Ion-ion plasma atomic layer etching process and reactor

Abstract

To form a plasma reactor having an electron beam plasma source in which there are no inherent asymmetries.SOLUTION: A reactor with an overhead electron beam source is capable of generating ion-ion plasma for performing an atomic layer etch process.SELECTED DRAWING: Figure 1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. patent application Ser. No. 14 / 660,531, filed Mar. 17, 2015, by Kenneth S. Collins et al., entitled "Ion-Ion Plasma Atomic Layer Etch Process and Reactor." Background

[0002] (Technical field) The present disclosure relates to a plasma reactor for processing a workpiece (eg, a semiconductor wafer) using an overhead electron beam source.

[0003] (Background discussion) A plasma source for processing a workpiece may include an electron beam source having a beam path that is transverse to the cylindrical symmetry axis of the plasma reactor. Such a transverse arrangement may introduce asymmetries into the process, whereas special configurations may be required within the reactor to avoid such asymmetries.

[0004] There is a need for a plasma reactor having an electron beam plasma source that is free of inherent asymmetry.

[0005] The electron beam plasma reactor includes: (1) an upper plasma chamber including: (a) a sidewall; (b) an upper electrode support including an electrically insulated electrostatic chuck and a thermal controller coupled to the upper electrode support; (c) an upper electrode thermally coupled to the upper electrode support and having an upper electrode surface; (d) an RF source power generator coupled to the upper electrode or to the upper electrode support or to an interior of the upper chamber; and a DC chucking voltage source coupled to the electrically insulated electrostatic chuck; (e) a gas distributor; and (f) a grid filter facing the upper electrode surface. The electron beam plasma reactor further includes (2) a lower plasma chamber, where the grid filter separates the upper plasma chamber from the lower plasma chamber, the lower plasma chamber including: (a) a vacuum chamber body enclosing a processing region; and (b) a workpiece support pedestal coupled to the workpiece support pedestal, the workpiece support pedestal having a workpiece support surface facing the grid filter, the workpiece support pedestal including an electrically insulated electrostatic chuck and a thermal controller.

[0006] In one embodiment, the reactor further includes a bias voltage generator coupled to the workpiece support pedestal.

[0007] In one embodiment, the top electrode comprises one of silicon, carbon, silicon carbide, silicon oxide, aluminum oxide, yttrium oxide, or zirconium oxide.

[0008] In one embodiment, the RF source power generator includes a first RF power generator at a VHF frequency and a second RF power generator at a frequency below VHF.

[0009] In one embodiment, the grid filter is conductive and the grid filter is either (a) electrically floating or (b) at a fixed potential.

[0010] An embodiment of the plasma reactor further includes a folded resonator coupled between the first RF power generator and the upper electrode, hi one embodiment, the folded resonator is coaxial with the sidewall.

[0011] In one embodiment, the RF source power generator includes a low VHF frequency generator having a first VHF frequency and a high VHF frequency generator having a second VHF frequency greater than the first VHF frequency.

[0012] In one embodiment, the grid filter includes first and second grids opposed to one another, and the plasma reactor further includes an accelerating voltage source connected to one of the first and second grids.

[0013] One embodiment further includes a first magnet adjacent one of the upper and lower chambers, each of which is circularly shaped and disposed at a respective axial position around the chamber. In the latter embodiment, the reactor further includes a second magnet adjacent each of the upper and lower chambers, the first and second magnets being circularly shaped and disposed at a respective axial position around the chamber, the first and second magnets generating one of: (a) a cusp-shaped magnetic field that is primarily axial in the upper chamber and primarily radial in the lower chamber, or (b) an axial magnetic field. In the latter embodiment, the reactor further includes a third magnet, the first and second magnets generating a first cusp-shaped magnetic field having a cusp surface in the upper chamber, and the second and third magnets generating a second cusp-shaped magnetic field having a cusp surface in the lower chamber.

[0014] In one embodiment, the reactor further comprises a magnet having a magnetic field in a transverse direction within said lower chamber.

[0015] In one embodiment, the reactor further includes a window in the sidewall, a coil antenna around the window, and an RF generator coupled to the coil antenna.

[0016] In one embodiment, the reactor further includes a remote plasma source having an output coupled to the chamber.

[0017] According to a further embodiment, a method for processing a workpiece in an electron beam plasma reactor includes dividing a chamber of the reactor into an upper chamber and a lower chamber by a grid filter and supporting a workpiece in the lower chamber with a surface of the workpiece facing the grid filter along an axis; supplying a gas into the chamber; coupling RF source power into or to electrodes in the upper chamber to generate a plasma including beam electrons in the upper chamber to generate an electron beam having a beam propagation direction corresponding to the axis; allowing at least a portion of the beam electrons to flow from the upper chamber to the lower chamber while preventing at least a portion of non-beam electrons and plasma ions from flowing from the upper chamber to the lower chamber; and generating a plasma in the lower chamber from the electron beam.

[0018] In one embodiment, the method further includes supplying a substantially inert gas to the upper chamber and a molecular process gas to the lower chamber.

[0019] In one embodiment, generating the plasma includes applying RF power to a plasma source electrode below a ceiling of the upper chamber, and the method further includes supporting the plasma source electrode by electrostatically chucking the electrode to the ceiling.

[0020] In one embodiment, the method further comprises controlling a temperature of the plasma source electrode by circulating a heat conducting medium within the ceiling.

[0021] In one embodiment, the method further includes coupling a bias voltage to the workpiece.

[0022] In one embodiment, the plasma source electrode comprises one of silicon, carbon, silicon carbide, silicon oxide, aluminum oxide, yttrium oxide, zirconium oxide.

[0023] In one embodiment, generating the plasma includes applying RF source power to a plasma source electrode below a ceiling of the upper chamber, the RF source power including RF power at a first frequency and RF power at a second frequency.

[0024] In one embodiment, the method further includes providing a magnetic field in the chamber from a first magnet, the first magnet comprising either a permanent magnet or an electromagnet, hi one embodiment, the method further includes providing a second magnet, the first and second magnets generating one of a cusp magnetic field or an axial magnetic field.

[0025] In one embodiment, generating the plasma further comprises applying RF source power to a coil antenna around a window in a sidewall of the upper chamber.

[0026] In yet another embodiment, a method for performing atomic layer etching in a process chamber using an electron beam plasma source includes the steps of: dividing the process chamber into upper and lower chambers by a grid filter; the upper chamber having a ceiling electrode, placing a workpiece in the lower chamber having a surface layer to be etched; supplying a molecular process gas to the chamber; and (I) performing a passivation process, the passivation process comprising: (A) performing at least one of the following steps: (a) coupling a high power level of VHF power into the upper chamber or into the ceiling electrode; or (b) coupling a high level of inductively coupled power into the upper chamber; and (B) depositing a passivation gas on the workpiece to etch the surface layer of the workpiece. (II) performing a passivation process comprising: (A) performing at least one of the following: (a) applying a high level of low frequency RF power to the ceiling electrode; or (b) reducing or eliminating a power level of at least one of (1) the VHF power or (2) the inductively coupled power; and (B) maintaining a bias voltage on the workpiece above a threshold value to etch the surface layer; and (III) alternately and continuously repeating the passivation process and the etching process.

[0027] In one embodiment, the step of supplying a molecular process gas to the chamber includes supplying the molecular process gas into the lower chamber, hi this latter embodiment, the method may further include supplying an inert gas into the upper chamber.

[0028] In one embodiment, the step of supplying a molecular process gas to the chamber includes supplying the molecular process gas into the upper chamber, hi this latter embodiment, the passivation process may further include supplying an inert gas into the upper chamber.

[0029] In one embodiment, the method further comprises carrying out the passivation process for a time period corresponding to passivation of a selected depth of material of the surface layer, which in one embodiment is one atomic layer.

[0030] In one embodiment, the molecular process gas includes a passivation species.

[0031] In one embodiment, reducing the dissociation during the etching process substantially stops or reduces passivation of the surface layer of the workpiece.

[0032] In one embodiment, enhancing the dissociation during the passivation process includes generating an electron beam propagating from the upper chamber to the lower chamber by ion bombardment of the ceiling electrode.

[0033] In one embodiment, (a) the VHF power of the high level of power is in the range of 300 to 10,000 watts, (b) the high level of inductively coupled power is in the range of 300 to 10,000 watts, and (c) the high level of low frequency RF power is in the range of 300 to 10,000 watts. [Brief description of the drawings]

[0034] So that a detailed understanding can be gained of the manner in which the exemplary embodiments of the invention are accomplished, a more particular description of the invention briefly summarized above can be made by reference to the embodiments thereof as illustrated in the accompanying drawings. It should be understood that in order not to obscure the invention, some well-known processes have not been discussed herein. [Figure 1] 1 shows a plasma reactor according to a first embodiment. [Figure 1A] 2 shows a variation of the plasma reactor of FIG. 1 having a pair of grids. [Diagram 2] 2 shows a plasma reactor according to a second embodiment. [Diagram 3] FIG. 3 is a partially cut-away elevational view of a VHF resonator used in the embodiment of FIG. 2. [Figure 4] FIG. 4 is a plan view corresponding to FIG. [Figure 5A] FIG. 4 is an orthographic view of a second embodiment of the VHF resonator of FIG. 3; [Figure 5B] FIG. 5B is a plan view corresponding to FIG. 5A. [Figure 5C] FIG. 5B is an enlarged view of a portion of FIG. 5A. [Figure 6] 1 shows an embodiment having a cusp-type magnetic field as a magnetic filter. [Figure 7] 1 illustrates an embodiment having an axial magnetic field for confining the electron beam. [Figure 8] 1 shows an embodiment having a transverse magnetic field as a magnetic filter. [Figure 9] 1 shows an embodiment having an upper cusp-type magnetic field to confine the plasma near the ceiling electrode and a lower cusp-type magnetic field as a magnetic filter. [Figure 10] 1 is a block diagram illustrating a method according to an embodiment. [Figure 11] FIG. 1 is a block diagram illustrating an atomic layer etching method according to an embodiment.

[0035] To facilitate understanding, the same reference numbers have been used, whenever possible, to designate identical elements common to the figures. It will be understood that elements and features of one embodiment may be beneficially incorporated in other embodiments without further description. It should be noted, however, that the appended drawings depict only illustrative embodiments of the invention and are therefore not to be construed as limiting the scope thereof, as the invention may include other equally effective embodiments. DETAILED DESCRIPTION

[0036] Referring to FIG. 1, an electron beam plasma reactor has a vacuum chamber body defining a chamber 100 including a cylindrical sidewall 102. The chamber 100 is divided into an upper chamber 100a and a lower chamber 100b by a grid filter 104. The lower chamber 100b is a drift space since there is no substantial electric field inside when no bias voltage is applied. A ceiling 106 is located above the upper chamber 100a and supports an electrode 108. In one embodiment, the electrode 108 is formed of a process compatible material (e.g., silicon, carbon, silicon carbon compounds, or silicon oxide compounds). In an alternative embodiment, the electrode 108 is formed of a metal oxide (e.g., aluminum oxide, yttrium oxide, or zirconium oxide). The ceiling 106 and the electrode 108 can be disk-shaped. The bottom surface of the electrode 108 faces the grid filter 104 and is exposed to the interior of the upper chamber 100a. In one embodiment, an insulator or dielectric ring 109 surrounds the electrode 108 .

[0037] A workpiece support stage 110 supporting a workpiece 111 in the lower chamber 100b has a workpiece support surface 110a facing the grid filter 104 and may be axially movable by a lift servo 112. In one embodiment, the workpiece support stage 110 includes an insulating puck 302 forming the workpiece support surface 110a, a workpiece electrode 304 inside the insulating puck 302, and a chuck voltage supply 305 connected to the workpiece electrode 304. Additionally, a base layer 306 below the insulating puck 302 has internal flow passages 308 for circulating a heat medium (e.g., liquid) from a circulating supply 310. The circulating supply 310 may function as a heat sink or a heat source.

[0038] An RF power generator 120 having a VHF frequency (e.g., 160 MHz) and a low frequency RF power generator 122 having a frequency below the VHF range or below the HF range (e.g., MF or LF range, e.g., 2 MHz) are coupled to the electrode 108 through an impedance matcher 124 via an RF feed conductor 123. In one embodiment, the impedance matcher 124 is adapted to provide impedance matching at different frequencies of the RF power generators 120 and 122 as well as filtering to isolate the power generators from each other. The output power levels of the RF power generators 120, 122 are independently controlled by a controller 126. As described in detail below, power from the RF power generators 120, 122 is coupled to the electrode 108. In one embodiment, the ceiling 106 is conductive and in electrical contact with the electrode 108, and power from the impedance matcher 124 is conducted through the ceiling 106 to the electrode 108. In one embodiment, the sidewall 102 is formed of metal and is grounded. In one embodiment, the surface area of ​​the grounded inner surface in the upper chamber 100a is at least twice the surface area of ​​the electrode 108. In one embodiment, the grounded inner surface in the chamber 100 may be coated with a process compatible material (e.g., silicon, carbon, silicon carbon compounds, or silicon oxide compounds). In an alternative embodiment, the grounded inner surface in the chamber 100 may be coated with a material such as aluminum oxide, yttrium oxide, or zirconium oxide.

[0039] In one embodiment, the RF power generator 120 may be replaced by two separately controlled VHF power generators 120a and 120b. The VHF generator 120a has an output frequency in the lower part of the VHF band (e.g., 30 MHz to 150 MHz), while the VHF generator 120b has an output frequency in the upper part of the VHF band (e.g., 150 MHz to 300 MHz). The controller 126 can control the plasma ion density by selecting the ratio between the output power levels of the VHF generators 120a and 120b. The two VHF power generators 120a and 120b can control the radial plasma uniformity in the upper chamber 100a by selecting the gap (the distance between the electrode 108 and the grid filter 104) of the upper chamber 100a, whereby the lower VHF frequency by itself produces an edge-high radial distribution of plasma ion density in the upper chamber 100a, and the upper VHF frequency by itself produces a center-high radial distribution of plasma ion density. With such a selection, the power levels of the two VHF power generators 120a, 120b are then set in a ratio that optimizes the uniformity of the radial distribution of plasma ion density.

[0040] In one embodiment, the ceiling 106 is a support for the electrode 108 and includes an insulating layer 150 including a chucking electrode 152 facing the electrode 108. A DC chucking voltage source 154 is coupled to the chucking electrode 152 via a feed conductor 155 to electrostatically clamp the electrode 108 to the ceiling 106. A DC blocking capacitor 156 may be connected in series with the output of the impedance matcher 124. A controller 126 may control the DC chucking voltage source 154. In one embodiment, an RF feed conductor 123 from the impedance matcher 124 may be connected to the electrode support or the ceiling 106 rather than directly to the electrode 108. In one such embodiment, RF power from the RF feed conductor 123 may be capacitively coupled from the electrode support to the electrode 108.

[0041] In one embodiment, the top gas injector 130 supplies process gas into the upper chamber 100a through a first valve 132. In one embodiment, the bottom gas injector 134 supplies process gas into the lower chamber 100b through a second valve 136. Gas is supplied from an array of process gas sources 138 through an array of valves 140 (which may include, for example, first and second valves 132 and 136). In one embodiment, the gas species and gas flow rates into the upper and lower chambers 100a, 100b are independently controllable. The controller 126 may control the array of valves 140. In one embodiment, an inert gas is supplied into the upper chamber 100a and a process gas is supplied into the lower chamber 100b. The flow rate of the inert gas may be selected to substantially prevent convection or diffusion of gas from the lower 100b into the upper chamber 100a, providing substantial chemical isolation of the upper chamber 100a.

[0042] In one embodiment, plasma can be generated in the upper chamber 100a by various bulk and surface processes involving high energy ion bombardment of the inner surface of the upper electron emission electrode 108. The ion bombardment energy and plasma density of the electrode 108 are functions of both RF power generators 120 and 122. The ion bombardment energy of the electrode 108 can be substantially controlled by the low frequency power from the RF power generator 122, and the plasma density in the upper chamber 100a can be substantially controlled (enhanced) by the VHF power from the RF power generator 120. High energy secondary electrons can be emitted from the inner surface of the electrode 108. The flux of high energy electrons from the emission surface can include an electron beam and can have a direction substantially perpendicular to the inner surface of the electrode 108, with the beam energy being approximately the ion bombardment energy of the electrode 108, which can typically range from about 10 eV to 5000 eV. The impact cross section of different processes depends on the electron energy. At low energies, the cross section for excitation (and dissociation in molecular gases) is larger than for ionization, and the reverse is true at high energies. RF power levels may be advantageously selected to target various inelastic electron collision processes.

[0043] In another embodiment having an optional RF source generator 174 and coil antenna 172 , the plasma density in the upper chamber 100 a can be substantially controlled (enhanced) by RF power from the RF power generator 174 .

[0044] In one embodiment, the grid filter 104 may be flat disk-shaped and coaxial with the sidewall 102. The grid filter 104 is formed by an array of multiple openings 104-1. In one embodiment, the axial thickness T of the grid filter 104 and the diameter d of the multiple openings 104-1 are selected to promote the flow of high energy directed beam electrons through the grid filter 104 while impeding the flow of non-beam (low energy) electrons and plasma ions through the grid filter 104, and the ratio of the grid filter hole area to the total grid filter area can be maximized. A high energy electron flux (electron beam) can pass through the grid filter 104 to reach the lower chamber 100b, where a plasma can be generated by various electron collision processes in the lower chamber 100b.

[0045] The plasma generated by the electron beam in the lower chamber 100b may have different characteristics than the plasma in the upper chamber 100a. The grid filter 104 may function as a filter to substantially electrically isolate the upper and lower chambers 100a, 100b from each other. In one embodiment, the grid filter 104 is formed of a conductive or semiconductive material and may be connected to ground or may be electrically floating. In another embodiment, the grid filter 104 is formed of a nonconductive material. In one embodiment, the grid filter 104 may be coated with a process compatible material (e.g., silicon, carbon, silicon carbon compounds, or silicon oxide compounds). In an alternative embodiment, the grid filter 104 may be coated with a material such as aluminum oxide, yttrium oxide, or zirconium oxide. In one embodiment, the plasma generated in the upper chamber 100a may have a high electron density and / or high electron temperature and may have high energy ions that bombard the electrode 108.

[0046] At least a portion of the electron beam, consisting of secondary electron flux emitted from the electrode 108 due to energetic ion bombardment of the electrode surface, propagates through the grid filter 104 into the lower chamber 100b, generating a low electron temperature plasma in the lower chamber 100b with a plasma density that depends on the beam energy and beam flux as well as other factors (e.g., pressure and gas composition). As the energetic beam electrons leave the plasma region of the lower chamber 100b, they may impinge on the workpiece 111 or the workpiece support pedestal 110. The remaining plasma can easily discharge the resulting surface charge caused by the electron beam flux.

[0047] In one embodiment, an electronegative or electron attaching gas (e.g., chlorine) is supplied into the chamber, RF and / or VHF power is applied to the electrode 108, optionally RF power is applied to the coil antenna 172, and optionally RPS power is applied to the remote plasma source (RPS) 280, a plasma is generated in the upper chamber 100a, and an accelerating voltage is generated on the electrode 108 with respect to ground and with respect to the plasma. The resulting high energy ion bombardment of the electrode 108 generates secondary electron emissions from the electrode surface, which constitute an electron beam flux from the electrode surface. The grid filter 104 allows at least a portion of the electron beam to propagate through the grid filter 104 into the lower chamber 100b, while preventing at least a portion of the non-beam electrons and plasma ions from passing through the grid filter 104, generating a low electron temperature plasma in the lower chamber 100b. The low electron temperature plasma achieved in an electronegative gas (e.g., chlorine) in the lower chamber 100b can produce a highly electronegative plasma having a density of negative ions much higher than the electron density and the approaching density of positive ions. Such a plasma is commonly referred to as an ion-ion plasma.

[0048] A substantially axially oriented magnetic field substantially parallel to the electron beam may optionally be used to help guide the electron beam and improve beam transport through the upper chamber 100a, the grid filter 104, and / or the lower chamber 100b. A low frequency bias voltage or any waveform with a low repetition frequency may be applied to the workpiece support 110 (e.g., to the workpiece electrode 304) to selectively or alternately extract positive and / or negative ions from the plasma and accelerate these ions to a desired energy level to impinge on the surface of the workpiece 111 for etching, cleaning, deposition, or other material modification. Radicals generated (a) in the upper chamber 100a, (b) in the lower chamber 100b by the electron beam, (c) by application of a bias voltage to the workpiece support 110, or (d) by the remote plasma source (RPS) 280 may convect or diffuse to the workpiece 111 and participate in reactions on the workpiece surface.

[0049] In another embodiment, a relatively inert gas (e.g., helium or argon) is provided in the upper chamber 100a, an electronegative or electron-attaching gas (e.g., sulfur hexafluoride) is flowed into the lower chamber 100b, RF and / or VHF power is applied to the electrode 108, optionally RF power is applied to the coil antenna 172, and optionally RPS power is applied to the RPS 280, a plasma is generated in the upper chamber 100a, and an accelerating voltage is generated on the electrode 108 relative to ground and the plasma. The resulting energetic ion bombardment of the electrode 108 generates secondary electron emissions from the electrode surface, which constitute an electron beam flux from the electrode surface. The grid filter 104 allows at least a portion of the electron beam to propagate through the grid filter 104 into the lower chamber 100b while preventing at least a portion of the non-beam electrons and plasma ions from passing through the grid filter 104, generating a low electron temperature plasma in the lower chamber 100b.

[0050] The resulting low electron temperature plasma in an electronegative gas (e.g., sulfur hexafluoride) in the lower plasma chamber can produce a highly electronegative plasma with a negative ion density much higher than the electron density and the approaching density of positive ions, commonly referred to as an ion-ion plasma. A substantially axially oriented magnetic field substantially parallel to the electron beam can optionally be used to help guide the electron beam and improve beam transport through the upper chamber 100a, the grid filter 104, and / or the lower chamber 100b. A low frequency bias voltage or any waveform with a low repetition frequency can be applied to the workpiece support 110 to selectively or alternately extract positive and / or negative ions from the plasma and accelerate the ion species to a desired energy level so that they can impinge on the workpiece surface for etching, cleaning, deposition, or other material modification. Radicals generated (a) in the upper chamber 100a, (b) by the electron beam in the lower chamber 100b, (c) by application of a bias voltage to the workpiece support 110, or (d) by the RPS 280 can convect or diffuse to the workpiece 111 and participate in reactions on the workpiece surface.

[0051] In one embodiment, the grid filter 104 is a gas distribution plate having internal gas passages 105a and gas injection outlets 105b. The internal gas passages 105a can be coupled to an array of valves 140.

[0052] In one embodiment, the RF bias power generator 142 is coupled to the workpiece electrode 304 of the workpiece support 110 via an impedance matcher 144. In a further embodiment, a waveform adjustment processor 147 may be connected between the output of the impedance matcher 144 and the workpiece electrode 304. The waveform adjustment processor 147 changes the waveform generated by the RF bias power generator 142 to a desired waveform. The ion energy of the plasma near the workpiece 111 is controlled by the waveform adjustment processor 147. In one embodiment, the waveform adjustment processor 147 generates a waveform whose amplitude is held at a level corresponding to a desired ion energy level during a particular portion of each RF cycle. The controller 126 may control the waveform adjustment processor 147.

[0053] In one embodiment, magnets 160 surround the chamber 100. In one embodiment, the magnets include a pair of magnets 160-1, 160-2 adjacent the upper and lower chambers 100a, 100b, respectively. In one embodiment, the pair of magnets 160-1, 160-2 provides an axial magnetic field suitable for confining an electron beam propagating from the upper chamber 100a to the lower chamber 100b.

[0054] In one embodiment, a side window 170 in the sidewall 102 faces the upper chamber 100a and is formed of a material (e.g., quartz or aluminum oxide) through which RF power can be inductively coupled. An inductive coil antenna 172 surrounds the side window 170 and is driven by an RF power generator 174 through an impedance matcher 176. A remote plasma source 280 can introduce plasma species into the lower chamber 100b.

[0055] In one embodiment, the flow of energetic electrons to workpiece 111 is blocked by a magnetic field having a predominantly radial component (i.e., transverse to the flow direction of the electron beam) in the region between grid filter 104 and workpiece 111. This magnetic field may be generated by one of magnets 160-1 or 160-2, or by another magnet or set of magnets.

[0056] In one embodiment, an internal passage 178 for conducting a thermally conductive liquid or medium inside the ceiling 106 is connected to a heat medium circulation source 180. The heat medium circulation source 180 functions as a heat sink or heat source. The mechanical contact between the electrode 108 and the ceiling 106 is sufficient to maintain a high thermal conductance between the electrode 108 and the ceiling 106. In the embodiment of FIG. 1, the force of the mechanical contact is regulated by an electrostatic clamping force provided by the DC chucking voltage supply 154.

[0057] 1A, the grid filter 104 is replaced by two spaced apart grids, an upper grid filter 104A and a lower grid filter 104B. In one embodiment, the upper and lower grid filters 104A, 104B are conductive and may be held at different voltages. For example, the upper grid filter 104A may be grounded while the accelerating voltage supply 300 may be connected to the lower grid filter 104B.

[0058] In an alternative embodiment, the RF drive coil antenna 290 may be located above the ceiling 106 .

[0059] Figure 2 shows a variation of the embodiment of Figure 1 in which VHF power (from RF generator 120) and lower frequency (low frequency) RF power (from RF generator 122) are supplied to electrode 108 via separate paths. In the embodiment of Figure 2, RF generator 120 is coupled to electrode 108 via a folded resonator 195 on the end of electrode 108. The lower frequency RF generator 122 is coupled to electrode 108 via RF feed conductor 123 through RF impedance matcher 194. A DC chucking voltage supply 154 is coupled to chucking electrode 152 via feed conductor 155 that extends through a passage in ceiling 106.

[0060] An embodiment of the folded resonator 195 of FIG. 2 will now be described with reference to FIGS. 3 and 4. The folded coaxial resonator 195 includes an inner conductive hollow cylinder 200 coaxial with the ceiling electrode 108. The inner conductive hollow cylinder 200 has a circular bottom end 200a that is in electrical contact with the top surface of the ceiling electrode 108. The folded coaxial resonator 195 further includes an outer conductive hollow cylinder 205 having a circular bottom end 205a that is in contact with the top surface of a dielectric ring 109 that surrounds the periphery of the electrode 108. The dielectric ring 109 can consist of an insulating support ring 109a and an insulating clamping ring 109b below the insulating support ring 109a. The inner and outer conductive cylinders 200, 205 are at least approximately the same axial length, such that their circular top ends 200b, 205b are at the same height above the ceiling electrode 108. The folded coaxial resonator 195 also includes a flat conductive annulus 210 that rests on and is electrically connected to the circular top ends 200b, 205b of the inner and outer hollow conductive cylinders 200, 205. The folded coaxial resonator 195 further includes a central conductive hollow cylinder 215 that is coaxial with and located between the inner and outer hollow conductive cylinders 200, 205. Preferably, the radius of the central conductive hollow cylinder 215 can be the geometric mean of the radii of the inner and outer hollow conductive cylinders 200, 205. The central conductive hollow cylinder 215 has a circular bottom end 215a that rests on and is in electrical contact with the top surface of the electrode 108.

[0061] A VHF power coupler 220 directs VHF power from the RF generator 120 to the central hollow conductive cylinder 215. The central hollow conductive cylinder 215 is thus the RF feed conductor of the folded coaxial resonator 195, while the inner and outer hollow conductive cylinders 200, 205 together with the planar conductive annulus 210 resemble the grounded outer conductor of a simple coaxial resonator. The electrical connection of the circular bottom ends 200a, 215a to the ceiling electrode 108 provides the necessary DC short, equivalent to the DC short at the ends of a simple (unfolded) coaxial tuning stub.

[0062] The VHF power coupler 220 includes an axial conductor 222 that extends through the top of the hollow inner cylinder 200 from a top end 222a on the outside of the hollow inner cylinder 200 to a bottom end 222b inside the inner cylinder 200. A first spoke conductor 224a extends radially from the axial conductor bottom end 222b through a hole 226a in the inner cylinder 200 to the central cylinder 215. As shown in FIG. 4, there are multiple spoke conductors 224a, 224b, 224c that are symmetrically arranged and extend radially from the axial conductor bottom end 222b through respective holes 226a, 226b, 226c in the inner cylinder 200 to the central cylinder 215 where their outer ends are electrically connected. In the illustrated embodiment, there are three spoke conductors 224 spaced at 120 degree intervals, although any suitable number n of spoke conductors 224 may be provided at 360 / n degree intervals.

[0063] In one embodiment, the VHF power coupler 220 is provided as a coaxial structure in which the axial conductor 222 and each spoke conductor 224 are coaxial transmission lines including a central conductor that is RF hot and surrounded by a grounded outer conductor or shield. This coaxial structure is shown in Figures 5A and 5B and is compatible with the magnetic field free environment inside the inner hollow conductive cylinder 200. In the embodiment of Figures 5A and 5B, the axial conductor 222 consists of a central axial conductor 222-1 connected to the output of the VHF generator 120 and a grounded outer axial conductor 222-2 surrounding the central axial conductor 222-1. Figure 5C shows a cross-sectional view of the axial conductor 222.

[0064] In the embodiment of Figures 5A-5C, each of the spoke conductors 224a, 224b, 224c embodies a coaxial transmission line structure. Thus, the spoke conductor 224a consists of a central spoke conductor 224a-1 and an outer spoke conductor 224a-2 surrounding the central spoke conductor 224a-1. The central spoke conductor 224a-1 extends radially from the axial central conductor 222-1 and terminates at and is electrically connected to the central cylinder 215. The central spoke conductor 224a-1 is RF hot due to its connection to the axial central conductor 222-1. The outer spoke conductor 224a-2 extends from the grounded axial outer conductor 222-2 and terminates at (and is electrically connected to) the inner cylinder 200. The central spoke conductor 224a-1 passes through the hole 226a (without contacting the inner conductive cylinder 200) and contacts the central conductive cylinder 215.

[0065] Each of the spoke conductors 224a, 224b, 224c has the same structure. Thus, the spoke conductor 224b consists of a central spoke conductor 224b-1 and an outer spoke conductor 224b-2 surrounding the central spoke conductor 224b-1. The central spoke conductor 224b-1 extends radially from the axial central conductor 222-1 and terminates at the central cylinder 215. The central spoke conductor 224b-1 is RF hot due to its connection to the axial central conductor 222-1. The outer spoke conductor 224b-2 extends from the grounded axial outer conductor 222-2 and terminates at (is electrically connected to) the inner cylinder 200, while the central spoke conductor 224b-1 passes through the hole 226b (without contacting the inner conductive cylinder 200) and contacts the central conductive cylinder 215.

[0066] Similarly, spoke conductor 224c consists of central spoke conductor 224c-1 and outer spoke conductor 224c-2 surrounding central spoke conductor 224c-1. Central spoke conductor 224c-1 extends radially from axial central conductor 222-1 and terminates at central cylinder 215. Central spoke conductor 224c-1 is RF hot due to its connection to axial central conductor 222-1. Outer spoke conductor 224c-2 extends from grounded axial outer conductor 222-2 and terminates at (is electrically connected to) inner cylinder 200, while central spoke conductor 224c-1 passes through hole 226c (without contacting inner conductive cylinder 200) and contacts central conductive cylinder 215.

[0067] A plurality of spoke center conductors 224a-1, 224b-1, 224c-1 extend radially from the axial center conductor 222-1 to electrically contact the central conductive cylinder 215. The contact area defines a circular plane. The axial location of the circular plane is selected such that the electrical or RF impedance at this location matches the characteristic impedance of 224a, 224b, 224c, respectively, at the VHF frequency of the RF generator 120. The characteristic impedance of the individual spoke conductors 224a, 224b, 224c is selected such that their total impedance at the junction (222b) matches the output impedance of the VHF generator 120 at the frequency of the VHF generator 120.

[0068] 6 shows a cusp-shaped magnetic field generated by magnets 160-1 and 160-2 in one embodiment. The cusp-shaped magnetic field is predominantly radial in the lower chamber 100b, thus deflecting electrons from reaching the workpiece 111. The cusp-shaped magnetic field is axial in a small region in the center. A central shield or blocker 400 may be provided to avoid leakage of high energy electrons through the center of the magnetic field due to the predominantly axial form of the magnetic field at the center.

[0069] 7 shows an axially shaped magnetic field produced by magnets 160-1 and 160-2 in another embodiment. The axial magnetic field is effective to confine the electron beam along an axial path.

[0070] 8 shows a transverse magnetic field M generated in the lower chamber 100b by magnet 161 to deflect electrons from reaching the work piece 111. Magnet 161 may be implemented, for example, as a Halbach array. Magnet 161 may also be a circular array of electromagnets, which allows the transverse magnetic field M to be electrically rotated about the cylindrical symmetry axis of the chamber 100 to enhance process uniformity.

[0071] FIG. 9 shows a magnetic field including an upper cusp-shaped magnetic field 500 generated by magnets 160-1 and 160-2 in the upper chamber 100a and a lower cusp-shaped magnetic field 504 generated by magnets 160-2 and 160-3 in the lower chamber 100b. The upper and lower cusp-shaped magnetic fields 500, 504 have symmetry planes 506, 508, respectively, above and below the grid filter 104. The upper cusp-shaped magnetic field 500 helps confine the plasma near the electrode 108. The lower cusp-shaped magnetic field 504 is predominantly radial in the lower chamber 100b, thus deflecting electrons from reaching the workpiece 111. The cusp magnetic field is axial in a small region at the center. A central shield or blocker 400 may be provided in the lower chamber 100b to avoid leakage of energetic electrons through the center of the magnetic field due to the predominantly axial form of the magnetic field at the center.

[0072] Using any one of the electron beam plasma reactors of Figure 1, Figure 1A, or Figure 2, the following method of processing a workpiece in an electron beam plasma reactor can be performed. Referring now to Figure 10, a grid filter 104 is provided to divide the chamber 100 into an upper chamber 100a and a lower chamber 100b (block 610 of Figure 10) while supporting a workpiece 111 in the lower chamber 100b opposite the grid filter 104. Gas is supplied to at least one of the upper and lower chambers 100a, 100b (block 612 of Figure 10). RF source power is introduced into the upper chamber 100a or to the electrode 108 to generate a plasma containing beam electrons in the upper chamber 100a to generate an electron beam having a beam propagation direction corresponding to the axis of symmetry (block 614 of Figure 10). The method further includes allowing at least a portion of the beam electrons to flow from the upper chamber 100a to the lower chamber 100b through the grid filter 104 (block 616 of FIG. 10) while simultaneously blocking at least a portion of the non-beam electrons and plasma ions from the upper chamber 100a to the lower chamber 100b through the grid filter 104 (block 618 of FIG. 10). The method further includes allowing the electron beam to generate a plasma in the lower chamber 100b (block 620 of FIG. 10). The method may further include supplying a substantially inert gas in the upper chamber 100a and a molecular process gas in the lower chamber 100b (block 622 of FIG. 10). The method may further include coupling a bias voltage to the workpiece 111 (block 624 of FIG. 10).

[0073] (Atomic Layer Etching) The reactor of FIG. 1, FIG. 1A, or FIG. 2 can be used to perform an atomic layer etching process. In one example, the workpiece 111 includes a semiconductor bulk layer (e.g., monocrystalline silicon), an overlayer (e.g., an oxide of silicon), and a surface layer (e.g., polycrystalline silicon), which can be partially masked. In this process, one of the gas sources 138 includes a precursor of an etching species (e.g., argon gas), while another of the gas sources 138 includes a precursor of a passivation species (e.g., chlorine gas). The passivation species is generated by dissociation (in a plasma) of the passivation precursor species (e.g., chlorine gas). Passivation is performed by exposing the workpiece 111 to the passivation species. Generally, the surface layer of the workpiece 111 is not easily etched (or is not susceptible to etching) by the etching species of a selected energy. The passivation makes the surface layer of the workpiece more susceptible to etching by the etching species. The depth of the passivated portion of the surface layer is determined by the time of exposure to the passivation species. In this process, the time of exposure to the passivation species is set to a period during which one atomic layer is passivated. The workpiece 111 is then exposed to an etching species to remove the one atomic layer. The aforementioned sequence is then repeated to remove the next atomic layer. This cycle is repeated, one atomic layer at a time, until the desired portion (e.g., 100%) of the surface layer has been removed. Thus, the process consists of alternating phases of passivation and etching.

[0074] 1, 1A, or 2, in one embodiment, an inert gas (e.g., argon) is supplied to the upper chamber 100a and a molecular process gas (e.g., chlorine) is supplied to the lower chamber 100b. As described above with reference to FIG. 1, the plasma is sustained by various bulk and surface processes, including energetic ion bombardment of the electrode 108 by the plasma ions. The density of the plasma is primarily controlled by the power level of the VHF power from the RF power generator 120, or by the power level of the RF power generator 174 that supplies power to the optional RF coil antenna 172, while the ion bombardment energy on the electrode 108, and therefore the resulting secondary electron beam energy, is primarily controlled by the power level of the low frequency power from the RF power generator 122. During the passivation phase, a high power level in the range of 300-10,000 watts of VHF power from RF power generator 120 (or optionally RF power generator 174 supplying power to optional RF coil antenna 172) generates a plasma in upper chamber 100a.

[0075] The above examples of high power levels are for reactors processing workpieces with diameters of 200 mm to 300 mm; larger substrates would use higher power levels. The voltage on electrode 108, which can optionally be increased by additional application of RF power from VHF power generator 120b to electrode 108, accelerates the electron beam propagating through grid filter 104 into lower chamber 100b, generating a plasma in lower chamber 100b. The high magnetic flux, low energy, electron beam conditions in lower chamber 100b promote dissociation of at least a portion of the molecular chlorine into atomic chlorine radicals, electrons, and ions. For a low electron temperature plasma, with no workpiece bias applied, the ion energy is below the threshold for etching silicon, and passivation of the workpiece surface occurs without significant etching. Next, in the etching phase, at least one of (A) a high level of low frequency RF power (in the range of 300-10000 watts) is applied to the electrode 108, or (B) a low VHF power or no VHS power is applied to the electrode 108, or (C) a low RF power or no RF power is applied to the coil antenna 172. The low power in this case is in the range of less than 300 watts. The above example of high power level is for a reactor processing workpieces with diameters of 200 mm-300 mm, larger substrates would use higher power levels. The higher voltage on the electrode 108 accelerates the higher energy electron beam, which propagates through the grid filter 104 into the lower chamber 100b, generating a plasma in the lower chamber 100b. The high energy electron beam conditions in the lower chamber 100b promote ionization and reduce dissociation of molecular chlorine into atomic chlorine radicals, electrons, and ions. Additionally, argon neutrals that pass through grid filter 104 into lower chamber 100b can be ionized by the beam electrons.By turning on a bias voltage (applied to the workpiece support 110) during the etching phase with a voltage corresponding to an energy sufficient to etch silicon in the presence of surface chlorine passivation species, but insufficient to etch silicon in the absence of the passivation species, ionic etchant species (argon or chlorine ions) can be extracted and accelerated to the workpiece surface to facilitate etching, and the cycle is then repeated.

[0076] Alternatively or additionally, a remote plasma source (RPS) 280 may provide the passivation radicals. In one variation of the embodiment detailed above, chlorine is supplied to the upper chamber 100a (optionally argon is supplied to the upper and / or lower chambers 100a, 100b) and chlorine radicals are generated in the upper chamber 100a by application of high power levels of VHF power from the RF power generator 120 (or optionally high power levels from the RF power generator 174 which supplies power to the optional RF coil antenna 172). High VHF power to the electrode 108 or optional power to the coil antenna 172 is used during passivation, while low frequency RF power (low or no VHF or coil power) to the electrode 108 is used along with a workpiece bias voltage during the etching phase.

[0077] During the above-mentioned etching phase, the RF power coupled to the electrode 108 can be low frequency RF power, or the frequency can be a higher frequency (eg, VHF).

[0078] A method for performing atomic layer etching using an electron beam plasma reactor of the type described above with reference to Figures 1, 1A, or 2 is provided. The method is illustrated in Figure 11. Referring to Figure 11, a grid filter 104 divides a processing chamber 100 into upper and lower chambers 100a, 100b, and a workpiece is placed in the lower chamber 100b (block 632 of Figure 11). A molecular process gas is supplied to the chamber 100 (block 634 of Figure 11). A passivation process is performed (block 636 of FIG. 11 ), which consists of (A) performing at least one of: (a) coupling a high power level of VHF power into the upper chamber 100a or to the electrode 108 (block 638 of FIG. 11 ); or (b) coupling a high level of inductively coupled power into the upper chamber 100a (block 640 of FIG. 11 ); and (B) maintaining a workpiece bias voltage at zero or below a threshold for etching the surface layer of the workpiece to reduce or prevent etching of the surface layer during the passivation process (block 642 of FIG. 11 ).

[0079] After the passivation process, an etching process is performed (block 644 of FIG. 11 ) by: (A) performing at least one of the following: (a) applying a high level of low frequency RF power to the ceiling electrode (block 646 of FIG. 11 ) or (b) reducing or eliminating the power level of at least one of (1) the VHF power or (2) the inductively coupled power (block 648 of FIG. 11 ), and (B) maintaining the bias voltage of the workpiece above a threshold for etching the surface layer (block 650 of FIG. 11 ).

[0080] The method then comprises repeating alternating passivation and etching processes in succession (block 652 of FIG. 11).

[0081] A molecular process gas may be supplied into the lower chamber 100b. Additionally, the method may further include supplying an inert gas into the upper chamber 100a. Alternatively, a molecular process gas may be supplied to the upper chamber 100a.

[0082] (advantage) The cylindrical symmetry of the VHF and RF power flow to the ceiling and the cylindrical symmetry of the electron beam distribution on the circular workpiece optimizes azimuthal uniformity in processing. The RF or VHF powered electrode provides the plasma source for generating the electron beam and does not require a non-insulated surface for the electrode or ground return. The electrode 108 may be consumable in certain plasma processes, and thus the support structure, which may include an electrostatic chuck, allows for fast electrode replacement and chamber maintenance recovery while ensuring repeatable electrical and thermal electrode performance, which is important for process stability. The grid filter 104 provides isolation between the upper and lower chambers 100a, 100b, allowing control of the workpiece processing environment in the lower chamber 100b independent of the plasma source environment in the upper chamber 100a. The upper and lower gas injectors 130 and 134 allow independent distribution of different gases or gas species to the upper and lower chambers 100a, 100b. For example, one gas that is particularly useful for generating the desired species in the upper chamber 100a (e.g., a "source" gas) is injected into the upper chamber 100a, while another gas (e.g., a "process" gas) required to process the workpiece 111 is injected into the lower chamber 100b. Gas may be injected through the gas jets 105b of the grid filter 104. For example, an inert gas may be injected through the gas jets 105b of the grid filter 104, thereby substantially preventing the process gas in the lower chamber 100b from convecting or diffusing into the upper chamber 100a. In an embodiment in which a molecular gas is supplied to the upper chamber 100a, dissociation of species in the upper chamber 100a may be enhanced by applying higher VHF power to the electrode 108 or RF power to the inductive coil antenna 172, without the need to expose the workpiece 111 to a plasma with a high ion density. The electron beam energy and magnetic flux may be adjusted to control the relative dissociation and ionization processes.In an embodiment where an inert gas flows in the upper chamber 100a and a molecular gas flows in the lower chamber 100b, the RF and / or VHF power to the electrode 108 and / or the RF power to the coil antenna 172 can be adjusted to adjust the electron beam energy and magnetic flux to the lower chamber 100b for relative control of the dissociation and ionization processes in the lower chamber 100b. The number (population) of radicals or dissociated species can be enhanced by the remote plasma source 280. Unlike commonly used direct current discharges, RF capacitively coupled plasmas, or inductively coupled plasmas, where the low electron temperature plasma may not be generated continuously (it is generated intermittently during the off-time of the pulsed DC or RF CCP / ICP discharge), the above embodiment can continuously generate a low electron temperature plasma with high uniformity on the workpiece 111 in the lower chamber 100b. Furthermore, using an electronegative gas, an electron-deficient, highly electronegative "ion-ion" plasma can be continuously generated with high uniformity over the workpiece, and by application of a low frequency bias voltage or any voltage waveform with a low repetition frequency applied to the workpiece support 110, positive and / or negative ions can be selectively or alternately extracted from the plasma and accelerated at desired energy levels into the workpiece surface for etching, cleaning, deposition, or other material modification processes.

[0083] While the forgoing is directed to embodiments of the present invention, other and further embodiments may be made without departing from the basic scope of the invention, which scope is defined by the following claims.

Claims

1. 1. A plasma reactor comprising: a body defining a vacuum chamber having a sidewall; an upper electrode support for holding an upper electrode, the upper electrode support comprising an electrically insulated electrostatic chuck and a thermal control device coupled to the upper electrode support; an RF source power generator coupled to the upper electrode or the upper electrode support, the RF source power generator comprising a first RF power generator having a first frequency and a second RF power generator having a second frequency; a gas distributor for injecting a process gas into the vacuum chamber; a folded resonator coupled between a first RF source power generator and an upper electrode or an upper electrode support; an RF impedance matcher coupled between the second RF source power generator and the upper electrode or the upper electrode support; A plasma reactor comprising: a workpiece support pedestal including an electrically insulated electrostatic chuck; and a thermal controller coupled to the workpiece support pedestal.

2. 10. The plasma reactor of claim 1 further comprising a DC chucking voltage source coupled to an electrically isolated electrostatic chuck.

3. 10. The plasma reactor of claim 1 further comprising a bias voltage generator coupled to the workpiece support pedestal.

4. 10. The plasma reactor of claim 1 comprising an upper electrode.

5. 5. The reactor of claim 4 wherein the top electrode comprises one of silicon, carbon, silicon carbide, silicon oxide, aluminum oxide, yttrium oxide, zirconium oxide.

6. 10. The plasma reactor of claim 1 further comprising a first electromagnet or permanent magnet adjacent the vacuum chamber.

7. 10. The plasma reactor of claim 1 further comprising a window in a sidewall, a coil antenna around the window, and an RF generator coupled to the coil antenna.

8. The plasma reactor of claim 1, wherein within the vacuum chamber an upper electrode emits an electron beam, a portion of which is controlled to collide with a gas to generate an ion-ion plasma.

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