Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2001-04-26
2003-04-08
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S020000, C117S066000, C117S073000, C117S076000, C117S930000, C117S932000
Reexamination Certificate
active
06544332
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing a silicon single crystal wherein size and density of grown-in defect incorporated in the crystal when growing the silicon single crystal by a Czochralski method (hereinafter may be abbreviated to CZ method) are controlled to be a desired value. The present invention also relates to silicon single crystals and silicon wafers produced by the method.
BACKGROUND ART
Along with a recent tendency to increase the degree of integration of semiconductor circuits, circuit elements have been becoming finer; thus quality requirements are becoming severer on silicon single crystals produced by CZ method which are used as a substrate. Particularly, there has been required a reduction of defects generated during single crystal growth, such as FPD (Flow Pattern Defect), LSTD (Laser Scattering Tomography Defect), and COP (Crystal Originated Particle), which are called grown-in defect and may cause a degradation in oxide dielectric breakdown voltage characteristics or device characteristics.
Recently, when a silicon single crystal is grown, there has been used a producing method wherein defects incorporated in the crystal during growth of the crystal are suppressed by changing growth conditions or by adjusting temperature distribution within a furnace of a pulling apparatus.
For example, an agglomeration temperature zone of grown-in defects of a silicon single crystal grown by a CZ method is usually in the range of 1150 to 1080° C., and size and density of the grown-in defects can be controlled to be desired values by increasing or decreasing a cooling rate of the crystal for passing through the temperature range. When the cooling rate of silicon single crystal in the agglomeration temperature zone of grown-in defects is decreased, an agglomeration of grown-in defects such as COP is promoted, with the result that a silicon single crystal having low crystal defect density can be obtained. Accordingly if thus-obtained silicon single crystal is processed to provide wafers and the wafer is used as a substrate material for integrated circuit device, a density of defects in the wafer surface is remarkably low so that devices having an excellent oxide dielectric breakdown voltage characteristics can be fabricated.
Meanwhile, in the above producing method, although it is possible to keep low density of grown-in defects, there is a drawback that the defect size is in inverse proportion to the defect density and thus the defect size becomes larger as the defect density is reduced (See Japanese Patent Application Laid-open (kokai) No. 10-208987). Along with miniaturization and high integration of integrated circuits, it is said to be undesirable that defects having large size exist in a wafer used as a substrate for integrated circuits, even if the defect density is low.
When the cooling rate of a crystal for passing through the agglomeration temperature zone of grown-in defects is increased by adjusting pulling conditions of the crystal or temperature distribution within a furnace, growth of grown-in defects is suppressed and the defect size itself can be suppressed to be extremely small. However, as the size of defects becomes smaller, the density of defects tends to be higher inversely. In case a number of defects exist on a wafer, a problem in terms of the oxide dielectric breakdown voltage characteristics is caused when the wafer is processed to integrated circuits. Thus, so far the producing method wherein the cooling rate in the agglomeration temperature zone is increased has not been employed so much.
However, recently it was confirmed that even in a silicon wafer in which grown-in defects are generated in the high density, if a size of the defects is very small, the defects can be eliminated by subjecting the wafer to heat treatment. The attention has been riveted to a method in which the defects in the surface of a wafer are suppressed effectively by combining a method for controlling the cooling rate of the crystal in the agglomeration temperature zone of grown-in defects when pulling the silicon single crystal with a heat treatment of the wafer obtained by processing the crystal.
Meanwhile, when nitrogen is added in a silicon single crystal, an agglomeration of defects generated in the crystal during growth of the single crystal is further suppressed. There was recently developed a method in which a size of grown-in defects is kept to be extremely small by controlling properly a time for passing the agglomeration temperature zone in addition to the above method by addition of nitrogen, and then by subjecting wafers processed from the single crystal to heat treatment, the defects in the wafer surface are eliminated (see Japanese Patent Application No. 10-170629). By adopting this method, the silicon single crystal can pass through the agglomeration temperature zone at high speed during the growth, and thereby the defects in the wafer surface can be eliminated without lowering a production efficiency of the crystal. As a result, the oxide dielectric breakdown voltage characteristics are good and the defects having large size do not exist on the wafer, so that the wafer can be used as a substrate material of high quality for integrated circuit. Thus, currently the technique with respect to that method has progressed with great speed.
However, recent test results show some cases where size or density of grown-in defects cannot be regulated evenly and the defect size is dispersed, for example, even though defects can be suppressed by adding nitrogen as impurity and adjusting properly the time for passing of the crystal in a temperature range of 1150-1080° C., i.e., an agglomeration temperature zone of grown-in defects, and even though the passing time of the crystal in the above temperature range, i.e. a cooling rate of the crystal in the range of 1150-1080° C. is controlled similarly by significantly changing the concentration of added impurity, i.e., nitrogen or by finely adjusting a temperature distribution within a furnace by changing Hot Zone of the pulling apparatus. Besides, even though the wafer obtained by processing is subjected to the heat treatment for eliminating the defects, there are some cases where the defects remain without being eliminated, which causes a problem in production of a wafer having a few defects.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problem, and the prime object of the present invention is to provide a silicon single crystal produced by CZ method wherein the dispersion in size and density of grown-in defects is suppressed effectively and the quality is stabilized regardless of the variety of crystals, a silicon wafer and a producing method therefor.
To achieve the above object, the present invention provides a method for producing a silicon single crystal in accordance with a Czochralski method, wherein before producing a crystal having a predetermined kind and concentration of impurity, another silicon single crystal having the same kind and concentration of impurity as the crystal to be produced is grown to thereby determine an agglomeration temperature zone of grown-in defects thereof, and then based on the temperature, growth condition of the crystal to be produced or temperature distribution within a furnace of a pulling apparatus is set such that a cooling rate of the crystal for passing through the agglomeration temperature zone is a desired rate to thereby produce the silicon single crystal.
It has been conventionally said that an agglomeration temperature zone when a silicon single crystal is grown by CZ method is generally in the range of 1150 to 1080° C. However, the above range corresponds to a case where any impurity such as nitrogen is not doped in the crystal. It is revealed that in case that impurity of high concentration is added in a growing crystal, the agglomeration temperature zone of grown-in defects varies slightly under the influence of impurities such as nitrogen added for suppression of defects, oxygen supp
Hayamizu Yoshinori
Iida Makoto
Kimura Masanori
Takeno Hiroshi
Hiteshew Felisa
Oliff & Berridg,e PLC
Shin-Etsu Handotai & Co., Ltd.
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