Electron beam plasma source with arrayed plasma sources for uniform plasma generation

A plasma reactor that generates plasma in workpiece processing chamber by a electron beam, has an electron beam source chamber and an array of plasma sources facing the electron beam source chamber for affecting plasma electron density in different portions of the processing chamber. In another embodiment, an array of separately controlled electron beam source chambers is provided.

BACKGROUND

A plasma reactor for processing a workpiece can employ an electron beam as a plasma source. Such a plasma reactor can exhibit non-uniform distribution of processing results (e.g., distribution of etch rate across the surface of a workpiece) due to non-uniform distribution of electron density and/or kinetic energy within the electron beam. Such non-uniformities can be distributed along the direction of beam propagation and can also be distributed in a direction transverse to the beam propagation direction.

SUMMARY

A plasma reactor for processing a workpiece, includes a workpiece processing chamber having a processing chamber enclosure comprising a ceiling and a side wall and an electron beam opening in said side wall, a workpiece support pedestal in said processing chamber having a work lace support surface facing said ceiling and defining a workpiece processing region between said workpiece support surface and said ceiling, said electron beam opening facing said workpiece processing region. The plasma reactor further comprises an electron beam source chamber comprising an electron beam source chamber enclosure that is open to said electron beam opening of said workpiece processing chamber, and an array of plasma sources distributed along a portion of said electron beam source chamber enclosure opposite from said electron beam opening, each of said plasma sources comprising a supply of plasma source power and a plasma source power applicator coupled to the supply of plasma source power. A controller governs each supply of plasma source power of each of said plasma sources.

The array of plasma sources is distributed along direction parallel with a plane of said workpiece support surface.

The plasma sources affect plasma electron density in respective portions of said electron beam source chamber, said respective portions distributed along a direction parallel with a plane of said workpiece support surface. The plasma reactor of claim3wherein said controller governs plasma electron density distribution along said direction.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary 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.

DETAILED DESCRIPTION

FIGS. 1A and 1Fare top and side views, respectively, of a plasma reactor having an electron beam plasma source employing a configurable array of plasma sources affecting uniformity of an electron beam, in accordance with a first embodiment. The reactor includes a process chamber100enclosed by a cylindrical side wall102, a floor104and a ceiling106. A workpiece support pedestal108supports a workpiece110, such as a semiconductor wafer, the pedestal.108being movable in the axial (e.g., vertical) direction. A gas distribution plate112is integrated with or mounted on the ceiling106, and receives process gas from a process gas supply114. A vacuum pump116evacuates the chamber through the floor104. A process region118is defined between the workpiece110and the gas distribution plate112. Within the process region118, the process gas is ionized to produce a plasma for processing of the workpiece110.

The plasma is generated in the process region118of the process chamber100by an electron beam from an electron beam source120. The electron beam source120includes a plasma generation chamber122outside of the process chamber100and having a conductive enclosure124. The conductive enclosure124has a gas inlet or neck.125. An electron beam source gas supply127is coupled to the gas inlet125. The conductive enclosure124has an opening124afacing the process region118through an opening102ain the sidewall102of the process chamber100through which the electron beam enters the process chamber100.

The electron beam source120includes an extraction grid126between the opening124aand the plasma generation chamber122, and an acceleration grid128between the extraction grid126and the process region118, best seen in the enlarged view ofFIG. 1C. The extraction grid126and the acceleration grid128may be formed as separate conductive meshes, for example. The extraction grid126and the acceleration grid128are mounted with insulators130,132, respectively, so as to be electrically insulated from one another and from the conductive enclosure124. However, the acceleration grid128is in electrical contact with the side wall102of the chamber100. The openings124aand102aand the extraction and acceleration grids126,128are mutually congruent, generally, and define a thin wide flow path for an electron beam into the processing region118. The width of the flow path is about the diameter of the workpiece110(e.g., 100-500 mm), while the height of the flow path is less than about two inches.

The electron beam source120further includes a pair of electromagnets134-1and134-2aligned with the electron beam source120, and producing a magnetic field parallel to the direction of the electron beam. The electron beam flows across the processing region118over the workplece110, and is absorbed on the opposite side of the processing region118by a beam dump136. The beam dump136is a conductive body having a shape adapted to capture the wide thin electron beam.

A negative terminal of plasma D.C. discharge voltage supply140is coupled to the conductive enclosure124, whereas a positive terminal of the voltage supply140is connected to the extraction grid126. In turn, a negative terminal of an electron beam acceleration voltage supply142is connected to the extraction grid126, and positive terminal is connected to the grounded sidewall102of the process chamber100. The electrons extracted from the DC discharge plasma through the extraction grid126are accelerated as they travel towards the acceleration grid128by the potential difference (typically of the order of a few kV) provided by the voltage supply142. In another example, the negative terminal of voltage supply142may be coupled to the conductive enclosure124, instead of the extraction grid126. In this case, the voltage supply142not only performs work to accelerate the electrons, but also to sustain DC discharge. The voltage supply140, in this case, only performs work on a small portion of a discharge current caused by electrons that do not make it through the openings and bombard the extraction grid. A coil current supply146is coupled to the electromagnets134-1and134-2. Plasma is generated within the chamber122of the electron beam source120by a D.C. gas discharge produced by power from the voltage supply140, which provides a voltage typically of the order of a few hundred volts. This D.C. gas discharge is the main plasma source of the electron beam source120. Electrons are extracted from the plasma in the chamber122through the extraction grid126, and accelerated through the acceleration grid128due to a voltage difference between the acceleration grid and the extraction grid to produce an electron beam that flows into the processing chamber100. Distribution of the plasma ion density and plasma electron density across the chamber122affects the uniformity of the electron beam. For example, referring toFIG. 1D, the extraction grid126includes a frame126-1and an array of spaced-apart blocking elements126-2defining an array of openings126-3. The frame126-1defines a narrow aperture126-4whose height H is relatively small (e.g., 2-4 cm) and whose width W (e.g., on the order of the workpiece diameter, or 300 mm or more) is generally parallel to the workpiece support plane of the pedestal108, so as to produce a correspondingly thin wide electron beam. The distribution of electron density across the width of the beam is liable to exhibit non-uniformities.

While the main plasma source in the electron beam source120is a D.C. gas discharge produced by the voltage supply140, any other suitable plasma source may be employed instead as the main plasma source. For example, the main plasma source of the electron beam source120may be a toroidal RF plasma source, a capacitively coupled RE plasma source, or an inductively coupled RF plasma source.

In the illustrated embodiment, the main plasma source of the electron beam source120is the D.C. gas discharge maintained within the chamber122by the D.C. discharge voltage supply140. This main plasma source is augmented by an array of plasma sources201,202,203and204distributed along a direction generally parallel to the workpiece support plane of the pedestal108. A controller150governs the rate at which each plasma source201,202,203and204generates plasma ions and electrons, each plasma source,201,202,203,204being controlled independently. The plasma sources201,202,203and204are RF plasma sources employing respective RE power generators215-1,215-2,215-3and215-4, and the controller150governs the RE power level of each RE generator215-1,215-2,215-3and215-4separately. Each plasma source201,202,203and204faces a region301,302,303and304of the chamber122. The output power level of each of the RF generators215-1,215-2,215-3and215-4affects plasma ion density and the plasma electron density in the corresponding region301,302,303and304of the chamber122. The distribution across the electron beam width of electron density reflects the distribution of plasma electron density and plasma ion density along the beam width among the regions301,302,303and304within the electron beam source chamber122. The controller150can therefore adjust plasma electron distribution across the width of the electron beam by changing the proportion of RF power output levels of the RF generators215-1,215-2,215-3and215-4. Such adjustments may be made in response to measurements of distribution across a test workpiece (processed in the process chamber100) of a process parameter (e.g., etch depth). Non-uniformities in distribution may be ameliorated or corrected by increasing RF power for those regions experiencing lower electron density and/or decreasing RF power for those regions experiencing higher electron density.

In the illustrated embodiment, each plasma source201-204is a toroidal RF plasma source consisting of an external reentrant conduit210having a pair of ports211,212through a back wall124-1of the chamber122, a ring213of a magnetically permeable material around the reentrant conduit210, a conductive coil214around the ring213, and an RF generator (e.g.,215-1,215-2,215-4) coupled to the coil214through an RF impedance match216.

In the embodiment ofFIGS. 2A,2B,2C, each plasma source201,202,203and204of the electron beam source120is a capacitively coupled RF plasma source. In this embodiment, the conductive housing124consists of an upper housing400and a lower housing402separated by the opening124aand by an insulator405. An insulator412overlies the upper housing400. The plasma sources201,202,203and204include separate electrodes410-1,410-2,410-2and410-4, respectively, overlying the insulator412. Respective ones of the RF generators215-1,215-2,215-3and215-4are coupled through the individual impedance matches216-1,216-2,214-3and216-4to respective ones of the electrodes410-1,410-2,415-2and410-4. An insulator413underlies the lower housing402. A common return (RF ground) electrode411underlies the insulator413. A first D.C. voltage supply420referenced to ground is connected to the upper and lower housings400,402. The negative terminal of the D.C. voltage supply420is connected through a choke inductor428to the upper housing400, and through a choke inductor422to the lower housing402. The choke inductors422and423enable each RF generator215-1,215-2,215-3and215-4to maintain RF voltage differences between the respective electrodes410-1,410-2,410-2and410-4and the lower housing402. Considering insulators412and413as blocking capacitors, the above scheme of connecting both RF and DC voltages to the same points (upper and lower housings400and402) resembles a well-known “bias tee” configuration. The first D.C. voltage supply420may provide a voltage in a high range (e.g., 2-3 kV). This voltage will determine the energy that electrons will gain when passing through the gap between the extraction grid126and the grounded acceleration grid128. In another example (not shown inFIG. 2A), a negative terminal of the high-voltage D.C. power supply420may be connected through a choke inductor to the extraction grid126, instead of the upper and lower housings400,402. A second D.C. voltage supply430is connected between the negative terminal of the first D.C. voltage supply420and the extraction grid126, the positive terminal of the second D.C. voltage supply430being connected through a choke inductor424to the extraction grid126, and the negative, terminals of the first and second D.C. voltage supplies420,430being connected together. The second D.C. voltage430supply may provide a voltage in a lower range (e.g., 0-300 volts). In one example, this voltage may be small and insufficient to autonomously produce and sustain a D.C. discharge. In this case, DC discharge is not the main plasma source for the electron beam source120. In this example, plasma is produced mostly by the capacitively coupled RF sources, and the DC voltage from the supply430is provided primarily to eliminate an electron-repelling sheath at the discharge side of the extraction grid, and thus ensure that electrons can leave the e-beam discharge chamber through the extraction grid.

In the embodiment ofFIGS. 3A and 3B, each one of the array of plasma source201,202,203and204of the electron beam source120is an inductively coupled RF plasma source, that includes a coil antenna510mounted over a dielectric window512formed on the back well124-1of the chamber122, and a respective one of the RF generators215-1,215-2,215-3and215-4coupled to the of510through a respective one of the RF impedance matches216.

In each of the foregoing embodiments, the electron beam source120has a single plasma source chamber122extending across the entire width of the plasma beam, corresponding to the width of the process region118of the process chamber100. In the embodiment ofFIG. 4, the electron beam source120is provided with an array of plasma sources601,602,603and604constituting separate smaller chambers distributed across the width of the electron beam. Each of the plasma sources601,602,603and604has a respective chamber622-1,522-2,622-3and622-4isolated from each other by insulators623. D.C. discharge voltage supplies642-1,642-2,642-3and642-4are connected between the walls of the respective chambers622-1,622-2,622-3and622-4and respective extraction grids626-1,626-2,626-3and626-4. The voltages V1, V2, V3and V4are independently controlled by the controller150, so that each chamber may be provided with different gas discharge voltages, so as to produce different electron densities. The chambers622-1,622-2,622-3and622-4are open toward the processing chamber100through the respective extraction grids626-1,626-2,626-3and626-4and respective acceleration grids628-1,628-2,628-3and628-4. An accelerating voltage supply646is coupled to the extraction grids626-1,626-2,626-3and626-4through respective variable resistors630-1,630-2,630-3and630-4, and is referenced to ground. The variable resistors630-1,630-2,630-3and630-4are independently controlled by the controller150, so that each extraction grid may be provided a different accelerating voltage, so as to accelerate beam electrons to different energies.

The four plasma sources601,602,603and604face respective regions501,502,503, and504of the processing chamber100and affect electron (and ion) density within those regions. The four plasma sources can provide different amounts of plasma to the different regions501,502,503, and504. The different D.C. discharge voltages provided to the e-beam sources601,602,603and604affect plasma ion density and the plasma electron density in the corresponding regions501,502,503and504of the processing chamber100. The distribution of electron density across the combined electron beam width (from all 4 sources) reflects the distribution of plasma electron density and plasma ion density along the beam width among the regions501,502,503and504within the processing chamber100. The controller150can therefore adjust plasma density distribution across the width of the electron beam by adjusting the voltages642-1,642-2,642-3and642-4to provide different D.C. gas discharge voltages to the different chambers622-1,622-2,622-3and622-4. Such adjustments may be made in response to measurements of distribution across a test workpiece (processed in the process chamber100) of a process parameter (e.g., etch depth).

In addition to providing different densities of beam electrons in the different regions501,502,503, and504, the plasma sources601,602,603and604may provide different energies of beam electrons in the different regions. This is done by the controller150adjusting the variable resistors630-1,630-2,630-3and630-4. This may be one so as to compensate for non-uniformities in the distribution of plasma density in the chamber100. Such non-uniformities may be detected by measuring process results on a test workpiece. While the electron energy levels of the different plasma sources601-604are depicted as being controlled by different variable resistors630-1,630-2,630-3,640-4from a shared accelerating voltage supply646, in one modification the same control may be realized by providing separate accelerating voltage supplies (not illustrated) controlled by the controller150, rather than separate variable resistors.