1. Field of the Invention
The present invention relates to a manufacturing method for a silicon single crystal, which grows a silicon single crystal by dipping a seed crystal into a silicon melt and then pulling the seed crystal therefrom. More particularly, the present invention relates to a manufacturing method for a silicon single crystal including a step of adding a dopant to the silicon melt while a straight body portion of the silicon single crystal is growing.
2. Related Art
The Czochralski method (CZ method) is a method that grows a silicon single crystal by dipping a seed crystal into a silicon melt and then pulling the seed crystal therefrom. In the CZ method, a dopant may be added to a melt while growing a silicon single crystal by pulling, for providing the silicon single crystal with the required electrical properties.
As a method for adding a dopant to a melt while pulling a single crystal, a method of disposing an open end of a supply unit of dopant above the melt and blowing carrier gas containing the dopant from the supply unit onto the melt is known. Inert gas such as argon gas is used as the carrier gas.
In addition, an invention of pulling and growing a silicon single crystal ingot having different resistivity discontinuously in a growing direction of the silicon single crystal, by: disposing a sample tube (doping tube) at a position not interfering with a pulling mechanism; lowering the sample tube down to just above an upper face of a crucible; melting a dopant inside the sample tube by radiant heat from the melt at the position; and then lowering the sample tube containing the dopant to a position so as to be immersed in the melt and thereby adding the melted dopant to the melt from an open surface of the sample tube, is disclosed in Japanese Unexamined Patent Application Publication No. 2005-336020.
Furthermore, an invention that supplies a dopant to a melt such that there is little or no concentration of dopant in a melt until a first half of a straight body portion of a silicon single crystal is formed and there is high concentration of dopant in the melt after that the first half of the silicon single crystal is formed, is disclosed in Japanese Unexamined Patent Application Publication No. 2008-266093. Here, a method of spraying a vapor, obtained by subliming a sublimable dopant, onto the melt is disclosed as a method for adding the dopant to the melt.
According to the prior arts disclosed in Japanese Unexamined Patent Application Publications No. 2005-336020 and 2008-266093, a silicon single crystal having desired electrical properties can be obtained since the concentration of the dopant in the melt can be changed while growing the silicon single crystal. In recent years, there has been a strong need for a silicon single crystal of low resistivity containing a high concentration of dopant. In order to obtain such a silicon single crystal, a large amount of dopant must be added while growing the silicon single crystal. Here, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-266093, it is known that a dopant should be added while growing a straight body portion of a silicon single crystal because a high concentration of dopant in the melt in growing of a shoulder portion to the straight body portion may lead to breakage of the single crystal.
However, the present inventors found that, by adding a large amount of dopant to a melt while growing a single crystal, a dislocation is introduced into the growing single crystal even while growing the straight body portion of the silicon single crystal. If a dislocation is introduced into a silicon single crystal, the silicon wafer obtained from the single crystal is inappropriate for manufacturing a semiconductor device, thus lowering yield of the silicon single crystal.