Device for producing single crystals

Details Device for producing single crystals Device for producing single crystals

2001-09-19

2004-03-30

Norton, Nadine G. (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Apparatus

For crystallization from liquid or supercritical state

C117S217000, C117S219000, C117S083000, C164S122000, C164S122100, C164S122200, C164S123000

Reexamination Certificate

active

06712904

ABSTRACT:

The invention concerns a device for producing monocrystals. In particular the invention concerns a device for producing monocrystals of various materials, for example III-V materials, for example of gallium arsenide monocrystals.
Familiar devices for producing monocrystals of various materials, for example III-V materials, for example of gallium arsenide monocrystals, generally comprise multiple temperature zone furnaces, such as those described in DE-OS-38 39 97 and in U.S. Pat. Nos. 4,086,424, 4,423,516 and 4,518,351.
These multiple temperature zone furnaces can consist not only of metal heat conductors but also of heating conductors containing carbon The so-called multiple zone tube furnaces enable a variable structure of a temperature field suitable for crystal growth and its displacement along the furnace's axis of rotation.
However, devices of this kind are characterized not only by an axial but also by a radial heat flow that can lead to a variable growth rate and to an unfavorable formation of the interphase melt-crystal.
In addition, multizone or multiple temperature zone furnaces are composed of a variety of thermal construction elements and this requires considerable expense for dismantling and assembling for maintenance work. As the number of zones increases the amount of automation increases and with it the susceptibility to faults of multizone furnaces.
In particular for the production of monocrystals with a large diameter, for example 2″, 3″, 100 mm, 125 mm, 150 mm 200 mm and above, there is the problem that a radial heat flow in the crystal has an effect on the isotherms, i.e. on the interphase melt-monocrystal in a vertical or axial direction respectively.
A device characterized by an insulating device being planned that is designed in such a way that a heat flow in a radial direction vertical to the rotation axis (M) of the furnace (
1
) can be restricted to a preset rate and whereby the insulating device (
6
) is designed so that its insulating effect is reduced from the cover heater (
3
) to the floor heater (
2
) is familiar from the Journal of Crystal Growth, NL, North-Holland Publishing Co. Amsterdam, Vol. 166, No. ¼, Sep. 1, 1996, pages 566-571.
The task of the invention is to provide a device for producing monocrystals, in particular monocrystals of various III-V materials, for example from gallium arsenide, in which the heat control is almost exclusively axial.
The task is solved by means of a device for producing a monocrystal by growing from a melt of raw materials of the monocrystal to be produced with a heating appliance (
1
) for generating a temperature gradient within the melt of raw material whereby the heating appliance (
1
) has a rotationally symmetrical furnace (
1
) with a rotation axis (M) and with an essentially level floor heater (
2
) and an essentially level cover heater (
3
) that can be controlled to different temperatures and characterized by an insulating device being planned that is designed in such a way that a heat flow in a radial direction vertical to the rotation axis (M) of the furnace (
1
) can be restricted to a preset rate and whereby the insulating device (
6
) is designed so that its insulating effect is reduced from the cover heater (
3
) to the floor heater (
2
).
In certain preferred embodiments of the invention, the device has a furnace designed cylindrically and a controller that is designed in such a way that the temperature of the floor heater (
2
) can be reduced in comparison with the temperature of the cover heater. In other preferred embodiments, the device has an insulator device (
6
) that is designed as a tapered cone body with a coaxial cylindrical hollow space that is open at the top and bottom and placed in the furnace (
1
) in such a way that the tapered end is towards the floor heater (
2
). Preferably, the insulator device is made, for example, of graphite. In other preferred embodiments, the device comprises a furnace (
1
) having a jacket heater (
5
). In still other preferred embodiments, the device comprises a heat transmission part (
6
) having a rotationally symmetrical profiled or unprofiled shape. In yet other preferred embodiments, the device includes a heating surface of the heaters being calculated in a ratio to the diameter of the monocrystal to be produced so that a temperature that is essentially homogeneous over the radial cross-section surface of the monocrystal to be produced can be generated together with a temperature gradient between the first heater (
2
) and the second heater (
3
) that is essentially homogeneous and constant. Preferably, the size of the surface of each heater (
2
,
3
) is at least 1.5 times the cross-sectional area of the monocrystal to be produced is calculated. Preferably, the controller is designed so that the temperature of the first level heater (
2
) can be lowered continuously as against the second level heater (
3
). In still other preferred embodiments, the clearance between the heaters is greater than the length of the monocrystal to be produced. In yet further preferred embodiments, a crucible (
4
) for receiving a melt of raw material of the monocrystal to be produced is provided between the first heater (
2
) and the second heater (
3
). Preferred devices of the present invention are particularly suited for the production of a monocrystal from a III-V composite semiconductor, for example, a monocrystal of gallium arsenide.
The device has the advantage that a homogeneous axial heat flow is guaranteed and that practically no heat at all can run off in a radial direction, i.e. of a radially homogeneous temperature at the upper and lower heating plates and the intermediate sections.
Other elements and expediencies can be seen in the description of a design example by means of FIG.
1
.


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Althaus et al., “Some new design features for vertical Bridgman furnaces and the investigation of small angle grain boundries developed during VB growth of GaAs.”, Journal of Crystal Growth 166 (1996) p. 566-571.

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