DE1261119B - Process for pulling NPN or PNP silicon or germanium single crystals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

BOIj

German KL: 12 g -17/18

Number:
File number:
Registration date:
Display day:

1 261119
K39630IVc / 12g
January 9, 1960
15th February 1968

Process for pulling NPN or PNP silicon or germanium single crystals from a Melts are known, with a redoping in each case to achieve the layers of changing conductivity the melt takes place. Since the redoping takes place through the addition of impurities, this increases in each case the concentration of contaminants in the melt, so that after this process the melt does not can be used repeatedly.

The so-called step drawing is also known, where layers of different conductivity are used obtained by changing the pulling speed. This effect is based on the fact that the segregation constant of the P-impurity and the N-impurity in each case depends on the pulling speed. The line type each zone depends on the size of the pulling speed and the length of each Zone from the time during which the relevant pulling speed is maintained.

When this process is carried out, the impurities are added to the melt in which they are evenly distributed. This takes place during this distribution of the contaminants in the melt Pulling the single crystal in each case at the intended pulling speed. At least during the initial period the distribution of impurities within the melt changes in the sense of each drawing stage the setting of a state of equilibrium. This means that the contaminant concentration is over the Cross-section of the single crystal changes, so that in the finished single crystal, the impurity profile over the Cross-section is different. As a result, have semiconductor bodies cut out of the single crystal different properties, in particular a different base thickness, depending on which one Cross-sectional area these semiconductor bodies are cut out. Through the occurring in practice Diffusion results in a further non-uniformity of the impurity profile over the cross-section.

In a process for pulling NPN or PNP silicon or germanium single crystals from a Donors and acceptors containing melt using different successive Pulling speeds, whereby initially a seed crystal of the first conductivity type with the Melt brought into contact and after production of the intermediate zone of the opposite conductivity type is drawn from the melt in such a way that the conductivity type that was initially present is generated again is, but homogeneous single crystals result within the entire cross section, if according to the invention the intermediate zone at the drawing speed

Method of pulling NPN or
PNP silicon or germanium single crystals

Applicant:

Kabushiki Kaisha Hitachi Seisakusho, Tokyo

Representative:

Dr.-Ing. E. Meier, patent attorney,

8000 Munich 22, Widenmayerstr. 5

Named as inventor:
Masami Tomono, Tokyo;
Shoji Tauchi, Fujisawa-Shi;
Hiroshi Kodera,
Kogo Sato, Tokyo (Japan)

Claimed priority:
Japan January 22, 1959 (1522),
of May 20, 1959 (15 796)

digkeitO is generated, so that neither a growth nor a melting of the with the melt in contact Brought crystal takes place and the dopants are built into the crystal exclusively by diffusion be, such donor-acceptor pairs are used that the type of The dopant determining the intermediate zone has the larger diffusion constant compared to the other dopant.

According to the invention, essentially only the different sizes of the diffusion constants of the donor-acceptor pairs are used. Before the start of the diffusion stage, the contaminants are uniformly distributed within of the melt, so that over the entire cross section of the single crystal one has the same impurity profile receives. As a result, the middle zone of the multilayer structure is uniform, and their Thickness can be predetermined. In particular, this middle zone can be made very thin.

According to a further development of the method according to the invention, before the intermediate stage is generated first a small part of the single crystal melted.

This melting is preferably carried out by increasing the melting temperature. During this On the one hand, melting takes place uniformly

809 508/327

Distribution of the impurities within the melt, and on the other hand a fresh interface between the solid and liquid phase created, from which the diffusion then proceeds in the manner described. This achieves a further equalization and improvement of the distribution of defects within the single crystal.

example

A single crystal of germanium is pulled up from the melt in the usual way. The pulling speed is then reduced to about 0.1 mm / min and a suitable amount of gallium and antimony is introduced into the germanium melt. The furnace temperature is increased by about 3 to 10 ^° C. at the same time, and 15 to 20 seconds are required to increase the temperature of the germanium melt. During this time the crystal should be pulled up and grow by about 0.03 mm. The crystal melts to a thickness of about 0.2 to 0.5 mm due to the increase in temperature of the melt. The furnace temperature is then held constant for about 20 to 30 seconds so that essentially no further growth or melting of the single crystal occurs. During this time, the impurities from the melt diffuse through the interface between the solid and liquid phase into the single crystal of germanium. Then, the furnace temperature is rapidly lowered at a cooling rate of about 100 ° C./min, and pulling out of the single crystal is completed at high speed. A single crystal is thus obtained in which the collector zone has grown on the characteristic crystal, the N-conductive base zone thereon, which is formed by the diffusion of the antimony from the melt into the collector zone, and the emitter zone has grown on the base zone. Gallium and antimony can also have been added to the germanium melt beforehand.

During the diffusion mainly antimony diffuses from the melt into the single crystal of germanium, because the diffusion constant of antimony in germanium is about 200 times greater than that of Galliums.

Substantially the same procedure is used to manufacture a silicon single crystal. It can e.g. B. an N-type silicon single crystal with a

35 specific conductivity of 1 μcm, which contains antimony as an impurity, can be used as a seed crystal and a silicon melt to which gallium and arsenic has been added in uniform distribution. Since the diffusion constant of gallium in the silicon crystal is 15 times greater than that of arsenic and since the concentration of gallium in the melt is selected such that its concentration in the crystal is greater than that of the antimony, a P-conductive intermediate zone is created.

By setting a sufficiently high pulling speed, the N-conductive emitter zone then becomes which is due to the higher segregation constant of arsenic.

Claims (2)

Patent claims: 1. Process for pulling NPN or PNP silicon or germanium single crystals from a Donors and acceptors containing melt using different successive Pulling speeds, whereby initially a seed crystal of the first conductivity type with the Melt brought into contact and after making the intermediate zone of the opposite Conductivity type is drawn from the melt in such a way that again the conductivity type present at the beginning is generated, characterized in that the intermediate zone at the drawing speed 0 is generated so that neither growth nor melting of the crystal brought into contact with the melt occurs and the dopants are incorporated into the crystal exclusively by diffusion, wherein such donor-acceptor pairs are used that the type of intermediate zone determines Dopant has the larger diffusion constant compared to the other dopant. 2. The method according to claim 1, characterized in that before generating the intermediate stage first a small part of the single crystal is melted. Documents considered: German Patent No. 964 708; U.S. Patent No. 2,851,341. 809 508/327 2.68 © Bundesdruckerei Berlin