HTCC antenna for plasma generation

Abstract

A plasma generating apparatus for generating a plasma includes a support having a first side and an opposing second side. The support is comprised of a ceramic matrix, and a split ring conductor is embedded in the ceramic matrix. A hermetic via extends from the split ring conductor to the second side of the support and connects to a power source. A ground plane is formed in the second side of the support. A plasma is generated proximate to the first side of the support, and the support seals to a wall of the chamber such that the first side is exposed to one or more gases in the chamber and the second side is isolated from the plasma and one or more gases in the chamber.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 124,401, filed December 11, 2020, the entirety of which is incorporated herein by reference.

[0002] The present invention relates generally to the field of electric antennas for igniting and sustaining a plasma, and in particular when the electric antenna is a component of a gas sensor that utilizes plasma emissions for spectroscopic analysis to determine the properties of a gas mixture. [Background technology]

[0003] Semiconductor processing tools require ultra-clean wafer processing chambers that tightly control the numerous gases used or generated during wafer processing. Accurate measurement of the composition of these process gases is critical to the operation of the processing tool. Accurate measurement of process gases helps optimize process recipes and also provides end-point control. Another element to ensure an ultra-clean wafer process is the rapid detection and location of leaks in semiconductor processing tools. Additionally, characterizing background contaminants such as water or hydrocarbons after routine maintenance is also important to maintain product yield and quality.

[0004] Many semiconductor tools use plasmas to facilitate deposition and etching processes. For example, plasmas are necessary for most sputter deposition processes and also play a role in plasma-enhanced atomic layer deposition, plasma-assisted chemical vapor deposition, and most etch processes. Light emitted directly from these plasmas may be monitored through a window in the process chamber to enable the aforementioned quality control measurements, in a method called optical emission spectroscopy (OES). However, it may be desirable to monitor gases in the process chamber when the plasma source is not active, or in chambers where a plasma source is not used, such as buffer / transport chambers and degassing chambers. In other cases, the plasma source may be located at a location separate or remote from the process chamber, such that only chemical products enter the process chamber. As a result, it is not always possible to use the plasma source of the process chamber to analyze the process gases, due to the above-mentioned circumstances.

[0005] In some instances, gases and leaks may be monitored using a mass spectrometry based residual gas analyzer. Unfortunately, mass spectrometers must operate at pressures lower than those used during most semiconductor processing. As a result, the use of mass spectrometers requires additional pumps to lower the sample pressure required for analysis. This additional pumping adds cost and slows the response time of the system. Furthermore, the ion-optical lens system of a mass spectrometer is particularly susceptible to damage from the many film depositions used in the manufacture of semiconductor devices. Even very thin layers of dielectrics can accumulate charge, degrading the performance of the spectrometer and causing the mass spectrometer to fail.

[0006] One alternative to either mass spectrometry or monitoring of the process plasma is the use of a sensor that provides its own plasma source. Such a sensor can operate in a manner similar to the plasma OES measurements described above, but can be installed in a chamber that does not have a plasma source, or can be used during times when the internal plasma source is not operating. This type of sensor is hereafter referred to as a SP-OES (self-plasma OES) sensor. (See, for example, Patent Documents 1 to 5. See also Non-Patent Documents 1 and 2.)

[0007] These sensors (INFICON Quantus LP-100, Nanotek AEGIS, etc.) can operate at pressures between about 1e-3 mbar and about 1 mbar. This pressure range covers several semiconductor processes, but many process chambers operate above this pressure range for at least part of the process. For example, critical processes such as ALD and CVD typically operate at pressures of tens of millibars. Generating plasma at low pressures allows the use of fairly low electric fields to provide electrons with enough energy to ionize gas molecules and generate the desired plasma, taking advantage of the long mean free path of electrons (e.g., about 380 μm or more at pressures below 1 mbar). For example, the first ionization energy of argon (Ar) is 15.8 eV. Therefore, in order for electrons to ionize argon, a high enough electric field is required to provide this much energy to the free electrons during collisions with the surrounding gas molecules. This suggests that the electric field required to ionize argon at 1 mbar pressure is 15.8 eV / (e*380 μm), or 41.6 kV / m (where e is the magnitude of the charge on the electron). Reducing the pressure increases the average path length that the electrons have to travel before colliding with the background gas, and therefore the electrons gain more energy during the collision for a given electric field. Thus, the lower the pressure, the smaller the electric field required to generate the plasma. This also means that generating plasma at higher pressures typically requires a higher electric field to obtain ionization energy with a shorter mean free path. For example, to ionize Ar at 50 Torr, the mean free path of the electrons at this pressure is about 8 μm, and 15.8 eV is required to ionize Ar, so about 2E6 V / m is required.

[0008] Several approaches have been investigated to generate microplasmas that can operate at higher voltages (these plasmas are often called microplasmas because they usually have a characteristic length of less than about 1 mm). These approaches include DC discharges, high frequency AC discharges, and microwave discharges. For example, a microwave resonant circuit including an antenna in the form of a microstrip split-ring resonator is one such approach. US Pat. No. 6,399,433 (Hopwood) discloses the construction of a microwave microstrip resonator in the shape of a ring with a small gap at the resonator end, i.e., a split-ring resonator. This structure is patterned with metal on a thin dielectric substrate, the opposite face of which has a metal ground plane. The resonant frequency is determined by the circumference of the ring, such that this length corresponds to half the wavelength of the conductor. The impedance is determined by the position along the resonator that drives the resonator and the characteristic impedance of the microstrip. Driving the resonator with a small, low-power RF amplifier, such as those currently used in communications and Bluetooth, generates potentials at the resonator ends that are 180° out of phase with each other. This generates an electric field near the resonator gap that is sufficient to ignite and sustain a microplasma at pressures from less than 1 mbar to just over 1000 mbar in many gases. Microplasmas have many potential applications, such as for sterilization and as a controlled light source. In some applications, the plasma source may be exposed to the process gas in a SP-OES.

[0009] Split-ring resonators, along with many other types of high-pressure plasma sources with exposed electrodes, have a limited lifespan because the tip of the resonator is quickly eroded by the plasma itself. This erosion reduces the generated electric field as the tip shape of the split-ring resonator changes. The change in tip shape also changes electrical properties such as resonant frequency and impedance. Another disadvantage of split-ring resonators is that the eroded split-ring conductor material can be newly deposited on other areas of the dielectric substrate, lowering the quality factor of the resonator. This lower quality factor reduces the maximum generated electric field, reduces the efficiency of the plasma source, and reduces the pressure range over which the plasma source can operate. Split-ring conductor material can also be newly deposited on the windows used to collect the OES light, causing undesirable losses of collected light. In addition, sputtering of the split-ring conductor into semiconductor process chambers is unacceptable. Contamination of the process with this sputtered material can destroy the wafers being produced. Sputtering of the conductor can also generate particles that can damage the semiconductor process.

[0010] Covering the device antenna with a thin layer of dielectric material such as glass has been shown to prevent ring erosion. However, differential thermal expansion and chemical incompatibility prohibit the use of most glasses in semiconductor processes. The maximum temperatures and process chemistries prohibit the use of materials that might be used to cover the resonator, such as silicon glass or polyimide resin. Furthermore, certain metals must never be exposed due to the risk of contaminating the semiconductor process. For example, traces of gold or copper detected by the sensor could destroy the electrical properties of the silicon wafers whose processing they are monitoring. As a result, the conductive material must be fully encapsulated in such a way that it is isolated from the process chamber even when exposed to excessive temperatures and / or etching chemistries.

[0011] Sensors designed to operate in the harsh environments of the semiconductor industry are limited in the acceptable wetted materials. Processes such as etching and chamber cleaning use corrosive gases such as nitrogen trifluoride (NF3) and high process temperatures, such as over 400°C. Therefore, sensors must be designed to be robust enough to withstand the harsh conditions of semiconductor processing while avoiding exposure to unacceptable materials. Plasma-generated antennas covered with mostly silicon-containing glass will fail because the glass will be quickly attacked by etching gases designed to remove silicon (e.g., NF3 reacts with Si to create volatile silicon tetrafluoride (SiF4)). Thin coatings of ALD alumina on the antenna (tens of nanometers) will not survive most semiconductor processes. Alternatively, thick alumina coatings on the antenna, such as plasma spraying, will cause adhesion problems. If a thick alumina coating fails, the release of alumina particles can destroy semiconductor tools and process wafers. Additionally, plasma source antennas must be low-cost enough to be easily replaced in the field.

[0012] Additional problems exist for measurement systems designed to operate at pressures between about 1 mbar and about 1000 mbar. In this pressure range, the mean free path of gas molecules is typically very short relative to the dimensions of the sensor. If the gas cell housing, plasma source, and collection window are constructed in such a way that the monitored gas must travel a long distance to enter and leave the cell, diffusion limitations mean that the sensor does not react quickly enough to address problems common in the semiconductor industry. For example, a type of leak can occur when a slit valve is briefly opened to move a wafer from the transfer chamber to the process chamber. This leak occurs very quickly, so a rapid response is required to detect the leak and identify its source. It is therefore important to design sensors that can communicate closely with the process environment with a minimum of intervening paths.

[0013] These are just a few of the issues associated with currently used auto-plasma OES sensors, particularly with respect to monitoring semiconductor processing tools. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] U.S. Patent No. 7,309,842 [Patent Document 2] U.S. Patent No. 7,123,361 [Patent Document 3] WO 10 / 129277 [Patent Document 4] US Patent Application Publication No. 2020 / 0273676 [Patent Document 5] U.S. Patent No. 10,262,841 [Patent Document 6] U.S. Patent No. 6,917,165 [Non-patent literature]

[0015] [Non-Patent Document 1] https: / / products.inficon.com / en-us / nav-products / product / detail / p-quantus-lp100 / [Non-Patent Document 2] http: / / www.nanotek.com / eng / products / products.php?ptype=view&prdcode=1608050006&catcode=181000&page=1&catcode=181000&searchopt=&searchkey= Summary of the Invention

[0016] The present disclosure is directed to sensors that can be directly exposed to the process environment with minimal intervening passages. An embodiment of a plasma source comprises a split-ring resonator microstrip comprising a split-ring conductor and a ceramic dielectric matrix. The dielectric matrix is ​​configured to support the split-ring resonator microstrip, and the split-ring features are embedded within the ceramic matrix. In an embodiment, the dielectric is comprised mostly of Al2O3 or other process compatible material. In an embodiment, the split-ring conductor is comprised of a refractory metal. In an embodiment, the ceramic matrix is ​​hermetic and configured to isolate the split-ring conductor from the process, and the plasma source is sealed at the front. The plasma generator may further comprise a focusing element configured to protrude from the flange. In an embodiment, the focusing element is a collimation lens located proximate to the split-ring conductor and comprises a curvature configured to focus the plasma light into the input field of view of the fiber or spectrometer.

[0017] One embodiment of a plasma generation apparatus for generating a plasma from one or more gases in a chamber includes a support comprising a ceramic matrix and having a first side and an opposing second side. A split ring conductor is embedded in the ceramic matrix and a hermetic via extends from the split ring conductor to the second side of the support. The hermetic via is configured to connect to a power source and a ground plane is formed in the second side of the support. A plasma is configured to be generated proximate to the first side of the support. The support is configured to seal to a wall of the chamber such that the first side is exposed to the one or more gases in the chamber and the second side is isolated from the plasma and the one or more gases in the chamber.

[0018] In one embodiment, the ceramic matrix is ​​comprised of at least one of Al2O3 and AlN. In one embodiment, the ceramic matrix is ​​comprised of one or more materials compatible with the plasma and one or more gases in the chamber. In one embodiment, the split ring conductor is comprised of a refractory metal. In another embodiment, the plasma generator comprises at least one plasma starting electrode, each electrode comprising a sealed via extending through the ceramic matrix from a first side to a second side of the support. In one embodiment, the at least one starting electrode is comprised of a refractory metal. In yet another embodiment, the plasma generator comprises a plurality of starting electrodes spaced apart relative to one another by a predetermined distance to initiate a plasma over a predetermined pressure range, such that the distance between the starting electrodes can be increased or decreased depending on what pressure range the plasma generator is used to generate the plasma.

[0019] In one embodiment, the plasma generation apparatus also includes a focusing element traversing the ceramic matrix and the ground plane. The focusing element is configured to collect light emitted by the plasma and transport the light through the ceramic matrix and the ground plane for observation from a second side of the support. The focusing element is hermetically sealed to the ceramic matrix. In one embodiment, the focusing element is a lens disposed proximate to the split-ring conductor. In one embodiment, the lens includes a curvature configured to optimize transfer of the light to an input field of view of one of: (1) an optical fiber, (2) an optical fiber bundle, and (3) a spectrometer.

[0020] An embodiment of the gas sensor comprises a split ring resonator microstrip configured to generate a plasma, the split ring conductor being surrounded by a ceramic matrix. An optical element configured to collect plasma light penetrates a via in the ceramic matrix. The optical element is sealed to the ceramic matrix using either a braze seal or a compression seal, the ceramic matrix being comprised of alumina. In one embodiment, the optical element is comprised of sapphire. The sapphire may be configured to thermally match the alumina of the ceramic matrix and the split ring conductor. In one embodiment, the optical element comprises a lens shape. In one embodiment, the optical element comprises a light pipe. The light pipe may accept light from near the center of both ends of the split ring resonator and terminate at an angle configured to direct the light through the split ring resonator. In another embodiment, the gas sensor further comprises an antenna connection configured to receive RF energy from the cable and transmit light by the fiber. In one embodiment, the gas sensor is configured to operate with remote electronics and at temperatures above 120° C. In one embodiment, the gas sensor is configured to be installed directly in the test chamber. In another embodiment, the gas sensor further comprises a plasma shield and a light baffle.

[0021] One embodiment of the gas sensor includes a plasma generation device having a first side and an opposing second side. The plasma generation device is configured to generate a plasma proximate to the first side, consisting of a split-ring conductor surrounded by a ceramic matrix. An optical element extends through the ceramic matrix between the first side and the second side, and is configured to collect light emitted by the plasma. A connector is electrically connected to the split-ring conductor. The optical element is sealed to the ceramic matrix using either (1) a brazed seal, and (2) a compression seal.

[0022] In one embodiment, the connector of the gas sensor is an antenna connector configured to receive RF energy from the cable, and the optical fiber is connected to the optical element and configured to receive light collected by the optical element. In one embodiment, the gas sensor further comprises remote electronics configured to interact with the gas sensor through the cable and the optical fiber, and operation occurs at a temperature greater than 120° C. In one embodiment, the plasma generator is configured to be exposed to one or more gases in the process chamber and functions as part of a wall of the process chamber. In one embodiment, the first side of the plasma generator comprises a polished surface.

[0023] One embodiment of a method for manufacturing a split-ring resonator microwave plasma source includes patterning a stack of ceramic tapes with conductors using a screen printing process to produce a hermetically sealed antenna including conductor traces. In another embodiment, the method further includes polishing the as-fired dielectric over the resonator electrodes. In another embodiment, the method further includes adding witness marks to the conductor trace layer. During the cutting process, the witness marks are exposed and used to guide the polishing step to a target thickness.

[0024] Another embodiment of a method for manufacturing a plasma generation device includes forming a support from a ceramic matrix in a green state, the support having a first side and an opposing second side. During the step of forming the support, split ring conductors and hermetic vias are embedded in the ceramic matrix, the vias extending from the split ring conductors to the second side of the support. The ceramic matrix with the embedded split ring conductors is fired, and a ground plane is disposed adjacent the second side of the support before or after firing. The first side of the support is polished to achieve a desired thickness of ceramic matrix between the first side and the split ring conductors, the desired thickness of ceramic matrix corresponding to a desired resonant frequency.

[0025] An embodiment of a self-plasma optical emission spectroscopy (SPOES) system comprises a plasma generator and a temperature sensor in thermal communication with the plasma generator to determine a temperature of the plasma generator. The temperature of the plasma generator is taken into account during operation of the SPOES system. In one embodiment, the SPOES system further comprises a heater in thermal communication with the plasma generator. The heater and the temperature sensor are configured to control the temperature of the plasma generator. In another embodiment, the SPOES system comprises a plasma generator and a collector, a VCR gland, and one of a ConFlat™ flange and a KF flange, and the plasma generator and the collector are brazed to the VCR gland, the ConFlat™ flange, and the KF flange. In one embodiment, the two-connection flow-through gas cell is constructed such that the gas flow is generally parallel to the plane of the antenna and the optical window, and no feature of the gas passage or plasma chamber is greater than about 10 mm in a direction generally perpendicular to the main direction of gas flow.

[0026] One embodiment of the gas sensing system includes a plasma generation device comprising a split-ring resonator microstrip. The split-ring resonator microstrip comprises a split-ring conductor and a ceramic matrix configured to surround and support the split-ring conductor. A temperature sensor is in thermal communication with the plasma generation device to determine a temperature of the plasma generation device such that the temperature of the plasma generation device is taken into account during operation of the gas sensing system. In one embodiment, the gas sensing system includes a heater in thermal communication with the plasma generation device. In this embodiment, the heater and the temperature sensor are configured to control the temperature of the plasma generation device.

[0027] Another embodiment of the gas sensing system includes a plasma generation device comprising a split-ring resonator microstrip. The split-ring resonator microstrip comprises a split-ring conductor and a ceramic matrix configured to support the split-ring resonator microstrip. The split-ring conductor is embedded within the ceramic matrix. In one embodiment, the gas sensing system also includes a two-connection flow-through gas cell defining a gas passageway through the plasma chamber. The optical window is disposed parallel from the ceramic matrix of the plasma generation device, generally across the plasma chamber. The gas cell is configured to provide a gas flow in a direction generally parallel to the plane of the plasma generation device and the plane of the optical window. The gas passageway and plasma chamber comprise features sized less than about 10 mm along a direction generally perpendicular to the gas flow direction.

[0028] High temperature co-fired ceramics (HTCC) is a process used to fabricate metal and ceramic components. In this process, layers of green ceramic tape are laid on top of each other. Between these layers, metallization made of refractory metals can be used to define the split-ring resonator electrodes. This metallization can be patterned using screen printing, inkjet printing, or other typical HTCC metallization processes. The green material and metallization are then fired at temperatures above 1200°C to sinter the material and remove the binder. The metal features of the split-ring resonator thus created are completely embedded within the ceramic, except for a connection to a single via that exits the ceramic from the backside opposite the side where the plasma is generated. This via is fitted with an electrical connector, allowing RF power to be delivered to the resonator from a suitable power source. By placing the resonator, or antenna, in the chamber and leaving the vias and connectors outside the process, all parts of the gas sensor exposed to the process can withstand the specific semiconductor processing, including resistance to high temperatures and aggressive chemicals. The use of split ring conductors made from refractory metals such as tungsten, and dielectrics made from alumina allows these portions of the device to withstand temperatures in excess of 1200°C. In high temperature environments above 300°C, a metal seal (e.g., a C-seal or wire seal) is required to seal the antenna to the sensor chamber, or to the flange if no sensor chamber is present. Because the antenna is constructed from high temperature materials, it is also compatible with brazing processes, allowing for brazed windows and brazed connections. [Brief description of the drawings]

[0029] A more detailed description of the invention briefly outlined above can be had by reference to the described embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings depict only typical embodiments of the invention and are therefore not to be considered as limiting the scope of the invention, as other equally effective embodiments of the invention may be recognized. For a further understanding of the nature and objects of the invention, therefore, reference can be made to the following detailed description read in conjunction with the drawings.

[0030] [Figure 1] FIG. 1 illustrates a top view of one embodiment of a plasma generating device. [Diagram 2] 2 shows a top view of an embodiment of a plurality of wafers of the plasma generating apparatus of FIG. 1. [Figure 3A] 3 shows a partial cross-sectional view of the plasma generating device taken along line GG in FIG. 2. [Figure 3B] 1A and 1B show schematic cross-sectional close-up views of embodiments of plasma generating devices; [Figure 4] 1 illustrates a cross-sectional view of an embodiment of a gas cell assembly including an embodiment of a plasma generation device. [Figure 5A] 1 shows a cross-sectional view of another embodiment of a gas sensor assembly having an embodiment of a plasma generating device. [Figure 5B] 1 shows a cross-sectional view of an embodiment of a gas sensor having an embodiment of an HTCC antenna that generates a plasma. [Figure 5C] 5C shows an enlarged schematic view of a portion of the embodiment of the gas sensor assembly of FIG. 5A and FIG. 5B. [Figure 6] 1 shows a schematic diagram of an embodiment of a shielding element. [Figure 7] 1 shows a schematic diagram of an embodiment of a gas cell assembly having an embodiment of a plasma generator and connected to an amplifier and spectrometer or filter photodiode system. [Figure 8] 1 shows a cross-sectional view of an embodiment of a gas cell assembly with an embodiment of a plasma generation device having both inlet and outlet connections for gas flow. [Figure 9A] 1 shows a perspective top view of another embodiment of a plasma generation device. [Figure 9B] 9B shows a schematic cross-sectional view of the embodiment along line HH in FIG. 9A. [Figure 10] 1 shows a perspective top view of another embodiment of a plasma generation device. [Figure 11] 11 shows a perspective top view of the embodiment of the plasma generation device of FIG. 10 with portions removed. [Figure 12] 11 shows a perspective side view of the embodiment of the plasma generation device of FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The following discussion relates to various embodiments of an HTCC antenna for generating plasma or microplasma. It will be understood that the embodiments described herein are examples illustrating certain inventive concepts as detailed herein. As such, other variations and modifications will be readily apparent to those skilled in the art. Additionally, certain terms are used throughout this discussion to provide an appropriate frame of reference with respect to the accompanying drawings. These terms, such as "upper", "lower", "front", "rear", "inner", "outer", "front", "rear", "upper", "lower", "inner", "outer", "first", "second", etc., are not intended to limit these concepts unless specifically indicated. The term "about" or "approximately" as used herein may refer to a range of 80% to 125% of the claimed or disclosed value. With respect to the drawings, the purpose is to depict salient features of the HTCC antenna for generating plasma or microplasma, and are not provided to scale.

[0032] 1-3, one embodiment of a microwave microstrip antenna used herein as a plasma generating device 100 is configured to generate high electric fields or electromagnetic waves that interact with the surrounding environment to generate a plasma 400, shown as a circle / ellipse. The generated plasma 400 acts as a light source, with a spectrum that depends, among other things, on the composition of the gas mixture from which it is generated. Analysis of this spectrum can be used to determine the composition of the gases in the surrounding environment. In this way, the presence of unwanted gases or vapors can be detected.

[0033] The plasma generating device 100 includes an antenna trace 110 embedded in a dielectric support made of a ceramic matrix 150. In one embodiment, the ceramic matrix 150 is a high temperature co-fired ceramic (HTCC) matrix. As used herein to refer to the position of the antenna trace 110 relative to the ceramic matrix 150, the terms "encapsulated" and "embedded" mean completely enclosed within the ceramic matrix 150 such that no portion of the antenna trace 110 is exposed. With reference to FIG. 1, the antenna trace 110 is shown with dashed lines indicating that it is embedded within the ceramic matrix 150, however, in some embodiments, the antenna trace 110 may still be visible through the ceramic matrix 150 even though no portion of it is exposed. In one embodiment, the antenna trace 110 is a split-ring conductor or split-ring resonator. The antenna trace 110 may be operated at a particular frequency at which it resonates, for example, 2.45 GHz. The choice of frequency will affect the size of the antenna trace 110. The antenna trace 110 defines a break or gap 107 having a width spanning the distance between both ends of the antenna trace 110. The gap 107 may vary in width, but is generally preferably in the range of 25-100 μm. A high electric field may be generated within or near the gap 107 to initiate the formation of a plasma 400 in the region near the gap 107, such as the region above the gap 107. In this embodiment, the gap 107 is completely filled with the ceramic matrix 150, and the generation of the plasma occurs near the top surface 130 of the first side 101. In one embodiment, the conductor of the antenna trace 110 is composed of tungsten, and the HTCC matrix may be composed of alumina (Al2O3), aluminum nitride (AlN), or other similar materials. Embedding the antenna trace 110 in the ceramic matrix 150 acts to isolate the antenna trace 110 from the corrosive environment that may be present in the process chamber.

[0034] Although the term "ring" has been used with reference to a particular embodiment of antenna trace 110, the term is not meant to be limited to circular rings, but may include resonators of all circular and non-circular shapes, such as rectangular, elliptical, and other shapes.

[0035] The plasma generating devices 100 may be formed on a wafer 200, as illustrated in FIG. 2. Each plasma generating device 100 comprises a support made of a ceramic matrix 150 having a first side 101, the process side or plasma side, which will be exposed to a semiconductor manufacturing process or process chamber in use, and a second side 102, the non-process side or non-plasma side (FIG. 3A), which is protected or otherwise not exposed to the semiconductor process or process chamber. Features 120 are added at the same level in the HTCC lamination process during metallization of the antenna traces 110. These will act as guides or witness marks during the final polishing step described below. The plasma generating devices 100 are fired and then cut from the wafer to produce individual devices as diced squares 112 as shown in FIG. 1, or laser cut or water jet cut into the desired shape (e.g., circles 114 as shown in FIG. 2, or other shapes as required). Cutting of the plasma generating devices 100 is done through the features 120. The features 120 are positioned to be cut open during the cutting process and are shown in FIG. 1 with dashed lines indicating that they are located within the ceramic matrix 150, although in some embodiments the features 120 may be visible through the ceramic matrix 150.

[0036] 3A-B show a cross section of one of the plasma generating devices 100 on the wafer 200 along the line GG in FIG. 2. As shown, the antenna traces 110 are embedded in the HTCC matrix 150. The features 120 are exposed at the end of the plasma generating device 100 after the dicing or sawing process and serve as a guide to measure the thickness 152 of the ceramic matrix 150 above the antenna traces 110, which can be better seen in the schematic cross section shown in FIG. 3B. As shown, the antenna traces 110 and the features 120 are disposed at the same distance from the top surface 130 or front surface. In other words, the plane P extends through both the antenna traces 110 and the features 120 such that they are disposed at the same depth within the ceramic matrix 150 relative to the top surface 130. Tight control of the thickness 152 of the ceramic matrix disposed above the conductor traces 110 is necessary to achieve the desired resonant frequency and generate the high electric field required for the generation of the plasma 400. The top surface 130 is polished until the feature 120 is at a target thickness (or distance) from the top surface 130, and thus the conductor trace 110 is at the same target thickness (or distance) from the top surface 130. In one embodiment, the feature 120 is a witness mark (such as a flat or a tab).

[0037] For example, with an RF power of 33 dBm and an antenna gap 107 of 100 μm, if the thickness 154 from the top surface 130 to the witness mark 120 is 0.001 inches, the antenna trace 110 can last for years because it provides good etch and sputter resistance while still generating a sufficient electric field to generate the desired plasma 400. In contrast, if the thickness 154 between the top surface 130 and the witness mark 120 is less than 0.001 inches, the resulting antenna trace 110 is not as well protected. However, if the thickness 154 is substantially greater than 0.001 inches, the desired high electric field in the gap is inhibited. Other techniques for assessing the thickness 154 of the ceramic matrix 150 between the top surface 130 and the witness mark 120, such as optical interferometry or spectral reflectance, typically fail due to the opaque optical quality of the ceramic matrix 150. The thickness 154 may be such that the antenna trace 110 (and witness mark 120 ) is visible through the ceramic matrix 150 even though the antenna trace 110 is embedded within the ceramic matrix 150 .

[0038] To complete the plasma generating device 100, a ground plane 160 is placed on the back or non-process side 102 of the ceramic matrix 150. In one embodiment, the ground plane 160 may be placed before or after sintering the plasma generating device. The ground plane 160 is a ground reference and is composed of an adhesion layer, such as titanium, followed by a plated layer of a highly conductive material, such as gold. This area is not exposed to the semiconductor process because a seal is made between the outer edge or top surface 130 (FIGS. 3A, 3B, and 4) of the ceramic matrix 150 and the wall of the cell chamber 408 (FIG. 4) where the plasma is generated and observed. A filled via 172 electrically couples the antenna trace 110 to a solder pad 170 (FIG. 3A) of the feed point 174 (FIG. 1). The solder pad 170 is generally placed at the same level as the ground plane 160, but is electrically isolated from the ground plane 160. Additionally, a ring 173 of nickel or other suitable metal can be plated onto the adhesion layer and used to make a brazed connection to a housing or flange. This feature can alternatively be on the outer cylindrical surface of the plasma generating device 100 in the case of a circular device. In certain embodiments not yet described that include a brazing process, the plating or gold or copper metallization of the ground surface 160 should be done after the brazing step so that the ground surface is not destroyed by the high brazing temperatures.

[0039] FIG. 4 shows a cross-sectional view of a gas cell assembly 429 including a plasma generator 100. The gas cell assembly 429 is configured to be connected to a semiconductor process chamber, a degassing chamber, or a transfer chamber. As shown, the process side 101 of the plasma generator 100 is a wall of the cell chamber 408 such that the encapsulated split ring conductor or antenna trace 110 would be exposed inside or otherwise in the cell chamber 408 of the gas cell assembly 429 without the ceramic matrix 150 surrounding it. RF energy is provided through a connector 406, which is soldered to vias 172 of the plasma generator 100 to provide the power necessary to resonate the plasma generator 100 and ignite and sustain a plasma 400 in the cell chamber 408. The cell chamber 408 is connected to the process chamber being monitored via a process connection flange 420, which may be KF-25 (although other flange styles may be used). The light baffle 410 protects the plasma generator 100 from other light sources and protects other light sensitive components of the semiconductor process chamber from light generated by the plasma 400 without significantly impeding gas flow. The dimensions of the cell chamber 408 are about 5 mm to about 20 mm, which is sufficient to contain the plasma 400 at most process pressures of interest, for example, between about 1 Torr and 50 Torr. The seal is made with O-rings 431 and 432, which may be placed in an O-ring groove 409. A window 405 is provided to allow light to exit the cell chamber for spectroscopic analysis. The baffle 410 also reduces deposition of process material from the process being monitored on the window 405 in a particular semiconductor tool installation. The cell chamber 408 may be made of stainless steel, Hastelloy, aluminum, Inconel, or any other suitable material. The clamp plate 444 presses the plasma generating device 100 against the O-ring 431 to create an airtight seal and also acts as a heat sink to reduce thermal expansion or contraction of the plasma generating device 100 that occurs due to changes in plasma impedance, after the plasma is extinguished or started, or after a change in the tool recipe.This thermal change can change the characteristic impedance of the plasma generating device 100 along with the resonant frequency, thus reducing the quality factor, preventing efficient operation, preventing plasma restart, causing signal drift, etc. The clamping plate 444 can be formed from stainless steel or from a more thermally conductive material such as aluminum or copper.

[0040] For some pressures and processes, the isolation of the plasma 400 provided by positioning the plasma generator 100 in the cell chamber 408 away from the process connection flange 420 is desirable. However, for other processes and pressures, such as when pressures are greater than 1 Torr and the process changes to be measured are fast (<10 seconds), the tortuous path to the plasma 400 becomes inappropriately long. The ratio of the mean free path of the molecules in a gas to the characteristic system dimensions is called the Knudsen number, Kn. When Kn is greater than 1, the gas molecules will bump into the chamber walls before bumping into each other and the flow is considered molecular. When Kn is between 1 and 0.01, the flow is considered transient and when Kn is less than 0.01, the gas molecules will bump into each other much more than they will bump into the chamber walls and the flow is called viscous. When the mean free path of the gas is much shorter than the dimensions of the sensor cell chamber and connecting components and Kn is low, the time-dependent gas composition in the cell chamber lags behind that in the process chamber being monitored and the effective sensor response time becomes too slow to be useful. For example, at typical atomic layer deposition (ALD) process conditions with an argon carrier at 40 Torr, the mean free path of a typical reagent molecule will be less than 1 μm, but the path length from the process connection flange 420 to the plasma 400 location is approximately 7 cm in the gas cell assembly 429. This means that the gas is flowing, if at all, in a viscous manner. However, in a dead-end arrangement such as the gas cell assembly 429, any changes in gas composition in the process being monitored will only be transmitted by diffusion into the plasma volume, which has a time constant on the order of many seconds, depending, among other things, on the molecular weight of the diffusing species and the square root of the process temperature. This is therefore too slow to monitor many modern semiconductor processes such as ALD, which have sub-second gas pulses and sub-10 second pump-out times.

[0041] 5A-C show another mounting arrangement of the plasma generator 100 intended to provide better response time in chamber pressure, where the mean free path is shorter than the dimensions of the cell chamber 408. A Kovar™ or other metal ring 189 can be brazed to the edge of the plasma generator 100 and then welded or brazed to the flange 191. A braze such as silver-copper, which has a melting point of about 780° C., can be used. In other embodiments, a higher temperature braze such as a 35:65 gold-copper braze may be used. Brazing to the backside provides the added benefit of isolating these materials from the plasma 400. As shown in FIG. 6, a shielding element 701, such as a step on the edge of the plasma generator 100, can be used to prevent the plasma from reaching the brazed metallization 702. This feature can be built into the ceramic tape stack used to form the plasma generator 100 before firing, or alternatively, it can be ground into the fired plasma generator 100 by ceramic processing.

[0042] In one embodiment, rather than using a separate window from the plasma generator for light collection, a window, light pipe, light collection element, or other light collection means can be sealed (attached via brazing, compression sealing, or other attachment process) through the ceramic matrix 150 of the plasma generator 100. The hole is laser cut after sintering, but can also be punched into the green ceramic tape during the manufacturing method described below. The light collection means can also be installed in this hole. Including the light collection means in the plasma generator allows the plasma generator 100 to be installed directly in the process chamber or transfer chamber, resulting in faster response times and allowing installation using a single port on the process chamber 500 or tool chamber. A more compact SP-OES system sensor is possible since a separate light collection device (window) is not required. This geometry also allows for O-ring seals, but does not allow for high temperature operation as desired in some applications. Still referring to Figures 5A-C, the window or light pipe 300 may be polished to collimate the light for efficient transfer to a fiber, fiber bundle, or spectrometer, or the window 300 may include a first end 320 and a second end 330. The first end 320 may be beveled to reflect light from the plasma 400 through the plasma generator 100 and acts as a light pipe defining an outer surface 321 and configured to efficiently transfer the light to a fiber optic connector 504. The optical element 505 may improve optical coupling of the collected light to the spectrometer. The use of sapphire optics allows for the transmission of light having wavelengths between 200-2000 nm, as well as the use of a brazing operation with the plasma generator 100 and thermal expansion matching (for high temperature operation). The connection of the chamber 500 to the flange is made at 191. This KF flange allows for O-ring and aluminum knife edge seals, but other flange configurations are also possible, such as VCR and ConFlat™, which typically use all-metal seals for high temperature operation.

[0043] FIG. 7 shows a process chamber 500 at least partially surrounded by process chamber walls 510, with a flange of an SP-OES sensor attached to the flange on the chamber 500. This allows the plasma generator 100 to be installed close, flush, or inserted into the chamber 500, which eliminates delays that arise from diffusion to the gas cell assembly 429, if one is used. The plasma generator 100 in this configuration is immersed in a semiconductor fabrication process. An RF compatible connector 503 is used to bring RF energy into the plasma generator, and a fiber optic connector 504 is used to carry the plasma generated light out. The amplifier 501 produces microwave frequency energy, and section 502 includes a spectrometer or filter photodiode system for measuring light from the process gases in the plasma 400. The spectrometer is configured to measure the light intensity as a function of wavelength over a range, for example 200-850 nm. From these spectra, information about the composition of the gases in the plasma can be derived. Alternatively, if only a particular known wavelength band is of interest, a filter that passes that band and a photodiode or photomultiplier tube can be used to monitor the plasma light. The cabling arrangement 532, 534 allows the plasma generator 100 to be placed in a limited space and the electronics and spectrometer or photodiode to be placed at some distance so that the electronics and spectrometer can remain adequately cooled, as determined by the component specifications, even when the process chamber 500 operates at high temperatures. In one embodiment, the electronics may allow remote operation of the gas cell assembly and / or the process chamber.

[0044] Figure 8 shows another alternative to the geometry of the attachment depicted in Figure 4. The flow-through cell 600 is shaped so that gas flows directly from the cell window 620 onto the plasma generator 100 located across the gas path. The cell is streamlined with no unswept volume so that it can provide a fast response to changes in gas concentration in a flowing gas stream, such as a gas delivery line or pump line. A limitation of this geometry is that it requires two connections 602, 603, which may not be desirable for installation in some other applications.

[0045] Another embodiment of the plasma generating device 100A is shown in Figures 9A-B. As with the other embodiments described above, the conductor trace 110 is surrounded by a ceramic matrix 150. As with those embodiments, the plasma generating device 100A includes a first hermetic via 506 that is used to transport power from an RF compatible connector 503, such as an SMA connector, soldered to the non-process or non-plasma side 102, partially through the ceramic matrix 150 to the encapsulated antenna trace 110 of the plasma generating device 100A, and generates an electric field near its end (within the gap 107) to ignite and sustain the plasma 400 (Figure 3A). The hermetic via 506 is hermetically sealed to be airtight with respect to the ceramic matrix 150. In one embodiment, a second hermetic via 508 also extends from a second SMA connector 513 or other suitable high voltage connector soldered to the non-process side 102. Rather than terminating in a buried conductor inside the ceramic matrix 150, the second via 508 extends through the process side of the ceramic matrix 150 with its end exposed to the process environment where it is monitored as a conductive electrode 514. The conductive electrode 514 has a sufficient thickness such that it remains exposed on the surface of the process side 101 of the plasma generator 100A after processing steps have been performed. For example, a polishing step may be performed to remove an amount of dielectric, leaving the antenna trace 110 buried under a layer of ceramic matrix 150, but this electrode 514 will remain.

[0046] Under some pressures or gas compositions, the electric field extending through the dielectric near the gap 107 of the antenna trace 110 is too low to initiate a plasma 400. In those cases, a high voltage signal, such as a -3 kV 10 Hz square wave, is applied to this second via 508 by connector 513 for a few seconds. This initiates a series of arc discharges between the wall of the process chamber 500 and the conductive electrode 514 exposed at the top of the via 508. This arc creates photons, electrons, and ions, and these species lower the breakdown potential near the gap 107 of the split ring conductor 110, thereby allowing the plasma 400 to be initiated under a wider range of pressures and / or gas conditions. Once initiated, this plasma 400 can generally be sustained without continued firing of the electrode 514.

[0047] In some embodiments, the second via 508 and the conductive electrode 514 are also tungsten, as are the first via 506 and the antenna trace 110. Tungsten is desirable because it has a high mass density and a small sputtering cross-section. The second via 508 is positioned so that the arc will occur to the grounded wall and close enough to the gap 107 in the antenna trace 110 to quickly ignite the plasma 400. At the same time, the second via 508 is positioned far enough away from the gap 107 in the antenna trace 110 so that it is not damaged during the generation of the plasma 400. In one embodiment, the second via 508 is positioned 1 mm to the wall of the process chamber 500 and 7 mm from the gap 107 in the split-ring conductor 110.

[0048] In some embodiments, the signal from the photodiode or the signal from the attached spectrometer is analyzed by an FPGA or microcontroller to detect the plasma off state and initiate a high voltage waveform at the plasma initiating electrode 514. Such a plasma initiating device can be added to the plasma generating device 100, 100A with little or no additional cost while still producing a low profile plasma generating device 100, 100A. Conventional plasma initiating devices such as brazed feedthrough pins are more expensive and they are more difficult to place close to the main plasma source. This is important at high pressures. In some embodiments, two or more additional conductive electrodes 514 are added. In such cases, the distance between the electrodes 514 and / or the distance between the electrodes and the wall of the process chamber 500 can be selected to facilitate plasma ignition at different pressures. Knowing the target pressure and gas species, the Paschen curve of the breakdown voltage as a function of the product of distance and pressure can be used to read the optimal spacing for a given power supply, or a power supply can be selected to fit the available geometry. In one embodiment, the conductive electrodes 514 are round or circular in shape and are an extension of the respective vias 508. In another embodiment, the conductive electrode 514 is of a shape other than round or circular (e.g., star-shaped, etc.) to generate a higher electric field. In yet another embodiment, more electrodes may be included in the plasma generating device 100A and positioned at various distances from each other and from the chamber wall 510 to allow for initiation of the plasma 400 at a wider pressure range. The electrodes may be driven from multiple connectors and voltage supplies. In other embodiments, multiple electrodes may be connected together and driven from the same connector if they are intended to arc to the chamber or sensor wall. Each may be located at a different distance from the wall. The only practical limitation is the acceptable size and complexity of the plasma generating device.

[0049] A method for manufacturing a plasma generator 100, 100A such as the embodiment described above will now be described. Typically, multiple layers of green ceramic tape are used to construct the support. Green ceramic tape is unfired (or unsintered) ceramic tape. Between any of these layers of green ceramic tape, metallization made of a refractory metal is used to define the split-ring resonator electrodes. This metallization can be patterned using screen printing, inkjet printing, or other typical HTCC metallization processes. Multiple layers of green ceramic tape are laminated (the lamination process may use one or more binders) and then fired at a temperature of about 1200°C to sinter the laminated material and remove the binders. The result is a sealed antenna structure with split-ring conductors 110 encapsulated in a ceramic matrix, except for a connection to a single via that extends through the second side 102 (the side opposite the side where the plasma is generated) of the ceramic matrix 150 of the support. The enclosed antenna structure is then polished in the area over the split ring conductor 110 to achieve a desired thickness of the ceramic matrix 150 between the first side 101 and the split ring conductor 110. The desired thickness of the ceramic matrix between the first side 101 and the split ring conductor 110 corresponds to a desired resonant frequency. In other words, by varying the thickness of the ceramic matrix 150 between the top surface 130 of the first side 101 and the split ring conductor 110, the resonant frequency of the plasma generation device 100, 100A can be tuned or changed.

[0050] 10-12, another embodiment of a plasma generation apparatus 800 is shown. In this embodiment, the plasma generation apparatus 800 includes a dielectric support 818 having a process-facing side 801 or first side that is exposed to the interior of the process chamber 500, cell chamber 408, or other semiconductor manufacturing process, and a non-process-facing side 802 or second side. The non-process-facing side 802 includes an antenna trace, resonator, or conductor trace 810 deposited on the dielectric support 818. In one embodiment, the dielectric support 818 and the conductor trace 810 are prepared by a HTCC process. As shown, the conductor trace 810 has a split ring configuration that defines a gap 807 similar to other embodiments previously discussed. The conductor trace 810 further connects to a connector 803, such as an RF connector, that provides power to the plasma generation apparatus 800. The non-process side 802 is positioned against a ground plane 860 such that there is a space 862 defined between the ground plane 860 and the non-process side 802 of the support 818. This space is generally most conveniently filled with ambient air at atmospheric pressure as a dielectric, although other materials may be selected to fill the space 862 for stability or increased breakdown voltage considerations. In one embodiment, the ground plane 860 is a ground reference for the conductor trace 810. Thus, it is possible to adjust the resonant frequency of the conductor trace 810 by increasing or decreasing the space 862 defined between the ground plane 860 and the non-process side 802 of the support 818. In one embodiment, this may be done by moving the ground plane 860 relative to the support 818. The space 862 may also be configured to stabilize the temperature of the plasma generating apparatus 800 to prevent the resonant frequency from shifting as the plasma generating apparatus 800 operates.

[0051] The process side 801 of the support 818 includes a plurality of emitters 806, 808 (e.g., two emitters) made of aluminum. In one embodiment, the emitters 806, 808 may be further coated or partially coated with a thin layer of dielectric material to enhance inertness in the presence of semiconductor manufacturing processes. As shown, there are two emitters 806, 808 positioned adjacent to one another defining a space or gap 817 between them. Each emitter 806, 808 is connected to a conductor trace 810 on the non-process side 801 of the support 818 through a hermetic via 805. Thus, the hermetic via 805 connects the emitters 806, 808 to the conductor trace 810 above a pressure threshold. As shown, the emitters 806, 808 are teardrop shaped and positioned such that a gap 817 is formed between the opposing pointed ends of the emitters 806, 808. In other words, emitters 806, 808 are positioned as mirror images of each other across plane P, as shown in FIG.

[0052] In operation, the high electric field created in the gap 817 between the emitters 806, 808 generates a plasma 400 (FIG. 3A) similar to the previously described embodiment. However, because the conductor trace 810 is disposed on the non-process side 802 of the support 818, it does not need to be embedded in a ceramic matrix, and therefore the conductor trace 810 can be made of a better, more highly conductive material, such as copper or silver. In one embodiment, the conductor 810 is prepared by conventional thick and thin film processes, rather than being limited to low conductive metals such as tungsten that are compatible with HTCC processes.

[0053] Although the present invention has been particularly shown and described with reference to certain exemplary embodiments, those skilled in the art will understand that various changes in details can be made therein without departing from the spirit and scope of the invention as may be supported by the written description and drawings. Moreover, when an exemplary embodiment is described with reference to a particular number of elements, it will be understood that the exemplary embodiment may be practiced utilizing either fewer or more than that particular number of elements.

Claims

1. 1. A plasma generating apparatus for generating a plasma from one or more gases within a chamber, the plasma generating apparatus comprising: a support having a first side and an opposing second side, the support comprising a ceramic matrix; a split-ring conductor embedded in the ceramic matrix; a hermetic via extending from the split ring conductor to the second side of the support and configured to connect to a power source; a ground surface formed on the second side of the support; Equipped with a plasma is generated proximate to the first side of the support; The support is configured to seal to a wall of the chamber such that the first side is exposed to the one or more gases in the chamber and the second side is isolated from the plasma and the one or more gases in the chamber.

2. The ceramic matrix is ​​Al ２ O ３ The plasma generating device according to claim 1 , comprising at least one of AlN and AlN.

3. 10. The plasma generating apparatus of claim 1, wherein the ceramic matrix is ​​made of one or more materials that are compatible with the plasma and the one or more gases in the chamber.

4. The plasma generating apparatus of claim 1 , wherein the split-ring conductor is made of a refractory metal.

5. 2. The plasma generating apparatus of claim 1, further comprising at least one plasma initiating electrode, each electrode comprising a hermetic via extending through the ceramic matrix from the first side to the second side of the support.

6. 6. The plasma generating apparatus of claim 5, wherein the at least one starting electrode is made of a refractory metal.

7. 6. The plasma generating apparatus of claim 5, wherein the plurality of starting electrodes are spaced relative to one another at a predetermined distance to initiate a plasma in a predetermined pressure range.

8. 2. The plasma generation apparatus of claim 1, further comprising a focusing element across the ceramic matrix and the ground plane, the focusing element configured to collect light emitted by the plasma and transport the light through the ceramic matrix and the ground plane for observation from the second side of the support, the focusing element being sealed to the ceramic matrix.

9. 9. The plasma generation apparatus of claim 8, wherein the focusing element is a lens positioned proximate to the split-ring conductor, the lens having a curvature configured to optimize transfer of the light to an input field of view of one of: (1) an optical fiber; (2) an optical fiber bundle; and (3) a spectrometer.

10. 1. A gas sensor comprising a plasma generating device having a first side and an opposing second side, the plasma generating device comprising: a split-ring conductor surrounded by a ceramic matrix and configured to generate a plasma proximate the first side; an optical element extending through the ceramic matrix between the first side and the second side, the optical element configured to collect light emitted by the plasma; and a connector electrically connected to the split ring conductor; Equipped with The gas sensor wherein the optical element is hermetically sealed in the ceramic matrix using either (1) a braze seal, and (2) a compression seal.

11. 11. The gas sensor of claim 10, wherein the connector is an antenna connector configured to receive RF energy from a cable, and an optical fiber is connected to the optical element and configured to receive light collected by the optical element.

12. 12. The gas sensor of claim 11, further comprising remote electronics configured to interact with the gas sensor through the cable and the optical fiber, and wherein operation occurs at a temperature greater than 120 degrees Celsius.

13. The gas sensor of claim 10 , wherein the plasma generator is configured to be exposed to one or more gases in a process chamber and functions as part of a wall of the process chamber.

14. The gas sensor of claim 10 , further comprising a ground plane formed on the second side of the plasma generating device.

15. 11. The gas sensor of claim 10, wherein the split-ring conductor is made of a refractory metal.

16. The gas sensor of claim 10 , wherein the first side of the plasma generating device comprises a polished surface.

17. 1. A method for manufacturing a plasma generating device, comprising the steps of: forming a support from a ceramic matrix in a green state, the support having a first side and an opposing second side; embedding a split ring conductor and a hermetic via in the ceramic matrix as part of forming the support, the hermetic via extending from the split ring conductor to the second side of the support; firing the ceramic matrix with the split-ring conductors embedded therein; placing a ground plane adjacent the second side of the support, either before or after the firing step; polishing the first side of the support to achieve a desired thickness of ceramic matrix between the first side and the split-ring conductor, the desired thickness of ceramic matrix corresponding to a desired resonant frequency; A method comprising:

18. 1. A method of manufacturing a split ring resonator plasma generator device, comprising the steps of: Providing a plurality of ceramic tapes; forming at least one metallization pattern on at least one of the plurality of ceramic tapes, the at least one metallization pattern comprising a split ring resonator; forming a laminate of the plurality of ceramic tapes; firing the laminate to produce a hermetically sealed antenna structure comprising a split-ring conductor in a ceramic matrix; polishing the antenna structure enclosed in an area over the split-ring conductor; A method comprising:

19. 20. The method of claim 18, wherein one or more measurements of one or more characteristics of the antenna structure, such as resonant frequency, quality factor, dielectric thickness, etc., are used to determine an endpoint of the polishing step.

20. 20. The method of claim 18, further comprising adding witness marks in the same metallization pattern as the split-ring conductors, wherein during a sawing process, the witness marks are exposed and used to guide the polishing step to a target thickness.

21. 1. A gas detection system comprising: A plasma generating device, comprising: A split ring resonator microstrip, A split ring conductor; a ceramic matrix configured to surround and support the split-ring conductor; A split ring resonator microstrip A plasma generating device comprising: a temperature sensor in thermal communication with the plasma generating device for determining a temperature of the plasma generating device, the temperature of the plasma generating device being taken into account during operation of the gas detection system; and A gas detection system comprising:

22. 22. The gas detection system of claim 21, further comprising a heater in thermal communication with the plasma generating device, the heater and the temperature sensor configured to control a temperature of the plasma generating device.

23. 1. A gas detection system comprising: A plasma generating device, comprising: A split ring resonator microstrip, A split ring conductor; a ceramic matrix configured to support the split-ring resonator microstrip, the split-ring conductors being embedded within the ceramic matrix; and A split ring resonator microstrip A plasma generating device comprising: a two-connection flow-through gas cell defining a gas passageway through a plasma chamber, the gas cell including an optical window disposed substantially parallel to the ceramic matrix of the plasma generating device across the plasma chamber; Equipped with the gas cell is configured to provide a gas flow in a direction substantially parallel to a plane of the plasma generating device and a plane of the optical window; A gas sensing system, wherein the gas passages and the plasma chamber have features sized less than about 10 mm along a direction substantially perpendicular to a direction of gas flow.

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