Atomic layer etching process system and method for achieving uniform control of substrate edge by using side wall coil arranged close to pedestal

Abstract

This invention discloses a system and method for achieving uniform control of substrate edges during atomic layer etching (ALE) using auxiliary sidewall coils arranged near the substrate. ALE includes a surface modification step and a sputtering step. The TCP source of this invention is equipped with auxiliary sidewall coils arranged near the substrate to increase plasma density in the surface modification step and to optimize control of ion density, energy, and angular distribution, particularly the control of ions at the substrate edges, in the sputtering step.

Description

[0001] Cross-reference to related applications

[0002] This invention claims priority to U.S. Patent Application No. 19 / 048,950, filed on February 9, 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 employing a transformer-coupled plasma (TCP) source and incorporating auxiliary sidewall coils arranged near the substrate to optimize control of substrate edge ions during the sputtering step of the ALE process. Background Technology

[0004] Atomic layer etching (ALT) is a high-precision etching technique that removes material layer by layer through alternating surface modification and sputtering steps. In some implementations, the surface modification step introduces reactive substances to chemically modify the outermost atomic layer of the substrate, and the subsequent sputtering step uses high-energy ions to remove the modified layer. This alternating cycle is repeated multiple times to achieve the desired etching depth with high precision.

[0005] While ALE offers advantages in etching selectivity and atomic-level precision control, the process is slow due to the use of different gases in the surface modification and sputtering steps. In some implementations, one approach to increase throughput is to use smaller reaction chambers to reduce the volume of gas exchanged between steps, thereby accelerating process changeovers. However, achieving atomic-level etching in smaller reaction chambers presents significant challenges, particularly in maintaining plasma homogeneity.

[0006] In some schemes, conventional transformer-coupled plasma (TCP) sources include a central coil and edge coils positioned at the top of the dielectric window to generate plasma. This configuration is effective in larger reaction chambers, but in smaller reaction chambers, especially during sputtering steps, it may not provide sufficient plasma homogeneity. In some schemes, the limited plasma diffusion distance in smaller reaction chambers leads to inhomogeneous ion density and angular distribution, resulting in inconsistent etching depth and profile.

[0007] Therefore, there is a need for an improved plasma source configuration that can achieve atomic layer etching in a smaller reaction chamber while maintaining plasma homogeneity, especially during the sputtering step. Summary of the Invention

[0008] In some implementations, systems and methods for atomic layer etching incorporate auxiliary sidewall coils based on conventional TCP sources, addressing the challenge of plasma homogeneity in smaller reaction chambers. The sidewall coils are arranged along the sidewalls of the reaction chamber adjacent to a base used to hold the substrate. During the sputtering step, plasma characteristics are enhanced by optimized control of ion density, energy, and angular distribution at the substrate edges. Furthermore, this facilitates more efficient and uniform modification of the substrate surface during the surface modification step.

[0009] In some implementations, the sidewall coils operate independently of the center and edge coils of the TCP source, receiving RF power at different frequencies from a dedicated radio frequency (RF) power generator. This independent control allows for customized, optimized plasma conditions for each atomic-layer etching step. In the surface modification step, the enhanced radical density facilitates more effective surface chemical modification. During the sputtering step, optimized ion control ensures etching consistency, particularly where etching inhomogeneities are more pronounced at the substrate edges in smaller reaction chambers.

[0010] In some implementations, by incorporating sidewall coils into the atomic layer etching (ALT) process system, plasma uniformity is significantly optimized, enabling ALT etching in a smaller reaction chamber while maintaining etching consistency and process stability. The system adjusts RF power parameters to optimize radical distribution, ion energy, and angular distribution, ensuring precise and repeatable ALT etching cycles.

[0011] Therefore, the systems and methods disclosed in this invention optimize the control of plasma characteristics, particularly in smaller reaction chambers, thereby improving etching uniformity, throughput, and overall process efficiency. Attached Figure Description

[0012] The implementation scheme can be more clearly understood by referring to the following description in conjunction with the accompanying drawings:

[0013] Figure 1 An exemplary ALE process system is shown, in which the TCP source has an auxiliary sidewall coil disposed near the base.

[0014] Figure 2 The flowchart of the ALE process using a TCP source with auxiliary sidewall coils is shown, detailing the execution steps of surface modification and sputtering, as well as the plasma control mechanism. Detailed Implementation

[0015] 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.

[0016] Terminology definition:

[0017] 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.

[0018] Reaction chamber: A vacuum-sealed space used for ALE processes, designed to maintain controlled plasma state, gas flow rate, and reaction chamber pressure.

[0019] Transformer-coupled plasma (TCP) source: A plasma generation system comprising central and edge RF coils positioned above dielectric windows in a vacuum reaction chamber, which generate plasma through electromagnetic field induction within the reaction chamber.

[0020] Base: A substrate carrier that holds the substrate in place during processing. In some embodiments, the base may be an electrostatic chuck (ESC) or a vacuum chuck, which can receive RF bias power to control ion energy and directionality.

[0021] Gas distribution unit: An assembly that introduces process gases into the reaction chamber. In some embodiments, the gas distribution unit may be a spray head or an injector, and includes separate channels for the different process gases used in the surface modification and sputtering steps.

[0022] Sidewall coils: One or more inductively coupled RF coils disposed along the sidewall of the reaction chamber adjacent to the substrate. Sidewall coils assist in the generation of free radicals during the surface modification step and enhance control over ion density, energy, and angle, particularly ion control at the substrate edges, during the sputtering step.

[0023] RF power generator: A power supply unit that can provide radio frequency power at different frequencies to maintain and control plasma characteristics.

[0024] Resonator: Impedance matching component used to optimize power transfer between the RF power generator and the reaction chamber.

[0025] Custom waveform generator: A device that generates a bias waveform applied to the base to optimize ion energy distribution.

[0026] Surface modification step: The first half of an ALE single cycle, in which free radicals in the plasma chemically react with the substrate surface to form a modified layer that is subsequently removed in the sputtering step. This process is typically self-limiting, ensuring precise material removal.

[0027] Sputtering step: The latter half of an ALE single cycle, in which the modified layer is physically removed by high-energy ions, thus completing an etching cycle with controlled material removal.

[0028] System controller: A computational system used to regulate process parameters such as RF power level, gas flow rate, pulse mode, and bias voltage to achieve accurate ALE process execution and etching uniformity.

[0029] Pulse mode: An RF power modulation method that uses timed pulses to control plasma ignition, ion energy, and free radical generation.

[0030] Bias voltage: The electric potential applied to the base to control the energy and directionality of ions in the plasma.

[0031] Process gas: The gas introduced into the reaction chamber during the ALE cycle. In some embodiments, a first process gas (such as chlorine) is used for the surface modification step, while an inert gas (such as argon) is used for the removal of the modified layer during the sputtering step.

[0032] Figure 1 An exemplary ALE process system 100 is shown. The process system 100 includes a reaction chamber 102 configured for performing plasma-based processes in a vacuum environment. The reaction chamber 102 is enclosed by a chamber wall 111, which includes a sidewall (or a portion thereof), designated as sidewall segment 113, which is made of a dielectric material such as quartz or ceramic.

[0033] The process system 100 also includes a TCP source comprising a center coil 114 and an edge coil 116. These coils are concentrically arranged on top of a dielectric window 107, which is made of a dielectric material such as quartz or ceramic. The distance between the outer edge of the edge coil 116 and the outer surface of the reaction chamber sidewall is 0 to 5 cm.

[0034] In one embodiment, the center coil 114 and the edge coil 116 are driven by the same RF power generator 104 via a resonator 106. A power divider 108 distributes the RF power from the RF power generator 104 to the two coils. The resonator 106 accommodates transmission line effects to match the impedance of the RF power generator 104 to the plasma impedance. The output RF power of the RF power generator 104 ranges from 50 to 5000 watts, and its operating frequency is selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz, and 400 kHz. The RF power generator 104 can also output RF power in pulse form according to a pulse mode, with power pulse frequencies ranging from 100 Hz to 100 kHz.

[0035] In another implementation scheme ( Figure 1 In the diagram (not shown), the center coil 114 and the edge coil 116 are driven by different RF power generators via their respective resonators, providing greater flexibility in selecting the frequency and pulse mode of each coil. For example, the center coil 114 receives 13.56 MHz of RF power, while the edge coil receives 1 MHz of RF power.

[0036] The process system 100 also includes an auxiliary sidewall coil 115, which receives RF power from the RF power generator 110 via a resonator 112. The sidewall coil 115 is disposed along a portion of the outer surface of a sidewall segment 113 made of a dielectric material such as quartz or ceramic to allow electromagnetic fields to penetrate into the interior of the reaction chamber 102. The sidewall coil 115 is positioned vertically at the shortest distance from the surface of the base 130.

[0037] The base 130 is used to fix the substrate 132 during processing. The base 130 can be an electrostatic chuck (ESC) or a vacuum chuck. The sidewall coil 115 can be configured as a single turn or multiple turns, and the distance between its lower edge and the surface of the base 130 is 0 to 4 cm, depending on the size of the reaction chamber 102.

[0038] The RF power generator 110 outputs RF power ranging from 50 to 1000 watts, and its operating frequency is selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz, 400 kHz, or 100 kHz. The RF power generator 110 can also output RF power in pulse form according to a pulse mode, with a power pulse frequency range of 100 Hz to 100 kHz. In another embodiment, the RF power generator 104 can also distribute a portion of its RF power to the sidewall coil 115 via a power divider 108.

[0039] The ALE process includes alternating surface modification and sputtering steps. During the surface modification step, sidewall coils 115 assist the center coil 114 and edge coils 116 to increase plasma density. Furthermore, sidewall coils 115 optimize the uniformity of free radical distribution within the reaction chamber 102.

[0040] During the sputtering step, sidewall coils 115, powered by RF power generator 110, generate plasma along the inner surface of the sidewalls of the reaction chamber 102. The plasma density can be adjusted according to process requirements and reaction chamber configuration. Sidewall coils 115 help control the ion density, energy, and angular distribution at the edges of the substrate 132, which is particularly critical when the plasma volume of the reaction chamber 102 is less than 10 liters. In smaller reaction chambers, ions generated by TCP sources (center and edge coils) may not have sufficient diffusion distance to achieve the required uniformity.

[0041] To increase ion energy during the sputtering step, the base 130 receives RF power from the RF power generator 118 via the resonator 120. The RF power generator 118 typically operates at a low frequency to enhance ion energy and achieve better directionality. The frequency of the RF power generator 118 can be selected from a frequency group including 2 MHz, 1 MHz, 400 kHz, or 100 kHz, and can output RF power in pulse form according to pulse patterns, with power pulse frequencies ranging from 100 Hz to 100 kHz. These pulse patterns can be synchronized or configured with specific timing control.

[0042] Gas distribution unit 126 receives process gas from gas source 128 and distributes the received process gas into reaction chamber 102. The gas distribution unit can be a spray head or an ejector. When configured as a spray head, the gas distribution unit can also simultaneously function as a dielectric window 107 to isolate reaction chamber 102. When the gas distribution unit is configured as an ejector, the dielectric window 107 includes an opening for accommodating the ejector, which needs to be adequately sealed to maintain a vacuum environment in reaction chamber 102.

[0043] In some embodiments, the spray head may include two separate lines for the first and second process gases used in the surface modification and sputtering steps, respectively. Additionally, in some embodiments, the gas distribution unit 126 may include a lateral injection mechanism located on the sidewall of the reaction chamber 102. The gas source 128 includes a gas box, various valves, and a mass flow controller (MFC).

[0044] A base 130 supports a substrate 132, which is typically a silicon substrate. Process gases, including reaction byproducts, are discharged from the reaction chamber 102 via a pump 136. A vacuum valve 134 located upstream of the pump regulates the gas discharge rate. The discharged gases pass through an exhaust line ( Figure 1 (Not shown in the image) Guided exhaust device. The pressure in the reaction chamber 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 and the reading of pressure gauge 138.

[0045] The operation of the process system 100 is coordinated by the system controller 140, which includes a computer and multiple software modules.

[0046] Figure 2 A flowchart of the ALE process 200 using process system 100 is shown.

[0047] Process 200 begins at step 202, where system controller 140 instructs gas distribution unit 126 to receive a first process gas (such as chlorine) from gas source 128. The first process gas is then distributed into reaction chamber 102.

[0048] In step 204, the center coil 114 and the edge coil 116 receive first RF power at a first frequency allocated according to a preset allocation rule from the RF power generator 104 via resonator 106. The first frequency can be selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz, and 400 kHz, and the output RF power ranges from 50 to 5000 watts. Furthermore, the RF power generator 110 can apply second RF power at a second frequency to the sidewall coil 115 via resonator 112. The second frequency can be selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz, 400 kHz, and 100 kHz, and the output RF power ranges from 50 to 1000 watts. The power generator can also output RF power in pulse form, with a frequency range of 100 Hz to 100 kHz. In this step, the base 130 is grounded to minimize ion bombardment.

[0049] In step 206, a surface modification step is performed, in which free radicals in the plasma react with the substrate 132 to form a modified layer with self-limiting properties. The duration of the substrate surface exposure to plasma is controlled to balance process performance and productivity; preferably, the exposure time is less than 200 milliseconds.

[0050] In step 208, an inert gas such as nitrogen may be used to purge the first process gas.

[0051] In step 210, the gas distribution unit 126 receives a second process gas (such as argon) and distributes the received second process gas into the reaction chamber 102.

[0052] In step 212, the center coil 114 and the edge coil 116 receive a third RF power at a third frequency from the RF power generator 104 via the resonator 106. The third frequency can be selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz, and 400 kHz, and the output RF power ranges from 50 to 5000 watts. Furthermore, the RF power generator 110 applies a fourth RF power at a fourth frequency to the sidewall coil 115. The fourth frequency can be selected from a frequency group including 2 MHz, 1 MHz, 400 kHz, and 100 kHz, and the output RF power ranges from 50 to 1000 watts. The power generator can also output RF power in pulse form, with a power pulse frequency range of 100 Hz to 100 kHz. The base 130 receives a fifth RF power from the RF power generator 118 via the resonator 120 to form a bias voltage of 50 to 5000 volts.

[0053] In step 214, a custom waveform generator 124 may be optionally applied to optimize the ion energy distribution.

[0054] In step 216, a sputtering step is performed to remove the modified layer by ions in the plasma. The bias voltage can be in the range of 50 to 5000 volts, and the RF power and custom waveform can be applied in pulses according to a preset pulse pattern.

[0055] In step 218, nitrogen may be used to purge the second process gas.

[0056] In step 220, steps 202 to 218 are repeated for a preset number of cycles until the ALE process is complete. The number of cycles can be adjusted according to the required etching depth and material removal rate. The system controller 140 dynamically manages process parameters, including RF power level, pulse mode, and gas flow rate, to ensure consistent etching performance and process uniformity.

[0057] By setting up multiple independent plasma sources and precisely controlling plasma characteristics, the process system 100, based on the TCP source and supplemented by sidewall coils, can optimize the performance of the ALE process. It is particularly suitable for use in smaller-volume reaction chambers where plasma homogeneity and process control are more challenging.

Claims

1. A process system, characterized by, include: A reaction chamber configured to operate under vacuum conditions, wherein at least a portion of the sidewalls of the reaction chamber are made of a dielectric material; A base, located within the reaction chamber, is configured to support a substrate during a plasma-based process. A gas distribution unit is configured to receive process gas and distribute the received process gas into the reaction chamber; A first radio frequency power generator is configured to apply a first radio frequency power to a central coil and an edge coil concentrically arranged at the top of the reaction cavity; A second radio frequency power generator is configured to apply a second radio frequency power to a sidewall coil, wherein the sidewall coil is arranged along a portion of the sidewall made of dielectric material; and A bias unit comprising a third RF power generator and / or a custom waveform generator, wherein the bias unit is coupled to the base.

2. The process system of claim 1, wherein, The distance between the outer edge of the edge coil and the outer surface of the sidewall is 0 to 5 centimeters.

3. The process system of claim 1, wherein, The dielectric material includes quartz and / or ceramic.

4. The process system of claim 1, wherein, The first radio frequency power generator is coupled to the center coil and the edge coil via a power divider, wherein the power divider is used to distribute radio frequency power to the center coil and the edge coil.

5. The process system of claim 1, wherein, The frequency of the first radio frequency power is selected from the frequency group including 13.56 MHz, 2 MHz, 1 MHz and 400 kHz.

6. The process system of claim 1, wherein, The power level of the first radio frequency power is 50 to 5000 watts.

7. The process system of claim 1, wherein, The first radio frequency power generator includes two radio frequency power generators, which are used to independently apply radio frequency power to the center coil and the edge coil, respectively.

8. The process system of claim 7, wherein, The two radio frequency power generators can operate at the same or different frequencies, selected from a frequency group including 13.56 MHz, 2 MHz, 1 MHz and 400 kHz.

9. The process system of claim 1, wherein, The sidewall coil includes a single-turn coil or a multi-turn coil.

10. The process system according to claim 1, characterized in that, The distance between the lower edge of the sidewall coil and the surface of the base is 0 to 4 centimeters.

11. The process system according to claim 1, characterized in that, The power level of the second radio frequency power is 50 to 1000 watts, and the frequency is selected from the frequency group including 13.56 MHz, 2 MHz, 1 MHz, 400 kHz and 100 kHz.

12. The process system of claim 1, wherein, The first RF power generator and the second RF power generator are integrated into a single RF power generator, and the RF power is distributed to the center coil, edge coil and sidewall coil via a power divider.

13. The process system of claim 1, wherein, The first radio frequency power, the second radio frequency power, and the third radio frequency power are output in pulse form according to their respective pulse modes, wherein their respective pulse modes can achieve pulse synchronization.

14. The process system of claim 1, wherein, The process system is configured as an atomic layer etching process system for performing an atomic layer etching process, wherein the atomic layer etching process includes a surface modification step and a sputtering step.

15. The process system of claim 1, wherein, All parts of the sidewall are made of dielectric material.

16. A method for processing a substrate with an atomic layer etching process, the method comprising: include: a. A reaction chamber for maintaining vacuum conditions, wherein the reaction chamber includes a transformer-coupled plasma source, sidewall coils, and a base, wherein the transformer-coupled plasma includes a central coil and an edge coil located at the top of the reaction chamber, the sidewall coils are arranged along the outer surface of the sidewall of the reaction chamber, and the base is coupled to a bias unit; b. Receive the first process gas through the gas distribution unit and distribute the received first process gas into the reaction chamber; c. Apply a first radio frequency power at a first frequency to the center coil and the edge coils through a power divider, apply a second radio frequency power at a second frequency to the sidewall coils, and ground the base; d. Perform surface modification steps using atomic layer etching (ALT) processes; e. Purge the first process gas from the reaction chamber; f. Receive the second process gas through the gas distribution unit and distribute the received second process gas into the reaction chamber; g. Apply a third radio frequency power at a third frequency to the center coil and the edge coils, apply a fourth radio frequency power at a fourth frequency to the sidewall coils, and apply a fifth radio frequency power to the base to establish a bias voltage; h. Apply a customized electrical waveform to the base using a customized waveform generator; i. Perform the sputtering step of the atomic layer etching process; j. Purging the reaction chamber with a second process gas; and k. Repeat steps b to j for a preset number of cycles until the atomic layer etching process is completed.

17. The method of claim 16, wherein, During the surface modification step, one or more of the radio frequency powers are output in pulse form according to their respective preset pulse patterns.

18. The method of claim 17, wherein, Each preset pulse mode includes pulse synchronization control.

19. The method of claim 16, wherein, During the sputtering step, one or more of the radio frequency powers are output in pulse form according to their respective preset pulse patterns.

20. The method of claim 19, wherein, Each preset pulse mode includes pulse synchronization control.

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