JPH05129411A - Compound semiconductor wafer for detecting metal element contamination and method of detecting metal element contamination - Google Patents

Abstract

PURPOSE:To detect a very small amount of heavy metal contamination by a very simple method, facilitate management and maintenance, and shorten working hour per specimen. CONSTITUTION:High purity GaAs wafer wherein heavy metal concentration is lower than or equal to 1015cm<-3>, carbon concentration is 1015cm<-3>, and three- step heat treatment has been performed is used as a wafer for detecting heavy metal contamination. When the wafer is dipped in chemical liquid containing heavy metal and dried, the heavy metal adheres to the GaAs wafer surface and remains. When the surface is heated at 700-850 deg.C, the heavy metal diffuses in GaAs, and forms impurity level in a band gap. The GaAs wafer is irradiated with laser light having energy larger than the band gap of GaAs, and photoluminescence is measured. Light emission corresponding with the heavy metal which emission is caused by recombination of excitated carrier and impurity level can be observed. By comparing the luminous intensity of the heavy metal with the band end luminous intensity corresponding with the band gap energy of GaAs, relative concentration can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal capable of easily detecting a metal element contained in a wafer manufacturing environment or a processing environment which is a source of metal element contamination of III-V group compound semiconductor wafers such as GaAs wafers. For elemental contamination detection III
-Group V compound semiconductor wafer and metal element contamination detection method.

[0002]

2. Description of the Related Art GaAs plays an important role in industry.
Group III-V compound semiconductor devices, including compound semiconductors, are manufactured through crystal manufacturing, wafer manufacturing processes such as grinding / polishing and etching, and wafer processing processes such as thin film formation and etching. In order to protect it, it is made under a very nervous clean management in its production. Fine pollution control is carried out on the dust in the atmosphere and metallic elements such as floating heavy metals, the chemical liquid used, the purity of the container in which it is contained, the purity of pure water, and the like. The most important point among them is pollution control in wet processes that use chemicals.

This will be examined for GaAs manufacturing. GaA
In a wide range of fields including not only the compound semiconductor device manufacturing stage but also the GaAs single crystal wafer manufacturing stage and processing that precedes it, cleaning and etching by a wet method using water, solvent, acid, alkali, etc. A so-called wet process is performed. Once the contamination of heavy metal elements affecting the semiconductor characteristics occurs in this process, it is extremely difficult to determine the source. This is because the whole process is complicated and diversified, and various kinds of chemicals and containers are used, and a problematic amount of contamination is so small that a highly accurate analysis is required.

Conventionally, a chemical solution is extracted for each process that may be contaminated and analyzed by an analyzer to search for a source and a range in which contamination is spread. As the analysis method, atomic absorption spectrometry, secondary ion mass spectrometry (SIMS), etc. are used exclusively.

[0005]

However, the conventional analytical methods used in the atomic absorption spectrometry are a flame generator for atomizing the constituent elements, a discharge tube serving as a light source,
Furthermore, it requires an absorbance measuring device, and SIMS requires a high-energy primary ion generator and a mass spectrometer.
Since large-scale and expensive equipment is used, it is not suitable for equipment for the purpose of checking each process of semiconductors. Moreover, the amount of contamination is often extremely small, and a large amount of cost is required for maintenance such as cleaning of the container used for analysis, control of the degree of vacuum of the device, and control of the mass spectrometer. Another problem is that the working time per sample is long.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art by using a III-V group compound semiconductor wafer which is not contaminated with metallic elements for detection, and to simply and inexpensively contaminate metallic elements. It is an object of the present invention to provide a III-V group compound semiconductor wafer for detecting metal element contamination and a method for detecting metal element contamination capable of detecting a metal element.

[0007]

A metal element contamination detection wafer of the present invention is a III-V group compound semiconductor wafer,
A metal element contamination detection wafer capable of detecting metal element contamination in a processing environment, which is of high purity and has been heat-treated to make the photoluminescence intensity uniform in the wafer surface. is there. In order to make the strength in the plane of the wafer particularly uniform, this heat treatment is preferably configured by a three-step heat treatment in a crystal ingot state or a wafer state. That is, after heating at 1000 ° C or higher,
Cool within a temperature range of 500-700 ° C, then 800
Reheat treatment is performed within a temperature range of up to 950 ° C.
In order to further improve the detection accuracy, it is desirable that the wafer to be detected has a metal element concentration of 10 ¹⁵ cm ^-3 or less and a carbon concentration of 10 ¹⁵ cm ^-3 or less. Here, the applicable III-V compound semiconductor is GaA.
In addition to s, there are InP, InAs, GaP, and the like, and a heavy metal is a typical example of the metal element to be the contamination detection target.

The metal element contamination detection method of the present invention is
A method for detecting a metal element contamination using a III-V compound semiconductor wafer for detecting a metal element contamination as described above, which comprises exposing a wafer to an environment for detecting metal element contamination to contaminate it with a metal element, and then taking out the environment. Diffusion heat treatment for diffusing the metal element into the wafer is performed, and then this wafer is subjected to photoluminescence analysis to show the peak of the band edge emission intensity corresponding to the band gap energy of the III-V group compound semiconductor. Then, the peak of the emission intensity of the metal element that appears corresponding to the metal element contained in the wafer is obtained, and the emission amount of both peaks is compared to obtain the amount of contamination of the metal element in the environment. In this case, the diffusion heat treatment is preferably performed in the range of 700 to 850 ° C. in order to ensure the fixing of the wafer to the metal element.

The environment in the present invention means a chemical solution such as an etching solution or a cleaning solution used in a wet process or a container, and an atmosphere in a dry process.

[0010]

In this case, the III-V compound semiconductor wafer of the present invention is GaAs, the contaminating metal element is a heavy metal,
The case where the environment is a chemical solution in the wet process will be described, but the same applies to other compound semiconductors, metal elements, and the environment. When a high-purity GaAs wafer is dipped in a chemical containing a heavy metal and dried, the heavy metal adheres to the surface of the GaAs wafer and remains. When this is subjected to an appropriate heat treatment, for example, at 700 to 850 ° C. for several tens of minutes, the heavy metal diffuses in GaAs and an impurity level is created in the band gap. Outside of this temperature range, phenomena other than the intended diffusion may occur, which is not preferable.

This GaAs wafer is irradiated with laser light having an energy larger than the band gap of GaAs, for example, light of 514.5 μm of Ar gas laser, and photoluminescence is measured. As a result, heavy metal is formed due to recombination of excited carriers and impurity levels. Corresponding luminescence is observed. By comparing this heavy metal emission intensity with the emission intensity of the band edge (hereinafter simply referred to as the band edge) that appears corresponding to the band gap energy of GaAs, the relative concentration can be obtained, and it can be compared with other analytical methods. The absolute value of the concentration can be obtained by comparing The photoluminescence method is a common apparatus most widely used for the analysis of physical properties of semiconductors, is easy to maintain, and allows simple measurement.

Next, a GaAs wafer for heavy metal contamination detection, which is necessary for the metal element contamination detection method of the present invention, will be described. The heavy metal concentration was set to 10 ¹⁵ cm ^-3 or less because
^This is because if it is larger than ¹⁵ cm ⁻³ , a measurement error will occur in the measurement of the concentration range of the amount of contamination equal to or higher than that.
Further, the carbon concentration is specified in particular as shown in FIG.
In addition to the band-edge emission peak appearing at 1.53 eV, a sharp emission peak for a shallow acceptor, which is said to involve carbon impurities that cannot be avoided during crystal growth, appears at 1.49 eV. For this reason, the light emission at the band edge largely depends on the carbon concentration.
This is because when it exceeds 0 ¹⁵ cm ⁻³ , the peak of the heavy metal element overlaps with the band edge emission peak and the two cannot be separated, and the peak intensity ratio cannot be obtained as a crystal.

There are many crystal defects in GaAs, and their non-uniform distribution and concentration affect the above measurement. In order to improve uniformity and enable accurate measurement, it is desirable to subject the crystal ingot before processing the wafer or the processed wafer to the following heat treatment. That is, it is heated at a temperature of 1000 ° C. or higher to 500 to 700.
It is cooled and held in the range of 800C, and then held in the range of 800 to 950C for a certain period of time. Such a three-step heat treatment
When applied to aAs crystals, the intrinsic defects in GaAs cannot be essentially eliminated, but since the photoluminescence intensity in the wafer surface is very uniform, it is possible to measure photoluminescence by the level within the band formed by crystal defects. The effect of can be suppressed. It should be noted that the strength can be made uniform by the three-step heat treatment because in the first-step or second-step heat treatment, the non-radiative centers having the levels near the center of the band gap, which are unevenly distributed in the wafer surface, are sufficiently eliminated. It seems that it is because it has not disappeared enough until the third stage. Therefore, it is possible to add heat treatment in four or more steps.

Thus, according to the present invention, high-purity GaA
s is exposed to the environment where heavy metal contamination is to be detected, and after heating it, the photoluminescence method, which is a highly versatile device, is used to detect heavy metal contamination. It is not necessary to use equipment, and it is therefore possible to devise the invention for the purpose of each semiconductor process check. In addition, even if the amount of contamination is extremely small, it is only necessary to prepare a high-purity GaAs wafer and a photoluminescence device. Therefore, cleaning the container used for contamination amount analysis, controlling the vacuum degree of the device, managing the mass spectrometer. It eliminates the need for maintenance and saves a great deal of cost. Also, the working time per sample is shortened.

Therefore, according to the present invention, in a GaAs compound semiconductor manufacturing process, which is often used for industrially important functional devices, process contamination due to heavy metal elements, which is a particularly serious problem, can be easily detected, so that the product yield is increased. It can be improved and the economic effect is great. Also, G
It can also be applied to detection of contamination by metal elements such as heavy metals on III-V group compound semiconductors other than aAs.

[0016]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

Example 1 From an undoped GaAs single crystal ingot grown by the pulling method (the boat method may be used), a GaAs wafer is cut into a rectangular shape having a thickness of 350 μm, 10 mm × 50 mm, and both surfaces are lapped, and then a sulfuric acid system The GaAs wafer for contamination detection was used after being etched with the etching solution of 1. and thoroughly washed with an organic solvent and pure water. Impurities analyzed by SIMS were all below the detection limit, 10 ¹⁵ cm ^-3
No more than. The carbon concentration determined by infrared absorption is of the order of 10 ¹⁴ cm ^-3 and 8 × 1
It was 0 ¹⁴ cm ^-3 . This GaAs wafer, in the state of a crystal ingot, was cut at 1150 ° C. for 24 hours for 50 hours before being cut out.
Three-step annealing at 0 ° C.-48 h and 850 ° C.-24 h was continuously performed.

In order to simulate the heavy metal element contamination of the wet process in the process step, an aqueous solution of copper sulfate having a varying copper concentration is prepared, the GaAs wafer is immersed in the solution for 5 minutes, and the wafer is taken out. The liquid was cut and naturally dried. After that, the wafer is placed in hydrogen gas at 750 ° C.
Heat treatment was performed for 30 minutes to diffuse copper in the wafer. Then, the photoluminescence measurement was performed while the wafer was cooled to about 77 K with liquid nitrogen so that the peak due to the impurities clearly appeared.

First, the uniformity of light emission at the band edge of 1.53 eV was measured at 9 points at a pitch of 5 mm in the lengthwise direction of the wafer. The variation in peak intensity within the plane was as small as 5% or less, and heavy metal contamination was detected. It was confirmed to be suitable for a wafer for use. Next, as light emission based on copper, which is a heavy metal element,
When the emission peak of 1.36 eV was observed, it was possible to separate from the peak of 1.53 eV without performing a treatment that is particularly difficult in measurement, and the peak intensity ratio of both was easily obtained. From the above results, the relationship as shown in FIG. 1 was obtained, and it was found that a very small amount of contamination to a high concentration of contamination can be detected by the method of this example and the wafer of this example. ..

Comparative Example 1 In the same manner as in Example 1, an experiment was conducted on a GaAs wafer in which the crystal ingot was not subjected to any heat treatment. As a result, the in-plane variation of the emission peak was large, and the two peaks overlap greatly, resulting in peak separation. Therefore, it was found that it was not suitable for detecting heavy metal contamination.

Comparative Example 2 Ingots were heat treated at 950 ° C. in the same manner as in Example 1.
When it was carried out in one step for -24 h, it was found that it could not be used for detection of heavy metal contamination in terms of in-plane variation and peak separation as in Comparative Example 1.

Comparative Example 3 In the same manner as in Example 1, a GaAs crystal having a high carbon concentration of 2 × 10 ¹⁵ cm ⁻³ was used. As a result, the peak of the band edge emission became strong and the peak separation from the heavy metal element could not be performed.

Comparative Example 4 In the same manner as in Example 1, a crystal for which 2 × 10 ¹⁵ cm ^{−3 of} copper was added from the beginning was used as a contamination detection wafer. The aqueous solution simulating heavy metal contamination was unusable because the difference in peak intensity between the one in which copper sulfate was not added and the one in which it was added was hidden by a measurement error.

Example 2 A GaAs wafer was prepared in the same manner as in Example 1, and an aqueous solution of manganese dissolved in nitric acid was used as the aqueous solution for simulating contamination, and the concentration of manganese, which is a heavy metal, was changed. , Contaminated the wafer. The treatments after the immersion method are the same as in Example 1. Photoluminescence is 1.
A peak due to 41 eV of manganese was observed. It was confirmed that there is no overlap or in-plane variation phenomenon as seen in the above-mentioned comparative example, and it is suitable for contamination detection in the wet process as in Example 1.

The results of Example 1, Comparative Examples 1 to 4 and Example 2 described above are summarized in Table 1.

[0026]

[Table 1]

The condition of * is as described above in the text.

◯ in the table is in a range suitable for the method,
X indicates unsuitability. Further, in Example 1 and Comparative Examples 1 to 4, the peak of photoluminescence caused by copper is observed, and in Example 2, the peak of photoluminescence caused by manganese is observed.

Other Embodiments The above-mentioned embodiment in which Cu and Mn are applied to the heavy metal impurities is F
When applied to other heavy metal impurities such as e, Mg, Zn and S, good results were obtained in all cases. Regarding the heat treatment applied to the ingot or the wafer in order to make the photoluminescence intensity uniform, a temperature of less than 1000 ° C., 50
Although the effects were compared by a combination of three processes of a temperature lower than 0 ° C. or higher than 700 ° C., a temperature lower than 800 ° C. or higher than 950 ° C., a wafer usable for detecting heavy metal contamination was obtained. 1000 ° C or higher, 80
Only combinations of temperature ranges of 0 to 950 ° C and 500 to 700 ° C were available.

[0030]

According to the present invention, the following effects can be obtained.

(1) GaA for detecting metallic element contamination of the present invention
According to the s-wafer, the III-V compound semiconductor wafer itself, which constitutes the III-V compound semiconductor device, is used for detecting the metal element contamination, so that the resources can be effectively used.

(2) According to the metal element contamination detection method of the present invention, metal element contamination can be detected very simply and inexpensively.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the peak intensity ratio of photoluminescence and the copper concentration in a copper sulfate aqueous solution according to this example.

FIG. 2 is an explanatory view showing a photoluminescence spectrum of undoped GaAs crystal.

Claims (5)

[Claims] 1. A III-V compound semiconductor wafer, a metal element contamination detection wafer capable of detecting metal element contamination in a processing environment, wherein the wafer has a high purity and is within a plane of the wafer. For metal element contamination detection, characterized by being heat-treated to make photoluminescence intensity uniform-
Group V compound semiconductor wafer. 2. The heat treatment is performed in a crystalline ingot state or a wafer state at a temperature of 1000.degree.
Cool in a temperature range of 0 to 700 ° C., then 800 to 9
The metal element contamination detection device according to claim 1, characterized in that it is reheated within a temperature range of 50 ° C.
III-V compound semiconductor wafer. 3. A metal element concentration of a wafer to be detected is 1
0 ¹⁵ cm ^-3 or less and a carbon concentration of 10 ¹⁵ cm ^-3
The III-V group compound semiconductor wafer for metal element contamination detection according to claim 1 or 2, wherein: 4. A metal element contamination detection method using the III-V compound semiconductor wafer for metal element contamination detection according to claim 1, wherein the wafer is used in an environment for detecting metal element contamination. Exposed to contaminate with metallic elements,
Diffusion heat treatment for diffusing the metal element into the wafer taken out from the environment is performed, and thereafter, this wafer is subjected to band edge emission corresponding to the band gap energy of the III-V group compound semiconductor by photoluminescence analysis method. Contamination of metallic elements characterized by determining the peak of intensity and the peak of luminous intensity of metallic elements appearing corresponding to metallic elements, and comparing the luminous intensity of both peaks to find the amount of metallic element contamination in the environment. Detection method. 5. The metal element contamination detection method according to claim 4, wherein the diffusion heating treatment is performed in a range of 700 to 850 ° C.