Atomic layer etching system and method with uniformity control mechanism

Abstract

The invention relates to an atomic layer etching system and method with a uniformity control mechanism. The ALE process includes a plurality of cycles, each cycle including a surface modification step and a sputtering step. The plasma source includes a center coil and an edge coil. The system supports the use of different selectable configurations in sputtering steps in different ALE cycles, capable of independently activating or closing the center coil and the edge coil. The flexibility provides a mechanism for adjusting the etching rate of the center and the edge of the substrate, so that non-uniformity (such as thickness difference) of the substrate to be processed is compensated. The system controller can generate a process formula based on the to-be-processed substrate data and the output specification so as to ensure that the etching process meets the expected performance requirement.

Description

Cross-references to related applications

[0001] This invention claims priority to U.S. Patent Application No. 18 / 898,599, filed on September 26, 2024. Technical Field

[0002] This invention relates to plasma-based semiconductor manufacturing processes, and more specifically, to an atomic layer etching (ALE) system and method that improves control over substrate etching uniformity. The invention provides selectable sputtering steps during the ALE cycle to compensate for non-uniformities in the substrate being processed, such as differences in target layer thickness, while maintaining the inherent precision and uniformity of ALE. 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 fluxes, which significantly improves 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 improved when using argon ion beams, XeF2 neutral particle beams, and combinations thereof. Efficient RIE etching requires both ion and neutral particle fluxes to maximize the synergistic effect. However, in modern etching processes, especially when etching dimensions are pushed down to the nanometer scale and structures have high aspect ratios, balancing these fluxes becomes increasingly complex. Furthermore, achieving uniformity on 300mm wafers and consistent repeatability in the manufacturing process also presents challenges.

[0004] The development of ALE technology aims to overcome the limitations of RIE. The ALE process system evolved from the RIE process system, which has less stringent requirements for achieving uniformity on 300mm wafers. However, ALE has unique requirements due to the characteristics of its process steps. Karanik et al. provided an overview of ALE technology in "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. The ALE process typically involves two steps: surface modification and material removal. The surface modification step forms a thin reactive layer of a predetermined thickness, which is easier to remove than the unmodified material. The material removal step removes the formed 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 an isotropic process for removing the modified layer (i.e., the thin reactive layer) using thermal energy. When using high-energy ions, the material removal step is achieved through a sputtering process. The anisotropic ALE process described in U.S. Patent No. 10,727,073 to Tan et al. demonstrates the versatility of this technology.

[0005] Although ALE itself has good uniformity, the substrate still exhibits some non-uniformity due to previous process steps, such as differences in target layer thickness. If left unaddressed, these differences can affect the overall performance of the final device. Advanced process control urgently requires systems capable of compensating for these non-uniformities without sacrificing etching process accuracy.

[0006] Existing ALE process systems typically lack the flexibility to dynamically adjust to address specific substrate variations. While conventional ALE cycles are designed to be consistent, they do not account for the need to personalize the etching process to compensate for non-uniformity in different areas of the substrate.

[0007] Therefore, there is an urgent need for a more flexible ALE process system to achieve precise control over the sputtering steps, thereby solving the problem of substrate non-uniformity and ensuring that the final etching results meet the stringent requirements of advanced semiconductor manufacturing processes. Summary of the Invention

[0008] This invention relates to a system and method for performing ALE (Advanced Etching Element) that enhances control over process uniformity, particularly in response to non-uniformity in the substrate to be processed. In some embodiments, the invention provides a system controller for managing an etching process across multiple ALE cycles, each ALE cycle including a surface modification step and a sputtering step. While ALE inherently possesses uniformity due to its self-limiting properties, in some processes, it is necessary to compensate for non-uniformity such as differences in target layer thickness to achieve the desired etching effect.

[0009] To address the aforementioned non-uniformity, in some embodiments, the system incorporates optional configurations for the sputtering steps. These configurations allow the system controller to adjust the etching characteristics of different substrate regions. For example, the system controller can selectively activate or deactivate the center or edge coils during the sputtering step to focus the etching process on specific areas, such as enhancing etching at the center or edges of the substrate. This flexibility enables precise control of the layer removal process and allows for customization of each ALE cycle based on the needs of the substrate being processed.

[0010] In some embodiments, the system controller can determine the optimal configuration for the sputtering steps by analyzing data related to substrate non-uniformity. This effectively compensates for thickness differences or other deviations on the substrate, thereby improving the overall uniformity of the final etched layer. The aforementioned optional configurations tailored to each ALE cycle provide a key mechanism for addressing complex process control requirements without affecting the inherent uniformity of the ALE process itself.

[0011] Therefore, this invention provides greater adaptability to the ALE process, enabling fine-tuning of the process to address specific substrate differences while maintaining the inherent uniformity of the ALE process. Attached Figure Description

[0012] To clearly describe the technical solution of the present invention, the following description will refer to the accompanying drawings:

[0013] Figure 1 This schematically illustrates the ALE process system.

[0014] Figure 2 The illustration schematically shows a transformer-coupled plasma (TCP) source configured with a central coil and edge coils.

[0015] Figure 3A This schematically illustrates a first implementation of a TCP source, where the center coil and edge coils are driven by a single RF power generator via an RF power divider.

[0016] Figure 3B The illustration shows a second implementation of the TCP source, in which the center coil and the edge coils are driven by different RF power generators to achieve independent control.

[0017] Figure 4 The flowchart of the ALE process with a uniformity control mechanism is illustrated.

[0018] Figure 5 The flowchart illustrates an ALE process with optional sputtering steps.

[0019] Figure 6 Table 1 shows the optional configurations of the sputtering steps in the ALE process to address substrate non-uniformity. Detailed Implementation

[0020] 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.

[0021] The terminology used in this invention is defined as follows:

[0022] 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 the etching depth and morphology. ALE operates in a cyclic manner and typically includes a surface modification step (chemically modifying the surface) and a sputtering step (removing the modified surface layer by physical ion bombardment).

[0023] Bias Unit: This unit generates a controlled voltage to accelerate ion bombardment of the substrate carried by the electrostatic chuck (ESC). The electric field generated by the bias unit enhances ion bombardment, ensuring precise control over ion energy and directionality during etching.

[0024] Chamber: A closed environment within a process facility used to perform semiconductor manufacturing processes (such as etching or deposition).

[0025] Chuck: A component used to carry and hold the position of a substrate in semiconductor manufacturing processes.

[0026] Electrostatic chuck (ESC): A chuck that uses electrostatic force to fix the position of a substrate in a semiconductor manufacturing process, providing uniform clamping force and stability.

[0027] Gas Distribution Unit: In some embodiments, this unit is used to distribute process gases to the substrate surface. This unit can achieve gas dispersion through injectors, showerhead structures, or lateral jet mechanisms, thereby improving the uniformity of gas distribution.

[0028] Gas Source: Refers to the origin or supply point of the process gas in the vacuum process chamber. In some embodiments, the gas box controls and regulates the gas flow rate under controlled pressure conditions.

[0029] Plasma Source: In some embodiments, a plasma source is used to generate plasma for processes such as etching or deposition. As examples, plasmas include inductively coupled plasma (ICP), TCP, and capacitively coupled plasma (CCP).

[0030] Process System: refers to the integrated equipment used in semiconductor manufacturing to perform various processes (such as deposition, etching, or surface modification).

[0031] Pulsing: A technique that modulates RF power in the form of pulses (discontinuous wave form) to better control plasma energy and improve process effects such as etching accuracy and uniformity.

[0032] Reactive ion etching (RIE) is a plasma etching technique that removes material from a substrate by combining physical ion bombardment with chemical reactions. RIE enables anisotropic etching, which is crucial for complex microfabrication processes.

[0033] A resonator is a device or component that generates resonance under specific RF conditions and is often used for RF impedance matching in semiconductor processing equipment applications.

[0034] RF Power Generator: A device that generates RF energy to sustain plasma in semiconductor manufacturing processes such as etching or deposition.

[0035] Substrate: The substrate used in the manufacture of semiconductor devices, usually a silicon wafer.

[0036] System Controller: The central control unit that coordinates and manages the operation of the process system to ensure the efficient and precise execution of semiconductor processes.

[0037] Tailored Waveform Generator: In some implementations, this generator can generate customized electrical waveforms to optimize ion energy distribution and improve etching or deposition performance.

[0038] Transmission line: In RF technology, a conductor used to transmit RF signals with minimal loss and distortion. Transmission lines ensure efficient power transfer in semiconductor manufacturing processes such as etching or deposition.

[0039] Vacuum Chamber: A closed space that removes air and other gases to create a low-pressure environment, which is crucial for precision semiconductor manufacturing processes.

[0040] Window: In a vacuum chamber, this window isolates the plasma generation area from external components. It is typically made of a non-conductive material, allowing electromagnetic waves such as RF or microwave energy to pass through.

[0041] See Figure 1 Gas distribution unit 104 introduces gas from gas chamber 106 via gas manifold 105. Gas distribution unit 104 can be configured as a shower head or injector according to design requirements. Gas manifold 105 mixes the gas before it enters process chamber 101. Gas chamber 106 typically includes components such as mass flow controllers (MFCs), pressure regulators, particulate filters, gas mixers, and safety sensors. Two valves 135 and 137 are provided between gas chamber 106 and gas manifold 105 to control the flow of first gas 108 and second gas 110, respectively. Although only two gas lines are shown in the figure, more gas lines may be used in some embodiments. Valve 116 is provided between gas manifold 105 and gas distribution unit 104 to regulate the flow rate of gas entering chamber 101. Gas chamber 106 is connected to gas source 107.

[0042] Plasma source 102 is connected to RF power generator 103 to generate plasma in the chamber. In the lower region of chamber 101, chuck 121 carries substrate 120 during the process. Chuck 121 is typically an ESC suitable for etching processes. To increase ion energy during etching (especially when etching high aspect ratio structures), bias unit 119 can be used when the plasma in the chamber is excited. Depending on the design, bias unit 119 can be an RF power generator connected to chuck 121 via a blocking capacitor, or it can be a specially configured custom waveform generator.

[0043] Gases, including reaction byproducts, are discharged from chamber 101 via pump 124. A vacuum valve 122, located upstream of pump 124, regulates the gas discharge rate. The discharged gas flows to exhaust port 126 via exhaust line 125. Chamber pressure control is achieved by balancing the gas injection and discharge rates; specifically, pressure regulation can be performed using a proportional-integral-derivative (PID) control loop based on readings from pressure gauge 127.

[0044] The ALE process operates in a cyclic manner, typically involving two gases supplied sequentially in two different steps: a surface modification step and a sputtering step. These are often referred to as two "half-cycles," together forming a complete ALE cycle. The surface modification step is usually called step A, and the sputtering step is called step B.

[0045] The operation of the process system 100 is coordinated by a system controller 128, which includes a computer and multiple software modules. The system controller 128 includes an ALE process recipe generator 130, which, when generating ALE process recipes, considers not only the final output specifications but also relevant information about the substrate to be processed. The ALE process recipe generator 130 is one of the software modules of the system controller 128. The information data about the substrate to be processed includes, but is not limited to, parameters such as the substrate's critical dimensions (CD) and target layer thickness.

[0046] Figure 2 A top view of two concentric coils 200 is shown, which are used to improve the homogeneity of the plasma within chamber 101. The plasma source 200 includes a center coil 202 and an edge coil 204. The center coil 202 is connected to an RF power generator via a pair of connectors 206, while the edge coil 204 is connected to the same or a different RF power generator via another pair of connectors 208. Although... Figure 2 Only single-turn coils are shown, but these coils can be multi-turn structures or employ various geometries known in the art.

[0047] In one embodiment, such as Figure 3A In a first implementation 300 of the plasma source 200 shown, a center coil 202 and an edge coil 204 are connected to an RF power generator 210 via a resonator 212. An RF power divider 214 is located between the resonator 212 and the coils to distribute RF power between the center coil 202 and the edge coil 204. The distribution ratio can be set by the process recipe. For example, the center coil 202 may receive 60% of the RF power from the RF power generator 210, while the edge coil 204 receives the remaining 40% of the RF power.

[0048] In another embodiment, such as Figure 3B In the second implementation 302 of the plasma source 200 shown, RF power generator 216 supplies power to the center coil 202 via resonator 218, while RF power generator 222 supplies power to the edge coil 204 via resonator 224. This embodiment provides greater flexibility by distributing different RF power to the center and edge coils via RF power dividers 220 and 226, respectively. Furthermore, the center and edge coils can also receive RF power of different frequencies or pulse patterns.

[0049] Figure 4 A flowchart of an ALE process 400 with a uniformity control mechanism is shown. The ALE process 400 begins at step 402, where a system controller 128 optionally receives data about the substrate to be processed. The system controller 128 optionally analyzes this data to determine the required etching performance, for example, to compensate for substrate non-uniformity. For example, the system controller 128 may determine that additional etching is needed in the central region of the substrate to correct for thickness differences in the target layer. Based on the required etching performance, the system controller 128 determines the cycle count for steps A and B in step 404.

[0050] A key feature of this invention is that different step B sputtering conditions can be optionally applied in different ALE cycles, such as... Figure 6 As shown in Table 1. In step B1, both the center coil and the edge coils (202 and 204) are activated to achieve uniform sputtering on the substrate; in step B2, only the center coil 202 is activated to enhance sputtering on the central region of the substrate; in step B3, only the edge coil 204 is activated to enhance sputtering on the edge region of the substrate.

[0051] In step 406, step A of the ALE cycle is performed, where chemically active neutral particles from the plasma diffuse and modify the substrate surface. Ideally, this step is a self-limiting process, meaning it can be performed after the substrate surface has been exposed to neutral particles for a sufficient time (typically several hundred milliseconds). To achieve the ideal ALE process, the bombardment of the substrate surface by ions needs to be eliminated in this surface modification step.

[0052] In step 408, system controller 128 selects one of the optional configurations of step B (including B1, B2, or B3). In step 410, the selected sputtering step is performed to remove the modified layer formed in step 406. Depending on the selected scheme, the removal of the modified layer may be region-selective. In step 412, system controller 128 updates the cycle count of the step. In step 414, system controller 128 determines whether the ALE process is complete; if complete, ALE process 400 ends; if not complete, it returns to step 406 to continue executing the cycle.

[0053] like Figure 5 As shown, ALE process formulation 500 includes three cycles in step 502 (each cycle performing steps A and B), followed by two cycles in step 504 (each cycle performing steps A and B1). The process formulation concludes with two additional cycles in step 506 (each cycle performing steps A and B). This specific process formulation produces a stronger etching effect in the central region of the substrate than in the edge regions, thereby achieving a customized etching profile for specific substrate non-uniformity.

[0054] It should be noted that the TCP source with two concentric coils shown in this invention is merely illustrative. More than two concentric coils may be used. In some designs, an ICP source including concentric coils may also be used. In other embodiments, TCP coils and ICP coils may be combined for use in the central and edge regions of the substrate. In other embodiments, the coils may be disposed on the dome structure at the top of the chamber or on the sidewall of the chamber. In still other designs, the plasma source may also provide enhanced or reduced sputtering capability to specific areas of the substrate in a particular cycle. All such variations are within the scope of the inventive concept.

Claims

1. A process system, characterized in that, include: The process chamber is configured as a vacuum environment; A chuck, located within the process chamber, is used to support the substrate to be processed during the ALE process; A gas distribution unit for introducing process gas into the process chamber; A plasma source for generating plasma in the process chamber, wherein the plasma source includes a central coil and an edge coil disposed above a window for sealing the process chamber; as well as A system controller configured to coordinate the operation of the process system to execute the ALE process according to a process recipe comprising multiple cycles, each cycle comprising a surface modification step and a sputtering step, wherein the sputtering step comprises multiple optional configurations, each of which can be used for different ALE cycles, wherein the optional configurations include selectively activating or deactivating the center coil and the edge coils.

2. The process system according to claim 1, wherein the center coil and the edge coil are connected to the RF power generator via a resonator, and the process system achieves power distribution between the center coil and the edge coil via an RF power divider.

3. The process system according to claim 1, wherein the center coil is connected to the first RF power generator via a first resonator, and the edge coil is connected to the second RF power generator via a second resonator.

4. The process system according to claim 1, wherein the optional configuration of the sputtering step includes: Activate the center coil and the edge coils; activate the center coil and deactivate the edge coils; The center coil is turned off and the edge coils are activated.

5. The process system according to claim 1, wherein the center coil has a single-turn structure or a multi-turn structure.

6. The process system according to claim 1, wherein the edge coil has a single-turn structure or a multi-turn structure.

7. The process system according to claim 3, wherein the first RF power generator and the second RF power generator have different operating frequencies.

8. The process system of claim 1, wherein the system controller determines the process formulation based on the data of the substrate to be processed and the output specifications of the ALE process.

9. A method for processing a substrate using ALE technology, characterized in that, include: Step a: Provide a process chamber with a vacuum environment and generate plasma through a plasma source, wherein the plasma source includes a central coil and edge coils arranged concentrically; Step b: Place the substrate to be processed onto the chuck inside the process chamber; Step c: Perform the surface modification step via the system controller; Step d: Select one of several optional configurations for the sputtering step via the system controller; Step e: Optional configuration for executing the selected sputtering step via the system controller; and Step f: Repeat steps c through e until the ALE process is complete.

10. The method of claim 9, wherein the optional configuration includes activating the center coil and the edge coils.

11. The method of claim 9, wherein the optional configuration includes activating the center coil and deactivating the edge coils.

12. The method of claim 9, wherein the optional configuration includes turning off the center coil and activating the edge coils.

13. The method of claim 9, wherein the center coil and the edge coil are connected to the RF power generator via an RF power divider.

14. The method of claim 9, wherein the center coil is connected to the first RF power generator and the edge coil is connected to the second RF power generator.

15. The method of claim 9, further comprising the system controller generating a process recipe based on data from the substrate to be processed and the output specifications of the ALE process.

16. A method for processing a substrate using ALE technology, characterized in that, include: Step a: Provide a process chamber with a vacuum environment and generate plasma through a plasma source, wherein the plasma source includes a central coil and edge coils arranged concentrically; Step b: Receive data from the substrate to be processed via the system controller; Step c: Generate a process recipe comprising multiple ALE cycles via the system controller, wherein each ALE cycle includes a surface modification step and a sputtering step, and the sputtering step includes optional sputtering steps for different ALE cycles; Step d: Place the substrate to be processed onto the chuck inside the process chamber; as well as Step e: Execute the ALE cycle according to the generated process recipe.

17. The method of claim 16, wherein the optional sputtering step includes activating the center coil and the edge coil.

18. The method of claim 16, wherein the optional sputtering step includes activating the center coil and deactivating the edge coils.

19. The method of claim 16, wherein the optional sputtering step includes shutting off the center coil and activating the edge coils.

20. The method of claim 16, wherein the center coil is connected to a first RF power generator and the edge coil is connected to a second RF power generator.

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