PLASMA UNTOIVFINEiViENT SENSOR AND METHODS THEREOF

BACKGROUND OF T HE INVENTION f 0001 j Plasma processing systems have long been employed to proeess substrates

(such as semiconductor wafers) to produce integrated circuits. Plasmas may be generated via many different methods, such as electron-cyclotron-resonance plasmas (ECR), inductively- coupled plasmas (ICP), or capadtive coupled plasmas (CCP). In many eases, confining the plasma to a specific region within the processing chamber, such as within the region directly above the substrate being processed, may provide certain advantages. J0θθ2] To facilitate discussion, Fig, 1 shows an example of a low-pressure plasma reactor 100 during which plasma is confined during processing. Consider the situation wherein, for example, a substrate 124 is placed on an electiode 1 10, w hich is mounted to a pedestal 120 that is connected to a chamber 102. Electrode 1 10 is connected to a remote power supply 1 14, such as a radio frequency (RP) power generator, through the interior of pedestal 120. A processing gas 150. which may be a mixture of chemicals, may be introduced into chamber 102 through an inlet 104 when the pressure in chamber 102, which may be lowered by a pump (not show n), has reached a desirable level to process substrate 124, electrode 1 10 may capaeitively couple the power from power supply 1 1-4 with processing gas 150 to form a plasma 106. Usually, plasma 106 is contained within a desired region of chamber 102 by a set of confinement rings 108. During substrate processing, gases from plasma 106, which may include a mixture of chemical components from processing gas 150, chemical components formed by reactions within plasma 106, and chemical byproducts from the processing of substrate 124. may flow through confinement rings 108 and a non- pi asm a chamber volume 128 before being removed from chamber 102 through an outlet 126. This route is illustrated by a path 136 and usually causes the interior of chamber 102 to be exposed to highly reactive gases e\ en w hen plasma 106 is contained. |OOOJj However, during processing of substrate 124, plasma 106 may unexpectedly or unconuoUably mijualε out of the desired iegi on within chamber 102, In otiiet vvoids. an unconfined plasma 138 may form in a region of chamber 102 that is outside of confinement rings 108 The formation of unconfined plasma 138 is undesirable because unconfined plasma 138 may alter the quality of processing plasma 106 in a way that may cause at least one of the following to occur: significantly degrade the performance on substrate 124, damage chamber 102, and damage pedestal 120. I- or example, substrate 124 may become damaged due to a change in an etch or deposition rate and or may be damaged by being

contaminated with particulate defects ot elemental contamination generated by unconfined plasma 138 Processing chamber 102 and or pedestal 120 may be physically damaged b> , for example, erosion or corrosion of chamber materials as a result of exposure to uneonfined plasma 138 In addition, components of processing chamber 102 may experience electrical damage because uneonfined piasma 138 ma> change the path by which plasma power is returned to ground through the chamber In an example, the plasma power from power- supply 1 14 may return to ground through chamber components which may not be designed to carry plasma pow er.

|0004j As can be appreciated from the foregoing, plasma imconfmeracnt e\ cuts may be caused by man> diffeient factors. For example, a plasma may become uneonfined if the plasma becomes unstable In another example, a plasma unconfϊnemcnt exeπt may occui if electrical arcing occurs within the processing chamber In yet another example, a plasma may become uneonfined if processing parameters, such as plasma power, plasma composition, gas supply flows, opetating pressure, and the like, fluctuate {0005] Also, the occurrence of the plasma uoeoofioement e\ents may be sporadic and may tend to be unpredictable One reason for the unpiedictability is that the uneonfined plasma diffeient forms In addition, die specific effects that a plasma imconfinement evem may c on substrate processing generally cannot be anticipated due to the \ariable and unpredictable form exhibited by uncon fined plasma. For example, an uneonfined plasma may have low density or high density. In another example, the space occupied by the uneonfined plasma may be large or small In vet another example, an υnconfined plasma may be a stable plasma or may be a fluctuating, sporadic plasma. the location of the uneonfined plasma within the reactor may change during processing {0006] Various methods have been employed to detect plasma uri confinement events.

One method includes utilizing an electrostatic probe that usually has multiple electrodes, such as a V! probe or a Langniun probe to detect a plasma unconfmement emit In an example, a l.angmuir-style probes, which may be unprotected electrodes (usually made from metal), may be exposed to the chamber environment Since the Langmuir-styie probe are typically electrically biased such that when the probe is exposed to plasma a direct current (DC) can flow fτom the plasma to the electrode. For example, a Langmuii -style probe 122 is positioned within the plasma ironrøeπt that is outside of the desired plasma confinement legion By employing a cuirent detectoi 148, DC' current changes on Langmuir-style probe 122 \ ia a power supply 1 18 may be detected Also, a DC power supply (not shown) may be employed to bias the probe.

[0Q07] However, the operational requirements of Langmuir-style probes (i.e. that the electrodes are unprotected and that a DC electrical contact with the plasma exist) limit the utility of the Langrnuir-style probes in detecting plasma uncønfmenieπt events. Also, due to the unpredictable nature of the piasnia unconfineinent events, the Langmuir-style probes may have to be operating continuously while the substrate is being processed in order to be effective. However, continuous usage may result in exposing the unprotected electrodes of the Langmuir-style probes to the mixture of chemical species that is usually present in the reactor chamber during plasma processing. The mixture of chemical species, which includes chemicals supplied for processing of the substrate, new chemical species generated within the processing plasma, and chemical byproducts formed daring the processing of the substrate, typically includes both corrosive components and depositing components that may detrimentally affect the ability of Langmuir-style probes to function properly, in an example, corrosive components {e.g. chlorine, fluorine, and bromine, etc.) may cause the electrodes to corrode, thereby causing the Langmuir-style probe to not function properly, such as failing to timely and/or accurately detect a plasma unconfinement event. In addition, corroded electrodes may become a source of particulate defects and or metallic contamination that may indirectly damage the substrate being processed. In another example, the depositing components of the mixture (e.g. inorganic SiOx-based byproducts and organic CFx-based polyrnerizers) may result in the formation of an electrically-insulating film on the electrodes of the probe; thus, the film may interfere with the required plasma-electrode DC contact, thereby preventing the probe from accurately and'or timely sensing the presence of a plasma. As can be appreciated from the foregoing, the Langmuir-style probes may not be ideal in detecting plasma unconfinement events. fθOθSj Another method that has been employed is to identity the changes in the bias voltage of a substrate during processing to detect plasma unconfinement events. With reference to Fig. 1, a bias voltage on substrate 124 may be produced when power provided by power supply 1 14 interact with plasma 106 within reactor iOO. Typically a sensor 140 may be installed {e.g. in electrode 1 10} to allow direct measurement of the bias voltage on substrate 124 during processing and a bias voltage detector 144 may be employed to compare the bias voltage against a threshold. Thus, when the characteristic of plasma 106 is altered due to unconfmed plasma 138, sensor 140 may be employed to measure the bias voltage and bias voltage detector 144 may be employed to detect the changes in the bias voltage. [0Q09] Additionally or alternat ely, a change in the bias voltage may be indirectly detected by measuring changes in parameters which are related to the substrate bias voltage.

FOT example, when the substiate bias voltage changes because of unconfined plasma 138, the power supplied by power supply 1 14 to electrode 1 10 to maintain plasma lOύ may also change, ^" t herefore, monitoring the power supplied to plasma 106 with a RF power detector 142 may allow detection of plasma unconfinement events. fOOiO] However, the utility of monitoring bias to detect plasma unconfinement e\ ents is limited by the difficulty in detecting changes in the bias voltage caused by plasma unconfmement events Detecting changes in bias voltage is particularly difficult when higher frequency generators (such as 60 MHz) are utilized to generate a plasma Bias \ oltagc generated by higher frequency generators arc small and since a plasma unconfinement e\ent usually occur at Sower power differentiating the plasma unconfinement c\ erst from the changes in the DC bias signal may be difficult or impossible to detect Therefore the utility of this technique is limited because of the mahilit) to reliably detect piasma unconfmement events.

[0011 j In vet another pπor ait appToach, an optical sensoτ raa\ be used to detect plasma unconfinerøeπt events. Those skilled in the art are aware that plasma generally emits light Thus, an optical sensor may be empiojed to detect the light emitted from an unconfined plasma In an example, with reference to Fig 1 , an optica! sensor 132 raa\ be installed adjacent to a transparent window 130 w ith a linc-of-sϊght into an area of chamber 102 in which monitoring is desired (denoted here as a passage 134). ^" t hus, when plasma 106 becomes unconfmed plasma 13 S. light from unconfined plasma ϊ38 may enter passage 134 and may pass tluough window 130 to be detected by optical sensor 132, Lpon detecting the light, optical sensor 132 may send a signal to an optical signal detector 146. If the signal is above a pre-defined threshold, optical signal detection 146 may provide an alert indicating that unconfined plasma 138 has been detected. jOOllj 1 lowever, employing the optical sensois to detect plasma unconfinement events may be limited because detecting the light emitted from unconfined plasma 138 may be difficult because the light emitted by uneon fined plasma 13S is significantly dimmer than the light emitted from processing plasma 106 In addition, the positioning of optical sensor 132 outside of chamber 102 may make "seeing ^"* the light difficult through transparent w mdow 130 since the reactive chemicals mav cause transparent window 130 to be less than transparent. In other words, the reactive chemicals may cause a layer of films to be deposited on transparent window 130. theieby significantly reducing the amount and/or quality of light that be detected optical sensor 132 Furthermore, the utility of optical sensors is dependent upon having \ iewiπg access into the processing cm ironmcnt. However, placing

windows and ^' or ing passages in all locations that may to be monitored may not alway s be feasible.

{0013 j Although -various methods ha\e been implemented, each of the methods does not preside a dependable and comprehensive solution for detecting plasma imconfinement events, In an example, the Ie pτobe is susceptible to corrosion, which may negatively impact the probe effectiveness in identifying plasma unconfmement e\ ents In another example, depending upon identifying changes in the bias voltage to determine plasma unconfmement may be dependent upon differentiating the changes in DC bias signal from a plasma uneonfinement event The ability to differentiate the two may be difficult when the DC bias signal is being generated b> a higher frequency generator {such as 60 MSHz) while the imcoiifmed plasma is occurring at a loxvei pow er lex el In yet another example, utilizing optical sensors to detect light emitted from unconfmed plasma is limited by the availability of v iewable passage and/or the inability to detect the light due to the obstruction that may cause the v tew able passage ^* "unv iewable"

BRlEh SUMMARY OF ^" IHh INVEN TION f00l4j The invention relates, in an embodiment, to an arrangement within a plasma reactor foτ detecting a plasma imconfinement ev ent The arrangement includes a sensoi, which is a capacim c-based sensor implemented w iihin the plasma reactor. The sensor is implemented outside of a plasma confinement region and is configured to produce a transient current when the sensor is exposed to plasma associated with the plasma unconfinement event The sensor has at least one electrically insulative laver oriented toward the plasma associated with the plasma unconfined The arrangement also includes a detection circuit, which is electrically connected to the sensor for converting the transient current into a transient voltage signal and for processing the transient voltage signal to ascertain whether the plasma unconfinement event exists

|00l5j The summary relates to onlv one of the main embodiments of the invention disclosed heieiπ and is not intended to limit the scope of the invention, which is act forth in the claims herein These and other features of the present irn ention will be described in more detail heiovv in the detailed description of the conjunction with the follow ing figures

BRIEF DtSCRlFtION OF ^" I HE DRAW INGS fOOiό] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the aceompam ing drawings and in which like ieference numerals refer to similar elements and in which

[OQI 7] Fig I shows an example of a piioi art plasma processing chamber in which the plasma is confined during processing, and illustrates current strategies for detecting plasma uπcoπfiπement events.

J0O18J Fig. 2 shows, in accordance with an embodiment of the present invention, a simple schematic of a plasma reactor duting plasma pioeessmg [00ϊ9] Fig 3A shows, in an embodiment of the invention, an implementation of sensor

{0020 j Fig. 3B shows, in an embodiment of the invention, an example of a rectangular capaαtive-bascd sensor

|0021 j Fig, K" shows, in an embodiment of the invention, an example of a cross- section of a sensor with two electrically insulative outei layers

|0022j 1-igs. 4A and 4B arc schematic \ iew s of embodiments of plasma detection circuits.

DFTAO FD DHSCRIPTK)K O\- THF PRFFhRRt-D HMBOPϊMi- NlS {0023] The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings In the following description, nunieious specific details aie set forth in order to pτo\ ide a thorough under standing of the present im cntion It will be apparent, however, to one skilled in the art, that the present invention may he practiced without some or all of these specific details. In other instances, well known process steps and/or structures not been described in detail in order to not unnecessarily obscure the present invention

J0O24J Various embodiments are described hereinbelow, including methods and techniques It should be kept in mind that the invention might also cover articles of manufacture that includes a computer readable medium on which computer-readable instructions for carrying out embodiments of the inventh e technique aie stored The computer teadable medium may include, for example, semiconductor, magnetic, opto- magnetie, optical, or other forms of computer readable medium for storing computer readable code Further, the invention may also apparatuses for practicing embodiments of the ention. Such apparatus may include circuits, dedicated and or programmable, to carry out tasks pertaining to embodiments of the im ention i-Xamples of such apparatus include a general-purpose computer and or a dedicated computing device when appropriately programmed and may include a combination of a computer computing device and dedicated/programmable cύeuits adapted for the \ arious tasks pertaining to embodiments of the invention

[0025] in accordance with embodiments of the invention, a plasma uneonfinement sensor, such as a eapacltive-based sensor, is provided for detecting plasma uπconfiπemem events within a plasma processing system. Embodiments of the invention include a sensor that is insensitive to corrosion and deposits that typify a plasma processing em iroαment. Embodiments of the invention also include the sensor to he attached to a detection circuit, which is configured at least to make a determination of an unconfinemem event within the plasma processing system.

J0026J In an embodiment, the sensor may include an electrically conductive substrate protected by one or more electrically insulative layers, in an embodiment. When the sensor is exposed to an unconfinement e\ent, the transient current that is developed across the electrically insulative layers may How through the sensor to a circuit converter The circuit converter is configured, in an embodiment, to translate the transient current into a transient voltage signal. The transient voltage signal may be sent through a low pass filter circuits to improve the signal-to-noise characteristics, such as to remove the high-frequency components from the transient voltage signal. Additionally or alternatively, the transient voltage signal may be sent through a set of resonance filters (such as LC filters), which is configured to at least remove additional frequencies. Once the transient voltage signal has been conditioned, the signal may be compared to a pre-defined threshold to determine the existence of a plasma uneonftnement e\ ent.

|0027] As can be appreciated from the foregoing, since the sensor Is configured to be insensitive to corrosion or deposition that may occur during plasma processing, the sensor can be continuously operating during plasma processing, thereby improving the likelihood and timeliness of uncoupled plasma event detection. Further, the detection circuit enables the transient current sensed by the sensor to be translated into a clear and robust signal that can be employed to determine the existence of a plasma unconfineiυent event |0028j The features and adv antages of the present invention may be better understood with reference to the figures and discussions that follow.

[0Q29] Fig, 2 shows, in accordance with an embodiment of the present invention, a simple schematic of a plasma reactor 200 during plasma processing. Plasma reactor 200 may include an electrode 210 {e.g., capacim e~based sensor), which is configured to be positioned within a region in which detection of plasma uneonftnement e\ ents is desired. In other words, the region may be outside of a plasma confinement region 214. In an example, electrode 210 may be mounted in a manner that enables the outer surface of electrode 210 to be exposed to υnconfmed plasma, such as υncon fined plasma 212,

[003θ] Due to the inherent characteristic of plasma, surfaces exposed to a plasma may clop an electrical charge as a result of the difference in velocity of the lighter plasma components (e g. electrons) interacting w ith the ier plasma components (e g molecular ions) Thus, w hen electrode 210 is exposed to unconfmed plasma 212, the outer surface of electrode 210 may undergo a charging process The outer electrode 210 smface may chaϊge negath ely or posith el\\ depending on the particular characteristics of unconfmed plasma 212. Usually, the charging process is a transient process since the charging process usually occurs until the outer surface of electrode 210 has an amount of charge which is at equilibrium w ith unconfmed plasma 212

{0031 j In an embodiment, while the transient charging process of the outer surface of electrode 210 is occurring, a transient charge with a charge that is opposite of the outer surface transient charge may be induced w itliiu electrode 210 In order to timely identify the existence of uneonfined plasma, the transient current induced by the transient charge is comerted into a transient signal by a conversion circuit 222 Since the transient \oltage signal may include by noise, a low -pass filter 224 may be utilized to remove the noise. In an example, low -pass filter 224 may be employed to remove high frequency components Ce g., high-frequency noise) thereby improving the ttansient voltage signal To transform the transient voltage signal into a conditioned signal, in an embodiment, a set of resonance LC filter 226 may be employed to block specific frequencies, such as those typically used to generate plasma The conditioned signal may then be forw arded to a threshold detector 228, which may be configuied to compare the conditioned signal against a pre-defmed threshold. If the conditioned signal is abo\e the pre-defmed threshold, threshold detector 228 may generate an alert indicating that unconfmed plasma has been detected, thereby enabling appropriate action to be taken (e.g., the plasma may be turned off and processing of the substrate stopped).

|0032j ϊMIJ 3λ shows, in an embodiment of the imention an implementation of a capacitixe-based sensor. As mentioned in Fig 2. a capacitn e~based sensor 302 may be physically mounted on a chamber wall 31 S of a plasma reactor hi an embodiment, capacitive-based sensor 302 may include at least two components: an electrically insulathe outet layer 308 and an electrically conducting substrate 304 In an embodiment, capacitive- based sensor 302 is electrically isolated from the mounting surface \ ia an insulator 316. When a transient charge is generated due to an uueoufmed plasma, tiie transient cuπem may be sent along to a conducting contact 314, which is coupled to electrically conducting substrate 304 \ ia an electrical contact 306 The transient charge rna> be sent to a detection

circuit (not shown) \ ia a wire 310 which rnav be secured to conducting contact 314 via a clamp 312

{0033 j Electrically conducting substrate 304 may be made from a variety of materials

In an embodiment electrically conducth e substrate 304 may be made from electrically conducting material such as a metal (e g AI, Cu. Ag, λu, Fe-based. etc } or a combination alloy of metals fcleetrieally substrate 304, in an embodiment, may also be made from a semiconducting material, such as highly-doped silicon, for example In an embodiment, electrically conducth e substrate 304 may be made from a conductiv e ceramic material ! eg silicon carbide) or a combination of conducts e ceramics. Additionally oi alternatively, electrically conductive substrate 304 may be made fiom either a conductive polymer oi a non-conductive polymer, in an embodiment ϊn an example, the conductive polymei may include but are not limited to an organic poiymet containing electrical l\ eonduethe "fillers ^" , an organic polyaniiine- based polymer, and a mixture of a polyanyline- based polymer In vet another embodiment electrically conductive substrate 304 may be made from an electrically conductive inorganic polymer, such as conducth e silicone, for example. As can be appreciated ftorn the foregoing, electrically conductive substrate 304 may be made from a combination of am or all of the abo\ e electrical!) conductive materials {0034] In an embodiment, electrically insυlative outer la>cr 308 may be made from an eiectrieally-tnsulame material, such as a form of SiO2 (e.g. quartz or glass), a ceramic (eg A120λ a commercial polymer (e g PTFE, polyimide, silicone, etc }, a polymer that is a byproduct of the plasma process (e g a CFx-based polymei ), or a combination of any or all of the above. Electrically insulath e outer layer 308 may be made of an electrically-insulating material that ma)- be compatible with the mixture of chemicals and plasma that may be typically used within the plasma reactor, m an embodiment In an example, anodized aluminum is a common component that maybe found within a plasma etch reactor (such as that illustrated in Hg 1 ) since anodi/ed aluminum is relatively inert to the chemicals typically used for substrate processing Therefore, electrically insulative outer layer 3OS made from electrically-insulating materials, such as anodized aluminum, that are compatible with the chemicals utilized during plasma processing may make the sensor protected by the electrically insulatne outer layet (30S) insensith e to the plasma environment and pte\ ent the electrically insuiathe outer layer from becoming a source of metal or particulate defects |0035] In another embodiment, electrically insulative outer layei 308 mav be grown from electrically conducth e substrate 304 In an example, anodized aluminum that may characterize electrically outer layer 308 may be grown from an aluminum substrate. In

0

anotheϊ example, electrical!) insuiathe outer layet 30S mav be grown from the film deposited on electrically conductive substrate 304. The film may be deposited by a plurality of common deposition techniques, including chemical deposition, plasnia enhanced chemical vapor deposition, sputtering, and the like In yet another example, electrically insulatKe outet laser 308 mas be applied onto electrically conduetn e substrate 304 bv a plurality of common application techniques, such as thermal spraying, sintering, thermal bonding, and the like,

{0036 j rhe thickness of electrically insulative outer layer 308 may \ ary depending upon the type of initiative material In an embodiment, the thickness of electrically insuiathe outer Saver 308 has to be sufficiently thick to electrically insulate electrically conductive substrate 304 while still enabling an appropriate capacitance to be generated when capacitive-based sensoϊ 302 is exposed to a plasma in order to create a measurable \oltage that is detectable in the detection circuit In one embodiment, the thickness of the film may range from 10 to 100 micrometers

{0037J λs can he appreciated from the foregoing, the number of electrically irssulame outer layer that may be applied to electrically conductive substrate 304 may as long as the set of electrically insulative outer layers electrically isolate electrical Iv conductiv e substrate 304 from the sensor's {302) outer surface 324. which is exposed to the υnconfϊned plasma. Fo illustrate. Fig. 30 shows, in an embodiment of the invention, an example of a cross-section of a capacϊtn c-bascd sensor 302 with two electrically insυlative outer !a\crs, 320 and 322 in an example, electrical!) msulatrve outeτ layeτ 322 mav be applied onto electrically insuiathe outer layer 320 as part of the fabrication of capacith e-based sensor 302. In this example, electrically insuiath e outer layer 320 may become an 'intermediate glue layer' to improve the adhesion of electrically insulative outer layer 322 onto electrically conductive substrate 304. In anothei example, electrically insulative outei Iayei 320 may a coefficient of thermal expansion winch is in-between electrically insulative outer laver 322 and electrical!} coπdueth e substrate 304 The thermal expansion coefficient may enable capacitive-based sensor 302 to he more resistant to cracking or flaking due to the effects of thermal cycling

|0038j In a third example, electrically insulative outer laver 322 may teptesent a layer of deposition that has formed on an electrically insuiathe outer layer 320 due to exposure to leactive gases that are present in the processing chamber while the substrate is being processed Because capacUhe-hased sensor 302 may operate like a capacitor, capacitive- based sensor 302 may be insensith c to the formation of an additional layer on the surface of

the sensor According, unlike Langmuir-type probes, the formation of an electrically insulative outer layer does not eliminate the ability of the sensor to detect imcon fined plasmas {0039 j Referring back to t- ig. 3 A, the specific combination of insulator 316, conductor contact 314, and clamp 312 may be custom-made for a particular application, or may be replaced by am number of commercial feed-through devices. {0040] Additionally, capacitive-based sensor 302 may be mounted to the chamber in many different ways In an embodiment, capacitive-based sensor 302 may be mounted within close proximity to chamber wall 3 i ts. as shown in Fig. 3A. In another embodiment, capaoim c-based sensor 302 may be flush with chamber wall 318 Sn yet another embodiment, capacitke-based sensor 302 may be mounted away (such as on the end of a rod or a pedestal) fioni chamber wall 31 S.

J0041) in an embodiment capacitύ c-based sensor 302 ma\ be of different geometrical shape. As can be appreciated from the foregoing, the shape of capacitive-based sensor 302 may be based on a manufacturer's preference oτ mas be dependent upon mounting location. In an embodiment as show n in Fig. 3B. capacitrve-based sensor 302 may be a rectangular "'button", with x and y dimensions of around one inch and a thickness / of 0 05 ^"" . In another embodiment capaeithe-based sensor 302 may be annular in shape, such as a ring, to account for the other components within the environment, such as a circular pedestal or a circular chamber. Usually, the sensiti\ ity is proportional to the surface area of the probe in contact with the unconfhied plasma ϊv _* hieh may not occupy the whole exterior volume!. Accordingly, a latget probe may provide a larger signal, but may also captuie moτe noise, l-urthermore, a very large probe may risk perturbing the normal plasma process, for example by changing the RF current return path Thus, the shape and si/e of the sensor may depend upon a manufacturer ^' s preference given the criteria discussed above, |0042j As aforementioned, once the transient current has been generated, the transient current may be sent to a detection circuit to determine the existence of an unconfined plasma The next few figures (Figs 4λ and 4B) aie examples of the flow of the transient circuit to the detection circuit

{0043] Fig 4A shows, in an embodiment of the invention, an example electrical model of both a capacim e~based sensoτ and a detection circuit A box 402 shows an example circuit model for a capacitive-based sensor. The outer surface of the capacitrve- based sensor (the surface which ts exposed to a plasma) is represented by a plate 404. Capacitois 406 and 408 each represents electrically insulathe outer layers which may be present on the electrically conducts e substrate of the capacitive-based sensor As can be

appreciated from the foregoing, additional layers on the electrically conductive substrate may be shown as additional capacitances in the electrical model {and \ ice \crsa} In an embodiment, the capacitance of the set of electrically outer layers on the electrically conductive substrate is the dominant capacitance In other words, the additional capacitance due to the formation of layets of plasma deposition products may be large relativ e to the capacitance of the outer layers of the detector, since the smallest capacitors in a series is the dominant one Usually, a typical capacitance value of the film may be about 0 1 nF per square centimeter of the surface area.

[0044] Boxes 410, 420, and 430 show an example circuit model for a detection circuit.

Box 410 shows an example of a model for a current- to- voltage converter (i e , circuit converter.). The euirein~to~s ullage consericr is configured to consort the transient current geneiated from an electrical chaige due to exposure of the plate 404 to a plasma In an example, the transient current that develop across capacitors 406 and 408 due to the exposure to the plasma may flow to an electπcal ground 416 \ ia a resistoT 414, thereby coin erting the transient current into to a transient voltage signal, which may be read at point 412. In an embodiment, resistor 414 may have a salυe of between i — 100 kohms {0045 j The transient voltage signal generated at point 412 may then be conditioned to improve signal-to-noise characteristics In an embodiment, the transient \ oitage signal may pass through a low. pass filter circuit, such as the example circuit shown in box 420. In an embodiment, low pass filter 420 may include, but are not limited to a resistor 422 connected to a capacitor 424. w Inch is connected to a gϊound 42c> The combination of elements 422 and 424 serve to remove high-frequency components from the transient \ oitage signal In an embodiment, resistor 422 may have a \ alue of 100 ohms and capacitor 424 may hax e a \ alue of about 10O nF.

J0046J The signal to noise characteristics of the Uansient xυitage signal may be further \ oitage signal through a set of resonance LC filteis such as the two examples presented in Box.430, m an embodiment. The first LC filter may include an inductor 432 in parallel w ith a capacitor 434 Similarly, the second LC filter may include an inductor 43ft in parallel to a capacitor 438 With the set of resonance LC filters, the transient voltage signal mas be improved by remov ing selectively blocking known and or expected frequencies For example, if a process plasma is powered by two separate Rh generators, that operate at diffeieni frequencies (e g . 13 56 MlIz and 28 Mlϊ/i, the transient \ oitage signal geneiated from a eapaciti\e-based sensor exposed to a plasma mas include both frequencies. Since the magnitude of these frequencies may interfere \\ ith the detection

of the transient \ oltage signal, the set of resonance LC filters may be employed to block the frequencies In an example, inductor 432 in parallel with capacitor 434 rna> block the 13 5ft MHz component and inductor 436 in parallel with capacitor 438 may block the 28 MHz component. Typically, the type of frequencies (e g., 2, 27 and 60 MHz) that may be commonly utilized ma> be the types of frequencies that may be blocked. However, the set of resonance LC filters are not limited to blocking just the afore mentioned frequencies and may block a range of frequencies (e g , 500 kl 1/ to 200 MHz). As can be appreciated from the foregoing, the type of frequencies that may be blocked may depend upon the user's preference.

{0047] Once the transient voltage signal has been filtered, a conditioned signal may be generated at a point 440 In an embodiment, the conditioned signal (i c, the output from resonance LC filter 430) ma> be sent to a threshold detector (not shown) The threshold detector may compare the conditioned signal to a pre -determined threshold to determine if a plasma unconfmement e\ ent has occuπed.

{0048J the detection circuit may be implemented as shown in Fig. 4B.

The detection circuit as shown in Fig. 4B is similar to the detection circuit of Fig. 4A except for an additional capacitot 418. In an embodiment, capacitor 418 may be implemented within the cυrrent-to-x oltage com crter of box 410 Since capacltn c-bascd sensor in box 402 may sometime experience short-circuit, capacitor 418 may prov ide some protection for the downstream components of the detection circuit ϊi.e. boxes 420, 430, threshold detector, etc.) fioni being damaged In an embodiment, capacitot 418 may ha \ e a \ alue of 10(* nF In an example, if the set of outer layers of the eapacith e-based sensor become damaged such that the electrically characteristic of the capacitive-based sensor is compromise, model capacitors 406 and 408 m box 402 are replaced by a direct electrical connection between the capacim e-based censor (i e plate 404) and the detection circuit components, which aie connected to point 412 in box 410. the detection cneuit mas also be short-circuited and be damaged Howevei. with capacitor 4! 8, a direct connection betw een the plasma and the detection components may be thereby preventing the detection circuit from being damaged. In addition, even if capacitor 418 becomes exposed to the unconfmed plasma due to (he short-en euit situation the transient \ oltage signal generated is detectably diffetent from the transient voltage signal that is associated with a non-short-circuited sensor. As a lesult, the threshold detector is able to differentiate between the two t>pes of transient \ oltage signal and may be able to make a determination that the capacim e-based sensoϊ has been damaged

[0Q49] As can be appreciated from the forgoing, one or more embodiments of the present invention provide for a plasma uiicoiifmement sensor for detecting unconfined plasma. By having a set of electrically iαsulative outer layers protecting the conduction substrate of the plasma υnconftnement sensor, the plasma unconfinement sensor is protected from the plasma em ironment, thereby enabling the plasma unconfuiement sensor to perform without experiencing performance degradation due to corrosion to critical sensor components and or deposition of electrically insulating Ohm on the conducting substrate of the sensor. With a detection circuit capable of filtering out extraneous noise from the v oltage signal, the voltage signal may be of higher quality; thus, providing the threshold detector with a clear signal from which a plasma unconfinement event may be determined. fOOSøj While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. Although \arious examples are provided herein, it is intended that these examples be illustrative and not limiting with respect to the invention. {0051 j Also, the title and summary are prov ided herein for con\enience and should not be used to construe the scope of the claims herein Further, the abstract is written in a highly iated form and is prov ided herein for convenience and thus should not be employed to construe or limit the overall invention, which is expressed in the claims. If the term "set" is employed herein, such term is intended to ha\ e its commonly understood mathematical meaning to cover zero, erne, or more than one member. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equiv alents as fall within the true spirit and scope of the present invention.