Abstract:
A plasma processing system includes a process chamber, a source configured to generate a plasma in the process chamber, a platen configured to support a workpiece in the process chamber, and a pressure sensor positioned adjacent to the workpiece. The pressure sensor is configured to monitor a local pressure adjacent to the workpiece. A method includes generating a plasma in a process chamber, supporting a workpiece in the process chamber, and monitoring a local pressure adjacent to the workpiece with a pressure sensor positioned adjacent to the workpiece.

Description:
FIELD  
       [0001]    This disclosure relates to workpiece processing systems, and more particularly to outgassing rate detection in a workpiece processing system. 
       BACKGROUND  
       [0002]    A workpiece processing system may include, but not be limited to, plasma processing systems such as doping, etching, and deposition systems. A workpiece processing system may also include a beam-line doping system such as a beam-line ion implanter. As a workpiece in such systems is treated, outgassing may occur from the workpiece. Such outgassing can lead to unstable and/or non-repeatable conditions. Therefore, it is desirable to sense and control such outgassing. 
         [0003]    For instance, two types of workpiece processing systems include plasma doping and beam-line ion implanters. In a plasma doping ion implanter, a source may generate plasma within a process chamber. A platen is positioned in the process chamber for supporting a workpiece, and ions may be accelerated from the plasma into the wafer. In a beam-line ion implanter, a desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at a front surface of the workpiece. 
         [0004]    In both the plasma doping and beam-line ion implanters, it may be desirable to operate the ion implanter at a relatively high dose rate in order to increase throughput. However, operating at such relatively high dose rates can exacerbate outgassing from the workpiece, e.g., a semiconductor wafer or wafer in one instance. Outgassing from the wafer may occur when ions strike films or layers on the wafer such as a photoresist layer. A photoresist layer is used to mask selected areas of the wafer surface so ions are implanted only in the unmasked areas. During ion implantation, the energetic ions may break up chemical bonds within the photoresist layer. As a result, outgassing byproducts such as volatile organic chemicals and/or other particles may be released. This may be referred to generally in the art as “outgassing,” or “photoresist outgassing” when the outgassing is attributable to the photoresist layer. 
         [0005]    High rates of outgassing from the wafer in ion implanters can lead to unstable and/or non-repeatable implant conditions. High rates of outgassing can also contribute to contamination in ion implanters as the energetic ions collide with the outgassing byproducts. In addition, in plasma doping ion implanters, outgassing byproducts can lead to arcing in the process chamber that can damage the devices being formed on the wafer. Therefore, it is desirable to sense a parameter representative of an outgassing rate. One conventional parameter that may be sensed in plasma doping ion implanters is global pressure in the process chamber sensed by a pressure sensor positioned relatively far away from the wafer. However, this pressure sensor has accuracy and time delay drawbacks. 
         [0006]    Accordingly, there is a need to provide another technique for outgassing rate detection that overcomes the above-described inadequacies and shortcomings. 
       SUMMARY  
       [0007]    According to a first aspect of the disclosure, a workpiece processing system is provided. The workpiece processing system includes a platen configured to support a workpiece, a source configured to provide an electromagnetic wave proximate a front surface of the workpiece, and a detector configured to receive at least a portion of the electromagnetic wave and provide a detection signal representative of an outgassing rate from the workpiece of outgassing byproducts. 
         [0008]    According to another aspect of the disclosure, a method of detecting outgassing is provided. The method includes providing an electromagnetic wave proximate a front surface of a workpiece, receiving at least a portion of the electromagnetic wave, and providing a detection signal representative of an outgassing rate from the workpiece of outgassing byproducts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are referenced with like numerals, and in which: 
           [0010]      FIG. 1  is a block diagram of a workpiece processing system consistent with the disclosure; 
           [0011]      FIG. 2  is a block diagram of one embodiment of a plasma doping ion implanter having a light source and light detector positioned within a process chamber; 
           [0012]      FIG. 3  is a block diagram of another embodiment of a plasma doping ion implanter having a light source and light detector positioned external to the process chamber; 
           [0013]      FIG. 4  is a plan view of a semiconductor wafer that may be treated in the systems of  FIGS. 1-3 ; 
           [0014]      FIG. 5  is a cross sectional view of the semiconductor wafer of  FIG. 4 ; and 
           [0015]      FIG. 6  illustrates plots of a detection signal versus time and an outgassing rate and dose rate over a similar time period. 
       
    
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  is a block diagram of a workpiece processing system  100  consistent with an embodiment of the disclosure. The workpiece processing system  100  may include, but not be limited to, doping systems, etching systems, and deposition systems. Doping systems may include a plasma doping ion implanter or a beam-line ion implanter. The workpiece processing system  100  includes a platen  114  to support a workpiece  120 . The workpiece processing system  100  also includes a source  160 , a detector  162 , a controller  146 , a user interface system  148 , and rate components  151 . The source  160  is configured to provide an electromagnetic wave  165  proximate a front surface  122  of the workpiece  120 . The source  160  may be a light source to emit a light wave or a microwave source to emit a microwave. The light source may be a laser, a light-emitting diode, or other light source known in the art. The light wave may have a frequency in the ultraviolet spectrum, the visible spectrum, and the infrared spectrum. The light source may provide a pulsed or continuous light wave. The microwave may have a frequency in the microwave spectrum. The detector  160  receives at least a portion of the electromagnetic wave  165  depending on the outgassing rate of outgassing byproducts  190  from the workpiece  120 . The source  160  may be positioned at one end of the workpiece  120 , while the detector  162  may be positioned on an opposing end of the workpiece  120 . The detector may be a light detector or a microwave detector. The light detector may by a photodiode, a photoresistor, or other light detector known in the art. The light detector may also include a collimator to redirect received light waves to the same area of the light detector. 
         [0017]    The controller  146  can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller  146  can also include other electronic circuitry or components, such as application specific integrated circuits, other hardwired or programmable electronic devices, discrete element circuits, etc. The controller  146  may also include communication devices, data storage devices, and software. The user interface system  148  may include, but not be limited to, devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the workpiece processing system  100  via the controller  146 . 
         [0018]    The rate components  151  can include differing components known in the art to control a rate of particles  141  directed to the workpiece  120 . When the workpiece processing system  100  is an ion implanter, the rate components  151  can include dose rate components to control the rate of ions directed to the workpiece  120 . For a beam-line ion implanter, the dose rate components may include an ion source, focusing elements such as lenses, a mass resolving slit, a scanner, and/or other beam line components known in the art. The dose rate components in a beam-line ion implanter may change the quantity of ions/second generated and/or reduce a cross sectional size of the ion beam having the same number of ions/second generated since dose rate may be given by ions/second/cm 2 . For plasma doping ion implanters, the dose rate components may include a source to change the plasma density, a biasing source to change the rate at which ions are accelerated from the plasma towards the wafer, and/or other components known to those skilled in the art. 
         [0019]    In operation, the workpiece processing system  100  may direct particles  141  towards the workpiece  120 . The particles  141  may break up chemical bonds within a layer, e.g., a photoresist layer  121 , of the workpiece  120 . As a result, outgassing byproducts  190  such as volatile organic chemicals and/or other particles may be released from the workpiece  120 . The outgassing byproducts  190  may include photoresist outgassing byproducts released from the photoresist layer  121 . The photoresist byproducts may include, but not be limited to, carbon compounds, water vapor, hydrogen, and nitrogen. 
         [0020]    The electromagnetic wave  165  may be partially deflected and/or absorbed by the released outgassing byproducts  190 . The amount of the electromagnetic wave deflected and/or absorbed depends on the outgassing rate of the outgassing byproducts  190 . Therefore, the intensity of the received electromagnetic wave by the detector  162  may be reduced compared to a nominal intensity in the presence of no outgassing. The controller  146  may determine the amount of reduction and correlate the same to an outgassing rate. 
         [0021]    The source  160 , the detector  162 , and the frequency of the electromagnetic wave  165  may be selected to maximize deflection and/or absorption by the expected outgassing byproducts  190 . In one embodiment, the expected outgassing byproducts  190  may include carbon compounds such as CH 4 . In this instance, the source  160  may be a light source and the electromagnetic wave  165  may be a light wave having a frequency in the infrared frequency spectrum. The detector  162  may be a light detector and the detection signal is representative of an outgassing rate of the carbon compounds. In one specific example, the wavelength of the light wave was selected at 3.392 microns to detect CH 4 . 
         [0022]    In another embodiment, the expected outgassing byproducts  190  may include water vapor. In this instance, the source  160  may be a microwave source and the electromagnetic wave  165  may be a microwave. The detector  162  may be a microwave detector and the detection signal is representative of an outgassing rate of the water vapor. In one specific example, the wavelength of the microwave was selected at 12 centimeters (2.45 GHz frequency) to detect water vapor. 
         [0023]    In yet another embodiment, the expected outgassing byproducts  190  may include hydrogen. In this instance, the source  160  may be a light source and the electromagnetic wave  165  may be a light wave having a frequency in the ultraviolet frequency spectrum. The detector  162  may be a light detector and the detection signal is representative of an outgassing rate of the hydrogen. In one specific example, the wavelength of the light wave was selected at 1216 angstroms to detect hydrogen atoms. 
         [0024]    The frequency range of the electromagnetic  165  wave may be selected to maximize deflection and/or absorption by the expected outgassing byproducts  190 . The detector  162  may therefore sense a decrease in the intensity of the received electromagnetic wave depending on the outgassing rate of the outgassing byproducts  190  and provide a detection signal to the controller  146 . The controller  146  may adjust the rate of the particles  141  in response to the detection signal. For example, in an ion implanter the controller  146  may lower a dose rate of ions directed towards the workpiece  120  in response to an excessive outgassing rate and increase the dose rate to a maximum level in response to a modest outgassing rate. 
         [0025]      FIG. 2  is a block diagram of one embodiment of a plasma doping ion implanter  200  consistent with the workpiece processing system  100  of  FIG. 1  where the source  160  is a light source  260 , the detector  162  is a light detector  262  and the electromagnetic wave  165  is a light wave  265 . The plasma doping ion implanter  200  may include a process chamber  210  defining an enclosed volume  212 . In this embodiment, the light source  260  and light detector  262  may be positioned within the process chamber  210 . The platen  114  may be positioned within the process chamber  210  to provide a holding surface for holding the workpiece  120 . In one instance, the workpiece  120  may be a semiconductor wafer having a disk shape. The workpiece  120  may, for example, be clamped to a flat surface of the platen  114  by electrostatic or mechanical forces. In one embodiment, the platen  114  may include conductive pins (not shown) for connection to the workpiece  120 . 
         [0026]    There are differing methods to generate a plasma  240  within the process chamber  210 . In one embodiment, a source  230  may cooperate with the anode  224  to generate the plasma  240 . The source  230  may be a high voltage power source to provide high voltage pulses to the anode  224 . In other embodiments, the source  230  may be a RF source such as an RF power supply to supply RF power to one or more antennas (not illustrated) to generate the plasma  240  in the process chamber  210 . Other sources and configurations for generating the plasma  240  in the process chamber  210  will be known to those skilled in the art. The plasma  240  may include a plasma sheath  242  in the region between the plasma  240  and the workpiece  120 . 
         [0027]    The plasma doping ion implanter  200  may also include a bias source  272  electrically coupled to the platen  114  to bias the platen  114  to accelerate ions from the plasma  240  into the workpiece  120 . The bias source  272  may be a DC pulsed power supply, an RF power supply, or other power supply known by those skilled in the art. When the bias source  272  is a DC pulsed power supply, the duty factor may be selected to provide a desired dose rate. A negative voltage pulse would accelerate positive ions from the plasma  240  towards the wafer  120 . The enclosed volume  212  of the process chamber  210  may be coupled thought a controllable valve  232  to a vacuum pump  234 . A gas source  236  may be coupled through a mass flow controller  238  to the chamber  210 . 
         [0028]    A shield ring  266  may be disposed around the platen  114 . As is known in the art, the shield ring  266  may be biased to improve the uniformity of implanted ion distribution near the edge of the workpiece  120 . Faraday sensors such as Faraday cups  250 ,  252  may also be positioned in an associated recess of the shield ring  266 . The Faraday sensors monitor ion current and may input a signal to the controller  146  representative of the dose rate. The controller  146  may process a signal from the Faraday sensors  250 ,  252  as well as the light detection signal from the light detector  262  to determine ion dose. For clarity of illustration, the controller  146  is illustrated as providing only an output signal to the bias source  172 . Those skilled in the art will recognize that the controller  146  may provide output signals to other components of the plasma doping ion implanter  200  and receive input signals from the same. 
         [0029]    In operation, the gas source  236  supplies an ionizable gas containing a desired dopant for implantation into the workpiece  120 . Examples of ionizable gas include, but are not limited to, BF 3 , N 2 , Ar, PH 3 , AsH 3 , B 2 H 6 , H 2 , Xe, SIH 4 , SIF 4 , GeH 4 , GeF 4 , CH 4 , CF 4 , AsF 5 , PF 3 , and PF 5 . The mass flow controller  238  regulates the rate at which gas is supplied to the process chamber  210 . The source  230  may generate the plasma  240  within the process chamber  210 , and the bias source  272  may bias the platen  114  to accelerate ions from the plasma  240  into the workpiece  120 . The energetic ions may cause outgassing byproducts  190  to be released from the wafer. The outgassing byproducts may include, but not be limited to, carbon compounds, water vapor, hydrogen, and nitrogen. The released outgassing byproducts  190  may absorb and/or deflect at least a portion of the light wave  265  provided by the light source  260 . The light source  260  may provide a pulsed or continuous light wave  265 . A pulsed light wave permits discrimination versus plasma generated light. The pulsed light wave may be pulsed synchronously with the bias signal provided by the bias source  272  or at higher sampling multiples. The pulsed light wave may therefore improve the signal to noise ratio of the portion of the received light wave. 
         [0030]    Regardless of whether the light source  260  provides a pulsed or continuous light wave  265 , the light detector  262  may sense a decrease in the intensity of the received light wave  265  depending on the outgassing rate of the outgassing byproducts  190  and provide a detection signal to the controller  146  representative of the same. The controller  146  may compare the actual intensity of the received light signal with a desired or nominal intensity and control the dose rate of the implanter  200  in response thereto. The controller  146  may control the dose rate in one embodiment by controlling the duty factor of a pulsed DC voltage signal provided to the platen  114 , e.g., by the bias source  272 . 
         [0031]      FIG. 3  is a block diagram of another embodiment of a plasma doping ion implanter  300  illustrating the light source  260  and light detector  262  positioned external to the process chamber  210 . Selected components of the implanter  300  similar to  FIG. 2  have been omitted from the drawing for clarity. A first window  302  is positioned relative to the light source to allow the light wave  265  from the light source to pass. A second window  304  is positioned relative to the light detector  262  to allow the light wave  265 , or a portion thereof depending on the amount of light absorbed and/or deflected by the outgassing byproducts  190 , to pass. The windows  302 ,  304  may be fabricated of quartz, glass, or some other transparent material known in the art. Positioning the light source  260  and light detector  262  external to the process chamber  210  protects them from adverse conditions within the interior volume  212  defined by the process chamber  210 . 
         [0032]    It is possible that over time the first and second windows  302 ,  304  may become partially opaque due to particle deposits forming thereon. This may reduce transmission of an electromagnetic wave such as a light wave. Such window coating may be compensated for by normalizing the light level received prior to processing the workpiece. For example, the light source  260  may provide a light wave prior to processing and the light detector  262  may quantify the intensity of the received light wave given the current conditions of the windows  302 ,  304 . The ratio of the received signal just prior to processing with the received signal during processing can be utilized to compensate for deposits on the windows  302 ,  304 . 
         [0033]    Although  FIGS. 2 and 3  illustrate, among other things, the light source  260  and light detector  262  positions relative to the process chamber  210  of plasma doping ion implanters, the light source  260  and light detector  262  could also be similarly positioned relative to another chamber such as an end station chamber of a different plasma processing chamber or a beam-line ion implanter. 
         [0034]      FIG. 4  is a plan view of a semiconductor wafer  420  having a disk shape and a diameter D 1 .  FIG. 5  is a cross sectional view of the semiconductor wafer of  FIG. 4 . The semiconductor wafer  420  may have a front surface  422  defining a plane  502 . The light wave  265  from the light source may be generally directed along a path  504  parallel to the plane  502 . The path  504  may be a distance (x) from the plane  502 . In one embodiment, the distance x may be less than or equal to 10% of the diameter D 1  of the wafer  420 . In this way, the light beam  265  is positioned on a path proximate the front surface  422  of the semiconductor wafer  420  to intercept outgassing byproducts  190  released from the same. For example, with a  300  mm diameter semiconductor wafer, the light beam  265  may be positioned a distance (x) from the semiconductor wafer of less than or equal to  30  mm. This positioning also enables the light wave to pass through the plasma sheath  242  in a plasma doping ion implanter. 
         [0035]      FIG. 6  illustrates a plot  602  of a detection signal that may be provided by the detector  162  over particular time period. A plot  604  of an outgassing rate of the outgassing byproducts  190  and a plot  606  of dose rate for an ion implanter over the same time period are also illustrated. In one embodiment, the detection signal may be a voltage signal. The voltage signal may have a maximum voltage level (V 2 ) indicating that substantially no portion of the electromagnetic wave  165  is absorbed and/or deflected by any outgassing byproducts  190  between times t 0  and t 1 . Hence the corresponding outgassing rate is effectively zero over the same time period and the dose rate may be at a maximum dose rate (dr 2 ). 
         [0036]    As illustrated by plot  602 , the detection signal may be at a desired voltage level (V 2 ) and then decrease until it reaches a threshold level (V 1 ) at time t 2 . As illustrated by plot  604 , the decrease in the detection signal is representative an increase in the outgassing rate from the wafer  120  over the same time period. The threshold voltage level (V 1 ) may be selected to be associated with a high outgassing rate (og 2 ). In response, the controller  146  may control the dose rate of an implanter by reducing the dose rate from an initial maximum dose rate (dr 2 ) to a comparatively lower dose rate (dr 1 ) at time t 2 . In one embodiment, the controller  146  may control the dose rate by controlling the duty factor of a pulsed DC voltage signal provided to the platen  114 , e.g., by the bias source  272 . In one example, the duty factor may be lowered by about 20% to 30% from its initial value at the maximum dose rate (dr 2 ). The controller  146  may then maintain the dose rate at the lower dose rate (dr 1 ) for a particular delay period or until time t 3  to give the outgassing time to dissipate relative to the high outgassing rate (og 2 ). The controller  146  may then start to ramp up the dose rate back to its maximum value (dr 2 ) at time t 4 . 
         [0037]    Advantageously, the detector  162  receives at least a portion of the electromagnetic wave  164  that is representative of an outgassing rate of the outgassing byproducts  190 . In an ion implanter, the dose rate can then be modulated in response to the outgassing rate. This enables improvements in throughput as the dose rate can be maximized as long as the detection signal is indicative of a relatively lower outgassing rate. In addition, the dose rate can be lowered if the detection signal is indicative of a relatively higher outgassing rate to control problems such as contamination and dose repeatability issues. Lowering the dose rate in a plasma doping implanter can also control arcing problems. 
         [0038]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.