JPS61120428A - Method of processing silicon substrate - Google Patents

Abstract

PURPOSE:To obtain clean surfaces on a substrate having an oxygen concentration of 6X10<17>atm/cm<3> or less, by diffusing an impurity having getter action into the first and second surfaces of the substrate and then removing the impurity diffusion layers. CONSTITUTION:P is diffused in the mirror finished faces (100) of a P type Si substrate 11 having a concentration of oxygen of 6X10<17>atm/cm<3> or less so as to provide N<+> type layers 13 on both the front and rear surfaces. These surfaces are covered with protection layers 14 of pure polysilicon, and the N<+> type lasers 13 are completely removed by mirror polishing them on one side thereof. According to this method, in which P is not locally concentrated and no residual diffusion layer 13 is left, clean surfaces of Si can be obtained with simplified processes. By using such substrates, the device manufacturing yield can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for processing a silicon substrate such as a silicon wafer,
In particular, it relates to a gettering treatment method using phosphorus or the like.

[Background technology and its problems]

Gettering processing methods in the manufacture of semiconductor devices are becoming more important as the crystals used are becoming dislocation-free. Impurities such as metals existing inside the crystal and various contaminants introduced in various processes affect crystals without dislocations more sensitively than crystals with dislocations, causing crystal defects and reducing carrier lifetime. It was connected to. For this reason, a method has been adopted in which a defect is intentionally generated on the back surface of the wafer, and the various contaminants mentioned above are gettered in the defect area.

For example, in the manufacturing process of silicon devices such as COD solid-state imaging devices, MOS-LSI C large-scale integrated circuits), and bipolar ICs, defects in the silicon wafer itself and heavy metal contamination introduced into the silicon wafer during the manufacturing process,
Gettering treatment is performed on the back surface and inside of the silicon wafer in order to reduce crystal defects and the like. Gettering methods include sandblasting, ion implantation, phosphorus diffusion, etc. (CIExtrinsic Getter)
and gettering (intrinsic getter) due to defects inside the crystal due to oxygen precipitation in the crystal itself.
Of these methods, the ring gettering method is used because it has the strongest and most sustainable gettering effect.

However, in the normal phosphorus gettering method, when the front surface of the silicon wafer is covered with a protective layer and phosphorus is diffused to the back surface,
Pinholes in the protective layer or abnormal phosphorus diffusion during phosphorus diffusion (
Phosphorus is locally diffused into the silicon surface by melt-through. For example, in a COD solid-state image pickup device, this local diffusion of phosphorus causes image defects, so a prevention method is necessary.

FIG. 1 is an example of a conventional ring-gettering processing method used in a COD solid-state image sensor.

First, as shown in Fig. 1A, a 5if2 film (2) with a thickness of about 1.0 μm is coated on the surface of a P-type silicon wafer (11) with a (100) plane. As a measure to reduce pinholes in this 5t02 film (2), 5102M was deposited by thermal oxidation at 1100°C in an HCl atmosphere.
Odor (1800 people thick) and 420℃ (7) CV D S
Two layers of tOJjM (8000 layers thick) are deposited and the 5t02 film on the back side of the silicon wafer (1) is removed.
Next, as shown in FIG. 1B, phosphorus is diffused onto the back surface of the silicon wafer (1) to form a phosphorus diffusion layer (3).In the conventional process, phosphorus diffusion is performed at 1100°C for 60 minutes, and the surface concentration is IXIQ21rx-3 or higher.Next, as shown in Figure 1C, in order to prevent the external diffusion of phosphorus to the wafer surface, a Si3N+ film (about 600mm thick) and a pure multilayer film were used. A protective layer (4) of crystalline silicon film (about 2500 mm thick) is deposited on both sides using low pressure CVD. Next, as shown in the first diagram, a silicon wafer (4) is deposited. The protective layer (4) and the 5t02 film (2) deposited on the surface of 1) are removed by etching so as not to expose the silicon surface (1a).

However, such conventional ring-gettering processing methods have the following problems. First, there is a problem with the pinholes of S i (h 1JIi (2)) on the wafer surface when performing phosphorus diffusion.If the 5iOd odor (2) is made into a single layer structure, the pinholes will decrease with the film thickness, but O In addition, pinholes do not completely disappear even if a two-layer structure of SiOz film and CVD 5i02 is formed by thermal oxidation (H (in J atmosphere)), and the 5i02 film (2) during phosphorus diffusion Even if there are no pinholes in the 5iOJ odor (2), phosphorus powder may adhere to the surface of the 5iOJ odor (2) during phosphorus diffusion, resulting in heterogeneous diffusion such as melt-through.
Therefore, it is important to select a protective film that has a masking effect, but at present there is no suitable material. In addition, in the step of the first drawing, the protective layer (4) on the wafer surface side and the S1Q21 odor (
2) must be completely removed from the entire surface, but some may remain locally due to non-uniformity in the thickness of the protective layer (5taN4Ill! and polycrystalline syringe film constituting the ooze) and dust.

, S i (h i *(2)) may also be similar.

Furthermore, as the number of steps for depositing and removing films increases, it becomes difficult to maintain the cleanliness of the silicon surface, so it is desirable to avoid increasing the number of steps as much as possible. Furthermore, in the conventional process, eight steps are required for the ring gettering process, which makes the process long.

Due to the above reasons, in actual COD solid-state image sensors,
Even if efforts are made to improve the process, there is no perfect method.
Pattern defects were caused by remaining film, etc.

The following methods can be used to reduce this drawback. That is, this is a method in which diffusion is performed on both sides of the wafer without a protective film, and then the diffusion layer is removed by polishing or the like on one side.

Compared to the above-described method, this method simplifies the process and eliminates concerns about diffusion due to pinholes. However, in this case, due to high concentration diffusion, a crystal defect region occurs deeper than the diffusion layer (approximately 10μ), and the silicon crystal obtained by the Czycochralski method contains a large amount of oxygen. It was found that defects were generated internally and that even if the polishing depth was varied, there was almost no good quality crystalline region that could form an active region.

Therefore, we focused on the saturation solubility of oxygen in Si at the diffusion temperature and performed getter treatment on a silicon substrate with an oxygen content below the saturation solubility to prevent defects from occurring inside the crystal due to oxygen precipitation. do.

[Purpose of the invention]

The present invention provides a method for processing semiconductor substrates that eliminates the above-mentioned drawbacks.

[Summary of the invention]

In the present invention, after impurities having a getter function are diffused into the first and second main surfaces of a silicon substrate having an oxygen concentration of 6 x 10" ato/d or less, the impurities are diffused onto the first main surface side. Polish until the layer is removed.

In the gettering treatment method of the present invention, there is no local penetration of impurities, and there is no remaining film, resulting in a clean surface of the semiconductor substrate.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to FIG.

In this example, a semiconductor substrate, for example, a P-type silicon wafer (11) having a (100) plane and an oxygen concentration of 4×10 17 atovas/− is prepared. In this case, the silicon wafer (11) is lapped and a chemically etched wafer is used. An ordinary wafer with mirror polishing on one side may be used, but since mirror polishing is required again, chemical etching finish on both sides is more cost-effective. Since a silicon wafer before mirror polishing is used, the thickness of the silicon wafer must be increased by the amount of polishing. For example, a 3-inch wafer has a final finished thickness of 400 μm, so it needs to be around 450 μm.

Then, as shown in Figure 2A, this silicon wafer (
11) Diffuse phosphorus on both the front and back principal surfaces to form an N+ type wide diffusion layer 1
3) Form. The temperature at this time was 1100℃ and the time was 6
It is 0 minutes.

Next, as shown in FIG. 2B, a protective layer (14) with a two-layer structure of Si3N+ film and polycrystalline silicon film or a pure polycrystalline silicon film is formed on both sides of the silicon wafer (11) by low pressure CVD. accumulate.

Note that in the normal pressure CVD method, it is sufficient to deposit only on the back side.

Next, as shown in FIG. 2C, one side, that is, the front side, of the silicon wafer (11) is mirror-polished. The amount of polishing at this time is sufficient to sufficiently remove the phosphorus diffusion layer (14).

According to this phosphorus gettering treatment method, phosphorus is diffused onto both main surfaces of the silicon wafer (11), and the protective layer (11) is further coated with the protective layer (11).
After depositing 4), the surface side is mirror-polished until the phosphorus diffusion layer (13) is removed, which essentially eliminates the local penetration of phosphorus as in the conventional method.
A clean silicon surface is obtained without any residual film such as bN4. Further, the process can be simplified and the yield can be improved. Therefore, when applied to a COD solid-state image sensor, black and white spots due to phosphorus absorption, 5iO2r
Pattern defects caused by remaining films such as Si3N+ are no longer generated.

Although phosphorus was used as an impurity having a getter effect on the upper side, impurities other than phosphorus may be used.

Although the basic configuration of the present invention is as described above, it is necessary to pay attention to the following two points when implementing it. One is stacking faults observed after mirror polishing, and the other is the occurrence of slip lines. In the present invention, after performing phosphorus diffusion, the silicon surface is polished and the interior of the silicon is used as the surface.

If this treatment method is applied to a commonly used CZ crystal, the oxygen in the silicon will precipitate during phosphorus diffusion (basically the same as oxidation) due to the high oxygen concentration in the silicon crystal, resulting in defects. It becomes the nucleus or the nucleus of a stacking fault.

This precipitation depends on the oxygen concentration in silicon, and the higher the oxygen concentration, the greater the amount of precipitation. For this reason, the silicon wafer (11) used in the present invention must have a controlled low oxygen concentration. The oxygen concentration of the silicon wafer (11) used is preferably in the range of 6 x 101017ato/crll or less.

On the other hand, when a silicon substrate having an oxygen concentration of I x 10'' atotas/cd or more was subjected to the same treatment, the defect density was 102 to 103 defects/-.

The solubility of oxygen in silicon at 1100℃ is approximately 4×1
01” atones/c11 This agrees with the above speculation.

When double-sided diffusion is performed, diffusion is also performed at the edges of the wafer.

In order to prevent out-diffusion of diffused impurities, an appropriate protective film is formed on the diffusion region before going through each process. Easily damaged. Therefore, the end diffusion portion is exposed, and out-diffusion of diffused impurities occurs, which may cause problems by being diffused into the operating region as unnecessary impurities.

In order to avoid this, the present invention is designed to stabilize the manufacturing process by performing double-sided diffusion, removing the diffusion layer by mechanically or chemically polishing the edge of the wafer, and then entering the above process. As a result, improvements in device yield and characteristics were achieved.

〔Effect of the invention〕

According to the above-described gettering treatment method of the present invention, a clean semiconductor substrate surface can be obtained without impurities locally infiltrating and without any remaining film.

Moreover, the process is simplified and the yield is improved. Therefore,
CCD solid-state image sensor, MOS-LS1. This makes it suitable for application to the manufacture of semiconductor devices such as bipolar ICs.

[Brief explanation of drawings]

1st rI! JA-D are process diagrams showing an example of a conventional gettering processing method, and FIGS. 2A-2C are process diagrams showing an example of a gettering processing method according to the present invention. (1) (11) are silicon wafers, +3 (13) are phosphorus diffusion layers, (41 (14) are protective layers.

Claims (1)

[Claims] a step of diffusing an impurity having a getter function into the first and second main surfaces of a silicon substrate having an oxygen concentration of 6×10^1^7 atoms/cm^3 or less, and forming the impurity diffusion layer on the first main surface. A method for processing a silicon substrate, comprising a step of removing it.