Inductive plasma source with metallic shower head using B-field concentrator

A method and apparatus for plasma processing of substrates is provided. A processing chamber has a substrate support and a lid assembly facing the substrate support. The lid assembly has a plasma source that comprises a coil disposed within a conductive plate, which may comprise nested conductive rings. The coil is substantially coplanar with the conductive plate, and insulated therefrom by an insulator that fits within a channel formed in the conductive plate, or nests within the conductive rings. A field concentrator is provided around the coil, and insulated therefrom by isolators. The plasma source is supported from a conductive support plate. A gas distributor supplies gas to the chamber through a central opening of the support plate and plasma source from a conduit disposed through the conductive plate.

FIELD

Embodiments described herein generally relate to manufacturing semiconductor devices. More specifically, embodiments described herein relate to methods and apparatus for plasma processing of substrates.

BACKGROUND

Plasma processing is commonly used for many semiconductor fabrication processes for manufacturing integrated circuits, flat-panel displays, magnetic media, and other devices. A plasma, or ionized gas, is generated inside a processing chamber by application of an electromagnetic field to a low-pressure gas in the chamber, and then applied to a workpiece to accomplish a process such as deposition, etching, or implantation. The plasma may also be generated outside the chamber and then directed into the chamber under pressure to increase the ratio of radicals to ions in the plasma for processes needing such treatments.

Plasma may be generated by electric fields, by magnetic fields, or by electromagnetic fields. Plasma generated by an electric field normally uses spaced-apart electrodes to generate the electric field in the space occupied by the gas. The electric field ionizes the gas, and the resulting ions and electrons move toward one electrode or the other under the influence of the electric field. The electric field can impart very high energies to ions impinging on the workpiece, which can sputter material from the workpiece, damaging the workpiece and creating potentially contaminating particles in the chamber. Additionally, the high potentials accompanying such plasmas may create unwanted electrical discharges and parasitic currents.

Inductively coupled plasmas are used in many circumstances to avoid some effects of capacitively coupled plasmas. An inductive coil is disposed adjacent to a plasma generating region of a processing chamber. The inductive coil projects a magnetic field into the chamber to ionize a gas inside the chamber. The inductive coil is frequently located outside the chamber, projecting the magnetic field into the chamber through a dielectric window. The inductive coil is frequently driven by high-frequency electromagnetic energy, which suffers power losses that rise faster than the voltage applied to the inductive coil. Thus, strong coupling of the plasma source with the plasma inside the chamber decreases power losses. Control of plasma uniformity is also improved by strong coupling between the plasma source and the plasma.

As device geometry in the various semiconductor industries continues to decline, process uniformity in general and plasma uniformity in particular, becomes increasingly helpful for reliable manufacture of devices. Thus, there is a continuing need for inductive plasma processing apparatus and methods.

SUMMARY

Embodiments described herein provide a lid assembly for a plasma chamber, the lid assembly having a first annular coil nested with a first conductive ring.

Other embodiments provide a processing chamber for a semiconductor substrate, the processing chamber having a chamber body that defines an interior region, a substrate support disposed in the interior region, and a lid assembly disposed in the interior region facing the substrate support, the lid assembly having a gas distributor and a plasma source with a first conductive surface that faces the substrate support, a second conductive surface that faces away from the substrate support, and a plurality of coils disposed in the conductive plasma source between the first surface and the second surface.

Other embodiments provide a method of processing a substrate by disposing the substrate on a substrate support in a processing chamber, providing a plasma source facing the substrate support, the plasma source comprising a plurality of conductive loops disposed in an electrode, to define a processing region between the plasma source and the substrate support, providing a gas mixture to the processing region, grounding the electrode, and forming a plasma from the gas mixture by applying electric power to the conductive loops.

DETAILED DESCRIPTION

FIG. 1is a schematic cross-sectional diagram of a processing chamber100according to one embodiment. The processing chamber100comprises a chamber body102, a substrate support104, and a gas distributor106facing the substrate support104, the gas distributor106and substrate support104defining a processing region118. The gas distributor106comprises a showerhead108, a gas conduit107, and a plasma source110surrounding the showerhead108. The plasma source110comprises a conductive spacer114and a coil112disposed inside the conductive spacer114. There may be one or more coils112disposed in the conductive spacer114. The conductive spacer114may be a disk-like member with channels or conduits housing the coils112. Alternately, the conductive spacer114may be a plurality of rings separating the coils112and nesting with the coils112. Each of the coils112is housed in a channel or recess116lined with an insulating material. The insulating material of the channel or recess116prevents electric current travelling from the coils112into the conductive spacer114. The coils112produce a magnetic field in the processing region118that ionizes a processing gas disposed therein to form a plasma. In some embodiments, the coil112may be a coil assembly featuring a removable insulating member, as further described below in connection withFIG. 2. In one embodiment, the coil112is conductive.

The conductive spacer114provides a large surface area grounded electrode that faces the substrate support104. The large grounded electrode allows generation of higher voltages at the substrate support using lower power levels. Disposing the coils112in the conductive spacer114also brings the plasma source close to the plasma generation area of the processing region118, improving coupling efficiency with the plasma. Additionally, the large grounded surface area of the conductive spacer114reduces plasma sheath voltage in the chamber, which reduces sputtering of chamber walls and chamber lid components, reducing contamination of workpieces disposed on the substrate support. Use of multiple coils112also provides the possibility of using different power levels on the coils to tune the plasma profile in the processing region118.

FIG. 2is a schematic cross-sectional diagram of a lid assembly200according to another embodiment. Similar to the gas distributor106ofFIG. 1, the lid assembly200comprises a showerhead202, a gas conduit206, and a plasma source204. The gas conduit206connects a gas source (not shown) to the showerhead202, placing the gas source in fluid communication with a processing chamber through openings208in the showerhead202.

The plasma source204comprises a support member228, conductive gas distribution rings214, and a coil210disposed in a channel212formed between the conductive gas distribution rings214. As illustrated inFIG. 2, the lid assembly200includes more than one channel212,211. For example, an innermost channel212is formed between an inner gas distribution ring214and the gas conduit206and an outermost channel211is formed between the gas distribution rings214. The gas conduit206is disposed through a central portion of the support member228. The gas distribution rings214may be metal or metal alloy, and may be coated with a dielectric material, if desired, or a chemically resistant or plasma resistant material, such as yttria, in some embodiments. The coil210, of which there may be more than one, may also be metal, metal alloy, or a conductive composite such as a metal coated dielectric or a metal composite featuring metals having different conductivities. The coil210may be conductive or inductive. Material selection for the coil210generally depends on the desired thermal and electrical conductivity. Materials with lower electrical conductivity are generally lower in cost, but a coil210made from low conductivity materials may generate unwanted heat, and may require excessive power to operate. Highly conductive materials such as copper and silver may be used proficiently for the coil210. Less conductive and lower cost materials such as aluminum, zinc, or nickel may be included as alloy or layer components.

Heat may be dissipated by forming the coil210with a conduit for a thermal control medium, which may be a cooling liquid such as water or a cooling gas such as nitrogen. The coil210may be an annular or torroidal tube in some embodiments. The tube wall thickness may be specified based on thermal and electrical conductivity needed. Cooling may be useful when high power, for example greater than about 500 W, is to be applied to the coil210. In one embodiment, the coil210is a torroidal tube comprising a layer of copper and a layer of silver. The power applied to the coil210may be radio frequency (RF) power.

Each channel212is generally lined with an insulating member216, which may be ceramic or plastic, Teflon, for example. The insulating member216confines the electric current to the coil210. The insulating member216may be an insert that fits into the channel212, or in other embodiments, may be a liner adhered to an inner surface of the channel212. The embodiment ofFIG. 2features two insulating members216, each of which is an annular member that fits inside a respective channel212, one of the insulating members216fitting inside the innermost channel212, which is a first channel in the embodiment ofFIG. 2, and the other insulating member216fitting inside the outermost channel211, which is a second channel in the embodiment ofFIG. 2. The second channel211is radially outward of the first channel212. Each of the first channel212and the second channel211has a coil210disposed therein. In the embodiment ofFIG. 2, a first conductive loop218includes a pair of coils210. For example, the first conductive loop218includes a first coil242aand a second coil242b. A second conductive loop219also comprises a pair of coils210. For example, the second conductive loop218includes a third coil248aand a fourth coil248b. Each conductive loop218,219rests inside a recess formed by the respective insulating members216. For example, the first conductive loop218rests in the inner channel212and the second conductive loop rests in the outer channel212.

Each coil210of the conductive loops218,219are electrically isolated from the other coil210of that conductive loop218,219, by respective isolators220, which at least partially surround the coils210. In the embodiment ofFIG. 2, each isolator220is an annular dielectric member having a recess224into which a coil210fits. The recess224of an isolator220and the recess formed by the insulating members216into which the isolator220fits generally face in opposite directions. Thus, each coil210is surrounded on three sides by an isolator220and on one side by an insulating member216. It should be noted that the isolators220may have any convenient cross sectional shape. For example, in an alternate embodiment, the isolators220may be rounded to follow the contours of a rounded, tube-like, coil210, such that the recess224has a rounded cross-sectional shape. In another embodiment, the cross-sectional profile of each isolator220and/or each recess224may be rectangular with beveled corners. In still other embodiments, each coil210may be formed with a coating that isolates the coils of a respective conductive loop218,219. The isolators220may be any insulating material, such as ceramic, glass, or plastic. In the embodiment ofFIG. 2, each isolator220is shown as a single piece covering a single coil210, but in alternate embodiments, an isolator220may be formed to cover two neighboring coils210while disposing a wall between the neighboring coils210.

A field concentrator222is disposed around each conductive loop218to amplify the magnetic field produced by each conductive loop218. In the embodiment ofFIG. 2, the field concentrator222is disposed around a pair of coils210and their respective isolators220, but in other embodiments, each coil210may be paired with a field concentrator222, or more than two coils210may be paired with a field concentrator222. The field concentrator222focuses the magnetic field produced by the respective conductive loop218,219toward the plasma generation area of the processing region, minimizing magnetic energy projecting away from the plasma generation area. Each field concentrator222generally comprises ferrite or other magnetically susceptible or magnetizable materials, such as low coercivity materials. Thermal control of the coils210minimizes temperature variation of the field concentrator222, maintaining the magnetic properties thereof for control of the magnetic field produced by the coils210.

The coils210are nested in the insulating members216which are interposed with the gas distribution rings214. Conductive members226may also be interposed with the coils210and the gas distribution rings214. In one embodiment, the conductive members226are rings that comprise metal, metal alloy, or metal mixtures, each of which may be attached to the support member228. The insulating members216fit between the conductive members226and the gas distribution rings214to provide a channel in which the coils210are disposed. The channel of the insulating members216is substantially coplanar with the gas distribution rings214and the conductive members226. That is, the coils210are substantially coplanar with the gas distribution rings214and the conductive members226. Additionally, the insulating members216form a flat surface with the gas distribution rings214.

The support member228is generally also conductive. In some embodiments, the support member228is a metal block (i.e., a plate). In another embodiment, the support member228is an electrode. The support member228has recesses230that, together with the gas distribution rings214or the conductive members226, define capture spaces232into which respective shoulder portions234of each insulating member216are captured to secure the insulating members216into the lid assembly200. The gas distribution rings214and the conductive members226may be grounded and thus allow for a large grounded surface to be brought into close proximity to the plasma, enabling higher bias voltage to be used on the substrate support at lower power levels and lower heat input (seeFIG. 1). The lid assembly200configuration ofFIG. 2also brings the plasma source energy of the coils210into close proximity with a gas in the processing region, resulting in a higher plasma density at lower power levels. Use of multiple coils, such as the coils210, also enables tuning of the plasma profile generated in the chamber by adjusting the power level applied to each individual coil.

The support member228comprises one or more conduits236(i.e., a plenum) that bring process gases to the gas distribution rings214. InFIG. 2, the conduit236is formed through the support member228above the gas distribution rings214and radially outward from the showerhead202. Additionally, in some embodiments, the gas distribution rings214may comprise conduits (not shown) to disperse gas from the conduit236around the circumference of the gas distribution member214for even gas distribution in the processing region. Additionally, the conduit236is in fluid communication with the processing region via a plurality of openings213formed through the gas distribution rings214. By interposing the gas distribution rings214with the coils210, the lid assembly200may be used as both a plasma source and a showerhead. Gas flow is distributed evenly across the face of the lid assembly200, and RF power is close-coupled to the process gas exiting the plurality of openings213formed through gas distribution rings214.

Thermal control may be enhanced by optionally including thermal control conduits240in the support member228. Locating thermal control conduits240in the support member228may enhance thermal control of the field concentrators222, which are otherwise at least partially insulated from any thermal control fluid circulating through the coils210by the isolators220. Thermal control in the vicinity of the field concentrators222may be advantageous for maintaining electromagnetic properties of the field concentrators222. Also optionally, a cushion238may be disposed between the field concentrators222and the support member228to avoid any damage to the field concentrators222, which may be easily damaged by direct contact with the metal surface of the support member228. The cushion238may be a thermally conductive material such as Grafoil®, which is a flexible graphitic sealing material manufactured by Natural Graphite Operations, of Lakewood, Ohio, a subsidiary of GrafTech International, and distributed by Leader Global Technologies, of Deer Park, Tex.

In general, the lid assembly200may have any convenient shape or size for processing substrates of any dimension. The lid assembly200may be circular, rectangular, or any polygonal shape. The lid assembly200may be of a size and shape adapted for processing semiconductor wafers for making semiconductor chips of any description, or the lid assembly200may be of a size and shape adapted for processing semiconductor panels such as large-area display or solar panels. Other types of substrates, such as LED substrates or magnetic media substrates, may also be processed using a lid assembly as herein described. In some embodiments, the coil (or coils)210may be disposed in a concentric circular shape, in a concentric non-circular (rectangular, polygonal, square, or irregular) shape, or in a non-concentric shape such as a boustrophedonic or zig-zag pattern. In another non-concentric embodiment, the coil (or coils)210may be disposed in a spiral pattern.

In some embodiments, a lid assembly may be similar to the lid assembly200ofFIG. 2, with some differences. In one embodiment, the lid assembly may have a curved surface facing the substrate support, curved in a convex or concave sense. In one aspect, the entire plasma source may be curved (i.e., the surface of the plasma source facing the substrate support and the surface facing away from the substrate support are both convex or concave). In another aspect, only the surface of the lid assembly facing the substrate support may be curved. In one embodiment, multiple showerheads may be provided, especially for large area lid assemblies. In one embodiment, gas may be injected through the conductive members226by providing one or more conduits through the support member228. In other embodiments, coils may be provided that comprise a single electrical circuit, rather than multiple discrete circuits. For example, in one embodiment, the coil may be arranged in a planar, circular or rectangular spiral shape nested with, or disposed in, a complementary conductive member such that the conductive member and the coil form a substantially planar plasma source. Such a spiral shape may also be z-displaced such that the plasma source is not planar, but has a z-dimension in a convex or concave sense.

FIG. 3is an exploded view of a lid assembly300according to another embodiment. The lid assembly300is similar in most respects to the lid assembly200ofFIG. 2, and identical features are labeled with the same identifying labels. The lid assembly300comprises a gas conduit206for delivering gas to the process region of the chamber on which the lid assembly300is installed. The lid assembly300further comprises a first conductive loop302and a second conductive loop304similar to the first conductive loop302, with the first conductive loop302shown in exploded format. The first conductive loop302comprises a plurality of coils306disposed in an insulating channel308. In the embodiment ofFIG. 3, the coils306are circular and concentric, but in alternate embodiments the coils306may be disposed in any convenient configuration, as described herein. Each of the coils306has a contact310for supplying power to the coils306. As described elsewhere herein, the coils306may be conductive tubes configured to carry a coolant in addition to electric power. Thus, the contacts310may also be used to provide coolant to the coils306.

The coils306are generally metal, or other electrically conductive material. The metal may be a single metal, an alloy, a mixture, or another combination of metals. The coils306may also be coated with a non-conductive material, such as ceramic or polymer, in some embodiments. In one embodiment, the coils306are copper tubes plated with silver. The metals to be used generally depend on the electrical and thermal properties needed for the particular embodiment. In high power applications, higher electrical conductivity will generally result in lower thermal budget, so more conductive materials may be advantageous. It should be noted that when multiple coils are used, each of the coils may have a different composition. For example, silver plated copper tubes may have different thicknesses of silver plating or different tube wall thicknesses to provide differential conductivity among the tubes. In other embodiments, each conductive loop302and304may have only one coil, or more than two coils.

An insulator312is disposed over the coils306so that the coils306are surrounded by insulative material. This prevents electric power from flowing to conductive rings314and316interposed between the first conductive loop302and the second conductive loop304. The insulator312comprises a wall that is not visible in the top-perspective view ofFIG. 3. The wall extends between the two coils306to prevent electrical cross-talk between the coils306in a given conductive loop302or304. Thus, each coil306is surrounded by insulative material. When power is provided to the coils306, a magnetic field is generated by the coils306. A field concentrator318is disposed partially around the coils306to focus and direct the magnetic field in the direction of the processing region for improved efficiency.

The insulator312further comprises a passage320for each contact310. The passages320pass through openings in the field concentrator318to provide a pathway for the contacts310to be coupled to electric power while preventing electrical contact between the contacts310and the field concentrator318. The contacts310protrude through the field concentrator318, where the contacts310may be coupled to an RF source.

As with the embodiment ofFIG. 2, any number of conductive loops, such as conductive loops302and304, may be disposed in the lid assembly300. Similar to the gas distribution rings214ofFIG. 2, process gases may also be provided through the conductive rings314and316, in addition to or in place of the gas conduit206, by providing a plurality of openings (not shown) through the conductive rings314and316to release process gases into the processing region. The lid assembly300may also be formed with a curvature according to any of the embodiments described herein.

Embodiments disclosed herein also provide a method of processing a substrate on a substrate support in a process chamber. A plasma source may be provided in a position facing the substrate support to form a plasma for processing the substrate. The method comprises providing a plasma source that has a plurality of coils disposed in an electrode, providing a processing gas to the chamber, grounding the electrode, and forming a plasma from the processing gas by applying power to the coils. The coils may be electrically insulated from the electrode by coating, wrapping, or situating the coils in an electrically insulating material, which may be a container, such as a channel formed in the electrode, or a liner disposed inside a channel formed in the electrode. RF power is applied to the coils, and may be controlled independently to shape the plasma density in the process chamber. The coils may be thermally controlled, if desired, by circulating a thermal control medium, such as a cooling fluid, through the tubular coils.

The coils may be substantially coplanar with the electrode in some embodiments. In other embodiments, the electrode may be non-planar, with the coils disposed therein. In still other embodiments, the coils may be partially disposed in the electrode and partially disposed outside the electrode, with any portions of the coils disposed outside the electrode contained or encapsulated in an insulating material.

The plasma may be further enhanced by providing a field concentrator disposed to concentrate the field inside the plasma region of the processing chamber. For example, the field concentrator may generally be disposed opposite the substrate support, such that the coils are between the field concentrator and the substrate support. Such positioning prevents development of magnetic field lines outside the chamber, and focuses the plasma source energy in the processing gas.