|Publication number||US2876147 A|
|Publication date||Mar 3, 1959|
|Filing date||May 21, 1956|
|Priority date||Feb 14, 1953|
|Also published as||DE1061527B, DE1210415B, US3030194, US3086856, US3216805, US3234012|
|Publication number||US 2876147 A, US 2876147A, US-A-2876147, US2876147 A, US2876147A|
|Inventors||Kniepkamp Heinrich, Ziegler Gunther|
|Original Assignee||Siemens Ag|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Referenced by (33), Classifications (34)|
|External Links: USPTO, USPTO Assignment, Espacenet|
March 3, 1959 H. KNIEPKAMP ET AL ,876,
METHOD OF AND APPARATUS FOR PRODUCING SEMICONDUCTOR MATERIAL Filed May 21, 1956 2 Sheets-Sheet 1 March 3, 1959 H. KNIEPKAMP ET AL 2,876,147
METHOD OF AND APPARATUS FOR pnonucmc SEMICONDUCTOR MATERIAL Filed 14:13:21, 1956 2 Sheets-Sheet 2 United States Patent METHOD OF AND APPARATUS FOR PRODUCING SEMICONDUCTOR MATERIAL Heinrich Kniepkamp and Giinther Ziegler, Karlsruhe,
Germany, assignors to Siemens & Halslre Aktiengesellschaft, Berlin and Munich, Germany, a corporation of Germany This invention is concerned with a method of and apparatus for producing semiconductor material by drawing rodlike bodies from a melt and applyingzone melting to said bodies, all in one workingoperation.
Copending application of Karl Siebertz Serial No. 409,420 filed February 10, 1954, having a common assignee, which describes a method of and apparatus for successively melting and solidifying semiconductor material in zones, applied primarily for purification purposes to an elongated preferably rodlike substantially perpendicularly disposed body fia'stened at its opposite ends, the melting zone being so small that it is supported by the adjacent solidified portions by adhering thereto. The advantage of the procedure is that it does not require a crucible, thereby avoiding contaminations which would otherwise result from the crucible material. The disadvantagewith the rod fastened at its ends--is that only one melting zone can be processed at any time. The procedure is, as compared with zone melting in a crucible, time consuming because it must be repeatedly applied while zone melting by means of a crucible, for example, a carbon well permits simultaneous processing of several melting zones. The simultaneous processing of several melting zones is in principle also possible with the rodlike body perpendicularly held at its ends provided that the rod is additionally supported at intermediate points, but these additional supports must be removed at the instant of passage of the melting zones through the corresponding regions.
The thought underlying the invention resides in recognition of the fact that the purification according to the zone melting process is the more effective the more the structure of the body to be purified approaches that of a monocrystal, the purification being most effective in the case of an ideal monocrystal.
The invention utilizes this fact by applying the zone melting described in the previously mentioned copending application directly and immediately upon drawing of crystals, especially monocrystals, from a crucible, thus combining the zone melting with the drawing in one working operation. The invention thereby contemplates to support the crystal, preferably a monocrystal, drawn from the crucible, at two widely separated points and to subject intervening areas to the zone melting. The operation according to the invention results not only in the advantage already mentioned, of accelerating the purification by the zone melting, but, in a particular embodiment, in giving the possibility to operate the zone melting in a continuous process. The supporting points are thereby to be altered, steadily or abruptly, in accordance with the length of the crystal drawn from the crucible. The speed at which the melting zone is drawn is to be matched to a certain extent with the speed at which the crystal is drawn from the crucible. However, inasmuch as the speed of drawing depends in part on the thickness of the rod, it will in some cases be necessary or suitable to interrupt or to slow down the crystal drawing at least Patented Mar. 3, 1959 for some intervals until the melting zones have been drawn once or several times through a predetermined portion of the rod-shaped crystal.
The. foregoing and other objects and features of the invention will appear from the description which is rendered below with reference to the accompanying schematic drawings, wherein- Fig. 1 shows an embodiment for drawing a crystal rod from a crucible in upward direction; and
Fig. 2 illustrates an embodiment for effecting the drawing of a crystal rod in downward direction.
Referring now to Fig. l, numeral 1 indicates a crucible made for example of graphite, containing molten silicon or germanium 21. The crucible 1 is provided with an extension 2 which is separately heated by means of a coil 3. The crystal 4 is in known manner drawn from the extension 2 in the direction of the arrow 5. Rollers 15 and 16 movably journalled in a bearing 7 are provided to support the upper end of the crystal 4. Numeral 8 indicates a belt extending from a drive roller 9 for rotating the rollers 15 and 16 to rotate the crystal rod 4 in the direction of the arrow 10. The crystal drawing is otherwise effected in known manner.
In accordance with the invention, there is provided a heating device 11, formed as an annulus, adapted to melt a narrow zone of the crystal rod 4. This heating device 11 may be disposed within a casing 26 provided with arms 27 carrying worm wheels 28 meshing with a worm 29, and may be displaced, for example, downwardly, in the direction of the arrow 12, by rotating the worm 29 in the direction of the arrow. The consequently produced melting zone 13 is thereby drawn downwardly along the solidified portion of the drawn monocrystal, effecting purification, and contaminations are deposited at the lower end engaging the flaring mouth 14 of the extension 2. The process is likewise employed in Fig. 2 though by opposite movement.
The pair of rollers 15-16 also serve for moving the crystal rod 4 upwardly. There is provided, for this purpose, a ratchet 17 supported on an annular carrier 18 which may be displaced downwardly, by suitable not illustrated means, to rotate a gear wheel 19 for correspondingly rotating the rollers 16 through the medium of a link 20, thereby advancing the crystal rod 4 upwardly.
The operation is as follows:
The heating coil 3 is in suitable manner connected to a current source, heating the neck of the extension 2. The crystal rod 4 is now drawn from the crucible 1 in known manner. The drawing operation is thereupon interrupted and the heating coil 3 is at the same time disconnected. A portion of the melt within the extension 2, at least within the flaring mouth 14, accordingly solidifies. The crystal rod 4 is thus fixedly supported at the bottom while being held at the top by the roller pairs 15-16. The heating coil 11 is thereupon moved from the upper end downward to the flaring mouth 14 of the extension 2, the melting zone 13 moving along the rod 4. This operation may be repeated, if desired. Upon conclusion of the zone melting, the heating coil is again connected to current. As soon as the material in the extension 2 and at least in part of the flaring mouth 14 has melted, the crystal drawing is continued, followed by zone melting, etc.
Upon remelting the material contained in the flaring mouth 14 of the extension 2, the contaminations collected therein, extracted in the zone melting, will enter into the melt 21 in the crucible 1, resulting in continually enriching the melt with contamination products. This effect is in part counteracted by continuously delivering to the melt 21 purified semiconductor material 23 from the supply receptacle 22, such delivery being automat- 3 ically efiected by means of a float 24 controlling a valve 25 disposed at the bottom of the receptacle 22. If desired, the contaminated melt may be drawn off at another point of the crucible, shown broken away at the right side, before delivering the new melt material.
It is in this manner possible to draw in a continuous process crystal rods 4 of desired length and uniform purity as well as crystalline structure. Portions of the crystal rod produced may be cut off at the upper end as desired or required.
The embodiment described above may be modified in several ways. Thus, several supporting means corresponding to the pairs of rollers 1516 may be provided, and several melting zones such as 13 may be arranged for simultaneous drawing relative -to the crystal rod. The heating coil 3 may under some circumstances be omitted and its function may be etfected by the heating coil 11. Additional supporting elements may be disposed at the lower end, and means may be provided for moving all supporting elements in the direction of drawing for the purpose of effecting a continuous drawing operation while simultaneously applying the zone melting.
Fig. 2 shows a modification in which the semiconductor crystal, if desired a monocrystal, is drawn downwardly from a melt 41 contained in a crucible 31. Rods are continuously drawn downwardly from the extensions 32 and 33. These rods may be supported at their ends by means corresponding to the elements described in connection with Fig. 1. vided tapering extensions 34 and 35. The functions of the pairs of rollers 36 and 37 shown in Fig. 2 correspond to those of the rollers 15-16 of Fig. l. The melting zones produced by the heating coils 38 and 39 are moved relative to the two rods, by suitable not illustrated means,'in opposite directions as indicated by arrows 40 and 41'. Contaminations are in this manner respectively transported to the lower end of the left hand crystal rod and to the upper end of the right hand rod. The right hand crystal rod is produced for further processing, while the left hand rod serves for regaining melt material which is delivered to the crucible 31 along the-path 42. The apparatus is encased in a housing 43 containing a suitable protective gas, preferably under pressure, to avoid dropping otf of melt at'the openings of the extensions 34 and 35. Numeral 44- indicates a manometer and 45 and 46 are locks or gates for the protective gas flowing-in the direction of the arrow 47 to prevent ingress of air into the housing 43.
The arrangement according to Fig. 1 may be modified to provide for dual rod operation by employing features analogous to those incorporated in Fig. 2.
Changes may be made within the scope and spirit the appended claims.
1. A method of producing elongated generally rodshaped semi-conductor crystal bodies, comprising'drawing a crystal body from a melt contained in a crucible while supporting said drawn crystal body at its ends, one end of said crystal body being in operative contact relation with the melt while subjecting said one end to heating, subjecting an intermediate area of said crystal body immediately upon conclusion of the drawing thereof to zone melting, andmoving relative to said crucible the consequently produced melting zone along the solidified portion of the drawn crystal, elfecting purification and causing deposit of contaminations at the end of said crystal body in contact with the melt.
2. A method according to claim 1, comprisingcontinuously delivering melt material to said crucible.
, 3. A method according to claim 1, comprising alternately drawing and zone melting said crystal body.
In the present case, there are pro 4. A method according to claim 1, comprising continuously drawing said crystal body and continuously zone melting portions of said drawn crystal body at a speed adapted to the speed of drawing.
5. A method according to claim 1, comprising drawing said crystal body from said crucible in upward direction.
6. A method according to claim 1, comprising drawing said crystal body from said crucible in downward dircction.
7. A method according to claim 5, comprising heating said crystal body during said drawing at a point adjacent the melt in said crucible, said crystal body solidifying at said point so that the solidified body is supported adjacent the melt during the subsequent zone melting thereof.
8. A method according to claim 6, comprising heating said crystal body during said drawing at a point adjacent I the melt in said crucible, said crystal body solidifying at said point so that the solidified body is supported adjacent the melt during the subsequent zone melting thereof.
9. Apparatus for producing semiconductor crystal bodies, comprising a crucible adapted to contain molten semiconductor material, a funnel-shaped extension projecting upwardly from said crucible, means for vertically upwardly drawing an elongated generally rodlike crystal body from said melt contained in said crucible, means for heating the material in said extension during drawing of said crystal body, the material in said extension par tially solidifying to serve as a support for said drawn crystal body at the lower end thereof with such lower end in operative contact relation with the melt in said crucible, means for supporti g the drawn crystal body at the upper end thereof, and vertically movable heating means concentric with said rodlike crystal bodyand intermediate the ends of said body for subjecting said body to zone melting immediately after the drawing thereof from said melt.
10. Apparatus for producing semi-conductor crystal bodies, comprising a crucible containing molten semiconductor material, means for vertically drawing anelongated generally rodlike crystal body from said melt contained in said crucible, guide rollers in engagement with said drawn crystal body, said guide rollers forming part of said drawing means, means for rotating said guide rollers about the axis of said crystal body to rotate such body, means for positively rotating a predetermined guide roller to move said crystal body relative to said melt with one end of said body in operative contact relation with said melt, heating means comprising a heating coil concentric with the rodlike crystal body and intermediate the ends thereof for subjecting said crystal body to zone melting immediately after concluding the draw ing of said body from said melt, and means for moving said heating means longitudinaly of said crystal body.
References Cited in the file of this patent UNITED STATES PATENTS 2,553,921 Jordan May 22, 1951 2,623,253 Harrison Dec. 30, 1952 2,631,356 Sparks et al. Mar 17, 1953 2,739,088 Pfann Mar. 20, 1956 2,743,200 Hannay Apr. 24, 1956 2,768,914 Buehler ct al. Oct. 30, 1956 2,770,022 Brennan Nov. 13, 1956 FOREIGN PATENTS 804,840 Germany Apr. 30, 1951 1,087,946 France Sept. 1, 1954
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|U.S. Classification||117/51, 117/209, 117/910, 117/23, 117/31, 117/933, 117/932, 117/936, 117/33, 23/301|
|International Classification||C30B13/16, C30B13/26, C30B13/32, C30B15/30, C30B15/00, C30B13/28, C30B15/02|
|Cooperative Classification||C30B15/30, Y10S117/91, C30B13/16, C30B15/02, C30B15/002, Y10S117/917, C30B13/28, C30B13/26, Y10S117/901, C30B13/32|
|European Classification||C30B15/02, C30B15/30, C30B13/32, C30B13/28, C30B15/00B, C30B13/16, C30B13/26|