JP7263676B2 - Method for controlling ion energy distribution in process plasma - Google Patents

Description

No. 62/657,301 entitled "Apparatus and Method for Controlling Ion Energy Distribution in Process Plasmas" by Yoshida et al. No. 62/657,272 entitled "Method for Ion Mass Separation and Ion Energy Control in Process Plasmas" by Yoshida et al. the disclosure of which is expressly incorporated by reference in its entirety.

The present disclosure relates to substrate processing in a plasma processing apparatus. In particular, the present disclosure provides apparatus and methods for controlling plasma generated in a plasma processing apparatus.

The use of plasma systems for processing substrates has been known for some time. For example, plasma processing of semiconductor wafers is well known. Plasma systems are typically utilized for plasma etching processes and/or plasma deposition processes. Plasma processing presents many technical challenges, and control of the plasma becomes more important as features and layer geometries on substrates continue to shrink. Generally, a plasma is generated by applying radio frequency power to a gas mixture in a chamber that separates the plasma from the surrounding environment. The performance of plasma processes is affected by many factors and variables, including ion species, ion density, ion kinetic energy, reactive neutrals, and the like.

Variable settings of the plasma processing apparatus can be adjusted to alter plasma characteristics to achieve desired process performance. These settings include, but are not limited to, gas flow rates, gas pressures, power for plasma excitation, bias voltages, etc., all of which are well known in the art. One of the challenges in achieving desired performance is the controllability of plasma properties. The variable settings have limited control since they are not directly related to plasma properties. As substrate processing requirements become more challenging, better controllability of plasma properties is required.

In one exemplary embodiment, innovative plasma processing methods and systems are described herein that utilize control of ion energy in a plasma by using multiple harmonic frequency components for plasma excitation. be. More specifically, the relative amplitudes and/or phase shifts between different frequency components are controlled to provide desired ion energy plasma characteristics. Relative amplitudes and/or phase shifts can be controlled without direct and/or manual ion energy measurements. Rather, the ion energy within the plasma is determined by one or more of the parameters within the plasma device, such as, for example, impedance levels, radio frequency (RF) generator electrical signals, matching circuit electrical signals, and other circuit electrical signals of the plasma processing device. can be dynamically controlled by monitoring the electrical properties of Therefore, since ion energy cannot be measured directly in plasma equipment for mass production of substrates, a technique is provided to quickly and accurately control ion energy distribution in a plasma processing system. Ion energy monitoring and control can be implemented dynamically during the plasma process to maintain the desired ion energy distribution. Thus, the techniques described herein can advantageously provide in-situ ion energy optimization in multiple harmonic frequency systems, e.g., without the use of ion energy sensors, and e.g. A dynamic control function can be provided to maintain optimum operating conditions of the distribution. Other advantages will be recognized with the benefit of the disclosure provided herein.

In one embodiment, a plasma processing system is provided that is capable of plasma processing a substrate. a process chamber, coupled to the process chamber and configured to provide RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency; and one or more RF power sources, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The system further includes control circuitry coupled to at least one other component of the plasma processing system for receiving at least one electrical characteristic of the plasma processing system during plasma processing of the substrate. The system comprises at least one output of a control circuit coupled to at least one of the one or more RF power sources, the one or more RF power sources providing a desired ion energy distribution during plasma processing of the substrate. It also includes at least one output configured to adjust characteristics of the fundamental frequency voltage and/or the second frequency voltage so as to obtain a .

In another embodiment, a method is provided for plasma processing a substrate. The method includes providing a process chamber and one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second voltage at a second frequency. Coupling the power source, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The method also includes monitoring at least one electrical characteristic of the plasma processing system during plasma processing of the substrate. The method includes adjusting the phase difference between the fundamental frequency voltage and the second frequency voltage and/or the amplitude of the fundamental frequency voltage and the second frequency voltage to obtain a desired ion energy distribution during plasma processing of the substrate. Further comprising adjusting the ratio during plasma processing.

In yet another embodiment, a method is provided for processing a substrate. The method includes providing a process chamber and one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second voltage at a second frequency. Coupling the power source, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The method also includes coupling a matching circuit between the process chamber and one or more RF power sources. The method further includes monitoring at least the impedance of the process chamber seen by the matching circuit during plasma processing of the substrate. The method also includes adjusting the phase difference between at least the fundamental frequency voltage and the second frequency voltage during plasma processing to obtain a desired ion energy distribution during plasma processing of the substrate.

In another exemplary embodiment, by controlling the application of the applied RF power, specifically the relationship between the fundamental RF frequency and the harmonic frequency, the ion energy distribution of ions of different masses is simultaneously controlled. Techniques for controlling the ion energy distribution within a plasma are described herein. Thus, the technique allows ion energy control for ions of different masses. By controlling the RF power distribution between the two frequencies, the characteristics of the plasma process can be changed. For example, the ions that dominate etching can be selectively based on whether the ions are lighter or heavier than other ions. Similarly, the atomic layer etch process can be controlled such that the process can be switched between layer modification and layer etch steps by adjusting the RF frequency. Such switching can be done within the same gas phase of the plasma process. Thus, a common gas phase of the plasma can be used for both the layer modification and layer etch steps while the system is in the layer modification or layer etch step with adjustment of the RF power supply. In one embodiment, controlling RF power includes controlling phase differences and/or amplitude ratios between the fundamental RF frequency and the harmonic frequencies. In addition, the control of the phase difference and/or the amplitude ratio can be controlled within the plasma device such as, for example, impedance levels, radio frequency (RF) generator electrical signals, matching circuit electrical signals and other circuit electrical signals of the plasma processing device. Detection of one or more electrical properties may be relied upon.

In one embodiment, a method is provided for plasma processing a substrate. The method includes providing a process chamber and one or more RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency. Coupling the RF power source, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The method comprises providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of The type of ions has a second mass, and the first mass and the second mass are different masses. By adjusting the relationship between the fundamental frequency voltage and the second frequency voltage to allow selective control of the ion energy distribution based on the first mass and the second mass, the method comprises: It also includes controlling the ion energy distribution of the first type of ions and the second type of ions.

In another embodiment, a method is provided for plasma etching a substrate. The method includes providing a process chamber and one or more RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency. Coupling the RF power source, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The method comprises providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of The type of ion has a second mass, the first mass and the second mass being different masses. By adjusting the relationship between the fundamental frequency voltage and the second frequency voltage to allow selective control of the ion energy distribution based on the first mass and the second mass, the method comprises: It also includes controlling the ion energy distribution of the first type of ions and the second type of ions. Controlling the ion energy distribution allows for selectively controlling the etching effects of at least one of the first type of ions and the second type of ions.

In yet another embodiment, a method is provided for plasma etching a substrate. The method includes providing a process chamber and one or more RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency. Coupling the RF power source, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency. The method comprises providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of The type of ion has a second mass, the first mass being heavier than the second mass, further comprising providing. The method includes adjusting the phase difference between the fundamental frequency voltage and the second frequency voltage and/or the amplitude ratio between the fundamental frequency voltage and the second frequency voltage to obtain the first type of ions and the second frequency voltage. and controlling the ion energy distribution of ions of the type Controlling the ion energy distribution produces an asymmetric ion energy distribution of at least one of the first type of ions or the second type of ions, and the asymmetric ion energy distribution for the first type of ions It is used to adjust the etching effect of the second type of ions.

A more detailed understanding of the invention and its advantages can be obtained by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals indicate like features. However, the accompanying drawings depict only exemplary embodiments of the disclosed concepts and are therefore not to be considered limiting of scope, but rather other equally effective embodiments of the disclosed concepts. Note that it is possible to allow

1 depicts an exemplary plasma processing system for implementing the plasma processing techniques described herein. 1 shows a plot of bimodal ion energy distribution in prior art plasma processing. Figure 2 shows the phase shift and amplitude difference between the fundamental frequency power supply and the harmonic frequency power supply; FIG. 4 shows plots of exemplary ion energy distributions that can be obtained when using a harmonic frequency power source in addition to a fundamental frequency power source; FIG. FIG. 4 shows plots of exemplary ion energy distributions without the use of a harmonic frequency source and with a harmonic frequency source at different phase shifts. FIG. Figure 3 shows the effect of different phase shifts of the harmonic frequency power supply on the amount of silicon oxide and silicon nitride etched as a function of bias power. Figure 2 shows the effect of different phase shifts of the harmonic frequency power supply on the etch selectivity between the silicon oxide etch rate and the silicon nitride etch rate as a function of the bias wave. Fig. 2 shows a plot of a typical symmetrical bimodal ion energy distribution in plasma processing with ions of different masses; FIG. 4 shows plots of asymmetric ion energy distributions, including etch thresholds, for plasma processing with ions of different masses utilizing the harmonic frequency technique described herein. FIG. 5 shows another asymmetric ion energy distribution plot including etch threshold for plasma processing with ions of different masses utilizing the harmonic frequency technique described herein. FIG. 11 shows plots of the asymmetric ion energy distributions of FIGS. 9 and 10 including different etch thresholds for use in an atomic layer etch process; FIG. 11 shows plots of the asymmetric ion energy distributions of FIGS. 9 and 10 including different etch thresholds for use in an atomic layer etch process; Figures 9 and 10 show plots of the asymmetric ion energy distributions of Figures 9 and 10 including different etch thresholds for use in different atomic layer etch processes; Figures 9 and 10 show plots of the asymmetric ion energy distributions of Figures 9 and 10 including different etch thresholds for use in different atomic layer etch processes; 1 illustrates an exemplary method for using the plasma processing techniques described herein. 1 illustrates an exemplary method for using the plasma processing techniques described herein. 1 illustrates an exemplary method for using the plasma processing techniques described herein. 1 illustrates an exemplary method for using the plasma processing techniques described herein. 1 illustrates an exemplary method for using the plasma processing techniques described herein.

It has been found that plasma processing results can be improved by controlling the application of fundamental frequency RF power and RF power at harmonic frequencies of the fundamental frequency. In one exemplary embodiment, innovative plasma processing methods are described herein that utilize control of ion energy in a plasma by using multiple harmonic frequency components for plasma excitation. More specifically, the relative amplitudes and/or phase shifts between different frequency components are controlled to provide desired ion energy plasma characteristics. Relative amplitudes and/or phase shifts can be controlled without direct and/or manual ion energy measurements. Rather, the ion energy within the plasma is a function of one of the plasma processing system, such as, for example, the impedance level, the electrical signal of a radio frequency (RF) generator, the electrical signal of a matching circuit, and/or the electrical signals of other circuits of the plasma processing apparatus. Or it can be dynamically controlled by monitoring multiple electrical properties. Therefore, since ion energy cannot be measured directly in plasma equipment for mass production of substrates, a technique is provided to quickly and accurately control ion energy distribution in a plasma processing system. Ion energy monitoring and control can be implemented dynamically during the plasma process to maintain the desired ion energy distribution. Thus, the techniques described herein can advantageously provide in-situ ion energy optimization in multiple harmonic frequency systems, e.g., without the use of ion energy sensors, and e.g. A dynamic control function can be provided to maintain optimum operating conditions of the distribution. Other advantages will be recognized with the benefit of the disclosure provided herein.

In another exemplary embodiment, by controlling the application of the applied RF power, specifically the relationship between the fundamental RF frequency and the harmonic frequency, the ion energy distribution of ions of different masses is simultaneously controlled. Techniques for controlling the ion energy distribution within a plasma are described herein. Thus, the technique allows ion energy control for ions of different masses. By controlling the RF power frequency, the characteristics of the plasma process can be changed. For example, the ions that dominate etching can be selectively based on whether the ions are lighter or heavier than other ions. Similarly, the atomic layer etch process can be controlled such that the process can be switched between layer modification and layer etch steps by adjusting the RF frequency. Such switching can take place within the same gas phase of the plasma process. In one embodiment, controlling RF power includes controlling phase differences and/or amplitude ratios between the fundamental RF frequency and the harmonic frequencies. In addition, the control of the phase difference and/or the amplitude ratio can be controlled within the plasma device such as, for example, impedance levels, radio frequency (RF) generator electrical signals, matching circuit electrical signals and other circuit electrical signals of the plasma processing device. Detection of one or more electrical properties may be relied upon.

The techniques described herein may be utilized in various plasma processing systems. For example, the techniques may be utilized in plasma etch processing systems, plasma deposition processing systems, or any other plasma processing system. FIG. 1 shows one exemplary plasma processing system 100 for purposes of illustration only. It will be appreciated that other plasma processing systems may similarly implement the concepts described herein. For example, the plasma processing system 100 may be a capacitively coupled plasma processing device, an inductively coupled plasma processing device, a microwave plasma processing device, a radial line slot antenna (RLSA) microwave plasma processing device, an electron cyclotron resonance (ECR) plasma processing device, or the like. could be. As such, those skilled in the art will appreciate that the techniques described herein may be utilized in any of a variety of plasma processing systems. Plasma processing system 100 may be used for a variety of operations including, but not limited to, etching, deposition, cleaning, plasma polymerization, plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and the like. The construction of plasma processing system 100 is well known and the specific construction presented herein is merely exemplary.

As shown in the exemplary system of FIG. 1, plasma processing system 100 may include process chamber 105 . Process chamber 105 may be a pressure controlled chamber, as is known in the art. A substrate 110 (a semiconductor wafer in one example) may be held on a stage or chuck 115 . A top electrode 120 and a bottom electrode 125 may be provided as shown. Top electrode 120 may be electrically coupled to top RF power supply 130 through top matching circuit 155 . Upper RF power supply 130 may provide upper frequency voltage 135 at upper frequency _fU . Bottom electrode 125 may be electrically coupled to bottom RF power supply 140 through bottom matching circuit 157 . Lower RF power supply 140 may provide multiple lower frequency voltages. For example, first lower frequency voltage 145 may be provided at a first lower frequency _f1 and second lower frequency voltage 150 may be provided at a second lower frequency _f2 . As discussed in more detail below, the second lower frequency _f2 can be a second or higher harmonic of the first lower frequency _f1 . Therefore, _f2 is equal to n* _f1 , where n can be an integer greater than one. Thus, the first lower frequency voltage 145 can operate as a fundamental frequency voltage, the second lower frequency voltage 150 can operate as a second voltage at a second frequency, and the second frequency is the second frequency of the fundamental frequency. Second harmonic or higher harmonic.

A feedback circuit 165 may be provided. As shown, feedback circuit 165 provides feedback between lower matching circuit 157 and lower RF power supply 140 . Specifically, in the illustrated example, feedback circuit 165 receives an input from lower matching circuit 157 and provides an output that is coupled to lower RF power supply 140 . The use of such feedback is merely exemplary, and as discussed below, the use of feedback to control the amplitude and phase shift of harmonic frequencies, as will be discussed below, can be achieved by using the feedback from lower matching circuit 157 It will be appreciated that feedback may be provided to lower RF power supply 140 from any of a variety of other components of plasma processing system 100, as it is not limited to feedback. Those skilled in the art will appreciate that many other components (not shown) may be included in the plasma processing system 100, or the components shown may be excluded, depending on the type of plasma processing system 100 utilized. would be

The components of plasma processing system 100 may be connected to and controlled by control unit 170, which may be connected to a corresponding memory storage unit and user interface (neither shown). Various plasma processing operations can be performed through the user interface, and various plasma processing recipes and operations can be stored in the storage unit. Accordingly, a given substrate can be processed in a plasma processing chamber using various microfabrication techniques. Since the control unit 170 can be coupled to and receive inputs from and provide outputs to various components of the plasma processing system 100, in one embodiment the function of the feedback circuit 165 is to provide additional feedback. It will be appreciated that it may be incorporated directly into the control unit 170 without the need for circuitry 165 .

Control unit 170 may be implemented in various ways. For example, control unit 170 may be a computer. In another example, the control unit may consist of one or more programmable integrated circuits programmed to provide the functionality described herein. For example, one or more processors (eg, microprocessors, microcontrollers, central processing units, etc.), programmable logic devices (eg, complex programmable logic devices (CPLDs)), field programmable gate arrays (FPGAs), etc.) and/or Other programmable integrated circuits can be programmed with software or other programming instructions to implement the functionality of the prohibited plasma process recipes. Software or other programming instructions may be stored on one or more non-transitory computer-readable media (e.g., memory storage devices, flash memory, DRAM memory, reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs). ), which, when executed by the programmable integrated circuit, cause the programmable integrated circuit to perform the processes, functions and/or capabilities described herein. Note further. Other variations may also be implemented. Feedback circuit 165 may consist of circuitry similar to that found in the control unit. Alternatively, feedback circuit 165 may provide feedback to the RF power supply based on measurements of certain electrical characteristics monitored in plasma processing system 100 to control the phase shift and amplitude ratio seen at the output of lower RF power supply 140 . It may be a specific circuit designed to provide specific feedback control of the RF power supply by being designed to provide the input.

In operation, the plasma processing apparatus uses the upper and lower electrodes to generate plasma 160 in process chamber 105 when power is applied to the system from upper RF power supply 130 and lower RF power supply 140 . Additionally, ions created in plasma 160 may be attracted to substrate 110, as is known in the art. The generated plasmas are of various types such as plasma etching, chemical vapor deposition, processing of semiconductor materials, glass materials and large panels such as thin film solar cells, other solar cells and organic/inorganic plates for flat panel displays. can be used to process a target substrate (such as substrate 110 or any material to be processed) in the process of.

When power is applied, a high frequency electric field is generated between the top electrode 120 and the bottom electrode 125 . The process gas delivered to the process chamber 105 can then be dissociated and converted into plasma. As shown in FIG. 1, the exemplary system described utilizes both a top RF power supply and a bottom RF power supply. For example, for an exemplary capacitively coupled plasma system, high frequency power in the range of approximately 3 MHz to 150 MHz may be applied from the upper RF power supply 130 and low frequency power in the range of approximately 0.2 MHz to 40 MHz may be applied from the lower RF power supply. obtain. It will be appreciated that the techniques described herein may be utilized with various other plasma systems. In one exemplary system, the power supply can be switched (higher frequency applied at the bottom electrode and lower frequency applied at the top electrode). Further, the dual power supply system is shown merely as an exemplary system, and the techniques described herein are such that frequency power is provided to only one electrode or a direct current (DC) bias power supply is utilized. or in other systems such as in which other system components are used.

As shown in FIG. 1, lower RF power supply 140 provides both a first lower frequency voltage and a second lower frequency voltage at first frequency _f1 and harmonic frequency _f2, respectively. The bottom RF power supply 140 can be considered a single RF power supply providing two or more frequencies, or alternatively, the bottom RF power supply 140 is a system having multiple RF power supplies each providing an RF voltage. It will be appreciated that it can be considered that Accordingly, lower RF power source 140 may consist of one or more RF power sources. Furthermore, as noted above, the use of each power supply as the upper and lower power supplies may be interchanged, thus the use of harmonics is not only limited to application to the lower electrode, but also to application to the upper electrode. can be utilized.

It is known in the art that conventional ion energy distributions in plasma systems often take the form of bimodal ion energy distributions. For example, FIG. 2 shows a conventional bimodal ion energy distribution plot 200 that can occur in a plasma etching system. Furthermore, for example, U.S.A. Czarnetzki et al, Plasma Sources Sci. Technol. , vol. 20, no. 2, p. 024010, it is known in the art that the ion energy distribution in the plasma can be controlled by applying harmonic frequencies in the power supply. More specifically, control of the amplitude ratios and relative phase shifts between different harmonic frequencies can affect the ion energy distribution. Thus, for example, in a plasma processing system 100 such as that shown in FIG. 1, the first lower frequency voltage 145 and the second lower frequency voltage 150 have a desired amplitude ratio between frequencies to affect the ion energy distribution. and a relative phase shift. FIG. 3 shows exemplary amplitudes A 1 and _{A 2 of} first lower frequency voltage 145 and second lower frequency voltage 150 . FIG. 3 also shows an exemplary phase shift θ between first lower frequency voltage 145 and second lower frequency voltage 150 .

Thus, for example, as shown in FIG. 4, a conventional bimodal ion energy distribution (as shown in FIG. 2) can be modified to obtain plot 400 through the use and control of harmonic frequencies. As shown in FIG. 4, the ion energy distribution is tuned by controlling the amplitude ratio and relative phase shift. FIG. 5 shows three exemplary ion energy distributions. Plot 505 shows the ion energy distribution when using a single lower frequency RF source (eg, 13.5 MHz). Plot 510 shows the effect of using a second (harmonic) frequency RF source in addition to the 13.5 MHz RF source. Plot 510 shows the ion energy distribution that occurs when the phase shift of the two sources is 0 degrees. Plot 515 also shows the effect of using a second (harmonic) frequency RF source in addition to the 13.5 MHz RF source, but in this case the phase shift is 180 degrees. As can be seen, using harmonics and changing the phase shift can affect the ion energy distribution. As shown, the ion energy distribution is graphed as a unit ion energy distribution f(E), which is the number of ions of a particular energy arriving on a unit surface area per unit time.

Depending on the particular plasma process, changes in the ion energy distribution can result in corresponding changes in the etch, deposition, etc. properties of the plasma process. 6 and 7 show exemplary variations. In Figures 6 and 7, the total bias power is the sum of power at both the fundamental and harmonic frequencies. In the example shown, each frequency contributes 50% of the power. Thus, for example, a total bias power of 400W can be provided by 200W at 13.56MHz and 200W at 27.12MHz. It will be appreciated that the particular percentage distribution of power and particular frequencies selected are merely exemplary, and the techniques disclosed herein are not limited to such examples. As shown in FIG. 6, etch rate is plotted against total bias power. More specifically, oxide and silicon nitride etch rates are shown using additional harmonic frequencies at 0 degree shifts and 180 degree shifts relative to the fundamental frequency. Thus, plot 605 shows the amount of silicon oxide etched at the 0 degree shift and plot 610 shows the amount of silicon oxide etched at the 180 degree shift. Similarly, plot 615 shows the amount of silicon nitride etched at the 0 degree shift, and plot 620 shows the amount of silicon nitride etched at the 180 degree shift. The selectivity results between silicon oxide and silicon nitride at the above phase shifts are shown in FIG. 7, where plot 705 is the selectivity at 0 degree phase shift and plot 710 is the is the selectivity at It will be appreciated that FIGS. 5-7 are exemplary only and that the use of harmonic control of RF power sources in plasma processing systems can be utilized in a wide variety of plasma processes.

It has been found desirable to control such ion energy distribution in situ and in real time in order to better control the properties of the plasma process. More specifically, optimal operating conditions, such as phase shifts and/or amplitude ratios at multiple frequencies utilized in a plasma process, may change as the operating or plasma conditions change. However, as noted above, direct measurement of ion energy distribution is generally not available in commercial mass-produced plasma equipment. As described herein, the optimal phase shift and/or amplitude ratio can be determined by monitoring other system characteristics and adjusting the ion energy distribution in real time in response to monitoring those other system characteristics. Selection can be made by providing feedback to the processing system.

Other system characteristics that are monitored can be any of a variety of characteristics. In one example, referring to FIG. 1 , the impedance of the process chamber seen by lower matching circuit 157 can be monitored by feedback circuit 165 and/or control unit 170 . The detected impedance condition is then used by feedback circuit 165 and/or control unit 170 to adjust the relative amplitude ratio and phase shift between first lower frequency voltage 145 and second lower frequency voltage 150. can be utilized to provide an input to the lower RF power supply 140 in the . Therefore, a control circuit (either a feedback circuit or a control unit) can be used to make the desired adjustments. In this way, during plasma processing, the lower RF power supply 140 can be adjusted on the fly to achieve a desired ion energy distribution shape during plasma processing. Although described in terms of the impedance seen by the matching circuit, it will be appreciated that other electrical signals may be monitored. For example, the electrical signal in the matching circuit can be monitored, the DC bias voltage can be monitored, various voltage levels of the RF power supply can be monitored, or various voltage and current levels in the system can be monitored. can be monitored (eg, AC peak-to-peak voltage (Vpp) level or voltage and current phase shift with respect to each other), and so on.

In one embodiment, amplitude ratios and relative phase shifts may be scanned within a specified range and electrical signals (eg, but not limited to impedance, etc.) of the plasma processing system 100 are collected. The plasma processing system 100 then determines the optimum amplitude between the multiple frequencies based on the collected data and a model of the correlation between the ion energy distribution and the electrical signal, depending on the desired shape of the ion energy distribution. Ratios and relative phase shifts can be calculated. Models can be either theoretical, experimental, or a combination of the two. It is thus understood that the correlation between the monitored electrical signal and the resulting realized ion energy distribution can result from the formation of a correlation table or graph obtained from experimental use, theoretical calculations or a combination thereof. will be done. Similarly, theoretical and/or experimental statistical correlations can be obtained. Similarly, simulated and/or experimental functions or models for correlation can be obtained. Thus, it will be appreciated that correlations can be obtained between one or more properties (e.g., electrical properties) of the system and ion energy distributions resulting from such properties in a variety of ways. be. In this way, for example, to achieve a desired ion energy distribution by adjusting the amplitude ratio and/or phase shift in real time in response to electrical measurements of the system (e.g., impedance of the process chamber in one embodiment). , real-time changes can be made to the lower RF power supply 140 .

In this way, a system can be provided that allows in-situ ion energy optimization in multiple harmonic frequency systems without the need to use ion energy sensors during the manufacturing process. In addition, the dynamic control feature provides the desired ion energy distribution even when operating conditions (e.g., pressure, source power, process chemistry, etc.) act to change the shape of the desired ion energy distribution during processing. allows it to maintain its shape. Although the above examples were made with one fundamental frequency voltage (first lower frequency voltage 145) and one harmonic frequency voltage (second lower frequency voltage 150), the concepts described herein are , may be utilized with one fundamental frequency voltage and two or more harmonic frequency voltages.

The ability to control ion energy distribution can be particularly useful in plasma processes that utilize ions of different masses. FIG. 8 shows a conventional bimodal ion energy distribution that can occur in a plasma etching system using two different ions of different masses. For example, plot 805 shows a plot of the ion energy distribution for ion _M2 and plot 810 shows the ion energy distribution for ion _M1 , where ion _M1 has a greater mass than ion _M2 . As described above, using RF harmonic frequency and phase shift and amplitude ratio control adjusts the conventional bimodal ion energy distribution to accentuate or enhance one of the peaks of the ion energy distribution. can be used to For example, controlling the harmonic frequency can provide the ion energy distribution of ions M1 and _M2 such that the light ion _M2 has _a higher energy compared to the heavy ion M1 _. Thus, as can be seen from FIG. 9, plot 905 shows the ion energy distribution for light ions _M2 and plot 910 shows the ion energy distribution for heavy ions _M1 . In FIG. 9 it can be seen that the light ion _M2 has a higher energy than the heavy ion _M1 . FIG. 9 includes an exemplary etch threshold 915, which is the threshold above which the energy of ion _M1 must perform an etching action and above which the energy of ion _M2 must perform an etching action. It includes an etch threshold 920 . It will be appreciated that the etch threshold will depend on the particular plasma chemistry and conditions utilized. Similarly, controlling the harmonic frequency can provide _the ion energy distribution of ions M1 and _M2 such that the light ion _M2 has _a lower energy compared to the heavy ion M1. Thus, as can be seen from FIG. 10, plot 1005 shows the ion energy distribution for light ions _M2 and plot 1010 shows the ion energy distribution for heavy ions _M1 . In FIG. 10 it can be seen that the light ion M2 has a lower energy than the heavy ion _M1 . FIG. 10 includes an exemplary etch threshold 1015, which is the threshold above which the energy of ion _M1 must perform an etching action, and above which the energy of ion _M2 must perform an etching action. It includes an etch threshold 1020 . It will be appreciated that the etch threshold will depend on the particular plasma chemistry and conditions utilized. Thus, as shown in the figure, an ion energy distribution for a process containing two different ions of different masses can exhibit at least two peaks for each ion, and the techniques described herein are useful for plasma processes. At least one peak of ions, such as the first peak or the second peak of ions, may be enhanced to alter performance characteristics.

Therefore, an asymmetric ion energy distribution can be obtained, as shown in the figure. Such asymmetry can be advantageously used in plasma processes that utilize two or more ions of different masses. For example, in a plasma etch process using lighter ions _M2 and heavier ions _M1 and the etch thresholds of FIG. ₉ , the asymmetric ion energy distribution as seen in FIG. becomes. Conversely, an asymmetric ion energy distribution and etch threshold as seen in FIG. 10 results in dominant etching by the heavier ions _M1 . One exemplary plasma etch process can be a chlorine (Cl ₂ )/helium (He) based etch. In such cases, the lighter ions, He ⁺ , may perform the dominant removal mechanism at the conditions of FIG. 9, while the heavier ions, Cl ₂ ⁺ or Cl ⁺ A removal mechanism may be implemented. Thus, as shown in FIGS. 9 and 10, the peaks of the ion energy distribution for some ions can be asymmetrically enhanced with one peak or the other to affect the processing characteristics of the plasma. In this way, control of the ion energy distribution can be used to affect processing characteristics (eg, but not limited to etching characteristics) of the plasma process utilized. Further, as explained above, control of the phase shift and amplitude ratio of harmonic frequencies can be utilized to achieve such variations in ion energy distribution as shown in FIGS. 9 and 10. FIG. Real-time in-situ control of phase shift and amplitude may be further based on the electrical properties of the plasma processing system, as discussed above.

In this way, selective etching with specific ion species can be achieved in plasma processing systems by adjusting phase shifts and/or amplitude ratios between harmonic frequencies and the fundamental frequency at which power is provided to the plasma processing chamber. It can be controlled in situ based on the application. Additionally, feedback from monitored electrical characteristics of the plasma processing system can be utilized to control phase shift and/or amplitude ratio adjustments.

The above techniques for utilizing and controlling ions of different masses can be particularly useful in atomic layer etching (ALE) processes. ALE processes are generally known to involve the sequential removal of thin layers through one or more self-limiting reactions. Such processes often involve a series of cyclical layer modification and etching steps. The modifying step can modify the exposed surface and the etching step can remove the modified layer. In this way a series of self-limiting reactions can occur. As used herein, an ALE process may include a Quasi-ALE process. Such a process can still use a cycle of series of modification and etching steps, but after removing the modified layer, the etching does not stop completely, but slows down considerably, so the removal is not required. The process is not purely self-limiting. In either case, the ALE-based process includes a series of cyclical modification and etching steps.

Use of the techniques described herein can be utilized in atomic layer etch processes to selectively change plasma processing between layer modification and etching steps. In one exemplary process, an atomic layer etch process may utilize heavier ions _M1 in a layer modification process and lighter ions _M2 in a layer removal process. For example, for use on silicon surfaces, ions M ₁ can be Cl ₂ ⁺ or Cl 2 ⁺ for silicon surface modification and ions M ₂ can be inert gas ions or noble gas ions such as He. obtain. Alternatively, depending on the materials and ions involved, the process may use the heavier ion _M1 in the layer removal process and the lighter ion _M2 in the layer modification process. In another embodiment, when used on a silicon anti-reflective coating surface, high-energy H ^{2 +} ions can be used for silicon anti-reflective coating surface modification, and fluorochemicals can be used for its selective removal. In yet another example, a _{C4F8 /} He plasma may be utilized. In such cases, a CF film may be formed on the surface when the He ions are of low energy, and the CF film may be removed by the energized He ions. In the example of a _C4F8 /He plasma, without changing the shape of the ion energy distribution, high bias voltages would be required, resulting in surface damage and/or etching by CF energetic ions _. FIGS. 11A and 11B correspond to the M ₁ and M ₂ ion energy distributions of FIGS. 9 and 10, except that different etch thresholds 1105 and 1110 have been added as indicated. Etch threshold 1105 indicates an ion energy threshold above which ions _M2 provide etching action and below which ions _M2 do not provide etching action. Etch threshold 1110 indicates an ion energy threshold above which ion _M1 provides etching action and below which ion _M1 does not provide etching action. If such energy of the ions is below the threshold for etching to occur, substantially no etching will occur and the layer modification process of ion _M1 will dominate. Therefore, the ion energy distribution shown in FIG. 11A primarily provides etching ions (lighter ions M ₂ ) at higher ion energies above the etching threshold to provide the etching or removal action of the atomic layer etching process. The ion energy distribution shown in FIG. _11B is primarily for etching ions (lighter ions M2). Figures 12A and 12B illustrate yet another atomic layer etch process. In this process, surface modification is achieved by lighter ions _M2 and etching or removal of the modified surface is performed by heavier ions _M1 or radicals in the plasma. As shown in FIG. 12A, an etch threshold 1205 is provided below which the lighter ions _M2 do not participate in etching or removal. Etch threshold 1210 indicates the etch threshold above which heavier ions _M1 etch or remove the modified surface.

The use of fundamental and harmonic power frequencies can be controlled such that the atomic layer etch process alternates between the states of FIGS. 11A and 11B and between the states of FIGS. 12A and 12B. Thus, by using control of the relationship between the fundamental frequency and the harmonic frequency, the modification and etching/removal steps can be separated and alternated. Moreover, such control can be utilized within the same gas phase of the plasma. It will be appreciated that frequency control can be obtained in situ as described above by controlling the phase shift and amplitude ratio of the various frequencies. Moreover, such control of phase shift and amplitude ratio may be based on the electrical characteristics of the plasma processing system as described in more detail above. Therefore, by controlling the RF power supply, the ion energy distribution selectively controls the layer modification step or the layer etching step of the atomic layer etching process.

In this way, simultaneous control of ion energies for ions of different masses can be achieved. Further, the control can be implemented to allow selective energy modulation of the ion mass of the target, such that the control can be used to implement high speed atomic layer etching. Such atomic layer etch control can be achieved even within the gas phase of plasma processes.

It will be appreciated that the applications described above are exemplary only, and that many other processes and applications may benefit from the techniques disclosed herein. 13-17 illustrate exemplary methods for using the plasma processing techniques described herein. It will be appreciated that the embodiments of FIGS. 13-17 are merely exemplary and that additional methods can utilize the techniques described herein. Moreover, the steps described are not intended to be exclusive, and further processing steps can be added to the methods shown in FIGS. 13-17. Additionally, the order of the steps is not limited to the order shown in the figures, as different orders may occur and/or various steps may be combined or performed simultaneously.

As shown in FIG. 13, a method is provided for plasma processing a substrate. Step 1305 includes providing a process chamber. Step 1310 is coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second frequency voltage at a second frequency. Thus, the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency, including coupling. Step 1315 includes monitoring at least one electrical characteristic of the plasma processing system during plasma processing of the substrate. Step 1320 adjusts the phase difference between the fundamental frequency voltage and the second frequency voltage and/or the amplitude of the fundamental frequency voltage and the second frequency voltage to obtain a desired ion energy distribution during plasma processing of the substrate. including adjusting the ratio during plasma processing.

As shown in FIG. 14, a method is provided for plasma processing a substrate. Step 1405 includes providing a process chamber. Step 1410 is coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second frequency voltage at a second frequency. Thus, the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency, including coupling. Step 1415 includes coupling matching circuits between the process chamber and one or more RF power sources. Step 1420 includes monitoring at least the impedance of the process chamber seen by the matching circuit during plasma processing of the substrate. Step 1425 includes adjusting the phase difference between at least the fundamental frequency voltage and the second frequency voltage during plasma processing to obtain a desired ion energy distribution during plasma processing of the substrate.

As shown in FIG. 15, a method is provided for plasma processing a substrate. Step 1505 includes providing a process chamber. Step 1510 is coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second frequency voltage at a second frequency. Thus, the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency, including coupling. Step 1515 is providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of ions. The type of ions has a second mass, the first mass and the second mass being different masses. Step 1520 adjusts the relationship between the fundamental frequency voltage and the second frequency voltage to allow selective control of the ion energy distribution based on the first and second masses by: Controlling the ion energy distribution of the first type of ions and the second type of ions.

As shown in FIG. 16, a method is provided for plasma etching a substrate. Step 1605 includes providing a process chamber. Step 1610 is coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second frequency voltage at a second frequency. Thus, the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency, including coupling. Step 1615 is providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of ions. The type of ions has a second mass, the first mass and the second mass being different masses. Step 1620 adjusts the relationship between the fundamental frequency voltage and the second frequency voltage to allow selective control of the ion energy distribution based on the first and second masses by: Controlling the ion energy distribution of the first type of ions and the second type of ions. Controlling the ion energy distribution, as shown in step 1620, allows for selectively controlling the etching effects of at least one of the first type of ions and the second type of ions.

As shown in FIG. 17, a method is provided for plasma processing a substrate. Step 1705 includes providing a process chamber. Step 1710 is coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at the fundamental frequency and a second frequency voltage at a second frequency. Thus, the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency, including coupling. Step 1715 is providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and a second type of ions. The type of ions has a second mass, the first mass being heavier than the second mass. Step 1720 adjusts the phase difference between the fundamental frequency voltage and the second frequency voltage and/or the amplitude ratio between the fundamental frequency voltage and the second frequency voltage to obtain the first type of ions and the second frequency voltage. and controlling the ion energy distribution of ions of the type Controlling the ion energy distribution produces an asymmetric ion energy distribution of at least one of the first type of ions or the second type of ions, as shown in step 1725 . As shown in step 1730, the asymmetric ion energy distribution is used to adjust the etching effect of the second type of ions on the first type of ions.

Further modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art how to carry out the invention. It is to be understood that the forms and methods of the invention shown and described herein are to be construed as presently preferred embodiments. Equivalent techniques may be substituted for those illustrated and described herein, and certain features of the invention may be utilized independently of the use of other features, all It will become apparent to those skilled in the art after having the benefit of this description of the invention.

Claims (17)

A method for plasma treating a substrate, comprising:
providing a process chamber;
coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency; combining, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency;
providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and the second type of ions; the ions of have a second mass, wherein the first mass and the second mass are different masses;
by adjusting the relationship between the fundamental frequency voltage and the second frequency voltage to enable selective control of the ion energy distribution based on the first mass and the second mass; and controlling said ion energy distribution of ions of a first type and said second type of ions. 3. The adjusting comprises adjusting a phase difference between the fundamental frequency voltage and the second frequency voltage and/or an amplitude ratio between the fundamental frequency voltage and the second frequency voltage. 1. The method according to 1. 3. The method of claim 2, wherein adjusting comprises adjusting a phase difference between the fundamental frequency voltage and the second frequency voltage. The plasma treatment is a plasma etching process, and the controlling the ion energy distribution is based on the difference between the first mass and the second mass, the first type of ions and the 3. The method of claim 2, providing selective control of the etching effects of the second type of ions. 5. The plasma etch process of claim 4, wherein the plasma etch process is an atomic layer etch process, and wherein the controlling the ion energy distribution selectively controls a layer modification step or a layer etch step of the atomic layer etch process. described method. A method for plasma etching a substrate, comprising:
providing a process chamber;
coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency; combining, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency;
providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and the second type of ions; the ions of have a second mass, wherein the first mass and the second mass are different masses;
by adjusting the relationship between the fundamental frequency voltage and the second frequency voltage to enable selective control of the ion energy distribution based on the first mass and the second mass; controlling the ion energy distribution of the first type of ions and the second type of ions;
The ion energy distribution has at least two peaks for the second type of ions, a first peak at a lower energy than the at least one peak for the first type of ions, and a second A peak is at a higher energy than the at least one peak for the first type of ions, and the controlling the ion energy distribution enhances the second peak for the second type of ions. used for
The method, wherein said controlling said ion energy distribution enables selectively controlling an etching effect of at least one of said first type of ions and said second type of ions. 7. The first type of ions are heavier than the second type of ions, and wherein the controlling the ion energy distribution provides for predominant etching by the second type of ions. The method described in . 7. The method of claim 6, wherein said controlling can be performed during plasma processing such that said ion energy distribution can vary within a common gas phase of said plasma etch. 7. The method of claim 6, wherein said plasma etching is an atomic layer etching process. 10. The method of claim 9 , wherein said controlling can be performed during plasma processing such that said ion energy distribution can vary within a common gas phase of said plasma etch. 10. The method of claim 9 , wherein said controlling said ion energy distribution is utilized to make said atomic layer etching process a layer modification step. 12. The method of claim 11 , wherein said controlling can be performed during plasma processing such that said ion energy distribution can vary within a common gas phase of said plasma etch. 10. The method of claim 9 , wherein said controlling said ion energy distribution is utilized to turn said atomic layer etch process into a layer etch step. 14. The method of claim 13 , wherein said controlling can be performed during plasma processing such that said ion energy distribution can vary within a common gas phase of said plasma etch. A method for plasma etching a substrate, comprising:
providing a process chamber;
coupling one or more RF power sources to the process chamber to provide RF power to the process chamber through at least a fundamental frequency voltage at a fundamental frequency and a second frequency voltage at a second frequency; combining, wherein the second frequency is a second harmonic frequency or a higher harmonic of the fundamental frequency;
providing at least a first type of ions and a second type of ions in the process chamber, the first type of ions having a first mass and the second type of ions; the ions of have a second mass, said first mass being heavier than said second mass;
to provide;
By adjusting the phase difference between the fundamental frequency voltage and the second frequency voltage and/or the amplitude ratio between the fundamental frequency voltage and the second frequency voltage, the ions of the first type and the controlling the ion energy distribution of the second type of ions;
The ion energy distribution has at least two peaks for the second type of ions, a first peak at a lower energy than the at least one peak for the first type of ions, and a second A peak is at a higher energy than the at least one peak for the first type of ions, and the controlling the ion energy distribution enhances the second peak for the second type of ions. used for
said controlling said ion energy distribution produces an asymmetric ion energy distribution of at least one of said first type of ions or said second type of ions;
The method, wherein the asymmetric ion energy distribution is used to adjust the etching effect of the second type of ions on the first type of ions. The plasma etching is an atomic layer etching process, and the controlling the ion energy distribution is utilized to switch the atomic layer etching process between a layer etching step and a layer modification step. Item 16. The method according to Item 15 . 17. The method of claim 16 , wherein said controlling said ion energy distribution is performed within the same gas phase of said atomic layer etch process.

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