Abstract:
A method of using a processing system that is operable to deposit liquid and to remove liquid by way of negative pressure. The method includes arranging a device to have at least one of the liquid deposited thereon by the processing system and the liquid removed therefrom by the processing system. The device has a sensor portion disposed thereon. The sensor portion can provide a sensor signal based on pressure related to the at least one of the liquid being deposited thereon by the processing system and the liquid being removed therefrom by the processing system. The method further includes performing at least one of depositing, by the processing system, the liquid onto the device and removing the liquid, by the processing system, from the device. The method still further includes providing the sensor signal, by the sensor portion, based on the pressure related to the at least one of the liquid being deposited onto the device and the liquid being removed from the device.

Description:
The present application claims priority from U.S. Provisional Application No. 61/254,544 filed Oct. 23, 2009, the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Within the semiconductor industry, there exists the need to improve yield, throughput, and the ever present quest to maintain pace with Moore&#39;s Law. The ideal way of accomplishing a process characterization is to provide a mechanism for real-time data collection of vital process parameters—explicitly the mechanical and electrical forces seen by the substrate. 
       FIG. 1  illustrates a portion of a conventional linear wet chemical cleaning system  100 . 
     As illustrated in  FIG. 1 , cleaning system  100  includes a holding tray  102 , a carrier tray  104 , a powered rail  112 , attachment devices  110 ,  114 ,  126  and  130 , a non-powered rail  128  and a cleaning portion  118 . Cleaning portion  118  includes a plurality of process shower heads  120 . 
     In operation, a wafer  108  may be disposed on carrier tray  104 . Attachment devices  110  and  114  and attachment devices  126  and  130  attached to carrier tray  104  enable carrier tray  104  to glide along a path D between powered rail  112  and non-powered rail  128 , respectively. As carrier tray  104  carrying wafer  108  passes underneath cleaning portion  118 , process shower heads  120  apply cleaning solutions to the surface of wafer  108 . Process shower heads  120  then remove the cleaning solution via vacuum. In this manner, any particulates on the surface of wafer  108  are removed. 
     In a wet cleaning process, cleaning solutions are applied to the surface of wafer  108  in conjunction with de-ionized water delivery &amp; mixed liquid-gas return lines. Goals during such a process include maintaining a balanced force on the surface of wafer  108  resulting from the application of liquid and gas flows and optimizing the efficiency of the wet clean process. Controlling forces applied to wafer  108  during a wet clean process may increase uniformity and residual removal rates across the entire wafer surface. 
     What is needed is a system and method for controlling forces applied to a wafer during a wet clean process in order to increase uniformity and residue removal rates across the entire wafer surface. 
     BRIEF SUMMARY 
     It is an object of the present invention to provide a system and method for controlling forces applied to a wafer during a wet clean process in order to increase uniformity and residue removal rates across the entire wafer surface. 
     In accordance with an aspect of the present invention, a method is provided for using a processing system that is operable to deposit liquid and to remove liquid by way of negative pressure. The method includes arranging a device to have at least one of the liquid deposited thereon by the processing system and the liquid removed therefrom by the processing system. The device has a sensor portion disposed thereon. The sensor portion can provide a sensor signal based on pressure related to the at least one of the liquid being deposited thereon by the processing system and the liquid being removed therefrom by the processing system. The method further includes performing at least one of depositing, by the processing system, the liquid onto the device and removing the liquid, by the processing system, from the device. The method still further includes providing the sensor signal, by the sensor portion, based on the pressure related to the at least one of the liquid being deposited onto the device and the liquid being removed from the device. 
     Additional objects, advantages and novel features of the invention are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an exemplary embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  illustrates a portion of a conventional linear wet chemical cleaning system  100 ; 
         FIG. 2  illustrates a characterization apparatus in accordance with an aspect of the present invention; 
         FIG. 3  shows a linear chemical cleaning and characterization system in accordance with an aspect of the present invention; 
         FIG. 4  shows a graph, which illustrates the signal response of each of the six sensors in a vibration sensor set during a particular cleaning process; 
         FIG. 5  shows a graph, which illustrates the signal response of two different sensors on a wafer during an example wet cleaning process; 
         FIG. 6  shows a graph, which illustrates the signal response of the sensors corresponding to functions in  FIG. 5  during an example wet cleaning process, after appropriate adjustments have been made; and 
         FIG. 7  is a flowchart illustrating an example method of operation of the cleaning and characterization system of  FIG. 3  in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with an aspect of the present invention, forces exerted on a wafer during semiconductor chemical cleaning process are monitored. Further, force vectors across the wafer surface area are extracted based upon wafer movement induced by liquids applied under pressure to the wafer surface during wet chemical clean processes. The monitored forces may then be used to adjust application of liquids and gases to the surface of a wafer and to adjust removal of materials from the surface of the wafer to optimize wafer yield. 
     Example embodiments of the present invention will now be described in reference to  FIG. 2-FIG .  5 . 
       FIG. 2  illustrates a characterization apparatus  200  in accordance with an aspect of the present invention: 
     As illustrated in  FIG. 2 , characterization apparatus  200  includes a wafer  202 , a sensor signal conduit  204 , an analog-to-digital converter (ADC)  206 , a digital signal processor (DSP)  208  and a tool controller  210 . Wafer  202  includes a set of vibration sensors  224  integrated on the surface. In an example embodiment, vibration sensors  224  are piezoelectric devices. In this particular embodiment, vibration sensor set  224  includes six sensors: sensor  212  (sensor # 6 ), sensor  214  (sensor # 4 ), sensor  216  (sensor # 2 ), sensor  218  (sensor # 1 ), sensor  220  (sensor # 3 ), and sensor  222  (sensor # 5 ). 
     In operation, wafer  202  is placed in cleaning system  100  and a given cleaning process begins. During the cleaning process, the sensors in vibration sensor set  224  each measure the local forces exerted on wafer  202 , such as the forces due to the application of cleaning solution, the application of de-ionized water, and the removal of such liquids, residues and particulates with a vacuum. The individual signals from vibration sensor set  224  are passed to ADC  206  via sensor signal conduit  204 , which are then passed through DSP  208  and eventually to tool controller  210 . Tool controller  210  may be a program that displays and records the signal responses from each sensor in vibration sensor set  224 . 
     The operation discussed above is illustrated in  FIG. 3 .  FIG. 3  shows a linear chemical cleaning and characterization system  300  in accordance with an aspect of the present invention. 
     Cleaning and characterization system  300  includes cleaning system  100  and characterization apparatus  200 . As shown in the figure, wafer  202 , which includes vibration sensors set  224 , is placed in cleaning system  100 . As discussed above, the signals from vibration sensor set  224  sense the various local forces on wafer  202  during the cleaning process. These individual sensor responses can be monitored and then correlated to specific process conditions, as will be discussed further with reference to  FIG. 4 . 
       FIG. 4  shows a graph  400 , which illustrates the signal response of each of the six sensors in vibration sensor set  224  during a particular cleaning process. 
     In graph  400 , the x-axis is time, in seconds, whereas the y-axis is the sensor output, in millivolts, of each particular sensor. Graph  400  includes function set  402 , a set of signal responses from the sensors in vibration sensor set  224 . In this embodiment, there are six individual functions, one from each sensor in vibration sensor set  224 . 
     Initially, the behavior of the responses in function set  402  is fairly constant, as wafer  202  begins gliding across holding tray  102 . However, around point  404 , a significant shift is present in each of the sensors responses. This can be correlated to wafer  202  beginning to move beneath process shower heads  120 , and may represent the forces of the cleaning solution being applied to the surface of wafer  202 . Shortly after point  404  in function set  402 , there is a very sharp transient at point  406 . This can be correlated to process shower heads  120  vacuuming the cleaning solution from the surface of wafer  202 . 
     After the transient near point  406  settles, the responses in function set  402  remain somewhat constant before experiencing a sharp negative transient around point  408 . This transient can be correlated to the point where wafer  202  has completed the pass beneath process shower heads  120  and the vacuum is no longer removing liquid from the surface of wafer  202 . 
     As mentioned earlier, the individual responses in function set  402  represent the forces seen by the individual sensors in vibration sensor set  224 . Therefore, the individual responses in function set  402  can provide a spatial map of the forces seen across wafer  202  during a given cleaning process. This allows any areas of non-uniformities or non-idealities in the way forces are applied to wafer  202  to be identified during the cleaning process. For example, for a given wafer  202 , there may be maximum threshold of pressure that may be applied to it, above which may potentially cause damage or even breakage. Therefore, by monitoring the local forces on wafer  202  during the cleaning process, one can check if the applied pressure at any location on wafer  202  (from the application of cleaning solution, vacuum, etc) exceeds this given threshold. If so, then various processing parameters (such as amount of water or cleaning solution dispensed during cleaning, force or duration of vacuum, etc) may be appropriately adjusted to reduce the pressure on wafer  202 . 
     In addition to maximum pressure threshold, there may be other pressure-related thresholds pertinent to a given wafer. For example, there may be a threshold for the maximum change in pressure over a given distance on the wafer. This may be monitored by examining the difference between individual sensor responses. Also, there may be a threshold for maximum change in pressure over a given time. This may be monitored by examining the gradient of the individual sensor responses as a function of time. In any case, if a threshold is exceeded, processing parameters may be adjusted to reduce the changes in pressure. For example, the rate at which water or cleaning solution is applied to wafer  202  or the force of the vacuum may be appropriately adjusted in order to reduce sudden changes in pressure during the cleaning process. Also, if process shower heads  120  are movable, they may be moved and rearranged such as to provide more uniform pressure across the surface of wafer  202 . 
     Once the processing parameters are adjusted, wafer  202  undergoes the cleaning process again and the resulting effects on the sensor responses are observed. The cycle of processing and observing followed by adjusting of processing parameters may be repeated several times until the results are deemed to be acceptable (all sensor outputs fall within set thresholds). In this manner, wafer damage during cleaning can be avoided or reduced, thereby improving the yield and efficiency of the wet cleaning process. Once the cleaning process has been sufficiently optimized, wafer  202  may be removed and the cleaning process may be performed on regular production wafers. 
     For the sake of discussion, the ability to adjust the cleaning system to account for sensor outputs surpassing given thresholds will now be described in reference to  FIGS. 5 and 6 . 
       FIG. 5  shows a graph  500 , which illustrates the signal response of two different sensors on wafer  202  during an example wet cleaning process. 
     In graph  500 , the x-axis is time, in seconds, whereas the y-axis is the sensor output, in millivolts, of each particular sensor. Graph  500  includes function  502  and function  504 , which represent signal responses from different sensors in vibration sensor set  224  on wafer  202 . For simplicity, in graph  500 , the signal responses from only two sensors are shown. 
     Graph  500  also includes maximum negative pressure threshold  506  and maximum positive pressure threshold  508 . These indicate a predetermined maximum amount of negative pressure and predetermined maximum amount positive pressure that may be applied to an area on wafer  202 , respectively, before a likelihood of damage to wafer  202  will exceed a predetermined likelihood of damage threshold. These thresholds may be experimentally determined by monitoring yield of batched of cleaned wafers. 
     As shown in graph  500 , at point  512 , function  502  exceeds maximum positive pressure threshold  508 . This indicates that the pressure at this sensor is too high and needs to be reduced, in order to reduce the likelihood of wafer damage below the predetermined likelihood of damage threshold. At point  516 , function  502  does not surpass the maximum negative threshold  506 , so the value of pressure there is acceptable. 
     However, note that there is a large change in pressure between point  514  on function  504  and point  516  on function  502 . Since the points are relatively close in time, the difference in pressure between points  514  and  516  (noted as d s1 ) represents the change in pressure sustained over the physical distance between the two sensors. In this example, presume the pressure change d s1  divided by the distance between the two sensors is found to exceed a predetermined threshold for pressure change per distance on wafer  202 . A predetermined threshold for pressure change per distance on wafer  202  is a threshold of pressure change per distance on wafer  202  before a likelihood of damage to wafer  202  will exceed a predetermined likelihood of damage. Since this threshold is exceeded, this is unacceptable and must be addressed. 
     In addition to changes in pressure over distance, there may also be established thresholds for changes in pressure over time. At point  518  on function  502 , the gradient with respect to time is indicated by a line (line  520 ). As one can see, line  520  is almost completely vertical, indicating a very large change in pressure over time. In this example, presume the gradient at point  518  exceeds a pre-determined threshold for change in pressure with respect to time. A predetermined threshold for pressure change with respect to time is a threshold of pressure change at a position on wafer  202  over time before a likelihood of damage to wafer  202  will exceed a predetermined likelihood of damage. Since this threshold is exceeded, this is unacceptable and must be addressed 
     Thus, in graph  500 , there are three different instances where pre-determined thresholds were exceeded: 1) at point  512 , the sensor corresponding to function  502  has exceeded the maximum (positive) pressure threshold; 2) between points  514  and  516 , the threshold for maximum change in pressure over distance was exceeded; 3) at point  518 , the sensor corresponding to function  502  has exceeded its threshold for maximum change in pressure with respect to time. All these must be addressed by appropriately adjusting the pressure sensed by the sensors corresponding to functions  502  and  504 . As previously mentioned earlier, these adjustments may be accomplished in a variety of ways, such as adjusting the rate at which water or cleaning solution is applied, or adjusting the force and/or duration of the vacuum. Also, if process shower heads  120  are moveable, they may be rearranged such as to provide more uniform pressure to all the sensors. Once adjustments are made, the cleaning process may be run again and the new sensor outputs can be monitored to check if they fall within the established thresholds. This will be described in more detail with respect to  FIG. 6 . 
       FIG. 6  shows a graph  600 , which illustrates the signal response of the sensors corresponding to functions  502  and  504  in  FIG. 5  during an example wet cleaning process, after appropriate adjustments have been made. 
     In graph  600 , the x-axis is time, in seconds, whereas the y-axis is the sensor output, in millivolts, of each particular sensor. Graph  600  includes function  602  and function  604 , which represent signal responses from different sensors in vibration sensor set  224  of wafer  202 . Function  602  corresponds to the same sensor that was associated with function  502  in  FIG. 5 , and function  604  corresponds to the same sensor that was associated with function  504  in  FIG. 5 . 
     As shown in  FIG. 6 , function  602  and  604  are now different from functions  502  and  504 , due to adjustments in the cleaning process. Specifically, the maximum value of function  602  (point  606 , which corresponds to point  512  on function  502 ) has been reduced, and now does not exceed the maximum positive pressure threshold  508 . Also, the minimum value of function  602  (point  610 , which corresponds to point  516  on function  502 ) has become less negative, such that the difference between point  608  of function  604  and point  610  of function  602  (denoted as d s2 ) is now smaller than the maximum threshold for change in pressure over distance. Further, at point  612  on function  602  (which corresponds to point  518  on function  502 ), the gradient with respect to time (shown by line  614 ) has been reduced, such that it now falls within the threshold for maximum change in pressure over time. Thus, one can see that in  FIG. 6  all the issues with sensors exceeding their predetermined pressure thresholds have been addressed via adjustments to the cleaning process. Now that the sensor outputs are within acceptable thresholds, there is less likelihood of wafer damage during the cleaning process, which thereby provides for a more efficient and higher-yield cleaning process. 
     An example method of operating cleaning and characterization system  300  in accordance with an aspect of the present invention will now be described with reference to  FIG. 7 . 
     Process  700  starts (step S 702 ) and process initializations occur (step S 704 ). Non-limiting examples of process initializations include, establishing data communications or positioning parts in cleaning and characterization system  300 . Process initializations may also include setting various process parameters such as the specific amount of water or cleaning solution to be applied (controlled by flow rate, etc), strength of the vacuum, and the specific time(s) when cleaning solution and/or vacuum is to be applied (and the duration of time applied). Also, initializations may include establishing thresholds for the pressure applied to wafer  202 , as discussed previously (e.g. maximum pressure, maximum change in pressure with respect to distance, time, etc). Further, if process shower heads  120  are moveable, their initial position would be set in this step. 
     Then, a sensor wafer is loaded (step S 706 ). Returning to  FIG. 3 , wafer  202 , with vibration sensor set  224  integrated on its surface, is disposed on carrier tray  104 . 
     Wafer  202  is then processed in cleaning and characterization system  300  (step S 708 ). 
     After wafer  202  is processed, the individual sensor outputs of vibration sensor set  224  are monitored (step S 710 ). The results are analyzed to determine if the individual sensor outputs of vibration sensor set  224  are all acceptable (all fall within the established thresholds) for the given process (step S 712 ). 
     If any of the individual sensor outputs of vibration sensor set  224  are not deemed to be acceptable, then the appropriate process parameters are adjusted (step S 714 ) and wafer  202  is processed again (step S 708 ) with the new parameters. As discussed previously with reference to  FIG. 4 , the adjustments to process parameters may include adjusting the flow rate of water and/or cleaning solution from process shower heads  120 , the position of process shower heads  120  (if movable), and/or the strength of vacuum used to remove cleaning solution and particles from the surface of wafer  202 . The adjustments may be implemented manually or via an automatic feedback control system. 
     Returning to step S 712 , if all individual sensor outputs of vibration sensor set  224  are deemed to be acceptable, then wafer  202  is removed from carrier tray  104  and a production wafer is loaded onto carrier tray  104  (step S 716 ). 
     The production wafer is then processed (step S 718 ). 
     After the production wafer is processed, it is determined whether more production wafers need to be processed (step S 720 ). If the determination is NO, then processing may conclude (step S 722 ). Otherwise the next production wafer is loaded (step S 716 ) and the process repeats. 
     In the above process, thresholds for certain parameters (maximum pressure on wafer, etc) are first established during initialization (step S 704 ) and later the sensor outputs are checked to ensure they are all within the given thresholds (step S 712 ). However, it may be the case that the parameter thresholds are not known prior to processing. Thus, in this case, the initialization step (step S 704 ) would just include the other process initializations (positioning of process shower heads  120 , setting strength of vacuum, etc) and step S 712  may just include a general overview of the sensor outputs to determine whether or not the results are acceptable. If the sensor outputs are deemed unacceptable, then the process would go on to step S 714  to adjust appropriate processing parameters, just as discussed previously. 
     In the embodiment discussed above with reference to  FIG. 2 , vibration sensor set  224  includes individual piezoelectric films. It should be noted however, that other embodiments may include sensors of other types, non-limiting examples of which include, sensors made of microelectrical mechanical systems (MEMs). Further, it should be noted that other embodiments may include any number of sensors integrated on the surface of wafer  202 , in any sort of pattern. 
     In the embodiments discussed above in  FIGS. 2-7 , sensors are used to measure forces on a wafer during a wet clean process. It should be noted, however, that other embodiments may include sensors or other measuring devices that measure other parameters on a wafer during processing, non-limiting examples of which include temperature or acidity. 
     In the embodiments discussed above in  FIGS. 3-7 , forces on a wafer during a wet chemical cleaning process are monitored and optimized. It should be noted, however, than an aspect of the present invention is not limited to use with wet chemical cleaning systems. On the contrary, an aspect of the present invention may be implemented with any semiconductor system of interest. For example, the methodology can be applied to chemical mechanical polishing (CMP) processing systems to monitor pressure distribution across a wafer, or in MEMs applications where a spatial analysis of these stresses exerted on a substrate is required. Further, the methodology may be used in other systems to characterize the chucking force applied to a wafer by an electrostatic chuck (ESC). Specifically, the characterization apparatus in  FIG. 2  may be used to measure the forces on a wafer applied by the chucking voltage of an ESC and therefore can allow for the examination of the uniformity of the clamping force across the wafer. By monitoring each sensor, a spatial map can be constructed of the relative clamp force at each sensor location, providing feedback to the user during ESC development as well as providing a problem-solving tool for chucking and de-chucking issues. 
     The foregoing description of various preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.