US3908586A

US3908586A - Apparatus for doping semiconductor rods during floating zone melt processing thereof

Info

Publication number: US3908586A
Application number: US447745A
Authority: US
Inventors: Ludwig Sporrer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1973-05-28
Filing date: 1974-03-04
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30
Also published as: DE2327085A1; BE815609A; JPS5020907A; DE2327085C3; IT1012869B; JPS5336403B2; DE2327085B2; DK286274A

Abstract

An apparatus for controllably doping semiconductor rods during a floating zone melt processing thereof which includes a selectively movable doping nozzle positioned in the vicinity of the induction heating coil and having an exhaust opening movable toward and away from the semiconductor rod.

Description

United States Patent Sporrer 1 Sept. 30, 1975 154] APPARATUS FOR DOPING [56] References Cited SEMICONDUCTOR RODS DURING UNITED STATES PATENTS FLOATING ZONE MELT PROCESSING 2550.899 5 1951 Zsamboky 239/587 x THEREOF -3.141848 7/1964 Enk et al. 75/65 ZM X Inventor: Ludwig p Munich n y 3,606,171 9/1971 Voelker 1. 239/587 [73] Assignce: Siemens Aktiengesellschaft, Berlin & FOREIGN PATENTS OR APPLICATIONS Munich Germany 1,017,795 10/1957 Germany 75/65 ZM X 969,903 9/1964 United Kingdom 219/1043 [22] Filed: Mar. 4, 1974 [2H APPL No: 447,745 Primary E.\'aminerMorris ldaplan Attorney, Agent, or Firm-H1ll, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [30] Foreign Application Priority Data May 28. 1973 Germany 2327085 [57] ABSTRACT 7 An apparatus for controllably doping semiconductor [5.] US. Cl ll8/49.l rods during a floating Zone melt processing thereof [5]] Int. CL- lf/LZ which includes a Selectively movable doping nozzle [58] held of Search 1 18/491 positioned in the vicinity of the induction heating coil 118/63, 620, 321; 117/932; 219/l043; 148/189, 187, 186, 174; 75/65 ZM; 166/4 El, 5 El; 239/587; 34/90, 91, 239

and having an exhaust opening movable toward and away from the semiconductor rod.

7 Claims, 2 Drawing Figures U.S. Patent Sept. 30,1975

APPARATUS FOR DOPING SEMICONDUCTOR RODS DURING FLOATING ZONE MELT PROCESSING THEREOF BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to an apparatus for doping semiconductor materials and somewhat more particularly to a crucible-free floating zone melt apparatus which includes a means of introducing a dopant in the vicinity of the zone of melt generated in a semiconductor rod.

2. Prior Art Doping of semiconductor rods generally occurs during deposition of semiconductor material from a gas phase by thermal and/or pyrolytic decomposition of a gaseous compound of the semiconductor material onto a heated rod-shaped carrier member composed of the same semiconductor material. Gaseous compounds of doping materials are mixed with gaseous compounds of semiconductor materials and both types of compounds decompose at the carrier member. The resulting crystal rods are polycrystalline in nature and must be transformed by a subsequent zone melting process into a monocrystalline form. During such transformation, the concentration of doping material often changes in an uncontrollable manner so that greater concentrations of doping material has to be provided in the initial polycrystalline rod if a desired concentration of dopant is to be attained in the final monocrystalline rods, which sometimes is attainable only after several passages of a melt zone through the rod. These procedures are very time-consuming and extremely inaccurate. Further, the prior art apparatus used to carry out these procedures are extremely expensive to operate and achieve, at best, only partially satisfactory results.

A method and device for doping semiconductor materials during floating zone melt processing thereof are described in German Offenlugungsshrift 2,016,574 and 2,020,l 82 which generally comprise transporting a gaseous doping material compound, for example, phosphorus nitrilochloride by means of a carrier gas stream directly to the melt zone on a rod. The gas is transported through a passageway within the induction heating coil and the exhaust of the passageway is permanently located at the innermost surface of the coil.

The aforesaid device necessarily has a fixed relation between the gas exhaust nozzle and the coil. However, the distance between a melt zone and an exhaust nozzle has a bearing on the concentration and/or distribution of dopant being incorporated within a rod. Accordingly, this type of device is not suitable for situations where a change in the diameter ofa semiconductor rod occurs during the treatment process. Changes in rod diameter occur, for example, in compression-stretch processing and this type of device fails to provide means of adjusting the distance between the gas exhaust nozzle and a melt zone so that it is not possible to control the concentration of doping material in a changing diameter semiconductor rod.

SUMMARY OF THE INVENTION The invention comprises an apparatus which provides an adjustable dopant concentration along a rod undergoing zone melt treatment in a simple and economical manner, even in a changing diameter semiconductor rod.

It is a novel feature of the invention to provide a zone melt apparatus which includes a means of adjusting the distance between a gas nozzle exhaust opening within the reaction chamber of the apparatus and a semiconductor rod mounted within the reaction chamber.

It is a further novel feature of the invention to provide an apparatus as described above wherein a distance scale is located on the gas exhaust nozzle and which is preferably calibrated in rod diameter units.

It is yet a further novel feature of the invention to provide an apparatus as described above wherein the gas exhaust nozzle is movably attached to a gas line. In certain embodiments, the exhaust nozzle is slidably attached to the gas line and in other embodiments, the nozzle is threadingly attached to a gas nozzle.

It is another novel feature of the invention to provide an apparatus as described above wherein a gas line is fixedly attached toan induction heating coil and the gas exhaust nozzle is movably attached to the gas line. Manual or machine means may be used to move the nozzle relative to the gas line.

Other and further objects of the present invention will be apparent from the following description and claims, and are illustrated in the accompanying drawings which, by way of illustration, show preferred em bodiments of the present invention and the principles thereof and what is now considered to be the best mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is apartial schematic illustration of an apparatus embodying the principles of the invention in an operational environment; and

FIG. 2 is a partial sectional view of another embodiment of apparatus constructed in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention provides a crucible-free floating zone melt apparatus which includes a means of adjusting the distance between the gas exhaust opening within the reaction chamber of the apparatus and a semiconductor rod mounted within the reaction chamber.

A zone melt apparatus incorporating the principles of the invention provides an adjustable concentration of dopant in a semiconductor rod undergoing zone melt treatment, even if the rod undergoes a change in its diameter dimensions during the treatment, such as during a compressionstretch process.

A preferred exemplary embodiment of the invention comprises a floating zone melt apparatus which includes a gas line fixedly attached, as by welding or soldering, to an induction heating coil within the reaction chamber of the apparatus and a gas exhaust nozzle movably attached to the gas line. This arrangement establishes the location of the gas exhaust nozzle relative to the induction heating coil and allows an operator to selectively adjust the distance between the exhaust opening and a zone of melt on a semiconductor rod annularly encompassed by the coil. Further, this arrangement allows the gas line to be combined with conduits of the coil which carry current and/or a heat-exchange medium to the coil. In such arrangements, the gaseous dopant compounds flowing through the gas line are maintained at a temperature below that of the melt and thus cannot decompose prematurely.

In certain preferred embodiments of the invention, the gas exhaust nozzle is moved as desired from outside the zone melt reaction chamber so that a uniform or non-uniform (i.e., stepped) dopant concentration can readily be achieved along the length of a rod. Means for moving the exhaust nozzle may be manual or mechanical, such as by a motor. Accordingly, the invention makes it possible to automatically carry out a selected doping program.

Preferably, the gas exhaust nozzle utilized in the practice of the invention is comprised of a material selected from the group consisting of quartz, a ceramic and a high melting metal, such as steel,

Apparatus constructed in accordance with the principles of the invention provides a simple and reproducible means of achieving, in a single passage (of the melt zone) of semiconductor rods having different rod diameters, a constant and exactly controllable concentration of dopants in semiconductor rods treated thereby. The apparatus of the invention is useful for zone melt treatment in a protective gas atmosphere or in a vacuum environment and the apparatus may be used with any desired doping material.

Referring now to FIG. 1 wherein a partial schematic view of a zone melting apparatus Zm is illustrated. All portions of such apparatus which are not essential to the understanding of the invention, such as carrier gas and doping material sources, rod and coil mounting means, reaction chamber walls, etc. have been omitted for the sake of clarity.

As shown, a semiconductor rod 1 is composed of a stock rod portion 2, a recrystallized or treated rod portion 3 and a melt zone 5 interconnecting rod portions 2 and 3. The rod is annularly encompassed at an axial portion thereof by an induction heating coil 4, which may be a multi-wound coil or a single wound fiat coil.

A gas line 7 is positioned in the vicinity of the induction heating coil 4 and is provided with a movable gas exhaust nozzle means 6, for example, comprising aquartz tube. A stream 8 of a gas comprised of a carrier gas, such as argon, and a doping material compound, such as phosphorus nitrilochloride, is fed from a source (not shown) at a select flow rate through gas line 7 and out exhaust opening 10.

In the embodiment shown, nozzle means 6 is movably connected with gas line 7 by thread means 9 so that the exhaust opening 10 can be axially moved toward and away from melt zone 5. The invention also includes embodiments having a slidable connection between the gas line and the nozzle means.

The gas line 7 may be fixedly attached to the induction heating coil 4 or it may be secured to a reaction chamber wall 13 (FIG. 2) by a gas impermeable seal member 19.

The nozzle means 6 is provided with a scale (vernier) 11 along a visible surface thereof for an exact indication of the distance the exhaust opening 10 is from the melt zone 5. Preferably, the scale 11 is calibrated in rod diameter units. An indicator 17 is attached to an end portion of gas line 7 and has a pointer which cooperates with scale 11 to show the exact position of opening 10 so that an operator may make whatever adjustments are desired. Accordingly, an optimum distance between the exhaust opening and the surface of a semiconductor rod can be easily attained for various rod diameters. This allows the concentration of doping material along a rod to be exactly as desired and the specific resistance of, for example, a doped silicon monocrystalline rod produced with the apparatus of the invention substantially corresponds to a given specification.

FIG. 2 illustrates an embodiment of the invention which includes a mechanical drive means 12 for effecting a desired movement of nozzle means 6. As illus trated, drive means 12 is capable of axial and rotational movement. A shaft 14 is coupled with drive means 12 outside a zone melt reaction chamber wall 13 and passes through wall 13 via seal member 19 so as to be movable relative to the wall. A gear 15 is fixed to the end of shaft 14 for cooperating with a pinion gear 16 fixed onto nozzle means 6. The gear 16 may be a pinion worm gear or a bevel gear. If desired, the shaft 14 may also be moved manually. The scale 11 is calibrated in rod diameter units and in cooperation with indicator 17 mounted on gas line 7 allows an operator to precisely position nozzle opening 10 as desired in relation to the surface of a semiconductor rod.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

I claim as my invention:

1. In an apparatus for doping a semiconductor rod during a floating zone melt processing thereof which includes means attached to the ends of said rod for vertically supporting said rod, an induction heating coil arranged to annularly encompass said rod and generate a melt zone on said rod and a doping nozzle arranged in the vicinity of said heating coil for guiding a doping material to the melt zone, the improvement comprising in that said doping nozzle is comprised of a stationary portion and a movable portion telescopically interconnected with one another, said movable portion having an exhaust opening facing said rod and having a visible vernier scale on a surface thereof, said scale being calibrated in accordance with rod diameter units and comprising indicator means for the spacing of nozzle discharge into said melt zone upon telescopic adjustment of said nozzle portions.

2. In an apparatus as defined in claim 1 wherein said movable portion of the doping nozzle is slidably interconnected with said stationary portion thereof.

3. In an apparatus as defined in claim 1 wherein said movable portion of the doping nozzle is threadingly interconnected with said stationary portion thereof.

4. In an apparatus as defined in claim 1 wherein said stationary portion of the doping nozzle is relatively rigidly attached to the induction heating coil at a surface of said stationary portion adjacent said movable portion of the doping nozzle.

5. In an apparatus as defined in claim 1 wherein said movable portion of the doping nozzle is actuatable from a position remote from said movable portion.

6. In an apparatus as defined in claim 5 wherein said movable portion of the doping nozzle includes a gear mounted on a surface thereof and an actuating means is provided in a cooperating relation with said gear for selectively moving said movable portion.

7. In an apparatus as defined in claim 1 wherein said gas nozzle is composed of a material selected from the group consisting of quartz, a ceramic and a high melting metal.