`
`[19]
`
`[11] Patent Number:
`
`5,429,070
`
`Jul. 4, 1995
`[45] Date of Patent:
`Campbell et al.
`
`US005429070A
`
`5,l22,251
`
`6/1992 Campbell et a].
`
`.............. 118/723 X
`
`FOREIGN PATENT DOCUMENTS
`
`63-77120 4/1988 Japan ................................... 156/345
`63-274148 11/1988 Japan .
`
`Primary Examiner—R. Bruce Breneman
`Assistant Examiner—Jonathan D. Baskin
`Attorney, Agent, or Firm—Skjerven, Morrill,
`MacPherson, Franklin & Friel; Alan H. MacPherson;
`David T. Millers
`
`[57]
`
`ABSTRACT
`
`Plasma deposition or etching apparatus is provided
`which comprises a plasma source located above and in
`axial relationship to a substrate process chamber. The
`plasma source may include a sapphire or alumina source
`tube for use with plasmas containing fluorine. Sur-
`rounding the plasma source are an inner magnetic coil
`and an outer magnetic coil arranged in the same plane
`perpendicular to the axis of the plasma source and the
`substrate process chamber. Preferably a first current is
`provided through the inner coil and a second current in
`a direction opposite to the direction of the first current
`is provided through the outer coil. The inner and outer
`coils are wrapped with a thin sheet of conducting mate-
`rial to shield the coils from RF signal generated by the
`plasma source. The result is to advantageously shape
`the magnetic field in the process chamber to achieve
`extremely uniform processing, particularly when a
`unique diamond shaped pattern of gas feed lines is used
`wherein the diamond is arranged to be approximately
`tangent at four places to the outer circumference of the
`workpiece being processed in the apparatus.
`
`13 Claims, 21 Drawing Sheets
`
`[54] HIGH DENSITY PLASMA DEPOSITION
`AND ETCHING APPARATUS
`
`[75]
`
`Inventors: Gregor A. Campbell, Glendale;
`Robert W. Conn, Los Angeles; Dan
`Katz, Beverly Hills; N. William
`Parker, Fairfield; Alexis de
`Chambrier, Glendale, all of Calif.
`
`[73] Assignee:
`
`Plasma & Materials Technologies,
`Inc., Chatsworth, Calif.
`
`[21] App1.No.: 979,574
`
`[22] Filed:
`
`Nov.20, 1992
`
`Related US. Application Data
`
`[63]
`
`Continuation-impart of Ser. No. 964,149, Oct. 19, 1992,
`which is a continuation-in-part of Ser. No. 887,278,
`May 21, 1992, abandoned, which is a continuation of
`Ser. No. 650,788, Feb. 4, 1991, Pat. No. 5,122,251,
`which is a continuation-in-part of Ser. No. 365,533,
`Jun. 13, 1989, Pat. No. 4,990,229.
`
`Int. 0.6 ....................... C23C 16/50; H01L 21/00
`[51]
`[52] US. Cl. ................................ 118/723 R; 118/719;
`118/723 MP; 118/723 AN; 156/345;
`204/298.37; 204/298.38
`[58] Field of Search ............... 118/723 MP, 723 Mw,
`118/723 ME, 723 MR, 723 MA, 723 AN, 723
`E, 723 BR, 723 IR, 723 R; 156/345;
`204/298.37, 298.38
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,433,228 2/ 1984 Nishimatsu et a1.
`4,963,242 10/ l990 Sato et al.
`.................. 204/298.37 X
`4,990,229 2/ 1991 Campbell et a].
`.
`..... 118/723 X
`5,089,441 2/ 1892 Moslehi ............................... 437/225
`
`.
`
`
`
`GILLETTE 1114
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`GILLETTE 1114
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`U.S. Patent
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`July 4, 1995
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`Sheet 1 of 21
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`5,429,070
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`US. Patent
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`July 4, 1995
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`Sheet 2 of 21
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`5,429,070
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`US. Patent
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`July 4, 1995
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`Sheet 3 of 21
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`July 4, 1995
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`July 4, 1995
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`US. Patent
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`July 4, 1995
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`July 4, 1995
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`Sheet 10 of 21
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`5,429,070
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`
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`
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`US. Patent
`
`July 4, 1995
`
`Sheet 11 of 21
`
`5,429,070
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`US. Patent
`
`July 4, 1995
`
`Sheet 12 of 21
`
`5,429,070
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`
`FIG. 13
`
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`US. Patent
`
`July 4, 1995
`
`Sheet 13 of 21
`
`5,429,070
`
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`US. Patent
`
`July 4, 1995
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`5,429,070
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`July 4, 1995
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`July 4, 1995
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`Sheet 21 of 21
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`5,429,070
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`3mTorr, MORI power 1000W
`85%Cl2-15%BCI3
`
`Selectivity (AVSiOg)
`Saleétivitv (AVPR)
`AI-SI-Cu Etch Rate
`Si-Og Etch Rate
`Resist Etch Rate
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`coatings and the coating of glass. In general, a plasma is
`produced at the sputter target material and the sputter
`target is biased to a negative voltage of around 700 V.
`Plasma ions (generally argon) impact the surface and
`sputter the material which then transports as neutral
`atoms to a substrate. Reactive gases can be introduced
`to chemically react with the sputtered atoms at the host
`substrate in a process called reactive sputter deposition.
`Rate is often important and it is therefore important to
`make the plasma as dense as possible. Ionization of
`reactive gases is also important and is helped by having
`plasma in the vicinity of the substrate material. Sputter-
`ing is also done by ions accelerated in an ion or plasma
`gun and then made to bombard the sputter target. In
`this case, a bias voltage on the target is not necessary.
`For sputtering insulating materials, RF voltage bias can
`be applied to the sputter target.
`
`Existing Methods
`
`There are presently two widely used methods for
`plasma deposition and etching, the parallel plate reactor
`and the ECR plasma deposition system. There are also
`methods based on the use of RF to produce plasma
`including ordinary induction techniques and techniques
`based on whistler waves.
`
`Parallel Plate Reactor (Diode)
`
`The RF diode has been widely used for both deposi~
`tion and etching. It is described in detail in the book by
`Chapman (“Glow Discharge Processes" John Wiley &
`Sons 1980). It uses RF at 13.56 MHz capacitively cou-
`pled to one electrode while the other electrode is
`grounded. The pressure in the system is typically 1
`mtorr to l torr and the plasma density is typically 1010
`electrons per cm3. The rate at which both deposition or
`etching occurs is dependent on the density of the plasma
`and the density (pressure) of the reactive gas used to
`etch, or, in CVD processes, to deposit.
`In etching, the high pressure needed to sustain the
`discharge causes collisions between the ions and the
`background gas. This causes the paths of the etching
`ions or atoms to be randomized or non-directional,
`leading to undercutting of the mask. This is referred to
`as an isotropic etch. It is desirable to have the etch
`atoms or ions be directional so that straight anisotropic
`etches can be achieved. At the high pressure used in RF
`diode discharges, it is necessary for the ions to have
`high energy (up to 1 KeV) to achieve an anisotropic
`etch. However, the high energy of the ions can cause
`damage to the substrate, film materials or photoresist.
`The plasma is sustained by secondary electrons that
`are emitted by ions impacting the cathode. These elec-
`trons are accelerated by the voltage drop across the
`sheath which is typically 400—1000 V. These fast elec-
`trons can bombard the substrate causing it to have a
`high voltage sheath drop. This high voltage can accel-
`erate the ions leading to damage of the substrate or film
`material. The presence of high energy electrons leading
`to high voltage sheath drops is undesirable.
`
`Electron Cyclotron Resonance Plasmas
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`HIGH DENSITY PLASMA DEPOSITION AND
`ETCHING APPARATUS
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is a continuation-in—part of US pa-
`tent application Ser. No. 07/964,149 filed Oct. 19, 1992
`which is a continuation-in-part of US. patent applica-
`tion Ser. No. 07/887,278 filed May 21, 1992, now aban-
`doned, which is a continuation of US patent applica-
`tion No. 07/650,788 filed Feb. 4, 1991 and issued Jun.
`16, 1992 as US. Pat. No. 5,122,251, which is a continua-
`tion-in-part of US. patent application Ser. No.
`07/365,533, filed Jun. 13, 1989 and issued Feb. 5, 1991 as
`us. Pat. No. 4,990,229, all of which are hereby incor-
`porated by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to a plasma deposition
`or etching method and various apparatus for depositing
`a thin film onto a substrate or for removal (etching) of
`a film from a substrate. The present invention includes
`the use of a new and significantly better high density
`plasma deposition and etching apparatus, a significantly
`improved magnetic means for the plasma source region
`and operation with a specified range of processes and
`gases. Applications of the present invention include the
`removal by etching of a layer from a surface, the re-
`moval by sputtering of a layer from a surface, or the
`deposition of a layer onto a surface.
`2. Related Art
`
`Etching
`
`Plasma etching involves using chemically active
`atoms or energetic ions to remove material from a sub-
`strate. It is a key technology in the fabrication of semi-
`conductor integrated circuits. However, before the
`advent of microwave plasmas utilizing electron cyclo-
`tron resonance (ECR), it was becoming difficult for
`conventional plasma etching techniques to satisfy the
`requirements dictated by the increase in device packing
`density. Specifically, the requirement for fine pattern
`etching without undercutting (anisotropic etching) and
`the requirements for low damage and high selectivity
`could hardly be satisfied at the same time.
`
`Deposition
`
`Plasma Enhanced Chemical Vapor Deposition
`(PECVD) is a widely used technique to deposit materi-
`als on substrates in a host of applications. In normal
`Chemical Vapor Deposition (CVD) the chemical reac-
`tion is driven by the temperature of the substrate and for
`most reactions this temperature is high (>800° C.). The
`high substrate temperature needed precludes use of this
`method in a number of applications particularly in mi-
`croelectronics, displays and optical coatings. The role
`of the plasma is to dissociate and activate the chemical
`gas so that the substrate temperature can be reduced.
`The rate of dissociation, activation and ionization is
`proportional to the density of the plasma. It is therefore
`of importance to make the plasma as dense as possible.
`
`Sputtering
`
`Sputtering is also a widely used method for deposit-
`ing materials onto substrates for a wide variety of appli-
`cations such as the production of hard or decorative
`
`65
`
`The advent of using microwaves at 2.45 GHz and a
`magnetic field of 875 Gauss to utilize electron cyclotron
`resonance allowed the generation of high density plas-
`mas at low pressure. The advantages of this technique
`for plasma etching are described by Suzuki in US. Pat.
`No. 4,101,411 and in an article entitled “Microwave
`
`
`
`3
`Plasma Etching” published in Vacuum, Vol. 34, No.
`10/ l l, 1984. Due to a low gas pressure (0.04-0.4 Pa) and
`high plasma density (l.7-7><10ll electrons/cm3) aniso-
`tropic etch with high etch rates is achievable.
`Suzuki, in U.S. Pat. No. 4,101,411, describes a plasma
`etching apparatus using ECR. Matsuo, in U.S. Pat. No.
`4,401,054 describes a plasma deposition apparatus utiliz-
`ing ECR. In U.S. Pat. No. 4,876,983 there is described
`a plasma etching apparatus to improve uniformity and
`have the specimen close to the source chamber.
`While this technique is desirable over the parallel
`plate reactor in many respects, it has several limitations.
`The magnetic field needed is very high (1—2 kGauss)
`which means that heavy, power consuming electromag-
`nets must be used. The maximum density is limited by
`either cut-off in certain configurations or by refraction
`in other configurations to the value of 1X1012 elec-
`trons/cm3 in the source. The expense of the power
`supply and necessary hardware to generate and transmit
`the microwaves is high. The uniformity (or width of the
`plasma profile) is not very good.
`RF Helicon Whistler Wave Plasmas
`The first use of helicon type whistler waves to gener-
`ate dense plasmas was described in 1970 by Boswell in
`the journal, Physics Letters, Vol. 33A, pp 457-458
`(1970) which showed an antenna configuration used by
`Ovchinnikov. This type of antenna excites an m=1
`mode. The frequency of excitation was 8 MHz. The
`density profile of the 10 cm plasma was found to be
`quite peaked, particularly at the higher magnetic field
`strengths needed for high densities. In Boswell, U.S.
`Pat. No. 4,810,935, two mathematical relationships are
`required to be satisfied. These equations are in fact
`overly restrictive and not applicable to the approach
`outlined by Campbell, Conn and Shoji in U.S. Pat. Nos.
`4,990,229 and 5,122,251.
`In these publications the mechanism for efficient cou-
`pling of the RF energy to the plasma could not be ex-
`plained. Chen,
`in an Australian National University
`report, explained the mechanism as Landau damping.
`Chen, in a paper presented in August 1988 and pub-
`lished in the journal, Plasma Physics and Controlled
`Fusion, Vol. 33, 1991, describes a system using whistler
`waves to generate dense plasmas for use in advanced
`accelerators. The type of antenna used in this arrange-
`ment was similar to that used by Boswell in that it ex—
`cited the m=1 mode and was a type known as the Na—
`goya Type III antenna. This type of antenna is ex-
`plained in a paper by Watari (1978). The frequency of
`excitation was 30 MHz.
`Campbell, Conn and Shoji, in U.S. Pat. No. 4,990,229
`and Pat. No. 5,122,251 describe new and highly efficient
`antenna means designed to excite the m=0 and the
`m=1 modes, and to control the wave number of the
`excited wave. This is important in obtaining the maxi~
`mum plasma density, in generating the broadest spatial
`plasma density profile in the source and process cham-
`ber regions, and in providing control over the electron
`temperature in the plasma.
`Efficiency of plasma production by low frequency
`whistler waves depends on the coupling of RF energy
`into the plasma. As discussed by Campbell et al. in U.S.
`Pat. No. 4,990,229, an important mechanism for damp-
`ing of the RF energy is Landau damping. The phase
`velocity of the whistler wave is given by m/kz, where
`k; is given by the dispersion relation and depends on the
`plasma density and vacuum magnetic field strength.
`Ideally, the phase velocity of the wave should be near
`
`10
`
`15
`
`20
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`25
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`30
`
`35
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`45
`
`50
`
`55
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`5,429,070
`
`4
`the maximum of the ionization potential of the gas we
`wish to ionize. From the dispersion relation for the
`m=0 mode, the higher the value of kz, the higher the
`density. However, the phase velocity of the wave is
`w/kz and so increasing kz decreases the energy of the
`electrons that are accelerated by the wave. If the k2 is
`too high then the energy of the electrons may fall below
`the ionization potential.
`Also, Campbell, Conn and Shoji in the above-men-
`tioned patents use a magnetic bucket means in conjunc-
`tion with the plasma generator to provide a uniform
`plasma density over large circular or rectangular areas.
`They use one or multiple plasma generators in conjunc-
`tion with cylindrical or rectangular magnetic buckets to
`provide a uniform density over a large area for the
`coating or etching of substrates such as are needed for
`1C or flat panel display processing. They use expansion
`of the magnetic field to allow deposition or etching
`over a large area.
`Other RF Induction Sources
`Other existing methods use RF circuit resonances to
`generate plasma. These methods are less efficient than
`those using low frequency whistler waves, and do not
`generate high density plasmas. Ogle, in U.S. Pat. No.
`4,948,458 describes an RF means to produce planar
`plasma in a low pressure process gas using an external
`planar spiral coil (or series of concentric rings) and
`connected to a second loop which is positioned to allow
`for effective coupling of the circuit and for loading of
`the circuit at the frequency of operation. Steinberg et
`al., in U.S. Pat. No. 4,368,092, describes a plasma gener-
`ating system employing a helical inductive resonator for
`producing the plasma external to an etching chamber.
`The plasma is non-uniform and passes through a tube
`before utilization. U.S. Pat. No. 4,421,898, describes
`an inductively-coupled plasma generating apparatus,
`where a transformer having a magnetic core induces
`electron circulation in an insulating tube carrying a
`process gas. Gas ionization is non-uniform, and expo-
`sure to the wafer occurs downstream. U.S. Pat. No.
`4,626,312, describes a conventional parallel plate plasma
`etcher where the wafer is situated on a lower electrode
`and a plasma is generated by applying radiofrequency
`energy across the lower electrode and a parallel upper
`electrode. U.S. Pat. Nos. 4,668,338 and 4,668,365, de—
`scribe magnetically—enhanced plasma processes for re—
`active ion etching and chemical vapor deposition, re-
`spectively. Flamm et al. in U.S. Pat. No. 4,918,031 de-
`scribes an L-C circuit referred to as a helical resonator
`which consists of an inner helically shaped copper coil
`surrounding a quartz tube and attached at one end to a
`cylindrical copper shield. The opposite end of the inner
`coil is unterminated. No external magnetic field is em-
`ployed in these approaches and all generate plasmas at
`low pressure in the 1—10 mtorr range but at moderate
`density in the quartz source tube or just below a planar
`spiral coil and without a high degree of spatial unifor-
`mity. No externally generated magnetic field is em—
`ployed in these RF plasma generators.
`SUMMARY OF THE INVENTION
`
`The present invention utilizes low frequency RF
`whistler waves to generate plasmas of high density for
`use in plasma etching, deposition, and sputtering equip-
`ment. Plasma is generated in a source tube which is
`typically made of quartz or a fluorine-resistant material
`such as alumina or sapphire. In conjunction with the
`source tube into which a gas is injected and along the
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`central axis of which a magnetic field is established, a
`single loop antenna is disposed in a plane transverse to
`the central axis. The angle of the antenna plane is 90“ if
`it is desired to excite only M=0 mode, or at less than
`90° if it is desired to excite components in both M=0
`and M=1 mode. The gas is a noble or reactive gas at a
`pressure of 0.] mtorr to 200 mtorr. The magnetic field
`strength is in the range of 10 to 1000 gauss and the
`antenna is driven with RF energy of 100 W to 5 KW at
`a frequency range of 2 MHz to 50 MHz. With the an-
`tenna placed along the tube source at a sufficient dis-
`tance along the axis from the gas injection end, the
`other end defining an open egress zone leading to a
`process chamber, the single loop antenna surprisingly
`provides highly efficient wave coupling to establish a
`high density and high current plasma.
`In accordance with other features of the invention,
`the plasma generated by this plasma source is supplied
`to a process chamber including a magnetic bucket sys-
`tem for holding the plasma away from the process
`chamber walls. The arrangement provides, in combina-
`tion, a uniform plasma density over a large circular
`area, so that a large substrate may be etched or other-
`wise processed. Another feature is that a magnetic cusp
`zone may be established, at the material surface being
`processed, to homogenize and make more uniform the
`plasma at that location. An aspect of this is that the
`magnetic cusp position relative to the substrate may be
`time modulated to enhance uniformity and reduce sensi-
`tivity to substrate location.
`Further, the magnetic field may be expanded to allow
`deposition or etching over a large area and current
`flows may be equalized by serial driving of antennas in
`systems having more than one antenna. Other features
`reside in configurations which employ one or more
`multiple geometrical areas for coating or etching of
`square or rectangular substrates, or a linear juxtaposi-
`tion for coating or etching large substrates.
`The invention provides a module with a highly effi-
`cient magnetic means of transporting plasma from a
`plasma generator means to a substrate located on a
`cooled substrate holder located in a substrate process
`chamber and in which the processing of the substrate is
`highly uniform and the substrate process module is
`compact. The invention shields the magnet means from
`- RF signals generated by the antenna and thereby pre-
`vents false signals from being received by a control
`system which drives the magnet means. The shielding
`may be a thin sheet of conducting material wrapped
`around the magnet means.
`The invention provides a gas distribution means in
`the top of the process chamber as an integral part of the
`process chamber structure in order to attain highly
`efficient plasma operation and highly uniform process-
`ing of the substrate while permitting the process module
`to be reduced in height.
`The invention attains highly efficient plasma opera-
`tion in a compact substrate process module which can
`attain excellent characteristics for the etching of IC
`wafers as represented by high etch rate, high unifor-
`mity, high selectivity, high anisotropy, and low dam-
`age.
`The invention achieves high density and highly uni-
`form plasma operation at low pressure from 0.3 mtorr to
`5 mtorr for etching an IC substrate and from 1 mtorr to
`30 mtorr for deposition of films on to substrates.
`The invention provides a substrate processing system
`capable of operating with a wide variety of gases and
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`combinations of gases, including highly reactive and
`corrosive gases.
`The invention provides such a substrate processing
`system capable of etching or depositing films listed in
`Table l and Table 2 using gases fed into the plasma
`generator region, into the process chamber region, or
`into both regions.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram depicting the principle
`of operation and RF current flow in an antenna con-
`structed according to the invention as shown in US.
`Pat. No. 4,990,229.
`FIGS. 2A, 2B and 2C are schematic views of anten-
`nas constructed according to the principles of the inven-
`tion.
`
`FIG. 3 is a schematic diagram depicting the principle
`of operation and RF current flow in a plasma source
`constructed according to the invention as shown in US.
`Pat. No. 5,122,251.
`FIGS. 4A and 4B illustrate in schematic form two
`basic configurations of a plasma deposition or etching
`apparatus accordance with this invention.
`FIG. 5A is a schematic diagram of a second example
`of a system in accordance with the present invention in
`which the plasma source region is connected to a mag-
`netic bucket region where uniformity requirements are
`important.
`FIG. SB is a plan view of the arrangement of FIG.
`5A, taken along the line 3A—3A in FIG. 5A.
`FIG. 6A is a perspective view of a third example of a
`system in the present invention for deposition or etch-
`ing over a large rectangular area where uniformity is
`important.
`FIG. 6B is a plan view of the arrangement of FIG.
`6A, taken along the line 4A—4A in FIG. 6A.
`FIG. 7A is a schematic diagram of yet another exam-
`ple of a system in accordance with the present invention
`in which a bottom magnet is added behind the plane of
`the substrate holder to provide a magnetic cusp field,
`the plane of the cusp being approximately the same as
`the plane of the substrate holder.
`FIG. 7B is a plan view of the arrangement of FIG.
`7A, taken along the line SA—SA in FIG. 7A.
`FIG. 8 is a schematic diagram of an example of a
`system in accordance with the invention for sputter
`deposition.
`FIG. 9 is a graph depicting the plasma current density
`at the substrate location according to the example of
`FIG. 5A using the plasma source depicted in FIG. 3 as
`a function of magnetic field in the source region.
`FIG. 10 is a graph of the same data as in FIG. 9 but
`graphed on a linear scale for magnetic field to show the
`plasma current density at the substrate location where
`the magnetic field is low, varying from zero to 160
`gauss.
`FIG. 11 is a graph depicting the total plasma current
`(or total flux) at the substrate location according to the
`invention as depicted in FIG. 5A using the plasma
`source as depicted in FIG. 3 as a function of RF power
`to the source at a gas pressure of 2 mtorr.
`FIG. 12 is a graph depicting the plasma current den-
`sity at the substrate location according to the invention
`as depicted in FIG. 5A using the antenna as depicted in
`FIG. 3 as a function of the gas pressure.
`FIG. 13 is a graph depicting the plasma current den-
`sity at the substrate location according to the invention
`as depicted in FIG. 5A and the plasma source of FIG. 3
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`as a function of position to show the excellent unifor—
`mity over a substantial width.
`FIGS. 14A to 14C are diagrams showing the arrange-
`ment of the electromagnetic system in the plasma gener-
`ator region according to the present invention to make
`efficient the transport of plasma from the plasma gener-
`ator tube to the substrate process chamber which in-
`cludes a magnetic bucket and where uniformity and
`high plasma flux to the substrate are required.
`FIG. 15A is a plot of the magnetic field lines obtained
`using one electromagnet surrounding the plasma source
`tube.
`FIG. 15B is a plot of the magnetic field lines obtained
`using two electromagnets surrounding the source tube
`and where the outer magnet coil carries a current in the
`opposite direction from the inner magnet coil and has a
`coil current that is 40% as large in magnitude as that of
`the inner coil.
`FIG. 16A is a schematic diagram of the configuration
`of a plasma etching or deposition apparatus.
`FIG. 16B is a plan view of the substrate process
`chamber section of the arrangement of FIG. 16A taken
`along the line 7A—7A in FIG. 16A.
`FIG. 17A is a plan view of the substrate process
`chamber showing the gas feed lines, the nozzle holes for
`gas injection into the chamber, the water cooling lines
`and the grooves for the ceramic permanent magnets.
`FIG. 17B is a detail showing the entrance to the gas
`feed line at the top of the substrate process chamber
`shown in FIG. 17A.
`FIG. 17C shows in larger size the gas feed structure
`of FIG. 17A.
`FIG. 18 is a cross sectional SEM image obtained for
`the etching of poly-Si
`in pure C12 using the MORI
`plasma source etching system. In this case, the SEM
`shows structure with 100% overetch. One sees highly
`anisotropic profiles, no notching, and less than 50 A
`oxide loss.
`FIG. 19 shows the aluminum etch rate, the oxide etch
`rate, and the PR etch rate (left ordinate) and selectivity
`to photoresist etching and to oxide etching (right ordi-
`nate) as a function of RF wafer bias power applied at
`13.56 MHz. The gas mixture is 85% C12—15% BC13, the
`MORI source power is 1 KW, and the substrate is lo-
`cated in the process chamber 20 cm below the end of
`the source tube.
`FIG. 20 is a cross sectional SEM image obtained for
`sub micron etching of W on a TiW adhesion layer on
`thermal oxide in pure SF6 using the MORI plasma
`source etching system. The anisotropy is excellent,
`there is no CD loss, and there are no residues.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIGS. 1A, 2B, and 2C illustrate schematically the RF
`current flow in two antennas constructed according to
`the invention disclosed in U.S. Pat. No. 4,990,229 issued
`Feb. 5, 1991. For a more detailed description of the
`operation of these antennas, U.S. Pat. No. 4,990,229 is
`incorporated herein by reference in its entirety.
`A simplified view of principal elements and relation-
`ships in a device in accordance with the invention is
`provided by the representation of FIG. 3, wherein high
`density plasma 9 is to be generated within a source tube
`10 of generally cylindrical form about a central (here
`vertical) axis. At one (here upper) end an injector 11
`feeds gas to be ionized into the interior volume of the
`source tube, where the gas is excited by an external loop
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`antenna 12 that encompasses an intermediate region of
`the source tube 10. The antenna loop 12 comprises in
`this example a not fully circular element lying in a plane
`that is at 90° or less in either sense relative to the central
`axis. The direction of propagation of the plasma is here
`downward toward an exit aperture 13. The antenna
`loop 12 has its opposite ends coupled to the outer con-
`ductor 14 and center conductor 15 of a coaxial driver
`line 16 which is energized through a matching box 18 by
`an RF energy source 19. A pair of variable vacuum
`capacitors 20, 21 in the matching box 18 are adjustable
`to tune the circuit so that the antenna loading plus the
`reactive load of the matching box 18 is approximately
`50 ohms to minimize the reflected power.
`The antenna tuning and wave spectrum are adjusted
`to match the conditions in the plasma field, and also in
`relation to an interior axial magnetic field 8 generated
`by at least one magnetic field coil (not shown) about the
`source tube 10. The matching condition is predicted by
`theory to be dictated by the dispersion relation:
`
`[w/wc— wpz/C2K22]2 = 1 + (3.:33/kza)2
`
`To effect wave coupling and establish a high plasma
`current density, measured in mA/cmz, the antenna loop
`12 is driven at 13.56 MHz and with RF energy of the
`order of 2.0 KW (in the range of 100 W to 5 KW) by the
`RF energy source 19. The magnetic field established by
`the magnetic field coil is in the range of 10 to 1000
`gauss, for different useful applications. The gas is argon
`and maintained at a pressure of about 1 mtorr in this
`example. However, in addition to a noble gas such as
`argon, reactive gases such as SFs, chlorine, oxygen, and
`mixtures with oxygen have been used with comparably
`useful results. A pressure range of 0.1 mtorr to 200
`mtorr can be used if other variables are properly taken
`into account. With a 5 KW power supply less than the
`maximum available power can be used, to a substan-
`tially lower level of several hundred watts, depending
`on the application. Although the 13.56 MHz frequency
`is available from many industrial sources, the range of 2
`MHz to 50 MHz can be usefully employed.
`In FIG. 3, the antenna loop 12 is shown at 90" to the
`longitudinal axis of the source tube 10. This orientation
`generates the M=0 mode, while reducing the angle
`from 90° in either sense introduces components of the
`M=l mode as well as components of the M=0 mode.
`Angles of less than 90‘ to the longitudinal axis require
`correspondingly longer antenna loops 12, so there is a
`practical limit of about 45° to the angle which can be
`used. Most orientations are preferred to be in the range
`of 60° to 90". It should be noted that the loop 12 is
`disposed within a flat plane that is directly perpendicu-
`lar or tilted to the longitudinal axis. In the prior art
`constructions with double loops and other configura-
`tions it has usually been postulated that the looped por-
`tions