US3136876A - Indicator and control system - Google Patents

Indicator and control system Download PDF

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US3136876A
US3136876A US65231A US6523160A US3136876A US 3136876 A US3136876 A US 3136876A US 65231 A US65231 A US 65231A US 6523160 A US6523160 A US 6523160A US 3136876 A US3136876 A US 3136876A
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coil
bar
sensing coil
inductive coupling
induced
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Jevon L Crosthwait
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Clevite Corp
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Clevite 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
    • 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
    • Y10T117/1004—Apparatus with means for measuring, testing, or sensing
    • Y10T117/1008—Apparatus with means for measuring, testing, or sensing with responsive control 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
    • Y10T117/1032—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
    • Y10T117/1076—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

  • This invention relates generally to systems for controlling, orindicating variations in, parameters effecting electromagnetic inductive coupling.
  • the invention pertains also to induction heating apparatus embodying such con trol and indicator systems, and specifically contemplates its application in zone melting apparatus, particularly vertical floating-zone type furnaces such as are used for melting and recrystallizing elongate cylindrical ingots of polycrystalline semiconductor materials to produce similarly shaped single crystals of predetermined diameter for ultimate fabrication into semiconductor devices.
  • the floating-zone technique and apparatus for carrying it out involve the disposition of an elongated bar of the fusible material being handled in a vertical position; establishing a molten zone at one end of the bar, usually by means of high frequency induction heating coils coaxially surrounding the bar; and
  • the molten zone travels slowly along the entire length of the bar.
  • the molten zone is moved upwardly from the bottom to the top of the bar and, if necessary or desirable, a single crystal seed is placed in contact with the end of the bar at Which the molten zone is initiated in order to promote single crystal growth.
  • the salient characterizing feature of the floating-zone procedure is the fact that, as the name implies, the molten zone is not provided with any external support; it is sustained solely and entirely by the characteristic surface tension of the fused material. As a result the material crystallizing at the trailing boundary (liquid/solid interface) of the zone, does so in the complete absence of any external physical contact which might exert a stress on the freezing material and cause polycrystalline growth.
  • Still another object is the provision of improved floating-zone type apparatus capable of growing bar crystals of a uniform cross-sectional dimension closely approaching the maximum limit imposed by the surface tension of the material crystallized.
  • a further object is the provision of an improved crystal size control system for floating-zone type crystallizing apparatus which is characterized by enhanced simplicity, sensitivity and reliability and which enables crystal diameter to be determined, within the limits imposed by surface tension of the material, to suit production convenience and economy for the particular size of the dice required for the device into which the crystal ultimately will be incorporated.
  • a still further object is the provision of a novel crystal size control system for floating-zone apparatus which is unaffected by frequency fluctuations in the service power supply.
  • apparatus in accordance with the present invention comprising an induction coil adapted to have a nominally conductive (i.e., conductive or. semiconductive) object disposed in its flux field.
  • a sensing coil and reference coil are coaxially disposed with respect to the inductioncoil and are so dimensioned and located relative to each other and to the induction coil and such an object in its flux field that there is induced, in the sensing coil an electrical voltage due to, and by means of, inductive coupling to both the intale for semiconductor device fabrication to obtain a uniform cross-section in the interests of convenience and improved yield in processing into dice or wafers.
  • dimensional uniformity reduces variations in structural perfection of the crystal and in concentration of doping additions.
  • Control of lateral dimensions has an additional importance where a floating-zone type operation is involved because each material operated upon has a characteristic maximum diameter beyond which the surface tension is not suflicient to sustain the molten zone. Therefore, to obtain a crystal of maximum possible cros section, desirable for economic reasons, Without risk of exceeding the critical limit requires delicate and precise control of the diameter of the molten zone which is, in turn, closely inter-related with that of the grown crystal.
  • Another general object is the provision of improved induction heating apparatus including a monitoring and/ or duction coil and the alternating currents induced thereby in such object and, in the reference coil, an electrical voltage substantially due only to, and by means of, inductive coupling to the induction coil.
  • Circuit means are provided for. comparing the respective electrical voltages in the sensing coil and reference coil to produce a difference signal indicative of changes in the inductive coupling between the sensingcoil and such an object and, therefore, of deviations by a parameter effecting inductive coupling from an established norm.
  • the signal generated in response to deviations of the parameter is utilized to correct the deviation.
  • FIGURE 1 is a schematic side elevational view, partially in section, illustrating the essential components of, and FlGURE 2 is a circuit "wiring diagram for, fioating-zone apparatus in accordance with the present invention.
  • charge bar Ida is illustrated as being cylindrical this shape is not essential. It may be of other non-cylindrical, geometric or irregular configurations and it may have a cross-sectional dimension substantially different from recrystallized ingot lllc. It is to such situation that the present invention can be applied with particular utility and advantage.
  • charge bar Ida and grown crystal ltlc may be considered as a monolithic bar of silicon (designated in its entirety by reference number along which molten zone ltlb is slowly traversed, the direction of travel assumed to be upward in the illustrated embodiment.
  • the solid-liquid interfaces ltla-b and ltlb-c, respectively contiguous to the charge bar and the grown crystal, will be referred to as the leading and trailing interfaces, respectively, with allusion to the direction of zone travel.
  • the vertical spacing between supports 12 and 14 is rendered adjustable by providing means for moving the supports vertically relative to one another, i.e., either or both of the supports may be movable.
  • lower support 12 is fixed
  • upper support 14 is movable by means of a worm gear 16 driven by a reversible electric servo-motor 18 through a suitable gear train 19.
  • the induction heating system also includes a pair of short-circuited coils 26, 23, respectively disposed above and below, and coaxial with, coil 26, at relatively short distances therefrom. Coils 26 and 28 serve to constrict the magnetic field generated by induction coil 20 and, therefore, define the length of the molten zone.
  • induction coil heating system 29, 22, 24, 26, 28 insofar as they effect the axial extent of the molten zone produced, its temperatures, and such variables are well known in the art and form no part of the present disclosure.
  • the induction heating system produces a molten zone encompassing a relatively short (as compared to the total length of bar ltl) segment of the bar.
  • zone 10b In its movement, zone 10b maintains a characteristic ogee profile configuration.
  • the concave curve 10d of the ogee is at a necked down region of minimum crosssection slightly above the mid-point of the zone; the convex curve 103 of the ogee encompasses the bottom portion of the molten zone adjacent trailing interface lltlb-c;
  • the convexly-curved segment ltle of the zone bulges outwardly beyond the circumference of interface 1@bc, tending to increase the diameter of the growing crystal.
  • the zone constricts radially so that the circumference of convexly-curved zone portion the is smaller than that of interface ltlb-c, the diameter of the growing crystal tends to decrease.
  • zone length 1% under equilibrium conditions is substantially constant and is determined by design and functioning of the induction coil heating system 20-25; the changes in zone length effected by relative physical displacement of interfaces like-b and lltlb-c is evanescent in nature as is the resultant change in zone geometry.
  • the curve bounding zone portion file In order to maintain a constant diameter in the grown crystal, the curve bounding zone portion file must be tangent to the sides of crystal 100. In accordance with the present invention this condition of tangencyis maintained by continuous monitoring of the cross-section of the grown crystal in the region of interface b-c to detect changes resulting from deviations in the desired tangency and applying a corrective adjustment to the spacing between interfaces lltlab and 1012-0.
  • a single-turn sensing coil 38 is coaxially disposed about bar it) in close proximity to interface ltlb-c, being sufficiently close thereto that R.-F. alternating currents induced in the bar by coil 2% induce a potential in the sensing coil.
  • An increase in the diameter of bar 2% at the location circumscribed by sensing coil 30 increases the degree of coupling between the bar and the sensing coil and, therefore, the magnitude of the potential induced in the latter. In like manner, a decrease in diameter has the converse effect.
  • Sensing coil 36 is disposed at a fixed axial distance from coil 29 (behind the coil as regards the direction of travel) and is movable therewith.
  • the distance between sensing coil 30 and induction coil Ztl is small enough that an R.-F. voltage is induced in the former, independently of that resulting from the coupling to bar ltl.
  • sensing coil 30 could be mechanically connected to the transport system, not shown, which moves the induction coil, and at such a distance therefrom that it is located at all times substantially in the plane of trailing interface ltlb-c.
  • Coaxially disposed with respect to induction heating coil 2% at a greater distance from bar it than sensing coil 39 is an additional single turn pickup coil 32, hereinafter termed the reference coil.
  • the distance between induction coil 20 and reference coil 32 is small enough to allow effective electromagnetic coupling therebetween wtih the result that an R.-F. potential is induced in thelatter similar, at least in order of magnitude, to the R.-F. voltage induced in sensing coil 36 by virtue of its coupling to the induction coil as.
  • reference coil 32 is far enough away from bar it) that inductive coupling thereto is negligible.
  • the spacing conditions required are conveniently obtained, as in the illustrated embodiment, by mahng reference coil 32 of considerably larger diameter than sensing coil 3%; the desired degree of coupling between induction coil 26 and the reference coil then may be attained by selection of the axial spacing therebetween.
  • the voltages of sensing coil 36 and reference coil 32 are compared so as to generate a control signal proportional to the deviation of the cross-sectional dimension of the grown crystal at interface b-c from a pro-established value.
  • This function is carried out by a circuit such as illustrated in FIGURE 2.
  • the circuit basically, comprises a load impedance and two substantially identical networks 36 and 38 for rectifying and attenuating the respective voltagesof the sensing and reference coils and applying them in opposition to one another across the load impedarrce so as to produce therein a current proportional to the voltage difference.
  • This circuit will now be de scribed in greater detail with reference to the FIGURE 2 wiring diagram.
  • the load impedance of the circuit is represented by resistorR connected in'series with a center zero ammeter M.
  • the series combination of meter M and load resistor R is common to both loops 36 and as, each of which comprises respective crystal diodes 40 and 42, arranged with opposite polarities relative to the load.
  • one terminal of sensing coil 30 is connected via a conductor 44 and a capacitive attenuator consisting of C and C to the positive terminal of diode 40 the negative side of which is connected through a dropping resistor R to one end 46 of the common load branch of networks 36 and 38.
  • one terminal of reference coil 32 is connected via a conductor 48 and a. capacitive attenuator consisting of C and C to the negative side of diode 42 the positive terminal of which is connected through variable resistor R to the same end 46 of the common branch.
  • the respective remaining terminals of sensing coil 30 and reference coil 32 are returned to the other end 50 of the common branch by conductors 52 and 54.
  • By-pass capacitors C3 and C are connected across networks 36 and 38 in parallel with the common branch and, respectively, resistors R and R
  • Radio frequency chokes L and L are connected across capacitors C and C respectively, to provide a return path for rectified D.-C. generated by the rectifying action of diodes 40 and 42.
  • a high gain amplifier 56 is connected across load resistance R bomb 56 is fed to, and utilized to control the operation of, servo-motor 18.
  • variable resistor R By adjustment of variable resistor R the voltages in the sensing coil and pickup coil, respectively, due to inductive coupling to the induction coil can be precisely balanced so that, for a given diameter of crystal 10c, i.e., the condition where the convex curvature of the molten zone is tangent to the sides of the grown crystal, no current flows in the load impedance branch of the circuit, the equal and opposite voltages producing a null.
  • R is adjusted to obtain a null when the crystal has the desired diameter (which can be achieved initially by manual control of motor 18,);
  • the null will be upset resulting in a current flowing in the load impedance generating an error signal across resistor R
  • the error signal is amplified by amplifier 56 and applied to servo-motor 18 to actuate it.
  • the direction of operation of the motor depends on the polarity of the signal, the relation between polarity and motor direction being selected so that a signal indicative of an excess diameter in the grown crystal operates the motor to increase the distance between upper and lower supports 12 and M- thus increasing the length of molten zone ltlb.
  • a signal indicative of a deficiency in the interface dimension causes reverse operation of motor 18 so that the upper support is moved toward the lower decreasing the length of the molten zone.
  • Gearing 19 of the servo-motor is selected in relation to the rate of growth of the crystal so that a correction to the crystal dimension is applied smoothly and without any tendency to spilling of the molten zone.
  • amplifier 56 may be omitted and servo-motor 18 operated manually in accordance with visual observation of center zero meter M as required to maintain a substantially zero reading thereon.
  • the apparatus described utilizes the fact that a voltage is induced in sensing coil 3t) which is a function of the size of the crystal. .However, the voltage induced is also a function of the resistivity of the object in the field of the R.-F. induction coil.
  • resistivity is virtually constant because the factors effecting resistivity, e.g., the identity of the material, and its temperature also are essentially constant, and the variable to be controlled in size.
  • the same basic principles and general arrangement can be utilized to measure or control one of the other variables, e.g., temperature Where size is constant.
  • One application of this type' would be to brazing apparatus employing an R.-F. induction heater.
  • the object to be brazed is composed of a material having an appreciable temperature coefficient of resistivity as is usually the case, the sensing arrangement described hereinabove could be incorporated as a temperature indicator or controller.
  • a monitoring and :control system for parameters effecting electromagnetic inductive coupling comprising: an induction coil adapted to have a nominally conductive object disposed in its fiux field; a sensing coil and a reference coil coaxially disposed with respect to said inducdue to, and by means of, inductive coupling to both said induction coil and the alternating currents induced thereby in such object and, in the reference coil, an electrical voltage substantially due only to, and b means of, inductive coupling to said induction coil; and circuit means or comparing the respective electrical voltages in said sensing coil and reference coil, to produce an electrical difference signal indicative of changes in the inductive coupling between said sensing coil and such an object and, therefore, of deviations by a parameter effecting said coupling from an established norm.
  • circuit means comprises a load impedance; means for rectifying the respective voltages induced in said sensing coil and said reference coil to obtain unidirectional voltages applied, in opposition to each other, across said load impedance to produce therein a current proportional to the difference between said unidirectional voltages, the potential drop across said load impedance constituting said difference signal.
  • circuit means includes means for adjusting the unidirectional voltage derived from said reference coil to a predetermined value correlated to a particular value of said parameter.
  • Induction heating apparatus comprising: a high frequency electrical induction heating coil efiective to heat an object in its flux field; a sensing coil coaxially disposed with respect to said heating coil, the size of said sensing coil and its location relative to said heating coil and to an object in the flux field of said heating coil being such that there is induced in said sensing coil an electrical voltage due to and by means of inductive coupling to high frequency alternating current produced in such an object by said heating coil, the magnitude of said voltage being directly proportional to the degree of said inductive coupling which, in turn, is variable in accordance with the proximity between such object and said sensing coil and with the resistivity of such object and, therefore, its temperature; and means for establishing a reference voltage and comparing thereto the induced voltage in the sensing coil to generate an electrical signal indicative of deviations of temperature, size and location of such an object from a pro-established datum.
  • induction heating apparatus comprising: a high frequency electrical induction heating coil effective to heat an object in its flux field; a sensing coil coaxially disposed with respect to said heating coilfthe size of said heating coil and its location relative to said heating coil and to an object in the flux field of said heating coil being such that there is induced in said sensing coil an electrical voltage due to and by means of inductive coupling to high frequency alternating current produced in such an object by said heating coil, the magnitude of said voltage being directly proportional to the degree of said inductive coupling which, in turn, is variable in accordance with the proximity between such object and said sensing coil and with the resistivity of such object and, therefore, its temperature; means for establishing a reference voltage and comparing thereto the induced voltage in the sensing coil to generate a control signal; and means utilizing said control signal to adjust a parameter affecting the inductive coupling.
  • Induction heating apparatus comprising: a radio frequency electrical induction heating coil effective to heat an object in its flux field; a sensing coil coaxially disposed with respect to said heating coil, the size of said sensing coil and its location relative to said heating coil and to an object in the flux field of said heating coil being such that there is induced in the sensing coil an electrical voltage due to, and by means of, inductive coupling to both said induction coil and the high frequency alternating current product thereby in such object, the portion of said voltage due to current in such object being directly proportional to the degree of said inductive coupling which, in turn, is variable in accordance with the proximity between such object and said sensing coil and with the resistivity of such object and, therefore, its temperature; an additional coil disposed at a location sulficiently remote from an object in the flux field of the heating coil that inductive coupling thereof to such an object is of negligible effect and sufiiciently close to said heating coil to cause a substantially constant reference voltage to be induced in said additional coil; circuit means for comparing the
  • Induction heating apparatus including means for utilizing said signal to adjust a parameter effecting the inductive coupling between said sensing coil and such object.
  • induction heating apparatus comprising: high frequency electrical induction heating coil means effective to heat an object disposed in its flux field; sensing coil means coaxially disposed with respect to said heating coil means, the size of said sensing coil means and its location relative to said heating coil means and to an object in the flux field of said heating coil means being such that there is induced in the sensing coil means an electrical voltage due to, and by means of, inductive coupling to both said induction heating coil means and the high frequency alternating current produced thereby in such object, the portion of said voltage due to current in such object being directly proportional to the degree of said inductive coupling which, in turn, is variable in accordance with the proximity between such object and said sensing coil means and with the resistivity of such object and, therefore, its temperature; additional coil means coaxially disposed with respect to said heating coil means at a location which normally would be sufficiently more remote than said sensing coil from such an object that inductive coupling thereof to such object is of negligible effect, said additional coil means being suificiently close to said heating coil means to cause
  • Apparatus for passing an unsupported molten zone along a vertically-disposed and elongated bar of fusible material comprising: respective support means fixedly engaging said bar at vertically spaced locations; means operative to adjust the spacing between said support means; high frequency electrical induction heating means effective to create a molten zone in said bar encompassing a relatively short longitudinal segment thereof; means for vertically displacing said heat-generating means relative to said bar with concomitant displacement of said molten zone therealong; a sensing coil, located at a constant vertical distance relative to said heat generating means, concentrically disposedabout said bar so as to be in close proximity to the liquid-solid interface at the trailing end of said molten zone whereby an induced electrical voltage is generated in said sensing coil by inductive coupling to high frequency alternating current produced in said bar by said heating means, the magnitude of said voltage being directly proportional to the degree of said inductive coupling which, in turn, is directly proportional to the proximity between said bar and said sensing coil and, therefore, to
  • Apparatus for passing an unsupported molten zone along a vertically-disposed and elongated bar of fusible material comprising: respective support means fixedly engaging said bar at vertically spaced locations; means operative to adjust the spacing between said support means; high frequency electrical induction heating means effective to create a molten zone in said bar encompassing a relatively short longitudinal segment thereof; means for vertically displacing said heating means relative to said bar with concomitant displacement of said molten zone therealong; a sensing coil, located at a constant vertical distance relative to said heating means, concentrically disposed about said bar so as to be in close proximity to the liquid-solid interface at the trailing end of said molten zone whereby an induced electrical voltage is generated in said sensing coil by inductive coupling to high frequency alternating current produced in said bar by said heating means, the magnitude of said voltage being directly proportional to the degree of said inductive coupling which, in turn, is directly proportional to the proximity between said bar and said sensing coil and, therefore, to the crosssectional
  • Apparatus for passing an unsupported molten zone along a vertically-disposed and elongated bar of fusible material comprising: respective support means fixedly I engaging said bar at vertically spaced locations; means operative to adjust the spacing between said support means; radio frequency electrical induction heating coil means effective to create a molten zone in said bar encompassing a relatively short longitudinal segment thereof; means for vertically displacing said induction heating coil means relative to said bar with concomitant displacement of said molten zone therealong; sensing coil means, located at a fixed vertical distance relative to said induction heating coil means, concentrically disposed about said bar so as to be in sufficiently close proximity to both said induction heating coil and the liquid-solid interface at the trailing end of said molten zone that there is induced in the sensing coil means an electrical voltage due to and by means of inductive coupling to both said induction coil means and the high frequency alternating current produced thereby in said bar, the portion of said voltage due to current in the bar being directly proportional to the degree of
  • Apparatus for passing an unsupported molten zone along a vertically-disposed and elongated bar of fusible material comprisingz respective support means fixedly engaging said bar at vertically spaced locations; means operative to adjust the spacing between said support means; radio frequency electrical induction heating coil means effective to create a molten zone in said bar encompassing a relatively short longitudinal segment thereof; means for causing relative axial displacement between said induction coil means and said bar with concomitant displacement of said molten zone along the bar; sensing coil means located at a fixed vertical distance relative to said induction heating coil, concentrically disposed about said bar so as to bein sufficiently close proximity to both said induction heating coil means and the liquid-solid interface at the trailing end of said molten zone that there is induced in the sensing coil means an electrical voltage due to and by means of inductive coupling to both said induction heating coil means and the high frequency alternating current produced thereby in said bar, the portion of said voltage due to current in the bar being directly proportional to the degree of said inductive coup
  • additional coil means disposed about said bar at a location sufliciently more remote from the bar than said sensing coil means that in ductive coupling thereof to the bar is of negligible effect and sufficiently close to said induction coil to cause a substantially constant reference voltageto be induced in the additional coil means; circuit means for comparing the induced voltage in said sensing coil means to said reference voltage; means included in said circuit means for adjusting said reference voltage to establish a null at a predetermined value of said induced voltage in the sensing coil and to generate a control signal upon the occurrence, and in proportion to the magnitude, of deviations from said null; and means utilizing said control signal to operate said spacing adjustment means and thus vary the vertical spacing between said support means.
  • Apparatus for passing an unsupported molten zone along a vertically-disposed and elongated bar of fusible material comprising: respective support means fixedly engaging said bar at vertically spaced locations; means operative to adjust the spacing between said support means; radio frequency electrical induction heating coil means effective to create a molten zone in said bar encompassing a relatively short longitudinal segment thereof; means for causing vertical displacement between said induction heating coil means and said bar with.
  • sensing coil means located at a fixed vertical distance relative to said induction heating coil means, concentrically disposed about said bar in substantially the same plane as and in sufficiently close proximity to the liquid-solid interface at the trailing end of saidmolten zone that there is induced in the sensing coil means an electrical voltage due to and by means of inductive coupling to both said induction heating coil means and the high frequency alternating current produced thereby in said bar, the portion of said voltage due to current in the bar being directly proportional to the degree of said inductive coupling which, in turn, is directly proportional to the proximity between said bar and said sensing coil means and, therefore, to the lateral dimension of said bar; additional coil means disposed about said bar at a location sufficiently more remote from the bar than said sensing coil means that inductive coupling thereof to the bar is of negligible effect and sufiiciently close to said induction coil to cause a substantially constant reference voltage to be induced in the additional coil means; circuit means for comparing the induced voltage in
  • circuit means comprises a load impedance; means for rectifying the respective voltages induced in said sensing coil means and said additional coil means to obtain unidirectional voltages applied, in opposition to each other, across said load impedance to produce therein at current proportional to the difference between said unidirectional voltages, the potential drop across said load impedance constituting said control signal.
  • Apparatus according to claim 14, wherein said cir- 1 1 cuit means includes means for adjusting the unidirectional voltage derived from said additional coil means to a predetermined value correlated to a particular dimension of said bar at said interface.
  • An induction heating apparatus for a movable object havingna variable, dimension comprising: a high frequency electrical induction heating coil effective to heat an object in its flux field; a sensing coil coaxially dis-, posed with respect to said heating coil and positioned adjacent the object whereby a voltage is induced in said sensing coil as a result of inductive coupling with the object and as a result of inductive coupling with said heating coil; a reference coil coaxially disposed with respect to said heating coil to be inductively coupled only thereto whereby a voltage is induced in said reference coil as a result of inductive coupling thereof with said heating coil; and circuit means for comparing the electrical voltages induced in said sensing coil and said reference coil respectively to produce an electrical difier- .Lufi! ence signal indicative of the changes in inductive coupling between said sensing coil and the object and thus indicative of variations in dimension of the object.

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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)
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US65231A 1960-10-26 1960-10-26 Indicator and control system Expired - Lifetime US3136876A (en)

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DEJ20667A DE1275298B (de) 1960-10-26 1961-10-17 Anordnung zum Messen und Regeln einer die induktive Kopplung zwischen Induktionsspulen beeinflussenden Groesse eines elektrisch leitenden Gegenstandes

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3293002A (en) * 1965-10-19 1966-12-20 Siemens Ag Process for producing tape-shaped semiconductor bodies
US3428436A (en) * 1963-12-16 1969-02-18 Monsanto Co Methods and apparatus for zone melting
US3515836A (en) * 1968-06-24 1970-06-02 Business Assets Corp Elevator means for a heat scanner device
US3604882A (en) * 1970-07-24 1971-09-14 Park Ohio Industries Inc Power control device for an inductor
US4032389A (en) * 1974-03-29 1977-06-28 National Research Development Corporation Apparatus for automatically controlling crystal growth
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US2691732A (en) * 1948-12-07 1954-10-12 Westinghouse Electric Corp Radio frequency generator
DE962006C (de) * 1954-07-01 1957-04-18 Siemens Ag Verfahren zum induktiven Schmelzen, insbesondere Zonenziehen, von Halbleitern mittels einer Hochfrequenzspule
US2913561A (en) * 1958-04-22 1959-11-17 Siemens Ag Processing semiconductor rods
US2916593A (en) * 1958-07-25 1959-12-08 Gen Electric Induction heating apparatus and its use in silicon production
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US3428436A (en) * 1963-12-16 1969-02-18 Monsanto Co Methods and apparatus for zone melting
US3293002A (en) * 1965-10-19 1966-12-20 Siemens Ag Process for producing tape-shaped semiconductor bodies
US3515836A (en) * 1968-06-24 1970-06-02 Business Assets Corp Elevator means for a heat scanner device
US3604882A (en) * 1970-07-24 1971-09-14 Park Ohio Industries Inc Power control device for an inductor
US4032389A (en) * 1974-03-29 1977-06-28 National Research Development Corporation Apparatus for automatically controlling crystal growth
US4619811A (en) * 1982-08-27 1986-10-28 Zaidan Hojin Handotai Kenkyu Shinkokai Apparatus for growing GaAs single crystal by using floating zone
US4857689A (en) * 1988-03-23 1989-08-15 High Temperature Engineering Corporation Rapid thermal furnace for semiconductor processing
US5601743A (en) * 1995-04-27 1997-02-11 Buhler Ag Apparatus for determining the solid contents of a slug by induction heating

Also Published As

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