(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATlON TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`30 August 2001 (30.08.2001)
`
`• I IIIII IIIIIII II IIIIII IIIII IIII I II Ill lllll lllll lllll lllll llll 111111111111111111
`
`(10) Iuternational Publication Number
`WO 01/63000 A2
`
`PCT
`
`(51) International Patent Classification 7:
`
`C23C 14/00
`
`(2.1) International A1>plication Number: PCf/USOl/04563
`
`(22) International Filing Date: 14 Febrnary 2001 (14.02.2001)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`60/185,068
`
`25 February 2000 (25.02.2000) US
`
`{71) Applicant (for all designated States except US): TOKYO
`ELECTRON LIMlTED [JP/JP]; TBS Broadcast Center,
`3-6 Akasaka 5-chorne, Minato-kn, Tokyo J07 (JP).
`
`{72) Inventor; and
`{75) Inventor/Applicant (for US only): JOHNSON, Wayne
`
`[US/US]; 14435 South 48th Street, Phoenix, AZ 85044
`(US).
`
`(74) Agents: LAZAR, Dale, S. et al.; Pillsbury Winthrop LLP,
`I 100 New York Avenue, N.W. Washi ngton, OC 20005
`(US).
`
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`l<Z, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, CZ,
`DE, DK, DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR,
`HU, ID, IL, IN, 1S, JP, KE, KG, KP, KR, KZ, LC, LK, LR,
`LS, J;r, LU, LV, MA, MD, MG, MK, .MN, MW, MX, MZ,
`NO, NZ, PT,, PT, RO, RU, SD, SE, SG, ST, SK, ST,, TJ, TM,
`TR, TI, 1Z, UA, UG, US, UZ, VN, YU, ZA, ZW.
`
`(84) Designated States (regional): ARIP() patent (GH, GM.
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent {AT, BE, CH, CY, DE, DK, BS, FI, FR, GB, GR, IE,
`
`[Continued on ne:xtpage]
`
`(54) Title: METHOD AND APPARATUS FOR DEPOSITING flLMS
`
`--i
`
`iiii
`
`------------------------------------------
`iiiii -
`iiiii --!!!!!!!!
`iiiii -
`
`(57) Abstract: A method and apparatus
`for performing physical vapor deposition
`of a layer or a sabstrate, composed of a
`deposition chamber enclosing a plasma
`region for containing an ionizable gas; an
`electmmagnetic
`field generating
`system
`surrounding the plasma region for inductively
`coupling an electromagnetic
`field
`into
`the p.lasma region to ionize the gas and
`generate and maintain a high density, low
`potential plasma; a source of deposition
`material including a solid target constituting
`a source of material to be deposited onto the
`substrate; a unit associated with the target
`for electrically biasing the target in order to
`cause ions in the plasma to strike the target
`and sputter material from the target; and a
`substrate holder for holding the substrate at
`a location to pem1it material sputte:red from
`the target to be deposited on the substrate.
`
`34
`
`32
`
`36
`
`iiiii ----iiiii
`N < = = = t"'l
`,..... = 0
`
`iiiii
`
`!!!!!!!!
`
`....._
`\C
`
`~
`
`20
`
`2
`
`18
`
`-=
`
`4
`
`40
`
`"'-10
`
`48
`
`-=
`
`Page 1 of 42
`
`APPLIED MATERIALS EXHIBIT 1018
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`

`

`WO O 1/63000 A2
`
`I IIIII IIIIIIII II IIIIII IIIII IIII I II Ill lllll lllll lllll lllll llll 1111111111111111111
`
`TT LU, MC NL, PT, SE, TR), OAPI patent (BF BJ, CF
`CO, Cl, CM. GA, GN, GW, ML, MR. NE, SN, TD, TGJ.
`
`Published:
`without international search report and to he repuhlished
`upon receipt of that report
`
`For two-lei/er codes and other abbreviations. re)cr to tlte "Guid(cid:173)
`ance /Votes on Codes and Abbreviations" appearing at the beiin(cid:173)
`ning of each regular issue of the PCT Gazelle.
`
`Page 2 of 42
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`

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`WO 01/63000
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`PCT/USOl/04563
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`1
`
`TITLE OF THE INVENTION
`
`METHOD AND APPARATUS FOR DEPOSITING FILMS
`
`This International Application claims benefit of U.S. Application No. 60/185,068
`
`5
`
`filed February 25, 2000.
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to the deposition of films, or layers, primarily in the
`
`fabrication of integrated circuits, but also in the manufacture of other products.
`
`Integrated circuit fabrication procedures are composed of a variety of operations,
`
`10
`
`including operations for depositing thin films on a semiconductor substrate, or wafer.
`
`Typically, a large number of identical integrated circuits are formed on such a wafer, which is
`
`then cut, or diced, into individual circuit chips.
`
`Given the small dimensions of these integrated circuits, the quality of each deposited
`
`layer or film has a decisive influence on the quality of the resulting integrated circuit.
`
`15
`
`Basically, the quality of a film is determined by its physical uniformity, including the
`
`uniformity of its thickness and its homogeneity.
`
`In particular, several process steps require the ability to deposit high quality thin
`
`conductive films and to deposit conducting material in both high aspect ratio trenches and
`
`vias (and/or contacts).
`
`20
`
`According to the current state of the art, films, or layers, are deposited on a substrate
`
`according to two types of techniques: physical vapor deposition (PVD), which encompasses
`
`various forms of sputtering; and chemical vapor deposition (CVD). According to each type
`
`of procedure, a layer of material composed of a plurality of atoms or molecules of elements
`
`or compounds, commonly referred to collectively as "adatoms", is deposited upon a substrate
`
`25
`
`in a low pressure region.
`
`In typical PVD procedures, a target material is sputtered to eject adatoms that then
`
`diffuse through the low pressure region and condense on the surface of the substrate on which
`
`the layer is to be deposited. This material forms a layer on the substrate surface.
`
`Continuation of this process leads to the growth of a thin film. The sputtering itself is a
`
`Page 3 of 42
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`

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`PCT/USOl/04563
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`2
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`physical process which involves accelerating heavy ions from an ionized gas, such as argon,
`
`toward the target surface, where the ions act to dislodge and eject adatoms of the target
`
`material as a result of momentum exchange which occurs upon collision of the ions with the
`
`target surface.
`
`5
`
`On the other hand, in CVD procedures, two or more gases are introduced into a
`
`vacuum chamber where they react to form products. One of these products will be deposited
`
`as a layer on the substrate surface, while the other product or products are pumped out of the
`
`low pressure region.
`
`Both types of deposition processes are advantageously performed with the assistance
`
`10
`
`of a plasma created in the low pressure region. In the case of PVD processes, it is essential to
`
`provide a primary plasma to generate the ions that will be used to bombard the target.
`
`However, in these processes, a secondary plasma may be formed to assist the deposition
`
`process itself. In particular, a secondary plasma can serve to enhance the mobility of adatoms
`
`in proximity to the substrate surface.
`
`15
`
`Although CVD processes are widely used in the semiconductor fabrication industry,
`
`processes of this type have been found to possess certain disadvantages. For example, in
`
`order to employ CVD for a particular deposition operation, it is necessary to be able to create
`
`a chemical reaction that will produce, as one reaction product, the material to be deposited. In
`
`contrast, in theory, any material, including dielectric and conductive materials, can be
`
`20
`
`deposited by PVD and this is the process of choice when deposition must be performed while
`
`maintaining the substrate temperature within predetermined limits, and particularly when
`
`deposition is to be performed while the substrate is at a relatively low temperature.
`
`A film composed of a dielectric material can be formed by PVD either by directly
`
`sputtering a target made of the dielectric material, or by performing a reactive sputtering
`
`25
`
`operation in which a conductive material is sputtered from a target and the sputtered
`
`conductive material then reacts with a selected gas to produce the dielectric material that is to
`
`be deposited. One exemplary target material utilized for direct sputtering is silicon dioxide.
`
`PVD can also be used for conductive layers.
`
`The simplest known PVD structure has the form of a planar diode which consists of
`
`30
`
`two parallel plate electrodes that define cathode constructed to serve as the target and an
`
`anode which supports the substrate. A plasma is maintained between the cathode and anode
`
`Page 4 of 42
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`

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`WO 01/63000
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`PCT/USOl/04563
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`3
`
`and electrons emitted from the cathode by ion bombardment enter the plasma as primary
`
`electroris and serve to maintain the plasma.
`
`While a target made of a conductive material can be biased with a DC power supply,
`
`a target made of a dielectric material must be biased with high frequency, and particularly RF
`
`5
`
`power, which can also assist the generation of ions in the plasma. The RF power is supplied
`
`to the target by a circuit arrangement including, for example, a blocking capacitor, in order to
`
`cause the applied RF power to result in the development of a DC self-bias on the target.
`
`Since the planar diode configuration is not suitable for efficient generation of ions,
`
`DC and RF magnetron configurations have been developed for producing a magnetic field
`
`10
`
`having field lines that extend approximately parallel to the target surface. This magnetic field
`
`confines electrons emitted from the target within a region neighboring the target surface,
`
`thereby improving ionization efficiency and the creation of higher plasma densities for a
`
`given plasma region pressure.
`
`Additional configurations followed including the variety of cylindrical magnetrons.
`
`15
`
`Several versions of the cylindrical magnetron variation have appeared in the patent prior art,
`
`in particular, the family of U.S. Patents Nos. 4,132,613, 4,132,613, 4,132,612, 4,116,794,
`
`4,116,793, 4,111,782, 4,041,353, 3,995,187, 3,884,793 and 3,878,085.
`
`As described in Thornton in "Influence of Apparatus Geometry and Deposition
`
`Conditions on the Structure and Topography of Thick Sputtered Coatings", J. Vac. Sci.
`
`20
`
`Technol., Vol 11, No 4, 666-670 (1974), the structure of a deposited metal film is dependent
`
`on both the temperature of the substrate and the gas pressure within the plasma region. The
`
`highest film quality can be achieved when the substrate is at a relatively low temperature and
`
`conditions are created to effect a certain level of bombardment of the substrate with ions
`
`from the plasma while the film is being formed. When optimum conditions are established, a
`
`25
`
`dense, high quality thin film which is substantially free of voids and anomalies can be
`
`achieved.
`
`It is known.in the art that bombardment of the substrate with ions having energies
`
`under 200 eV, and preferably not greater than 30 eV, and more preferably between 10 and 30
`
`e V, can result in the formation of dielectric films having optimum characteristics. This has
`
`30
`
`been found to be true in the case of, for example, thin films of Si02 and Ti Oz.
`
`Page 5 of 42
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`WO 01/63000
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`4
`
`Achievement of high deposition rates and optimum quality of the deposited layer
`
`requires a high energy density in the plasma adjacent both the target and the substrate. Plasma
`energy flux (with units of J/m2 -sec) is the product of the ion flux (with units of number of
`ions/m2-sec) and ion energy (with units of J/ion).
`
`5
`
`However, whereas the highest possible ion energy is desired adjacent the target to
`
`maximize the target sputtering rate, it has been found that the ion energy adjacent the
`
`substrate, i.e., the energy of ions that bombard the substrate, should be less than the
`
`maximum achievable for reasons relating primarily to layer quality.
`
`For example, a reduced ion energy in the plasma adjacent the substrate reduces the
`
`10
`
`rate of implantation of plasma gas ions into the substrate, as well damage to the substrate
`
`subsurface, and the creation of voids and mechanical stresses in the layer being formed.
`
`Therefore, while it is desirable to have a high ion density in the plasma adjacent both
`
`the target and the substrate, different desiderata exist with respect to plasma ion energy. The
`
`plasma density in these systems are quite uniform, ie within +/-20% due _to diffusion.
`
`15
`
`The plasma energy flux to the target and to the substrate are each limited by the
`
`ability to remove heat from the target or substrate/chuck, respectively. Moreover, the ion
`
`energy associated with ions striking the substrate surface is desired to be limited to a
`
`maximum value to assure layer deposition quality. Therefore, it is imperative to use a plasma
`source capable of generating a dense plasma(> 1012 cm "3
`) or, equivalently, a high ion current
`
`20
`
`density at the target and substrate surfaces while enabling direct control of the ion energy via
`
`other means.
`
`For PVD of conductive material, an electron cyclotron resonance (ECR) plasma
`source is known, capable of generating plasmas with a density in the range of 1012 cm·3 and
`
`higher. However, the plasma density proximate the substrate is often significantly reduced
`
`25
`
`since the substrate is generally downstream from the plasma source.
`
`In general, known systems are not suitable for both generating a high density plasma
`
`and allowing appropriate control of the ion energy delivered to the substrate. Specifically,
`
`when, in the known systems, the plasma density is increased, the plasma potential is
`
`correspondingly raised and this leads to high sheath voltages and high ion energies in the
`
`30
`
`vicinity of the substrate.
`
`Page 6 of 42
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`5
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`Furthermore, a growing problem associated with many PVD chambers is a lack of
`
`directivity for the adatom specie. Subsequently, when filling high aspect vias and trenches,
`
`the feature may be "pinched off' prematurely due to deposition coating growth on the feature
`
`side-walls. Therefore, the concept of "ion plating" was introduced wherein a fraction of the
`
`5
`
`adatom specie is ionized and attracted to the substrate surface by means of a substrate bias.
`
`Consequently, the directed (normal) flow of ionized adatom specie enabled a uniform coating
`
`growth without pinch-off; see U.S. Patent No. 5,792,522.
`
`In addition, an inherent problem associated with the use ofinductively coupled
`
`plasma sources for conductive material PVD applications is the development of conductive
`
`10
`
`coatings on the chamber walls. Once this thin coating exceeds some thickness (-400 A), the
`
`wall coating becomes sufficiently conductive that the plasma source ceases to sustain a
`
`plasma. In both U.S. Patent No. 5,800,688 and 5,763,851, a circumferential shield
`
`comprising longitudinal and transverse structures is employed to limit the field of view of
`
`sputtered material migrating towards the chamber walls, hence, interrupting the generation of
`
`15
`
`a continuous wall coating of conducting material. Figure 1 of U.S. Patent No. 5,800,688
`
`shows a series of angular blade sections displaced circumferentially, whereas Figure 2 U.S.
`
`Patent No.5, 763,851 shows a series of concentric shields comprising longitudinal slots, with
`
`slots alternately placed between adjacent layers.
`
`BRIEF SUMMARY OF THE INVENTION
`
`20
`
`A primary object of the present invention is to form high quality films on a substrate.
`
`Another object of the present invention to provide a method and apparatus for
`
`performing PVD in a plasma region which contains a high density plasma and in which the
`
`target is bombarded with high energy ions and the substrate is bombarded with comparatively
`
`low energy ions.
`
`25
`
`A further object of the invention is to allow independent control of the target and
`
`substrate bombardment ion energies.
`
`A further object of the invention is to achieve high target material sputter rates in
`
`order to produce corresponding high film deposition rates.
`
`Yet another object of the invention is to provide a novel target electrode structure
`
`30 which allows the desired high sputtering rate to be achieved.
`
`Page 7 of 42
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`6
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`Further objects of the invention are to reduce particle contamination due to complex
`
`geometric features in the process chamber, and to improve the efficiency of coupling RF
`
`power to the plasma.
`
`Another object of the invention is to eliminate certain obstacles to the plasma-assisted
`
`5
`
`deposition of conductive layers on substrates.
`
`A still further object of the invention is to control the buildup of sputtered material on
`
`the chamber walls.
`
`The above and other objects are achieved, according to the present invention, by
`
`apparatus for performing physical vapor deposition of a layer on a substrate, which apparatus
`
`10
`
`includes a deposition chamber enclosing a plasma region for containing an ionizable gas, and
`
`electromagnetic field generating means surrounding the plasma region for inductively
`
`coupling an electromagnetic field into the plasma region to ionize the gas and generate and
`
`maintain a high density, low potential plasma. A source of deposition material including a
`
`solid target is installed in the chamber. The solid target contains a material which is to be
`
`15
`
`deposited onto the substrate. The target is electrically biased in order to cause ions in the
`
`plasma to strike the target and sputter material from the target.' The apparatus further includes
`
`a substrate holder for holding the substrate at a location to permit material sputtered from the
`
`target to be deposited on the substrate.
`
`In preferred embodiments of the apparatus according to the invention, the
`
`20
`
`electromagnetic field generating means comprise an electrostatically shielded radio frequency
`
`electromagnetic field source that includes an electrostatic shield surrounding the plasma
`
`region and a coil surrounding the shield for converting RF power into an electromagnetic
`
`field that is coupled into the plasma through the electrostatic shield.
`
`It has been found that a source of this type is capable of generating a high density
`
`25
`
`plasma, which makes possible the achievement of high target sputter rates and high substrate
`
`deposition rates while maintaining a low plasma potential and, hence, enabling independent
`
`control of the DC self-bias induced in each of the target and substrate.
`
`Objects according to the invention are further achieved by the provision, in such
`
`apparatus, of a target assembly constructed to have the following features: the area of the
`
`30
`
`target is small relative to the unbiased area of the chamber, thereby maximizing DC self-bias
`
`of the target; a match network is provided for permitting application of a high frequency RF
`
`Page 8 of 42
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`7
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`voltage to create the self-bias, the target presenting a low impedance to high frequencies; the
`
`match network is constructed to minimize harmonics of the high frequency on the target;
`
`some RF power is capacitively coupled to the target; the target is brazed to a stainless steel
`
`plate which maximizes heat transfer from the target to a heat removal system; the heat
`
`5
`
`removal system is constructed to be capable of high heat removal rates, typically in excess of
`10 W/cm2
`
`; and a network for monitoring electrode arcing is provided.
`
`Objects according to the invention are further achieved by the provision of a substrate
`
`holder in the form of a chuck having the following features: the chuck is constructed to
`
`electrostatically clamp the substrate to the chuck; a system for delivering gas to the lower
`
`10
`
`surface of the substrate is provided; the chuck is constructed to remove heat at a high rate
`
`from the substrate; and a RF bias is applied to the chuck in order to induce a DC self-bias in
`
`the substrate. The combination. of all four of these features will facilitate the delivery of a
`
`high ion flux to the substrate and, consequently, high deposition rates, while ions having a
`
`relatively low energy also impact on the substrate. As noted earlier herein, a certain amount
`
`15
`
`oflow energy in bombardment is needed to produce the highest quality depositing films.
`
`fu further accordance with the invention, the electrostatic shield of the
`
`electromagnetic field generating means is arranged to be electrically and/or thermally biased.
`
`The application of such bias during a sputtering process or between sputtering operations can
`
`serve to remove material that has been deposited on the inner surface of the shield, which
`
`20. constitutes a lateral wall of the deposition chamber. This at least reduces, if not completely
`
`eliminating, wall contamination and, thus, subsequent substrate contamination. The thickness
`
`of material deposited on the wall can be monitored, and this will provide an indication of
`
`when a wall cleaning is required.
`
`Also in accordance with the invention, the apparatus may be configured to permit
`
`25
`
`deposition of conductiye material by providing a dielectric process tube that surrounds and
`
`delimits the plasma region and a bias shield that surrounds the process tube and is used for
`
`monitoring the thickness of a conductive material layer deposited on the process tube and to
`
`provide a bias voltage that acts to sputter the conductive material off of the process tube.
`
`Page 9 of 42
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`8
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`BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
`
`FIG. 1 is an elevational view, partly in cross-section and partly pictorial, of a first
`
`embodiment of a PVD apparatus according to the invention.
`
`FIG. 2 is a cross-sectional, detail view of one structural feature of the apparatus of
`
`5
`
`FIG. 1.
`
`FIG. 3 is a view similar to that of FIG 1 of a second embodiment of PVD apparatus
`
`according to the invention.
`
`FIG. 4 is a cross-sectional, detail view of a portion of a modified version of the
`
`apparatus of FIG. 1 or FIG. 3 for PVD of conductive materials.
`
`10
`
`FI Gs. 5A and 5b are developed views, FIG. 5A being a top plan cross-sectional detail
`
`view and FIG. 5B being a side elevational detail view, of one embodiment of components of
`
`the apparatus shown in FIG. 4.
`
`FIG. 6 is a developed side elevational detail view of a second embodiment of one of
`
`the components shown in FIGs. 5A and 5B.
`
`15
`
`FIG. 7A is partially a developed cross-sectional plan view and partially a schematic
`
`diagram showing one embodiment of a coating thickness monitoring arrangement according
`
`to the invention.
`
`FIG. 7B is a diagram showing an equivalent circuit of the arrangement of FIG. 7A.
`
`FIG. 8 is a diagram showing the variation of sputtering yield with ion energy for
`
`20
`
`several target compositions.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`The first embodiments to be described are particularly suitable for sputtering and
`
`depositing dielectric material.
`
`25
`
`FIG. 1 illustrates a first embodiment of an apparatus according to the present
`
`invention for performing physical vapor deposition, on a substrate, of a layer of a dielectric
`
`material sputtered from a target. The apparatus is composed of a housing 2 that encloses a
`
`Page 10 of 42
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`9
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`plasma chamber 4, an annular coil enclosure 6, a target assembly 8 and a substrate holder 10.
`
`Plasma chamber 4 is separated from coil enclosure 6 by a cylindrical conductive sheet 14 that
`
`serves as an electrostatic shield.
`
`Coil enclosure 6 contains a multi-tum helical coil 16 connected between ground and a
`
`5
`
`series arrangement of a RF power generator 18 and a matching network 20.
`
`Housing 2 is also connected to ground and conductive sheet 14 is connected to
`
`ground, at least during the major portion of a deposition process. Target 8 is composed
`
`basically of a metal plate 24 and a dielectric sheet, or plate, 26 constituting the source of
`
`material to be sputtered and deposited on a substrate. Metal plate 24 is provided with
`
`10
`
`passages forming part of a coolant flow path 30 through which a coolant fluid flows during
`
`deposition operation. Plate 24 is conductively connected to a RF power generator 32 via a
`
`series arrangement of a matching network 34 and a blocking capacitor 36.
`
`Substrate holder 10 provides a support surface for a substrate 40 on which the layer is
`
`to be deposited. Substrate holder 10 is provided with :flow passages forming part of a coolant
`
`15
`
`flow path 44 for flow of a coolant that will remove heat from substrate 40. Substrate holder
`
`10 is connected to a RF power generator 46 via a matching network 48 provided to maximize
`
`power transfer to holder 10.
`
`As shown in FIG. 4, to be described in detail below, it is desirable that electrostatic
`
`shield 14 be well ground at the top and bottom and maintained permanently at ground
`
`20
`
`potential. A second electrically isolated shield, or bias shield, 80 is provided between shield
`
`14 and a process tube 82 made of dielectric material. Shield 80 may be used for imposing an
`
`electrical wall bias to remove deposited layers thereon.
`
`Conductive sheet 14 is provided with an array of slots 60 via which electromagnetic
`
`energy generated by coil 16 is coupled into plasma chamber 4. Slots 60 will be closed by
`
`25
`
`dielectric windows, or sh.eet 14 may entirely encircle a cylindrical process tube, such as tube
`
`82 of FIG. 4.
`
`In the arrangement illustrated in Figure 1, coil 16 and conductive sheet 14 constitute
`
`the essential components of an electrostatically-shielded radio frequency (ESRF) plasma
`
`source that is already known in the art. For example, generators of this type are described in
`
`30 U.S. Patents Nos. 4,938,031 and 5,234,529, as well as in Lieberman and Lichtenberg,
`
`Principles of plasma discharges and materials processing, Chapter 12, John Wiley and Sons,
`
`Inc. (1994). As described in the latter text, coil 16 can be configured to form a helical
`
`Page 11 of 42
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`10
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`resonator by giving coil 16 a length equal to an integral number of quarter wavelengths of the
`
`RF input signal. The point on coil 16 to which RF power is supplied from generator 18 is
`
`located close to one end of the coil which is grounded. This portion of the coil effectively
`
`serves as part of the matching network, enabling selection of a tap position for achieving a
`
`5 match condition. Under certain conditions, proper selection of the tap point location can
`
`provide the desired impedance matching for the circuit. The open-circuited part of coil 16
`
`provides a termination that is resonant at the RF.
`
`In accordance with the usual practice in the art, enclosure 6 is filled with a bath of a
`
`dielectric fluid, one example of which is sold under the trademark Fluorinert, in order to
`
`10 maintain coil 16 at a desired temperature.
`
`The purpose of matching network 20 is to match the power supply output impedance
`
`to the load impedance as represented by the intrinsic impedance of coil 16 and the impedance
`
`of the plasma established in chamber 4, in order to maintain efficient energy transfer to the
`
`plasma. Matching networks for achieving this result are already known in the art.
`
`15
`
`According to preferred embodiments of the invention, metal plate 24 and other target
`
`components connected to generator 32 are preferably made of stainless steel and the target
`
`material is attached to plate 24 in a manner dictated by the nature of the materials involved.
`
`For example, the target, or dielectric plate, 26 may be made of alumina, which will be brazed
`
`to copper plate 24. One advantage of brazing is that it will maximize the heat transfer
`
`20
`
`conductance between plates 24 and 26.
`
`The load impedance on power supply 18 is a :function of the intrinsic impedance of
`
`coil 14 and the impedance presented by a plasma created in chamber 4. The impedance of
`
`the plasma will vary significantly between that which exists prior to plasma ignition and that
`
`which exists while a plasma is being maintained. Matching network 20 is provided
`
`25
`
`essentially to maintain efficient energy transfer from generator 18 to the plasma despite such
`
`load impedance variations.
`
`Each matching network 20, 34, 48 and 58 may be an L-network composed of two
`
`variable capacitors and an inductor, the capacitors being mechanically adjustable by an
`
`30
`
`automatic control network in order to maintain the desired impedance match. Typically, the
`source impedance of an RF generator is of the order of 50 n and the variable match network
`components will be adjusted so that the output impedance of the match network is the
`
`complex conjugate of the input impedance to the plasma source. Under matched conditions,
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`the forward power at the match network junction is maximized and the reflected power is
`
`minimized. Use can be made of known matching network designs which, while differing
`
`from one another in speed, robustness and controllability, are based upon the same
`fundamental principles which are abundantly described in the art. The provision of series
`
`5
`
`connected blocking capacitor 36 serves to promote the development of a high level DC self(cid:173)
`
`bias voltage on plates 24 and 26.
`
`The RF bias applied to target 26 must exceed the sputtering threshold of the target,
`
`which is typically between 60 and 100 volts. The sputtering yield will then increase linearly
`
`as a function of voltage until reaching a level between 500 and 1000 volts. The optimum
`
`10
`
`operating point for a target is that at which the sputtering yield per unit power absorbed is a
`
`maximum. The sputtering yield itself is basically dependant on the power dissipated at the
`
`target. This power is limited by the thermal conductivity of the target material and the rate of
`
`heat conduction to the coolant flow path. A typical, efficient target design can dissipate on
`the order of 1 OW/cm2
`
`•
`
`15
`
`Furthermore, the area of target 26 should be small relative to the area of the grounded
`
`or unbiased surfaces delimiting the plasma chamber in order to assure a high DC self-bias at
`
`target 26. This derives from the known fact that when a potential exists between two
`
`electrodes, and one electrode has an area substantially different from the other, the resulting
`
`DC self-biased will be relatively large.
`
`20
`
`In further accordance with the present invention, the RF power produced by generator
`
`32 should be at a very high frequency, preferably higher than 50MHz. When dielectric target
`
`26 has a thickness of several millimeters, it is necessary that capacitive coupling to the front,
`
`or exposed, surface of target 26 provide the mechanism for transmitting power through target
`
`26. The following Table 1 provides one preferred exemplary set of specifications for
`
`25
`
`perfom1ance of a deposition process according to the invention in apparatus of the type
`
`shown in Figure 1.
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`Table 1
`
`Target Specifications
`
`Target power density (W/cm1")
`
`10
`
`Target voltage (volts)
`
`333.33
`
`Target current density (amps/cm.t)
`
`0.03
`
`Target diameter (in (cm))
`
`8 (20.32)
`
`Target area (in.t (cm:.:))
`
`50.3 (324.3)
`
`Target power (W)
`
`3242.9
`
`Total target current (amps)
`
`Target impedance (ohms)
`
`9.7
`
`34.3
`
`In further accordance with the invention, the structure for supplying RF power from
`
`generator 32 to target electrode 24 may be constructed to reduce the amplitude,ofharmonic
`
`5
`
`components of the RF power. The presence of harmonic components having significant
`
`amplitudes can lead to a non-uniform spatial distribution of the electric field that is coupled
`
`from electrode 24 into the plasma in chamber 4. Even though only the fundamental RF
`
`power :frequency is coupled to target electrode 24 and ultimately couples power at this
`
`frequency into the plasma, harmonics of that fimdamental frequency can be generated within
`
`10
`
`the plasma due to the inherent nonlinearity of the plasma, and in particular the plasma
`
`sheaths, which are thin boundary layers of the plasma adjacent to electrode surfaces. Within
`
`the plasma sheath adjacent to dielectric plate 26, power at the fundamental RF frequency can
`
`be redistributed to harmonic frequencies by a nonlinear waveform rectification mechanism.
`
`Electric field components at these harmonic frequencies can then appear in target 24, 26
`
`15
`
`because it directly interfaces with the plasma. In many cases, harmonic energy can then be
`
`reflected at impedance mismatches, such as may exist at the base of the match network, and
`
`this reflected energy is returned to the plasma.
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`fu order to obtain an improved target sputtering uniformity