JPH0350200A - Method for vanishing oxygen as thermal donor in epitaxial wafer - Google Patents

Abstract

PURPOSE:To easily vanish oxygen as a thermal donor in a wafer formed by epitaxial growth after pulling by Czochralski method by cooling the wafer under specified conditions. CONSTITUTION:When a single crystal formed by epitaxial growth after pulling by Czochralski method is cooled, cooling is carried out at >=2 deg.C/sec cooling rate in the temp. range of at least 650-300 deg.C. The O2 remaining in a wafer and acting as a donor is vanished and the shortening of the service life of the wafer and the slip of the wafer due to contamination by heavy metals are suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a method of #element-Maldner erasure in epitaxial wafers.

[Prior Art 1] FIG. 3 shows a wafer processing process for performing conventional epitaxial wafer growth. Oxygen acts as a donor in a wafer made by slicing a single crystal produced by the Czochralski method as a substrate, so it is necessary to eliminate this oxygen.

Conventionally, the oxygen thermal donor erasure heat treatment of the epitaxial wafer was performed after the substrate wafer etching step 3, as shown in FIG. However, in this case, since the wafer is subjected to two heat treatments: oxygen thermal donor erasure 8 and epitaxial growth 6, there are problems in that the wafer tends to slip and is easily contaminated by impurities such as heavy metals.

[Problem to be Solved by the Invention 1] The purpose of the present invention is to improve the above-mentioned drawbacks, and it is possible to omit the conventional oxygen thermal donor elimination heat treatment process, reduce slip, and achieve a long minority carrier life. A method for manufacturing a wafer is provided.

[Means for Solving the Problems] The present invention provides at least 650° C. after epitaxial growth.
This is a method for eliminating oxygen thermal donors in an epitaxial wafer, which is characterized in that oxygen thermal donor elimination is achieved by setting the cooling rate between 300° C. and 300° C. to 2° C./Sec or more.

[Effect 1] In the present invention, as shown in FIG. 2, which shows an example of a heat pattern for epitaxial growth, in the conventional cooling process, gradual cooling was performed as shown by the broken line.
By performing rapid cooling at a cooling rate of 2°C/sec or more -F during this time, it has become possible to omit the conventional oxygen thermal donor elimination. The reason for this will be explained with reference to FIG. Figure 4 shows data for a wafer in which the oxygen thermal donor erasing process of the substrate wafer was omitted and cooling was performed rapidly after epitaxial wafer growth.6 In Figure 4, ρ
0 is the substrate resistivity before epitaxial growth, and ρ is the substrate resistivity after epitaxial growth. The vertical axis in FIG. 4 indicates the ratio ρ/ρ0 between the two fronts. The horizontal axis shows the cooling rate. ρ/ρ0 is saturated at about 1.5, indicating that oxygen thermal donor elimination is complete. From this graph, the cooling rate is 2.
It can be seen that epitaxial oxygen thermal donor elimination is completed at 0° C./sec or lower.

Next, the reason why the cooling rate is limited to 2° C./sec or more is at least between 650° C. and 300° C. will be explained. FIG. 5 shows the change in ρ/ρ0 when the cooling start temperature is changed at a cooling rate of 2.0° C./sec. If the temperature is higher than 650'C, ρ/ρ0 is approximately 1.5. FIG. 6 shows the change in ρ/ρ0 when the end temperature of cooling of 2° C./sec or more was changed. p/ρ0 is saturated below 300°C. As a result of the above, the objective was achieved if the temperature was set to 2° C./see or higher between 650° C. and 300° C., so this limitation was made.

[Example] FIG. 1 shows a process diagram of an example of the present invention. Figures 1 and 3
It is clear from a comparison with the figures that the conventional substrate wafer oxygen thermal donor erase step 8 is omitted.

Figure 2 shows the heat pattern after epitaxial growth.The solid line is the heat pattern of the example in which cooling was performed rapidly, and the cooling curve shown in the broken line in the figure is the one in which conventional oxygen thermal donor elimination was performed. The cooling is the same as before. Table 1 shows the slip occurrence and minority carrier life of Examples of the present invention and Comparative Examples. In addition,
Even when the cooling start temperature of the present invention was set at 800°C, the results were the same as when the cooling start temperature was set at 650°C.

Minority carrier lifetime represents shortening of lifetime due to heavy metal contamination, and was determined by a photoconductive attenuation method using a laser beam with a wavelength of 904 nm as a light source and microwave reflection as a resistivity measurement method.

[Effect of the invention 1] By omitting the substrate wafer oxygen thermal donor erasing step during the epitaxial manufacturing process and changing the cooling rate, epitaxial wafer slip and heavy metal contamination were reduced.

[Brief explanation of drawings]

Fig. 1 is a process diagram of an example of the present invention, Fig. 2 is a heat pattern of an example and a comparative example, Fig. 3 is a process diagram of a conventional example, and Fig. 4 is a graph showing the relationship between cooling rate and resistance ratio. , Figure 5,
FIG. 6 is a graph showing the resistance ratio when the cooling start temperature and the cooling end temperature are changed, respectively. 1...Slicing 2...-Wrapping 3...
Etching 4...Polishing 5...Cleaning
6...Epitaxial growth 7...Rapid cooling 8...Oxygen thermal donor elimination

Claims (1)

[Claims] 1 From at least 650°C after epitaxial growth 3
A method for erasing oxygen thermal donors in an epitaxial wafer, characterized in that oxygen thermal donor erasure is achieved by setting a cooling rate between 00C and 2C/sec or more.