Optical emission spectroscopy for advanced process characterization

Abstract

A method for characterizing a plasma in a plasma processing system is provided, the method including: generating a pulsed plasma in a plasma processing chamber of the plasma processing system, the pulsed plasma being powered with a pulsed power signal, each pulse of the pulsed plasma including three periods: an overshoot period, a stable-on period, and a decay period; and performing repetitive optical emission spectroscopy (OES) measurements of the pulsed plasma, the repetitive OES measurements including acquiring first OES data during one of the three periods from two or more pulses of the pulsed plasma; and acquiring characteristics of the pulsed plasma for one of the three periods based only on the first OES data.

Description

[Technical Field]

[0001] Cross-references to related patents and applications This application claims priority to and the benefit of the filing date of U.S. Non-Provisional Patent Application No. 17 / 948,407, filed September 20, 2022, which is incorporated herein by reference in its entirety.

[0002] The present invention relates generally to systems and methods for process characterization, and in particular embodiments to optical emission spectroscopy for advanced process characterization. [Background technology]

[0003] Generally, semiconductor devices, such as integrated circuits (ICs), are fabricated by sequentially depositing and patterning layers of dielectric, conductive, and semiconducting materials onto a substrate to form a network of electronic components and interconnect elements (e.g., transistors, resistors, capacitors, metal lines, contacts, and vias) integrated into a monolithic structure. The process flows used to form the constituent structures of semiconductor devices often involve the deposition and removal of various materials, which may expose patterns of several types of materials on the surface of the engineered substrate. Summary of the Invention [Problem to be solved by the invention]

[0004] Advanced process control, including in-situ process characterization and fault detection, is essential for the repeatable fabrication of complex structures during semiconductor manufacturing. As minimum feature dimensions in patterned layers shrink regularly and new materials continue to be introduced into ICs, the need for improved process characterization to ensure process compliance and cost reduction is increasing. [Means for solving the problem]

[0005] According to one embodiment of the present invention, there is provided a method for characterizing a plasma in a plasma processing system, the method including: generating a pulsed plasma in a plasma processing chamber of the plasma processing system, the pulsed plasma being powered with a pulsed power signal, each pulse of the pulsed plasma including three periods: an overshoot period, a stable-on period, and a decay period; performing repetitive optical emission spectroscopy (OES) measurements of the pulsed plasma, the repetitive OES measurements including acquiring first OES data during one of the three periods from two or more pulses of the pulsed plasma; and acquiring characteristics of the pulsed plasma for one of the three periods based solely on the first OES data.

[0006] According to one embodiment of the present invention, there is provided a method of processing a substrate, the method including: performing plasma processing on a substrate in a plasma processing chamber by exposing the substrate to a pulsed plasma in the plasma processing chamber, the pulsed plasma being provided with a source power and a pulsed bias power at a bias power frequency; and repeatedly acquiring first optical emission spectroscopy (OES) data when the bias power is off and the source power is provided, the first OES data being acquired at the bias power frequency.

[0007] According to one embodiment of the present invention, there is provided an optical emission spectroscopy (OES) apparatus including: a plasma processing chamber configured to hold a substrate to be processed; an RF power source configured to generate a pulsed plasma in the plasma processing chamber; an OES detection device connected to the plasma processing chamber, the OES detection device configured to measure an OES signal from the pulsed plasma; a microprocessor; and a non-transitory memory storing a program executed by the microprocessor, the program including instructions for generating a first pulse train and a second pulse train, the first pulse train and the second pulse train being synchronized; powering the RF power source and generating the pulsed plasma based on the first pulse train; and collecting an OES data set with the OES detection device based on the second pulse train. [Brief explanation of the drawings]

[0008] For a more complete understanding of the present invention and its advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings.

[0009] [Figure 1] 1 shows a schematic block diagram of a method for synchronizing optical emission spectroscopy (OES) with plasma power modulation, according to various embodiments. [Figure 2] 1 illustrates an example of a plasma processing system having an OES configured to operate synchronously with a plasma process, according to various embodiments. [Figure 3] 1 shows a schematic diagram of an OES detection device and its components according to various embodiments. [Figure 4] 1 illustrates an example of a pulsed regime for generating a pulsed plasma, according to various embodiments. [Figure 5] 10 illustrates modeled temporal profiles of radical density, electron density, and electron temperature for a pulsed plasma according to various embodiments. [Figure 6A]10 illustrates an exemplary scheme for acquiring OES data synchronously with power pulsing of a pulsed plasma, according to an embodiment with source power pulsing. [Figure 6B] 10 illustrates an exemplary scheme for acquiring OES data synchronously with power pulsing of a pulsed plasma according to an embodiment with bias power pulsing. [Figure 7A] 1 shows a process flow diagram of a method for characterizing a pulsed plasma using OES, according to one embodiment. [Figure 7B] 1 shows a process flow diagram of a method for characterizing a pulsed plasma using OES, according to another embodiment. [Figure 7C] 10 shows a process flow diagram of a method for characterizing a pulsed plasma using OES according to an alternative embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] This application relates to systems and methods for process characterization, and more particularly, to optical emission spectroscopy (OES) for advanced process characterization. In semiconductor manufacturing, plasma processing is used at various stages to deposit and etch various materials and build complex structures with nanometer-scale precision. Because plasma is a high-energy, complex system containing ionic and radical species, accurately characterizing the plasma and monitoring the progress of plasma processing during operation is often challenging. Optical emission spectroscopy (OES) is a powerful spectroscopic tool for analyzing atoms and ions present in plasma by detecting optical emissions from excited species. OES systems have been incorporated into some plasma processing systems for process characterization, as described, for example, in U.S. Pat. Nos. 5,862,060 and 10,453,653. For example, using OES to collect optical emission signals from process plasma can enable endpoint detection (EPD) of plasma etching processes such as reactive ion etching (RIE) and atomic layer etching (ALE). However, the time resolution of OES techniques during plasma processing is often limited to the subsecond scale, posing a significant challenge for advanced process characterization by OES. New OES techniques with improved time resolution are desirable, particularly for pulsed plasma processing involving power modulation. Current OES techniques tend to miss important information about the stability of the power modulation pulse due to insufficient sensitivity. Conventional OES techniques may typically be based on continuous (time-averaged) signal acquisition that is not time-synchronized with the RF generator. Embodiments of the present application disclose methods that employ time synchronization between a pulsed RF generator and OES data acquisition. In various embodiments, this synchronization enables OES data collection only during selected periods of interest during power modulation (e.g., only a portion of the source power-on period). This technique advantageously enables selective OES signal observation and characterization at different stages of interest during a single modulation pulse cycle, extending time resolution to millisecond or submillisecond scales.Therefore, the present method can improve the capability of plasma stability monitoring during various Advanced Pulsing Technology (APT) processes. Furthermore, the present method can also eliminate the step of averaging signals over different periods during power modulation by separately collecting OES data from different periods, which can lead to an improvement in the signal-to-noise ratio of the OES signal.

[0011] A scheme for synchronizing optical emission spectroscopy (OES) with power modulation of a plasma is described below, first with reference to FIG. 1, followed by a description of an exemplary plasma processing system in FIG. 2 and an OES detection device in FIG. 3. An exemplary RF pulsing scheme for source power and bias power is described in FIG. 4. Example profiles of radical density, electron density, and electron temperature of a pulsed plasma as a result of power modulation are then described with reference to FIG. 5. An example scheme for OES data acquisition synchronized with power pulsing of a pulsed plasma is then described with reference to FIGS. 6A-6B. An exemplary process flow diagram is shown in FIGS. 7A-7C. All figures in this disclosure are for illustrative purposes only and are not drawn to scale.

[0012] FIG. 1 shows a schematic block diagram of a method for synchronizing optical emission spectroscopy (OES) with plasma power modulation, according to various embodiments.

[0013] To enable synchronization of OES data acquisition with pulsed plasma processing, function generator 100 may be used to generate a synchronized set of commands for both the plasma processing units (e.g., plasma power sources 110 and 120 and bias power source 130) and OES detection device 140. An exemplary implementation of function generator 100 and OES detection device 140 in a plasma processing system is described below with reference to Figure 2. The schematic block diagram of Figure 1 is merely an example, and the number of power sources, either plasma power sources or bias power sources, is not limited to any particular number.

[0014] FIG. 2 illustrates an example of a plasma processing system 20 having an OES configured to operate synchronously with a plasma process, according to various embodiments.

[0015] 2 shows substrate 200 disposed on substrate holder 210 (e.g., a circular electrostatic chuck (ESC)) near the bottom inside plasma processing chamber 220. Substrate 200 may optionally be maintained at a desired temperature using a heater / cooler 215 surrounding substrate holder 210. The temperature of substrate 200 may be maintained by a temperature controller 230 connected to substrate holder 210 and heater / cooler 215. The ESC may be coated with a conductive material (e.g., a carbon-based or metal nitride-based coating) so that it can be electrically connected to substrate holder 210.

[0016] Process gases may be introduced into the plasma processing chamber 220 by a gas delivery system 270. The gas delivery system 270 includes multiple gas flow controllers for controlling the flow of multiple gases into the chamber. Each gas flow controller of the gas delivery system 270 may be assigned to each of the fluorocarbons, noble gases, and / or equilibrating agents. In some embodiments, an optional center / edge splitter may be used to independently adjust the gas flow rates at the center and edge of the substrate 200. Process gases or any exhaust gases may be exhausted from the plasma processing chamber 220 using a vacuum pump 280.

[0017] As shown in FIG. 2 , the substrate holder 210 can be the bottom electrode of the plasma processing chamber 220. In the illustrative example of FIG. 2 , the substrate holder 210 is connected to two RF bias power supplies 240 and 242. In some embodiments, a conductive circular plate near the top inside the plasma processing chamber 220 is the top electrode 250. In FIG. 2 , the top electrode 250 is connected to an RF power supply 244 of the plasma processing system 20. The three RF power supplies 240, 242, and 244 can correspond to the bias power supply 130, the plasma power supplies 110, and the plasma power supplies 120 shown in FIG. 1 . In various embodiments, all of the power supplies for plasma processing (e.g., the RF power supplies 240, 242, and 244) are connected to a function generator 100 to enable synchronized operation of the power supplies. Additionally, the function generator 100 is also connected to an OES detection device 140. The OES detection device 140 can be positioned to measure optical emissions from a processing region 260 of the plasma between the substrate 200 and the top electrode 250.

[0018] In various embodiments, function generator 100 includes appropriate digital and / or analog circuitry, such as oscillators, pulse generators, modulators, and couplers. The function generator may be part of or include a controller unit for plasma processing system 20, enabling feedback control of the plasma process, for example, based on process monitoring using OES techniques. Function generator 100 can generate one or more arbitrary waveforms that can be used for both power modulation of the RF power supply and OES data acquisition. In certain embodiments, some of the power modulation may be performed by the RF power supply itself instead of the function generator. In such cases, function generator 100 may generate a pulse train synchronized with the power modulation by the RF power supply to acquire OES data. In certain embodiments, additional components (e.g., a wideband amplifier and a wideband impedance matching network) may be connected to the RF power supply, although not shown.

[0019] In certain embodiments, the power source may include a DC power source. The RF and / or DC power sources (e.g., RF power sources 240, 242, and 244) may be configured to generate continuous wave (CW) RF, pulsed RF, DC, pulsed DC, high frequency rectangular (e.g., square wave) or triangular (e.g., sawtooth) pulse trains, or a combination or superposition of two or more such waveforms. Additionally, the power sources may be configured to generate periodic functions, such as sine waves, whose characteristics, such as amplitude and frequency, can be adjusted during the plasma process.

[0020] A typical frequency of the RF source power can range from about 0.1 MHz to about 6 GHz. In certain embodiments, RF sources 242 and 244 can be used to simultaneously provide low-frequency RF power and high-frequency RF power, respectively.

[0021] In this disclosure, OES techniques are primarily directed to characterizing pulsed plasma processes. Pulsed plasma, in this disclosure, refers to any type of plasma in which the source power, bias power, or both are pulsed at any frequency. In various embodiments, pulsing at frequencies between 0.1 kHz and 100 kHz can be used to modulate the plasma source power or bias power. In certain embodiments, RF pulsing in the kHz range can be used to power the plasma. In various embodiments, any duty cycle (e.g., 0.1% to 99.9%) can be used for any plasma tool. In certain embodiments, moderate duty cycles of 10% to 70% or 10% to 80% can be used for capacitively coupled plasma (CCP), and 3% to 90% can be used for inductively coupled plasma (ICP). In one embodiment, a 1 MHz sinusoidal RF signal can be modulated with a 100 Hz on-off frequency. In another embodiment, a DC signal can be modulated with a 100 Hz on-off frequency. In yet another embodiment, a 1 MHz rectangular DC pulse signal may be modulated with an on-off frequency of 100 Hz. In an alternative embodiment, algorithms may be used to perform repetitive modulation of RF or fast DC pulse waveforms at lower frequencies (e.g., less than 100 Hz).

[0022] In RF pulsed plasmas, various parameters such as radical density, electron density, and electron temperature can change rapidly in response to power modulation, and their temporal profiles may not be adequately resolved using time-averaged, non-time-synchronized OES data acquisition methods employed for plasma process characterization. In various embodiments, the methods described in this disclosure use function generator 100 to synchronize power modulation for plasma control with OES data acquisition, thereby allowing selective acquisition of OES spectra for portions of one pulse cycle during power modulation.

[0023] Various configurations may be used for the plasma processing system 20 with the OES detection device 140. For example, the plasma processing system 20 may be a capacitively coupled plasma (CCP) system, as shown in FIG. 2, or an inductively coupled plasma (ICP) system. In alternative embodiments, the plasma processing system 20 may include a resonator, such as a helical resonator. Additionally, microwave plasma (MW) or other suitable systems may also be used. In various embodiments, RF power, chamber pressure, substrate temperature, gas flow rates, and other plasma processing parameters may be selected according to a respective process recipe.

[0024] FIG. 3 shows a schematic diagram of an OES detection device 140 and its components according to various embodiments.

[0025] OES detection device 140 may include sensor 300, transceiver 302, filter 304, memory 306, and processor 308. In various embodiments, OES detection device 140 may be configured to receive commands from function generator 100 (FIGS. 1 and 2) and, in response, perform a series of operations: acquire OES data with sensor 300, receive OES data with transceiver 302, filter the OES data with filter 304, and determine characteristics of the pulsed plasma with processor 308. The characteristics of the pulsed plasma may be, for example, plasma density and / or concentrations of reactive ion species, etch by-products, or other species of interest. The characteristics of the pulsed plasma may also include information about electron temperature. In certain embodiments, OES detection device 140 may further be configured to process the acquired OES data, for example, by averaging and / or smoothing, before determining the characteristics of the pulsed plasma.

[0026] When acquiring OES data, sensor 300 may include, for example, a spectrometer that samples the optical emission spectrum of the plasma. In this example, the spectrum may include light intensity as a function of wavelength or frequency. Sensor 300 may include a charge-coupled device (CCD) sensor, a complementary metal-oxide semiconductor (CMOS) image sensor, or other type of light-detecting device, or may utilize an optical sensor to measure light intensity in the plasma processing chamber of plasma processing system 20. In certain embodiments, sensor 300 may include a CCD sensor with millisecond time resolution. In other embodiments, sensor 300 may include a CMOS image sensor with microsecond time resolution.

[0027] In various embodiments, memory 306 may include a non-statutory computer-readable storage medium for storing instructions executed by processor 308 to perform the various functions described herein. For example, memory 306 may generally include both volatile and non-volatile memory (e.g., RAM, ROM, etc.). Memory 306 may be referred to herein as a memory or a computer-readable storage medium. Memory 306 may store computer-readable, processor-executable program instructions as computer program code that may be executed by processor 308 as a particular machine configured to perform the operations and functions described in the implementations herein.

[0028] The OES detection device 140 can collect multiple wavelength emission spectra resulting from the glow discharge of gases in the plasma processing chamber. These wavelengths can be associated with specific chemical species generated from the incoming reactant gases and can result from gas-phase reactions as well as reactions at the wafer and chamber surfaces. The OES detection device 140 can be configured to detect a variety of chemical species, including silicon halides and halogen species themselves (e.g., Cl, F, Br). In certain embodiments, the plasma process can include etching silicon oxide using fluorine-containing chemicals such as fluorocarbon or hydrofluorocarbon gases. In such embodiments, dynamic detection of silicon halides and halogen species (F) released by decomposition of the fluorocarbon or hydrofluorocarbon gas is useful for monitoring the progress and stability of the etching process. Other detectable by-products include carbon monoxide (CO) and carbon dioxide (CO), formed by the reaction of oxygen (O) from the film or gas mixture with carbon (C) from the fluorocarbon or hydrofluorocarbon gas.

[0029] As the structure of the wafer's surface shifts from steady-state etching to complete removal of the etched material, the wavelength of the emission spectrum may also shift. Detecting this shift can provide useful information about the plasma process, such as information for determining the etch endpoint, indicating completion of the required etch.

[0030] In various embodiments, the configuration of OES detection device 140 may be specifically tailored to the type of plasma discharge typically used in plasma processing system 20. For example, the species and wavelength ranges for detection may differ for high density ICP, low density CCP, electron cyclotron resonance (ECR) plasma, etc.

[0031] FIG. 4 illustrates an example of a pulsing scheme for generating a pulsed plasma, according to various embodiments.

[0032] Various pulsing schemes may be used for plasma processes characterized by OES techniques. Exemplary embodiments are shown in Figure 4: (a) source power pulsed with a pulse train without bias power (source pulsing), (b) source power pulsed with a pulse train with constant bias power (source pulsing), (c) constant source power with bias power pulsed with a pulse train (bias pulsing), (d) source power pulsed with a first pulse train with bias power pulsed with a second pulse train offset from the first pulse train (synchronous pulsing with offset), and (e) source power pulsed with a first pulse train with bias power pulsed with a second pulse train identical to the first pulse train (synchronous pulsing without offset). These are merely examples, and other pulsing schemes may be possible in other embodiments. Furthermore, plasma processes may employ power modulation including any combination of these or other schemes, thereby having three or more distinct stages for each pulse period. 4 shows the pulse train as switching only between an on state and an off state, in one or more embodiments, the source power or bias power pulse train may instead switch between two on states: a high power level and a low power level. Furthermore, in alternative embodiments, the pulse train may include more than two power levels (e.g., two on states and an off state).

[0033] FIG. 5 shows modeled temporal profiles of radical density, electron density, and electron temperature for a pulsed plasma according to various embodiments.

[0034] In response to the pulsing of the plasma power, the parameters of the pulsed plasma change rapidly with time. Figure 5 shows the radical density (n r ), electron density (n e ) and electron temperature (T e5 shows several example time-normalized decay profiles for a given time period (t1). In this example, source power is turned on at t1 and turned off at t2. In FIG. 5, the time profile has three periods: overshoot period 1, stable on period 2, and decay period 3. First, in response to providing sufficient source power at t1, if an appropriate gas flows under an appropriate pressure, a plasma can be generated in the plasma processing chamber. Overshoot period 1 is an initial, short, transient period that shows a rapid change from the plasma off state to the on state before the plasma stabilizes. During this period, as shown in FIG. 5, the electron temperature T e may spike before dropping to a stable level, while the radical density (n r ) and electron density (n e ) may increase without overshooting the stable level. This profile in FIG. 5 is only an example, and in other embodiments, any parameter may behave differently (e.g., with or without overshoot). In one embodiment, the overshoot period may be assumed to be the first 10 μs or less after t1.

[0035] The stable on-period 2 is the subsequent period, during which n r , n e and / or T e is considered stable, with period 2 ending at t2 when the source power is turned off. In one embodiment, a parameter is considered stable if its rate of change is below a set threshold rate and maintained for at least a set threshold duration. In another embodiment, the start of stable on period 2 may be determined based on the expected duration of overshoot period 1. In yet another embodiment, OES techniques may be used to monitor the plasma to thereby determine the transition from overshoot period 1 to stable on period 2.

[0036] Decay period 3 is the period from after t2 to the start of the next pulse cycle (not shown in FIG. 5), during which n r , n e and T edecay at significantly different rates. In one embodiment, the decay times taken for these parameters to decrease to negligible levels are r About 1ms or more, n e About 100 μs, T e The pulse frequency determines the duration of each pulse (i.e., the total duration of the overshoot period 1, the stable on period, and the decay period 3). For example, according to certain embodiments, for a pulse frequency in the range of 0.1 kHz to 10 kHz, each pulse may be 100 μs to 10 ms. In one or more embodiments, each pulse may be 1 ms to 100 ms (i.e., a pulse frequency of 10 Hz to 1 kHz). Thus, depending on the pulse frequency, the parameters (e.g., n r or n e ) decays to a negligible level, the next pulse cycle can begin.

[0037] In various embodiments, OES techniques can be used to selectively acquire OES data for any one or more periods of interest (i.e., overshoot period 1, stable-on period, or decay period 3) to characterize a pulsed plasma with power modulation. OES data collected only for a selected period of interest during power modulation can be used to determine characteristics of the pulsed plasma (e.g., plasma density) for that selected period of interest. Because OES detects optical emissions from excited species in the plasma, particularly in the example shown in FIG. 5 where source power is pulsed without bias power, the window for OES data acquisition during decay period 3 can be limited due to little or no optical emission. However, this window for OES detection during decay period 3 can be substantially expanded and enabled by the use of bias power that maintains a certain level of plasma heating.

[0038] It should also be noted that Figure 5 shows only a portion of one pulse cycle of power modulation. For plasma processes on time scales substantially longer than one pulse cycle, n r , n e , Te and other parameters may vary periodically with the pulse cycle. In certain embodiments, similar or identical time-normalized decay profiles may be reproduced for each pulse cycle. However, under certain conditions, it may still occur that a stable plasma may not be established even with power modulation, or that a certain induction time may be required to establish a stable plasma. In such cases, the temporal profile may vary from pulse to pulse. In various embodiments, selective OES data acquisition advantageously enables a method for characterizing such stability, or lack thereof, of a pulsed plasma by collecting data from multiple pulse cycles.

[0039] 6A-6B show example schemes for OES data acquisition synchronized with power pulsing of a pulsed plasma, according to various embodiments. Several exemplary embodiments of selective OES data acquisition synchronized with plasma pulsing are described. FIG. 6A shows an exemplary time diagram of source power pulsing with selective OES data acquisition.

[0040] In this embodiment of FIG. 6A , the source power is pulsed while continuous bias power is provided. The source power pulsing mode can advantageously enable separation of the gas excitation phase (source power on) and the excited species consumption phase (source power off) in a plasma etching process. Such separation is made possible by the rapid changes in plasma parameters caused by plasma pulsing. However, characterizing the plasma separately during each phase is difficult with conventional OES techniques, such as continuous OES data acquisition. According to various embodiments, synchronizing OES data acquisition with plasma pulsing enables selective acquisition of OES data for regions of interest. In the illustrated example, the first set of OES measurements (a in FIG. 6A ) may be performed only during the source power on phase. In certain embodiments, a single OES measurement may take less than 10 ms, and in one or more embodiments, approximately 4 ms. In other embodiments, submillisecond (microsecond-scale) time resolution may also be achieved using appropriate sensors. Although FIG. 6A shows only one OES measurement for the source power-on phase per pulse cycle, more than one OES measurement may be performed. The number of OES measurements per pulse cycle may be selected based on the pulsing frequency and duty cycle. Collecting multiple OES data may help improve the signal-to-noise ratio of the data through averaging, filtering, and / or smoothing. In an alternative embodiment, each set of OES data for each pulse cycle may be compared to each other to determine plasma stability over the duration of multiple plasma pulse cycles. Furthermore, the number of OES measurements per pulse cycle may be less than one. For example, each OES measurement may be performed every 10 pulse cycles.

[0041] Additionally, a second set of OES measurements (FIG. 6A, b) can be performed during the source power-off phase. In one embodiment, the second set of OES data can be analyzed and used to compare with the first set of OES data. Such analysis can aid in understanding plasma characteristics using source power pulsing. For example, selective OES data acquisition for two periods can quantitatively characterize the high-power plasma excitation period and the low-power "source power-off" period. These trends can therefore indicate a discharge transition from a high-density plasma (inductively coupled) to a low-density plasma (capacitively coupled). Without wishing to be limited by any theory, OES data analysis in these embodiments can be used to provide information about the total emission intensity, which reflects plasma density and electron temperature.

[0042] An exemplary time diagram of bias power pulsing with selective OES data acquisition is shown in Figure 6B. In this embodiment, the bias power is pulsed while continuous source power is provided.

[0043] The bias power pulsing mode can advantageously improve by-product removal in plasma etching processes, where etching occurs primarily when the bias power is on and by-product evacuation (removal) occurs when the bias power is off. In these embodiments, a first set of OES measurements can be performed when the bias power is off (FIG. 6B, a). Without wishing to be limited by any theory, OES data analysis in these embodiments can be used to provide information about specific chemical species (e.g., etch by-products). OES data selectively acquired during the bias power off phase can be assumed to reflect the concentration of etch by-products and can be used to monitor the progress of by-product evacuation (removal). Based on the acquired information, the plasma etching process recipe can be updated to optimize process parameters such as pulsing frequency and duty ratio.

[0044] Additionally, a second set of OES measurements (b in FIG. 6B) may be performed during the bias power-on phase. The second set of OES data may be analyzed separately from the first set of OES data to, for example, monitor the generation of etch by-products in the plasma etch process. The first and second sets of OES data may also be compared to each other to calculate the difference in etch rate between the two time periods based on the quantification of the etch by-products. In certain embodiments, information obtained by OES data analysis may further be used to update process recipes and optimize plasma etch processes. For example, the OES techniques herein may advantageously help reduce dissociation and redeposition of etch by-products on surfaces, which are detrimental to effective etching.

[0045] While one or two sets of selective OES data acquisition are described above with reference to Figures 6A and 6B, the OES technique can also employ three or more sets to characterize more periods during a pulse cycle. In one embodiment, three sets of selective OES data acquisition may be performed for the overshoot period, the stable-on period, and the decay period, as previously shown in Figure 5. OES data from the overshoot period may be particularly useful for understanding rapid changes in plasma properties during transient periods.

[0046] As previously described with reference to FIG. 4 , various types of pulsing schemes can be used and applied with the OES techniques of the present disclosure. Thus, each pulse cycle can include a different temporal profile of plasma parameters than those shown in FIGS. 6A and 6B . For example, both the source power and the bias power can be pulsed (synchronous pulsing) to obtain a pulsed plasma. In one or more embodiments, the two powers can be pulsed at a common pulsing frequency. The duty ratios of each power can be the same or different. Furthermore, the source power and the bias power can be offset from one another or fully synchronized (e.g., FIG. 4 ). In some examples, more than three distinct periods can be obtained per pulse cycle. The selective OES data acquisition of the OES techniques described above can also be applied to such examples. In one embodiment, the OES techniques can be applied to study ignition instabilities specific to the synchronous pulsing mode of pulsed plasma.

[0047] In various embodiments, OES techniques can be used as a plasma diagnostic tool to examine plasma characteristics (e.g., plasma density and radical density) as a function of plasma conditions (e.g., source power, bias power, gas flow rate, pressure, and / or power modulation). As a result, OES techniques can be useful for identifying plasma stability conditions for various advanced pulsing regimes. OES techniques can also be applied to plasma processes (e.g., deposition and / or etching processes) for real-time monitoring of the plasma process. OES techniques can be advantageously versatile regardless of the type of plasma process, as OES can measure as long as sufficient radiation is available from the plasma and the OES detection device can operate without interfering with any plasma process detection devices. In one example, OES techniques can be used to determine the endpoint of a plasma etching process. Alternatively, OES techniques can include a plasma stability diagnostic step before initiating the plasma process. Selective OES data acquisition and subsequent analysis can be configured to determine that the pulsed plasma is stable for at least a specific duration exceeding one pulse cycle. The plasma process can be initiated when the pulsed plasma is determined to be stable (e.g., FIG. 7C).

[0048] 7A-7C show process flow diagrams of methods for characterizing pulsed plasma using OES according to various embodiments.

[0049] In FIG. 7A, process flow 70 begins with generating a pulsed plasma in a plasma processing chamber (block 710). In various embodiments, each pulse of the pulsed plasma includes three periods: an overshoot period, a stable-on period, and a decay period. Next, repetitive optical emission spectroscopy (OES) measurements may be performed on the pulsed plasma using an OES system of the plasma processing system (block 720). The repetitive OES measurements may include acquiring first OES data during one of the three periods from two or more pulses of the pulsed plasma (block 722) and acquiring characteristics of the pulsed plasma during one of the three periods based solely on the first OES data (block 724). Characteristics of the pulsed plasma that may be derived from the first OES data include plasma density, radical density, and concentration of the species of interest.

[0050] In FIG. 7B, process flow 72 begins with performing plasma processing on a substrate in a plasma processing chamber by exposing the substrate to a pulsed plasma in the plasma processing chamber, where the pulsed plasma is provided with a source power and a pulsed bias power at a bias power frequency (block 712). First OES data may then be repeatedly acquired at the bias power frequency when the bias power is off and the source power is on (block 723). In various embodiments, the bias power frequency may be between 0.1 kHz and 100 kHz. In certain embodiments, the process may further proceed to performing a temporal analysis of the chemical composition of the pulsed plasma based on the first OES data (block 730).

[0051] In FIG. 7C , process flow 74 begins by providing a source power and a bias power to produce a pulsed plasma process in a plasma processing chamber according to initial conditions of process parameters, where the source power or the bias power is pulsed (block 710). In various embodiments, each pulse of the pulsed plasma includes three periods: an overshoot period, a stable-on period, and a decay period. Next, OES data may be acquired during one of the three periods from two or more pulses of the pulsed plasma (block 722). The process then proceeds to determining whether the pulsed plasma is stable by comparing the OES data between pulses of the pulsed plasma (block 740). If it is determined that the pulsed plasma is not stable, one or more process parameters may be changed from the initial conditions of the process parameters (block 760). In certain embodiments, after changing one or more process parameters, the steps of selectively acquiring OES data (block 722) and determining (block 740) may be repeated until it is determined that the pulsed plasma is stable. If the pulsed plasma is determined to be stable, then in certain embodiments, plasma processing may be performed by exposing a substrate in the plasma processing chamber to the pulsed plasma (block 750).

[0052] Illustrative embodiments of the present invention are summarized here, with other embodiments being apparent from the specification as a whole and from the claims filed herewith.

[0053] Example 1. A method for characterizing a plasma in a plasma processing system, the method comprising: generating a pulsed plasma in a plasma processing chamber of the plasma processing system, the pulsed plasma being powered with a pulsed power signal, each pulse of the pulsed plasma including three periods: an overshoot period, a stable-on period, and a decay period; performing repetitive optical emission spectroscopy (OES) measurements of the pulsed plasma, the repetitive OES measurements comprising acquiring first OES data from two or more pulses of the pulsed plasma during one of the three periods; and acquiring characteristics of the pulsed plasma for one of the three periods based only on the first OES data.

[0054] Example 2. The method of Example 1, wherein the pulsed power signal is for source power or bias power and is pulsed at a frequency between 0.1 kHz and 100 kHz.

[0055] Example 3. The method of example 1 or 2, wherein one measurement of the first plurality of OES data takes less than 100 ms.

[0056] Example 4. The method of any one of Examples 1-3, wherein the first OES data is collected during an overshoot period, and the repeat OES measurement further includes acquiring second OES data during a stable-on period or a decay period from two or more pulses of the pulsed plasma, and acquiring characteristics of the pulsed plasma for the stable-on period or the decay period based solely on the second OES data.

[0057] Example 5. The method of any one of Examples 1-3, wherein the first OES data is collected during a stable on period, and the repeat OES measurement further includes acquiring second OES data during a decay period from two or more pulses of the pulsed plasma, and acquiring a characteristic of the pulsed plasma for the decay period based solely on the second OES data.

[0058] Example 6. The method of any one of Examples 1-5, wherein the pulsed plasma characteristic includes plasma density.

[0059] Example 7. A method of processing a substrate, the method including: performing plasma processing on a substrate in a plasma processing chamber by exposing the substrate in the plasma processing chamber to a pulsed plasma, the pulsed plasma being provided with a source power and a pulsed bias power at a bias power frequency; and repeatedly acquiring first optical emission spectroscopy (OES) data when the bias power is off and the source power is provided, the first OES data being acquired at the bias power frequency.

[0060] Example 8. The method of Example 7, wherein the bias power frequency is between 0.1 kHz and 100 kHz.

[0061] Example 9. The method of example 7 or 8, wherein each of the first OES data is acquired by an OES measurement of less than 100 ms.

[0062] Example 10. The method of any one of Examples 7-9, further comprising performing a temporal analysis of the chemical composition of the pulsed plasma based on the first OES data.

[0063] Example 11. The method of any one of Examples 7-10, wherein acquiring the first OES data and temporal analysis is performed while performing a plasma treatment.

[0064] Example 12. The method of any one of Examples 7-11, wherein the plasma treatment is a plasma etching treatment and the temporal analysis of chemical composition includes monitoring etching by-products.

[0065] Example 13. The method of any one of Examples 7-12, further comprising repeatedly acquiring second OES data when the bias power is on, the second OES data being acquired at the bias power frequency.

[0066] Example 14. The method of any one of Examples 7-13, wherein the source power is pulsed source power at a source power modulation frequency, and the method further includes repeatedly acquiring third OES data when the source power is on, the third OES data being acquired at the source power frequency.

[0067] Example 15. An optical emission spectroscopy (OES) apparatus comprising: a plasma processing chamber configured to hold a substrate to be processed; an RF power source configured to generate a pulsed plasma in the plasma processing chamber; an OES detection device connected to the plasma processing chamber, the OES detection device configured to measure an OES signal from the pulsed plasma; a microprocessor; and a non-transitory memory storing a program executed by the microprocessor, the program comprising instructions for generating a first pulse train and a second pulse train, the first pulse train and the second pulse train being synchronized; powering the RF power source and generating the pulsed plasma based on the first pulse train; and collecting an OES data set with the OES detection device based on the second pulse train.

[0068] Example 16. The OES apparatus of Example 15, wherein the two pulse trains are configured such that the OES data set is collected only when the RF power is on.

[0069] Example 17. The OES apparatus of Example 15, wherein the two pulse trains are configured such that the OES data set is collected only when the RF power is off.

[0070] Example 18. The OES apparatus of any one of Examples 15-17, wherein the program further comprises instructions for performing a temporal analysis of the pulsed plasma based on the OES data set.

[0071] Example 19. The OES apparatus of any one of Examples 15-18, wherein the program further includes instructions for determining whether the pulsed plasma is stable based on the temporal analysis, and if the pulsed plasma is determined to be not stable, updating the first pulse train and the second pulse train, powering the RF power source based on the updated first pulse train, and collecting another set of OES data with the OES detection device based on the updated second pulse train.

[0072] Example 20. An OES apparatus according to any one of Examples 15-19, wherein the OES detection device has a time resolution of detection of less than 100 ms.

[0073] Example 21. A method for characterizing a plasma in a plasma processing system, the method comprising: generating a pulsed plasma process in a plasma processing chamber according to an initial condition of process parameters, the pulsed plasma being provided with a source power and a bias power, wherein the source power or the bias power is pulsed, and each pulse of the pulsed plasma includes three periods: an overshoot period, a stable-on period, and a decay period; selectively acquiring OES data during one of the three periods from two or more pulses of the pulsed plasma; determining whether the pulsed plasma is stable by comparing the OES data between the pulses of the pulsed plasma; and if the pulsed plasma is determined to be not stable, modifying one or more process parameters from the initial condition of the process parameters.

[0074] Example 22. The method of Example 21, further comprising repeating the steps of selectively acquiring OES data after modifying one or more process parameters and determining until the pulsed plasma is determined to be stable.

[0075] Example 23. The method of Example 21 or 22, further comprising, after the pulsed plasma is determined to be stable, performing a plasma treatment by exposing a substrate in the plasma treatment chamber to the pulsed plasma.

[0076] Example 24. The method of Example 5 or 6, wherein the repetitive OES measurements further include selectively acquiring third OES data during an overshoot period from two or more pulses of the pulsed plasma, and acquiring a characteristic of the pulsed plasma during the overshoot period based on the third OES data.

[0077] While the present invention has been described with respect to exemplary embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the exemplary embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art upon reference to this description. It is therefore intended that the appended claims cover any such modifications or embodiments.

Claims

1. 1. A method for characterizing a plasma in a plasma processing system, comprising: generating a pulsed plasma in a plasma processing chamber of the plasma processing system, the pulsed plasma being powered using a pulsed power signal, each pulse of the pulsed plasma including three periods: an overshoot period, a stable on period, and a decay period; and performing repetitive optical emission spectroscopy (OES) measurements of the pulsed plasma, the repetitive OES measurements comprising: acquiring first OES data during one of the three time periods from two or more pulses of the pulsed plasma; and obtaining a characteristic of the pulsed plasma for the one of the three time periods based solely on the first OES data.

2. 10. The method of claim 1, wherein the pulsed power signal is for source power or bias power and is pulsed at a frequency between 0.1 kHz and 100 kHz.

3. The method of claim 1 , wherein one measurement of the first OES data takes less than 100 ms.

4. The first OES data is collected during the overshoot period, and the repeat OES measurements are acquiring second OES data during the stable-on period or the decay period from two or more pulses of the pulsed plasma; The method of claim 1 , further comprising: obtaining a characteristic of the pulsed plasma for the stable-on period or the decay period based solely on the second OES data.

5. The first OES data is collected during the stable on-period, and the repeat OES measurements are acquiring second OES data during the decay period from two or more pulses of the pulsed plasma; The method of claim 1 , further comprising: obtaining a characteristic of the pulsed plasma for the decay period based solely on the second OES data.

6. The method of claim 1 , wherein the characteristics of the pulsed plasma include plasma density.

7. 1. A method of processing a substrate, comprising: performing a plasma process on a substrate in a plasma processing chamber by exposing the substrate to a pulsed plasma in the plasma processing chamber, the pulsed plasma being provided with a source power and a pulsed bias power at a bias power frequency; repeatedly acquiring first optical emission spectroscopy (OES) data when the pulsed bias power is off and the source power is provided, the first OES data being acquired at the bias power frequency.

8. The method of claim 7, wherein the bias power frequency is between 0.1 kHz and 100 kHz.

9. The method of claim 7 , wherein each of the first OES data is acquired by an OES measurement lasting less than 100 ms.

10. The method of claim 7 , further comprising performing a temporal analysis of the chemical composition of the pulsed plasma based on the first OES data.

11. The method of claim 10 , wherein the acquiring of the first OES data and the temporal analysis are performed while the plasma processing is being performed.

12. The method of claim 10 , wherein the plasma process is a plasma etching process, and the temporal analysis of chemical composition includes monitoring etching by-products.

13. The method of claim 7 , further comprising repeatedly acquiring second OES data when the pulsed bias power is on, the second OES data being acquired at the bias power frequency.

14. 8. The method of claim 7, wherein the source power is pulsed source power at a source power modulation frequency, the method further comprising repeatedly acquiring third OES data when the source power is on, the third OES data being acquired at the source power modulation frequency.

15. 1. An optical emission spectroscopy (OES) apparatus comprising: a plasma processing chamber configured to hold a substrate to be processed; an RF power source configured to generate a pulsed plasma within the plasma processing chamber; an OES detection device connected to the plasma processing chamber, the OES detection device configured to measure an OES signal from the pulsed plasma; a microprocessor; a non-transitory memory for storing a program to be executed by the microprocessor, the program including: generating a first pulse train and a second pulse train, the first pulse train and the second pulse train being synchronized; powering the RF power source and generating the pulsed plasma based on the first pulse train; collecting an OES data set with the OES detection device based on the second pulse train.

16. 16. The OES apparatus of claim 15, wherein the first and second pulse trains are configured such that the OES data set is collected only when the RF power source is on.

17. 16. The OES apparatus of claim 15, wherein the first and second pulse trains are configured such that the OES data set is collected only when the RF power source is off.

18. 16. The OES apparatus of claim 15, wherein the program further comprises instructions for performing a temporal analysis of the pulsed plasma based on the OES data set.

19. The program determining whether the pulsed plasma is stable based on the temporal analysis; and updating the first pulse train and the second pulse train when it is determined that the pulsed plasma is not stable; energizing the RF power source based on the updated first pulse train; 20. The OES apparatus of claim 18, further comprising instructions to: collect another set of OES data with the OES detection device based on the updated second pulse train.

20. 20. The OES apparatus of claim 18, wherein the OES detection device has a time resolution of detection of less than 100 ms.

Images