Method of manufacturing epitaxial wafer, epitaxial wafer and cz silicon wafer for epitaxial growth

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a method for manufacturing an epitaxial wafer, an epitaxial wafer, and a CZ silicon wafer for epitaxial growth, which have excellent IG capability.

【0002】

[Conventional technology]

Epitaxy produced by epitaxially (hereinafter, simply referred to as epi) growth on a CZ silicon wafer for epitaxial growth (hereinafter, may be simply referred to as a substrate) manufactured by the Czochralski (CZ) method. Wafers (hereinafter, may be simply referred to as epiwafers) are widely used for manufacturing highly integrated devices because of the good crystallinity of the epitaxial layer.

【0003】

However, such an epitaxial wafer is usually manufactured by subjecting it to a high temperature process of 1000 ° C. or higher when performing epitaxial growth. Therefore, the core of oxygen precipitation dissolves during the high temperature process, oxygen does not precipitate in the bulk in the subsequent device process, and a sufficient amount of BMD (Bulk Micro Defect) cannot be obtained. Therefore, there was a problem that the IG (internal gettering) ability was insufficient.

【0004】

Therefore, the following measures are taken to solve the above problems. First, oxygen is precipitated by increasing the oxygen concentration of the CZ silicon wafer used as the substrate. Second, it prevents insufficient precipitation by lowering the temperature of the epitaxial growth process and suppressing the dissolution of precipitated nuclei. Third, by heat-treating before or after the epi, the former grows the precipitated nuclei to a stable size at high temperature, and the latter secures oxygen precipitation by creating new precipitated nuclei.

【0005】

However, these measures have the following problems. When the first oxygen concentration is increased, that is, when high oxygen crystals are grown, the deterioration rate of the crucible is accelerated in the Czochralski method, so that the durability of the crucible is lowered and the crystals are easily dislocated. It was. The second epitaxial wafer grown at a low temperature of less than 1000 ° C is certainly more prone to precipitation in the subsequent device process than the high temperature growth, but its density is still insufficient for a gettering site. The heat treatment before and after the third epi requires a long time (4 hours or more) of heat treatment at a low temperature (600 to 1000 oC), which increases the cost.

【0006】

In addition to the above measures, an attempt was also made to improve the IG ability by adding a dopant that promotes oxygen precipitation into the silicon single crystal. Nitrogen and carbon are well known as impurities that affect such oxygen precipitation characteristics. Among them, nitrogen-doped CZ silicon wafers form stable oxygen precipitate nuclei at high temperatures, so even if epitaxial growth is performed at a high temperature of 1000 ° C or higher, the oxygen precipitate nuclei do not disappear, and in the subsequent device process. There is an advantage that sufficient oxygen precipitates can be secured. However, when an extremely high oxygen precipitate density is required, it is necessary to dope nitrogen at a high concentration. Therefore, when epitaxial growth is performed on a wafer doped with nitrogen at such a high concentration, crystals are formed on the epitaxial layer. Defects may occur.

【0007】

On the other hand, carbon-doped CZ silicon wafers have also been known to have a function of promoting oxygen precipitation. For example, Japanese Patent Application Laid-Open No. 10-229093 and Japanese Patent Application Laid-Open No. 11-204534 describe inventions for improving IG ability by doping a silicon single crystal with carbon. However, when epitaxial growth is performed using a carbon-doped silicon wafer as a substrate, the function of promoting oxygen precipitation is inferior to that when epitaxial growth is performed using a nitrogen-doped silicon wafer as a substrate, and sufficient IG capability is obtained. There was a drawback that it could not be done.

【0008】

[Problems to be Solved by the Invention]

The present invention has been made to solve the above problems, and an epitaxial wafer having excellent crystallinity and high IG capability can be manufactured by a simple method without adding a special process to increase the cost. The purpose is.

【0009】

[Means for solving problems]

The present invention for solving the above problems is a method for producing an epitaxial wafer, which comprises performing epitaxial growth on a carbon-doped CZ silicon wafer at a temperature of less than 1000 ° C (claim 1). In this way, by performing low-temperature epitaxial growth at less than 1000 ° C on a carbon-doped CZ silicon wafer, more oxygen precipitation can be obtained as compared with the case where epitaxial growth is performed on a conventional carbon-doped silicon wafer. Better IG capability can be obtained.

【0010】

In this case, it is preferable that the carbon concentration of the CZ silicon wafer is 1.0 ppma or more (claim 2). In this way, if the carbon concentration of the CZ silicon wafer used as the substrate is 1.0 ppma or more, the effect of reliably promoting oxygen precipitation can be obtained even with a wafer having a relatively low oxygen concentration, and the IG capability can be improved. This is because it can be improved. The carbon concentration is preferably 5 ppma or less because it may interfere with single crystal formation when the CZ single crystal is pulled up.

【0011】

In this case, it is preferable to heat-treat the CZ silicon wafer before epitaxial growth at a temperature of 600 to 1000 ° C. for at least 1 hour (claim 3). As described above, by performing the low temperature heat treatment at 600 to 1000 ° C. before the epitaxial growth, the oxygen-precipitated nuclei can be grown to a stable size, and more BMD can be obtained. Further, in the present invention, since carbon is doped in the CZ silicon wafer that performs epitaxial growth, a long-time heat treatment is not required as in the conventional pre-epitaxial growth heat treatment.

【0012】

In this case, it is preferable to heat-treat the epitaxial wafer after the epitaxial growth at a temperature of 600 to 1000 ° C. for at least 1 hour (claim 4). As described above, new precipitated nuclei can be produced and the BMD density can be increased by low-temperature heat treatment at 600 to 1000 ° C after epitaxial growth. In this case as well, since the epitaxial wafer is doped with carbon in the present invention, a long-time heat treatment is not required as in the conventional heat treatment after epitaxial growth.

【0013】

The epitaxial wafer (claim 5) manufactured by such a manufacturing method of the present invention includes, for example, a substrate which is a carbon-doped CZ silicon wafer and an epitaxial layer grown at a temperature of less than 1000 ° C. It is an epitaxial wafer characterized in that it is composed of (claim 6). As described above, the epitaxial wafer in which the epitaxial layer was grown at a temperature of less than 1000 ° C on the substrate which is the carbon-doped CZ silicon wafer of the present invention has high IG capability and is doped with nitrogen. Unlike the epitaxial wafer using a substrate, the epitaxial layer does not have crystal defects, and the epitaxial wafer is of extremely high quality.

【0014】

The present invention is a CZ silicon wafer for epitaxial growth for performing epitaxial growth at a temperature of less than 1000 ° C. The CZ silicon wafer is a CZ silicon wafer for epitaxial growth characterized in that it is doped with carbon. Yes (claim 7). If the carbon-doped CZ silicon wafer is used as a CZ silicon wafer for epitaxial growth for epitaxial growth at a temperature of less than 1000 ° C., an epitaxial wafer having a much larger IG capability than the conventional one can be obtained. Obtainable.

【0015】

In this case, the carbon concentration of the CZ silicon wafer is preferably 1.0 ppma or more (claim 8). This is because, as described above, with such a carbon concentration, a sufficient IG effect can be obtained even at a relatively low oxygen concentration.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in more detail, but the present invention is not limited thereto. First, the present inventors investigated in detail the effects of carbon-doped CZ crystals on OSF (Oxidation-induced Stacking Fault) and Grown-in defects. As a result, it was confirmed that unlike the nitrogen-doped crystal, the carbon-doped crystal is less likely to generate an OSF ring and no dislocation loop is generated at that position. That is, there are no (small) crystal defects in the CZ silicon wafer for epitaxial growth, which is a source of crystal defects in the epitaxial layer generated by epitaxial growth. In this respect, the carbon-doped wafer can be said to be a suitable material as a substrate. I found out.

【0017】

However, as described above, when epitaxial growth is performed on a carbon-doped wafer, oxygen precipitation is not promoted so much in the subsequent device process and the IG capacity is low as compared with the case where epitaxial growth is performed on a nitrogen-doped wafer. is there.

【0018】

Therefore, the present inventors investigated the oxygen precipitation characteristics of the carbon-doped wafer in order to improve the IG capability of the carbon-doped wafer. In Fig. 1, carbon is doped at a low concentration (Fig. 1 (a): target value 0.1 ppma) and a high concentration (Fig. 1 (b): target value 1.0 ppma), and the oxygen concentration is 10 to 19 ppma-JEIDA (Nippon Denshi). 800 ° C / 4h + 1000 ° C / 16h for wafers made from 6-inch, crystal orientation <100>, p-type, 10Ω · cm CZ single crystals raised within the range of the Industrial Promotion Association standard). The results of investigating the oxygen precipitation characteristics after performing two types of heat treatment at 1000 ° C / 16h are shown.

【0019】

The carbon-doped crystal was pulled up by using an 18-inch quartz crucible and immersing the carbon rod in the silicon melt in the crucible. The surface area of the carbon rod is about 2500 mm, assuming that the crucible rotation speed and crystal rotation speed are 2 rpm and 15 rpm, respectively.²The region was immersed, and the immersion time was 15 minutes (0.1 ppma) or 120 minutes (1.0 ppma).

【0020】

From Fig. 1 (a), when a wafer sample with a low carbon concentration (0.1 ppma) is heat-treated at 800 + 1000 ° C, it is about 1 × in a wafer having an oxygen concentration of about 15 ppma-JEIDA or higher. Ten¹⁰(Piece / cm³) It can be seen that a degree or more of BMD was observed.

【0021】

In addition, as shown in Fig. 1 (b), when a wafer sample with a high carbon concentration (1.0 ppma) is heat-treated at 800 + 1000 ° C, the wafer having an oxygen concentration of about 12 ppma-JEIDA or higher is about 1 ×. Ten¹⁰(Piece / cm³) It can be seen that a degree or more of BMD was observed.

【0022】

On the other hand, as shown in FIGS. 1 (a) and 1 (b), the BMD when heat-treated at 1000 ° C / 16h is very small, especially when the oxygen concentration is 14 ppma-JEIDA or less, the carbon concentration is low or high. Approximately 1 x 10 in each case⁷(Piece / cm³) BMD was observed.

【0023】

In other words, carbon doping promotes oxygen precipitation only in the precipitated nuclei that are stable (not extinguished) at a temperature of around 800 ° C in the first stage heat treatment, and disappears at high temperatures of 1000 ° C or higher in the first stage. Since it is easy, it was confirmed that it does not precipitate much. This is because even if the epitaxial layer is grown on a carbon-doped substrate in a normal high-temperature process of 1000 ° C or higher, the oxygen precipitation nuclei disappear, and high IG capability cannot be expected in the subsequent device process. means.

【0024】

In addition, Secco etching was performed on these carbon-doped wafers for 30 minutes, and an etch pit called LEP (Large Etch Pit) was observed. LEP is a defect caused by dislocation clusters, and it is known that when an epitaxial layer is formed on a wafer in which LEP is present, an epi layer defect is generated in the region where LEP is present (see Japanese Patent Application No. 11-294523). ). As a result of observation, it was confirmed that no such LEP was observed in the carbon-doped wafer. Therefore, it was confirmed that if an epitaxial layer is formed on the carbon-doped wafer, secondary defects unlike the nitrogen-doped wafer do not occur.

【0025】

From the above, the present inventors have experimentally grasped the above-mentioned characteristics of the carbon-doped substrate with respect to oxygen precipitation for the first time experimentally. Then, the present invention was completed as a result of studying to obtain an epitakisha wafer having a high BMD density, that is, a high IG ability by utilizing this characteristic. That is, in the present invention, a carbon-doped crystal is used as a substrate of an epitaxial wafer, and epi-growth at a low temperature of less than 1000 ° C. is performed in order to obtain a high BMD. Epi-growth at this temperature will result in approximately 1x10 in subsequent device processes.¹⁰(Piece / cm³) Or higher BMD density can be obtained, and an excellent epitaxial wafer without the occurrence of secondary defects can be obtained without adding a special step. However, if the temperature is less than 600 ° C, the oxygen-precipitated nuclei may not grow sufficiently during epi-growth, and may dissolve depending on the subsequent heat treatment conditions. Therefore, the epi-growth temperature is 600 ° C or higher. Is preferable.

【0026】

It is more preferable that the BMD density can be further increased by performing a low-temperature heat treatment at 600 to 1000 ° C before and after epi-growth and adding a treatment for growing oxygen-precipitated nuclei as in the prior art. In this case, since the substrate is doped with carbon, oxygen precipitation is sufficiently promoted even in a short heat treatment time of about 1 hour, so that the heat treatment cost can be reduced.

【0027】

Next, in order to investigate the carbon concentration dependence of the BMD density, a sample having an oxygen concentration of 13.5 to 15.5 ppma (JEIDA) was extracted from the carbon-doped sample obtained in the above experiment, and the relationship between the carbon concentration and the BMD density was examined. Plotted in Figure 2.

【0028】

From Fig. 2, when carbon is doped at 1.0 ppma or more and heat treatment is performed at less than 1000 ° C in the first stage, even a wafer with a relatively low oxygen concentration is about 1 × 10.¹⁰(Piece / cm³It can be seen that an extremely high density BMD density above) can be obtained. That is, if epi-growth is performed on such a wafer at a temperature of less than 1000 ° C, it can be expected that an epi-wafer capable of producing a high-density BMD in the subsequent device process can be obtained. Furthermore, a large margin is given to the oxygen concentration when pulling up a crystal for a wafer having a specific BMD density, and the limitation of the variation in oxygen concentration of the pulled up crystal is relaxed. In addition, this ripple effect enables high-speed growth of single crystals, leading to a reduction in production costs.

【0029】

[Example]

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto. (Example) Using an 18-inch quartz crucible, the raw material polycrystalline is put into the crucible and melted, and the carbon rod is immersed in the silicon melt in the crucible to have a diameter of 6 inches and a crystal orientation <100>. , P-type, 10 ~ 20Ω · cm carbon-doped CZ silicon single crystal rod was pulled up.

【0030】

The crystal pulling speed is 1.0 mm / min, the rutsubo rotation speed and the crystal rotation speed are 2 rpm and 15 rpm, respectively, and the carbon rod has an area of about 2500 mm.²The area of was immersed for 120 minutes. Wafers are cut out from a position 30 cm from the top of the straight body of this single crystal rod, and multiple mirror-polished wafers are prepared by a normal processing method, and the carbon concentration and oxygen concentration are measured by the FT-IR method (Fourier transform infrared spectroscopy). Measured by. As a result, the carbon concentration was about 1.1 ppma and the oxygen concentration was about 15.3 ppma (JEIDA).

【0031】

Then, after performing the following treatment on these four mirror-polished wafers (A, B, C, D), heat treatment at 1000 ° C / 16h is performed to grow precipitated nuclei, and the BMD density in the wafer is adjusted to infrared. It was measured by the scattering tomograph method (measuring device MO-401: manufactured by Mitsui Mining &amp; Smelting Co., Ltd.). The results are shown in Table 1.

【0032】

[table 1]

<img file="JP2001237247A_D0001.tif" />【0033】

From Table 1, the epitaxial wafer composed of the substrate which is the carbon-doped CZ wafer of the present invention and the epitaxial layer grown at a temperature of less than 1000 ° C has a high BMD density and has a high IG capability. It turns out that there is. It can also be seen that this IG capacity is further improved by applying a low-temperature short-time heat treatment before and after the epitaxial growth. Furthermore, Secco etching was performed on these wafers (A to D) for 30 minutes, and LEP was observed. As a result, it was confirmed that no such LEP was observed in these carbon-doped wafers.

【0034】

(Comparative Example) A mirror-polished wafer was prepared by doping with carbon under the same conditions as in the example, and then an epitaxial layer was formed by an epitaxial growth heat treatment at 1125 ° C. and 5 μm to prepare an epitaxial wafer. The BMD density of this wafer E was measured in the same manner as in the examples, and the results are also shown in Table 1. From Table 1, the BMD density of wafer E is 6.0 × 10.⁶(Piece / cm³), And it can be seen that the IG capability is far inferior to that of the epitaxial wafer of the example, even though the substrate is a carbon-doped CZ silicon wafer.

【0035】

The present invention is not limited to the above embodiment. The above embodiment is an example, and any one having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. It is included in the technical scope of the invention.

【0036】

For example, in the above embodiment, the case of growing an epitaxial wafer having a diameter of 6 inches has been described with an example, but the present invention is not limited to this, and the epitaxial wafer having a diameter of 8 to 16 inches or more is also included. It can be applied and can work more effectively.

【0037】

[Effect of the invention]

As is clear from the above, according to the present invention, an epitaxial wafer having a high IG capability can be produced even from a wafer having a relatively low oxygen concentration. In addition, this leads to giving a large margin to the initial oxygen concentration range, the limitation of the oxygen concentration variation of the raised crystal is relaxed, and as a ripple effect, high-speed growth of the single crystal becomes possible, which leads to a reduction in production cost. In addition, it is possible to obtain an epitaxial wafer having an epitaxial layer having excellent crystallinity without causing defects in the epitaxial layer as seen when a nitrogen-doped wafer is used for a substrate.

[Simple explanation of drawings]

[Figure 1]

(a) and (b) are diagrams showing the relationship between the carbon concentration, oxygen concentration, heat treatment temperature and BMD density of an epitaxial wafer using a carbon-doped wafer as a substrate.

[Figure 2]

It is a figure which showed the relationship between the carbon concentration and the BMD density of an epitaxial wafer using a carbon-doped wafer as a substrate.