DE1215658B - Process for the production of doped semiconductor material - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

BOIj

German class: 12 g

Number: 1215 658

File number: W 23291IV c / 12 g

Filing date: May 8, 1958

Opening day: May 5, 1966

In the manufacture of semiconductor material for semiconductor components, ζ. Β. Transistors and rectifiers, it is often required that the semiconductor material has uniform electrical conductivity. Since the size of the conductivity in semiconductors depends on the concentration of the conductivity type determining dopant in the semiconductor material depends, the dopant must be evenly distributed.

When the doped semiconductor material crystallizes out of a melt, the given Distribution coefficient of the dopant involved (i.e. the dopant preferably either the liquid one or the solid phase) to an increasing or decreasing concentration of the dopant in the melt. The partition coefficient is given by the ratio of the concentration in the solid phase defined to the concentration in the liquid phase.

To compensate for this enrichment of the dopant, z. B. the crystal pulling The pulling speed of the crystal is changed in such a way that the distribution coefficient also changes. at Another method to compensate for this changing concentration in the melt is the Material to which the melt is depleted, added gradually and in such an amount that the through the amount removed from crystallization is being compensated.

According to another method, a melt of constant volume and constant composition is obtained which are maintained by the use of a second solid-liquid interface becomes (zone melting).

Changes in concentration in grown crystals, which were caused by accidental changes in the growth conditions were previously switched off tries to eliminate the accidental changes itself. For this purpose, mainly steeper temperature gradients were used on the solidification front, extremely small growth rates, extraordinary precise control of temperature and cooling conditions as well as special furnace shapes are used.

In a process for the production of doped semiconductor material with uniform electrical conductivity by directional crystallization of a melt of the semiconductor material which contains at least two dopants 1 and 2 dissolved, no special efforts need to be made to avoid these random changes if - using the The fact that with the dopant concentrations customary in semiconductor bodies, the conductivity properties do not depend on the total amount of dopants present, but on the over-process for the production of doped
Semiconductor material

Applicant:

Western Electric Company,

New York, N.Y. (V. St. A.)

Representative:

Dipl.-Ing. H. Fecht, patent attorney,

Wiesbaden, Hohenlohestr. 21

Named as inventor:

George Sanford Indig, Bronxville, N. Y .;

William Gardner Pfann,

Far Hills, N.J. (V. St. A.)

Claimed priority:

V. St. v. America dated June 25, 1957 (667 956)

shot of the dopant determining the conductivity type compared to the existing dopant of the opposite type are dependent - according to the invention, the dissolved substances are selected so that one the following two properties, viz

a) the conductivity type and

b) the sign of the quantity (1 - Ic),

is opposite for the two solutes and the other is the same for the two solutes, the ratio of the concentration of the solute 2 to the concentration of the solute 1 in the liquid phase in the range from 0.8 to 1.2 times the absolute value of size ii * is chosen when R * is the ratio of the increase in the distribution coefficient of the solute 1 at different crystal growth rates to the increase in the distribution coefficient of the solute 2 at different crystal growth rates and k is the distribution coefficient.

In this way, with comparable growth conditions, the evenness of the specific Resistance of the end product improved by several orders of magnitude compared to a semiconductor material, that contains only one dopant.

In a fusible semiconductor, e.g. B. germanium or silicon, which is the desired Contains conductivity type of the leading dopant 1,

609 567/514

The dopant 2 thus compensates for the changes in the concentration of the excess dopant 1.

Several dopants can also be used as dopant 1 and / or several dopants as dopant 2 be used.

Because the concentration in the main part of the melt is more or less depending on the growth conditions deviates from the concentration at the solidification front, is that present in the crystallizing material Concentration not the one that corresponds to the partition coefficient. this fact has given rise to the use of so-called "effective partition coefficients", the empirical and are numerically closer to one compared to the distribution coefficient. the Dependence of the effective partition coefficient on both the growth rate of the crystal as well as the degree of movement, e.g. B. The degree of agitation of the melt is known and follows in both Cases of the same law.

A change d / in the growth rate (and / or a corresponding change in the degree of movement of the melt) produces the changes Ok ₁ and dk _{2 of} the effective distribution coefficient.

The ratio - ^ - can therefore for all dopant α Ar ₂

combinations are determined. It is set equal to R * . The ratio of the

Concentrations of dopants in the melt -

C ₁

correspond or at least come close.

This applies when the two dopants have opposite conductivity types , both dopants then having values for Jc that are either both greater or both smaller than one or when the two dopants have the same conductivity type, one then having a value for k greater than one and the other has a value for k less than one.

The four possible combinations of these properties with two dopants A and B are listed in the table below:

Table I.

Dopant A
type

L acceptor

2. Donor

3. acceptor

4. Donor

Sign of

45

type

Dopant B

Sign of

Acceptor
Donor
Donor
Acceptor

example 1

55

From test data from Bridgers (Journal of Applied Physics, Vol. 27, pp. 746 to 751 [1956]) for the system germanium plus antimony (a donor) plus gallium (an acceptor) it results that the critical ratio R * has the value 0.14 at a growth rate / of 0.0025 cm / sec for a pulled crystal rotated at 144 revolutions per minute. Thus the ratio is the

Concentrations of antimony to gallium, - ~, in the

Melt equal to 7, whereby the index 2 should be assigned to antimony.

The desired concentration of dopants in the solid phase Z = k _x C ₁ - Jt ₂ C ₂ is 0.73 · 10 ¹⁴ atoms per cubic centimeter, corresponding to a specific p-type resistance in the solid phase of about 10 ohm-cm Room temperature. The individual values for k that can be taken from the literature under these growth conditions are:

Ai = 0.105 and / c ₂ = 0.0046.

Using the relationship C ₂ = 7 C ₁ , the required value for C _{1 is} given by

0.73 · 10 ¹⁴ = 0.105 C ₁ - 0.0046 · 7 C ₁ ,
C ₁ = 1.0 · 10 ¹⁵ atoms of gallium per cubic centimeter, C ₂ = 7.0 · 10 ^ls atoms of antimony per cubic centimeter.

Example 2

Let us consider a germanium system that only contains gallium as the conductivity-determining dopant contains. The mean growth rate / is 0.0025 cm / sec at a crystal rotation speed of 30 revolutions per minute. Increasing the growth rate by 50% results in one Increase in the gallium concentration in the growing crystal by 25%, which is a conductivity deviation generated by 25%.

Let us now consider a germanium system that contains gallium as dopant 1 and antimony as dopant 2, in amounts such that the difference between the concentrations of the two dopants at an average growth rate of 0.0025 cm / sec and a crystal rotation rate of 30 revolutions per minute leads to the same value for the conductivity as in the above germanium system. The gallium and antimony additions to the melt are as determined by the critical ratio R * according to the above equations. The growth rate of the growing crystal is increased by 50%. Under these conditions, the change in the differential concentration in the growing crystal and the percentage deviation in the conductivity is less than 1%.

Furthermore, consider a germanium system which contains gallium and antimony, the additions being so large that the same differential concentration for gallium results as under the same growth conditions in the first-mentioned system germanium-gallium. This time, however, the addition of gallium and antimony to the melt is such that deviations from the critical ratio R * of up to ± 20% are permitted. The growth rate is now to be increased by 40%. Even under these conditions, the excess gallium concentration in the crystallizing material only deviates by about 6%, as does the conductivity.

Example 3

Let us consider a germanium system that again only contains gallium as the only dopant, where the crystal growth rate is 0.0025 cm / see and the crystal rotation speed is 144 revolutions per minute. An increase in A growth rate of 50% leads to an increase in the concentration of gallium in the growing Crystal of 20%.

Let us now consider a germanium system that contains both gallium and boron as dopants,

in such amounts that the total concentration of the two dopants in the growing crystal at an average growth rate of 0.05 cm / sec and at a crystal rotation rate of 144 revolutions per minute is such that a crystal of the same conductivity as in the germanium system described above - Gallium is produced. The gallium and boron additions are such that the boron concentration in the liquid phase divided by the gallium concentration in the liquid phase equals R * (numerically equal to 0.0038). An increase in the growth rate by 50% results in a conductivity deviation in the growing crystal of less than 2%.

Let us also consider a germanium-gallium-boron system in which the gallium and boron additions to the melt are such that the same conductivity results as in the germanium-gallium system described above under the same growth conditions. The gallium and boron additions to the melt are chosen this time so that deviations from the critical ratio R * of up to ± 20% are permitted. Even under these conditions, an increase of 50 ° / _{0 in} the growth rate only results in a conductivity deviation in the growing crystal of about 5 ° / 0-

Examples 2 and 3 show that a deviation of the ratio of the concentrations of dopants 1 and 2 in the melt from the critical value R * does not result in an ideally compensated product, as this crystallizes out of a melt for which the ratio R * applies , but nevertheless represents a significant improvement over the use of only a single dopant. For the usual two-doped system of the invention, 0.8 R * to 1.2 R * represents a reasonable working range of the ratio R. It should be noted, however, that deviations outside of the specified range still result in somewhat improved conductivity uniformity .

The conditions required for dopants 1 and 2 according to the invention are, for. B. at fulfills the following combinations:

45

■ G Table II Dopant 2 Main ingredient Dopant 1 antimony Germanium gallium arsenic Germanium Indium antimony Germanium Indium antimony Silicon gallium boron Silicon arsenic boron Silicon phosphorus boron Germanium gallium cadmium Indium antimonide zinc

55

Even if the method is based on random changes in the rate of growth over time has been described, it can also be used with success in stationary, non-uniform conditions become: if z. B. a temporally constant, but spatially different degree of agitation in the If melt is present in front of the solidification front, the presence of a compensation dopant is ensured for the same reasons a uniform resistivity over the whole Solidification front, because, as mentioned, the change in the distribution coefficient with the degree of movement the melt follows the same regularity as the change in the distribution coefficient with the Growth rate, and because both changes are independent of each other to a good approximation are, so the total change is a complete differential that results from the sum of the corresponding partial changes composed. The expression "dependence on the rate of growth" and the like should therefore be understood in this generalized sense.

Claims (6)

Patent claims: 1. Process for the production of doped semiconductor material with uniform electrical Conductivity through directed crystallization of a melt of the semiconductor material, which is at least contains two dopants 1 and 2 dissolved, characterized in that the dissolved Substances are chosen so that one of the following two properties, namely a) the conductivity type and b) the sign of the quantity (l-k), is opposite for the two solutes and the other is the same for the two solutes, the ratio of the concentration of the solute 2 to the concentration of the solute 1 in the liquid phase in the range from 0.8 to 1.2 times the Absolute value of the size R * is chosen if R * is the ratio of the increase in the distribution coefficient of the solute 1 at different crystal growth rates to the increase in the distribution coefficient of the solute 2 at different crystal growth rates and k is the distribution coefficient. 2. The method according to claim 1, characterized in that germanium as the semiconductor material and the solute 2 used is antimony. 3. The method according to claim 1, characterized in that the semiconductor material and silicon as solute 2 antimony is used. 4. The method according to claim 1, characterized in that the semiconductor material and silicon boron and phosphorus are used as solutes. 5. The method according to claim 1, characterized in that germanium as the semiconductor material and boron and gallium are used as solutes. 6. The method according to claim 1, characterized in that indium antimonide as the semiconductor material and zinc and cadmium are used as solutes. Considered publications:
Belgian Patent No. 528,916;
J. appl. phys., 1956, pp. 746 to 751. A priority document was displayed when the registration was announced. 609 567/514 4.66 © Bundesdruckerei Berlin