Control of spatial density of plasma with process stations by return path reactance tuning

Abstract

Disclosed herein are techniques for control of spatial density of plasma with process stations by return path reactance tuning. In some embodiments, a semiconductor fabrication chamber comprises a pedestal configured to support a wafer undergoing processing. The chamber may further comprise a showerhead. The chamber may further comprise two or more unpowered electrodes operatively coupled to the showerhead or to the pedestal. The chamber may further comprise one or more variable reactances coupled to at least one of the two or more unpowered electrodes, wherein reactances of the one or more variable reactances are modified to control a spatial density of plasma within the fabrication chamber.

Description

CONTROL OF SPATIAL DENSITY OF PLASMA WITH PROCESS STATIONS BY RETURN PATH REACTANCE TUNINGINCORPORATION BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claim benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes.BACKGROUND

[0002] Plasma-based fabrication processes are utilized for various semiconductor fabrication processes. Plasma may be formed using a high power radio frequency (RF) signal provided to an electrode of a process station. It may be useful to control spatial density of the plasma within the station, e.g., to control thickness of a deposited film on a wafer undergoing processing. However, control of plasma density may be difficult to achieve.

[0003] The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0004] Disclosed herein are techniques for control of spatial density of plasma with process stations by return path reactance tuning. In some embodiments, a semiconductor fabrication chamber comprises a pedestal configured to support a wafer undergoing processing. The chamber may further comprise a showerhead. The chamber may further comprise two or more unpowered electrodes operatively coupled to the showerhead or to the pedestal. The chamber may further comprise one or more variable reactances coupled to at least one of the two or more unpowered electrodes, wherein reactances of the one or more variable reactances are modified to control a spatial density of plasma within the fabrication chamber.

[0005] In some examples, modification of the reactances of the one or more variable reactances reduces a likelihood of arcing in a vicinity of the wafer.

[0006] In some examples, the two or more unpowered electrodes are separated by at least one of: a non-gas dielectric material, a vacuum, or a gas-filled gap. In some examples, a body ofthe showerhead comprises the dielectric material, and wherein the two or more unpowered electrodes are disposed in the showerhead body. In some examples, the two or more unpowered electrodes are separated by the dielectric material within a conducting body of the showerhead.

[0007] In some examples, at least one electrode of the two or more electrodes are affixed to a periphery of the showerhead.

[0008] In some examples, the two or more unpowered electrodes are operatively coupled to the showerhead, and wherein an RF source is operatively coupled to the pedestal.

[0009] In some examples, the two or more unpowered electrodes are operatively coupled to the pedestal, and wherein an RF source is operatively coupled to the showerhead.

[0010] In some examples, the reactances of the one or more variable reactances are modified to control the spatial density of the plasma in a radial direction within the fabrication chamber.

[0011] In some examples, the reactances of the one or more variable reactances are modified to control the spatial density of the plasma in an azimuthal direction within the fabrication chamber.

[0012] In some examples, the one or more variable reactances comprise variable capacitors.

[0013] In some examples, the one or more variable reactances comprise variable inductors.

[0014] According the some embodiments, a method of controlling spatial density of plasma within a process station comprises: obtaining information associated with an ongoing plasmabased fabrication process within the process station; and modifying one or more variable reactances based on the information, the one or more variable reactances each operatively coupled to a corresponding one of two or more unpowered electrodes disposed in or connected to a showerhead or a pedestal, wherein the modification of the one or more variable reactances causes plasma density to be spatially controlled within the process station.

[0015] In some examples, the information is obtained from one or more sensors or cameras disposed in the process station.

[0016] In some examples, the information is indicative of a film thickness at a current time point on a surface of a wafer undergoing the fabrication process. In some examples, values of the one or more variable reactances are determined to increase a likelihood of the film thickness being modified toward target film thickness properties. In some examples, the target film thickness properties comprise film thickness across a spatial extent of the wafer undergoing the fabrication process.

[0017] In some examples, the two or more unpowered electrodes are separated by at least one of: a non-gas dielectric material, a vacuum, or a gas-filled gap. In some examples, the one or more variable reactances comprise one or more variable capacitors.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a diagram that illustrates voltages at different regions of a station.

[0019] FIGS. 2A, 2B, 2C, and 2D illustrate example configurations that utilize variable reactances operatively coupled to electrodes of a showerhead in accordance with some embodiments.

[0020] FIG. 3 illustrates an example configuration that utilizes variable reactances operatively coupled to electrodes of a pedestal in accordance with some embodiments.

[0021] FIG. 4 is a flowchart of an example process for modifying reactances operatively coupled to electrodes of a showerhead in accordance with some embodiments.DETAILED DESCRIPTION

[0022] In the following description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments.

[0023] Plasma-based fabrication operations, which may include etching operations, deposition operations, etc. may be performed in a process station. Plasma may be generated by applying one or more radio frequency (RF) signals to one or more electrodes of the process station, which are generally referred to herein as “powered electrodes.” For example, in some embodiments, a capacitively-coupled plasma (CCP) may be generated using a powered electrode operatively coupled to a pedestal of a process station on which a wafer is to reside when undergoing processing. In some examples, the powered electrodes may be operatively coupled to variable reactances. As used herein, a “variable reactance” may be used interchangeably with the term “variable reactance element.” A “variable reactance” may be a component with a modifiable reactance, such as a variable capacitor or a variable inductor. Note that reactance is understood to be the imaginary component of impedance. By utilizing variable capacitors or variable inductors, the reactance may be changed, and accordingly, variable capacitors and / or variable inductors may be considered to be variable reactances.

[0024] A variable reactance may be used to perform tuning. For example, the relative impedance between a first electrode of the pedestal and a second electrode of the pedestal may be modified, which may in turn change the distribution of power coupling between eachelectrode and the nearby plasma. The change in power coupling or power distribution between an electrode and the plasma may in turn modify plasma density spatially. Modification of the spatial plasma density may be desirable, e.g., to increase or decrease film deposition radially and / or azimuthally. For example, film deposition may be increased or decreased in a radial direction to modify thickness at outer edges of the wafer relative to an inner portion.

[0025] Disclosed herein are techniques, systems, and apparatuses for performing tuning to control spatial density of plasma utilizing variable reactances operatively coupled between unpowered electrodes and the ground return path. By performing tuning using variable reactances associated with these electrodes, the nearby plasma region associated with each electrode will be driven by different RF voltages, spatially modulating the power coupling to the plasma. In particular, spatially modulating the power coupling to the plasma may occur in a radial and / or azimuthal direction due to generation of a corresponding spatial differential in impedance and / or RF voltage.

[0026] In some embodiments, as shown in and described below in connection with FIGS. 2A- 2D, a showerhead may have two or more unpowered electrodes, at least one of which may be operatively coupled to a variable reactance used to generate the impedance / voltage differential in a spatial direction. Alternatively, in some embodiments, as shown in and described below in connection with FIG. 3, one or more unpowered electrodes may be associated with a pedestal of a process station, and at least one of the unpowered electrodes may be operatively coupled to a variable reactance used to generate the impedance / voltage differential. As used herein, a variable reactance may include a variable capacitor and / or a variable inductor. The variable reactance may be used to modify a relative impedance of the two or more electrodes, thereby creating a voltage differential which can be used to modify plasma density in a radial and / or azimuthal direction. A variable reactance, such as a variable capacitor and / or a variable inductor, may be a mechanically-actuated component, e.g., a rotational capacitor that may be rotated to form different capacitances.

[0027] A process station may include a pedestal on which a wafer is to reside during processing. In some cases, the pedestal may include multiple electrodes. An RF signal may be provided to one or more electrodes. In some cases, these electrodes may be powered with opposite polarity, which may allow for electro-static clamping of the wafer to the pedestal.

[0028] In cases in which the RF signal is provided to electrodes of the pedestal, a showerhead of the station may comprise an unpowered electrode. In other words, the showerhead, when unpowered, may be operatively coupled to ground. The showerhead may be configured to distribute various gases (e.g., precursor gases) into the station. Due to the provision of the RFsignal, a plasma may be struck within the station, which may be used to perform plasma-based fabrication operations on the wafer (e.g., a deposition operation and / or an etching operation).

[0029] In some cases, an outer electrode of the pedestal may be operatively coupled to a variable capacitor that is used to change the reactance, and therefore the impedance of the variable capacitor. Because the impedance of the variable capacitor is changed, the relative impedance associated with the outer electrode relative to the impedance of the inner electrode may also be changed. FIG. 1 illustrates the relative impedance difference associated with the outer electrode (where the impedance is depicted as Zi) relative to the impedance associated with the inner electrode (the impedance is depicted as Z2). As illustrated in FIG.l, due to the impedance differences, the voltage with respect to ground associated with each electrode, referred to as V / and V2, respectively, are also different for the outer electrode and inner electrode.

[0030] Often an additional electrode is placed in the pedestal near the clamping electrodes to prevent direct current (DC) current leakage. In order to prevent DC current leakage, the wafer must be positioned over this additional electrode. The wafer may couple preferentially to one of these electrodes and accordingly has an RF voltage potential determined by that electrode. Different circuit impedance elements connected to each electrode can result in a different RF voltage of each electrode. This difference in RF voltage (corresponding to the value of Vi - V2, as shown in and described above in connection with FIG. 1) in proximity to the pedestal or wafer may be problematic. When the wafer preferentially couples to one or more of the multiple electrodes, it reduces the degree to which the other electrodes in the pedestal can modify the plasma density above the wafer, because the incurred RF voltage difference is between the wafer and pedestal and is not between the wafer and the showerhead.

[0031] Disclosed herein are techniques for performing tuning using one or more variable reactances operatively coupled to one or more unpowered electrodes along the RF return path of a process station or process chamber. In the case of a powered pedestal (e.g., in which the RF source is operatively coupled to the pedestal), the unpowered electrode or electrodes are associated with a showerhead. Alternatively, in the case of a powered showerhead, the unpowered one or more electrodes are associated with the pedestal. Note that although the electrodes associated with the RF return path are unpowered, the variable reactance may be utilized to induce a voltage differential proximate to the electrodes. In some implementations, the voltage differential may be spatially separated from the wafer, which may be advantageous. For example, in the case in which the showerhead comprises unpowered electrodes operatively coupled to one or more variable reactances, a voltage differential may be induced between acenter region below the showerhead and an edge region, which may lead to corresponding changes in plasma density between the center and the edge regions. Accordingly, plasma density may be controlled in a spatial direction (e.g., radially and / or azimuthally). Note that tuning using variable reactance elements coupled to unpowered electrodes along the RF return path may allow for generation of RF voltage differences between the showerhead and the wafer when the RF return path is via the showerhead, which may in turn allow modification of plasma density above the wafer.

[0032] The variable reactances may be any suitable type of elements or combination of elements. For example, a variable reactance may comprise one or more capacitors, and / or one or more inductors. Electrodes of the RF return path may be spatially separated by a physical dielectric material. A physical dielectric material may comprise any material or gas that is non or weakly conducting, and may include aluminum nitride, aluminum, oil, air, etc. For example, the electrodes may be separated by a condensed or non-gas (e.g., a solid, a liquid, etc.) dielectric material, a vacuum gap, or a gas-filled gap (e.g., air, or another non or weakly conducting gas). The electrodes may be coupled to or attached to the showerhead, or, alternatively, may be disposed within the showerhead. Example configurations are shown in and described below in connection with FIGS. 2A-2D.

[0033] It should be noted that, in instances in which tuning is performed using a variable reactance associated with a showerhead electrode using the techniques disclosed herein, an additional electrode of the pedestal may still be utilized to prevent or limit DC leakage current.

[0034] In some implementations, a showerhead may comprise two or more electrodes, or a segmented electrode (e.g., divided into two or more portions). In some embodiments, at least one of the two or more unpowered electrodes may be operatively coupled to a variable reactance (e.g., a variable capacitor and / or a variable inductor) such that the reactance may be tuned to allow for control of the spatial density of plasma (e.g., in the region below the showerhead). In some embodiments, the two or more electrodes may be separated by a nonconducting material, which may be a dielectric material, air, vacuum, or a gas-filled region.

[0035] FIG. 2A illustrates a portion of an example process station that includes a segmented showerhead electrode in accordance with some embodiments. As illustrated, the showerhead includes two electrodes 202 and 206 that together comprise what is sometimes referred to herein as a “segmented electrode.” Note that, in the example shown in FIG. 2A, the showerhead electrodes are unpowered in that both are operatively coupled to ground. First electrode 202 is operatively coupled to ground via variable capacitor 214, and second electrode 206 is operatively coupled to ground via variable capacitor 218. The capacitances of variablecapacitor 214 and / or variable capacitor 218 may be modified in order to generate a voltage differential between first electrode 202 and second electrode 206, that, in turn, allows a spatial density of the plasma to be modified in the azimuthal and / or radial directions. For example, note that the density of plasma is higher in plasma region 215 relative to plasma region 216. In particular, the voltage differential may be generated between a center region and an edge region, thereby causing a corresponding differential in the spatial density of plasma between the center and edge regions. First electrode 202 and second electrode 206 are separated by a dielectric material 210. In some embodiments, dielectric material 210 may be replaced by air, vacuum space, or a gas-filled region. In the example shown in FIG. 2A, the pedestal comprises an inner electrode 204 which is operatively coupled to an RF source 208. Accordingly, the pedestal is powered, and the showerhead is unpowered. Wafer 212 resides on the pedestal.

[0036] In some implementations, one or more electrodes associated with a showerhead may be affixed to a peripheral portion of the showerhead. In instances in which the showerhead is unpowered, the one or more periphery electrodes may be operatively coupled to ground via a variable reactance. A configuration with one or more showerhead periphery electrodes may be advantageous for controlling plasma density in a peripheral region (e.g., in the radial direction).

[0037] FIG. 2B illustrates a portion of an example process station that includes a peripheral electrode 226 in accordance with some embodiments. As illustrated, peripheral electrode 226 is operatively coupled to ground via variable capacitor 228. A showerhead electrode 222 is operatively coupled to ground via variable capacitor 224. Capacitances of variable capacitor 224 and / or variable capacitor 228 may be utilized to control a spatial plasma density of plasma 216. In particular, due to the voltage differential generated between center and edge regions (e.g., based on actuation of variable capacitors 224 and / or 228), density of plasma at an edge region 217 may be modified (e.g., increased or decreased). Note that peripheral electrode 226 is separated from a conducting portion of showerhead electrode 222 via a dielectric material 230. In some embodiments, dielectric material 230 may be replaced by air, vacuum space, or a gas-filled region.

[0038] In some embodiments, showerhead electrodes may be disposed in a dielectric showerhead body. In some implementations, the pedestal may be a conducting pedestal (e.g., the pedestal may be comprised of a conducting electrode to which an RF generator is operatively coupled). FIG. 2C illustrates a portion of an example process station that includes showerhead electrodes disposed in a dielectric showerhead body in accordance with some embodiments. As illustrated, a first showerhead electrode 240 and a second showerheadelectrode 244 are disposed in a dielectric showerhead body 248. First showerhead electrode 240 is operatively coupled to ground via a variable capacitor 242, and second showerhead electrode 244 is operatively coupled to ground via a variable capacitor 246. As described above, capacitances of variable capacitor 242 and / or variable capacitor 246 may be modified to control a spatial plasma density of plasma 216. For example, a voltage differential between the center and edge regions may lead to a change in plasma density in edge region 217 (e.g., an increase or decrease in plasma density). In the example shown in FIG. 2C, pedestal 250 is a conducting pedestal that is operatively coupled to RF generator 208.

[0039] The examples shown in and described above in connection with FIGS. 2A, 2B, and 2C utilize two electrodes associated with the showerhead. In some embodiments, three or more electrodes may be utilized. Use of additional electrodes may allow for more fine-grained tuning of spatial plasma density. For example, plasma density in a region between two electrodes may be controlled, and an increased number of electrodes may be used to increase a number of regions in which plasma density may be controlled.

[0040] FIG. 2D illustrates a portion of an example process station that utilizes three showerhead electrodes in accordance with some embodiments. As illustrated, the showerhead comprises a first electrode 252, a second electrode 256, and a third electrode 260. First electrode 252 is operatively coupled to ground via a variable capacitor 254, second electrode 256 is operatively coupled to ground via a variable capacitor 258, and third electrode 260 is operatively coupled to ground via a variable capacitor 262. Capacitances of variable capacitor 254, variable capacitor 258, and / or variable capacitor 262 may be modified to control a spatial density of plasma 216, e.g., in edge region 217 as shown. First electrode 252 is separated from second electrode 256 via a dielectric material 264, and second electrode 256 is separated from third electrode 260 via a dielectric material 266. Note that one or both of dielectric materials 264 and / or 266 may be replaced by an air gap, a vacuum filled gap, and / or a gas filled gap.

[0041] It should be noted that although FIG. 2D illustrates three electrodes that are part of the showerhead body, in some embodiments, any combination of electrodes as part of the showerhead body and / or affixed to a showerhead periphery (e.g., as shown in FIG. 2B) may be utilized. For example, three electrodes may be used where two electrodes are part of the showerhead body, and where one electrode is affixed to a periphery of the showerhead.

[0042] Additionally, it should be noted that although FIGS. 2A-2D illustrate each showerhead electrode as operatively coupled to ground via a variable reactance, in some implementations, only one electrode may be operatively coupled to ground via a variable reactance, and the remaining electrodes may be operatively coupled to ground via a fixed reactance (e.g., a fixed-value capacitor).

[0043] FIGS. 2A-2D illustrate a configuration in which a pedestal is powered and a showerhead is unpowered. Accordingly, variable reactances along the RF return path are operatively coupled to unpowered electrodes of the showerhead to control spatial plasma density. In instances in which the showerhead is powered (e.g., the RF source is operatively coupled to the showerhead) and the pedestal is unpowered, variable reactances along the RF return path may be operatively coupled to one or more unpowered electrodes of the pedestal. The variable reactance(s) may be controlled to control a plasma density in a spatial direction (e.g., radially and / or azimuthally), e.g., to control plasma density in a center region relative to an edge region.

[0044] FIG. 3 illustrates an example configuration of variable reactances along the RF return path in an instance in which the showerhead is powered in accordance with some embodiments. As illustrated, a showerhead 302 is operatively coupled to the RF source 208. A pedestal 304 comprises two unpowered electrodes, 306 and 308. These may be an inner and outer electrode, respectively. Note that each of electrodes 306 and 308 are operatively coupled to ground. Electrodes 306 and 308 are operatively coupled to ground via variable capacitors 310 and 312, respectively. Wafer 212 resides on the pedestal 304. Control of the capacitances 310 and / or 312 generates a voltage differential that in turn controls a density of plasma 216. For example, plasma density in an edge region 217 may be modified (e.g., increased or decreased) relative to a center region based on the capacitances of variable capacitors 310 and / or 312.

[0045] In some embodiments, a value of a variable reactance associated with a showerhead electrode may be determined based on obtained information associated with an ongoing plasma-based fabrication process. For example, the obtained information may be in situ information indicative of a current film thickness of deposited film on a wafer undergoing processing. Such information may be obtained from one or more sensors, cameras, etc. disposed in a process station. In some embodiments, a processor or controller associated with the process station or the process chamber may modify one or more variable reactances associated with one or more showerhead electrodes based on the obtained information. Continuing with this example, the processor or controller may determine values for the one or more variable reactances that will, when implemented, generate a voltage differential across the two or more showerhead electrodes that will be likely to yield a change in spatial plasma density that is likely to bring film thickness in alignment with a target film thickness. The modification of variable reactances may also be based on information obtained after wafer processing is complete (e.g., one or more ex situ metrology metrics). For example, the obtainedinformation may indicate a difference in deposited film thickness across a particular spatial direction (e.g., a radial and / or azimuthal direction), whereas a target thickness is to be uniform across the wafer surface. In some embodiments, values of variable reactances may be determined using a trained machine learning model, a lookup table, or the like. Such a trained model or lookup table may be generated using, e.g., experimental data that relates reactance values or voltage differentials to plasma densities and / or deposited film thicknesses.

[0046] FIG. 4 is a flowchart of an example process 400 for modifying variable reactances associated with a showerhead in accordance with some embodiments. Blocks of process 400 may be performed by one or more processors or controllers associated with a process station or process chamber. The one or more processors or controllers may be proximate to the process station or process chamber (e.g., as an edge device), or may be remote. In some embodiments, blocks of process 400 may be executed in an order other than what is shown in FIG. 4. In some embodiments, two or more blocks of process 400 may be executed substantially in parallel. In some embodiments, one or more blocks of process 400 may be omitted.

[0047] Process 400 can begin at 402 by obtaining information associated with an ongoing plasma-based fabrication process within a process station or chamber. The information may be indicative of plasma uniformity within the process station or process chamber, indicative of thickness of deposited film at different regions of a wafer undergoing processing, or the like. The information may be obtained from one or more sensors, cameras, etc. disposed in the process station or chamber.

[0048] At 404, process 400 can cause one or more variable reactances to be modified based on the information. The one or more variable reactances may each be operatively coupled to a corresponding electrode of two or more electrodes disposed in or connected to a showerhead. Modification of the one or more variable reactances may cause plasma density to be spatially controlled within the process station or chamber. For example, plasma density may be controlled in a radial and / or azimuthal direction. Control of plasma density may result in control of film deposition thickness, e.g., to be uniform across the wafer.

[0049] Values of the one or more variable reactances may be determined based on the obtained information. For example, in some embodiments, the reactance values may be identified as ones likely to generate a plasma density that is closer to a target plasma density (e.g., a uniform plasma density). As another example, in some embodiments, the reactance values may be identified as ones likely to generate a plasma density that is in turn likely to generate film thickness that is within a predetermined range of a target film thickness. In some embodiments, reactance values may be determined using a model (e.g., a pre-trained machine learning model,a numerical simulation of the fabrication process, etc.), a look up table, etc. For example, such a model or look up table may relate reactance values to voltage differentials, plasma density metrics, film thickness metrics, or the like, which may allow a reactance value to be determined for a given target voltage differential, plasma density, or film thickness.

[0050] Note that, as described above, the one or more variable reactances may each be operatively coupled to an electrode of a showerhead. The one or more variable reactances may include variable capacitors and / or variable inductors. The showerhead may be an unpowered showerhead such that each of the two or more electrodes are operatively coupled to ground.CONCLUSION

[0051] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.

Claims

CLAIMSWhat is claimed is:

1. A semiconductor fabrication chamber comprising: a pedestal configured to support a wafer undergoing processing; a showerhead; two or more unpowered electrodes operatively coupled to the showerhead or to the pedestal; and one or more variable reactances coupled to at least one of the two or more unpowered electrodes, wherein reactances of the one or more variable reactances are modified to control a spatial density of plasma within the fabrication chamber.

2. The semiconductor fabrication chamber of claim 1, wherein modification of the reactances of the one or more variable reactances reduces a likelihood of arcing in a vicinity of the wafer.

3. The semiconductor fabrication chamber of claim 1, wherein the two or more unpowered electrodes are separated from one another by at least one of: a non-gas dielectric material, vacuum, or a gas-filled gap.

4. The semiconductor fabrication chamber of claim 3, wherein a body of the showerhead comprises the dielectric material, and wherein the two or more unpowered electrodes are disposed in the showerhead body.

5. The semiconductor fabrication chamber of claim 3, wherein the two or more unpowered electrodes are separated by the dielectric material within a conducting body of the showerhead.

6. The semiconductor fabrication chamber of any one of claims 1-5, wherein at least one electrode of the two or more unpowered electrodes are affixed to a periphery of the showerhead.

7. The semiconductor fabrication chamber of any one of claims 1-5, wherein the two or more unpowered electrodes are operatively coupled to the showerhead, and wherein an RF source is operatively coupled to the pedestal.

8. The semiconductor fabrication chamber of any one of claims 1-5, wherein the two or more unpowered electrodes are operatively coupled to the pedestal, and wherein an RF source is operatively coupled to the showerhead.

9. The semiconductor fabrication chamber of any one of claims 1-5, wherein the reactances of the one or more variable reactances are modified to control the spatial density of the plasma in a radial direction within the fabrication chamber.

10. The semiconductor fabrication chamber of any one of claims 1-5, wherein the reactances of the one or more variable reactances are modified to control the spatial density of the plasma in an azimuthal direction within the fabrication chamber.

11. The semiconductor fabrication chamber of any one of claims 1-5, wherein the one or more variable reactances comprise variable capacitors.

12. The semiconductor fabrication chamber of any one of claims 1-5, wherein the one or more variable reactances comprise variable inductors.

13. A method of controlling spatial density of plasma within a process station, the method comprising: obtaining information associated with an ongoing plasma-based fabrication process within the process station; and modifying one or more variable reactances based on the information, the one or more variable reactances each operatively coupled to a corresponding one of two or more unpowered electrodes disposed in or connected to a showerhead or a pedestal, wherein the modification of the one or more variable reactances causes plasma density to be spatially controlled within the process station.

14. The method of claim 13, wherein the information is obtained from one or more sensors or cameras disposed in the process station.

15. The method of claim 13, wherein the information is indicative of a film thickness at a current time point on a surface of a wafer undergoing the fabrication process.

16. The method of claim 15, wherein values of the one or more variable reactances are determined to increase a likelihood of the film thickness being modified toward target film thickness properties.

17. The method of claim 16, wherein the target film thickness properties comprise film thickness across a spatial extent of the wafer undergoing the fabrication process.

18. The method of any one of claims 13-17, wherein the two or more unpowered electrodes are separated by at least one of: a non-gas dielectric material, a vacuum, or a gas- filled gap.

19. The method of any one of claims 13-17, wherein the one or more variable reactances comprise one or more variable capacitors.

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