United States Patent
`
`[19]
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`Celestino et a1.
`
`[11]
`
`[451
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`Patent Number:
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`4,579,618
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`Date of Patent:
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`Apr. 1, 1986
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`[54]
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`[75]
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`[73]
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`[21]
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`[22]
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`[63]
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`[51]
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`[52]
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`[53]
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`[56]
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`PLASMA REACTOR APPARATUS
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`Inventors: Salvatore A. Celestino, Novato;
`Georges J. Gorin, Pinole; Stephen E.
`Hilliker; Gary B. Powell, both of
`Petaluma, all of Calif.
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`Assignee:
`Appl. No.:
`Filed:
`
`Tegal Corporation, Novato, Calif.
`665,098
`
`Oct. 29, 1984
`
`Related US. Application Data
`Continuation of Ser. No. 568,859. Jan. 6, 1984. aban-
`doned.
`
`Int. Cl.‘ ........................ B44C 1/22; C03C 15/00;
`C03C 25/06; C23F 1/02
`U.S. Cl. .................................... 156/345; 156/643;
`156/646; 204/298; 204/192 E
`Field of Search ....................... 156/345, 643, 646;
`204/164, 192 EC, 192 E, 298; 118/728, 50.1,
`620; 427/38, 39; 134/1
`References Cited
`
`U.S. PATENT DOCUMENTS
`Suzuki et al.
`................... 204/298 X
`
`£98,419 11/1981
`
`4
`
`4.316.791
`2/1982 Taillet
`4.352.725 10/ 1982 Tsukada ........
`4,411,733 10/1983 Macklin ct al.
`4.464.223
`8/1984 Gorin
`
`156/345 X
`.. 156/345 X
`
`.. 156/345 X
`...... 156/643
`
`FOREIGN PATENT DOCUMENTS
`
`Japan ................................... 156/643
`4/1981
`0033839
`0186937 11/1983 Japan .
`
`Primary Examiner—William A. Powell
`Attorney, Agent, or Firm—Paul F. Wille
`
`[57]
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`ABSTRACT
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`Plasma processing is accomplished with an improved
`single electrode reactor apparatus. High and low fre-
`quency power supplies are coupled to the single elec-
`trode to provide increased process flexibility, control
`and residue removal. A multi-stage passive filter net-
`work is disclosed which performs the functions of cou-
`pling both power supplies to the electrode, isolating the
`low frequency power supply from the high frequency
`power supply and attenuating the undesired frequencies
`produced by mixing of the two frequencies in the non-
`linear load represented by the reactor.
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`3 Claims, 2 Drawing Figures
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`'V‘kfl“\\\\
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`NEI'WORK 13.58 MHz
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`100 KHz
`MATCHING
`
`POWER
`SU PPLY
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`Page 1 of 6
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`APPLIED MATERIALS EXHIBIT 1016
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`

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`U. S. Patent Apr. 1, 1986
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`Sheet 1 of 2
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`4,579,618
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`Noz_Io._.<z
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`I}mmfi;
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`2
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`A power supply apparatus, which is coupled to the
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`single electrode by an RF transmission line, comprises a
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`low frequency power supply and a high frequency
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`power supply. Typically,
`the low frequency power
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`supply operates at approximately 100 KHz and the high
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`frequency power supply operates at approximately
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`13.56 MHz. Both power supplies are coupled to the
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`electrode through coupling networks which serve to
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`optimize RF transmission through impedance match-
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`ing. It is necessary to efficiently couple both the high
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`and low frequency power supplies to the electrode
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`while providing isolation between the power supplies.
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`Furthermore, the problem of coupling RF power to a
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`non-linear load such as a plasma reactor is very com-
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`plex. This is especially true in the case of commercial
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`units which must meet stringent FCC limits on emitted
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`radiation. To meet these needs, a specialized filter/com-
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`biner is provided which couples both power supplies to
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`the electrode and provides isolation while suppressing
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`mixing products of the two frequencies caused by the
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`non-linear nature of the load.
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`A particular embodiment of the invention comprises
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`a method of metal etching utilizing the previously de-
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`scribed apparatus which has proved particularly useful
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`for aluminum etching. For instance, it has been found
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`that a reactive atmosphere comprising carbon tetrachlo-
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`ride, chlorine, and argon which is subjectd simulta-
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`neously to 250 watts at 13.56 MHz and 20 watts at 100
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`KHz provides excellent etching of an aluminum/-
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`silicon/ 1% copper layer. The surface remaining after
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`such an etching process is substantially cleaner than that
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`left by prior art processes.
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`These and other objects and advantages of the pres-
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`ent invention will be apparent to one skilled in the art
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`from the detailed description below taken together with
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`the drawings.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a schematic cross-sectional view of an appa-
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`ratus according to a particular embodiment of the pres—
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`ent invention; and
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`FIG. 2 is a schematic diagram of a filter/combiner
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`according to a particular embodiment of the present
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`invention.
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`DETAILED DESCRIPTION TO THE
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`INVENTION
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`1
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`PLASMA REACTOR APPARATUS
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`4,579,618
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`5
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`This application is a continuation of application Ser.
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`No. 568,859, filed Jan. 6, 1984, abandoned.
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`FIELD OF THE INVENTION
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`The present invention relates, in general, to plasma
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`reactors and their use. More particularly, the invention
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`relates to a single electrode, multi-frequency plasma 10
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`reactor.
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`BACKGROUND OF THE INVENTION
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`Various forms of processing with ionized gases, such
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`as plasma etching and reactive ion etching, are increas- 15
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`ing in importance particularly in the area of semicon-
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`ductor device manufacturing. Thus, the investigation of
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`the effects of the variation of various process parame-
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`ters defining a plasma process has been pursued. Of
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`particular interest are the various etching processes 20
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`used in semiconductor device manufacturing. It is in—
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`creasingly necessary to produce very fine lines with
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`such processes, which requires a high degree of process
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`uniformity, flexibility and control. A further need exists
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`for apparatus which provides efficient wafer handling. 25
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`As disclosed in US. Pat. No. 4,464,223, it has been
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`discovered that a plasma reactor which is capable of
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`applying power of more than one frequency to energize
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`the plasma offers significant advantages in terms of
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`process flexibility, control, and uniformity. However, 30
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`the advantages of such a dual frequency process have
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`only been achievable in multi-electrode plasma reac-
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`tors. Such reactors are structurally more complex and
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`therefore may be commercially disadvantageous in
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`some circumstances.
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`A particular need exists in the area of metal etching
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`processes. In order to achieve the desired end result, it
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`is necessary to adequately remove any organic and/or
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`inorganic residues from the etched surface. Prior art
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`etching processes have proved lacking in one respect or 40
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`another in providing an adequately clean surface fol-
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`lowing a metal etching step.
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`SUMMARY OF THE INVENTION
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`Accordingly, it is an object of the present invention 45
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`to provide an improved plasma reactor apparatus and
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`method.
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`A further object of the present invention is to provide
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`a plasma reactor apparatus and method by which a
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`single electrode may be used to apply power of more 50
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`than one frequency to the reaction volume.
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`Yet a further object of the present invention is to
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`provide an improved method and apparatus for metal
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`etching whereby surface residues, both organic and
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`inorganic, are effectively removed.
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`A particular embodiment of the present invention
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`comprises a plasma reactor apparatus having an enclo-
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`sure and an electrode. The electrode is adapted to carry
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`the workpiece and also mates to the lower portion of
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`the enclosure to seal the reaction volume. In addition, 60
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`the electrode is electrically insulated from the enclo-
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`sure. A manifold is provided within the enclosure to
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`distribute the input reactive gases and to allow reaction
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`products to be exhausted by means of a vent connected
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`to a vacuum pump. Typically,
`temperature control 65
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`means such as water jackets are provided in the enclo-
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`sure and the electrode. Also, an optical window is pro-
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`vided for purposes of process monitoring.
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`55
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`Referring to FIG. 1, a plasma reactor apparatus ac-
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`cording to the principles of the present invention is
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`illustrated in cross-section. Plasma reactor 10 is de-
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`signed, in broad terms, to enclose a reaction volume 11,
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`supply a reactive gas mixture 12 thereto, exhaust reac-
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`tion products 13 therefrom, and impose an RF electric
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`field therein. An enclosure 15 which includes a ceramic
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`insulator lower portion 16, a manifold 17 and an elec—
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`trode 18 serve to define reaction volume 11. Enclosure
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`15 is conductive and electrically grounded. Electrode
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`18 is adapted to sealably engage ceramic insulator 16
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`and is supplied wlth an O-ring seal 19 to accomplish an
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`adequate seal therebetween. Manifold 17 is coupled to a
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`supply means 21 and is adapted to supply reactive gas 12
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`to reaction volume 11. In addition, manifold 17 directs
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`reaction products 13 comprising used and unused reac-
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`tive gas and chemical products of the reaction to a vent
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`22 so that they may be exhausted by a vacuum pump
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`which is not shown. Manifold 17 may be of the type
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`disclosed in US. Pat. No. 4,209.357 issued June 24. 1980
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`and assrgned to the assignee of the present invention.
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`Page 4 of 6
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`3
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`Plasma reactor apparatus 10 also includes an optical
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`window 23 in enclosure 15 whereby the optical proper-
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`ties of the plasma in reaction volume 11 may be moni—
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`tored. In addition, a temperature control device such as
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`water jacket 24 is provided. As is well—known in the art,
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`it is also common to provide temperature control de-
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`vices such as water jackets and/or heating devices in
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`electrode 18.
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`Electrode 18 serves the dual purpose of energizing
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`reactive gas 12 and providing the means by which
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`workpieces are loaded and unloaded from reaction
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`volume 11. During the loading process electrode 18 is
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`lowered away from ceramic insulator 16, whereby ac—
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`cess to reaction volume 11 is provided. In addition,
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`electrode 18 is adapted to serve as a workpiece holder.
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`A semiconductor wafer 25, which is surrounded and
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`carried by a wafer ring 26, is supported by electrode 18.
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`This single electrode arrangement is particularly advan—
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`tageous in that it readily interfaces with an automated
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`wafer transport system.
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`A power supply apparatus 30 is coupled to electrode
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`18 to supply RF power thereto. According to the pres-
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`ent invention, power supply apparatus 30 comprises a
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`low frequency portion 31 and a high frequency portion
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`32. In the nomenclature associated with plasma reactors
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`and plasma processes it is common to describe as “high
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`frequency” any frequency greater than about 10 MHz.
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`Similarly, “low frequency” is used to describe any fre-
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`quency less than approximately 1 MHz. The use of
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`combined high and low frequencies in plasma processes
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`has been described in US. Pat. No. 4,464,223. How-
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`ever, that disclosure describes the use of multiple fre—
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`quencies in a multiple electrode reactor apparatus. It
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`has not been known heretofore that multiple frequen-
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`cies could be successfully combined in a single elec-
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`In the particular case of this embodiment of the pres—
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`ent invention, low frequency portion 31 of power sup-
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`ply 30 comprises a 100 KHz power supply 33, a power
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`meter 34 and a 100 KHz matching network 35. Power
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`meter 34 serves to monitor the power level of the 100
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`KHz power being supplied to reaction volume 11.
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`Matching network 35 serves to optimize the transmis—
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`sion of 100 KHz power to electrode 18 by means of
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`impedance matching. Matching network 35 may com—
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`prise, for instance, an impedance transformer. Similarly,
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`high frequency portion 32 of power supply 30 com-
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`prises a 13.56 MHZ power supply 37, a power meter 38
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`and a 13.56 MHz matching network 39. Matching net-
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`work 39 may comprise, for instance, an automated slug—
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`tuning apparatus.
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`A filter/combiner 40 is coupled between low fre-
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`quency power supply 31, high frequency power supply
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`32 and electrode 18. Ports A and B of filter/combiner
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`40 are coupled to high frequency power supply 31 and
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`low frequency power supply 32, respectively. Port X of
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`filter/combiner 40 is coupled to electrode 18. Filter/-
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`combiner 40 must serve three purposes which are
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`unique to a single electrode, dual frequency plasma
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`reactor. First, the high frequency power must be largely
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`prevented from reaching the low frequency power
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`supply to prevent damage. The converse of this isola-
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`tion problem is provided by 13.56 MHz matching net-
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`work 39. Second, the mixing products caused by the
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`coupling of two different frequencies to a non-linear
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`load (the plasma reactor) must be attenuated in order to
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`comply with FCC regulations. Third,
`the radiation
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`4,579,618
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`4
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`emitted by the reactor and the various interconnections
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`must be minimized.
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`Referring now to FIG. 2, filter/combiner 40 is shown
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`schematically. Ports A, B and X are shown schemati—
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`cally as coaxial connectors, since the interconnection of
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`the various elements is generally accomplished with
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`coaxial cable. Each of the indicated ground connections
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`in filter/combiner 40 is coupled to the same ground as is
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`enclosure 15 (FIG. 1). This minimizes ground currents.
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`1n broad terms,
`filter/combiner 40 comprises first
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`through sixth stages 45, 46, 47, 48, 49 and 50, respec-
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`tively, coupled between port X and port B. Port A is
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`coupled out between first stage 45 and second stage 46.
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`First stage 45 of filter/combiner 40 is a parallel tank
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`circuit made up of inductor 51 and capacitor 52. In a
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`particular embodiment, first stage 45 is intended to at-
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`tenuate the 40.68 MHz mixing product. Inductor 51 has
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`a value of 0.153 [.Lh and capacitor 52 has a value of 100
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`pf.
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`Second stage 46 is also a tank circuit which comprises
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`an inductor 53 and a capacitor 54. In the particular
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`embodiment, second stage 46 is intended to attenuate
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`the 13.56 MHz signal between ports A and B. This
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`provides the required isolation and prevents stages
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`three through six from altering the 13.56 MHz match-
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`ing. Inductor 53 has a value of 1.38 ph and capacitor 54
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`has a value of 100 pf.
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`Third stage 47, which is connected in series with first
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`stage 45 and second stage 46, comprises a cored induc-
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`tor 55 and its parallel parasitic capacitance 56. In the
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`particular embodiment, third stage 47 serves to attenu-
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`ate the 27.12 MHz mixing product between ports X and
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`B. Inductor 55 has a value of 10 ph and parasitic capaci-
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`tance 56 has a value of 3.4 pf.
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`Fourth stage 48 is coupled between the line between
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`ports X and B and ground. In addition, electro-mag—
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`netic coupling between third stage 47 and fourth stage
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`48 is prevented by grounded shield 57. Fourth stage 48
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`combines with first stage 45 and firth stage 49 to attenu-
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`ate the 40.68 MHz mixing product between ports X and
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`B. Fourth stage 48 comprises an inductor 58 and a ser-
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`ies-connected capacitor 59. Inductor 58 has a value of
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`0.2 uh and capacitor 59 has a value of 75 pf.
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`Fifth stage 49, another parallel tank circuit series-con-
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`nected between ports X and B, comprises a cored induc-
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`tor 60 and its parallel parasitic capacitance 61. Like
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`fourth stage 48, it is resonant at 40.68 MHz in the partic-
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`ular embodiment. Inductor 60 has a value of 5 uh and
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`parasitic capacitance 61 has a value of 3 pf.
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`A second grounded shield 62 separates fifth stage 49
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`from sixth stage 50. Sixth stage 50, which serves to
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`attenuate the 67.8 MHz mixing product between ports
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`X and B, comprises an inductor 63 and a series-con-
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`nected, grounded capacitor 64. Inductor 63 has a value
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`of 0.07 ph and capacitor 64 has a value of 75 pf.
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`Filter/combiner 40 is typically augmented by ensur-
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`ing good RF contact between the various panels which
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`make up the cabinet of the plasma reactor apparatus to
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`contain any radiation which might exist. Filter/com-
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`biner 40 represents a delicate compromise between
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`being able to provide good impedance matching and
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`providing the necessary attenuation of harmonics.
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`As is disclosed in US. Pat. No. 4,464,223, the combi—
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`nation of high and low frequencies in plasma processes
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`has been found to offer increased flexibility and control.
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`Generally,
`this is due to the fact that the degree of
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`dissociation and the ion energy cross-section in the
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`plasma are strong functions of frequency, as is the ion
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`Page 5 of 6
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`Page 5 of 6
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`

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`6
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`While the present invention has been disclosed with
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`reference to a particular embodiment thereof, various
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`modifications and changes will be apparent to those
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`skilled in the art and may be made without departing
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`from the spirit and scope of the invention.
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`We claim:
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`1. In a plasma reactor apparatus having a reaction
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`volume for containing a reactive gas and electrode
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`means for producing as electric field within said vol-
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`ume, the improvement comprising:
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`means for supplying electrical power to said elec-
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`trode means at a low frequency;
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`means for supplying electrical power to said elec-
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`trode means at a high frequency; and
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`a filter/combiner interconnecting said low frequency
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`power supply, said high frequency power supply,
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`and said electrode means; said filter/combiner
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`being adapted to couple said low and high fre—
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`quency power supplies to said electrode means,
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`isolate said low frequency power supply from said
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`high frequency power supply and attenuate unde-
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`sired mixing products of said high and low frequen-
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`cres.
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`2. The apparatus as set forth in claim 1 wherein an
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`enclosure means partially defines said reaction volume
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`and wherein said enclosure means is grounded.
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`3. The apparatus as set forth in claim 1 wherein said
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`filter/combiner comprises a multi-stage passive filter
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`network having at least one stage for attenuating high
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`frequency electrical power between said high fre-
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`quency power supply and said low frequency power
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`supply and at least one stage for attenuating undesired
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`mixing products.
`Ik
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`4,579,618
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`5
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`energy. In other words, different percent dissociations
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`and ion energy cross-sections are produced at the high
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`and low frequencies with higher ion energies being
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`present in the low frequency discharge. Therefore, by
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`controlling the relative power levels of the two power
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`supplies in the disclosed apparatus a process which
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`combines a high etch rate with excellent residue re-
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`moval is achievable.
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`In particular,
`the dual frequency, single electrode
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`reactor apparatus disclosed herein is well—suited to
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`metal etching processes. By way of example, a process
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`for etching aluminum/silicon with an admixture of 1%
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`copper is described. In this process,
`the 13.56 MHz
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`power supply is operated at 250 watts and the 100 KHz
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`power supply is operated at 20 watts. The reactive gas
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`comprises 50 standard cubic centimeters per minute
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`(sccm) of carbon tetrachloride, l5 sccm of chlorine and
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`40 sccm of argon. The system operating pressure is
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`maintained at 270 mtogr. The etch rate of this process is
`roughly 7000 to 8000 A/min. It has been found that the
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`described process provides excellent etching character-
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`istics and further provides a surface which is substan-
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`tially clear of organic and inorganic contaminants. Prior
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`art metal etching processes generally leave substantial
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`residues which may affect subsequent processing steps
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`and the long term reliability of the finished device.
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`The plasma reactor apparatus and method described
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`above provide an improvement in plasma processes.
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`The present invention combines the advantages of a
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`dual frequency plasma process with the simplicity and
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`commercial advantage of a single electrode reactor. In
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`addition, the disclosed method for etching metals pro-
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`vides a substantially cleaner surface than did prior art
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`methods.
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`Page 6 of 6
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`Page 6 of 6
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