Abstract:
Apparatus and methods for diagnosing status of a consumable part of a plasma reaction chamber, the consumable part including at least one conductive element embedded therein. The method includes the steps of: coupling the conductive element to a power supply so that a bias potential relative to the ground is applied to the conductive element; exposing the consumable part to plasma erosion until the conductive element draws a current from the plasma upon exposure of the conductive element to the plasma; measuring the current; and evaluating a degree of erosion of the consumable part due to the plasma based on the measured current.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/706,612, filed on Dec. 6, 2012, which is a divisional of U.S. application Ser. No. 11/896,637, filed on Sep. 4, 2007, the entire contents of each of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Plasma has been used in many applications, such as semiconductor processing steps. A conventional plasma processing equipment generates plasma having harsh thermal and/or chemical properties, which causes wear to numerous parts that are exposed thereto during the processing steps. Due to the aggressive nature of the plasma, repeated contact with the plasma may cause one or more of the parts to erode gradually and/or fail abruptly, degrading the performance of the equipment and causing the process result to change over time. 
         [0003]    As such, it is important to carefully monitor the states of these parts and change the parts at the appropriate time. If they are changed too soon, the production cost is increased by throwing away the parts which could still be used further. If they are left too long before changing, damage may result to other parts of the equipment leading to additional cost. For instance, eroding an edge ring in a semiconductor processing chamber beyond the safe limit may result in destroying an electrostatic chuck which is a far more costly part. The ideal case is to use the part to the maximum safe limit and no further. 
         [0004]    The useful lifetime of each part may be estimated through statistical analysis of degradation and failure when placed in specific environments. However, it is always possible that the part may fail or need to be replaced earlier than expected. Also, in practice, the lifetime of the part may depend on exactly how the equipment is run, which may not be known or closely monitored. Furthermore, it may be necessary to open the equipment to perform an inspection, which is disruptive to production and leads to a certain down-time. Thus, it would be desirable to provide an ability to detect events indicative of the end of useful lifetime, faults, or failure of the part during the operation of the equipment and independent of application in any specific plasma process. It would be further desirable to provide an ability to monitor the state of each part in real time and calling of an alarm when the end of effective operational lifetime of the part is reached. 
       SUMMARY 
       [0005]    According to one embodiment, a method of diagnosing status of a consumable part of a plasma reaction chamber wherein the consumable part includes at least one conductive element embedded therein, includes the steps of: coupling the conductive element to a power supply so that a bias potential relative to the ground is applied to the conductive element; exposing the consumable part to plasma thereby causing the conductive element to draw a current from the plasma upon exposure of the conductive element to the plasma; measuring the current; and evaluating a degree of erosion of the consumable part due to the plasma based on the measured current. 
         [0006]    According to another embodiment, a consumable part of a plasma reaction chamber wherein the consumable part is formed of dielectric material and including a surface to be exposed to plasma, includes: one or more conductive elements embedded in the consumable part; a probe circuit coupled to the conductive elements; and a power supply coupled to the probe circuit and ground to apply a bias potential to the conductive elements relative to the ground, wherein the conductive elements are operative to draw a current from the plasma upon exposure of the conductive element to the plasma and the probe circuit is operative to measure the current. 
         [0007]    According to yet another embodiment, a consumable part of a plasma reaction chamber wherein the consumable part is formed of conductive material and including a surface to be exposed to plasma, includes: one or more conductive elements embedded in the consumable part and electrically insulated from the consumable part by a dielectric layer; a probe circuit coupled to the conductive elements; and a power supply coupled to the probe circuit and ground thereby to apply a bias potential to the conductive elements relative to the ground, wherein the conductive elements are operative to draw a current from the plasma upon exposure of the conductive element to the plasma and the probe circuit is operative to measure the current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic cross sectional diagram of a plasma processing chamber having a diagnostic sensor in accordance with one embodiment. 
           [0009]      FIG. 2  shows an exemplary plot of signal from the diagnostic sensor in  FIG. 1  as a function of time. 
           [0010]      FIGS. 3A-3B  show schematic side and top cross sectional views of an edge ring in accordance with another embodiment. 
           [0011]      FIGS. 4A-4B  show schematic cross sectional views of various embodiments of an edge ring. 
           [0012]      FIG. 5  shows a schematic cross sectional diagram of an exemplary embodiment of an upper electrode of the type to be used in the plasma processing chamber in  FIG. 1 . 
           [0013]      FIG. 6  shows a schematic cross sectional diagram of the upper electrode in  FIG. 5 , taken along the line VI-VI. 
           [0014]      FIGS. 7A-7C  show schematic cross sectional diagrams of various exemplary embodiments of an upper electrode of the type to be used in the plasma processing chamber in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring now to  FIG. 1 , there is shown a schematic cross sectional diagram of a plasma processing chamber  100  in accordance with one embodiment. It is noted that the chamber  100  is an exemplary device that generates plasma and includes a diagnostic sensor according to one embodiment. Hereinafter, for brevity, the following discussion is limited to sensors for diagnosing components in the chamber  100 . However, it should be apparent to those of ordinary skill that the similar sensor embodiments can be applied to other suitable plasma generating devices. 
         [0016]    As depicted, the chamber includes a wall  117  for forming a space within which various components for generating capacitively coupled plasma are disposed. The chamber also includes an electrostatic chuck  106  for holding a substrate  112  in place during operation and an upper electrode  102 . The upper electrode  102  and chuck  106  form a pair of electrodes coupled to an RF power source (not shown in  FIG. 1 ) and generate plasma over the top surface of the substrate  112  when powered by the RF source. The chamber  100  also includes a ceramic ring  108 , a coupling ring  110  disposed between the ceramic ring and the chuck  106 , and an edge ring  114  disposed around the edge of substrate  112 . The plasma is confined by confinement rings  104  disposed in the gap between the upper electrode  102  and chuck  106 . Some of the gas particles in the plasma pass through the spacing/gaps between the rings  104  and thence are exhausted from the chamber by a vacuum pump. 
         [0017]    The edge ring  114  performs several functions, including positioning the substrate  112  relative to the chuck  106  and shielding the underlying components not protected by the substrate itself from being damaged by the plasma. The edge ring  114  also enhances plasma uniformity across the substrate  112 . Without the edge ring  114 , the substrate  112  electrically defines the outer edge of the chuck and the equipotential lines would curve upward sharply in the vicinity of the substrate edge. As such, without the edge ring  114 , the substrate edge would experience a different plasma environment from the plasma environment that exists at the center of the substrate, resulting in poor production yield near the edge. More detailed description of the chamber can be found in commonly owned U.S. Pat. No. 6,986,765. 
         [0018]    Due to the aggressive nature of the plasma, the edge ring  114  can wear away over time. As the edge ring  114  wears away, the plasma properties in the vicinity of the damaged regions of the edge ring may change. The changes to the plasma properties in turn may cause the process result to change over time and the chamber may reach a point where the edge ring  114  needs to be replaced. 
         [0019]    To monitor the operational condition and structural status of edge ring  114  in real time and to provide an indication of an event, such as the end of useful lifetime of the edge ring, a diagnostic sensor  115  can be coupled to the edge ring  114 . The sensor  115  includes a pickup unit or probe  116  and a probe circuit  118  connected to the probe  116  via a conductor wire  119 . The probe  116  is embedded in the edge ring  114  such that the probe is completely surrounded by the edge ring  114 . In one exemplary embodiment, the probe  116  has the shape of a wire segment or pin. The probe  116  is formed of, but not limited to, conducting material, such as metal, while the edge ring  114  is formed of, but not limited to, electrically insulating or dielectric material. 
         [0020]    The probe circuit  118  includes a power supply  122  for applying an electrical potential between the probe  116  and ground. The circuit  118  also includes a resistor  120  and a measuring device  124 , such as voltmeter, for measuring the voltage across the resistor or the electrical current flowing through the resistor. The conductor wire  119  is shown to extend from the probe  116  through the chamber wall  117  to the circuit  118 . In an alternative embodiment, the circuit  118  may be disposed inside the chamber and the measuring device  124  may be coupled to a display unit that is located outside the chamber wall  117  and operative to display the signal measured by the device  124  to the operator. 
         [0021]    The probe  116  is embedded in the edge ring  114  at a depth corresponding to a diagnostic event, such as the end of useful lifetime of the edge ring  114 . The probe  116  is biased to a negative dc potential, preferably of 10-15 volts, relative to the ground. During operation, the portion of the edge ring  114  covering the probe  116  from the plasma prevents the energetic positive ions of the plasma from reaching the probe  116 . However, upon repeated exposures to the plasma, the covering portion of the edge ring  114  may be eroded and expose the probe  116  to the plasma, causing the probe to draw an ion current from the plasma. The drawn ion current flows through the resistor  120  of the probe circuit  118  and can be measured by measuring the voltage across the resistor. The plasma can be coupled to the ground via the wall  117 , upper electrode  102 , or other suitable components and complete a path for the ion current drawn by the probe, i.e., the plasma is a source of the ion current and forms a part of the electrical path for the ion current, wherein the ground also forms a part of the electrical path. 
         [0022]    In an alternative embodiment, the probe  116  can be biased to a positive dc potential (not shown in  FIG. 1 ), preferably of 10-15 volts, relative to the ground. In this embodiment, the positive terminal of the power supply  122  in  FIG. 1  may be connected to the resistor  120  while the negative terminal of the power supply  122  is connected to the ground. The positively biased probe  116  may draw a negative electron current from the plasma when the edge ring  114  is worn out to expose the probe  116  to the plasma. The plasma can be coupled to the ground via the wall  117 , upper electrode  102 , or other suitable components and complete a path for the electron current drawn by the probe, i.e., the plasma is a source of the electron current and forms a part of the electrical path for the electron current, wherein the ground also forms a part of the electrical path. 
         [0023]      FIG. 2  shows an exemplary plot of signal from the measuring device  124  in  FIG. 1  as a function of plasma exposure time. As the portion of the edge ring  114  covering the probe  116  from the plasma is worn out, the ion current flowing through the resistor  122 , or, equivalently, the voltage across the resistor measured by the device  124  may suddenly increase, as depicted in  FIG. 2 . This sudden increase in signal intensity may be used as an indicator of the point when the probe  116  is exposed to the plasma. In one embodiment, a warning or notification requiring operator attention or intervention may be triggered when the voltage increases to a preset threshold voltage V T  that corresponds to a diagnostic event, such as the end of effective operational lifetime of the edge ring  114 . In another embodiment, warning or notification may be triggered when the voltage shows a sudden change in value. Thus, by monitoring the signal from the measuring device  124 , an in situ diagnosis of condition, such as degree of erosion, and performance of the edge ring  114  can be performed in real time. 
         [0024]    As discussed above, the probe  116  may be biased to a positive dc potential relative to the ground and draw negative electron currents. In such a case, the vertical axis of the plot in  FIG. 2  may represent the absolute value of the voltage across the resistor  120 . 
         [0025]    In one exemplary embodiment, the sensor  115  may include multiple probe pins embedded in the edge ring  114  in order to provide redundancy or to monitor the overall integrity of the edge ring.  FIG. 3A  shows a schematic side cross sectional view of an edge ring  300  within which multiple probes  302  are embedded.  FIG. 3B  shows a schematic top cross sectional view of the edge ring  300  with eight probes  302 , taken along the line IIIA-IIIB. For brevity, the probe circuit coupled to the probes via conductor wire  304  is not shown in  FIG. 3A . 
         [0026]    As depicted in  FIGS. 3A-3B , multiple probes or probe pins  302  are arranged circumferentially at a preset angular interval about the central axis of the edge ring  300 . It is noted that any other suitable number of probes  302  may be embedded in the edge ring  300 . In another exemplary embodiment, the probes  302  may be electrically connected to each other via an optional connection wire  306 , wherein the connection wire  306  may be formed of electrically conducting material and embedded in the edge ring  300 . In this embodiment, all of the probes  302  may be coupled to the probe circuit. 
         [0027]    The shape, dimension, and material compositions of the probe are selected according to the type of application thereof. In one exemplary embodiment, the diagnostic sensor may include a plurality of thin plates coupled to a probe circuit, each plate having a generally polygonal or circular plate/disk shape. For instance,  FIG. 4A  shows a schematic cross sectional view of an exemplary embodiment of an edge ring  400 . As depicted, the multiple probes  402  are circumferentially arranged and embedded in the edge ring  400 . Each probe  402  has a flat circular disk shape and coupled to a probe circuit (not shown in  FIG. 4A ) via a conductor wire  404 . It is noted that the probe  402  may have other suitable shapes, such as rectangular. 
         [0028]    Optionally, the multiple probes  402  embedded in the edge ring  400  may be connected to each other by a connection wire  406 , wherein the connection wire  406  may be formed of electrically conducting material and embedded in the edge ring. In this embodiment, all of the probes may be coupled to the probe circuit via a conductor wire. 
         [0029]      FIG. 4B  shows a schematic cross sectional view of another embodiment of an edge ring  410 . As depicted, a probe  412  having an annular shape is embedded in the edge ring  410 . For brevity, the probe circuit coupled to the probe  412  via a conductor wire  404  is not shown in  FIG. 4B . 
         [0030]    The diagnostic sensors of  FIGS. 1-4B  can be applied to other suitable components, such as confinement rings, that can be eroded by actions of the plasma and made of electrically insulating or dielectric material. Signals from multiple diagnostic sensors associated with these components can be simultaneously monitored to diagnose the conditions of the components in real time. For components made of conducting or semiconductor material, such as the upper electrode  102  ( FIG. 1 ), the probe can be surrounded by dielectric material in order to prevent a direct contact between the probe and host component in which the probe is embedded, as discussed in conjunction with  FIGS. 5-7B . Hereinafter, for the purpose of illustration, an upper electrode is described as an exemplary host component formed of conducting material. 
         [0031]      FIG. 5  shows a schematic cross sectional diagram of an exemplary embodiment of an upper electrode  500  that might be used in the plasma processing chamber in  FIG. 1 .  FIG. 6  shows a schematic cross sectional diagram of the upper electrode  500 . For brevity, the detailed configuration of the electrode, such as gas injection mechanism, is not shown in  FIGS. 5-6 . As depicted, the upper electrode  500  is associated with a diagnostic sensor  501  that includes one or more probe units  503  embedded in the upper electrode. Each probe unit  503  has a probe  502  including a pin or wire segment formed of conducting material, such as metal, and an insulating layer  504  surrounding the probe to electrically insulate the probe from the upper electrode  500 . The insulating layer  504  may be formed by, for example, a coating of dielectric material on the probe  502 . The sensor  501  also includes a sensor circuit  506  and one or more conductor wires  508 , each of the conductor wires  508  being coupled to the sensor circuit  506  and a corresponding one of the probes  502 . The conductor wires  508  can be electrically insulated from the upper electrode  500 . 
         [0032]    In one exemplary embodiment, each probe  502  can be individually coupled to the probe circuit  506  via a conductor wire  508 . In another exemplary embodiment, the probes  502  can be electrically connected to each other by an optional connection wire  506 , wherein the wire  506  is embedded in the upper electrode  500  and insulated from the upper electrode by an insulating layer, such as dielectric coating, surrounding the wire  506 . In this embodiment, all of the probes  502  are coupled to the probe circuit  506 . The probe circuit  506  may have components and operational mechanisms similar to those of the circuit  118  in  FIG. 1 . 
         [0033]    In yet another exemplary embodiment, each probe can include a thin plate that is formed of, but not limited to, conducting material and has a generally round or polygonal shape. For instance,  FIG. 7A  shows a schematic cross sectional view of an exemplary embodiment of an upper electrode  700 , taken along a direction parallel to the line VI-VI ( FIG. 5 ). As depicted, each of the multiple probe units  703  embedded in the upper electrode  700  includes a probe  704  having a flat circular disk shape and an insulating layer  702  surrounding the probe to electrically insulate the probe from the upper electrode  700 . It is noted that the probe  704  may have other suitable shapes, such as rectangular. It is also noted that any suitable number of probes may be used in the upper electrode. 
         [0034]    Optionally, the multiple probes  704  may be connected to each other by a connection wire  706  that is similar to the connection wire  506  ( FIG. 5 ). In this embodiment, all of the probes are coupled to the probe circuit via a conductor wire. 
         [0035]    In still another exemplary embodiment, the probe embedded in the upper electrode may have a generally annular shape, as shown in  FIG. 7B .  FIG. 7B  shows a schematic cross sectional view of an upper electrode  710 . As depicted, a probe unit  713  embedded in the upper electrode  710  includes an annular probe  714  and an insulating layer  712  surrounding the probe  714  and electrically insulating the probe  714  from the upper electrode  710 . The probe  714  may be formed of a conducting material, such as metal, and coupled to a probe circuit similar to the circuit  118  in  FIG. 1 . 
         [0036]      FIG. 7C  shows a schematic top cross sectional view of another exemplary embodiment of an upper electrode  720 . As depicted, multiple probe units  723  may be concentrically embedded in an upper electrode  720  and each probe unit  723  includes an annular probe  724  and an insulating layer  722  surrounding the probe and electrically insulating the probe  724  from the upper electrode  720 . In the case where the upper electrode  720  includes multiple gas holes to have a showerhead configuration, the radial spacing between probe units can include gas outlets therein. The insulating layer  722  and probe  724  may be respectively formed of materials similar to those of layer  712  and probe  714 . 
         [0037]    It is noted that the probes described in  FIGS. 3A-7C  can be biased to a positive dc potential, preferably of 10-15 volts, relative to the ground. For instance, the positive terminal of the power supply in  FIG. 5  is connected to the resistor while the negative terminal of the power supply is connected to the ground. For brevity, the probes positively biased with respect to the ground are not described in detail. However, it should be apparent that the operational and structural features of the sensor embodiments having negatively biased probes are similar to those of the sensor embodiments having positively biased probes. 
         [0038]    While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.