US3757071A - Method for crucible free zone melting - Google Patents

Method for crucible free zone melting Download PDF

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Publication number
US3757071A
US3757071A US00231182A US3757071DA US3757071A US 3757071 A US3757071 A US 3757071A US 00231182 A US00231182 A US 00231182A US 3757071D A US3757071D A US 3757071DA US 3757071 A US3757071 A US 3757071A
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melting zone
rod
zone
melting
pulses
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H Stut
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Siemens AG
Siemens Corp
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Siemens Corp
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/28—Controlling or regulating
    • C30B13/30—Stabilisation or shape controlling of the molten zone, e.g. by concentrators, by electromagnetic fields; Controlling the section of the crystal

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  • ABSTRACT Method for crucible free zone melting of a vertically oriented semiconductor rod wherein the melting zone is monitored by a television camera and the information taken from the electric pulses supplied by the television cameras, not only regarding the cross section of the crystallizing material, but regarding the angle of two tangents of the melting zone profile and are used for the regulation and control of the melted zone.
  • One tangent is applied in the crystallization boundary and the other tangent, beyond the bulge of the melting zone at a distinctive point of the melting zone profile, in particular at an inversion point.
  • the invention concerns a method for the crucible free zone melting of a vertically oriented rod of semiconductor material, particularly silicon, with a heating device coaxially surrounding the rod and movable parallel to its axis, for the generation of the melting zone, in which pictures of the melting zone successively recorded in its various positions in the rod by a television camera, with the recording conditions kept constant, serve to generate electric pulses with information regarding the cross section area of the section of the rod crystallizing from the melting zone.
  • This information is used for controlling the power supply for the heating device and/or the axial distance of the solid portions of the rod supporting the melting zone and/or of an electromagnetic support field in the sense of controlling the cross section of the material crystallizing at a given instant from the melting zone to a preset desired value.
  • the present invention provides information serving for controlling the melting zone regarding the angles between two lines tangent to the profile of the melting zone and the vertical axis of the rod be taken from the pulses supplied by the television camera.
  • One tangent is placed in the point of origin of the melting zone profile at the crystallization boundary, while the other tangent is at a distinctive point of the melting zone profile beyond its bulge.
  • FIG. 1 depicts a melting zone being monitored by a television camera
  • FIG. 2 depicts a semiconductor rod with the molten zone shifted toward the upper solid rod end
  • FIG. 3 shows a television image from the television camera
  • FIG. 4 shows the qualitative shape of some pulses occurring during the scanning of the television image
  • FIG. 5 shows another semiconductor rod with molten zone.
  • the profile of the melting zone normally adjusts itself, provided the diameters of the two solid parts of the rod 1 and 2, supporting the melt 3, as well as the diameter of the melting zone 3, have mutually identical or approximately identical magnitudes.
  • lllustratory external forces acting upon the melting zone are the surface adhesion of the liquid material at the two solid parts of the rod 1 and 2 and the force of gravity. Further external forces such as electromagnetic support fields or a force effect due to the heating device, respectivelymay have to be taken into consideration. These external forces are counteracted by the cohesion in the melt and thus by the surface tension resulting from it.
  • the force of gravity causes a downward direction gradient of the hydr'ostatic pressure in the melting zone 3.
  • FIG. 1 three tangents A, B and C are laid to the profile of the melting zone.
  • the tangent A touches the melting zone profile at its lower point of origin y. and forms the acute angle a with the vertical axis X of the rod.
  • the tangent B touches the profile of the melting zone at the upper point of origin b and forms the actuve angle B with the vertical axis X of the rod.
  • the tangent C touches the melting zone profile at the inversion of deflection point W between the bulge 3a and the constriction 3b. It forms the acute angle 7 with the rod axis X.
  • the acute angles a and B open toward the top, while the angle 7 opens toward the bottom.
  • the melting zone profile shown in FIG. I is normally present if the melted zone is passed from the bottom to the top through the rod to be zone melted and the diameter of the rod crystallizing from the melting zone and if the part ll of the rod supporting the melting zone 3, differs by not more than 40 percent from the diameter of the part of the rod 2, which is to be remelted, and borders the top of the melting zone, then the magnitude of the angle 0: determines whether the diameter of the rod 1 to be crystallized from the melting zone increases, remains constant or even decreases. For silicon, a critical value of this angle is at about 8.
  • the diameter of the material crystallizing from the melt increases to an extent, depending on the difference of the actual value of a from the value of 8, while for an angle a less than 8, the diameter of the crystallizing material becomes continuously smaller in a similar manner.
  • the angle a must be 8. As the melting zone 3, seen from FIG. 1, has a bulge 3a in its lower part, the acute angle a is open toward the top. If furthermore, silicon is the semiconductor material used, the angle a has approximately the correct value of 8 under customary conditions, (the melting zone height H is 10 40 mm and inductive heating of the melting zone) so that it is possible. to cause a cylindrical rod grow from the bottom to the top through the rod to be zone-melted without using further auxiliary means, for instance, of an electromagnetic support field generated by a special support coil.
  • the invention can be carried out with a melting zone traveling through the rod from the bottom to the top (FIG. 1) as well as with a melting zone (FIG. 2) traveling from the top to the bottom.
  • a melting zone traveling through the rod from the bottom to the top (FIG. 1)
  • a melting zone traveling from the top to the bottom.
  • I tangent angles a and 3 are used to control and/or regulate parameters, in addition to the diameter d of the material crystallizing in each case.
  • the tangent angles B and a are used.
  • a and 'y or B while in the second case, a serves as stability parameters.
  • a in the first case and B in the case is used as the control parameter for the behavior of the cross section of the material crystallizing from the melting zone.
  • the method of the invention is preferably carried out with a melting zone traveling from the bottom to the top.
  • a melting zone traveling from the bottom to the top.
  • the melting zone has the shape described in FIG. 1. It generates in the television camera an image of the melting zone and its environment on an image screen, which has known special electrical properties, for instance, a vidicon target.
  • the image is' then systematically scanned by a fine electron beam, which closes at least one electric circuit.
  • the image screen offers locally different electric resistance depending on the exposure, the electric current caused by the electron beam will have different intensities, depending on whether it impinges on'a brighter or darker point of the image of the melting zone on the image screen of the' television camera.
  • the-current flowing in the electron beam which is controlled by the image of the melting zone 3 becomes the larger, the brighter, the corresponding point of the image becomes in the television camera and therefore in the imaged system also.
  • the brightness of the melting zone 3 is approximately constant and is appreciably less than the brightness at the end of the rod parts I and 2 supporting it.
  • the heating source is a perponderantly flat horizontal induction coil l
  • a horizontal partial zone of the melting zone 3 is shielded off and appears in the image of the television camera as a dark area.
  • a similar situtation applies for the further surroundings of the melted zone as care is taken by suitable filters in the pick-up optics of the television camera that the image of the melting zone stands out with as much contrast as possible against the image of its surrounding.
  • the imaging of the melting zone 3 projected in the television camera occurs under constant conditions. This will be achieved practically by arranging the heating device and the melting zone stationery in space and by pushing the rod through the annular shaped heating device in the axial direction, according tothe intended speed of the melting zone.
  • the optical system of the camera is advantageously aligned so that its optical axis is perpendicular to the axis of the rod X and is directed approximately v toward the center of the melting zone.
  • the electron beam should scan the image on the image screen of the television camera in unilaterally directed mutually'parallel lines.
  • the lines are perpendicular to the image X of the axis X by suitable orientation of the camera.
  • the spacing of two adjacent lines should have s 4 .92 23. 292 .9 rel? h, f instance, h total image height 625.
  • the shape of the melting zone corresponds here to the conditions according to FIG. 1.
  • the image of the melting zone is designated 3', that of the lower part of the rod 1', that of the upper part of the rod 2', and the image of the heat source (induction coil) I.
  • This image is now scanned line by line by the electron beam in the television camera.
  • the spacing between two scanning lines is h.
  • 13 lines are shown although in practice the number of lines is, of course, many times larger.
  • the lines will be designated with z,, 2 i
  • FIG. 4 shows qualitative shape of some of these pulses. P, as they occur during the scanning of the image of the melting zone according to FIG. 3.
  • the pulse P corresponds to the lower boundary and the pulse P. to the upper boundary of the melting zone.
  • These pulses P P. have correspondingly high amplitudes av. because of the particularly brightly radiatingsolid rod ends 1 and 2.
  • the width of the pulse P will be designated with P...
  • the width P. can
  • the image of the melting zone 3 is continuously recorded during the entire process by the optical pick-up system of the television camera.
  • the evalutation that is the generation of the pulses Pf
  • the melting zone changes correspondingly slowly within the range of stability.
  • as many pulses Pff as desired can be derived per scanning cycle.
  • the pulses P appear also in the current at the output of the television camera and are evaluated according to the teachings of the invention.
  • the pulses P supplied by the television camera can be evaluated in different ways as a control process.
  • the inversion point w of the melting the pulses Pf as to both their amplitude a and width Pf.
  • two groups must be distinguished regarding the amplitude ag of the pulses P;
  • the pulses of particularly high amplitude which correspond to theespecially brightly radiating rod ends 1 and 2 at the transition to the melting zone *3, and which become successively smaller with increasing distance from the pulses associated with the melting zone.
  • the scanning lines 2, corresponding to the dark points of the image to be scanned, particularly at the place of the image I, of the induction coil I which produces the melting zone. These lines, however, do not lead to pulses with appreciable amplitude.
  • pulses P1? are obtained with successively increasing amplitude and of a duration (width Pl) corresponding to the diameter d at each instance of the image I of the lower rod portion 1.
  • the largest amplitude a is given to the last pulse associated with the image I. i.e., the pulse 1 f, with the width Pf, (FIG. 4, pulse Pg).
  • the following of the pulses I. are associated with the image proper 3 of the melting zone 3.
  • the first of these pulses. namely the pulse I, ;t should be noted particularly.
  • the amplitude 0,. is distinctly smaller as c ompared to the amplitude a of the last pulse P associated with the rod portion 1.
  • the amplitudes have practically the same value for all of these pulses P. (pulses P P in FIG. 4).
  • the pulses practically disappear (pulse P9 in FIG. 4) and reappear again as soon as the electron beam reaches those scanning lines 2,, which correspond to the portion of the melting zone image 3' proper which is located above the image I and is not shielded.
  • the pulses Pf ⁇ regain their former amplitude. which corresponds to the brightness of the melting zone image.
  • the last of these pulses namely the pulse jf corresponding to the point 1 of the melting zone profile, should be noted particularly.
  • the scanning electron beam reaches the image 2 of the upper portion of the rod 2 which delineates and supports the melting zone. Pulses P; then show immediately again a high amplitude corresponding to the more brightly glowing solid material at the end of the rod (pulse P5 in FIG. 4).
  • the first of the pulses P corrgsponding to the solid rod portion 2 is designated .by Ff. Its amplitude a- --a is also a maximum.
  • the pulses 1 and 1 which just still or already, respectively, correspond to the solid material at the l oundar of the melting zone 3. Their widths P and to the diameter d of the solid material at the points-in question of the solid portions of the rod ,1 and 2, respectively.
  • I 2. the first and the last of the pulses associated with the melting zone, and particularly the pulses, PT. and Pf.
  • the melting zone has a construction 3b, one must derive above the bulge 3a of the melting zone further pulses P5 24 for the determination of the value of the angle A; the pulses 1 and P; are distinguished from the pulses P which are situated between them in time and belong to the melting zone 3, by their particularly high amplitude a one will first filter out from the individual sequences of pulses P obtained per scanning cycle, those, the amplitude of which has the-value a One will therefore provide a suitable separator, which makes the desired choice.
  • proportional PL (It subdivides each pulse sequence into three partial V, respectively, are proportional PL) can be evaluated as a measure for the magnitude of the diameters of the solid rod portions 1 and 2 at the phase boundary or of the images 1 amd 2, respectively, corresponding to them.
  • the width p, of the pulse P is considered as the measgre for the diameter of the crystallizing material and 17., is used as the control quantity for the following.
  • the difference between the two pulses P, and P, are particularly monitored as they are used for the monitoring and control of the melted zone. Nevertheless, the computing processes to be described in the following, canbe p erformed successively for all pulses P., of each scanning cycle.
  • the sequence of first order differences A; P5, Pi? are now formed between thewidtlisTIBf successive pulses P, of each pulse sequence. If the adjacent pulses P, in each case differ with respect to their width P., the difference has an finite value; in the event these widths are equal the difference A.., be-
  • the index 1/ which is initially provided correlated to the values 5 h, 2h, 3h, nh of the axial image coordinate 5.
  • these 5 are nothing but a similar image of the axial coordinates x for the different points of the melting zone 3 and its surroundingsfone is, therefore, justified to consider the pulse widths p as different values of a function P P '(6) wherein the function p can be assumed to be continuously differentiable.
  • Its first derivative with respect to E is defined by For the values Q, h, 2h nh it assumes the values p, p,, p, p,,.
  • the value of the first derivative is related to the associated first order difference according to the equation 9/ E) v P(( "P( l ?E the point uh 5 (v+ l) h.
  • the identity dD /dx dpldg exists, where D corresponds to the diameter of the melting zone at the point corresponding to the line z... Consequently, one obtains for the angle (1; of the tangent to the melting zone profile with the x-axis (rod axis) the relation which is valid in good appfoximation. From the difference of the widths of the first two pulses after the pulse P5, i.e., the pulse P ⁇ ; and the immediately following pulse P5 one obtains the value of the tangent of the angle a.
  • the pulses Pf, delivered by the television camera are first fed to a measured value converter.
  • each of th e pu lses Pf initiates the generation of a sequence of equally spaced switching pulses and identical shape, the numbe r of which in each case is a measure for th e corresponding width P5 of the res'pi tivejaulsePf.
  • a bin ary code corresponding to the individualrouefif, is geaerated: This code, in turn, is fed to a digital computer in which the described computations for determining thediameter D of the material crystallizing out from the melting zone and gftan p are carried out with emphasis of tan.
  • the pulses P; and Pf Of the two pulses with maximum amplitude a i.e. the pulses P; and Pf, only the pulse belonging to the crystallization front needs to be retained. If the the materialto be remelted, the pulse P., is accordthe material to be remelted, the pulse F is accordingly to be emphasized particularly. This is possible, for instance, by means of an amplitude peak detecting circuit;
  • the image of the melting zone and its surroundings, projected by the optical system of the television camera is not scanned continuously but, for instance, at regular time intervals, for instance, only once per second or per minute or even less frequently.
  • One then obtains a number of successively following scanning cycles, to which one can assign, according to their order, the numbers 1. l, 2, 3, m.
  • the corresponding reference values Dy, tana p. tany and/or tanB are preprogrammed, where of course, these values must be in accordance with the mechanical stability of the melting zone. If these pulses P; of the ,u" scanning cycle then arrive gt the computer, the corresponding reference values D tan a,
  • the index 11. can also be assigned the meaning of a longitudinal coordinate via the travel velocity of the crystallization front'of the melting zone or via the length increase of the material crystallized from the course of the individual desired values D, tan a tan 7, tan 3,. via the distance from the heat source f the o er for.thei2 rt. zn.2 .v the o s ns rqm the melting zone. 1
  • a device can be combined without difficulty which permits determining in the tan 4); value immediately preceding, i.e., tan ,B and to evaluate it.
  • a change of the volume of the melting zone is necessary.
  • the power supplied to the melting zone and therefore the heating of the melting zone can remain constant unless excessively large changes are involved.
  • a change of the volume of the melted zone is also possible by changing the frequency of the electric current causing the heating of th melting one. lftthe possibility of an absolute measurement of the diameter exists, it is recommended to correct the volume of the meltingzone via a subrodinated control circuit until the diameter of thl melting zone is correct.
  • the information necessary for regulation or program control, respectively, of the process can in all cases be derived only from the profile of the melted zone itself. in the case of non rotation symmetrical conditions, it may here be necessary to provide two television cameras with optical systems oriented perpendicularly to each otherfThe afigEs a and y, or a and ,8, respectively, which are to be monitored and controlled, respectively, according to the invention, are entirely usuable as the information sources, as discussed above. From experience, at least with respect to zone melting of silicon rods, the following can be stated with regard to the control of their values 1. According to experience, the angles a and B depend, in the case of inductive heating of the melting zone (FIGS. AND 96), to a particular degree of the axial distance of the solid portions of the rod supporting the melted zone, and the angle 7 depends on the heating of the meltingzone. A similar statement applies for the distances of the lower edge of the melted zone from the induction coil.
  • the data processing digitially, especially since the television camera supplies the diameter by counting the width of the melting zone an therefore in digital form.
  • the generator frequency can most practically be determined by counting.
  • the power supplied to the melting zone or to the heating device, respectively can simply be displayed in this form by a digital voltmeter.
  • control circuits for single parameter control and regulation particularly with respect to the diameter of the material crystallized from the melting zone, reference can be made to German Pat. Nos. 1,209,551 an 1,231,671 which correspond respectively to U. S. Pat. No. 3,198,929 and 3,243,509.
  • control and regulation with respect to at least three parameters is involved, the arrangement must be expanded accordingly.
  • the method of claim 1, which further comprises, when melting zone travels through the rod to be zone melted from the bottom to the top, monitoring the angle a of the tangent to the profile of the melting zone at the crystallization front, with the vertical axis of the rod and at least one of the angle 7 of the tangent at the inversion point of the profile of the melting zone, with the vertical axis of the rod and the angle )3 of the tangent to the profile of the melting zone at the melting front with the vertical axis of the rod.
  • the method for crucible free zone melting of a vertically held semiconductor rod wherein a melting zone, which passes through the semiconductor rod, is produced by a heating device coaxially surrounding the rod and movable parallel to its axis, which comprises monitoring the semiconductor rod with the melting zone by a television camera under constant recording conditions; adjusting the television camera in relation to the semiconductor rod so that the image of the axis of the semiconductor rod upon the target of the television camera is perpendicular to equidistant scanning lines on the target of the television camera; modulating the electron beam, which scans the image of the semiconductor rod and of the melting zone along the indicated scanning line in the form of electrical pulses; said modulating being efiected by the image of the semiconductor rod and the emitting zone; said electrical pulse correspond directly to the bright image of the glowing melting zone and to the glowing portions of the solid semiconductor rod; during the individual scanning cycles the electron beam selecting two retained pulse groups which consist of at least two immediately adjacent pulses and through limiting to the respective pulse group determining half the difference between the lengths of respectively adjacent pulses
  • the second pulse group is selected so that the pulses belonging thereto belong to the scanning line which coincides with the image of the melting side of the emlting zone an to the scanning lineqadjacent to said first scanning line which falls in the image proper of the interior of the melting zone.
  • the melting zone is guided frmm above, downward through the semiconductor rod, the second group of pulses is selected so' that it consists of three adjacent pulses and that the middle of said pulses corresponds to the scanning line which passes through a turning point of the image of the melting zone profile.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)
US00231182A 1971-03-22 1972-03-02 Method for crucible free zone melting Expired - Lifetime US3757071A (en)

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DE2113720A DE2113720C3 (de) 1971-03-22 1971-03-22 Verfahren zur Durchmesserregelung beim tiegellosen Zonenschmelzen von Halbleiterstäben

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4023520A (en) * 1975-04-28 1977-05-17 Siemens Aktiengesellschaft Reaction container for deposition of elemental silicon
US4866230A (en) * 1987-04-27 1989-09-12 Shin-Etu Handotai Company, Limited Method of and apparatus for controlling floating zone of semiconductor rod
US4931945A (en) * 1987-12-05 1990-06-05 Shin-Etsu Handotai Company Limited Method of controlling floating zone
US20050051539A1 (en) * 2003-09-10 2005-03-10 Yablochnikov Boris A. Method for monitoring the performance of a magnetic pulse forming or welding process
WO2014033212A1 (de) * 2012-08-30 2014-03-06 Forschungsverbund Berlin E.V. Modellprädiktive regelung des zonenschmelz-verfahrens

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2332968C3 (de) * 1973-06-28 1981-12-10 Siemens AG, 1000 Berlin und 8000 München Vorrichtung zur Steuerung des durchmessers eines Halbleiterstabes
US4185233A (en) * 1978-03-30 1980-01-22 General Electric Company High efficiency ballast system for gaseous discharge lamps
JP2014240338A (ja) * 2013-06-12 2014-12-25 信越半導体株式会社 半導体単結晶棒の製造方法
JP6642234B2 (ja) * 2016-04-20 2020-02-05 株式会社Sumco 単結晶の製造方法および装置

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4023520A (en) * 1975-04-28 1977-05-17 Siemens Aktiengesellschaft Reaction container for deposition of elemental silicon
US4866230A (en) * 1987-04-27 1989-09-12 Shin-Etu Handotai Company, Limited Method of and apparatus for controlling floating zone of semiconductor rod
US4931945A (en) * 1987-12-05 1990-06-05 Shin-Etsu Handotai Company Limited Method of controlling floating zone
US20050051539A1 (en) * 2003-09-10 2005-03-10 Yablochnikov Boris A. Method for monitoring the performance of a magnetic pulse forming or welding process
US7026585B2 (en) * 2003-09-10 2006-04-11 Torque-Traction Technologies, Inc. Method for monitoring the performance of a magnetic pulse forming or welding process
WO2014033212A1 (de) * 2012-08-30 2014-03-06 Forschungsverbund Berlin E.V. Modellprädiktive regelung des zonenschmelz-verfahrens

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JPS5233042B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1977-08-25
GB1373718A (en) 1974-11-13
DE2113720C3 (de) 1980-09-11
BE781067A (fr) 1972-07-17
NL7115341A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1972-09-26
FR2130453A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1972-11-03
DE2113720B2 (de) 1980-01-10
CA970255A (en) 1975-07-01
DK140822C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1980-05-12
FR2130453B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1975-04-11
DE2113720A1 (de) 1972-09-28
CH538885A (de) 1973-07-15
DK140822B (da) 1979-11-26
IT962055B (it) 1973-12-20

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