JPH0964137A - Detecting method of crystal defect of single-crystal silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the crystal defects of a single-crystal silicon surface easily by measuring the light and shade of an anodic oxide film by the difference of the growth thickness of the anodic oxide film formed on the surface of a single-crystal silicon substrate. SOLUTION: A single-crystal silicon substrate 4 and a platinum counter electrode 3 are dipped in an electrolytic bath 2. The single-crystal silicon substrate 4 is used as an anode and the platinum counter electrode 3 as a cathode, and a specified current is made to flow between the single-crystal silicon substrate 4 and the platinum counter electrode 3. An Al evaporated film 8 is formed on the whole rear of the silicon substrate 4, the Al evaporated film and a lead wire 5 are fixed with conductive paints 9, and an insulating film 10 is formed. When the silicon substrate 4 is anodized, an anodizing electrolytic current is concentrated to crystal defects on the surface of the silicon substrate 4, oxide films 7 are grown in the crystal defects more thickly, and light and shade are generated in the oxide films 7. Accordingly, the crystal defects on the outermost surface of the silicon substrate are detected easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting crystal defects in a silicon single crystal substrate, and more particularly to a method for detecting crystal defects on the surface of a substrate.

[0002]

2. Description of the Related Art Dislocations, which are imperfections in silicon single crystals,
Liquid etching has been used to detect stacking faults, precipitates, surface contamination, and diffusion. For this liquid etching method, for example, Ziltor solution is known. The Siltor solution is a 1: 1 mixed solution of hydrofluoric acid and chromic acid, and is used to detect the above various defects by etching the surface of a silicon single crystal by 10 μm or more.

In addition to the above liquid etching method, a method using a scanning electron microscope or a transmission electron microscope, X-ray topography, etc. are known. X-ray topography is an X-ray diffraction image obtained by irradiating a silicon single crystal with X-rays.
The crystal defect is detected from the line topography.

[0004]

However, in the above-mentioned conventional liquid etching method, it is necessary to etch the surface of the silicon single crystal by 10 μm or more as described above, and therefore the crystal defects on the outermost surface of the silicon single crystal should be detected. Was impossible. Further, the liquid etching method has an environmental hygiene problem because the etching liquid contains harmful chromium, and the treatment of the waste liquid is one of the problems when the liquid etching method is used.

Scanning electron microscope, transmission electron microscope, X
Line topography lacks simplicity because it requires expensive equipment and advanced handling technology, and these methods detect bulk crystal defects in silicon single crystals and detect crystal defects on the outermost surface of silicon single crystals. It was impossible. This invention has been made in view of the above points, and its object is a method for detecting crystal defects on the outermost surface of a silicon single crystal by using a method that reflects the physical properties of the outermost surface of a silicon single crystal, which is simple and environmentally friendly. To provide.

[0006]

According to the present invention, the above object is to anodic oxidize a silicon single crystal substrate to form an anodic oxide film on the surface of the silicon single crystal substrate, and to increase the growth thickness of the anodic oxide film. It is achieved by measuring the distribution of the light and shade of the anodic oxide film according to. In the above-mentioned invention, the anodic oxidation uses a mixed aqueous solution of boric acid and sodium borate as an electrolytic solution, or, when anodizing a silicon single crystal substrate having a high specific resistance of 1000 Ω · cm or more, a silicon single crystal substrate is used. It is effective to cover one of the main surfaces with a conductive thin film.

[0007]

Function: Anodizing electrolytic current concentrates on crystal defects on the surface of the silicon single crystal. Therefore, non-uniformity occurs in the anodic oxidation electrolytic current on the surface of the silicon single crystal, and the oxide film grows thicker due to crystal defects. In this way, shading occurs in the oxide film. Crystal defects include dislocations, diffusion layers, strained layers, and the like. The diffusion layer includes, for example, a p-type substrate on which an n-layer is selectively formed, a p-type substrate on which a p ⁺ diffusion layer is formed, and the like.

Since the mixed aqueous solution of boric acid and sodium borate is weakly alkaline, the silicon single crystal substrate is stable in the electrolytic bath, and the polarization of the anode causes discharge of hydroxide ions, and the outermost surface of the silicon single crystal substrate. Oxidizes. When one main surface of the silicon single crystal substrate is covered with a conductive thin film, the potential distribution of the silicon single crystal substrate becomes uniform.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. Example 1 FIG. 1 is a principle diagram showing an anodizing method for a silicon single crystal. Silicon single crystal substrate 4 and platinum counter electrode 3 are electrolytic bath 2
Is soaked in. A predetermined current is passed between the silicon single crystal substrate 4 and the platinum counter electrode 3 by using the silicon single crystal substrate 4 as an anode and the platinum counter electrode 3 as a cathode. 5 is a lead wire. A silicon oxide film grows on the surface of the silicon single crystal substrate.

The electrolytic bath 2 is an aqueous solution of 6 g of boric acid and 38 g of sodium borate and has a temperature of 22 to 25 ° C. The surface of the silicon single crystal substrate was mirror-finished, and the platinum counter electrode 3 was used with dimensions of 30 mm × 50 mm × 0.1 mm. The DC power supply voltage was adjusted so that the current flowing through the silicon single crystal substrate was 0.5 to 1.0 mA. FIG. 6 is a sectional view showing a silicon single crystal substrate anode according to an embodiment of the present invention. On the entire back surface of the silicon single crystal substrate 4.
An Al vapor deposition film 8 is formed, the Al vapor deposition film 8 and the lead wire 5 are fixed with a conductive paint 9, and then an insulating film 10 is formed. 7
Is a silicon oxide film. This anodic structure is effective when the specific resistance of the silicon single crystal substrate is 1000 Ω · cm or more, and a uniform anodic oxide film 7 can be obtained. When the specific resistance of the silicon single crystal substrate is 100 Ω · cm or less, the silicon single crystal substrate may be simply pinched with a clip. When the specific resistance is 1000 Ω · cm or more, a uniform anodic oxide film cannot be formed only by pinching with a clip.

FIG. 2 (a) is a photograph of the crystal structure showing the light and shade of the anodic oxide film on the silicon single crystal substrate according to the embodiment of the present invention. Silicon single crystal substrate (diameter 40 mm, thickness 40
0 μm) is a dislocation-free single crystal substrate having a specific resistance of 40 to 50 Ω · cm. Diffuse phosphorus from both sides of the silicon single crystal substrate (surface concentration 1 × 10 ²¹ atoms / cm ³ depth about 150 μm)
After that, the phosphorus diffusion layer on one side was removed and mirror finishing was performed.
The center of the silicon single crystal substrate is covered with Al foil and boron is ion-implanted (accelerating voltage 100 keV, dose 1 × 10 ¹⁵ /
cm ² ). After ion implantation of boron, anodic oxidation was performed.

Crystal defects generated by ion implantation are observed as black dots except for the portion covered with Al foil. In addition, so-called striation in which the dopant is distributed like a tree ring when producing a silicon single crystal is also observed. Comparative Example 1 FIG. 2B is an X-ray photograph of an X-ray topography showing crystal defects of the silicon single crystal substrate according to the comparative example of the present invention.

X without anodic oxidation of the silicon single crystal substrate
The procedure is the same as in Example 1 except that the line topography is measured. A dislocation network due to the one phosphorus diffusion layer remaining on the silicon single crystal substrate is observed. The crystal defects obtained by the methods of Example 1 and Comparative Example 1 are different from each other. The crystal defects obtained by the method of Example 1 are those on the outermost surface of the silicon single crystal substrate, and the crystal defects obtained in Comparative Example 1 are bulk crystal defects of the silicon single crystal substrate. Example 2 FIG. 3A is a photograph of a crystal structure showing the light and shade of an anodized film of a silicon single crystal substrate according to a different example of the present invention.

A silicon single crystal substrate (diameter 40 mm, thickness 400 μm) has a specific resistance of 40 to 50 Ω · cm and an etch pit density of 2 × 10 ⁴ / cm ² . After removing the surface-treated layer with hydrofluoric nitric acid, anodization was performed. Black spots on the anodic oxide film due to the etch pits are observed. FIG. 4 is an enlarged photograph (× 200) of a crystal structure showing the shade of the anodic oxide film of a silicon single crystal substrate according to another embodiment of the present invention.
Times).

It can be seen that crystal disorder of about 50 to 100 μm occurs around dislocations. Comparative Example 2 FIG. 3B is an X-ray photograph of an X-ray topography showing crystal defects of a silicon single crystal substrate according to a different comparative example of the present invention.

X without anodic oxidation of the silicon single crystal substrate
The procedure is the same as in Example 1 except that the line topography is measured. It can be seen that the distribution of the etch pits is close to that of the anodic oxide film of Example 2. The crystal defects obtained by both the methods of Example 2 and Comparative Example 2 are in agreement. Example 3 FIG. 5 (a) is a photograph of a crystal structure showing the light and shade of the anodic oxide film of a silicon single crystal substrate according to a further different example of the present invention.

The silicon single crystal substrate (diameter 40 mm, thickness 400 μm) is a dislocation-free single crystal substrate having a specific resistance of 40 to 50 Ω · cm. After mirror finishing, the letter 8 was drawn with a diamond pen and then anodized. Since the character 8 has crystal defects, only the character 8 is observed. Comparative Example 3 FIG. 5B is an X-ray photograph of an X-ray topography showing crystal defects of a silicon single crystal substrate according to a further different comparative example of the present invention.

Since the character 8 has a crystal defect, only the character 8 is observed. The crystal defects obtained by any of the methods of Example 3 and Comparative Example 3 are in agreement.

[0019]

When the silicon single crystal substrate is anodized, the anodizing electrolytic current concentrates on the crystal defects on the surface of the silicon single crystal substrate, the oxide film grows thicker on the crystal defects, and the oxide film has density. Therefore, crystal defects on the outermost surface of the silicon single crystal substrate are easily detected.

When a mixed aqueous solution of boric acid and sodium borate is used as an electrolytic solution for anodic oxidation, discharge of hydroxide ions occurs due to anodic oxidation and the silicon single crystal substrate is oxidized. When one main surface of the silicon single crystal substrate is covered with a conductive thin film and anodized, the potential distribution on the other main surface of the silicon single crystal substrate becomes almost uniform. An oxide film is formed, which makes it possible to detect crystal defects in the entire silicon single crystal substrate.

[Brief description of drawings]

FIG. 1 is a principle diagram showing an anodizing method for a silicon single crystal.

FIG. 2 (a) is a photograph of the crystal structure showing the light and shade of the anodic oxide film of the silicon single crystal substrate according to the example of the present invention. (B) shows the crystal defects of the silicon single crystal substrate according to the comparative example of the present invention. X-ray photograph of X-ray topograph

FIG. 3A is a photograph of a crystal structure showing the light and shade of an anodized film of a silicon single crystal substrate according to a different embodiment of the present invention. FIG. 3B is a crystal defect of a silicon single crystal substrate according to a different embodiment of the present invention. X-ray photograph of X-ray topograph showing

FIG. 4 is an enlarged photograph (× 2) of a crystal structure showing the density of an anodized film of a silicon single crystal substrate according to a different embodiment of the present invention.
00 times)

FIG. 5 (a) is a photograph of a crystal structure showing the light and shade of an anodized film of a silicon single crystal substrate according to a further different embodiment of the present invention. (B) is a silicon single crystal substrate according to a still further comparative example of the present invention. X-ray photograph of X-ray topograph showing crystal defects

FIG. 6 is a sectional view showing a silicon single crystal substrate anode according to an embodiment of the present invention.

[Explanation of symbols]

 2 Electrolytic bath 3 Platinum counter electrode 4 Silicon single crystal substrate 5 Lead wire 7 Silicon oxide film 8 Al vapor deposition film 9 Conductive paint 10 Insulating film

Claims (3)

[Claims] 1. A method of anodizing a silicon single crystal substrate to form an anodized film on the surface of the silicon single crystal substrate, and measuring the distribution of the anodized film density due to the difference in the growth thickness of the anodized film. A method for detecting a crystal defect on the surface of a silicon single crystal substrate. 2. The detection method according to claim 1, wherein the anodic oxidation uses a mixed aqueous solution of boric acid and sodium borate as an electrolytic solution. 3. The crystal defect detection of a silicon single crystal substrate according to claim 1, wherein one main surface of the silicon single crystal substrate is covered with a conductive thin film to carry out anodization. Method.