Tuned focus ring for uniformity improvement of plasma-assisted processes

Abstract

Described herein is a plasma processing apparatus that comprises a tuned focus ring. The tuned focus ring comprises an inner sidewall having an upper portion and a lower portion extending below the upper portion, and a ledge extending from the inner sidewall between the upper portion and the lower portion. The ledge extends around a circumference of the lower portion of the inner sidewall. The upper portion of the inner sidewall extends a first height over the ledge along a first annular segment of the tuned focus ring. The upper portion extends a second height over the ledge along a second annular segment of the tuned focus ring. The first height is greater than the second height.

Description

TUNED FOCUS RING FOR UNIFORMITY IMPROVEMENT OF PLASMA- ASSISTED PROCESSESCLAIM FOR PRIORITY

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 664,572, filed on June 26, 2024, titled “TUNED FOCUS RING FOR UNIFORMITY IMPROVEMENT OF PL ASMA- ASSISTED PROCESSES,” and which is incorporated by reference in entirety.BACKGROUND

[0002] Substrate processing for etch and deposition form a backbone of the semiconductor industry. While a variety of processing techniques may be utilized, virtually all processes utilize a showerhead to deliver process gases to a substrate awaiting process. A showerhead can be used to distribute gas over an entire substrate. In capacitively-coupled plasma deposition processes, a showerhead metallic body may provide a source or sink electrode opposite plasma electrodes within the pedestal supporting a semiconductor substrate. A plasma may be ignited and confined within the gap between substrate and showerhead. The uniformity of films deposited by a plasma deposition process such as a plasma-enhanced chemical vapor deposition (PECVD) may be influenced by the uniformity of the plasma. Ion densities may be skewed by non-uniformities of gas distribution, for example, or by electric field asymmetries. The latter may result from asymmetric arrangement of metallic objects within a process chamber in the vicinity of the plasma generation area, specifically near the showerhead and / or pedestal. Resulting asymmetry in the plasma can be mirrored by asymmetries in the deposited film. An example of such an asymmetry is a non-uniform film thickness or gradually increasing or decreasing thickness (e.g., tilting) along a diameter of the film.BRIEF DESCRIPTION OF DRAWINGS

[0003] Material described herein is illustrated by way of example and not by way of limitation in accompanying figures. For simplicity and clarity of illustration, elements illustrated in figures are not necessarily drawn to scale. For example, dimensions of some elements may be exaggerated relative to other elements for clarity. Also, various physical features may be represented in their simplified “ideal” forms and geometries for clarity of discussion, but it is nevertheless to be understood that practical implementations mayapproximate illustrated ideals. For example, smooth surfaces and square intersections may be drawn in disregard of finite roughness, comer-rounding, and imperfect angular intersections characteristic of structures formed by nanofabrication techniques. Further, where considered appropriate, reference labels have been repeated among figures to indicate corresponding or analogous elements.

[0004] Fig. 1 illustrates a profile interior view of a plasma chamber, in accordance with at least one implementation.

[0005] Fig. 2A illustrates an enlarged cross-sectional view of a wafer and a focus ring supported on a pedestal platen, in accordance with at least one implementation.

[0006] Fig. 2B illustrates a perspective view of the focus ring shown in Fig. 2A, in accordance with at least one implementation.

[0007] Fig. 3A illustrates a perspective view of a tuned focus ring, in accordance with at least one implementation.

[0008] Fig. 3B illustrates a profile view of the tuned focus ring shown in Fig. 3A, in accordance with at least one implementation.

[0009] Fig. 4A illustrates a perspective view of a tuned focus ring having a tapered thickness, in accordance with at least one implementation.

[0010] Fig. 4B illustrates a cross-sectional view of the tuned focus ring shown in Fig. 4A, in accordance with at least one implementation.

[0011] Fig. 4C illustrates a cross-sectional view of the tuned focus ring shown in Fig. 4B, having a non-linear taper, in accordance with at least one implementation.

[0012] Fig. 4D illustrates a cross-sectional view of the tuned focus ring shown in Fig. 4B, having a series of discontinuous steps, in accordance with at least one implementation.

[0013] Fig. 5 illustrates a perspective view of a plasma process system comprising a showerhead and a pedestal disposed below the showerhead, in accordance with at least one implementation.

[0014] Figs. 6A - 6D respectively illustrate a contrast in PECVD film NU% performance between a typical focus ring and tuned focus rings described herein for the same plasma asymmetry, in accordance with some implementations.

[0015] Fig. 7 illustrates a method flowchart summarizing a method for using a locus ring, in accordance with at least one implementation.DETAILED DESCRIPTION

[0016] One or more apparatus and methods are described to improve uniformity of plasma-deposited films or plasma-etched substrates by introducing a tuned focus ring having a non-uniform thickness profile to compensate for plasma asymmetries. Focus rings may also be known as carrier rings in the art, whereby a carrier ring is configured to cradle a semiconductor wafer substrate during transfer between workstations in process chambers having multiple process workstations. The designation of “focus ring” may stem from the fact that the ring accompanies a wafer substrate on an electrostatic chuck, or wafer chuck not having electrostatic clamping capability, on a pedestal during a plasma deposition or etch process at a workstation within a plasma chamber. An inner sidewall of the focus ring surrounds the edge of the wafer and may modify the local plasma in the vicinity of the wafer edge by altering the electric field distribution or shielding the wafer edge from sputtering by energetic ions.

[0017] The focus ring may draw in or direct (e.g., focus or concentrate) or deflect electric field lines within the plasma to or from the wafer edge. A focus ring may comprise a composition and / or geometry that may attract or repel charged particles from the plasma to concentrate over the wafer, particularly at the edge region, where the local electric field distribution, plasma temperature, and reactive species (e.g., ions and neutral radicals) density distributions may diverge from the bulk of the plasma. This divergence may influence deposition or etch rate at the wafer edge in relation to deposition or etch rate over the interior region of the wafer.

[0018] A non-uniformity in film deposition or wafer etch may develop due to this disparity of plasma characteristics between the wafer edge in relation to the bulk of the wafer interior. The proximity of the focus ring to the wafer edge (e.g., lateral distance of a gap between the wafer edge and the inner sidewall of the ring) and the height of the focus ring relative to the surface of the wafer are adjustable parameters that can have a large influence on the deposition and etch rate at the periphery (e.g., edge portion) of the wafer relative to the interior of the wafer. The influence of the focus ring can extend several millimeters from the wafer edge toward the interior portion of the wafer. The proximity and height of the focus ring with respect to the wafer edge may influence the electric fields, as well as plasma particle densities, within the gap region between the focus ring and the wafer edge. In general, the gap region is small, less than one millimeter. In at least one implementation, the gap region can be larger, extending to several millimeters.

[0019] The height of the focus ring relative to the wafer surface can be less than one millimeter to several millimeters. The electric fields may influence the positive / negative ion, electron, and neutral radical densities within the plasma in the neighborhood of the wafer edge. The presence of a focus ring may extend the uniformity of a plasma electric field beyond the wafer edge, whereas in the absence of a focus ring, the plasma electric field can be highly non-uniform in the vicinity of the wafer edge. The plasma electric field may be more intense in the vicinity of the wafer edge in the absence of a focus ring relative to the interior portions of the wafer.

[0020] To an extent, the material composition of a focus ring may influence the plasma properties also near the edge region of a wafer. For example, a focus ring may comprise a dielectric material, such as silicon carbide or a ceramic composite, such as ytterbium oxide. The dielectric constant of the material may be tuned by addition of small amounts of ruthenium, for example.

[0021] Asymmetries in the process chamber environment may also affect the symmetry of a plasma. For example, electric fields and reactive species density distributions within a plasma may be skewed by proximity of metallic objects around a pedestal in a process workstation. The skewing of electric fields and densities of reactive species (e.g., ions and neutral radicals) may cause asymmetrical etch or deposition rates primarily at or near the edge of the wafer. In the case of plasma enhanced deposition, the edge thickness of a deposited film may be reduced or increased at one side of a wafer relative to an average film thickness. This occurrence of asymmetry in plasma reactions at the edge may not be controllable by adjustment of the gap distance or height of the focus ring. In at least one implementation, some correction of non-uniformity of film deposition, for example, may be achieved by adjustment or tuning plasma parameters such as gas flow, gas pressure, RF power, and pedestal temperature.

[0022] In at least one implementation, film thickness non-uniformities may be offset to some extent by hardware adjustments within the environment of the plasma, such as distance to other metal pieces within the process chamber. If the process chamber has multiple deposition workstations or etch workstations, these may be arranged bilaterally or in quadrants within the process chamber. Plasma density asymmetries may be introduced at one station by the other workstations. For example, capacitive coupling of a radio frequency (RF) electric field from the plasma electrodes to metallic objects associated with adjacent workstations, such as metal showerheads and metal portions of pedestals, may cause skewing of plasma density at an active station where a deposition or etch is in progress.

[0023] To a limited extent, tilting the active showerhead (e.g., at the workstation having an ignited plasma) can correct the asymmetry. However, tilting of the showerhead, a plasma electrode, places portions of the showerhead in greater proximity to the pedestal than other portions, and may lead to arcing and wafer sliding. Uneven distribution of the electric field within a plasma caused by tilting of the showerhead may also cause plasma instabilities, possibly leading to greater non-uniformity in a deposited film thickness or in an etching process.

[0024] Steady state offset may be used to correct for edge non-uniformity, where the wafer may be laterally moved relative to the focus ring. However, gap distances between the inner sidewall of the focus ring and the wafer edge is generally small, for example, 1 mm or less, leaving little room to entirely correct for the non-uniformity.

[0025] The thickness of the focus ring has a distinct impact on the edge thickness of a PECVD film. In at least one implementation, a focus ring having a variable thickness profile is disclosed, whereby the thickness of the focus ring is tapered along the circumference or is stepped. In at least one implementation, the thickness profile of the focus ring is varied to compensate for asymmetries in the process chamber that lead to PECVD film nonuniformities. For example, a process chamber workstation may systematically produce PECVD films that have an edge thickness non-uniformity in a particular quadrant or half of the wafer. Such asymmetries may not be mitigatable by hardware reconfiguration as process chamber hardware may have a fixed configuration that cannot be changed, for example. In at least one implementation, the focus ring may enable mitigation of PECVD film nonuniformities in such situations, as the geometry of the disclosed focus ring may be tailored to a process workstation that may be exhibit plasma asymmetries due to a particular process chamber configuration or for other reasons.

[0026] Fig. 1 illustrates a profile interior view of a plasma chamber 100, in accordance with at least one implementation. In at least one implementation, plasma chamber 100 is configured to perform PECVD for fabrication of thin films on semiconductor wafers, or dry etching (e.g., reactive ion etching) to create structures on semiconductor wafers. In at least one implementation, plasma chamber 100 comprises a chamber wall 102, a showerhead 104, and a pedestal 106. In at least one implementation, showerhead 104 and pedestal 106 are components of a process workstation within plasma chamber 100, as depicted in the figure. In at least one implementation, plasma chamber 100 comprises multiple workstations that comprise a showerhead and pedestal as shown in Fig. 1. In at least one implementation, plasma chamber 100 comprises a transfer arm and end effector (not shown) or an indexer (notshown) between multiple workstations. In at least one implementation, pedestal 106 comprises a platen 108, which supports a wafer 110. In at least one implementation, wafer 110 is lifted to a height d over platen 108 by lift pins 112. In at least one implementation, wafer 110 is seated within a focus ring 114.

[0027] In at least one implementation, plasma chamber 100 is configured to generate and support a plasma 116. In at least one implementation, plasma 116 is a capacitively coupled plasma or an inductively coupled plasma. In at least one implementation, showerhead 104 is or comprises an upper plasma electrode electrically coupled to an RF generator. In at least one implementation, platen 108 is held at a reference potential (e.g., electrically grounded) as a lower plasma electrode. Plasma 116 may be initiated and sustained by RF fields extending within the space between showerhead 104 and platen 108. Plasma 116 comprises a sheath that may have a profile like that shown in the figure. Plasma 116 may have a substantially uniform ionic density distributions of ions and neutrals across most of wafer 110. Near the edge of wafer 110 and focus ring 114, plasma 116 may have characteristics, such as ion and neutral distributions, as well as electric field distributions, that diverge from the bulk of plasma 116. Such divergence of plasma properties at the wafer edge and the influence of the focus ring to even out the plasma properties at the wafer edge (e.g., focus ring 114) is described below.

[0028] Fig. 2A illustrates an enlarged cross-sectional view of wafer 110 and focus ring 114 supported on platen 108, in accordance with at least one implementation. In at least one implementation, PECVD film 118 has been deposited over wafer 110 by a PECVD process. In at least one example, PECVD film 118 may be an insulating film, such as a silicon oxide (e.g., SiCh), silicon nitride, or nitrogen doped silicon carbide (SiCN). PECVD film 118 may comprise semiconductive materials, such as polysilicon, epitaxial gallium arsenide, gallium nitride, and the like. PECVD film 118 may also comprise carbon-based materials, such as graphene, carbon nanotubes, and metals.

[0029] In at least one implementation, the thickness profile of PECVD film 118 is highly exaggerated relative to wafer 110 to show thickness variations. For example, PECVD film 118 may have a nominal thickness t of 5000 angstroms (A), whereas wafer 110 may have a thickness of 500 microns (e.g., 5xl06A). The illustration shows that PECVD film 118 is generally thickest at the center portion, indicated by the vertical dashed line at the center of wafer 110. PECVD film 118 may generally be thickest at the center of wafer 110 and may smoothly taper to a slightly smaller thickness at the edge, as shown. For example, a thicknessvariation Ati may be approximately 50 A -100 A, accounting for a non-uniformity (NU%) of approximately 1% or less. A non-uniformity below 1% may be substantially uniform.

[0030] In at least one implementation, PECVD film 118 may have a film defect 120 on the right edge of PECVD film 118, as depicted in the cross-sectional view. Here, the film thickness descends precipitously from a gradual decrease in thickness in the central portion of PECVD film 118. A thickness deviation At2 of 200 A or greater may be measured at the right edge due to film defect 120, contributing to a non-uniformity of PECVD film 118. For example, aNU% may be calculated to be 1.5% for PECVD film 118 having film defect 120. The precipitous drop in thickness may indicate that film precursor radicals may have been excluded from the edge region along the right-side edge of wafer 110, or that an overabundance of ions may have been concentrated by focus ring 114 over the right-side edge, effectively sputter-etching the film along the right edge.

[0031] In at least one implementation, focus ring 114 has an inner sidewall 122 that is separated from wafer edge 124 by gap g. In at least one implementation, gap g may range between 100 microns to several millimeters. In at least one implementation, focus ring 114 has a thickness hi ranging between 1 mm to 5 mm, where hi is substantially uniform along the circumference of focus ring 114, where the circumference extends between inner sidewall 122 and an outer sidewall 123. In at least one implementation, focus ring 114 has an outer diameter Di and a first inner diameter D2 across an upper portion of inner sidewall 122. In at least one implementation, inner sidewall 122 comprises a ledge 126 that protrudes inwardly. Ledge 126 may enable seating of wafer 110 within focus ring 114. In at least one implementation, an upper portion of inner sidewall 122 extends a height I12 over ledge 126. A lower portion 127 of sidewall 122 extends below ledge 126, where a second inner diameter D3 may depend on the width of ledge 126.

[0032] In at least one implementation, inner sidewall 122 may extend above or below a surface 128 of wafer 110 by a distance Ah. In at least one implementation, distance Ah may be zero. In at least one implementation, height hi of focus ring 114 and distance Ah relative to surface 128 of wafer 110 may influence thickness of PECVD film 118 near wafer edge 124. For example, a negative Ah may permit a thicker deposit near wafer edge 124, whereas a positive Ah may suppress deposition near the wafer edge 124, producing a thinner deposition near wafer edge 124 relative to the bulk of PECVD film 118.

[0033] The inset shows an illustrative example of a PECVD deposition asymmetry in the form of film defect 120 in PECVD film 118. The inset shows a plan view of PECVD film118, illustrating the extent of disposition of film defect 120 at the edge of PECVD film 118. Dashed contours are also included to map thickness variations of PECVD film 118, in accordance with the cross-sectional view. Film defect 120 is shown as the hatched portion of PECVD film 118. In the illustrative example, film defect 120 has a crescent shape, extending a small distance (e.g., a few millimeters) into the interior of PECVD film 118, primarily along the top and bottom right quadrants of the circumference of PECVD film 118. Film defect 120 may be due to asymmetric plasma fields and skewed distributions of reactive plasma species during deposition of PECVD film 118, as described above. Such asymmetry in the plasma may arise by asymmetrical arrangement of hardware within plasma chamber 100, causing asymmetric coupling of RF fields to platen 108, for example, and / or by asymmetric electric fields within plasma 116, and / or asymmetric reactive gas flow rates from showerhead 104.

[0034] Fig. 2B illustrates a perspective view of focus ring 114, in accordance with at least one implementation. In at least one implementation, focus ring 114 is completely symmetrical, having a circular cylindrical shape. In at least one implementation, focus ring 114 has a uniform thickness hi, extending around the circumference of focus ring 114. The symmetrical geometry of focus ring 114 may be a conventional design. Focus ring 114 comprises horizontal surfaces, comprising ledge 126 extending between diameters D2 and D3, and top surface 130 extending between diameters Di and D2. As noted above, ledge 126 enables seating of wafer 110 within focus ring 114, for example to shield the edge region of wafer 110. Upper portion 132 of inner sidewall 122 extends a height I12 over ledge 126. In at least one implementation, I12 may range between 2 mm (approximately 0.1 inch) to 5 mm (approximately 0.2 inch). A lower portion 127 of sidewall 122 extends a distance hi-h2 below ledge 126.

[0035] In at least one implementation, focus ring 114 comprises a dielectric material. In at least one implementation, the dielectric material may have a relative dielectric constant ranging from 2 up to 100. In at least one implementation, focus ring 114 may partially comprise a conductive material. Dielectric materials having higher dielectric constants may support larger negative surface charging due transient electron flux during the positive portion of RF cycles, whereas materials having lower dielectric constants may support smaller negative surface charging. The negative surface charging may attract positive ions (e.g., Ar+), drawing them toward the top surface 130 and inner sidewall 122 (e.g., specifically upper portion 132) of focus ring 114. The ion attraction by inner sidewall 122 of focus ring 114, for example, may increase or decrease ion flux near the wafer edge (e.g., wafer edge124). Highly energetic Ar+ions, for example, may sputter newly deposited material near the wafer edge, reducing thickness and possibly enabling film defect 120 to develop. However, less energetic Ar+ions may assist deposition of material near the wafer edge, allowing buildup of film structure at the wafer edge. The height of top surface 130 of focus ring 114 relative to wafer surface 128 may also reduce or enhance the effect of ion flux on film growth at the wafer edge. For example, a positive height differential, where top surface 130 is higher than wafer surface 128, may shield the wafer edge from ion flux. Ions may be deflected away from wafer surface 128 near wafer edge toward inner sidewall 122 and top surface 130. For a negative height differential, where top surface 130 is lower than wafer surface 128, the opposite may be true, where shielding by focus ring is removed, and ion flux may be concentrated over the wafer edge.

[0036] Due to plasma asymmetries discussed above and the influence exerted by the focus ring on edge deposition rates, the local edge deposition rate may be modulated by tuning the shape of the focus ring to mitigate disparities in deposition rate due to plasma asymmetries, as described below.

[0037] Fig. 3A illustrates a perspective view of a tuned focus ring 300, in accordance with at least one implementation. In at least one implementation, tuned focus ring 300 has a stepped profile. Tuned focus ring 300 comprises upper surface 302 extending around a first annular segment that follows a first circular arc (where the first circular arc is a portion of the total circumference of tuned focus ring 300) of the circumference of tuned focus ring 300, whereby the circular arc of the first annular segment is subtended by an angle 0 (e.g., first angle). In at least one implementation, 0 may be adjusted to range between 10 degrees to 360 degrees, depending on the extent of asymmetry correction desired along the wafer edge. In at least one implementation, tuned focus ring 300 comprises lower surface 304 extending around a second annular segment having a second circular arc subtended by an angle of 360 degrees - 0 (e.g., second angle).

[0038] In at least one implementation, tuned focus ring 300 further comprises ledge 306 extending from upper sidewall 308 of the inner sidewall of tuned focus ring 300. In at least one implementation, upper sidewall 308 may extend over lower surface 304 by a height d. In at least one implementation, upper surface 302 is at a height F13 over ledge 306. Ledge 306 may enable seating a wafer in tuned focus ring 300 for transfer between workstations, or to seat a wafer onto a pedestal when transferring the wafer into the plasma chamber. When positioned on a pedestal, the wafer may be lifted off ledge 306 by lift pins (e.g., lift pins 112)as shown in Fig. 2A. The portion of lower sidewall 310 of the inner sidewall of tuned focus ring 300 perpendicularly extends below ledge 306 to the base of tuned focus ring 300.

[0039] In at least one implementation, lower surface 304 is at a height tu (see Fig. 3B) over ledge 306. Both height hs and height tu may be adjusted to provide a desired degree of screening of the adjacent portion of the wafer edge, for example. In at least one implementation, height hs may range between 100 microns to several millimeters.

[0040] In at least one implementation, tuned focus ring 300 comprises one or more dielectric materials. The material composition of a focus ring can influence the plasma properties also near the edge region of a wafer. In at least one implementation, tuned focus ring 300 comprises silicon carbide or a ceramic composite. In at least one implementation, tuned focus ring 300 comprises a ceramic composite material coated with silicon carbide or other recalcitrant and / or plasma compatible dielectric. In at least one implementation, the ceramic composite comprises ytterbium oxide. In at least one implementation, the ceramic composite may contain small amounts of ruthenium or other plasma resistant transition metal or lanthanide to tune the overall dielectric constant.

[0041] In at least one implementation, tuned focus ring can comprise semiconductive and conductive materials to modify the local effects on a plasma near the wafer edge. In at least one implementation, different portions of tuned focus ring 300 may comprise different compositions. For example, lower surface 304 may be coated with a first dielectric, semiconductive, or conductive material, and upper surface 304 and upper sidewall 308 in the vicinity of upper surface 302 may be coated with a second dielectric, semiconductive, or conductive material.

[0042] Fig. 3B illustrates a profile view of tuned focus ring 300, in accordance with at least one implementation. The profile view shows the relation between height d and overall height I13 (e.g., first height) and height tu (e.g., second height) of tuned focus ring 300. In at least one implementation, height d is the difference between hs and tu. In at least one implementation, hs may range between 1 mm to 5 mm, whereas d may range between 100 microns to 2 mm. In at least one implementation, d may be up to 50% of height hs.

[0043] Lateral dimensions of tune focus ring 300 are also shown in Fig. 3B. Diameter D4 is the overall diameter of tuned focus ring 300, whereas D5 is the diameter of upper sidewall 308 and De is the diameter of lower sidewall 310, where D4 > D5 > De. Width w of upper surface 302 and lower surface 304 is D4-D5.

[0044] Fig. 4A illustrates a perspective view of a tuned focus ring 400 having a tapered thickness, in accordance with at least one implementation. In at least one implementation,tuned focus ring 400 comprises top surface 402 extending along the entire circumference of tuned focus ring 400. In at least one implementation, at least a portion of top surface 402 is at least partially sloped, as described presently. In an exemplary implementation shown in Fig. 4A, top surface 402 comprises upper flat surface 404, lower flat portion 406, and two sloped portions 408 extending between, upper flat surface 404 and lower flat portion 406. Top surface 402 may have a width w that is constant around the entire circumference. In at least one implementation, width w may be non-constant around the circumference. For example, some portions of top surface 402 may be narrower than other portions. In at least one implementation, upper flat surface 404 follows a first circular arc subtended by an azimuthal angle 0 (e.g., first angle), forming a first annular portion of top surface 402. In at least one implementation, 0 may range between 30 and 120 degrees, for example.

[0045] In at least one implementation, lower flat portion 406 follows a second circular arc subtended by an azimuthal angle c|) (e.g., second angle), forming a second annular portion of top surface 402. In at least one implementation, c|) may range between 30 and 120 degrees, for example. In at least one implementation, sloped portions 408 follow a third and a fourth circular arc (e.g., third annular segment and fourth annular segment) subtended by an azimuthal angle (e.g., third angle) forming third and fourth annular portions of top surface 402. Angle 5, may range between 30 and 120 degrees, the value of which is the difference between angle 0 and angle (|). Arclengths of upper flat surface 404, sloped portion 408 and lower flat portion 406 may be demarked where portions of top surface 402 are subtended by azimuthal angles 0, (|) and Arclengths of upper flat surface 404, lower flat portion 406 and sloped portions 408 may be determined by (angle) x D? / 2, where D? is the diameter of tuned focus ring 400, and angle is any of 0, (|), or 5, expressed in radians.

[0046] In at least one implementation, angles 0 and (|) may be adjusted to compensate plasma asymmetries. The slope of sloped portions 408 is related to the height difference between upper flat surface 404 and lower flat portion 406, and azimuthal angle The arclength of sloped portions 408 is also related to azimuthal angle 5, by ^D? / 2, as noted above.

[0047] In at least one implementation, an upper sidewall 410 of the inner sidewall extends between a ledge 412 and upper flat surface 404. Upper sidewall 410 has a variable height around the circumference of tuned focus ring 400, for example, tapering along sloped portions 408 from maximum height hs to minimum height he (e.g., third height in Fig. 4B). In at least one implementation, upper sidewall 410 extends to a maximum height hs above a ledge 412 along upper flat surface 404, whereas upper sidewall 410 extends to a minimumheight he above ledge 412 along lower flat portion 406. As noted, ledge 412 provides a means to seat a wafer within tuned focus ring 400.

[0048] Adjustment of the taper of sloped portions 408 may fine tune mitigation of gradually changing plasma asymmetries in a PECVD process, for example. For example, upper flat surface 404, having a height hs above the surface of a wafer, may be azimuthally positioned where enhanced shielding of the wafer edge is desired to mitigate sputtering of the edge by Ar+ ions, or to mitigate undesired deposition on the backside of the wafer edge. In at least one implementation, height hs may be adjusted to extend a desired distance above a wafer surface to obtain maximal shielding against sputtering, for example.

[0049] Some wafer edges are beveled, enabling infiltration of neutrals to deposit on the backside of the wafer edge. For example, for a PECVD process, if sputtering of the wafer edge is predominant in a particular orientation due to a plasma asymmetry, tuned focus ring 400 may be oriented such that the highest portion of sidewall 410 and upper flat surface 404 are positioned in the direction of the plasma asymmetry. In at least one implementation, height he of lower flat portion 406 may be adjusted to realize a desired distance above the wafer surface to reduce any shielding where the plasma will not have significant tendency to sputter the wafer surface and permit normal deposition.

[0050] With regards to material composition of tuned focus ring 400, similar considerations may apply to tuned focus ring 400 as did to tuned focus ring 300, described above. In at least one implementation, different portions of tuned focus ring 400 may comprise different compositions comprising dielectric, semiconductive, or conductive materials.

[0051] Fig. 4B illustrates a cross-sectional view of tuned focus ring 400, in accordance with at least one implementation. Outer diameter D7, first inner diameter Ds and second inner diameter D9 (of lower portion 411) are shown, where D7 > Ds > D9. The cross-sectional view shows the linear taper of sloped portion 408 of upper sidewall 410 along length L between height hl of upper flat surface 404 and height h2 of lower flat portion 406. Length L may be approximately the arclength of sloped portions 408 (e.g., L = cord length D?sin[^ / 2]). Width w of top surface 402, where top surface 402 extends laterally between outer diameter D7 and first inner diameter Ds of upper sidewall 410, may be adjusted to maximal effect on the plasma in the edge region of the wafer, thus affecting the thickness of upper sidewall 410. In at least one implementation, sloped portions 408 of top surface 402 have a linear taper. In at least one implementation, sloped portions 408 of top surface 402 have a non-linear taper. Inat least one implementation, sloped portions 408 of top surface 403 comprise a series of discontinuous steps. Fig. 4C illustrates an example of a non-linear curved taper 414 exhibited by sloped portions 408, in accordance with at least one implementation. Fig. 4D illustrates an example showing sloped portions 408 comprising a series of discontinuous stepped segments 416, in accordance with at least one implementation.

[0052] Fig. 5 illustrates a perspective view of a plasma process system 500, comprising a showerhead 502 and a pedestal 504 disposed below showerhead 502, in accordance with at least one implementation. In at least one implementation, plasma process system 500 is a workstation within a plasma chamber (e.g., plasma chamber 100). In the illustrative example, a plasma 506 is struck between showerhead 502 and pedestal 504. Tuned focus ring 400 is additionally shown in the illustrative example seated on platen 508 of pedestal 504, having wafer 510 seated within. While tuned focus ring 400 having a tapered sidewall is shown in the example, it will be understood that tuned focus ring 300 having a stepped sidewall may also be equally employed without changing the context of the scope of the example.

[0053] Plasma process system 500 may have asymmetries due to layout of process hardware in the vicinity of plasma process system 500, as discussed above that may be reflected in plasma 506 as plasma asymmetries. Such plasma asymmetries may skew a film deposition or an etch, in particular, reducing film thickness near the wafer edge for example. In the illustrative implementation, sidewall 410 tapers downward toward the front of the figure (e.g., in the y-direction).

[0054] Figs. 6A, 6B, 6C, and 6D respectively illustrate a contrast in PECVD film NU% performance between a focus ring 114, as shown in Fig. 2A, and tuned focus rings 300 and 400 for the same plasma asymmetry, modified in accordance with at least one implementation of this disclosure. In at least one implementation, the views shown in Figs. 6A-6D are cross-sectional views to contrast changes in NU% of PECVD film 118 due to the focus ring. Referring to Fig. 6A, focus ring 114 may be a conventional focus ring because height hi of sidewall 122 above ledge 126 is constant about the circumference of focus ring 114. Due to an asymmetry in plasma conditions (plasma not shown), film defect 120 develops along the edge of wafer 110 in the left-hand quadrant. In the illustrative example, film defect 120 is manifested as an abrupt decrease in film thickness near the left side of wafer 110. Focus ring 114, having a constant ring thickness around the circumference, does not correct local plasma conditions occurring near the edge in the side or quadrant where the plasma asymmetry is most present. The left-hand inset of Fig. 6A shows a profilometry graph 600 of the center and edge of PECVD film 118, showing an exemplary profilometricmeasurement of film defect 120 relative to the interior portion of PECVD film 118. In the exemplary profilometric measurement, thickness of PECVD film 118 is approximately 200 angstroms lower than the central portion of PECVD film 118, having a nominal thickness of 4900 A, for example. The right-hand inset of Fig. 6A shows a plan view of PECVD film 118, showing film defect 120 extending along most of the left edge of PECVD film 118. Here, the NU% of PECVD film 118 may be 1.5%.

[0055] Referring now to Fig. 6B, the plasma asymmetry may be compensated by tuned focus ring 300, having a stepped sidewall height between hs and tu (I13 > tu). The stepped profile of upper sidewall 308 is shown by the dashed line. In the illustrative example, NU% of PECVD film 118 is improved by substantial elimination of film defect 120. Tuned focus ring 300 may enable a complete deposition along the edge of wafer 110, for example by a shielding effect afforded by positioning the higher portion of upper sidewall 308 (e.g., hs) along the left side of wafer 110. In the illustrative example, the larger height hs of upper sidewall 308 may shield the left side of wafer 110 against excessive high energy Ar+ ion intrusion at the edge of wafer 110, and hence against excessive sputtering of the edge region of PECVD film 118 by high energy Ar+ ions. On the right side of wafer 110, high energy Ar+ ions may not be abundant, thus little sputtering wear of PECVD film 118 may occur on the right-hand side of PECVD film 118, obviating the need to provide shielding by tuned focus ring 300. Thus, the lower height tu of upper sidewall 308 may be appreciably lower than hs or even negative (e.g., below wafer surface 128).

[0056] Still referring to Fig. 6B, the left-hand inset shows a profilometry graph 602, showing an exemplary profilometric measurement of PECVD film 118 formed with tuned focus ring 300 present. Here, film defect 120 is substantially filled in by film material at the left edge of wafer 110, due to the higher portion of upper sidewall 308 shielding the left-hand side of wafer 110 against high-energy Ar+ ions, for example. A thickness difference of approximately 50 angstroms between the edge region and central portion of PECVD film 118 may be realized by replacement of focus ring 114 by tuned focus ring 300, and judicious positioning of tuned focus ring 300 such that the higher portion of upper sidewall 308 is in the region of the plasma asymmetry causing creating of film defect 120. The right-hand inset of Fig. 6B shows a plan view of PECVD film 118, showing that PECVD film 118 is substantially more symmetrical, where film defect 120 has been eliminated.

[0057] Referring now to Figs. 6C and 6D, tuned focus ring 300 is replaced by tuned focus ring 400 and focus ring 450, respectively. In at least one implementation, tuned focus ring 400 and focus ring 450 have a tapered upper sidewall 410, as described previously. Thetapered upper sidewall 410 of focus rings 400 and 450, respectively, may be tailored to enable fine-tuning of the plasma asymmetry compensation effect that was afforded by tuned focus ring 300, having a stepped profile. The profile of focus ring 450 has a longer taper (e.g., sloped portions 408 shown in Figs. 4A-4C) than exhibited by tuned focus ring 400.

[0058] Fig. 7 illustrates a flowchart 700 summarizing a method for using a locus ring in accordance with at least one implementation. While the following examples concern a PECVD film deposition, similar considerations may also apply to plasma-assisted etch processes. In at least one implementation, flowchart 700 may include a single workstation or multiple workstations within a process chamber (e.g., plasma chamber 100 in Fig. 1). In at least one implementation, the method summarized by flowchart 700 comprises operations 702 - 704.

[0059] At operations 702 and 704, a wafer is seated within a tuned focus ring, such as tuned focus ring 300 or 400 as described herein. In at least one implementation, a wafer may be transferred from a vacuum transfer module into the plasma chamber having at least one plasma workstation with a robot arm and end effector attached to the robot arm. The wafer may be held by the end effector, and seated on a tuned focus ring already positioned on a pedestal within the plasma chamber. Prior to introduction of the wafer, the focus ring may be placed on the pedestal by a human or by the robot arm / end effector, where the tuned focus ring is held by the end effector. In at least one implementation, the end effector may be configured to rotate the tuned focus ring to position it in a desired orientation. The desired orientation may be related to hardware asymmetries within the plasma chamber.

[0060] At operation 706, the tuned focus ring may be oriented manually or by an indexer having a rotating functionality in a multi -workstation plasma chamber, in accordance with at least one implementation. For example, the indexer may rotate the tuned focus ring by a desired number of degrees to orient the tuned focus ring with respect to a plasma asymmetry within the plasma chamber.

[0061] At operation 708, a plasma may be struck to initiate a plasma process. In at least one implementation, the plasma process may be a PECVD process or an etch process.

[0062] In some instances, well-known methods and devices are shown in block diagram form, rather than in detail, to avoid obscuring at least one implementation. Reference throughout this specification to “an implementation,” “one implementation,” “in at least one implementation,” or “some implementations” means that a particular feature, structure, function, or characteristic described in connection with implementation is included in at least one implementation. Thus, appearances of phrase “in an implementation,” “in at least oneimplementation,” or “in one implementation” or “some implementations” in various places throughout this specification are not necessarily referring to same implementation of disclosure. Furthermore, particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more implementations. For example, a first implementation may be combined with a second implementation anywhere particular features, structures, functions, or characteristics associated with two implementations are not mutually exclusive.

[0063] As used in herein, singular forms “a”, “an,” and “the” are intended to include plural forms as well, unless context clearly indicates otherwise. It will also be understood that term “and / or” as used herein refers to and encompasses all possible combinations of one or more of associated listed items. General term definitions are given below.

[0064] Here, “coupled” and “connected,” along with their derivatives, may be used herein to describe functional or structural relationships between components. These terms are not intended as synonyms for each other. Rather, in particular implementations, “connected” may be used to indicate that two or more elements are in direct physical, optical, or electrical contact with each other. “Coupled” may be used to indicated that two or more elements are in either direct or indirect (with other intervening elements between them) physical, electrical or in magnetic contact with each other, and / or that two or more elements co-operate or interact with each other (e.g., as in a cause an effect relationship).

[0065] Here, “over,” “under,” “between,” and “on” as used herein refer to a relative position of one component or material with respect to other components or materials where such physical relationships are noteworthy. For example, in context of materials, one material or material disposed over or under another may be directly in contact or may have one or more intervening materials. Moreover, one material disposed between two materials may be directly in contact with two layers or may have one or more intervening layers. In contrast, a first material “on” a second material is in direct contact with that second material / material. Similar distinctions are to be made in context of component assemblies. As used throughout this description, and in claims, a list of items joined by term “at least one of’ or “one or more of’ can mean any combination of listed terms.

[0066] Here, “adjacent” may generally refer to a position of a thing being next to (e.g., immediately next to or close to with one or more things between them) or adjoining another thing (e.g., abutting it).

[0067] Unless otherwise specified in explicit context of their use, terms “substantially equal,” “about equal,” and “approximately equal” mean that there is no more than incidentalvariation between two things so described. Such variation is typically no more than + / - 10% of a predetermined target value.

[0068] Here, “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and similar terms are used for descriptive purposes and not necessarily for describing permanent relative positions. For example, terms “over,” “under,” “front side,” “back side,” “top,” “bottom,” “over,” “under,” and “on” as used herein refer to a relative position of one component, structure, or material with respect to other referenced components, structures, or materials within a device, where such physical relationships are noteworthy. These terms are employed herein for descriptive purposes only and predominantly within context of a device z-axis and therefore may be relative to an orientation of a device. Hence, a first material “over” a second material in context of a figure provided herein may also be “under” second material if device is oriented upside-down relative to context of figure provided. Similar distinctions are to be made in context of component assemblies.

[0069] Here, a device that is “configured to” perform a task or function may be configured (e.g., programmed and / or hardwired) at a time of manufacturing by a manufacturer to perform the function. In at least one example, the device may be configurable (or reconfigurable) by a user after manufacturing to perform the function and / or other additional or alternative functions. In at least one example, the configuring may be through firmware and / or software programming of the device, through a construction and / or layout of hardware components and interconnections of the device, or a combination thereof.

[0070] Here, “between” may be employed in context of z-axis, x-axis, or y-axis of a device. A material that is between two other materials may be in contact with one or both of those materials. In another example, a material that is between two or other material may be separated from both of other two materials by one or more intervening materials. A material “between” two other materials may therefore be in contact with either of other two materials. In another example, a material “between” two other materials may be coupled to other two materials through an intervening material. A device that is between two other devices may be directly connected to one or both of those devices. In another example, a device that is between two other devices may be separated from both of other two devices by one or more intervening devices. Specific terms are defined below.

[0071] Here, “plasma process chamber” may generally refer to a semiconductor processing chamber wherein plasma may be created to assist a film deposition process or an etch process.

[0072] Here, “plasma” may generally refer to a fourth state of matter consisting of a gas of charged particles such as positive ions and free electrons. Plasmas may assist in film deposition by creating reactive species in the gas phase, for example, molecular and atomic radicals, and forming atomic and molecular ions in the gas phase. Atom ions may be accelerated by direct current (DC) fields in the plasma to activate a deposition surface by gentle sputtering.

[0073] Here, “plasma asymmetry” may generally refer to an azimuthal non-uniformity in a plasma, generally concerning distributions of electric fields and reactive species.

[0074] Here, “focus ring” may generally refer to an annular device that generally accompanies a wafer for processing in a plasma process chamber. A focus ring may improve uniformity of plasma-assisted deposition processes by changing plasma characteristics in the vicinity of a wafer edge. A conventional focus ring has a constant thickness around its circumference.

[0075] Here, “tuned focus ring” may generally refer to a focus ring that has a varying thickness around its circumference. It is “tuned” by engineering the variations of thickness to compensate plasma asymmetries that may cause film deposition non-uniformities at the edge of wafer substrates, as described herein.

[0076] Here, “annulus” may generally refer to a circular ring-shaped structure. An annulus may have a circular or rectangular cross section, having an outer circumference and an inner circumference encircling a central aperture.

[0077] Here, “annular segment” may generally refer to a portion of an annulus, generally subtended by a circular angle.

[0078] Here, “arc” may generally refer to a portion of a circle.

[0079] Here, “sidewall” may generally refer to a vertically extending wall from a horizontal wall.

[0080] Here, “inner sidewall” may generally refer to a sidewall of an annulus having a rectangular cross section, where the annulus has an outer sidewall along an outer circumference and an inner sidewall along an inner circumference. The inner sidewall encircles the center aperture of the annulus.

[0081] Here, “taper” may generally refer to a slope or non-constant height or thickness. The taper may be linear or non-linear.

[0082] Here, “ledge” may generally refer to a shelf structure or a flat horizontal protrusion from a wall or sidewall of a structure.

[0083] Here, “wafer” may generally refer to a semiconductor substrate that is processed to produce microelectronic circuitry or micro-electrical and mechanical system (MEMS) devices.

[0084] Here, “wafer chuck” generally refers to a support configured to receive wafers for processing within a process chamber. A wafer chuck may incorporate electrostatic clamping to hold the wafer in place. A wafer chuck may be included on a pedestal.

[0085] Here, “dielectric material” generally refers to an insulative material.

[0086] The structures of various examples described herein can also be described as method(s) of forming those structures or apparatuses, and method(s) of operation of these structures or apparatuses. The following examples are provided that illustrate the various examples of the disclosure. The examples can be combined with other examples. As such, various examples can be combined with other examples without changing the scope of the invention.

[0087] Example l is a plasma processing apparatus, comprising: a tuned focus ring, wherein the tuned focus ring comprises: an inner sidewall having an upper portion and a lower portion extending below the upper portion; a ledge extending from the inner sidewall between the upper portion and the lower portion, wherein the ledge extends around a circumference of the lower portion of the inner sidewall, wherein the upper portion of the inner sidewall extends a first height over the ledge along a first annular segment of the tuned focus ring, wherein the upper portion extends a second height over the ledge along a second annular segment of the tuned focus ring, and wherein the first height is greater than the second height.

[0088] Example 2 is a plasma processing apparatus as in any of the examples, particularly example 1, wherein the first annular segment extends along a first circular arc subtended by a first angle, and wherein the second annular segment extends along a second circular arc subtended by a second angle.

[0089] Example 3 is a plasma processing apparatus as in any of the examples, particularly example 2, wherein the first height is constant along the first circular arc, and wherein the second height is constant along the second circular arc.

[0090] Example 4 is a plasma processing apparatus as in any of the examples, particularly example 3, wherein a third annular segment extends along a third circular arc between the first circular arc and the second circular arc.

[0091] Example 5 s a plasma processing apparatus as in any of the examples, particularly example 4, wherein a fourth annular segment extends along a fourth circular arc between the first circular arc and the second circular arc and opposite the third circular arc.

[0092] Example 6 is a plasma processing apparatus as in any of the example, particularly example 5, wherein the third annular segment extends a third height over the ledge, and wherein the third height is between the first height and the second height.

[0093] Example 7 is a plasma processing apparatus as in any of the examples, particularly example 6, wherein the third height is constant along the third annular segment.

[0094] Example 8 is a plasma processing apparatus as in any of the examples, particularly example 6, wherein the third height is variable along the third annular segment.

[0095] Example 9 is a plasma processing apparatus as in any of the examples, particularly example 8, wherein the third height is tapered along the third annular segment.

[0096] Example 10 is a plasma processing apparatus as in any of the examples, particularly example 9, wherein the third height has a linear taper along the third annular segment.

[0097] Example 11 is a plasma processing apparatus as in any of the examples, particularly example 9, wherein the third height has a non-linear taper along the third annular segment.

[0098] Example 12 is a plasma processing apparatus as in any of the examples, particularly example 8, wherein the third height is stepped along the third annular segment.

[0099] Example 13 is a tuned focus ring, comprising; a first annular segment and a second annular segment; an inner sidewall comprising: an upper sidewall portion; and a lower sidewall portion extending below the upper sidewall portion, wherein a ledge extends from the inner sidewall and extends along a circumference of the lower portion between the upper sidewall portion and the lower sidewall portion, wherein the upper sidewall portion extends a first height over the ledge along the first annular segment, wherein the upper sidewall portion extends a second height over the ledge along the second annular segment, and wherein the first height is greater than the second height.

[0100] Example 14 is a tuned focus ring as in any of the examples, particularly example13, comprising at least one dielectric material.

[0101] Example 15 is a tuned focus ring as in any of the examples, particularly example14, wherein the first annular segment comprises a first dielectric material, and wherein the second annular segment comprises a second dielectric material.

[0102] Example 16 is a tuned focus ring as in any of the examples, particularly example 15, wherein the first dielectric material comprises ytterbium oxide, and wherein the second dielectric material comprises ruthenium.

[0103] Example 17 is a method comprising placing a tuned focus ring on a wafer chuck within a plasma chamber; seating a wafer on the tuned focus ring; depositing a film on the wafer by a plasma deposition process; and orienting the tuned focus ring with respect to a plasma asymmetry within the plasma chamber such that the film is uniform along an edge of the wafer.

[0104] Example 18 is a method as in any of the examples, particularly example 17, wherein placing the tuned focus ring on the wafer chuck within the plasma chamber comprises transferring the tuned focus ring to the wafer chuck by a robot arm, and wherein the tuned focus ring is held by an end effector.

[0105] Example 19 is a method as in any of the examples, particularly example 17, wherein seating the wafer on the tuned focus ring comprises transferring the wafer from a vacuum transfer chamber by a robot arm, and wherein the wafer is held by an end effector attached to the robot arm.

[0106] Example 20 is a method as in any of the examples, particularly example 17, wherein orienting the tuned focus ring with respect to the plasma asymmetry within the plasma chamber comprises rotating the tuned focus ring by a desired number of degrees to orient the tuned focus ring with respect to the plasma asymmetry within the plasma chamber.

Claims

CLAIMSWhat is claimed is:

1. A plasma processing apparatus, comprising: a tuned focus ring, wherein the tuned focus ring comprises: an inner sidewall having an upper portion and a lower portion extending below the upper portion; and a ledge extending from the inner sidewall between the upper portion and the lower portion, wherein the ledge extends around a circumference of the lower portion of the inner sidewall, wherein the upper portion of the inner sidewall extends a first height over the ledge along a first annular segment of the tuned focus ring, wherein the upper portion extends a second height over the ledge along a second annular segment of the tuned focus ring, and wherein the first height is greater than the second height.

2. The plasma processing apparatus of claim 1, wherein the first annular segment extends along a first circular arc subtended by a first angle, and wherein the second annular segment extends along a second circular arc subtended by a second angle.

3. The plasma processing apparatus of claim 2, wherein the first height is constant along the first circular arc, and wherein the second height is constant along the second circular arc.

4. The plasma processing apparatus of claim 3, wherein a third annular segment extends along a third circular arc between the first circular arc and the second circular arc.

5. The plasma processing apparatus of claim 4, wherein a fourth annular segment extends along a fourth circular arc between the first circular arc and the second circular arc and opposite the third circular arc.

6. The plasma processing apparatus of claim 5, wherein the third annular segment extends a third height over the ledge, and wherein the third height is between the first height and the second height.

7. The plasma processing apparatus of claim 6, wherein the third height is constant along the third annular segment.

8. The plasma processing apparatus of claim 6, wherein the third height is variable along the third annular segment.

9. The plasma processing apparatus of claim 8, wherein the third height is tapered along the third annular segment.

10. The plasma processing apparatus of claim 9, wherein the third height has a linear taper along the third annular segment.

11. The plasma processing apparatus of claim 9, wherein the third height has a non-linear taper along the third annular segment.

12. The plasma processing apparatus of claim 8, wherein the third height is stepped along the third annular segment.

13. A tuned focus ring comprising; a first annular segment and a second annular segment; an inner sidewall comprising: an upper sidewall portion; and a lower sidewall portion extending below the upper sidewall portion, wherein a ledge extends from the inner sidewall and extends along a circumference of the lower sidewall portion between the upper sidewall portion and the lower sidewall portion, wherein the upper sidewall portion extends a first height over the ledge along the first annular segment, wherein the upper sidewall portion extends a second height over the ledge along the second annular segment, and wherein the first height is greater than the second height.

14. The tuned focus ring of claim 13, comprising at least one dielectric material.

15. The tuned focus ring of claim 14, wherein the first annular segment comprises a first dielectric material, and wherein the second annular segment comprises a second dielectric material.

16. The tuned focus ring of claim 15, wherein the first dielectric material comprises ytterbium oxide, and wherein the second dielectric material comprises ruthenium.

17. A method comprising: placing a tuned focus ring on a wafer chuck within a plasma chamber; seating a wafer on the tuned focus ring; depositing a film on the wafer by a plasma deposition process; and orienting the tuned focus ring with respect to a plasma asymmetry within the plasma chamber such that the film is uniform along an edge of the wafer.

18. The method of claim 17, wherein placing the tuned focus ring on the wafer chuck within the plasma chamber comprises transferring the tuned focus ring to the wafer chuck by a robot arm, and wherein the tuned focus ring is held by an end effector.

19. The method of claim 17, wherein seating the wafer on the tuned focus ring comprises transferring the wafer from a vacuum transfer chamber by a robot arm, and wherein the wafer is held by an end effector attached to the robot arm.

20. The method of claim 17, wherein orienting the tuned focus ring with respect to the plasma asymmetry within the plasma chamber comprises rotating the tuned focus ring by a desired number of degrees to orient the tuned focus ring with respect to the plasma asymmetry within the plasma chamber.

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