Method and apparatus for controlling RF parameters at multiple frequencies

Abstract

To provide a method and an apparatus for controlling radio-frequency (RF) plasma attributes for an RF plasma processing system.SOLUTION: Some embodiments of the present disclosure provide voltage-current (V / I) sensors 151 and 152 in a process chamber 120 that can be used at high temperatures. Some embodiments provide a method for using the voltage-current (V / I) sensors 151 and 152 in the process chamber 120 to measure RF plasma attributes and provide feedback control to an RF generator 130.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to radio-frequency (RF) plasma processing systems, and more particularly to a voltage-current (V / I) probe for measuring RF power in high temperature environments. Some embodiments of the present disclosure relate to a method for calibrating the probe of the present disclosure. Some embodiments of the present disclosure also utilize an RF sensor disposed within a processing chamber. [Background technology]

[0002] In semiconductor manufacturing, direct information on the substrate processing can be crucial to process performance. Unfortunately, the majority of vendor-supplied systems have RF sensors outside the chamber. Also, such sensors may not always be properly calibrated against known reactive loads, or the phase of the voltage and current may not be properly characterized. As a result, they do not directly provide information on the RF voltage, current, and phase during the deposition process. Similarly, they lack the ability to control these factors.

[0003] There are not two sets of sensors placed upstream and downstream of the wafer that are cross-triggered so that the propagation delay between the two can be used to derive the wafer coupled power.

[0004] Therefore, there is a need for a method and apparatus for providing direct information regarding RF voltage, RF current, and RF phase, as well as a need for a method and apparatus for controlling RF voltage, RF current, and RF phase during processing. Summary of the Invention

[0005] One or more embodiments of the present disclosure are directed to a method of controlling a plasma processing chamber, the method including measuring a first voltage, a first current, and a phase difference between the first voltage and the first current with a first RF voltage-current (V / I) sensor disposed in the plasma processing chamber, and an RF generator coupled to the plasma processing chamber is controlled based on the measurements provided by the first RF voltage-current sensor.

[0006] Further embodiments of the present disclosure are directed to a plasma processing chamber including a susceptor disposed within the process space and configured to support one or more substrates during processing. The RF plasma generator is configured to output a variable voltage, a variable current, and a variable phase of the variable voltage and the variable current. At least one RF voltage-current (V / I) sensor is disposed within the process space and configured to measure a first voltage, a first current, and a phase difference between the first RF voltage and the first RF current. A controller is connected to the RF plasma generator and the at least one RF voltage-current sensor, the controller configured to control the RF generator based on an input from the at least one RF voltage-current sensor.

[0007] A further embodiment of the present disclosure is directed to a non-transitory computer readable medium including instructions that, when executed by a controller of a plasma processing system, cause the plasma processing system to: operate an RF generator; measure an RF voltage, an RF current, and a phase difference between the RF voltage and the RF current with an RF voltage-current sensor; determine a measurement of the coupled plasma output (power) at the voltage-current sensor; and modify an output of the RF generator.

[0008] In order that the previously mentioned features of the present disclosure may be more fully understood, the present disclosure briefly summarized above may be more fully described by reference to embodiments, some of which are illustrated in the accompanying drawings, which should be noted, however, that the accompanying drawings depict only typical embodiments of the present disclosure and should not be considered as limiting its scope, as the present disclosure may embrace other equally effective embodiments. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram illustrating a radio frequency (RF) plasma processing system in accordance with one or more embodiments of the present disclosure. [Diagram 2] 2 is a schematic cross-sectional view of a plasma processing chamber of the RF plasma processing system of FIG. 1, configured in accordance with one or more embodiments of the present disclosure. [Figure 3A] 2 is a schematic plan view of a V / I sensor in the RF plasma processing system of FIG. 1 in accordance with one or more embodiments of the present disclosure. [Figure 3B] 3B is a schematic cross-sectional view of a V / I sensor in the RF plasma processing system of FIG. 1 taken along the section AA of FIG. 3A. [Figure 4A] FIG. 4 is a functional schematic diagram of a V / I probe of the V / I sensor of FIGS. 3A and 3B in accordance with one or more embodiments of the present disclosure. [Figure 4B] FIG. 4 is a functional schematic diagram of a V / I probe of the V / I sensor of FIGS. 3A and 3B in accordance with one or more embodiments of the present disclosure. [Diagram 5] FIG. 13 illustrates a flowchart of process steps for calibrating a V / I sensor in accordance with one or more embodiments of the present disclosure. [Figure 6] FIG. 13 illustrates a flowchart of process steps for controlling RF power in accordance with one or more embodiments of the present disclosure. [Figure 7A] FIG. 1 shows a schematic diagram of a thin film deposition system and its equivalent circuit, including the location of the RF sensor relative to the RF delivery circuit. [Figure 7B]FIG. 1 shows a schematic diagram of a thin film deposition system and its equivalent circuit, including the location of the RF sensor relative to the RF delivery circuit. [Figure 7C] FIG. 1 shows a schematic diagram of a thin film deposition system and its equivalent circuit, including the location of the RF sensor relative to the RF delivery circuit. [Figure 8A] 1A-1D illustrate various test fixtures for calibrating sensors in accordance with one or more embodiments of the present disclosure. [Figure 8B] 1A-1D illustrate various test fixtures for calibrating sensors in accordance with one or more embodiments of the present disclosure. [Figure 8C] 1A-1D illustrate various test fixtures for calibrating sensors in accordance with one or more embodiments of the present disclosure. [Figure 8D] 1A-1D illustrate various test fixtures for calibrating sensors in accordance with one or more embodiments of the present disclosure. [Figure 8E] 1A-1D illustrate various test fixtures for calibrating sensors in accordance with one or more embodiments of the present disclosure. [Figure 9] FIG. 1 illustrates a data acquisition architecture for real-time sampling and control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] For clarity, the same reference numbers have been used wherever possible to designate identical elements common to the figures, and it is contemplated that elements and features of one embodiment may be advantageously incorporated in other embodiments without further detail.

[0011] In the following description, numerous specific details are set forth to provide a more thorough understanding of the embodiments of the present disclosure. However, it will be apparent to one skilled in the art that one or more of the embodiments of the present disclosure may be implemented without one or more of these specific details. In other cases, well-known features are not described so as not to obscure one or more of the embodiments of the present disclosure.

[0012] 1 is a block diagram illustrating a radio frequency (RF) plasma system 100 in accordance with one or more aspects of the present invention. The RF plasma system 100 includes a plasma processing chamber 120 and a first RF generator 130 coupled to the plasma processing chamber 120 via a first RF match 131 and a transmission line 132. In some embodiments, the RF plasma system 100 also includes a second RF generator 140 coupled to the plasma processing chamber 120 via a second RF match 141 and a transmission line 142. The RF plasma system 100 further includes control circuitry 150 (also referred to herein as a "controller") and voltage-to-current (V / I) sensors 151 and 152.

[0013] The plasma processing chamber 120 may be any technically feasible plasma deposition or plasma etch chamber, including a capacitively or inductively coupled plasma system for generating plasma therein, including a Plasma-Enhanced Chemical Vapor Deposition (PECVD) system, a physical vapor deposition system, an epitaxial layer deposition system, a plasma etch system, and the like. The first RF generator 130 may be any technically feasible RF power generator configured to drive plasma generation in the plasma processing chamber 120 by providing RF power to one or more discharge electrodes in the plasma processing chamber 120. The first RF generator 130 may provide RF power at one or more RF frequencies. For example, in some embodiments, the first RF generator 130 may be configured to provide power at an RF frequency of 13.56 MHz to a distribution manifold (also referred to as a showerhead) or other components suitable for use as discharge electrodes in the plasma processing chamber 120. Similarly, the second RF generator 140, if provided, may be any technically feasible RF power generator, at one or more RF frequencies, configured to drive plasma generation in the plasma processing chamber 120. For example, in some embodiments, the second RF generator 140 may be configured to provide power at a low RF frequency, such as 360 kHz, to a substrate support (also referred to as a susceptor) or other component suitable for use as a discharge electrode in the plasma processing chamber 120.

[0014] As shown, the first RF generator 130 transmits RF power, i.e., power through a first RF match 131 and a transmission line 132, to an RF load in the plasma processing chamber 120. A V / I sensor 151 is disposed in the plasma processing chamber 120 and transmits a voltage induced by a voltage associated with the RF power and a voltage induced by a current associated with the RF power to the control circuitry 150 via a signal lead 153, thereby enabling measurement of the current, voltage, and phase of the RF power. Because the V / I sensor 151 is provided at the connection points 221, 222 of the transmission line 132 and is disposed in the plasma processing chamber 120, there is little need for the control circuitry 150 to correct for the effects of standing wave components in the transmission line 132. Similarly, the second RF generator 140 transmits RF power to an RF load in the plasma processing chamber 120 via a second RF match 141 and a transmission line 142. The V / I sensor 152 enables measurement of the current, voltage, and phase of the RF power coupled to the plasma processing chamber 120 via the transmission line 142. Specifically, the V / I sensor 152 transmits a voltage induced by a voltage associated with the RF power and a voltage induced by a current associated with the RF power to the control circuitry 150 via signal lead 154.

[0015] In embodiments in which the plasma processing chamber 120 is configured with a pedestal or substrate support heater, the RF plasma system 100 further includes a heater power supply 160 coupled to a heating element (not shown in FIG. 1 ) in the plasma processing chamber 120 via conductive leads 161 and 162. In such embodiments, the RF plasma system 100 also includes an RF filter 170 electrically disposed between the heating element in the plasma processing chamber 120 and the heater power supply 160. Although the heating element disposed in the pedestal or substrate support is not nominally part of the RF system of the plasma processing chamber 120, such heating elements typically include a coiled conductive component having many windings, and as a result can couple to the RF energy provided in the processing region (not shown in FIG. 1 ) of the plasma processing chamber 120. Thus, the RF filter 170 is an electronic system or device configured to provide a portion of the conductive path formed between the heater coil and the heater power supply 160 while protecting the heater power supply 160 from the RF energy provided in the plasma processing chamber 120. RF filter 170 is typically located outside of plasma processing chamber 120, i.e., adjacent to or in contact with a surface exposed to air. As a result, RF filter 170 may reach temperatures of 100° C. to 200° C. during operation of plasma processing chamber 120.

[0016] The control circuitry 150 includes logic circuitry configured to receive signals from the V / I sensor 151 and determine the current, voltage, phase, and magnitude of the coupled RF power entering the plasma processing chamber 120 via the transmission line 132. In some embodiments, such logic circuitry is embodied as magnitude and phase detection circuitry. In embodiments in which the first RF generator 130 transmits RF power via the transmission line 132 to multiple connection points 221, 222 in the plasma processing chamber 120, the control circuitry 150 includes logic circuitry configured to receive multiple signals from the V / I sensor 151 to determine the current, voltage, phase, and magnitude of the coupled RF power entering the plasma processing chamber 120 via each such transmission line 132. Similarly, the control circuitry 150 includes logic circuitry configured to receive signals from the V / I sensor 152 and determine the current, voltage, phase, and magnitude of the coupled RF power entering the plasma processing chamber 120 via the transmission line 142.

[0017] In embodiments in which the plasma processing chamber 120 is configured with a pedestal or substrate support heater, the V / I sensor 152 is configured to transmit a signal voltage induced by RF power passing from a heater element in the pedestal or substrate support heater through conductive leads 161 and 162 to the control circuitry 150 via signal lead 154. The V / I sensor 152 is further configured to transmit a voltage signal induced from a current flow associated with a portion of the RF power provided to the pedestal through signal lead 154 to the control circuitry 150, which voltage signal is passed through conductive leads 161 and 162 to an external ground (not shown). In such embodiments, the control circuitry 150 is further configured to determine the current, voltage, phase, and magnitude of the RF power passing through conductive leads 161 and 162 based on the voltage transmitted through signal lead 154. Thus, the RF power losses through the conductive leads 161, 162 and the heater power supply 160 can be quantified based on the current and voltage measurements provided by the V / I sensor 152. As a result, chamber-to-chamber variations in processes performed at various instances of the plasma processing chamber 120 can be prevented by quantifying and compensating for instance-to-instance variations (i.e., from one chamber to the next) in the electrical behavior of the electrical circuitry that the RF filter 170 is in.

[0018] For example, in such an embodiment, the process performed in the plasma processing chamber 120 can be based on the actual or near actual RF power delivered to the processing region 246 of the processing chamber 120 via the transmission line 142, not only by measuring the RF power provided by the second RF generator 140, but also by correcting for the RF power lost via the conductive leads 161 and 162.

[0019] In some embodiments, the V / I sensor 152 is located in a region of the processing chamber that is at least partially surrounded by grounded or shielded processing chamber elements to isolate the V / I sensor 152 components from various external noise sources. In some configurations, a minimum fixed gap (e.g., 1-10 mm) is maintained between all of the V / I sensor 152 components and other processing chamber elements in the region of the processing chamber in which the V / I sensor is located. As a result, chamber-to-chamber variations in processes performed at various instances of the plasma processing chamber 120 are prevented by reducing instance-to-instance variations in the electrical measurements provided by the V / I sensor 152. In one example, the V / I sensor 152 is located in the plasma processing chamber 120.

[0020] 1, only one controller 150 is depicted in RF plasma system 100. In other embodiments, a different controller 150 may be incorporated into each RF generator included in RF plasma system 100. In still other embodiments, the functionality of control circuitry 150 may be incorporated into a central system controller for RF plasma system 100. In any case, the functionality of control circuitry 150 may include any technically feasible implementation, including via software, hardware, and / or firmware.

[0021] 2 is a schematic cross-sectional view of a plasma processing chamber 120 configured according to various embodiments of the present disclosure. By way of example, the embodiment of the plasma processing chamber 20 of FIG. 2 is described in terms of a PECVD system, but any other plasma processing chamber, including other plasma deposition chambers or plasma etch chambers, may fall within the scope of the embodiments. The plasma processing chamber 120 includes a wall 202, a bottom 204, and a chamber lid 224 that together enclose a susceptor 208 and a processing region 246. The plasma processing chamber 120 further includes a vacuum pump 214, a gas source 218, a first RF generator 130 and a first RF match 131, a second RF generator 140 and a second RF match 141, and an RF filter 170, each of which is coupled to the exterior of the plasma processing chamber 120.

[0022] Additionally, the plasma processing chamber 120 includes one or more V / I sensors 151 and 152 that are directly coupled to or otherwise mounted within the plasma processing chamber 120. In the embodiment shown in FIG. 2, the plasma processing chamber 120 includes a V / I sensor 151 such that the voltage and current passing through the transmission line 132 may be accurately measured in close proximity to the processing region 246 and the substrate 210. Additionally, the plasma processing chamber 120 includes a V / I sensor 152 such that the voltage and current passing through the transmission line 142 may be accurately measured in close proximity to the processing region 246 and the substrate 210. In some embodiments, the V / I sensor 152 is mounted on or near the bottom 204 of the plasma processing chamber 120 or is directly coupled to the bottom 204 of the plasma processing chamber 120. Alternatively, the V / I sensor 152 may be mounted on or near the susceptor 208. In some embodiments, the V / I sensor 152 may be directly bonded to the surface of the susceptor 208. Alternatively, the V / I sensor 152 may be attached to the susceptor 208 via a bracket or other support structure. In either case, the V / I sensor 152 is located within a few centimeters of the substrate 210 and the processing region 246.

[0023] It is noted that V / I sensors 151 and 152 are specifically located within plasma processing chamber 120. Sensors 151 and 152 may be directly coupled to an interior surface thereof or may be attached to a bracket or other support structure that is directly coupled to an interior surface of plasma processing chamber 120. In some embodiments, sensors 151 and 152 are exposed to elevated temperatures during processing of substrate 210.

[0024] The walls 202 and bottom 204 may be constructed of a conductive material, such as aluminum or stainless steel. Within the plasma processing chamber 120 is a shadow frame 238 configured to prevent or reduce unwanted deposition on the surface of the susceptor 208 that is not covered by the substrate 210 during processing. The shadow frame 238 sits on a ledge 240 when the plasma processing chamber 120 is idle and may be coupled to the inner surface of the walls 202 by one or more straps 243. Through one or more of the walls 202 may be a slit valve opening 206 configured to facilitate insertion and removal of the substrate 210 into and from the plasma processing chamber 120. A slit valve configured to seal the slit valve opening 206 may be provided inside or outside the plasma processing chamber 120.

[0025] A vacuum pump 214 is coupled to the plasma processing chamber 120 and configured to adjust the vacuum level therein. As shown, a valve 216 may be coupled between the plasma processing chamber 120 and the vacuum pump 214. The vacuum pump 214 evacuates the plasma processing chamber 120 prior to substrate processing and removes process gases therefrom during processing through the valve 216. The valve 216 may be adjustable to facilitate adjustment of the amount of vacuum pumped out of the plasma processing chamber 120. The amount of vacuum pumped out through the valve 216 and the incoming gas flow rate from the gas source 218 determine the chamber pressure and process gas residence time in the plasma processing chamber 120.

[0026] The susceptor 208 may include any technically feasible device for supporting a substrate 210, such as substrate 210 of FIG. 2, during processing by the plasma processing chamber 120. In some embodiments, the susceptor 208 is configured to be raised and lowered. In some embodiments, the susceptor 208 may be at least partially formed from or include a conductive material, such as tungsten, copper, molybdenum, aluminum, or stainless steel. In embodiments where the plasma processing chamber 120 is a capacitively coupled plasma chamber, the susceptor 208 may be configured to include an electrode (not shown). In such an embodiment, the metal rod 242 is electrically coupled to a recessed electrode disposed within the susceptor 208 and configured to provide RF power to the recessed electrode through a connection point 247. In this manner, the recessed electrode and the metal rod 242 are electrically coupled to the second RF generator 140 via the transmission line 142.

[0027] In some embodiments, the susceptor 208 includes one or more heating elements 209 for heating the substrate 210 during processing. In such embodiments, the heating elements 209 are coupled to a heater power supply 160 via conductive leads 161 and 162. Each of the conductive leads 161 and 162 passes through a respective measurement aperture (not shown in FIG. 1 ) of the V / I sensor 151 such that RF current and RF voltage can be measured thereby.

[0028] The gas source 218 is coupled to the plasma processing chamber 120 via a tube 223 that passes through the chamber lid 224. The tube 223 is coupled to the backing plate 226 to allow process gases to pass through the backing plate 226 and enter a plenum 248 between the backing plate 226 and the gas distribution showerhead 228. The gas distribution showerhead 228 may be held in position adjacent to the backing plate 226 by the suspension 234 such that the gas distribution showerhead 228, backing plate 226, and suspension 234 together form an assembly sometimes referred to as a gas box. Thus, in operation, process gases introduced into the plasma processing chamber 120 from the gas source 218 fill the plenum 248 and then pass through gas passages 230 formed in the gas distribution showerhead 228 and uniformly enter the processing region 246. In an alternative embodiment, process gases may be introduced into the processing region 246 through inlets and / or nozzles (not shown) attached to the wall 202 in addition to or instead of the gas distribution showerhead 228.

[0029] The first RF generator 130 is coupled to the backing plate 226 at coupling points 221 and / or 222 via one or more transmission lines 132. Thus, the coupling points 221 and 222 function as RF power feed points to the backing plate 226. Alternatively, the first RF generator 130 may be coupled to the backing plate 226 at one coupling point. The transmission lines 132 may include coaxial cables, which in some embodiments are configured with additional shielding on the exterior of these coaxial cables to prevent excessive leakage of RF power to ground. In one embodiment, the first RF generator 130 may include an RF generator capable of generating RF current at a frequency of about 13.56 MHz. In another embodiment, the first RF generator 130 may include a VHF generator capable of generating VHF power, such as VHF power at frequencies from about 40 MHz to 200 MHz or higher. As shown, each of the transmission lines 132 passes through a respective measurement aperture of the V / I sensor 151.

[0030] In some embodiments, the first RF generator 130 provides radio frequency power through the first RF match 131 to a discharge electrode disposed adjacent to the processing region 246. Such a discharge electrode may include a process gas distribution element, such as a gas distribution showerhead 228 (as shown in FIG. 2), or a gas injection nozzle array through which process gas is introduced to the processing region 246. The discharge electrode, e.g., the gas distribution showerhead 228, may be oriented approximately parallel to the surface of the substrate 210 to capacitively couple plasma source power to the processing region 246 disposed between the substrate 210 and the gas distribution showerhead 228. During processing, the susceptor 208, the shadow frame 238, and the substrate 210 are elevated and positioned near (e.g., within 1-30 mm) the lower surface of the showerhead 228 to form an at least partially enclosed processing region 246.

[0031] In some embodiments, the plasma processing chamber 120 may include a machine-compatible controller (e.g., control circuitry 150) configured to control the operation of the plasma processing chamber 120, including the output power level of the first RF generator 130, the flow rates of various process gases directed to the processing region 246 via the gas source 218, adjustment of the valves 216, etc. Typically, such a controller includes one or more processors, memory, and instructions suitable for controlling the operation of the plasma processing chamber 120. Alternatively, in some embodiments, a system controller configured to control the operation of a multi-chamber processing system may instead be configured to control the operation of the plasma processing chamber 120 as well as one or more other processing chambers.

[0032] Plasma processing, such as PECVD processing, is typically performed in plasma processing chamber 120 by placing substrate 210 on susceptor 208 and introducing one or more precursor gases from gas source 218 into processing region 246. One or more precursor gases in processing region 246 are energized (e.g., excited) into a plasma state by applying RF power from RF generator 130 to gas distribution showerhead 228 at coupling points 221 and 222 and / or RF power from RF generator 140 to susceptor 208. This type of plasma is typically referred to as a capacitively coupled plasma (CCP) because the electronic heating mechanism is primarily through a capacitive plasma sheath near the gas distribution showerhead 228 and / or a grounded electrode, such as susceptor 208 or wall 202. The excited gases react to form a material layer on the surface of substrate 210.

[0033] Typically, RF current seeks the shortest path back to the source that sent it. Thus, during plasma processing, the sent RF current travels from the first RF generator 130, through the plasma generated in the processing region 246, to an RF path such as the wall 202. In an embodiment in which the susceptor 208 is coupled to the second RF generator 140, the RF current travels from the second RF generator 140, through the rods 242, the recessed electrodes, and the plasma provided in the processing region 246, to an RF return path such as the wall 202 and the bottom 204. However, in an embodiment in which the susceptor 208 includes a heating element 209, the heating element 209 may be coupled to the RF energy delivered to the plasma processing chamber 120, and a certain percentage of the RF energy provided to the susceptor 208 may not return to the second RF generator 140. Instead, a portion of the RF energy provided by the second RF generator 140 may flow to the heater power supply 160 via the conductive leads 161 and 162. Although the filter 170 is configured to reduce the flow of RF energy along the conductive leads 161 and 162, the filter 170 is rarely perfectly efficient. As a result, a large portion of the RF energy may flow to the heater power supply 160 with or without the filter 170. Therefore, in addition to power losses due to reflections, the RF power losses through the conductive leads 161 and 162 may also affect the amount of RF energy actually delivered to the processing region 246. Also, because the operation of the filter 170 typically varies from instance to instance, the effects of the RF power losses through the conductive leads 161 and 162 may vary at each instance of the plasma processing chamber 120. Therefore, if nominally identical processes are performed in two different instances of the plasma processing chamber 120, the process results, such as film thickness, uniformity, etc., may suffer from unpredictable variations unless the RF power actually delivered to the processing region 246 can be accurately measured.

[0034] Conventional V / I sensors for RF applications often include organic substrates, such as FR-4, that may be thermally damaged at 70° C. or higher. As a result, in high temperature applications, such as PECVD chambers, conventional V / I sensors are typically located some distance away from the processing chamber. As a result, measurements taken with such sensors and used in RF matching components of electrical circuits are subject to extrapolation techniques to compensate for the position dependency of RF measurements made away from the processing chamber along imperfectly matched transmission lines due to this induced error in the sensed electrical measurements. Such extrapolations are highly dependent on the construction details of the plasma processing chamber 120, are very difficult to experimentally validate, and even if validated for one process, they usually vary for other processes depending on the process chemistry and chamber operating conditions. Furthermore, due to the nonlinear nature of the standing waves in the transmission lines 132 and 142, conventional extrapolation techniques based on ideal transmission line models cannot accurately capture the RF power losses that reside between the substrate 210 and the remote measurement points, and therefore may significantly underestimate or overestimate such power losses.

[0035] Thus, in embodiments of the present disclosure, V / I sensors 151 and / or 152 enable more accurate measurement of the voltage, current, and phase of the RF power delivered to processing region 246. In particular, V / I sensors 151 and / or 152 are configured for high temperature environments and are therefore suitable for placement within plasma processing chamber 120 even as high temperature processes are performed thereby. One such embodiment is illustrated in Figures 3A and 3B.

[0036] FIG. 3A is a schematic plan view of the V / I sensor 152 according to various embodiments of the present disclosure. FIG. 3B is a schematic cross-sectional view of the V / I sensor 152 taken at section AA of FIG. 3A. The V / I sensor 152 is configured to accurately measure RF current and RF voltage in a high temperature environment, such as a location in the plasma processing chamber 120 during a high temperature PECVD process. In the embodiment shown in FIG. 3A and FIG. 3B, the V / I sensor 152 is configured to measure RF current and RF voltage at the metal rod 242 and the conductive leads 161, 162. In one embodiment, the V / I sensor 152 is configured to measure RF voltage and RF current provided to the distal end of the metal rod 242 relative to the susceptor 208 and the distal ends of the conductive leads 161, 162. In some embodiments, the V / I sensor 152 includes a plane body 301 having a first V / I probe 310, a second V / I probe 320, a third V / I probe 330, and a ground plane 302 that surrounds and electrically isolates the first V / I probe 310, the second V / I probe 320, and the third V / I probe 330 from one another.

[0037] The planar body 301 is constructed of an inorganic-containing electrically insulating material, such as ceramic, mica, ferrite, or similar materials. For example, suitable ceramic materials include aluminum oxide and aluminum nitride. The aforementioned inorganic electrically insulating materials have higher thermal resistance than organic substrates typically employed in conventional V / I sensors, such as FR-4. Thus, the planar body 301 and the V / I sensor 152 are adapted to be mounted within the plasma processing chamber 120. As a result, the V / I sensor 152 may be located in close proximity to the processing region 246 of the plasma processing chamber 120. However, for some high temperature applications, the planar body 301 may be formed of a polyimide, such as Kapton®.

[0038] The first V / I probe 310 includes a voltage pickup 311 and a current pickup 312, each of which is disposed around a measurement aperture 315. The measurement aperture 315 is configured to accommodate a conductive structure suitable for transmitting RF power, such as the conductors of the transmission line 142 or metal rod 242 that provide RF power to a recessed electrode in the susceptor 208. Thus, the V / I probe 310 is configured to provide accurate voltage and current measurements of the RF power delivered to the plasma processing chamber 120 at a location proximate to the processing region 246.

[0039] The voltage pickup 311 shown in FIG. 4B is configured to emit a voltage signal induced by RF power passing through a measurement aperture 315 formed in the planar body 301, for example, via a transmission line 142 or a metal rod 242. The voltage signal emitted by the voltage pickup 311 is approximately proportional to the voltage of the RF power passing through a portion of a conductive element disposed in the measurement aperture 315. In some embodiments, the voltage pickup 311 is configured as a conductive ring 311A, which is provided around or formed on the surface of the measurement aperture 315. The conductive ring 311A ​​is typically surrounded by a ground element 320. Both the conductive ring 311A ​​and the ground element 320 are connected in an electrical circuit, such as an RF voltage measurement circuit 455 shown in FIG. 4B, and are used together to measure the voltage of the RF power passing through a portion of an RF conductive element disposed in the measurement aperture 315. The ground element 320 typically includes one or more ground layers 302A and 302B disposed on or within the surface of the V / I sensor 152 and electrically coupled to one another by a number of interconnect vias 302C. The one or more ground layers 302A and 302B and the number of interconnect vias 302C may be formed from a conductive material (e.g., a metal containing Al, Ag, Au, Mo, Sn, or Cu) and are used to electrically shield the first V / I probe 310, the second V / I probe 320, and the third V / I probe 330 from one another and from other external components. In some configurations, the number of interconnect vias 302C are disposed around each of the V / I probes 310, 320, and 330 to provide shielding that minimizes crosstalk between components within each of the V / I probes. In some embodiments, the ground element 320 may be connected to an outer shield conductor 402 of a coaxial transmission line (not shown), such as the signal lead 154 .

[0040] The current pickup 312 shown in FIG. 4A is configured to generate a voltage signal induced by RF power passing through a portion of a conductive element located within the measurement aperture 315 by use of an electrical circuit, such as the RF current measurement circuit 454 shown in FIG. 4A. The magnetic field flux induced voltage signal is approximately proportional to the RF current induced in the current pickup 312 and passing through the portion of the conductive element located within the measurement aperture 315. In some embodiments, the current pickup 312 is configured as a toroidal shaped coil, or a close approximation thereof. For example, in the embodiment shown in FIGS. 3A and 3B, the current pickup 312 includes a substantially planar circuit trace 313 on the top surface 301A of the planar body 301, a substantially planar circuit trace 314 on the bottom surface 301B of the planar body 301, and a conductive via 316 formed through the planar body 301. Each conductive via 316 connects a circuit trace 313 with a corresponding circuit trace 314 such that the serially interconnected circuit traces 313, 314, and conductive vias 316 together form an uninterrupted conductive loop structure.

[0041] 3A and 3B minimizes or otherwise reduces crosstalk between the voltage pickup 311 and the current pickup 312. In particular, because the voltage pickup 311 and the current pickup 312 are disposed in a plane, i.e., a plane defined by the planar body 301 (e.g., the XY plane), and because this plane is perpendicular to the direction of RF power transmission through the measurement aperture 315, an RF voltage in the transmission line provided in the measurement aperture 315 induces little voltage in the current pickup 312, and an RF current flowing in the transmission line provided in the measurement aperture 315 induces little voltage in the voltage pickup 311. Thus, it is believed that the voltage and current measurements of the transmission line can be considered mutually exclusive of each other, and therefore crosstalk between these sensing elements is negligible. That is, there is no significant measurement error caused by the voltage signal from voltage pickup 311 including a contribution from the RF current passing through measurement aperture 315, and there is no significant measurement error caused by the voltage signal from current pickup 312 including a contribution from the RF voltage passing through measurement aperture 315. Thus, the product of the measured voltage times the measured current times the cosine of the phase difference between voltage pickup 311 and current pickup 312 is approximately proportional to the instantaneous transmission line power at the measurement point. In some embodiments, the size of voltage pickup 311 and current pickup 312 in V / I probe 310 is proportional to the size or cross-sectional area of ​​the portion of the conductive element that passes through aperture 315 formed therein, or proportional to the generated field across aperture 315 formed therein.

[0042] A second V / I probe 320 and a third V / I probe 330 may be generally similar in configuration and operation to the first V / I probe 310 and are included in the V / I sensor 152 to provide voltage and current measurements to additional RF transmission lines associated with the plasma processing chamber 120, such as conductive leads 161 and 162. It should be noted that conductive leads 161 and 162 are not intended as RF transmission lines, but may nevertheless operate as such in some embodiments of the plasma processing chamber 120.

[0043] The second V / I probe 320 includes a voltage pickup 321 and a current pickup 322, each of which are disposed around a measurement aperture 325. The measurement aperture 325 is configured to accommodate a particular RF conductive lead associated with the plasma processing chamber 120 that is not coupled between the RF source and a ground that is coupled to the plasma processing chamber 120, such as conductive lead 161. In some embodiments, the size of the voltage pickup 321 and current pickup 322 in the V / I probe 320 is proportional to the size or cross-sectional area of ​​a portion of a conductive element that passes through the measurement aperture 325 formed therein, or proportional to the field across the measurement aperture 325 formed therein.

[0044] Similarly, the third V / I probe 330 includes a voltage pickup 331 and a current pickup 332, each of which is disposed around a measurement aperture 335. The measurement aperture 335 is configured to accommodate another RF conductive lead associated with the plasma processing chamber 120 that is not coupled between the RF source and a ground that is coupled to the plasma processing chamber, such as conductive lead 162. In some embodiments, the voltage pickup 331 and current pickup 332 in the V / I probe 330 are sized in proportion to the size or cross-sectional area of ​​a portion of a conductive element that passes through the measurement aperture 335 formed therein, or in proportion to the field across the measurement aperture 335 formed therein. Because the second V / I probe 320 and the third V / I probe 330 enable measurement of the RF power loss through the conductive leads 161 and 162, the actual RF power coupled into the processing region 246 can be more accurately determined by simply measuring the RF power delivered to the plasma processing chamber 120 through the metal rod 242 or the upstream portion of the transmission line 142. Thus, chamber-to-chamber variations in the efficiency of the filter 170 can be detected, quantified, and compensated for through the use of various V / I probes and chamber RF matching elements.

[0045] 4A and 4B are functional schematic diagrams of a first V / I probe 310 of a V / I sensor 152 in accordance with one or more embodiments of the present disclosure. As shown, a signal lead 154B of signal lead 154 (FIG. 1) is coupled to a voltage pickup 311, and another signal lead 154A of signal lead 154 is coupled to a current pickup 312. In some embodiments, each of these signal leads 154A and 154B is configured as part of one or more coaxial cables having a 50 ohm resistance between a center conductor 401 and an outer shield conductor 402.

[0046] In some embodiments, for optimal or otherwise improved operation of the plasma processing chamber 120, each V / I sensor associated therewith can be calibrated. In such an embodiment, a particular signal voltage emitted by the voltage pickup of the V / I sensor can be precisely correlated to a particular known RF voltage passing through the measurement aperture of the V / I sensor. Similarly, a particular signal voltage emitted by the current pickup 312 of the V / I sensor can be precisely correlated to a particular known RF current passing through the measurement aperture of the V / I sensor. In this manner, a calibration factor can be developed for the voltage pickup and another calibration factor can be developed for the current pickup 312. In a subsequent step, the signal voltage emitted by the voltage pickup and multiplied by the appropriate calibration factor can be precisely indicative of the RF voltage passing through the measurement aperture at any point in time. Similarly, the signal voltage emitted by the current pickup 312 and multiplied by the appropriate calibration factor can be precisely indicative of the RF current passing through the measurement aperture at any point in time. One such embodiment is described below in conjunction with FIG. 5.

[0047] FIG. 5 sets forth a flow chart of a process for calibrating a V / I sensor according to various embodiments of the present disclosure. The process is described in the context of the RF plasma system 100 in FIGS. 1-4, but one skilled in the art will appreciate that the process may also be performed in other types of RF plasma systems. The control algorithm for the method 500 resides in the machine compatible controller 150 configured to control the operation of the plasma processing chamber 120, or in a separate computing device that is coupled to the RF plasma system 100 during the calibration process. Such control algorithms may be embodied in whole or in part as software or firmware implemented logic and / or as hardware implemented logic circuitry.

[0048] Prior to this process, a suitable RF generator is coupled to a dummy load of known impedance via an RF match of known impedance and a suitable transmission line. More specifically, the RF generator, dummy load, and RF match are selected to form a matched RF system, i.e., an RF system without any reflections. For example, in one embodiment, a second RF generator 140 is coupled to a 50 ohm dummy load via a second RF match 142 and a transmission line 142. Additionally, prior to this process, the transmission line is fed into the measurement aperture of the V / I sensor to be calibrated, such as V / I sensor 152.

[0049] Method 500 begins at block 501, where RF power is generated at a particular RF frequency by second RF generator 140. For example, in one embodiment, second RF generator 140 generates 2500 W at 27 MHz. In some embodiments, the magnitude of the RF power generated at block 501 is equal to the maximum RF power expected to be employed by second RF generator 140 at the particular frequency.

[0050] In block 502, a V / I probe into which transmission line 141 is fed, for example first V / I probe 310, emits a first voltage signal and a second voltage signal. Voltage pickup 311 emits a first voltage signal proportional to the RF voltage found at measurement aperture 315 of first V / I probe 310. Current pickup 312 emits a second voltage signal proportional to the RF current passing through measurement aperture 315 of first V / I probe 310. Control circuitry 150 can then store these received measurement signals in memory.

[0051] In block 503, a calibration factor is determined for the voltage pickup 311 based on the first voltage signal passing through the measurement aperture 315 and the known RF voltage. Note that since there are no reflections in the matched RF system employed in method 500, the RF voltage is equal to the square root of the product of the RF power and resistance of the system. Since both the RF power and resistance of the system are known, the RF voltage is also known. Thus, after completing blocks 501-503 at least twice, a curve of known magnitude of V / I probe voltage versus RF voltage can be formed. Since the calibration curve will be linear with an intercept at zero volts, the coefficient will be equal to the slope of the formed curve, which will later be used as the calibration factor for the V / I probe voltage.

[0052] Also in block 503, a calibration factor is determined for the current pickup 312 based on the second voltage signal passing through the measurement aperture 315 and the known RF current. Since there are no reflections in the matched RF system employed in method 500, the RF current is also known since the current is equal to the square root of the ratio of the RF power to the resistance of the system. Since both the RF voltage and resistance of the system are known, the RF current is also known. Thus, after completing blocks 501-503 at least twice, a curve of known magnitude of the V / I probe current measurement (e.g., voltage signal) versus RF current can be formed. Since the calibration curve will be linear with an intercept at zero volts, the coefficient will be equal to the slope of the formed curve, which is later used as a calibration factor during V / I probe current measurements.

[0053] In some embodiments, the calibration coefficients determined for the voltage pickup 311 and / or the current pickup 312 for each V / I probe are stored in a memory of the control circuitry 150 and used by a portion of the control circuitry to adjust the measured RF current and RF voltage values ​​by the V / I probes that are subsequently used by the RF matching and / or RF power elements used in the process chamber.

[0054] In some embodiments, RF generators may be employed in the RF plasma system to provide mixed operating frequencies. For example, in some circumstances, two RF frequencies simultaneously allow the PECVD plasma to control the plasma density and ion energy adjacent to the substrate 210 being processed. Also, pulsing steps may be employed to optimize certain film properties. In either case, when there is more than one frequency in the RF system, the signals emitted by the current and voltage pickups of the V / I sensor are typically fed into bandpass filters (not shown) at each of the operating frequencies before reaching the magnitude and phase detection circuitry. The insertion of such bandpass filters may result in a magnitude difference (attenuation) and a phase difference between the signals emitted by the current pickup 312 and the voltage pickup, which may then be used to adjust the RF power provided by each of the RF generators and / or adjust the RF match parameters corresponding to the respective RF matching elements of each RF source.

[0055] According to some embodiments, an RF generator is employed in the RF plasma system to provide the mixed operating frequency, and the calibration process of method 500 can be employed at different RF power levels for each of the RF frequencies used in the process chamber to generate accurate calibration factors for each of the provided RF frequencies. Specifically, the calibration process of method 500 can be employed at each operating frequency to generate a calibration factor for each of the operating frequencies, thereby allowing correction for the attenuation of the generated signal caused by the bandpass filter. Furthermore, since the RF system employed in method 500 is a matched RF system without reflections, when a phase difference between the first voltage signal and the second voltage signal is detected, the phase difference is actually the phase difference of the RF system caused by the bandpass filter included in the RF system and detected by the measurement circuitry. In multiple frequency steps of the RF system, a different system phase shift is typically employed for each of the provided RF frequencies, and each such phase shift is determined in a different implementation of method 500. Therefore, the phase difference measured by method 500 at a particular frequency can be considered a system phase shift that can be adopted for that particular operating frequency for use in correcting RF power parameters detected by the V / I probe, which can be used to control the RF power provided by each of the RF generators and / or adjust the RF match parameters corresponding to each RF matching element of each RF source.

[0056] FIG. 6 sets forth a flow chart of a process for controlling RF power applied to a plasma processing chamber 120 according to various embodiments of the present disclosure. The process is described in the context of RF plasma system 100 in FIGS. 1-4, but one of ordinary skill in the art will appreciate that the process may also be performed in other types of RF plasma systems. The control algorithms in this method reside in the controller 150 or in machine-compatible control circuitry configured to control the operation of the plasma processing chamber 120. Such control algorithms may be embodied in whole or in part as software- or firmware-implemented logic and / or as hardware-implemented logic.

[0057] Prior to this process, an appropriate calibration factor for each V / I probe associated with RF plasma system 100 is determined, for example, by method 500. For example, for V / I sensor 152, an appropriate calibration factor is determined for each of voltage pickup 311, current pickup 312, voltage pickup 321, current pickup 322, voltage pickup 331, and current pickup 332. Also, in embodiments where second RF generator 140 is configured to generate mixed frequencies, a system phase shift from measurement circuitry of RF plasma system 100 is determined for each frequency.

[0058] The method 600 begins at block 601, where RF power is generated by the second RF generator 140 at a particular RF frequency and power magnitude. The RF power magnitude generated in block 601 is intended to result in a targeted RF power being coupled into the processing region 246. Typically, the targeted RF power corresponds to a particular process ongoing in the plasma processing chamber 120. Thus, for each process, a different targeted RF power may be employed in block 601.

[0059] In block 602, V / I sensor 152 emits at least a first voltage signal and a second voltage signal, where voltage pickup 311 emits the first voltage signal and current pickup 312 emits the second voltage signal. The first voltage signal is proportional to the RF voltage passing through measurement aperture 315 of V / I probe 310, and the second voltage signal is proportional to the RF current passing through measurement aperture 315 of V / I probe 310. In an embodiment in which V / I sensor 152 includes multiple probes, the V / I sensor emits an additional voltage signal, such as a voltage signal that is a measure of the RF voltage and RF current associated with conductive leads 161 and 162.

[0060] In some embodiments, the V / I sensor 152 emits the first and second voltage signals at an interval of 1 μs to 1 sec. In some embodiments, the interval is in the range of 1 μs to 1 ms. In doing so, it may be possible to generate respective RF voltage and RF current waveforms.

[0061] At block 603, an actual RF power delivered to the processing region 246 in the plasma processing chamber 120 is determined. In some embodiments, determining the actual RF power delivered includes applying a first calibration factor to the first voltage signal and applying a second calibration factor to the second voltage signal. As previously indicated, the first calibration factor and the second calibration factor are typically determined in a calibration process performed prior to method 500, etc.

[0062] During the process of determining the actual RF power delivered to the processing region 246, the control circuitry 150 retrieves the first and second calibration factors from memory, then multiplies the corresponding measurement signal values ​​collected from the corresponding V / I probes by the corresponding calibration factors to determine corrected measurement signal values, which can then be used to control the RF power provided by each of the RG generators and / or adjust the RF match parameters corresponding to each of the RF matching elements of the RF source. For example, in some embodiments, the first voltage signal is multiplied by the first calibration factor to produce a measured voltage value that accurately indicates the actual voltage passing through the V / I sensor 152, and the second voltage signal is multiplied by the second calibration factor to produce a measured current value that accurately indicates the actual current passing through the V / I sensor 152. The actual RF power coupled to the processing region 246 can then be calculated by a computer based on the measured voltage and current values. This allows software running within the control circuitry 150 to use the actual RF power coupled to the processing region 246 to more precisely control processes taking place in the processing chamber and / or displayed on a graphical user interface (e.g., a monitor or display) coupled to the control circuitry 150 and accessible to a user.

[0063] In some embodiments, the actual RF power coupled into the processing region 246 is further based on a measured phase difference between the measured voltage and current values. Specifically, in such embodiments, the instantaneous transmission line power at the measurement point is the product of the measured voltage value times the measured current value times the cosine of the measured phase difference between the voltage pickup 311 and the current pickup 312. The measured phase difference can thereby be used by software operating within the control circuitry 150 to more accurately control RF related processes taking place in the processing chamber and / or displayed on a graphical user interface (e.g., a monitor or display) coupled to the processing circuitry 150 and accessible to a user.

[0064] In embodiments where the mixed frequency is generated by the second RF generator 140, the previously determined system phase shift is first subtracted from the measured phase difference between the first voltage signal (from the voltage pickup 311) and the second voltage signal (from the current pickup 312). In this manner, in block 603, the actual phase difference between the voltage pickup 311 and the current pickup 312 can be determined prior to calculating the actual RF power coupled into the processing region 246.

[0065] In some embodiments, the actual RF power coupled to processing region 246 is also based on lost RF power not delivered to processing region 245. For example, in such embodiments, the actual RF power delivered to processing region 246 is also based on the RF power measured at conductive leads 161 and 162.

[0066] At block 604, a determination is made whether the actual RF power coupled to the processing region 246 is within a predetermined range of the target RF power coupled to the processing region 246. If it is within the predetermined range, the current output is maintained unchanged, if it is outside the predetermined range, 600 proceeds to block 605.

[0067] In block 605, the magnitude of the current output is adjusted so that the actual RF power coupled to the processing region 246 is equal to or approximately equal to the target RF power coupled to the processing region 246. The method 600 then returns to block 601.

[0068] Implementation of method 600 allows for improved measurement and control of RF voltage, RF current, RF phase, and coupled RF power in high temperature environments. Because RF voltage and RF current can be measured in close proximity to the processing region of the plasma processing chamber 120, more accurate measurements of coupled RF power can be obtained, improving performance of the plasma processing chamber 120 and reducing chamber-to-chamber variations in plasma processing.

[0069] In some embodiments disclosed herein, the V / I sensor includes a planar body of an inorganic, electrically insulating material, a measurement aperture formed in the planar body 301, a voltage pick-up centered about the measurement aperture, and a current pick-up centered about the measurement aperture. Due to the planar configuration and material composition of the V / I sensor, the V / I sensor may be placed in close proximity to or even in contact with a hot surface of the plasma processing chamber 120. In fact, the inventors have recently and surprisingly discovered that the V / I sensor described herein may be placed within the plasma processing chamber 120. As previously indicated, in some embodiments, a voltage signal proportional to the RF voltage passing through the V / I sensor is derived from the voltage pick-up portion of the V / I sensor, and a voltage signal proportional to the RF current passing through the V / I sensor is derived from the current pick-up portion of the V / I sensor, thereby minimizing induced errors in the measurements due to the nature of the sensed signals, which does not result in any significant measurement interaction between the sensors. Therefore, based on one or more of these factors, the RF voltage and RF current measurements provided by one or more of the embodiments disclosed herein are often more accurate than V / I sensors placed outside the plasma processing chamber.

[0070] Aspects of the present embodiments may be embodied as a system, method, or computer program product. Accordingly, aspects of the present disclosure may take the form of an all-hardware embodiment, an all-software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be generally referred to herein as a "circuit," "module," or "system." Aspects of the present disclosure may also take the form of a computer program product embodied in one or more computer-readable medium(s) having computer-readable program code embodied therein.

[0071] Any combination of one or more computer readable media may be utilized. The computer readable media may be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium may be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. A more specific (non-exhaustive) list of computer readable storage media would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or flash memory), an optical fiber, a portable compact disk read only memory (CD-ROM), an optical storage element, a magnetic storage element, or any suitable combination thereof. In the context of this disclosure, a computer readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, an instruction execution device, or an instruction execution device.

[0072] Embodiments of the present disclosure relate to methods and apparatus for controlling various parameters of radio frequency (RF) at multiple frequencies. Some embodiments of the present disclosure may advantageously utilize sensors located within a processing chamber to minimize the distance between the sensor and the substrate during processing. Some embodiments of the present disclosure may advantageously acquire and / or process data related to the RF to dynamically control the RF in real time.

[0073] Disclosed herein are methods and apparatus for acquiring and processing RF voltage, RF current, and RF phase information based on real-time streamed time domain waveforms, and some embodiments of the present disclosure provide for the application of digital signal processing techniques to extract coupled RF power at multiple frequencies at multiple RF sensor locations in CVD equipment operating in elevated temperature environments.

[0074] A new sensor and a new method for calibrating such a sensor under high power are disclosed that enable the use of the sensor in a plasma processing chamber for process monitoring; heretofore, there have been no RF sensors in plasma processing chambers that provide direct data.

[0075] Figures 7A-7C show schematics of a typical CVD system with simplified RF equivalent circuits. Figure 7A shows the equivalent of a real precision chamber operating at high wafer temperatures of approximately 500°C to approximately 650°C. Figure 7B shows the simplified equivalent of the RF-only circuit. Figure 7C shows an ideal 50 ohm RF transmission line model.

[0076] 7A-7C show possible RF leakage paths that need to be controlled in a modern CVD system to obtain a production-worthy thin film. To heat the wafer and chamber to high temperatures, an RF filter is used to block RF energy, usually in the DC or 50 / 60 Hz frequency range, from entering the heater driver circuit. Without being bound by theory, it is noted that since a practical filter cannot present infinite impedance at RF frequencies, some leakage current passes through the filter and escapes from the main RF control circuit. The leakage current results in loss of RF current to the wafer as well as loss of control of the power coupled to the wafer. In a modern semiconductor manufacturing environment, it is preferable to maintain better than percent level control on the main RF control.

[0077] Therefore, some embodiments of the present disclosure place the embedded RF sensor in the system, rather than external to the system. Although it would be preferable for the embedded RF sensor to be directly on the wafer for reliable measurements, high wafer temperatures may preclude this placement. Therefore, some embodiments place the embedded RF sensor as close to the wafer as possible.

[0078] Some embodiments of the present disclosure provide a dual sensor configuration where a first sensor is placed above the wafer and a second sensor is placed below the wafer. Some embodiments of the present disclosure provide a single sensor placed below the wafer where a current sensor coil and a voltage ring encase the RF rods that connect to the ESC electrodes.

[0079] Further embodiments of the present disclosure provide methods and apparatus to do the same for an RF transmission line at a power level equivalent to that of the CVD equipment, but with known characteristics such as voltage, current, phase, and propagation delay, etc. In some embodiments, the RF transmission line is used as a calibration tool to enable conversion of the RF sensor signal to voltage, current, and phase against a timestamp with microsecond to millisecond time resolution.

[0080] 4A and 4B, the sensor emits a voltage signal related to the RF voltage and RF current, but the emitted voltage signal is not the RF voltage (V) or RF current (A). The voltage signal needs to be calibrated against a known voltage and current at the operating frequency or frequencies before being deployed in the chamber for measurement.

[0081] 8A-8E show examples of how to build and use a test fixture to calibrate a sensor under high power. Without being bound by theory, it is believed that the calibration should be performed at a power level that is the same or equivalent to the power level in the chamber, e.g., such that power dissipation is dependent on the driving power level, to account for any possible non-linear effects on power.

[0082] It can be seen from Figures 8A-8E that a high power RF generator and a dummy load with a 50 ohm characteristic impedance is used to draw power through either the 50 ohm impedance transmission line shown in Figures 8A-8E or through a non-50 ohm impedance transmission line. In the non-50 ohm case, a reactive RF load consisting of a network of capacitors and inductors presents an impedance of R+jX that is known to the tester (Figures 8C and 8D).

[0083] The inventors have also seen phase shifts picked up by the top and bottom sensors due to changes in the coax cable length: As can be seen in Figure 8A, a 1 foot coax cable results in a different phase shift than a similar fixture with a shorter or no cable (Figure 8B).

[0084] In Figures 8A and 8B, it can be seen that test fixtures #1 and #2 have 50 ohm transmission lines that induce a voltage that is in phase with the current everywhere along the line. The reflected power back to the RF generator is zero for a matched 50 ohm transmission line. When full power is applied to the 50 ohm transmission line, the full power is delivered to the dummy load at 100%, i.e., zero reflections.

[0085] This can be confirmed with power meters located before and after the sensor. If the characteristic impedance of the transmission line is 50 ohms and the delivered power is 1000 W, the voltage signal (V) will correspond to 233.6 Vrms and the current signal (V) will correspond to 4.472 Arms, and the phase difference at this point is zero degrees. The described calibration procedure may be performed by one skilled in the art for a second or third RF frequency.

[0086] Following the described calibration procedure, the resulting compensation coefficients can be applied back to the RF voltage, RF current, and RF phase measurements for each of the operating frequencies. This calibration is done at maximum delivery current for each frequency such that all operating powers are low to ensure that any nonlinear effects that may be introduced by the sensor measurement system are factored into the power.

[0087] In Figures 8C and 8D, it can be seen that test fixtures #3 and #4, which contain reactive elements such as inductors and capacitors, are not 50 ohm transmission lines throughout the entire transmission line. However, careful selection of reactive elements can create a transmission line that appears to be 50 ohms to the RF generator. In this way, full power can be delivered to a 50 ohm dummy load. For example, in test fixture #4 (Figure 8D), the -j170 ohm capacitive load is offset by the j170 ohm inductive load, leaving the RF generator with an appearance of a 50 ohm load impedance. In doing so, one skilled in the art can calibrate the inductive load against a known reactive load.

[0088] In one example, an inductive load of approximately j170 ohms was shown to result in a 44% reflection, where the top sensor picked up 55.5W and the bottom sensor pair picked up 50.6W, both roughly matching the alternate power measurements coming from the power meter.

[0089] Some embodiments of the present disclosure relate to Digital Signal Processing (DSP) techniques corresponding to the methods described above and are further elaborated upon, including digital filtering techniques such as low pass, high pass, and band pass, FIR filtering, RF harmonic analysis including fast Fourier transform, phase determination based on zero crossing and cycle averaging, transmission line delay time based on voltage probe signal cross referencing, and coupled power calculation based on time domain waveforms. All of these techniques are implemented with hard time loops running on the FPGA hardware that controls the data streaming and manipulation.

[0090] Some embodiments of the present disclosure relate to DSP techniques and Data Acquisition (DAQ) hardware compatible with the DSP algorithms. Figure 8 shows a block diagram of a DAQ with an RF front end of at least 200 MHz, but preferably 1 GHz or higher, on 4 channels simultaneously, typically based on Texas Instruments Inc. Model ADC32RF4x, 14-bit, 3Gsps ADC converters compatible with an FPGA controller based on the Altera ArriaV model when integrated into a TI evaluation board model TSW14J56.

[0091] In some embodiments, alternative architectures can be used, including those marketed by Pico Technology Ltd. that integrate a high speed ADC with an FPGA controller, such as the Picoscope6000 series.

[0092] A typical DSP algorithm includes RMS value detection, taking the entire streamed waveform for multiple cycles, and calculating the root mean square value over the sampled cycles. In some embodiments, the waveform and the voltage and current RMS values ​​are plotted against time in millisecond resolution. An FFT is also performed on the waveform after applying a windows filtering function or Hanning window function, which shows the fundamental frequency of 27.12 MHz and its harmonics up to the 5th order.

[0093] Phase detection is based on a zero crossing algorithm where the timestamp of a particular waveform is detected when the voltage signal changes sign as it passes through zero and the same is done to a reference waveform resulting in two zero crossing timestamp arrays. By subtracting the two arrays resulting in the time difference between the two waveforms in nanoseconds, either ahead or behind, a delta timestamp array is obtained and the phase shift angle between the two waveforms is the average time difference over a full cycle divided by the cycle time and then multiplied by 360 / 6.18.

[0094] A figure of merit matrix can be developed to fully characterize the chamber behavior for one or multiple RF frequencies. In the case of multiple frequencies, the algorithm can be applied separately for each frequency after digitally bandpass filtering the mixed frequency waveform. These variations are within the scope of this invention disclosure.

[0095] For example, one further algorithm is Total Harmonics Distribution (THD), which is derived based on FFT magnitude that can characterize the total power distributed among the harmonics relative to the total power at the fundamental frequency, e.g., 10% power at THD, which means 90% of the power at the fundamental frequency under system control, and where variations over time can change the power delivered to the wafer.

[0096] Another example of an applicable algorithm is to calculate the coupled power based on the waveform. At any time, the power is the product of the voltage and current, i.e., P(t)=V(t)×I(t), where V(t) and I(t) are the waveforms acquired by the V, I sensors embedded in the chamber. The average power over time is therefore the average of P(t) over multiple RF cycles. This can be done by multiplying the voltage and current arrays together before taking the average over the product. If the load is resistive, the voltage and current are in phase and the coupled power is maximized by averaging, and if they are 90 degrees out of phase, the coupled power is minimized, i.e., near zero.

[0097] Some embodiments of the present disclosure relate to how multiple sets of sensors located upstream and downstream of the wafer are used to derive the power coupled to the wafer. Control schemes are also disclosed in which the power coupled to the wafer may be kept constant throughout the thin film deposition or may be varied to a particular step or steps throughout the deposition process based on the power coupled to the wafer. The same measurement and control methods apply whether the monitored or controlled is changed to, for example, voltage, or current and phase, depending on which particular thin film property figure of merit is of interest, including but not limited to, deposition rate, modulus, refractive index, wet etch rate, single layer thin film thickness uniformity, single layer thin film stress and uniformity, stacked thin film thickness uniformity, stacked thin film stress and uniformity, and lithography aspects such as step-to-step variations.

[0098] The methods and techniques described above may be applied to single RF frequency powering systems as well as multiple frequency powering systems.

[0099] In a method using multiple RF sensors in a high temperature PECVD chamber operating at multiple frequencies, the magnitude of the RF voltage, RF current, and phase difference between the RF voltage and RF current are provided to a host controller for further accomplishment and are used as feedback control targets either individually or collectively.

[0100] Based on the RF voltage, RF current, and RF phase measurements described above, an average voltage x current product number is constructed that corresponds to the coupled RF power at a particular frequency, and then stored and used as a real-time control target to obtain desirable, consistent wafer deposition results.

[0101] The sensor design and construction described thus far works well both in high power bench test fixtures for calibration purposes as well as in high temperature CVD chambers.

[0102] In a method of calibrating the implantable sensor using a high power 50 ohm resistive load or a non-50 ohm reactive load, the reactive load may consist of an inductive, capacitive, or inductive-capacitive network that may appear to the RF generator as either 50 ohms with no reflection or as a non-50 ohm with a non-zero power reflection to the RF generator. In the case of a non-zero reflection, the reflected power may be known based on existing network element values ​​or may be measured separately, either by using a separate power meter or by using an equivalent power measurement built into the RF generator. Such an RF network with known characteristics is constructed in a manner that is geometrically similar to the chamber in which the sensor will be used or is electrically equivalent to the chamber in terms of RF wave propagation at one or more operating frequencies.

[0103] The data acquisition system capable of streaming waveforms to a host computer RAM in real time or in hard time droop, consisting of a multi-channel ADC capable of sampling rates greater than 1 Gsps and a minimum of 14-bit ADC voltage resolution, further comprises an FPGA-based controller that transfers acquired raw waveform data to the host computer for further DSP processing or transfers processed data based on the raw waveform data to the host computer in real time or in hard time droop, and further comprises a RT (real time) chamber controller that can log either pre-processed or post-processed RF sensor data or take action when the post-processed RF sensor data is exposed to the chamber RT controller through the RF tuning system, such action including, but not limited to, feedback or feedforward adjustments or some combination thereof of any RF sensor's figure of merit based on optimization in the wafer results, such adjustments including holding fast certain aspects of the sensor feedback or partially altering it during the deposition process during the deposition recipe selection step.

[0104] In a further claim of use for chamber matching purposes, the embedded sensors individually or collectively act as indicators that provide for the isolation or identification of individual parts, assemblies, or collections thereof when a root cause of some thin film property fails to meet the use or excludes the same as the root cause in such cases.

[0105] Digital signal processing techniques and algorithms are developed based on the waveform, including, but not limited to, RMS detection, peak detection, FFT based harmonic detection and quantification, phase detection based on suitable techniques such as zero crossing algorithms, filtering based on probability techniques such as FIR, crossing correction analysis, combined power detection, etc.

[0106] Throughout this specification, the reference to "an embodiment," "a particular embodiment," "one or more embodiments," or "one embodiment" means that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the disclosure. Thus, the appearance of phrases such as "in one or more embodiments," "in a particular embodiment," "in an embodiment," or "in one embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0107] Although the present disclosure has been described in connection with specific embodiments, those skilled in the art will understand that the described embodiments merely reflect the principles and applications of the present disclosure. Those skilled in the art will understand that various modifications and changes may be made to the method and apparatus of the present disclosure without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure also includes modifications and changes that fall within the scope of the appended claims and their equivalents.

Claims

1. 1. A method for controlling a plasma processing chamber, comprising: measuring a first voltage, a first current, and a phase difference between the first voltage and the first current with a first RF voltage-current (V / I) sensor disposed in the plasma processing chamber; and controlling an RF generator coupled to the plasma processing chamber based on measurements provided by the first RF voltage-current sensor.

2. 10. The method of claim 1, further comprising measuring a second RF voltage, a second RF current, and a phase difference between the second RF voltage and the second RF current with a second RF voltage-current sensor disposed in the plasma processing chamber.

3. The method of claim 2 , wherein the first RF voltage and current sensor is positioned above a substrate during processing and the second RF voltage and current sensor is positioned below the substrate.

4. The method of claim 2 , wherein the plasma processing chamber operates at multiple frequencies.

5. The method of claim 1 , wherein the RF generator is controlled to maintain a predetermined plasma power.

6. 6. The method of claim 5, wherein controlling the RF generator to maintain the predetermined plasma power comprises determining a product of the first RF voltage and the first RF current to determine a combined plasma power at the first RF voltage-current sensor, and controlling the RF generator to maintain the predetermined plasma power.

7. The method of claim 5 , further comprising determining an average plasma power using the root mean square of the first RF voltage and the first RF current.

8. The method of claim 1 , wherein the first RF voltage-current sensor measurements are taken at intervals between 1 μs and 1 second.

9. The method of claim 7, wherein the interval is in the range of 1 μs to 1 ms.

10. a susceptor disposed within the processing space and configured to support one or more substrates during processing; an RF plasma generator configured to output a variable voltage, a variable current, and a variable phase of said voltage and said current; at least one RF voltage-current (V / I) sensor disposed in the process space and configured to measure a first voltage, a first current, and a phase difference between the first RF voltage and the first RF current; a controller coupled to the RF plasma generator and the at least one RF voltage and current sensor and configured to control the RF generator based on input from the at least one RF voltage and current sensor; A plasma processing chamber comprising:

11. The plasma processing chamber of claim 10, wherein at least two RF voltage-current sensors are disposed within the processing space.

12. 12. The plasma processing chamber of claim 11, wherein a first RF voltage and current sensor is disposed above the substrate support apparatus and a second RF voltage and current sensor is disposed below the substrate support apparatus.

13. 12. The plasma processing chamber of claim 11, further comprising a second RF plasma generator operating at a different frequency than the RF plasma generator.

14. The plasma processing chamber of claim 10 further comprising a substrate heater powered at 50 / 60 Hz.

15. 15. The plasma processing chamber of claim 14, wherein the at least one RF voltage-current (V / I) sensor is configured to measure voltage, current, and phase on both conductive leads between the substrate heater and an external power source.

16. 11. The plasma processing chamber of claim 10, wherein the at least one RF voltage-current sensor is configured to stream waveforms of each of the first RF voltage, the first RF current, and the phase difference to the controller.

17. The plasma processing chamber of claim 16, wherein the resolution of each waveform is in the range of 1 μs to 1 ms.

18. The plasma processing chamber of claim 16 , wherein each waveform is streamed in real time.

19. controlling the RF generator based on input from the at least one RF voltage-current sensor, multiplying the root mean square of the first RF voltage and the root mean square of the first RF current to determine a coupled power at the at least one RF voltage-current sensor; comparing the coupled power to a predetermined plasma power; and modifying the RF generator output if outside a predetermined range of a predetermined plasma power to modify the coupled power at the at least one RF voltage-current sensor.

20. 1. A non-transitory computer readable medium comprising instructions that, when executed by a controller of a plasma processing system, cause the plasma processing system to: activating an RF generator; measuring an RF voltage, an RF current, and a phase difference between the RF voltage and the RF current with an RF voltage-current sensor; determining a measurement of the coupled plasma power at the voltage-current sensor; and modifying an output of the RF generator.

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