US3635802A - Method of anodizing a thin-film device - Google Patents

Method of anodizing a thin-film device Download PDF

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Publication number
US3635802A
US3635802A US87370A US3635802DA US3635802A US 3635802 A US3635802 A US 3635802A US 87370 A US87370 A US 87370A US 3635802D A US3635802D A US 3635802DA US 3635802 A US3635802 A US 3635802A
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Prior art keywords
anodizing
current
thin
film device
steps
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US87370A
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Robert A Manning
Donald H Raymond
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AT&T Corp
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Western Electric Co Inc
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Assigned to AT & T TECHNOLOGIES, INC., reassignment AT & T TECHNOLOGIES, INC., CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE JAN. 3,1984 Assignors: WESTERN ELECTRIC COMPANY, INCORPORATED
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/22—Apparatus or processes specially adapted for manufacturing resistors adapted for trimming
    • H01C17/26—Apparatus or processes specially adapted for manufacturing resistors adapted for trimming by converting resistive material
    • H01C17/262—Apparatus or processes specially adapted for manufacturing resistors adapted for trimming by converting resistive material by electrolytic treatment, e.g. anodic oxydation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/10—Regulating voltage or current
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N97/00—Electric solid-state thin-film or thick-film devices, not otherwise provided for

Definitions

  • ABSTRACT Thin-film resistors and other devices are precision adjusted by a regular, geometric progression of steps.
  • Each step of a binary step anodization pattern for adjusting a resistor to a nominal resistance value is designed to decrease by one-half the percentage deviation in resistance from the nominal value at the end of the preceding step.
  • Successive binary step decreases in the percentage resistance deviation are attained by a series of binary step decreases in the product of anodizing current and anodizing time for each step.
  • the resultant, decreasing rate adjustment pattern tends to render negligible any chance of substantially overshooting the desired nominal value while permitting rapid attainment of the nominal value.
  • a general purpose, process control computer is equipped with a series of tapes or other program devices storing anodizing current and anodizing time information for carrying out successive steps of the subject anodizing technique.
  • Such information is that which has been derived for given sets of conditions and resistor codes, incorporating various regular, geometric progression anodizing patterns and linear approximations, such as a linear approximation of a binary step pattern.
  • Each resistor is anodized in successive steps, after each of which steps a resistance measurement is made and the anodizing current and anodizing time for the next step are determined. Anodization is terminated when the tolerance zone about the nominal resistance value is entered.
  • This invention relates to methods of anodizing a thin-film device and, more particularly, to methods of anodizing a thinfilm device according to a selected pattern of anodizing steps to adjust a parameter of the thin-film device to a desired value.
  • a high degree of precision is often required either in the absolute value of a parameter of a finished device or in matching values of the parameter in two or more finished devices.
  • tolerance requirements for finished resistors may be of the order of i0.0l percent of a design resistance value or of the resistance value of a resistor to be matched.
  • a wellknown method of adjusting thin-film resistors to value involves anodization, a process according to which a portion of the thickness of a resistor, which may be made of a thin film of tantalum, tantalum nitride, or other material, is oxided to form a dielectric layer, thereby reducing the thickness of the remaining, unoxidized portion of the film to increase the resistance of the film.
  • a typical method of manufacturing thin-film resistors employs a two-stage resistance adjusting operation.
  • a first stage of resistance adjustment involves the anodization of each thin-film resistor at a first, relatively high rate by a series of relatively high current anodizing steps which may be interspersed with resistance measuring steps. This first stage of anodization continues until the resistance of the thin-film resistor is found by measurement to have been increased to within a first rough tolerance range of the nominal resistance value, typically -5 percent.
  • a second stage of resistance adjustment then provides a more precise, relatively low rate anodization by a series of relatively low current anodizing steps.
  • This second stage of anodization continues until the resistance of the thinfilm resistor is found by measurement to fall within the typical :05 percent or more tolerance requirement.
  • a multiplexed system is often utilized, whereby a number of thin-film resistors are anodized simultaneously with sequential testing determining instantaneous resistances of the resistors during anodization.
  • An object of the invention resides in new and improved methods of anodizing a thin-film device, e.g., in order to adjust a parameter of the device, such as resistance, to a desired value.
  • the invention contemplates the anodization of a thin-film device in accordance with a selected pattern of anodizing steps which will bring a parameter of the device, e.g., the resistance of a thin-film resistor, within a very narrow tolerance zone in a minimum time period, yet with a minimal likelihood of overshooting the nominal value of such a degree as to pass out of the tolerance zone.
  • the contemplated pattern of anodizing to accomplish these ends involves a multiple step procedure under which each successive step is designed to decrease by a fixed fractional multiple the percentage deviation of the parameter of interest from a desired final value of the parameter.
  • Such pattern is achieved by a series of steps wherein the product of anodizing current and anodizing time for each succeeding step is equal to such fixed fractional multiple of the product of anodizing current and anodizing time for each preceding step.
  • a preferred fixed fractional multiple utilized in carrying out the method of the invention is equal to one-half, such that the percentage deviation of the parameter of interest from the desired value is decreased continually in binary fashion.
  • the binary pattern has been selected for its capability of changing rapidly the value of the parameter of interest, while eliminating any chance of shooting the desired nominal value by more than one binary step, an insignificantly small quantity once adjustment has brought the parameter into the vicinity of the desired nominal value.
  • the invention further contemplates adjustment of thin-film devices according to a pattern of steps of decreasing the anodizing current and anodizing time in binary fashion or other geometric progression wherein one of the anodizing current and the anodizing time may be held constant during several successive steps while the other is decreased in accordance with the pattern.
  • a method in accordance with the principles of the invention employs a number of steps wherein constant anodizing current is applied to a thin-film device for time periods decreasing in fixed geometric progression, followed by a number of steps wherein the anodizing time period is maintained constant and the anodizing current is decreased according to the fixed geometric progression.
  • Anodization may be interrupted briefly after each anodization cycle during this process, e.g., after each step, to allow testing equipment to check the progress of the thin-film device toward nominal value. Multiplexing may be utilized in connection with such method to produce finished anodized thin-film devices at an increased rate.
  • FIG. I of the drawing is a plot depicting the first three steps of a pattern of anodization illustrative of the principles of the invention, the plot displaying an anodizing current-time product versus the percentage deviation from a nominal resistance value of a thin-film resistor;
  • FIG. 2 constitutes an expanded vertical scale continuation of the plot of FIG. I, depicting several additional steps according to the FIG. I pattern of anodization;
  • FIG. 3 is a plot of anodizing time versus percentage deviation from value for the first three steps of the pattern of FIGS. 1 and 2;
  • FIG. 4 is a plot of anodizing current versus percentage deviation from value for several additional steps of the pattern DETAILED DESCRIPTION
  • a thin-film device such as a thin-film resistor
  • a characteristic parameter of the thin-film device such as its resistance
  • the specified tolerance zone is represented at the right-hand end 21 (FIG. 2) of the horizontal scale used in the plot of FIGS. I and 2, FIG.
  • FIG. 2 constituting an expanded vertical scale, rightward continuation of the portion of the plot shown in FIG. 1.
  • the parameter of the thin-film device be adjusted to within the very close tolerance of the nominal resistance value in as short as possible a total time period, yet with a minimal likelihood of overshooting the tolerance zone associated with the nominal value.
  • Each successive step may be seen to reduce by one-halfthe percentage deviation in resistance existent at the end of the preceding step.
  • any errors in resistor measurements should affect the final resistance value of the resistor by no more than one binary step, i.e., at most something of the order of 0.01 percent of the nominal value for a 0.02 percent tolerance zone. Such effect would still fall within the tolerance zone for the resistor.
  • a product I,,T, Represented by the vertical scale of FIGS. 1 and 2 is a product I,,T,, of anodizing current I and anodizing time T for each step n.
  • This pattern of binary decreases in the current-time product for successive anodizing steps has been selected in order that the desired binary pattern of decreases in percentage deviation from nominal resistance, provides rapid anodization such that a minimal likelihood of overshooting the tolerance zone, will result.
  • a second phase of anodization in accordance with the method (FIG.
  • a typical minimum anodizing period to be utilized is 25 milliseconds, a period still providing a feasible anodizing time for accurately timed, anodization switching operations to take place.
  • a rate of voltage rise is calculated by dividing the 0.0l67 volts voltage rise by the 25 millisecond minimum time period value, the calculated rate of voltage rise being 0.667 volts per second, or 40 volts per minute.
  • D percentage resistance deviation
  • v./min. rate of voltage rise in volts per minute
  • step N6 would be characterized by a rate of voltage rise of 2,560 volts per minute, a value in excess of the 2,000 volts per minute absolute maximum, if the constant anodizing time phase (Phase II) of the method were continued in the reversed order progression of steps.
  • step N-5 is takenas a crossover point X, at which the constant anodizing time phase (Phase II) will begin in the forward order actual performance of the calculated pattern.
  • Step N 6 is assigned to Phase I of anodization, the constant anodizing current phase.
  • V is the rate of voltage rise in vol'ts per minute
  • I is current in microamps.
  • An advantageous manner of employing a method in accordance with the principles of the invention involves the use of a conventional process control computer having a memory, or peripheral systems such as an associated library of tapes, storing information derived in accordance with the above calculations and tabulation for a wide range of materials of differing resistivity values.
  • Initial values of anodizing current I and anodizing time T plus proper crossover points x are provided for the various resistivities.
  • Intermittent resistance tests may be interspersed between anodizing steps through the use of any conventional measuring circuitry. Exemplary of such circuitry are either intermittent, anodize and then test circuits,
  • Multiplexing may be advantageously employed to anodize a number of thin-film resistors simultaneously with a momentary coupling of each successive resistor undergoing anodization into testing relationship with the resistance measuring circuitry.
  • the particular apparatus to be used is not material to the methods of the invention.
  • FIG. 4 horizontal scale, percentage resistance deviation
  • K ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇
  • FIG. 5 constitutes a flow chart illustrating a series of operations, which may be performed by a conventional, general purpose, process control computer device, in the production of such resistors.
  • the operations to be performed according to this flow chart are to anodize precisely resistors previously roughly adjusted to approximately a -5 percent tolerance, utilizing conventional anodizing circuitry and electrolytes, e.g., an electrolyte composed of 0.01 percent citric acid solution, in a carboxyl cellulose vehicle.
  • Rp represents the programmed nominal resistance value for any individual thin-film resistor
  • n having a resistance R
  • Numerical values of the subscript l will be used to identify specific resistors, for example, resistors r and r having resistances R and R respectively.
  • the term i refers to the total number of resistors to be anodized in a particular group of resistors.
  • the tolerance zone about the nominal value Rp for each resistor n i.e., the 10.0I percent deviation zone 0.9999 Rp R, I.000l Rp, is defined as the limit range L.
  • the term n indicates a maximum number of anodizing steps to be permitted with respect to any resistor r,.
  • the anodization of a number of i of thin-film resistors commences at START" position 31 in FIG. 5.
  • the memory of the computer apparatus for example, asprovided' by a program tape associated with a particular code of resistor to be anodized, is searched (box 32) to provide (box 33) a programmed nominal resistance value Rp for the first resistor r
  • the resistance R, of the resistor r is measured by conventional resistance testing equipment.
  • Such equipment determines whether the resistance R, is more than a value of 5 percent above the resistance Rp programmed for the resistor r, (box 36); if not, whether the resistance R is greater than the maximum resistance of the programmed tolerance zone L associated with the resistor r i.e., whether R l.000l Rp for the resistance Rp programmed for the re 'sistor r (box 37); and, if not, whether the resistance R initially falls-within the programmed tolerance zone L associated with the resistor r i.e., whether 0.9999 Rp R, l.000l Rp for the resistance r, programmed for the resistor r (box 38).
  • the computer is programmed to indicate that the resistor r, is HIGH" (box 41) by activating conventional recording mechanisms (not shown). If the resistance R, is
  • boxes 36 and 37 are not necessary for an anodization program, but are useful only in a sorting operation, which may be performed either separate from or as a part of a program of anodization.
  • the program tape associated with the particular code of thin-film resistor to undergo anodization provides the computer with the information of the type illustrated by the plots of FIGS. 3 and 4 and the calculations and tabulation previously described. It is assumed that linear approximation b" of the nonlinear binary step pattern has been selected as a most convenient pattern of anodization to be employed for this code of resistor.
  • the conventional resistance testing equipment indicates a percentage deviation in resistance R, of the resistor r, from the resistance Rp programmed for the resistor r, this percentage deviation corresponding to a first position along the horizontal scale, presumably in FIG. 3. Let us say that the corresponding point on dotted line b is that shown in FIG. 3 at 51.
  • the anodizing time T determined by the computer for use in a first anodizing step corresponds to the position of the point 51 with respect to the vertical scale of FIG. 2.
  • the program directs the computer to carry out a first anodizing step (box 48), the resistor being anodized in conventional manner in the presence of an electrolyte after which a new resistance value R, of the resistor r, is measured (box 34). If anodization has resulted in the predicted binary pattern of decrease in percentage deviation in resistance, point 52 on dotted line b will have been reached.
  • the constant anodizing time will have thereafter been the predetermined value of 25 milliseconds.
  • Boxes 61 and 62 involve the making of a comparison of the number of anodizing steps n, after each step, with the number n and the signalling of associated recording equipment to indicate a "stalled condition once the number n of steps has been equalled.
  • the value of R is recorded (box 64).
  • Matching operations will thereafter occur through the use, in anodizing the matching resistor, of a value of a target nominal resistance value Rp corresponding to the recorded value of R,, multiplied (box 66) by a desired resistance ratio, if other than unity, provided by the computer memory (box 67), e.g., in the form of the program tape for the code of resistor undergoing anodization.
  • Such matching operation might be employed in the manufacture of thin-film resistor networks including the resistors r,, r,, etc.
  • Anodization of successive resistors r,, r etc. continues until a comparison at box 44 indicates that a final resistor has been trimmed to value. Thereupon, the anodizing operation is terminated (box 68).
  • a method of anodizing a thin-film device to adjust a parameter of the device to within a tolerance range of a desired final value which comprises:
  • n is the number of each step
  • 1, is the anodizing current applied to the device in the presence of an electrolyte during each step n
  • T is the time for which the anodizing current 1,,is applied during each step n
  • K is a constant greaterthan I
  • T is the time for which the anodizing current I is applied during said initial step.
  • anodizing the device by performing at least three steps according to a linear approximation of the nonlinear pattern of steps 9.
  • K a linear approximation of the nonlinear pattern of steps 9.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electromagnetism (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Apparatuses And Processes For Manufacturing Resistors (AREA)
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US87370A 1970-11-06 1970-11-06 Method of anodizing a thin-film device Expired - Lifetime US3635802A (en)

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US (1) US3635802A (xx)
BE (1) BE774895A (xx)
CA (1) CA928433A (xx)
DE (1) DE2155220A1 (xx)
FR (1) FR2112510B1 (xx)
GB (1) GB1363528A (xx)
IT (1) IT942267B (xx)
NL (1) NL7115203A (xx)
SE (1) SE393133B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3956081A (en) * 1973-04-09 1976-05-11 General Radio Method of high speed resistor trimming
US3962049A (en) * 1971-05-13 1976-06-08 Kabushiki Kaisha Aiden Process for coloring aluminum anodic oxide film
US20060011492A1 (en) * 2002-04-03 2006-01-19 Gerhard Moeckl Method for machining workpieces using a machining process in particular an electrochemical machining process
US20080102543A1 (en) * 2000-11-14 2008-05-01 Ballantine Arne W Increasing an electrical resistance of a resistor by oxidation

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3004149A1 (de) * 1980-02-05 1981-08-13 Siemens AG, 1000 Berlin und 8000 München Verfahren zur reproduzierbaren herstellung metallischer schichten
CN111863365B (zh) * 2019-04-28 2022-04-26 深圳市杰普特光电股份有限公司 调阻机及其调阻方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2920018A (en) * 1957-04-22 1960-01-05 Electro Chem Mfg Co Inc Anodizing process and system
US3520783A (en) * 1967-02-10 1970-07-14 Northern Electric Co Method of adjusting a resistor by anodizing

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2920018A (en) * 1957-04-22 1960-01-05 Electro Chem Mfg Co Inc Anodizing process and system
US3520783A (en) * 1967-02-10 1970-07-14 Northern Electric Co Method of adjusting a resistor by anodizing

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3962049A (en) * 1971-05-13 1976-06-08 Kabushiki Kaisha Aiden Process for coloring aluminum anodic oxide film
US3956081A (en) * 1973-04-09 1976-05-11 General Radio Method of high speed resistor trimming
US20080102543A1 (en) * 2000-11-14 2008-05-01 Ballantine Arne W Increasing an electrical resistance of a resistor by oxidation
US20080314754A1 (en) * 2000-11-14 2008-12-25 Ballantine Arne W Increasing an electrical resistance of a resistor by nitridization
US8440522B2 (en) 2000-11-14 2013-05-14 International Business Machines Corporation Increasing an electrical resistance of a resistor by oxidation
US20060011492A1 (en) * 2002-04-03 2006-01-19 Gerhard Moeckl Method for machining workpieces using a machining process in particular an electrochemical machining process

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SE393133B (sv) 1977-05-02
FR2112510B1 (xx) 1974-08-19
FR2112510A1 (xx) 1972-06-16
GB1363528A (en) 1974-08-14
NL7115203A (xx) 1972-05-09
DE2155220A1 (de) 1972-05-10
BE774895A (fr) 1972-03-01
IT942267B (it) 1973-03-20
CA928433A (en) 1973-06-12

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