DE1175445B - Process for the formation of preferably narrow orientation facets on a semiconductor single crystal rod - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Cl .:

German class:

Number:
File number:
Registration date:
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40d-3 / 00Pai

New

1175 445
115852 VI a / 40d
December 30, 1958
August 6, 1964

The invention relates to a method for forming preferably narrow orientation facets a semiconductor single crystal rod, in particular made of germanium, which preferred crystal faces, in particular [lll] crystal surfaces, make it visually recognizable during the manufacture of the rod Pulling from the melt at the temperature of the melting point of the semiconductor.

Most of the bars have sections of the surface that can be referred to as "flats". A closer look at these flats reveals that they consist of a multitude of stages, similar to the Sequence of steps of a staircase, in which the step treads of largely flat, reflective Surfaces or facets are formed which run parallel to a [III] plane. The flattening a rod consists of one, two or up to several hundred facets.

It is already a method of orienting one single crystal rod has been proposed (German Patent 1 108 944), which in connection with cutting the rod into semiconductor bodies for semiconductor components such as diodes and transistors, is used, which have certain planes parallel to certain crystallographic planes. This previously proposed method includes the use of optical reflections on the Surfaces of small areas or facets of the rod.

Difficulties were encountered in using this method in that not all of the rods were used Facets showed. According to the earlier German patent 1 108 944 it is then necessary by application selected etching processes to produce facets.

A well-known method of making single crystal rods for the fabrication of semiconductor devices, like diodes and transistors, consists in putting a seed crystal in the mother melt, z. B. of germanium, and that one then slowly pulls the seed crystal out of the melt, at the same time the melt is largely kept at the melting temperature of the material will. As a result, it grows on the crystal nucleus in accordance with the crystallographic orientation of the nucleus a crystal. In general, it is advantageous if the drawing direction is as precise as possible with a desired crystallographic axis is kept coincident.

Several have an effect on the formation of the orientation facets during the manufacture of a rod Factors. An important factor is the particularity of the furnace in which the rod is produced.

Method of forming preferably
narrow orientation facets on one
Semiconductor single crystal rod

Applicant:

IBM Germany Internationale Büro-Maschinen Gesellschaft mb H.,
Sindelfingen (Württ), Tübinger Allee 49

Named as inventor:
James Smart Hanson,
New York, NY (V. St. A.)

Claimed priority:

V. St. v. America December 31, 1957

(706449)

The ovens for making drawn rods usually tend to form cylindrical rods. Man has found that some ovens provide bars which are almost entirely cylindrical, but which are Facets are missing. The specifics are apparently determined by the furnace design, and it is impossible to predict immediately before the furnace is built and put into operation whether its construction is carried out in the sense of a requirement for faceting.

Another factor affecting faceting is an excessive angular error between the direction in which the rod is pulled out of the Melt and the desired crystallographic axis of the rod. Bars made in this way have a lot few or no facets at all.

The object on which the invention is based is now to provide an improved method of formation of orientation facets on a semiconductor single crystal rod during the manufacture of the rod to create by pulling from the melt. This process should be independent of the furnace design and larger angular errors between the pull axis and the preferred crystal axis direction can be operated with success.

♦ 09 639/303

A particular object of the invention is to provide a method with which facets for any desired pull shaft can be produced.

For a process for the formation of preferably narrow orientation facets on a semiconductor single crystal rod, in particular from germanium, which has preferred crystal faces, in particular [III] crystal faces, Make it visually recognizable during the manufacture of the rod by pulling it out of the Melt at the temperature of the melting point of the semiconductor, the invention consists in that after reaching the desired length of the drawn single crystal rod in the drawing process rapid reduction in the temperature of the melt by about 10 to 20 ° C. and / or by reducing it the pulling speed caused an expansion of the interface at the lower end of the rod and the semiconductor single crystal is then suddenly removed from the melt.

It is essential that the conditions or states are changed during crystal formation, before the crystal is pulled from the melt, so as to expand the surface in an outward direction of the crystal, which is usually cylindrical at the bottom. However, this expansion should be quite small, e.g. B. about 0.13 to 0.25 mm in radial width. This becomes beneficial in that desired extent by a rapid and sufficient lowering of the temperature of the Melt reached for a long enough time. For some materials, the crystal expansion can also be formed by reducing the pull rate of the crystal from the melt.

The invention is explained in more detail with reference to the drawings.

F i g. 1 is a geometric representation of an octahedron, the faces of which are the [lll] crystal faces reproduce;

F i g. 2 shows a schematic representation of the device which is used for the optical orientation of the single crystal rod is used;

F i g. Fig. 3 is a schematic illustration for a common crystal pulling process;

F i g. 4 is a schematic illustration for a preferred method step for carrying out the inventive concept;

F i g. 5 shows a further and essential method step according to the invention;

F i g. Figure 6 shows, in elevation and partly in section, a single crystal rod made in accordance with the invention was produced;

F i g. 7 shows a part on an enlarged scale the rod of Figure 6;

Fig. 8 gives a detail from the plan of the rod shown in Fig. 7 again.

In Fig. 1 an octahedron is shown, the corners of which are labeled A, B, C, D, E and F. All surfaces of such an octahedron correspond to the [III] crystallographic planes. The planes determined by the quadrangles ABDE, ACEF and BCDF are known under the name crystallographic [100] planes. The octahedron shown in Fig. 1 can be viewed as the representation of an ideal perfect crystal made of certain substances including germanium.

During the formation of the crystal from any crystallized substance, it tends extremely easily to become in certain directions to grow. In the case of germanium, it tends to grow in directions which receive the [lll] planes as outer surfaces. When growing germanium crystals for For transistors, it is essential that the rods are single crystalline; that is, they have a single crystal lattice follow through the entire crystal. The process for the production of germanium crystals, which are constantly in use, are in particular because of their adaptability for the Production of monocrystalline structures has been selected. While those produced by this process Crystals occasionally have polycrystalline components, which in the case of the transistor are rejected had to separate out, the main parts of the crystals so produced are nonetheless monocrystalline.

It is essential that some transistors be made with certain faces parallel to a [III] face of the crystal. To ensure such parallelism, the location of the [III] surfaces can be precisely determined.

An axis that is perpendicular to a [III] surface is hereinafter referred to as a [III] axis. In Fig. 1, the Y-Y ' axis is such an axis because it is perpendicular to the surface ABC . Note that there is a set of three planar surfaces which are equated to the triangles ACD, ABF and BCE and which, when the [III] axis is extended, intersect at the same point and at equal angles with the [III] axis at that point form. This angle is approximately 19% ° and is indicated in the drawing as angle α.

Another set of flat surfaces, which are marked by the triangles CDE, BEF and ADF , intersects the [Hl] axis at point P ' with equal angles <* when elongated. If a bundle of light rays is directed onto the crystal and the crystal is slowly rotated about an [III] axis, the light rays reflected from the three surfaces at the same angle to this axis will follow the same paths when the crystal rotates. By defining three light-reflecting facets on the crystal surface in such a way that the same target is hit when the rod is rotated about a given axis, the axis of rotation can be arranged to coincide with the [III] axis. When cutting the crystal perpendicular to this axis of rotation, it can be ensured that each cube cut out of the crystal for transistor production has surfaces which lie parallel to a [Hl] plane.

FIG. 2 shows a crystal rod 1 which is inserted into an optical device for determining the [III] axis of the crystal is incorporated. At one end of the crystal is a shaft 2 with sealing wax 3 or Cement or other suitable means. The shaft 2 is in a cylinder 4 through two sets 5 and 6 held by three screws each. The cylinder 4 rests in a pair of V-shaped support frames 7 and 8, so that the cylinder is freely rotatable about its geometrical axis. This holding device including of the cylinder and the screw sets 5 and 6 allow the geometrical axis of the rod 1 to adjust or tilt with respect to the axis of rotation of the cylinder 4. About the setting or the location the [lll] axis of the crystal 1 to be determined light beam directed from a suitable source

len or direct sunlight via a mirror against the facets on the crystal 1 and from there to a receiver 10 reflected. When three facets at different points on the surface of one Crystals can be found whose reflections hit the target 10 when the crystal is rotated then it is determined that the crystal rotates about an [III] axis.

The crystal and its holder are constructed so that the light comes from a suitable collimator is reflected from one of the required three surfaces on the crystal towards the target 10. Of the When the cylinder is rotated by approximately 120 °, the crystal is then turned around to make the next flat one Position the surface for reflection. The position of the reflected light on the receiver 10 will be an indication of the amount and direction in which the crystal's [III] axis has pivoted must be in order to bring them parallel to the axis of rotation of the cylinder 4. Adjusting the two Screw sets 5 and 6 will make this shift. The crystal is rotated again, and although on the third flat surface, the position of the reflected light on the receiver 10 is again observed and a precise adjustment of the rod's crystallographic axis is made again.

This continues until a point of light reflected from each of the three flat faces of the row after hitting the same point on the interceptor 10, when the cylinder 4 is rotated.

A common crystal pulling process is shown in FIG. A seed crystal as shown at 11 is introduced into a melt 12 made of the same material. The melt is in a crucible 13, the material of which is chosen so that it does not contaminate the melt. The crucible is in brought a furnace, the temperature of which is kept at the melting point of the material. Of the The seed crystal is then slowly rotated and slowly pulled out of the melt. When pulling out of the crystal nucleus, the material recrystallizes from the melt or grows on the crystal nucleus, so that a wide, usually cylindrical, crystal rod as shown at 14 is formed.

As soon as the crystal 14 has reached the desired length, according to the invention, the temperature the melt suddenly by a sufficient amount, e.g. B. 10 to 20 ° C, reduced. this runs on a very sudden increase in the diameter of the rod at the solid-liquid interface and forms a widening at the bottom of the rod. This lowered temperature is held until the expansion is a desired one has reached radial width, preferably in the amount of 0.13 to 0.25 mm. As soon as the requested Once the size has expanded, the crystal is suddenly lifted from the melt (cf. Fig. 5).

In common crystal pulling processes, the growing rod is mainly in or light below the melting point of the material, while the melt is usually slightly above that temperature is held. This is best done by reducing the amount of heat supplied by an amount which depends on the furnace design and other factors. It is considered that a decrease in temperature the melt from 10 to about 20 ° C gives the best results. This drop in temperature easily causes expansion, but does not endanger the recrystallization of the melt in the crucible. The temperature used must remain above the melting point of the material for this purpose.

While it is of course impossible to determine exactly what is in the liquid-solid boundary happens between the rod and the melt 12, it can be assumed that there is a strong There is a tendency for the crystal to grow at that boundary in directions which are preferred Search to get [lll] levels. Hence, those coinciding with those planes exist Facets entirely at the liquid-solid boundary of the crystal rod. When the crystal slowly comes out of the Melt is pulled, as in the case of the earlier crystal pulling technique, these facets are by flattening of the lower end of the crystal obscured. By suddenly pulling out the stick after the expansion is formed, the facets are preserved.

The facet formation is greatly increased by the described method according to the invention, even for drawing directions which are far from any crystallographic axis.

The increase in the rate of growth, which - albeit otherwise undesirable - through this expansion technique is made necessary is limited to the lower end of the rod. This End becomes undesirable in common semiconductor technology because of crystallographic disturbances and Resistance changes eliminated.

Although in the embodiment of the present invention described above, the extension by Lowering the temperature of the melt is achieved, it is also possible to expand it Variation of other melting states, e.g. B. by lowering the drawing speed or by simultaneous reduction of the temperature and the drawing speed to achieve.

F i g. 6 shows a crystal 14 that is in accordance is bred with the present invention. This has an expansion 15, which is at the lower periphery is formed. FIG. 7 shows the crystal 14 and the expansion 15 according to FIG. 6 in greatly enlarged scale. The facet appears here at 16. FIG. 8 is a plan view of the Crystal according to FIG. 7 again and shows the facet 16 as it appears from below.

It is essential that the facets become narrow for the orientation process described above. The facets should preferably be 2.38 to 3.18 mm long and no more than 0.25 mm wide. Ever the narrower the dimensions, the more precise the orientation of the rod generally becomes.

After a single crystal rod is formed according to the method described and its axis [111] has been set up precisely, it can then be used for any desired angular orientation using a goniometer or the like. Set and cut out semiconductor bodies, the surfaces of which have any desired angular relationship to the crystallographic axis.

If you use the method described, you get facets that are reliably effective are in the optical orientation process, regardless of the furnace design and without Consider the angle between the direction of drawing and the various crystallographic axes.

Claims (2)

Patent claims: 1. Process for the formation of preferably narrow orientation facets on a semiconductor single crystal rod, in particular from germanium, which are preferred crystal surfaces, in particular [III] crystal surfaces, make them visually recognizable during the manufacture of the rod by drawing from the melt at the temperature of the melting point of the semiconductor, thereby characterized in that after reaching the desired length of the drawn single crystal rod in the drawing process by rapid Lowering the temperature of the melt by about 10 to 20 ° C and / or by lowering it the pulling speed caused an expansion of the interface at the lower end of the rod and thereafter the semiconductor single crystal is suddenly taken out of the melt. 2. The method according to claim 1, characterized in that the sudden drop in temperature the mother melt is maintained until the expansion of the single crystal rod at the liquid-solid boundary layer an amount of 0.13 to 0.25 mm, measured radially, has reached. Considered publications:
British Patent Nos. 706 849, 769 426. 1 sheet of drawings 409 639/303 7.64 © Bundesdruckerei Berlin