Samsung Electronics Co., Ltd. v. Demaray LLC
`Samsung Electronic's Exhibit 1018
`Exhibit 1018, Page 1
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`WO 01/63000 A2
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`—_MIUIIINIIIINTATITARITIARTNTATMTTi
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`Il, LU, MC, NL, PL, SK, TR), OAPI patent (BF, BJ, CK, Aor two-letter codes and other abbreviations, refer to the "Guid-
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`ance Notes on Codes andAbbreviations" appearing at the begin-
`ning ofeach regular issue ofthe PCT Gazette.
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`Published:
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`—_without international search report and to be republished
`upon receipt of that report
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`Ex. 1018, Page 2
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`Ex. 1018, Page 2
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`TITLE OF THE INVENTION
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`METHOD AND APPARATUS FOR DEPOSITING FILMS
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`This International Application claims benefit of U.S. Application No. 60/185,068
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`filed February 25, 2000.
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`BACKGROUND OF THE INVENTION
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`The present invention relates to the deposition offilms,or layers, primarily in the
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`fabrication of integrated circuits, but also in the manufacture of other products.
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`Integrated circuit fabrication procedures are composed ofa variety of operations,
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`including operations for depositing thin films on a semiconductor substrate, or wafer.
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`Typically, a large numberof identical integrated circuits are formed on such a wafer, which is
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`then cut, or diced, into individual circuit chips.
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`Given the small dimensionsof these integrated circuits, the quality of each deposited
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`layer or film has a decisive influence on the quality ofthe resulting integrated circuit.
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`15
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`Basically, the quality of a film is determined byits physical uniformity, including the
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`uniformity of its thickness and its homogeneity.
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`In particular, several process steps require the ability to deposit high quality thin
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`conductive films and to deposit conducting material in both high aspectratio trenches and
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`vias (and/or contacts).
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`20
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`According to the current state of theart, films, or layers, are deposited on a substrate
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`according to two types of techniques: physical vapor deposition (PVD), which encompasses
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`various forms of sputtering; and chemical vapor deposition (CVD). According to each type
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`ofprocedure, a layer of material composed of a plurality of atoms or molecules of elements
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`or compounds, commonlyreferred to collectively as “adatoms”, is deposited upon a substrate
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`in a low pressure region.
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`In typical PVD procedures, a target material is sputtered to eject adatomsthat then
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`diffuse through the low pressure region and condense on the surface of the substrate on which
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`the layer is to be deposited. This material forms a layer on the substrate surface.
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`Continuation ofthis process leads to the growth of a thin film. The sputtering itself is a
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`Ex. 1018, Page 3
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`physical process which involves accelerating heavy ions from an ionized gas, such as argon,
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`toward the target surface, where the ions act to dislodge and eject adatomsofthe target
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`material as a result of momentum exchange which occurs upon collision of the ions with the
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`target surface.
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`Onthe other hand, in CVD procedures, two or more gases are introduced into a
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`vacuum chamber where they react to form products. One of these products will be deposited
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`as a layer on the substrate surface, while the other product or products are pumped out of the
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`low pressure region.
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`Both types of deposition processes are advantageously performed with the assistance
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`10
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`of a plasma created in the low pressure region. In the case of PVD processes,it is essential to
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`provide a primary plasmato generate the ions that will be used to bombardthetarget.
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`However, in these processes, a secondary plasma may be formedto assist the deposition
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`process itself. In particular, a secondary plasma can serve to enhance the mobility of adatoms
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`in proximity to the substrate surface.
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`15
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`Although CVD processes are widely used in the semiconductor fabrication industry,
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`processes ofthis type have been foundto possess certain disadvantages. For example, in
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`order to employ CVD fora particular deposition operation,it is necessary to be ableto create
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`a chemical reaction that will produce, as one reaction product, the material to be deposited. In
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`contrast, in theory, any material, including dielectric and conductive materials, can be
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`deposited by PVD andthis is the process of choice when deposition must be performed while
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`maintaining the substrate temperature within predetermined limits, and particularly when
`deposition is to be performed while the substrate is at a relatively low temperature.
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`A film composedofa dielectric material can be formed by PVD either by directly
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`sputtering a target madeof the dielectric material, or by performingareactive sputtering
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`operation in which a conductive materialis sputtered from a target and the sputtered
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`conductive material then reacts with a selected gas to producethedielectric material thatis to
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`be deposited. One exemplary target material utilized for direct sputtering is silicon dioxide.
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`PVDcan also be used for conductive layers.
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`The simplest known PVD structure has the form of a planar diode which consists of
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`two parallel plate electrodes that define cathode constructed to serve as the target and an
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`anode which supports the substrate. A plasma is maintained between the cathode and anode
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`Ex. 1018, Page 4
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`and electrons emitted from the cathode by ion bombardmententer the plasma as primary
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`electrons and serve to maintain the plasma.
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`While a target made of a conductive material can be biased with a DC power supply,
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`a target madeofa dielectric material must be biased with high frequency, and particularly RF
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`power, which can also assist the generation of ions in the plasma. The RF poweris supplied
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`to the target by a circuit arrangement including, for example, a blocking capacitor, in orderto
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`cause the applied RF powerto result in the development of a DC self-bias on thetarget.
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`Since the planar diode configuration is not suitable for efficient generation of ions,
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`DC and RF magnetron configurations have been developed for producing a magneticfield
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`having field lines that extend approximately parallel to the target surface. This magnetic field
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`confines electrons emitted from the target within a region neighboring the target surface,
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`thereby improving ionization efficiency and the creation of higher plasmadensities for a
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`given plasmaregion pressure.
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`Additional configurations followed including the variety of cylindrical magnetrons.
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`15
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`Several versions of the cylindrical magnetron variation have appeared in the patentprior art,
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`in particular, the family of U.S. Patents Nos. 4,132,613, 4,132,613, 4,132,612, 4,116,794,
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`4,116,793, 4,111,782, 4,041,353, 3,995,187, 3,884,793 and 3,878,085.
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`Asdescribed in Thornton in "Influence of Apparatus Geometry and Deposition
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`Conditions on the Structure and Topography of Thick Sputtered Coatings", J. Vac. Sci.
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`Technol., Vol 11, No 4, 666-670 (1974), the structure of a deposited metalfilm is dependent
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`on both the temperature of the substrate and the gas pressure within the plasma region. The
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`highest film quality can be achieved when the substrate is at a relatively low temperature and
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`conditions are created to effect a certain level of bombardmentof the substrate with ions
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`from the plasma while the film is being formed. When optimum conditions are established, a
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`dense, high quality thin film which is substantially free of voids and anomalies can be
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`achieved.
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`It is known in the art that bombardmentofthe substrate with ions having energies
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`under 200 eV, and preferably not greater than 30 eV, and more preferably between 10 and 30
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`eV, can result in the formation ofdielectric films having optimum characteristics. This has
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`30
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`been found to be true in the case of, for example, thin films of SiOz and Ti02.
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`Ex. 1018, Page 5
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`Achievementof 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/m’-sec) is the product ofthe ion flux (with units ofnumber of
`ions/m?-sec) and ion energy (with units ofJ/ion).
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`However, whereas the highest possible ion energy is desired adjacent the target to
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`maximize the target sputtering rate, it has been found that the ion energy adjacent the
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`substrate,i.e., the energy of ions that bombard the substrate, should be less than the
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`maximum achievable for reasonsrelating primarily to layer quality.
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`For example, a reduced ion energy in the plasma adjacent the substrate reduces the
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`rate of implantation ofplasma gas ions into the substrate, as well damageto the substrate
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`subsurface, and the creation of voids and mechanicalstresses in the layer being formed.
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`Therefore, while it is desirable to have a high ion density in the plasma adjacent both
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`the target and the substrate, different desiderata exist with respect to plasma ion energy. The
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`plasma density in these systems are quite uniform, ie within +/-20% due to diffusion.
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`The plasma energyflux to the target and to the substrate are each limited by the
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`ability to remove heat from the target or substrate/chuck, respectively. Moreover, the ion
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`energy associated with ions striking the substrate surface is desired to be limited to a
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`maximum value to assure layer deposition quality. Therefore, it is imperative to use a plasma
`source capable of generating a dense plasma (107 cm”) or, equivalently, a high ion current
`density at the target and substrate surfaces while enabling direct control of the ion energy via
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`20
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`other means.
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`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 10°? cm? and
`higher. However, the plasma density proximate the substrate is often significantly reduced
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`25
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`since the substrate is generally downstream from the plasma source.
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`In general, known systemsare not suitable for both generating a high density plasma
`and allowing appropriate control of the ion energy deliveredto the substrate. Specifically,
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`when, in the known systems, the plasma density is increased, the plasmapotentialis
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`correspondingly raised and this leads to high sheath voltages and high ion energies in the
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`30
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`vicinity of the substrate.
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`Furthermore, a growing problem associated with many PVD chambersis a lack of
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`directivity for the adatom specie. Subsequently, whenfilling high aspect vias and trenches,
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`the feature may be “pinched off’ prematurely due to deposition coating growth on the feature
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`side-walls. Therefore, the concept of “ion plating” was introduced wherein a fraction of the
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`adatom specie is ionized and attracted to the substrate surface by meansofa substrate bias.
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`Consequently, the directed (normal) flow of ionized adatom specie enabled a uniform coating
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`growth without pinch-off; see U.S. Patent No. 5,792,522.
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`In addition, an inherent problem associated with the use of inductively coupled
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`plasma sources for conductive material PVD applicationsis the development of conductive
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`coatings on the chamber walls. Oncethis thin coating exceeds somethickness (~400 A), the
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`wall coating becomessufficiently conductive that the plasma source ceasesto sustain a
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`plasma. In both U.S. Patent No. 5,800,688 and 5,763,851, a circumferential shield
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`comprising longitudinal and transverse structures is employed to limit the field of view of
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`sputtered material migrating towards the chamber walls, hence, interrupting the generation of
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`a continuous wall coating of conducting material. Figure 1 of U.S. Patent No. 5,800,688
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`showsa series of angular blade sections displaced circumferentially, whereas Figure 2 U.S.
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`Patent No.5,763,851 showsa series of concentric shields comprising longitudinal slots, with
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`slots alternately placed between adjacent layers.
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`BRIEF SUMMARYOF THE INVENTION
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`20
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`A primary object of the present invention is to form high quality films on a substrate.
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`Another object of the present invention to provide a method and apparatus for
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`performing PVD in a plasmaregion which contains a high density plasma and in which the
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`target is bombarded with high energy ions and the substrate is bombarded with comparatively
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`low energy ions.
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`A further object of the invention is to allow independent controlofthe target and
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`substrate bombardmention energies.
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`A further object of the invention is to achieve high target material sputter rates in
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`order to produce corresponding high film deposition rates.
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`Yet another object of the invention is to provide a noveltarget electrode structure
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`which allows the desired high sputtering rate to be achieved.
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`Ex. 1018, Page 7
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`Further objects ofthe invention are to reduce particle contamination due to complex
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`geometric features in the process chamber, and to improvethe efficiency of coupling RF
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`powerto the plasma.
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`Another object of the invention is to eliminate certain obstacles to the plasma-assisted
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`deposition of conductive layers on substrates.
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`A still further object ofthe invention is to control the buildup of sputtered material on
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`the chamberwalls.
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`The aboveand other objects are achieved, according to the present invention, by
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`apparatus for performing physical vapor deposition of a layer on a substrate, which apparatus
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`includes a deposition chamber enclosing a plasma region for containing an ionizable gas, and
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`electromagnetic field generating means surrounding the plasmaregionfor inductively
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`coupling an electromagneticfield into the plasma region to ionize the gas and generate and
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`maintain a high density, low potential plasma. A source of deposition material including a
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`solid target is installed in the chamber. Thesolid target contains a material whichis to be
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`deposited onto the substrate. The target is electrically biased in order to cause ions in the
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`plasmatostrike the target and sputter material from the target. The apparatus further includes
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`a substrate holder for holding the substrate at a location to permit material sputtered from the
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`target to be deposited on the substrate.
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`In preferred embodiments of the apparatus according to the invention, the
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`electromagnetic field generating means comprise an electrostatically shielded radio frequency
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`electromagnetic field source that includes an electrostatic shield surrounding the plasma
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`region and a coil surrounding the shield for converting RF power into an electromagnetic
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`field that is coupled into the plasma through the electrostatic shield.
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`It has been found that a source of this type is capable of generating a high density
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`plasma, which makespossible the achievementof high target sputter rates and high substrate
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`deposition rates while maintaining a low plasmapotential and, hence, enabling independent
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`control of the DC self-bias induced in each of the target and substrate.
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`Objects according to the invention are further achieved by the provision, in such
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`apparatus, of a target assembly constructed to have the following features:
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`the area of the
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`target is small relative to the unbiased area of the chamber, thereby maximizing DCself-bias
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`of the target; a match network is provided for permitting application of a high frequency RF
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`voltage to create the self-bias, the target presenting a low impedanceto high frequencies; the
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`match network is constructed to minimize harmonicsof the high frequency on the target;
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`some RF poweris capacitively coupled to the target; the target is brazed to a stainless steel
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`plate which maximizes heat transfer from the target to a heat removal system; the heat
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`removal system is constructed to be capable of high heat removalrates, typically in excess of
`10 W/cm’; and a network for monitoring electrode arcing is provided.
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`Objects according to the invention are further achieved by the provision of a substrate
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`holder in the form of a chuck having the following features:
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`the chuck is constructed to
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`electrostatically clamp the substrate to the chuck; a system for delivering gas to the lower
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`surface of the substrate is provided; the chuck is constructed to removeheat at a high rate
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`from the substrate; and a RF bias is applied to the chuck in order to induce a DC self-bias in
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`the substrate. The combination. ofall four of these features will facilitate the delivery of a
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`high ion flux to the substrate and, consequently, high deposition rates, while ions having a
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`relatively low energy also impact on the substrate. As noted earlier herein, a certain amount
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`of low energy in bombardmentis needed to produce the highest quality depositing films.
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`In further accordance with the invention, the electrostatic shield of the
`electromagnetic field generating meansis arranged to be electrically and/or thermally biased.
`The application of such bias during a sputtering process or between sputtering operations can
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`serve to remove material that has been deposited on the inner surface of the shield, which
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`constitutes a lateral wali of the deposition chamber. This at least reduces,if not completely
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`eliminating, wall contamination and, thus, subsequent substrate contamination. The thickness
`ofmaterial deposited on the wall can be monitored, and this will provide an indication of
`when a wall cleaning is required.
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`Also in accordance with the invention, the apparatus may be configured to permit
`deposition of conductiye material by providing a dielectric process tube that surrounds and
`delimits the plasma region andabias shield that surrounds the process tube and is used for
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`monitoring the thickness of a conductive material layer deposited on the process tube and to
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`provide a bias voltage that acts to sputter the conductive material off of the processtube.
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`BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
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`FIG.1 is an elevational view,partly in cross-section and partly pictorial, of a first
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`embodiment of a PVD apparatus according to the invention.
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`FIG.2 is a cross-sectional, detail view of one structural feature of the apparatus of
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`FIG. 1.
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`FIG.3 is a view similar to that ofFIG 1 of a second embodiment ofPVD apparatus
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`according to the invention.
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`FIG.4 is a cross-sectional, detail view of a portion of a modified version of the
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`apparatus ofFIG. 1 or FIG. 3 for PVD of conductive materials.
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`FIGs. 5A and 5b are developed views, FIG. 5A being a top plan cross-sectional detail
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`view and FIG. 5B being a side elevational detail view, of one embodiment of components of
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`the apparatus shown in FIG.4.
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`FIG.6 is a developed side elevational detail view of a second embodiment of one of
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`the components shown in FIGs. 5A and 5B.
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`FIG. 7A is partially a developed cross-sectional plan view and partially a schematic
`diagram showing one embodimentof a coating thickness monitoring arrangement according
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`to the invention.
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`FIG. 7B is a diagram showing an equivalent circuit of the arrangement of FIG. 7A.
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`FIG.8 is a diagram showing the variation of sputtering yield with ion energy for
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`several target compositions.
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`DETAILED DESCRIPTION OF THE INVENTION
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`The first embodiments to be described are particularly suitable for sputtering and
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`depositing dielectric material.
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`25
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`FIG.1 illustrates a first embodiment of an apparatus according to the present
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`invention for performing physical vapor deposition, on a substrate, of a layer of a dielectric
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`material sputtered from a target. The apparatus is composedof a housing 2 that encloses a
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`Ex. 1018, Page 10
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`plasma chamber4, an annular coil enclosure 6, a target assembly 8 and a substrate holder 10.
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`Plasma chamber4 is separated from coil enclosure 6 by a cylindrical conductive sheet 14 that
`Serves as an electrostatic shield.
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`Coil enclosure 6 contains a multi-turn helical coil 16 connected between ground and a
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`series arrangement of a RF powergenerator 18 and a matching network 20.
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`Housing 2 is also connected to ground and conductive sheet 14 is connected to
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`ground,at least during the major portion of a deposition process. Target 8 is composed
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`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
`passages forming part of a coolant flow path 30 through which a coolant fluid flows during
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`10
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`deposition operation. Plate 24 is conductively connected to a RF powergenerator 32 via a
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`series arrangement of a matching network 34 and a blocking capacitor 36.
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`Substrate holder 10 provides a support surface for a substrate 40 on which the layeris
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`to be deposited. Substrate holder 10 is provided with flow passages forming part of a coolant
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`flow path 44 for flow of a coolant that will remove heat from substrate 40. Substrate holder
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`10 is connected to a RF powergenerator 46 via a matching network 48 provided to maximize
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`powertransfer to holder 10.
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`As shown in FIG.4, to be described in detail below,it is desirable that electrostatic
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`shield 14 be well ground at the top and bottom and maintained permanently at ground
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`20
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`potential. A secondelectrically isolated shield, or bias shield, 80 is provided between shield
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`14 and a process tube 82 madeofdielectric material. Shield 80 may be used for imposing an
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`electrical wall bias to remove deposited layers thereon.
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`Conductive sheet 14 is provided with an array of slots 60 via which electromagnetic
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`energy generated by coil 16 is coupled into plasma chamber 4. Slots 60 will be closed by
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`dielectric windows,or sheet 14 may entirely encircle a cylindrical process tube, such as tube
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`82 of FIG. 4.
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`In the arrangement illustrated in Figure 1, coil 16 and conductive sheet 14 constitute
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`the essential components of an electrostatically-shielded radio frequency (ESRF) plasma
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`source that is already known in the art. For example, generators of this type are described in
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`30
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`USS. Patents Nos. 4,938,031 and 5,234,529, as well as in Lieberman and Lichtenberg,
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`Principles ofplasma discharges and materials processing, Chapter 12, John Wiley and Sons,
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`Inc. (1994). As described in the latter text, coil 16 can be configured to formahelical
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`resonator by giving coil 16 a length equal to an integral numberof quarter wavelengths of the
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`RF input signal. The point on coil 16 to which RF poweris supplied from generator 18 is
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`located close to one end ofthe coil which is grounded. This portion ofthe coil effectively
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`serves as part of the matching network, enabling selection of a tap position for achieving a
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`match condition. Under certain conditions, proper selection of the tap point location can
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`provide the desired impedance matchingforthe circuit. The open-circuited part of coil 16
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`provides a termination that is resonant at the RF.
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`In accordance with the usual practice in the art, enclosure 6 is filled with a bath ofa
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`dielectric fluid, one example of which is sold underthe trademark Fluorinert, in order to
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`maintain coil 16 at a desired temperature.
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`The purpose ofmatching network 20 is to match the power supply output impedance
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`to the load impedanceas represented by the intrinsic impedanceof coil 16 and the impedance
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`ofthe plasma established in chamber 4,in order to maintain efficient energy transfer to the
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`plasma. Matching networks for achieving this result are already knownin the art.
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`According to preferred embodiments of the invention, metal plate 24 and othertarget
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`components connected to generator 32 are preferably madeofstainless steel and the target
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`material is attached to plate 24 in a mannerdictated by the nature of the materials involved.
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`For example, the target, or dielectric plate, 26 may be made of alumina, which will be brazed
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`to copper plate 24. One advantage of brazing is that it will maximize the heat transfer
`conductance between plates 24 and 26.
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`20
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`The load impedance on powersupply 18 is a functionofthe intrinsic impedance of
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`coil 14 and the impedance presented by a plasma created in chamber 4. The impedance of
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`the plasma will vary significantly between that which exists prior to plasma ignition andthat
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`which exists while a plasma is being maintained. Matching network 20 is provided
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`25
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`essentially to maintain efficient energy transfer from generator 18 to the plasma despite such
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`load impedance variations.
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`Each matching network 20, 34, 48 and 58 may be an L-network composed of two
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`variable capacitors and an inductor, the capacitors being mechanically adjustable by an
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`automatic control network in order to maintain the desired impedance match. Typically, the
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`30
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`source impedance of an RF generatoris of the order of 50 © and the variable match network
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`components will be adjusted so that the output impedance of the match networkis the
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`complex conjugate ofthe input impedanceto the plasma source. Under matched conditions,
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`Ex. 1018, Page 12
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`the forward powerat the match network junction is maximized and the reflected poweris
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`minimized. Use can be made of known matching network designs which, while differing
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`from one another in speed, robustness and controllability, are based upon the same
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`fundamental principles which are abundantly described in the art. The provision ofseries
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`connected blocking capacitor 36 serves to promote the development of a high level DC self-
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`bias voltage on plates 24 and 26.
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`The RF bias applied to target 26 must exceed the sputtering threshold ofthe target,
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`whichis typically between 60 and 100 volts. The sputtering yield will then increase linearly
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`as a function of voltage until reaching a level between 500 and 1000 volts. The optimum
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`operating point for a target is that at which the sputtering yield per unit power absorbedis a
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`maximum. Thesputtering yield itself is basically dependant on the powerdissipated at the
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`target. This poweris limited by the thermal conductivity of the target material and the rate of
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`heat conduction to the coolant flow path. A typical, efficient target design can dissipate on
`the order of 10W/cm?.
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`15
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`Furthermore, the area of target 26 should be small relative to the area of the grounded
`or unbiased surfaces delimiting the plasma chamberin order to assure a high DC self-bias at
`target 26. This derives from the known fact that when a potential exists between two
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`electrodes, and one electrode has an area substantially different from the other, the resulting
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`DC self-biased will be relatively large.
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`20
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`In further accordance with the present invention, the RF power produced by generator
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`32 should be at a very high frequency, preferably higher than 50MHz. Whendielectric target
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`26 has a thickness of several millimeters, it is necessary that capacitive coupling to thefront,
`
`or exposed, surface of target 26 provide the mechanism for transmitting power through target
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`26. The following Table 1 provides one preferred exemplary set of specifications for
`
`25
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`performance of a deposition process according to the invention in apparatus of the type
`
`shown in Figure 1.
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`Ex. 1018, Page 13
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`Ex. 1018, Page 13
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`12
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`Table 1
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`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
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`
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`In further accordance with the invention, the structure for supplying RF power from
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`generator 32 to target electrode 24 may be constructed to reduce the amplitude. ofharmonic
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`components ofthe RF power. The presence ofharmonic components having significant
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`amplitudes can lead to a non-uniform spatial distribution of the electric field that is coupled
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`from electrode 24 into the plasma in chamber 4. Even though only the fundamental RF
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`power frequency is coupled to target electrode 24 and ultimately couples powerat this
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`frequency into the plasma, harmonicsof that fundamental frequency can be generated within
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`10
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`the plasma due to the inherent nonlinearity of the plasma, and in particular the plasma
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`sheaths, which are thin boundary layers of the plasma adjacent to electrode surfaces. Within
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`the plasma sheath adjacentto dielectric plate 26, powerat the fundamental RF frequency can
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`be redistributed to harmonic frequencies by a nonlinear waveform rectification mechanism.
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`Electric field components at these harmonic frequencies can then appear in target 24, 26
`
`15
`
`becauseit directly interfaces with the plasma. In many cases, harmonic energy can then be
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`reflected at impedance mismatches, such as may exist at the base of the match network, and
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`this reflected energy is returned to the plasma.
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`Ex. 1018, Page 14
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`Ex. 1018, Page 14
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`In order to obtain an improved target sputtering uniformity, it is therefore desirable to
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`incorporate harmonic reduction techniques. One such approach would be the construction of
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`a conical, coaxial RF transmission line for feeding the RF powerto target 24, 26 in order to
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`make the line transparent to harmonic frequencies. Wave propagation along the line may be
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`attenuated using a dielectric material having a significant dielectric or magnetic loss tangent,
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`6 within a coaxial conductoror by using RF filtering techniques. Construction of such
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`arrangements can be based on knowledge already existing in theart, as disclosed, for
`
`example, in a Provisional application filed by Windhorn on February 14, 2000, Attorney
`Docket No. 258426. When, for example, a high density plasma, of the order of 10'ions/cm?
`, is generated in chamber4, with ion current densities ofthe order of 30mA/cm’flowing to
`
`10
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`the surface ofdielectric plate, or sputter target plate 26, together with the creation of high ion
`
`energies, a high energy flux can be created at the target surface. By maximizing the energy
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`flux to the target surface and optimizing its breakdown between ion flux and ion energy, a
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`maximum sputter yield can be created.
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`15
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`Substrate holder 10 includes a chuck, which may be an electrostatic chuck, for
`
`holding substrate 40 in place. Substrate holder 10 is mounted to be capable of undergoing
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`vertical movementin order to bring substrate 40 to a desired level with respect to chamber4.
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`Vertically moveable substrate holders are already well known in the art. In accordance with
`
`the present invention, this capability may be employedto position the upper surface of
`
`20
`
`substrate 40 just slightly below the lower extremities of slots 60. The density ofthe
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`inductively coupled plasma produced in chamber 4 decays rapidly below the lower
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`extremities, and above the upper extremities, of slots 60. The rate of decayis strongly
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`dependent upon the pressure within chamber 4. The density becomesnearly zero within a
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`few centimeters above and below theslot extremities. This allows the upper surface of
`
`25
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`substrate 40 to be located in proximity to a region ofhigh plasma density, while itself being
`
`in a region of low plasmadensity, thereby allowing a low level of ion energy to be achieved
`
`at the substrate surface. This level can be controlled by suitable selection of the substrate
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`self-bias voltage.
`
`Substrate holder 10 is further constructed to maintain the substrate at a specified
`
`30
`
`temperature by incorporating therein a cooling system, including a coolant flow path 44,
`capable ofremovingheat from substrate 40 at a rate of the order of 5-10W/cm’. Thermal
`
`conduction between substrate 40 and substrate holder 10 is improved by supplying a layer of
`
`gas therebetween and bycreating electrostatic forces to hold substrate 40 against holder 10.
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`Ex. 1018, Page 15
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`Ex. 1018, Page 15
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`14
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`The combination of a layer of gas and electrostatic clamping, each of which is conventional
`
`in the art, serves to increase the thermal conductivity in the interface region between substrate
`
`40 and substrate holder 10. One such devicein the priorart is described in U.S. Patent #
`
`5,625,526 (Watanabeet al.) entitled “Electrostatic Chuck”.
`
`At the bottom of chamber4, holder 10 is surrounded by an annular region whichis in
`
`communication with a ducting system (not shown) leading to a vacuum pump, such as a
`
`turbomolecular pump, that maintains a desired vacuum pressure within chamber 4. RF power
`
`is supplied by generator 46 to substrate holder 10 for the purpose of establishing a DC self-
`bias on substrate 40.
`
`10
`
`The RF bias supplied to holder 10, a