Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With plasma generation means remote from processing chamber
Reexamination Certificate
2000-08-07
2002-08-13
McDonald, Rodney G. (Department: 1753)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With plasma generation means remote from processing chamber
C156S345380, C156S345480, C156S345490, C118S7230MP, C118S7230ER, C118S7230IR, C118S7230IR, C118S7230AN, C315S111510, C204S298060, C204S298070, C204S298160, C204S298310, C204S298330, C204S298340
Reexamination Certificate
active
06432260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plasma source apparatus and method by which to produce a high power density gaseous plasma discharge within a nearly all-metal, fluid cooled vacuum chamber by means of an inductively coupled RF power means. The invention is particularly useful for generating a high charged particle density source of ions and electrons with either chemically inert or reactive working gases for processing materials.
2. Brief Description of the Prior Art
Numerous forms of inductively coupled plasma (ICP) sources or transformer coupled plasma (TCP) sources have been described along with their applications to materials processing. These devices make use of at least one induction coil element disposed in close proximity to, around or within a vacuum chamber that is excited with RF power. Electromagnetic fields about the induction coils sustain a gas plasma discharge within the vacuum apparatus and induce RF electron drift currents within the plasma. In addition to the RF induction coils, auxiliary DC or AC magnetic fields and Faraday shields may also be imposed on the ICP or TCP apparatus so as to enhance RF heating or spatial properties of the gas plasma discharge. References have disclosed unique design embodiments of the induction coils, the application of Faraday shields to reduce electrostatic coupling from high voltages on the coils, RF coupling and impedance matching techniques to the ICP source, and unique embodiments that improve the RF electron heating and spatial uniformity of the plasma.
In those instances where the induction coil is not immersed within the vacuum, the RF fields are coupled to the plasma discharge through a ridged dielectric vacuum wall. The plasma discharge body formed by various ICP sources can be closely coupled to a materials processing vacuum region to facilitate surface treatment, material etching, sputter deposition, chemical vapor deposition, and other related vacuum based operations. In other applications it is desirable to remotely couple ICP sources to process vacuum systems in order to generate heated, reactive gaseous species which then flow into the materials processing vacuum region or system to enhance etching or deposition processes and to facilitate chamber and vacuum component surface cleaning. This latter application may require a high plasma density state that is commonly associated with an ICP source in the presence of high gas flows several hundreds of standard cubic centimeters per minute (sccm) and with plasma discharge pressure vacuum pressures greater than several hundreds of milliTorr.
The following references are indicative of inductively coupled plasma sources used in materials processing applications:
U.S. Pat. No. 4,065,369, Ogawa et al., Dec. 27, 1977
U.S. Pat. No. 4,368,092, Steinberg et al., Jan. 11, 1983
U.S. Pat. No. 4,431,898, Reignberg et al., Feb. 14, 1984
U.S. Pat. No. 4,948,458, Ogle, Aug. 14, 1990
U.S. Pat. No. 5,008,593, Schilie et al., Apr. 16, 1991
U.S. Pat. No. 5,280,154, Cuomo et al., Jan. 18, 1994
U.S. Pat. No. 5,397,962, Moslehi, Mar. 14, 1995
U.S. Pat. No. 5,534,231, Keller et al., Jul. 9, 1996
There are several shortcomings of the prior art methods for producing inductively coupled plasma for many applications. In particular, these sources which use non-conductive dielectric (i.e. fused-quartz, glass, alumina, sapphire, aluminum nitride, or boron nitride) walls to separate the induction coil(s) from the plasma discharge body can limit range of the power density (Watts per cubic centimeter) disposed through the dielectric wall and into the process plasma discharge. These dielectric vacuum wall materials pass the RF fields into the vacuum plasma discharge. They are then selected and applied on the basis of their chemical compatibility with the reactive plasma discharge byproducts, thermal-mechanical resilience, and UV transmission properties. However, at higher pressures and power densities, the restrictions of collisional, ambipolar diffusion of ions and electrons results in a spatial constriction of the plasma discharge within the vacuum chamber, and often in close proximity to the induction coil current carrying elements. In such cases the heated plasma discharge gases readily transfer thermal energy to the wall in close proximity to the induction coil as disposed about the plasma source. The localized thermal flux from the plasma gases can be so high and localized that the plasma discharge may damage the dielectric materials by means of thermally enhanced chemical erosion, thermally induced mechanical stresses, or even softening and melting as in the case of fused quartz or glass. Moreover, the spatial constriction of the diffusive plasma body can result in a lower coupling efficiency from the primary induction coils to the gas plasma discharge.
In order to accommodate these dielectric materials under high power density conditions, special fluid cooling measures such as forced air cooling or circulating liquid coolants in direct or near contact to the dielectric vacuum wall is required to extract waste heat from the plasma apparatus. Exemplary of this approach are Schile et al. in U.S. Pat. No. 5,008,593, Holber et al. in U.S. Pat. No. 5,568,015, and Shang et al. in U.S. Pat. No. 5,892,328. The inclusion of fluid cooling measures directly on the dielectric vacuum plasma discharge walls can make the design of the source complicated and expensive and can reduce the coupling efficiency of RF or microwave power to the plasma. Also, direct water cooling of the dielectric wall can incur high operational risks because air or water can readily leak into the vacuum based process should the dielectric wall be cracked or damaged when mechanically or thermally shocked or when under cooled.
In some cases, workers can avoid the problems with the high power density inductively coupled state at high pressures and power by operating ICP plasma discharge apparatus in a substantially weaker plasma density, capacitively coupled state. In this lower plasma density state, the plasma discharge is driven by sheath electron heating through the spatially distributed quasi-static electric fields from the RF voltage on the induction coil rather than through induced electric fields associated with the RF currents on the induction coil. Unfortunately, the capacitively coupled state of conventional ICP sources does not support the high excitation, ionization, and molecular dissociation levels as desired from the inductively coupled state of an ICP source.
Most existing ICP and TCP sources are limited in their scale, power range and pressure range of operation due to the following:
1. extensive use of dielectric vacuum wall materials and their common thermal mechanical constraints when used in high power density, chemically reactive and ultraviolet light emitting plasma applications;
2. low coupling efficiency within non-immersed coil ICP source designs (<0.5 typically) due to spatial design constraints between induction coils and this plasma discharge body;
3. constraints in cooling dielectric vacuum walls, vacuum seals, vacuum power feedthroughs, and induction coil elements in high power density applications; and
4. RF quasi-electrostatic fields on the coil and within the plasma as driven by the induction coil elements and the need for Faraday shields and fluid cooling means with high AC voltage standoff ratings.
Relevant to the background of this invention is an alternative means of producing an inductively coupled plasma discharge using a ferrite transformer core such that the conductive gas plasma discharge works as a single turn secondary winding about the ferrite core. This method has been described by Anderson in U.S. Pat. No. 3,500,118, U.S. Pat. No. 3,987,334, and U.S. Pat. No. 4,180,763 for lighting applications and by Reinberg et al. in U.S. Pat. No. 4,431,898 for plasma resist strip applications. These references describe how at least one ferrite core disposed about a closed path, topologically toroidal shaped dielectric vacuum chamber or chamber embod
Carter Daniel C.
Mahoney Leonard J.
Roche Gregory A.
Advanced Energy Industries Inc.
Hudson, Jr. Benjamin
McDonald Rodney G.
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