JPS59200425A - Treating method of semiconductor base body - Google Patents

Abstract

PURPOSE:To eliminate the partial injection of an impurity having gettering action while removing the remaining of a film, and to clean the surface of a base body by each diffusing the impurity to the first and second main surfaces of the base body, forming a protective layer on the second main surface and polishing the first main surface side until an impurity diffusion layer is removed. CONSTITUTION:With a silicon wafer 11, a wafer such as a lapped and chemical etching-finished wafer is used, phosphorus is diffused to both surface and back main surfaces of the silicon wafer 11, and N<+> type diffusion layers 13 are formed. Two layer structure of Si3N4 films and polycrystalline silicon films or protective layers 14 consisting of pure polycrystalline silicon films are deposited on both main surfaces of the silicon wafer 11 through a decompression CVD method. Said structure or layer may be deposited only on the back side through a normal pressure CVD method. One surface, the surface side, of the silicon wafer 11 is mirror-ground. The quantity of the surface side ground at that time shall be sufficient to completely remove the diffusion layer 14 of phosphorus.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for processing semiconductor substrates such as silicon wafers, and in particular to a gettering saturation method using phosphorus or the like.

Background technology and its problems In the manufacturing process of silicon devices such as CCD solid-state image sensors, MOS-LSIs (large-scale integrated circuits), and bipolar ICs, defects in the silicon wafer itself and defects introduced into the silicon wafer during the manufacturing process are In order to reduce heavy metal contamination, crystal defects, etc., gettering embedding is performed on the backside and inside of silicon wafers. Sandblasting is the gettering method.

Gettering (Extrin) such as ion implantation and phosphorus diffusion
sic Getter) and gettering (Intri) due to defects inside the crystal due to oxygen precipitation in the crystal itself.
nsic Getter). In this method, a ring gettering method is used which has a strong and persistent gettering effect. However, in the normal phosphorus gettering method, when the front surface of a silicon wafer is covered with a protective layer and phosphorus is diffused to the back surface, pinholes in the protective layer or abnormal diffusion (melt-through) of phosphorus during phosphorus diffusion occur. Phosphorus is locally diffused into the silicon on the surface. For example, C
In CD solid-state imaging devices, this local diffusion of phosphorus causes image defects, so a method for preventing this is necessary.

FIG. 1 is an example of a conventional ring-gettering processing method used in a CCD solid-state image sensor. This is first, number x
As shown in vAA, a 5to2 film (2) with a thickness of about 1.0 μm is deposited on the surface of a P-type silicon wafer (1) of (100) ifl, for example, to serve as a protective film during v diffusion.

As a measure to reduce pinholes in this Si0g film (2), HC
5toz expansion (thickness 1800A) by thermal oxidation at 1100℃ in t atmosphere (420℃f) eVD 5i02 w
A (Ji[Sa8000A) (1) Deposit two layers,
The 5inz film on the back side of the silicon cube (1) is removed. Next, as shown in FIG. 1B, a silicon wafer (1) is
A phosphorus diffusion layer (8) is formed by diffusing phosphorus on the back surface of the substrate.

In the conventional process, phosphorus diffusion was performed at 1100° C. for 60 minutes, and the surface concentration was greater than 1×1 g”i3.

Next, as shown in FIG.
Then, a protective layer (4) of pure polycrystalline silicon family (about 250 OA thick) is deposited. This protective layer (4) was formed by low pressure CVD.
When using this method, it is deposited on both sides. Next, as shown in the first diagram, a protective layer (
4) and 5i02J [(2) are etched away to expose the silicon surface (la).

However, such conventional ring-gettering processing methods have the following problems. First, there is a problem with the pinholes in the 8102 film (2) on the surface of the sea urchin when performing phosphorus diffusion. When the 5i02 film (2) is formed into a single layer structure, the pinholes decrease as the film thickness increases, but they do not become 0″'/2. Even with a layered structure, pinholes cannot be completely eliminated.Also, 5i during phosphorus diffusion
Even if there are no pinholes in the 02 membrane (2), 5
Phosphorus powder or the like may adhere to the surface of the in2 film (2), causing abnormal 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 protective film. In addition, in the step of the first plan, it is necessary to completely remove the protective layer (4) and the 5i02 film (2) on the surface side of the sea urchin, but it is also necessary to completely remove the protective layer (4) on the surface side of the sea urchin. Some parts may remain locally due to non-uniformity in the thickness of the silicon film or dust. 5i02!
(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, making the process longer.

Due to the above reasons, in actual CCD solid-state image sensors,
Despite efforts to improve the process, there is no perfect method, and pattern defects occur due to black and white dots due to phosphorus penetration, and residual 5i02 film, Si3N4 film, etc.

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

SUMMARY OF THE INVENTION The present invention involves diffusing impurities having a getter function into the first and second main surfaces of a semiconductor substrate, forming a protective layer on at least the second main surface, and then dispersing the impurities on the first main surface side of the substrate. is polished until the impurity diffusion 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.

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

In this example, a semiconductor substrate, for example, a P-type 7 silicon wafer (11) having a (100) plane is prepared. In this case, the silicon wafer is wrapped and finished with chemical etching. 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.

In order to use a silicon wafer before mirror polishing, it is necessary to increase the thickness of the silicon wafer by the amount of polishing.

For example, a 3-inch wafer has a final finishing thickness of 400 mm.
Since it is μm, it needs to be around 450 μm.

Therefore, as shown in FIG. 2A, this silicon wafer αυ
Phosphorus is diffused on the front and back main surfaces to form an N-type diffusion layer.

Next, as shown in FIG. 2B, a protective layer (14) made of a two-layer structure of Si3N4 glands and a polycrystalline silicon film or a pure polycrystalline silicon film is formed by low pressure CVD on both sides of the silicon wafer. Deposit. Note that in the normal pressure CVD method, it is good to deposit only on the back side.

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

According to such a phosphorus gettering treatment method, phosphorus is diffused on both main surfaces of a silicon wafer (Lυ), and a protective layer (14
) is deposited, the surface side is mirror-polished until the phosphorus diffusion layer a31 is removed, which essentially eliminates the local penetration of phosphorus as in the conventional method, and 8i02, S
A clean silicon surface is obtained without any residual film such as i3N4. Further, the process can be simplified and the yield can be improved. Therefore, when applied to a CCD solid-state image sensor, a black and white point due to phosphorus penetration, 5i02
, pattern defects caused by remaining films such as Si3N4 are eliminated.

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 used as a surface.

If this treatment method is applied to a commonly used C2 crystal, the oxygen in the silicon will precipitate during phosphorus diffusion (basically the same even when oxidized) due to the high oxygen concentration in the silicon crystal, causing 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, it is necessary to use a silicon wafer I used in the present invention whose oxygen concentration is controlled to be low.

Silicon wafer used Ql) 17) Oxygen concentration halo x1
A range of 017crIV3 to 10×101 eyes 3 is preferable.

FIG. 3 shows experimental results regarding the oxygen concentration in silicon and the stacking fault density. The measurement was performed at a phosphorus diffusion temperature of 1100°C.
After the steps shown in FIG. 2A to C, the measurement was carried out after further thermal oxidation at 1100°C. Stacking faults were observed after 5ecco etching. In addition, as a crystal growth method to control the oxygen concentration, a static magnetic field is applied to the silicon surface in the container, and the silicon crystal is pulled up while rotating relative to the container. This experiment was conducted using a silicon wafer obtained by this method.

From FIG. 3, the oxygen concentration at which the stacking fault becomes 0 cIn is about 7.0×10 cm or less. In addition, the slip line is 1xlOcIn for thermal oxidation at 1100°C.
It will no longer be generated at higher oxygen concentrations. From this experiment, there are no suitable conditions for a wafer process temperature of 1100°C, and it is necessary to lower the temperature to 1050°C or lower. In addition, from the point of view of the phosphorus gettering effect, the higher the phosphorus diffusion temperature, the stronger and more durable the effect. For this reason, it is better to have a higher temperature for phosphorus diffusion, but this can be covered to some extent by increasing the diffusion time.
000° C. for 120 minutes, and the ring gettering effect seems to be slightly lower than that of 1100° C., but no difference in device characteristics has been found.

In heat treatment at 1000° C., the critical oxygen concentration for generating stacking faults as shown in FIG. 3 becomes 1×10 crn or more, and the occurrence of slip lines becomes 6×10 cm or less. This range tends to widen if the heat treatment temperature is further lowered, but in the current wafer process, the temperature is around 1000"C, and from the point of view of the ring getter effect, phosphorus diffusion is 1000"C.
It is thought that the gettering effect will be insufficient below.

The oxygen concentration in the silicon used in this example is determined by the absorption coefficient α (Crn) of the absorption peak of 1110 on infrared measurement.
A conversion factor of 4.81×10 α is used for the conversion coefficient between the concentration and the concentration 7 (Oi).

Effects of the Invention According to the gettering treatment method of the present invention described above, not only is there no local penetration of impurities, but also a clean semiconductor substrate surface is obtained with no remaining film.

Moreover, the process is simplified and the yield is improved. Therefore,
It is suitable for application to the manufacture of semiconductor devices such as CCD solid-state image sensors, MOS-LSIs, and bipolar ICs.

[Brief explanation of the drawing]

1A-D are process diagrams showing an example of a conventional gettering processing method, FIGS. 2A-C are process diagrams showing an example of a gettering geographical method according to the present invention, and FIG. FIG. 2 is a characteristic diagram showing the relationship between concentration and stacking fault degree. (1) (lυ is silicon wafer, (3) (lal&!
(4) a phosphorus diffusion layer and a Q-retention layer. Figure 2 Figure 8

Claims (1)

[Claims] a step of diffusing an impurity having a gettering effect into the first and second main surfaces of the semiconductor substrate, a step of depositing a protective layer on at least the second main surface, and a step of depositing a protective layer on at least the second main surface; A method for processing a semiconductor substrate comprising the step of polishing until an impurity diffusion layer is removed.