Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
1999-10-05
2001-07-31
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
Reexamination Certificate
active
06267815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for pulling a silicon single crystal which has a monocrystalline solid seed crystal of silicon being brought into contact with molten silicon material and an interface being formed between solid seed crystal and molten material, and the molten silicon material being caused to solidify with the formation of a thin-necked crystal and a cylindrical single crystal. The method is one wherein, during the pulling of the thin-necked crystal, it is ensured that the ratio V/G(r) is above a constant C
crit
having the value 1.3*10
−3
cm
2
/Kmin, with V being the pulling rate, with G(r) being the axial temperature gradient at the interface and r being the radial distance from the center of the thin-necked crystal.
2. The Prior Art
The most frequently used methods for pulling a single crystal by solidifying molten material are the Czochralski method (CZ method) and the float zone method (FZ method). These methods are described, for example, in
Semiconductor Silicon Crystal Technology
by F. Shimura (Academic Press, London 1988, pages 124-127, 130-131 and 135) with reference to the example of producing silicon single crystals.
The production of silicon single crystals using the aforementioned methods is divided into several phases. After polycrystalline silicon (polysilicon) has been melted, a seed crystal of given crystal orientation is brought into contact with the melt. Then a 2-3 mm wide and several centimeters long thin-necked crystal is pulled, whose diameter is subsequently increased to the target diameter of the silicon single crystal to be produced. The phase of pulling the thin-necked crystal is used to eliminate dislocations present in the seed crystal and is carried out in the prior art according to Dash's principle (
W. C. Dash, J. Appl. Phys.
29 (1958), 736-737). If, during this phase, the dislocations are not successfully eliminated, then it is not subsequently possible to produce a dislocation-free silicon single crystal.
Such silicon single crystals are the basic material for electronic components whose functional capacity depends, for example, on the freedom of the basic material from defects. Thus there is the requirement for defect-free and therefore also dislocation-free single crystals as a result.
In relation to the production of silicon single crystals, a study has been published (
E. Dornberger and W. v. Ammon, Journal of the Electrochem. Soc.
, Vol. 143, No. 5, May 1996, 1648-1653). This study links the occurrence of particular crystal defects when pulling a single crystal with particular parameters which play a role in the pulling of the single crystal.
SUMMARY OF THE INVENTION
It has now been found according to the present invention that, for the production of a single crystal, it is not only the conditions during the pulling of the single crystal that are of particular importance. The single crystal can be made from semiconductor material, preferably from silicon.
The present invention relates to a method for pulling a single crystal, in which a monocrystalline solid seed crystal is brought into contact with molten material and an interface is formed between solid and molten material. Molten material is then caused to solidify with the formation of a thin-necked crystal and a cylindrical single crystal. During the pulling of the thin-necked crystal, it is ensured that the ratio V/G(r) is above a constant C
crit
having the value 1.3*10
−3
cm
2
/Kmin, with V being the pulling rate, G(r) being the axial temperature gradient at the interface and r being the radial distance from the center of the thin-necked crystal. The solid seed crystal and the molten material are semiconductor material, preferably silicon.
It has been found that, when employing the method of the invention, the risk of forming dislocations is reduced when the single crystal is being pulled. Therefore, the dip-in frequency (number of attempts needed to produce a dislocation-free single crystal) decreases as well as the dip-in time (time from first contact between the seed crystal and the silicon melt to completion of the pulling of the thin-necked crystal) decreases.
The ratio V/G(r) can be increased, and thus brought into the desired range, by increasing the pulling rate for given thermal conditions. Another alternative is to reduce the axial temperature gradient at the interface, for example by providing an appropriately designed heat shield around the thin-necked crystal which is preferably removable and adjustable.
REFERENCES:
patent: 5078830 (1992-01-01), Shirata et al.
patent: 6048395 (2000-04-01), Iida et al.
patent: 6120599 (2000-09-01), Iida et al.
patent: 0 866 150 (1998-09-01), None
W.C. Dash, J. Appl. Phys. 29 (1958), 736-737.
E. Dornberger and W.U. Ammar, Journal of the Electrochem. Soc., vol. 143, No. 5, May 1996, 1648-1653 English Abstract Corresponding to EP 0 866 150 A1.
Ammon Wilfried Von
Dornberger Erich
Ehlert Andreas
Collard & Roe P.C.
Hiteshew Felisa
Wacker Siltronic Gesellschaft fur Halbleitermaterialien AG
LandOfFree
Method for pulling a single crystal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for pulling a single crystal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for pulling a single crystal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2495154