Detection and mitigation of abnormal plasma events in semiconductor processing

Abstract

SOLUTION: In certain embodiments, anomalous plasma events, which may include the formation of electrical arcs in a semiconductor processing chamber, may be detected and mitigated. In certain embodiments, the method may include detecting an optical signal emitted by the plasma, converting the optical signal into a voltage signal, and forming a conditioned voltage signal. In response to determining that the change associated with the adjusted voltage signal exceeds the threshold, the output power of the RF signal coupled to the chamber may be adjusted. Such adjustments can mitigate the formation of abnormal plasma events occurring within the chamber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] [Incorporated by reference] A PCT application is being filed concurrently herewith as part of this application, and each application identified in that concurrently filed PCT application to which this application claims benefit or priority is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] Semiconductor processing frequently involves the use of plasma in fabrication chambers, and during such operations, anomalous plasma events may occur in response to the electrical conditions used to generate the plasma. An anomalous plasma event may include, for example, the formation of an electric arc or other type of visible event generated by an electrical discharge between two or more localized plasma regions within a process station. An anomalous plasma event may cause excessive heating and / or excessive current flow, which may damage semiconductor wafers being processed. In some cases, an anomalous plasma event may result in damage to a semiconductor process station. Summary of the Invention

[0003] One embodiment may include a method for detecting an anomalous plasma event in a semiconductor processing chamber. Such an embodiment may include detecting an optical signal emitted by a plasma in the semiconductor processing chamber, the plasma being formed in response to an RF signal from an RF generator. The method may also include converting the optical signal to a voltage signal and adjusting the voltage signal to form a regulated voltage signal. The method may further include determining whether a change associated with the regulated voltage signal exceeds a threshold and adjusting an output parameter of the RF signal from the RF generator based at least in part on the determination.

[0004] In certain embodiments, the method may include adjusting the voltage signal to form an adjusted voltage signal by filtering the voltage signal with a low-pass filter. Determining whether a change associated with the adjusted voltage exceeds a threshold may include comparing the change in the voltage signal to the adjusted voltage signal. Adjusting the voltage signal to form the adjusted voltage signal may include applying an offset to the adjusted voltage signal. Adjusting the voltage signal to form the adjusted voltage signal may include taking a first derivative of the voltage signal. Adjusting the output parameter of the RF generator may include reducing the output power of the RF generator from a first power level to a second power level. The method may further include, after reducing the output power of the RF generator from the first power level to the second power level, maintaining the output power of the RF generator at the second power level for a first period of time. The method may also include, after maintaining, increasing the output power of the RF generator from the second power level to the first power level for a second period of time. The second power level may be a non-zero power level. Alternatively, the second power level may be zero. The method may further include determining a first amount of RF power reduction based at least in part on light intensity or process parameters in the semiconductor processing chamber, and reducing the output power level of the RF generator by the first amount, wherein the process parameters may include one or more process parameters selected from the group consisting of a DC power level, an RF bias power level, a station-to-station RF power variation, a frequency adjustment parameter, a pressure, and a temperature.

[0005] In one or more embodiments, the semiconductor processing tool can include a semiconductor processing chamber. The semiconductor processing tool can include an RF generator configured to provide RF power to the semiconductor processing chamber to generate and maintain a plasma. The semiconductor processing tool can also include a photodetector configured to detect an optical signal indicative of an optical emission of the plasma in the semiconductor processing chamber. The optical detector can be configured to convert the optical signal into a voltage signal utilizing a slope change detection unit. The semiconductor processing tool can also include receiving the voltage signal and adjusting the voltage signal to form an adjusted voltage signal. The semiconductor processing tool can be configured to determine whether a change associated with the adjusted voltage signal exceeds a threshold. In one embodiment, in response to the determination, the semiconductor processing tool can send a signal to the RF generator configured to cause an adjustment to the RF generator.

[0006] In some embodiments, the semiconductor processing tool may further include a lens on the semiconductor processing chamber configured to allow light within the semiconductor processing chamber to pass through the lens. The semiconductor processing tool may also include a fiber optic cable between the lens and the photodetector configured to transmit at least a portion of the light that passes through the lens to the photodetector. The tilt change detection unit of the semiconductor processing tool may further include a filter that filters the voltage signal and converts the voltage signal to a regulated voltage signal. The semiconductor processing tool may also include a comparator that compares a change between the regulated voltage signal and the voltage signal. The comparator of the semiconductor processing tool may include a transistor-transistor logic (TTL) configured to send a TTL signal to the RF generator. The RF generator may be configured to reduce RF power from a first power level to a second power level in response to receiving the signal from the tilt change detection unit. The tilt change detection unit may include a differentiator configured to take the derivative of the voltage signal and convert the voltage signal to a regulated voltage signal. The semiconductor processing tool may also include a comparator configured to determine whether a change in the regulated voltage signal exceeds a threshold. The semiconductor processing tool may further include a fiber optic cable between the semiconductor processing chamber and the photodetector, configured to transmit light generated by the plasma in the semiconductor processing chamber to the photodetector. The photodetector may be electrically connected to the RF generator, and the optical signal from the semiconductor processing chamber is supplied from the semiconductor processing chamber to the RF generator. The photodetector and tilt change detection unit may be positioned outside the semiconductor processing chamber. Alternatively, the photodetector and tilt change detection unit may be positioned between the semiconductor processing chamber and the RF generator. The photodetector and tilt change detection unit may be positioned on the semiconductor processing chamber.

[0007] In certain embodiments, a method for detecting an anomalous plasma event can include forming a plasma using a signal from an RF generator and detecting a fluctuating optical signal produced by the plasma. The detecting method can include calculating a spectral density of the fluctuating optical signal and determining that the spectral density of the fluctuating optical signal differs from one or more reference spectral densities of the fluctuating optical signal produced by the plasma by a threshold amount.

[0008] In certain embodiments, calculating the spectral density of the varying optical signal may utilize a Fast Fourier Transform (FFT). The method may include one or more reference spectral densities of the varying optical signal corresponding to the spectral density of the varying optical signal generated by a plasma maintained under nominal conditions. The threshold amount may correspond to one standard deviation relative to the spectral density of the varying optical signal from a plasma maintained under nominal conditions. The threshold amount may correspond to two standard deviations relative to the spectral density of the varying optical signal from a plasma maintained under nominal conditions. The spectral density of the varying optical signal may include determining the spectral density of an optical signal varying at a frequency of about 400 kHz. Calculating the spectral density of the varying optical signal may include determining the spectral density of an optical signal varying at a frequency between about 400 kHz and about 4 MHz. Calculating the spectral density of the varying optical signal may include determining the spectral density of an optical signal varying at multiple frequencies generated by one or more RF generators.

[0009] In certain embodiments, the apparatus may include a signal processor configured to analyze an output signal from a photodetector that receives the optical signal from the multi-station processing tool. The signal processor may be further adapted to detect a fluctuating optical signal generated by a plasma formed in the semiconductor fabrication chamber, calculate a spectral density of the fluctuating optical signal, and determine that the spectral density of the fluctuating optical signal differs from one or more reference spectral densities of the fluctuating optical signal generated by the plasma by a threshold amount.

[0010] In certain embodiments, the one or more reference spectral densities of the fluctuating optical signal may correspond to a spectral density calculated while the plasma is maintained under nominal conditions. The threshold amount may correspond to one standard deviation relative to the spectral density of the fluctuating optical signal from a plasma maintained under nominal conditions. Alternatively, the threshold amount may correspond to two standard deviations relative to the spectral density of the fluctuating optical signal from a plasma maintained under nominal conditions. The spectral density of the fluctuating optical signal may be calculated while an RF signal having a frequency of approximately 400 kHz is coupled into the multi-station processing tool. The spectral density of the fluctuating optical signal may be calculated to determine the spectral density of the fluctuating optical signal at frequencies between 400 kHz and 4 MHz. The spectral density of the fluctuating optical signal may be calculated at the frequency of the RF signal coupled into the multi-station processing tool. [Brief explanation of the drawings]

[0011] Various embodiments disclosed herein are illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which:

[0012] [Figure 1] FIG. 1 is a diagram illustrating a first example of an anomalous plasma event detection device.

[0013] [Figure 2] FIG. 2 is a diagram illustrating a first exemplary slope change detection unit capable of detecting an anomalous plasma event.

[0014] [Figure 3A] FIG. 3A is a diagram illustrating a waveform representing an exemplary detection response of a slope change detection unit. [Figure 3B] FIG. 3B is a diagram illustrating a waveform representing an exemplary detection response of the slope change detection unit.

[0015] [Figure 4]FIG. 4 is a schematic diagram of an exemplary electrical circuit capable of detecting an anomalous plasma event.

[0016] [Figure 5] FIG. 5 is a diagram illustrating a waveform representing RF power coupled into a process station of a fabrication chamber as a function of time.

[0017] [Figure 6A] FIG. 6A shows another waveform illustrating the RF power output along with the signal output of the slope change detection unit.

[0018] [Figure 6B] FIG. 6B is a diagram illustrating a group of profiles representing the spectral density of light energy fluctuations under nominal operating conditions within a process station.

[0019] [Figure 6C] FIG. 6C is a diagram illustrating a group of profiles representing the spectral density of light energy fluctuations under nominal operating conditions within a process station, as well as a profile representing the spectral density of light energy fluctuations while an anomalous plasma event occurs within the process station.

[0020] [Figure 6D] FIG. 6D is a diagram illustrating an alternative configuration of the first exemplary anomalous plasma event detection apparatus of FIG. [Figure 6E] FIG. 6E is a diagram illustrating an alternative configuration of the first exemplary anomalous plasma event detection apparatus of FIG.

[0021] [Figure 7A] FIG. 7A is a flowchart of a first exemplary technique for detecting and mitigating the effects of an anomalous plasma event.

[0022] [Figure 7B] FIG. 7B is a flowchart of a second exemplary technique for detecting and mitigating the effects of an anomalous plasma event.

[0023] [Figure 8] FIG. 8 is a block diagram of an exemplary device that can be used to implement the disclosed embodiments.

[0024] [Figure 9] FIG. 9 is a schematic diagram of one embodiment of a multi-station processing tool.

[0025] [Figure 10] FIG. 10 is a diagram showing a substrate processing apparatus for depositing a film on a semiconductor substrate.

[0026] [Figure 11] FIG. 11 is a diagram illustrating one embodiment of a multi-station processing tool.

[0027] [Figure 12] FIG. 12 is a diagram illustrating the Paschen curve for helium gas. DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, numerous specific details are set forth in order 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 in order to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments are described in conjunction with specific embodiments, it will be understood that they are not intended to limit the disclosed embodiments.

[0029] In this application, the terms "semiconductor wafer," "wafer," "substrate," "wafer substrate," and "partially fabricated integrated circuit" are used interchangeably. Those skilled in the art will understand that the term "partially fabricated integrated circuit" can refer to a silicon wafer at any of the many stages of fabricating an integrated circuit. Wafers or substrates used in the semiconductor device industry may have diameters of 200 mm, 300 mm, or 450 mm. The following detailed description assumes that the invention is practiced on a wafer. However, the invention is not so limited. Workpieces can be of various shapes, sizes, and materials. In addition to semiconductor wafers, other workpieces that can utilize the invention include various products such as printed circuit boards, glass panels, etc.

[0030] Many semiconductor processes use plasma for one or more aspects of processing. Plasma is typically generated in a processing chamber between two electrodes, one connected to a radio frequency (RF) power source and the other connected to RF ground. The RF power supplied to the electrodes can range from about 200 watts to about 3000 watts. The frequency used to drive plasma formation can include a high frequency (HF) component, a low frequency (LF), or both HF and LF components. HF frequencies can be about 13.56 MHz or about 27 MHz, and LF frequencies can be about 300-400 kHz. "High" frequency generally refers to signal frequencies several orders of magnitude higher than "low" frequency, e.g., megahertz compared to kilohertz, although other frequencies of high or low frequency RF power can also be used.

[0031] One type of abnormal plasma event that can occur during plasma formation is a high-voltage breakdown, "light-up," or arcing within a processing chamber, such as the area around a showerhead or a substrate support structure like an electrostatic chuck (ESC). When two structures that can serve as electrodes are separated by a gap, arcing or high-voltage breakdown can occur under certain circumstances. These circumstances typically depend on the voltage difference between the electrodes, the composition of the gas between the electrodes, the pressure of the gas between the electrodes, and the size of the separation between the electrodes. The interaction between these factors can be characterized by Paschen's Law, which provides the high-voltage breakdown voltage as a function of pressure, gap distance, and two gas-dependent parameters. The voltage required to initiate an abnormal plasma event, such as a light-up or arc, is sometimes referred to as the "breakdown voltage" and is a function of the gas filling the volume between the two electrodes, the pressure of that gas, and the distance between the potential endpoints of the electric arc. This relationship is expressed as:

number

[0032] FIG. 12 (embodiment 1200) illustrates the Paschen curve for helium gas. The logarithmic vertical axis represents breakdown voltage in volts (e.g., the voltage required to cause an arc or other type of anomalous plasma event), and the horizontal axis (also logarithmically scaled) represents pressure multiplied by distance in Torr-cm. As shown in FIG. 12, the lowest or minimum breakdown voltage of approximately 150 V is at the lowest point of the Paschen curve and occurs at approximately 4 Torr-cm. This characteristic creates two regions where semiconductor processing may occur before the lowest breakdown voltage is reached: one to the "left" of the curve's lowest point and one to the "right" of the curve's lowest point. The vertical dashed line in FIG. 12 approximates the dividing line between these two sides.

[0033] Some semiconductor processes utilize higher RF power to reduce deposition times and increase substrate throughput. However, using higher RF power can increase the risk of voltage breakdown, arcing, or other types of abnormal plasma events within the processing chamber. Such events can damage the substrate, electrodes (such as the showerhead or substrate support structure), and the chamber itself. Unacceptable damage to the substrate can result in scrapping the substrate and / or damage to the electrodes. In addition, a damaged chamber may require time-consuming, expensive, and / or extensive repairs of the electrodes (e.g., showerhead or pedestal replacement), which can result in additional costs and downtime for the semiconductor processing chamber.

[0034] Therefore, it is desirable to detect arcs or other types of abnormal plasma events in a processing chamber and then mitigate such events. Many conventional abnormal plasma event detection techniques can result in missed or false arc detections. For example, one conventional method may include a voltage detection method that measures the RF voltage delivered to a powered electrode to generate a plasma and determines whether that voltage reaches a threshold voltage or approaches within a certain amount of the threshold voltage. If so, such a system assumes that an arc discharge may occur in the processing chamber. In response to the detection of the threshold voltage, the RF power is reduced or completely shut off, thereby reducing the voltage in the processing chamber and preventing the occurrence of an abnormal plasma event. This threshold voltage is typically a predetermined value obtained using experimental measurements. However, this detection method has drawbacks, such as being limited to a single predetermined voltage threshold. Additionally, this detection method can be computationally intensive and difficult to implement because it may require very fast voltage monitoring speeds that may not accurately reflect the real-time occurrence of an abnormal plasma event. The inability to accurately reflect the real-time occurrence of an abnormal plasma event may be due to potential time displacement between the occurrence of an arc event and the measured voltage. Additionally, the detection method can be insensitive to small arcing events, is subject to system noise, and can require significant time and experimentation to determine and optimize the appropriate threshold voltage.

[0035] Threshold voltage detection methods may have other detection limitations. For example, such methods generally detect whether a measured voltage increases beyond a certain threshold. However, because the RF drive signal contains a time-varying voltage driven at various frequencies (e.g., a periodic waveform such as a sinusoidal signal operating at 13.56 MHz), the intensity of light emitted by the plasma may oscillate at a similar frequency component of the detector output signal due to the normal intensity of light emitted by the plasma in response to the RF signal being at its nominal peak. If the threshold voltage is set appropriately, an anomalous plasma event causing additional light emission may be detectable. However, if the anomalous plasma event occurs between successive peaks of the voltage cycle, the anomalous plasma event may not be detected, especially if the component of the detector output signal attributable to the anomalous plasma event has a smaller magnitude than the amplitude of the component of the detector output signal attributable to the RF signal. For example, assuming the measured voltage of the detector output signal has a peak amplitude of 0.2 V (average 2 V), application of the RF drive signal may cause the voltage to increase to 2.2 V at the peak and then decrease to 1.8 V at the bottom (so that the peak-to-peak is 0.4 V). If an arc occurs during a cycle in which the voltage peaks at 2.2 V and the detector output signal increases by 0.3 V, the measured voltage will be 2.5 V, above the 2.4 V threshold (which may indicate an arc, as determined experimentally). However, if an arc occurs during a cycle in which the voltage troughs at 1.8 V, the measured voltage will be 2.1 V (1.8 V + 0.3 V), below the 2.4 V threshold. The threshold for such a system cannot be set lower than the magnitude of the peak output signal generated by application of a normal RF drive signal. Therefore, this detection method may not be useful for detecting small-voltage abnormal plasma events that occur during certain portions of an AC (e.g., sinusoidal) voltage cycle.

[0036] Another similar technique can optically monitor for anomalous plasma events. Here, similar to the method described above, voltage is measured. However, the voltage can be derived from the output of a photodetector configured to measure light intensity within the chamber and generate a voltage signal indicative of that light intensity. For example, a plasma formed within the chamber may emit varying amounts of light depending on the plasma's behavior. Thus, the photodetector can generate a voltage output signal representative of the intensity of the light emitted by the plasma. However, arcing events can generate additional light, resulting in a corresponding increase in the voltage generated by the photodetector. This voltage can then be monitored in a manner similar to that described above for direct voltage monitoring. However, this technique suffers from many of the same drawbacks as direct voltage monitoring, in that it is insensitive to low-intensity discharge events, which may not be detected, especially if they occur during local minima in the photodetector signal.

[0037] Another limitation of these detection methods is that they may not be able to detect anomalous plasma events smaller than the difference between the peak voltage and the threshold voltage. For example, the threshold voltage may be offset above the peak voltage by a certain amount so that each peak voltage and / or small, insignificant voltage deviations do not approach the threshold voltage and therefore trigger an alarm or other corrective action. However, harmful anomalous plasma events may occur at voltages lower than the offset between the peak voltage and the threshold voltage. Therefore, anomalous plasma events smaller than the difference between the peak voltage and the threshold voltage may not be detected. For example, if an anomalous plasma event of 0.15 V occurs at a peak voltage of 2.0 V, the measured voltage will be below the 2.2 V threshold and will therefore remain undetected and unmitigated.

[0038] These conventional detection methods are also undesirably sensitive to parameter settings of the process occurring within the processing chamber. For example, each time a process parameter is changed (e.g., RF power, RF frequency, gas species, chamber pressure, etc.), multiple new threshold voltages may be required, for example, in response to the effect of the modified process parameter on the voltage threshold at which arcing occurs. Therefore, modifying parameter settings may require additional experimentation and optimization time, which may also result in undesirable downtime for the semiconductor processing tool.

[0039] Thus, the present disclosure includes novel techniques and apparatus for detecting anomalous plasma events in semiconductor processing. Generally, plasmas can emit light that can be detected by photodetectors, such as optical detectors. The light emitted by plasmas can oscillate or fluctuate at various frequencies based on plasma parameters, such as chemical species, RF power parameters (such as voltage), and RF frequency components (e.g., high-frequency components, low-frequency components, or both). Some exemplary plasma illumination oscillation frequencies can be on the order of one cycle per tens of milliseconds, such as approximately one cycle per 20 milliseconds. In contrast, the occurrence of anomalous plasma events generally occurs relatively quickly and at high frequencies compared to other light emitted by plasmas, e.g., on the order of one cycle per nanosecond.

[0040] The techniques described below exploit the differences between light energy fluctuations that occur during anomalous plasma event frequencies compared to light energy fluctuations that occur during nominal plasma operation. Such differences can be utilized to identify anomalous plasma events. In some embodiments, anomalous plasma events, due to their much higher frequency, can cause abrupt (e.g., high-frequency) changes in the slope of the photodetector output signal, allowing a determination to be made regarding the change in slope of the photodetector signal at a given instant. In other embodiments, the photodetector signal can be normalized by removing the low-frequency portion of the signal, leaving only the high-frequency portion, which may indicate an anomalous plasma event. In still other embodiments, the photodetector signal can be subjected to, for example, Fourier analysis (e.g., fast Fourier transform) or other types of frequency spectrum analysis to determine the magnitude of the intensity of various frequency components. In certain embodiments, if the analyzed photodetector signal exhibits high-frequency components greater than a certain magnitude, these frequency components may indicate an anomalous plasma event. These anomalous plasma event detection techniques may differ from conventional techniques, such as those described above, because, in certain embodiments, the anomalous plasma event detection techniques consider the rate of change of the optical signal. This is in contrast to conventional approaches that simply rely on the magnitude of the detected signal.

[0041] FIG. 1 illustrates a first exemplary anomalous plasma event detection apparatus according to an embodiment 100. As shown, the embodiment 100 includes a semiconductor processing chamber 102, a lens 104 (which may be omitted in certain embodiments), a fiber optic cable 106 coupled to the lens 104 and a signal processor 108, and an RF generator 110. The semiconductor processing chamber 102, described in more detail below, can be used for plasma-based semiconductor processes such as plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and atomic layer etching (ALE). The RF generator 110, also described in more detail below, can include an LF generator, an HF generator, or both. The lens 104 is positioned within the semiconductor processing chamber 102 and allows light generated within a chamber included in any processing station within the semiconductor processing chamber 102 to pass through the lens 104, through the fiber optic cable 106, and to the signal processor 108.

[0042] The signal processor 108 may include a photodetector, such as a photodetector 112 (which may include a photodiode), capable of receiving optical signals from the semiconductor processing chamber 102 and converting the received optical signals into voltage signals. The photodetector 112 may include any other type of photodetector electronics capable of detecting any number of photons carrying energy at various wavelengths in the infrared, visible, and / or ultraviolet, and may include, for example, a spectrometer. The signal processor 108 may also include a tilt change detection unit 114, which is configured to receive a voltage signal from the photodetector 112, as represented by the dashed line between the photodetector and the tilt change detection unit 114. The signal processor 108 may be further configured to determine a change in the voltage signal from the photodetector 112 and determine whether the change in the voltage signal is indicative of an anomalous plasma event occurring within the semiconductor processing chamber 102.

[0043] In some implementations, the slope change detection unit 114 may compare the raw photodetector signal with a filtered version of the same signal to determine high-frequency changes between the raw and filtered signals. Comparing the raw and filtered signals may enable determining that an anomalous plasma event has occurred. In some such implementations, a signal containing high-frequency components caused by an anomalous plasma event is compared to a signal that does not have high-frequency components (particularly due to the use of a low-pass filter applied to the raw voltage signal). Such a comparison may enable determining the relative changes between the filtered and unfiltered versions of the signal.

[0044] 2 illustrates a first exemplary slope change detection unit according to embodiment 200. Here, photodetector 112 is shown with first exemplary slope change detection unit 214 enclosed by a dashed rectangle. A raw voltage signal 215 from photodetector 112 is split and sent to a filter, which in some embodiments may include a buffer amplifier 216, a low-pass filter 218, and a feedback amplifier 220 with a threshold / enable signal 222. This filtered signal, along with the raw voltage signal 215, is then sent to a high-speed comparator 224. The buffer amplifier 216 can operate to isolate the raw analog data from the low-pass filter 218, which filters out high-frequency signals, and the threshold / enable signal 222 provides an offset for the filtered signal.

[0045] In the embodiment of FIG. 2, the high-speed comparator 224 operates to compare the raw photodetector voltage signal and the filtered photodetector voltage signal to determine whether there has been a change between the signals. For example, a determination can be made as to whether the difference between the two signals at a given moment exceeds a threshold amount. In response to the difference between the filtered and unfiltered signals being greater than the threshold amount, this can indicate a change in slope in the raw signal, thus indicating an anomalous plasma event. In certain embodiments, the filtered signal can be offset from the unfiltered signal by a predetermined offset amount, as described above, which can operate to avoid scenarios in which the two signals may cross each other (except due to an anomalous plasma event). The high-speed comparator 224 can also include transistor-transistor logic (TTL) that can change the output signal 226 from a first voltage to a second voltage in response to a detected change between the filtered and unfiltered signals that is greater than a first threshold.

[0046] 3A and 3B illustrate waveforms representing an exemplary detection response of a slope change detection unit, according to one embodiment. In FIG. 3A (embodiment 300A), the simulated raw photodetector voltage signal (305) is represented by a dashed line, the filtered and offset voltage signal (310) is represented by a dotted line, and the output TTL signal 315 is represented by a solid line. The vertical axis is scaled in volts, and the horizontal axis is scaled in time (in seconds). As shown, the detected light emission of the plasma oscillates as a sine wave with an amplitude of approximately 0.2 V. In the example of FIG. 3B, a detailed view of a portion of FIG. 3A is illustrated. Here, an abnormal plasma event has occurred, and the filtered signal remains constant because the high-frequency arc signal has been filtered out. However, the abnormal plasma event, which in this case may correspond to an arc, has caused a change in the photodetector voltage signal. In this case, the change in the photodetector output voltage signal corresponds to an increase in the slope of the photodetector output voltage signal. In response to a comparison between the simulated raw photodetector signal 305 and the filtered output signal 310, which are offset from one another by a first threshold (e.g., approximately 0 volts in FIG. 3B ), the high-speed comparator causes the output TTL signal 315 to change from approximately 0.2 V to approximately 3.8 V. As further shown in FIG. 3B (embodiment 300B), in response to an abnormal plasma event (e.g., an arc) occurring, the simulated raw photodetector voltage signal 305 again changes (e.g., decreases in slope). In response to the simulated raw photodetector signal 305 decreasing in slope, the high-speed comparator causes the output TTL signal 315 to change from approximately 3.8 V back to approximately 0.2 V, such that the simulated raw photodetector signal 305 and the low-pass signal 310 are no longer offset from one another by a value greater than the first threshold.

[0047] FIG. 4 illustrates an exemplary electrical circuit capable of detecting an anomalous plasma event according to embodiment 400. This circuit in embodiment 400 may represent aspects of the signal processor 108 in FIG. 1 and the first exemplary slope change detection unit 214 in FIG. 2. In the embodiment of FIG. 4, the "simulated photodetector input" may represent the photovoltage signal generated by the photodetector 112 in FIG. 2. Additionally, the "threshold from Ethernet input / output controller (EIOC)" (V3) in FIG. 4 may represent the threshold / monitor enable signal 222 that may be sent from the EIOC as part of a control program executed by the system controller 950 in FIG. 9. Furthermore, the "buffer" in FIG. 4 may represent the buffer amplifier 216 in FIG. 2. The feedback amplifier 220 (shown as "feedback amplifier" in FIG. 4) adds (or sums) the threshold from the EIOC (V3) signal to the output signal from the buffer in FIG. 4. The output signal from the buffer in FIG. 4 is filtered by the combination of R1 / C1 / C2, thereby forming a low-pass filter corresponding to the low-pass filter 218 in FIG. 2. The output signal from the buffer of Figure 4 is compared to a combination of the simulated photodetector input (V2) signal and the sine wave input (V4) signal via a comparator of Figure 4 (corresponding to comparator 224 of Figure 2). In response to comparing the combined ensemble of the simulated photodetector input and the sine wave input to the output signal from the feedback amplifier, the comparator of Figure 4 detects an anomalous plasma event. In certain embodiments, the detection of an anomalous plasma event occurs when the combined ensemble of the simulated photodetector input and the sine wave is greater in magnitude than the output signal from the feedback amplifier by a threshold amount.

[0048] While the functionality of the slope change detection unit of FIG. 2 can be implemented using the analog electronic circuitry of FIG. 4, in some other embodiments, the functionality of FIG. 2 may be implemented digitally, such as via a field-programmable gate array (FPGA). In some other embodiments, the slope change detection unit may use a differentiator that can operate to take the derivative of a raw optical data signal, such as the optical data signal from the photodetector 112, to determine whether a change has occurred in the slope of the output signal from the photodetector. The output signal from the differentiator may be proportional to the rate of change of the input signal voltage (e.g., the derivative with respect to time). The derivative of the raw optical data signal, such as from the photodetector, may be transmitted to an input port of a comparator, such as the high-speed comparator 224. The high-speed comparator may perform a comparison between the raw optical data signal and a threshold value to determine whether the difference in slope of the raw optical data signal exceeds the threshold value. In some cases, the threshold sensitivity may be adjusted in response to process changes during deposition to avoid false alarms. If the change exceeds the change threshold value, the comparator 224 may again output a TTL signal at a second voltage having an increased magnitude relative to the first voltage.

[0049] In some implementations, the slope change detection unit can convert the raw photovoltage signal into the frequency domain using a fast Fourier transform (FFT). The signal represented in the frequency domain can be used to determine whether a particular frequency component, such as one associated with an arcing (or other anomalous plasma event), is present at an intensity greater than a particular threshold amount. In some implementations, an output signal can be generated if an unexpected frequency is detected (or detected at a level above a threshold) in response to the occurrence of an anomalous plasma event.

[0050] In response to detecting an anomalous plasma event, such as by generating a TTL signal, various responses and actions can be taken, such as adjusting the RF power coupled to the fabrication chamber. In some cases, the adjustment may include reducing (or completely stopping) the RF power (e.g., LF, HF, or both). In some such cases, the RF power magnitude may be reduced to zero, and then the RF power may be increased to its previous level after a period of time sufficient to allow arcing (or other anomalous plasma events in the fabrication chamber) to cease. Such an increase in RF power may correspond to a linear or nonlinear increase. In some other cases, the adjustment of RF power may include reducing the RF power (e.g., LF, HF, or both) to a non-zero level for a period of time, and then increasing the power to a level corresponding to the original level.

[0051] FIG. 5 shows a waveform 500 representing RF power coupled to a process station of a chamber as a function of time. As shown in FIG. 5, the RF power (e.g., the power supplied by the RF generator 110 of FIG. 1) at time t1 corresponds to power level P1. At time t1, in response to the detection of an anomalous plasma event, the RF power is reduced to power level P2 and maintained for a period from time t1 to time t2. The RF power gradually increases (e.g., ramps) between times t2 and t3 until the RF output power reaches level P1 at time t2. In some embodiments, the RF power reduction can be a percentage reduction, such as a 10% or 30% reduction. However, it will be understood that the disclosed embodiments are not limited to such examples and are intended to encompass any percentage RF power reduction, such as 5%, 10%, 20%, 30%, etc.

[0052] In some implementations, a determination can be made regarding the magnitude of a detected anomalous plasma event by, for example, determining the intensity of the anomalous plasma event by subtracting low-pass filtered data points of the photodetector signal from corresponding unfiltered data points. Subtracting the low-pass filtered data points from the corresponding unfiltered data points can result in an estimate of the arc light intensity, for example. Such a determination (or other determination that can provide some indication of the intensity of the anomalous plasma event) can, in such implementations, be used to determine the extent of RF system adjustment in response to the anomalous plasma event. For example, if the magnitude of the detected anomalous plasma event decreases, the system may switch the RF generator to a lower power mode at a first level. However, if the magnitude of the detected RF event reaches a certain threshold magnitude, the system may switch the RF generator to another lower power mode at a second level lower than the first level. In such systems, multiple power levels may be supported, and the supported power levels may correspond to different threshold magnitudes of the anomalous plasma event intensity. In these cases, the system may select a power level associated with a range of arc intensity magnitudes within which the detected arc event falls.

[0053] 6A shows another waveform representing RF power along with the output signal of the slope change detection unit according to embodiment 600A. As shown, the RF power output of the RF generator oscillates, while the output signal of the slope change detection unit corresponds to a relatively flat, constant line. When an abnormal plasma event is detected, the amplitude of the output signal of the slope change detection unit increases, causing the RF power unit to shut off the RF power output signal. In some cases, the response time between the signal increase of the slope change detection unit and the adjustment of the RF power output may correspond to approximately 2 microseconds.

[0054] In some embodiments where an abnormal plasma event (e.g., the formation of an electric arc) occurs above or below the edge of the semiconductor wafer, the arc intensity and process parameters can define the amount by which RF power should be reduced. For example, in some embodiments, high RF power results in a more dispersive RF plasma. Therefore, reducing the RF power coupled to the process station can operate to confine the plasma to the region between the electrodes. For example, reducing RF power in response to the occurrence of an electric arc at the edge of the semiconductor wafer can reduce the plasma density at the wafer edge, thus concentrating the generated plasma in the region between the electrodes more toward the center of the wafer. Reducing RF power can also operate to reduce the voltage of the electrodes, which helps reduce the occurrence of abnormal plasma events (e.g., arcing), even if they occur toward the center of the wafer (away from the edge). The intensity of the abnormal plasma event and process parameters can also be used to define the amount by which RF power should be reduced. For example, the greater the arc intensity, the greater the reduction in RF power. Additionally, for very low-pressure processes, the plasma can be more dispersive compared to high-pressure processes (for the same power, gas, and other parameters). Therefore, in such cases, the power may need to be reduced further to provide greater confinement of the plasma.

[0055] Anomalous plasma event detection equipment, such as the devices described above, may be arranged in alternative configurations. More specifically, signal processor 108 may be located in different locations and may include different configurations. As noted above, in FIG. 1 , the signal processor may be positioned at different locations within the processing chamber, such as in a different part of the tool. In some implementations, an optical signal may be transmitted from a location within processing chamber 102 to a photodetector in the signal processor via fiber optic cable 106 or the like.

[0056] FIG. 6B illustrates a group of profiles 600B representing the spectral density of light energy fluctuations under nominal operating conditions in a process station, according to one embodiment. The vertical axis of FIG. 6B indicates a measurement of the spectral density (e.g., a percentage of the full spectrum), and the horizontal axis of the logarithmic scale of FIG. 6B indicates frequency. Thus, the profiles in the group of profiles 600B represent the spectral density of light energy fluctuations over a predetermined period of time in response to RF power coupled at frequencies of approximately 400 kHz (i.e., ±10%) and approximately 13.56 MHz (i.e., ±10%). In the particular example of FIG. 6B , the spectral density of light energy fluctuations is shown over four sampling periods, with each profile representing the spectral density of light energy fluctuations over one of the four sampling periods. Thus, in response to the coupling of RF power (e.g., including frequencies of 400 kHz and 13.56 MHz) into the fabrication chamber, the optical signal from the plasma may fluctuate or oscillate not only at a first peak corresponding to a fundamental frequency of 400 kHz (±10%), but also at harmonics of 400 kHz, e.g., about 800 kHz (±10%), and 1600 kHz (±10%). In addition, it can be seen that the spectral density of the fluctuating optical signal from the plasma varies only slightly at frequencies between about 100 kHz and about 50 MHz. For example, at a frequency of about 100 kHz, the spectral density of the optical signal generated by the plasma may range from about 0.8% to about 1.2% of the full spectrum of the fluctuating optical signal from the plasma.

[0057] 6C illustrates a group of profiles representing the spectral density of light energy fluctuations under nominal operating conditions within a process station, as well as a profile representing the spectral density of light energy fluctuations while an anomalous plasma event occurs within the process station, according to embodiment 600C. Similar to FIG. 6B, the vertical axis of FIG. 6C represents a measurement of spectral density (e.g., a percentage of total light energy), and the horizontal axis of the logarithmic scale of FIG. 6C represents frequency. The profiles in the group of profiles 610 represent the spectral density of the optical energy of the plasma fluctuating over a predetermined period in response to the coupling of RF power (e.g., 400 kHz and 13.56 MHz) to the fabrication chamber. In the particular example of FIG. 6C , the spectral density of the optical energy fluctuations is shown over three sampling periods, each corresponding to one of the profiles 610. In response to the coupling of RF power (e.g., 400 kHz and 13.5 MHz) to the fabrication chamber, the optical signal generated by the plasma may fluctuate or oscillate at a first peak frequency corresponding to a fundamental frequency of 400 kHz. The optical signal generated by the plasma may further fluctuate or oscillate at harmonics such as approximately 800 kHz and (1600 kHz) 1.6 MHz. Additionally, it can be seen that the spectral density of each of the profiles 610 varies only slightly between frequencies of approximately 100 kHz and approximately 50 MHz.

[0058] However, in addition to profile 610, FIG. 6C further illustrates profile 620, which represents the spectral density of light energy fluctuations in response to an anomalous plasma event (e.g., an arc) occurring within the fabrication chamber. Thus, as shown in FIG. 6C, during an anomalous plasma event, the spectral density of light energy fluctuations increases significantly between about 600 kHz and about 3.6 MHz. In other embodiments, during an anomalous plasma event, the spectral density of light energy fluctuations may increase significantly in a different frequency range, such as from about 400 kHz (±10%) to about 4 MHz (±10%). For example, at about 1 MHz (1000 kHz), the spectral density of profile 620 that may be observed during an anomalous plasma event in the chamber corresponds to a value of about 2%. This can be compared to the spectral density observed under nominal conditions, as shown by profile 610, which corresponds to a value of about 1%. Thus, as shown in FIG. 6C, an anomalous plasma event (e.g., as evidenced by profile 620) may be indicated by observing a significant increase in the spectral density of plasma fluctuations between specific frequency ranges.

[0059] In the particular example of FIG. 6C , an anomalous plasma event is indicated by observing or detecting an increase in spectral density of about 100% at a particular frequency or across a particular frequency range relative to the nominal plasma conditions of the fabrication chamber (e.g., from about 1% spectral density to about 2% spectral density). Additionally, such an increase in spectral density may be observed at frequencies between about 400 kHz (±10%) and 4 MHz (±10%), although it will be understood that the disclosed embodiments are not limited to such examples and may encompass spectral densities and / or spectral density profiles observed at other frequency ranges, such as frequencies below about 400 kHz and frequencies above about 4 MHz. Additionally, in other embodiments, an anomalous plasma event may be indicated by a slight increase in the spectral density of fluctuations or vibration signals from the plasma compared to nominal operating conditions. For example, in certain embodiments, an anomalous plasma event may be identified in response to an increase in spectral density of less than 100%, e.g., 75%, 50%, or less, although the disclosed embodiments are not limited to such examples and may encompass other increases in spectral density.

[0060] In certain embodiments, an anomalous plasma event may be identified in response to an increase in spectral density relative to the standard deviation of the spectral density observed under nominal operating conditions. Thus, in one example, an anomalous plasma event may be identified by first calculating the standard deviation of the spectral density for a group of profiles, such as profile 610, representing nominal (or reference) plasma conditions. In another example, a moving average (along with a moving standard deviation) may be calculated over a particular period of time. In another example, the standard deviation may be calculated continuously using a time window that increases in size as a function of time. The methodology for calculating the standard deviation, or other statistical measure, may depend on the particular process being performed at the process station and may change during the processing of wafers.

[0061] In response to calculating the standard deviation utilizing the reference spectral density, an anomalous plasma event can be identified in response to observing a fluctuating signal from the plasma characterized by a spectral density profile having an amplitude that is (e.g.,) one standard deviation greater than the calculated standard deviation (e.g., the standard deviation utilizing the reference spectral density). In another example, an anomalous plasma event can be identified in response to observing a spectral density profile having an amplitude that is two standard deviations greater than the calculated standard deviation (e.g., the standard deviation utilizing the reference spectral density). However, the disclosed embodiments are intended to encompass spectral density profiles indicative of an anomalous plasma event that differ by any number of standard deviations with respect to the spectral density profile of the fluctuating signal from a plasma operating under nominal conditions.

[0062] Returning briefly to FIG. 1 , in certain embodiments, the signal processor 108 may be programmed to perform analysis on the raw output signal from the photodetector 112. In one or more such embodiments, analysis of the output signal from the photodetector 112 may be utilized to determine the spectral density of light energy fluctuations under various operating conditions within the process station. Thus, with reference to FIG. 6C , a profile representing plasma energy fluctuations over a predetermined time period may be analyzed to determine the spectral density at various frequencies as a proportion or percentage of the total spectrum of the light energy fluctuations of the plasma source. In some cases, such analysis performed by the signal processor 108 may include performing a fast Fourier transform (FFT) on the output signal from the photodetector 112. Following performance of the FFT on the output signal from the photodetector 112 over one or more predetermined time periods, the spectral density of the light energy fluctuations may be plotted in a manner similar to the spectral densities of FIGS. 6B / 6C . In response to analyzing the spectral density of the light energy fluctuations, the signal processor 108 may determine that an anomalous plasma event has occurred. In certain embodiments, an anomalous plasma event may be identified in response to detecting an increase in spectral density at a particular frequency of optical energy fluctuations, such as between about 400 kHz and about 4 MHz. An anomalous plasma event may be identified in response to observing a spectral density having an amplitude greater than a threshold amount compared to the spectral density observed during nominal plasma conditions. In certain embodiments, the threshold amount may correspond, for example, to one or two standard deviations with reference to the spectral density calculated during nominal plasma conditions. An anomalous plasma event may be identified in response to observing a spectral density having an amplitude other than one or two standard deviations with reference to the spectral density calculated during nominal plasma conditions, although the disclosed embodiments are not limited to such examples. Additionally, an anomalous plasma event may be identified by detecting an increase in spectral density at a frequency other than between about 400 kHz and about 4 MHz, although the disclosed embodiments are not limited to such examples. Rather, the embodiments are intended to encompass detection of spectral densities over any range of oscillations or fluctuations in the optical energy of the plasma.

[0063] 6D and 6E illustrate alternative configurations of the first exemplary anomalous plasma event detection apparatus of FIG. 1. In FIG. 6D, the anomalous plasma event detection apparatus 600D may not include a fiber optic cable. Rather, the anomalous plasma event detection apparatus 600D may include a signal processing unit 608A positioned in or on the processing chamber 602A such that a photodetector obtains an optical signal of the plasma in the processing chamber 602A. The output signal from the photodetector 612A can be processed utilizing a high-speed comparator 614A. The output signal from the high-speed comparator 614A is then transmitted to the RF generator 610A. In some embodiments, the apparatus may include a lens 604 between the processing chamber 602A and the photodetector 612A. In FIG. 6E, the anomalous plasma event detection apparatus 600E includes a lens 604B coupled to the signal processing unit 608B as part of the RF generator 610B via a fiber optic cable 606B. In such cases, the photodetector 612B may also be a component of the RF generator 610B. In some such examples, the RF generator 610A may include a high-speed comparator 614B so that an additional high-speed comparator is not utilized. An advantage of the anomalous plasma event detection apparatus 600E is that noise around the processing chamber 602B and the signal processing unit 608B cannot affect the signals utilized and generated by the signal processing unit 608B.

[0064] Various techniques can also be used to detect and mitigate arcing events in a processing chamber. FIG. 7A illustrates a flowchart of a first exemplary technique for detecting and mitigating an anomalous plasma event according to embodiment 700A. The technique begins at 701, where an optical signal generated by the fluctuating optical emission of the plasma is detected at 703. As described above, the plasma emits light of various wavelengths, and an optical sensor or detector (such as optical detector 112) is configured to detect the light emitted by the plasma. Additionally, at 705, the optical signal is converted to a voltage signal, which may be performed by an optical sensor or detector. At 707, the voltage signal is conditioned to form a conditioned voltage signal. This conditioning can follow any of the techniques described above, such as filtering and / or offsetting the raw optical voltage signal as described with respect to FIG. 2, taking the derivative of the raw optical voltage signal, or using FFT analysis of the raw optical voltage signal.

[0065] In response to the raw optical voltage signal being conditioned, 709 determines whether a change associated with the conditioned voltage signal exceeds a threshold. The determination can be any of the comparisons described above, such as comparing the filtered and / or offset voltage signal (i.e., the conditioned voltage signal) to the raw optical voltage signal and determining whether the change between these two signals exceeds a threshold. As noted above, in some embodiments, a determination is made whether the change between these two signals exceeds a threshold, which may indicate an arc or other type of abnormal plasma event occurring within the processing chamber. In these embodiments (i.e., embodiments utilizing a filtered optical signal), the determination is based not solely on a change in the filtered and / or offset signal itself, but on a change in the raw voltage signal relative to the filtered and / or offset signal. For example, as shown in FIG. 3B, a change in the raw voltage signal relative to the filtered signal indicates the occurrence of an arc or other type of abnormal plasma event. In response to utilizing both signals, this comparison is a determination associated with the conditioned voltage signal. The threshold can be selected according to various parameters, such as, for example, the rate of change and the magnitude of the change.

[0066] In some other embodiments of 709, determining that an abnormal plasma event is occurring can be based on a change in the conditioned voltage signal relative to a threshold, such as utilizing derivative and / or FFT techniques. Here, the determination can be based on the change in the conditioned voltage signal. For example, the output signal of the derivative technique can include a direct correlation with the rate of change of the optical signal, such that determining this conditioned voltage signal can directly indicate the occurrence of an arc.

[0067] If it is determined at 711 that the change associated with the adjusted voltage signal exceeds a threshold, mitigation actions may be taken. These mitigation actions may include adjusting the output parameters of the RF generator, such as by reducing the RF power output to a lower power level for a period of time and then returning the RF power output to the initial power level, as described above.

[0068] 7A, as described above, the technique may also include indicating that the determination of 709 generates and sends a TTL signal to the RF generator. In some embodiments, the RF generator is configured to receive the TTL signal and trigger a response to one or more parameters of the RF generator, such as reducing the output power of the RF generator. Additional aspects of the technique may also include generating a plasma in the processing chamber by coupling RF power to the processing chamber prior to or simultaneously with 703.

[0069] FIG. 7B illustrates a flowchart of a second exemplary technique for detecting and mitigating an anomalous plasma event, according to embodiment 700A. The technique begins at 751, where a plasma is formed in response to a signal of sufficient amplitude from an RF generator at 752. In some embodiments, the RF generator may generate signals at, for example, approximately 400 kHz (±10%) and approximately 13.56 MHz (±10%). It will be understood that the disclosed embodiments are not limited to such examples and may encompass various additional frequencies. At 754, a fluctuating optical signal generated by the plasma may be detected. The detection may be performed by an optical sensor or a photodetector. At 755, a signal processor may calculate the spectral density of the fluctuating optical signal. In certain embodiments, such calculation may occur while the plasma is operating under nominal conditions and may occur over several periods of time. In certain embodiments, a determination may be made at 756 that the spectral density of the fluctuating optical signal differs from one or more previously calculated spectral densities of the fluctuating optical signal. However, in certain other embodiments, 756 may include determining that the spectral density of the varying optical signal differs from a reference spectral density. In response to the spectral density of the varying optical signal differing from a previously calculated spectral density or other type of reference spectral density, often by a threshold amount, the signal processor may indicate that an anomalous plasma event has occurred.

[0070] In some embodiments, a semiconductor processing chamber may include two or more processing stations, as described below, and the optical emissions of each station may be monitored separately. For example, a processing chamber may include four processing stations, each of which may utilize a separate photodetector configured to detect the optical emissions from the corresponding processing station.

[0071] The devices and techniques described herein offer many advantages over conventional anomalous plasma event detection techniques. In some cases, these described techniques enable faster detection and mitigation response times because the optical signal can be processed with analog circuitry that can generate a signal directly to an RF generator that can respond to the signal. This direct connection between the RF generator and the optical signal allows for fast and efficient response times. In contrast, conventional techniques may require the detected signal to be sent to a processor for analysis, and then another signal sent by the processor to the RF generator. Because certain anomalous plasma events, such as electrical arcs, can form quickly, the delays associated with some conventional techniques can result in undesirable damage to wafers and / or other equipment. Additionally, as discussed above, these described techniques and devices can detect small-magnitude anomalous plasma events that cannot be detected by conventional methods.

[0072] As noted above, the apparatus and techniques described herein are applicable to any semiconductor process that uses a plasma, and to any semiconductor processing chamber in which a plasma is generated. Examples of these processes and apparatus are described below.

[0073] Plasma-enhanced chemical vapor deposition (PECVD) equipment In some embodiments, wafer fabrication equipment can include one or more PECVD process stations included in a process tool that can include the features described above in Figures 1, 6A, and 6B, for example, along with other features described below.

[0074] FIG. 8 provides a block diagram of an exemplary apparatus that can be used to implement the disclosed embodiments. As shown, the reactor 800 of FIG. 8 includes a process chamber 824 that surrounds the other components of the reactor and functions to contain a plasma generated by a capacitor-type system including, for example, a showerhead 814 operating in conjunction with a grounded heater block 820. A high-frequency RF generator 802 connected to a matching network 806 and a low-frequency RF generator 804 are connected to the showerhead 814. The power and frequency provided by the matching network 806 are sufficient to generate a plasma from the process gases, e.g., 400-700 W of total energy. In one embodiment of the invention, both an HFRF generator and an LFRF generator can be used during deposition, while in some other embodiments, only the HFRF generator is used. In a typical process, the high-frequency RF component is generally between about 2 and 60 MHz, and in at least one embodiment, the HF component is about 13.56 MHz. The low-frequency LF component is generally between about 250 and 400 kHz. In some embodiments, the RF generator can be considered to include both an HFRF generator and an LFRF generator, and possibly a matching network.

[0075] Within the reactor, a wafer pedestal 818 supports a substrate 816. The pedestal typically includes a chuck, forks, or lift pins for holding and transferring the substrate during deposition and / or plasma processing reactions. The chuck can be an electrostatic chuck, a mechanical chuck, or various other types of chucks available in industry and / or research.

[0076] Process gases are introduced through an inlet 812. Multiple source gas lines 810 are connected to a manifold 808. The gases may or may not be premixed. Appropriate valves and mass flow control mechanisms are used to ensure the correct gases are delivered for the deposition and post-deposition stages of the process. If the chemical precursors are delivered in liquid form, a liquid flow control mechanism is used. The liquid is then vaporized and mixed with other process gases during transport in a manifold heated beyond its point of vaporization before reaching the deposition chamber.

[0077] The process gas exits the chamber 824 via an outlet 822. A vacuum pump 826 (e.g., a one- or two-stage mechanical dry pump and / or a turbomolecular pump) typically draws the process gas and maintains an appropriate low pressure within the reactor by means of a closed-loop controlled flow restriction device such as a throttle valve or pendulum valve.

[0078] The present invention can be implemented in multi-station or single-station tools. In a specific embodiment, a 300 mm Novellus Vector™ tool with a four-station deposition scheme or a 200 mm Sequel™ tool with a six-station deposition scheme is used.

[0079] 9 shows a schematic diagram of one embodiment of a multi-station processing tool 900 including an inbound load lock 902 and an outbound load lock 904, either or both of which may utilize a remote plasma source, according to embodiment 900. A robot 906 is configured to move wafers at atmospheric pressure from a cassette loaded through a pod 908 to the inbound load lock 902 via an atmospheric pressure port 910. The wafer is placed by the robot 906 on a pedestal 912 of the inbound load lock 902, the atmospheric pressure port 910 is closed, and the load lock is pumped down. If the inbound load lock 902 utilizes a remote plasma source, the wafer may undergo remote plasma processing in the load lock before being introduced into the processing chamber 914. Additionally, the wafer may also be heated in the inbound load lock 902, for example, to remove moisture and adsorbed gases. The chamber transfer port 916 to the processing chamber 914 is then opened and another robot (not shown) moves the wafer into the reactor and places it on a pedestal in the first station shown in the reactor for processing. Note that although the embodiment shown in Figure 9 includes a load lock, it will be understood that in some embodiments the wafer may enter the process station directly.

[0080] The illustrated processing chamber 914 includes four process stations, numbered 1 through 4 in the embodiment shown in FIG. 9 . Each station has a heated pedestal (shown at 918 for station 1) and a gas line inlet. It will be understood that in some embodiments, each process station may have a different purpose or multiple purposes. While the illustrated processing chamber 914 includes four stations, it will be understood that a processing chamber according to the present disclosure may have any suitable number of stations. For example, in some embodiments, a processing chamber may have five or more stations, while in other embodiments, a processing chamber may have three or fewer stations.

[0081] FIG. 9 also illustrates one embodiment of a wafer handling system 990 for transferring wafers within the processing chamber 914. In some embodiments, the wafer handling system 990 can transfer wafers between various process stations and / or between process stations and load locks. It will be understood that any suitable wafer handling system may be used. Non-limiting examples include a wafer carousel and a wafer handling robot. FIG. 9 also illustrates one embodiment of a system controller 950 used to control the process conditions and hardware states of the process tool 900. The system controller 950 can include one or more memory devices 956, one or more mass storage devices 954, and one or more processors 952. The processor 952 can include a CPU or computer, analog and / or digital input / output connections, stepper motor controller boards, etc.

[0082] Although not shown in FIG. 9, tool 900 may include any of the features of reactor 800, such as gases and piping for each station described above, as well as vacuum pumps.

[0083] In some embodiments, the system controller 950 controls all of the activity of the process tool 900. The system controller 950 executes system control software 958, which is stored on the mass storage device 954, loaded into the memory device 956, and executed on the processor 952. The system control software 958 may include instructions for controlling the timing, mixture of gases, chamber and / or station pressures, chamber and / or station temperatures, purge conditions and timing, wafer temperature, RF power levels, frequencies, substrate, pedestal, chuck and / or susceptor positions, and other parameters of a particular process being performed by the process tool 900. The system control software 958 may be configured in any suitable manner. For example, various process tool component subroutines or control objects may be written to control the operation of the process tool components necessary to perform various process tool processes in accordance with the disclosed methods. The system control software 958 may be coded in any suitable computer-readable programming language.

[0084] In some embodiments, the system control software 958 may include input / output control (IOC) sequence instructions for controlling the various parameters described above. For example, each PECVD process may include one or more instructions for execution by the system controller 950. Instructions for setting process conditions for a PECVD process step may be included in the corresponding PECVD recipe step. In some embodiments, the PECVD recipe steps may be arranged in sequence such that all instructions for a PECVD process step are executed simultaneously with that process step.

[0085] In some embodiments, other computer software and / or programs may be used that are stored on the mass storage device 954 and / or memory device 956 associated with the system controller 950. Examples of programs or sections of programs for this purpose include a substrate positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program.

[0086] The substrate positioning program may include program code for process tool components used to load the substrate onto the pedestal 918 and control the spacing between the substrate and other parts of the process tool 900 .

[0087] The process gas control program can include code for controlling gas composition and flow rates to stabilize the pressure of the process station, and optionally code for flowing gases to one or more process stations prior to deposition. The process gas control program can include code for controlling the gas composition and flow rates within any of the disclosed ranges. The pressure control program can include code for controlling the pressure of the process station by, for example, adjusting a throttle valve in the exhaust system of the process station, gas flow to the process station, etc. The pressure control program can include code for maintaining the pressure of the process station within any of the disclosed pressure ranges.

[0088] The heater control program can include code for controlling current to a heating unit used to heat the substrate. Alternatively, the heater control program can control the delivery of a heat transfer gas (such as helium) to the substrate. The heater control program can include instructions for maintaining the temperature of the substrate within any of the disclosed ranges.

[0089] The plasma control program can include code for setting the RF power level and frequency supplied to the process electrodes of one or more process stations, for example, using any of the RF power levels disclosed herein. The plasma control program can also include code for controlling the duration of each plasma exposure.

[0090] In some embodiments, the system controller 950 may be part of, coupled to, or a combination of a computer integrated with, coupled to, or otherwise networked to the system. For example, the controller may be in the “cloud” or all or part of a fab host computer system. This allows for remote access to wafer processing. The computer may provide remote access to the system to monitor the current progress of a fabrication operation, review the history of past fabrication operations, review trends or performance criteria from multiple fabrication operations, modify parameters of a current process, configure processing steps following a current process, or initiate a new process. In some examples, a remote computer (e.g., a server) can provide process recipes to the system over a network. Such a network may include a local network or the Internet. The remote computer may include a user interface that allows entry or programming of parameters and / or settings, which are then communicated to the system from the remote computer. In some examples, the system controller 950 receives instructions in the form of data. Such data may identify parameters for each processing step performed during one or more operations. It should be understood that the parameters may be specific to the type of process being performed and the type of tool the controller is configured to interface with or control. Thus, as described above, system controller 950 may be distributed by including, for example, one or more individual controllers networked together and working together toward a common purpose (such as the processes and controls described herein).An example of a distributed controller for such purposes would include one or more integrated circuits on the chamber that communicate with one or more integrated circuits located remotely (e.g., at the platform level or as part of a remote computer) and coupled to control the process in the chamber.

[0091] In some embodiments, there may be a user interface associated with the system controller 950. The user interface may include a display screen, a graphical software display of equipment and / or process conditions, and user input devices such as a pointing device, keyboard, touch screen, microphone, etc.

[0092] In some embodiments, the parameters adjusted by the system controller 950 may relate to process conditions. Non-limiting examples include process gas composition and flow rates, temperature, pressure, plasma conditions (such as RF power level, frequency, and exposure time), etc. These parameters may be provided to the user in the form of a recipe and may be entered using a user interface.

[0093] Signals for monitoring the process may be provided by analog and / or digital input connections of the system controller 950 from various process tool sensors. Signals for controlling the process can be output at analog and digital output connections of the process tool 900. Non-limiting examples of process tool sensors that may be monitored include mass flow controllers, pressure sensors (such as pressure gauges), thermocouples, etc. Appropriately programmed feedback and control algorithms can be used with data from these sensors to maintain process conditions.

[0094] Any suitable chamber may be used to practice the disclosed embodiments. Exemplary deposition equipment includes, but is not limited to, equipment from the ALTUS® product family, VECTOR® product family, and / or SPEED® product family, each available from Lam Research Corporation of Fremont, California, or any of a variety of other commercially available processing systems. Two or more stations may perform the same function. Similarly, two or more stations may perform different functions. Each station may be designed / configured to perform a specific function / method as desired.

[0095] PECVD processing Many semiconductor fabrication processes deposit materials using plasma-enhanced chemical vapor deposition ("PECVD"). In a typical PECVD reaction, a substrate is exposed to one or more volatile precursors, which react and / or decompose to produce a desired deposit on the substrate surface. A PECVD process typically begins with flowing one or more reactants into a reaction chamber. The delivery of reactants may continue as a plasma is generated to which the substrate surface is exposed, causing deposition on the substrate surface. This process continues until the desired film thickness is reached, after which the plasma is typically extinguished and the flow of reactants is terminated. The reaction chamber may then be purged, and post-deposition steps may be performed.

[0096] As noted above, in some embodiments, the frequency used to drive plasma formation during PECVD can include a high frequency ("HF") component, a low frequency ("LF") component, or both. The HF frequency can be about 13.56 MHz or about 27 MHz. The HF RF power used to drive plasma formation can be about 200-3,000 W. These power levels represent the total power delivered and can be divided among stations in a multi-station processing chamber. The plasma can be generated at a first power level, which can be any power within this range, for example, 600 W for a single station or 2,400 W for a four-station processing chamber, resulting in 600 W for each of the four stations. The duration of plasma exposure depends on the desired thickness of the deposited film. In some embodiments, pulsed PECVD methods can be used. These methods can include pulsed precursor and / or RF power levels. In some embodiments, the frequency used to drive plasma formation during PECVD can include both an LF component and an HF component. The LF frequency can be about 300-400 kHz. The LF RF power used to drive plasma formation can be approximately 200-2,500 W.

[0097] Atomic layer deposition In some embodiments, some semiconductor processes involve multiple film deposition cycles, each resulting in a "discrete" film thickness. While atomic layer deposition (ALD) is one such film deposition method, any technique that deposits thin layers of film and is used in repeated successive materials can be considered to involve multiple deposition cycles, and the methods and apparatus disclosed herein can also be used generally to control film thickness in such multi-cycle deposition operations.

[0098] As device and feature sizes continue to shrink in the semiconductor industry, and as 3D device structures (e.g., Intel's Tri-Gate transistor architecture) become more prevalent in integrated circuit (IC) designs, the ability to deposit thin, conformal films (films of material that have a uniform thickness relative to the shape of the underlying structure, even if non-planar) continues to grow in importance. ALD is a film formation technique well-suited for depositing conformal films because only a single, thin layer of material is deposited in one ALD cycle, with the thickness limited by the amount of one or more film precursor reactants that can adsorb to the substrate surface (i.e., form an adsorption-limiting layer) prior to the film-forming chemical reaction itself. Multiple "ALD cycles" can then be used to build up films of desired thickness, each layer being thin and conformal so that the resulting film substantially matches the shape of the underlying device structure. In certain embodiments, each ALD cycle comprises the following steps: 1. Exposing the substrate surface to a first precursor. 2. Purging the reaction chamber in which the substrate is located. 3. Activation of the reaction of the substrate surface, typically with a plasma and / or a second precursor. 4. Purging the reaction chamber in which the substrate is located.

[0099] The duration of each ALD cycle is typically less than 25 seconds or less than 10 seconds. The plasma exposure step(s) in an ALD cycle can be short, such as less than 1 second in duration. Because of the short duration, controlling the plasma consistency can enhance process uniformity. Variations in plasma impedance and delivered power are two factors that can affect process uniformity.

[0100] An apparatus and method are provided for controlling RF power used in multi-cycle deposition operations in a semiconductor tool having multiple processing stations that share an RF power source, where the frequency of the RF power and the power applied to each of the stations that share the RF power source are controlled.

[0101] FIG. 10 illustrates a substrate processing apparatus for depositing a film on a semiconductor substrate, according to one embodiment. The processing apparatus 1000 of FIG. 10 has a single processing chamber 1002 with a single substrate holder 1008 within an interior volume that can be maintained under vacuum by a vacuum pump 1018. Also, a gas delivery system 1001 and a showerhead 1006 are fluidly coupled to the chamber for delivering (for example) film precursors, carrier and / or purge and / or process gases, secondary reactants, etc. Equipment for generating plasma within the processing chamber is also illustrated in FIG. 10. The apparatus illustrated schematically in FIG. 10 provides basic equipment for performing film deposition operations, such as chemical vapor deposition (CVD) or ALD, on semiconductor substrates.

[0102] For simplicity, the processing apparatus 1000 is illustrated as a stand-alone process station having a process chamber body for maintaining a low-pressure environment. However, it will be understood that, as described herein, multiple process stations may be included in a common process tool environment, e.g., within a common reaction chamber. For example, FIG. 11 illustrates one implementation of a multi-station processing tool, according to embodiment 1100. Furthermore, it will be understood that in some implementations, one or more hardware parameters of the processing apparatus 1000 (including those described in detail below) may be programmably adjusted by one or more system controllers.

[0103] The processing apparatus 1000 is in fluid communication with a reactant delivery system 1001 for delivering process gases to a distribution showerhead 1006. The reactant delivery system 1001 includes a mixing vessel 1004 for blending and / or conditioning the process gases delivered to the showerhead 1006. One or more mixing vessel inlet valves 1020 can control the introduction of process gases into the mixing vessel 1009.

[0104] Some reactants may be stored in liquid form prior to vaporization and subsequent delivery to the process chamber 1002. The embodiment of Figure 10 includes a vaporization point 1003 for vaporizing the liquid reactants provided to the mixing vessel 1009. In some embodiments, the vaporization point 1003 may be a heated liquid injection module. In some other embodiments, the vaporization point 1003 may be a heated vaporizer. In still other embodiments, the vaporization point 1003 may be eliminated from the process station.

[0105] In some embodiments, a liquid flow controller (LFC) can be provided upstream of the vaporization point 1003 to control the mass flow rate of the liquid that is vaporized and delivered to the processing chamber 1002 .

[0106] The showerhead 1006 delivers process gases and / or reactants (e.g., film precursors) to a substrate 1012 in a process station, the flow of which is controlled by one or more valves (e.g., valve 1020) upstream of the showerhead. In the embodiment shown in Figure 10, the substrate 1012 is shown positioned below the showerhead 1006 and resting on a pedestal 1008. The showerhead 1006 can have any suitable shape and can have any suitable number and arrangement of ports for delivering process gases to the substrate 1012.

[0107] A volume 1007 is located below the showerhead 1006. In some implementations, a pedestal 1008 can be raised or lowered to expose a substrate 1012 to volume 1007 and / or to change the volume of volume 1007. Optionally, the pedestal 1008 can be lowered and / or raised during portions of the deposition process to adjust the process pressure, reactant concentration, etc. within volume 1007.

[0108] 10, the showerhead 1006 and pedestal 1008 are electrically connected to an RF power source 1014 and matching network 1016 for supplying power to the plasma. In some implementations, the plasma energy may be controlled (e.g., via a system controller having appropriate machine-readable instructions) by controlling one or more of the process station pressure, gas concentration, RF source power, RF source frequency, and plasma power pulse timing. For example, the RF power source 1014 and matching network 1016 may be operated at any suitable power to form a plasma having a desired composition of radical species. Similarly, the RF power source 1014 may provide RF power at any suitable frequency.

[0109] In some embodiments, the plasma may be monitored in situ by one or more plasma monitors. In one scenario, plasma power may be monitored by one or more voltage and current sensors (e.g., load sensors such as VI probes). Examples of such sensors include the MKS VI-Probe-4100 and 350. Such sensors can measure voltage, current, and phase difference. In certain embodiments, the sensors may be electrically connected to the RF power source and located at or near the showerhead. In such embodiments, the impedance presented to the RF generator output port may represent the impedance of the plasma. In another scenario, one or more optical emission spectroscopy sensors (OES) may measure plasma density and / or process gas concentration. In some embodiments, one or more plasma parameters may be programmably adjusted based on measurements from such in situ plasma monitors. For example, a load sensor may be used in a feedback loop to provide programmable control of plasma power. It will be understood that in some embodiments, other monitors may be used to monitor the plasma and other process characteristics. Such monitors may include, but are not limited to, infrared (IR) monitors, acoustic monitors, and pressure transducers.

[0110] In some implementations, the plasma may be controlled via input / output control (IOC) sequence instructions. In one example, instructions for setting plasma conditions for plasma activation may be included in a corresponding plasma activation recipe of a process recipe. In some cases, process recipes may be arranged in a sequence, whereby all instructions for a process are executed simultaneously. In some implementations, instructions for setting one or more plasma parameters may be included in a recipe preceding a plasma process. For example, a first recipe may include instructions for setting the flow rate of an inert gas (e.g., helium) and / or a reactant gas, instructions for setting a plasma generator to a power setpoint, and a time delay instruction for the first recipe. A subsequent second recipe may include instructions for enabling the plasma generator and a time delay instruction for the second recipe. A third recipe may include instructions for disabling the plasma generator and a time delay instruction for the third recipe. It will be understood that these recipes may be further subdivided and / or repeated in any suitable manner within the scope of the present disclosure.

[0111] In some deposition processes, plasma strikes last for periods on the order of several seconds or longer. In certain embodiments described herein, much shorter plasma strikes can be applied during a processing cycle. These can be on the order of less than 50 milliseconds, with 25 milliseconds being a specific example. Such short RF plasma strikes require rapid stabilization and regulation of the plasma. To achieve rapid stabilization and regulation of the plasma, the plasma generator can be configured through a two-stage tuning process including a coarse tuning component and a fine tuning component. The coarse tuning component can preset the impedance match to a specific impedance. The coarse tuning component can preset the impedance magnitude to a value, for example, 50 ohms. In certain embodiments, the coarse tuning component may be limited to adjustments that affect the impedance magnitude. The fine tuning component can float the RF frequency from a baseline frequency to attempt to match the phase to a target value, such as a zero phase value. Traditionally, high-frequency plasmas have been generated at a frequency of approximately 13.56 MHz. In various embodiments disclosed herein, the frequency can be floated to a value different from this standard value to match the phase to a target value. In certain embodiments, the fine tuning component may be limited to adjustments that affect the phase of the impedance. By floating the frequency while fixing the impedance match to a predetermined impedance, the plasma can stabilize much more quickly. Very short plasma strikes, such as those associated with ALD or atomic layer etching (ALE) cycles, can benefit from rapid plasma stabilization.

[0112] The first 1-2 milliseconds of a typical deposition cycle involves igniting the plasma. After ignition, fine tuning of the RF frequency is performed to match the plasma phase to the target value.

[0113] As described above, one or more process stations may be included in a multi-station substrate processing tool. FIG. 11 illustrates an example of a multi-station substrate processing apparatus that may utilize plasma balancing hardware. Using a multi-station processing apparatus such as that illustrated in FIG. 11 can achieve various efficiencies in terms of both equipment and operating costs. For example, a single vacuum pump can be used to evacuate all four process stations, thereby creating a single high-vacuum environment. Depending on the implementation, each process station may have a dedicated showerhead for gas delivery, but may share the same gas delivery system. Similarly, certain elements of plasma-generating equipment may be shared between process stations (e.g., power supplies), but depending on the implementation, certain aspects may be process-station-specific (e.g., using a showerhead to apply plasma-generating potentials). Again, it should be understood that such efficiencies may be achieved to a greater or lesser extent by using a greater or fewer number of process stations per processing chamber (e.g., 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 or more process stations per reaction chamber).

[0114] The substrate processing apparatus of Figure 9 can also be used to perform ALD processes. Here, a single substrate processing chamber 914 includes multiple substrate processing stations, each of which can be used to perform a processing operation on a substrate held in that process station's wafer holder. In this particular embodiment, a multi-station substrate processing tool 900 is shown having four process stations 1, 2, 3, and 4. Other similar multi-station processing apparatuses may have a greater or lesser number of processing stations, depending on the implementation and, for example, the desired level of parallel wafer processing, size / space constraints, cost constraints, etc.

[0115] In FIG. 9, RF power is generated by an RF power system 913 and distributed to each of stations 1-4. The RF power system may include one or more RF power sources, e.g., high-frequency (HFRF) and low-frequency (LFRF) power sources, an impedance matching module, and a filter. In certain embodiments, the power source may be limited to only high-frequency or low-frequency power sources. Unless otherwise specified, it is assumed that the deposition process described uses only high-frequency power. The RF power system distribution system is symmetrical with respect to the reactor and has a high impedance. This symmetry and impedance ensure that approximately equal amounts of power are delivered to each station. Minor differences in RF power (on the order of 5-15%) can result from tolerances in the distribution system components, station placement, temperature differences, and process conditions.

[0116] Small variations in RF power can cause wafer-to-wafer non-uniformities in various film properties, such as composition, thickness, density, amount of crosslinking, chemistry, reaction completion point, stress, refractive index, dielectric constant, hardness, etch selectivity, stability, hermeticity, etc. The ability to fine-tune plasma power at individual stations and dynamically respond to changes in station conditions can reduce wafer-to-wafer non-uniformities. Note that the methods and apparatus of the present invention are not limited to multi-station reactors. The methods and apparatus disclosed herein apply to other RF power systems in which multiple processing regions share an RF power source.

[0117] The system controller 950 can also be used to control the process conditions and hardware states of the process tool 900 and its process stations for performing ALD. The system controller 950 can provide machine-readable instructions for performing the deposition process. The instructions can control various process parameters such as DC power levels, RF bias power levels, station-to-station variations such as RF power parameter variations, frequency adjustment parameters, pressure, temperature, etc. The instructions can control parameters for operating the in situ deposition of a film stack according to various embodiments described herein.

[0118] FIG. 11 is a schematic diagram illustrating various components of an exemplary multi-station plasma reactor with multiple stations sharing RF power using RF frequency adjustment. As shown, RF power source 1101, which may be a high-frequency RF power source, is distributed to multiple stations 1151 via a distribution network 1121. The HFRF may have a frequency of about 2 to 60 MHz, or about 13.56 MHz. In other embodiments, a low-frequency RF power source may be used in addition to or instead of the high-frequency RF power source. The low-frequency RF power source may have a frequency of about 100 kHz to about 1 MHz, or about 400 kHz. Certain commercially available RF power sources include the ability to adjust the frequency of the RF power. Examples of such RF power sources include Advanced Engineer's Paramount series, MKS's SurePower series, Comdel's CB, CLX, and CDX series, and Huettinger's TruPlasma series.

[0119] Power from the RF power source 1101 may be routed through an impedance matching system that may include a fixed matching module 1103. In certain embodiments that include both high-frequency and low-frequency RF power sources, high-pass and / or low-pass filters may also be present. Additionally, in certain embodiments, power from the RF power source may be routed through an automatic matching module. In embodiments that include a low-frequency RF power source in addition to or instead of a high-frequency RF power source, the low-frequency power may be routed through either fixed or automatic matching. In certain embodiments, an automatic matching module may be used to match the RF power frequency to the set impedance of the plasma load. In other embodiments, a fixed matching module may be used that does not automatically match the RF power frequency to the set impedance of the plasma load.

[0120] In the embodiment shown in FIG. 11 , the RF power source 1101 is connected to a distribution network 1121. The distribution network 1121 can distribute RF power generated by the RF power source 1101 to each of the multiple stations 1151. The distribution network 1121 is connected to an RF adjuster 1123 for each of the multiple stations 1151. For each of the multiple stations 1151, the RF adjuster 1123 is connected to a power parameter sensor 1133 in front of the showerhead 1153. The power parameter sensor 1133 can be any type of sensor previously disclosed, such as a load sensor or an OES sensor. The RF power source 1101 can receive commands from an RF controller 1143 to vary the frequency of the RF power distributed to the stations. The command can be a frequency adjustment in response to impedance detected by one or more power parameter sensors 1133. In other embodiments, additional sensors can measure a final phase, which represents the phase of the plasma at all of the stations 1151. The RF controller 1143 can then vary the frequency of the RF power delivered to the stations according to the final phase measured by the additional sensor. In certain implementations, the RF controller 1143 can include instructions, e.g., code, for varying the frequency of the RF power so that the phase of the impedance is zero or near zero. In the implementation shown in FIG. 11, the RF controller 1143 can vary the frequency of the RF power from the RF power source 1101 upstream of each station.

[0121] The RF adjusters 1123 are controlled by an RF controller 1143. The RF controller 1143 can change the RF power of individual stations by a determined amount based on measurements from the sensors 1133 at each station 1151. In certain embodiments, the RF adjusters 1123 can be variable capacitors. The RF controller 1143 can control a stepper motor (not shown) that can change the capacitance of the variable capacitor. Other methods of changing the capacitance can also be used. For example, the RF adjusters 1123 can also be a bank of capacitors with individual switches. RF power can be controlled by activating (turning on) several capacitors with specified values. For example, capacitors can be selected to add 1 pF, 2 pF, 4 pF, 8 pF, and 16 pF of shunt capacitance to the station. In this example, all combinations of active (on) and inactive (off) capacitors cover a range of 0 pF to 31 pF with 1 pF resolution. By selecting which capacitors are activated, the controller can vary the RF power to the station. This digital control is faster than using a stepper motor to control a variable capacitor, especially if a wide range of capacitance needs to be covered. Depending on the available space and the amount of control required, one skilled in the art could design an RF adjuster that uses one or more capacitors to vary the RF power by a specific amount.

[0122] In other embodiments, the RF adjuster 1123 can be a variable coil inductor. The RF controller 1143 can control the variable coil inductor to affect the RF power delivered to the station. In certain embodiments, the RF adjuster is not limited to capacitors and inductors. In certain embodiments, other RF adjusters 1123 can utilize different mechanisms to change the RF power, such as a resonator circuit or a resistor circuit.

[0123] The sensor 1133 measures at least one RF power parameter. The measured RF power parameter can be voltage, current, impedance, phase, or load power. Commercially available probes can be used to measure RF power parameters and provide the measurements to the RF controller 1143. It is also possible to measure non-RF parameters and use them as source signals for the RF controller 1143. For example, light emission from station plasma or substrate temperature sensors can measure station characteristics and provide them to the RF controller 1143. Light-emitting systems can be installed near each station to collect light emitted by the station plasma. The substrate temperature sensor may use a remote infrared detection system built below the substrate. The sensor 1133 can also measure multiple RF power parameters, or multiple sensors can be used in a particular implementation to measure multiple RF power parameters.

[0124] In some embodiments, the RF adjusters can be set to a fixed value or range of values ​​over a multi-step process, such as a multi-cycle ALD process, with little or no need to sense RF power parameters in real time and adjust the distribution of RF power among stations.

[0125] Each station 1151 includes a showerhead 1153 operating in conjunction with a grounded pedestal 1157. The power and frequency provided are sufficient to generate a plasma from the process gases, for example, in the range of about 50 W to about 6000 W per station. Power levels can vary depending on the implementation. RF power is connected to the station processing region through the showerhead 1153, and when RF power is applied, it generates or sustains a plasma. The plasma deposits material on the substrate by various mechanisms. For example, the plasma can decompose the process gases and cause them to react on the substrate surface. In the illustrated implementation, the RF current is grounded at the pedestal 1157, which is connected to ground 1131. In certain other implementations, the RF current can be grounded at a different location within the chamber, such as the showerhead.

[0126] The plasma activation step of a multi-step deposition process with short cycle duration may be short. The duration of the plasma activation step can be about 150 milliseconds or less (e.g., about 50 milliseconds). Because of the short duration, controlling the plasma consistency affects the process uniformity. Plasma balancing can be used to control the plasma consistency.

[0127] Although not shown in Figures 8-11, any of the tools in these figures can include any features of the other tools, such as controller 950, which can be configured to execute any of the instructions described herein for reactor 800. Additionally, the chambers identified in the embodiments 800, 900, and 1000 of Figures 8-10, respectively, can be considered chamber 102 of Figure 1 and chambers 602A and 602B of Figures 6D and 6E, respectively. Additionally, RF generators 110, 610A, and 610B can also be considered either or both of the HFRF and LFRF generators of Figures 8-11.

[0128] Unless the context of this disclosure clearly requires otherwise, throughout the claims, words like "comprises," "comprising," and the like should be construed in an inclusive sense, i.e., "including but not limited to," rather than an exclusive or exhaustive sense. Words using the singular or plural generally also include the plural or singular, respectively. In addition, the words "herein," "below," "on," "below," and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word "or" is used in reference to a list of two or more items, the word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. The term "embodiment" refers to an embodiment of the technology and methods described herein, as well as a physical object embodying a structure and / or incorporating the technology and / or methods described herein. The terms "substantially," "approximately," and "about" are understood to include ±10% of the indicated amount.

Claims

1. 1. A method for detecting an anomalous plasma event in a semiconductor processing chamber, comprising: detecting an optical signal emitted by a plasma in the semiconductor processing chamber, the plasma being formed in response to an RF signal from an RF generator; converting the optical signal into a voltage signal; adjusting the voltage signal to form a adjusted voltage signal; determining whether a change associated with the regulated voltage signal exceeds a threshold; adjusting an output parameter of the RF signal from the RF generator based at least in part on the determination; and A method comprising:

2. 10. The method of claim 1, adjusting the voltage signal to form the adjusted voltage signal includes filtering the voltage signal with a low pass filter; the determining includes comparing the change in the voltage signal to the regulated voltage signal. method.

3. 3. The method of claim 2, The method, wherein adjusting the voltage signal to form a regulated voltage signal further comprises applying an offset to the regulated voltage signal.

4. 10. The method of claim 1, The method, wherein adjusting the voltage signal to form a adjusted voltage signal includes taking a first derivative of the voltage signal.

5. 10. The method of claim 1, The method, wherein the adjusting the output parameter of the RF generator includes decreasing an output power of the RF generator from a first power level to a second power level.

6. 6. The method of claim 5, reducing the output power of the RF generator from the first power level to the second power level, and then maintaining the output power of the RF generator at the second power level for a first period of time; after said maintaining, increasing the output power of the RF generator from the second power level to the first power level for a second period of time; The method further comprises:

7. 6. The method of claim 5, The method, wherein the second power level is a non-zero power level.

8. 6. The method of claim 5, The method, wherein the second power level is zero.

9. 10. The method of claim 1, determining a first amount of RF power reduction based at least in part on a light intensity or process parameter within the semiconductor processing chamber; reducing the output power level of the RF generator by the first amount; further comprising the process parameters include one or more process parameters selected from the group consisting of DC power level, RF bias power level, station-to-station RF power variation, frequency adjustment parameters, pressure, and temperature; method.

10. 1. A semiconductor processing tool comprising: a semiconductor processing chamber; an RF generator configured to provide RF power to the semiconductor processing chamber to generate and maintain a plasma; a photodetector configured to detect an optical signal indicative of an optical emission of a plasma within the semiconductor processing chamber, the photodetector configured to convert the optical signal into a voltage signal; A tilt change detection unit, comprising: receiving the voltage signal; adjusting the voltage signal to form a regulated voltage signal; determining whether a change associated with the regulated voltage signal exceeds a threshold; a slope change detection unit configured to send a signal to the RF generator in response to the determination, the signal being configured to cause an adjustment to the RF generator; 1. A semiconductor processing tool comprising:

11. 11. The semiconductor processing tool of claim 10, a lens on the semiconductor processing chamber configured to allow light within the semiconductor processing chamber to pass through the lens; a fiber optic cable between the lens and the photodetector, the fiber optic cable configured to transmit at least a portion of the light passing through the lens to the photodetector; 10. The semiconductor processing tool of claim 9, further comprising:

12. 11. The semiconductor processing tool of claim 10, The tilt change detection unit a filter that filters the voltage signal to convert the voltage signal into the conditioned voltage signal; a comparator for comparing a change between the regulated voltage signal and the voltage signal; 10. The semiconductor processing tool of claim 9, further comprising:

13. 13. The semiconductor processing tool of claim 12, The semiconductor processing tool, wherein the comparator includes a transistor-transistor logic (TTL) configured to send a TTL signal to the RF generator.

14. 11. The semiconductor processing tool of claim 10, The semiconductor processing tool, wherein the RF generator is configured to reduce the RF power from a first power level to a second power level in response to receiving the signal from the slope change detection unit.

15. 11. The semiconductor processing tool of claim 10, The tilt change detection unit a differentiator configured to take the derivative of the voltage signal and convert the voltage signal to the regulated voltage signal; a comparator configured to determine whether the change in the regulated voltage signal exceeds the threshold; 10. The semiconductor processing tool of claim 9, further comprising:

16. 11. The semiconductor processing tool of claim 10, a fiber optic cable between the semiconductor processing chamber and the photodetector, the fiber optic cable being configured to transmit light generated by the plasma in the semiconductor processing chamber to the photodetector; 10. The semiconductor processing tool of claim 9, further comprising:

17. 11. The semiconductor processing tool of claim 10, the photodetector is electrically connected to the RF generator; the optical signal from the semiconductor processing chamber is provided to the RF generator from the semiconductor processing chamber; Semiconductor processing tools.

18. 11. The semiconductor processing tool of claim 10, the photodetector and the tilt change detection unit are positioned outside the semiconductor processing chamber; Semiconductor processing tools.

19. 20. The semiconductor processing tool of claim 18, the photodetector and the tilt change detection unit are positioned between the semiconductor processing chamber and the RF generator; Semiconductor processing tools.

20. 11. The semiconductor processing tool of claim 10, the photodetector and the tilt change detection unit are positioned above the semiconductor processing chamber; Semiconductor processing tools.

21. 1. A method for detecting an anomalous plasma event, comprising: forming a plasma using a signal from an RF generator; detecting a fluctuating optical signal produced by the plasma; calculating a spectral density of the varying optical signal; determining that the spectral density of the fluctuating optical signal differs from one or more reference spectral densities of fluctuating optical signals generated by the plasma by a threshold amount; A method comprising:

22. 22. The method of claim 21, A method, wherein calculating the spectral density of the varying optical signal includes utilizing a Fast Fourier Transform.

23. 22. The method of claim 21, The method, wherein the one or more reference spectral densities of the varying optical signal correspond to the spectral density of the varying optical signal produced by a plasma maintained under nominal conditions.

24. 24. The method of claim 23, The method, wherein the threshold amount corresponds to one standard deviation for the spectral density of the fluctuating optical signal from the plasma maintained under nominal conditions.

25. 24. The method of claim 23, The method, wherein the threshold amount corresponds to two standard deviations for the spectral density of the fluctuating optical signal from the plasma maintained under nominal conditions.

26. 22. The method of claim 21, The method, wherein calculating the spectral density of the varying optical signal includes determining the spectral density of the varying optical signal at a frequency of about 400 kHz.

27. 22. The method of claim 21, The method, wherein calculating the spectral density of the varying optical signal includes determining the spectral density of the varying optical signal at a frequency between about 400 kHz and about 4 MHz.

28. 22. The method of claim 21, The method, wherein calculating the spectral density of the varying optical signal includes determining the spectral density of the varying optical signal at multiple frequencies generated by one or more RF generators.

29. 1. An apparatus comprising:

1. A signal processor configured to analyze an output signal from a photodetector receiving an optical signal from a multi-station processing tool, the signal processor comprising: Detecting a fluctuating optical signal generated by a plasma formed in the semiconductor fabrication chamber; calculating a spectral density of the varying optical signal; determining that the spectral density of the fluctuating optical signal differs from one or more reference spectral densities of the fluctuating optical signal generated by the plasma by a threshold amount; a signal processor further configured to:

30. 30. The apparatus of claim 29, The apparatus, wherein the one or more reference spectral densities of the varying optical signal correspond to spectral densities calculated while the plasma is maintained under nominal conditions.

31. 31. The apparatus of claim 30, The apparatus, wherein the threshold amount corresponds to one standard deviation for the spectral density of the fluctuating optical signal from the plasma maintained under nominal conditions.

32. 31. The apparatus of claim 30, The apparatus, wherein the threshold amount corresponds to two standard deviations for the spectral density of the fluctuating optical signal from the plasma maintained under nominal conditions.

33. 30. The apparatus of claim 29, An apparatus wherein the spectral density of the varying optical signal is calculated while an RF signal having a frequency of about 400 kHz is coupled into the multi-station processing tool.

34. 34. The apparatus of claim 33, The spectral density of the varying optical signal is calculated to determine the spectral density of the varying optical signal at frequencies between 400 kHz and 4 MHz.

35. 35. The apparatus of claim 34, The apparatus, wherein the spectral density of the varying optical signal is calculated at a frequency of the RF signal coupled to the multi-station processing tool.

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