US3154623A - Devices for purifying materials by zone refining methods - Google Patents

Devices for purifying materials by zone refining methods Download PDF

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Publication number
US3154623A
US3154623A US144460A US14446061A US3154623A US 3154623 A US3154623 A US 3154623A US 144460 A US144460 A US 144460A US 14446061 A US14446061 A US 14446061A US 3154623 A US3154623 A US 3154623A
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bar
thermo
molten zone
magnitudes
heating element
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US144460A
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English (en)
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Reich Robert
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Centre National de la Recherche Scientifique CNRS
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Centre National de la Recherche Scientifique CNRS
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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
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1927—Control of temperature characterised by the use of electric means using a plurality of sensors
    • G05D23/193—Control of temperature characterised by the use of electric means using a plurality of sensors sensing the temperaure in different places in thermal relationship with one or more spaces
    • G05D23/1931—Control of temperature characterised by the use of electric means using a plurality of sensors sensing the temperaure in different places in thermal relationship with one or more spaces to control the temperature of one space
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G05D23/22—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element being a thermocouple
    • 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
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S148/00—Metal treatment
    • Y10S148/074—Horizontal melt solidification

Definitions

  • the present invention relates to the technique for producing high purity materials by the zone refining method, which consists in causing a relatively narrow molten zone to travel from one end to the other of a small ingot or bar, otherwise solid and the length of which is great as compared with the width of the molten zone, so as to modify the distribution of the solid impurities having coeificients of solubility different in the solid phase and in the molten phase respectively.
  • This method permits, in particular, of preparing very pure metals and semi-conductors, either pure or doped in a very accurate manner.
  • the devices used for the purification of materials by the zone refining method comprise a heating element which is given a relative movement with respect to the element to be treated so as to obtain the desired displacement of the molten zone.
  • efficiency of treatment depends in particular upon the regularity of movement or" the solidification surface, upon the dimension of the molten zone and upon the thermal gradient between the liquid phase and the solid phase.
  • T and T are the maximum temperatures in the molten zone, in the two cases respectively.
  • T is the melting point of the material to be purified.
  • t and t are the temperatures of the ends of the bar.
  • the easier method consists in modifying the heating conditions of the source of heat so as to compensate for the thermal losses but such a compensation, which must necessarily be performed in a continuous manner, is difiicult to obtain in a correct manner with the means presently available because said means only permit of effecting the compensation either too early or too late and in both cases in a very sudden manner.
  • This invention is based upon the fact that a relation has been found to exist between the heating power and a 2 thermal factor depending directly upon the position of the molten zone during its displacement along the bar, this thermal factor being the temperature of twoor sevoral-points located on opposite sides of the middle of the bar.
  • FIG. 3 of the appended drawings shows the variations of the power of the heating element and of the temperatures of the ends of the bar for a molten zone of a given ⁇ gidth in accordance with the position thereof along the In FIG. 3, the position of the molten zone, measured from the starting end of the bar, was plotted in abscissas and the temperature in ordinates and curves at, b, c, d were thus traced.
  • Curve :1 shows the variation of the temperature of the starting end of the bar.
  • Curve b shows the variation of the temperature of the finishing end of the bar.
  • Curve 0 shows the variation of the sum of the temperatures of the respective ends of the bar that is to say the sum of the ordinates of curves at and 1).
  • Curve d shows the variation of the heating power of the source of heat necessary to maintain a molten zone of constant width, this heating power being indicated by the temperatures of a point of the heating element.
  • the present invention is based upon the application of these curves in order to maintain at a substantially constant value the width of the molten zone travelling at a given rate along a given element made of a material having a good thermal conductivity. It permits of obtaining a correct regularity of the displacement of the solidification surfaces.
  • means are provided for maintaining at least one molten zone of a bar at a substantially constant width, or length, by causing the variations of power of the heating means to be controlled by the variations of temperature of at least two points of the bar disposed on opposite sides of the middle part thereof.
  • the temperature of said points of the bar and the heating power are transformed into magnitudes all of the same nature, for instance electric voltages.
  • a linear function, continuous and definite, of the tem peratures and of the heating power is kept constant so as to produce, in response to any increase of the sum of these temperatures, a reduction of the heating power and inversely.
  • the heating power is represented by a temperature which is combined with at least the temperatures of the respective ends of the bar to be treated.
  • thermocouples disposed in the following manner: one is electrically insulated in the heating element and each of the two others are electrically and chemically insulated at the respective ends of the bar.
  • thermo-couples are disposed in a portion of the bar kept 3 at a temperature compatible with their normal operation without deterioration and for this purpose, if necessary, in a portion of the bar sufliciently removed from the extreme molten zones.
  • thermo-couple may be placed in an auxiliary solid body subjected to the direct action of said field.
  • thermo-couples instead of determining the heating power of the source of heat by means of the temperature of one of its points, it is possible to use means supplying a direct voltage of the order of one rnillivolt varying in accordance with this power, which is combined with the electromotive forces of the thermo-couples disposed at the starting and finishing ends of the bar respectively.
  • the invention is applicable to all devices permitting the various treatments requiring the formation of a molten zone, in particular in order to prepare single crystals, to incorporate and distribute in a homogeneous manner one or several impurities in a solid phase as in the case of semi-conductor dopings, and so on.
  • thermocouples to transform into magnitudes of the same nature the temperatures to be combined together and the heating power.
  • T and T are the temperatures of two points located on opposite sides of the middle of the bar.
  • P is the instantaneous supply power of the heating source.
  • F and F are continuous functions of T and T respectively, these functions increasing when T and T increase.
  • F is a function of the instantaneous power P, which may either increase or decrease when P increases.
  • F F and F are determined by the nature of the detecting means that are used (such as thermo-couples).
  • a, b, c are coefficients depending upon the lay-out of the apparatus, the thermal constants of the bar and the length, or width, of the molten zone.
  • Coefficients a and b are always of the same sign, coefficient c being either positive or negative;
  • F is a function of the heating power P which increases when P increases in the case of coefiicient being positive and decreases when P increases in the case of coefficient 0 being negative;
  • (3) C is a constant depending upon the characteristics of the measurement apparatus and which is chosen as great as possible in order to increase sensitivity.
  • the corresponding values of temperature T and T 0n the one hand and the heating power on the other hand are unique for a given layout, that is to say for given values of ratios abc
  • the corresponding values of T T and P or those of their functions F (T F (T and F (P)) are determined experimentally after thermal equilibrium has been reached, a system of three equations is obtained which permits of calculating the values of the constants with respect to one of them, for instance a, b, and c with respect to C their absolute values being determined by practical considerations relative to their order of magnitude (such for instance as the scale of the measurement apparatus that is used).
  • the width of this zone will be compelled to pass during its displacement along the bar, through the value chosen for the three positions that are considered.
  • thermo-couples it is possible to dispose along the bar to be treated a number of thermo-couples greater than two, in the case of a single molten zone.
  • T T T T being the temperatures of the hot welds of the n thermo-couples.
  • the power of each of the external sources of heat may be corrected separately by the only temperature of the bar end nearer thereto, adjustment of the power of the intermediate sources being kept constant. It will therefore be seen that the invention permits of causing the length of one or several molten zones to pass through different values chosen according to the needs during their displacement along the bar.
  • the device according to the invention does not require moving the molten zone from one end of the bar to the other end.
  • the displacement of the molten zone may be limited to a given portion of the bar, in such manner as to dispose the thermo-couples in the sutficiently cooled portion comprised between the end position of the molten zone and each of the ends of the bar.
  • thermo-couples permits of avoiding any deterioration of the apparatus and any soiling of the material to be treated so that the invention may be applied to the treatment of refractory elements.
  • FIG. 4 is a plan view of a device according to the in- Vention wherein the thermo-couples are mounted in series each of them being connected to a potentiometer.
  • FIG. 5 shows on an enlarged scale the mounting of the thermo-couples and potentiometer in the device of FIG. 4.
  • FIG. 6 relates to a lay-out for the measurement of the thermo-electric forces in the case where the thermocouple at the starting end and the thermo-couple at the finishing end of the bar are mounted in shunt and the whole of these two thermo-couples is connected in series with that of the heating element.
  • FIG. 7 is also concerned with a lay-out for the measureent of the thermoelectric forces but it applies to the case where the thermo-couples disposed at the respective ends of the bar are mounted in series at the ends of a common potentiometer.
  • FIG. 8 relates to a lay-out for the measurement of thermo-electric forces wherein the measurement potentiometer is mounted on the thermo-couple provided in the heating element.
  • FIGS. 9, 10 and 11 illustrate lay-outs for placing the instantaneous heating power under control of the sum of the thermo-electric forces of the thermo-couples disposed at the ends of the bar, the regulating apparatus comprising a zero galvanometer or a millivoltmeter.
  • FIG. 12 shows a device of the same kind as those of FIGS. 9, 10 and 11 consisting of several auto-transformers mounted in series.
  • a device comprises a bar 1 of the material to be treated, a motor 2 for moving along bar 1 the source of heat 3, which may be an electric furnace, a regulating apparatus 4 comprising a suitable measurement apparatus and receiving electromotive forces from thermo-couples 5-6-7, the hot welds 8-9-1tl of which are disposed in the following manner: welds 8 and 9, corresponding to thermocouples 5 and 6, at the respective ends of bar 1, weld 10 of thermo-couple 7 in the source of heat 3 which produces the molten zone 11 and elements 12, connected to a source 13 for the supply of calories, for controlling the heating power of this source 3.
  • FIG. 4 also shows a general lay-out for the thermocouples that are used and which may consist of any suitable elements and in particular suitable metals and alloys as commonly used in the manufacture of thermo-couples such as:
  • Copper-constantan Cu Ni 45% Platinum-platinum and rhodium alloy (Pt from 87 to 90%, Rh from 13 to 10%);
  • each of the thermo- 5 couples 5-6-7 is connected with a potentiometer 14-15- 16 respectively and the whole of these potentiometers is connected to regulator 4 comprising any measurement device such as millivoltmeter or zero galvanometer.
  • FIG. 4 does not show the means for producing and adjusting the displacements of heating element 3 along bar 1, such means being well known in the prior art.
  • Adjustment of the heating element will be advantageously obtained through any devices working either by gradual adjustment or by switching on and off.
  • thermo-couples For the thermo-couples, the cold Welds at 23-24, 25- 26, 27-28 being kept at a constant temperature (room temperature) the thermo-electric forces e e e obtained respectively at the terminals of potentiometer 14, 15, 16 are equal to the contact potentials of the elements constituting the thermocouple, with the possible difference of a constant.
  • thermal forces 2 e 6 are those active in the device and which are meas ured by the opposition method for three static positions of a molten zone of given width along the bar to be treated, after thermal equilibrium has been obtained.
  • thermo-electric forces The sum of the elementary thermo-electric forces being kept constant since it is sent to regulator 4, of a known type for a thermo-couple, having a fixed index the too cold and too hot positions of which respectively deliver the hole and part heating powers, the following relation exists between these electromotive forces:
  • a, f, g and C are constants depending upon the lay-out characteristics of the bar to be treated and upon the Width that is chosen for the molten zone 11,
  • 0 is a given function of the heating power of the heating element 3.
  • thermo-couple circuit For practical purposes, knowing the value R of the resistance imposed for the thermo-couple circuit and the values of the thermo-electric forces e e of the respective thermo-couples for two or three static positions of the heatin element along the bar, it is possible to determine the value of the total resistance R of every potentiometer. Known formulas then permit of determining from this value of the total resistance, the positions of the sliding members 29, 3t 31 of the respective potentiometers.
  • thermo-couples may be effected in many different ways and in particular as shown by way of indication on FIGS. 6, 7 and 8.
  • thermo-couples 5 and 6 are mounted in series or in shunt, and on the other hand when the potentiometer is mounted on the thermo-couple 7 disposed in the heating element.
  • reference numerals 5, 6 and 7 designate the thermo-couples, 8, 9 and ill) the hot welds, 23-24, 25- 26, 27-28 the cold welds and 4 the regulator.
  • thermo-couples 5 and 6 mounted in shunt and to the common terminal 35 of switches 36 and 37;
  • thermo-couple 5 through its end 38 to the junction point 39 of thermo-couple 5 and mounted in series with thermo-couple 6 and through the other end til to the terminal 41 of switch 42;
  • thermo-couple 7 which is disposed in the heating element, and through 45 to the terminal 46 of switch 47;
  • switches 52 and 53 which are each of the two positions type, that is to say which may be placed on contact studs in or I.
  • thermo-electric forces e e e of the potential across the terminals of the regulator or to couple them in normal working conditions
  • This heating power may be adjusted in particular by action upon the feed voltage in the case where an electric heating is used or upon the biasing of the grid of a triode of the oscillatory circuit when heating is obtained by means of a high frequency field.
  • This reference voltage which will be designated by e and is a continuous function of the heating power, may be either a well defined fraction of the feed voltage or a potential difference obtained for instance by means of the arrangement diagrammatically illustrated by FIGS. 9, l0 and 11.
  • This arrangement comprises an auxiliary direct current source 54, two potentiometers 55 and 56, the displacement of the sliding member 57 being linked with that of the brush 58 of the auto-transformer 59 which controls the power of the heating element.
  • thermo-electric forces of thermo-couples 5 and 6 on the one hand and of the reference voltage on the other hand, opposing their sum to a direct voltage obtained by means of source 60 and potentiometer 61 and using for this purpose a temperature regulator i with a zero galvanometer, mounted in such manner that the too hot position corresponds to an increase of the sum of the electromotive forces and therefore to a reduction of the heating power and also of the value of the reference voltage.
  • the arrangement must be such that an increase of the reference voltage corresponds to a decrease of the feed voltage.
  • the feed network being still connected to the terminals 65 and 66 of the auto-transformer, to dispose the heating element between the terminals 66 and 67. 7
  • FIG. 12 corresponds to a construction comprising two auto-transformers.
  • the apparatus of FIG. 12 comprises essentially the following elements:
  • a motor 68 capable of rotating in both directions (either from left to right or from right to left) which drives a shaft 69 carrying a sliding member 7 6 moving along potentiometer 55; this potentiometer permits of obtaining the reference voltage and comprises for this purpose terminals 62-63 and 64 which are connected in the same manner as illustrated with reference to FIG. 9.
  • Two auto-transformers 71 and 72 comprising brushes 73 and 74 rigid with shaft 69 and movable along windings 75 and '76, these parts being electrically connected together, as shown by the drawings, that is to say in such manner that the primary of one is fed from the secondary of the other in order to obtain, in response to variations of the reference voltage, variations of power different from those obtained by means of a single auto-transformer; for this purpose, the feed network is connected with the terminals 77 and 78 of the first auto-transformer whereas the heating element is connected with the terminals 79 and 81B of the secondary transformer, the terminal 81 of the brush of auto-transformer 71 is connected with a terminal 82 of auto-transformer 72 and finally the terminal 83 of auto-transformer 71 is connected with a terminal 84 of auto-transformer 72.
  • the reference voltage e added to the sum of the thermo-electric forces (e +e varies linearly as a function of the voltage V across the terminals of the heating element.
  • Ratio a, voltage V, and power P of the heating source are magnitudes which are always positive.
  • a device for the treatment of a bar of a heat conducting material which comprises, in combination, a heating element movable along said bar to form a molten zone thereof travelling along said bar, two means for measuring the temperatures of said bar at two points thereof located on opposite sides of its middle part, respectively, means for translating the values thus measured of said temperatures into respective magnitudes, both of the same nature, means for measuring the power of said heating element, means for translating the value thus measured of said heating power into a magnitude also of the same nature, and means operatively connected with said heating element to vary the heating power thereof, to maintain the width of the molten zone substantially constant, said means being responsive to variations of said three magnitudes for keeping at a substantially constant value a linear function of said three magnitudes, this linear function being the sum of three terms, the two first terms being of the same sign and being each a function of one of the two first mentioned magnitudes, respectively, which increases in absolute value when the corresponding magnitude inreases and inversely, the third term being of a sign opposed to that of the two first mentioned magnitudes which
  • a device according to claim 1 wherein said means for measuring the heating power of said heating element are means for measuring the temperature of one of the points of said element.
  • a device wherein said magnitudes are potential differences, and said third magnitude is a direct voltage proportional to said heating power.
  • thermo-couples means for measuring said temperatures and said means for translating the values thus measured of said temperatures into said two first mentioned magnitudes are combined together in the form of thermo-couples, whereas said means for measuring said heating power and said means for translating the value thus measured of said heating power into the third mentioned magnitude are combined together in the form of a thermo-couple, the means for keeping said linear function at a substantially constant value comprising potentiometers connected with said thermo-couples to form said function and a regulator connected with said potentiometers.
  • thermocouples are mounted in portions of said bar remote from the end positions of the molten Zone.
  • a device according to claim 1 wherein said magnitudes are potential differences and the last mentioned means comprise an auto-transformer having a brush the position of which determines the heating power.
  • a device according to claim 1 wherein said magnitudes are potential differences and the last mentioned means comprise a feed rheostat having a brush the position of which determines the heating power.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
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  • Automation & Control Theory (AREA)
  • Electromagnetism (AREA)
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  • Crystallography & Structural Chemistry (AREA)
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US144460A 1960-10-14 1961-10-11 Devices for purifying materials by zone refining methods Expired - Lifetime US3154623A (en)

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Application Number Priority Date Filing Date Title
FR841136A FR1281269A (fr) 1960-10-14 1960-10-14 Perfectionnements aux dispositifs de purification de divers matériaux par le procédé des zones fondues

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4473433A (en) * 1982-06-18 1984-09-25 At&T Bell Laboratories Process for producing dielectrically isolated single crystal silicon devices

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2691732A (en) * 1948-12-07 1954-10-12 Westinghouse Electric Corp Radio frequency generator
US2743199A (en) * 1955-03-30 1956-04-24 Westinghouse Electric Corp Process of zone refining an elongated body of metal
US2792317A (en) * 1954-01-28 1957-05-14 Westinghouse Electric Corp Method of producing multiple p-n junctions
US2870309A (en) * 1957-06-11 1959-01-20 Emil R Capita Zone purification device
US2972525A (en) * 1953-02-26 1961-02-21 Siemens Ag Crucible-free zone melting method and apparatus for producing and processing a rod-shaped body of crystalline substance, particularly semiconductor substance
US2992311A (en) * 1960-09-28 1961-07-11 Siemens Ag Method and apparatus for floatingzone melting of semiconductor rods

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2691732A (en) * 1948-12-07 1954-10-12 Westinghouse Electric Corp Radio frequency generator
US2972525A (en) * 1953-02-26 1961-02-21 Siemens Ag Crucible-free zone melting method and apparatus for producing and processing a rod-shaped body of crystalline substance, particularly semiconductor substance
US2792317A (en) * 1954-01-28 1957-05-14 Westinghouse Electric Corp Method of producing multiple p-n junctions
US2743199A (en) * 1955-03-30 1956-04-24 Westinghouse Electric Corp Process of zone refining an elongated body of metal
US2870309A (en) * 1957-06-11 1959-01-20 Emil R Capita Zone purification device
US2992311A (en) * 1960-09-28 1961-07-11 Siemens Ag Method and apparatus for floatingzone melting of semiconductor rods

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4473433A (en) * 1982-06-18 1984-09-25 At&T Bell Laboratories Process for producing dielectrically isolated single crystal silicon devices

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BE609017A (fr) 1962-02-01
GB962010A (en) 1964-06-24
FR1281269A (fr) 1962-01-12

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