JP5614394B2 - Cleanliness evaluation method for vapor phase growth apparatus - Google Patents

Description

  The present invention relates to a method for evaluating the cleanliness of a vapor phase growth apparatus used for producing an epitaxial wafer.

  As a method for detecting metal impurities in a silicon wafer, there is a wafer lifetime (hereinafter sometimes referred to as WLT) method (see, for example, Non-Patent Document 1). As a typical method of this WLT method, microwave photoconductive decay is used. There is a legal minority carrier lifetime method (hereinafter referred to as a μPCD method). In this method, for example, light is applied to a sample (substrate), and the lifetime of the minority carriers generated is detected by a change in the reflectance of the microwave, thereby evaluating the metal impurities in the sample.

  When the metal is taken into the wafer, the WLT value becomes small. Therefore, the metal contamination in the heat treatment furnace can be managed by measuring and evaluating the WLT value of the heat-treated or vapor-grown wafer. Can do. In other words, by preparing a monitor wafer for cleanliness evaluation and performing heat treatment in a heat treatment furnace used in the actual process, and measuring the WLT value of the wafer after heat treatment, it is determined whether or not the heat treatment furnace is contaminated with metal impurities. Can be determined.

"Issues with Silicon Crystal / Wafer Technology" (Realize Inc., issued on January 31, 1994) pp. 265-269 “Chemistry of Silicon” (Realize, issued on June 28, 1996), pages 705-711

Since this method is simple but can detect even a small amount of contamination with high sensitivity, it is widely used for the management of a heat treatment furnace and the cleanliness evaluation of a vapor phase growth apparatus. In particular, in the case of a vapor phase growth apparatus, a wafer having a P ⁻ or N ⁻ conductivity type is prepared, an epitaxial layer is formed on the wafer using the vapor phase growth apparatus to be evaluated, and the epitaxial wafer is formed. By measuring by the above-mentioned μPCD method, the cleanliness of the vapor phase growth apparatus can be evaluated.

  On the other hand, it is known that the influence of the lifetime measured by the μPCD method varies depending on the conductivity type of the monitor wafer and the type of contaminating element (for example, Non-Patent Document 2). Specifically, when the impurity is Cu, the sensitivity to the amount of contamination is low when the conductivity type of the monitor wafer is P / P type. Further, when the impurity is Fe, the sensitivity of the P / P conductivity type monitor wafer is higher. As described above, since the detection sensitivity varies depending on the type of impurity and the conductivity type of the monitor wafer, in order to evaluate contamination with high sensitivity to various impurities, the conductivity type of the monitor wafer must be used properly. It was necessary to evaluate using a single monitor wafer.

  The present invention has been made in view of the above problems, and it is possible to accurately evaluate cleanliness with high sensitivity without the need to use different conductivity types of monitor wafers depending on the types of contaminating impurities in the vapor phase growth apparatus. An object of the present invention is to provide a method for evaluating the cleanliness of a phase growth apparatus.

The present invention has been made to solve the above problems, and is a method for evaluating the cleanliness of a vapor phase growth apparatus,
Using the vapor phase growth apparatus, a monitor wafer in which a P type epitaxial layer and an N type epitaxial layer are continuously grown in random order on a silicon wafer is manufactured, and the lifetime value of the monitor wafer Measure and
A cleanliness evaluation method for a vapor phase growth apparatus is provided, wherein the cleanliness of the vapor phase growth apparatus is evaluated from a lifetime value of the monitor wafer.

  With such a method for evaluating the cleanliness of a vapor phase growth apparatus, it is possible to accurately evaluate the cleanliness with high sensitivity without having to use a different conductivity type of the monitor wafer depending on the type of contaminating impurities in the vapor phase growth apparatus. . Moreover, since the cleanliness can be accurately evaluated with high sensitivity with a single monitor wafer, the evaluation cost can be reduced.

  The lifetime value of the monitor wafer is preferably measured by the μPCD method.

  By using the μPCD method in this way, the lifetime value can be easily measured with high accuracy.

  Furthermore, in the evaluation of the cleanliness of the vapor phase growth apparatus, the contamination degree of Cu and the contamination degree of Fe can be simultaneously evaluated.

  Thus, without using different conductivity types of monitor wafers, the contamination of an element that hardly lowers the lifetime value in a P-type epitaxial layer such as Cu with one wafer and the lifetime value in an N-type epitaxial layer such as Fe. It is possible to simultaneously evaluate the contamination of elements that are difficult to lower.

  The present invention also provides a method of manufacturing an epitaxial wafer using the vapor phase growth apparatus evaluated by the above-described method for evaluating the cleanliness of the vapor phase growth apparatus.

  If an epitaxial wafer is manufactured by a vapor phase growth apparatus that has been evaluated to be free of contamination by the cleanliness evaluation method of the present invention, various high-quality epitaxial wafers with little contamination can be manufactured with a high yield.

  As described above, according to the method for evaluating the cleanliness of the vapor phase growth apparatus of the present invention, it is not necessary to use the conductivity type of the monitor wafer depending on the type of contaminating impurities in the vapor phase growth apparatus, and the cleanliness is accurately and accurately. Can be evaluated. Moreover, since the cleanliness can be accurately evaluated with high sensitivity with a single monitor wafer, the evaluation cost can be reduced. Furthermore, if an epitaxial wafer is manufactured with a vapor phase growth apparatus that has been evaluated to be free of contamination by the cleanliness evaluation method of the present invention, it is possible to manufacture various high-quality epitaxial wafers with low contamination at a high yield. .

It is a flowchart of the cleanliness evaluation method of the vapor phase growth apparatus of this invention. It is sectional drawing of the monitor wafer which has two epitaxial layers whose conductivity type is P type and N type. Each of the monitor wafers in the case where the monitor wafers of Examples and Comparative Examples 1 and 2 were manufactured using a vapor phase growth apparatus previously contaminated with Cu, a vapor phase growth apparatus previously contaminated with Fe, and a vapor phase growth apparatus not contaminated. It is a graph which shows a wafer lifetime value.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto. As described above, there has been a demand for a method for evaluating the cleanliness of a vapor phase growth apparatus that can accurately evaluate cleanliness with high sensitivity by using a single monitor wafer without the need to use different conductivity types for monitor wafers.

  As a result of intensive studies on the above problems, the present inventors pay attention to the fact that there are pollutant element species that are easy to detect depending on the conductivity type of the monitor wafer, and the monitor wafer has two conductivity types, that is, P type and N type. It was found that if both epitaxial layers were provided, impurities easily detected by the P-type and N-type conductivity types could be detected simultaneously with high sensitivity, and the present invention was completed. Hereinafter, the present invention will be described in more detail.

  FIG. 1 shows a flowchart of the cleanliness evaluation method for the vapor phase growth apparatus of the present invention. First, in the cleanliness evaluation method of the present invention, a monitor in which a P type epitaxial layer and an N type epitaxial layer are continuously grown in random order on a silicon wafer using a vapor phase growth apparatus to be evaluated. A wafer is manufactured (FIG. 1A). At this time, the P-type and N-type epitaxial layers are grown to form a two-layer epitaxial layer, but the growth order of the P-type and N-type epitaxial layers is not particularly limited. Accordingly, the N type may be formed after the P type is formed, or the P type may be formed after the N type is formed. The silicon wafer to be used may be either a P type or an N type.

  Next, the lifetime value of the monitor wafer is measured (FIG. 1B). The measurement of the lifetime value is not particularly limited, but is preferably performed by the μPCD method that allows easy measurement.

  Finally, the cleanliness of the vapor phase growth apparatus is evaluated from the lifetime value of the monitor wafer (FIG. 1C). When impurities, particularly metal, are taken into the epitaxial layer of the monitor wafer, the lifetime value becomes small. Therefore, if a monitor wafer is manufactured using the vapor phase growth apparatus to be evaluated and the monitor wafer is contaminated and the lifetime value is small, it is evaluated that the cleanness of the vapor phase growth apparatus is low. it can. Conversely, if the lifetime value decrease is small, it can be evaluated that the contamination of the monitor wafer derived from the vapor phase growth apparatus is small, and the cleanliness of the vapor phase growth apparatus can be evaluated to be high.

As shown in FIG. 2, the monitor wafer 4 used in the present invention has a structure in which P-type and N-type epitaxial layers are stacked in layers on a silicon wafer 3 as a first epitaxial layer 1 and a second epitaxial layer 2. In this case, the wafer lifetime value is approximately represented by the reciprocal combination of the lifetime values of each layer.
1 / Tw = 1 / T1 + 1 / T2
Tw: Wafer lifetime value of the monitor wafer 4 T1: Lifetime value of the first epitaxial layer 1 T2: Lifetime value of the second epitaxial layer 1

  For this reason, when several epitaxial layers are piled up like FIG. 2, the epitaxial layer with the lowest lifetime value becomes dominant with respect to a wafer lifetime value. This makes it possible to accurately evaluate the cleanliness with high sensitivity without having to use the conductivity type of the monitor wafer depending on the type of contaminating impurities in the vapor phase growth apparatus.

  For example, in the present invention, even when there is contamination of an element that is difficult to lower the lifetime value in the P-type epitaxial layer, such as Cu, the lifetime value decreases in the N-type epitaxial layer, so the total wafer lifetime value is It is lowered by the lifetime value of the N-type epitaxial layer, and contamination can be detected with high sensitivity. On the other hand, in the case of Fe contamination, the lifetime value is hardly lowered in the N-type epitaxial layer, but the lifetime value is greatly lowered in the P-type epitaxial layer. In this case as well, the contamination can be detected with high sensitivity. In this way, it is possible to simultaneously evaluate the contamination degree of an element whose lifetime value is difficult to be lowered in a P-type epitaxial layer such as Cu and the contamination degree of an element such as Fe which is difficult to reduce a lifetime value in an N-type epitaxial layer. it can.

  Furthermore, it is preferable to manufacture an epitaxial wafer using the vapor phase growth apparatus evaluated by the method for evaluating the cleanliness of the vapor phase growth apparatus of the present invention. By using a monitor wafer in which two layers of a P-type epitaxial layer and an N-type epitaxial layer are deposited in this way, the contamination of impurity species that has been overlooked in the conventional monitor wafer of a single P-type or N-type epitaxial layer is overlooked. Impurities can be detected with high sensitivity. Therefore, if an epitaxial wafer is manufactured by a vapor phase growth apparatus that has been evaluated for contamination by the cleanliness evaluation method of the present invention, a high-quality epitaxial wafer with little contamination can be manufactured with a high yield.

  EXAMPLES Hereinafter, although the Example and comparative example of this invention are given and demonstrated further in detail, this invention is not limited to the following Example.

〔Example〕
A P-type silicon wafer having a diameter of 200 mm and a substrate resistivity of 10 Ωcm was prepared. Next, a vapor phase growth apparatus previously contaminated with Cu, a vapor phase growth apparatus previously contaminated with Fe, and an uncontaminated vapor phase growth apparatus were prepared. Using these vapor phase growth apparatuses, monitor wafers were prepared in which a 10 Ωcm P-type epitaxial layer was deposited on this silicon wafer by 10 μm and a 10 Ωcm N-type epitaxial layer was further deposited by 10 μm.

  Each monitor wafer thus produced was subjected to a surface treatment by chemical passivation, and a wafer lifetime value was measured using a μPCD wafer lifetime measuring device. FIG. 3 shows an in-plane average value of the wafer lifetime value of each monitor wafer of the example. As is apparent from FIG. 3, the wafer lifetime value of the monitor wafer manufactured with the vapor phase growth apparatus previously contaminated with Cu and Fe is the wafer lifetime value of the monitor wafer manufactured with the vapor phase growth apparatus without contamination. The presence or absence of contamination of Cu and Fe could be detected with high sensitivity.

[Comparative Example 1]
Next, a P-type silicon wafer having a diameter of 200 mm and a substrate resistivity of 10 Ωcm was prepared. As in the example, a 10 Ωcm P-type epitaxial layer was formed on this P-type silicon wafer by using a vapor phase growth apparatus previously contaminated with Cu, a vapor phase growth apparatus previously contaminated with Fe, and an uncontaminated vapor phase growth apparatus. A monitor wafer was prepared by depositing 10 μm of layers.

  Each monitor wafer thus produced was subjected to a surface treatment by chemical passivation, and a wafer lifetime value was measured using a μPCD wafer lifetime measuring device. FIG. 3 shows in-plane average values of the wafer lifetime values of the monitor wafers in Comparative Example 1.

  In the case of the P / P monitor wafer of Comparative Example 1 in which the P-type epitaxial layer was deposited on the P-type silicon wafer, the wafer lifetime value of the monitor wafer produced by the Fe-contaminated vapor phase growth apparatus was the vapor phase without contamination. Although the value is greatly lower than that of the growth apparatus, the value is almost the same as that of the vapor growth apparatus that was not contaminated when manufactured by the vapor growth apparatus contaminated with Cu.

[Comparative Example 2]
An N-type silicon wafer having a diameter of 200 mm and a substrate resistivity of 10 Ωcm was prepared. As in the embodiment, an N-type epitaxial layer of 10 Ωcm is formed on this N-type silicon wafer using a vapor phase growth apparatus previously contaminated with Cu, a vapor phase growth apparatus previously contaminated with Fe, and an uncontaminated vapor phase growth apparatus. A monitor wafer was prepared by depositing 10 μm of layers.

  Each monitor wafer thus produced was subjected to a surface treatment by chemical passivation, and a wafer lifetime value was measured using a μPCD wafer lifetime measuring device. FIG. 3 shows an in-plane average value of the wafer lifetime value of each monitor wafer in Comparative Example 2.

  In the case of the N / N monitor wafer of Comparative Example 2 in which the N-type epitaxial layer is deposited on the N-type silicon wafer, the wafer lifetime value of the monitor wafer produced by the vapor-phase growth apparatus contaminated with Cu is the vapor phase in which there is no contamination. Although the value is significantly lower than that of the growth apparatus, the value is almost the same as that of the vapor growth apparatus that was not contaminated when manufactured with a vapor-contaminated vapor growth apparatus.

  As described above, in the case of an N / N monitor wafer or a P / P monitor wafer as in Comparative Examples 1 and 2, contamination of either Cu or Fe can be detected, but the detection capability of the other impurity is low. It was confirmed that there was a problem in the cleanliness evaluation of the phase growth apparatus. Compared to this, in the case of an N / P / P monitor wafer as in the embodiment, both Cu and Fe can be detected with high sensitivity, and it is necessary to use the conductivity type of the monitor wafer depending on the type of contaminating impurities in the vapor phase growth apparatus. It was shown that the cleanliness can be accurately evaluated with high sensitivity. In addition, in the example, it was also shown that the evaluation cost can be reduced because both Cu and Fe can be detected with high sensitivity by one monitor wafer.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

DESCRIPTION OF SYMBOLS 1 ... 1st epitaxial layer, 2 ... 2nd epitaxial layer, 3 ... Silicon wafer, 4 ... Monitor wafer

Claims (3)

A method for evaluating the cleanliness of a vapor phase growth apparatus,
Using the vapor phase growth apparatus, a monitor wafer in which a P type epitaxial layer and an N type epitaxial layer are continuously grown in random order on a silicon wafer is manufactured, and the lifetime value of the monitor wafer Measure and
Evaluating the cleanliness of the vapor phase growth apparatus from the lifetime value of the monitor wafer ,
In the evaluation of the cleanliness of the vapor phase growth apparatus, the cleanliness evaluation method of the vapor phase growth apparatus, wherein the contamination level of Cu and the contamination level of Fe are simultaneously evaluated .   2. The method for evaluating the cleanliness of a vapor phase growth apparatus according to claim 1, wherein the lifetime value of the monitor wafer is measured by a μPCD method. An epitaxial wafer manufacturing method comprising manufacturing an epitaxial wafer using the vapor phase growth apparatus evaluated by the method for evaluating the cleanliness of the vapor phase growth apparatus according to claim 1 .

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