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  Plasma reactor apparatus with a toroidal plasma source and a vhf capacitively coupled plasma source with variable frequencyUSPTO Application #: 20070246161Title: Plasma reactor apparatus with a toroidal plasma source and a vhf capacitively coupled plasma source with variable frequency Abstract: A plasma reactor for processing a workpiece includes a reactor chamber and a workpiece support within the chamber, the chamber having a ceiling facing the workpiece support, a toroidal plasma source comprising a hollow reentrant conduit external of the chamber and having a pair of ends connected to the interior of the chamber and forming a closed toroidal path extending through the conduit and across the diameter of the workpiece support, and an RF power applicator adjacent a portion of the reentrant external conduit, and an RF source power generator coupled to the RF power applicator of the toroidal plasma source. The reactor further includes a capacitively coupled plasma source power applicator comprising a source power electrode at one of: (a) the ceiling (b) the workpiece support, and plural VHF power generators of different fixed frequencies coupled to the capacitively coupled source power applicator, and a controller for independently controlling the power output levels of the plural VHF generators so as to control an effective VHF frequency applied to the source power electrode. (end of abstract) Agent: Robert M. Wallace Law Office Of Robert M. Wallace - Ventura, CA, US Inventors: Alexander Paterson, Valentin N. Todorow, Theodoros Panagopoulos, Brian K. Hatcher, Dan Katz, Edward P. Hammond, John P. Holland, Alexander Matyushkin USPTO Applicaton #: 20070246161 - Class: 156345380 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070246161. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] In semiconductor fabrication processes, conventional sources of plasma source power, such as inductively coupled RF power applicators or capacitively couple RF power applicators, introduce inherent plasma density non-uniformities into the processing. In particular, inductively coupled plasma sources are characterized by an "M"-shaped radial distribution of plasma ion density over the semiconductor workpiece or wafer. As device geometries have continued to shrink, such non-uniformities become more critical, requiring better compensation. Presently, the non-uniformity of an overhead inductively coupled source is reduced or eliminated at the wafer surface by optimizing the coil design and ceiling-to-wafer distance, aspect ratio, of the chamber. This distance must be sufficient so that diffusion effects can overcome the effects of the nonuniform ion distribution in the ion generation region before they reach the wafer. For smaller device geometries on the wafer and the inductive plasma source located near the ceiling, a large ceiling-to-wafer distance is advantageous. However, a large ceiling-to-wafer distance can prevent the beneficial gas distribution effects of a ceiling gas distribution showerhead from reaching the wafer surface, due to diffusion over the large distance. For such large ceiling-to-wafer distances, it has been found that the gas distribution uniformity is not different whether a gas distribution showerhead is employed or a small number of discrete injection nozzles are employed. [0002] In summary, the wafer-ceiling gap is optimized for ion density uniformity which may not necessarily lead to gas delivery optimization. [0003] One limitation of such reactors is that not all process parameters can be independently controlled. For example, in an inductively coupled reactor, in order to increase reaction (etch) rate, the plasma source power must be increased to increase ion density. But, this increases the dissociation in the plasma, which can reduce etch selectivity and increase etch microloading problems, in some cases. Thus, the etch rate must be limited to those cases where etch selectivity or microloading are critical. [0004] Another problem arises in the processing (e.g., etching) of multi-layer structures having different layers of different materials. Each of these layers is best processed (e.g., etched) under different plasma conditions. For example, some of the sub-layers may be best etched in an inductively coupled plasma with high ion density and high dissociation (for low mass highly reactive species in the plasma). Other layers may be best etched in a capacitively coupled plasma (low dissociation, high mass ions and radicals), while yet others may be best etched in plasma conditions which may be between the two extremes of purely inductively or capacitively coupled sources. However, to idealize the processing conditions for each sub-layer of the structure being etched would require different process reactors, and this is not practical. SUMMARY OF THE INVENTION [0005] A plasma reactor for processing a workpiece includes a reactor chamber and a workpiece support within the chamber, the chamber having a ceiling facing the workpiece support, a toroidal plasma source comprising a hollow reentrant conduit external of the chamber and having a pair of ends connected to the interior of the chamber and forming a closed toroidal path extending through the conduit and across the diameter of the workpiece support, and an RF power applicator adjacent a portion of the reentrant external conduit, and an RF source power generator coupled to the RF power applicator of the toroidal plasma source. The reactor further includes a capacitively coupled plasma source power applicator comprising a source power electrode at one of: (a) the ceiling (b) the workpiece support, and plural VHF power generators of different fixed frequencies coupled to the capacitively coupled source power applicator, and a controller for independently controlling the power output levels of the plural VHF generators so as to control an effective VHF frequency applied to the source power electrode. BRIEF DESCRIPTION OF THE DRAWINGS [0006] FIG. 1 is a simplified block diagram of a plasma reactor in accordance with an embodiment of the invention. [0007] FIGS. 2A and 2B together constitute a block diagram depicting a method of one embodiment of the invention, and these drawings are hereinafter referred to collectively as "FIG. 2". [0008] FIG. 3A is a graph depicting a radial distribution of plasma ion density that is typical of an inductively coupled plasma. [0009] FIG. 3B is a graph depicting the radial distribution of plasma ion density that is typical of a capacitively coupled plasma. [0010] FIG. 3C is a graph depicting the radial distribution of plasma ion density obtained in the reactor of FIG. 1 in accordance with a method of the invention. [0011] FIG. 4 illustrates ion radial distribution non-uniformity (deviation) as a function of the ratio of the power levels of inductively and capacitively coupled power. [0012] FIG. 5 illustrates ion radial distribution non-uniformity (deviation) as a function of the ratio of the pulse duty cycles of inductively and capacitively coupled power. [0013] FIG. 6 is a graph illustrating lines of constant plasma ion density for pairs of values of inductively and capacitively coupled power levels. [0014] FIG. 7 is a graph illustrating lines of constant plasma ion density for pairs of values of inductively and capacitively coupled power pulsed duty cycles. [0015] FIG. 8 is a graph illustrating the dependency of electron density in the bulk plasma as a function of source power levels for different VHF frequencies of the capacitively coupled power. [0016] FIGS. 9A and 9B together constitute a block diagram depicting a method of another embodiment of the invention, and are hereinafter referred to collectively as "FIG. 9". [0017] FIG. 10 is a graph illustrating different bulk plasma electron energy distribution functions obtained for different mixtures of capacitively and inductively coupled power. [0018] FIG. 11 depicts the change in electron energy distribution functions for different source power levels obtained when capacitively coupled power is added to inductively coupled power. [0019] FIG. 12 depicts different optical emission spectra obtained for different degrees of dissociation (electron energy distributions). [0020] FIG. 13 is a graph depicting how the degree of dissociation (e.g., population of free carbon or free fluorine) increases with increasing ratio of inductively coupled power to capacitively coupled power. [0021] FIG. 14 is a graph depicting how the degree of dissociation (e.g., population of free carbon or free fluorine) increases with increasing ratio of inductively coupled power pulsed duty cycle to capacitively coupled power duty cycle. Continue reading... Full patent description for Plasma reactor apparatus with a toroidal plasma source and a vhf capacitively coupled plasma source with variable frequency Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Plasma reactor apparatus with a toroidal plasma source and a vhf capacitively coupled plasma source with variable frequency patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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