United States Patent [19J
`Sproul et al.
`
`[54] METHOD FOR SPUTTERING COMPOUNDS
`ON A SUBSTRATE
`
`[75]
`
`Inventors: William D. Sproul, Palatine; Michael
`E. Graham, Evanston, both of Ill.
`
`[73] Assignee: Northwestern University, Evanston,
`Ill.
`
`[ *] Notice:
`
`This patent issued on a continued pros(cid:173)
`ecution application filed under 37 CFR
`1.53( d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`[21] Appl. No.: 08/635,472
`
`[22] Filed:
`
`Apr. 22, 1996
`
`Int. Cl.6
`..................................................... C23C 14/34
`[51]
`[52] U.S. Cl. ................................ 204/192.13; 204/192.15;
`204/192.16; 204/192.22; 204/192.23; 204/192.25;
`204/298.03; 204/298.07; 204/298.06; 204/298.08;
`204/298.14
`[58] Field of Search ......................... 204/192.13, 192.15,
`204/192.22, 192.23, 192.25, 298.03, 298.07,
`298.08, 298.14, 298.26, 298.06, 192.16
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,428,811
`4,963,239
`5,303,139
`5,492,606
`5,556,520
`
`1/1984 Sproul et al. ...................... 204/192.13
`10/1990 Shimamura et al.
`.............. 204/298.08
`4/1994 Mark .................................. 204/298.08
`2/1996 Stauder et al. ..................... 204/298.08
`9/1996 Latz ................................... 204/192.13
`
`FOREIGN PATENT DOCUMENTS
`
`0 564 789 10/1993 European Pat. Off ..
`
`I 1111111111111111 11111 111111111111111 1111111111 1111111111 111111111111111111
`US005942089A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,942,089
`* Aug. 24, 1999
`
`OTHER PUBLICATIONS
`
`Sellers, "Asymmetric Bipolar Pulsed DC-The Enabling
`Technology for Reactive PVD", ENI Tech Note, pp. 1-8,
`Feb. 1996.
`
`William D. Sproul, High Rate Reactive Sputtering Process
`Control, Surface and Coatings Technology, 33 (1987)
`73-81.
`
`William D. Sproul and Paul J. Rudnik, The Effect of Target
`Power on the Nitrogen Partial Pressure Level and Hardness
`of Reactively Sputtered Titanium Nitride Coatings, Thin
`Solid Films, 171 (1989) 171-181.
`
`W. D. Sproul and P. J. Rudnik, Advances in Partial-Pressure
`Control Applied to Reactive Sputtering, Surface and Coat(cid:173)
`ings Technology, 39/40 (1989) 499-506.
`
`(List continued on next page.)
`
`Primary Examiner-Nam Nguyen
`Assistant Examiner-Rodney G. McDonald
`Attorney, Agent, or Firm-Banner & Witcoff, Ltd.
`
`[57]
`
`ABSTRACT
`
`A method and apparatus for monitoring and controlling
`deposition of metal, insulating compounds or other com(cid:173)
`pounds on a substrate by sputtering techniques includes
`maintaining pulsed, constant, direct current power to the
`target, sensing the voltage of the target material used in the
`process, simultaneously rapidly sensing the partial pressure
`of the reactive gas, and simultaneously biasing the substrate
`to activate the reactive gas or otherwise energizing the
`reactive gas in the vicinity of the substrate. An apparatus for
`practicing the invention is also disclosed.
`
`13 Claims, 5 Drawing Sheets
`
`Schematic of Sputtering System
`
`22
`
`24
`
`26
`
`/0
`
`28
`
`Jo~ Pressure
`$~SITT
`r:------:-------:---=====--144-______ .,j
`,-L---....,___.. 16
`Power Pulsed DC/RF Other
`
`50
`
`Substrate Holder
`
`,,
`Target!\ ,,
`:: ,,
`/4
`i!
`substrate
`~
`,,
`:,
`
`Reactive
`Gas
`34
`-----------1---- 44
`:
`42
`' ' I
`
`l-'4--- control I er
`Target
`Voltage~~~
`48 To the set point
`of the contro Iler
`Mass
`Spectrometer
`
`cryo
`Pump
`
`12
`
`D.C.Pulsed Power 32
`constant Source
`
`Page 1 of 12
`
`APPLIED MATERIALS EXHIBIT 1011
`
`

`

`5,942,089
`Page 2
`
`OIBER PUBLICATIONS
`
`W. D. Sproul, P. J. Rudnik and M. E. Graham, The Effect of
`N2Partial Pressure, Deposition Rate and Substrate Bias
`Potential on the Hardness and Texture of Reactively Sput(cid:173)
`tered TiN Coatings, Surface and Coatings Technology,
`39/40 (1989) 355-363.
`X. Chu, M.S. Wong, W. D. Sproul, S. L. Rohde and S. A
`Barnett, Deposition and Properties of Polycrystalline TiN/
`NbN Superlattice Coatings, J. Vac Sci. Technol. A 10( 4),
`Jul./Aug. 1992.
`William D. Sproul, Control of A Reactive Sputtering Process
`For Large Systems, Presented at the Society of Vacuum
`Coaters 36th Annual Technical Conference, Dallas, Texas,
`Apr. 30, 1993.
`J. Affinito and R. R. Parsons, Mechanisms of Voltage
`Controlled, Reactive, Planar Magnetron Sputtering of Al in
`Ar/N2 and AR/0 2 Atmospheres, J. Vac. Sci. Technol. A 2(3),
`Jul.-Sep. 1984.
`
`S. Schiller, K. Goedicke, J. Reschke, V. Kirchhoff, S.
`Schneider and F. Milde, Pulsed Magnetron Sputter Technol(cid:173)
`ogy, Surface and Coatings Technology, 61 (1993) 331-337.
`P. Prach, U. Reisig, Chr. Gottfried and H. Walde, Aspects
`and Results of Long-Term Stable Deposition of Al2 0 3 With
`High Rate Pulsed Reactive Magnetron Sputtering, Surface
`and Coatings Technology, 59 (1993) 177-182.
`W. D. Sproul, M. E. Graham, M. S. Wong, S. Lopez, and D.
`Li, Reactive Direct Current Magnetron Sputtering of Alu(cid:173)
`minum Oxide Coatings. J. Vac. Sci. Technol. A 13(3),
`May/Jun. 1995.
`William D. Sproul, Michael E. Graham, Ming-Show and
`Paul J. Rudnik, Reactive DC Magnetron Sputtering of the
`Oxides of Ti, Zr, and Hf, Presented at the International
`Conference on Metallurgical Coatings and Thin Films,
`Town and Country Hotel, San Diego, California, Apr. 24-28,
`1994 and Submitted for publication in Surf ace and Coatings
`Technology.
`
`Page 2 of 12
`
`

`

`.... = 00
`"'-' N
`\0
`....
`Ul
`
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`
`:
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`
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`
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`
`constant Source
`D.C. Pu Is ed Power L--32
`
`Pump
`cryo J-12
`
`of the controller
`Q
`;a 48j To the set point
`
`4
`
`S pect ram et er
`
`Mass
`
`Voltage
`Target· controller
`
`Substrate Holder
`
`/6
`
`Substrate
`
`/4
`Target
`
`20
`
`50
`
`Power Pulsed DC/RF Other
`
`Sensor
`30----1 Pressure
`
`2a~ 1 controller
`
`42
`
`I
`I
`I
`
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`
`38
`
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`
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`26
`
`24
`
`22
`
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`
`34
`
`Reactive
`
`Gas
`
`36-iMeter
`Flow
`
`Schematic of Sputtering System
`
`FIG.I
`
`Page 3 of 12
`
`

`

`U.S. Patent
`US. Patent
`
`Aug. 24, 1999
`Aug. 24, 1999
`
`Sheet 2 of 5
`Sheet 2 0f5
`
`5,942,089
`5,942,089
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`Page 4 of 12
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`Page 4 of 12
`
`

`

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`FIG.3
`Asymmetric Bipolar Pulsed DC Power
`100
`
`0 ---r- -
`
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`0
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`20
`30
`40
`50
`60
`70
`80
`
`Time) µseo
`
`Source= J. Sellers) ''Asymmetric Bipolar Pulsed DC)''
`ENI Tech Note 1 ENIJ Rochester, NY
`
`d •
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`.... = 00
`
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`
`Page 5 of 12
`
`

`

`FIG.4
`AIOx-Target Voltage vs.Oxygen Partial Pressure
`
`-o- Increasing
`--1:r- Decreasing
`
`400
`
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`
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`.... = 00
`
`\0
`
`Page 6 of 12
`
`

`

`U.S. Patent
`
`Aug. 24, 1999
`
`Sheet 5 of 5
`
`5,942,089
`
`LO
`(\J
`
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`Page 7 of 12
`
`

`

`1
`METHOD FOR SPUTTERING COMPOUNDS
`ON A SUBSTRATE
`
`5,942,089
`
`2
`Sputtering techniques for the application of pure metals
`are fairly well refined and effective. Additionally, sputtering
`techniques for conductive or non-insulating compounds
`have been somewhat successful utilizing the techniques
`described in the aforesaid publications. However, certain
`materials, which provide an insulating, hard coating upon a
`substrate are difficult to apply as a film or may not be
`efficiently applied using such sputtering techniques. Alumi(cid:173)
`num oxide, for example, has heretofore been applied by
`10 sputtering techniques to a substrate at only a small fraction
`of the rate and efficiency of the application associated with
`the pure aluminum metal. Thus, low deposition rates of
`insulating or non-conductive metal compounds have con(cid:173)
`tinued to pose a challenge. Publications that reflect research
`15 regarding the sputtering of such compounds include the
`following, which are incorporated herewith by reference:
`9. "Aspects and Results of Long-Term Stable Deposition
`of Al2 O2 with High Rate Pulsed Reactive Magnetron
`Sputtering," published in Surf ace and Coatings Technology,
`1993;
`10. "Reactive Direct Current Magnetron Sputtering of
`Aluminum Oxide Coatings," J. Vac. Sci. Technol. A 13(3),
`May/June 1995; and
`11. "Reactive DC Magnetron Sputtering of the Oxides of
`Ti, Zr, and Hf," presented at the International Conference on
`Metallurgical Coatings and Thin Films, Town and Country
`Hotel, San Diego, Calif., Apr. 24-28, 1995, and accepted for
`publication in Surf ace and Coatings Technology.
`In sum, there has remained a need to provide an improved
`method and apparatus for the deposition of metallic, insu(cid:173)
`lating compounds such as aluminum oxide, on a substrate
`using sputtering techniques.
`
`25
`
`30
`
`BACKGROUND OF THE INVENTION
`Briefly, the present invention relates to a method and 5
`apparatus for sputtering of a thin film of a compound onto
`a substrate workpiece by means of cathodic, magnetron
`sputtering.
`Application of metals and metallic compounds by use of
`a reactive deposition process is known and is the subject, for
`example, of U.S. Pat. No. 4,428,811, "Rapid Rate Reactive
`Sputtering Of A Group IVE Metal" issued Jan. 31, 1984,
`incorporated herewith by reference. U.S. Pat. No. 4,428,811
`discloses a method and apparatus for rapid rate deposition of
`metallic compounds such as titanium nitride onto a substrate
`in a vacuum chamber. In the process, the chamber is filled
`with inert gas that is ionized and bombards the metal target
`within the chamber to initiate the sputtering process. A
`substrate is positioned within the chamber for coating, and
`a second reactive gas is fed into the chamber at a measured 20
`rate to combine at the substrate with the atomized metal
`from the target to form the coating. Control systems for such
`sputtering operations are also disclosed in the aforesaid
`patent.
`Over the years, the technology associated with sputtering
`processes has been improved so that additional compounds
`and materials can be applied to a substrate by. A series of
`papers by the co-inventor reflect research in this area includ(cid:173)
`ing the following:
`1. "High Rate Reactive Sputtering Process Control,"
`published in Surface and Coatings Technology, 1987;
`2. "The Effect of Target Power on the Nitrogen Partial
`Pressure Level and Hardness of Reactively Sputtered Tita(cid:173)
`nium Nitride Coatings," published in Thin Solid Films, 35
`1989;
`3. "Advances in Partial-Pressure Control Applied to Reac(cid:173)
`tive Sputtering," published in Surface and Coatings
`Technology, 1989;
`4. "The Effect of N2 Partial Pressure, Deposition Rate and
`Substrate Bias Potential on the Hardness and Texture of
`Reactively Sputtered TiN Coatings," published in Surface
`and Coatings Technology, 1989;
`5. "Deposition and Properties of Polycrystalline TiN/NbN
`Superlattice Coatings," published in J. Vac. Sci. Technol. A
`10/4, July/August 1992; and
`6. "Control of a Reactive Sputtering Process for Large
`Systems," a paper presented at the Society of Vacuum
`Coaters, 36th Annual Technical Conference, Dallas, Tex.,
`Apr. 30, 1993.
`The text of these publications is incorporated herewith by
`reference.
`The energy source which effects the ionization of the inert
`gas in a sputtering system has evolved over time so that now
`pulsed, direct current electrical power is known to be a
`preferred energy source to the target material. Publications
`relating to this technique and technology include the fol(cid:173)
`lowing:
`7. "Mechanisms of Voltage Controlled, Reactive, Planar
`Magnetron Sputtering of Al in Ar/N 2 and Ar/O 2
`Atmospheres," published in J. Vac. Sci. Technol. A 2(3),
`July-September 1984; and
`8. "Pulsed Magnetron Sputter Technology," published in
`Surface and Coatings Technology, 1993.
`These publications are incorporated herewith by refer(cid:173)
`ence.
`
`SUMMARY OF THE INVENTION
`
`In a principal aspect, the present invention comprises a
`method for deposition of various compounds, especially
`insulating, metallic compounds such as aluminum oxide, on
`a substrate as a thin film by sputtering techniques utilizing
`40 a pulsed, constant power, direct current electric power
`supply to cause ionization of an inert gas that bombards a
`target thereby releasing the atoms of the target into a vacuum
`chamber and further controlling the rate of admission and
`thus the reaction of a second, reactive gas to the chamber
`45 with a combination of control signals. Specifically, the rate
`of admission is controlled by a first signal derived from the
`measured voltage of the target which is maintained at a
`constant power setting. The rate of admission is further
`controlled by a second signal derived from the measured
`50 partial pressure of the reactive gas. The partial pressure of
`the reactive gas is sensed by means such as an optical gas
`controller or mass spectrometer, as well as the target voltage,
`is sensed to provide control signals representative of the
`desired composition and physical characteristics of the thin
`55 film. The desired composition and physical characteristics
`are derived empirically for given target materials, reactive
`gases and power settings. To further enhance the thin film
`deposition process, the reactive gas at or near the substrate
`is subjected to local energy input, for example, by applying
`60 pulsed direct current to the substrate. By the method, it is
`possible to carefully control the amount of reactive gas in the
`system and thereby increase the rate of deposition of the
`compound multiple times the rate of deposition using prior
`sputtering techniques.
`Thus, it is an object of the invention to provide an
`improved method and apparatus for deposition of com(cid:173)
`pounds on a substrate by sputtering techniques.
`
`65
`
`Page 8 of 12
`
`

`

`5,942,089
`
`3
`It is a further object of the invention to provide an
`improved method for deposition by sputtering of com(cid:173)
`pounds including oxides, nitrides, fluorides, sulfides,
`chlorides, borides and mixtures thereof.
`Another object of the invention is to provide an improved
`and highly efficient method and apparatus for deposition of
`insulating, metal compounds on a substrate utilizing
`improved control techniques.
`Another object of the invention is to provide an improved
`method for deposition of thin films of insulating, metal
`compounds on a substrate at rates which are multiples of the
`rates of prior art sputtering techniques.
`Another object of the invention is to provide an improved
`method for deposition of metal and semi-conductor com(cid:173)
`pounds as thin films using sputtering techniques.
`A further object of the invention is to provide a method for
`effecting efficient deposition of compounds by sputtering
`techniques utilizing a constant power, pulsed direct current
`power supply for the target material and control signals for
`controlling the admission of reactive gas wherein one signal
`is reflective of the voltage of the target power source and
`another signal is reflective of the partial pressure of the
`reactive gas used in the practice of the process.
`These and other objects, advantages and features of the 25
`invention will be set forth in the detailed description as
`follows.
`
`20
`
`30
`
`4
`source 32 is preferably asymmetric as depicted in FIG. 3
`with the cathode negatively biased, although a symmetric
`source 32, as depicted in FIG. 2, may be utilized.
`A reactive gas, such as oxygen, is provided from a source
`5 34 through a flow meter 36 and control valve 38 via a
`conduit 40 to the vicinity of the target 18 where its proximity
`to atoms from the target will enhance reaction therewith. The
`reactive gas control valve 38 is responsive to a plurality of
`sensing or feedback signals which are input to a controller
`42 which, upon proper processing, provides a control signal
`10 via link 44 to valve 38.
`The signals to the controller 42 are derived from two
`sources, first the voltage of the target 18 is constantly
`monitored. Second, the partial pressure of the reactive gas is
`monitored. Regarding the voltage target 18, this voltage may
`15 vary since the power to the target 18 is maintained at a
`constant value. For each set of conditions within the
`chamber, therefore, for a given target and reactive gas, it is
`possible to derive the relationship between such constant
`power voltage and the partial pressure of the reactive gas
`thereby identifying the optimal range of partial pressure and
`voltage for formation of the compound comprised of the
`target material and reactive gas. An example of this empiri(cid:173)
`cal derivation is depicted in FIG. 4 for a target material of
`aluminum in an argon/oxygen atmosphere for increasing and
`decreasing oxygen partial pressure wherein the target power
`was 2 kilowatts from a 20 kHz3 pulsed direct current source
`and the total chamber pressure was 4 mTorr. Note that partial
`pressure of about 0.03 mTorr at a target voltage of 270 to 380
`volts is indicative of highly efficient film formation. This
`information or information of this type is derived from an
`experimental or test run, and the results are programmed into
`controller 42 thus enabling the controller 42 the capability to
`provide almost instantaneous feedback control input
`because voltage measurements provided to the controller 42
`from target 18 are inherently rapid. Thus, the voltage feed-
`35 back signal provides a highly sensitive, rapid response,
`control function, when empirical or full range test run,
`hystersis information derived from an experiment or full
`range test run of the type reflected by FIG. 4 is programmed
`into the controller 42.
`Simultaneous with the rapid control signal derived from
`the voltage of target 18, a second less rapid signal is derived
`by directly measuring the partial pressure of the reactive gas,
`e.g. oxygen. Thus, as depicted in FIG. 1, a mass spectrom(cid:173)
`eter 46, for example, or a partial pressure controller, e.g. an
`45 analyzer (OGC made by Leybold Infilon of East Syracuse,
`N.Y.) is provided to determine the partial pressure of the
`specific reactive gas. Note the signal derived from sensor 46
`is species specific, e.g. oxygen; whereas the target voltage
`signal is not. Thus, the target voltage signal, previously
`50 described, may result, at least in part, due to phenomena
`other than the partial, pressure of the reactive gas. For
`example, out gassing from the substrate or chamber walls
`may have an impact on the signal. Thus, the reactive gas
`sensor 46 provides a signal 48 to the controller which is
`55 reflective of the true partial pressure of the reactive gas
`(oxygen) albeit a slowly developed or slowly derived signal
`relative to the target voltage signal because of the instru(cid:173)
`mentation involved.
`In any event, the meaning of the signal 48 is also
`60 dependent upon the empirical relationship between reactive
`gas partial pressure and flow rate. This relationship is
`derived simultaneously with the empirical power voltage/
`partial pressure relationship discussed with regard to FIG. 4
`for each specific set of conditions. FIG. 5 is a graph
`65 depicting the relationship for the same conditions (in fact,
`derived during the same empirical experimental run) as FIG.
`4.
`
`BRIEF DESCRIPTION OF IBE DRAWING
`In the detailed description which follows, reference will
`be made to the drawing comprised of the following figures:
`FIG. 1 is a schematic of a vacuum chamber and the
`control circuitry associated therewith for the practice of the
`method of the invention;
`FIG. 2 is a graph depicting a symmetric, bipolar pulsed,
`direct current power supply wave;
`FIG. 3 is a graph depicting an asymmetric, bipolar pulsed
`direct current power supply wave;
`FIG. 4 is a graph depicting the target voltage/oxygen
`partial pressure hysteresis curve for the reactive sputtering 40
`of aluminum in an argon/oxygen atmosphere; and
`FIG. 5 is a graph depicting the oxygen reactive gas
`flow/oxygen partial pressure hysteresis curve for the reactive
`sputtering of aluminum in an argon/oxygen atmosphere;
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Overview And General Description
`The method of the invention as well as the associated
`apparatus are designed to optimize the conditions for reac(cid:173)
`tion between atomized target material and reactive gas to
`form and deposit a thin film compound in a sputtering
`system. Thus referring to FIG. 1 , there is depicted the
`component parts of a sputtering system used to practice the
`invention.
`A vacuum chamber 10 is evacuated by a pump 12 after a
`substrate material 14, e.g. quartz or a piece of steel is
`mounted on a holder 16 within the chamber 10. A target
`material 18, e.g. Aluminum or some other metal or semi(cid:173)
`conductor material, is also mounted within the chamber 10.
`The target 18 serves as a cathode in the process and the
`inside walls 20 of chamber 10 serve as an anode. An inert
`gas, e.g. Argon (Ar), is admitted to chamber 10 from a
`source 22 via a meter 24 and valve 26 controlled by a
`controller 28 responsive to a pressure sensor 30.
`The target 18 is subject to a bipolar, pulsed, direct current
`power source 32 of the type generally known in the art. The
`
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`5,942,089
`
`5
`Referring to FIG. 5, for the reported conditions and
`materials, which is the same as specified for the data of FIG.
`4, the optimal partial pressure is in the range of about 0.02
`mTorr, at which point the oxygen flow is in the range of 15
`to 20 Seem. Thus, the signal 48 from sensor 46 can be 5
`utilized to "zero" or set the controller 42 so that the target
`voltage signal to controller 42 is working from an appro(cid:173)
`priate base line.
`One further input to the system is provided to enhance the
`film deposition process. An energy source 50 provides a 10
`means for activating the reactive gas, e.g. Oxygen, at or near
`the substrate 14. For example, a pulsed direct current power
`supply may be applied to the substrate 14. Other energy
`sources include a radio frequency voltage source, lasers,
`electron beams, a microwave source, or an inductively 15
`coupled plasma source. A radio frequency source of 13.56
`MHZ or a harmonic multiple thereof may be used. The
`energy input at the substrate 14 has the effect of enhancing
`the process efficiency as reflected by the data derived in
`FIGS. 4 and 5, by way of example, so as to increase flow rate 20
`and voltage at optimal conditions.
`Also by correlating the data of the type derived in FIGS.
`4 and 5 with various physical parameters of the film
`compound, it becomes possible to apply films having cus(cid:173)
`tomized characteristics. For example, each of the data points 25
`of FIGS. 4 and 5 are representative of compounds having
`associated therewith a variety of measurable physical char(cid:173)
`acteristics including conductivity, modulus, hardness,
`extinction coefficient, index of refraction, reflectivity, trans(cid:173)
`mission and constituent composition. By controlling the 30
`sputtering process to such data points, as it is possible to do
`with this process, the desired custom film may be sputter
`applied to a substrate 14.
`The process is especially useful in the deposition of
`insulating, metal compounds such as aluminum oxide. 35
`Experimental results demonstrate application rates 15 to 20
`times better than prior techniques. For example, with the
`reactive sputtering of stoichiometric Al2 0 3 , the deposition
`rate had been increased from about 5% of the metal depo(cid:173)
`sition rate to 70% or more of the metal deposition rate. Also, 40
`the process is useful with many compounds including
`oxides, nitrides, carbides, sulfides, fluorides, chlorides,
`borides and mixtures thereof. Numerous metals, including
`aluminum, titanium, hafnium, zirconium, tantalum, silicon,
`and chromium have been successfully used as the target 45
`material.
`Specific Example:
`Following is a specific
`invention:
`
`example of the practice of the
`
`6
`Two nominally 5"x15" rectangular MRC Inset targets are
`mounted vertically, opposing one another about 11" apart
`with the substrate table in between. The cathodes are an
`unbalanced magnetron design, which enhances the plasma
`density in the vicinity of the substrate, and at least one target
`is aluminum with a metallic purity of at least 99.99%.
`The cathodes (targets) are each connected to Advanced
`Energy MDX 10 kW de power supplies through 20 kHz
`Spare-Le (or higher frequency) units which together provide
`a pulsed de power and suppression of arcing on the target
`surface during sputtering.
`The substrate table is connected to a 3 kW rf power
`supply, and the induced de voltage is read out through a
`meter which is shielded from rf power by means of an
`appropriate filter.
`The total gas pressure in the chamber is monitored by a
`Baratron (capacitance manometer) for sputtering pressures
`(1-10 mTorr), and lower pressures are monitored with a
`Bayard-Alpert type ionization gauge. The ionization gauge
`is also used as a reference in checking the calibration of the
`partial pressure sensors (OGC or mass spec.), or a more
`stable instrument such as a spinning rotor gauge can be used
`and is preferred if available.
`The partial pressures of all gases in the system are
`monitored with an Inficon Quadrex 100, quadrupole mass
`spectrometer, and two of the gases (oxygen and argon) are
`monitored with an Inficon OGC (Optical Gas Controller).
`The mass spectrometer is attached to a sampling system
`which is differentially pumped, since it requires an operating
`pressure that is typically in the 10- 6 Torr range, and is
`mounted to the top of the chamber. The OGC is attached
`directly to the back of the chamber through a standard KF
`flange, since it operates at sputtering pressures.
`The gas flow controllers are MKS model 260 with modi(cid:173)
`fications that allow them to respond to pressure signals
`instead of flow signals. In this case, the total pressure is
`maintained constant by a feedback control involving the
`Baratron and the MKS controller. The target voltage on the
`aluminum target is used as the primary indicator of oxygen
`partial pressure during sputtering and is used as a feedback
`signal to the MKS controller which operates the inlet valve
`for a quick response to any deviations in partial pressure
`(voltage). Since the voltage is not a unique signal with
`respect to the partial pressure of oxygen, the OGC or the
`mass spectrometer is used to provide a feedback signal for
`the voltage set point, which is thus tied to the actual desired
`level of oxygen partial pressure. This OGC or mass spec(cid:173)
`trometer value is updated more slowly than the voltage. This
`50 dual feedback loop provides a fast response that optimizes
`the process control and maintains a unique relationship
`between the control set points and the selected partial
`pressure of oxygen.
`In order for the process to function in the preferred
`55 manner, one desires to also establish an anode surface in
`close proximity to the plasma but shielded from deposition,
`since the insulating film produced in the process will cause
`the anode to become non-functional if not protected and
`would cause the process to stop.
`Deposition protocol:
`The appropriate partial pressure of oxygen has been
`previously selected from an initial determination of the
`hysteresis curve, which relates the gas flow (see FIG. 5) and
`the target voltage (see FIG. 4) to the set partial pressure of
`oxygen in a fixed and determinable way for a given system
`and given operating conditions. The partial pressure that is
`selected will be that which uses the least amount of reactive
`
`Deposition of Aluminum Oxide by Means of
`Reactive DC Sputtering
`Aluminum oxide (stoichiometric composition but non(cid:173)
`crystalline) may be deposited using the following deposition
`system hardware:
`The substrate to be coated is placed in a stainless steel
`vacuum chamber, approximately 29" o.d. and about 30"
`high, which is electrically grounded to earth potential and is
`pumped with a 6" diffusion pump and a 1500 1/s turbo(cid:173)
`molecular pump, which are both backed up with appropri- 60
`ately sized mechanical pumps (in this case, Edwards EM2-
`80's) capable of achieving a base pressure of lxl0- 6 Torr.
`The substrate may be a flat glass slide or other material of
`choice, which is mounted on the 5"-diameter, rotatable
`substrate table. The closest approach of the substrate to the 65
`target is about 3" and it may be rotated or held stationary
`during coating.
`
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`5,942,089
`
`7
`gas and still makes a coating with the desired properties.
`Once the partial pressure of 0 2 has been determined that
`corresponds to the desired properties of the oxide coating
`( e.g., optically clear), and the target voltage for that partial
`pressure is known, the necessary set points for the process 5
`can be inserted into the controllers.
`The following operating parameters are set:
`The power supply (with Spare-Le unit) is set for a
`constant power of 2 kW.
`The target voltage set point is set to achieve a level of 10
`-340 volts.
`The MKS controller/Baratron is set to adjust the argon
`flow to maintain a constant total pressure of 8 mTorr.
`The partial pressure set-point is set for 0.03 mTorr on the
`OGC (actual numbers may vary depending on the calibra- 15
`tion of the pressure gauges used, but the relative location on
`the hysteresis curve will not vary for a coating of a given
`composition, deposited at a given rate).
`It is preferred, for example, to bias the substrate by
`adjusting the rf power supply to 1 kW.
`The coating thus produced is clear and insulating and the
`rate of deposition is about 1600 A/min3 compared to the pure
`metal deposition rate of about 2000 Nmin.
`Following is a table which summarizes experimental
`results associated with various film compounds applied by 25
`the process using the apparatus of the invention:
`
`20
`
`8
`( d) providing an anode in the chamber;
`( e) admitting the reactive gas into the chamber, said
`reactive gas capable of forming the compound in
`combination with atoms and ions from the target;
`(t) supplying pulsed, direct current, electrical power to the
`target to effect ionization of the inert gas and thereby
`effect bombardment of the target to release atoms and
`ions from the target into the chamber for combination
`with the reactive gas; and
`(g) controlling the admission and reaction of the reactive
`gas by:
`(i) maintaining constant power to the target;
`(ii) measuring substantially instantaneously a target
`voltage and providing a first voltage measurement
`signal for controlling the rate of admission of the
`reactive gas to the chamber to achieve partial pres(cid:173)
`sure reflective of a compound composition having
`defined physical characteristics, said first voltage
`measurement signal comprising an independent
`measurement indicative of the partial pressure in the
`system which is not reactive gas species specific,
`which provides a signal characteristic of the optimal
`range of partial pressure for reaction of the reactive
`gas;
`(iii) simultaneously measuring the species specific par(cid:173)
`tial pressure of the reactive gas and providing a
`
`TABLE OF METAL-OXIDE DEPOSITION EXPERIENCE
`
`Compound
`(could choose non-
`stoichiometric)
`
`Target
`Target
`Power, Voltage,
`V
`kW
`
`