DE1275032B - Method for crucible-free zone melting of a crystalline rod, in particular a semiconductor rod - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN -007W ^ PATENT OFFICE

EDITORIAL

Int. CL:

Number:
File number:
Registration date:
Display day:

BOId

BOIj

German class: 12 c-2

12 g-17/10

P 12 75 032.2-43 (S 98115)

July 10, 1965

August 14, 1968

The main patent 1218 404 relates to a method for crucible-free zone melting of a perpendicular its ends held crystalline rod, in particular semiconductor rod, the holders of at least one of which is set in rotation about its vertical axis, relative to one another and to a heating device surrounding the rod in the shape of a ring in the direction of the rod axis with such one another coordinated speeds are moved that the thickness of the melt solidifies again Rod part is enlarged beyond the clear width of the heating device.

According to the main patent, this method is designed so that the rotating holder of the re-solidifying rod part is shifted laterally relative to the heating device.

The method according to the main patent has the particular advantage that working in the field of The transition from the original cross-section to the new, enlarged cross-section is made much easier will. In addition, there is the possibility of using semiconductor rods using previously known methods produce enlarged cross-section. And finally there is also the option of removing the end of the rod, whose cross-section is enlarged, to be arranged above the heating coil.

The present method represents a modification and further improvement of the method according to the Main patent. It is characterized in that after reaching the desired thickness of the re-solidifying Rod part the holder of each rod part is continuously moved back and forth laterally relative to the heating device. This modification of the procedure according to the main patent has the particular advantage that the resistance curve over the rod cross-section becomes comparative.

The invention is to be explained in more detail on the basis of exemplary embodiments. In the

Figures 1 through 5 are different phases of the invention Procedure shown;

F i g. 6 shows another embodiment;

Fig. 7 is a schematic diagram of the distribution the specific resistance across the cross section of a zone melting process concentric rod holders treated semiconductor rod.

In Fig. 1 is in a semiconductor rod 2 with the help of an induction heating coil 3, which with high frequency current is fed, a melting zone 4 is generated. At the lower end of the rod 2 a seed crystal 5 is melted, which z. B. can be a single crystal used for single crystal growth. The seed crystal 5 Method for crucible-free zone melting of a crystalline rod, in particular a semiconductor rod

Addendum to the patent: 1218 404

Applicant:

Siemens Aktiengesellschaft, Berlin and Munich, 8520 Erlangen, Werner-von-Siemens-Str. 50

Named as inventor:

Dr. rer. nat. Wolfgang Keller, 8551 Pretzfeld - -

and thus the lower rod part are set in rotation about the vertical axis by z. B. the lower bracket is driven with the help of an electric motor. As can be seen from the drawing,

as is the melting zone at the point in time shown in FIG. 1 has reached the point at which the transition from the thin seed crystal to the normal rod thickness is reached.
In FIG. 2, the further procedural measures are shown at a later point in time by corresponding arrows. The seed crystal 5 is not only moved downward with respect to the heating coil 3, which is assumed to be stationary, but at the same time to the right in the image plane. This also pulls the melting zone 4 apart to the right. Since the lower rod part 5 rotates about its own axis, the material which crystallizes out of the melt grows essentially symmetrically to the axis of rotation of the lower rod holder.

The upper rod part 2 is pushed in from above in the corresponding ratio. He can also be around its longitudinal axis can be rotated.

In Fig. 3 shows a still later stage in the procedure is shown, up to the target diameter is reached in which, by displacement of the seed crystal 5 to the right a further increase of the rod diameter of the lower rod part 2 a. At this point in time, the direction of the lateral displacement of the lower bracket is reversed and this bracket is now moved from right to left.

4 shows a later point in time in the method in which the left end point of the

809 590/384

Movement of the lower rod holder holding the seed crystal 5 is achieved. As the arrow indicates becomes down here as both rod parts continue to move in the direction of the rod axis again reversed the direction of the lateral displacement.

In Fig. 5 another state is reached in which the direction of the reciprocating movement is reversed again will.

In the example it is assumed that the rod is to be enlarged to double its diameter, i.e. that the rod cross-section is quadrupled. In this case, with respect to the heating coil 3, the upper rod part 2 must be pushed in at four times the speed with which the lower rod part Za is pulled away from the heating coil. You can z. For example, assume that the lower rod part Za is moved downwards at a speed of 2 mm / min, while the upper rod part 2 is moved downwards at a speed of 8 mm / min. The speed of rotation of the lower rod part can be approximately 5 to 100 rpm, preferably approximately 20 rpm. The reciprocating movement of the lower bracket can be performed about 5 to 20 times per minute.

In Fig. 6 is another embodiment of the Illustrates the method according to the invention, in which the resolidifying rod part 12 ″ above the Heating coil 13 is pulled upwards and the rod part 12 is also moved upwards relative to the heating coil 13 will. The melting zone 14 can be held due to the large adhesive surface on the upper rod part 12 a if it is dimensioned particularly short in the direction of the rod axis. This is special heating by a flat induction heating coil with spirally arranged windings is advantageous.

In Fig. 7, the distribution of the specific resistance values is plotted over a rod diameter, which was observed as the result of some crucible-free zone melting processes. The aim is to achieve a distribution that is as even as possible. Without special measures, however, the in FIG. 7, namely that the values of the specific resistance ρ starting from an edge of the rod denoted by zero are initially uniform and decrease significantly by several percent towards the center of the rod denoted by r , while they decrease towards the other edge D of the rod rise again to the first amount symmetrically to the center and maintain this amount up to the edge D of the rod. In contrast, by constantly moving the rotating support of the re-solidifying rod part, the material particles crystallizing out of the melt with a reduced specific resistance are distributed over almost the entire cross-section of the re-solidifying rod part, so that practically no differences can appear.

Claims (1)

Claim: Method for crucible-free zone melting of a crystalline held vertically at its ends Rod, in particular semiconductor rod, its holders, of which at least one is set in rotation about its vertical axis, relative to one another and to a ring-shaped rod surrounding heating device in the direction of the rod axis with such coordinated Speeds are moved that the thickness of the melt resolidifies Rod part is enlarged beyond the clear width of the heating device, the rotating Holder of the re-solidifying rod part is shifted laterally relative to the heating device, according to patent 1218404, characterized in that after reaching the desired Thickness of the re-solidifying rod part, the holder of this rod part relative to the heating device is continuously moved back and forth laterally. 1 sheet of drawings 809 590/384 8.68 © Bundesdruckerei Berlin