US3198929A - Electric control apparatus for zone melting of semiconductor rods - Google Patents

Electric control apparatus for zone melting of semiconductor rods Download PDF

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Publication number
US3198929A
US3198929A US243973A US24397362A US3198929A US 3198929 A US3198929 A US 3198929A US 243973 A US243973 A US 243973A US 24397362 A US24397362 A US 24397362A US 3198929 A US3198929 A US 3198929A
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rod
travel
zone
counting
diameter
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US243973A
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English (en)
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Stut Hans
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Siemens Schuckertwerke AG
Siemens Corp
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Siemens Corp
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Program-control systems
    • G05B19/02—Program-control systems electric
    • G05B19/04—Program control other than numerical control, i.e. in sequence controllers or logic controllers
    • G05B19/08—Program control other than numerical control, i.e. in sequence controllers or logic controllers using plugboards, cross-bar distributors, matrix switches, or the like
    • 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
    • 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
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/20—Pc systems
    • G05B2219/23—Pc programming
    • G05B2219/23199—Reference value, setpoint for regulator
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/20—Pc systems
    • G05B2219/25—Pc structure of the system
    • G05B2219/25475—Sequence synchronized with machine axis, like knitting machine
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1032—Seed pulling
    • Y10T117/1068—Seed pulling including heating or cooling details [e.g., shield configuration]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1032—Seed pulling
    • Y10T117/1072—Seed pulling including details of means providing product movement [e.g., shaft guides, servo means]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1076—Apparatus for crystallization from liquid or supercritical state having means for producing a moving solid-liquid-solid zone
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10T117/10—Apparatus
    • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
    • Y10T117/1076—Apparatus for crystallization from liquid or supercritical state having means for producing a moving solid-liquid-solid zone
    • Y10T117/1088—Apparatus for crystallization from liquid or supercritical state having means for producing a moving solid-liquid-solid zone including heating or cooling details

Definitions

  • FIG. 1 ELECTRIC CONTROL APPARATUS FOR ZONE MELTING OF SEMICONDUCTOR RODS Filed Dec. 6, 1962 5 Sheets-Sheet 1 FIG. 1
  • My invention relates to electric apparatus for controlling the zone melting of rod material, particularly semiconductor rods to be employed, for example, as an intermediate product in the manufacture of semiconductor junction diodes, transistors, semiconductor switching devices of the p-n-p-n type and others,
  • semiconductor rods amenable to zone melting may consist of germanium, silicon, gallium arsenide, indium antimonide or various other intermetallic compounds.
  • Zone melting is employed for various purposes. it may serve for purifying a semiconductor rod of undesired impurities, for uniformly distributing a dopant in the rod (zone levelling), or for converting a polycrystalline rod to a monocrystal with the aid of a crystal seed fused to one end of the rod.
  • One and the same zone-melting operation may simultaneously perform two or more of such functions.
  • zone-melting operations require a considerable amount of attention and skill on the part of attendant personnel. This is the case particularly when converting a polycrystalline rod into a monocrystal with the aid of a monocrystalline seed.
  • the seed has a smaller diameter than the rod to which the seed is fused, because a seed of smaller diameter can be more easily and more reliably produced in perfect monocrystalline constitution and with fewer crystal-latticed dislocations than are apt to occur in larger crystals,
  • the use of relatively small crystal seeds may render it difiicult to reliably perform the zone-melting operation at the locality where the small cross-sectional area of the seed merges with the larger area of the rod proper.
  • heating energy and the digital control of the rod cross section in accordance with respective programs so that the increase or decrease of the heating energy and the conjoint increase or decrease in cross-sectional diameter take place in increments depending upon passage of the zoneheating device through one or a given number of steps along its travel relative to the semiconductor rod.
  • a threaded feed spindle or other device for displacing the zone-heating device along the rod is employed for controlling the issuance of digital counting pulses, for example to a binary chain of counters.
  • the above-mentioned chain of binary counters is composed of a first portion comprising a number of counting stages, and a subsequent, second portion which also comprises a number of sequential counting stages.
  • the first counting stage of the second portion in the chain feeds pulses .to a conversion unit which converts the incoming digital coding of the travel points into a continuous travel image in accordance with the natural number sequence and thereby puts into effect the particular program storer or memory with which the conversion unit is connected by a corresponding number of leads.
  • Thev program storer or memory system consists, for example, of a cross-bar distributor or coordinate-type selector which possesses two systems of mutually crossing groups of contact rails, although other suitable mechanical memory devices, for example punch-card, punch-tape or magnetic memory devices, are also applicable. Connecting contacts can be plugged or screwed into the cross bars at the intersection points of each distributor, thus interconnecting the corresponding two rails in each memory system in accordance with the preselected program.
  • the above-mentioned cross-bar distributor is used for issuing the travel-dependent signal through connecting leads to the input circuit of AND-gates. Simultaneously these AND-gates receive through respective connecting leads the corresponding counting pulses from the counting stages in the first portion of the counter chain. Each of these AND-gates issues a different number of pulses per rotation of the heater transport spindle depending I further preset the digital control of the o upon the programmed datum value preset in the cross-bar distributor, and each of these issuing pulses represents or controls a unit step with respect to the change in heating energy or change in rod diameter.
  • the output pulses of the AND-gates are supplied through a common output lead to a digital-analog converter of the heating-energy control system and to a corresponding digital-analog converter of the diameter control system. Consequently, the output circuit of the particular digital-analog converter provides an electrical control magnitude which corresponds to the desired absolute value of heating power to be supplied to the molten zone or to the absolute value of diameter or cross section to be adjusted in the molten zone of the rod.
  • FIG. 1 shows schematically the essential features of the zone-melting apparatus together with a diagram of the electrical system.
  • FIGS. 2 and 3 are graphs explanatory of the system performance.
  • FIG. 4 is an electric circuit diagram of one of the various counting stages according to FIG. 1;
  • FIG. 5 is a circuit dagram of details adjacent to one of the counting stages according to FIG. 4 in the system of FIG. 1; and
  • FIGS. 6, 7. and 8 are circuit diagrams of other components in the system of FIG. 1.
  • a semiconductor rod to be zonemelted has a crystal seed 2 fused to one end.
  • the two ends of the rod-seed structure are clamped in axially spaced holders in the conventional manner.
  • One of the holders can be placed in rotation about the common axis relative to the other for uniform distribution of the molten material in the molten zone la.
  • the two holders and hence the ends of the semiconductor rod are displaceable axially one relative to the other by means of a control device 74 in order to stretch or compress the molten zone 1a in order to thereby maintain a constant diameter of the rod portion solidifying out of the molten zone.
  • the molten zone 1a in the semiconductor rod is produced by means of an inductive heater coil schematically shown at 3 whose design and mounting may also be in accordance with details known from the patents just mentioned.
  • the heater coil 3 constitutes the primary winding of an electric induction system operating with a current whose frequency is sufficiently high for good regulation. Suitable, for example, is a frequency of 40 megacycles per second.
  • the heater winding 3 is carried by a transporting device that comprises a vertically mounted, rotatable screw spindle 5 with a traveling nut 4 which is prevented from rotation so that it becomes displaced upwardly or downwardly by revolution of the spindle 5, thus moving the heater winding 3 axially along the rod 1.
  • the revolution of spindle 5 is simultaneously used for driving an electric contact device serving as a digital pulse transmitter.
  • This device comprises a cam disc 6 with a number of lobes 7 for controlling a switch lever 8 cooperating with a fixed contact 9.
  • the lobes '7 for example sixteen, are uniformly distributed over the cam periphery, only eight lobes being shown in FIG. 1 for simplicity.
  • the contact is between lever S and fixed contact 9 made and broken sixteen times, and corresponding pulses are transmitted from a voltage source 8 to the input circuit of a chain 10 of binary counters whose individual, sequential stages are denoted by 11 to 1?.
  • the internal circuitry of each of the stages will be described in a later place with reference to FIG. 4.
  • the counting stages 11 to 13 according to FIG. 1 constitute a first portion of the chain it).
  • the active input lead of each counting stage 11 and 12, as well as the corresponding active input leads of other digital counting stages mentioned hereinfater, are denoted by 121, whereas the identifying numeral 122 is applied to the output lead of the respective counting stages.
  • the stages 11 to 13 in the first portion of chain 10 have their output leads 122 connected through respective leads 21 to 23 with respective AND-gates 25E to 27E for the heating-energy control system, and also with respective AND- gates 25D to 27D of the rod-diameter control system.
  • Two AND-gates 24E and 24D are directly connected to the switch contact 9.
  • the counting stages 14 to 19, as well as any additional, not illustrated stages in chain 10, constitute together the second position of the counting chain 10.
  • the respective output leads of these counting stages are connected to a conversion unit 28 composed of switching and gate circuits for converting the binary coding of the travel-step points into a continuous travel-path image or signal according to the natural numerical sequence.
  • the output leads of the converter 28 are connected to respective vertical bars 29 to 45 of a double cross-bar distributor.
  • the distributor further comprises a set of horizontal bars 47E to 50E of a program storer system for heating-energy control, and another set of horizontal bars 47D to 50D forming a program control system for diameter control.
  • Each of the horizontal distributor bars 47E to 50E is connected to an input lead of respective AND-gates 2413 to 27E.
  • Each of the horizontal distributor bars 47]) to StiD is analogously connected to an input lead of one of the respective AND gates 24D to 27D.
  • the vertical bars 29 to 45, on the one hand, and the bars 47E to 59B and 47D to 50D, on the other hand, can be selectively connected with each other at the respective intersections by means of plugs or screws S in order to preset a travel-responsive program for power control as well as a travel-responsive program for diameter control.
  • FIG. 1 Selected connections of this kind are indicated in FIG. 1 by two concentric circles surrounding at each locality S the intersection point between a vertical bar and one of the horizontal cross bars in each of the two programming systems.
  • the cross-bar selector 45 in FIG. 1 thus exemplifies two preset programs for heat control and diameter control respectively, both programs being dependent upon the digital pulses issued in response to the travel of the heater along the rod.
  • the AND-gates 24E to 27E have a common output lead 51E connected to a digital-analog converter 52E.
  • the AND-gates 24D to 27D have a common output lead 51D connected to another digital-analog converter 52D.
  • Each of converters 52B and 52D comprises counting stages a to f and a direct-voltage supply denoted by a source 68B and 68D respectively.
  • Each of converters 52E, 52D further comprises a series-connected resistor 53E, 53D and a number of transverse resistors 54E to 59E and 54D to 59D respectively. The latter resistors are connected to the respective counting stages a to f in each converter.
  • the output terminals 60E and 61E of converter 52E furnish an electric voltage whose magnitude is determined by the voltage division to which the direct voltage between input terminals 62B and 63E is subjected by the series connection of the resistor 53E with the particular transverse resistor or resistors 54E to 59E that are switched into operation at a time.
  • the output voltage between the output terminal 60D and 61D of the digital analog converter 52D is determined by the division to which the direct voltage impressed upon input terminal 62D and 63D is subjected by the series connection of the resistor 53D with the one or more of resistors 54D to 59D switched into activity at a time.
  • the regulator 64 is supplied through a connecting lead 65 with a converted measuring value indicative of the current which a high-frequency generator 67 supplies through a measuring instrument 66 to the heater winding 3.
  • the lead 65 is shown connected to the current-measuring instrument 66 to indicate that the signal supplied to the regulator 64 is proportional to the heating current.
  • Another lead 69 connects the regulator 64 with the high-frequency generator 67 and supplies a control magnitude corresponding to the departure of the pilot (actual current) magnitude supplied through lead 65 from the datum value set by the programming system and supplied from terminal 60E, so that the generator 67 is controlled to increase or decrease the heating current as is needed to have the actual amount of heating energy correspond to the program value.
  • the latter value issues from the output terminals 60D, MD of the converter 52D to the regulator '76.
  • the regulator 70 further receives through an input lead 72 a signal indicative of the actual diameter of the molten zone.
  • This diameter pilot signal is produced in the illustrated embodiment by means of an inductive loop 71 which surrounds the semiconductor rod 1 at the location where the molten zone commences to freeze.
  • the inductive loop 71 is connected to a transformer 72 or converter which issues a corresponding signal through the lead 72 to the regulator 70.
  • the datum value from the program system is compared with the actual diameter value as manifested by the pilot signal, and a corresponding difference voltage is impressed through an output lead 73 upon the displacement control system 74 of the zonemelting apparatus.
  • the system 74 in response to the regulating signal, displaces the lower holder of the rod upwardly or downwardly to cause a compression or axial expansion of the molten zone, thus regulating the diameter of the rod where it freezes out of the molten zone, to the value preset in the program system.
  • the crystal seed used for this purpose and fused to one end of the rod is generally given a much smaller cross section than the rod itself.
  • One or more zone-melting passes must be commenced at the seed crystal near its fusion junction with the semiconductor rod proper.
  • the heating energy supplied to the rod zone in order to melt it and heat it up to a given temperature, so that the supply of heat is adapted to change in cross section occurring along the rod-seed assembly.
  • the shape of the assembly components prior to zone melting, as Well as the desired shape after zone melting, is predetermined. Hence these given shapes determine the program to be preset in the programming system 46 in dependence upon the travel of the heater relative to the rod.
  • a travel-responsive program could be 6. stored in such a manner that the control of the change in heat supply and the control of axial displacement for obtaining the desired diameter, take place continuously. This, however, would require an excessive amount of equipment. It is considerably more advantageous, according to the invention, to provide separate programming systems of digital performance which control the stretching-compressing motion of the seciconductor rod and the heat supply to the molten Zone, so that, depending upon the steepness of the transition from seed to rod, the absolute value of the rod diameter and of the heat supply to the molten zone are changed by a correspondingly greater or smaller number of individual, uniform steps.
  • FIG. 2 indicates on the ordinate the amount of heating energy, and on the abscissa a number of successive, equal steps of travel traversed by the inductive heating device relative to the rod in the axial direction of the latter.
  • FIG. 3 shows along the ordinate the diameter values of the molten zone, also versus incremental steps of heater travel indicated along the abscissa.
  • a program is assumed to be desired according to which the diameter of the rod-seed assembly is to increase from the value D to a larger value D corresponding to the conditions existing, for example, at the junction between the seed and the rod proper. Since the volume to be converted to molten condition increases with increasing diameter, it is necessary to accordingly increase the electric heating energy supplied by the induction heater to the molten zone.
  • the transfer from the diameter D to the larger diameter D is performed in unit steps as indicated by the stepped curve train in FIG. 3.
  • the control in these unit steps is dependent upon the steps of heater travel between the points A and B on the abscissa. Consequently, during each unit of travel, for example A-C, or C-D, or DE, traversed during continuous travel of the heater, a preselected number of individual steps in the direction of increasing diameter is added to the preceding absolute magnitude of the diameter.
  • the merger curve exemplified in the graph possesses differen degrees of steepness in different portions.
  • the corresponding performance would subtract for each step of heater travel a number of unit changes in diameter as correspond to the steepness of the curve for that particular travel step.
  • the travel steps AC and DE are of equal size, but the steepness of the merger curve in the range of step AC is considerably smaller than in the range of step D-E. Consequently, for satisfying the slight gradient of step A-C, a smaller number of individual unit steps is needed for correspondingly changing the diameter than in the range of step DE.
  • step A-C is represented in FIG. 3 to comprise only two unit steps of diametrical change, whereas the step DE comprises four such unit steps.
  • the particular number of these unit steps is predetermined over the entire zone-melting travel of the heater along the rod by the setting chosen in the programming system 46 (FIG. 1).
  • the change in diameter must be accompanied by a travel-responsive change in supply of heating energy.
  • the heating energy is changed from the value E to the higher value E of the above-mentioned travel distance from point A to B. This is done incrementally in such a manner that whenever the heater coil passes through one unit step of its travel, a corresponding, preselected number of unit changes in heating energy is effected, depending upon the steepness of the transition between the absolute energy value at the beginning and the value at the end of tie travel step, thus correspondingly increasing, or reducing as the case may be, the tot-a1 amount of heat supplied to the molten zone.
  • This control performance will again be exemplified by comparing the travel steps A-C and DE with each other.
  • the program curve shown in FIG. 2 shows that during the travel step A-C of the inductance heater the characteristic curve has a relatively slight steepness in comparison with the steepness during travel step D-E. Therefore, as exemplified, four individual unit steps of change in heating energy are applied during travel step AC, but eight unit steps are effective during travel step DE. In this manner, a proper adaptation of the change in diameter and the correlated change in electric heating is obtained as required for maintaining the desired median temperature value in the molten zone of the semiconductor rod.
  • FIG. 4 shows by way of example the circuit of a bistable flip-flop stage applicable in each of the counting stages 11, 12, 13, 14, 15 etc. as well as in the counting stages 52Ea to f and 52Da to f.
  • the terminals 111, 112, 121, 122 correspond to the equally denoted leads of the counting stage 525a, for example; and the lead 107 in FIG. 4 corresponds to lead 17 in FIG. 1.
  • Terminals 1%9 and 1113 indicate the positive and negative terminal or lead of a direct-current supply of constant voltage, not shown in FIG. 1.
  • the flip-flop stage according to FIG. 4 comprises two transistors 101 and 102 for example of the p-n-p type.
  • An ohmic resistor 103, 164 is connected in series with the collector of each transistor 1111, 192.
  • the collector of transistor 1111 is further connected through an ohmic resistor 105 with the base of transistor 1112.
  • the collector of transistor 102 is analogously connected through a resistor 196 with the base of transistor 1tl1.
  • Capacitors 124 and 125 lie across respective resistors 1&5 and 1116.
  • the common emitter lead 1117 of the transistors is attached to the positive terminal 1119 of the direct-voltage source.
  • the negative terminal 110 of the same directvoltage source is connected to the common collector lead 108.
  • the signal terminal 111 is attached to the base of transistor 1&1, and the signal terminal 112 to the base of transistor 102.
  • a capacitor 113, two opposingly poled diodes 114 and 115, as well as a capacitor 115 lie all in series between the respective bases of transistors 1 31 and 1112.
  • the lead 117 joining capacitor 113 with diode .114 is connected through an ohmic resistor 118 with the collector of transistor 1112.
  • the corresponding lead 119 between capacitor 116 and diode 115 is in connection with the collector of transistor 1121 through an ohmic resistor 124).
  • the signal terminal 121 is connected between the two diodes 114 and 1115. Leads and terminals 122, 123, constitute the output mmebers of the flip-flop circuit.
  • the operation of the bistable circuit is as follows.
  • the output lead 122 assumes the potential of the minus pole 111 in the same manner as was previously the case for the output lead 123 when transistor 1132 was turned off.
  • the lead 123 has zero potential, and the lead 122 has a finite potential relative to the plus pole 1119, determined by the voltage of the source connected between terminals 189 and 111
  • the circuit can be switched to its opposite stable condition by applying a corresponding negative signal to the signal terminal 1111. Thereafter the output lead 123 furnishes an output signal of a predetermined voltage value relative to plus pole 1119, whereas the output lead 122 again assumes zero potential relative to the same pole 10?.
  • the triggering of the bistable flip-flop circult from one to the other stable condition is effected by appyling a negative potential to the base of the one transistor that is turned ofr at a time so that in this manher a current will flow through its emittter-base path.
  • This particular mode of operation is employed in the counting stages 52Ea to f and 52Da to f in conjunction with additional circuit components described hereinafter with reference to FIG. 5.
  • the same bistable switching circuit can also be operated in a different mode according to which sequential pulses are applied to one and the same control lead with the eflect that the circuit will trigger from its stable condition then occupied to the other stable condition.
  • This particular mode of operation is employed in the counting stages of the chain 10 according to FIG. 1. It requires using the control terminal 121 and involves the further circuit components described above, namely the capacitors 113, 116 and the diodes 114, 115.
  • this terminal is abruptly placed at the potential of the plus pole 109.
  • this terminal is abruptly placed at the potential of the plus pole 109.
  • such as abrupt change in potential is effected by the closing of contacts 8, 9 in the earn-operated switch responsive to the steps of travel performed by the inductance heater.
  • the capacitor 113 (FIG. 4) discharges through the still conductive emitter-base of transistor 161 in te direction from the base to the emitter.
  • the emitter-base path is connected to the polarity of the capacitor 113 acting as a voltage source.
  • the base received a positive potential and the emitter a negative potential. This causes the flow of current in the control path of transistor 101 to cease, and the transistor is turned off. As a result, the potential of the collector of transistor 1111 becomes more negative.
  • the above-described circuit operating in the mode last referred to, is employed in the counting stages 11, 12 etc. of chain 10 by issuing sequential control signals to the input lead 121 and employing each time the output value resulting between the reference potential at the terminal 109 and the output lead 122. This output value is issued to the input lead 121 of the next following counting stage in the chain 10.
  • FIG. 1 the stages 11 and 12 in counting chain 16 are provided with reference numerals 121, 122 indicating the respective signal leads and output leads in the same manner as these numerals are employed for the corresponding signal and output terminals in FIG. 4.
  • a bistable circuit according to FIG. 4 is used in each of the counting stages of the two digital analog converters 52E and 52D together with the supplement shown in FIG. 5. It is assumed in FIG. 5 that the supplemental components relate to the first stage a in the counting chain 52E. Accordingly, there is shown in FIG. 5 the series-connected resistor 53E preceding the counting chain, as well as the first transverse resistor 54E, corresponding to the two equally denoted resistors in FIG. 1. Connected in series with resistor 54E is the emitter-collector path of a transistor 126 whose base is connected through an ohmic resistor 127 to the output lead 123 according to FIG. 4. When the output lead 122. (FIG.
  • the output voltage furnished by each of the counting chains 52E and 52D is a function of the transverse connections that are switched on at any time through the resistor 54B and 54D to 59D respecti-vely.
  • the leads and connections of the counting stages a to f by the same reference characters as used in FIGS. 4 and 5.
  • the signal terminals and leads 111, 112 are also employed.
  • the leads 112 are used for presetting signals into the counting stages by means of switches l to q.
  • the leads 11 1 serve for issuing clearing signals to the same counting stages of the counting chains.
  • the length of the travel steps during wln'ch the diameter and energy control is performed in unit steps during zone-melting operation can also be varied, for example by correspondingly varying the number of control pulses issuing per revolution of the transport spindle 5 and displacing the heating device.
  • a group of coaxial cam discs may be provided which can be selectively placed into mechanical connection with the switch 8 to be driven. With a smaller number of cam lobes, the travel steps are larger than with a greater number of lobes.
  • the number of the counting stages in the first portion of the two-part counting chain 10' can be varied. By increasing or decreasing the number of these stages, the size of the travel step is increased or decreased accordingly.
  • the base value of the rod diameter and the base value of the heating energy are first preset into the counting chains 52D and 52B by closing the corresponding switches l to q.
  • the switches l to q are only signal contacts, such as keys or pushbutton contacts, which after entering the signal or counting value return to the illustrated open position.
  • a mechanically coupled mechanism can be used operating as a selector switch which, after being adjusted to the selected setting, is used for supplying a corresponding voltage pulse through a common supply lead.
  • the presetting of base values for rod diameter and heating energy is effected as follows.
  • the purpose of the digital-analog converters 52B and 52D is to convert the signal voltages received from the preceding portion of the system into analog voltages and to supply them to the respective regulating devies 64 and which in turn control the supply of heating energy and the rod diameter respectively.
  • each of the converters 52B and 52D must be set for a desired initial output voltage to be impressed upon the regulating device 64 or 70. This is done by closing a selected number of the switches l, m, n, 0, p, q of each converter 52E, 52D in accordance with a binary code combination.
  • the above-described entering of presetting and clearing signals into the respective binary counter stages a to f in converters 52B and 52D will be further understood by reverting to the circuit diagram of such a stage shown in FIG. 4 and generally described above.
  • the signal pulse for presetting the stage is applied to the signal input terminal E (112). Due to the signal, the transistor 1&2 is turned on and the transistor 161 is turned oif so that the signal appears at output terminal A (lead 122.).
  • the clearing signal is applied to the input terminal E (111). This signal switches the bistable network to its other stable condition in which the transistor N52 is turned off Whereas the transistor 191 is turned on.
  • each of the converters 52E and 52D has been set, by closing of a selected binary code combination of switches l to q to furnish a proper output voltage to the respective regulating devices 64 and 7% so that the subsequent counting operation of the system commences from these entered base values for the diameter of the semiconductor rod and for the electric heating energy to be supplied to the melting Zone.
  • the heater winding must now be placed to the zero position of its travel relative to the rod. This can be done in response to a signal and in conjunction with a limit switch or stop which termniates the displacement to the zero position after that position is reached.
  • the travelling nut commences to shift upwardly.
  • the spindle thread has a pitch of 1 mm. height and that the cam 6 produces eight pulses for each revolution of the spindle, which pulses are issued to the counter chain It and also to one of the input leads for the AND-gates 24E to 27E for the energy counting chain 52E, and to one of the input leads of the AND-gates 24D to 27D for the diameter counting chain 52D.
  • the first portion of the counter chain it) possesses four counting stages 11 to 14- for binary coding.
  • the second portion of the counter chain 16 receives a signal at its first stage 15.
  • the individual travel step in the example here being discussed amounts to 2 mm.
  • the change in energy supply and in diameter of the rod 1 is performed in accordance with the number of unit steps pre-adjusted at the cross-bar distributor 46. For example, if for the travel step under observation four unit steps are to be performed for energy change and also for change in diameter, then the cross-bar distributor must release for this travel step the AND-gate 26E as well as the AND-gate 26D. These two gates then pass the output values to the input stages of the respective digital-analog converters constituted by the counting chains 52B and 52D.
  • the converter 28 translates the binary coding of the travel points into analog voltage values continuously representing the travel in accordance with a natural sequence of numbers.
  • the converter 28 may be given the electrical design exemplified in FIG. 6.
  • FIG 6 shows the same counting stages 14-, 15, 16 etc., as illustrated in FIG. 1.
  • each of these counting stages is equipped with two amplifier units a and b for respectively amplifying the yes signals and no signals which each of the counting stages 14 etc. furnishes at the respective output terminals A and A of its bistable lip-flop network according to FIG. 4. All components which, according to FIG. 6, form part of the converter are shown within a dot-and-dash enclosure for more clearly indicating the relation of FIG. 6 to FIG. 1.
  • the converter 28 further comprises diodes designated by D with a numerical subscript, and ohmic resistors analogously denoted by W.
  • D diodes
  • W ohmic resistors
  • FIG. 6 shows a smaller number of counting stages 14 etc. but a larger number of output leads 261-232 corresponding to those denoted by 29 to 45 in FIG. 1, which issue from the converter 28 for connection to the vertical bars of the crossbar distributor 46.
  • the counting system comprising the counting stages 14 etc.
  • the output terminals of the amplifiers b are conductively connected with the zero potential of the voltage source feeding the system.
  • the source terminal that constitutes this zero potential in the system is designated by (-1-).
  • the amplifiers a in each of the respective counting stages are not connected to the voltage source and hence cannot apply a potential to any other component of the system.
  • distributor bar 261 or 29
  • corresponding signals are given onto the AND-gates in accordance with the selected distributor connections exemplified by the above-described contact plugs or screw bolts S (FIG. 1).
  • FIG. 7 shows more in detail an example of a regulating circuit applicable for controlling the power supply to the heater coil 3 according to FIG. 1.
  • a regulating circuit applicable for controlling the power supply to the heater coil 3 according to FIG. 1.
  • Represented in FIG. 7 and identified by dot-and-dash enclosures are the same regulating device 64 and high-frequency generator 67 as shown in FIG. 1, as well as the sensing device 66 to which the components 64 and 67 are connected.
  • the high-frequency generator .67 comprises a tube circuit 67a with an output transformer 67b whose inductive coupling between primary and secondary winding is adjustable.
  • the coupling is controlled by an electric motor 670, depending upon the running direction of the motor, the connection of motor 670 with the coupling control device of the transformer being indicated by a broken line 67d.
  • the measuring device 66 comprises a current transformer 66a to which an ohmic resistor 66!; is connected in parallel. A series-connection of a diode 66c and a capacitor 66d lies in parallel to the resistor 66b. This circuit serves for measuring the peak value of rectified voltage by means of an indicating instrument 66a. The peak value occurring at capacitor 66d is simultaneously impressed between two leads 65 connected to the regulating device 64.
  • the regulator 64 is equipped with a polarized relay whose winding 64a controls two interconnected movable contacts 64! and 640 cooperating with respective pairs of fixed contacts which are connected by leads 69 with the motor 67c.
  • the relay contacts 64b and 64c operate as a reversing switch for connecting the motor 670 to a voltage source with one or the other voltage polarity, so that the motor runs in one or the other direction, depending upon occurrence and direction of current flow through the relay 64a.
  • the regulator 64 i further equipped with two ohmic resistors 64k and MI.
  • the relay winding 64a is connected to the zero potential of the voltage source (D).
  • the right-hand end of resistor 64l is connected to the output lead 69E of the digital-analog converter 52E (FIG. 1).
  • the components 66d, 64k, 641, connected to the relay winding 64a and across the voltage source (60E-O), constitute a Wheatstone bridge network.
  • Two branches of the bridge network contain respective voltage ources 66:! and (6EO), whereas the relay winding 64a lies in the output diagonal. Consequently, the bridge network compares the voltages furnished from 66d and 60E-O respectively.
  • a corresponding difference voltage is impressed upon the relay winding 64a.
  • the current in the relay thus depends as to magnitude and direction upon the magnitude and polarity of the voltage difference.
  • the relay contacts 64b, 640 are displaced accordingly and cause the motor 67c in the generator assembly 67 to correspondingly vary the degree of coupling between the two windings of the transformer 6712. This reduces or increases the heating power supplied to the inductive heater coil 3, depending upon the error voltage formed in the regulating device 64.
  • FIG. 8 illustrates by way of example an embodiment of circuitry applicable for the control components 72 and 74 shown in FIG. 1. These components serve for controlling the rod diameter in response to a diameter measurement in the region of the freezing front of the molten zone 1a. This diameter is sensed, according to FIGS. 1 and 8, by means of a winding 71 surrounding the rod 1 at the freezing front. The change in rod diameter modifies the inductance of the winding.
  • the end of the winding are connected to the device 72 identified by dot-anddash confines in FIG. 8.
  • the device comprises a highfrequency generator 72a of about 20 megacycles per second which is connected in the input diagonal of a bridge network whose branches comprise respectively two ohmic resistors 72b, 72c and an inductance coil 72d.
  • the inductance or coil 72d constitutes, in effect, the datum value in the network, and as soon as the reactive impedances of components 71 and 72d are equal, the bridge network is in an electrical condition at which a given output value of voltage appears in its output diagonal comprising the primary Winding 7 2c of a transformer 72k.
  • the regulator 70 may be given a design and performance as described above with reference to the regulator 64 shown in FIG. 7. Accordingly, there is connected to the regulator 70 the pole O of the voltage source and a lead coming from the terminal 60D of the digital-analog converter 52D, as is also apparent from FIG. 1. As explained with reference to FIG. 7, the regulator contains a bridge network whose output diagonal comprises a polarized relay which, in turn, energizes the reversible motor 74a in control device 74 to run in one or the other direction, depending upon the direction in which the rod diameter departs from the programmed datum value.
  • the motor 74a acts through a transmission gear 74 upon the lower holder 2 of the semiconductor rod 1 for axially displacing the holder in one or the other direction, thus subjecting the molten zone to compression or stretching as required for maintaining a constant diameter at the freezing front of the molten zone.
  • Electric control apparatus for floating-zone melting of semiconductor rods, comprising two coaxial rod-end holders jointly defining a rod axis, an electric heating device movable along said axis for producing a molten zone in the rod being processed, holder displacing means for axially displacing one of said holders relative to the other to vary the cross section of the molten zone, electric power supply means connected to said device and being controllable for varying the heating energy transmitted to the rod being processed, a digital control system connected to said displacing means and said power supply means for conjointly controlling said cross section and said heating power in dependence upon the travel of said heating device along the rod axis, said control system having counting-pulse transmitter means in operative connection with said heating device for issuing a given number of pulses for given travel steps of said device, and said system having two programming means for presetting a travel-responsive power program and a travel-responsive cross-section program respectively, whereby the heating power supplied to the zone and the zone cross section are controlled in unit increments of change corresponding
  • said heating device comprising an inductance heater winding extending about said axis, and a transport mechanism for moving said heater along the rod axis, said pulse transmitter means of said digital control system being connected with said transport mechanism for issuing said given number of counting pulses for each of equal steps of travel of said heater.
  • Electric control apparatus for floating-zone melting of semiconductor rods, comprising two coaxial rod-end holders jointly defining a rod axis, an electric heating device movable along said axis for producing a molten zone in the rod being processed, holder displacing means for 1 axially displacing one of said holders relative to the other to vary the cross section of the molten zone, electric power supply means connected to said device and being controllable for varying the heating energy transmitted to the rod being processed, a digital control system connected to said displacing means and said power supply means for conjointly controlling said cross section and said heating power in dependence upon the travel of said heating de vice along the rod axis, said control system having counting-pulse transmitter means in operative connection with said heating device for issuing a given number of pulses for given travel steps of said device, and said system having two programming means for presetting a travel-responsive power program and a travel-responsive cross section program respectively, whereby the heating power supplied to the zone and the zone cross section are controlled in unit increments of change
  • each of said digital-analog converters comprising two voltage supply buses, a resistor, a voltage source connected to said buses in series with said resistor, a plurality of counter stages and resistors, said latter counter stages being connected across said two buses in series with one of said latter resistors respectively to jointly form a chain network of counter stages, whereby a travel-responsive and program-controlled output voltage appears between said buses at the end of said chain network remote from said source.
  • said programming means comprising a cros bar selector having groups of members selectively interconnectable at respective intersection points for setting the desired control program.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Automation & Control Theory (AREA)
  • General Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Electromagnetism (AREA)
  • Liquid Deposition Of Substances Of Which Semiconductor Devices Are Composed (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
US243973A 1961-12-07 1962-12-06 Electric control apparatus for zone melting of semiconductor rods Expired - Lifetime US3198929A (en)

Applications Claiming Priority (1)

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DES77026A DE1209551B (de) 1961-12-07 1961-12-07 Verfahren zum tiegelfreien Zonenschmelzen eines stabfoermigen Halbleiterkoerpers miteiner Steuerung seines Durchmessers- bzw. Querschnittsverlaufs und Vorrichtung zur Durchfuehrung dieses Verfahrens

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3880599A (en) * 1972-04-26 1975-04-29 Siemens Ag Control of rod diameter responsive to a plurality of corrected parameters
US4292487A (en) * 1977-07-07 1981-09-29 Topsil A/S Method for initiating the float zone melting of semiconductors
US4866230A (en) * 1987-04-27 1989-09-12 Shin-Etu Handotai Company, Limited Method of and apparatus for controlling floating zone of semiconductor rod
US4873063A (en) * 1986-01-06 1989-10-10 Bleil Carl E Apparatus for zone regrowth of crystal ribbons
US4925636A (en) * 1987-12-14 1990-05-15 Grumman Aerospace Corporation Apparatus for directional solidification of a crystal material
US4931945A (en) * 1987-12-05 1990-06-05 Shin-Etsu Handotai Company Limited Method of controlling floating zone
US5074952A (en) * 1987-11-13 1991-12-24 Kopin Corporation Zone-melt recrystallization method and apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3712772A (en) * 1970-09-23 1973-01-23 Hunkar Instr Dev Labor Inc Control system for parison extruders

Citations (3)

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Publication number Priority date Publication date Assignee Title
US2992311A (en) * 1960-09-28 1961-07-11 Siemens Ag Method and apparatus for floatingzone melting of semiconductor rods
US3002115A (en) * 1957-08-22 1961-09-26 Bendix Corp Electrical system for controlling movement of objects
US3046379A (en) * 1959-09-11 1962-07-24 Siemens Ag Method and apparatus for zone melting of semiconductor material

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Publication number Priority date Publication date Assignee Title
DE890420C (de) * 1951-09-02 1953-09-17 Guenther Dipl-Ing Budnick Verfahren zum Messen von Strecken und zum Teilen von Kreisen
AT194444B (de) * 1953-02-26 1958-01-10 Siemens Ag Verfahren und Einrichtung zur Behandlung einer längserstreckten Halbleiterkristallanordnung
AT215481B (de) * 1958-04-22 1961-06-12 Siemens Ag Verfahren zum tiegellosen Zonenziehen von Halbleitermaterial
DE1094238B (de) * 1959-03-09 1960-12-08 Licentia Gmbh Verfahren zum Konstanthalten der Breite der Schmelzzone beim tiegelfreien Zonenschmelzen

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3002115A (en) * 1957-08-22 1961-09-26 Bendix Corp Electrical system for controlling movement of objects
US3046379A (en) * 1959-09-11 1962-07-24 Siemens Ag Method and apparatus for zone melting of semiconductor material
US2992311A (en) * 1960-09-28 1961-07-11 Siemens Ag Method and apparatus for floatingzone melting of semiconductor rods

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3880599A (en) * 1972-04-26 1975-04-29 Siemens Ag Control of rod diameter responsive to a plurality of corrected parameters
US4292487A (en) * 1977-07-07 1981-09-29 Topsil A/S Method for initiating the float zone melting of semiconductors
US4873063A (en) * 1986-01-06 1989-10-10 Bleil Carl E Apparatus for zone regrowth of crystal ribbons
US4866230A (en) * 1987-04-27 1989-09-12 Shin-Etu Handotai Company, Limited Method of and apparatus for controlling floating zone of semiconductor rod
US5074952A (en) * 1987-11-13 1991-12-24 Kopin Corporation Zone-melt recrystallization method and apparatus
US4931945A (en) * 1987-12-05 1990-06-05 Shin-Etsu Handotai Company Limited Method of controlling floating zone
US4925636A (en) * 1987-12-14 1990-05-15 Grumman Aerospace Corporation Apparatus for directional solidification of a crystal material

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GB1032217A (en) 1966-06-08
CH407958A (de) 1966-02-28

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