Simplified gas delivery system for atomic layer etching

Abstract

The invention relates to a simplified gas delivery system for atomic layer etching. According to the system, the overall cost is reduced by omitting the requirements of a gas tank and a pressure gauge. A preset mass flow controller (MFC) and a three-way valve can accurately control the gas flow in the surface modification step and the sputtering step of the ALE process. By means of the self-limiting property of the ALE process, the system does not need to maintain the steady-state pressure of the chamber, and the efficiency can be improved only by controlling the volume of the conveyed gas.

Description

Cross-references to related applications

[0001] This invention claims priority to U.S. Patent Application No. 18 / 904,028, filed on October 1, 2024. Technical Field

[0002] This invention relates to atomic layer etching (ALE) systems and methods, and more particularly to a simplified gas delivery system that can reduce overall costs and improve the efficiency of the ALE process. Background Technology

[0003] Reactive ion etching (RIE) is a major etching technique in semiconductor manufacturing. During RIE, various substances, including neutral particles, free radicals, and ions, interact and influence the etching process. A key feature of RIE is the synergistic effect of ion and neutral particle flux, which significantly increases the etching rate. The concept of this synergistic effect first appeared in Coburn and Winters' paper "Ion-and electron-assisted gas-surface chemistry—an important effect in plasma etching" published in J. Appl. Phys. (Vol. 50, pp. 3189-3196, 1979). They found that the etching rate of silicon was significantly increased when using argon ion beams, XeF2 neutral particle beams, and combinations thereof.

[0004] Efficient RIE etching requires both ion and neutral particle fluxes to maximize synergistic effects. However, balancing these fluxes becomes increasingly complex in modern etching processes, especially as etching dimensions advance to the nanometer scale and structures have high aspect ratios. Furthermore, achieving uniformity on 300mm wafers and consistent repeatability throughout the manufacturing process also presents challenges.

[0005] The development of ALE technology aims to overcome the limitations of RIE. The ALE process system evolved from the RIE process system, and its requirements for achieving uniformity on 300mm wafers are less stringent. However, ALE has unique requirements due to the characteristics of its process steps. Karanik et al. provided a brief overview of ALE technology in their article "Overview of atomic layer etching in the semiconductor industry" published in J.Vac.Sci.Technol. (A33, 020802 1-14, 2015), while Lill further explored ALE technology in "Atomic layer processing: semiconductor dry etching technology" (Wiley-VCH GmbH, 12 Boschstrasse, Weinheim, Germany, 69469, 2021). ALE enables atomically precise control of material layer removal and is an etching technique utilizing sequential self-limiting reactions.

[0006] ALE processes typically involve two steps: surface modification and material removal. The surface modification step creates a thin reactive layer of a predetermined thickness, which is easier to remove than the unmodified material. The material removal step removes the thin reactive layer while preserving the underlying unmodified substrate material, thus resetting the surface for subsequent cycles. Material removal can be achieved using thermal energy obtained by increasing wafer temperature or by utilizing the kinetic energy provided by inert gas ions. U.S. Patent No. 10,208,383 to George et al. discloses a process for removing the modified layer (i.e., the thin reactive layer) using thermal energy. U.S. Patent No. 10,727,073 to Tan et al. describes a process for removing the modified layer using ion bombardment.

[0007] Despite the numerous advantages of ALE, traditional ALE systems often operate slowly, primarily due to their complex and costly gas delivery mechanisms. Therefore, the industry urgently needs a more cost-effective and efficient gas delivery system to meet or even exceed current performance standards. Summary of the Invention

[0008] This invention relates to an ALE system with a simplified gas delivery system, which can reduce operating costs and increase process speed. The ALE process (especially anisotropic ALE) comprises two distinct steps: in the first step (surface modification step), a first gas (such as chlorine) is introduced into a chamber to modify the substrate surface and weaken chemical bonds in the material to be etched. This step can be accelerated by generating chemically active neutral particles through plasma generation.

[0009] In the second step (sputtering step), the modified layer is removed using a sputtering process. After the first gas is exhausted, a second gas (such as argon) is introduced into the chamber; by applying a bias voltage, the ions generated by the plasma are accelerated towards the substrate, thereby removing the modified layer.

[0010] In some embodiments, the first and second gases are directly sourced from a central gas supply unit, eliminating the need for separate gas tanks. During the surface modification step, the flow rate of the first gas is controlled by a mass flow controller (MFC) and introduced into the gas distribution unit of the chamber via a three-way valve. This three-way valve can direct the first gas into the chamber or a branch line. Atomic layer deposition (ALD) valves are recommended due to their millisecond-level rapid switching capability. The second gas is controlled similarly during the sputtering step.

[0011] In some embodiments, the pressure gauge can be completely omitted. The total amount of the first gas required for the chemical modification step is controlled by adjusting the flow rate and the step duration; similarly, the total amount of the second gas required for the sputtering step can also be adjusted.

[0012] This invention abandons the traditional goal of "maintaining steady-state pressure in the chamber" and instead utilizes the inherent self-limiting properties of the ALE process in the surface modification and sputtering steps. This method improves the speed of the ALE process without sacrificing performance. Attached Figure Description

[0013] To clearly describe the technical solution, the following explanation will refer to the accompanying drawings:

[0014] Figure 1 This illustrates the structure of a traditional ALE process system.

[0015] Figure 2 : This shows a flowchart of the traditional ALE process;

[0016] Figure 3 The present invention provides an exemplary ALE process system with a simplified gas delivery system.

[0017] Figure 4 The ALE process steps using a simplified gas delivery system are shown in detail. 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] Terminology definition:

[0020] Aspect Ratio: The ratio of the height to the width of a structure on a semiconductor wafer, which is crucial for defining the geometry and performance of microstructures.

[0021] Bias Unit: This unit generates a controlled voltage to accelerate ion bombardment of the wafer carried by the electrostatic chuck (ESC). The electric field generated by the bias voltage enhances ion bombardment, ensuring precise control over ion energy and directionality during etching.

[0022] Chamber: A closed environment used to perform semiconductor manufacturing processes (such as etching or deposition).

[0023] Chuck: A component used to carry and hold the position of a wafer in semiconductor manufacturing processes.

[0024] Electrostatic Chuck (ESC): A type of chuck that uses electrostatic force to fix the position of a wafer in a semiconductor manufacturing process, providing uniform clamping force and stability.

[0025] Gas Distribution Unit: A component within the plasma process chamber used to introduce and distribute process gases onto the substrate surface. For example, injectors can be placed centrally or arranged at a specific angle, or a showerhead-like structure can be used to achieve uniform gas dispersion. Furthermore, lateral injection mechanisms can be used to promote transverse gas flow, thereby improving distribution uniformity.

[0026] Gas pressure regulator: A device that controls and stabilizes gas pressure, providing precise pressure conditions for processes such as etching and deposition. Even if the supply gas or flow rate fluctuates, the device can maintain stable pressure.

[0027] Facility Gas Supply: The source of process gases used in vacuum process chambers, typically connected to a centralized gas distribution system. It regulates and controls gas flow and ensures that gas composition and purity meet requirements.

[0028] Anisotropic Atomic Layer Etching (ALE) is a precision etching process used in semiconductor manufacturing. This process removes material layer by layer at the atomic scale, allowing for precise control over etching depth and morphology. ALE operates in a cyclic manner and typically includes a surface modification step (chemically modifying the surface to form a reactive layer) and a sputtering step (removing the reactive layer through physical ion bombardment). It is characterized by high precision and high selectivity.

[0029] Plasma Process Chamber: A vacuum chamber designed specifically for processes involving plasma, such as etching or deposition, where plasma provides the energy needed to activate chemical reactions or remove materials.

[0030] Plasma Source: Used to generate plasma for etching, deposition, or surface modification. Examples of plasma sources include inductively coupled plasma (ICP), transformer-coupled plasma (TCP), and capacitively coupled plasma (CCP). ICP generates plasma using an RF magnetic field produced by a coil; TCP generates plasma through the induction of RF energy between a planar coil; and CCP generates plasma by applying RF power between two electrodes.

[0031] Process System: refers to the integrated equipment used in semiconductor manufacturing to perform various processes (such as deposition, etching, and cleaning).

[0032] Reactive ion etching (RIE) is a plasma-based etching technique that combines physical ion bombardment and chemical reaction to synergistically remove substrate material. In RIE, reactive gases are ionized in the plasma to generate ions and neutral particles; the ions are accelerated toward the substrate under the influence of an electric field, physically sputtering the material, while the active neutral particles enhance the chemical etching effect.

[0033] A resonator is a device or circuit component that generates resonance at a specific RF frequency, used in applications such as RF impedance matching. Resonators can be manufactured using various components (such as inductor-capacitor circuits) and exhibit high selectivity and stability at the resonant frequency.

[0034] RF Power Generator: A device that generates RF power to excite plasma in processes such as etching or deposition.

[0035] Substrate: The basic material upon which semiconductor devices are manufactured, usually a silicon wafer.

[0036] System Controller: The central unit that manages and controls the operation of the process system, ensuring the coordinated and efficient operation of the semiconductor manufacturing process.

[0037] Tailored Waveform Generator: This generator produces customized electrical waveforms to optimize plasma processes. By adjusting the shape, frequency, and amplitude of the waveform, plasma characteristics can be precisely controlled, improving the uniformity, performance, and selectivity of etching and deposition processes.

[0038] Transmission line: In RF technology, a conductor used to transmit RF signals with minimal loss and distortion. In semiconductor manufacturing, transmission lines are used to transfer RF power from a generator to a plasma source, aiding in impedance matching to reduce reflections and power loss.

[0039] Figure 1 A conventional ALE process system 100 is shown. This system includes a plasma process chamber 101 situated in a vacuum environment, equipped with a plasma source 102 powered by an RF power generator 103. The plasma source 102 can be configured as TCP or ICP. In some configurations, a matching network (such as a resonator, not shown) can be provided between the RF power generator 103 and the plasma source 102, taking into account the effects of transmission lines, to achieve impedance matching between the RF power generator output and the plasma load in the chamber 101; in other configurations, a direct connection can also be used.

[0040] The ALE process system 100 also includes a gas distribution unit 104, which draws gas from the gas tank 106 via a gas manifold 105. Depending on specific design requirements, the gas distribution unit 104 can be configured as a spray head or an injector. Before introducing gas into the chamber 101, gases from different pipelines are mixed via the gas manifold 105. Valves 112 and 114 control the flow of gases 108 and 110 from the gas tank 106 to the gas manifold 105, and valve 116 controls the flow of gas from the gas manifold 105 to the gas distribution unit 104. For simplicity, only two gas pipelines are shown in the figure, but various ALE processes may involve multiple gases. The gas tank 106 is connected to a central gas supply unit 107.

[0041] Inside chamber 101, chuck 121 supports substrate 120. Chuck 121 is typically an electrostatic chuck (ESC), particularly suitable for etching applications. To ensure optimal ion energy (especially when etching high aspect ratio structures), bias unit 119 is activated when plasma is generated within the chamber. Depending on system design specifications, an RF power generator connected to chuck 121 supplies power to the bias unit via a DC blocking capacitor, or a custom waveform generator can supply power to the bias unit.

[0042] Pump 124 expels the gas and reaction byproducts from chamber 101. Vacuum valve 122, located near the pump, controls the gas expiratory rate, and the gas is directed to exhaust port 126 via exhaust line 125. The steady-state pressure within the chamber is maintained by balancing the gas injection and expiratory rates: pressure gauge 127 collects pressure data and manages the pressure using a proportional-integral-derivative (PID) control loop.

[0043] In a typical ALE process, two different steps (surface modification and sputtering) use two different gases. These two steps are often referred to as a "half-cycle" and together they constitute a complete ALE cycle.

[0044] Figure 2 The flow chart 200 of a conventional ALE process is shown. Step 201: A first gas 108 from a gas box 106 is introduced into a chamber 101 via a gas distribution unit 104. Step 202: The first gas chemically modifies the surface of a substrate 120. For example, chlorine gas can be used to form silicon-chlorine bonds, which are weaker than the underlying silicon-silicon bonds. Plasma generated by an RF power generator 103 and a plasma source 102 can assist this chemical modification process. In this step, the chuck bias unit is off to minimize ion bombardment of the substrate surface.

[0045] Step 204: The surface modification step ends. At this point, the supply of the first gas 108 is stopped, and the second gas 110 (usually an inert gas) is introduced into the chamber 101. Step 206: In the sputtering step, the modified layer is removed by ion bombardment—ions generated by the second gas are accelerated under the action of the bias unit 119, thereby removing the modified layer.

[0046] Since each ALE cycle can only remove a few single-atom layers of material, multiple cycles are required to achieve the desired etching depth. In some cases (especially when etching high aspect ratio structures), the number of ALE cycles may exceed 100. Step 208: Count the number of cycles and compare it with the preset process formulation; if the target number of cycles is reached, the process ends; otherwise, in step 210, the second gas is replaced with the first gas, and a new ALE cycle is started. A delay can be set between gas switches to avoid generating unintended RIEs.

[0047] Figure 3 An embodiment of an ALE process system 300 is shown, featuring a simplified gas delivery system. This embodiment differs significantly from the conventional ALE process system 100 in several ways: first, the gas chamber is eliminated, reducing system cost (the gas chamber is a relatively expensive component in ALE process systems); second, the pressure gauge 327 becomes an optional component and can be omitted in some embodiments. In conventional systems, the pressure gauge is used to measure the vacuum pressure within the chamber and works in conjunction with pumps and valves to achieve the stable pressure required for the etching process through PID control.

[0048] This embodiment employs a novel control strategy: instead of aiming to stabilize the chamber pressure, process control is achieved by controlling the total amount of gas introduced into the chamber during the surface modification and sputtering steps. The total gas amount is determined by both the gas flow rate and the duration of gas introduction into the chamber.

[0049] The ALE process exhibits inherent self-limiting characteristics in both the surface modification and sputtering steps. For example, once a sufficient amount of chemically active neutral particles are adsorbed onto the substrate surface, further modification ceases; similarly, the sputtering step has a relatively stable process window within which increasing ion energy or ion density does not significantly improve the material removal rate. These self-limiting characteristics make it possible to reduce costs without sacrificing performance.

[0050] The ALE process system 300 includes a plasma process chamber 301 capable of maintaining a vacuum environment, and the chamber 301 is equipped with a plasma source 302 connected to an RF power generator 303. A gas distribution unit 304 (configurable as a spray head or ejector) draws gas directly from a central gas supply unit 310, eliminating the need for a gas tank. A first gas 312 enters the gas distribution unit 304 sequentially through a first MFC 306 and a first three-way valve 316, which can direct the gas to the chamber, a first branch line 315, or remain closed. A first gas pressure regulator 309 is provided between the central gas supply unit 310 and the MFC 306 to ensure that the gas pressure meets requirements.

[0051] MFC 306 is used to control the flow rate of the first gas 312, but due to its inherent delay characteristics, it takes tens of milliseconds to reach the specified flow rate by initiating the PID control within the MFC. In one implementation, the flow rate setpoint (such as the electromagnetic coil current) can be predetermined during the setup process and stored for later use; in another implementation, the flow rate of the MFC can be stabilized before the ALE process begins and remain stable throughout the process.

[0052] Similarly, a second gas pressure regulator 311 is provided between the second MFC 308 and the central gas supply device 310; the second three-way valve 318 can guide the second gas 314 to the chamber or the second diversion line 317.

[0053] ALD valves are recommended due to their millisecond-level fast switching capability; in some implementations, combinations of various valves known in the art may also be used.

[0054] The system controller 307 coordinates and controls the operation of the ALE process system 300: analyzes the process recipe to determine the gas flow rate, monitors the operation of the first three-way valve 316 and the second three-way valve 318 (by providing pulse electrical signals to control the valve timing), and manages the start-up and shutdown of the ALE process.

[0055] A chuck 321 (typically an ESC) is located at the lower part of chamber 301 for securing substrate 320 during the process. For processes involving high aspect ratio structures, bias unit 319 is used to provide higher ion energy, which can be powered by an RF generator or a custom waveform generator.

[0056] Pump 324 discharges the gas and reaction byproducts from chamber 301 through vacuum valve 322. Unlike conventional systems, this embodiment does not require reaching the steady-state pressure of the chamber, thus eliminating the need for a pressure gauge; however, the set value of the vacuum valve can be determined during setup and controlled by system controller 307.

[0057] Figure 4 The detailed process flow of the ALE process system 300 is shown, labeled 400. Step 402: Before starting the ALE process, MFC 306 and MFC 308 are preset to a specified flow rate according to the process recipe. This flow rate can be achieved by directly generating the electromagnetic coil current of the MFC (without using internal PID control), or by allowing the MFC to reach a steady state before the process starts; at this time, the gas is initially directed to the first branch line 315 and the second branch line 317.

[0058] Step 404 includes two parallel sub-steps (sub-step 404A and sub-step 404B): In sub-step 404A, the first three-way valve 316 opens, allowing the first gas 312 to flow into the chamber 301 at a flow rate preset by the MFC 306; the total gas volume is calculated by the flow rate and the opening duration of the first three-way valve 316 (controlled by the pulse electrical signal of the system controller 307); simultaneously, in sub-step 404B, the second three-way valve 318 directs the second gas 314 to the second branch line 317.

[0059] Step 406: Perform surface modification by chemically modifying the substrate surface, thereby weakening the chemical bonds in the material to be etched.

[0060] Step 408: The system executes two synchronized sub-steps (sub-step 408A and sub-step 408B): In sub-step 408A, the first three-way valve 316 switches the first gas 312 to the first branch line 315; in sub-step 408B, the second three-way valve 318 introduces the second gas 314 into the chamber for the sputtering step. These two sub-steps can be performed simultaneously or with a set delay (controlled by the system controller 307) to ensure complete discharge of the first gas.

[0061] Step 410: Perform the sputtering step, where high-energy ions generated by the plasma and bias unit remove the chemically modified layer. This completes one ALE cycle; subsequently, the second gas 314 is exhausted from the chamber while the first gas 312 is reintroduced to initiate the next cycle.

[0062] Finally, in step 412, the system controller 307 determines whether the required number of ALE cycles has been completed: if not, the cycle repeats; if completed, the process ends.

[0063] The concept of this invention can be extended to other process systems, such as ALD process systems, other thermal process systems, or any process system that requires rapid switching of gas or precursor.

Claims

1. A process system, characterized in that, include: The plasma processing chamber is configured as a vacuum environment; A plasma source, which is connected to an RF power generator; Gas delivery system, comprising: Central gas supply system; A gas distribution unit is used to distribute gas from the central gas supply device to the chamber; A first MFC and a first valve are sequentially disposed between the central gas supply device and the gas distribution unit for conveying a first gas. The first valve may deliver the first gas to the chamber or the first branch line, or may be in a closed state. A second MFC and a second valve are sequentially disposed between the central gas supply unit and the gas distribution unit for supplying a second gas. The second valve can supply the second gas to the chamber or the second branch line, or be in a closed state. A system controller is configured to execute an ALE process comprising multiple cycles, each cycle including a surface modification step and a subsequent sputtering step, wherein the system controller is further configured to: During the surface modification step, the first valve is operated to deliver the first gas through the gas distribution unit to the chamber, and the second valve is operated to direct the second gas to the second branch line; During the sputtering step, the second valve is operated to deliver the second gas through the gas distribution unit to the chamber, and the first valve is operated to direct the first gas to the first branch line; Before the ALE process begins, the first MFC and the second MFC are preset to the specified flow rates of the first gas and the second gas, respectively, and remain unchanged during the ALE process.

2. The process system according to claim 1, wherein, The gas delivery system further includes a first gas pressure regulator and a second gas pressure regulator to regulate the first gas and the second gas, respectively.

3. The process system according to claim 2, wherein, The gas delivery system is configured to eliminate the need for a gas tank.

4. The process system according to claim 1, wherein, The system controller is configured to perform the ALE process without reaching the chamber steady-state pressure, and the process system does not require a pressure gauge to measure the chamber pressure.

5. The process system according to claim 1, wherein, The first valve and the second valve are ALD valve.

6. The process system according to claim 1, wherein, The first valve and the second valve are controlled by the system controller via pulse electrical signals.

7. The process system according to claim 6, wherein, The signal to stop the flow of the first gas into the chamber is synchronized with the signal to introduce the second gas into the chamber.

8. The process system according to claim 6, wherein, The signal to stop the flow of the first gas into the chamber is not synchronized with the signal to introduce the second gas into the chamber, and a delay is set to ensure that the first gas is emptied from the chamber.

9. The process system according to claim 6, wherein, The signal to stop the flow of the second gas into the chamber is synchronized with the signal to introduce the first gas into the chamber.

10. The process system according to claim 6, wherein, The signal to stop the flow of the second gas into the chamber is not synchronized with the signal to introduce the first gas into the chamber, and a delay is set to ensure that the second gas is emptied from the chamber.

11. The process system according to claim 1, wherein, The setpoints of the first MFC, the second MFC, and the vacuum valve are determined during the setup process and remain unchanged throughout the ALE process.

12. The process system according to claim 1, wherein, The first MFC, the second MFC, and the vacuum valve include PID control, and the PID control remains off throughout the ALE process.

13. The process system according to claim 11, wherein, The settings for the first MFC and the second MFC include the electromagnetic coil current.

14. A gas delivery system for an ALE process system, characterized in that, include: The first MFC and the second MFC are preset to the predetermined flow rates of the first gas and the second gas, respectively, wherein the set values ​​of the first MFC and the second MFC remain unchanged throughout the ALE process; the first three-way valve and the second three-way valve are configured to direct one of the first gas and the second gas to the process chamber, while directing the other of the first gas and the second gas to the diversion line. as well as A first gas pressure regulator and a second gas pressure regulator are used to maintain the first gas and the second gas at a specified pressure before they enter the first MFC and the second MFC, respectively.

15. The gas delivery system according to claim 14, wherein, The ALE process system does not require reaching the steady-state pressure of the chamber and does not require a pressure gauge to be installed in the process chamber when used for ALE processes.

16. The gas delivery system according to claim 14, wherein, The gas delivery system is configured to eliminate the need for a gas tank.

17. The gas delivery system according to claim 14, wherein, The system controller is configured to provide pulsed electrical signals to the first three-way valve and the second three-way valve to control their operation.

18. The gas delivery system according to claim 14, wherein, The first MFC, the second MFC, and the vacuum valve each contain set values, which are determined during the setting process and remain unchanged during the ALE process.

19. The gas delivery system according to claim 14, wherein, The first MFC, the second MFC, and the vacuum valve include PID control, and the PID control remains off during the ALE process.

20. The gas delivery system according to claim 18, wherein, The settings for the first MFC and the second MFC include the electromagnetic coil current.

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