JPH0362031B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing n ⁺ PP ⁺ junction silicon wafers used in solar cells by means of P-type silicon wafers.

Traditionally efficient BSF (Back Surface
Silicon wafers are used in solar cells, and the wafers are manufactured through the following steps.

In other words, as shown in the process diagram of FIG. 1, by first diffusing trivalent impurities such as phosphorus and boron into the P-type silicon wafer prepared in step A, the P-type silicon wafer is An n ⁺ layer covered with a silicon oxide film A is formed on the entire surface to obtain a P n ⁺ junction.

Next, after removing the silicon oxide film A with a hydrogen fluoride solution, screen printing Al paste B on the back side of the n ⁺ layer and baking it in the air.
By diffusing Al from the n ⁺ layer into the P layer of a P-type silicon wafer, thereby forming a P ⁺ layer.
A BSF process is performed to form an n ⁺ PP ⁺ bond, and at this time, the Al paste oxide C remaining attached to the lower surface of the P ⁺ layer is removed with a solution of HCl, NaOH, etc.

Of course, n ⁺ PP ⁺ obtained as above
The bonded silicon wafer becomes a solar cell by forming a back electrode on the back side and a front electrode on the front side, but in the above state shown in Figure 1 F, the n ⁺ layer Since the outer periphery of the P ⁺ layer contacts the P + layer, this contact reduces the output of the solar cell. By removing the outer circumferential portion of ^{the +} layer and the outer circumferential portion of the P ⁺ layer, a final silicon wafer as shown in (g) is obtained.

For this reason, when using the conventional method, it is necessary to perform a cumbersome process such as polishing the outer periphery of an extremely thin silicon wafer, resulting in poor productivity and the possibility of damaging the wafer during polishing. There was a defect that the edge D became a rough surface, resulting in a decrease in efficiency as a solar cell.

In view of the above-mentioned difficulties, the present invention makes it possible to manufacture an n ⁺ PP ⁺ bonded silicon wafer without contact between the n ⁺ layer and the P ⁺ layer without applying any grinding means, thereby improving its productivity and solar cells. The main feature is that SiO ₂ , TiO ₂ , MgO ₂ is added to the outer periphery of the back surface of the P-type silicon wafer
Print an impurity diffusion prevention layer using a paste such as
By performing a diffusion treatment using phosphorus, boron, etc., an n ⁺ layer covered with a silicon oxide film is formed on the entire surface except for the impurity diffusion prevention layer, and then by a solution treatment using hydrogen fluoride, etc. After removing the silicon oxide film and the impurity diffusion prevention layer, an Al paste is printed on the lower surface of the backside n ⁺ layer exposed at the center of the backside, and this is baked in the air. Diffuse the paste from the n ⁺ layer at the center of the back surface to the P layer of the P-type silicon wafer, thereby forming a P ⁺ layer to form n ⁺ PP ⁺ .
After BSF treatment, the Al paste oxide layer formed on the bottom surface of the above P ⁺ layer is treated with HCl.
The reason is that it is removed by solution treatment with NaOH or the like.

The present invention will be described in detail with reference to the process diagram of FIG. 2. As shown in FIG.
A P-type silicon wafer 1 of 300 μm and a specific resistance of 1 Ωcm is prepared, and first, on the back side 1' of the wafer 1,
An impurity diffusion prevention layer 2 is printed on the outer periphery in a ring shape by a screen printing method or the like.

At this time, the material for the diffusion prevention layer 2 is as follows:
Ceramic oxides such as SiO ₂ , TiO ₂ and MgO ₂ are preferably used, and when printing, for example, the above
A paste containing SiO ₂ as a main component is used, and in order to obtain the paste, SiO ₂ and the like are mixed with a cellulose-based organic binder and an organic solvent, as is known.

Next, by applying the diffusion treatment using impurities such as phosphorus and boron to the above item B in the same manner as shown in Fig. 1B, an n ⁺ layer is formed on the entire surface except for the impurity diffusion prevention layer 2 as shown in C Therefore, the n ⁺ layer includes the front side n + layer 3 from the front surface to the outer peripheral side, and the back side n ⁺ layer 3 at the center of the back surface ^.
The layer 3' is formed in a segmented manner, and the silicon oxide film 4 is formed on the surface of these n ⁺ layers 3 and 3', which reduces the sheet resistance of the n ⁺ layer. was 50Ω/□, and the depth of the diffusion layer was 0.2 μm.

Next, by treating the above material with a hydrogen fluoride solution, the silicon oxide film 4 and
By removing the impurity diffusion prevention layer 2 made of SiO ₂ etc., the state shown in (D) in the same figure is obtained. Next, as shown in (E), Al paste 5 is applied to the lower surface of the n ⁺ layer 3' on the back side.
is printed by means such as screen printing, and the Al paste 5 used at this time may be one containing aluminum powder of 350 mesh or more as a main component and prepared in the same manner as the SiO ₂ paste described above. The layer thickness due to the printing is 20 ~
It was set to 40 μm.

Furthermore, the above-mentioned material is fired in air at a temperature of 800°C to 900°C for 1 to 5 minutes, and by this process, the Al of the Al paste 5 ^is
It penetrates through the layer 3' and diffuses into the P layer of the P type silicon wafer 1, thereby forming a P ⁺ layer adjacent to the P layer as shown in f, thus n ⁺ P.
The BSF processing to form a P ⁺ junction is completed.

Finally, by removing the Al paste oxide layer 6 formed on the lower surface of the P ⁺ layer with HCl or the like in the above step, a silicon wafer 7 for solar cells can be manufactured as shown in FIG. A back electrode is formed on the lower surface of the ⁺ layer, a front electrode is formed on the upper surface of the n ⁺ layer 3 on the front side, and the electrode is further coated with an antireflection film to obtain a solar cell.

As is clear from the above explanation, in the present invention, an impurity diffusion prevention layer is formed in advance on the outer periphery of the back surface of the P-type silicon wafer before the diffusion treatment for forming the n-layer. On the back side, the n ⁺ layer on the front side is separated from the n + layer on the front side, and the n ⁺ layer on the back side is formed only in the center. As a result, the product can be easily manufactured without contact between the n ⁺ layer and the P ⁺ layer. Since the polishing work required in the conventional method is not required, workability can be improved, and since no rough surfaces are generated due to polishing, highly efficient solar cells can be obtained, and the disadvantages of damaging the wafer during work can be avoided. It will be resolved.

[Brief explanation of drawings]

I to I in FIG. 1 are process explanatory diagrams showing a conventional method for manufacturing silicon wafers for solar cells, and I to I in FIG. 2 are process explanatory diagrams showing the same manufacturing method according to the present invention. 1... P-type silicon wafer, 2... Impurity diffusion prevention layer, 3... Front side n ⁺ layer, 3'... Back side n ⁺
Layer, 4... silicon oxide film, 5... Al paste,
6...Al paste oxide layer.

Claims (1)

[Claims] 1 SiO ₂ ,
By printing an impurity diffusion prevention layer made of a paste such as TiO ₂ or MgO ₂ and performing a diffusion treatment using phosphorus, boron, etc., the entire surface except for the impurity diffusion prevention layer is covered with a silicon oxide film. ⁺ layer is formed, and then the silicon oxide film and the impurity diffusion prevention layer are removed by solution treatment such as hydrogen fluoride, and then Al paste is applied to the bottom surface of the n ⁺ layer on the back side exposed at the center of the back side. By printing this and firing it in the air, the Al of the Al paste is diffused from the N ⁺ layer at the center of the back surface to the P layer of the P type silicon wafer, thereby forming a P ⁺ layer. By doing this, we perform BSF processing to form an n ⁺ PP ⁺ junction.
A method for manufacturing a silicon wafer for a solar cell, further comprising removing the Al paste oxide layer formed on the lower surface of the P ⁺ layer by solution treatment with HCl, NaOH, or the like.