DE1256202B - Process for producing homogeneous, rod-shaped crystals from a melt - Google Patents

Description

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GERMAN

PATENT OFFICE

EDITORIAL

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German class: 12 g- 17/06

Number: 1256 202

File number: N18903IV c / 12 g

Filing date: September 14, 1960

Opened on: December 14, 1967

A rod-shaped crystal made of semiconducting material with a diamond structure is said to be used in Transistors, diodes or photocells are as homogeneous as possible with regard to their specific resistance be. It has been found that in such a rod-shaped, by pulling from a melt or crystal produced by zone melting often has the specific resistance in the transverse directions is not homogeneous and that in particular in a generally centrally located, extending in the longitudinal direction of the crystal extending part the resistivity differs significantly from that in the adjacent Sharing is different. As a result of this phenomenon, hereinafter referred to as "nucleation" the resistivities can if they are in different places on one Cross-section of the crystal can be measured, relative differences of more than 30%, even 50% and have more. Below the relative difference between two resistivities becomes here the ratio, expressed as a percentage, between the difference and half of the sum of these understood specific resistances. The reason for this core formation was not known. It was already proposed to reduce this phenomenon by rotating the growing crystal and / or vibrated, but it has been found that doing so is not sufficiently suppressed.

It has also already been proposed to use single-crystal semiconductor rods in the production Zone melting to melt the seed crystal in such a way that its [III] direction is different from the direction of growth of the crystal.

To now the homogeneity of a rod-shaped single crystal, especially with regard to its specific Resistance to increase and to prevent the occurrence of any nucleation becomes more rod-shaped in manufacturing Crystals from a semiconducting material with diamond structure containing melt through Growing of a single crystal whose [III] directions are different from the growing direction of the crystal are, according to the invention, the seed crystal is oriented so that the [100] and [110] directions, as well as the [111! directions deviate by angles of at least 5 ° from the direction of growth of the crystal.

The invention is explained in more detail below with reference to the drawing, in which

1 shows a device for growing a seed crystal by zone melting without a crucible,

Fig. 2 shows the orientation of the crystal shown in Fig. 1,

Method of making more homogeneous
rod-shaped crystals from a melt

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. EE Walther, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Named as inventor:

Johannes Aloysius Maria Dikhoff,

Eindhoven (Netherlands)

Claimed priority:

Netherlands 18 September 1959 (243 511)

3 shows a device for pulling up a crystal from a melt,

4 shows the orientation of the crystal shown in FIG. 3,

F i g. 5 a device for. Zone melting in an elongated crucible and

F i g. 6 the orientation of the in F i g. 5 schematically represents the seed crystal shown.

In Fig. 1 denotes 1 a silicon seed crystal which is fixed at the top in a holder 2 which rotates about its vertical axis X at a speed of 100 revolutions per minute. A silicon rod 3 arranged vertically along the ΑΓ axis is fastened in a holder 4 at the bottom. Between the rod 3 and the crystal 1 there is a melting zone 5, which is generated by means of a high-frequency coil 6 symmetrically surrounding this zone, the molten material not flowing down due to the high surface tension. The high-frequency coil is moved downward at a speed of 1 mm per minute in the direction indicated by an arrow, the rod 3 gradually melting and the crystal 1 gradually growing into a rod in the vertical direction. The solidification front 7 between the growing seed crystal 1 and the melting zone 5 has a somewhat curved shape that is almost symmetrical with respect to the X axis. The orientation of the crystal 1 is shown in FIG. 2 shown by means of a cube 8, whose

709 708/370

Claims (3)

3 4 Position of that of a cubic unit cell of, for example, the orientation of the given in Fig. 4 Crystal corresponds. The [lll] -direction can be used with 9 be crystal application, which with the help of the draws. It closes an angle of 25 ° with the cube 26 is indicated. The [lll] direction 27 Growth direction 10 of the crystal. The other, lies in the plane of the drawing and closes one [III] directions (not shown) close a 5 'angle of 15 ° with the growing direction 28 of the larger angles with the direction of growth, while the others are crystallographic the [100] directions (according to the edges of the main directions see larger angles with this Cube) and the [110] direction not shown. The crystal obtained gen (according to the surface diagonals of the cube) can in turn be perpendicular to the [III] direction 27 Divide angles of more than 5 ° into sections with the direction of growth io. Will be in such a lock in. In this case, there is no nucleation in the section of the specific resistance on differently growing ones Crystal on. borrowed places measured, it turns out that the The rod-shaped crystal obtained in this way sometimes measured values from one another can be easily distinguished by sawing perpendicular to the [Hl] -, but the relative differences are Divide direction 9 into sections. Will always wear less than 10% in a 15. such a section shows the specific resistance at Fig. 5 shows a likewise not claimed Measured at different locations, it turns out, an apparatus for producing rod-shaped crystals that although the measured values sometimes differ by zone melting, in which a crucible 30 is made differ from each other, but the relative sub-quartz in the form of an elongated boat differences are always less than 10%. 20 horizontally in the longitudinal direction opposite one of the F i g. 3 represents a high-frequency coil 31 surrounding the pre-crucible, which is not claimed here. direction for pulling crystals from a bar. Melt, in which 11 is a crucible made of graphite, a germanium rod 32 is located in the crucible of the crucible so that its [111! -direction that there is an angle of 10 ° with the longitudinal direction of the 14 two cavities 15 and 16 between the crucible 11 and the container. The crucible 30 includes. The orientation of such holder 14 consists of a cylinder 17 with an arranged seed crystal is again piston 18 in FIG des 30 [HI] direction is denoted by 36.
Container 14 is attached and through a The crucible 30 (Fig. 5) is now arranged, rod-shaped intermediate part 20, which is passed through an opening 21 in the disc 12 that the high-frequency coil 31, the contact point between the rod 32 and the seed crystal 33, the container 14 is connected to the interior of the crucible 11, after which the coil is excited. The whole thing is created by a melting zone 37. Then high frequency coil 22 is surrounded so that it can be heated the crucible at a rate of 2 mm per. Due to the presence of the graphite minute with respect to the coil in the direction indicated by a disk 12 with the edge 13 and the cavities 15 arrow, so that the and 16 can the bottom of the crucible 11 additional melting zone the rod 32 in its longitudinal direction Heat can be supplied. The container 14 and the 40 passes through, this rod gradually melting. Channel 19 are completely filled with a melt 23 of Ger- and to a rod-shaped crystal with an orienmanium, which also becomes the crucible 11 up to an orientation according to FIG. Because the heating at the height of only 6 mm from the bottom of the crucible fills the top of zone 37 (FIG. 5) more than at the calculated. A rod-shaped growing Germa underside is, the zone on the upper side is wider niumkristall 24 with a diameter of 2 cm, 45 than on the underside, whereby the solidification front is obtained by the partial growth of a pre-oriented 38 relative to the longitudinal axis of the growing seed crystal , with an equal part of the crystal has an asymmetrical shape at a constant speed of 1 mm per minute and is pulled up on its underside almost perpendicular to the vertical from the melt in the crucible, direction 39, in which the crystal grows while it moves with it a speed of 50 but strongly deviates from this position at the top - 50 revolutions per minute around its Γ-axis. In that the [Hl] -direction 36 of the rotates, whereby it gradually increases further. Because the seed crystal is gradually raised in relation to the direction of growth 39, the piston 18 is gradually raised (FIG. 6) by an angle of 10 ° downwards from the level of the melt in the crucible at a constant level, it is nowhere perpendicular to the height of the Er. 55 starrungsfront 38 (Fig. 5), so that in the growing No nucleation occurs as a result of the additional heating of the bottom of the crystal. Let it be crucible here and due to the small distance between notices that in this case the choice of direction in the bottom of the crystal 24 and the bottom of the [III] axis 36 by a proportion there is at the solidification front 25 the growing small angle deviates from the growing direction, Everywhere crystals are practically vertical heat - 60 is not arbitrary, but in direct transport, while the heat transport is related to the asymmetrical shape of the Ertaler Direction is almost negligible. As a result, the stiff front stands. the solidification front 25 is almost flat and ■ '.- runs practically perpendicular to the growing patent claims everywhere: direction of the crystal. 65 1. Process for producing homogeneous rod In order to prevent nucleation, it is now sufficient to have a shaped crystal made of a semiconducting material at a relatively small angle between one of the melts containing a rial with a diamond structure [lll] directions and the growing direction, so that by growing a single crystal, its [lll] directions from the growing direction of the Crystal are different, characterized that the seed crystal is oriented so that the [100] and [110] directions, as well as the [III] directions at angles of at least 5 ° from the direction of growth of the Crystal differ. 2. The method according to claim 1, characterized in that the seed crystal is oriented in this way becomes that the smallest of the angles between the growing direction and the [lll] directions of the crystal is at least 20 °. 3. The method according to at least one of the preceding claims, characterized in that that the seed crystal is oriented so that the smallest of the angles between the direction of growth and the [III] directions of the crystal is at most 30 °. 1 sheet of drawings