Abstract:
A method and apparatus for scanning multiple scanning probe microscopes in close proximity, to scan overlapping scan areas at the same time while avoiding collision employs a control system providing drive signals to a first Atomic Force Microscope (AFM) and calculated drive signals to additional AFMs based on the first drive signals and the relative position of the additional AFMs to the first AFM for consistent spaced motion. Scanning and Failure Analysis (FA) probing of multiple feature of interest using multiple APMs allows for reduced time for locating FA features to set up measurements.

Description:
RELATED APPLICATION  
       [0001]     This application claims priority to U.S. provisional application serial No. 60/394,414, filed Jul. 8, 2002, and is a continuation of U.S. patent application Ser. No. 11/015,945 filed Dec. 17, 2004 which is in turn a continuation of Ser. No. 10/615,223 filed Jul. 7, 2003, all entitled “Software Synchronization of Multiple Scanning Probes”, the disclosures of which are fully incorporated herein by reference. 
     
    
     COPYRIGHT NOTICE  
       [0002]     Certain software programs or routines disclosed in this application are subject to copyright protection and all rights thereto are specifically reserved. No dedication to the public of those copyrights is intended or made by such disclosure in this specification.  
       BACKGROUND  
       [0003]     1. Field of the Invention  
         [0004]     This invention generally relates to scanning probe microscopy (SPM) and failure analysis (FA), and more specifically to a system of control of multiple probe scanning when SPM is used to locate features for FA.  
         [0005]     2. Description of the Related Art  
         [0006]     Location of features in semiconductor microcircuits for failure analysis (FA) work has often been a difficult task. With advancing technology the size of features of interest for FA has decreased. Traditional methods of making electrical contact to features of interest in FA, also called probing, involved using mechanical positioners with fine probing needles and an optical microscope. The positioners are precision, 3-axis stages that can be manual or motorized. Attached to the positioners are sharp, probing needles. Using a traditional optical microscope and the positioner, a user would probe the FA device of interest with the needle. The small size of current semiconductor technology has made location and probing of FA features difficult or even impossible because of the limits of optical microscopy.  
         [0007]     Scanning probe microscopy (SPM) is one technique that can be used to locate these features. SPM can be used to create and image and locate features of interest that are much smaller than features that could be located using traditional optical microscopy. Since SPM can probe only one FA feature of interest per scanning probe microscope, multiple scanning probes are needed to contact multiple features. The field of using SPM, also called Atomic Force Microscopy (AFM), for the purpose of FA probing is called Atomic Force Probing (AFP). The acronym AFP is used to describe the field as well as instruments designed for use in the field, Atomic Force Probes.  
         [0008]     The prior art contains many examples of using SPM to locate FA features including using a single SPM to locate FA features. However, only a limited number of FA experiments can be performed with a single probe as many devices of interest for FA require 2 probes, in the case of diodes, 3 probes, in the case of transistors, or even more probes.  
         [0009]     The limited prior art relating to multiple scanning probes for FA shows the probes scanning one at a time in order to avoid collisions. This method is effective at avoiding collisions, at least until the probes move to their respective features of interest. However, this method takes longer to perform the scanning. This allows more time for drift, such as thermal drift, to occur. Also, the simple fact of longer measurement time is a serious weakness of the prior art.  
         [0010]     One embodiment of the prior art for 2 probes is shown pictographically in  FIGS. 1   a - 1   d.  A sample  110  contains features of interest  112 . These features of interest  112  may be too small to be probed easily using traditional methods.  FIG. 1   a  shows the scanning probe tips  114  grossly positioned on the sample  110  and near the features of interest  112 . Each scanning probe tip  114  will scan and image a scan area  116 .  FIG. 1   b  shows the first scanning probe tip  114  starting at a start point  118  and scanning its area of interest  116 .  FIG. 1   c  shows the same process for the second scanning probe tip  114 . At any given point during scanning the scan direction  120  for the different scanning probe tips  114  may or may not be the same direction.  FIG. 1   b  and  FIG. 1   c  show different scanning directions, as is common in the prior art.  FIG. 1   d  shows the scanning probe tips  114  positioned on the features of interest  112  and ready for an FA experiment. This process took twice the amount of time as was required for one scan. Similarly, if more probes are needed in the experiment the time delay scales with the number of probes used.  
         [0011]     This process also requires a difficult initial gross positioning setup. When the scanning probes tips are initially placed, they must be sufficiently far apart so that when one scanning probe tip is scanning, it does not collide with any other scanning probe tip that is not scanning. This requires initially placing the scanning probe tips sufficiently far apart to avoid the collision, and makes placing the scanning probe tips sufficiently close together to scan and image the same area difficult.  
         [0012]     It is, therefore, desirable to perform SPM using multiple probes and provide scanning of multiple probes in the same amount of time as would be taken to perform a scan of a single probe. This provides the advantage of less time for SPM drift effects, as well as the simple advantage of less measurement time. This also provides the advantage of a more simple and efficient initial gross positioning setup, because collision with scanning probe tips that are not scanning does not need to be avoided.  
       SUMMARY OF THE INVENTION  
       [0013]     A device and method to simultaneously scan multiple scanning probes over overlapping or non-overlapping areas of interest to locate respective features of interest in a minimum amount of time employs at least two scanning probes, each probe supported by cantilever to an atomic force microscope (AFM) having a special reference frame. A motion control signal is generated for a first one of the AFMs and an offset motion control signal is determined for a second one of the AFMs. The offset motion control signal is responsive to the first motion control signal and the special reference frames of the AFMs for non-interfering simultaneous scanning of a probe supported by the second one of the AFMS to a probe supported by the first one of the AFMs. A controller in the first AFM receives the motion control signal and a controller in the second AFM receives the offset motion control signal to operate the scanning of the AFMs and their associated probes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0015]      FIGS. 1   a  to  1   d  depict prior art technique of scanning multiple scanning probes one after another to scan and probe features of interest;  
         [0016]      FIGS. 2   a  to  2   c  depict employment of an embodiment of the present invention for scanning multiple scanning probes simultaneously to scan and probe features of interest;  
         [0017]      FIGS. 3   a  to  3   c  depict an embodiment of the present invention for 3 probes;  
         [0018]      FIG. 4  shows three scanning probe tips and the sample, as viewed from the top;  
         [0019]      FIG. 5   a  is a block diagram of the hardware configuration of an embodiment of the invention;  
         [0020]      FIG. 5   b  is a detailed side view of an embodiment of the probe tip and cantilever  FIG. 6   a  is a flow chart for software implementation of certain control aspects for an embodiment of the invention;  
         [0021]      FIG. 6   b  is a continuation of the flow chart of  FIG. 6   a;    
         [0022]      FIGS. 7   a  to  7   f  are schematic representations of some of the electrical waveforms in the embodiment described;  
         [0023]      FIGS. 8   a  to  8   c  show employment of an embodiment of the present invention scanning multiple scanning probes simultaneously to scan and probe features of interest while avoiding a certain area;  
         [0024]      FIG. 9  is a flow chart for the software implementation of the Z axis control for area avoidance; and,  
         [0025]      FIGS. 10   a  to  10   c  show waveforms representative of the control signals for the control routine defined in  FIG. 9   
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     As shown in  FIG. 2   a,  an embodiment of the present invention employs two or more scanning probe tips  114   a  and  114   b  that are located near a sample  110 . The sample  110  contains the features of interest  112   a  and  112   b.    FIG. 2   b  shows the scanning probe tips in relation to desired scan areas  116   a  and  116   b  respectively. Note that in the embodiment shown, the scan areas  116   a  and  116   b  are overlapping. Each scan area has a start point  118   a  and  118   b  where the respective scanning probe tip will begin its scan. Each scanning probe tip also has a scan direction  120   a  and  120   b  respectively. In the embodiment shown the scan directions  120   a  and  120   b  are always parallel and offset for all scanning probe tips. This provides for simultaneous motion of the probe tips in spaced relation thereby avoiding collision.  FIG. 2   c  shows the scanning probe tips positioned on the features of interest and ready for an electrical measurement or force measurement.  
         [0027]      FIGS. 3   a,    3   b  and  3   c  show an embodiment of the invention adding a third probe  114   c  for simultaneously scanning a third desired scan area  1116   c.  A third feature of interest  112   c  is also depicted.  
         [0028]      FIG. 4  shows the geometrical relationship of three scanning probe tips  114   a,    114   b  and  114   c  positioned over the sample  110 . The scanning probe tips are at different angles from one another. The platen angle  122   a,    122   b  and  122   c  of scanning probe tips  114   a,    114   b  and  114   c,  respectively, is the angle of the probe centerline  124   a,    124   b  and  124   c,  respectively, as measured from a reference axis  126 . Each scanning probe tip has a unique platen angle. The present invention employs the platen angle for the probe tips for generation of control signals as will be described in greater detail subsequently.  
         [0029]      FIG. 5   a  shows a schematic diagram of the elements of an AFP system embodying the present invention. The user accesses the software via a computer  130 . The computer is of a standard configuration, such that it is connected to a screen  132 , a mouse  134 , and a keyboard  136 . The scan image  137  is displayed on the computer screen. The computer  130  generates scan waveforms  138   a,    138   b  and  138   c.  A generalized case for more than three probes is represented by waveform  138   i.  The generation of the scan waveforms is described subsequently with respect to  FIG. 6 . There is one complete, independent set of scan waveforms to control motion of a probe tip for each feature of interest  112 . The scan waveforms are output to digital to analog converters (DACs)  140   a,    140   b  and  140   c  respectively. There is one DAC  140  for each probe tip control. The DACs share a clock signal  142  provided by clock generator  143  that ensures the scan waveforms remain synchronized. The DACs also share a synchronization pulse  144  provided by sync generator  145  that ensures that the scanning starts at the same time. The DACs drive control electronics  146   a,    146   b  and  146   c.  Control electronics for SPM operation are well known to one skilled in the art. There is one complete, independent set of control electronics for each probe. The control electronics are each connected to an AFM head  148   a,    148   b  and  148   c  respectively. Each AFM head contains a 3-axis actuator  150 , a feedback position sensor  152  and a deflection sensor  154 . The 3-axis actuator provides for scanning along the sample  110 . The feedback position sensor  152  in conjunction with the control electronics provide calibrated scanning. The deflection sensor  154  in conjunction with 1-axis of the 3-axis actuator provides for constant force AFM scanning. This system may also be operated without force feedback, where the deflection sensor is used to generate the scan image. There is one complete, independent AFM head for each feature of interest for which simultaneous probing is desired. Attached to the AFM heads are the cantilever  156  and scanning probe tips  114 . In the embodiment shown, the AFM heads are able to position multiple scanning probe tips in close proximity to one another. The control electronics generate the image data  157 . The image data is passed to the analog to digital converters (ADCs)  158 . The ADCs convert the image data to digital format pass the image to the computer. The computer can then display the image data to the user on the computer screen.  
         [0030]      FIG. 5   b  shows a detailed side view of an embodiment of the probe tip employed with the present invention attached to a cantilever. In this embodiment the deflection sensor uses the reflective back of the cantilever to determine the deflection of the cantilever. The arrangement of the probe tip and cantilever shown allows the greatest clearance between multiple probes operating in close proximity. The angled attachment of the probe tip to the cantilever, or in alternative embodiments, the angling of the cantilever attachment to the AFM, to position the extreme end of the probe tip as far as possible from the AFM is employed to achieve this feature.  
         [0031]      FIG. 6  is a flow chart of the mathematical operations of the software. The standard SPM scan parameters input  159  consists of X scan size  160 , Y scan size  162 , X resolution  164 , Y resolution  166 , X offset  168  and Y offset  170  which are used by subsequent routines to create a scan waveform for the AFM manipulating each probe tip.  
         [0032]     The drive waveform generation routine  172  takes the SPM scan parameters input and outputs a drive waveform  174 , identified as W, that contains both an X value output  176  and Y value output  178 . In one embodiment, shown in  FIG. 7   c  and  FIG. 7   d  and described subsequently, the drive waveform is a triangle wave with the peaks and valleys rounded off, at the last 5 points. For this embodiment, the waveform generation is accomplished in the following sequence. The X values of the drive waveform are centered about the value ‘X offset’. The X values of the drive waveform have amplitude of ‘X scan size’ divided by 2. The X values of the drive waveform have the number of points per cycle equal to 2 multiplied by the value ‘X resolution’. The X values of the drive waveform have a number of cycles equal to 2 times the value ‘Y resolution’. The Y values of the drive waveform are centered about the value ‘Y offset’. The Y values of the drive waveform have amplitude of ‘Y scan size’ divided by 2. The Y values of the drive waveform have the number of points per cycle equal to 2 multiplied by the value ‘X resolution’ multiplied by the value ‘Y resolution’. The Y values of the drive waveform have 1 cycle. The X offset and Y offset values define the location of the scan area.  
         [0033]     The code described herein to achieve the desired AFM control has been programmed in existing embodiments using a LabVIEW compiler available from National Instruments Corporation, 11500 N Mopac Expwy, Austin, Tex. 78759-3504, as shown in Appendix A hereto which is incorporated herein by reference.  
         [0034]     The start point rotation routine  180  takes the drive waveform, W, and based on desired start point input  181  rotates the X values of the drive waveform and the Y values of the drive waveform so the X start point  182  and Y start point  184  are the first points in the waveforms. This calculation places the probe tips at start points  118   a,    118   b  or  188   c,  as described previously with respect to  FIGS. 2   b  and  3   b,  are the locations where the probes will begin scanning. In the start point routine, rotation is defined in the software-programming context; taking a 1 dimensional array of numbers, moving a section of the numbers from the rear to the front, and placing the numbers that use to be at the front, at the rear. The start point rotated X value output  176 ′ and the Y value output  178 ′ of the new waveform W′  174 ′ are the resulting output of the start point rotation routine.  
         [0035]     The scan rotation routine  186  transforms the drive waveform W′ to the spatial reference frame of the individual AFM heads  148 . The input parameter platen angle R  187  for each AFM head and associated probe tip, is the angle  122   a,    122   b  or  122   c  of the probe tip centerline  124   a,    12   b  or  124   c,  respectively, measured relative to the arbitrary reference axis  126  on the sample as described previously with respect to  FIG. 4 . The output result of this routine is a rotated drive waveform W″ 174 ″ having an X value output  176 ″ and a Y value output  178 ″. For the embodiment described herein, a multiplication by a rotation transformation matrix M  189 , formed based on an angle value equal to the platen angle R for each AFM probe tip, is performed. In scan rotation routine, rotation is defined in the linear algebra context; to multiply by a matrix of the form given in the scan rotation routine to rotate the input array about the origin by the given angle.  
         [0036]     If all rotated drive waveforms W″ as determined by interrogatory  190 , have been generated. If some AFM control electronics have not been generated, then the process repeats itself for the next SPM starting with the waveform generation routine  172 . Because the invention assumes more than one AFM, the above routines will execute at least twice, corresponding to two or more AFMs. If all AFMs have generated their respective rotated drive waveform, W″, then waveforms are generated in routine  191  to position the probe tip of each AFM at its respective start point. The positioning waveform is then loaded into the AFM control electronics in routine  192  and each AFM moves its respective probe tip to its start point. All AFM control electronics start with a common synchronization pulse  144 , so all begin at the same time. All AFM control electronics also share a common clock signal  142 , so they all proceed at the same rate.  
         [0037]     Upon reaching the start points, the rotated drive waveform W″ is loaded in routine  193  to the AFM control electronics  146   a,    146   b  or  146   c  respectively. Then scanning routine  194  begins. All AFM control electronics  146  start with a common synchronization pulse  144 , so all begin at the same time. All AFM control electronics also share a common clock signal  142 , so they all proceed at the same rate.  
         [0038]     The data from the AFM control electronics  146  is gathered in step  195  and displayed as an image on the computer screen  132  to the user. During operation of the scanning routine, a monitoring function  196  is concurrently checking if the user has selected the probe button on the computer screen  132 . If the probe button has not been selected the scanning routine continues to gather data and update the display image. Note that in the embodiment shown the probe button is a software button and does not have a physical location. If the user has selected the probe button, reflected by operation  197 , then the probe point routine takes the user&#39;s probing locations input, calculates a waveform  198  to move from the current location of the scanning probe tips to the user&#39;s probing locations and outputs the waveform, as reflected in routine  200 , to the AFM control electronics. The scanning probe tips are moved by the AFM control electronics to the location specified by the user&#39;s probing location as shown in block  201 . This routine is identical in function, but different in input to the start point positioning generation routine. The input to this function is the probing point, rather than the start point.  
         [0039]      FIGS. 7   a  through  7   f  show examples of some of the electrical signals during the execution of the scanning operation.,  FIG. 7   a  is the shared clock  142  that is used to make sure all AFMs remain synchronized.  FIG. 7   b  shows the synchronization pulse  144  that signals for all AFMs to begin at the same time.  FIG. 7   c  shows the X values of the drive waveform  176  generated by the waveform generation routine  172 .  FIG. 7   d  shows the Y values of the drive waveform  178  also generated by the waveform generation routine  172 .  FIG. 7   e  shows an example of the X values of the rotated drive waveform W″  188 , for an AFM head that is rotated to an exemplary arbitrary platen angle relative to the sample  110 .  FIG. 7   f  shows an example of the Y values of the rotated drive waveform W″ for the AFM head. These waveforms are generated by the scan rotation routine  186 . Note that after the scan rotation routine  186  the rotated drive waveform  188 , W′, depend greatly on the platen angle  122 .  
         [0040]     Operation of the embodiment of the invention disclosed herein is accomplished as follows. The system employs multiple scanning probe microscopes. The scanning probe tips may be in close proximity to one another, such as a few microns to under 1 micron. Additionally, the scanning probe tips are centered in their travel, engaged on a sample and may be able to scan an overlapping scan area. As previously described with respect to  FIG. 2   a,    2   b,    2   c,    3   a,    3   b,  and  3   c,  the scan area  116  contains multiple features of interest  112 .  
         [0041]     Using the computer  130  the user enters various scanning parameters such as X scan size  160 , Y scan size  162 , X offset  168 , Y offset  170 , X resolution  164 , Y resolution  166 , X start point  182 , Y start point  184  and platen angles for the AFM probe tips ( 122   a,    122   b  and  122   c  for the three probe example disclosed herein).  
         [0042]     The user tells the computer to begin scanning and the software routine running on the computer  130  starts the procedure illustrated in  FIG. 6 . The waveform generation routine  172  generates a drive waveform W, so that each scanning probe tip will raster an area described by the scanning parameters.  
         [0043]     The drive waveforms W are rotated by the start point rotation routine  180  so that all scanning probe tips will start at the same point in their respective drive waveforms. This will ensure that the spacing between the AFM probe tips  114  will be constant for the start of scanning.  
         [0044]     Next, the drive waveforms are rotated by the scan rotation routine  186  to result in the rotated drive waveforms W″. This rotation ensures that even though all AFM heads and their associated scanning probe tips have a different platen angle they will all scan at the same direction at the same time and further ensures that the spacing between scanning probe tips will remain substantially constant for the duration of scanning.  
         [0045]     Next, the rotated drive waveforms W″ are loaded to the DACs  140   a,    140   b  and  140   c  respectively. The AFMs are positioned placing the probe tips at the start points. Once the rotated drive waveforms have been loaded, all AFM control electronics share a common clock  142 . This ensures that the scanning probe tips will stay synchronized. Then the synchronization circuit issues a synchronization pulse  144 , which signals all AFM control electronics  146  to begin scanning. This ensures that all of the AFMs start scanning at the same time. The DACs then output their respective rotated drive waveform to their AFM control electronics. During scanning the scanning probe tips move in spaced relation to maintain constant spacing to when they first started scanning. Each set of AFM control electronics controls the feedback position sensors  152  and the 3-axis actuator  150  in the associated AFM head  148  to scan in a calibrated manner. Each deflection sensor  154  monitors the deflection of the cantilever  156  to which the scanning probe tip  114  is attached. This deflection signal is returned to the SPM control electronics  146  and displayed to the user on the computer screen  132 .  
         [0046]     During scanning the AFM probe tips move in an identical scanning direction  120  at all times, as shown in  FIGS. 2   a - c  and  3   a - c.  Similarly, the starting points  118   a,    118   b  and  118   c  are in the same relative location for the scan areas  116   a,    116   b  and  116   c  for all scanning probe tips. Additionally, the spacing between the scanning probe tips is constant at all times.  
         [0047]     During scanning the computer  130  gathers data from the AFM control electronics  146  and displays it on the computer screen  132 . When the user locates the features of interest  112  on the computer screen, he or she can choose to probe those features. The user then selects the location of the features of interest to be probed as the probing location  196  and selects the probe button  194 . Then the computer  130  will calculate and output a waveform to the DACs  140  which will drive the AFM control electronics  146 , which will drive the scanning probe tips to a respective point on the sample  110  corresponding to the probing location  196 . The DACs  140  will share their common clocks  142  and synchronization pulse  144  as before. The DACs  140  will then drive the AFM control electronics  146 . This will cause the scanning probe tips to move to the probing locations  196 . Note that, for the first time since scanning began, the spacing between scanning probe tips  114  is no longer constant once the scanning probe tips  114  begin to move toward the probing locations  196 .  
         [0048]     For an alternative embodiment of the invention with enhance functionality,  FIG. 8   a  shows the sample  110 , features of interest  112   a  and  112   b  and an area to be avoided  198 . In  FIG. 8   a  the scanning probe tips  114   a  and  114   b  are positioned on the sample  110 .  FIG. 8   b  shows each of the scanning probe tips has its own scan area  116   a  and  116   b,  respectively, that excludes the area to be avoided  198 . In the embodiment shown, the spacing between scanning probe tips  114   a  and  114   b  may not always be constant. In this embodiment the probes retract in Z, the out of the plane of the sample direction, to avoid the area to be avoided. Each scan area  116  has a start point  118  that is where the scanning probe tip  114  will begin. Each scanning probe tip  114  also has a scanning direction  120 . In the embodiment shown the scanning directions  120  are substantially the same for all probe tips  114 .  
         [0049]      FIG. 9  shows in flow chart form the generation of the Z axis probe retraction waveform consistent with the area to be avoided which is overlaid on the waveform generation for the X and Y components of the AFM motion.  FIGS. 10   a,    10   b,  show the waveforms of  FIGS. 7   c  and  7   d  expanded and truncated for clarity.  FIG. 110   c  show the corresponding Z axis actuation for the avoided area associated with the X and Y motion. Referring to  FIG. 9 , the X and Y extents of the area to be avoided are provided as parameter input  202  to generation routine  204  for a control matrix  206  for the excluded area. A simple rectangular area is shown for the embodiment in the drawings, but is not a limitation on the invention. For purposes of explanation the operation of only one probe tip and AFM is described herein. The control electronics monitor the X/Y position  208  of the probe tip as driven by the appropriate waveform  178  for X position and  176  for Y position shown in expanded form in  FIGS. 10   b  and  10   a  respectively. If the probe tip position has entered the exclusion matrix values  210 , the probe is lifted  212  by the Z axis control in the AFM. The X/Y position is then monitored to determine when the probe tip is clear of the exclusion matrix values  214  at which time the probe is lowered  216  to resume generation of image data.  
         [0050]     The exclusion area is graphically demonstrated in  FIG. 10   a  as Y exclusion zone  218  and  FIG. 10   b  as X exclusion zone  220 . The resulting Z axis waveform  222  shown in  FIG. 10   c  demonstrates the lifting of the probe tip when in the exclusion area.  FIG. 8   c  shows the scanning probe tips  114  positioned on the features of interest  112  and ready for an FA experiment.  
         [0051]     A commercially available version of an embodiment of the invention is the Atomic Force Probe (AFP) system available from MultiProbe, Inc, 10 E. Islay Street, Santa Barbara, Calif. 93101, the assignee of the present application. This system is capable of placing the scanning probe tips in close proximity, being less than a few microns, as shown in  FIG. 2   c  or  3   c.  This system has feedback position sensors  152  for the 3-axis actuator  150  and supporting SPM control electronics  146  as shown in  FIG. 5 . This system also executes the software routine shown in block diagram form in  FIG. 6 . For 3 scanning probe tips  114  this microscope performs the operation shown pictographically in  FIG. 3 .  
         [0052]     An additional commercially available atomic force microscope (AFM) is the Veeco Metrology AFM head with supporting control electronics available from Veeco Metrology Group, 112 Robin Hill Road, Santa Barbara, Calif. 93117. This commercially available system does not presently support the invention, however, this system contains the elements shown in  FIG. 5 . The most noteworthy of these elements are the feedback position sensors  152  for the 3-axis actuator  150  and the supporting AFM control electronics  146  as shown in  FIG. 5 . This system also does not have the ability to place multiple scanning probe tips in close proximity.  
         [0053]     Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.