Abstract:
An apparatus for controlling a temperature of a substrate during semiconductor substrate processing including a semiconductor substrate processing chamber and a substrate support disposed in the chamber. The substrate support includes heater electrode adapted for connection to a power source and disposed within the substrate support, and a meter coupled to the heater electrode for measuring resistivity of the heater electrode as an indicator of the temperature of the heater electrode. A controller is also coupled to the meter and the power source wherein the controller regulates power distribution from the power source to the heater electrode based upon a temperature of the heater electrode, where the temperature is determined from a measured resistivity of the heater electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 09/565,199 filed May 4, 2000, which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE DISCLOSURE  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to an apparatus for processing a semiconductor wafer. More particularly, the invention relates to an apparatus for controlling the temperature of a wafer support pedestal.  
           [0004]    2. Description of the Background Art  
           [0005]    Substrate supports are widely used to support substrates (i.e., semiconductor wafers) within semiconductor processing systems. These supports are used to support and/or retain semiconductor wafers, or other substrates, in a stationary position in the process chamber during processing.  
           [0006]    Typically, the substrate support contains one or more electrodes (i.e., heating electrodes) embedded within the substrate support body. The heater electrode may be used to raise the temperature of the wafer and thereby enhance the process that such wafer is undergoing (e.g. etching, physical vapor deposition, or chemical vapor deposition). Additionally, the temperature of the substrate support is usually monitored via thermocouples placed in vicinity of the heater electrode. However, the temperature that is measured by the thermocouples is dependent upon their proximity to the heater electrode. Thus, the closer to the heater electrode, the greater the accuracy in monitoring temperature.  
           [0007]    One disadvantage of using thermocouples is that the thermocouples are not in close proximity to the heater electrode, and thereby result in inaccurate temperature readings. As such, the temperature may exceed design constraints during the processing before corrective action can be taken. Additionally, there is increased design and manufacturing complexity of a substrate support caused by the thermocouple feed-through wiring and similar wiring. Therefore, a need exists in the art for an apparatus that is capable of monitoring and self-regulating the temperature of the substrate support.  
         SUMMARY OF THE INVENTION  
         [0008]    The disadvantages associated with the prior art are overcome by the present invention of an apparatus for controlling a temperature of a substrate during semiconductor substrate processing, comprising a semiconductor substrate processing chamber and a substrate support disposed in the chamber. The substrate support includes a heater electrode adapted for connection to a power source and disposed within the substrate support, and a meter coupled to the heater electrode for measuring a characteristic of the heater electrode as an indicator of temperature of the heater electrode.  
           [0009]    A controller is also coupled to the meter and the power source, wherein the controller regulates power distribution from the power source to the heater electrode based upon a temperature of the heater electrode. It is noted that the temperature is determined by a measured resistivity of the heater electrode.  
           [0010]    Thus, the apparatus for actively-controlling a heater electrode embedded within a substrate support advantageously allows greater accuracy in determining the temperature of the substrate support, as opposed to the use of thermocouples. Furthermore, the apparatus inventively provides the ability to self-regulate the temperature by adjusting the power source to the heater electrode. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 depicts a schematic diagram of a plasma processing apparatus containing the present invention;  
         [0013]    [0013]FIG. 2 depicts a detailed view of a substrate support of the present invention;  
         [0014]    [0014]FIGS. 3A and 3B depict graphs of resistivity versus temperature for various metals; and  
         [0015]    [0015]FIG. 4 depicts a flowchart of a method of controlling temperature of a substrate support in accordance with the present invention. 
     
    
       [0016]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION  
       [0017]    The present invention relates to improvements in an apparatus for supporting a substrate during a silicon etching or deposition process. Such substrate processing may be conducted (but not necessarily required) in a plasma-based environment. Specifically, the invention relates to an apparatus for actively controlling a heating electrode embedded in a semiconductor substrate (wafer) support utilizing the properties of electrical resistivity of the electrode material.  
         [0018]    [0018]FIG. 1 depicts a simplified schematic diagram of an etch processing chamber  110 . Although the preferred embodiment will be described in terms of a decoupled plasma source (DPS) etching chamber manufactured and sold by Applied Materials, Inc. of Santa Clara, Calif., one skilled in the art will recognize that the inventive substrate support utilizing a heating electrode as a sensor may be incorporated into any other semiconductor wafer processing chamber. Such chambers may illustratively include physical vapor deposition (PVD) chambers or chemical vapor deposition CVD chambers.  
         [0019]    The process chamber  110  is constructed to include at least one inductive coil antenna segment  112 , positioned exterior to a dielectric, dome-shaped ceiling  120  (referred to herein as the dome  120 ), and connected to a radio-frequency (RF) source  118  (which is generally capable of producing an RF signal having a tunable frequency of about 12.56 MHz). The RF source  118  is coupled to the antenna  112  through a matching network  119 . Process chamber  110  also includes a substrate support (cathode)  116  for supporting a substrate  114  to be processed. The substrate support  116  is connected to a second RF source  122 . The RF source  122  is generally capable of producing a RF signal having a frequency in the range of 50 kHz to 15 MHz. For example, in the case of a deep trench etch process conducted in the chamber  110 , a bias frequency of about 400 kHz is used. The source  122  is coupled to the cathode  116  through a matching network  124 . The chamber  110  also contains a conductive chamber wall  130  that is connected to an electrical ground  134 . A controller  140  comprising a central processing unit (CPU)  144 , a memory  142 , and support circuits  146  for the CPU  144  is coupled to the various components of the chamber  110  to facilitate control of process parameters (i.e., temperature, pressure, applied power, gas flow, and the like).  
         [0020]    Additionally, the substrate support  116  comprises a heater electrode  151  that is coupled to a power source assembly  150 . The heater electrode  151  is utilized to maintain the substrate support  116  and resultantly the substrate  114  at a desired temperature, such as 350 degrees Celsius (C.).  
         [0021]    [0021]FIG. 2 depicts a detailed view of the substrate support  116 . In particular, the substrate support  116  comprises a heater electrode  151  having a first lead  153  and second lead  155  coupled to a power source assembly  150  that is positioned external to the conductive chamber wall  130 . The power source assembly  150  comprises a power source  152  coupled to the first lead  153  of the heater electrode  151 , and a meter  156  coupled between the power source  152  and the second lead  155  of the heater electrode  151 . Furthermore, a controller  154  is coupled between the power source  152  and the meter  156  to control the power source  152  based upon heater electrode condition. Specifically, the resistance of the heater electrode  151 , as a function of temperature, is used to control power applied to the heater electrode.  
         [0022]    It is well known in the art that the resistance of any material with a uniform cross-sectional area is influenced by the kind of material, length, cross-sectional area and temperature of the conductor. The resistivity is a measurement of the characteristic of the material at some specified temperature. Under normal conditions, the resistivity (i.e., of metals) increases linearly with temperature.  
         [0023]    As such, Resistance R (ohms)=r(L/A) where  
         [0024]    r=resistivity of the specific type of conductor,  
         [0025]    L=length of the conductor, and  
         [0026]    A=cross-sectional area.  
         [0027]    [0027]FIGS. 3A and 3B depict graphs of resistivity versus temperature for various metals. Specifically, the graph in FIG. 3A illustrates the change in resistivity for copper and aluminum conductors as a function of temperature. The graph  300  comprises resistivity values on the Y-axis  302  and temperature values on the X-axis  304 . The graph  300  shows that the curves for both copper  310  and aluminum  312  are linear in shape. Likewise, the graph in FIG. 3B illustrates the same linear relationship as between the resistivity and temperature values for the metal Molybdenum  314 . For most metal conductors, resistivity and accordingly, resistance rises with increases in temperature, due to the increased molecular vibrations within the conductor, which hinders the flow of mobile electron charges. Thus, the slope of the curve is positive.  
         [0028]    These aforementioned properties of a conductor are advantageously utilized in the subject invention. The heater electrode  151  is fabricated from a conductive material suitable for use in high temperature (i.e., approximately 350° C.) conditions. Preferably, the electrode  151  is fabricated from Molybdenum. The resistance of the heater electrode  151  is periodically measured, and the current flow through the heater electrode  151  and the substrate support  116  may be adjusted to thereby control the temperature of the conductor. For example, the measured resistivity of Molybdenum is 5.17×10 −8  ohm-meter at 20° C. Alternately, the resistivity of Molybdenum is approximately 7.5×10 −8  ohm-meters at 350° C.  
         [0029]    Referring to FIG. 2, in operation, the power source  152  supplies a steady flow of charge through the heater electrode  151 . The flow of charge thereby causes the temperature of the heater electrode  151  to rise as a result of the increased molecular movement. Coincidental to the heater electrode  151  receiving power, the meter  156  measures the current flow through the heater electrode  151  and generates a corresponding signal. The resulting signal is then sent to the controller  154  for conversion under Ohm&#39;s law to a resistive value, i.e., ohms. It is understood by those skilled in the art that any type of meter  156  may be utilized, such as a voltage meter, ohm meter, or resistivity meter, as long as the measured value may subsequently be converted by the controller  154  to a resistivity measurement, i.e., ohm-meter.  
         [0030]    Once the controller  154  has received or converted the meter&#39;s  156  measured signal in ohms, the controller  154  then converts the resistance value into a temperature value. The conversion is based upon the known length, cross-sectional area and resistivity values of the heater electrode  151 . Such values are constant to the specific design and manufacture of the heater electrode. In particular, a heater electrode fabricated from Molybdenum has a known resistivity value of 5.17×10 −8  ohm-meters. The controller  154  periodically samples the resistance of the heater electrode  151  via the meter  156 . Alternately, the controller  154  may continuously sample the resistance of the heater electrode  151  via the meter  156 . Regardless of the sampling method used, the resistivity versus temperature curve for the heater electrode  151  is known (and provided by the controller  154 ) and the corresponding temperature of the heater electrode  151  is determinable. By sampling the resistance, and knowing the resistivity vs. temperature characteristic of the heater electrode  151 , the temperature of the heater electrode  151  is tracked. Thus, the controller  154  can increase or decrease the temperature of the heater electrode  151  by increasing or decreasing the power provided by the power source  152 . In this manner, the temperature of the heater electrode  151  and consequently, the substrate support may be monitored and controlled.  
         [0031]    Referring to FIG. 1, in operation, the substrate  114  is placed on the substrate support  116  and gaseous components are supplied from a gas panel  138  to the process chamber  110  through entry ports  126 . The plasma is ignited in the process chamber  110  by applying RF power from the RF sources  118  and  122  respectively to the antenna  112  and the substrate support  116 .  
         [0032]    The pressure within the interior of the etch chamber  110  is controlled using a vacuum pump  136  and a throttle valve  127  situated between the chamber  110  and the vacuum pump  136 . The temperature at the surface of the chamber walls  130  is controlled using liquid-containing conduits (not shown) which are located in the walls  130  of the chamber  110 .  
         [0033]    The heater electrode  151  embedded in the substrate support  116  is used to generate heat through the substrate support  116  for temperature control. By using an appropriate heat transfer medium, either heating or cooling of the substrate support  116  can be accomplished. A helium gas flow from source  148  to channels formed by the back of the substrate  114  and grooves (not shown) on the substrate support surface is used to facilitate heat transfer between the substrate  114  and the substrate support  116 . During an etch process, the substrate  114  is gradually heated by the plasma to a steady state temperature of approximately 30-130 degrees C.  
         [0034]    To facilitate control of the chamber  110  as described above, the CPU  144  may be one of any form of general purpose computer processor that can be used in an industrial setting for controlling various chambers and subprocessors. The memory  142  is coupled to the CPU  144 . The memory  142  may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of computer readable media or digital storage, and may be a part of a host computer at some remote location. The support circuits  146  are coupled to the CPU  144  for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. The control software that is used for implementing the etching process of the present invention is generally stored in memory  142  as a software routine. The software may also be stored and/or executed by a CPU that is remotely located from the hardware being controlled by the CPU. When executed by the CPU  144 , the software routine contained in the computer readable memory transforms the general-purpose computer into a specific purpose computer (controller  140 ) that controls the chamber operation such that the etching process and the necessary temperature control is performed.  
         [0035]    [0035]FIG. 4 depicts a flowchart of a method  400  of controlling temperature of a substrate support. It is to be understood that this method  400  can be practiced by hand or as part of the software routine discussed above. Specifically, the method  400  begins at step  401 , and proceeds to step  402  where a meter, such as an amperage, voltage, resistance (ohms), or resistivity meter, measures the respective value across a heater electrode embedded in the substrate support. In step  404 , the measured value, e.g., current flow (amps) is then sent to the controller for conversion to a temperature value. In step  406 , the value measured by the meter is converted into a resistive value in accordance with Ohm&#39;s law. Once the controller has determined a resistive value, the resistivity value for the heater electrode is determined in step  408 . The resistivity value is then stored in the memory (not shown) of the controller, and the method  400  proceeds to step  410 .  
         [0036]    In step  410 , the measured resistivity is compared to the known resistivity value for the heater electrode stored in the memory of the controller. For example, the known resistivity value for a Molybdenum based heater electrode is 5.17×10 −8  ohm-meter at 20° C.  
         [0037]    In step  412 , the determination of the temperature is based upon the linear attributes of the resistivity curve of a metal with respect to temperature. Therefore, since the slope of the curve is constant (see FIG. 3B), the temperature of the heater electrode may be readily calculated based upon the known and measured resistivity values. As such, in step  414 , the temperature as observed from the reading of the meter is stored in the memory (not shown) of the controller. The controller will receive periodic updates of the meter readings for the heater electrode.  
         [0038]    In step  416 , the controller determines whether the temperature is a desired temperature for the heater electrode, and subsequently, the substrate support. If, in step  416 , the temperature is the desired temperature, then the method  400  proceeds to step  418  where the controller maintains the present amount of output power at the power source. If, however, the temperature is not the desired temperature of the heater electrode, then the method  400  proceeds to step  420 . In step  420 , a determination is made by the controller as to whether the temperature of the heating electrode is too high or low. If, in step  420 , the temperature is determined by the controller to be too low, then the method  400  proceeds to step  422 , where the power source output is increased. Conversely, if in step  420 , the determination is made that the temperature is too high, then the method  400  proceeds to step  424 . In step  424 , the power source output is decreased. In this manner, the controller may track the incremental readings of the heater electrode and make the appropriate adjustments to the power source in order to maintain a controlled temperature. Once a decision has been made and executed through any of steps  418 ,  422 , or  424 , the method returns to step  402  to take another measurement. This process continues until the particular wafer process ends and the method  400  ends at step  426 .  
         [0039]    Thus, the method and apparatus of actively-controlling a heater electrode embedded in a substrate support, advantageously allows the greater accuracy in determining the temperature of the substrate as opposed to the use of thermocouples. Furthermore, the apparatus and method inventively provide the ability to self-regulate the temperature by adjusting the power source to the heater electrode. Although several preferred embodiments that incorporate the teachings of the present invention have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.