Plasma vessel cleaning for ion beam systems
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-07-29
- Publication Date
- 2026-08-14
Smart Images
Figure 2026527519000001_ABST
Abstract
Description
Background Art
[0001] In plasma ion beam applications (either or both of ion beam film deposition and ion beam etching), stable and consistent performance of the ion beam source is always desired. There are several factors that directly affect the performance and stability of ion beam systems and ion sources, such as plasma density, efficiency of RF power supply, uniformity of gas distribution, grid optics, etc. Among these, the efficiency of RF power supply particularly affects the long-term performance of the system and process. A more efficient RF power supply can be obtained when the plasma container (also called the discharge chamber) is "clean" and there is little or no conductive coating on the inner wall of the container. However, during film deposition and etching applications, some of the sputtered material inevitably scatters towards the ion source and deposits on the inner wall of the plasma container. Therefore, during the long-term use of an ion beam system, there is always material accumulating on the container wall. Excessive material deposition can cause peeling (flaking) and lead to the generation of contaminating particles, whether it is conductive or dielectric, which is a serious problem in wafer processing.
[0002] A method for restoring the plasma container to avoid the above problems will be described below.
Summary of the Invention
[0003] The present disclosure relates to in-situ cleaning of the container of an ion film deposition / etching system, including accelerating ions towards the container wall to remove the material deposited on the wall. The method of the present disclosure can be applied to any ion source system with or without grids, including those using assist ion beams.
[0004] During the use of an ion system or ion source, a significant amount of sputtered material is typically scattered (or sputtered) backward onto the inner wall of the plasma vessel, resulting in reduced radio frequency (RF) power supply and process drift, requiring time for system and process readjustment, and ultimately necessitating ex situ cleaning. When the vessel becomes coated, system uptime and operability decrease, ultimately increasing the cost of system ownership. The cleaning method described herein reduces system downtime, improves productivity, and lowers operating costs. The method can be performed during or between substrate processing.
[0005] The method includes having plasma present in a plasma vessel, not performing beam extraction, and using a minimum gas flow rate and a high RF power level. This disclosure describes a method for cleaning an ion beam system vessel in situ in a particular embodiment. The method includes supplying sufficient initial RF power and a low gas flow rate through the ion beam system to maintain the plasma, turning off any grid bias, and increasing the RF power to the plasma to at least 500 W, for example, 500 W to 3000 W, depending on the size of the plasma vessel.
[0006] This disclosure also describes a method for cleaning an ion beam system vessel in situ by transitioning the system from H mode to E mode, turning off any grid bias, increasing the plasma potential after turning off any grid bias, increasing the RF power, and causing the energized ions to collide with the inner wall of the vessel.
[0007] The document also describes a method for cleaning an ion beam system vessel in situ, which involves colliding capacitively coupled ions with a coating on the inner wall of the vessel.
[0008] This summary is provided to introduce, in a simplified form, a selection of concepts that will be further explained in the detailed description below. This summary is not intended to identify any key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. These, and various other features and benefits, will become apparent upon reading the detailed description below. [Brief explanation of the drawing]
[0009] [Figure 1] Figure 1 is a schematic side view of a part of the ion beam deposition system. [Figure 2] Figure 2 is a flowchart illustrating an example of a step-by-step method for cleaning the vessel of an ion beam system. [Figure 3] Figure 3 is a schematic side view of a container showing cleaning by the method described herein. [Modes for carrying out the invention]
[0010] The supply of RF power is a critical factor in the performance and stability of the ion system, as well as in other factors such as plasma density, gas distribution uniformity, and grid optics. These factors affect process stability, maintenance intervals, plasma vessel temperature, and plasma density, which in turn affect ion beam divergence. In etching or deposition applications, some of the sputtered target material is scattered back to the plasma vessel and deposited on the inner wall. In the case of etching or deposition of metals, the backscattered metallic material forms a thin conductive layer on the inner wall of the plasma vessel. This metallic layer absorbs and reflects RF power via eddy currents. This reduces the effective RF power supplied to the plasma. Attempts have been made to mitigate the effects of eddy currents, such as by using slotted deposition shields. However, while these methods are somewhat effective in extending the life of the plasma vessel, they do not completely eliminate the accumulation of coatings on the vessel walls and their impact on the RF power supply. The following disclosure describes an in situ process for cleaning the plasma vessel, thereby restoring efficient RF power supply and stabilizing the entire ion beam process.
[0011] Typically, when using inductively coupled plasma, it is desirable to operate in H-mode (also called inductively coupled plasma or transformer-coupled plasma), where the plasma density is high, RF coupling is efficient, and the electron temperature is relatively low. Under such conditions, the plasma potential (sheath potential) remains low, and ions moving towards the vessel wall through the near-wall sheath have low energy below the sputtering threshold. As will be further explained below, a decrease in neutral gas pressure can cause an increase in electron temperature and thus an increase in plasma potential. This increased plasma potential provides sufficient energy for ions moving towards the inner wall of the plasma vessel to produce significant sputtering at the wall, and thus remove material present on the vessel wall. An increase in RF power also increases the attenuation length of the RF electromagnetic field, resulting in a partial transition to E-mode (also called capacitively coupled plasma). In this E-mode, the electric field component of the RF electromagnetic field increases the energy of ions moving towards the wall, further increasing the material removal rate.
[0012] The method described herein for cleaning a vessel operates the ion source in plasma-only mode without ion extraction, although cleaning can also be performed during ion extraction. Furthermore, the gas flow rate is reduced to a minimum while maintaining the plasma. The cleaning time is adjusted according to the physical permeability of the grid, the coating thickness, and the chamber's pumping speed.
[0013] Conventionally, vessels are formed from dielectric materials and are cleaned ex situ by interrupting system operation and breaking the vacuum of the ion beam system. This leads to increased ownership costs due to process time loss and maintenance costs. The method described herein does not require breaking the system vacuum, thus reducing system operational downtime. In situ cleaning can be performed between substrate processing, for example, when it is determined that the metal layer on the vessel wall has grown to an undesirable thickness, based on factors such as loss of RF power efficiency or process drift. In addition, periodic in situ cleaning by these methods can not only significantly extend the average time between larger system maintenance but also suppress unplanned system shutdowns caused by process instability or contamination. By cleaning the vessel at regular intervals, the thickness of deposited material can be controlled and maintained below a desired level, thus eliminating ambiguity in determining the optimal timing for performing maintenance.
[0014] The method of this disclosure can be applied to any gridded or ungridded ion source or plasma source, including those using an assisted ion beam. The method is suitable for ion systems or ion sources operating at any pressure, power, and / or sputtering speed. Figure 1 shows a typical ion beam system to which the method of this disclosure can be applied.
[0015] The following description refers to the accompanying drawings, which form part of this specification and illustrate at least one specific implementation. The following description provides additional specific implementations. It should be understood that other implementations may be contemplated and implemented without departing from the scope or spirit of this disclosure. Therefore, the following detailed description should not be construed as restrictive. This disclosure is not so limited, but an understanding of the various aspects of this disclosure will be gained through the descriptions of the examples provided below. In some examples, reference numbers may have associated sublabels in lowercase to indicate one of several similar components. Where a reference number is referenced without the designation of a sublabel, the reference is intended to refer to all such several similar components.
[0016] Figure 1 is a schematic diagram of the ion beam system 100. While the implementation of the ion beam system 100 is shown as an ion beam sputtering deposition system, the components of the ion beam system 100 can also be used to implement any or all of the following: an ion beam etching system, an ion implantation system, an ion beam deposition system, an ion beam assisted deposition system, etc., with some modifications. The system 100 can be used, for example, to deposit, deposit and modify, and / or deposit and etch materials.
[0017] The ion beam system 100 includes an ion beam source 102, a target assembly 104, and a substrate assembly 106 for supporting the substrate 116. Note that the substrate assembly 106 may include a single large substrate 116 or sub-assembly holders for holding multiple smaller individual substrates 116. The substrate 116 may be formed from one or more layers of a metal, such as a silicide, nitride, oxide, alloy, or ceramic.
[0018] An ion beam source 102, including a dielectric vessel, generates an ion beam 120 comprising multiple ion beamlets directed towards or irradiated onto a target assembly 104, the target assembly 104 including at least one target 114 fixed to the target assembly 104, which contains material to be deposited on a substrate 116. The ion beam 120 has a central axis 125 that targets or is directed towards the target assembly 104, such that the ion beam 120 collides with the target assembly 104 completely or nearly completely. The target assembly 104 is placed on a platform that can rotate the target assembly 104 about a given axis 115 as needed. In some designs, the target assembly 104 may be tilted. When the ion beam 120 collides with the target assembly 104, a sputter plume 140 of material is generated from the target 114.
[0019] Examples of target 114 materials include, but are not limited to, metals such as titanium (Ti), tungsten (W), molybdenum (Mo), tantalum (Ta), ruthenium (Ru), cobalt (Co), copper (Cu), and rhodium (Rh); metallic and semiconductor nitrides such as titanium nitride (TiN), tantalum nitride (TaN), silicon nitride (Si3N4), molybdenum nitride (MoN), and tungsten nitride (WN, W2N, WN2); metallic and semiconductor oxides such as silicon oxide (SiO2), titanium oxide (TiO), and aluminum oxide (Al2O3); metallic and semiconductor silide such as tungsten silide (W5Si3), molybdenum silide (MoSi2), and titanium silide (Ti5Si3); and other types of metallic, dielectric, and semiconductor targets.
[0020] The ion beam 120 collides with the target 114 at an angle such that the sputter plume 140 generated from the target 114 propagates toward the substrate assembly 106 and the substrate 116. In some configurations of the ion beam system 100, the sputter plume 140 may diverge as it travels from the target 114 toward the substrate assembly 106, and may partially overspray beyond the substrate 116. However, in other configurations, the sputter plume 140 can be more or less concentrated, resulting in a more effective distribution of the resulting material deposition over specific areas of the substrate 116.
[0021] The substrate assembly 106 is positioned so that the sputter plume 140 also impacts the substrate 116 at a desired angle. In one exemplary configuration of the ion beam system 100, the substrate assembly 106 is mounted on a fixture 118, which allows the substrate assembly 106 to be moved in a desired manner, including rotating the substrate assembly 106 about its axis 119, or rotating the fixture 118 to tilt the substrate assembly 106 and change its angle with respect to the sputter plume 140.
[0022] In one example of the ion beam system 100, the ion source 102 generates positively charged ions. However, in another example, the ion source 102 generates negatively charged ions. The ion source 102 is a radio frequency (RF) or microwave type gridded ion source.
[0023] System 100 may include one or more grids 110 proximate to ion beam source 102 for directing ion beam 120 from ion beam source 102 toward target assembly 104. In one configuration of ion beam system 100, grid 110 deflects the ion beamlets such that ion beam 120 diverges from central axis 125 of the ion source 102, as compared to the case where no overall deflection of the ion beam occurs. In another configuration, grid 110 deflects the ion beamlets such that ion beam 120 does not diverge from central axis 125. Other structures and configurations may also be provided. Grid 110 can be configured such that ion beam 120 has a symmetric or asymmetric cross-sectional profile about the beam axis.
[0024] Grid 110 has holes or apertures therethrough to allow beamlets of ion beam 120 to pass through grid 110. The individual holes of grid 110 can be arranged such that the density of holes per unit area is maximized to maximize the ions extracted from ion source 102. Grid 110 may have a pattern of holes that are linear, elliptical, or asymmetric in shape. The number and size of the holes affect the transmissivity of grid 110.
[0025] As described above, illustrated system 100 is a general and versatile system. System 100 may include a reactive gas source, an assist ion source, an assist gas source, various heaters, a neutralizer, a turret for multiple rotating targets, and any additional features such as diagnostic probes and sensors.
[0026] System 100 can operate with any conventional operating parameters under any operating conditions. For example, system 100 may be under an inert atmosphere, or a reactive gas and / or a noble gas may be added. For example, the gas introduction can range from a low flow rate of 1 sccm to a high flow rate of 100 sccm. System 100 typically operates at less than 10 torr, for example, 1×10 -5 ~1×10-3 It operates at a process (chamber) pressure of torr. The system 100, particularly the ion source 102, can utilize a high-energy ion beam having a voltage in the range of, for example, 40 V to 2000 V. The system can provide a net deposition rate exceeding 10 angstroms per minute and, in some cases, exceeding 200 angstroms per minute.
[0027] After the system 100 has been used for a long time, material from at least one target 114 and / or substrate 116 is backscattered and deposited on the grid 110 and inside the ion beam source 102. The amount of backscattered material deposited inside the ion beam source generally increases as the transparency of the grid 110 increases. Although not shown in FIG. 1, the ion beam source 102 includes a plasma vessel into which a neutral gas is injected and the neutral gas is ionized, and the backscattered material is deposited on the inner wall of this vessel. When the backscattered material is a metal, a thin conductive layer is formed on the vessel wall. As described above, this metal layer is undesirable because it absorbs and reflects RF power, reducing the efficiency and stability of the system 100.
[0028] To remove the undesirable material, in an in situ method, the system 100 transitions from the inductively coupled H mode, which is the normal operation, to the capacitively coupled E mode having a relatively high plasma potential. In the E mode, the ions from the ion source 1O2 couple to a high-frequency electric field rather than a high-frequency magnetic field and are thus accelerated radially. This radial movement facilitates the collision of ions with the vessel wall. Further explanation regarding the collision of ions with the coated vessel wall is provided below with respect to FIG. 3.
[0029] Typically, during deposition and etching operations, the plasma is inductively coupled, also known as magnetic coupling or operating in H-mode. Ideally, during H-mode, the plasma density is high, RF coupling is efficient, the electron temperature is relatively low, and the stray potential (sheath potential) remains low. Under these process conditions, backscattering and accumulation on the vessel walls occur, albeit at low velocities. However, under certain conditions, such as low neutral pressure and high RF power, the plasma potential is higher, and ions moving towards the wall through the sheath near the wall are accelerated to energies higher than the sputtering threshold, thereby causing significant backscattering on the vessel walls. Whether the accumulation on the vessel walls is slow or fast, it ultimately leads to an undesirable decrease in RF power. If a decrease of approximately 5% or 10% from the desired RF power is observed, it is beneficial to remove this material from the vessel walls.
[0030] To remove material from the container wall, the system transitions to E-mode, i.e., to generate a capacitively coupled plasma, i.e., to a high plasma potential. By reducing the gas flow rate and increasing the input RF power compared to H-mode, the plasma potential and the attenuation length of the RF electromagnetic field increase, thus transitioning to E-mode.
[0031] During this E-mode cleaning process according to this disclosure, the ion source operates in plasma-only mode without ion extraction, with high RF power (e.g., at least 500 W), and the gas flow rate is reduced to the minimum value at which the plasma is maintained (e.g., less than 30 sccm, e.g., about 2-30 sccm). The exact value of the gas flow rate depends on the size of the plasma vessel, the permeability of the grid 110, and the gas exhaust capacity of the chamber. Ions from the ion source collide with the vessel wall, etching away the deposited metal layer from the vessel wall. It should be noted that it is desirable to etch only the backscattered (e.g., metallic) coating from the plasma vessel and not the dielectric wall itself. Over-etching would result in the deposition of etched dielectric material upstream of the grid 110, which could cause arc discharge and source instability. However, the deposition of etched metallic material on the grid 110 should not have any harmful effects.
[0032] The cleaning time for the vessel is adjusted according to the physical permeability of the grid 110, the thickness of the backscattering material on the vessel wall, the gas exhaust capacity of the chamber, the size of the plasma vessel, and the amount of material to be removed. When the RF power is high (e.g., at least 500W, e.g., 500W to 3000W) and the gas flow rate is low (e.g., 30 sccm or less, e.g., 2 to 30 sccm), the cleaning time is at least 30 seconds, or at least 60 seconds or 1 minute, or at least 2 minutes, and in some embodiments, about 2 hours, this time does not include the ramp-up time. Typically, the time required for cleaning is 4 hours or less, and in some embodiments, 2 hours or less.
[0033] Figure 2 shows a typical in situ method 200 for cleaning a vessel in an ion beam system. In the first step 202, the ignited plasma is maintained at low power and low gas flow rate, which may be done by reducing the power and gas flow rate from a previously higher level, or by initially turning on the system at low power and gas flow rate. Examples of appropriate power and gas flow rates are approximately 500 W or less, e.g., 150 W to 500 W, and approximately 10 to 60 sccm, depending on the size of the vessel. In the second step 204, which may be before, after, or simultaneously with step 202, any grid bias is turned off.
[0034] In the third step 206, the RF power to the plasma is increased to, for example, more than 500W, or more than 1000W, or between 500W and 3000W. Other examples of high RF power are at least 1500W and at least 2000W. Also in step 206, depending on the initial gas flow rate, the gas flow rate is reduced to 30 sccm or less, for example, 2 to 30 sccm. The power and gas flow rate are selected according to specific parameters of the system, including the properties of the material on the vessel wall (e.g., thickness), the characteristics of the chamber, the structure of the vessel (e.g., size, material, dimensions, etc.), the type of gas, the downstream grid, and a specific plasma source.
[0035] In step 208, ions from the plasma collide with the container wall, removing material (e.g., metallic material) from it. The cleaning process is typically operated for a period of at least 30 seconds and no more than 4 hours, and in some embodiments no more than 2 hours, based on the material removal rate, which depends on the ion collision rate on the container wall and the amount of material to be removed.
[0036] Method 200 can be performed between substrate processing steps, for example, based on a decrease in RF power over time, if it is determined that the metal layer on the container wall has grown to an undesirable thickness, or at scheduled intervals.
[0037] Method 200 and its variations do not require breaking the system vacuum, thus reducing system downtime. As described above, in situ cleaning can be performed between substrate processing without causing significant disruption to system operation. In addition, scheduled periodic in situ cleaning using these methods can not only significantly extend the average time between larger system maintenance but also suppress unplanned system shutdowns caused by unacceptable processing conditions or process instability, such as drift. By cleaning the container at regular intervals, the thickness of the deposited material can be controlled and maintained below a desired level, thereby reducing, and in some cases eliminating, ambiguity in determining the optimal timing for performing maintenance.
[0038] Figure 3 schematically and schematically shows the interior of an ion beam source 300 having a plasma vessel 302 and an RF coil 304 (the coil 304 is also referred to herein as the plasma source) that generates plasma within the vessel 302. One grid 306 is shown, but other systems may have multiple grids. The inner wall 303 of the plasma vessel 302 has a thick coating 310 thereon, which is formed of material sputtered and backscattered from a target and / or a substrate being coated (the target and substrate are not shown in Figure 3).
[0039] In Figure 3, the RF power to the plasma source is increased (for example, at least 500W, e.g., 500W to 3000W) so that ions from the plasma collide with the coating 310 on the wall 303 of the plasma vessel 302, etching or removing the material 310.
[0040] As shown, the specific operating parameters of the adjustment process are determined by the conditions and parameters of the ion beam system itself (e.g., deposition and / or etching), as well as the type and amount of material to be removed from the vessel wall. A skilled operator of the ion beam system can determine the desired cleaning parameters for a particular deposited material based on the system parameters.
[0041] The vessel cleaning process described herein offers numerous advantages. The cleaning extends the vessel's operational life in situ, without the need to break the system's vacuum. System operational stability is improved by cleaning and removing material layers that cause RF electromagnetic wave dissipation and reflection. This improved stability leads to reduced process drift and variability, resulting in less need for process readjustment and enabling more productive operating time and more consistent output from one product to the next.
[0042] The cleaning process is applicable to any ion source system and is system or material independent. The above description and examples provide a complete description of the processes and uses of exemplary implementations of the present invention. The above description provides specific implementations. It should be understood that other implementations may be contemplated and implemented without departing from the scope or spirit of this disclosure. Therefore, the above detailed description should not be construed as restrictive. Features and elements from one implementation or embodiment may be readily applied to a different implementation or embodiment, insofar as this does not contradict the above. Furthermore, features from one implementation or embodiment may be combined with features from another implementation or embodiment to form yet another implementation or embodiment. This disclosure is not limited in this way, but an understanding of the various aspects of this disclosure will be gained through the description of the examples provided.
[0043] Unless otherwise indicated, all numerical values representing the size, quantity, and physical properties of features should be understood as being modified by the term "approximately." Therefore, unless otherwise indicated, the numerical parameters described are approximations that may vary depending on the desired properties sought by those skilled in the art using the teachings disclosed herein.
[0044] As used herein, the singular forms "a," "an," and "the" encompass implementations having multiple references unless the context clearly indicates otherwise. As used herein and in the appended claims, the term "or" is used generally to include "and / or" unless the context clearly indicates otherwise.
[0045] Spatially related terms, including but not limited to "below," "upper," "directly below," "downward," "upper," and "top," are used herein to facilitate descriptions of the spatial relationship of one element to another. Such spatially related terms encompass different orientations of the device, in addition to the specific orientations shown in the figures and described herein. For example, if the structure shown in the figures is inverted or turned inside out, a part previously described as being below or beneath other elements would become above or beneath those other elements.
[0046] Since many embodiments and implementations of the present invention are possible without departing from the spirit and scope of the present invention, the present invention is contained in the claims appended below.
Claims
1. A method for cleaning the container of an ion beam system in situ, wherein the ion beam system is used to clean the container. Maintaining the plasma with low initial RF power and low initial gas flow rate, Turn off any grid bias. After turning off any grid bias, increase the RF power to the plasma to at least 500 W and supply a gas flow rate of 2 to 30 sccm. Methods that include...
2. The method according to claim 1, wherein the initial low RF power is approximately 500W or less.
3. The method according to claim 1, wherein the initial low gas flow rate is 10 to 60 sccm.
4. The method according to claim 1, wherein increasing the RF power to the plasma includes increasing the RF power to 500W to 3000W for at least 30 seconds.
5. The method according to claim 4, wherein increasing the RF power to the plasma includes increasing the RF power for a period of four hours or less.
6. The method according to claim 1, wherein the method is used between processing the first substrate and processing the second substrate without breaking the vacuum of the ion beam system.
7. A method for cleaning the vessel of an ion beam system in situ, Transitioning the aforementioned system from H mode to E mode, Increasing the plasma potential after turning off any grid bias, The RF power is increased, causing the energized ions to collide with the inner wall of the container. Methods that include...
8. The method according to claim 7, wherein the transition from the H mode to the E mode includes increasing the RF power and decreasing the gas flow rate.
9. The method according to claim 8, wherein reducing the gas flow rate includes reducing the gas flow rate to 2 to 30 sccm.
10. The method according to claim 7, wherein increasing the RF power and colliding the energized ions includes increasing the RF power to at least 500 W.
11. The method according to claim 10, wherein increasing the RF power includes increasing the RF power from 500W to 3000W.
12. The method according to claim 7, wherein increasing the RF power and causing the ions to collide includes causing the ions to collide for at least 30 seconds.
13. The method according to claim 7, wherein the method is carried out between the processing of the first substrate and the processing of the second substrate without breaking the vacuum of the ion beam system.
14. A method for cleaning an ion beam system vessel in situ, comprising colliding ions with a metal coating on the inner wall of the vessel.
15. The method according to claim 14, wherein the method is performed in E mode and ions sputter the inner wall of the container.
16. The method according to claim 14, comprising increasing the RF power of the system to at least 500 W with a gas flow rate of 2 to 30 sccm.
17. The method according to claim 16, comprising increasing the RF power of the system from 500W to 3000W.
18. The method according to claim 14, wherein the method is carried out without breaking the vacuum of the ion beam system.