Abstract:
An assembly, for example an electrostatic chuck, is provided including a substrate, an electrostatic chuck, a heating plate, and a bond layer comprising a phosphorescent material. In one form, an optical sensor is disposed proximate the bond layer to detect a temperature of the bond layer in the field of view of the optical sensor. The phosphorescent material is illuminated and the subsequent decay is observed by the optical sensor. From this information, the temperature of the electrostatic chuck and substrate is determined and heating elements may be adjusted by a controller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the filing date under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62/021,937 filed Jul. 8, 2014, the entire contents of each of which are hereby incorporated herein by reference 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to heated assemblies, and more particularly to temperature detection and control systems for such assemblies, including by way of example, electrostatic chucks and substrates in semiconductor processing equipment. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Heated assemblies are frequently used in applications having limited space and requiring precise control. In the art of semiconductor processing, for example, a chuck or susceptor is used to hold a substrate (or wafer) and to provide a uniform temperature profile to the substrate during processing. 
         [0005]    Referring to  FIG. 1 , a prior art support assembly  110  for an electrostatic chuck is illustrated, which includes an electrostatic chuck  112  with an embedded electrode  114 , and a heating plate  116  that is bonded to the electrostatic chuck  112  through an adhesive layer  118 . A heater  120  is secured to the heating plate  116 , which may be an etched-foil heater, by way of example. This heater assembly is bonded to a cooling plate  122 , again through an adhesive layer  124 . The substrate  126  is disposed on the electrostatic chuck  112 , and the electrode  114  is connected to a current source (not shown) such that electrostatic power is generated, which holds the substrate  126  in place. A radio frequency (RF) power source (not shown) is connected to the electrostatic chuck  112 , and a chamber that surrounds the support assembly  110  is connected to ground. The heater  120  thus provides requisite heat to the substrate  126  when a material is deposited or a thin film on the substrate  126  is etched. The heater  120  thus provides requisite heat to the substrate  126  when a material is deposited onto or etched from the substrate  126 . 
         [0006]    During processing of the substrate  126 , it is important that the temperature profile of the electrostatic chuck  112  be highly uniform in order to reduce variations within the substrate  126  being etched. Improved devices and methods for improving temperature uniformity are continually desired in the art of semiconductor processing, among other applications. 
       SUMMARY 
       [0007]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
         [0008]    In one form of the present disclosure, an assembly is provided comprising a first member, and a second member disposed proximate to the first member. The first member may take the form of an electrostatic chuck or a substrate. The second member may take the form of a heating plate. The assembly further comprises a bond layer disposed between the first member and the second member. The bond layer secures the second member to the first layer and at least a portion of the bond layer is comprised of a phosphorescent material. The assembly also includes an optical sensor which is disposed proximate the bond layer to detect the temperature of the first member. 
         [0009]    In another form of the present disclosure, an electrostatic chuck support assembly is provided, comprising an electrostatic chuck and a heating plate disposed below the electrostatic chuck. The support assembly further comprises a first bond layer disposed between the electrostatic chuck and the heating plate. At least a portion of the first bond layer comprises a phosphorescent material. The support assembly also comprises an optical sensor positioned to observe the portion of the first bond layer comprised of phosphorescent material. The support assembly also includes a cooling plate, disposed proximate the heating plate and a second bond layer disposed between the heating plate and the cooling plate. 
         [0010]    In yet another form of the present disclosure, a method of detecting and controlling temperature of an electrostatic chuck is provided, comprising having a bond layer between an electrostatic chuck and a heating plate. At least a portion of the bond layer comprises a phosphorescent material. The method further comprises positioning an optical sensor proximate the bond layer and receiving signals from the optical sensor regarding a decay rate of light emitting from the phosphorescent material. The method further comprises determining the temperature of the bond layer based on the signal received from the optical sensor, and controlling the temperature of the heating plate. 
     
    
     
       DRAWINGS 
         [0011]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0012]      FIG. 1  is an elevated side view of a prior art electrostatic chuck; 
           [0013]      FIG. 2  is a cross-sectional side view of an assembly, showing a substrate, electrostatic chuck, bond layer, heating plate, and an optical sensor constructed in accordance with the principles of the present disclosure; 
           [0014]      FIG. 3  is a cross-sectional side view of another form of an assembly, showing a substrate, electrostatic chuck, a heating plate, a cooling plate, two bond layers, and two optical sensors constructed in accordance with the principles of the present disclosure; 
           [0015]      FIG. 4  is a cross-sectional side view of yet another form of an assembly, showing a substrate, electrostatic chuck, bond layer, and a heating plate with an aperture disposed on the side of the assembly constructed in accordance with the principles of the present disclosure; 
           [0016]      FIG. 5  is a partial plan view of another form of an assembly, showing a heating element and optical sensors constructed in accordance with the principles of the present disclosure; 
           [0017]      FIG. 6  is a chart showing an example of intensity of a phosphorescent material with respect to time; and 
           [0018]      FIG. 7  is a chart showing an example of the calibration data used by a controller correlating decay rate to temperature of the electrostatic chuck. 
       
    
    
       [0019]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0021]    Generally, with fiber optic sensing, a light source is used to illuminate a phosphorescent material for a brief time period, and an optical signal conditioner is used to detect the light radiation that the phosphorescent material emits in response. The rate of decay of phosphorescent radiation is proportional to its temperature, and thus the temperature of the object can be determined. Such fiber optic sensing is set forth in greater detail in, for example, in U.S. Pat. Nos. 4,652,143 and 4,776,827, which are hereby incorporated by reference in their entireties. 
         [0022]    As used herein, the term “optical sensor” should be construed to mean both a fiber optic light guide and an optical signal conditioner used to sense and determine temperature of a phosphorescent material. 
         [0023]    Referring to  FIG. 2 , an assembly  10  is shown comprising a substrate  12 , an electrostatic chuck  14 , a heating plate  20  and a bond layer  16  disposed between the electrostatic chuck  14  and the heating plate  20 . The bond layer  16  secures heating plate  20  to the electrostatic chuck  14  and comprises a phosphorescent material  26  disposed within an optically clear matrix  27 . The matrix  27  may be the actual bond material, such as a silicone bonding material. Alternatively, the phosphorescent material  26  may be mixed with the matrix  27 , and then this composite material combined with the bond layer  16  material. Additionally, the phosphorescent material  26 , with or without a matrix  27  that is separate from the bond layer  16 , may be mixed evenly throughout the entire bond layer  16 , or it may be located only specific areas throughout the bond layer  16 . Accordingly, the specific illustrations shown herein should not be construed as limiting the scope of the present disclosure. 
         [0024]    In one form, the heating plate  20  also defines an aperture  22  exposing the phosphorescent portion of the lower side  28  of the bond layer  16  to an optical sensor  24 , disposed within the aperture  22 . In operation, the optical sensor  24  illuminates the phosphorescent material  26  and then receives light from the decay of the phosphorescent material  26  to determine the temperature of the bond layer  16 , which is thermally coupled to the electrostatic chuck  14  and the substrate  12  by conduction. This information is sent to a controller  54 , which determines and controls the temperature of the electrostatic chuck  14  and substrate  12 . 
         [0025]    The heating plate  20  provides support for the electrostatic chuck  14 . It also may contain one or more heating elements  18  which may be used to alter the temperature of the electrostatic chuck  14 . The heating plate  20  may be made of metal or another thermally conductive material. 
         [0026]    The bond layer  16  secures the heating plate  20  to the electrostatic chuck  14 . It may be made from a number of substances such as a silicone elastomer, a pressure sensitive adhesive, a glass frit, a ceramic epoxy, or a layer of indium. The bond layer  16  should be capable of effectively securing the heating plate  20  and the electrostatic chuck  14  throughout the operational temperature range of the assembly  10 , as well as being capable of incorporating a phosphorescent material  26  prior to application. The bond layer  16  may also be made of a transparent, thermally conductive, elastomeric material such as Sylgard® 184 brand silicone compound manufactured by Dow Corning. Adhesion may be improved with the addition of a primer to the mating surfaces. Various optically transparent silicone elastomers may be used depending on the requirements for bond strength, temperature range, thermal conductivity, viscosity, durometer, cure-time, and bond layer  16  thickness. 
         [0027]    The phosphorescent material  26  is mixed into the bond layer  16 , and should be capable retaining its phosphorescent properties after mixing. The phosphorescent material  26  may be more easily mixed into the bond layer  16  if it is made of a small particle size powder, which may be between about 1 to about 100 microns in size. The mix ratio of the bond layer  16  material to the phosphorescent material  26  is dependent on application requirements. Higher signal strength may be obtained from a higher concentration of phosphorescent material, such as approximately 25% by weight. Alternatively, improved bond strength and elasticity may be achieved with a lower concentration ratio of phosphorescent material, such as approximately 1% by weight. 
         [0028]    The phosphorescent material  26  is generally an inorganic phosphor that can be excited by conventional LED sources. Examples of suitable phosphorescent materials  26  include, by way of example, Al 2 O 3 :Cr 3+ , Mg 28 Ge 10 O 48 :Mn 4+ , or Mg 4 FGeO 6 :Mn 4+ . These specific compounds are merely exemplary and should not be construed as limiting the range of compounds that may be used as the phosphorescent material  26 . Generally, in this application, the compounds that may be employed will exhibit absorption bands between about 380 nm to about 650 nm, and excitation bands between about 500 nm and about 950 nm with strong time decay dependence on temperature over the required temperature range of the application. Materials selected with shorter decay time constants at a given temperature may enable faster update rates. Various other materials may be employed, and may be selected based on their application suitability for temperature range, phosphorescent decay rate, cost, and commercial availability. 
         [0029]    The process of mixing the phosphorescent material  26  into the bond layer  16  is dependent on whether the phosphorescent material  26  will be disposed only in a portion of the bond layer  16  or the entirety of the bond layer  16 . If the phosphorescent material  26  will be mixed into the entirety of the bond layer  16 , the phosphorescent powder can be added as the bond layer  16  material is mixed. However, if the phosphorescent material  26  will be disposed only on a portion of the bond layer  16  material, it may be desirable to apply the bond layer  16  material to either the heating plate  20  or the electrostatic chuck  14  first. Then, the phosphorescent material  26  may be mixed into the bond layer  16  where it will align with the optical sensor  24 , such as aligning with the aperture  22  of the heating plate  20 . Optionally, the phosphorescent material  26  can be mixed into the bond layer  16  in specific locations after the entire bond layer  16  has been applied. 
         [0030]    With reference to  FIG. 3 , a cross-section of another possible form of the assembly  30  is shown. Similar to the form of  FIG. 2 , this form includes a substrate  12 , an electrostatic chuck  14 , a heating plate  20  with heating elements  18  and an aperture  22  allowing disposition of an optical sensor  24 , and a first bond layer  16  between the heating plate  20  and the electrostatic chuck  14  comprising the phosphorescent material  26 . However,  FIG. 3  shows an additional cooling plate  34  with cooling elements  36 . Between the heating plate  20  and the cooling plate  34  may be a second bond layer  32 . 
         [0031]    The cooling plate  34  transfers heat from the heating plate  20  and the electrostatic chuck  14  to the cooling plate  34 . The cooling plate  34  may be made of a metal or another material which efficiently conducts heat. The cooling elements  36  of the cooling plate  34  may comprise fluid passage to provide convective heat transfer. The cooling plate  34  may also define first and second apertures  22 ,  40 . The first aperture  22  of the cooling plate  34  may be aligned with the aperture  22  defined by the heating plate  20  to allow an optical sensor  24  to be disposed in the aperture  22  to observe the first bond layer  16 . The second aperture  40  may be aligned with phosphorescent portion of the lower side  50  of the second bond layer which comprises a phosphorescent material  26 . 
         [0032]    A second optical sensor  38  may be disposed in the second aperture  40  to illuminate and observe the decay rate of the phosphorescent material  26 . This information may be used to model the thermal gradients across the two bond layers  16 ,  32  and more accurately control the rate of heating or cooling of the electrostatic chuck  14  and heating plate  20 . The second optical sensor  38 , or further additional optical sensors (not shown) may be employed for additional accuracy or redundancy as needed. It should also be understood that the optical sensors  24  and  38  in this form of the present disclosure need not be disposed within apertures  22 ,  40  as shown, which are merely exemplary and should not be construed as limiting the configuration of the optical sensors with respect to the bond layers having phosphorescent material. 
         [0033]    The second bond layer  32  may be made of a similar range of materials as the first bond layer  16 . Likewise, the range of phosphorescent material  26  which may be mixed into a portion of the second bond layer  32  may be similar to the first bond layer  16 . 
         [0034]    Additionally, the assembly  30  may comprise an additional tuning layer (not shown) to achieve high precision control over the temperature of the substrate  12 . This tuning layer may comprise additional heating elements used to finely tune the heat distribution of the substrate  14  in addition to the heating elements  18  of the heating plate  20 . Details on the composition, function, and integration of such a tuning layer may be found by way of example in U.S. Patent Publication 2013/0161305 and its related family of applications, which are commonly owned with the present application and the entire contents of which are incorporated herein by reference in their entirety. 
         [0035]    With reference to  FIG. 4 , a cross-section of yet another form of the assembly  48  is shown. Similar to  FIG. 2 , this form includes a substrate  12 , an electrostatic chuck  14 , a heating plate  20  with heating elements  18 , and a bond layer  16 . However, the form shown in  FIG. 4  has a heating plate  20  which defines an aperture  44  on the side of the assembly. An optical sensor  24  may be disposed within this aperture to observe the profile of the bond layer  16 . Although only a portion of the bond layer  16  may contain phosphorescent material  26 , at least a portion of the periphery of the bond layer  16  of  FIG. 4  comprises a phosphorescent material  26 . This allows the optical sensor  24  to be positioned anywhere around the circumference of or embedded within the bond layer  46  to observe the bond layer  46  and measure the temperature of the electrostatic chuck  14  in that region. In an additional form, the optical sensor  24  itself may be embedded within the bond layer  16  rather than remaining physically outside the bond layer  16 . 
         [0036]    The heating plate  20  may define the aperture  44  on the side of the bond layer  46  in at least two ways. As shown in  FIG. 4 , the heating plate  20  may include a sidewall  42 , which rises above the base of the heating plate  20  to enclose a portion of the electrostatic chuck  14 . This sidewall  42  may be in segments arranged circumferentially about the base  20  or completely encircle the base of the heating plate  20 . The aperture  44  of the heating plate  20  may be defined by an opening  45  in this sidewall  42  exposing the bond layer  46  in the space between the electrostatic chuck  14  and the base of the heating plate  20 . 
         [0037]    Alternatively, the optical sensor  24  may be disposed on the base of a heating plate  20  without a sidewall  42  to observe the profile of the bond layer  46 . In such a configuration, the aperture  44  would be defined by the space between the electrostatic chuck  14  and the heating plate  20 . 
         [0038]    Referring to  FIG. 5 , a partial plan view of the heating plate  20  for yet another form of the assembly  58  is shown. In this form, one possible configuration of a heating element  18  is shown. Additionally, numerous apertures  22  are shown in the heating plate  20  indicating positions where optical sensors  24  may be disposed. Further optical sensors  24  are shown around the circumference of the heating plate  20 , as well as a controller  54  and a heating element power supply  56 . 
         [0039]    The heating elements  18  shown in  FIG. 5  comprises a single resistive heating element  18 , which may be arranged in evenly spaced traces to cover the surface of the heating plate  20 . The ends of the resistive heating element  18  are connected by wires  52  to the power supply  56 . Alternatively, the heating elements may be arranged as individual heating elements, which cover individual regions or zones of the heating plate&#39;s  20  surface  60 . These heating elements may be connected to the power supply  56  by wires  52  in series or in parallel, or other circuit configurations. Additionally, a variety of arrangements of heating elements, in addition to different types of heaters such as layered, Kapton®, and ceramic, among others, may be employed while remaining within the scope of the present disclosure and thus the specific illustrations and descriptions herein should be construed as limiting the scope of the present disclosure. 
         [0040]    Multiple apertures  22  defined on the surface and around the circumference of the heating plate  20  allow flexibility and redundancy in measuring the temperature of electrostatic chuck  14 . Each aperture  22  may be occupied by an array of optical sensors  24  to provide constant temperature monitoring of many portions of the electrostatic chuck  14 . Alternatively, fewer optical sensors  22  may be inserted into or removed from any aperture to allow monitoring of specific areas of the electrostatic chuck  14  as needed. 
         [0041]    Referring to  FIG. 6 , a chart is shown giving an example of how the optical sensor  24  measures the decay of the phosphorescent material  26  mixed into the bond layer  16 . Initially, the optical sensor  24  excites the phosphorescent material  26  by illuminating it with a pulse of light. The phosphorescent material  26  then emits phosphorescent radiation with a determinable intensity which decays over a period of time. The optical sensor uses this intensity rate of decay to determine the time constant (τ) according to the formula I(t)=I O e −kt/τ , where I is intensity, t is time, and k is a constant value. The time (τ) constant of the phosphorescent radiation is dependent on the specific phosphorescent material  26 . 
         [0042]    The assembly  10  may be calibrated, along with the optical sensor(s)  24  and the controller  54  prior to use. As a result, the controller  54  can receive the information regarding the time constant of decay of the phosphorescent material  26  and determine the temperature of the bond layer  16  at the various optical sensor locations. 
         [0043]    Referring to  FIG. 7 , a chart is shown giving an example of data that may be used to calibrate the controller  54  for the assembly  10 . The controller  54  may be configured to associate decay rate of the phosphorescent material  26  to temperature of the electrostatic chuck  14  or of the substrate  12 . As discussed above, the temperature of the bond layer  16  may be determined by observing the decay rate of the phosphorescent material  26  in the bond layer  16 . Through experimental use or thermodynamic modeling, the temperature in the electrostatic chuck  14  can be predicted from the temperature in the bond layer  16 . Therefore the controller  54  can be calibrated to associate a range of decay rates to a correlating range of electrostatic chuck  14  temperatures. A similar process may be used to predict the temperature in the substrate  12  if desired. As the controller  54  determines the temperature of the electrostatic chuck  14 , the controller  54  may alter the power supply  56  to change the output of the heating elements  18  and adjust the temperature of the electrostatic chuck  14  as needed. 
         [0044]    The present disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the present disclosure. For example, the composite bond layer (i.e., having the bond material and the phosphorescent material, with or without a separate binder) may be employed between any members of an assembly where temperature detection is desired, and whether or not those members function as heating members, cooling members, combinations thereof, or other functional members. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.