US3296036A

US3296036A - Apparatus and method of producing semiconductor rods by pulling the same from a melt

Info

Publication number: US3296036A
Application number: US502054A
Authority: US
Inventors: Keller Wolfgang
Original assignee: Siemens AG
Current assignee: Siemens Schuckertwerke AG; Siemens AG
Priority date: 1965-03-19
Filing date: 1965-10-22
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03
Also published as: DE1296132B; NL6602568A; BE677920A; GB1065187A; DK120943B

Description

Jan. 3, 1967 w. KELLER 3,296,036

APPARATUS AND METHOD OF PRODUCING SEMICONDUCTOR RODS BY PULLING THE SAME FROM A MELT Filed Oct. 22, 1965 2 Sheets-Sheet 1 Fig.1

Fig.2

Fig.3

Jan. 3, 1967 W. LLER 3,296,036

ICON TOR ROD APPARATUS AND THOD OF P UCING SEM 5 BY U LING THE SAME FROM A MEL Filed Oct. 22, 1965 2 Sheets-Sheet 2 nit "sent 3,296,036 APPARATUS AND METHOD OF PRODUCING SEMICONDUCTOR RODS BY PULLIN G TIE SAME FROM A MELT Wolfgang Keller, Pretzfeld, Germany, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt, Germany, a corporation of Germany Filed Oct. 22, 1965, Ser. No. 502,054 Claims priority, applicatiggfigrmany, Mar. 19, 1965, 19 Claims. (Cl. 148--1.6)

This application is a continuation-in-part of my application Serial No. 351,032, filed March 11, 1964, now abandoned.

My invention relates to apparatus and method for producing semiconductor rods by pulling the same from a melt of semiconductor material.

Monocrystalline semiconductor rods have been produced in the past by pulling them from a melt according to the Czochralski method and by crucible-free zone melting according to the method of Theuerer. More recently, the so-called Podest process has become known (see the article by Dash on page 363 of Growth and Perfection of Crystals, edited by Doremus, Roberts and Turnbull, pulished by John Wiley & Sons, Inc., New York, and Chapman and Hall, Ltd., London, 1958). A drop-shaped melt is produced on a slotted or split semiconductor rod, for example by means of induction heating, and a monocrystal is drawn out of this melt after immersing a monocrystalline seed therein.

In the method of pulling monocrystals from a melt in a crucible, the diameter of the growing semiconductor material is controlled by regulating the temperature of the melt and the speed at which the pulling takes place or both. By using a monocrystalline seed, semiconductor monocrystals of larger diameters can be produced in this manner. This method, however, has a disadvantage in that impurities, such as oxygen, can diffuse into the melt from the heated crucible Wall. With materials that melt at high temperatures, such as silicon for example, further difficulties arise due to the fact that the crucible wall becomes plastically deformable at those high temperatures. With the crucible-free zone melting method, monocrystals with a diameter of more than 25 mm. can be produced only with great difficulty, and it is almost impossible to produce monocrystals of more than 35 mm. diameter.

It is accordingly an object of my invention to provide an apparatus and method of producing semiconductor rods which avoids the disadvantages of the previously known apparatuses and methods and which permits the production of semiconductor rods of relatively large diameters with ease.

It is another object of my invention to provide an apparatus and method of producing semiconductor rods in which the semiconductor rods that are grown are of relatively large diameter and are monocrystalline.

It is an additional object of my invention to provide an apparatus and method of producing semiconductor rods wherein contamination by diffusion from the crucible walls is prevented by making the crucible walls proper of the same highly purified semiconductor material.

It is a concomitant object of my invention to provide an apparatus and method of producing semiconductor bodies wherein the body that is grown is practically undisturbed while it is being heated and the growing crystal accordingly has exceptionally few dislocations, a feature which is known to be particularly important in the production of monocrystalline semiconductor bodies that are to be used as electronic components.

In accordance with an aspect of my invention, I provide an apparatus and method of producing semiconduc tor rods by pulling the same from a melt in which a rod component, i.e. a seed crystal particularly, is immersed in a melt and is enlarged as it is pulled out. A substantially cylindrical semiconductor carrier element is provided, having a longitudinal axis extending in a vertical direction, and the semiconductor carrier element is rotated continuously about this axis. The semiconductor body is heated from above by means of a heating device disposed at one side of the rotational axis and extending up to about the center of the body cross section, and the rod portion beyond the heated portion of the melt is pulled out of the latter.

In accordance with another aspect of my invention and in order to avoid imperfections of the growing semiconductor monocrystal, it is pulled from the melt outside of the field of the induction heating coil in the case where heating is carried out by induction.

In accordance with a further aspect of my invention, the semiconductor body is heated from below by means of a heating device disposed at one side of the rotational axis thereof and extending to the center of the body cross section, and the rod portion beyond the heated portion of the melt is pulled out of the latter in a downward direction.

The novel features which are considered as characteris tic for the invention are set forth in particular in the appended claims.

While the invention has been illustrated and described as apparatus and methtod of producing semiconductor rods by drawing them from a melt, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. Such adaptations should, and are intended to be comprehended within the meaning and range of equivalents of the claims herein.

The invention itself, however, both as to its construction and its method of operation, together with addition al objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross section of, a vacuum chamber in which the method of this invention can be carried out;

FIG. 2 is an enlarged perspective view of the central components shown in the vacuum chamber of FIG. 1;

FIGS. 3 and 4 are top plan views of modifications of the components shown in FIG. 2;

FIG. 5 is a perspective view of an additional modification of the components shown in FIG. 2;

FIG. 6 is an enlarged partial front elevational view of a modification of the components shown in FIG. 2; and

FIG. 7 is a partly sectional bottom plan view of FIG. 6 taken along the lines VIIVII in the direction of the arrows.

Referring now to the drawings and particularly to FIG. 1 thereof, there is shown a vacuum chamber comprising a box-type housing 2 provided with a viewing glass or window 3 through which the method carried outin accordance with my invention inside the chamber can be observed. Instead of a vacuum, a protective gas can be supplied to the housing 2 in order to carry out the method of this invention. The chamber can be evacuated or supplied wtih protective gas through the connecting tube 4. A thick rod 5 as well as a slender rod 6, both consisting either of silicon or germanium, are located inside the chamber, the slender rod 6 being produced or grown from and carried by the thick rod 5. A melt 7 is located between the

rods

5 and 6 and is formed by heating and melting the top of the rod 5 3 With an induction coil 8, but can also be formed similarly by radiation heating or electron radiation. The induction coil 8 is secured to a support 9 of suitable insulating material which does not melt or vaporize at the employed temperatures. The support 9 extends outwardly from the chamber 2 through a vacuum-proof or protective-gas-proof fitting 10, as the case may be, located in an opening at the bottom wall of the chamber 2. The support 9 has at least one longitudinal bore through which the electrical leads to the heating coil 8 and a coolant supply and discharge means for cooling the heating coil extend. The two-headed arrow 11 indicates that the heating coil 8 and the support 9 are displaceable from outside the vacuum chamber in a vertical direction as viewed in FIG. 1.

The thick rod is supported by a lower holder 12 that is secured at an end of a guide rod 13 which is also led to the outside through a vacuum-proof or protective-gas-proof fitting 14, as the case may be, also mounted in an opening provided in the base wall of the chamber. The guide rod 13 can also be actuated from the outside for displacement in the vertical direction as viewed in FIG. 1 as well as for turning about its axis as indicated by the pertinent two-headed and curved arrows. The slender rod 6 is held in a similar manner as the thick rod 5 in an upper holder 15 which is secured at the end of a shaft 16. The shaft 16 also passes through a vacuumor protective-gas-proof fitting 17, as the case may be, mounted in an opening in the top Wall of the chamber and is also displaceable in a vertical direction from the outside as viewed in FIG. 1, as well as rotatable about its own axis as shown by the related arrows.

In FIG. 2, portions of the thick rod and the slender rod are shown in an enlarged view as engaging one another in a melt. As is apparent from the drawing, the slender rod portion 6 lies remote from the effects of the heating coil 8 and is therefore able to grow completely undisturbed thereby. The heating coil 8 produces a heating effect on the portion of the end surface of the thicker rod 5 which lies beneath it, causing it to melt. By continuous rotation of the thicker rod 5 about its longitudinal axis, every portion of the outer end surface of the thick rod is subjected to the heating efiect of the coil 8. On the other hand, the slender rod 6 which is located eccentrically with respect to the longitudinal axis of the thick rod 5 is not affected by the heating device. It is understood, of course, that instead of the single Winding of the illustrated heating coil 8, a heating coil with several windings, such as two or three, for example, can be employed. The slender rod 6 is advantageously rotated about its own axis so as to ensure symmetrical crystalline growth thereof. The thick rod 5 is suitably a cylindrical semiconductor body of silicon or germanium. Slight variations in the diameter of the cylindrical rod 5 are of no significance. Also slight variations in the shape of the cylinder, for example where a slight taper of the surface gives it a somewhat conical appearance, are not harmful for carrying out the method of this invention. Naturally, it is particularly advantageous when the rod is substantially a geometrically perfect cylinder.

In FIG. 3 there is illustrated a slightly modified heating coil 8a in which one of the leads is shown as being drawn off straight from the heating loop rather than having a bend as in the embodiment of FIG. 2.

In FIG. 4 there is shown another heating coil 8b which differs from that of FIGS. 2 and 3. The induction heating coil 8b of FIG. 4 has the form of a segment of a circle. The point of the circular segment is located at the rotational axis of the cylindrical thick rod 5. Such a shape of the induction heating coil produces a fairly uniform depth penetration of the applied heat overthe entire surface of the melt 7 as the rod 5 is rotated.

The entire upper surface of the thick rod 5 is advantageously not heated but rather, a predetermined margin located between the arc-shaped portion of the coil 8b and the edge of the rod 5 remains unheated, which prevents dripping of the melt from the upper surface of the rod.

It is advisable to supply the melt continuously with new semiconductor material from an outside source and thereby prevent the cylindrical semiconductor body 5 from being entirely consumed. In such a case the cylindrical semiconductor body 5 can be kept relatively short in length as shown in FIG. 5. The semiconductor material which is supplied to the melt is preferably in the form of another semiconductor rod and is also preferably introduced in the vicinity of the heater so that it will melt as soon as possible. In the case where heating is effected by an induction-type heating coil as shown in FIG. 5, the additional semiconductor material in the form of the rod 18 is introduced into the melt through the circular turn of a heating coil 8c. The cylindrical semiconductor body 5 in such a case is not necessarily but preferably surrounded by a graphite crucible 19. In order to reduce the heating capacity or necessary heating power for the induction heating coil 80, the graphite crucible 19 is preheated; for example in the case where silicon is the semiconductor, the cylindrical semiconductor body and crucible are preheated to about 1200 C. Other types of preheating can also be provided, for example by means of an induction heating coil which surrounds the thick rod 5 in the vicinity of the melt 7.

It is of course also contemplated within the scope of my invention to apply heat to the top of the thick rod 5 on one side of the vertical axis and to rotate the rod 5 to produce the melt 7 by other heating means than the

induction coil

8, 8a, 8b, 80. As aforementioned, such applications can be made by radiation heating, electron radiation heating, or the like.

In the embodiment of FIGS. 6 and 7, the lower end of a preferably cylindrical semiconductor body 22 is heated by a liquid cooled induction coil 24 which can have one or more windings and can also have other forms such as a segment of a circle having an acute central angle or having a crescent shape as in FIG. 7. By employing lowfrequency heating current the magnetic supporting effect exerted by the coil on the melt can be increased to such an extent in comparison to its heating effect that engage ment of the heating coil 24 by the melt 25 is prevented. This can also be achieved by providing an additional coil beneath the semiconductor body which is supplied with an alternating current of for example 10 kilocycles. Due to the rotation of the semiconductor body about its longitudinal axis, the heating output therefrom is distributed uniformally over the entire cross section so that the melt 25 spreads out over the entire end surface of the semiconductor body. After dipping a seed crystal into the melt, the monocrystalline thin semiconductor rod 23 is drawn therefrom, its growth being uninfluenced by the heating action. To obtain a symmetrical growth of the semiconductor rod 23 it is rotated about its longitudinal axis. The direction of the arrow 27 indicates the direction in which the semiconductor rod 23 is being pulled from the melt 25. The semiconductor body 22 can be preheated by the coil 26 or in any other manner so that the required heat output of the coil 24 is reduced. The

coils

24 and 26 are secured to a carrier (not shown) displaceable in a vertical direction as viewed in FIG. 6 which can also contain the electrical leads as well as the coolant loop conduits. Since the semiconductor body 22 becomes shorter in length during the pulling operation, the

coils

24 and 26 are made to follow after it as it reduces in length in the direction shown by the arrow 28. Naturally, the

coils

24 and 26 can also remain at rest and the semiconductor body 22 can be guided in a downward direction as the lower end of the rod is being diminished. Since the process is preferably carried out in vacuum, the holders of the semiconductor body 22 and of the thin semiconductor rod 23 as well as the carrier for the

coils

24 and 26 must extend outwardly from the vacuum vessel through suitably apertured, vacuum-tight inserts in the wall thereof similar to the

inserts

10, 14, 17 of the embodiment shown in FIG. 1. The consumption of the cylindrical semiconductor body 22 can be reduced by continually supplying new semiconductor material preferably in rod form to the melt. The new semiconductor material is expediently supplied to the vicinity of the heating action, through the heating coil when induction heating is employed, in order to achieve a rapid melting thereof. Thus in the embodiment of FIG. 7, in a manner similar to that of FIG. 5, except for the fact that the melt is at the bottom end of the semiconductor body rather than at the top end thereof, a supply of semiconductor material, in the form of a rod 30 (FIG. 7), for example, can be continuously added to the melt through the space within the coil 24.

I claim:

1. Method of producing a monocrystalline semiconductor body which comprises horizontally rotating a melt of semiconductor material simultaneously with a carrier of the same material underlying and supporting the melt; applying heat at a radially extending area overlying the rotating melt so as to heat the melt as it passes beneath the area to at least the melting temperature of the material; and pulling with the aid of a crystal seed a mono crystalline semiconductor body from a portion of the melt distantly located from the applied heating area.

2. Method of producing a monocrystalline semiconductor body which comprises horizontally rotating a melt of semiconductor material simultaneously with a carrier of the same material underlying and supporting the melt; applying heat at a radially extending area overlying the rotating melt so as to heat the melt as it passes beneath the area to at least the melting temperature of the material; pulling with the aid of a crystal seed a monocrystalline semiconductor body from a portion of the melt distantly located from the applied heating area; and supplying additional semiconductor material in solid form to the melt to replenish the material pulled from the melt.

3. Method of producing a monocrystalline semiconductor rod which comprises horizontally rotating a substantially cylindrical block of semiconductor material simultaneously with a melt of the same material carried by the block; applying heat at a radially extending area overlying the rotating melt so as to heat the melt as it passes beneath the area to at least the melting temperature of the material; and pulling with the aid of a crystal seed a monocrystalline semiconductor rod from a portion of the melt distantly located from the heating area.

4. Method of producing a monocrystalline semiconductor rod which comprises horizontally rotating a substantially cylindrical block of semiconductor material simultaneously with a melt consisting of the same material which is supported by the block; applying heat at a radially extending area overlying the rotating melt so as to heat the melt as it passes beneath the area to at least the melting temperature of the material; pulling with the aid of a crystal seed a monocrystalline semiconductor rod from a portion of the melt distantly located from said heating area; and introducing semiconductor material in rod form to said melt from above the same to replace the material pulled from said melt.

5. Method of producing a monocrystalline semiconductor rod which comprises horizontally rotating a substantially cylindrical carrier of semiconductor material simultaneously with a melt consisting of the same material and supported on the carrier; applying heat at a radially extending area overlying the rotating melt so as to heat the melt as it passes beneath the area to at least the melting temperature of the material; pulling with the aid of a crystal seed a monocrystalline semiconductor rod from a portion of the melt distantly located from said heating area; and introducing semiconductor material in solid form to the melt through the heating area from above the melt so as to replace the material pulled from the melt.

6. Method of producing a monocrystalline semiconductor rod which comprises horizontally rotating a substantially cylindrical carrier of semiconductor material simultaneously with a melt consisting of the same material overlying and supported by the carrier; applying heat at a fixed area overlying the rotating melt and extending radially to a marginal area adjacent the periphery of the cylindrical carrier so as to heat all of the melt encircled by the marginal area as it passes beneath the heating area to at least the melting temperature of the material; and pulling with the aid of a crystal seed a monocrystalline semiconductor rod from a portion of the melt distantly located from said heating area.

7. Apparatus for producing a monocrystalline semiconductor body comprising a semiconductor carrier, means for rotating said semiconductor carrier about a vertical axis, means for applying heat from a position above said carrier, onto an upper face of said carrier over a fixed area extending radially outwardly from the vicinity of said vertical axis, said upper face of said carrier being rotatable through said area to form a melt of semiconductor material around said vertical axis; and means for pulling a crystal seed and consequent semiconductor growth thereon from said melt at a location distant from said heating area.

8. Apparatus according to claim 7 including means for supplying semiconductor material to said melt from above the same so as to replace the material pulled therefrom.

9. Apparatus according to claim 8 wherein said heat applying means comprises an induction heating coil located above and spaced from said melt, said coil having the shape of a sector of a circle with its vertex directed toward said vertical axis, the area defined by said sectorshaped coil corresponding substantially to said heat-applying area.

10. Apparatus according to claim 9 including means for adjusting the spacing between said induction heating coil and said melt.

11. Method of producing a monocrystalline semiconductor body which comprises horizontally rotating a melt of semiconductor material and supporting the melt on a carrier simultaneously rotating therewith, applying heat at a radially extending area adjacent the surface of the rotating melt so as to heat the melt as it passes the applied heating area to at least the melting temperature of the material; and pulling with the aid of a crystal seed a monocrystalline semiconductor body from a portion of the melt distantly located from the applied heating area.

12. Method according to claim 11, wherein the melt underlies the carrier, the applied heating area underlies the melt so as to heat the melt from below and the monocrystalline semiconductor body is pulled from the melt in a downward direction.

13. Method according to claim 12 wherein the melt is supported by a magnetic field.

14. Method according to claim 12 including preheating the semiconductor material in the vicinity of the melt.

15. Apparatus for producing a monocrystalline semiconductor body comprising a semiconductor carrier, mean-s for rotating said semiconductor carrier about a vertical axis, means for applying heat from a position adjacent an axial end of said carrier onto an end face of said carrier over a fixed area extending radially outwardly from the vicinity of said vertical axis, said end face of said carrier being rotatable through said area to form a melt of semiconductor material around said vertical axis; and means for pulling a crystal seed and consequent semiconductor growth thereon from said melt at a location distant from said heating area.

16. Apparatus according to claim 15 wherein the position of said heat applying means is located below said carrier for applying heat onto a lower face of said carrier.

17. Apparatus according to claim 16 including means 7 8 -for supplying semiconductor material to said melt from 1 for preheating said semiconductor carrier in the vicinity below the same so as to replace the material pulled thereof said melt.

from.

18. Apparatus according to claim 16 wherein said heat 1 l d f 0d l t' app ylng means me u es means or pr uclng a magne 1c 5 DAVID L. RECK Primary Examinerfield for supporting the melt.

19. Apparatusaccording to claim 15 including means N. F. MARKVA, Assistant Examiner.

No references cited.

Claims

1. METHOD OF PRODUCING A MONOCRYSTALLINE SEMICONDUCTOR BODY WHICH COMPRISES HORIZONTALLY ROTATING A MELT OF SEMICONDUCTOR MATERIAL SIMULTANEOUSLY WITH A CARRIER OF THE SAME MATERIAL UNDERLYING AND SUPPORTING THE MELT; APPLYING HEAT AT A RADIALLY EXTENDING AREA OVERLYING THE ROTATING MELT SO AS TO HEAT THE MELT AS IT PASSES BENEATH THE AREA TO AT LEAST THE MELTING TEMPERATURES OF THE MATERIAL; AND PULLING WITH THE AID OF A CRYSTAL SEED A MONOCRYSTALLINE SEMICONDUCTOR BODY FROM A PORTION OF THE MELT DISTANTLY LOCATED FROM THE APPLIED HEATING AREA.