Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – With means for measuring – testing – or sensing
Patent
1992-12-28
1995-04-25
Breneman, R. Bruce
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
With means for measuring, testing, or sensing
117217, 117218, C30B 1526
Patent
active
054089522
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an improvement on a procedure for growing a single crystal in accordance with the Czochralski method (hereafter abbreviated as the CZ method).
PRIOR ART
As a process for manufacturing such crystals as silicon single crystals, a method known as the CZ method for growing single crystal is generally being used. In this method, the crystalline raw material that has been placed into the crucible is melted and, following contact of the seed crystal with the molten liquid, while the seed crystal and the crucible rotate in opposite direction to each other, resulting the seed crystal growing.
In an existing similar single crystal growth method, when the crystal is pulled up, the molten liquid level decreases and the surface of the melt, i.e. the condition of the single crystal growth surface, is altered thus after a while the single crystal comes to a point where it cannot be pulled up. Additionally, when the molten liquid level shifts, the quantity of oxygen dissolved from the molten liquid also changes, thus the axial oxygen concentration of the single crystal obtained is altered as well. Recently, an IG (Intrinsic Gettering) process which makes use of the oxygen precipitates has come into effect requiring a strict control over the oxygen concentration.
In dealing with this problem, the prior art carried out control of the molten liquid level using only a rate controller. The present process attempts to maintain the position of the molten liquid level in countering the crystal pulling up speed by fixing the lifting of the crucible at a constant speed such that volume of the displaced liquid portion is properly offset.
But in the prior art when drawing up single crystals using an automatic diameter controller, in the initial stages, during what is-known as "shoulder forming" before the body section of the crystal becomes fixed in diameter, the ratio of the rate controller is too small and the uniformity of the liquid level cannot be maintained. Thus, as a result, the precise liquid level corresponding to the constant section of the crystal could not be established. Furthermore, the thermal deformation that occurs at the single crystal pulling temperature in addition to change in the interior volume of the crucible both produced variation of the melt level. Consequently, through just the use of the aforementioned rate controller, precise control of the melt level was not possible in this prior method. Additionally, the oxygen concentration of the single crystal depends on both the temperature of the melt surface and the cooling rate of the crystal. Control of both, the amount of flow of the argon gas covering the liquid surface and the quantity of silicide evaporation were essential as was the precise control of the melt level position during the entire pulling period, from beginning to end.
However, in the CZ method, during the "seed" process in which the seed crystal is dipped into the melt and tapered upon pull up, if the temperature of the melt following melting of the raw material is even slightly off, dislocation-free crystal pulling is not possible. As a result, in this CZ method, after perfectly melting the raw material and overshooting 1500.degree. C., it was essential to calm down the melt and stabilize the molten liquid convection inside the crucible. Additionally, it was essential that the oxygen concentration be fixed at a constant level at the melt surface in the initial pull up stage. However, the interior of the heat furnace is kept at an extremely high temperature and a thermometer cannot be set up, thus, in the prior art, detection of the melt temperature depends on the operator's perception. In actuality, the dipping and tapering draw up of the seed crystal was carried out using this detection method. But in the aforementioned process in which detection depends on the operator's perception, it is very difficult to measure precisely the temperature of the liquid. As well, an enormous amount of time is taken leading up to the aforementione
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Anbe Toshio
Saitoh Masao
Wakabayashi Daisuke
Breneman R. Bruce
Garrett Felisa
Mitsubishi Materials Corporation
Mitsubishi Materials Silicon Corporation
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