JPS61135128A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To contrive the restraint of generation of defects in the vicinity of a surface of a wafer and the reduction of cost of products by depositing a polysilicon film or a silicon nitride film on a semiconductor substrate after forming an oxide film on the substrate and further subjecting it to a heat treatment at 1,150-1,250 deg.C. CONSTITUTION:An N type silicon substrate 1 is subjected to a heat treatment at 950 deg.C in an oxygen atmosphere and a thermal oxidation film 2 is formed on the surface of it. A polysilicon film 3 is deposited over the whole surface by an LPCVD method and wafers are inserted in the four heat-treatment reactors which are different in a degree of purification, and in which a heat treatment is effected in N2 atmosphere at 1,200 deg.C for 5hr thereby forming a low-oxygen layer 4 on a surface of the substrate 1. Further a heat treatment is carried out in N atmosphere at 700 deg.C for 10hr thereby forming an oxygen deposited nucleus layer 5 inside the substrate. After removing the polysilicon film 3 by chemical dry etching, the thermal oxide film 2 is removed followed by mirror finishing of the surface of substrate 1. The elements are formed on the surface of substrate 1 to fabricate a semiconductor device. Thus the density of defects on a surface can be kept at a low level constantly of a constantly for a long time regardless of the purification degree of the heat-treatment reactors.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for reducing crystal defects in a semiconductor substrate.

[Technical background of the invention and its problems]

As is well known, in order for various functional elements formed on the surface of a silicon substrate (wafer) to operate normally, it is desirable that there be no defects in or near the element. There are many causes for these defects, but mainly due to heavy metal contamination during the element manufacturing process, and oxygen contained in the silicon crystal precipitates during heat treatment during the element manufacturing process. For this reason, various attempts have been made to avoid the occurrence of defects.

A first method is to use a wafer with a low oxygen concentration obtained by applying a magnetic field to a melt during crystal growth. It has been reported that by using a wafer with such a low oxygen concentration, fewer defects occur in the wafer surface area (Hoshi et al.: Semiconductor Research 20, p. 254 (1)
983)). However, with the current trend of using large-diameter crystals, obtaining wafers with such a low oxygen concentration requires a huge magnetic field application device. therefore,
Considering the cost of the device and the cost of electricity required to apply the magnetic field, the cost is high except for some special elements.

It has some drawbacks.

In addition, as a second means, one wafer is processed before the device manufacturing process.
A method of reducing the oxygen concentration near the wafer surface by performing heat treatment at 000 to 1250° C. has been adopted. (Matsushita, Usami, Watanabe 2 Semiconductor Research 20, Pl 98 (1983))
. However, it is difficult to obtain industrially stable defect-free surface wafers using such methods. As a practical example, we used a heat treatment furnace that was kept clean to begin with.
After performing a heat treatment at a predetermined temperature of ~1250° C. for 4 hours to form a device, the density of defects near the wafer surface was examined, and the results shown in Table 1 were obtained.

Table 1 also shows the defect occurrence density when the same heat treatment as above was performed after using the same furnace for three months under the same temperature conditions.

Table 1 From Table 1, it can be seen that when the heat treatment temperature is high, the initial defect density near the wafer surface is low, and the generation of defects is suppressed. On the other hand, in order to keep the heat treatment furnace clean, it is desirable that the temperature is lower in the range of 1000 to 1250°C. This is due to the following reasons. In other words, the material of the reaction tube used in the heat treatment furnace is usually high-purity quartz or high-purity silicon carbide, but in either case, it is empirically known that the higher the temperature in the above temperature range, the faster the deterioration occurs. . Therefore, as the heat treatment temperature increases, the number of times the reaction tube must be replaced increases, leading to an increase in the cost of the product.

In addition, in Table 1 above, the heat treatment temperature is 1250°C,
In the case of 1200°C, the defect occurrence density after 3 months on the wafer is as high as 40.23 x 1011"), so the deterioration changes slowly over time, and due to this deterioration, the wafer It can be seen that there is contamination inside the furnace.

Based on the above, in the second method, heat-treating the wafer at high temperature has a certain effect on suppressing the occurrence of defects, but if this method is to be applied industrially, the selection of temperature is a problem. becomes. That is, 1000-1100℃
The occurrence of defects is not sufficiently suppressed in the temperature range of
There is a risk that defects will occur in the solder. ” [Object of the Invention] The present invention has been made in view of the above circumstances, and provides a method for manufacturing a semiconductor device that can suppress the occurrence of defects near the wafer surface regardless of the cleanliness of the heat treatment furnace, and can reduce product costs. This is what we are trying to provide.

[Summary of the invention]

The method for manufacturing a semiconductor device of the present invention is characterized in that after forming an oxide film on a semiconductor substrate, a polycrystalline silicon film or a silicon nitride film is deposited, and further heat treatment is performed at a temperature of 1150 to 1250°C. It is something.

According to this method, since the polycrystalline silicon film or silicon nitride film has a blocking effect against contamination, it is possible to suppress the occurrence of defects on the wafer surface for a long period of time regardless of the cleanliness of the heat treatment furnace. Product costs can be reduced.

The heat treatment temperature was set at 1150 to 1250°C because
Below 1150°C, the effect of suppressing defect generation is small;
On the other hand, if the temperature exceeds 1250°C, the deterioration of the heat treatment furnace will be accelerated and problems will arise in terms of heat resistance of the heat treatment furnace.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

First, the surface crystal orientation (100), specific resistance 20-40Ω
- Place the scratched N-type silicon substrate 1 in an oxygen atmosphere.

A heat treatment was performed at 950° C. to form a thermally oxidized lI2 film with a thickness of 800 μm on the surface (as shown in FIG. 1). Next, LPCV
A polycrystalline silicon film 3 with a thickness of 1000 is applied to the entire surface using the D method.
was deposited (as shown in Figure 2). Next, the above-mentioned wafers were loaded into four heat treatment furnaces (A-D') under various management conditions and with different degrees of cleanliness, and each was heated for 1200 min in an N2 atmosphere.
℃ for 5 hours to form a low oxygen layer 4 on the surface of the substrate 1.
was formed. Furthermore, a heat treatment is performed at 700''C for 10 hours in an N2 atmosphere to form an oxygen precipitation nucleus layer 5 inside the substrate 1 (as shown in FIG. 3).Then, the polycrystalline silicon film 3 is peeled off by chemical dry etching. After that, the thermal oxide film 2 was peeled off, and the surface of the substrate 1 was mirror-finished again by 4 pL (as shown in FIG. 4).

After that, elements are formed on the surface of the substrate 1 by a normal method,
Manufactured semiconductor devices.

Regarding the above process, the defect occurrence density (number/Ql
+2) was investigated. The results are shown in Table 2 below. In addition,
In the comparative example in Table 2, after forming a thermal oxide film on the substrate surface,
The results are for a substrate processed under the same conditions as in the above example except that the step of depositing a polycrystalline silicon film was omitted. In addition, the comparison in Table 2 is for heat treatment at 1000°C using the heat treatment furnace (A-) after using the heat treatment furnace (A), which was initially kept clean, at 1200°C for 3 months. .

Table 2 As is clear from Table 2, by forming a thermal oxide film on the substrate and depositing a polycrystalline silicon film, heat treatment is performed at high temperature for a long period of time regardless of the cleanliness of the heat treatment furnace. The surface defect density can be stably kept at a low level.

The cause of this effect is currently presumed to be that the polycrystalline silicon film has some kind of blocking effect against contamination inside the furnace.

In addition, the number of times the heat treatment furnace needs to be replaced can be reduced.
Product costs can be reduced.

Note that in the above example, after forming an oxide film on the substrate surface,
Although a polycrystalline silicon film is deposited on the entire surface, the same effect can be obtained not only by forming a polycrystalline silicon film but also by forming another film having a blocking effect against contamination in the furnace, such as a silicon nitride film. Further, in the above embodiments, a low temperature heat treatment was also performed after the high temperature heat treatment, but even if this low temperature heat treatment is not performed, the effects of the present invention are not affected in any way.

〔Effect of the invention〕

As detailed above, the method of the present invention has remarkable effects such as suppressing long-term stagnation and the occurrence of defects near the wafer surface and reducing product costs, regardless of the cleanliness of the heat treatment furnace. be.

[Brief explanation of drawings]

1 to 4 are cross-sectional views showing a method of manufacturing a semiconductor device according to an embodiment of the present invention. 1...P-type silicon substrate, 2...thermal oxide film, 3...
・Polycrystalline silicon film, 4... surface low oxygen layer, 5...
Oxygen precipitation nucleation layer. 5 Applicant's agent Patent attorney Takehiko Suzue Figure 4

Claims (1)

[Claims] After forming an oxide film on the semiconductor substrate, a polycrystalline silicon film or a silicon nitride film is deposited, and further 1150 to 125
A method for manufacturing a semiconductor device, characterized in that heat treatment is performed at a temperature of 0°C.