Abstract:
A method comprising processing a substrate exposed to a plasma in a processing chamber, obtaining a metric indicative of a parameter of the plasma during the processing of the substrate, and determining a defect in the substrate by comparing the metric to a predefined criteria.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to a method and system for detecting substrate defects during processing. More specifically, a method and system for detection of substrate breakage by tracking process parameters. 
         [0003]    2. Description of the Related Art 
         [0004]    Substrate processing systems are used to process substrates, such as silicon wafers in the production of integrated circuit devices as well as large area substrates in the manufacture of flat panel displays, solar collection devices, among other electronic devices. Particularly in the production of flat panel displays, manufacturers face new challenges due to shrinking pixel size, fast refresh rate and reduced substrate thickness. These challenges require manufacturers to improve defect control, film properties and thickness. 
         [0005]    Typically, robots are disposed in the substrate processing system to transfer the substrates through a plurality of process chambers for conducting a sequence of processing steps of the fabrication process. The use of robots in the processing of substrates is essential to processing a large number of substrates through many different types of processing technologies with minimal contamination (e.g., substrate handling contamination). To be profitable, these systems feature high processing and transfer speed, and greater accuracy to minimize defects to provide a high throughput system. 
         [0006]    One of the key issues facing manufacturers includes glass breakage. A glass breakage incident brings the tool to a costly unscheduled shut down that typically takes 12-18 hrs to correct and may require wet cleaning of the process or transfer chambers. In certain cases, the initial incident contaminates panels processed subsequent to the incident, resulting in defects in the processed panels, and may include scrapping the defective panels. Thus, glass breakage typically results in tool downtime, loss of production, and ultimately the loss of profits for the manufacturer. 
         [0007]    What is needed is a method for detecting defects in substrates during processing to minimize defective substrates that would otherwise require scrapping. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the invention generally provide a method for determining defects and/or imperfections in substrates during processing by tracking or monitoring processing parameters during processing. 
         [0009]    In one embodiment, a method is provided. The method includes processing a substrate exposed to a plasma in a processing chamber, obtaining a metric indicative of a parameter of the plasma during the processing of the substrate, and determining a defect in the substrate by comparing the metric to a predefined criteria. 
         [0010]    In another embodiment, a method is provided. The method includes processing a substrate exposed to a plasma in a processing chamber, obtaining a metric indicative of a parameter of the plasma during the processing of the substrate, ceasing the processing when the parameter of the plasma is outside of a predetermined limit indicating a defective substrate, and removing the defective substrate from the processing system. 
         [0011]    In another embodiment, a method is provided. The method includes transferring n substrates into one or more chambers in a processing system, plasma processing each of the n substrates sequentially, monitoring parameters of the plasma during plasma processing of the n substrates, ceasing plasma processing when the parameters of one of the n substrates are outside of a predetermined limit indicating a defective substrate, and removing the defective substrate from the processing system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is a top plan view of a multi-chamber substrate processing system. 
           [0014]      FIG. 2  is a schematic cross-sectional view of one embodiment of a processing chamber that may be part of the substrate processing system of  FIG. 1 . 
           [0015]      FIG. 3A  is a graph comparing a typical Vdc trace with an abnormal Vdc trace during a deposition process. 
           [0016]      FIG. 3B  is a graph showing deposition runs on four substrates. 
           [0017]      FIG. 4  is a graph showing deposition runs on multiple substrates. 
           [0018]      FIG. 5  is another graph showing deposition runs on multiple substrates. 
       
    
    
       [0019]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0020]    Embodiments described herein provide a method for determining defects and/or imperfections in substrates during processing by tracking or monitoring processing parameters during processing. Embodiments of the invention are exemplarily described in a processing system available from Applied Materials, Inc., of Santa Clara, Calif., but some embodiments may be successfully practiced in systems available from other manufacturers. 
         [0021]      FIG. 1  is a top plan view of a multi-chamber substrate processing system  100  suitable for the fabrication of structures and devices on a large area substrate for use in the fabrication of liquid crystal displays (LCD&#39;s), flat panel displays, organic light emitting diodes (OLED&#39;s), or photovoltaic cells for solar cell arrays, on flat media. The processing system  100  includes a plurality of processing chambers  105  and one or more load lock chambers  110  positioned around a central transfer chamber  115 . The processing chambers  105  may be configured to complete a number of different processing steps to achieve a desired processing of flat media, such as a large area substrate  120  (outlined in dashed lines). The processing chambers  105  may be of any type for performing a plasma process, such as a plasma enhanced chemical vapor deposition (PECVD) chamber, a sputtering chamber, or plasma etching chamber. 
         [0022]    Positioned within the transfer chamber  115  is a transfer robot  125  having an end effector  130 . The end effector  130  is configured to be supported and move independently of the transfer robot  125  to transfer the substrate  120 . The end effector  130  includes a wrist  135  and a plurality of fingers  138  adapted to support the substrate  120 . In one embodiment, the transfer robot  125  is configured to be rotated about a vertical axis and/or linearly driven in a vertical direction (Z direction) while the end effector  130  is configured to move linearly in a horizontal direction (X and/or Y direction) independent of and relative to the transfer robot  125 . For example, the transfer robot  125  raises and lowers the end effector  130  (Z direction) to various elevations within the transfer chamber  115  to align the end effector  130  with openings  140  (one is shown in  FIG. 1 ) in the processing chambers  105  and the load lock chambers  110 . When the transfer robot  125  is at a suitable elevation, the end effector  130  is extended horizontally (X or Y direction) to transfer and/or position the substrate  120  into and out of the openings  140  in any one of the processing chambers  105  and the load lock chambers  110 . Additionally, the transfer robot  125  may be rotated to align the end effector  130  with other processing chambers  105  and the load lock chambers  110 . A controller  145  may be coupled to the processing system  100  to control and/or monitor processing parameters within the processing system  100 . 
         [0023]    The trend towards increasingly larger substrates and smaller device features requires increasingly precise positional accuracy of the substrate in the various process chambers  105  in order to ensure repetitive device fabrication with low defect rates. Increasing the positional accuracy of substrates throughout the processing system  100  is a constant challenge. In one example, flat-panel display substrates (e.g., glass substrates) are transferred on the end effector  130  (e.g., a blade or fingers) of the transfer robot  125  to and from the various chambers  105  of the processing system  100 . During this transfer it is difficult to ensure that flat-panel display substrates align properly with the end effector  130 , and once aligned, that the substrate can pass through the openings  140  in the load lock chambers  110  or the processing chambers  105  without collisions due to a shift in alignment (i.e., misalignment) during transfer. A collision may not only chip or crack the flat-panel display substrate, but also create and deposit debris in the load lock chamber  110 , the transfer chamber  115 , or the processing chambers  105 . Such debris may cause processing defects or other damage to the substrate from which the debris originated as well as subsequently processed substrates. Thus, the presence of debris often requires shutting down the processing system  100 , or a portion thereof, to thoroughly remove the potentially contaminating debris. Moreover, with larger dimension substrates and increased device density, the value of each substrate has greatly increased. Accordingly, damage to the substrate or yield loss because of substrate misalignment is highly undesirable due to consequential increase in cost and reduction in throughput. 
         [0024]    Embodiments of the processing system  100  described herein alleviate the challenge in identifying glass breakage or debris from glass breakage in the processing system  100 . Embodiments of a defect detection method will be explained in conjunction with an exemplary processing chamber  105  and its operation. 
         [0025]      FIG. 2  is a schematic cross-sectional view of one embodiment of a processing chamber  105  that may be part of the substrate processing system  100  of  FIG. 1 . The processing chamber  105  is configured to process the large area substrate  120  using plasma in forming structures and devices. The substrate  120  may be thin sheet of metal, plastic, organic material, silicon, glass, quartz, or polymer, among other suitable materials. The substrate  120  may have a surface area greater than about 1 square meter, such as greater than about 2 square meters. In other embodiments, the substrate  120  may include a plan surface area of about 15,600 cm 2 , or greater, for example about a 90,000 cm 2  plan surface area (or greater). The structures may be thin film transistors which may comprise a plurality of sequential deposition and masking steps. Other structures may include p-n junctions to form diodes for photovoltaic cells. 
         [0026]    As shown in  FIG. 2 , the processing chamber  105  generally comprises a chamber body  200  including a lid  202 , a bottom  205   a  and sidewalls  205   b  that at least partially defines a processing volume  210 . A substrate support  215  is disposed in the processing volume  210 . The substrate support  215  is adapted to support the substrate  120  on a top surface during processing. The substrate support  215  is coupled to an actuator  216  adapted to move the substrate support at least vertically to facilitate transfer of the substrate  120  and/or adjust a distance D between the substrate  120  and a showerhead assembly  220 . One or more lift pins  218   a - 218   b  may extend through the substrate support  215 . The lift pins  218   a - 218   b  are adapted to contact the bottom  205   a  of the chamber body  200  and support the substrate  120  when the substrate support  215  is lowered by the actuator  216  in order to facilitate transfer of the substrate  120  where the substrate support  215  is lowered allowing the lift pins  218   a - 218   d  to contact and support the lower surface of the substrate  120 . In a processing position as shown in  FIG. 2 , the lift pins  218   a - 218   b  are adapted to be flush with or slightly below the upper surface of the substrate support  215  to allow the substrate  120  to lie flat on the substrate support  215 . 
         [0027]    The showerhead assembly  220  is configured to supply a processing gas to the processing volume  210  from a processing gas source  222 . The processing chamber  105  also comprises an exhaust system  224  configured to apply negative pressure to the processing volume  210 . The showerhead assembly  220  is generally disposed opposing the substrate support  215  in a substantially parallel relationship. 
         [0028]    In one embodiment, the showerhead assembly  220  comprises a gas distribution plate  226  and a backing plate  228 . The backing plate  228  may function as a blocker plate to enable formation of a gas volume between the gas distribution plate  226  and the backing plate  228 . The gas source  222  is connected to the gas distribution plate  226  by a conduit  230 . 
         [0029]    The gas distribution plate  226 , the backing plate  228 , and the conduit  230  are generally formed from electrically conductive materials and are in electrical communication with one another. The chamber body  200  is also formed from an electrically conductive material. The chamber body  200  is generally electrically insulated from the showerhead assembly  220 . In one embodiment, the showerhead assembly  220  is mounted on the chamber body  200  by an insulator  232 . 
         [0030]    In one embodiment, the substrate support  215  is also electrically conductive, and the substrate support  215  and the showerhead assembly  220  are configured to be opposing electrodes for generating a plasma  234  of processing gases therebetween during processing of the substrate  120 . The controller  145  may be used to monitor the state of the plasma  234  during processing, in one embodiment. 
         [0031]    A radio frequency (RF) power source  236  is generally used to generate the plasma  234  between the showerhead assembly  220  and the substrate support  215  before, during and after processing. In one embodiment, the RF power source  236  is coupled to the showerhead assembly  220  by a first output  238   a  of an impedance matching circuit  239 . A second output  238   b  of the impedance matching circuit  239  is electrically connected to the chamber body  200 . 
         [0032]    In one embodiment, the processing chamber  105  includes a plurality of RF return devices  240 . Each of the RF return devices  240  are coupled between the substrate support  215  and a grounded component of the chamber body  200 . Each of the RF return devices  240  may be selectively activated to be open or closed to electrical current. Each of the plurality of RF devices  240  may be spring forms, straps, wires, or cables adapted to provide a RF conductive medium between the substrate support  215  and a grounded component of the chamber body  200  (i.e., a component of the chamber body  200  that is in electrical communication with the RF power source  236 ). 
         [0033]    During processing, one or more processing gas is flowed to the processing volume  210  from the gas source  222  through the showerhead assembly  220 . A RF power is applied between the showerhead assembly  220  and the substrate support  215  to generate a plasma  234  from the processing gases for processing the substrate  120 . 
         [0034]    One embodiment of an RF current path is schematically illustrated by arrows in  FIG. 2 . The RF current path may be indicative of RF current flow during processing of the substrate  120 . The RF current generally travels from a first lead  242   a  of the RF power source  236  to the first output  238   a  of the impedance matching circuit  239 , then travels along an outer surface of the conduit  230  to a back surface of the backing plate  228 , then to a front surface of the gas distribution plate  226 . From the front surface of the gas distribution plate  226 , the RF current goes through plasma  234  and reaches a top surface of the substrate  120  or the substrate support  215 , then through one or more of the plurality of RF return devices  240  to an inner surface  244  of the chamber body  200 . From the inner surface  244 , the RF current returns to a second lead  242   b  of the RF power source  236  from the impedance matching circuit  239 . 
         [0035]    The controller  145  may be coupled to the processing chamber  105  to monitor conditions of the RF power and/or the plasma  234  within the processing chamber  105 . The controller  145  may include a central processing unit (CPU), a memory, and support circuits for the CPU that is coupled to the various components of the processing chamber  105  to facilitate control and monitoring of the processes performed therein. The controller  145  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, or computer-readable medium, 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 digital storage, local or remote that is in communication with the CPU. The support circuits are in communication with the CPU for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. Processing recipes and transfer routines as well as metrics indicative of the plasma parameters, such as described herein, is generally stored in the memory as a software routine. The software routine may also be stored and/or executed by a second CPU that is remotely located from the hardware being controlled by the CPU. 
         [0036]    In one embodiment, the controller  145  monitors RF related data, such as RF reflected power, direct current voltage (Vdc), voltage peak-to-peak (Vpp), RF current, and other properties of the applied RF power during processing of the substrate  120 . The controller  145  may be a database with configurable software modules having sensors that monitor the RF input and/or output to track RF parameters within the processing chamber  105 . In one embodiment, the controller  145  may be an automation and equipment engineering system (EES) platform sold by Applied Materials, Inc. as the Applied E3 module, although controllers from other manufacturers could be used. 
         [0037]    In one embodiment, the controller  145  uses historical RF data (obtained using a manufacturers particular recipe) as a baseline and limits are established such that RF parameters outside of those limits represents breakage and/or contamination due to a previous breakage event. The controller  145  provides the ability to monitor RF related data items such as RF reflected power, Vdc, or Vpp, along with any desired chamber parameter. In one aspect, the changes in RF parameters may be changes in local impedance on each substrate that is recognized by the controller  145 . The data collected and/or monitored by the controller  145  may be provided by the impedance matching circuit  239 . Using data mining and comparing the signature (i.e., trace(s)) of broken glass to that of intact glass for the whole recipe (one example of which is shown in  FIG. 3A ), the RF signals are reliable indicators to determine when glass has broken and/or other defects are present. For example, if a previous breakage event contaminates subsequent substrates, a defect in the subsequent substrates may appear. The defects include a short-circuit, arcing, as well as local non-uniformity in the films deposited on the substrates. The defects may affect the final product such that any displays formed thereon will not operate properly. 
         [0038]    The following figures are graphical representations of testing results of the defect detection method as described herein. 
         [0039]      FIG. 3A  is a graph  300  comparing a typical Vdc trace  305  with an abnormal Vdc trace  310  during a deposition process. The ordinate represents voltage and the abscissa represents time (in seconds). The typical Vdc trace  305  represents an undamaged or defect-free substrate (indicated by the “Vdc intact 1” and “Vdc intact 2” traces in this graph) while the abnormal Vdc trace  310  represents a defective substrate (indicated by the “Vdc broken” trace). As shown, a Vdc shift occurs when deposition is performed on the defective substrate indicated by the abnormal Vdc trace  310 . A large shift in Vdc may be indicative of a large defect (e.g., a non-uniformity, a crack or chip) while a relatively small shift may be indicative of a smaller defect. 
         [0040]      FIG. 3B  is a graph  315  showing deposition runs on four substrates represented by traces  320 A- 320 D. The ordinate represents voltage and the abscissa represents time (in seconds). Each of the traces  320 A- 320 C indicates a defect-free substrate based on Vdc parameters (e.g., typical Vdc trace  305 ). However, trace  320 D indicates a defective substrate (e.g., abnormal Vdc trace  310 ), which is representative of a glass breakage event in the processing system. 
         [0041]      FIG. 4  is a graph  400  showing multiple deposition runs over many days. Each data point represents a substrate that has been plasma processed in a processing system such as the processing chamber  105  of  FIG. 2 . Each data point is referred to as a substrate  402   n , wherein n represents an integer greater than zero. Regions  405  and  410  are shaded and each region  405  and  410  represent hundreds of substrates  402   n  produced over multiple days (the data points are very close to each other and are difficult to show individually given the scale of the graph  400 ). 
         [0042]    According to the defect detection method as described herein, lines  415 A and  415 B indicate soft limits for a specific recipe. As shown in the graph  400 , a substrate  402   n ′ is outside of the limit indicated by line  415 A and indicates a glass breakage event. When the limit is exceeded, such the excess shown with respect to the substrate  402   n ′, an alert may be provided to personnel to shut down the processing system  100 . Region  420  indicates a time period where the substrate  402   n ′ is removed, and the processing system  100  is inspected and cleaned to remove remnants of the substrate  402   n ′. The substrate  402   n ′ may be removed through the transfer chamber  115  (shown in  FIG. 1 ) or removed directly from the processing chamber  105  (shown in  FIG. 2 ) such as through the lid  202  (shown in  FIG. 2 ). 
         [0043]    Following the inspection and cleaning of the processing system  100 , substrates  402   n ″ may be plasma processed for qualification. A region  425  indicating a time period for metrology of the substrates  402   n ″ may follow the qualification run and the plasma processing resumes at region  410 . Region  430  indicates a time period for preventative maintenance (PM) of the processing system  100  and plasma processing of the substrates  402   n  resumes after the PM. 
         [0044]      FIG. 5  is a graph  500  showing multiple deposition runs over many days. The ordinate represents voltage and the abscissa represents time (in days). Each data point represents a substrate that has been plasma processed in a processing system such as the processing system  100  of  FIG. 1 . Each data point is referred to as a substrate  502   n  wherein n represents an integer greater than zero, a substrate  504 , a substrate  512 . Region  505  indicates a time period for PM of the processing system  100  after which substrates  504  are plasma processed for qualification. After a time period  510  for metrology of the substrates  504 , processing of substrates  502   n  resumes. 
         [0045]    The data point indicated by substrate  512  indicates a breakage event. The breakage event according to the graph  500  may be a minor glass break, such as about 5% or less of the surface area of the substrate, as compared to the breakage event shown in the graph  400  of  FIG. 4 . It has been found that a large shift in the plasma parameters corresponds with a large break, and vice versa. After the breakage event, plasma processing parameters decline in subsequent substrates, and as such, quality of the final product declines. The substrates  502   n  represented by data points within the lines  415 A and  415 B may be deemed as acceptable; however, lines  515 A and  515 B indicate hard limits where the system should be shut down. For example, substrates between the lines  415 B and  515 B were tested and passed quality control, but substrates below line  515 B were unacceptable and included defects (e.g., the “mura effect”) and were scrapped. 
         [0046]    The breakage event shown in  FIG. 5  may be a case where glass pieces (small glass shards) were left in the processing chamber after processing the substrate  512 , and the product quality suffered. The subsequent decline in the plasma parameters of the substrates processed subsequent to the substrate  512  indicates defects in the films deposited thereon and final testing indicated evidence of the mura effect. In this situation, the fabrication facility could have saved about 120 substrates from scrap if the defect detection method would have been used. For example, the system could have been stopped at substrate  525  and removed from the system, thus saving subsequent substrates from scrap. 
         [0047]    Embodiments of the invention provide detection of glass breakage in a processing chamber  105  during deposition by tracking RF process parameters. A controller  145  is utilized to collect chamber data and analyze RF signals for abnormal behavior that deviates from the normal trends according to a specific product recipe. 
         [0048]    According to one embodiment, a plasma environment is initiated and maintained in the processing chamber  105 . The glass substrate acts as a dielectric and the paths of the ions and the electrons are determined in the chamber for a specific RF power delivery, and these paths through the chamber define the chamber impedance. If a defect appears on the glass substrate, then new paths are formed (a number of them reaching the susceptor directly without going through the glass substrate). The subsequent paths lead to a modified chamber impedance and this impedance difference is tracked to identify if the glass substrate is intact or broken. The controller  145  (shown in  FIG. 2 ) may be provided with a data mining algorithm to track the evolution of RF parameters and thus the impedance during deposition in the processing chamber  105  through a time window. 
         [0049]    The deposition and all power lift steps are monitored, and the algorithm utilizes historical data for the same deposition recipe for the given chamber and compares the data to a time weighted average. Limits are then determined based on a review of the historical data, which allows for soft limits that depend on the chamber conditions. When limits are exceeded, an alarm, audible, visual and/or electronic (i.e., e-mail) can be provided to the technicians to alert that there is a problem with the chamber. 
         [0050]    The time weighted average of the algorithm serves a dual purpose. The average effectively filters fluctuations that arise from the RF parameter measurements and provides a smooth reading throughout each deposition run. The average also takes into account the chamber condition or “aging” between PM intervals. 
         [0051]    The invention uses a relatively inexpensive and non-intrusive method of tracking RF parameter changes in the processing chamber  105  to detect glass breakage in PECVD chambers. 
         [0052]    Embodiments of the invention provide a way to minimize the effect of RF parameter measurement fluctuations in the detection of the glass breakage during a deposition recipe run. Embodiments of the invention provide a notification to the relevant parties that glass breakage has occurred in a processing chamber. Early notification is provided to minimize the tool downtime. Broken glass is contained to the processing chamber where the deviation in RF parameters occurs and other chambers, such as the transfer chamber, is not contaminated. This saves considerable time as only one processing chamber will need to be cleaned (as opposed to the whole tool being down for unscheduled maintenance). 
         [0053]    By detecting a deviation from the normal (historical) RF parameter values that may be used as a predefined criteria to establish predetermined limits, embodiments of the invention can also detect if small glass pieces have been left in the processing chamber  105  where the deviation occurred. The contamination caused by small glass pieces in a chamber affects the final product quality (i.e., the mura effect). Early notification of leftover small glass pieces in the CVD processing chamber  105  may be beneficial in saving time and minimizing cost of ownership. For example, in a typical display fabrication facility, substrates are only sampled periodically for quality. Full testing only occurs at the end of the line when many substrates may have been processed in a contaminated processing chamber  105  and may exhibit defects caused by the contamination. Thus, at this final check, it is possible that multiple fully processed substrates are scrapped. Utilizing the method described herein provides early identification of a contaminated processing chamber and the chamber may be isolated and cleaned prior to processing other substrates. 
         [0054]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.