Improved Separation Of The Deposition Mandrel From A Vapor Phase Deposited Semiconductor Body

Abstract

An at least unilaterally open, hollow body of semiconductor material, such as a tubular or cup-shaped body for example, is produced by precipitating the semiconductor material from a gaseous phase upon a heatable carrier consisting of a different material whose thermal coefficient of expansion is greater than that of the semiconductor material. During the process the carrier is heated to a temperature at which the difference in thermal expansion causes fissures or cracks to appear in the precipitated semiconductor material. Thereafter the precipitation of semiconductor material is continued until the cracks are closed by the further growth of precipitating semiconductor material. Ultimately the carrier is removed by pulling or dropping it out of the resulting cooled semiconductor body.

Description

My invention relates to producing an at least unilaterally open, hollow body of semiconductor material by precipitating the semiconductor material from a gaseous compound or phase of the material upon a heatable carrier structure consisting of a different material, and removing the carrier upon precipitation of a sufficiently thick layer of semiconductor material. The semiconductor body thus produced may have an annular or tubular shape open at both sides, or it may consist of a unilaterally closed tubular or cup-shaped structure. Thus the accompanying drawing exemplifies in FIG. 1 a tubular body 1 of silicon or other semiconductor material shown in perspective, and FIG. 2 shows in cross section an example of a cup-shaped body or crucible boat made of such a material.

A method of this type proposed previously requires removing the carrier structure from the hollow semiconductor body produced thereupon, by burning the carrier out of the body.

It is an object of my invention to devise a different process of manufacture which, while generally involving a precipitation method of the above-mentioned type, affords removing the carrier structure without endangering the soundness or quality of the semiconductor layer produced thereupon.

Another object subsidiary to the one just mentioned is to enable the removal of the carrier structure from the precipitated hollow semiconductor body without destruction or damage to the carrier structure so that it remains applicable for performing one or more further precipitation processes.

To achieve these objects, and in accordance with my invention I precipitate the semiconductor material from the gaseous phase upon a carrier consisting of a different material whose thermal coefficient of expansion is greater than that of the semiconductor material. During the precipitation process, or at some intermediate stage, I heat the carrier to an elevated temperature at which the difference in expansion occurring between the carrier and the semiconductor body causes fissures or cracks to occur in the precipitated semiconductor material. Thereafter I continue the precipitation of semiconductor material until the further growth of precipitated material closes and thus eliminate the cracks. Ultimately I remove the carrier out of the resulting hollow semiconductor body. This is done, for example, by simply pulling the carrier out of the body or by permitting it, when cooled, to drop out of the body.

For the purpose of the invention the carrier preferably is made of graphite or the like industrial carbon material.

According to another preferred feature of the invention I first heat the carrier to the processing temperature required or advantageous for the precipitation of the semiconductor material from the gasous phase until the precipitated layer has reached a given thickness at which the semiconductor body remains sufficiently self-supporting and coherent despite the subsequent formation of fissures or cracks. I then temporarily raise the temperature of the carrier above that employed during the precipitation stage with the result of causing the cracks. Thereafter I again reduce the temperature of the carrier to the one employed during the first precipitation stage, thus causing a further growth of semiconductor material upon the previously precipitated semiconductor layer to make the cracks grow closed.

The method according to the invention is performed by mounting a carrier, for example a rod or other structure of graphite, in a hermetically closed reaction vessel and then heating the carrier within the vessel while simultaneously passing a gaseous compound of the semiconductor material into the vessel. In these respects the process and the processing equipment need not differ from the processes and equipment known for the production of electronic silicon material, described for example in the U.S. Pat. No. 2,999,735 of Reuschel, U.S. Pat. No. 3,146,123 of Bischoff, and U.S. Pat. No. 3,042,494 of Gutsche.

The accompanying drawing on which;

FIGS. 1 and 2 show a tubular body 1 and a cup-shaped body 2, respectively, as described above, and

FIG.. 3 illustrates schematically and partly in section a tubular body 1 of silicon precipitated upon a rod-shaped cylindrical carrier 3 of graphite.

During the process the carrier 3 is clamped at both ends and is heated by passing electric current longitudinally through the carrier. The heating may also be effected by electric induction heating which is preferably applied for heating the carrier used in the production of a cup-shaped or other unilaterally closed semiconductor body such as the one exemplified in FIG. 2.

When, for example, if silicon is to be precipitated upon the carrier structure, the gaseous phase to be passed into the reaction vessel may consist, for example, of SiHC1.sub.3 mixed with molecular hydrogen H.sub.2. When the carrier of graphite is heated to the precipitation temperature, for example about 1,050.degree. C to about 1,200.degree. C, the introduction of the gaseous mixture into the reaction vessel causes crystalline silicon to precipitate upon the carrier. This pyrolytic precipitation and deposition process is continued until a desired layer thickness of the semiconductor material is attained, this thickness being dependent upon the dimensions of the hollow semiconductor body to be produced. For example, if a unilaterally open tube having an inner diameter of 30 mm and a wall thickness 2 mm is to be produced, the precipitation can be interrupted when a wall thickness of about 1 mm is attained. Then the carrier is heated to a higher temperature. This has the consequence that the carrier structure of graphite expands more than the precipitated layer of silicon due to the fact that the thermal coefficient of expansion of graphite is greater than that of silicon. The difference in expansion causes the silicon layer to crack. The temperature increase during this stage of the process is so chosen that the silicon layer will not completely crack away from the carrier. It has been found advantageous, referring to a tubular semiconductor body of the above-mentioned dimensions, to apply a temperature increase of about 50.degree. to about 100.degree. C. Such a temperature increase has the effect that the inner diameter of the precipitated layer of silicon will slightly widen but the silicon layer will remain a coherent entity.

After the fissures or cracks have thus been formed in the silicon layer, the temperature of the carrier structure can be reduced to a value which may be the minimum at which a further precipitation of crystalline silicon will just remain possible, or the temperature may be maintained at the increased value at which the fissures or cracks have formed in the semiconductor material. Subsequently an additional quantity of crystalline silicon is precipitated until the cracks grow closed.

The precipitation process need not necessarily be interrupted during the stage of increased temperature. The process rather can also be performed so that further silicon will precipitate during the interval of increased temperature.

When the desired ultimate layer thickness is attained, the precipitation process is terminated and the carrier structure together with the precipitated layer of silicon is permitted to cool. Thereafter the carrier structure can be removed from the tubular or other semiconductor body simply by letting the carrier drop out of the opening of the semiconductor body. Due to its weight and somewhat smaller diameter, the carrier structure will readily slide out of the tubular body and can again be used for the production of another semiconductor body.

While the method according to the invention has been specifically described with reference to the production of a tube of silicon, similar structure can be produced in the same manner from germanium, silicon carbide, III-V semiconductor compounds and II-VI compounds. Aside from tubular structures, various other hollow bodies that are open on at least one side are producible in the same manner.

To those skilled in the art it will be obvious from a study of this disclosure, that with respect to shapes, materials and other processing data, my invention is amenable to various modifications and hence may be given embodiments other than those particularly illustrated and described herein, without departing from the essential features of the invention and within the scope of the claims annexed hereto.

Claims

I claim:

1. The method of producing an at least unilaterally open hollow body of silicon which comprises precipitating a layer of silicon from a gaseous compound thereof onto a graphite carrier, the precipitation temperature being in the range from about 1,050.degree.C to about 1,200.degree.C, heating the carrier upon precipitation of the layer of semiconductor material to a temperature of about 50.degree.C to about 100.degree.C above the precipitation temperature, whereby cracks occur in the layer of precipitated semiconductor material, then continuing the precipitation of semiconductor material until the cracks are eliminated by further growth of precipitated semiconductor material, cooling the carrier and pulling the carrier from the resulting hollow semiconductor body without destroying said hollow semiconductor body.

2. The method according to claim 1 which comprises reducing, upon occurrence of said cracks, the temperature of the carrier to a value between 1,050.degree.C and 1,200.degree.C.

3. The method of claim 1 which comprises heating the carrier to the precipitation temperature until the precipitating semiconductor material layer has attained a wall thickness of about 1 mm, then temporarily heating the carrier a 50.degree. to 100.degree.C higher temperature, and thereafter maintaining the carrier at 1,050.degree. to 1,200.degree.C during said continuing precipitation of semiconductor material.