Rapid gas delivery system and method for atomic layer etching

Abstract

The invention relates to a rapid gas delivery system and method for atomic layer etching. The system utilizes a compact gas buffer disposed near the gas distribution unit, enabling faster and more efficient delivery of gas to the chamber. The controller manages the gas flow of the gas buffer to maintain an amount of gas within the gas buffer required to perform a single ALE cycle. When one gas buffer delivers gas to the chamber for a partial ALE step, gas is concurrently delivered to the other gas buffer. The configuration not only can improve the efficiency, but also can save components such as a pressure gauge, thereby saving the cost.

Description

[0001] Cross-references to related applications

[0002] This invention claims priority to U.S. Patent Application No. 18 / 740,634, filed on June 12, 2024. Technical Field

[0003] This invention relates to atomic layer etching (ALE) systems and methods. Specifically, this invention relates to an improved gas delivery mechanism designed to rapidly introduce gas into the chambers of an ALE process system. Background Technology

[0004] 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 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 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 (also known as high depth-to-width ratios), balancing these fluxes becomes increasingly complex. Furthermore, achieving uniformity on 300mm wafers and consistent repeatability in 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, 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.

[0006] However, in traditional ALE process systems, the slow gas introduction rate into the chamber affects process efficiency. This is especially critical when etching high aspect ratio structures, where multiple ALE cycles may be required.

[0007] Leeser's U.S. Patent No. 2020 / 0126758 discloses a charge design for accelerating precursor delivery system processes. However, rapid gas delivery systems specifically designed for ALE process systems still require development. Clearly, ALE process systems urgently need innovation to simplify gas management, accelerate gas replacement, shorten process cycles, and improve the consistency of etching results. Against this technological backdrop, the present invention was conceived. Summary of the Invention

[0008] This invention provides an ALE process system with an improved gas delivery system designed to rapidly introduce gas into the ALE process chamber. The system includes different gas buffers for different process gases, each storing a sufficient amount of gas for one ALE cycle. Due to the compact structure of these gas buffers, the gas stored within them has a higher pressure than the gas inside the chamber. By placing these gas buffers adjacent to the gas distribution unit, the gas flow rate can be further increased.

[0009] In some implementations, the state of these gas buffers (including gas inflow and gas evacuation) is controlled by pulse signals generated by a controller, thereby ensuring that gas can be delivered to the chamber quickly and efficiently. This method can shorten ALE cycle time, reduce unwanted RIE, and thus improve overall process efficiency.

[0010] In some embodiments, a first gas buffer is used to store a first gas. In some embodiments, a second gas buffer is used to store a second gas. During the surface modification step, the first gas in the first gas buffer is delivered to the chamber via a gas distribution unit. During the sputtering step, the second gas in the second gas buffer is delivered to the chamber. Simultaneously, the first gas buffer delivers the first gas to the chamber, while the second gas is delivered to the second gas buffer via a central gas supply device, and vice versa. The gas buffer of the present invention has a smaller structure to save valuable space above the process chamber. Typically, the space above the process chamber is quite congested. The small size of the gas buffer also increases the internal gas pressure, thereby enabling rapid gas delivery to the chamber.

[0011] In other embodiments, a corresponding valve is provided between each gas buffer and the gas distribution unit. The operation of the valve is controlled by a pulse signal generated by the controller.

[0012] In other embodiments, a corresponding three-way valve and MFC are provided between each gas buffer and the central gas supply unit. These three-way valves are controlled by pulse signals generated by the controller. When the passage of the three-way valve to the corresponding gas buffer is closed, gas from the central gas supply unit will be delivered to the corresponding branch line. Atomic layer deposition (ALD) valves are preferably used to achieve rapid switching control.

[0013] The amount of gas stored in the gas buffer depends on two factors. The first factor is the flow rate of the MFC. Given that the MFC is a relatively slow device with a setup time of approximately several hundred milliseconds, its setup will remain constant throughout the ALE process. The MFC setup will be performed before the ALE process begins. The second factor is the duration of connection between the gas buffer and the central gas supply unit.

[0014] In some implementations, the ALE process system does not require a gas box, thus significantly reducing costs.

[0015] In other implementations, the ALE process system also does not require a pressure gauge.

[0016] As described above, the present invention provides a gas delivery system that is both efficient and economical, enabling rapid and precise gas delivery and laying the foundation for improving the ALE process. Attached Figure Description

[0017] The embodiments of the present invention will become clear by referring to the following description and the accompanying drawings.

[0018] Figure 1 A conventional ALE process system is shown.

[0019] Figure 2 A flowchart illustrating the operating steps of a conventional ALE process system is shown.

[0020] Figure 3A An ALE process system with an improved gas delivery system according to an embodiment of the present invention is shown.

[0021] Figure 3B A gas buffer according to an embodiment of the present invention is shown, which is designed to rapidly introduce gas into a chamber.

[0022] Figure 4 This is a schematic diagram of the operation of a gas delivery system according to an embodiment of the present invention.

[0023] Figure 5 This is a flowchart illustrating the operation steps of the ALE process system according to an embodiment of the present invention. Detailed Implementation

[0024] For thorough understanding, embodiments of the present invention are described in detail below. Although embodiments have been described in detail for clarity, modifications and variations adapted to the principles of the invention are within the scope of protection of the invention. The present invention selectively describes some conventional steps and components to highlight the unique aspects of the invention.

[0025] Figure 1A conventional ALE process system 100 is shown. A chamber 101 is in a vacuum environment and is equipped with a plasma source 102. The plasma source 102 is powered by a radio frequency (RF) power generator 103. The plasma source 102 can employ various designs, including transformer-coupled plasma (TCP) and inductively coupled plasma (ICP). In some embodiments, the RF power generator 103 and the plasma source 102 can be directly connected, or they can be indirectly connected via a matching network (not shown).

[0026] like Figure 1 As shown, the gas distribution unit 104 draws gas from the gas tank 106 via the gas manifold 105. Depending on specific design requirements, the gas distribution unit 104 can be in the form of a spray head or an injector. The gas manifold 105 mixes various gases before they enter the chamber 101. Typically, the gas tank 106 includes components such as MFCs, gas pressure regulators, particulate filters, gas mixers, and safety sensors. Valves 135 and 137 are located between the gas tank 106 and the gas manifold 105, and are used to control the flow of the first gas 108 and the second gas 110, respectively. It should be noted that although only two gas lines are configured for clarity, the ALE process can support the delivery of more gases. Valve 116 is located between the gas manifold 105 and the gas distribution unit 104, and is used to control the flow of gas entering the chamber 101. The gas tank 106 is connected to a central gas supply unit 107.

[0027] The base 121 is located at the lower part of the chamber 101 and is used to provide support for the substrate 120 during processing. The base 121 is typically an electrostatic chuck (ESC) used for etching processes. To increase the ion energy during etching (especially when etching high aspect ratio structures), the bias unit 119 is activated immediately once plasma is formed in the chamber 101. Depending on the design requirements, the bias unit 119 can be an RF power generator connected to the base 121 via a blocking capacitor, or it can be a specific waveform generator.

[0028] The ALE process system 100 uses pump 124 to discharge gases and reaction byproducts from chamber 101. A vacuum valve 122, located above pump 124, regulates the discharge rate. The gas discharged from vacuum valve 122 is then delivered to exhaust port 126 via exhaust line 125. Chamber 101 maintains constant pressure by balancing the gas input and output flow rates. This balance is achieved using a proportional-integral-derivative (PID) control loop, which acquires real-time pressure data from pressure gauge 127.

[0029] The ALE process operates in cycles, and the two distinct steps of surface modification and sputtering typically require the use of different gases (108 and 110). These two steps are often referred to as two “half-cycles,” which are combined to form a complete ALE cycle. Figure 2 A flowchart of the operation of a conventional ALE process system 100 is shown, labeled as process 200. Process 200 may also involve two or more gases. In step 201, a first gas 108 is delivered from a gas tank 106 to a chamber 101 via a gas distribution unit 104. In step 202, the surface of the substrate 120 is chemically modified (i.e., a surface modification step). For example, chlorine gas can be used to weaken silicon-silicon bonds, unlike the intrinsic bonds between silicon atoms. Plasma generated by the combined excitation of an RF power generator 103 and a plasma source 102 can assist in this chemical modification operation. When plasma is used during surface modification, the bias device needs to be turned off to avoid generating high-energy ions that could interfere with the ALE process. Ideally, the ALE process system 100 performs only the surface modification step during surface modification, without involving an etching step.

[0030] In step 204, the surface modification step is ended, the delivery of the first gas 108 is stopped, and the second gas 110 is delivered simultaneously. Depending on design requirements, the stopping of the first gas 108 delivery and the starting of the second gas 110 delivery can be performed simultaneously, or a short delay can be set between these two operations to ensure that the first gas has been completely purged from the chamber before the second gas is delivered. This short delay avoids undesirable RIE caused by the simultaneous presence of multiple gases. In step 206, a sputtering etching step is performed. Specifically, the second half-cycle of the ALE process involves removing weakened atoms on the surface by performing a sputtering step. Since the ions in the plasma generated by the plasma source 102 and the RF power generator 103 lack sufficient energy, a bias voltage needs to be applied to the base 121 to increase the ion energy, which is crucial for the sputtering step.

[0031] Since each ALE cycle can only etch a few material layers, multiple cycles are necessary to achieve the desired etching depth. In some cases, the number of ALE cycles may exceed 100, especially when processing high aspect ratio structures. In step 208, the number of cycles is calculated and compared with a predetermined process formulation. If all cycles have been completed, the ALE process ends. If not, in step 210, the second gas 110 is switched back to the first gas 108, and a new ALE cycle begins. Similar to the previous steps, a short delay can be set during gas replacement to avoid undesirable RIE caused by the simultaneous presence of multiple gases.

[0032] Figure 3A An ALE process system 300 with an improved gas delivery system according to an embodiment of the present invention is shown. The ALE process system 300 and... Figure 1 The ALE process system 300 differs significantly from the previous one. Specifically, the ALE process system 300 is equipped with a gas buffer 109 for the first gas 108 and a gas buffer 111 for the second gas 110. More specifically, as... Figure 3B As shown, the gas buffer is essentially a compact container with an inlet 1127 and an outlet 1129 for receiving and discharging gas. In the ALE process, the gas buffer stores enough process gas for one ALE cycle. Because the volume of the gas buffer is much smaller than that of the chamber 101, the gas within the gas buffer has a higher pressure. In some embodiments, a pressure gauge or pressure sensor may be provided within the gas buffer to measure the gas pressure. One problem with this approach is that it increases the size of the gas buffer, resulting in an undesirable complex structure. For example, the pressure sensor may need to be connected to a power supply and may need to communicate with a controller. Therefore, a gas buffer with a compact structure is preferred.

[0033] Gas buffer 109 and gas distribution unit 104 are connected via valve 118, and similarly, gas buffer 111 is connected to gas distribution unit 104 via valve 116. Given the critical importance of rapid valve response, ALD valves are recommended.

[0034] When valve 118 is opened, pressurized gas from gas buffer 109 is rapidly delivered to gas distribution unit 104. By positioning gas buffers 109 and 111 close to gas distribution unit 104, the rapid inflow of gas can be further accelerated, thereby significantly shortening the time for gas to be delivered to the chamber.

[0035] MFC 113 is connected to gas buffer 109 via valve 112, and MFC 115 is connected to gas buffer 111 via valve 114. Given the time requirements of the process, ALD valves are preferred. When valve 112 is closed, valve 118 is open. Simultaneously, valve 116 is closed, and valve 114 is open. After valve 114 is open, MFC 115 controls the delivery of second gas 110 from the central gas supply unit 107 to gas buffer 111. The gas flow rate set by the MFC determines the volume of second gas 110 introduced into gas buffer 111. This volume can be adjusted by controlling the charging time. Since conventional MFCs require hundreds of milliseconds to achieve flow regulation, it is not feasible to use conventional MFCs for flow control in a fast ALE process. In one embodiment, the MFCs are always in an "operating" state to achieve a stable flow rate for all gases. In one embodiment, both valves 112 and 114 are three-way valves. When valve 112 controlling gas buffer 109 is closed, the first gas 108 can be diverted to the diversion line 131 via three-way valve 112. Similarly, when valve 114 controlling gas buffer 111 is closed, the second gas 110 can be diverted to the diversion line 133 via three-way valve 114. The diverted gas can be discharged directly or recycled.

[0036] Both MFC113 and MFC115 are connected to the central gas supply unit 107. Typically, the ALE process system 300 uses a gas pressure regulator ( Figure 3A (Not shown), the gas pressure is adjusted to the value required by the MFC. In one embodiment, some MFCs are equipped with pressure regulators. In some embodiments, the ALE process system 300 may be equipped with a particle filter to reduce the number of particles. These components for gas delivery are well known to those skilled in the art and will not be described in detail.

[0037] Figure 4 This is a schematic diagram of the operation of a gas delivery system 400 according to an embodiment of the present invention. Figure 4 An improved control scheme for an ALE process system 300 according to an embodiment of the present invention is illustrated.

[0038] The core of this improved control scheme is the controller 402. The controller 402 generates four pulse signals 404, 406, 408, and 410 to control valves 112, 114, 116, and 118, respectively. These four pulse signals are controlled by the controller 402 and have the same period. In one embodiment, the pulse signal 410 for valve 118 can be the inverted signal of pulse signal 408 for valve 116. The pulse signal 406 for valve 114 can be the inverted signal of pulse signal 404 for valve 112. In another embodiment, the “on-time” of these pulse signals can be individually adjusted to achieve optimal process performance. For example, a delay can be intentionally introduced to ensure that the current gas has been completely purged from chamber 101 before another gas is introduced. In other embodiments, these pulse signals can be introduced a few milliseconds earlier than their preset time to compensate for valve opening time. In other embodiments, these pulse signals are square wave signals with an adjustable duty cycle generated by the controller 402. In other embodiments, these pulse signals have a rising ramp phase and a falling ramp phase.

[0039] Figure 5 This is a flowchart illustrating the operation steps of the ALE process system 300 according to an embodiment of the present invention. In step 502, valve 112 is opened by pulse signal 404, while valve 118 is closed by pulse signal 410. Subsequently, first gas 108 is delivered to gas buffer 109 via MFC 113. The volume of first gas 108 in gas buffer 109 depends on the gas flow rate (set to a value by controlling MFC 113) and the opening duration of valve 112 (determined by the conduction time of pulse signal 404). Given the inherent delay of MFC 113 (approximately several hundred milliseconds), MFC 113 should be kept active at all times. Before opening valve 112, first gas 108 is introduced into split line 131.

[0040] Step 504 includes two parallel operations: steps 504A and 504B. In step 504A, valve 112 is closed by pulse signal 404, while valve 118 is opened by pulse signal 410. Subsequently, the first gas 108 in gas buffer 109 is delivered to chamber 101. Simultaneously, in step 504B, valve 114 is opened by pulse signal 406, while valve 116 is closed by pulse signal 408. At this time, the second gas 110 is delivered to gas buffer 111 through MFC 115. The volume of the second gas 110 in gas buffer 111 depends on the gas flow rate (controlled by setting MFC 115 to a set value) and the opening duration of valve 114 (determined by the conduction time of pulse signal 406). After the passage from valve 114 to gas buffer 111 is closed, the second gas 110 is delivered to the diversion line 133 through another passage of valve 114.

[0041] In step 506, the surface modification step of the ALE process is performed. During this time, the first gas 108 is ionized by the RF power generator 103 to generate plasma, and the generated energy is transferred to the plasma source 102. This process causes chemically active neutral particles to diffuse into the substrate 120, thereby weakening the chemical bonds of one or more monolayers on the surface of the substrate 120. It is noteworthy that during the surface modification process, the bias unit 119 of the base 121 remains inactive.

[0042] Step 508 includes two parallel operations: step 508A and step 508B. In step 508A, valve 114 is closed by pulse signal 406, and valve 116 is opened by pulse signal 408, at which time the second gas 110 is delivered from gas buffer 111 to chamber 101. In step 508B, valve 112 is opened by pulse signal 404, and valve 118 is closed by pulse signal 410. When valve 112 is open relative to gas buffer 109, the first gas 108 is delivered to gas buffer 109 through MFC 113.

[0043] Subsequently, in step 510, the sputtering step of the ALE process is performed within chamber 101. During sputtering, the RF power generator 103 is activated, generating ions by transmitting RF power to the plasma source 102. Activating the bias unit 119 of the pedestal 121 helps generate high-energy ions, which can then diffuse to the surface of the pedestal 121, thereby facilitating the removal of the chemically modified layer formed in the surface modification step of the ALE process. In step 512, if it is determined that the ALE process has been completed, process 500 ends; otherwise, the next ALE cycle is executed.

Claims

1. An ALE process system, characterized in that, include: A chamber that operates in a vacuum environment; A base, located within the cavity, is used to provide support to the substrate during the ALE process; A gas distribution unit, used to introduce gas into the chamber; and A gas delivery system includes a first gas buffer, a second gas buffer, and a controller, wherein the first gas buffer stores a first gas required for a surface modification step, and the second gas buffer stores a second gas required for a sputtering step. When the first gas buffer releases the first gas into the chamber through the gas distribution unit, the second gas is supplied from the central gas supply device to the second gas buffer. When the second gas buffer releases the second gas into the chamber through the gas distribution unit, the first gas is supplied from the central gas supply device to the first gas buffer.

2. The ALE process system as claimed in claim 1, wherein the first gas buffer obtains a first gas from the central gas supply device via a first MFC, and the second gas buffer obtains a second gas from the central gas supply device via a second MFC.

3. The ALE process system as claimed in claim 2, wherein the volume of the first gas entering the first gas buffer is determined by the first MFC, and the volume of the second gas entering the second gas buffer is determined by the second MFC.

4. The ALE process system as claimed in claim 3, wherein the volume of the first gas further depends on the connection duration between the first gas buffer and the central gas supply device, and the volume of the second gas further depends on the connection duration between the second gas buffer and the central gas supply device.

5. The ALE process system as claimed in claim 1, wherein the ALE process system further includes a first three-way valve located between the first MFC and the first gas buffer, wherein when the passage of the first three-way valve to the first gas buffer is closed, the first three-way valve delivers the first gas to the first diversion line; wherein the first three-way valve switches its conduction state according to a pulse signal issued by the controller.

6. The ALE process system of claim 1, wherein the ALE process system further comprises a second three-way valve located between the second MFC and the second gas buffer, wherein when the passage of the second three-way valve to the second gas buffer is closed, the second three-way valve delivers the second gas to the second diversion line; wherein the second three-way valve switches its conduction state according to a second pulse signal issued by the controller.

7. The ALE process system of claim 1, wherein the ALE process system further comprises a third valve located between the first gas buffer and the gas distribution unit, the third valve switching its conduction state according to a third pulse signal issued by the controller.

8. The ALE process system of claim 1, wherein the ALE process system further comprises a fourth valve located between the second gas buffer and the gas distribution unit, the fourth valve switching its conduction state according to a fourth pulse signal issued by the controller.

9. The ALE process system as described in claim 1, wherein the ALE process system does not require a gas box.

10. The ALE process system as claimed in claim 1, wherein the ALE process system does not require a pressure gauge.

11. A method using an ALE process system, characterized in that, Includes the following steps: a. Place the substrate in the chamber; b. Performing a surface modification step, wherein the surface modification step includes: i. The first gas stored in the first gas buffer is delivered to the chamber. ii. A third pulse signal associated with the surface modification step is issued by a controller to control the flow rate of the first gas into the chamber, wherein the third pulse signal is used to manage the on / off state of a third valve located between the first gas buffer and the gas distribution unit, and iii. Activate a plasma source to generate plasma within a chamber, wherein chemically active neutral particles in the plasma interact with the substrate to generate a modified layer; c. Performing a sputtering step, wherein the sputtering step includes: i. The second gas stored in the second gas buffer is delivered to the chamber. ii. A fourth pulse signal associated with the sputtering step is issued by a controller to control the flow rate of the second gas into the chamber, wherein the fourth pulse signal is used to manage the on / off state of a fourth valve located between the second gas buffer and the gas distribution unit, and iii. Applying a bias voltage to the substrate to increase the ion energy in the plasma, thereby accelerating the sputtering of the modified layer; and d. The surface modification step and the sputtering step are performed alternately.

12. The method of claim 11, wherein the method further comprises supplying a second gas to the second gas buffer when the first gas is supplied from the first gas buffer to the chamber.

13. The method of claim 12, wherein the method further comprises determining a setpoint for a second MFC located between the second gas buffer and the central gas supply unit via the controller, and controlling the setpoint to remain constant throughout the ALE process.

14. The method of claim 12, wherein the method further comprises generating a second pulse signal by the controller when the first gas is delivered from the first gas buffer to the chamber, to control the gas flow rate entering the second gas buffer.

15. The method of claim 11, wherein the method further comprises supplying a first gas to the first gas buffer when the second gas is supplied from the second gas buffer to the chamber.

16. The method of claim 15, wherein the method further comprises generating a first pulse signal by the controller when the second gas is delivered from the second gas buffer to the chamber, to control the gas flow rate entering the first gas buffer.

17. A gas delivery system that performs multiple ALE process cycles, characterized in that, include: A first gas buffer is used to store the first gas required for the surface modification step; The second gas buffer is used to store the second gas required for the sputtering step; A first group of valves and a second group of valves, wherein the first group of valves is connected between the first gas buffer and the chamber and between the second gas buffer and the chamber, and the second group of valves is connected between the first gas buffer and the central gas supply device and between the second gas buffer and the central gas supply device. as well as A controller, connected to the first group of valves and the second group of valves, is used to generate pulse signals to control the gas delivery. When one of the first gas buffer and the second gas buffer releases the gas it stores into the chamber, gas is supplied to the other of the first gas buffer and the second gas buffer. This operation is performed alternately and synchronously with the ALE cycle within the chamber.

18. The gas delivery system of claim 17, wherein a first MFC is provided between the first gas buffer and the central gas supply device, and the flow rate of the first MFC is set by the controller before the start of the ALE process, the flow rate of the first MFC remaining constant during the ALE process.

19. The gas delivery system of claim 17, wherein a second MFC is provided between the second gas buffer and the central gas supply device, and the flow rate of the second MFC is set by the controller before the start of the ALE process, the flow rate of the second MFC remaining constant during the ALE process.

20. The gas delivery system of claim 17, wherein the gas delivery system does not require a gas tank.

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