Optical temperature sensor with monolithic crystalline phosphor

Abstract

This invention discloses an optical temperature sensor for a plasma processing chamber. The optical temperature sensor includes a light source, a photodetector, and a component for transmitting light through a wall of a plasma processing chamber. An optical temperature sensing element is thermally coupled to a plasma processing chamber assembly within the plasma processing chamber. The optical temperature sensing element includes a monolithic phosphor element configured to be excited by light from the light source and to emit light indicating a temperature of the monolithic phosphor element back to the photodetector.

Description

[Technical Field]

[0001] The specific examples disclosed in this invention generally relate to temperature sensing devices, and more specifically, to crystal optical temperature sensing devices. [Previous Technology]

[0002] Fiber optic temperature sensors have several unique advantages over other temperature measurement devices, especially when operating in the presence of strong electromagnetic fields or when measuring extremely low temperatures (such as -100°C). More specifically, fiber optic temperature sensors are well-suited for measuring the temperature of plasma processing chamber components; however, the harsh environment inside plasma processing chambers often limits the effectiveness of such fiber optic temperature sensors.

[0003] Currently, fiber optic temperature sensors are typically integrated into the electrostatic chuck of a plasma processing chamber and operate outside the harsh environment of the plasma processing chamber and in the atmosphere. This external positioning of the fiber optic temperature sensor makes it difficult, or in some cases impossible, to measure the temperature of individual plasma processing chamber components located within the plasma processing chamber.

[0004] The temperature inside the chamber can be monitored remotely using a pyrometer and a window or light tube; however, the variable emissivity of the components involved presents considerable challenges, especially when the components are coated with chemicals from the harsh environment of the plasma processing chamber (such as redeposition etching residues from etching processes). In addition, some plasma processes may require monitoring at extremely low temperatures, such as -70°C in some etching processes, for which pyrometers are not suitable.

[0005] In-cell operation of many current fiber optic temperature sensors is impractical due to the harsh environment of most plasma processing chambers. Specifically, any component of a fiber optic temperature sensor operating within a plasma processing chamber must be chemically resistant to the harsh environment and chemically compatible with the processes occurring within the plasma processing chamber to maintain functionality while avoiding process contamination. For example, many current fiber optic temperature sensors are made with polysiloxane, epoxy, or inorganic ceramic adhesives, which may contain known ionic contaminants (such as sodium, potassium, etc.). These fiber optic temperature sensors may degrade or contaminate the process when exposed to the plasma processing chamber environment.

[0006] Therefore, there is a need in the art for a novel optical temperature sensor design to address some of the current shortcomings, particularly those related to the placement of optical temperature sensor components within a plasma processing chamber in order to measure the temperature of individual plasma processing chamber components. [Summary of the Invention]

[0007] The following is a simplified summary of one or more of the modes and / or specific instances disclosed herein. Therefore, the following summary should not be considered an exhaustive overview of all covered modes and / or specific instances, nor should it be thought to identify key or essential elements concerning all covered modes and / or specific instances, or to define the scope associated with any particular mode and / or specific instance. Thus, the sole purpose of the following summary is to present, in a simplified form, certain concepts related to one or more modes and / or specific instances of the mechanisms disclosed herein before the detailed descriptions presented below.

[0008] Some embodiments of the present invention may be characterized as an optical temperature sensor for a plasma processing chamber, comprising a light source, a light tube configured to transmit light through the wall of the plasma processing chamber, and a photodetector. The optical temperature sensing element may be thermally coupled to and embedded in a plasma processing chamber assembly within the plasma processing chamber. The optical temperature sensing element may include a monolithic phosphor element configured to be excited by light transmitted from the light source through the light tube and to emit light indicating the temperature of the monolithic phosphor element back to the photodetector via the light tube.

[0009] Another aspect of the present invention may be characterized as a plasma chamber optical temperature sensor, comprising a light source, a component for transmitting light through the wall of the plasma chamber, and a photodetector. The plasma chamber optical temperature sensor may also include a component for thermally coupling an optical temperature sensing element to a plasma chamber assembly within the plasma chamber. The optical temperature sensing element may include a monolithic phosphor element configured to be excited by light from the light source transmitted through the component for transmitting light and to emit light back to a photodetector indicating the temperature of the monolithic phosphor element via the component for transmitting light.

Implementation Method

[0013] The word “illustrative” is used in this document to mean “serving as an example, illustration or explanation”. Any specific instance described as “illustrative” in this document is not necessarily to be understood as better or more advantageous than other specific instances.

[0014] This invention enables a highly durable plasma chamber optical temperature sensor to be located within the plasma chamber for accurate measurement of the temperature of individual plasma chamber components. Furthermore, this invention enables the plasma chamber optical temperature sensor to be chemically resistant to the harsh environment within the plasma chamber and chemically compatible with the processes occurring within the plasma chamber, thus maintaining functionality and reducing process contamination. In addition, this invention enables the plasma chamber optical temperature sensor to highly shield stray light, thereby improving temperature sensing accuracy. By implementing the apparatus of this invention, significant improvements can be achieved in plasma chamber optical temperature sensors, potentially realizing more reliable and durable plasma chamber optical temperature sensors capable of accurately measuring the temperature of individual plasma chamber components, which can be used to improve process control.

[0015] Some specific embodiments of the present invention may include a plasma chamber optical temperature sensor having a light source, a photodetector, and a component for transmitting light through the wall of the plasma chamber. For example, the component for transmitting light may include at least one of a light pipe, an optical fiber, a window, a mirror, a lens, a light guide, and any other optical component configured to transmit light through the wall of the plasma chamber. The plasma chamber optical temperature sensor may further include an optical temperature sensing element and a component for thermally coupling the optical temperature sensing element to a plasma chamber assembly (such as a focusing ring or showerhead electrode) within the plasma chamber. For example, the component for thermal coupling may include at least one of the following: direct contact between the optical temperature sensing element and the plasma chamber assembly, such as by embedding the optical temperature sensing element within the plasma chamber assembly; a thermal interface material located between the optical temperature sensing element and the plasma chamber assembly; and close proximity between the optical temperature sensing element and the plasma chamber assembly. The optical temperature sensing element may comprise a monolithic phosphor element configured to be excited by light from a light source transmitted through a component for transmitting light, and to indicate the temperature of the monolithic phosphor element via the same component. For example, the monolithic phosphor element may be a single-crystal or polycrystalline bulk material exhibiting thermosensitive phosphorescence, such as any of various doped Al₂O₃, yttrium aluminum garnet (YAG), spinel (MgAl₂O₄), or a variety of known crystalline materials exhibiting temperature-dependent phosphorescence with suitable decay times. Such bulk crystals may be grown with high purity and high consistency, for example via a Czochralski crystal pulling process, and may be cut into specific shapes, such as disks, to achieve better mounting or retention, depending on the application. One or more dopants, such as chromium, europium, cerium, manganese, etc., can be selected and included in a particular crystal bulk, at least in part, based on the phosphorescence decay time and the sensitivity within a specific temperature range of the resulting doped crystal bulk. In some specific instances, the monocrystalline phosphor element can be a single crystal bulk and can be oriented to minimize birefringence, such as on the c-axis of an Al₂O₃-based monocrystalline phosphor element.

[0016] Unlike many prior art phosphors, monolithic phosphor elements do not require the use of adhesives, binders, or encapsulating materials. Furthermore, monolithic phosphor elements can exhibit advantageous material properties typically associated with crystalline materials, such as excellent chemical resistance and heat resistance from low temperatures to well above 1000°C. Therefore, the monolithic phosphor element can be exposed to the harsh environment of the plasma chamber, enabling the plasma chamber optical temperature sensor to be chemically resistant to the harsh environment of the plasma chamber and compatible with the process chemistry occurring within the plasma chamber. This allows the plasma chamber optical temperature sensor to be located within the plasma chamber and accurately measure the temperature of individual plasma chamber components.

[0017] In some specific examples, the plasma chamber optical temperature sensor may include a component for mechanically engaging the optical temperature sensing element to the plasma chamber assembly. The component for mechanical engagement may include at least one of an O-ring and a retaining ring. For example, the optical temperature sensing element may be embedded in the plasma chamber assembly, such as by means of a recess within the plasma chamber assembly, and held or secured in place by an O-ring, thereby forming a mechanical engagement. The O-ring may comprise a compressible, elastic material capable of withstanding the environment within the plasma chamber, such as a fluoropolymer, high-performance polysiloxane, or polysiloxane encapsulated with a fluoropolymer, which allows the optical temperature sensing element to be retained even under varying thermal expansion conditions and to be easily disassembled for repair, such as by flip-polishing repair, and reused in another plasma chamber assembly.

[0018] In another example, the optical temperature sensing element can be embedded in the plasma chamber assembly, for example, by means of a recess located within the plasma chamber assembly, and held by a retaining ring, thereby forming a mechanical connection. The retaining ring can be made of the same material as the plasma chamber assembly, such as SiC or Si, and is sized to allow for different thermal expansions between the plasma chamber assembly and the optical temperature sensing element. The retaining ring can be attached to the plasma chamber assembly by at least one of soldering and brazing, such as by fillerless laser soldering or soldering with filler material, which is compatible with the plasma process occurring within the plasma chamber. In applications where the elastic material of the O-ring is chemically or thermodynamically incompatible with the plasma process, the retaining ring enables a mechanical connection between the optical temperature sensing element and the plasma chamber assembly.

[0019] In some specific examples, the plasma chamber optical temperature sensor may include, where appropriate, a component for providing a compressible thermal interface between the optical temperature sensing element and the plasma chamber assembly. The component for providing the compressible thermal interface may include a compressible pyrolytic graphite thermal interface material or other compressible thermal interface materials compatible with the plasma process occurring within the plasma chamber, located between the optical temperature sensing element and the plasma chamber assembly. For example, in the retaining ring example discussed above, the compressible pyrolytic graphite thermal interface material may be located between the optical temperature sensing element and the plasma chamber assembly, which can help compensate for the different thermal expansions of the plasma chamber assembly and the optical temperature sensing element, thereby potentially filling any gaps between them and enhancing thermal coupling.

[0020] In some specific examples, the plasma chamber optical temperature sensor may include a component for directly bonding a monolithic phosphor element of the optical temperature sensing element to the plasma chamber assembly. The component for direct bonding may include laser-bonding the monolithic phosphor element to the plasma chamber assembly. For example, the optical temperature sensing element may be embedded in the plasma chamber assembly, such as by means of a recess located within the plasma chamber assembly, and the monolithic phosphor element may be directly laser-bonded to the plasma chamber assembly, such as along the periphery of the recess. The optical temperature sensing element may have a coefficient of thermal expansion matching the plasma chamber assembly, such as a ruby ​​optical temperature sensing element and a sintered alumina ceramic plasma chamber assembly, and may be configured to directly connect to each wall of the recess over a wide temperature range, thereby providing robust thermal coupling and enabling the optical temperature sensing element to be held in place without the need for additional components such as O-rings or retaining rings.

[0021] In some specific examples, the plasma chamber optical temperature sensor can highly shield stray light, thereby improving temperature sensing accuracy. For example, the optical temperature sensing element can be embedded in the plasma chamber assembly to provide light shielding on all non-exposed sides and can be configured such that any exposed side faces the wall of the plasma chamber, thereby potentially reducing stray light from the plasma process occurring within the plasma chamber. In another example, a component for allowing light transmission through the wall of the plasma chamber can shield stray light within the plasma chamber, such as by positioning behind the plasma chamber assembly and shielding stray light (e.g., ambient light) outside the plasma chamber, such as by encapsulation or coating known in the art to provide light shielding. Such shielding of stray light can improve temperature sensing accuracy by reducing stray light excitation of the monolithic crystalline phosphor element and reducing stray light transmission to the photodetector. Furthermore, monolithic phosphor elements can incorporate narrowband emitting materials, such as ruby, which allows for the use of narrowband filters to help reduce the impact of stray light on the photodetector, thereby providing more accurate temperature measurements. Additionally, fault detection algorithms or other methods for filtering noisy data can be implemented to mitigate errors introduced by stray light.

[0022] Referring now to the figures, FIG1 illustrates a cross-sectional view of an exemplary embodiment of an optical temperature sensor 101 for a plasma chamber, wherein the optical temperature sensing element 102 is mechanically engaged to the plasma chamber assembly 104 using an O-ring 106. The plasma chamber optical temperature sensor 101 may have a light source (not shown) and a photodetector (not shown), and a light tube 110 configured to transmit light through the wall 116 of the plasma chamber. The light source may be located outside the plasma chamber and may be configured to emit light transmitted via the light tube 110 to the optical temperature sensing element 102, which may contain a monolithic crystal phosphor element. The photodetector may also be located outside the plasma chamber and may be configured to receive light emitted by the monolithic crystal phosphor element of the optical temperature sensing element 102 via the light tube 110. In some embodiments, additional optical elements, such as optical fibers, may optically connect the light tube 110 to the light source and the photodetector.

[0023] The optical temperature sensing element 102 can be directly thermally coupled to and embedded in the plasma chamber assembly 104 within the plasma chamber. The plasma chamber assembly 104 can be any component within the plasma chamber, such as a focusing ring or a showerhead electrode, and can be made, for example, of silicon, silicon carbide, or sintered alumina ceramic. As shown, the optical temperature sensing element 102 can be positioned in a recess 105 of the plasma chamber assembly 104. The recess 105 can be generally cylindrical, having an annular flange with a tapered wall configured to receive and retain an O-ring 106. The optical temperature sensing element 102 can have a tapered cylindrical shape and can be configured to directly connect to the bottom wall of the recess 105, thereby providing thermal coupling. O-ring 106 can be wedged between the sidewall of optical temperature sensing element 102 and the tapered wall of annular flange to hold optical temperature sensing element 102 and mechanically engage it to plasma chamber assembly 104. Considering the different thermal expansion of optical temperature sensing element 102 and plasma chamber assembly 104, a small gap can be maintained between the sidewall of optical temperature sensing element 102 and one or more sidewalls of recess 105. O-ring 106 may comprise a compressible elastic material capable of withstanding the environment within the plasma chamber, such as a fluoropolymer, high-performance polysiloxane, or polysiloxane encapsulated with a fluoropolymer, which allows the optical temperature sensing element 102 to be held even under different thermal expansion conditions and easily disassembled for repair, such as by flip-polishing repair, and reused in another plasma chamber assembly. Although the optical temperature sensing element 102 and the recess 105 are shown as generally cylindrical, it is considered that other geometries such as cubes and cones, as well as configurations for O-ring retention such as conical walls with notches rather than annular flanges, may be used without departing from the scope of the invention.

[0024] The monolithic phosphor element of the optical temperature sensing element 102 can be configured to be excited by light transmitted from a light source through a light tube 110 and to emit light indicating the temperature of the monolithic phosphor element back to a photodetector via the light tube 110. For example, the light source can emit light guided to the light tube 110, such as via an optical fiber or direct line of sight. The light tube 110 can then transmit light from the light source to the monolithic phosphor element of the optical temperature sensing element 102, thereby exciting the monolithic phosphor element, which then emits light. The light emitted by the monolithic phosphor element depends on the temperature of the monolithic phosphor element, which can be thermally coupled to the plasma processing chamber assembly 104 as an assembly of the optical temperature sensing element 102. The light tube 110 can then transmit the light emitted by the monolithic phosphor element to a photodetector, such as via an optical fiber or direct line of sight. The photodetector can interpret the light emitted by the monolithic phosphor element to determine the temperature of the monolithic phosphor element. Due to thermal coupling, this temperature can be used to determine the temperature of the plasma processing chamber assembly 104.

[0025] The optical tube 110 can pass through the vacuum-sealed feedthrough interface 112, the wall shielding layer 114, and the wall 116 of the plasma processing chamber to access the interior of the plasma processing chamber. The vacuum-sealed feedthrough interface 112 can be integrated into the wall 116 and can provide an airtight seal for the plasma processing chamber while allowing the optical tube 110 to enter. In addition, the vacuum-sealed feedthrough interface 112 can provide an interface and optical connection to the optical tube 110 and the optical fiber, for example, through a central aperture, which assists in transmitting light from the light source to the photodetector. The optical tube 110 can be located in the well 109 of the wall shielding layer 114, extending toward the optical temperature sensing element 102, but with a gap between the optical temperature sensing element 102 and the optical tube 110. The optical tube 110 can be constructed without the use of adhesives, bonding agents, or encapsulating materials, such as a sapphire optical tube with excellent chemical resistance. Depending on the circumstances, window 108 may cover well 109, thereby isolating light tube 110 from the environment within the plasma processing chamber and protecting light tube 110. However, whether window 108 is included depends on any chemicals or residues that may be present within the plasma processing chamber. For example, window 108 may not be included in a harsher environment due to potential problems, such as those related to the deposition of chemical residues that affect emissivity as discussed above.

[0026] In other specific embodiments, the light tube 110 may be replaced with other components for transmitting light, such as encapsulated optical fibers, windows, lenses, light guides, or any other optical components configured to transmit light through the wall shielding layer 114 and the wall 116 of the plasma processing chamber; however, such optical components may introduce problems regarding the harsher plasma processing chamber environment. For example, the encapsulating material around the optical fiber may degrade under harsh conditions and may contaminate the plasma processing chamber. Additionally, other preferred configurations (such as narrow apertures) and components for providing a hermetically tight seal, such as gaskets or welding techniques, may be implemented without departing from the scope of the invention.

[0027] The optical temperature sensing element 102 shown is composed entirely of a monolithic crystal phosphor element; however, it is considered that, without departing from the scope of the present invention, in other specific embodiments, the optical temperature sensing element 102 may include other components, such as a mounting bracket, a housing of the monolithic crystal phosphor element, a light shielding element, etc.

[0028] In some specific examples, the monocrystalline phosphor element of the optical temperature sensing element 102 may be a monocrystalline bulk material exhibiting thermosensitive phosphorescence, or alternatively, a polycrystalline bulk material exhibiting thermosensitive phosphorescence. For example, the monocrystalline phosphor element may be a monocrystalline bulk material of various doped Al2O3, yttrium aluminum garnet (YAG), spinel (MgAl2O4), or any of a variety of known crystalline materials having temperature-dependent phosphorescence with suitable decay times. One or more dopants, such as chromium, europium, cerium, manganese, etc., may be selected and included in a particular monocrystalline bulk material, at least in part, based on the phosphorescence decay time and the sensitivity within a specific temperature range of the resulting doped monocrystalline bulk material. The birefringence associated with such crystalline materials, especially in monocrystalline form, may be mitigated, for example, by oriented monocrystalline phosphor elements to minimize the birefringence along the c-axis of, for example, an Al2O3-based monocrystalline phosphor element. These crystalline materials exhibit excellent chemical resistance and heat resistance from low temperatures to well above 1000°C. Furthermore, the monolithic form of these monolithic crystal blocks allows for the fabrication of monolithic crystalline phosphor elements without the need for adhesives, binders, or encapsulating materials, thus avoiding some of the problematic aspects associated with chemical deposition on phosphor compositions and components within the plasma processing chamber in previous technologies. Therefore, monolithic crystalline phosphor elements can be directly exposed to the harsh environment of the plasma processing chamber, allowing the optical temperature sensing element 102 to be located within the plasma processing chamber while remaining chemically resistant to the harsh environment and compatible with the process chemistry occurring within the plasma processing chamber. Positioning the optical temperature sensing element 102 within the plasma processing chamber enables excellent thermal coupling with individual plasma processing chamber components (such as plasma processing chamber component 104) through direct contact, thereby allowing for accurate temperature measurement of individual plasma processing chamber components.

[0029] In some specific embodiments, the plasma chamber optical temperature sensor 101 can highly shield stray light, thereby improving temperature sensing accuracy. The optical temperature sensing element 102 can be embedded in the plasma chamber assembly 104 to provide light shielding on all non-exposed sides. Additionally, as shown, any exposed side of the optical temperature sensing element 102 can face the wall shielding layer 114 of the plasma chamber, and the optical temperature sensing element 102 can be embedded in a portion of the plasma chamber assembly 104 closely adjacent to the wall shielding layer 114. Therefore, the plasma chamber assembly 104 can block most of the stray light generated by the plasma process occurring within the plasma chamber. Furthermore, the light tube 110 can be located behind the plasma chamber assembly 104, thereby shielding the light tube 110 from stray light generated within the plasma chamber, and the external portion of the light tube 110 can be encapsulated by a vacuum-sealed feedthrough interface 112, thereby shielding the light tube 110 from external stray light while providing access to the light source and photodetector. Such shielding of stray light can improve temperature sensing accuracy by reducing stray light excitation of monolithic phosphor elements and reducing stray light transmission to the photodetector.

[0030] Referring now to FIG2, FIG2 illustrates a cross-sectional view of an exemplary specific example of the internal portion of a plasma chamber optical temperature sensor, wherein the optical temperature sensing element 202 is mechanically engaged with the plasma chamber assembly 204 within a recess 205 of the plasma chamber assembly 204 using a retaining ring 206. The plasma chamber optical temperature sensor of FIG2 is substantially the same as the plasma chamber optical temperature sensor 101 of FIG1, except that the optical temperature sensing element 202, the plasma chamber assembly 204, and the recess 205 are configured for the retaining ring 206 rather than the O-ring 106, and may include a compressible thermal interface material 207.

[0031] The optical temperature sensing element 202 is thermally coupled to and embedded in the plasma chamber assembly 204 within the plasma chamber. The thermal coupling between the optical temperature sensing element 202 and the plasma chamber assembly 204 can be achieved through direct contact, close proximity, or, as appropriate, through a compressible thermal interface material 207. The optical temperature sensing element 202 may be located in a recess 205 of the plasma chamber assembly 204, and the recess 205 may be generally cylindrical with an annular flange configured to receive a retaining ring 206. The optical temperature sensing element 202 may have a cylindrical shape at one end and a conical cylindrical shape at the other end configured to connect the retaining ring 206. The optical temperature sensing element 202 shown is entirely composed of a monolithic crystal phosphor element; however, in other specific embodiments, the optical temperature sensing element 202 may include other components.

[0032] The retaining ring 206 may be generally annular, with a tapered inner wall configured to connect to the plasma chamber assembly 204. The retaining ring 206 may be placed on an annular flange and attached to the plasma chamber assembly 204 to retain the optical temperature sensing element 202 and mechanically engage it to the plasma chamber assembly 204. For example, the retaining ring 206 may be attached to the plasma chamber assembly 204 by at least one of welding and soldering, such as by fillerless laser welding or welding with filler material, which is compatible with specific plasma processes occurring within the plasma chamber. Considering the different thermal expansion of the optical temperature sensing element 202 and the plasma chamber assembly 204, a small gap may be maintained between the optical temperature sensing element 202 and one or more walls of the recess 205. The retaining ring 206 may be made of the same material as the plasma chamber assembly 204, such as silicon, silicon carbide, or sintered alumina ceramic, and is sized to allow for different thermal expansions of the plasma chamber assembly 204 and the optical temperature sensing element 202. In some configurations, a small gap is left between the retaining ring 206 and the optical temperature sensing element 202. In applications where the elastic material of the O-ring is incompatible with certain plasma processes, such as chemically or thermodynamically, the retaining ring 206 enables mechanical engagement between the optical temperature sensing element 202 and the plasma chamber assembly 204.

[0033] Depending on the circumstances, the compressible thermal interface material 207 may be located between the optical temperature sensing element 202 and the plasma processing chamber assembly 204. For example, the compressible thermal interface material 207 may be a compressible pyrolytic graphite thermal interface material or other compressible thermal interface material compatible with the plasma process occurring within the plasma processing chamber, and the compressible thermal interface material 207 may be shaped into a disc and located between the bottom wall of the recess 205 and one end of the optical temperature sensing element 202. The compressible thermal interface material 207 can help compensate for the different thermal expansions of the plasma processing chamber assembly 204 and the optical temperature sensing element 202, such as by compressively filling the gap between them, thereby enhancing thermal coupling.

[0034] Although the optical temperature sensing element 202 and the recess 205 are shown as cylinders, it is considered that other geometries such as cubes and cones and the retaining ring 206 configuration, such as a retaining circular plate with a plurality of holes or a retaining ring integrated into the optical temperature sensing element 202, may be used without departing from the scope of the invention.

[0035] Referring now to FIG3, FIG3 illustrates a cross-sectional view of an exemplary specific example of the internal portion of a plasma chamber optical temperature sensor, wherein the optical temperature sensing element 302 is directly coupled to the plasma chamber assembly 304 within the recess 305 of the plasma chamber assembly 304. The plasma chamber optical temperature sensor of FIG3 is substantially the same as the plasma chamber optical temperature sensor 101 of FIG1, except that the optical temperature sensing element 302, the plasma chamber assembly 304, and the recess 305 are configured for direct coupling without the need for the O-ring 106.

[0036] The optical temperature sensing element 302 is thermally coupled to and embedded in the plasma chamber assembly 304 within the plasma chamber. Thermal coupling between the optical temperature sensing element 302 and the plasma chamber assembly 304 can be achieved through direct contact. The optical temperature sensing element 302 can be configured to reside in a recess 305 of the plasma chamber assembly 304, and can be directly attached to the plasma chamber assembly 304, for example, by directly bonding a monolithic phosphor element of the optical temperature sensing element 302 to the plasma chamber assembly 304. For example, the monolithic phosphor element of the optical temperature sensing element 302 can be directly laser-welded to the plasma chamber assembly 304, such as along the periphery 303 of the recess 305. The illustrated optical temperature sensing element 302 is entirely composed of a monolithic phosphor element; however, in other specific embodiments, the optical temperature sensing element 302 may include other components.

[0037] The optical temperature sensing element 302 and the recess 305 can be configured to maintain contact over a wide temperature range and thus maintain good thermal coupling. For example, the optical temperature sensing element 302 and the recess 305 may each have a matching cylindrical shape and a matching coefficient of thermal expansion, such that each wall of the optical temperature sensing element 302 facing the recess 305 maintains contact with the recess 305. The materials of the optical temperature sensing element 302 and the monolithic phosphor element can be selected to match the coefficient of thermal expansion of the plasma chamber assembly 304, such as selecting a ruby ​​optical temperature sensing element and a monolithic phosphor element to match the coefficient of thermal expansion of the sintered alumina ceramic plasma chamber assembly. This direct engagement of the optical temperature sensing element 302 and the plasma chamber assembly 304 achieves robust thermal coupling and allows the optical temperature sensing element 302 to be held in place without the need for additional components such as O-rings or retaining rings. Other optical temperature sensing elements and recess geometries, such as cubes and cones, may be used in other specific embodiments without departing from the scope of the invention.

[0038] The prior description of the disclosed specific examples is provided to enable anyone skilled in the art to make or use the invention. Various modifications to these specific examples will readily become apparent to those skilled in the art, and the general principles defined herein can be applied to other specific examples without departing from the spirit or scope of the invention. Therefore, the invention is not intended to be limited to the specific examples shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. [Simplified Explanation of the Diagram]

[0010] [Figure 1] A cross-sectional view illustrating an exemplary specific example of an optical temperature sensor for a plasma processing chamber, wherein the optical temperature sensing element is mechanically engaged to the plasma processing chamber assembly using an O-ring;

[0011] [Figure 2] illustrates an exemplary specific example of the internal portion of an optical temperature sensor in a plasma processing chamber, wherein the optical temperature sensing element is mechanically engaged to the plasma processing chamber assembly using a retaining ring; and

[0012] [Figure 3] is a cross-sectional view illustrating an exemplary specific example of an internal portion of an optical temperature sensor in a plasma processing chamber, wherein the optical temperature sensing element is directly coupled to the plasma processing chamber assembly.

Claims

1. An optical temperature sensor for a plasma processing chamber, comprising: a light source; a light tube configured to transmit light through a wall of a plasma processing chamber; a photodetector; and an optical temperature sensing element having a conical cylindrical shape and being thermally coupled to the bottom wall of a recess of a plasma processing chamber assembly within the plasma processing chamber via direct contact, the optical temperature sensing element being embedded in the recess of the plasma processing chamber assembly within the plasma processing chamber, the recess having a conical wall; an O-ring positioned between the conical wall of the recess and a side wall of the optical temperature sensing element; and the optical temperature sensing element comprising a monocrystalline phosphor element configured to be excited by light transmitted from the light source through the light tube and to emit light indicating the temperature of the monocrystalline phosphor element back to the photodetector via the light tube.

2. The plasma processing chamber optical temperature sensor of claim 1, wherein a compressible thermal interface material is located between the optical temperature sensing element and the plasma processing chamber assembly.

3. The plasma processing chamber optical temperature sensor of claim 1, wherein the monolithic phosphor element is a monolithic block exhibiting thermosensitive phosphorescence.

4. The plasma processing chamber optical temperature sensor of claim 1, wherein the monocrystalline phosphor element is a polycrystalline bulk exhibiting thermosensitive phosphorescence.

5. An optical temperature sensor for a plasma processing chamber, comprising: a light source; a component for transmitting light such that the light is transmitted through a wall of the plasma processing chamber; a photodetector; a single-crystal bulk sensing element exhibiting thermosensitive phosphorescence, the single-crystal bulk sensing element including a cylindrical end and a conical cylindrical end, the single-crystal bulk sensing element being thermally coupled to the bottom wall of a recess of a plasma processing chamber assembly within the plasma processing chamber, and the single-crystal bulk sensing element being embedded in the recess of the plasma processing chamber assembly within the plasma processing chamber, the recess having a conical wall; and a retaining ring having one end engaged with the recess and having a conical inner wall to overlap with the conical cylindrical shape of the single-crystal bulk sensing element.

6. The plasma chamber optical temperature sensor of claim 5, wherein the retaining ring system is attached to the plasma chamber assembly by at least one of welding and brazing.

7. The plasma chamber optical temperature sensor of claim 5, further comprising: a component for providing a compressible thermal interface between the single-crystal bulk sensing element and the plasma chamber assembly.

8. The plasma chamber optical temperature sensor of claim 5, further comprising: a component for direct bonding to directly bond the monocrystalline bulk sensing element to the plasma chamber assembly.

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