CN107623056A - A method for repairing surface defects of nano-textured surfaces formed by reactive ion etching - Google Patents

Abstract

The invention relates to a method for repairing surface defects of a nano-texture surface formed by a reactive ion etching method, comprising steps: (1) removal of a damaged layer on the surface of a nano-texture surface formed by a reactive ion etching method and surface micro-modification: configuring a HF ozone mixed solution , put the silicon wafer processed by reactive ion etching in HF ozone mixed solution to form a silicon oxide layer on the surface of the silicon wafer; In the mixed solution made of deionized water, the silicon oxide layer and metal ions on the surface of the silicon wafer are removed, and then dried to enter the normal process of polycrystalline cells. This method can precisely control the thickness of the damaged layer to be removed, so that the range of reflectance is concentrated after the damage is removed, and the color and appearance of the cell are uniform; compared with the existing damage layer removal process, the chemical consumption is low; _O3 can not only remove the surface damage layer, and also has a good ability to remove organic matter and metal ions on the surface of the silicon wafer.

Description

A method for repairing surface defects of nano-textured surfaces formed by reactive ion etching

technical field

The invention belongs to the technical field of solar energy manufacturing, and in particular relates to a method for repairing surface defects of a nano suede surface formed by a reactive ion etching method.

Background technique

As an emerging clean and renewable energy source, photovoltaic power generation can directly convert solar energy into electrical energy. The photoelectric conversion efficiency of cells is one of the keys to reducing the cost of photovoltaic power generation. The development of diamond wire cutting technology can effectively reduce the cost of slicing. However, the polycrystalline silicon wafer formed by diamond wire cutting cannot form a good surface light-trapping structure by using the conventional acid texturing process. The light-trapping structure on the surface of the battery is very important for the conversion efficiency of the battery. Form a uniform nano-scale suede, effectively reduce the reflectivity of the silicon wafer surface, increase light absorption, and increase the photogenerated current of the solar cell. However, during the RIE texturing process, the ion bombardment will cause certain damage to the surface of the silicon wafer, and the damaged layer will further form a recombination center, reducing the opening voltage and conversion efficiency of the solar cell. Therefore, after RIE texturing, it is necessary to increase the damage removal process. The depth of RIE nano-scale suede is in the range of 100-200nm, and it is necessary to remove the 5-20nm thick damage layer, which requires precise control, otherwise the suede will be damaged and the reflectivity will increase. , the light absorption becomes worse; the existing damage removal processes include HF-HNO3 system, HF-H2O2 system, and KOH system, which cannot be accurately controlled, which makes it difficult to control the surface reflectance distribution after damage removal.

Contents of the invention

The technical problem to be solved by the present invention is: to overcome the problems that the de-damage process is difficult to accurately control, and the reflectivity range of the silicon wafer is wide after de-damaging, etc., and provide a method for repairing surface defects of nano-textured surfaces formed by reactive ion etching.

The technical solution adopted by the present invention to solve its technical problem is: provide a method for repairing surface defects of nano suede surface formed by reactive ion etching method, comprising steps:

(1) Removal of the damaged layer formed by the reactive ion etching method and micro-modification of the surface: configure a HF ozone mixed solution, place the silicon wafer after RIE treatment in the HF ozone mixed solution, so that a silicon oxide layer is formed on the surface of the silicon wafer ;

(2) After the suede surface is prepared, place the silicon wafer in a mixed solution of HF, HCl and deionized water to remove the silicon oxide layer and metal ions on the surface of the silicon wafer, then dry it and enter the polycrystalline The normal process of the cell.

As a preferred embodiment of the present invention, the mass concentration of the HF ozone mixed solution in step (1) is 1%-10%.

As a preferred embodiment of the present invention, the HF ozone mixed solution described in the step (1) is under normal temperature conditions, and the O concentration is in the range of _30-150ppm .

As a preferred embodiment of the present invention, the ozone described in step (1) is produced using an ozone generator.

As a preferred embodiment of the present invention, the reaction time between the RIE-treated silicon wafer and the HF-ozone mixed solution in step (1) is 5 min-15 min.

As a preferred embodiment of the present invention, the mass concentration of HF in the mixed solution formed by mixing HF, HCl and deionized water in step (2) is 1%-2.5%.

As a preferred embodiment of the present invention, the mass concentration of HCl in the mixed solution formed by mixing HF, HCl and deionized water in step (2) is 2%-5%.

As a preferred embodiment of the present invention, the reaction time of the mixed solution formed by mixing the silicon wafer with the HF, HCl and deionized water in step (2) is 500s-700s.

As a preferred embodiment of the present invention, the reaction time of the mixed solution formed by mixing the silicon wafer with the HF, HCl and deionized water in step (2) is 600s.

The beneficial effects of the present invention are:

(1) The thickness of the damaged layer formed by the removed reactive ion etching can be precisely controlled, so that the reflectance range is concentrated after the damage is removed, and the color and appearance of the cell are uniform;

(2) Compared with the conventional HF-HNO3 system and HF-H2O2 system to remove the damaged layer, the consumption of chemicals is lower;

(3) O ₃ can not only remove the surface damage layer, but also has a good ability to remove organic matter and metal ions on the surface of the silicon wafer, and the cleanliness of the silicon wafer surface is increased.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort. in:

Fig. 1 is the SEM picture of the nano-textured surface that forms after the reactive ion etching process of the silicon chip surface among the embodiment one of the present invention;

Fig. 2 is the SEM figure of the nano suede surface after defect repairing on the surface of the silicon chip in embodiment one of the present invention;

Fig. 3 is the contrast of the reflectivity of the surface of the silicon wafer before and after repairing the defective layer of the silicon wafer in Embodiment 1 of the present invention;

Fig. 4 is a volt-ampere curve of the battery in Example 1 of the present invention under 500W/m ² and 1000W/m ² light.

detailed description

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Reference herein to "one embodiment" or "an embodiment" refers to a particular feature, structure or characteristic that can be included in at least one implementation of the present invention. "In one embodiment" appearing in different places in this specification does not all refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

A method for repairing surface defects of the nano suede surface formed by a reactive ion etching method of the present invention includes the following two steps of step 3 and step 4. For ease of understanding, the steps of the previous process are also expressed together:

Step 1, removing the damaged layer on the surface of the silicon wafer;

Specifically, the HF:HNO ₃ :H ₂ O ₂ solution system is used to remove the damaged layer and surface dirt caused by the cutting of the silicon wafer; the etching amount of the silicon wafer during this process is between 0.1-0.3g.

Step 2, preparation of nano suede;

Specifically, after removing the damaged layer, use RIE method to prepare nano-scale suede, the reaction gas is SF ₆ , O ₂ , Cl ₂ , the gas volume ratio is about 2:3:1.2, and the radio frequency power range is 8kw-15kw, where , the prepared suede has a depth of 100-200nm and a width of 200-500nm.

Step 3, RIE damage layer removal and surface micro-modification;

Specifically, configure 1%-10% mass concentration of HF ozone mixed solution, use an ozone generator to generate an ozone solution, and ensure that the O concentration in the solution is within the range of _30-150ppm , at room temperature; the silicon wafer after RIE is placed here In solution, the reaction time is 5min-15min.

Step 4, after the suede is prepared, place the silicon wafer in a mixed solution of HF (1%-2.5% in mass concentration), HCL (2%-5% in mass concentration) and deionized water, and the reaction time is 500s-700s. Remove the surface oxide layer and metal ions, dry, and enter the normal process of polycrystalline cells.

The above method takes advantage of the strong oxidizing properties of ozone, and adopts the solution system of ozone plus HF to replace the traditional HF/HNO ₃ solution system or alkaline solution (such as KOH) for removing the damaged layer. The process is highly controllable, the surface is corroded uniformly, and the technical cost is low.

The nano suede surface defect repairing method that combines reactive ion etching method to form below introduces three embodiments that can fully embody the content of the present invention:

Embodiment one:

(1) Removing the damaged layer on the surface of the silicon wafer: use a solution system of HF:HNO ₃ :H ₂ O=1:16:5 (mass ratio) to remove the damaged layer and surface dirt caused by the cutting of the silicon wafer. In this process, the thinning amount of the silicon wafer is 5-10 μm.

(2) Preparation of nano-sized suede: After removing the damaged layer, use RIE method to prepare nano-sized suede. The reaction gas is SF ₆ , O ₂ , Cl ₂ , the gas volume ratio is about 2:3:1.2, and the radio frequency power range 8kW-15kW. The prepared texture has a depth of about 100-200nm and a width of about 200-500nm, and the surface reflectance can be controlled at 4%-8%.

(3) RIE damage layer removal and surface micro-modification: configure ₅ % (mass concentration) HF ozone mixed solution, use an ozone generator to generate an ozone solution, and ensure that O in the solution Concentration is at 70ppm, normal temperature; Silicon wafer after RIE , placed in this solution, the reaction time can be adjusted to ensure that the surface reflectance after corrosion reaches the target value, and the reflectance range is controlled at 10% to 18%.

(4) After the suede surface is prepared, the silicon wafer is placed in a mixed solution of HF (mass concentration 2%), HCl (mass concentration 3%), deionized water, and the reaction time is 600s to remove the surface oxide layer and metal ions, Dry and enter the normal process of polycrystalline cells.

Please refer to Figure 1 to Figure 4 for the test situation of the above method. Fig. 1 is the SEM figure of the nano-velvet surface formed after the RIE treatment of the silicon chip surface in the embodiment of the present invention; Fig. 2 is the nano-velvet surface after the defect repair on the silicon chip surface in the embodiment of the present invention SEM image. From the comparison of Figure 1 and Figure 2, it can be seen that after the defect repair on the surface of the silicon wafer, the concave-convex surface is smoother, and it is easier to accurately control in the subsequent steps. FIG. 3 is a comparison of the reflectivity of the surface of the silicon wafer before and after repairing the defective layer of the silicon wafer in Embodiment 1 of the present invention. It can be seen from Figure 3 that the reflectivity after defect repair is more concentrated. Fig. 4 is a volt-ampere curve of the battery in Example 1 of the present invention under 500W/m ² and 1000W/m ² light. It can be seen from FIG. 4 that the opening voltage and conversion efficiency of the solar cell after defect repairing are higher.

Embodiment two:

(1) Removing the damaged layer on the surface of the silicon wafer: use a solution system of HF:HNO ₃ :H ₂ O=1:16:5 (mass ratio) to remove the damaged layer and surface dirt caused by the cutting of the silicon wafer. In this process, the thinning amount of the silicon wafer is 5-10 μm.

(2) Preparation of nano-sized suede: After removing the damaged layer, use RIE method to prepare nano-sized suede. The reaction gas is SF ₆ , O ₂ , Cl ₂ , the gas volume ratio is about 2:3:1.2, and the radio frequency power range 8kW-15kW. The prepared texture has a depth of about 100-200nm and a width of about 200-500nm, and the surface reflectance can be controlled at 4%-8%.

(3) RIE damage layer removal and surface micro-modification: configure 1% (mass concentration) HF ozone mixed solution, use an ozone generator to generate ozone solution, ensure that O concentration in the solution is at 30ppm, normal temperature _; silicon wafer after RIE , placed in this solution, the reaction time can be adjusted to ensure that the surface reflectance after corrosion reaches the target value, and the reflectance range is controlled at 10% to 18%.

(4) After the suede surface is prepared, the silicon wafer is placed in a mixed solution of HF (mass concentration 1%), HCl (mass concentration 2%), deionized water, and the reaction time is 500s to remove the surface oxide layer and metal ions, Dry and enter the normal process of polycrystalline cells.

Embodiment three:

(1) Removing the damaged layer on the surface of the silicon wafer: use a solution system of HF:HNO ₃ :H ₂ O=1:16:5 (mass ratio) to remove the damaged layer and surface dirt caused by the cutting of the silicon wafer. In this process, the thinning amount of the silicon wafer is 5-10 μm.

(2) Preparation of nano-sized suede: After removing the damaged layer, use RIE method to prepare nano-sized suede. The reaction gas is SF ₆ , O ₂ , Cl ₂ , the gas volume ratio is about 2:3:1.2, and the radio frequency power range It is 8kw-15kw. The prepared texture has a depth of about 100-200nm and a width of about 200-500nm, and the surface reflectance can be controlled at 4%-8%.

(3) RIE damage layer removal and surface micro-modification: configure 10% (mass concentration) HF ozone mixed solution, use an ozone generator to generate ozone solution, ensure that O concentration in the solution is at 150ppm, normal temperature _; , placed in this solution, the reaction time can be adjusted to ensure that the surface reflectance after corrosion reaches the target value, and the reflectance range is controlled at 10% to 18%.

(4) After the suede surface is prepared, the silicon wafer is placed in a mixed solution of HF (2.5% mass concentration), HCl (5% mass concentration), and deionized water, and the reaction time is 700s to remove the surface oxide layer and metal ions, Dry and enter the normal process of polycrystalline cells.

Those of ordinary skill in the art should be able to understand that one of the characteristics or purposes of the present invention is: the method utilizes the strong oxidizing properties _of O to form thin silicon oxide on the surface of the silicon wafer, and is equipped with HF solution and oxidation Silicon reaction, so as to achieve the purpose of removing the damaged layer; the advantage of this method is that the concentration of O ₃ is precisely controlled, and the thickness of silicon oxide has no strong correlation with the concentration of HF solution, so the thickness of the removed damaged layer is precisely controlled and uniform; at the same time, using O _3. Good cleaning ability, which can effectively remove metal ions and organic matter on the surface of silicon wafers. In addition, the O ₃ cleaning process only needs a small amount of chemicals, which reduces the consumption of chemicals, and has certain cost advantages and environmental protection advantages.

Inspired by the above-mentioned ideal embodiment according to the present invention, through the above-mentioned description content, relevant workers can make various changes and modifications within the scope of not departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims (9)

1. the nanometer suede surface defect repair method that a kind of reactive ion etching method is formed, it is characterised in that including step：

(1) removal of reactive ion etching method damaging layer and the micro- modification in surface：HF ozone mixed solutions are configured, will be through RIE processing Silicon chip afterwards is positioned in the HF ozone mixed solution so that silicon chip surface forms silicon oxide layer；

(2) after the completion of nanometer suede preparation, silicon chip is positioned over to the mixed solution mixed by HF, HCl and deionized water In, the silicon oxide layer and metal ion of silicon chip surface are removed, is then dried, into polycrystalline cell piece normal flow.

2. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：The mass concentration of HF ozone mixed solutions described in step (1) is 1%-10%.

3. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：HF ozone mixed solution is under normal temperature condition described in step (1), O₃Concentration is in the range of 30-150ppm.

4. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：Ozone is made using ozone generator described in step (1).

5. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：The reaction time of silicon chip and the HF ozone mixed solution described in step (1) after RIE is handled is 5min- 15min。

6. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：In the mixed solution that HF, HCl and deionized water mix described in step (2) HF mass concentration be 1% ~ 2.5%。

7. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：HCl mass concentration is 2% ~ 5% in the mixed solution that HF, HCl and deionized water mix described in step (2).

8. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：The reaction time of silicon chip and described HF, HCl and deionized water mixed solution mixed is described in step (2) 500s-700s。

9. the nanometer suede surface defect repair method that reactive ion etching method according to claim 1 is formed, it is special Sign is：The reaction time of silicon chip and described HF, HCl and deionized water mixed solution mixed is described in step (2) 600s。