Abstract:
A probe apparatus configured to measure a set of electrical characteristics in a plasma processing chamber, the plasma processing chamber including a set of plasma chamber surfaces configured to be exposed to a plasma is disclosed. The probe apparatus includes a collection disk structure configured to be exposed to the plasma, whereby the collection disk structure is coplanar with at least one of the set of plasma chamber surfaces. The probe apparatus also includes a conductive path configured to transmit the set of electrical characteristics from the collection disk structure to a set of transducers, wherein the set of electrical characteristics is generated by an ion flux of the plasma. The probe apparatus further includes an insulation barrier configured to substantially electrically separate the collection disk and the conductive path from the set of plasma chamber surfaces.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates in general to substrate manufacturing technologies and in particular to apparatus for measuring a set of electrical characteristics in a plasma. 
   In the processing of a substrate, e.g., a semiconductor wafer, MEMS device, or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate (chemical vapor deposition, plasma enhanced chemical vapor deposition, physical vapor deposition, etch, etc.) for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon. 
   In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck. Appropriate etchant source gases (e.g., C 4 F 8 , C 4 F 6 , CHF 3 , CH 2 F 3 , CF 4 , CH 3 F, C 2 F 4 , N 2 , O 2 , Ar, Xe, He, H 2 , NH 3 , SF 6 , BCl 3 , Cl 2 , etc.) are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate. 
   Subsequently, it is often beneficial to measure the electrical characteristics in a plasma (i.e., ion saturation current, electron temperature, floating potential, etc.) in order to ensure consistent plasma processing results. Examples may include detecting the endpoint of a chamber conditioning process, chamber matching (e.g., looking for differences between chambers which should nominally be identical), detecting faults and problems in the chamber, etc. 
   Referring now to  FIG. 1 , a simplified diagram of an inductively coupled plasma processing system is shown. Generally, an appropriate set of gases may be flowed from gas distribution system  122  into plasma chamber  102  having plasma chamber walls  1117 . These plasma processing gases may be subsequently ionized at or in a region near injector  109  to form a plasma  110  in order to process (e.g., etch or deposit) exposed areas of substrate  114 , such as a semiconductor substrate or a glass pane, positioned with edge ring  115  on an electrostatic chuck  116 . 
   A first RF generator  134  generates the plasma as well as controls the plasma density, while a second RF generator  138  generates bias RF, commonly used to control the DC bias and the ion bombardment energy. Further coupled to source RF generator  134  is matching network  136   a , and to bias RF generator  138  is matching network  136   b , that attempt to match the impedances of the RF power sources to that of plasma  110 . Furthermore, vacuum system  113 , including a valve  112  and a set of pumps  111 , is commonly used to evacuate the ambient atmosphere from plasma chamber  102  in order to achieve the required pressure to sustain plasma  110  and/or to remove process byproducts. 
   Referring now to  FIG. 2 , a simplified diagram of a capacitively coupled plasma processing system is shown. Generally, capacitively coupled plasma processing systems may be configured with a single or with multiple separate RF power sources. Source RF, generated by source RF generator  234 , is commonly used to generate the plasma as well as control the plasma density via capacitively coupling. Bias RF, generated by bias RF generator  238 , is commonly used to control the DC bias and the ion bombardment energy. Further coupled to source RF generator  234  and bias RF generator  238  is matching network  236 , which attempts to match the impedance of the RF power sources to that of plasma  220 . Other forms of capacitive reactors have the RF power sources and match networks connected to the top electrode  204 . In addition there are multi-anode systems such as a triode that also follow similar RF and electrode arrangements. 
   Generally, an appropriate set of gases is flowed through an inlet in a top electrode  204  from gas distribution system  222  into plasma chamber  202  having plasma chamber walls  217 . These plasma processing gases may be subsequently ionized to form a plasma  220 , in order to process (e.g., etch or deposit) exposed areas of substrate  214 , such as a semiconductor substrate or a glass pane, positioned with edge ring  215  on an electrostatic chuck  216 , which also serves as an electrode. Furthermore, vacuum system  213 , including a valve  212  and a set of pumps  211 , is commonly used to evacuate the ambient atmosphere from plasma chamber  202  in order to achieve the required pressure to sustain plasma  220 . 
   In view of the foregoing, there are desired apparatus for measuring a set of electrical characteristics in a plasma. 
   SUMMARY OF THE INVENTION 
   The invention relates, in an embodiment, to a probe apparatus configured to measure a set of electrical characteristics in a plasma processing chamber, the plasma processing chamber including a set of plasma chamber surfaces configured to be exposed to a plasma. The probe apparatus includes a collection disk structure configured to be exposed to the plasma, whereby the collection disk structure is coplanar with at least one of the set of plasma chamber surfaces. The probe apparatus also includes a conductive path configured to transmit the set of electrical characteristics from the collection disk structure to a set of transducers, wherein the set of electrical characteristics is generated by an ion flux of the plasma. The probe apparatus further includes an insulation barrier configured to substantially electrically separate the collection disk and the conductive path from the set of plasma chamber surfaces. 
   The invention relates, in another embodiment to a probe apparatus configured to measure a set of electrical characteristics in a plasma processing chamber, the plasma processing chamber including a set of plasma chamber surfaces configured to be exposed to a plasma. The probe apparatus includes a collection disk structure configured to be exposed to the plasma, whereby the collection disk structure is recessed with respect to a plasma chamber surface within which the collection disk structure is disposed. The probe apparatus also includes a conductive path configured to transmit the set of electrical characteristics from the collection disk structure to a set of transducers, wherein the set of electrical characteristics is generated by an ion flux of the plasma. The probe apparatus further includes an insulation barrier configured to substantially electrically separate the collection disk and the conductive path from the set of plasma chamber surfaces. 
   These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  illustrates a simplified diagram of an inductively coupled plasma processing system; 
       FIG. 2  illustrates a simplified diagram of a capacitively coupled plasma processing system; 
       FIG. 3  illustrates a simplified diagram of a probe, according to an embodiment of the invention; 
       FIG. 4  illustrates a simplified diagram of a probe, in which direct contact is made between a conductive path and a collection disk structure, according to an embodiment of the invention; and, 
       FIG. 5  illustrates a simplified diagram of a conductive path including a wire, according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   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, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
   While not wishing to be bound by theory, it is believed by the inventor herein that a set of electrical characteristics of a plasma in a plasma processing system may be determined by measuring ion flux with a sensor that is substantially coplanar with the plasma chamber surface or, alternatively, a sensor that is recessed into a plasma chamber wall. 
   Flux is generally defined as the rate at which a given quantity passes through a fixed boundary per unit time. For a plasma processing system, ion flux commonly signifies the energy per unit time (or power) created by ions in a plasma passing through a plasma chamber surface or boundary. Subsequently, this plasma-surface (or boundary) interaction may be analyzed in order to determine a set of electrical characteristics in the plasma itself. 
   Coplanar refers to the position of the sensor in relation to a plasma chamber surface, wherein a measuring surface of the sensor and the surface of the plasma chamber are substantially on the same plane. Recessed refers to the position of the sensor in relation to a plasma chamber surface, wherein the surface of the plasma chamber is between the measuring surface of the sensor and the plasma. 
   Unlike other indirect measurement techniques, such as the use of a non-coplanar or non-recessed interferometer which are subject to distortion, a coplanar or recessed sensor can directly measure a condition inside the plasma chamber. For example, a coplanar ion flux probe may be used to detect the endpoint of a chamber conditioning process, to measure plasma properties (e.g., ion saturation current, electron temperature, floating potential, etc.), for chamber matching (e.g., looking for differences between chambers which should nominally be identical), for detecting faults and problems in the chamber, etc. 
   In an embodiment, the parts of the probe exposed to plasma and reactive gases are composed of materials which do not contaminate the plasma with particles or unwanted chemicals. For example in a dielectric etching system, suitable materials would include silicon, silicon dioxide, and fluoropolymers. In addition, in order to properly function, the connection between the conductive surface of the probe and the powering/sensing electronics (e,g, transducers, etc.) should have a low and stable resistance, when cycled between room temperature and elevated temperatures (routinely at or above 200° C.) commonly found in plasma processing. 
   Referring now to  FIG. 3 , a simplified diagram of a probe is shown, according to an embodiment of the invention. In general, the probe is comprised of a collection disk structure, a conductive path, and an insulation barrier. The collection disk structure  302  faces the plasma and is generally constructed of a conductive surface area  303  that is coplanar with or recessed with respect to a plasma chamber surface. In an embodiment, collection disk structure  302  is comprised of metalized silicon. Collection disk structure  302  is further coupled to conductive path  306  which, in turn, is commonly connected to power/sensing electronics [not shown] that may measure I-V characteristics of the ion flux probe, as slow transient currents charge and conductive path  306 ) is sputtered with a metal. In an embodiment, conductive path  306  is comprised of aluminum. In an embodiment, conductive path  306  is comprised of stainless steel. In an embodiment, collection disk structure  302  is further coupled to conductive path  306  via a leaf spring  308 . In an embodiment, leaf spring  308  is substantially cylindrical. 
   Further isolating collection disk structure  302  and conductive path  306  from the plasma chamber [not shown] is insulation barrier  304 . In an embodiment, insulation barrier  304  is a ground shield. In an embodiment, insulation barrier  304  comprises a dielectric, such as quartz. In an embodiment, insulation barrier  304  comprises ceramic such as aluminum nitride, aluminum oxide, etc. In an embodiment, insulation barrier  304  comprises an air (vacuum) gap which is small enough to prevent plasma forming within the gap, but large enough to prevent arcing between conductive path  306  and plasma chamber [not shown]. 
   Referring now to  FIG. 4 , a simplified diagram of a probe is shown, in which direct contact is made between a conductive path and a collection disk structure, according to an embodiment of the invention. In general, as before, the probe is comprised of a collection disk structure, a conductive path, and an insulation barrier. The collection disk structure  402  faces the plasma  110  and is generally constructed of a conductive surface area  403  that is coplanar with or recessed with respect to a plasma chamber surface. 
   In an embodiment, collection disk structure  402  is comprised of metalized silicon. In general, metalized silicon is preferable to more commonly used probe materials, such as tungsten and aluminum oxide, which may contaminate the plasma. Collection disk structure  402  is further coupled to conductive path  406  which, in turn, is commonly connected to power/sensing electronics [not shown] that may measure I-V characteristics of the ion flux probe, as slow transient currents charge and discharge the capacitance. In an embodiment, the back surface (i.e. the surface in contact with conductive path  406 ) is sputtered with a metal. In an embodiment, conductive path  406  is comprised of aluminum. In an embodiment, conductive path  406  is comprised of stainless steel. In an embodiment, collection disk structure  402  is further coupled to conductive path  406  via a leaf spring  408 . In an embodiment, leaf spring  408  is substantially cylindrical. Further isolating collection disk structure  402  and conductive path  406  from the plasma chamber [not shown] is insulation barrier  404 . In an embodiment, insulation barrier  404  is a ground shield. In an embodiment, insulation barrier  404  comprises quartz. In an embodiment, insulation barrier  404  comprises ceramic such as aluminum nitride, aluminum oxide, etc 
   In an embodiment, a gap  415   a  exists between conductive path  406  and insulation barrier  404  in order to provide space for thermal expansion. In an embodiment, gap  415   a  is small enough to prevent plasma forming within the gap. In an embodiment, a gap  415   b  exists between insulation barrier  404  and plasma chamber wall structure  414  in order to provide space for thermal expansion. In an embodiment, gap  415   b  is small enough to prevent plasma forming within the gap. 
   In an embodiment, an O-ring  410  is positioned between collection disk structure  402  and insulation barrier  404 . In an embodiment, an O-ring  411  is positioned between collection insulation barrier  404  and the plasma chamber wall structure  414 . In an embodiment, O-ring  410  and O-ring  411  are comprised of a perfluoronated elastomer (i.e., Perlast, Parofluor, Kalrez, etc.). In an embodiment, O-ring  410  and O-ring  411  are comprised of Teflon. In an embodiment, O-ring  410  substantially reduces arcing or light up in gaps between collection disk structure  402  and conductive path  406 . In an embodiment, O-ring  411  substantially reduces arcing or light up in gaps between and conductive path  406  and insulation barrier  404 . In an embodiment, O-rings  410  and  411  may substantially reduce contamination of the plasma from metal that may have been sputtered on the back surface of collection disk structure  402 , as previously described. 
   In an embodiment, the temperature of the probe is substantially the same as the temperature of the plasma chamber. In general, because plasma recipes tend to be highly sensitive to temperature fluctuations of components in a plasma processing system (i.e., etch quality, etc.) temperature uniformity is beneficial. 
   In an embodiment a layer of thermally conductive adhesive is placed between conductive path  406  and insulation barrier  404 . In an embodiment, closed loop control of temperature may be accomplished by embedding a thermocouple [not shown] in disk structure  402 , and a resistive wire [not shown] around conductive path  406   
   Referring now to  FIG. 5 , conductive path includes a wire, according to an embodiment of the invention. In general, as before, the probe is comprised of a collection disk structure  502 , a conductive path  506 , and an insulation barrier  504 . The collection disk structure  502  faces the plasma  110  and is generally constructed of a conductive surface area  503  that is coplanar to or recessed with a plasma chamber surface. 
   In an embodiment, collection disk structure  502  is comprised of metalized silicon. Collection disk structure  502  is further coupled to conductive path  506  which, in turn, is commonly connected to power/sensing electronics [not shown] that may measure I-V characteristics of the ion flux probe, as slow transient currents charge and discharge the capacitance. In an embodiment, the back surface (i.e. the surface in contact with conductive path  506 ) is sputtered with a metal. In an embodiment, conductive path  506  is comprised of aluminum. In an embodiment, conductive path  506  is comprised of stainless steel. Further isolating collection disk structure  502  and conductive path  506  from the plasma chamber  514  is insulation barrier  504 . In an embodiment, insulation barrier  504  is a ground shield. In an embodiment, insulation barrier  504  comprises quartz. In an embodiment, insulation barrier  504  comprises ceramic, such as aluminum nitride, aluminum oxide, etc. In an embodiment, insulation barrier  504  comprises an air gap which is small enough to prevent plasma forming within the gap, but large enough to prevent arcing between conductive path  1006  and plasma chamber  514   
   In an embodiment, an O-ring  510  is positioned between collection disk structure  502  and the plasma chamber wall structure  514 . In an embodiment, O-ring  510  is comprised of a perfluoronated elastomer (i.e., Perlast, Parofluor, Kalrez, etc.). In an embodiment, O-ring  510  is comprised of Teflon. In an embodiment, O-ring  510  provides pressure between the back of the probe  507  and the plasma chamber [not shown]. Such pressure substantially improves the ability of the probe to dissipate heat during operation. 
   In an embodiment, the temperature of the probe is substantially the same as the temperature of the plasma chamber. In an embodiment a layer of thermally conductive adhesive is placed between conductive path  506  and insulation barrier  504 . In an embodiment, closed loop control of temperature may be accomplished by embedding a thermocouple [not shown] in disk structure  502 , and a resistive wire [not shown] around conductive path  506 . In an embodiment, conductive path  506  includes a wire  509  connected to the power/sensing electronics. In an embodiment, the wire is connected to conductive path  506  with a screw. In an embodiment, the wire is connected to conductive path  406  with a BNC connector [not shown]. In an embodiment, conductive path  506  directly physically contacts collection disk structure  502  at  512 . 
   In an embodiment, the probe bias is not substantially biased above the nominal floating potential, the probe bias being generally derived entirely from the plasma in conjunction with applied RF potentials. In an embodiment, thermal grounding of the probe may be accomplished by the use of pressure and materials which provide low thermal contact resistance, such as graphite  507 . In an embodiment, closed loop control of temperature may be accomplished by embedding a thermocouple [not shown] in disk structure  502 , and a resistive wire [not shown] around conductive path  506 . 
   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. It should also be noted that there are many alternative ways of implementing the methods of the present invention. 
   Advantages of the invention include an apparatus for measuring a set of electrical characteristics in a plasma. Additional advantages include the maintenance of substantial temperature uniformity between the probe and a plasma chamber surface, and the avoidance of materials such as tungsten and aluminum oxide which may contaminate the plasma environment. 
   Having disclosed exemplary embodiments and the best mode, modifications and variations may be made to the disclosed embodiments while remaining within the subject and spirit of the invention as defined by the following claims.