JPH02177321A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To reduce minute defects in an epitaxial film by heat-treating an Si single crystal substrate at specific temperature ranges respectively in two processes of dry oxygen atmosphere and wet oxygen atmosphere. CONSTITUTION:By a vapor phase reaction method, an Si single crystal film is epitaxially grown on an Si single crystal substrate. In this process, the Si substrate is heat-treated in advance in the temperature range of 650-1000 deg.C in dry oxygen atmosphere, and then it is done in the temperature range of 1100-1200 deg.C in wet oxygen atmosphere, and thereafter the Si single crystal film is epitaxially grown on this substrate. According to this method, minute defects consisting of deposit or dislocation occur inside the substrate, and by intrinsic gettering effect which absorbs minute defects and their unclei by the distorting field, minute defects in the epitaxial film can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor substrate, and more particularly to a method for reducing microdefects found in an epitaxial surface layer during epitaxial growth of a silicon single crystal thin film by a vapor phase reaction method.

Silicon epitaxial layers are essential as substrates for ICs and LSIs, and even as substrates for VLSIs.
Used for bipolar devices. Crystal defects such as stacking faults, dislocations, and micro defects (shallow bits) are found in this epitaxial layer. It is well known that these crystal defects deteriorate the electrical characteristics of devices. Suppressing at least one of these crystal defects can contribute to improving the yield of devices.

Various methods have been proposed to suppress crystal defects.

Currently, the density of stacking defects in epitaxial layers can be reduced to 10 pieces or less 1 cm2 by gas etching before epitaxial growth, and as for dislocations, the defect density can be reduced to 10 pieces or less by improving the uniform heating method during epitaxial growth. It is becoming less than 1Cm2. The problem here is the micro defects found in the epitaxial surface layer. Micro defects grow as the device process progresses, becoming large stacking faults and causing a decrease in yield. This microdefect density is found to be 106 to 107 lCm2 in an epitaxial layer using a conventional untreated wafer, and its correlation with device characteristics, such as a decrease in breakdown voltage, is being clarified.

It is presumed that the cause of these microdefects is heavy metal contamination, which has a high diffusion rate.

It is currently unclear whether the heavy metals are due to contamination of the wafer surface during epitaxial growth pretreatment, or whether they come flying from the inner walls of the surrounding equipment during epitaxial growth.

As a gettering method for heavy metals, (1
) forming a mechanically strained layer. Proposals include (2) forming a strained layer by ion implantation, (3) forming a Si2N4 film and introducing misfit dislocations, and (4) forming a strained layer by laser. The effectiveness of the gettering effect of these backside treatments has been confirmed in MOS devices, but the process is more complex in bipolar devices, and the effectiveness gradually disappears as high-temperature processes are repeated. It is also said that

The present invention heat-treats a silicon single crystal substrate in two steps, one in a dry oxygen atmosphere and one in a wet oxygen atmosphere, to generate micro-defects consisting of precipitates and dislocations inside, and then use the resulting strain field to destroy the micro-defects or their nuclei. This is an attempt to reduce micro defects in the epitaxial film by the so-called intrinsic gettering (IG) effect.

For example, in the process of epitaxially growing a silicon single-crystal thin film on a silicon single-crystal substrate by a gas-phase reaction method, the substrate is pre-heated in a dry oxygen atmosphere for 60 minutes.
After heat treatment in the temperature range of 50°C to 1000°C, two types of heat treatment steps are successively performed in the temperature range of 11000°C to 1200'C in a wet oxygen atmosphere. Regarding the effectiveness of the IC effect in a method for manufacturing a semiconductor substrate, see, for example, G, A.

Rozgonyi et al: Appl, Phy
s, Lett, vol, 32°747-749 (
(1978), it has been reported that the lifetime of MOS devices has been improved. The inventors I
It was considered that the C effect is particularly effective in reducing micro defects in the epitaxial layer. A detailed explanation will be given below based on examples.

Example 1: The epitaxial substrate was heated in advance in a dry oxygen atmosphere at a temperature range of 6008C to 1200C.
After heat treatment for 6 to 64 hours to remove the oxide film, epitaxial growth was performed. In order to evaluate micro defects in the epitaxial film, the temperature was set at 1140℃12 in a wet oxygen atmosphere.
The film was heat treated for a period of time, etched for 30 seconds using a Zirtle etching solution, and observed using a Nomarski interference microscope. As a result, micro defects in epitaxial films grown epitaxially using substrates heat-treated in dry oxygen at a temperature range of 700'C to 1000'C were significantly reduced, and 5X103
The size of each piece was 1 cm2 or less.

Example 2: Substrates having various oxygen concentrations were heat-treated in the above dry oxygen atmosphere, and the occurrence of internal defects and the amount of interstitial oxygen were measured by etching and infrared spectroscopy. As a result, it was found that the reduction in interstitial oxygen significantly depends on the oxygen concentration of the starting wafer and the heat treatment temperature and time. The amount of decrease in interstitial oxygen is proportional to the amount of precipitated internal defects, and as a result of etching observation, such a correlation was clearly seen at temperatures below 1000°C. Measurement of the amount of decrease in interstitial oxygen As described above, the rate of decrease in interstitial oxygen is 1) larger as the heat treatment time is longer, 2) larger as the oxygen concentration of the starting wafer is higher under the same heat treatment conditions, and 3) at a specific temperature. It was found that the reduction rate was the highest, and so on.

Example 3: Next, as shown in Example 2 above, after removing the oxide film of the wafer that had been heat-treated in dry oxygen,
After heat treatment in wet oxygen at 1100° C. to 1200° C. for 2 hours, the reduction rate of interstitial oxygen and the state of precipitation of internal defects were measured. As a result, in the temperature range of 6506C to 1000C,
It was found that when a substrate heat-treated in dry oxygen was subsequently heat-treated in wet oxygen, the rate of decrease in interstitial oxygen was even more remarkable, and the increase in internal defects was also remarkable. When the samples listed in Table 1 are further heat-treated in wet oxygen at 1140°C for 12 hours, the result is that the samples are heat-treated in dry oxygen at an appropriate temperature range and then heat-treated in wet oxygen. It was found that the rate of decrease in interstitial oxygen concentration may increase by one order of magnitude or more compared to the first treatment.

Since the second treatment only takes a short time, by performing these two heat treatment steps in succession, it became possible to shorten the heat time as a whole. For example, to achieve a reduction rate of 40% or more, it takes 64 hours for sample E with the first treatment alone, whereas 18 hours is sufficient for sample A with the second and second treatments. . In other words, by adding the second process, the first process time can be significantly shortened.

Furthermore, by adding the second treatment to a wafer with a low oxygen concentration of about 710 m3 after 13 cuttings, a reduction rate of 17.1% could be achieved, and the IG effect was recognized.

Example 4: In order to confirm the effectiveness of successive first and second treatments, the interstitial oxygen concentration did not decrease even if heat treatment was performed only in wet oxygen in the second treatment without performing the first treatment. No visible defects were observed, and no internal defects occurred.

Example 5: Therefore, when epitaxial growth was performed using a wafer that had undergone the first and second heat treatment steps described above, a remarkable IG effect was observed, and with an appropriate combination of heat treatment conditions, the epitaxial layer The microdefect density inside was less than 5 x 103/cm2.

Claims (1)

[Claims] In the process of epitaxially growing a silicon single crystal thin film on a silicon single crystal substrate by vapor phase reactivity, the substrate is heat treated in a dry oxygen atmosphere at a temperature range of 650°C to 1000°C, and then heated in a wet oxygen atmosphere at a temperature of 1100°C to 1000°C.
A method for manufacturing a semiconductor substrate, comprising performing heat treatment in a temperature range of 1200° C. and then epitaxially growing the substrate.