Systems and methods for high synergy atomic layer etching using capacitively coupled plasma

Abstract

A system and method for high synergistic atomic layer etching using a capacitively coupled plasma is disclosed. The atomic layer etching includes a surface modification step and a sputtering step. A capacitively coupled plasma (CCP) source with a sidewall coil is used to increase plasma density and reduce ion bombardment during the surface modification step. During the sputtering step, the chamber operates the CCP source in a sidewall coil disabled state.

Description

[0001] Cross-references to related applications

[0002] This invention claims priority to U.S. Patent Application No. 19 / 046,554, filed on February 6, 2025. Technical Field

[0003] This invention relates to atomic layer etching (ALE) processes and systems. More specifically, this invention relates to an ALE process system that utilizes a capacitively coupled plasma (CCP) source with auxiliary sidewall coils to reduce ion bombardment during surface modification steps. Background Technology

[0004] Anisotropic atomic layer etching (ALE) is a plasma-based etching technique that includes a surface modification step and a sputtering step. The different chemical reactions, material compositions, and plasma energy distributions involved in the surface modification and sputtering steps allow for more precise control over the flux of ions, electrons, and neutral particles, thus broadening the process window. This step separation facilitates self-limiting reactions, which are crucial for maintaining the ideality of the etching process, manifested in etching uniformity, surface smoothness, and selectivity. Kanarik et al., in "Predicting synergy in atomic layer etching" (J. Vac. Sci. Technol. A35, pp. 05C302 1–7, 2017), defined the ALE synergy factor as follows:

[0005]

[0006] Here, EPC (Etch Per Cycle) represents the total thickness of material removed in one cycle (usually the average of multiple cycles); "and" The values ​​of "" represent the (non-ideal) contributions from the surface modification step and the sputtering step, respectively. Ideally, these two steps would not etch independently, but when combined, the synergy factor would approach 100%. However, in reality, the presence of ions in the plasma makes reactive ion etching (RIE) unavoidable in the surface modification step; similarly, physical sputtering of the underlying unmodified layer is unavoidable in the sputtering step.

[0007] In the surface modification step of ALE (Alternating Electrode Process), it is desirable to avoid ion bombardment by the plasma. However, the unintended introduction of RIE (Residual Injection Effusion) in this step presents a challenge. Since ion bombardment of the substrate surface is difficult to completely avoid, conventional ALE struggles to maintain ideal etching characteristics. Traditional ALE methods are ineffective at eliminating these RIEs, resulting in suboptimal etching performance, especially as device structures become increasingly complex and their dimensions shrink. RIEs in the ALE process cause non-uniform layer removal and undesirable etching profiles, which is particularly severe in advanced device manufacturing; even small deviations can significantly impact device performance and yield.

[0008] Most ALE processes are based on inductively coupled plasma (ICP) sources. Capacitively coupled plasma (CCP)-based ALE faces a fundamental challenge: the high plasma density required for rapid surface modification leads to high ion bombardment. While high density (or high concentration) of radicals is needed for rapid and uniform surface modification, the associated ion energy results in undesirable radical energy exchange (RIE), compromising the self-confining properties of ALE. Because plasma density and ion energy are inherently correlated in CCP systems, reducing ion bombardment without decreasing radical concentration is difficult. Adjusting process parameters such as radio frequency (RF) power or pressure simultaneously affects plasma density and sheath potential, making it nearly impossible to maintain the required radical flux while minimizing ion bombardment. Summary of the Invention

[0009] To overcome this limitation, auxiliary plasma sources (such as sidewall coils) can be introduced to generate additional radicals without increasing ion energy. By combining an inductively coupled plasma (ICP) assembly with a CCP, radical generation can be enhanced without significantly increasing ion energy. This hybrid approach allows for better control of plasma properties and effective decoupling of radical generation and ion bombardment, thereby improving the fidelity of the ALE process.

[0010] In some embodiments, the present invention provides an atomic layer etching (ALE) system comprising a capacitively coupled plasma (CCP) source with auxiliary sidewall coils to generate high-density free radicals during a surface modification step while minimizing ion bombardment. A key technology of the present invention lies in the introduction of the sidewall coils as an auxiliary plasma source.

[0011] In ALE processes, rapid surface modification requires high plasma density. However, in CCP process systems, high density leads to high ion bombardment, resulting in undesirable RIE and reduced synergistic effects. The problem can be solved by incorporating sidewall coils, which enhance radical generation without significantly increasing ion energy, thus decoupling radical flux from ion bombardment. This enables precise surface modification while maintaining the self-confining properties of ALE.

[0012] In some embodiments, the ALE system utilizes sidewall coils alone to generate free radicals during the surface modification step. In other embodiments, the sidewall coils are combined with a high-frequency RF power generator connected to the anode to further increase plasma density while minimizing ion bombardment. Furthermore, the sputtering step may employ a custom waveform generator to apply low-frequency RF power to the anode to optimize ion energy distribution and improve ion directionality during the sputtering step.

[0013] Pulsed schemes can also be introduced to precisely control plasma characteristics. In some implementations, the pulse duration of the RF power applied to the anode is shorter than that of the RF power applied to the sidewall coils to further mitigate ion bombardment while maintaining efficient radical generation. These configurations enhance process flexibility and ensure better control over etching selectivity, uniformity, and precision.

[0014] By utilizing a hybrid plasma configuration combining CCP and ICP components (including sidewall coils) and multiple RF power delivery modes, this invention enhances ALE synergy while configuring the CCP reaction chamber with a small plasma volume for faster gas exchange. The system controller coordinates RF power supply, pulse schemes, and waveform customization to optimize ALE performance, making this approach suitable for advanced semiconductor manufacturing processes requiring non-destructive, atomic-level precision. Attached Figure Description

[0015] Embodiments of the present invention can be clearly illustrated by referring to the following description and accompanying drawings:

[0016] Figure 1 An exemplary ALE process system is shown, which includes a CCP source with auxiliary sidewall coils to enhance free radical generation and reduce ion bombardment during surface modification.

[0017] Figure 2 The flowchart of the ALE process using a CCP source with sidewall coils is shown to illustrate the execution of the surface modification and sputtering steps. Detailed Implementation

[0018] To facilitate a full understanding of the invention, specific embodiments thereof will be described in detail below. While specific details are provided for ease of explanation, any modifications and variations consistent with the technical principles of the invention are considered appropriate. Certain well-known procedures and components are described selectively only to highlight the unique features of the invention.

[0019] The terminology is defined as follows:

[0020] Atomic Layer Etching (ALE): A plasma-based etching process that removes material layer by layer by alternating surface modification and sputtering steps, thereby achieving atomic-level precision control.

[0021] Chamber: A vacuum-sealed space for performing ALE processes, designed to maintain a controlled plasma state.

[0022] Capacitively Coupled Plasma (CCP) source: A plasma generation method that uses an electric field between an anode (suction cup) and a cathode (grounded spray head) to maintain the plasma, commonly used in semiconductor processing.

[0023] Suction cup: A substrate carrier used as the anode in a CCP system. It can be an electrostatic chuck (ESC) or a vacuum chuck, used to hold and hold the wafer during processing.

[0024] Grounding spray head: A component used as the cathode in a CCP system to distribute process gases into the chamber.

[0025] Sidewall coils: One or more inductively coupled RF coils that help generate free radicals for surface modification while minimizing ion bombardment.

[0026] RF power generator: supplies RF power at different frequencies to maintain and control the plasma, where high frequencies can increase plasma density and low frequencies can increase ion energy.

[0027] Resonator: An impedance matching component used to optimize power transfer between the RF power generator and the chamber, ensuring stable plasma operation at different process steps.

[0028] Custom waveform generator: A device for regulating the bias applied to the chuck, narrowing the ion energy distribution to optimize the sputtering process.

[0029] Surface modification step: The first half of the ALE cycle, in which free radicals in the plasma chemically react with the substrate surface to form a modified layer that can be selectively removed in the next step.

[0030] Sputtering step: The latter half of the ALE cycle, in which high-energy ions physically remove the modified layer, completing a full etching cycle and achieving controlled material removal.

[0031] System controller: A computing system with software modules used to adjust process parameters, RF power application, gas flow rate and pulse scheme to maintain precise ALE operation.

[0032] Pulse scheme: Optimize plasma ignition, ion energy and free radical generation in different ALE process steps by controlling the application of RF power through timed pulses.

[0033] Bias: The bias applied to the chuck is used to control the energy and directionality of ions in the plasma, which is crucial for achieving anisotropic etching in high aspect ratio structures.

[0034] Process gases: reactive gases (e.g., chlorine) used for surface modification and inert gases (e.g., argon) used for sputtering play different roles in each ALE cycle.

[0035] Figure 1 An exemplary ALE process system 100 is illustrated. The process system 100 includes a chamber 102 configured to perform a plasma-based process in a vacuum environment. The chamber 102 is surrounded by chamber walls 111. The chamber walls include chamber sidewalls 113 made of a dielectric material, such as quartz or ceramic. The chamber 102 also includes a capacitively coupled plasma (CCP) source, comprising a chuck 124 as an anode and a grounded spray head 120 as a cathode. Depending on the application, the chuck 124 may be an electrostatic chuck (ESC) or a vacuum chuck. The grounded spray head 120 may be made of a conductive material, such as silicon. The grounded spray head 120 receives process gas from a gas source 122 and distributes the received gas into the chamber 102. The gas source 122 includes a gas box, multiple valves, and a mass flow controller (MFC). The chuck 124 adsorbs a substrate 126, which is typically a silicon wafer.

[0036] Process gases, including reaction byproducts, are discharged from chamber 102 via pump 130. A vacuum valve 128 located upstream of the pump regulates the gas discharge rate. The discharged gas passes through an exhaust line ( Figure 1 (Not shown) is supplied to the exhaust device. The chamber pressure is controlled by balancing the injection and exhaust rates of the gas, and the pressure is regulated by a proportional-integral-derivative (PID) control loop based on the reading of pressure gauge 132.

[0037] The suction cup 124, which serves as the anode, receives RF power from one or more RF power generators. Figure 1 An example with two RF power generators (104 and 106) is shown, which can operate at different frequencies. RF power generator 104 can operate at 60 MHz, while RF power generator 106 can operate at 400 kHz. Higher RF frequencies can increase plasma density, while lower frequencies can increase ion energy. The RF power generators are connected to the chuck 124 via a resonator 108, which is used to match the impedance of the RF power generators to the impedance of the CCP. It should be noted that the plasma can exhibit different states during the ALE process. For example, the surface modification step and the sputtering step can correspond to different plasma impedances. The resonator 108 is configured to incorporate impedance variations to match the impedance of the RF power generators.

[0038] A custom waveform generator 110 can be used to optimize the ion energy distribution during the sputtering step. The custom waveform generator 110 is typically used in conjunction with one of the RF power generators.

[0039] The process system 100 also includes one or more sidewall coils 116. An RF power generator 112 applies RF power to the sidewall coils 116 via a resonator 114 at a predetermined frequency (e.g., 13.56 MHz). In one embodiment, a single coil with one or more turns is used. In another embodiment, multiple separate coils are used, each driven by a single RF power generator operating at a different power level or frequency. One of the key challenges of using CCP sources for ALE is the difficulty in eliminating ion bombardment during the surface modification step, which requires a high concentration of free radicals to modify the substrate surface within a short step time (less than 200 ms). It is well known that for CCP sources, higher plasma densities lead to higher free radical concentrations, resulting in higher ion energies. This makes it difficult to achieve highly synergistic ALE processes using CCP sources due to excessive ion bombardment during the surface modification step.

[0040] The application of the sidewall coil 116 solves this problem by introducing an auxiliary plasma source without increasing ion energy.

[0041] In some implementations, during the surface modification step, the output duration of RF power generator 104 or 106 is shorter than that of RF power generator 112 to reduce ion bombardment.

[0042] In other embodiments, RF power is output in pulses according to a predetermined pulse pattern. The pulse output duration of RF power generator 104 or 106 is shorter than the pulse output duration of RF power generator 112.

[0043] In some respects, the start time of the pulse output of RF power generator 112 can be controlled to have a time delay with the pulse output of RF power generator 104 or 106 in order to effectively ignite the plasma, especially when an electronegative process gas (e.g., chlorine) is used during the surface modification step.

[0044] The ALE process cycle typically involves delivering different process gases in two distinct steps (a surface modification step and a sputtering step). The surface modification step and the sputtering step are each two half-cycles of an ALE cycle. The grounded spray head 120 can have two different gas distribution modes, including different gas channels and different injection holes for the first and second process gases, respectively.

[0045] The operation of the process system 100 is controlled by the system controller 134, which includes a computer and multiple software modules.

[0046] Figure 2 A flowchart of the ALE process 200 of process system 100 is shown. Process 200 begins at step 202, where system controller 134 instructs grounded spray head 120 to receive a first process gas (e.g., chlorine) from gas source 122. Subsequently, grounded spray head 120 distributes the first process gas into chamber 102. In step 204, sidewall coil 116 receives first RF power at a first frequency from RF power generator 112 via resonator 114. The first frequency may be 13.56 MHz, and the power level range is 50 watts to 5000 watts. During step 204, RF power generator 104 may apply a second RF power at a second frequency to the anode. The second frequency may be 60 MHz or 27 MHz, and the power level range is 50 to 500 watts.

[0047] In step 206, the substrate 126 is surface-modified using free radicals in the plasma to ensure the formation of a modified layer with self-limiting properties. The duration of the substrate surface exposure to plasma is controlled to balance process performance and productivity.

[0048] In step 208, a gas such as nitrogen may be used to purge the first process gas.

[0049] In step 210, the grounded spray head 120 receives a second process gas (e.g., argon) and distributes it into chamber 102. In step 212, the anode (i.e., the chuck 124) receives third RF power at a third frequency from the RF power generator 106. The sidewall coil 116 is deactivated at this time. The ion energy of the sputtering step is optimized by the third RF power at the third frequency. The third frequency can be selected from: 2 MHz, 1 MHz, 400 kHz, and 100 kHz.

[0050] In step 214, a custom waveform generator 110 may be used to optimize the ion energy distribution.

[0051] In step 216, a sputtering step is performed, in which ions in the plasma remove the modified layer. The bias voltage is approximately in the range of 50 to 5000 volts, and the RF power and custom waveform are output in pulse form according to a predetermined pulse scheme.

[0052] In step 218, nitrogen or other inert gases may be used to purge the second process gas.

[0053] In step 220, steps 202 through 218 are repeated for a predetermined number of cycles to complete the ALE process. The predetermined number of cycles can be adjusted according to the desired etching depth and material removal rate. The system controller 134 dynamically manages process parameters, including RF power level, pulse pattern, and gas flow rate, to ensure consistent etching performance and process uniformity.

[0054] By setting up independent plasma sources (CCP source and ICP source arranged along the sidewall of the chamber) and precisely controlling plasma characteristics, the process system 100 can achieve highly coordinated ALE.

Claims

1. A system for performing atomic layer etching processes, characterized in that, include: A chamber for maintaining a vacuum environment, and the sidewalls of the chamber are made of a dielectric material; A suction cup, located within the cavity, is configured to adsorb a substrate during atomic layer etching processes; A spray head configured to receive process gas and distribute the received process gas into a chamber, wherein the spray head is grounded; One or more radio frequency power generators connected to the suction cup are used to apply radio frequency power to a capacitively coupled plasma source, wherein the suction cup is configured as the anode of the capacitively coupled plasma source and the spray head is configured as the cathode of the capacitively coupled plasma source; One or more sidewall coils, wherein the sidewall coils are arranged along the outer surface of the sidewall of the chamber; and A system controller configured to control the chamber during the surface modification and sputtering steps to activate the sidewall coils during the surface modification step and deactivate the sidewall coils during the sputtering step.

2. The system according to claim 1, characterized in that, The system also includes a custom waveform generator, which is activated during the sputtering step.

3. The system according to claim 2, characterized in that, The custom waveform generator and one of the radio frequency power generators connected to the chuck cooperate to provide a bias voltage ranging from 50 to 5000 volts to accelerate ions in the chamber.

4. The system according to claim 1, characterized in that, The system also includes one or more radio frequency power generators connected to the sidewall coil.

5. The system according to claim 4, characterized in that, The radio frequency power generator connected to the sidewall coil can operate at the same or different frequencies, including: 13.56 MHz, 2 MHz, 1 MHz, 400 kHz and 100 kHz.

6. The system according to claim 1, characterized in that, The radio frequency power generator connected to the suction cup can operate at the same or different frequencies, including: 100 MHz, 60 MHz, 27 MHz, 13.56 MHz, 2 MHz, 1 MHz, 400 kHz and 100 kHz.

7. The system according to claim 1, characterized in that, In the surface modification step and the sputtering step, the radio frequency power generator connected to the chuck applies radio frequency power of different frequencies to the chuck, wherein the frequency used for the sputtering step is lower than the frequency used for the surface modification step.

8. The system according to claim 1, characterized in that, At least one of the radio frequency power generators connected to the suction cup outputs radio frequency power in pulse form.

9. The system according to claim 8, characterized in that, The pulse duration of the RF power applied to the chuck is shorter than the output duration of the RF power applied to the sidewall coil.

10. The system according to claim 1, characterized in that, During the surface modification step, at least one of the radio frequency power generators connected to the chuck is deactivated.

11. The system according to claim 1, characterized in that, The spray head is configured with different gas distribution modes corresponding to the first process gas and the second process gas, respectively.

12. The system according to claim 1, characterized in that, The dielectric material includes quartz or ceramic.

13. The system according to claim 1, characterized in that, The plasma volume of the chamber is less than 5 liters.

14. A method for processing a substrate using atomic layer etching (ALTI) technology, characterized in that, include: a. A chamber for maintaining a vacuum environment to perform an atomic layer etching process, wherein a capacitively coupled plasma source is disposed within the chamber, a chuck is configured as the anode of the capacitively coupled plasma source, a grounded spray head is configured as the cathode of the capacitively coupled plasma source, wherein one or more sidewall coils arranged along the dielectric sidewall of the chamber serve as an auxiliary plasma source to provide radio frequency power during a surface modification step; b. Receive the first process gas through the spray head and distribute the received first process gas into the chamber; c. Apply a first radio frequency power at a first frequency to the sidewall coil, and apply a second radio frequency power at a second frequency to the anode; d. Perform surface modification steps using atomic layer etching (ALT) processes; e. Remove the first process gas from the chamber; f. Receive the second process gas through the spray head and distribute the received second process gas into the chamber; g. Apply a third radio frequency power at a third frequency to the anode; h. Apply a customized electrical waveform output from a customized waveform generator to the anode during the sputtering step; i. Perform the sputtering step of the atomic layer etching process; j. Remove the second process gas from the chamber; and k. Repeat steps b to j for a predetermined number of cycles until the atomic layer etching process is completed.

15. The method according to claim 14, characterized in that, The method further includes stopping the application of the first radio frequency power to the sidewall coil after the surface modification step is completed.

16. The method according to claim 14, characterized in that, The first radio frequency power includes multiple frequencies.

17. The method according to claim 16, characterized in that, Each of the sidewall coils receives a first radio frequency power at a different frequency.

18. The method according to claim 16, characterized in that, The system controller controls the radio frequency power according to a predetermined pulse pattern.

19. The method according to claim 18, characterized in that, During the surface modification step, the pulsed radio frequency power applied to the sidewall coil and the pulsed radio frequency power applied to the anode are synchronized.

20. The method according to claim 18, characterized in that, During the surface modification step, the system controller is configured to make the pulse output duration of the RF power applied to the anode shorter than the pulse output duration of the RF power applied to the sidewall coil.

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