysilicon wafer with a thickness of 200 μm;

(2) The cleaned polycrystalline silicon wafer was reacted in H ₂ CrO ₄ -HF mixed acid to remove the mechanical damage layer on the surface of the silicon wafer; Figure 1 is a photo of the surface of the polycrystalline silicon wafer with the surface mechanical damage layer removed;

Among them, H ₂ CrO ₄ acid is made of analytically pure CrO ₃ powder and pure water to make a solution with a concentration of 1mol/L, and the concentration of HF acid is 49%; the volume ratio of the two acids is H ₂ CrO ₄ :HF=1: 1～3:1, response time 40～80s;

(3) Soak the polysilicon wafer reacted with H ₂ CrO ₄ -HF mixed acid in deionized water, and rinse off the residual acid on the surface of the polysilicon wafer;

(4) Soak the rinsed polysilicon wafer in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching;

Among them, the K ₂ Cr ₂ O ₇ solution is prepared from analytically pure K ₂ Cr ₂ O ₇ powder and pure water to a solution with a concentration of 0.15mol/L, and the concentration of HF is 49%; the volume ratio of the two solutions is K ₂ Cr ₂ O ₇ :HF=1:1～1:4, the reaction time is 7～10min;

(5) The polysilicon wafer etched with the K ₂ Cr ₂ O ₇ -HF mixed solution was soaked in deionized water, the residual solution on the surface of the polysilicon wafer was rinsed, and then dried in an oven; Figure 2 shows the dislocation corrosion Photo of the surface of a polycrystalline silicon wafer.

As shown in Figures 1 and 2, after the polycrystalline silicon wafer is etched, the microstructures such as grains, grain boundaries, and twins on the surface of the polycrystalline silicon wafer can be clearly seen, and the dislocation accumulation area presents a black fuse morphology.

Select different positions of the dislocation-etched polysilicon wafer, observe through a metallographic microscope, and read out the number of dislocations in the field of view, take the average value, divide by the area of the field of view, and obtain the dislocation density;

According to calculation, the dislocation density of the polycrystalline silicon wafer selected in Example 1 is 100 cm ^-2 .

Example 2

A method for detecting the dislocation density of a polysilicon wafer, comprising the steps of ① dislocation etching; ② observing the corrosion results, and calculating the dislocation density; wherein, the dislocation etching includes the following steps:

(1) Clean the cut polysilicon wafer with a thickness of 160 μm;

(2) The cleaned polycrystalline silicon wafer is reacted in H ₂ CrO ₄ -HF mixed acid to remove the mechanical damage layer on the silicon wafer surface; among them, the mass ratio of H ₂ CrO ₄ acid to HF acid is 1:1; the reaction time is 80s ;

(3) Soak the polysilicon wafer reacted with H ₂ CrO ₄ -HF mixed acid in deionized water, and rinse off the residual acid on the surface of the polysilicon wafer;

(4) The rinsed polysilicon wafer was soaked in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching; wherein, the mass ratio of K ₂ Cr ₂ O ₇ to HF acid in the mixed solution was 1:4.5, and the reaction Time 7min;

(5) Soak the polysilicon wafer etched with the K ₂ Cr ₂ O ₇ -HF mixed solution in deionized water, rinse off the residual solution on the surface of the polysilicon wafer, and then dry it in an oven;

The distribution and density calculation of dislocations are the same as in Example 1.

Example 3

A method for detecting the dislocation density of a polysilicon wafer, comprising the steps of ① dislocation etching; ② observing the corrosion results, and calculating the dislocation density; wherein, the dislocation etching includes the following steps:

(1) Clean the cut polysilicon wafer with a thickness of 80 μm;

(2) The cleaned polycrystalline silicon wafer is reacted in H ₂ CrO ₄ -HF mixed acid to remove the mechanical damage layer on the silicon wafer surface; among them, the mass ratio of H ₂ CrO ₄ acid to HF acid is 1:4.5; the reaction time is 40s ;

(3) Soak the polysilicon wafer reacted with H ₂ CrO ₄ -HF mixed acid in deionized water, and rinse off the residual acid on the surface of the polysilicon wafer;

(4) The rinsed polysilicon wafer is soaked in K ₂ Cr ₂ O ₇ -HF mixed solution for dislocation etching; wherein, the mass ratio of K ₂ Cr ₂ O ₇ to HF in the mixed solution is 1:1, and the reaction time 10min;

(5) Soak the polysilicon wafer etched with the K ₂ Cr ₂ O ₇ -HF mixed solution in deionized water, rinse off the residual solution on the surface of the polysilicon wafer, and then dry it in an oven;

The distribution and density calculation of dislocations are the same as in Example 1.

comparative example

The HNO ₃ -HF mixed acid dislocation etching method for polycrystalline silicon wafers was used to dislocation etch polycrystalline silicon wafers with a thickness of 200 μm. The etching solution was HNO ₃ and HF mixed acid with a volume ratio of 1:18. After 10 seconds, the center of the silicon wafers reacted and penetrated. .

The applicant declares that the present invention illustrates the detailed test process of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed test process, that is, it does not mean that the present invention must rely on the above-mentioned detailed test process to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. a method that detects the polysilicon chip dislocation density comprises the steps: 1. dislocation corrosion; 2. observe Corrosion results, calculate dislocation density, it is characterized in that, described dislocation corrosion is immersed in K for the polysilicon chip that will remove mechanical damage layer ₂Cr ₂O ₇Carry out dislocation corrosion in the-HF mixed solution.

2. the method for claim 1 is characterized in that, described K ₂Cr ₂O ₇In-HF the mixed solution, K ₂Cr ₂O ₇With the mass ratio of HF be 1:1～1:4.5.

3. method as claimed in claim 1 or 2 is characterized in that, described K ₂Cr ₂O ₇-HF mixed solution is the K of 1:1～1:4 by volume ratio ₂Cr ₂O ₇Solution and HF acid solution mix;

Preferably, described K ₂Cr ₂O ₇Solution is K ₂Cr ₂O ₇The aqueous solution, described K ₂Cr ₂O ₇The concentration of solution is 0.1～0.2mol/L, preferred 0.15mol/L,

Preferably, described HF acid solution is the HF aqueous acid, and described HF acid solutions is 45～55wt%, preferred 49wt%.

4. as the described method of one of claim 1～3, it is characterized in that described polysilicon chip is at K ₂Cr ₂O ₇Soak time in the-HF mixed solution is 7～10min.

5. as the described method of one of claim 1～4, it is characterized in that described dislocation corrosion comprises the steps:

(1) cleans polysilicon chip;

(2) be immersed in H ₂CrO ₄In-HF the mixed acid, remove mechanical damage layer;

(3) the remaining acid solution on removal polysilicon chip surface;

(4) polysilicon chip is immersed in K ₂Cr ₂O ₇Carry out dislocation corrosion in the-HF mixed solution;

(5) remove the residual solution on polysilicon chip surface, and dry.

6. method as claimed in claim 5 is characterized in that, described H ₂Cr ₂O ₇In-HF the mixed acid, H ₂Cr ₂O ₇With the mass ratio of HF be 1:1～1:4.5, preferred 1:1.3～1:4.2.

7. as claim 5 or 6 described methods, it is characterized in that described H ₂Cr ₂O ₇-HF mixed acid is the H of 1:1～3:1 by volume ratio ₂Cr ₂O ₇Acid solution and HF acid solution mix.

8. method as claimed in claim 7 is characterized in that, described H ₂Cr ₂O ₇Acid solution is by CrO ₃Powder and water are formulated, described H ₂Cr ₂O ₇The concentration of acid solution is 0.8～1.2mol/L, preferred 1mol/L;

Preferably, described HF acid solution is the HF aqueous acid, and described HF acid solutions is 45～55wt%, preferred 49wt%.

9. as the described method of one of claim 5～8, it is characterized in that described polysilicon chip is at H ₂Cr ₂O ₇Soak time in the-HF mixed acid is 40-80s.

10. as the described method of one of claim 1～9, it is characterized in that described dislocation corrosion comprises the steps:

(1) polysilicon chip with well cutting cleans;

(2) polysilicon chip of process cleaning is at H ₂CrO ₄The mechanical damage layer of silicon chip surface is removed in reaction in the-HF mixed acid;

Wherein, H ₂CrO ₄Acid is by analytically pure CrO ₃Powder and pure water are mixed with the solution that concentration is 1mol/L, and the HF acid concentration is 49%; The volume ratio of two kinds of acid is H ₂CrO ₄: HF=1:1～3:1, reaction time 40～80s;

(3) will with H ₂CrO ₄The reacted polysilicon chip of-HF mixed acid is immersed in the deionized water, and the remaining acid solution on polysilicon chip surface is rinsed well;

(4) be soaked into K through the polysilicon chip after the flushing ₂Cr ₂O ₇Carry out dislocation corrosion in the-HF mixed solution;

Wherein, K ₂Cr ₂O ₇Solution is by analytically pure K ₂Cr ₂O ₇Powder and pure water are mixed with the solution that concentration is 0.15mol/L, and HF concentration is 49%; The volume ratio of two kinds of solution is K ₂Cr ₂O ₇: HF=1:1～1:4, reaction time 7～10min;

(5) and K ₂Cr ₂O ₇The polysilicon chip that-HF mixed solution corrodes is immersed in the deionized water, and the residual solution on polysilicon chip surface is rinsed well, puts into oven for drying subsequently.

Images