JPH10247629A - Manufacture of semiconductor wafer, semiconductor wafer and solar cell using the semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with the removal process of impurity diffused layer side surface for a P-N junction isolation in the manufacturing method of a semiconductor wafer by a method wherein an insulating film is formed on the surface of a semiconductor ingot or the surface of a semiconductor block, which is obtained by cut-processing this ingot, and after that, the ingot or the block is cut into the wafer. SOLUTION: A CZ method pulling P-type single crystal silicon ingot is processed by cutting into a silicon block having a prescribed dimension. After that, a surface damaged layer generated by the cutting is etched away using the so-called mixed acid solvent, such as a hydrofluoric acid, a nitric acid and an acetic acid, then, the silicon block is cleaned in pure water and is dried. After that, a silicon nitride film 2 of a thickness of 0.1μm is formed on the surface of a P-type silicon block 1 using an LPCVD device. As the condition for the formation at this time, an SiH2 Cl2 gas and an NH3 gas, for example, are used and a temperature of 800 deg.C is set. A P-type silicon block 3 formed with the film 2 is cut using a wire-saw cutting device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor wafer, a semiconductor wafer, and a solar cell using the semiconductor wafer.

[0002]

2. Description of the Related Art In manufacturing a silicon crystal solar cell, a single crystal or polycrystalline P-type silicon wafer is usually used as a substrate, and an N-type impurity diffusion layer is provided on the substrate to form a PN junction. Used.

In the above manufacturing process, when the PN junction (j) is formed by diffusing an N-type impurity into the front side of the P-type silicon wafer (w), the side surface and, if necessary, the back surface of the wafer are simultaneously diffused to the wafer surface. N-type diffusion layer
(n) is formed (see FIG. 5). For this reason, when electrodes are formed on the front side and the back side, respectively, and when operated as a solar cell, a short circuit or a leak state occurs between the electrodes on the front side and the back side due to the diffusion layer on the side peripheral surface of the wafer. Satisfactory operation as a battery cannot be obtained.

Therefore, a step of cutting and removing (C) the diffusion layer on or near the side surface of the wafer after the formation of the impurity diffusion layer or the electrode pattern and joining and separation is required (see FIG. 6). Such joining separation method uses a mechanical grinding,
Etching methods using chemicals or plasma, removal methods by laser processing method or ultrasonic processing method, etc. are applied, but problems such as difficulty of removal process, uniformity, reproducibility, etc.,
There are many problems to be solved, such as the problem of bonding characteristics after removal.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor wafer, which does not require a step of removing a lateral impurity diffusion layer for separating a PN junction as in the prior art, a semiconductor wafer, and a solar cell using the semiconductor wafer. To provide.

[0006]

According to the invention of claim 1 of the present application, there is provided a semiconductor ingot or a semiconductor block (1) obtained by cutting the ingot.
Forming an insulating film (2) on the surface of the semiconductor wafer and then cutting the wafer into wafers ". According to the invention of claim 4 of the present application,
`` Semiconductor wafer with insulating film (2) formed on side peripheral surface
(4)] is provided.

The semiconductor ingot used in the manufacturing method of the present invention is preferably a "silicon crystal type" as described in claim 2 of the present application. The silicon crystal system may be either single crystal silicon or polycrystalline silicon. Usually, these silicon crystal systems are configured and used as P-type or N-type.

In the present invention, the object for forming the insulating film may be a semiconductor ingot, or a semiconductor block cut from the ingot to a predetermined size. Blocks. In short, any material may be used as long as it is in the stage before cutting into wafers.

The above-mentioned semiconductor ingot or block is preferably a silicon crystal system particularly from the viewpoint of solar cell production, and includes a single crystal silicon ingot obtained by the CZ method, a single crystal silicon ingot by the FZ method, and a polycrystalline silicon ingot. Can be

In the present invention, the insulating film (2) has a thickness of 0.05
A range of ５5 μm is suitable. When the thickness is less than 0.05 μm, the function as a diffusion mask at the time of impurity diffusion is insufficient, and when the thickness is more than 5 μm, cracks and the like are liable to be formed in the film, which is disadvantageous. Further, as a type of the insulating film, when a silicon crystal system is selected as the semiconductor ingot, a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon thermal oxide film, and the like are preferable. The thickness of the silicon nitride film is 0.1 to 0.3 μm, and the thickness of the silicon thermal oxide film is 0.2 to 1 μm.
It is optimal in that it satisfies the function required for the insulating film and takes into consideration the formation cost.

According to the present invention, there is provided a semiconductor wafer according to the present invention, wherein an impurity diffusion layer is formed to provide a PN junction and a desired electrode is formed on each of the front and back surfaces of the wafer by means known in the art. Thereby, it can be provided as a solar cell.

In the present invention, the ingot or block is cut into wafers by a wire saw cutting method,
A method known in the art, such as an inner peripheral blade cutting method, a cutting method using a laser, or a cutting method using electric discharge machining, can be used as it is.

The semiconductor wafer of the present invention can be sufficiently applied to a diode device, a transistor device, and the like using the whole surface of the wafer, in addition to the solar cell.

[0014]

According to the present invention, an insulating film (2) is formed on the surface of a semiconductor ingot or a semiconductor block (1) at a stage prior to cutting into a wafer.
Is formed, so the wafer obtained when cutting (4)
The insulating film (2) remains on the side peripheral surface of the wafer (4), which functions as a mask when forming an impurity diffusion layer on the wafer (4), and the wafer (4)
Since the PN junction is separated between the front and rear surfaces, the step of dividing the junction becomes unnecessary. In addition, the insulating film (2) also functions as a mechanical protective film at the time of cutting into a wafer and at the time of processing a solar cell and other semiconductor devices.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments, but the present invention is not limited thereto. Example 1 FIG. 1 is a cross-sectional view of an example of a P-type silicon block according to the present invention, and FIG. 2 is a cross-sectional view (a) and a plan view of an example of a P-type silicon wafer cut from the P-type silicon block of FIG. FIG. 3 is a cross-sectional view when an N-type impurity diffusion layer (PN junction) is formed on the P-type silicon wafer of FIG.

First, a P-type single crystal silicon ingot pulled up by the CZ method is cut into a silicon block having a predetermined size, and the surface damaged layer generated by the cutting is treated with hydrofluoric acid.
It is removed by etching using a so-called mixed acid solution such as nitric acid and acetic acid, and then washed and dried in pure water. Then, the above P
A silicon nitride film (2) having a thickness of 0.1 μm is formed on the surface of the mold type silicon block (1) using an LPCVD apparatus (FIG. 1).
reference). The formation conditions at this time include, for example, SiH ₂ C
The temperature is 800 ° C. using l ₂ and NH ₃ gas.

The P-type silicon block (3) on which the silicon nitride film (2) was formed as described above was cut using a wire saw cutting device to obtain a P-type silicon wafer (4) shown in FIG. The resulting P-type silicon wafer (4) has a 0.1 μm silicon nitride film on the side surface around the wafer as shown in FIG.
(2).

The process of manufacturing a solar cell (see FIG. 4) using the P-type silicon wafer (4) as a substrate is a known process. That is, etching with a concentrated NaOH solution for removing a processing layer on the wafer surface, and thin Na for forming irregularities on the surface (so-called textured state).
It consists of steps of etching with an OH solution, forming an N-type diffusion layer (5) by N-type impurity diffusion (forming a PN junction (6)), and forming electrodes (7) on the front and back surfaces.

In the above process, when the PN junction (6) is formed by diffusing the N-type impurity, as shown in FIG. Therefore, when the N-type impurity diffuses, the nitride film (2) functions as a mask, which inevitably divides the front and back surfaces of the wafer and insulates the conduction therebetween. Therefore, a processing step for separating the PN junction at the peripheral portion of the wafer after the formation of the PN junction has conventionally been required. However, in the present embodiment, the PN junction separation step is unnecessary.

In the above embodiment, the insulating film provided on the surface of the silicon block is a silicon nitride film formed by the LPCVD method. However, other types of insulating films that can withstand the etching process using a NaOH solution and can function as a diffusion mask during impurity diffusion. Thin film of material such as another CVD method (PECV
D, ATCVD, etc.), a silicon nitride film, a silicon oxynitride film, a silicon oxide film, a silicon thermal oxide film, and the like are also possible.

[0021]

According to the present invention, the insulating film functions as a mask during the formation of the PN junction, so that a step for separating the PN junction after diffusion is not required. Also, when cutting a wafer from a silicon ingot or silicon block,
It also acts as a mechanical protective film on the side peripheral surface of the wafer, and can prevent the occurrence of chipping, cracking, and the like on the peripheral surface of the wafer. Further, chipping, chipping, cracks, and the like of the peripheral surface on the wafer side can be effectively prevented in all processing steps after the wafer is cut.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a P-type silicon block according to the present invention.

2A is a cross-sectional view of an example of a P-type silicon wafer cut from the P-type silicon block in FIG. 1;
Plan view of an example of a silicon wafer

3 is a sectional view when an N-type impurity diffusion layer (PN junction) is formed on the P-type silicon wafer of FIG. 2;

FIG. 4 is a schematic cross-sectional view of a solar cell using an example of a P-type silicon wafer of the present invention.

FIG. 5 is a cross-sectional view of a wafer in which a PN junction of a conventional example is formed.

FIG. 6 is a schematic diagram illustrating a PN junction separation step in a conventional example.

[Explanation of symbols]

(1) P-type silicon block (2) Silicon nitride film (3) P-type silicon block with silicon nitride film formed (4) P-type silicon wafer as an example of the present invention (5) N-type diffusion Layer (6)… PN junction (7)… Electrode

Claims (7)

[Claims] 1. A method of manufacturing a semiconductor wafer, comprising: forming an insulating film on a surface of a semiconductor ingot or a semiconductor block obtained by cutting the ingot, and thereafter cutting the wafer into wafers. 2. The semiconductor ingot or block is made of a silicon crystal, and the insulating film is one selected from a silicon nitride film, a silicon oxynitride film, a silicon oxide film, and a silicon thermal oxide film. Semiconductor wafer manufacturing method. 3. The method for manufacturing a semiconductor wafer according to claim 2, wherein the silicon crystal system is single crystal silicon or polycrystalline silicon. 4. A semiconductor wafer having an insulating film formed on a side peripheral surface. 5. The semiconductor wafer according to claim 4, comprising a silicon crystal system, wherein the insulating film is one selected from a silicon nitride film, a silicon oxynitride film, a silicon oxide film, and a silicon thermal oxide film. 6. The semiconductor wafer according to claim 5, wherein the silicon crystal system is single crystal silicon or polycrystalline silicon. 7. A solar cell, wherein a PN junction is formed on a predetermined surface of the semiconductor wafer according to any one of claims 4 to 6, and electrodes are formed on each of the front and back surfaces of the wafer.