Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2001-06-14
2003-04-15
Hiteshew, Felisa (Department: 1765)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C117S013000, C117S019000, C117S020000
Reexamination Certificate
active
06548035
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a silicon single crystal wafer suitable for a substrate of epitaxial wafer used in fabrication of semiconductor devices and an epitaxial wafer utilizing it, as well as methods for producing them, and the present invention further relates to a method for evaluating a silicon single crystal wafer suitable for a substrate of epitaxial wafer.
BACKGROUND ART
It is well known that grown-in defects existing in CZ silicon single crystals pulled by the Czochralski method (CZ method) degrade oxide dielectric breakdown voltage characteristics of wafers, cause isolation failures in the device production step and so forth, and various methods are proposed to obviate such problems.
For example, there are a method of reducing grown-in defects during the pulling by the CZ method, a method of eliminating surface defects by subjecting a wafer to annealing at high temperature in a hydrogen or argon atmosphere, a method of using an epitaxial wafer in which an epitaxial layer is grown, and so forth.
Further, as the integration degree of semiconductor devices becomes higher in recent years, it is becoming more important to reduce crystal defects in semiconductors, in particular, crystal defects on and near surfaces thereof. For this reason, the demand for epitaxial wafers in which an epitaxial layer excellent in crystallinity is formed on a wafer surface increases every year.
Meanwhile, when devices are produced by using an epitaxial wafer, various heat treatment steps are usually used in addition to the epitaxial growth. If contaminations such as heavy metal impurities are present during these steps, they will markedly degrade device characteristics. Therefore, such contaminants must be eliminated from the epitaxial layer as much as possible. Accordingly, a substrate having high gettering effect is required as a substrate for the epitaxial growth.
Gettering includes extrinsic gettering (EG) and intrinsic gettering (IG). As typical EG techniques, there are technique of polysilicon back seal in which a polysilicon film is deposited on a back surface of substrate, technique of mechanically damaging the back surface and so forth. However, not only these techniques suffer from problems of particle generation and so forth, but also they are extremely disadvantageous in view of cost since they require special process steps.
On the other hand, in IG, a CZ method silicon wafer containing oxygen is subjected to a heat treatment to generate oxide precipitates that become gettering sites in a bulk portion of substrate. However, in the case of an epitaxial wafer, it suffers from a problem that oxide precipitate nuclei originally existing in a substrate are eliminated during the epitaxial growth at a high temperature, and gettering ability becomes insufficient because oxide precipitates are not likely to be formed and to grow during the subsequent device heat treatment.
Therefore, the conventional production of epitaxial wafers utilizes the fact that a substrate containing boron at a high concentration (p
+
substrate) has the gettering effect, that is, there is often used a p
−
/p
+
epitaxial wafer, in which an epitaxial layer of low boron concentration (p
−
) is formed on a p
+
substrate. However, when epitaxial growth is performed on a p
+
substrate, there are caused a problem of autodoping, in which boron doped at a high concentration is evaporated from the substrate and taken up into the epitaxial layer during the epitaxial growth, or a problem that boron is taken up from the substrate surface into the epitaxial layer due to solid phase out-diffusion. Further, since demand for epitaxial wafers utilizing p
−
substrates is increasing in recent years for CMOS devices, insufficient gettering ability becomes to constitute a problem.
Furthermore, fairly recently, there is frequently seer effective use of techniques utilizing characteristics of crystals doped with nitrogen as methods for obtaining CZ wafers having reduced grown-in defects existing near wafer surfaces. For example, there can be mentioned a technique in which defects in a deeper region are eliminated through annealing by doping nitrogen into crystals to make a size of grown-in void defects smaller in order to enhance easiness of elimination of defects during the annealing at a high temperature, a technique of producing epitaxial wafers showing enhanced IG ability by using crystals doped with nitrogen for substrates of the epitaxial wafers so as to enhance formation of oxide precipitates during the device heat treatment and thus increase BMDs (Bulk Micro Defects) and so forth.
As an example of use of such nitrogen-doped crystals for substrates for epitaxial growth, in the technique described in Japanese Patent Laid-open (Kokai) Publication No. 11-189493, a silicon single crystal grown with doping of nitrogen at a level of 10
13
atoms/cm
3
or more is used for epitaxial wafers. This technique was based on the finding that, if an epitaxial layer was formed on a substrate containing an OSF (Oxidation induced Stacking Fault) region, which was generated in a ring shape depending on the pulling conditions of single crystal in the CZ method, oxygen precipitation nuclei existing in the OSF ring region were not eliminated, but they functioned as effective gettering sites in the device production process after the epitaxial formation, and the finding that the width of the OSF ring could be made larger by doping nitrogen during the single crystal growth, and if the amount of nitrogen to be doped was 10
13
atoms/cm
3
or more, the nuclei of OSFs effective for the gettering could be uniformly distributed over the whole single crystal.
However, according to the investigation of the inventors of the present invention, it became clear that, if an epitaxial layer was formed on a wafer doped with nitrogen, defects called LPDs (Light Point Defects, generic term for referring to bright spot defects observed by using a wafer surface analysis apparatus utilizing laser light), which were harmful to devices, were likely to be formed on the OSF region of the epitaxial layer. Further, it was also found that these LPDs were particularly notably observed, when the nitrogen concentration was high. That is, if an epitaxial layer is formed utilizing the technique described in the aforementioned Japanese Patent Laid-open (Kokai) Publication No. 11-189493 as it is, there are likely to be obtained an epitaxial wafer in which many LPDs are generated. Therefore, as a countermeasure for this, decrease in nitrogen concentration is contemplated. However, the decrease in nitrogen concentration results in reduction of two of the intrinsic effects of doping with nitrogen, that is, the reduction in void size, i.e., improvement effect of elimination efficiency of defects by the annealing, and the improvement effect of IG ability brought by the enhancement of oxygen precipitation.
DISCLOSURE OF THE INVENTION
The present invention was accomplished in view of the aforementioned problems, and its object is to provide a substrate for an epitaxial wafer that suppresses crystal defects to be generated in an epitaxial layer when epitaxial growth is performed on a CZ silicon single crystal wafer doped with nitrogen and also has superior IG ability and an epitaxial wafer utilizing such a substrate, as well as methods for producing them. Further, another object of the present invention is to provide a method for evaluating such a substrate suitable for an epitaxial wafer.
In order to achieve the aforementioned objects, the present invention provides a silicon single crystal wafer for epitaxial growth grown by the CZ method, which is doped with nitrogen and has a V-rich region over its entire plane.
Such a silicon single crystal wafer as described above, which is obtained by processing a silicon single crystal ingot doped with nitrogen in the CZ method and has a V-rich region over its entire plane, can suppress crystal defects to be generated in the epitaxial layer during the epitaxial growth, and moreover, it c
Aihara Ken
Hayamizu Yoshinori
Iida Makoto
Kimura Akihiro
Kimura Masanori
Hiteshew Felisa
Oliff & Berridg,e PLC
Shin-Etsu Handotai & Co., Ltd.
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