Apparatus and method for producing silicon semiconductor...

Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For crystallization from liquid or supercritical state

Reexamination Certificate

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C117S013000, C117S218000, C117S222000

Reexamination Certificate

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06764548

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an apparatus for producing a silicon semiconductor single crystal using the Czochralski method (referred to as a CZ method hereinafter), and a method for producing a silicon semiconductor single crystal with the apparatus.
BACKGROUND ART
Conventionally, in the growth of a silicon semiconductor single crystal using the CZ method, polysilicon is charged in a crucible provided in a growth furnace of an apparatus for producing a silicon semiconductor single crystal, the polysilicon is melted to silicon melt by heating the polysilicon with a heater provided around the crucible, and after a seed crystal is dipped into the melt, the seed crystal is pulled above the silicon melt while rotating it gently to grow a silicon semiconductor single crystal having a substantially cylindrical constant diameter portion. Then the pulled silicon semiconductor single crystal is cut and ground to leave the constant diameter portion, and becomes a silicon semiconductor wafer through a wafer shaping process. The thus obtained silicon semiconductor wafer is used as a semiconductor device substrate for fabricating an integrated circuit or the like on the surface layer of which is formed an electric circuit.
In the process of forming an electric circuit on the surface layer of the silicon semiconductor wafer, oxygen atoms contained in the silicon semiconductor wafer bond to silicon atoms to form oxide precipitates such as BMD (Bulk Micro Defect) inside the silicon semiconductor wafer. It is known that the oxide precipitates such as BMD capture (or getter) excess contamination atoms such as heavy metal atoms contaminated in the semiconductor device fabricating process to improve properties and yields of semiconductor devices. Therefore, by using a silicon semiconductor wafer substrate containing larger amounts of oxide precipitates such as BMD, it is possible to improve yields of semiconductor devices formed on a surface layer of the substrate.
The amount of oxide precipitates depends on a concentration of oxygen originally contained in the silicon semiconductor wafer as well as on thermal history of the silicon semiconductor wafer for a period from during the crystal growth up to just prior to the semiconductor device fabricating process. However, generally there is a standard for a concentration of oxygen contained in a silicon semiconductor wafer, which cannot be changed readily.
Also it is known that in the silicon semiconductor single crystal, even if distribution of an oxygen concentration in the direction of the growth axis is homogeneous, distribution of the amount of precipitated oxygen exists in a state where it is relatively large in the seed side of the grown crystal and is relatively small in the melt side. It is considered that this phenomenon is due to the distribution in the axial direction of thermal history in a relatively low temperature zone where nuclei of the oxide precipitates are formed and grow in the single crystal.
Then there is disclosed a technique for adjusting the thermal history to a desired value during a processing period from growing a silicon semiconductor single crystal up to manufacturing a silicon semiconductor wafer therefrom. For instance, JPA 83-120591 discloses a method of increasing oxygen precipitation by heating a silicon semiconductor single crystal during its growth to adjust the thermal history, and in JPA 90-263792, the method of annealing a silicon semiconductor single crystal after its growth and the like are examined.
In the method of heating a silicon semiconductor single crystal during its growth, however, there are required large scale reconstruction for installing a heating apparatus of heating a grown silicon semiconductor single crystal in a producing apparatus and a power for heating the grown crystal; the method cannot be regarded as an efficient method from the viewpoint of cost and operability. Further, a temperature balance during growth of a silicon semiconductor single crystal is forcibly changed, so that dislocations are created in the grown crystal, thereby the commercialization thereof being disadvantageously impossible.
On the other hand, in the method of annealing a silicon semiconductor single crystal after its growth, it is conceivable to anneal the silicon semiconductor single crystal in the ingot state or in the wafer state, but an expensive apparatus is required in either case, and in addition, running cost for the apparatus for annealing as described above is generally high, and therefore this method is inefficient in view of the production cost. Further, this method in which oxygen precipitation in a crystal is controlled by means of annealing has such troubles as contamination by heavy metals during the annealing process; so such problems persist in this method.
DISCLOSURE OF THE INVENTION
With the foregoing drawbacks of the prior art in view, it is an object of the present invention to provide an apparatus and a method for producing a silicon semiconductor single crystal which can stabilize and homogenize an amount of precipitated oxygen in the direction of the crystal growth axis when growing a silicon semiconductor single crystal.
To achieve the above described object, an apparatus for producing a silicon semiconductor single crystal according to the present invention resides in an apparatus for producing a silicon semiconductor single crystal by the Czochralski method which comprises a main growth furnace having a crucible retaining silicon melt disposed therein for growing a silicon semiconductor single crystal, and an upper growth furnace for housing therein and cooling the silicon semiconductor single crystal pulled from the silicon melt, wherein the upper growth furnace communicated to a ceiling section of the main growth furnace is provided with an upper insulating member for surrounding a pulled silicon semiconductor single crystal.
To make oxygen precipitated more in a silicon semiconductor single crystal, it is necessary to form therein nuclei for causing oxygen precipitation during crystal growth and to make the nuclei grown to large sizes. When a silicon semiconductor single crystal is subjected to heat treatment at a constant temperature, nuclei of oxide precipitates larger than the critical radius at the temperature grow to larger sizes, while those smaller than the critical radius are annihilated from inside of the silicon semiconductor single crystal. The critical radius of the nuclei of oxide precipitates becomes larger as the heat treatment temperature becomes higher. Therefore, to form BMD capable of gettering contaminants in a silicon semiconductor wafer, it is important to make the nuclei of oxide precipitates to sizes where the nuclei are not annihilated with heat treatment in the semiconductor device fabricating process. For that purpose, it is necessary to make the nuclei of oxide precipitates larger by adding heat treatment or thermal history more at a lower temperature than the heat treatment temperature in the semiconductor device fabricating process.
After a silicon semiconductor single crystal is formed in a growth furnace in a silicon semiconductor single crystal producing apparatus, the silicon semiconductor single crystal is pulled into the upper growth furnace and is allowed to cool down therein; therefore by adjusting the cooling rate at the low temperature section to a desired value, the silicon semiconductor single crystal is able to receive thermal history more to promote the formation of BMD.
To easily grow the silicon semiconductor single crystal having such quality as described above, the simple and best method is to arrange an upper insulating member for keeping warm a crystal pulled into the upper growth furnace such that the silicon semiconductor single crystal receives sufficiently thermal history at the low temperature section when the silicon semiconductor single crystal cools down. The upper insulating member may have a length almost similar to the full length of the upper growth furnace or may be arranged so as to keep warm at l

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