WO2015108548A1

WO2015108548A1 - Electrical contact method between fixed electrode and removable target piece

Info

Publication number: WO2015108548A1
Application number: PCT/US2014/017457
Authority: WO
Inventors: Edward P. Hammond, Iv; Eric Ruhland; Alexander S. Polyak; Tsutomu Tanaka; Christopher T. Lane; James L. L'HEUREUX
Original assignee: Applied Materials, Inc.
Priority date: 2014-01-17
Filing date: 2014-02-20
Publication date: 2015-07-23
Also published as: TW201531588A

Abstract

Embodiments of the present invention relate to a plasma source that includes an electrode and a plurality of target pieces covering an outer side surface of the electrode. The target pieces are electrically coupled to the electrode by one or more springs or spring-like elements. Alternatively, the target pieces may be pushed against the outer surface of the electrode by clamps or brackets. Since the target pieces are not bonded to the electrode, replacing the target pieces becomes more convenient

Description

ELECTRICAL CONTACT METHOD BETWEEN FIXED ELECTRODE AND

REMOVABLE TARGET PIECE

BACKGROUND

Field

[0001] Embodiments of the invention generally relate to processing chambers, and more particularly, to one or more plasma sources in the processing chambers.

Description of the Related Art

[0002] In-line processing tools deposit material on substrates, such as solar cells, in a continuous manner for dozens to hundreds of hours. As a result of continuous deposition, several millimeters of film can accumulate on chamber components, such as a plasma source. The plasma source may include an electrode and target pieces, and because of the brittle nature of the target pieces and the shape of the electrode, the target pieces may be occasionally loosely fit against the electrode. The accumulated deposition material may be a dielectric material and may be formed between the target pieces and the electrode, which causes the target pieces to have poor electrical contact with the electrode. In addition, deposition gases may diffuse into the area between the target pieces and the electrode, and form a dielectric film therein. The poor contact caused by the dielectric film formed between the target pieces and the electrode can lead to localized arcing and melting of the target pieces, which can eventually expose the electrode to plasma erosion.

[0003] Therefore, there is a need for an improved plasma source that is used to deposit dielectric materials.

SUMMARY

[0004] Embodiments of the present invention relate to a plasma source that includes an electrode and a plurality of target pieces covering an outer side surface of the electrode. The target pieces are electrically coupled to the electrode by one or more springs or spring-like elements. Alternatively, the target pieces may be pushed against the outer surface of the electrode by clamps or brackets. Since the target pieces are not bonded to the electrode, replacing the target pieces becomes more convenient. [0005] In one embodiment, a plasma source is disclosed. The plasma source comprises an electrode, where the electrode is a closed loop having an outer side surface, and a plurality of target pieces covering the outer side surface of the electrode, where one or more springs or spring-like elements electrically couple the target pieces to the electrode.

[0006] In another embodiment, a plasma source is disclosed. The plasma source comprises an electrode, where the electrode is a closed loop having an outer side surface, and a plurality of target pieces, a top clamp disposed over the electrode and the target pieces. The top clamp has a plurality of tabs and each tab is configured to push the target pieces against the outer side surface of the electrode. The plasma source further comprises a bottom clamp, where the electrode and the target pieces are disposed over the bottom clamp.

[0007] In another embodiment, a plasma source is disclosed. The plasma source comprises an electrode, where the electrode is a closed loop having an outer side surface, a plurality of target pieces, a plurality of brackets disposed on the target pieces and a pulling device connecting the plurality of brackets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0009] Figure 1A is a schematic isometric view of a substrate processing system according to one embodiment.

[0010] Figure 1 B is a schematic side cross sectional view of a deposition chamber according to one embodiment.

[0011] Figure 2 is a schematic sectional view of a deposition source, according to one embodiment. [0012] Figures 3A - 3D are cross sectional views of a spring connecting a target piece and an electrode according to one embodiment.

[0013] Figure 3E is a perspective view of a plunger device according to one embodiment.

[0014] Figures 4A - 4B show a spring connecting target pieces to an electrode according to one embodiment.

[0015] Figures 5A - 5D illustrate utilizing clamps to push the target pieces against the electrode according to one embodiment.

[0016] Figures 6A - 6B illustrate utilizing springs to push the target pieces against the electrode according to one embodiment.

[0017] Figure 7 illustrates utilizing a wire to push the target pieces against the electrode according to one embodiment.

[0018] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

[0019] Embodiments of the present invention relate to a plasma source that includes an electrode and a plurality of target pieces covering an outer surface of the electrode. The target pieces are electrically coupled to the electrode by one or more springs.

[0020] Figure 1A is a schematic isometric view of a substrate processing system 100 according to one embodiment. Embodiments of the present invention generally provide a high throughput substrate processing system 100, or in-line processing system, for in-situ processing of a film stack used to form regions of a solar cell device. In one configuration, one or more film stacks formed on each of the substrates 101 contains one or more passivating or dielectric layers that are deposited and further processed within one or more processing chambers 140, 141 , 142 contained within the high throughput substrate processing system 100. The processing chambers 140, 141 , 142 may include, for example, one or more of plasma enhanced chemical vapor deposition (PECVD) chambers, low pressure chemical vapor deposition (LPCVD) chambers, atomic layer deposition (ALD) chambers, plasma enhanced atomic layer deposition chambers (PEALD), physical vapor deposition (PVD) chambers, thermal processing chambers (e.g., RTA or RTO chambers), substrate reorientation chambers (e.g., flipping chambers) and/or other similar processing chambers.

[0021] The high throughput substrate processing system 100 may include one or more deposition chambers, such as process chambers 140, 141 , 142 in which substrates 101 are exposed to one or more gas-phase materials and an RF plasma. In one embodiment, the processing system 100 includes at least one plasma enhanced chemical vapor deposition (PECVD) processing chamber that has been adapted to process a plurality of substrates 101 , such as solar cell substrates, as the substrates 101 pass through the system 100 in a linear direction. In one embodiment, the substrates 101 are simultaneously transferred in a vacuum or inert environment through the high throughput substrate processing system 100 to prevent substrate contamination and improve substrate throughput.

[0022] In one embodiment, the substrate processing system 100 includes a substrate receiving chamber 105, a pre-processing chamber 107, at least one processing chamber maintained at a pressure below that of atmospheric pressure, such as a first processing chamber 140, a second processing chamber 141 , and a third processing chamber 142, at least one transferring chamber, such as transferring chambers 109 and 1 1 1 , a buffer chamber 1 14 and a substrate unload chamber 1 16. The substrate processing system 100 may also include one or more support components 1 10, such as a control unit, user interface, buffer, and the like.

[0023] Figure 1 B is a schematic side cross sectional view of a processing chamber 140, according to one embodiment of the invention. The processing chamber 140 comprises one or more deposition sources, such as deposition sources 160A-160D, gas sources 128 and 129, one or more power sources 131 (four are shown), chamber walls 102 that at least partially enclose a portion of the chamber volume 106, and at least a portion of the conveyor transfer system 1 15. Deposition sources 160A-160D are adapted to form a layer on the surface of the substrates 101 as the substrates 101 pass under and adjacent to the deposition sources 160A-160D. The walls 102 generally comprise a material that can structurally support the loads applied by the environment 143, which is external to the chamber volume 106, when it is heated to a desirable temperature and pumped to a vacuum pressure by a vacuum pump 145. The walls 102 generally comprise a material such as aluminum, an aluminum alloy, or stainless steel.

[0024] In one configuration, the portion of the conveyor transfer system 1 15 comprises a conveyor 121 that is adapted to support, guide, and move the substrates 101 through the processing chamber 140 by use of one or more actuators (not shown), for example, a stepper motor or servo motor. In one configuration, the conveyor 121 comprises two or more rollers 1 12 (four are shown) and a belt 113 that are configured to support and move the substrates 101 in a positive X-direction during processing. However, it is to be noted that processing in a reverse configuration is also contemplated.

[0025] In one embodiment of the processing chamber 140, each of the deposition sources 160A-160D is coupled to at least one gas source, such as gas sources 128 and 129, that is configured to deliver one or more process gases to a processing region 125 formed with the chamber volume 106, and below each of the deposition sources 160A-160D and over the surface of a substrate 101 disposed there under. Gas lines 148 and 149 facilitate transfer of gases from the gas sources 128, 129 to the deposition sources 160A-160D.

[0026] The deposition sources 160A-160D will generally include at least one gas delivery element, such as a first gas delivery element 181 and second gas delivery element 182, which are each configured to direct the process gases to the processing region 125. The first gas delivery element 181 includes a fluid plenum 161 that is configured to receive the process gas from a gas source 128 and deliver the received gas to the processing region 125 through one or more openings 163 formed therein. Similarly, the second gas delivery element 182 comprises a fluid plenum 162 that is configured to receive the process gas from a gas source 129 and deliver the received gas to the processing region 125 through one or more openings 164 formed therein. The gas sources 128 and 129 are generally configured to provide one or more precursor gases and/or carrier gases that are used to deposit a layer on the surface of the substrates 101 via deposition process, such as a PECVD process.

[0027] In one example of a process performed in the process chamber 140, at least one of the gas sources 128 and 129 is configured to deliver a silicon-containing gas to the deposition sources 160A-160D. The silicon-containing gas may be selected from a group consisting of silane, disilane, chlorosilane, dichlorosilane, trichlorosilane, dibromosilane, trimethylsilane, tetramethylsilane, tridimethylaminosilane (TriDMAS), tetraethoxysilane (TEOS), triethoxyfluorosilane (TEFS), silicon tetrachloride, silicon tetrabromide, 1 ,3,5,7- tetramethylcyclotetrasiloxane (TMCTS), dimethyldiethoxy silane (DMDE), octomethylcyclotetrasiloxane (OMCTS), methyldiethoxysilane (MDEOS), bis(tertiary- butylamino)silane (BTBAS), or combinations thereof. The oxygen-containing gas may be selected from a group consisting of oxygen (O2), nitrous oxide (N₂0), ozone (O3), and combinations thereof. In one embodiment, the silicon-containing gas is silane and the oxygen-containing gas is 0₂. The silicon-containing gas and the oxygen-containing gas may form a dielectric layer on the surface of the substrates 101 .

[0028] In another process sequence, such as processing performed in a first processing chamber 140, at least one of the gas sources 128 and 129 is configured to deliver a silicon-containing gas and nitrogen-containing gas to a deposition source 160A-160D. The nitrogen-containing gas may be, for example, diatomic nitrogen, nitrous oxide, or ammonia.

[0029] It is contemplated that in some embodiments, the gas sources 128 and 129 may be adapted to provide multiple precursor gases, either independently or simultaneously. In such an embodiment, the gases sources 128, 129 may be gas cabinets housing multiple precursor and/or carrier gas sources or reactive gases.

[0030] It is contemplated that any of deposition sources 160A-160D may be configured to deliver other precursor gases in addition to those listed above, including an aluminum-containing gas. The deposition sources 160A-160D, and the precursor gases provided thereto, may be used to facilitate the formation of a desired passivation layer stack deposition. It is also contemplated that more gas sources may be added to the chamber 140 to accommodate more types of gas delivery.

[0031] It is contemplated that each of the deposition sources 160A-160D may be adapted to deposit different film materials on the substrates 101 . For example, the deposition sources 160A-160D may be adapted to deposition one or more films of silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, and the like.

[0032] Figure 2 is a schematic sectional view of a deposition source according to one embodiment. As shown in Figure 2, the first deposition source 160A includes the gas delivery element 181 , such as a nozzle, for introducing processing gas into the processing region 125. Gas delivery elements 182 (two are shown) are disposed adjacent to the gas delivery element 181 , and are adapted to deliver a second process gas to the processing region 125. Each of the gas delivery elements 181 , 182 are coupled to a gas source, such as the gas source 128 or 129. For example, the gas delivery element 181 may be coupled to the gas source 128, and the gas delivery element 182 may be coupled to the gas source 129.

[0033] The deposition source 160A also includes a housing 208 in which a plasma source 209 is enclosed. The plasma source 209 may include an electrode 210 and a target 283. The electrode 210 may be a closed loop having an inner side surface 212 and an outer side surface 214. In one embodiment, the top surface of the electrode 210 has a racetrack shape (having the long axis into and out of the paper). The electrode 210 may be made of any suitable material such as iron. The electrode 210 may be coupled to a common power supply 131 (shown in Figure 1 B). In one embodiment, the power supply 131 is an AC power supply. The outer surface 214 of the electrode 210 may be covered by the target 283 that protects the electrode 210 from plasma erosion during deposition processes. To accommodate the shape of the electrode 210 as well as thermal expansion, the target 283 may be a close-fitting collection of individual pieces. The target pieces 283 may be made of crystalline silicon. The target pieces 283 are a sacrificial material and may contribute to the formation of material on the substrate 101 via sputtering. In one example, the material formed on the substrate 101 includes less than 1 percent of material originating from the target pieces 283. The target pieces 283 may also include materials other than silicon. In one example, the target pieces 283 may share a common element with a precursor gas. The target pieces 283 may be secured using one or more tabs 216, and electrical insulators 286a, 286b may be disposed at upper and lower end of the target pieces 283. The electrical insulators 286a, 286b may also facilitate electrical isolation of the electrode 210. One or more clamps (described in detail below) may be disposed between the electrical insulators 286a, 286b and the target pieces 283 to push the target pieces 283 against the electrode 210.

[0034] A cooling block 284 is also disposed in the housing 208 and includes cooling passages 219a formed therein to facilitate cooling of deposition source components. A cooling jacket 285 having cooling passages 219b formed therein may also be disposed within the housing 208 to further enhance cooling. The gas delivery elements 182 include cavity portions 222 that are bound by a shield 223. Magnets 224, 225, 226 may be disposed adjacent the shield assembly 223 and the electrode 210. The electromagnetic field between the magnets 225, 226 facilitates plasma formation within the cavity 222. The electromagnetic field between the magnets 224, 226 helps shape the plasma in the cavity 222. The magnets 226 may be enclosed or protected by a pole cover 287.

[0035] In one embodiment, power supply 131 is an alternating current power supply with a frequency range between 20 kHz to 500 kHz, such as 40 kHz. During operation, reactive and/or inert gases are supplied from a gas source, such as gas source 129, and introduced to the processing region 125 through the cavity portions 222. Simultaneously, a second gas is introduced to the processing region 125 through the gas delivery element 181 . The magnets 224 and magnetic shunts 226 facilitate formation of plasma from process gases located in the processing region 125, thereby inducing deposition of material on a substrate located within the processing region 125.

[0036] To avoid chipping or fracturing the target pieces 283 and to accommodate thermal expansion, target pieces 283 may be loosely fit against each other and against the electrode 210. Processing gases may diffuse into the gap between the target pieces 283 to form a dielectric film in the gap. In addition, dielectric particles may accumulate within the gap. The presence of the dielectric material between the electrode 210 and the target pieces 283 can cause poor electrical contact and lead to localized arcing and melting of the target pieces 283. Figures 3A - 3D and 4A - 4B illustrate designs that can maintain electrical contact between the electrode 210 and the target pieces 283 while not unduly stressing the target pieces 283.

[0037] Figures 3A - 3D are cross sectional views of a spring 304 connecting a target piece 283 and the electrode 210 according to one embodiment. As shown in Figure 3A, a cavity 302 is formed on the outer surface 214 of the electrode 210, and there are may be a plurality of cavities surrounding the electrode 210. Each cavity 302 may include a spring 304 that provides electrical contact between the target piece 283 and the electrode 210. The spring 304 may be made of an electrical conductive material that can operate under high temperature, such as stainless steel, INCONEL®, tungsten, tantalum or titanium. In one embodiment, the electrode 210 has a length of about 400 mm and there are 44 springs 304 disposed in the outer surface 214 of the electrode 210. One end of the spring 304 may be contacting the electrode 210 by a securing device 305 and the other end of the spring may be contacting the non-plasma facing side of the target piece 283 by a force exerted by the spring 304. The springs 304 are not bonded to the electrode 210, allowing easy replacement of the springs 304 should one become damaged or defective after extended use. The spring 304 at its natural state may have a length that's greater than the distance "D", thus, the target piece 283 exerts a compressive force on the spring 304, and the force exerted by the spring 304 provides constant contact with the target piece 283. The springs 304 are not fixed or fastened to the target pieces 283, which provide a convenient way to replace the target pieces 283. A gap 310 may be formed between the target piece 283 and the outer surface 214 of the electrode 210, and the gap 310 ranges from about 0 mm to about 1 .5 mm.

[0038] The securing device 305 may include a screw 306 and a washer 308, as shown in Figure 3A. The screw 306 is screwed into the electrode 210 and one end of the spring 304 is wrapped around the screw 306 and secured by a washer 308. The washer 308 helps holding the spring 304 in position since in the implementation the spring 304 could easily be pulled out of position by gravity if the target piece 283 was not holding the spring 304 in place. The securing device 305 may be made of an electrical conductive material and may be made of the same material as the spring 304. In one embodiment, both the spring 304 and the securing device 305 are made of stainless steel. In case the end of the spring 304 is not contacting the electrode 210, the securing device 305 serves as an electrical contact between the spring 304 and the electrode 210.

[0039] In one embodiment, the securing device 305 may be a set screw 312, as shown in Figure 3B. The set screw 312 may be drilled into the electrode 210 and one end of the spring is wrapped around the portion of the set screw 312 that is not inside the electrode 210. Because the spring 304 is under compressive force, the end of the spring 304 would not be pulled out of the set screw 312. In one embodiment, the set screw 312 is made of stainless steel.

[0040] Figure 3C shows that one end of the spring 304 is directly contacting the electrode 210, and the securing device 305 is a press fit material 314 that holds the spring 304 in place by friction. The press fit material 314 may be made of any suitable material, such as stainless steel. Figure 3D shows that the securing device 305 includes filling material 316 and a plunger device 318 threaded into the filling material 316. As shown in Figure 3E, the plunger device 318 may have a threaded body 320 encapsulating a compression spring 322. The threaded body 320 has a first end 326 that is threaded into the filling material 316 and a second end 328 opposite the first end 326. A plunger 324 may be disposed at the second end 328, and a portion of the plunger 324 may be disposed in the threaded body 320. As the target piece 283 is placed near or adjacent to the threaded body 320, the target piece 283 pushes the plunger 324 into the threaded body 320, exerting a compressive force on the spring 322. The spring 322 is also exerting a force pushing the plunger 324, so the plunger 324 is in constant contact with the target piece 283. The filling material 316, the threaded body 320, the spring 322 and the plunger 324 may be all made of an electrical conductive material such as stainless steel. The threaded body 320 provides thermal isolation of the spring 322 from the target piece 283, which may be at an elevated temperature during operation.

[0041] Figures 3A - 3E illustrate designs relying on the axial force of a plurality of springs to maintain electrical contact between the target pieces and the electrode. Figures 4A - 4B illustrate a design that relies on the radial compression force of one spring to maintain electrical contact between the target pieces and the electrode. Figure 4A is a cross sectional view of the electrode 210 and the target pieces 283. A continuous trench 402 may be formed in the outer surface 214 of the electrode 210. A single spring 404 may be placed in the trench 402. Instead having one axial end contacting the electrode 210 and the other axial end contacting the target piece 283, the radial points (i.e., one or more points on each coil) of the spring 404 may be in contact with the electrode 210, and other radial points of the spring 404 may be in contact with the target piece 283. The radial compression force of the spring 404, as indicated by "F" in Figure 4A, helps maintaining electrical contact between the target pieces 283 and the electrode 210. Figure 4B is a plan view of the electrode 210 and the spring 404. As shown in Figure 4B, the spring 404 circumscribes the outer surface 214 of the electrode 210, and the electrode 210 has a racetrack shape.

[0042] Conventionally, the target pieces may be bonded or fixed to the electrode, which makes replacing target pieces more difficult. It would be beneficial to have a plasma source that has the target pieces in contact with the electrode, yet the target pieces are not bonded or fixed to the electrode. Figures 5A - 5D illustrate utilizing clamps 502, 504 to push target pieces 501 against the electrode 210. Figure 5A is a cross sectional view of the target pieces 501 being pushed against the outer surface 214 of the electrode 210 by a top clamp 502 and a bottom clamp 504. The clamps

502, 504 may be made of titanium. Each target piece 501 may have two outer edges 510 that are chamfered. The top clamp 502 may include a plurality of tabs

503, and each tab 503 may have a chamfer 512 that matches the chamfer of the top outer edge 510. As the tabs 503 are driven down by a force, the chamfer 512 pushes the target piece 501 downward and inward against the outer surface 214 of the electrode 210. The bottom clamp 504 may also have a chamfer 513 that matches the chamfer of the bottom outer edge 510, and as the target piece 501 is pushed downward, the chamfer 513 helps pushing the target piece 501 inward against the outer surface 214 of the electrode 210. Shields 506, 508 may cover the top clamp 502 and bottom clamp 504, respectively, to reduce ion bombardment of the clamps 502, 504 and to protect the clamps 502, 504 from subsequent heating.

[0043] The force that is driving the tabs 503 toward the target pieces 501 may be generated by screws. Figure 5B is a top view of the top clamp 502 according to one embodiment. The top clamp 502 may have the plurality of tabs 503A - 503N. As shown in Figure 5B, tabs 503A - 503E are disposed along one straight side of the clamp 502 and tabs 503H - 503M are disposed along another straight side of the clamp 502. Tab 503G is disposed at one round end and tab 503N is disposed at the other round end. In one embodiment, tabs 503A and 503B secure a first straight target piece, tabs 503C and 503D secure a second straight target piece, tabs 503E and 503F secure a third straight target piece, tabs 503H and 5031 secure a fourth straight target piece, tabs 503J and 503K secure a fifth straight target piece, tabs 503L and 503M secure a sixth straight target piece, tab 503G secure a first curved target piece and tab 503N secure a second curved target piece. Other numbers and configurations of the tabs 503 and target pieces 501 may be utilized. As shown in Figure 5B, each tab 503 may have a screw 518 to couple the clamp 502 to the electrode 210 and the screw 518 may be tightened to generate the force that drives the tab 503 toward the target piece 501 . The top clamp 502 may include holes 520 for cooling channels to pass through.

[0044] Figure 5C is a top view of the top clamp 502 according to another embodiment. The top clamp 502 has a plurality of tabs 522, and each tab 522 does not include a screw for generating the force to drive the tab 522 toward the target piece 501 . Instead, the screws 524 are disposed outside of the tabs 522 to couple the clamp 502 to the electrode 210. As shown in Figure 5D, a block 530 may be disposed on the chamfer 523 of each tab 522. The block 530 may be fixed to the chamfer 523 of the tab 522, and as the clamp 502 is secured to the electrode 210, the block 530 provides an interference fit with the target pieces 501 and some measure of preload to drive the target pieces 501 against the electrode 210. In other words, the blocks 530 and the target pieces 501 exert mutual and opposite forces onto each other, causing the target pieces 501 to be pushed against the electrode 210 at one end, and the tabs 522 to flex away from the target pieces 501 at the other end. Shields (not shown) may cover the top clamp 502 and bottom clamp 504 to reduce ion bombardment of the clamps 502, 504 and to protect the clamps 502, 504 from subsequent heating.

[0045] Figures 6A - 6B illustrate utilizing a plurality of brackets 602 and a pulling device 603 to push the target pieces 283 against the electrode 210 according to one embodiment. The target pieces 283 may have substantially right-angled outer edges and each bracket 602 may be disposed on a target piece 283 so the two inside surfaces 604, 606 of the bracket 602 are in contact with a top surface 608 and a bottom surface 610 of the target piece 283, respectively. The brackets 602 may be disposed evenly spaced apart on the target pieces 283, as shown in Figure 6B, or the brackets 602 may not be disposed evenly spaced apart on the target pieces 283. The inside surface 604 of the bracket 602 may be disposed on the target piece 283, as shown in Figure 6A, or disposed on both the target piece 283 and the electrode 210, as shown in Figure 6B. A pair of brackets 602 may be aligned on opposite sides of the electrode 210, and the pulling device 203 coupling the pair of brackets 602 exerts a force to pull on the brackets, which in turn pushes the target pieces 283 against the electrode 210. The pulling device 603 may be a plurality of springs. As shown in Figure 6B, 7 pairs of brackets 602 are disposed on the target pieces 283 and the electrode 210, and 7 elongated springs are pulling on each pair of brackets 602. The brackets 602 and the springs 603 may be made of titanium.

[0046] Figure 7 illustrates utilizing the plurality of brackets 602 and pulling device 702 to push the target pieces 283 against the electrode 210 according to another embodiment. Instead of using a plurality of springs 603, a wire 702 is used as the pulling device to pull on all brackets 602. The wire 702 is connected to the brackets 602 in a shoelace configuration, as shown in Figure 7, so as the wire 702 is tightened, all of the brackets 602 are pulled inwardly, causing the target pieces 283 to be pushed against the electrode 210. The brackets 602 and the wire 702 may be made of titanium.

[0047] In summary, one or more springs or clamps are utilized to help maintaining electrical contact between a plurality of target pieces and an electrode. Even if a dielectric film is formed in the gap between the target pieces and the electrode, electrical contact is maintained by the one or more springs. The clamps are utilized to push the target pieces against the electrode so no gap is formed between the target pieces and the electrode.

[0048] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

Claims:

1 . A plasma source, comprising:

an electrode, wherein the electrode is a closed loop having an outer side surface; and

a plurality of target pieces covering the outer side surface of the electrode, wherein one or more springs electrically couple the target pieces to the electrode.

2. The plasma source of claim 1 , further comprising a plurality of cavities formed in the outer surface of the electrode, wherein one spring of the one or more springs is disposed in each cavity.

3. The plasma source of claim 2, wherein the spring is secured to the electrode by a securing device.

4. The plasma source of claim 3, wherein the securing device comprises an electrical conductive material.

5. The plasma source of claim 3, wherein the securing device further comprises a filling material, wherein the spring is encapsulated by an electrically conductive material and the encapsulated spring is threaded into the filling material.

6. A plasma source, comprising:

an electrode, wherein the electrode is a closed loop having an outer side surface;

a plurality of target pieces;

a top clamp disposed over the electrode and the target pieces, wherein the top clamp has a plurality of tabs and each tab is configured to push the target pieces against the outer side surface of the electrode; and

a bottom clamp, wherein the electrode and the target pieces are disposed over the bottom clamp.

7. The plasma source of claim 6, wherein the top clamp and the bottom clamp are made of titanium.

8. The plasma source of claim 6, wherein each target piece has chamfered outer edges and each tab has a matching chamfer.

9. The plasma source of claim 8, wherein each tab includes a screw, and the chamfer of each tab is in contact with a top chamfered outer edge of each target piece.

10. The plasma source of claim 8, wherein each tab includes a block disposed on the chamfer and each block is in contact with a top chambered outer edge of each target piece.

1 1 . A plasma source, comprising:

a plurality of target pieces;

a plurality of brackets disposed on the target pieces; and

a pulling device connecting the plurality of brackets.

12. The plasma source of claim 1 1 , wherein the plurality of brackets are disposed on the target pieces and on the electrode.

13. The plasma source of claim 11 , wherein the pulling device comprises a plurality of springs.

14. The plasma source of claim 11 , wherein the pulling device comprises a wire connecting the brackets in a shoelace configuration.

15. The plasma source of claim 1 1 , wherein the pulling device comprises titanium.