Patent Application
20110278260
Embodiments described herein generally relate to manufacturing semiconductor devices. More specifically, embodiments described herein relate to methods and apparatus for plasma processing of substrates.
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.
Embodiments described herein provide a lid assembly for a plasma chamber, the lid assembly having a first annular inductive 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 definines 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 conductive 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.
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.
The conductive spacer 114 provides a large surface area grounded electrode that faces the substrate support 104. The large grounded electrode allows generation of higher voltages at the substrate support using lower power levels. Disposing the conductive coils 112 in the conductive spacer 114 also brings the plasma source close to the plasma generation area of the processing region 118, improving coupling efficiency with the plasma. Additionally, the large grounded surface area of the conductive spacer 114 reduces 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 conductive coils 112 also provides the possibility of using different power levels on the coils to tune the plasma profile in the processing region 118.
The plasma source 204 comprises a conductive coil 210 disposed in a channel 212 formed between conductive gas distribution members 214. The gas distribution members 214 may 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 conductive coil 210, 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. Material selection for the conductive coil 210 generally depends on the desired thermal and electrical conductivity. Materials with lower electrical conductivity are generally lower in cost, but a conductive coil made 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 a conductive coil. 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 conductive coil 210 with a conduit for a thermal control medium, which may be a cooling liquid such as water or a cooling gas such as nitrogen. The conductive coil 210 may 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 conductive coil 210. In one embodiment, a conductive coil is a torroidal tube comprising a layer of copper and a layer of silver.
The channel 212 is generally lined with an insulating member 216, which may be ceramic or plastic, Teflon, for example. The insulating member 216 confines the electric current to the conductive coil 210. The insulating material may be an insert that fits into the channel 212, or in other embodiments, may be a liner adhered to the inner surface of the channel 212. The embodiment of
The two conductive loops 218 are electrically isolated, one from the other, by respective isolators 220, which serve to surround each conductive loop 218. In the embodiment of
A field concentrator 222 is disposed around each conductive coil 210 to amplify the magnetic field produced by each conductive coil 210. In the embodiment of
The inductive coils 210 are interposed within the gas distribution members 214 that nest with the insulating members 216 and cooperatively define the channels 212. Conductive members 226 may also be interposed with the inductive coils 210 and the gas distribution members 214. In one embodiment, the conductive members 226 are rings that comprise metal, metal alloy, or metal mixtures, each of which may be attached to a support member 228. The insulating members 216 fit between the conductive members 226 and the gas distribution members 214 to provide the channel 212 in a substantially coplanar configuration with the conductive members 214 and 226, such that the inductive coils 210 are substantially coplanar with the conductive members 214 and 226.
The support member 228 is generally also conductive. In some embodiments, the support member 228 is a metal block. The support member 228 has recesses 230 that, together with the conductive members 226, define capture spaces 232 into which respective shoulder portions 234 of each insulating member 216 are captured to secure the insulating members 216 into the lid assembly 200. The conductive members 214 and 226 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 (
The support member 228 comprises one or more conduits 236 that bring process gases to the conductive gas distribution members 214. Additionally, in some embodiments, the conductive gas distribution members 214 may comprise conduits (not shown) to disperse gas from the conduit 236 around the circumference of the gas distribution member 214 for even gas distribution. By interposing conductive gas distribution members 214 with inductive coils 210, the apparatus 200 may be used as both a plasma source and a showerhead. Gas flow is distributed evenly across the face of the apparatus, and RF power is close-coupled to the process gas exiting the various openings.
Thermal control may be enhanced by optionally including thermal control conduits 240 in the support member 228. Locating thermal control conduits in the support member 228 may enhance thermal control of the field concentrators 222, which are otherwise at least partially insulated from any thermal control fluid circulating through the loops 218 by the isolators 220. Thermal control in the vicinity of the field concentrators 222 may be advantageous for maintaining electromagnetic properties of the field concentrators 222. Also optionally, a cushion 238 may be disposed between the field concentrators 222 and the support member 228 to avoid any damage to the field concentrators 222, which may be easily damaged by direct contact with the metal surface of the support member 228. The cushion 238 may 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 assembly 200 may have any convenient shape or size for processing substrates of any dimension. The lid assembly 200 may be circular, rectangular, or any polygonal shape. The lid assembly 200 may be of a size and shape adapted for processing semiconductor wafers for making semiconductor chips of any description, or the lid assembly 200 may 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 conductive coil (or coils) 210 may 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 conductive coil (or coils) 210 may be disposed in a spiral pattern.
In some embodiments, a lid assembly may be similar to the lid assembly 200 of
The conductors 306 are generally metal, or other electrically conductive material. The metal may be a single metal, an alloy, a mixture, or another combination of metals. The conductors 306 may also be coated with a non-conductive material, such as ceramic or polymer, in some embodiments. In one embodiment, the conductors 306 are 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 RF 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 RF coil may have only one conductor, or more than two conductors.
An insulator 312 is disposed over the conductors 306 so that the conductors 306 are surrounded by insulative material. This prevents electric power from flowing to the conductive rings 314 and 316 interposed between the first and second RF coils 302 and 304. The insulator 312 comprises a wall that is not visible in the top-perspective view of
The insulator 312 further comprises a passage 320 for each contact 310. The passages 320 pass through openings in the field concentrator 318 to provide a pathway for the contacts 310 to be coupled to electric power while preventing electrical contact between the contacts 310 and the field concentrator 318. The contacts protrude through the field concentrator 318, where they may be coupled to an RF source.
As with the embodiment of
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 conductive loops 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 conductive loops. The conductive loops may be electrically insulated from the electrode by coating, wrapping, or situating the loops in an electrically insulating material, which may be a container, such as a channel formed in the electrode, a coating applied to the conductive loops, or a liner disposed inside a channel formed in the electrode. RF power is applied to the loops, and may be controlled independently to shape the plasma density in the process chamber. The conductive loops may be thermally controlled, if desired, by circulating a thermal control medium, such as a cooling fluid, through tubular conductive loops.
The conductive loops may be substantially coplanar with the electrode in some embodiments. In other embodiments, the electrode may be non-planar, with conductive loops disposed therein. In still other embodiments, the conductive loops may be partially disposed in the electrode and partially disposed outside the electrode, with any portions of the conductive loops 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 conductive loops 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.
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.
