WO2000022646A1

WO2000022646A1 - Water-cooled coil for a plasma chamber

Info

Publication number: WO2000022646A1
Application number: PCT/US1999/022893
Authority: WO
Inventors: Anantha Subramani; Michael Rosenstein; Timothy C. Lommasson; Peter Satitpunwaycha
Original assignee: Applied Materials, Inc.
Priority date: 1998-10-15
Filing date: 1999-10-01
Publication date: 2000-04-20
Also published as: KR20010080191A; KR100649278B1; JP2002527900A; JP4564660B2

Abstract

A feedthrough assembly for a plasma chamber for mounting an RF coil onto a wall of the chamber and passing through the chamber wall in an electrically insulated and pressure-tight manner. The feedthrough assembly defines a darkspace gap between an electrically grounded member and a member electrically coupled to the RF coil, the darkspace being located between the plasma generation area of the chamber and insulator members of the feedthrough assembly to protect the insulator members from the plasma and from deposition of the sputtered material.

Description

WATER-COOLED COIL FOR A PLASMA CHAMBER

FIELD OF THE INVENTION The present invention relates to ionized deposition and etching processes and apparatus, and more particularly, to a method and apparatus for mounting a coil to a chamber for the fabrication of semiconductor devices.

BACKGROUND OF THE INVENTION To improve bottom coverage of high aspect ratio vias, channels and other openings in a wafer or other substrate during a deposition process, the deposition material may be ionized in a plasma prior to being deposited onto the substrate. The ionized deposition material may be redirected by electric fields to ensure more material reaches the bottom areas. It has been found that it is desirable to increase the density of the plasma to increase the ionization rate of the sputtered material in order to decrease the formation of unwanted cavities in the deposition layer. Such a plasma is also useful for other semiconductor processes such as etching a wafer. There are several known techniques for exciting a plasma with RF fields including capacitive coupling, inductive coupling and wave heating. In a standard inductively coupled plasma (ICP) generator, RF current passing through an antenna in the form of a coil surrounding the plasma induces electromagnetic currents in the plasma. These currents heat the conducting plasma by ohmic heating, so that it is sustained in steady state. As shown in U.S. Pat. No. 4,362,632, for example, current through a coil is supplied by an RF generator coupled to the coil through an impedance matching network, such that the coil acts as the first windings of a transformer. The plasma acts as a single turn second winding of a transformer. As described in copending application Serial No. 08/680,335, entitled "Coils for Generating a Plasma and for Sputtering," filed July 10, 1996 (Attorney Docket # 1390CIP/PVD/DV) and assigned to the assignee of the present application, it has been recognized that the coil itself may provide a source of sputtered material to supplement the deposition material sputtered from the primary target of the chamber. Application of an RF signal to a coil insulatively positioned on a shield wall in the chamber can cause the coil to develop a negative bias which will attract positive ions which can impact the coil causing material to be sputtered from the coil. Because relatively large currents are passed through the coil to energize the plasma, the coil often undergoes significant resistive heating. In addition, ions impacting the coil can further heat the coil if the coil is used as a sputtering source. As a result, an internal coil can reach relatively high temperatures which can have an adverse effect on the wafer, the wafer deposition process or even the coil itself. Moreover, the coil will cool once the deposition is completed and the current to the coil is removed. Each heating and subsequent cooling of the coil causes the coil to expand and then contract. This thermal cycling of the coil can cause target material deposited onto the coil to generate particulate matter which can fall onto and contaminate the wafer. To reduce coil heating, it has been proposed in some applications to form the coil from hollow tubing through which a coolant such as water is passed. However, because the source of coolant is most conveniently located outside the chamber, the vacuum chamber in which the coil is located will typically require a feedthrough to permit coolant to pass through the chamber wall, through the coil and back to the exterior of the chamber. In addition, because the RF source may be located exterior to the chamber as well, a feedthrough for the RF power to the coil may also be needed in the chamber wall. However, the chamber wall is usually maintained at ground potential for safety and other reasons. Hence, the RF feedthrough should be capable of electrically insulating the coil from the chamber wall. Still further, the coolant and RF feedthroughs should be capable of maintaining a large pressure differential between the exterior of the chamber which is typically at ambient pressure, and the interior of the chamber which may be at 1 milliTorr or lower pressure. As a consequence, known RF and fluid feedthroughs tend to be relatively complex and difficult to install. For example, one known feedthrough comprises a conduit having an external end to which sources of RF energy and coolant are coupled, and an internal end to which the coil is welded or otherwise joined. In such a feedthrough, however, the internal joint between the coil and the feedthrough is a potential leakage point which could significantly disrupt the semiconductor processes performed in the chamber and potentially damage the chamber itself. In a copending application entitled "Improved coil and coil feedthrough" (attorney Docket No. 1802/MD/PVD/DV), filed by Peter Satitpunwaycha and assigned to the assignee of the present application, an RF coil is described, which includes a continuous, one-piece conduit of conductive material having first and second ends positioned on the chamber exterior, a coil portion positioned in the chamber interior and a feedthrough portion positioned in an aperture of the chamber wall. This design eliminates a potential source of coolant leak because the conduit lacks any joints between the feedthrough and coil portions. In a coil feedthrough such as the one described in the above-referenced copending application, an insulating member is typically used to electrically insulate the RF coil which is at a potential supplied by the RF source ("RF-hot"), from the chamber wall which wall is typically grounded. The shield wall which is also usually at ground potential has a spaced aperture through which the RF coil also passes. It is desirable to protect the surfaces of the feedthrough insulating member from deposition of the sputtered material, as well as to protect it from the plasma generated in the plasma generation region of the chamber. For example, when the deposition material is a conductive material such as a metal, an unprotected surface of the insulating member may be coated with the deposition material and become conducting. SUMMARY OF THE PREFERRED EMBODIMENTS It is an object of the present invention to provide an improved method and apparatus for mounting a coil, which obviates, for practical purposes, the above- mentioned limitations, particularly in a manner requiring a relatively uncomplicated arrangement. This and other objects and advantages are achieved by, in accordance with one aspect of the invention, an RF coil feedthrough assembly having an insulating member for electrically insulating the coil from the chamber wall, and a blocking member defining a darkspace gap for protecting the insulator from the sputtered material and to confine the plasma inside the chamber. The darkspace gap is formed between the blocking member electrically coupled to the chamber wall and a member electrically coupled to the RF coil, and positioned along the coil between the interior plasma region and the insulator. In one embodiment, the coil passes through an aperture in a block that is electrically coupled to the chamber wall, and a darkspace gap is formed between the outer surface of the coil and an inner surface of the aperture. In another embodiment, a sleeve is provided around and electrically coupled to the RF coil, the sleeve and the coil passing through an aperture in a chamber shield that is electrically coupled to the chamber wall. In this embodiment, a darkspace gap is formed between the sleeve and an inner surface of the aperture on the shield. Because the sleeve typically has higher structural rigidity than the coil and is less likely to move inside the aperture through which it passes, the darkspace gap formed between the sleeve and the aperture may be more readily maintained. According to another aspect of the present invention, the entire RF feedthrough assembly may be carried by the RF coil. The feedthrough assembly may be adapted to be fastened onto an exterior surface of the chamber wall in a pressure-tight manner. Because the feedthrough assembly is secured to the chamber from the exterior, installation of the RF coil is significantly facilitated. Moreover, the feedthrough can fully support the coil so that no other connection or support for the coil need be provided in the interior of the chamber. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of electrical interconnections to a plasma generating coil in accordance with the present invention. Fig. 2 is a cross-sectional view of a portion of a coil and a feedthrough assembly in accordance with an embodiment of the present invention. Fig. 2a is a side view of the feedthrough of Fig. 2. Fig. 3 is an exterior view of the feedthrough of Fig. 2. Fig. 4 is a cross-sectional view of a portion of a coil and a feedthrough assembly in accordance with another embodiment of the present invention. Fig. 5 is an exterior view. DETAILED DESCRIPTION OF THE DRAWINGS Referring to Figs. 1 and 2, a plasma generator utilizing an RF coil in accordance with a first embodiment of the present invention comprises a substantially cylindrical plasma chamber 100 which is received in a vacuum chamber 102 (shown schematically in Fig. 1). The plasma chamber 100 of this embodiment has a one-turn or multiple-turn fluid-cooled tubular coil 104 which includes a portion 104a positioned in a generally cylindrical shield 106 and within an interior plasma generation area 108 within the shield 106. The shield 106 is electrically coupled to an exterior wall 114 of the chamber 102, which is typically grounded. Radio frequency (RF) energy from an RF generator 110 coupled to an external portion 104b of the coil 104 which passes through a feedthrough assembly 112 mounted in the exterior wall 114 of the chamber 102 to an interior coil portion 104a and the remainder of the RF coil 104. The RF energy is inductively coupled into the interior area 108 of the deposition system 100, which energizes a plasma within the deposition system 100. As explained in greater detail below, the RF coil 104 of the illustrated embodiment includes a continuous, one piece tubular conduit which passes from the exterior of the chamber (coil portion 104b), through the feedthrough assembly 112 (coil portion 104d), around the interior of the chamber (coil portion 104a) and back through the feedthrough assembly 112 (coil portion 104e) to the exterior of the chamber (coil portion 104f) without any joints which may cause leaks of the fluid coolant carried within the coil. In addition, the feedthrough assembly 112 has a block member 202 (Fig. 2) which is adapted to be fastened to the exterior wall 114 of the chamber 102 to significantly facilitate installation of the coil 104 into the chamber. During a sputter deposition process, an ion flux strikes a negatively biased target 120 positioned at the top of the chamber 102. The target 120 is preferably negatively biased by a DC power source 122. The coil 104 may develop a negative bias to attract ions. The plasma ions eject material from the target 120 and possibly also the coil 104 onto a substrate 124 which may be a wafer or other workpiece which is supported by a pedestal 126 at the bottom of the deposition system 100. A rotating magnet assembly 128 provided above the target 120 produces magnetic fields which sweep over the face of the target 120 to promote a desired erosion pattern over the target face. The atoms of material ejected from the target 120 and coil 104 are in turn ionized by the plasma being energized by the coil 104 which is inductively coupled to the plasma. The RF generator 110 is preferably coupled to the external end 104b of the coil 104 through an amplifier and impedance matching network 130. The other external end 104f of the RF coil 104 is coupled to ground, preferably through a blocking capacitor 132 which may be a variable capacitor, if sputtering of the coil is desired. The ionized deposition material is attracted to the substrate 124 and forms a deposition layer thereon. The pedestal 126 may be negatively biased by an RF (or DC or AC) source 136 so as to externally bias the substrate 124. Also, the substrate 124 may self bias in some applications such that external biasing of the substrate 124 may optionally be eliminated. Figs. 2, 2a and 3 illustrate an RF feedthrough assembly for a water-cooled coil according to one embodiment of the present invention. As described in greater detail below, the feedthrough 112 is designed in such a manner as to inhibit the deposition of conductive deposition material onto insulative surfaces, which could cause a short between the coil and adjacent grounded surfaces and yet accommodate a degree of flexing of the coil during operation without causing a short. In addition, a darkspace is formed between the coil and adjacent grounded surfaces to retard the passage of the plasma ions to inhibit arcing between the coil and the adjacent grounded surfaces. Fig. 2 is a cross-sectional view of the feedthrough 112 in a plane passing through the axes of the coil portions 104d and 104e and substantially normal to the cylindrical axis of the chamber. Fig. 2a is a side view of the feedthrough of Fig. 2 viewed in the direction indicated by the arrow A in Fig. 2. Fig. 3 is a schematic illustration of the feedthrough of Fig. 2 viewed along the direction indicated by the arrow B in Fig. 2. As shown in Figs. 2 and 3, the portions 104b, 104d, 104e and 104f of the illustrated embodiment of the RF coil 104 are substantially cylindrical. The portions 104d and 104e are positioned substantially parallel to each other and pass through two apertures 202a and 202b, respectively (Fig. 2), of a block member 202. The inner diameters of the apertures are slightly larger than the outer diameters of the coil portions 104d and 104e passing therethrough, so that an annular space may be formed between the outer surface of the coil portions and the inner surface of the associated aperture to inhibit passage of conductive material and create a darkspace as described below. The structural components of the feedthrough are typically identical with respect to the two coil portions 104d and 104e, although the two end portions 104b and 104 f of the coil may be adapted to be coupled to different electrical circuitry, for example, as described above and shown in Fig. 1. As shown in Fig. 2, an insulator tube 204 is disposed around a portion of the external coil portion 104b between the block member 202 and the end of the coil. The insulator tube 204 may be made of ceramic or other suitable insulating materials. A ring-shaped member 206 is welded or otherwise secured to the outside surface of a portion of the coil portion 104b between the insulator tube 204 and the end of the coil. The ring member 206 may be formed of titanium or other suitable conductive material. The insulator tube 204 is joined at one end 204a to the ring member 206 by a first sleeve 208 disposed around the coil portions between the insulator tube 204 and the ring member 206, and at the other end 204b to the block member 202 by a second sleeve 210 disposed around the coil portion between the insulator tube 204 and the block member 202. The first and second sleeves 208 and 210 may be made of kovar or other suitable material. The first sleeve 208 is joined at one end 208a to the ring member 206, and at the other end 208b to the end 204a of the insulator tube 204. The second sleeve is joined at one end 210a to the end 204b of the insulator tube 204. The end portion 208b of the first sleeve and the end portion 210a of the second sleeve are spaced apart along the insulator tube 204, so that the first and second sleeves 208 and 210 are electrically insulated from each other. The other end 210b of the second sleeve 210 extends into the aperture 202a of the block member 202, and is joined to an inner surface of the aperture. The inner diameters of the second sleeve 210 are larger than the outer diameter of the coil portion passing therethrough by a sufficient amount so that the second sleeve 210 does not contact the outer surface of the coil portion 104d. Further, the diameter of the inner surface of aperture 202a is larger than the outer diameter of the coil portion 104d passing therethrough by a predetermined amount, so that an annular space 212 is formed between the inner surface of the aperture 202a and the outer surface of the coil portion 104d. Since the block member 202 is mechanically coupled to the coil 104 through the insulator tube 204, the coil 104 and the block member 202 are electrically insulated from each other. In this manner, the coil 104 is insulatively supported by the block member 202. The block member 202 may be made of titanium, aluminum, stainless steel or other suitable structural material. The sleeves 208 and 210 may be joined to the ring member 206, the insulator tube 204 and the inside surface of the block member 202 at points 208a, 208b, 210a and 210b, respectively, by high temperature brazing at a melting temperature of, for example, approximately 800°C. Such brazing forms a secure joint for most applications as the operating temperature of the feedthrough is typically well below 800 °C. Other suitable means may also be used to join the above components, such as welding. The connections between the coil, the ring structure 206, first sleeve 208, the insulator tube 204, the second sleeve 208, and the block member 202 are preferably pressure-tight. In addition, a nipple 214 is provided at the end of the coil portion 104d to provide coupling with a coolant source for a coolant fluid such as gas or water. The nipple 214 may be made of titanium or other suitable materials. As shown in Figs. 2 and 3, the coil portion 104e passes through a matching aperture 202b of the block member 202. The structure for coupling the coil portion 104e to the block member 202 is the same as the structure described above for the coil portion 104d. Through these structures, the block member 202 carries the coil 104 in a pressure-tight and insulated manner. The feedthrough assembly 112 may be installed in the chamber 100 by passing the feedthrough assembly through an aperture 106a in the shield wall 106 and an aperture in the wall 114 of the chamber and fastening the block member 202 onto the wall using, for example, bolts 216 as shown in Fig. 3. The bolts 216 may be received directly in the main wall of the chamber or a separate adaptor plate as described below in connection with another embodiment. Vacuum seals may be provided between the block member 202 and the wall 114 to ensure a pressure tight filling. The feedthroughs 112 can fully support the coil so that no other connection or support need be provided in the interior of the chamber. However, in this embodiment, the aperture 106a of the shield wall 106 may be sized so as to snugly receive the block member 202 of the feedthrough so as to prevent the passage of deposition material and plasma ions between the block member 202 and the shield wall. Thus, the block member 202 may be supported by and fastened to the shield wall to provide additional support for the feedthrough 112 and the coil 104. When the feedthrough 112 is installed, the block member 202 will be electrically coupled to the chamber, which is typically grounded. The coil 104, which is electrically insulated from the block member 202 by the insulator tube 204, is typically at a relatively high voltage supplied by the RF source (referred to as being "RF-hot") when the apparatus is operating. As described above, the coil 104 and the block member 202 are spaced from each other to define an annular space 212 between the block member 202 and the coil portion 104d having a predetermined size. As best seen in Fig. 2, the annular space 212 in effect forms a constricted passageway between the insulator member 204 and the plasma generation area 108 in which the sputtered deposition material is being ionized. The relatively narrow width of the space 212 and the relatively long length of the space 212 acts to inhibit the passage of sputtered deposition material to the insulator member 204. Hence, the formation of a conductive path of conductive sputtered deposition material across the insulator member 204 which could short the coil 104 to the block member 202 may be substantially slowed or completely arrested, thereby lengthening the effective life of the coil feedthrough 112. At the same time, the width of the space 212 is preferably sufficiently wide to permit a degree of flexure of the coil 104 without the coil coming into contact with and electrically shorting to the feedthrough block member 202. In the illustrated embodiment, the space 212 between the conductive outer surface of the coil 104 and the grounded inner surface of the block apertures 202a and 202b has a width of approximately 0.04 - 0.08 inches (1-2 mm) and a length of approximately Vz - 1 inches (12-25 mm) for a width to length ration of about 1:12. It is preferred that this ratio be at least 1 :2. These dimensions may vary depending upon the. particular application. Other dimensions are of course possible, depending upon the particular application. In the illustrated embodiment, the block member 202 extends the length of the well defined space 212. The annular space 212 is also preferably sized to form a "darkspace" gap. A darkspace gap is a space formed between two conductors maintained at different voltages in a plasma generation environment in which the distance between the two conductors is sufficiently small to retard the formation of a plasma between the two conductors yet spaced sufficiently to inhibit arcing between the conductors. Hence, the plasma is prevented from penetrating into the darkspace from the adjacent plasma area 108. The maximum distance between the two conductors that can produce such a darkspace depends on factors such as the relative voltages of the two conductors, the pressure of operation, and the density of the plasma in the plasma generation area. In the embodiment illustrated in Fig. 2, the darkspace gap 212 is sufficiently small to form such a darkspace between the coil portion 104d and the inner surface of the aperture 202a in the block member 202. Thus, darkspace gap 212 functions to retard the formation of a plasma in the space 212 to inhibit arcing between the coil and the adjacent surfaces of the block member apertures 202a and 202b. For a chamber pressure in the range of a few milliTorr to approximately 30 milliTorr, a darkspace gap of 0.06 inches (1.5 mm) is preferred. In the illustrated embodiment, the block member 202 has an opening 220 which provides a gap between the coil 104 and the block member adjacent the opening 220 which is substantially greater than the darkspace gap but is large enough such than arcing and inadvertent contact between the coil and the opening 220 are unlikely. The opening 220 may be formed into the block member 202 to define the desired length of the apertures 202a and 202b. Figs. 4 and 5 illustrate an RF feedthrough assembly for a water-cooled coil according to another embodiment of the present invention. Fig.4 is a cross- sectional view of the feedthrough in a plane containing the axis of the coil portion 104d and substantially parallel to the cylindrical axis of the chamber. The coil portion 104e (Figs. 1 and 5) is parallel to the coil portion 104d and is not shown in Fig. 4. Fig. 5 is a front elevation view of the feedthrough of Fig. 4 viewed along the direction indicated by the arrow C in Fig. 4. As shown in Figs. 4 and 5, the portions 104d and 104e of the RF coil 104, which are substantially cylindrical, are substantially parallel to each other and pass through two apertures 301 in an adaptor plate 302. Fig. 4 also shows the plasma generation area 108 inside the chamber. As shown in Fig. 4, a tubular member 304 is disposed around and joined with coil portion 104d and extends along substantially the entire portion of the coil that passes through the aperture 301 of the adaptor plate 302. The tubular member 304 has an annular flange 304a at or near an "interior" end of the tube 304 (i.e., the end of the tube inside the pressure vessel of the chamber), and threads are provided on the outside surface of a portion 304b of the tube 304 on the exterior end of the tube (i.e., the end of the tube outside the pressure vessel of the chamber). A cylindrical sleeve 306 is disposed around the coil portion 104d and extends from the tubular member 304 at the flange 304a of the tubular member 304. The sleeve 306 has an inner diameter that is larger than the outer diameter of the coil portion 104d, so that the sleeve is spaced from the coil. Both the sleeve 306 and the tubular member 304 are in electrical contact with the coil portion 104d. As described below, the sleeve 306 passes through an aperture 316 in the shield 106 (Figs. 1 and 4). The tubular member 304 is joined to the coil by welding or other suitable means, and the sleeve 306 is similarly joined to the tubular member 304. Alternatively, the sleeve 306, the tubular member 304 and possibly even the coil may be made as an integral single piece. The coil 104 is insulatively fastened to the plate 302 by a fastening and insulating assembly comprising the flange 304a of the tubular member 304, an insulator ring 308, disposed between the flange 304a and the adaptor plate 302, an insulator sleeve 310 disposed between the tubular member 304 and the adaptor plate 302, and a nut 312 threaded onto the threaded portion 304b of the tubular member 304. The insulator sleeve 310 has a portion 310a having a relatively small outer diameter which passes through the aperture 301 of the block 302, and a flange portion 310b having a relatively large outer diameter which is received by a shoulder 302a of adaptor block 302. The nut 312 is in turn received by the shoulder 310c of the flange 310b. The insulating ring 308 and the insulating sleeve 310 may be made of vespel or other suitable material. As shown in Fig. 4, the adaptor plate 302 is received between the insulator ring 308 and the flange portion 310b of the insulator sleeve 310. When the nut 312 is tightened, the nut 312 presses against the flange portion 310b of the insulator sleeve 310, thereby causing the flange 304a of the tubular member 304 to press against the insulator ring 308. The insulator ring 308 and the flange portion 310b of the insulator tube in turn compress adaptor plate 302, thereby insulatively fastening the coil 104 to the adaptor plate 302. Vacuum seals 314 may be provided between the flange 304a and the insulator ring 308, and between the insulator ring 308 and the block 302. As shown in Fig. 5, the coil portion 104e passes through another aperture 302b of the block 302. The structure for coupling the coil portion 104e to the block 302 is, in the illustrated embodiment, substantially the same as the structure described above for the coil portion 104d. When the feedthrough shown in Fig. 4 is installed in the deposition apparatus 100, the adaptor plate 302 may be fastened to the chamber wall 114 by suitable fasteners such as bolts 318. Vacuum seal 314a may be provided between the plate 302 and the chamber wall ^'114. The plate 302 will typically be at the same voltage as the chamber wall 114, which is typically grounded. Referring back to Fig. 4, when the feedthrough assembly is installed in the deposition apparatus 100, the circular sleeve 306 which extends along a portion of the coil 104 passes through an aperture 106a in the shield 106 (also shown in Fig. 1). The aperture 106a of the shield has an inner diameter which is greater than the outer diameter of the circular sleeve 306 by a predetermined amount. As explained above, the shield 106 is typically electrically coupled to the chamber wall 114, which is typically grounded; while the flange 306 is electrically coupled to the RF coil 140, which is RF-hot during operation. Thus, a darkspace gap 316 may be provided between the flange 306 and the inner surface of the aperture 106a of the shield 106. As shown in Fig. 4, the darkspace gap 316 is positioned between the interior plasma generation area 108 and the insulating ring 308 such that the insulator ring 308 is not otherwise exposed to the plasma area 108. Thus, the darkspace gap protects the insulating ring 308 from the plasma ions and the sputtered deposition material that are present in the plasma generation area 108. The feedthrough assembly 112 may be installed in the chamber 100 by passing the feedthrough assembly through an aperture in the wall 114 of the chamber and fastening the plate 302 onto the wall using, for example, bolts 318 as shown in Figs. 4 and 5. A vacuum seal may be provided between the plate 302 and the wall 114. The shield 106 may be formed in one or more sections in which a lower section 106b which includes the lower portion of the aperture 106a, is installed before the coil 104. After the coil 104 is installed, the remaining sections 106c of the shield 106 may be installed to complete the shield aperture 106a about the sleeve 306. The feedthroughs 112 can fully support the coil so that no other connection or support need be provided in the interior of the chamber. In the feedthrough assembly of the second embodiment shown in Fig. 4, the darkspace gap is defined between a grounded member (the shield 106) and an RF-hot sleeve 306 disposed around the coil 104. By comparison, in the embodiment of Fig. 2 the darkspace gap is formed between a grounded member (the block member 202) and the coil itself. As a consequence, a degree of precision may be required in machining the coil so that the coil portion passing through the aperture 202a is correctly positioned with respect to the aperture to form the darkspace gap 212 therebetween. In addition, due to the size and weight of the coil, the coil may tend to wobble inside the aperture, so that the size of the annular darkspace formed between the aperture 212 and the coil may vary along the periphery of the aperture. In the design of the second embodiment of Fig. 4, on the other hand, the sleeve 306 tends to be more rigid than the coil portion. Consequently, the darkspace gap 316 formed between the sleeve 306 and the inner surface of the aperture 106a in the shield 106 may be more rigidly defined. Another advantage of the embodiment of Fig. 4 is that the entire feedthrough assembly with the exception of the sleeve, is protected by the shield 106 and the darkspace gap 316. Alternatively, a grounded member other than the shield 106, such as a portion of the plate 302 or a portion of the chamber wall, may also be used to form a darkspace gap with the sleeve 306. Two embodiments of the present invention have been described in detail. It should be recognized, however, that the detailed structures of the illustrated embodiments may be varied without deviating from the spirit of the inventions. The preferred coil embodiments discussed herein can be used to deposit many different types of metals, such as Al, Ti, Ta, Cu, etc., and metal nitrates, such as TiN, TaN, etc. If one or more additional coils are used with the tubular coil, then the tubular coil and additional coils may be comprised of the same material or, alternatively, different materials. Still further, additional tubular cooling coils as well as sputtering coils may be added to the embodiments discussed herein. In addition to the circular shape depicted herein, it is anticipated that the central portion of the coil within the chamber may have a variety of shapes. For example, the coil may have flat spiral or frusto-conical multi-turn shapes as well as described in copending application Serial No. 08/857,719, entitled "Central Coil Design for Ionized Metal Plasma Deposition," filed May 16, 1997 (Attorney Docket 1752/PVD/DV), for example. Still further, a one-piece tubular coil in accordance with the present invention may have sputtering surfaces or deposition blocking surfaces attached or formed on the exterior of the tubular coil as described in copending application Serial No. 08/857,944, entitled "Hybrid Coil Design for Ionized Deposition," filed May 16, 1997 (Attorney Docket 1871/PVD/DV), for example. The appropriate RF generators and matching circuits are components well known to those skilled in the art. For example, an RF generator such as the ENI Genesis series which has the capability to "frequency hunt" for the best frequency match with the matching circuit and antenna is suitable. The frequency of the generator for generating the RF power to the coil 104 is preferably 2 MHz but it is anticipated that the range can vary. For example, 1 MHz to 28 MHz may be satisfactory. An RF power setting of 1.5 kW is preferred but a range of 1.5-5 kW is satisfactory. In addition, a DC power setting for biasing the target 128 of 8-12 kW is preferred but a range of 2-24 kW and a pedestal 126 bias voltage of -30 volts DC are satisfactory. The above parameters may vary depending upon the particular application. A variety of sputtering gases may be utilized to generate the plasma including Ar, and a variety of reactive gases such as NF₃, CF₄ H₂, 0₂ and many others may be used. Various sputtering gas pressures are suitable including pressures of 0.1 - 50 mTorr. For ionized PVD, a pressure between 10 and 100 mTorr such as 30 mTorr often provides better ionization of sputtered material. It will, of course, be understood that modifications of the present invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study others being matters of routine mechanical and electronic design. Other embodiments are also possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. An RF feedthrough for a plasma chamber having a wall and an interior plasma generation area, comprising: an elongated conductor member having a surface for carrying an RF signal; an insulator member coupled to said conductor member; and a block member coupled to said insulator member and electrically insulated from said conductor member, said block member having a surface spaced from said surface of said conductor member by a distance less than a predetermined maximum distance to define a darkspace gap therebetween.

2. The RF feedthrough of claim 1 , wherein said insulator member is mounted to said conductor member and wherein said block member is mounted to said insulator member.

3. The RF feedthrough of claim 1 , wherein said insulator member is carried around said conductor member.

4. The RF feedthrough of claim 3, wherein said surface of said block member defines an annular-shaped darkspace gap around said surface of said conductor member.

5. The RF feedthrough of claim 1 , wherein said block member is adapted to be fastened to said wall of said chamber such that said darkspace gap is located between said plasma generation area of said chamber and said insulator member.

6. The RF feedthrough of claim 1 , wherein said block member is adapted to be electrically coupled to said wall.

7. The RF feedthrough of claim 1 , further comprising a pressure tight seal between said block member and said insulating member.

8. The RF feedthrough of claim 4, further comprising a first sleeve disposed around said conductor member between said insulator member and said block member, said first sleeve having a first and a second end, said first end being sealingly joined to said insulating member and said second end being sealingly joined to said block member.

9. The RF feedthrough of claim 8, further comprising a second sleeve disposed around said conductor member, said second sleeve having a first and a second end, said first end being sealingly joined to said insulating member and said second end being joined to said conductor member, whereby said insulator member is carried by said conductor in a pressure-tight manner.

10. The RF feedthrough of claim 1 wherein said insulator member is made of ceramic.

11. The RF feedthrough of claim 1 wherein said block member is made of stainless steel.

12. The RF feedthrough of claim 9 wherein said first and second sleeves are made of covar.

13. The RF feedthrough of claim 1 wherein said elongated conductor defines a coolant-carrying channel within said conductor member, and wherein said conductor has a first end adapted to be coupled to a coolant supply.

14. An RF feedthrough for a plasma chamber having a wall and an interior plasma generation area, comprising: an elongated conductor member having a surface for carrying an RF signal; an insulator member carried by said conductor member; and a block member carried by said insulator member and electrically insulated from said conductor member, said block member being fastened to said wall, said block member having a surface spaced from said surface of said conductor member by a distance less than a predetermined maximum distance to define a darkspace gap therebetween; wherein said darkspace gap is positioned between said insulator member and said plasma generation area.

15. The RF feedthrough of claim 14, wherein said insulating member has a tubular cross-section and is carried around said conductor member.

16. The RF feedthrough of claim 15, wherein said surface of said block member defines an aperture in said block around a portion of said conductor member.

17. The RF feedthrough of claim 14, wherein said block member is electrically coupled to said wall.

18. An RF feedthrough for a deposition chamber having a wall and an interior plasma generation area, comprising: an elongated conductor member for carrying an RF signal; a first insulating member positioned between said conductor member and said wall, to electrically insulate said conductor from said wall; an extended member carried by and electrically coupled to said conductor member, said extended member having a surface; and an electrically grounded member having a surface spaced from said surface of said extended member by a distance less than a predetermined maximum distance to define a darkspace gap therebetween, wherein said darkspace gap is positioned between said insulating member and said plasma generation area.

19. The RF feedthrough of claim 18, wherein said insulating assembly is disposed around said conductor member.

20. The RF feedthrough of claim 18, wherein said extended member is a sleeve disposed around said conductor member and wherein said surface of said electrically grounded member defines an aperture around said sleeve.

21. The RF feedthrough of claim 20, wherein said electrically grounded member is a shield substantially enclosing the interior plasma generation area.

22. The feedthrough of claim 31 further comprising an adapter member adapted to be coupled to said chamber wall.

23. The feedthrough of claim 18 wherein said extended member has a flange, said first insulating member being disposed between said flange and said adapter member.

24. The feedthrough of claim 22 wherein said first insulating member has an aperture to receive said extended member and a first shoulder to engage said flange and a second shoulder to engage said adapter member.

25. The feedthrough of claim 24 further comprising a fastener to compress said first insulating member between said flange of said extended member and adapter member.

26. The feedthrough of claim 25 wherein said fastener comprises a nut and threads carried by said extended member and positioned to threadably receive said nut.

27. The feedthrough of claim 22 further comprising a second insulating member which is sleeve-shaped and positioned around said adapter member and between said adapter member and said extended member.

28. The feedthrough of claim 26 further comprising a second insulating member which is sleeve-shaped and positioned around said adapter member and between said adapter member and said extended member, said second insulating member having a shoulder positioned to be engaged by said nut received by said extended member.

29. The feedthrough of claim 28 wherein said second insulating member has a second shoulder positioned to engage said adapter member wherein said adapter member is compressed between said first and second insulating members.

30. The RF feedthrough of claim 18 wherein said elongated conductor member defines a coolant-carrying channel within said conductor member, and wherein said conductor has a first end adapted to be coupled to a coolant supply.

31. A semiconductor fabrication system, comprising: a low pressure chamber having a wall which defines an exterior of said chamber and an interior of said chamber, said chamber interior being adapted to be maintained at a pressure substantially below the pressure of said chamber exterior; an adapter plate coupled to said chamber wall and defining an aperture; a shield wall positioned within said chamber and having a surface which defines an aperture an RF coil adapted to generate a plasma in said chamber interior, said RF coil including a coil portion positioned in said chamber interior and a feedthrough portion positioned in said adapter plate aperture and said shield wall aperture; an insulating member positioned between said RF coil feedthrough portion and said adapter plate; a sleeve carried by said RF coil feedthrough portion and having a surface spaced from said shield wall surface by a distance less than a predetermined maximum distance to define a darkspace gap therebetween, wherein said darkspace gap is positioned between said insulating member and said plasma generation area.

32. The system of claim 31 further comprising a flange carried by said RF coil feedthrough portion and positioned to engage said insulating member.

33. The system of claim 33 further comprising a second insulating member positioned between said adapter plate and said RF coil feedthrough portion, and a fastener carried by said RF coil feedthrough portion and positioned to compress said adapter plate between said first and second insulating members.

34. A method of providing RF current and a coolant through a feedthrough in a semiconductor processing chamber having a plasma, comprising: insulating a coolant filled RF coil from a wall of said chamber using an insulating member positioned between said chamber wall and said RF coil; and retarding formation of a plasma in a darkspace gap positioned adjacent to said insulating member.

35. The method of claim 34 wherein said darkspace gap is defined by a sleeve carried by said RF coil and having a surface spaced from a shield wall surface by a distance less than a predetermined maximum distance to define said darkspace gap therebetween, wherein said darkspace gap is positioned between said insulating member and said plasma generation area.

36. The method of claim 34 wherein said darkspace gap is defined by a block member coupled to said insulator member and electrically insulated from said RF coil, said block member having a surface spaced from a surface of said RF coil by a distance less than a predetermined maximum distance to define said darkspace gap therebetween.