US2913383A - Jet-electrolytic method of configuring bodies - Google Patents

Jet-electrolytic method of configuring bodies Download PDF

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Publication number
US2913383A
US2913383A US656728A US65672857A US2913383A US 2913383 A US2913383 A US 2913383A US 656728 A US656728 A US 656728A US 65672857 A US65672857 A US 65672857A US 2913383 A US2913383 A US 2913383A
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jet
etching
current
germanium
electrolyte
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US656728A
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Alvin R Topfer
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Space Systems Loral LLC
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Philco Ford Corp
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Priority to BE567337D priority Critical patent/BE567337A/xx
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Priority to US656728A priority patent/US2913383A/en
Priority to GB14060/58A priority patent/GB866382A/en
Priority to FR1206041D priority patent/FR1206041A/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/3063—Electrolytic etching
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C25F3/12—Etching of semiconducting materials

Definitions

  • the present invention relates to methods for the removal of material from electrically-conducting bodies, and particularly to electrolytic methods for the shaping of such bodies.
  • the high frequency performance of such devices is usually enhanced by providing the emitter and/ or collector barriers adjacent substantially llat, plane-parallel surfaces of the semiconductive material.
  • the emitter and collector barriers may be made substantially plane-parallel, even though the pits have substantial curvature compared to their diameters, by making the area of the bottoms of the: pits large and utilizing only a small part of the bottom area of each pit for the active element of the transistor, this expedient requires removal of an unnecessarily large amount of material, thereby adding to the expense of the manufacturing process.
  • the pit can be made initially with a relatively flat bottom and relatively steep sides, the desired planeparallel configuration of material can be obtained by the removal of less material and with consequent commercial advantage.
  • a flat-bottomed, steep-sided geometry of pit produces a lower base resistance in transistors made therefrom.
  • Flat-bottomed pits in semiconductive materials have also been found desirable from another viewpoint when the depth of the depressions is determined by infra-red thickness control such as that described in the copending application Serial No. 449,347 of Robert N. Noyce, led August l2, 1954, and entitled Electrical Method and Apparatus.
  • the thickness of the material remaining under the pit may face of the semiconductive material subjected to the etching process remain smooth, and, in fact, it is often desirable that the etching action be such as to reduce any surface roughnesses originally present, thus eliminating or reducing the need for chemical etching prior to electrolytic jet-etching.
  • Another object is to provide an improved method for the jet-electrolytic configuring of bodies of material such as germanium, arsenic or antimony.
  • Another object is to provide an improved method for the jet-electrolytic removal of material from a body of germanium, which operates at a higher rate than prior art methods. It is another object to provide a method forV the rapid yet smooth electrolytic machining of materials such as germanium, arsenic or antimony.
  • Still another object is to provide a novel electrolytic method for producing pits having substantially flat bottoms in germanium, and particularly in lll-oriented germanium.
  • a still further object is to provide such a method of electrolytic material removal in ywhich the electrical supply requirements are especially compatible with those required for electroplating of the same body.
  • the above objectives are realized by the provision of a process in which a jet of electrolyte is directed against a body of a material such as germanium, arsenic or antimony, while a potential negative with respect to the jet is applied to the body so that the electrical current in the jet flows in a direction opposite to that normally employed in etching.
  • the density of the current employed is in general substantially greater than is employed in conventional jet etching or plating, and is for example of the order of hundreds or thousands of amperes per square inch.
  • the electrolyte is one having cations which are principally of a non-platable type, such as hydrogen. Under these conditions very rapid removal of material has been produced in the region of jet impingement. In the case of germanium such as is utilized in semiconductor devices, the rate of removal may readily be about six times greater than has been found practical with conventional jet-etching in which the semiconductive body is maintained positive with respect to the jet.
  • etching While the exact type of etching obtained in any particular application depends in some degree upon the nature of the material etched, the electrolyte used and the density of the electrical current ilowing through the jet, it has been found that by suitable adjustment of the operating conditions, depressions having very flat, smooth bottoms may readily be obtained, as is desirable for certain purposes such as those mentioned hereinbefore-namely, production of high frequency transistor devices and/or jet-etching of germanium with simultaneous infra-red measurement of thickness. Furthermore, it has been found that the process in some of its forms can be employed to smooth out roughnesses which may exist in the surface of the semiconductive body prior to initiation of the etching process, particularly in the case of lll-oriented germanium single crystals.
  • semiconductor blanks which have been produced by sawing or similar abrasive method may be subjected to the present process to provide a localized region of precise small thickness therein without requiring a preliminary chemical etching to smooth the rough surfaces produced by the sawing action.
  • the process can readily be performed without producing random etching or blast holes in the semiconductor material, as sometimes occurs in conventional etching processes.
  • the process of the invention also makes possible simplification of semiconductor shaping procedures, particularly in that strong illumination of the region subjected to treatment does not appear to be necessary for rapid, smooth removal of material and, where the material removal process is to be followed by an electroplating process, a single source of potential of predetermined polarity is sucient for both processes.
  • sequential local removal of material and local electroplating can readily be accomplished with the body maintained negative with respect to the electrolyte at all times by utilizing rst a large current tot produce etching and then a lower current in the same direction to produce plating.
  • the electrical current density is raised above a predetermined minimum value characteristic of the material and the electrolyte employed, typicaldensities being of the order of between one-hundred and onethousand amperes per square inch.
  • typicaldensities being of the order of between one-hundred and onethousand amperes per square inch.
  • the optimum current density may readily be determined experimentally merely by increasing the current until the desired results are obtained.
  • the method may be practiced by the application of a current of constant value between electrolyte and body, I have found it also advantageous in some circumstances to utilize a varying current, such as a rectified sine wave or other pulsatile waveform, having values in the current range required for the present type of material removed.
  • etching will be utilized herein to include removal of material by the method of the invention, although the mechanism of the removal appears to be greatly different from that involved in conventional etching. While all of the details of this mechanism are not fully understood, it-is believed that there is involved the formation of a hydride of the material being etched. Since germanium, arsenic and antimony can combine with nascent hydrogen during come more readily apparent from a consideration of the following ⁇ detailed description taken in connection with the accompanying drawings, in which:
  • FIG. l is a diagram illustrating apparatus useful for practicing the invention in one of its forms
  • Figures 2 and 3 are sectional views of bodies of germanium to which reference will be made in describing typical results of practicing my method.
  • Figures 4 and 5 are diagrammatic representations illustrating arrangements for practicing the invention in two of its other forms.
  • the apparatus shown therein comprises one preferred arrangement which may be used in accordance with the invention rapidly to produce a pit in a wafer- 10 of single-crystalline germanium while monitoring the thickness of the material remaining beneath the pit by an infra-red measuring technique. It will be understood that the drawingis illustrative only, and that the various parts thereof are not necessarily to scale.
  • Wafer 10 in which the pit is to be produced is disposed between the jet-forming apparatus 12 and the gas-blast generator 14 so as to be impinged on its lower surface by the electrolytic jet 16.
  • generator 14 is merely to direct a drying blast of a gas such as nitrogen or air against the upper surface of Wafer 10, thereby to prevent wetting of this surface by the electrolyte which might interfere with stable infra-red transmission.
  • gas inlet 18 may be connected to a source (not shown) ot compressed nitrogen, which gas then iiows through orifice 20 onto the upper side of wafer 10.
  • let-forming apparatus 12 is constructed so as to permit infra-red radiations from source 24 to be directed through the jet 16 to the region of body 10 impinged by the jet, while the gas-blast generator is constructed to accommodate and support an infra-red sensitive cell'26 disposed to detect infra-red radiations transmitted through body 10.
  • Suction tubes 28 and 30, shown diagrammatically, may also be provided to produce regions of reduced air pressure adjacent the region of iet impingement, thereby to improve the stability and smoothness of the jet as described in the copending application Serial No. 637,972 of R. T. Vaughan, filed February 4, 1957, and entitled Method and Means for Fabricating Semiconductive Devices and the Like.
  • Germanium wafer 10 is in this case ohrnically soldered to a base tab 32, by which it is held between jet-forming means 12 and gas-blast generator 14. Jet-forming means 12, gas-blast generator 14 and wafer 10 may be supported in their proper relative positions by any appropriate means; although for convenience a common Lucite case 34 has been indicated in the drawing, it will be understood that, for greater accuracy in positioning of the several elements, precision-machined parts may be'used.
  • Electrolyte from electrolyte source and pump 36 supplies electrolyte under pressure to jet-forming apparatus 12 by way of inert tubing 38.
  • the iet forming apparatus comprises a chamber 40, closed at one end by the nozzle 42 which may be of ceramic and which contains a small orifice 44 from which the jet of electrolyte emanates.
  • the electrolyte and any associated parts in the path between the source 24 and the wafer 10 are composed of materials which exlhibit substantial transmittance for infra-red radiations of the wavelength to be utilized in the measuring process.
  • 5 appropriate condensing lenses and collimating means may be included in infra-red source 24 to direct radiations principally into the electrolyte in nozzle 42 and thence to the jet 16.
  • a light chopper 44 in the form of a peripherally-serrated disc 46 having its serrated portion interposed in the path of the infra-red radiations and rotated by a synchronous motor 48 as shown, whereby the radiations are periodically interrupted.
  • Leads from infra-red detector 26 supply the output signal thereof to an amplifier 50 and indicator S2 which together are operative to produce an output indication which varies in predetermined fashion as the thickness of the semiconductive body approaches and attains the desired value.
  • the electrolyte impingent upon the under-surface of wafer 10 is maintained at a potential positive with respect to the wafer by means of potential source 56, one terminal of which is connected by way of switch 58 to the base tab 32, and the other terminal of which is connected by way of a variable resistor 60 to an inert metallic electrode 62 immersed in the electrolyte.
  • the electrode 62 is located in Ia side-arm of the tubing such as 64 provided with a gas pressure release arrangement represented schematically as element 66, so that any bubbles formed about electrode 62 are prevented from passing into jet 16 and interfering with the infra-red thickness measurements.
  • Potential source 56 may in some instances comprise a source of direct voltage, and in other cases a varying voltage such as a rectified half sine-wave.
  • Variable resistor 60 permits adjustment of the current supplied to the jet by the potential source.
  • the pump and suction devices are actuated so that the desired jet of electrolyte is impinged against the germanium wafer 10.
  • Switch 58 is closed and resistor 60 is adjusted to apply the appropriate positive potential difference between electrode 62 and wafer 10, and to cause the desired electrolytic current to flow through the jet.
  • the infra-red source 243 and the associated light-chopper 44 simultaneously provide a beam of periodically-interrupted infra-red radiations which passes through the jet 16 and wafer 10 to the infra-red detection cell 26, and the resultant cell output signal is supplied to amplier S and indicating device 52.
  • the effect of the jet and the applied current is then swiftly and smoothly to remove material adjacent the region of impingement of the germanium, provided the electrolytic current is sufficiently high.
  • the jet 16 is 16 mils in diameter, about 2 millimeters long and composed of 1.0 normal hydrochloric acid
  • wafer 10 is of 2 ohm-centimeter
  • N- type germanium of 111 crystal orientation rand when the electrolytic current is about 170 milliamperes
  • the thickness of the germanium body beneath the jet decreases from about mils to about 0.2 mil in about 12 seconds, corresponding to a thickness reduction rate of about 0.4 mil per second.
  • the average current density in the jet in this case is about 850 amperes per square inch.
  • the resultant etch pit is smooth and essentially flat-bottomed, having the general form illustrated in Figure 2.
  • the infra-red radiations are transmitted etiiciently through the flat- 6 bottomed pit tothe infra-red detecting' apparatus to provide the desired accurate indications of the .remaining thickness of the germanium wafer.
  • any of a variety of common electrolytes may also be utilized, including various normalities of sulphuric acid, hydrochloric acid and a mixture of hydrouoric acid and sodium uoride.
  • acids appear generally to be most convenient in readily producing rapid, smooth etching
  • non-acidic electrolytes such as potassium hydroxide and ammonium chloride have also been used to produce material removal.
  • transient stimuli such as a ash of bright light or a momentary change in the magnitude or direction of the current, have been found helpful in initiating the etching action should it be difficult to start with certain electrolytes or material.
  • the nature of the etching action obtained generally depends in substantial measure upon the electrolytic current density.
  • etching rate The precise relation between etching rate and electrical current density has been found to depend in some degree upon the nature of the electrolyte and the mate-rial treated, but the general form of the relationship has been found to be similar for many different applications.
  • the material etched was N-type germanium, the jets were 15 mils in diameter and were of sulphuric acid of 0.4, 0.6, 1.0 ⁇ and 1.5 normality in different cases.
  • the etching current was half-Wave rectified, 60-cycle alternating current, measured with a direct-current meter indicating the average value of the current.
  • the variations of etching rate with current were similar for al1 four normalities of electrolyte, the values given in the following table being typical.
  • the shape of the etched depression also depends upon the current employed. For example, in the foregoing experiments it was found that mounds or plateaus in the bottom of the depression often occur when the current is relatively low, which do not appear when higher currents are used.
  • Example I An electrolytic jet 16 mils in diameter of 1.0 Normal hydrochloric acid was directed from a distance of about 2 millimeters against a body of N-type germanium 5 mils thick, of about 3 ohm-centimeter resistivity and cut in the 111 crystal orientation.
  • the voltage applied to the electrode 62 was 500 volts D.-C. positive with respect to the germanium body, and the distance from the anode to the body through the electrolyte was about 3 inches; the current through the jet was about 140 milliamperes D.C.
  • the resultant etch rate was about 0.4 mil per second, so that the 5 mil body was etched to about 0.2 mil in 12 seconds, and the etch pit had the geometry shown in Figure 3 in which the bottom of the pit comprises a smoothsurfaced peripheral groove surrounding a central plateau having a relatively rough surface.
  • Example Il Increasing the current from 140 to 170 milliamperes but otherwise using the same conditions as in Example I, the smooth, flat-bottomed pit shown in Fig. 2 was obtained with an etching rate of about 0.4 mil per second.
  • Example III Utilizing 11G-oriented germanium, 0.75 Normal HCl and a current of about 125 milliamperes, but with conditions otherwise as in Examples I and II, rapid, localized etching occurred.
  • Example IV Utilizing 0.5 Normal HCl and a current of about 80 milliamperes but with conditions otherwise as in Example III, rapid and smooth etching was obtained.
  • Example V Utilizing the same arrangement of apparatus as in Example 1V, but employing P-type germanium instead of N-type germanium, and l Normal HCl, rapid etching at the rate of about 0.4 mil per second was obtained with a direct-current of about 120 milliamperes.
  • Example Vl Utilizing the same apparatus as in Example V, but
  • Example VII With the same semiconductive material and waveform of current as in Example VI, but employing an electrolyte consisting of a mixture of 0.2 Normal NaF and 0.2 Normal HF, rapid but rough etching was obtained.
  • Example VIII Utilizing apparatus of the type shown in Figure l, with a jet of 0.4 Normal H2504 of 9 mils diameter, antimony was etched rapidly with a direct-current of 42 milliamperes.
  • Example IX Under the same conditions as were used in Example VIII, arsenic was similarly etched with a direct-current of 62 milliamperes.
  • the method has also been employed using non-aqueons electrolytes to ellect etching, although the etching usually proceeds at a lower rate.
  • HCl in ethylene glycol was found to produce slow etching at about 500 amperes/square inch, D.C.
  • FIG. 4 there is represented schematically an arrangement of a pair of electrolytic jets 100 and 102 directed against opposite surfaces of semiconductive wafer 104.
  • the potential source 106 supplies a positive potential to jet 102 by way of variable resistor 108 and switch 110, and at the same time supplies a positive potential to jet 100 by way of variable resistor 114 and switch 116.
  • variable resistor 108 and switch 110 supplies a positive potential to jet 100 by way of variable resistor 114 and switch 116.
  • Example X Using a pair of opposed jets each 16 mils in diameter and composed of 0.4 Normal H2804, a wafer of N-type germanium was rapidly etched using a half-Wave rectied current of milliamperes total for the two jets together as measured by a D.C. meter, with the applied potential in the direction to make the jets positive with respect to the wafer.
  • Example XI Using one jet of 8 mils diameter and 2 Normal H2SO4 and another, opposed jet of 16 mils diameter and 1 Normal H2504, and applying current to the 16 mil jet only, when the current was 100 milliamperes, etching was obtained under the 8 mil unbiased jet only; when the current was increased to milliamperes, etching was obtained under both jets; and with a current of to 270 milliamperes, etching was obtained under the l6-mil, biased jet only.
  • the process involves the production of a hydride of the material under treatment; thus the process has been found effective to produce rapid removal of material from bodies of germanium, antimony and arsenic which form hydrides cathodically, but inelective on silicon, carbon, aluminum, zinc and other material which do not readily form hydrides cathodically.
  • germanium hydride is formed in the treatment of germanium by the process of the invention.
  • the method of removing a portion of a body of material selected from the class consisting of germanium, arsenic and antimony comprising the steps of directing against said portion of said body a jet of an electrolyte containing hydrogen ions While maintaining said jet positive with respect to said body lto pass a current between said jet and said body, said jet being maintained sufficiently positive with respect to said body to produce in the portion of said jet impinging said body portion an average electrical current density of at least 50 amperes per square inch and to cause etching of said body portion by said jet.

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US656728A 1957-05-02 1957-05-02 Jet-electrolytic method of configuring bodies Expired - Lifetime US2913383A (en)

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BE567337D BE567337A (US07935154-20110503-C00006.png) 1957-05-02
US656728A US2913383A (en) 1957-05-02 1957-05-02 Jet-electrolytic method of configuring bodies
GB14060/58A GB866382A (en) 1957-05-02 1958-05-02 Improvements in and relating to the electrolytic shaping of bodies
FR1206041D FR1206041A (fr) 1957-05-02 1958-05-02 Procédé d'enlèvement de matière d'un corps électriquement conducteur

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Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3039514A (en) * 1959-01-16 1962-06-19 Philco Corp Fabrication of semiconductor devices
US3041258A (en) * 1960-06-24 1962-06-26 Thomas V Sikina Method of etching and etching solution for use therewith
US3075903A (en) * 1960-02-23 1963-01-29 Motorola Inc Method of electrolytically etching a semiconductor element
US3109792A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109793A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109795A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109788A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Electrolytic production of phosphine
US3109794A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109786A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Process for the preparation of phosphine
US3109791A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109787A (en) * 1959-07-31 1963-11-05 Hooker Chemical Corp Production of phosphine
US3137645A (en) * 1961-10-04 1964-06-16 Philco Corp Jet electrolytic treating apparatus
US3196094A (en) * 1960-06-13 1965-07-20 Ibm Method of automatically etching an esaki diode
US3218248A (en) * 1961-10-12 1965-11-16 Anocut Eng Co Electrolytic cavity sinking apparatus and method
US3228862A (en) * 1960-10-04 1966-01-11 Gen Instrument Corp Esaki diode manufacturing process, and apparatus
US3928154A (en) * 1973-04-12 1975-12-23 Trw Inc Electrochemical radius generation
US3959098A (en) * 1973-03-12 1976-05-25 Bell Telephone Laboratories, Incorporated Electrolytic etching of III - V compound semiconductors
US20130303055A1 (en) * 2012-05-14 2013-11-14 John P. Rizzo, JR. Component machining method and assembly

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2557823A (en) * 1946-10-26 1951-06-19 Gen Motors Corp Method of forming a composite article comprising steel and silver
US2755238A (en) * 1955-03-25 1956-07-17 Sprague Electric Co Electrolytic etching and oxidizing of aluminum

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2557823A (en) * 1946-10-26 1951-06-19 Gen Motors Corp Method of forming a composite article comprising steel and silver
US2755238A (en) * 1955-03-25 1956-07-17 Sprague Electric Co Electrolytic etching and oxidizing of aluminum

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3039514A (en) * 1959-01-16 1962-06-19 Philco Corp Fabrication of semiconductor devices
US3109787A (en) * 1959-07-31 1963-11-05 Hooker Chemical Corp Production of phosphine
US3075903A (en) * 1960-02-23 1963-01-29 Motorola Inc Method of electrolytically etching a semiconductor element
US3196094A (en) * 1960-06-13 1965-07-20 Ibm Method of automatically etching an esaki diode
US3041258A (en) * 1960-06-24 1962-06-26 Thomas V Sikina Method of etching and etching solution for use therewith
US3109793A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109792A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109794A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109786A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Process for the preparation of phosphine
US3109791A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109795A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Method of preparing phosphine
US3109788A (en) * 1960-07-27 1963-11-05 Hooker Chemical Corp Electrolytic production of phosphine
US3228862A (en) * 1960-10-04 1966-01-11 Gen Instrument Corp Esaki diode manufacturing process, and apparatus
US3137645A (en) * 1961-10-04 1964-06-16 Philco Corp Jet electrolytic treating apparatus
US3218248A (en) * 1961-10-12 1965-11-16 Anocut Eng Co Electrolytic cavity sinking apparatus and method
US3959098A (en) * 1973-03-12 1976-05-25 Bell Telephone Laboratories, Incorporated Electrolytic etching of III - V compound semiconductors
US3928154A (en) * 1973-04-12 1975-12-23 Trw Inc Electrochemical radius generation
US20130303055A1 (en) * 2012-05-14 2013-11-14 John P. Rizzo, JR. Component machining method and assembly
US8764515B2 (en) * 2012-05-14 2014-07-01 United Technologies Corporation Component machining method and assembly

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GB866382A (en) 1961-04-26
BE567337A (US07935154-20110503-C00006.png)

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