CN103730347B - Recycled silicon wafer texturing method - Google Patents

Abstract

The present invention provides a method for reusing silicon wafers for texturing, comprising the following steps: step S10: emptying the chemical solution in the top tank of the process tank of texturing equipment or wet etching equipment; step S20: making the The silicon wafers are used to pass through the top tank of the process tank and then enter the alkali washing tank for alkali washing; step S30: making the reused silicon wafers after alkali washing enter the acid tank. The technical scheme of the invention effectively solves the problems of sequins and thinning in the prior art when reusing silicon wafers.

Description

Texturing method of reusing silicon wafers

technical field

The invention relates to the technical field of battery manufacturing technology, in particular to a texturing method for reusing silicon wafers.

Background technique

Figure 1 shows a schematic diagram of the manufacturing process of the battery sheet in the prior art. As shown in Figure 1, the manufacturing process of the battery sheet mainly includes texturing, diffusion, wet etching, PECVD (plasma enhanced chemical vapor deposition) , printing and sintering, and testing and packaging steps. The functions of the above steps are as follows:

Texturing: use a mixed solution of nitric acid and hydrofluoric acid to texture the surface of the silicon wafer; remove the surface damage layer caused by the cutting of the silicon wafer; form a rough surface and a large number of holes on the surface of the silicon wafer to increase the surface of the cell. The light-receiving area reduces the reflectivity, thereby improving the conversion efficiency of the solar cell.

Diffusion: A layer of phosphorus is diffused on the P-type substrate silicon to form a P-N junction.

Wet etching: Etch the silicon wafer with a mixed solution of nitric acid and hydrofluoric acid; etch the P-N junction on the edge of the silicon wafer to avoid battery leakage; polish the back of the battery to have a mirror effect, so that sunlight can be reflected back into the silicon wafer , used multiple times.

PECVD: Using low-temperature plasma as the energy source, the sample is placed on the electrode of glow discharge under low pressure, and the sample is heated to a predetermined temperature by glow discharge (or an additional heating element), and then an appropriate amount of reaction gas is introduced. The gas forms a solid film on the surface of the sample through a series of chemical reactions and plasma reactions.

Printing and sintering: screen printing is printed by using the principle that the screen holes of the non-graphic part of the printing plate are closed and cannot pass through the ink, and the screen holes of the graphic part are transparent and can pass through the ink. Tension the screen and firmly fix it on the screen frame, and use manual or photochemical methods to make graphic and text parts that can penetrate ink and non-graphic and text parts that cannot penetrate ink when the mesh is closed. When printing, put the ink on one side of the printing plate, apply a certain pressure on the ink part on the screen printing plate with a squeegee (squeegee), and move to the other end of the screen at the same time. In this process, the ink leaks from the screen through holes in the graphic part to the substrate under the extrusion of the scraper, thus completing a printing.

Each process of texturing, diffusion, wet etching, PECVD, and printing will produce unqualified products. The above-mentioned unqualified products are called recycled silicon wafers, and the above-mentioned recycled silicon wafers need to be processed again. Fig. 2 shows a schematic flow chart of the texturing method for reusing silicon wafers. As shown in Figure 2, the texturing method of reusing silicon chips comprises the steps: loading; making the reusing silicon chips pass through the texturing tank (containing the mixed liquid of _HNO3 and HF in it), the alkali washing tank (containing KOH in it) liquid) and acid tank (which contains a mixed liquid of HCL and HF); hot air drying. There is also a DI water (deionized water) washing tank after the texturing tank, alkali washing tank and acid tank.

After one or more texturing treatments on silicon wafers, different degrees of sequins will appear, and some sequin lattices are more obvious, which is easy to cause module mosaics. The reuse of silicon wafers will increase the number of sequins and flowers of the cells, reduce the appearance level of the finished cells, and increase the production cost. In addition, recycled silicon wafers become relatively thin and easily broken. The secondary reuse treatment method of silicon wafers will lead to low conversion efficiency of cells and a high proportion of unqualified cells.

Contents of the invention

The present invention aims to provide a texturing method for reusing silicon wafers to solve the problems in the prior art that the reused silicon wafers are prone to sequins and thinning.

In order to achieve the above object, according to one aspect of the present invention, there is provided a method for reusing silicon wafers for texturing, comprising the following steps: Step S10: the top tank of the process tank of texturing equipment or wet etching equipment Evacuating the liquid medicine; step S20: making the reused silicon chips pass through the top tank of the process tank and then enter the alkali cleaning tank for alkaline cleaning; step S30: making the recycled silicon chips after alkali cleaning enter the acid tank.

Further, an upper roller and a lower roller are arranged oppositely in the top tank of the process tank, and in step S10, the upper roller and the lower roller are cleaned after the chemical solution is emptied, so as to remove the residual chemical solution on the upper roller and the lower roller.

Further, in step S20, make the textured surface of the recycled silicon wafer pass the upper roller and the lower roller downward.

Further, a water washing step is also included between step S20 and step S30 and after step S30.

Further, the top tank of the process tank is built with a mixed solution of HNO ₃ and HF.

Further, the alkali washing tank is built with KOH solution.

Further, a mixed solution of HCL and HF is built in the acid tank of the texturing equipment; HF solution is built in the acid tank of the wet etching equipment.

Applying the technical scheme of the present invention, the chemical solution in the top tank of the process tank of the texturing equipment or wet etching equipment is emptied, so that when the reused silicon wafer passes through the top tank of the process tank, it only reacts with the residual chemical solution , or do not react with the liquid medicine, but directly enter the alkali washing tank and acid tank. In this way, the suede effect of the first texture of the silicon wafer and the thickness of the silicon wafer can be preserved to the greatest extent, which can effectively reduce the consumption of acid, reduce the fragmentation rate, improve the conversion efficiency, improve the qualified rate of finished products and reduce the sequins of the cell , to reduce the increase in the appearance of components due to battery sequins.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

FIG. 1 shows a schematic diagram of the manufacturing process of a battery sheet in the prior art;

Fig. 2 shows the schematic flow sheet of the texturing method of reusing silicon chip in the prior art; And

Fig. 3 shows a schematic flow chart of an embodiment of the texturing method for reusing silicon wafers according to the present invention.

detailed description

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and examples.

Aiming at the problem of sequins and thinning in the reuse of silicon wafers mentioned in the background technology, the inventor conducted a series of experimental verifications and found that the reasons for the easy occurrence of sequins and thinning are as follows:

When the silicon wafer passes through the texturing tank, the surface of the silicon wafer is textured by a mixed solution of nitric acid and hydrofluoric acid. The purpose of the above process is to 1) remove the surface damage layer caused when the silicon wafer is cut. 2) Form uneven surfaces and a large number of holes on the surface of the silicon wafer to increase the light-receiving area on the surface of the cell and reduce the reflectivity, thereby improving the conversion efficiency of the solar cell. The texturing method of reusing silicon wafers is the same as the first texturing method of silicon wafers, and also needs to pass through the texturing tank, so that the liquid medicine inside will damage the suede surface, and even the uneven surface of the silicon wafer (texture surface) ) gradually become flat, which makes the silicon wafer easy to become a mirror-like sequin. In addition, passing through the texturing tank again or multiple times will cause multiple reactions on the texturized surface of the silicon wafer, which will reduce the thickness of the silicon wafer, which is prone to thinning problems.

For the above reasons, the present application proposes an effective solution. As shown in Figure 3, the preferred embodiment of the texturing method of reusing silicon chip comprises the following steps:

Step S10: Empty the chemical solution in the top tank (texture tank or etching tank) of the process tank of the texturing equipment or wet etching equipment;

Step S20: Make the reused silicon wafer pass through the texturing tank and then enter the alkali washing tank for alkali washing, and the alkali washing is used to remove the PN junction;

Step S30: Make the reused silicon wafer after alkali cleaning enter the acid tank.

In this preferred embodiment, texturing equipment or wet etching equipment can be used for texturing the reused silicon wafers. The process tank includes a top tank and a bottom tank, the bottom tank stores the chemical solution, and the chemical solution in the top tank is in direct contact with the silicon wafer. In this preferred embodiment, the chemical solution in the top tank of the process tank is emptied, so that when the reused silicon wafer passes through the texturing tank, it only reacts with the residual chemical solution, or does not react with the chemical solution, but directly enters the Alkali and acid tanks. In this way, the suede effect of the first texture of the silicon wafer and the thickness of the silicon wafer can be preserved to the greatest extent, which can effectively reduce the consumption of acid, reduce the fragmentation rate, improve the conversion efficiency, improve the qualified rate of finished products and reduce the sequins of the cell , to reduce the increase in the appearance of components due to battery sequins.

Preferably, when using texturing equipment, a certain concentration of HF and HCL mixed chemical solution needs to be proportioned in the acid tank, wherein the concentration of HCL is higher than that in the prior art, because HCL can remove metal impurities on the surface of silicon wafers , while HF can purify the cleanliness of silicon wafers.

An upper roller and a lower roller are arranged oppositely in the texturing tank, and in step S10, the upper roller and the lower roller are cleaned after the liquid medicine is discharged, so as to remove the liquid medicine remaining on the upper roller and the lower roller. Clear water can be utilized to clean the upper roller and the lower roller after the medicinal solution in the texturing tank is discharged, so that there is no medicinal solution on the upper roller and the lower roller.

Alternatively, in step S10 , there is no need to clean the upper roller and the lower roller after the liquid medicine is discharged, and there is residual medicine liquid on the upper roller and the lower roller. Like this, when making reused silicon chip, some reused silicon chip can carry away the liquid medicine remaining on the upper roller and the lower roller when passing through, so also can make there is no liquid medicine on the upper roller and the lower roller completely.

In order to facilitate the subsequent diffusion process, in step S20 , the textured side of the recycled silicon wafer passes the upper roller and the lower roller downward. In addition, it has been verified by experiments that when there is residual liquid medicine on the upper roller and the lower roller, after the textured side of the reused silicon wafer passes through the alkali cleaning tank and the acid tank, it is found that the textured side of the recycled silicon wafer has Roller print. Like this, affect the color attractive in appearance of reused silicon wafer after coating, cause the surface to be unqualified. The main reason is that there is a mixed drug of HF and HNO ₃ on the roller, and the place where the silicon wafer contacts the roller is corroded too much, forming a roller mark. And when there is residual liquid medicine on the upper roller and the lower roller, after the textured surface of the reused silicon wafer passes through the alkali washing tank and the acid tank, there is no roller print on the textured surface of the reused silicon wafer. The contact area between the silicon wafer and the lower roller increases, and the entire area of the silicon wafer will touch the roller, and the reaction of the liquid medicine is relatively uniform.

The beneficial effects of the present invention will be further described below in conjunction with specific examples.

Embodiment one

Drain the chemical solution from the top tank of the texturing tank (HF, HNO ₃ mixed solution tank) back to the bottom tank to ensure that there is no mixed drug of HF and HNO ₃ on the upper and lower rollers in the texturing tank liquid. After mixing a certain concentration of KOH, HF, and HCL, the conductivity of the KOH tank is 12-15, and the conductivity of the acid tank is 650-690. After reusing the silicon wafer directly through the alkali washing tank and acid tank, the surface of the reused silicon wafer is clean, the dark lines are normal, the brightness of the wafer is similar to that of the textured surface of the normal original silicon wafer, and the uniformity of the diffusion resistance is poor 5.1 %, the efficiency of the cells is 17.31%, and the unqualified ratio is 4.8%.

Embodiment two

Change the concentration of the alkali tank, increase the conductivity of the alkali tank to 18, and drain the liquid medicine from the top tank of the texturing tank (HF, HNO3 mixed liquid tank) of the texturing equipment back to the bottom tank to ensure that the upper roller in the texturing tank There are some mixed liquid medicines of HF and HNO3 on the lower and lower rollers. Turn the textured side of the recycled silicon wafer up, and pass through the alkali tank and acid tank directly, and found that some recycled silicon wafers still have roller marks on the textured side. The reason is that the local corrosion of the silicon wafer is too high, not because the silicon wafer is involved in the process. Porous silicon produced by a chemical reaction.

According to the experimental conditions of Example 2, the operating speed of the texturing equipment is set to 2.1 to track the efficiency of the reused cells, and the data are as follows:

Other parameters are set unchanged, and the operating speed of the equipment is changed to 1.8, and the efficiency of the reused cells is tracked. The data are as follows:

Among them, Uoc refers to the voltage of the cell, Isc refers to the current, Rser refers to series connection, Rsh refers to parallel connection, FF refers to filling, Ncell refers to conversion efficiency, Irev1 refers to leakage, and Count refers to the number of cells.

Embodiment Three

Drain the chemical liquid from the top tank of the process tank (HF, HNO ₃ mixed liquid tank) of the texturing equipment back to the bottom tank to ensure that there are some HF, HNO ₃ mixed chemical liquid, alkali Groove, acid tank concentration ratio is the same as embodiment two. The textured surface of the silicon wafer is facing down, and after directly passing through the alkali tank and the acid tank, there is no roller mark on the textured surface of the silicon wafer. The main reason is that the contact area between the silicon wafer and the lower roller increases (the entire silicon wafer The area of the silicon wafer will be in contact with the roller, and participate in the liquid reaction more evenly. The lower roller carries a certain amount of mixed liquid of HF and HNO ₃ , which can clean the surface of the silicon wafer to a certain extent.

Under the premise that the conductivity of the alkaline cleaning tank and the acid tank are the same, and the operating speed of the equipment is the same, the statistics of surface flakes, fragmentation rate statistics and component flower flakes of the prior art reuse process and the reuse process of the present application are as follows:

Among them, during the experiment, the operating speed of the equipment was 2.0m/min, the conductivity of the alkali tank was 15ms, and the conductivity of the acid tank was 660ms. The automatic rehydration volume is 25 tablets/45ml for HNO3 and 25 tablets/92ml for HF. The parameters of the reutilized texturing tank of the prior art are speed 2.5m/min and temperature 10°.

Comparative Experiment proportion of surface Fragmentation rate Component flower current technology 2.2% 3.95% 65% this application 2.7% 1.67% 16.5%

Among them, a module is generally connected in series by 60 cells, and the proportion of the surface refers to 39 cells with bright lattices in a module.

Through the comparison of small batch production, the parameters of the cells produced by the recycling process of the prior art and the recycling process of the present application are as follows:

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. a method for making texture of reusing silicon chips, is characterized in that, comprises the following steps: Step S10: Empty the chemical solution in the top tank of the process tank of the texturing equipment or wet etching equipment; Step S20: making the reused silicon wafers pass through the top tank of the process tank and then enter the alkaline cleaning tank for alkaline cleaning; Step S30: Make the reused silicon wafer after alkali cleaning enter the acid tank. 2. The texturing method according to claim 1, characterized in that, an upper roller and a lower roller oppositely arranged are arranged in the top groove of the process tank, and in the step S10, after the liquid medicine is emptied, Cleaning the upper roller and the lower roller to remove the liquid medicine remaining on the upper roller and the lower roller. 3 . The texturing method according to claim 2 , characterized in that, in the step S20 , the textured surface of the reusable silicon wafer passes through the upper roller and the lower roller facing downward. 4 . 4. The texturing method according to claim 1, characterized in that, between the step S20 and the step S30 and after the step S30, a water washing step is also included. 5. method for making texture according to claim 1, is characterized in that, the top tank of described process tank is built-in the mixed solution of HNO ₃ and HF. 6. method for making texture according to claim 1, is characterized in that, KOH solution is built-in in described alkali washing tank. 7. The texturing method according to claim 1, wherein the acid tank of the texturing equipment is provided with a mixed solution of HCL and HF; the acid tank of the wet etching equipment is provided with a HF solution.