Managing the impact of beam power by varying base emissivity

Abstract

A workpiece mounting system is disclosed that includes a chuck and a base. Increasing the emissivity of the base increases heat transfer from the chuck to the base. In some embodiments, the emissivity of the base can be controlled, so that for lower power levels of the ion beam, the emissivity remains low, allowing the chuck to quickly reach a desired temperature. For higher power levels of the ion beam, the emissivity increases, increasing heat transfer to the base and allowing the chuck to maintain a desired temperature. A high-emissivity coating can also be applied to the top surface of the base. In other embodiments, a pair of movable shields can be positioned between the chuck and the base. The position of the shields can be a function of the power level of the incident ion beam.

Description

[Technical Field]

[0001] This application claims priority to U.S. Patent Application No. 17 / 943,753, filed September 13, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] Embodiments of the present disclosure relate to a system for changing the emissivity of the base to improve heat transfer from the electrostatic chuck to the base, allowing for higher power implants. [Background technology]

[0003] The manufacturing of semiconductor devices involves multiple separate and complex processes. Typically, a semiconductor workpiece undergoes many processes during the manufacturing process. When the workpiece is processed, it is typically secured (clamped) to a chuck. This clamping can be mechanical or electrostatic in nature. Electrostatic chucks are traditionally composed of multiple layers. The top layer, also known as the top dielectric layer, is made of an electrically insulating or semiconductive material that contacts the workpiece and generates an electrostatic field without creating a short circuit. Multiple electrodes can be positioned below the top dielectric layer to generate the electrostatic force. The multiple electrodes are made of a conductive material, such as a metal.

[0004] In certain applications, such as the manufacture of power devices, implantation at elevated temperatures may be beneficial. To increase the temperature of the workpiece, the workpiece is typically heated by contact, such as by using a gas trapped between the workpiece and the chuck, such as when the workpiece is held in place by electrostatic forces. The workpiece may also be heated directly by the chuck. In either embodiment, heat is applied to the underside of the workpiece by the chuck. To achieve these elevated temperatures, the chuck is typically maintained at elevated temperatures using an embedded resistive heating element.

[0005] At low beam power levels, the chuck can dissipate heat at a faster rate than the heat supplied by the ion beam. At these beam power levels, a heating element is used to maintain the desired temperature of the chuck. However, at higher beam power levels, the chuck cannot dissipate heat fast enough, and the temperature of the workpiece cannot be controlled. This phenomenon, known as thermal runaway, can limit the beam power levels that can be used. Using a lower-than-desired beam power level increases implant times and reduces throughput.

[0006] It would therefore be advantageous to have a system that can dissipate the energy delivered by an ion beam so that higher beam power levels can be utilized. Furthermore, it would be beneficial if this system were useful for both low and high power levels. Summary of the Invention

[0007] A workpiece mounting system is disclosed that includes a chuck and a base. Increasing the emissivity of the base increases heat transfer from the chuck to the base. In some embodiments, the emissivity of the base can be controlled, so that for lower power levels of the ion beam, the emissivity remains low, allowing the chuck to quickly reach a desired temperature. For higher power levels of the ion beam, the emissivity increases, increasing heat transfer to the base and allowing the chuck to maintain a desired temperature. A high-emissivity coating can also be applied to the top surface of the base. In other embodiments, a pair of movable shields can be positioned between the chuck and the base. The position of the shields can be a function of the power level of the incident ion beam.

[0008] According to one embodiment, a system for mounting and heating a workpiece is disclosed. The system includes an electrostatic chuck and a base spaced from the electrostatic chuck, with a material disposed on an upper surface of the base having an emissivity different from that of the base. In some embodiments, the material includes a high-emissivity coating. In specific embodiments, the high-emissivity coating has an emissivity of 0.4 or greater. In specific embodiments, the high-emissivity coating has an emissivity of 0.6 or greater. In some embodiments, the high-emissivity coating includes at least one of anodized aluminum, anodized titanium, SiC, alumina, graphite, silicon, silicon dioxide, nichrome, and a ceramic coating. In certain embodiments, the material includes an electrochromic material. In some embodiments, the electrochromic material includes electrochromic glass. In certain embodiments, the electrochromic glass has a transmittance that changes by at least 30% depending on a voltage applied to the electrochromic glass.

[0009] According to another embodiment, a system for mounting and heating a workpiece is disclosed. The system includes an electrostatic chuck, a base spaced from the electrostatic chuck, and a controller configured to vary heat transfer between the electrostatic chuck and the base based on the power level of an incident ion beam. In some embodiments, an electrochromic material is disposed on an upper surface of the base, and the system further includes an electrochromic power supply in communication with the electrochromic material and the controller, the controller controlling the voltage supplied to the electrochromic material by the electrochromic power supply. In some embodiments, the emissivity of the electrochromic material is greater than the emissivity of the upper surface of the base. In some embodiments, the transmittance of the electrochromic material is a first value when a low-power ion beam is used and a second value lower than the first value when a high-power ion beam is used. In certain embodiments, when the transmittance is the second value, the heat transfer between the electrostatic chuck and the base is greater than the heat transfer when the transmittance is the first value. In some embodiments, the system further includes a movable shield disposed between the electrostatic chuck and the base. In certain embodiments, the upper surface of the base is coated with a high-emissivity material having an emissivity of 0.4 or greater. In certain embodiments, the movable shield is made of a material having an emissivity lower than that of the high-emissivity material. In some embodiments, the movable shield is in a closed position when a low-power ion beam is used and in an open position when a high-power ion beam is used, wherein in the closed position, the movable shield is positioned so that the top surface of the movable shield is parallel to the bottom surface of the electrostatic chuck. In some embodiments, the movable shield is in a closed position when a low-power ion beam is used and in an open position when a high-power ion beam is used, wherein in the closed position, the movable shield is positioned so that more than 80% of the heat radiated by the electrostatic chuck is blocked by the movable shield, thereby preventing heat from being transferred directly from the electrostatic chuck to the top surface of the base.

[0010] For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a side view of a chuck and a base according to one embodiment. [Figure 2] FIG. 10 is a side view of a chuck and a base according to another embodiment. [Figure 3A] FIG. 10 is a side view of the chuck and base in a closed position according to a third embodiment. [Figure 3B] FIG. 10 is a side view of the chuck and base in an open position according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] As explained above, in many applications it may be advantageous to heat the workpiece while it is secured to the electrostatic chuck. Traditionally, this heating is performed using conduction, where the heat contained in the electrostatic chuck is transferred to the workpiece, often using a backside gas.

[0013] Several embodiments of a system for mounting and heating a workpiece are disclosed. A first embodiment is shown in FIG.

[0014] The chuck may be an electrostatic chuck 100 and may have one or more electrodes 110 disposed therein. The electrodes 110 are in communication with an electrode power supply 120. The electrode power supply 120 may supply a DC or AC voltage to the electrodes 110. The frequency and amplitude of the voltage supplied to the electrodes 110 are determined by design and are not limited by the present disclosure. In certain embodiments, the electrodes 110 are arranged in pairs, and voltages of opposite polarity are supplied to the pairs.

[0015] The electrostatic chuck 100 may also include heaters 130 embedded within the electrostatic chuck 100. These heaters 130 may be used to heat the electrostatic chuck 100 to a desired temperature. These heaters 130 may be resistive elements, and a temperature is increased by passing an electric current through the heaters 130. The heaters 130 may be in communication with a heating power supply 135.

[0016] A backside gas channel may pass through the electrostatic chuck 100 and terminate at the top surface of the electrostatic chuck 100. The backside gas channel 150 may be in communication with a source of backside gas that allows for thermal conduction between the electrostatic chuck 100 and the workpiece 10.

[0017] The system also includes a base 180, which is typically cooled. The base 180 may be constructed of a metal such as aluminum. The base 180 may be water-cooled. The base 180 may be maintained at a lower temperature than the electrostatic chuck 100. The electrostatic chuck 100 may be separated from the base 180 using a standoff or another mechanism, particularly for high-temperature implants where proper thermal management is important. The standoff allows the wafer to remain at high temperatures (e.g., 300°C or higher) while maintaining appropriate temperature gradients and acceptable thermal stresses within the electrostatic chuck 100. In some embodiments, the electrostatic chuck 100 and the base 180 are separated by a distance of, for example, 0.5 mm to 50 mm. In certain embodiments, the distance between the electrostatic chuck 100 and the base 180 may be 1.0 mm to 10 mm. Of course, other dimensions are also possible.

[0018] A controller 190 can communicate with the electrode power supply 120 and the heating power supply 135. The controller 190 has a processing unit and an associated memory device. The memory device contains instructions that, when executed by the processing unit, enable the system to perform the functions described herein. The memory device may be non-volatile memory, such as flash ROM, electrically erasable ROM, or other suitable device. In other embodiments, the memory device may be volatile memory, such as RAM or DRAM. In certain embodiments, the controller 190 may be a general-purpose computer, an embedded processor, or a specially designed microcontroller. The actual implementation of the controller 190 is not limited by this disclosure.

[0019] The heat transfer (Q) between the electrostatic chuck 100 and the base 180 is determined by the following equation: TIFF2025529360000002.tif7170 where σ is the Stefan-Boltzmann constant, TIFF2025529360000003.tif16170 is the effective emissivity between the electrostatic chuck and the base, and ε chuck is the emissivity of the electrostatic chuck, ε base is the emissivity of the surface of the base 180, and the view factor between the electrostatic chuck and the base is assumed to be 1. A is the surface area of ​​the top surface of the base, and T chuck and T base are the temperatures of the electrostatic chuck 100 and the base 180, respectively.

[0020] As mentioned above, the base 180 is typically aluminum, with an emissivity of approximately 0.1 to 0.2 depending on the surface finish. Therefore, increasing the emissivity of the base 180 results in more heat being transferred to the base 180. In the embodiment shown in FIG. 1 , a high-emissivity coating 181 is applied to the upper surface of the base 180. This high-emissivity coating 181 can be any material that controls surface emissivity and meets semiconductor processing constraints, such as anodized aluminum, anodized titanium, SiC, alumina, graphite, silicon, silicon dioxide, nichrome, or a ceramic coating such as Cerablak™. Coating methods can include, but are not limited to, atomic layer deposition (ALD), plasma vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, and the like. To achieve higher emissivity, the coating thickness can be 2 μm or greater, as long as good adhesion can be achieved between the high-emissivity coating 181 and the base 180. The high-emissivity coating 181 may be any coating that can be applied to the upper surface of the base 180 and has an emissivity of at least 0.4. Such a coating can approximately double the amount of heat transferred to the base 180, depending on the emissivity of the chuck. In some embodiments, the emissivity of the high-emissivity coating is at least 0.6. Such a coating can approximately triple the amount of heat transferred from the electrostatic chuck 100 to the base 180, depending on the emissivity of the chuck. The emissivity of the high-emissivity coating 181 can be customized by modifying the material selection or chemical composition of the coating to control the radiation and absorption of thermal energy. The emissivity of the coating is controlled accordingly. The energy absorption of the base 180 can also be further controlled by modifying the surface roughness, such as Ra > 0.5 μm, which is an effective way to increase the surface area A as shown in Equation (1). Increasing the roughness has the added benefit of increasing adhesion between the high-emissivity coating 181 and the base 180.

[0021] FIG. 2 illustrates a second embodiment. In this embodiment, the electrostatic chuck 100 is the same as that described with reference to FIG. 1. The distance between the electrostatic chuck 100 and the base 180 may be as described above. In this embodiment, an electrochromic material 182 is applied to the upper surface of the base 180. The thickness of the electrochromic material 182 may be 0.1 to 10 μm, although other thicknesses may be used. The electrochromic material 182 may be in communication with an electrochromic power supply 183. During operation, the transmittance of the electrochromic material 182 changes based on the voltage supplied by the electrochromic power supply 183. The electrochromic material 182 may be switchable glass, also known as smart glass, or may be a different material. The electrochromic material 182 may be NbO x The electrochromic material 182 may include oxides of transition metals, such as WO3, MoO3, IrO2, NiO, and VO5. In one particular embodiment, the electrochromic material 182 may be tin-doped indium tin (ITO) nanocrystals in niobium oxide glass. It has been reported that changing the applied voltage from 1.5 V to 4 V changes the optical transmittance of glass containing ITO nanocrystals from approximately 60% to approximately 95%. In other words, depending on the voltage applied to the electrochromic material 182, the transmittance can change by at least 30%. Of course, different voltages can also be used. Furthermore, the electrochromic material 182 typically has a much higher emissivity than aluminum, such as 0.9.

[0022] The controller 190 may be in communication with the electrochromic power supply 183. Thus, the controller 190 can vary the transmittance of the electrochromic material 182.

[0023] In this embodiment, the thermal energy exchange between the chuck and the base is expressed as follows: TIFF2025529360000004.tif7170 where τ is the transmittance, TIFF2025529360000005.tif16170 is the effective emissivity between the electrostatic chuck and the electrochromic material 182.

[0024] Therefore, the first part of the equation represents the heat transfer between the electrostatic chuck and the base, and the second part of the equation represents the heat transfer between the electrostatic chuck and the electrochromic material 182. When a high voltage, for example 4 V, is applied, the electrochromic material 182 becomes nearly transparent, i.e., τ → 1, and equation (2) is equivalent to equation (1). When the base is heated to the original surface (ε base = 0.2), this configuration would represent a low emissivity configuration. Reducing the voltage can reduce the transmittance τ to 60%. In this scenario, equation (2) can be written as base =0.2) and high emissivity surfaces (ε glass =0.9).

[0025] 1-2, the top surface of base 180 is covered with a material that has a different emissivity than base 180. The material may be high-emissivity coating 181, as described with respect to FIG. 1. Alternatively, the material may be electrochromic material 182, as described with respect to FIG. 2. This material may have a higher emissivity than the top surface of base 180.

[0026] 3A-3B illustrate a third embodiment. In this embodiment, the electrostatic chuck 100 is the same as that described with reference to FIG. 1. The distance between the electrostatic chuck 100 and the base 180 may be as described above. In this embodiment, one or more movable shields 185 are disposed between the base 180 and the electrostatic chuck 100. The movable shields 185 may be made of metal or other suitable material. Each movable shield 185 has a width defined as the horizontal direction in FIG. 3A, a thickness defined as the vertical direction in FIG. 3A, and a length defined as the direction into the page. The length of each movable shield 185 may be at least as long as the portion of the electrostatic chuck under which it is disposed. The width of each movable shield 185 may also be such that, when multiple movable shields are positioned adjacent to each other in the width direction, their combined width is at least as long as the width of the electrostatic chuck 100. The thickness of the movable shields may be significantly smaller than the width of each shield. For example, in some embodiments, the width-to-thickness ratio of the movable shields 185 may be at least 5:1. In other embodiments, it may be 10:1 or greater.

[0027] Additionally, the movable shield 185 is configured to be rotatable about an axis, as shown in FIG. 3B. In some embodiments, the movable shield may be rotatable at least 90 degrees. A rotation motor 186 is in communication with the movable shield 185 and is operable to rotate the movable shield 185 from the closed position shown in FIG. 3A to the open position shown in FIG. 3B. A controller 190 may be in communication with the rotation motor 186.

[0028] Additionally, the emissivity of the upper surface of the movable shield (the surface closest to the electrostatic chuck 100) may be different from the emissivity of the lower surface. In some embodiments, the emissivity of the upper surface may be greater than the emissivity of the lower surface. In other embodiments, the emissivity of the two surfaces is the same.

[0029] In some embodiments, the movable shield 185 may have a low emissivity. In certain embodiments, the emissivity of the movable shield 185 may be 0.4 or less. In other embodiments, the emissivity of the movable shield 185 may be 0.2 or less. In other embodiments, the emissivity of the movable shield 185 may be 0.1 or less. As shown in FIG. 3A , when in the closed position, most of the heat radiated from the electrostatic chuck 100 is reflected toward the chuck, allowing the chuck to retain more heat. In the closed position, the top surface of the movable shield 185 may be positioned in a plane parallel to the bottom surface of the electrostatic chuck 100. The top surface of each movable shield is defined as the side closest to the chuck when in the closed position. In the closed position, more than 80% of the heat radiated from the electrostatic chuck may be blocked by the movable shield 185, preventing direct conduction from the chuck to the top surface of the base 180. In other embodiments, more than 90% of the heat is blocked. Since almost all of the heat is transferred first to the movable shield and then from the movable shield to the base, the effective emissivity between the electrostatic chuck 100 and the base 180 is: TIFF2025529360000006.tif12170

[0030] ε shield is maintained in the range of less than 0.1, and the base is coated with a high emissivity coating, so that the emissivity is at least 0.4. eff,sh is much lower than in the configuration without the movable shield 185. For example, assuming the following: ε chuck =0.9, ε base =0.9, ε shield = 0.1, the effective emissivity when the shield is closed is expressed as follows: TIFF2025529360000007.tif12170

[0031] This represents a low emissivity configuration.

[0032] As shown in FIG. 3B , when in the open position, heat radiated from the electrostatic chuck can be transferred directly to the top surface of the base 180. This is because the thickness of the movable shield 185 is much smaller than the width of the shield. In some embodiments, in the open position, the movable shield 185 can be rotated so that the top surface of the movable shield 185 is perpendicular to the bottom surface of the electrostatic chuck 100. This configuration minimizes the effect of the movable shield 185 on heat transfer between the electrostatic chuck 100 and the base 180. Of course, in other embodiments, the rotation of the movable shield 185 can be less than 90°. In the open position, more than 80% of the heat radiated from the electrostatic chuck can be transferred directly from the chuck to the top surface of the base 180. In other embodiments, more than 90% of the heat is transferred directly to the top surface of the base 180.

[0033] In this configuration, a high emissivity coating can be applied to the base 180. Assuming the same emissivity as above, the effective emissivity is expressed as: TIFF2025529360000008.tif13170

[0034] This represents a high emissivity configuration.

[0035] Of course, other emissivities can be used. For example, if the high-emissivity coating on the base has an emissivity of 0.5, the emissivity when the shield is closed is 0.047 and when the shield is open is 0.473. In some embodiments, the emissivity of the top surface of base 180 is greater than the emissivity of movable shield 185.

[0036] Thus, in certain embodiments, a material having an emissivity different from that of the base 180 can be applied to the top surface of the base 180. For example, a high-emissivity coating 181, such as that described with respect to Figure 1, can be applied to the top surface of the base 180. Alternatively, an electrochromic material 182, such as that described with respect to Figure 2, can be applied to the top surface.

[0037] The embodiment of Figures 2-3 allows for adaptive heat transfer rates from the chuck.

[0038] For example, assume that a low-power ion beam is used. A low-power level is defined as a power level that allows the electrostatic chuck 100 to dissipate heat through radiative heating faster than the ion beam can transfer heat to the chuck. In these embodiments, a heater 130 within the chuck is used to maintain a high temperature of the electrostatic chuck 100. In some embodiments, a low-power beam refers to a beam power of less than 100 W. A high-power level is defined as a power level at which a conventional chuck cannot dissipate the thermal energy provided by the ion beam, causing thermal runaway. In some embodiments, a high-power level is defined as a beam power greater than 100 W. In other embodiments, a high-power level may be defined as greater than 500 W. In yet other embodiments, a high-power level may be greater than 1000 W.

[0039] In the embodiment of FIG. 2 , the controller 190 can control the electrochromic power supply 183 to set the transmittance of the electrochromic material 182 to a first value. This first value can be approximately 100%. In this mode, the electrochromic material 182 is nearly transparent, so the system operates similarly to when the electrochromic material 182 is not utilized. When a high power level of the ion beam is used, the controller 190 can control the electrochromic power supply 183 to set the transmittance of the electrochromic material 182 to a second value that is lower than the first value, e.g., less than 70%. Because the emissivity of the electrochromic material 182 is higher than the emissivity of the base 180, more heat is transferred from the electrostatic chuck when a high power ion beam is used.

[0040] Similar techniques can be applied to the embodiment of Figures 3A-3B. When a low-power ion beam is used, the controller 190 can control the rotation motor 186 to close the movable shield 185, thereby reflecting heat toward the electrostatic chuck 100. When a high-power ion beam is used, the controller 190 can control the rotation motor 186 to move the movable shield 185 to an open position. In this position, heat is reflected from the underside of the shield to the base 180 and can be transferred directly to the base 180. This improves heat transfer between the electrostatic chuck 100 and the base 180 when a high-power ion beam is used.

[0041] The embodiments described above in this application can have many advantages. In one simulation, the emissivity of the base 180 was increased from 0.2 to 0.8. The maximum ion beam current that could be implanted without thermal runaway increased by 50%. This simulation was verified by testing the base 180 with a high-emissivity coating. As predicted, the maximum ion beam current without thermal runaway increased by 50%. Increasing the maximum allowable ion beam current can improve the throughput of the implantation system. Furthermore, as shown in Figures 2-3, the heat transfer coefficient can be adaptively changed, allowing the same chuck and base combination to be used for ion beams with both low and high power levels.

[0042] The scope of the present disclosure is not limited by the specific embodiments described herein. Indeed, various other embodiments and modifications of the present disclosure, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Moreover, while the present disclosure has been described herein in the context of particular implementations in particular environments for particular purposes, those skilled in the art will recognize that its utility is not limited in this respect, and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in light of the full scope and spirit of the present disclosure as described herein.

Claims

1. 1. A system for mounting and heating a workpiece, comprising: an electrostatic chuck; a base spaced from the electrostatic chuck; Equipped with A system wherein a material having an emissivity different from that of the base is disposed on an upper surface of the base.

2. The system of claim 1 , wherein the material comprises a high-emissivity coating.

3. 3. The system of claim 2, wherein the high-emissivity coating has an emissivity of 0.4 or greater.

4. 3. The system of claim 2, wherein the high-emissivity coating has an emissivity of 0.6 or greater.

5. 3. The system of claim 2, wherein the high-emissivity coating comprises at least one of anodized aluminum, anodized titanium, SiC, alumina, graphite, silicon, silicon dioxide, nichrome, and a ceramic coating.

6. The system of claim 1 , wherein the material comprises an electrochromic material.

7. The system of claim 6 , wherein the electrochromic material comprises electrochromic glass.

8. 8. The system of claim 7, wherein the electrochromic glass has a transmittance that varies by at least 30% in response to a voltage applied to the electrochromic glass.

9. 1. A system for mounting and heating a workpiece, comprising: an electrostatic chuck; a base spaced from the electrostatic chuck; a controller configured to vary the amount of heat transfer between the electrostatic chuck and the base based on a power level of the incident ion beam; A system comprising:

10. 10. The system of claim 9, wherein an electrochromic material is disposed on an upper surface of the base, the system further comprising an electrochromic power supply in communication with the electrochromic material and the controller, the controller controlling the voltage supplied to the electrochromic material by the electrochromic power supply.

11. The system of claim 10 , wherein the emissivity of the electrochromic material is greater than the emissivity of the top surface of the base.

12. 11. The system of claim 10, wherein the transmittance of the electrochromic material is a first value when a low-power ion beam is used and a second value lower than the first value when a high-power ion beam is used.

13. 13. The system of claim 12, wherein when the permeability is at the second value, the amount of heat transfer between the electrostatic chuck and the base is greater than the amount of heat transfer when the permeability is at the first value.

14. The system of claim 9 , further comprising a movable shield disposed between the electrostatic chuck and the base.

15. 15. The system of claim 14, wherein a top surface of the base is coated with a high-emissivity material having an emissivity of 0.4 or greater.

16. The system of claim 15 , wherein the movable shield is made from a material having an emissivity lower than the emissivity of the high emissivity material.

17. 15. The system of claim 14, wherein the movable shield is in a closed position when a low-power ion beam is being used and is in an open position when a high-power ion beam is being used, and wherein in the closed position the movable shield is positioned such that a top surface of the movable shield is parallel to a bottom surface of the electrostatic chuck.

18. 15. The system of claim 14, wherein the movable shield is in a closed position when a low-power ion beam is being used and is in an open position when a high-power ion beam is being used, and wherein in the closed position the movable shield is positioned such that more than 80% of heat radiated by the electrostatic chuck is blocked by the movable shield from being conducted directly from the electrostatic chuck to a top surface of the base.

Images