Abstract:
A scanning probe nanolithography system comprising a probe to create nanostructures line ( 60 ) by line through writing said nanostructures ( 74 ) pixel by pixel along lines ( 61 ) on a sample. A positioning system is adapted to provide a positioning of the probe at a sequence of predetermined positions to the sample and its surface towards the probe and a control unit ( 50 ) is provided to control the positioning system for positioning the probe for a pixel-wise writing of said lines ( 61 ) through a writing unit. It further comprises a sensor unit adapted to detect a predetermined property of the written nanostructure ( 74 ), the sensor unit being connected to the control unit to adapt the control signals to be provided to the writing unit for writing the following line ( 61; 62 ) based on the measured signals ( 65; 66 ) of the predetermined property.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a scanning probe nanolithography system and a control method of scanning probe nanolithography processes. 
       PRIOR ART 
       [0002]    Scanning probe nanolithography systems are known from a plurality of prior art documents, e.g. U.S. Pat. No. 8,261,662, reciting further publications. 
         [0003]    Nanolithography is usually done in an open-loop way, meaning that all writing/patterning parameters have to be set prior to the writing/patterning process. No information from the written nanostructure is obtained during the writing process. Therefore, all external (temperature, humidity, pressure, . . . ) or internal (thermal drift, noise, fluctuations, degradations, ageing . . . ) influences, that potentially disturb the writing/patterning process have to be shielded, eliminated or accounted for during the writing process in order to obtain nanostructures of high quality and good reproducibility. 
         [0004]    Feedback loops as mentioned in U.S. Pat. No. 8,261,662 are used to control system writing parameters of the writing process, e.g. control of writing current through measurements of said current. 
         [0005]    Scanning Probe Lithography techniques use sharp tips/probes to create nanostructures. This can be done, for example, by mechanical interactions (nano-shaving or nanoscratching as e.g. described by Yan et al.,  Small,  6(6):724-728, (2010)), with electrical fields between the tip and the sample (local anodic oxidation, see e.g. Chen et al.,  Optics letters,  30(6):652-654, (2005), field-induced deposition, see e.g. Rolandi et al.  Angewandte Chemie International Edition,  46(39):7477-7480, (2007), field emission of electrons), light enhancement at the tip (near-field lithography, see e.g. Srituravanich et al.,  Nature Nanotechnology,  3.12 733-737, (2008)), deposition of material from the tip (dip pen lithography, see e.g. Radha et al.,  ACS nano,  7.3:2602-2609, (2013)) or local heating of the tip (thermochemical, thermal desorption lithography, see e.g. Pires et al.,  Science,  328, 732, (2010)). Usually, scanning probe lithography methods scan the surface line by line and write the nanostructures pixel by pixel along the lines. 
         [0006]    In many cases, the same tip that creates the nanostructures can be used to image/read (like an Atomic Force Microscope (AFM) or a Scanning Tunneling Microscope (STM)) the nanostructures also in a line by line and pixel by pixel manner. The information/property to image/read the surface with the nanostructures is most of the time topography, but can also be e.g. friction, thermal conductivity, electrical conductivity, electrostatic potential, magnetic moment, adhesion, elastic modulus or further surface properties that can be measured by standard scanning probes microscopy techniques. 
         [0007]    US201126882A1 is an example how external parameters (in this case leveling of the substrate) need to be measured and adjusted prior to the patterning of nanostructures. 
         [0008]    In contrast to prior art US201126882A1, the present invention starts with the patterning process and takes the information from deviations of the target nanostructure to adjust the external parameters. This closed-loop lithography concept could potentially be applied also to solve the problem described in patent US201126882A1, which is the leveling of multiple cantilevers, in a more elegant and faster way. 
         [0009]    U.S. Pat. No. 7,060,977B1 describes a typical calibration process that is used for many scanning probe nanolithography processes. First a “nanoscale test pattern” is fabricated. The test pattern is measured afterwards by some other means to deduct the relevant calibration parameters for the real patterning. The method allows doing the calibration and the actual application “on the same day”. 
         [0010]    The present invention does the measurement of the nanostructures continuously and during the lithography process for each line and hence within typically 10 ms to 100 ms. 
         [0011]    U.S. Pat. No. 5,825,670A describes a method how the information from imaging of a calibration sample using scanning probe microscope can be used to reduce errors due to non-linearity in the scanner motion. It is mentioned that this calibration can also be used to better control the positioning for scanning probe lithography, where a precise positioning is even more important than for imaging. 
         [0012]    The present invention images during the lithography process. The information of each imaged line can also be used to detect deviations from the xy position, e.g. through thermal drift, and correct for them. 
         [0013]    Scanning probe microscopy has been combined with scribing methods like in U.S. Pat. No. 5,327,625A. Here, a scribing tool indents nanostructures into a surface and a separate scanning probe microscope is used to measure the indentations. 
         [0014]    In the present invention the same probe is used for writing and imaging. 
         [0015]    In Scanning Tunneling Microscopy (STM) the imaging speed depends a lot on the feed-back loop of the imaging process. Previous imaged lines can be used to predict the topography of the next imaged line and can hence help to make the feed-back loop faster, as is described in U.S. Pat. No. 4,889,988 A. 
         [0016]    The present invention uses the fact that for each line the imaging information meaning the property of the nanostructure, like the topography in thermal scanning probe lithography, is already roughly known before the actual imaging process because the target property of the nanostructure of the writing process is known at the respective line. Hence, the imaging parameters can be optimized for speed and nondestructive imaging. This can mean for example in the case of topography that the z-positioning moves according to the target writing topography so that the probe is still in contact to measure the actual topography but without strong potentially destructive forces because the cantilever exerts a weaker force on the surface. 
       SUMMARY OF THE INVENTION 
       [0017]    According to prior art procedures, such imaging/reading of the written nanostructures is done after complete writing of the nanostructures. Hence, if the writing parameters (force, electric current, contact time, temperature, . . . ) are adjusted during the writing process, this is done in a feedback loop with a measurement of the writing parameter. 
         [0018]    It is therefore an object of the invention to provide an improved nanolithography writing method and device. 
         [0019]    The presented invention provides—inter alia—an improved control of the writing process and especially a way to monitor the surface and the written nanostructures during the write process and use this information to improve the write process on the fly. The method according to the invention therefore provides for a closed-loop feedback. In short, the invention provides an alternative: scanning probe closed-loop nanolithography and in-situ inspection system and method. 
         [0020]    A scanning probe nanolithography system according to the invention comprises a probe to create nanostructures line by line through writing said nanostructures pixel by pixel along lines on a sample. It has a position system, preferably a XYZ position system, adapted to provide a positioning of the probe at a sequence of predetermined positions to the sample and its surface towards the probe and a control unit adapted to control the position system for positioning the probe for a pixel-wise writing of said lines through a writing unit. A write/actuation mechanism is used for the creation of the nanostructures. A sensor unit is adapted to detect a predetermined property of the written nanostructure and is connected to the control unit to adapt the control signals to be provided to the writing unit for writing the following line based on the measured signals of the predetermined property. Following is to be understood as the next line in time, not necessarily the adjacent line. 
         [0021]    A tip scans over the surface of a sample. The tip is used to write/create/pattern a structure onto/into a sample and to read/image the structure and the surface of the sample as well and optional also monitor/read the distance of the tip to the surface of the sample. The information of the read process is used as feedback for the write process, e.g. for the next line. Thereby, the write process is directly controlled and stabilized with a higher frequency than uncontrolled alterations of external or internal influencing parameters can usually affect the patterning process. This method results in reliable and uniform patterning across the whole write field and less necessary calibrations prior to the writing. Also, it enables to display the written nanostructure on the computer screen already during the write process. The scan movement is done line by line (X=line direction), typically with the write process in one direction and the read process on the return. Reading the same line as the previously written line may not provide sufficient or correct information about the write process, because of the reading process itself (smaller size of the read pixel than write pixel) and the potential influence of the following write lines (finite write pixel size) on the structure. Therefore, the read line that follows the write line is preferably not done at the same line position Y, but at or between positions of earlier write lines. Hence, the scan motion in Y may go forward and backwards, depending on if the next line is a write or a read line. 
         [0022]    In other words, the control unit is adapted to control a XY portion of the position system to position the read line that follows the write line in a constant distance in parallel at or between positions of earlier write lines. The distance can be zero, then the previous written line is re-written; or the distance can be a multiple of the distance between write lines; then there are further previously written lines between the line just being read and the “next” line to be written. 
         [0023]    The control unit can be adapted to use the signal from the sensor unit to determine the distance between the tip and the sample surface and to use the acquired data from the sensor unit to adapt the control signals to be provided to the positioning system and consequently control the distance at all positions XY of the raster scanned area by adjusting the Z position motion. 
         [0024]    The information of the programmed property and hence expected property of the written nanostructure can be used to adjust the Z position motion the tip to be positioned at an optimized height for reading the said written nanostructure. 
         [0025]    Further embodiments of the invention are laid down in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, 
           [0027]      FIG. 1  shows a schematical representation of a scanning probe setup according to an embodiment of the invention; and 
           [0028]      FIG. 2  shows a closed-loop lithography process through visualization of the write and read process according to an embodiment of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]      FIG. 1  shows a schematical representation of a scanning probe setup according to an embodiment of the invention. Such a setup comprises the scanning probe lithography system and incorporates in the electronic parts control elements of the system showing a method according to the invention. 
         [0030]    The scanning probe lithography system comprises a positioning system  10  for positioning a writing element (tip  31 ) in the plane over the sample  20 . Here the positioning system  10  is a XYZ position system  10 . Such a XYZ position system  10  can comprise e.g. piezo stages or magnetic voice-coil stages. These are shown as a xy-piezo 2D displacement unit  11  and a z-piezo displacement unit  12 . The z-piezo displacement unit  12  is positioned in a direct relationship with the xy-piezo table  11  for a sample  20  where the nanostructure is produced. There is provided a tip  31  e.g. on a cantilever  30 . The cantilever  30  is connected with the piezo displacement unit  12  to be displaced over the surface  21 . 
         [0031]    It is noted that the z piezo displacement is not necessarily done to write the structure. In the method according to an embodiment of the invention the displacement for the writing is done via an electrostatic actuation mechanism. The Z piezo is used to level the tip to the right position. 
         [0032]    The cantilever  30  further comprises a write/actuation mechanism  41  to write a nanostructure with the tip  31  on or into the surface. The creation of the nanostructure originates from interactions between the tip  31  and the sample surface  21  that locally modify the sample surface  21 . Such modifications can originate from mechanical scratching or grinding, dip pen deposition of various inks from the tip to the sample, heat flow from the tip to the sample, electrical current between tip and the sample, an electric field that creates a liquid meniscus between the tip and the sample, an electric field that changes and deposits molecules in a liquid or gas between the tip and the sample, emission of electrons from the tip to the sample, local flip of the magnetic moment of the sample by a magnetic tip, enhanced light interaction through near field effects of the tip or any other tip induced local modification of the sample surface. The interactions and hence the modifications are turned on by applying a capacitive force, switching on a heating current, switching on field emission of electrons, switching on a laser that is focused on the tip, displacement of the z-piezo, a bimorph bending or switching on an electric field between the tip and the sample. Depending on the write/actuation mechanism  41 , parameters like temperature, duration of the interaction time, electrical current, electrical potential, displacement of the tip or light/laser intensity can be controlled and varied and hence influence the resulting write pixel in size, shape and/or degree of modification. 
         [0033]    A sensor unit  40  is provided and adapted to detect read/image a specific property/signal of the written nanostructure using the tip  31 . The property in relationship with the written nanostructure can be detected by any suitable kind of scanning probe microscopy technique for example based on the laser deflection or interferometry of the cantilever  30  or comprise a thermal sensor or piezoresistive sensor within the cantilever  30 . The specific property/signal can be a physical property based on friction, thermal conductivity, electrical conductivity, electrostatic potential, magnetic moment, adhesion, elastic modulus or topography or other properties typically measured using scanning probe microscopy techniques. 
         [0034]    Furthermore a controller unit  50 , usually a computer working as a real-time system, is provided. 
         [0035]    The XYZ positioning system  10  moves the sample  20  and/or the tip  31 . The controller  50  commands the movement in XY  52  and the movement in Z  53  of the XYZ positioning system  10  and hence controls the position of the tip  31  relative to the sample surface  21 . The XYZ positioning system  10  comprises positioning sensors (not shown) which send the coordinates of the position in XY  52  and the position in Z  53  to the controller unit  50 . The height signal is the exemplary read signal, it is not necessarily the piezo signal in other embodiments. The sensor unit  40  sends the measured specific property/signal from the interaction of the tip  31  with the sample surface  21  via an information path  51  to the controller unit  50 . 
         [0036]    The controller unit  50  sends continuously commands for the writing process to the positioning unit  10  with control in XY  52  and control in Z  53  and commands via an information path  54  to the write/actuation mechanism  41  and hence the writing tip  31  (which is done according to usual and known procedures in the art) and receives continuously and subsequently the position of the XYZ system  10  and the one or more signals of the sensor unit  40  relating to the reading process. 
         [0037]    Such a scanning probe system setup is provided to be used to monitor the writing process in various ways within different embodiments which are all considered encompassed by the principle of the invention. 
         [0038]    One way to monitor the writing process is to measure/read after one or more written lines, i.e. after having written a predetermined number of pixels of one or more writing lines. Switching between writing and reading for each line or between several lines provides information about the writing process that can be used as feedback signal for the writing parameters. Simple switching between the lines (trace and retrace) may not be sufficient to measure the final write result because the extension of the read pixels  66  is usually not of the same size as the write pixels  62  and write pixels of the next line may influence the final nanostructure if the distance in Y between write lines is smaller than the extension of the write pixels  62 . 
         [0039]      FIG. 2  shows, inter alia, on the right side a scheme for a scan path  60  to overcome the previously mentioned limitations and really use only information of final written lines (written pixel extensions  62 ) as input for the ongoing writing process. The scan path  60  that goes both forward  61  and backwards  65  in the Y direction and not just forward as done in all usual scanning probe technologies. In a simpler embodiment, the forward write path  61  and the backward read pass comprise a simple switching between read and write lines as a basic approach for a feedback implementation. In another embodiment the direction of the write path  61  and the read path  65  are in the same direction, wherein the next write path after a read path  65  can comprise a turn in the side areas  23  as will be explained below. 
         [0040]    Thermal desorption nanolithography is an exemplary scanning probe nanolithography technique, which is suitable and has been demonstrated to work for the presented closed-loop nanolithography scheme. This technique uses a heatable tip  31  and resist materials like polyphthalaldehyde (PPA) that are responsive to heat. The resist evaporates at the locations where it comes into contact with the hot tip. The write/actuation mechanism (in this case an electrostatic force that pulls a heated tip into contact with the sample for a certain time) determines how deep the tip penetrates the resist and hence determines the depth of the pattern. The force is varied e.g. according to the gray-level of a bitmap. Thereby, the bitmap can be converted into a relief in the resist where the depth at each position corresponds to the gray-level of the bitmap. However, effects like drift in Z direction, non-parallelism between the scan plane and the sample plane or physical and chemical changes within the tip, the cantilever  30  and the sample  20  influence the patterning force (as exerted through control signals  54 ) and the distance between tip  31  and sample  21  and hence influence the depth during the write process. A full control over all these effects during the write process of fields of typical sizes between 0.1 μm 2  and 100,000 μm 2  is hardly possible. Therefore, in this example the force and Z piezo position are adjusted during the write process according to the measured topography of the previous lines. 
         [0041]      FIG. 2  further displays the closed-loop lithography process for the example of thermal desorption nanolithography through visualization of the write and read process according to an embodiment of the invention. A grayscale bitmap of physicist Richard Feynman was written into PPA as sample  20  using a heatable tip  31 . Piezo motors were used to scan the tip  31  in X and Y over the surface  21  in a raster scan manner. The pattern image  24  was written within a central area  22  of the piezo scanner movement, where the movement is linear, meaning the scan speed of typically between 0.1 and 10 mm/s in X was constant. In the surrounding turnaround zone  23  the scan movement in X turns around. The time during which the tip  31  is in this region (typically 1 ms to 100 ms) was not used for patterning but for positioning in Y (go to next line) and for processing of the feedback data. The turnaround zone  23  is part of the example and not an inevitable part of the invention as the data processing and the positioning in Y can also be done within the central area  22 , however, with an possible loss in positioning accuracy. 
         [0042]    The writing with the heated tip  31  was done in trace (to the right, positive X) direction along line  61  and creating write pixel extensions  62 . During the turnaround  63  in zone  23 , the tip  31  was cooled down and moved backwards (negative Y direction). On the retrace (to the left, negative X) direction along line  65  the cold tip  31  was used to measure the topography of the sample surface  21  via an integrated thermal sensor as sensor unit  40 . This is shown in the exemplary height diagram (cross section at the position of the eyes of Richard Feynman) on the lower left part of  FIG. 2 , wherein the height  0  is the surface position and the double arrow  75  shows the depth amplitude (in this case around 30 nm) of the topography towards the lower dotted line, wherein the intermediate line of the two dotted parallel lines is related to the mean depth (in this case around 12 nm). Within the writing step at tip height  71  the sample  20  was structured using the heated tip  31  and the write/actuation mechanism  41  (in this case the patterning force) to write the programmed depth of the pattern. Upon the way back with the lowered cold tip  31 , said tip followed the solid line  73  as measured/read depth, predetermined by the written structure and the sensor unit (in this case the integrated thermal sensor) sent the topography signal to the control unit ( 50 ). 
         [0043]    The measured topography was compared to the programmed/target depth at this line (Y position). Deviations from the target were detected. This can be done for each X position (corresponding to an applied patterning force) or global deviations like the deviation of the mean depth (to adjust the mean writing force) and/or the depth amplitude  75  (to adjust the force range) can be calculated. In the next turnaround zone, the tip is moved forward (positive Y direction) to the next write line. Which write line  61  is the next write line can depend on the measured deviation (e.g. a line can be repeated). For this next write line  61  the patterning forces were adjusted according to the measured deviations. In this example, if the depth was too shallow, the patterning force was increased accordingly to meet the target depth. As a consequence, the patterning depth  73  matches the target depth  74  with exceptional precision for the whole nanostructure  24 . 
         [0044]    Both the write and the read pixels  62  and  66  have a finite extension (typically 0.1 nm to 100 nm depending on the tip size and the kind of interaction with the sample surface  21 ). It is important that the reading occurs in the area where the writing is “finished”, meaning that it is out of reach of a not yet written line which could still influence the nanostructure at this Y position. Therefore the backwards step before reading should be large enough, so that it is guaranteed that the extensions of the subsequent write line do not intersect with the extension of this read line. The reading line  66  does not necessarily read (in this example measure the depth) of the previously written line  61 , but read lines that have been written one or more steps before. If the specific just written line should be monitored, then the backwards step before reading should be smaller than half the write pixel extension  62  plus half the read pixel extension  66  as shown in the embodiment of  FIG. 2 . Here each read pixel  66  is smaller than the neighboring write pixel  62 . However, the parallel distance between write line  61  and read line  65  is small enough that such circles intersect. 
         [0045]    The sensor  40  can also be used to gain additional information for feedback control of the writing process besides reading the written pattern and compare it with the target pattern as described above. If the sensor  40  is capable of measuring the distance between the tip  31  and the sample surface  21 , like it is possible with a thermal height sensor, then this information about the distance can be used as a further feedback input for the writing process. For this feedback, a frame around the image pattern  24  was left in the example of  FIG. 2  within the field  22  of linear scanner motion. 
         [0046]    This reading frame is used to determine the distance  81  between the surface  72  and the tip  31  at write height  71 . In the example, the tip  31  was cooled down and the read sensor  40  switched on inside that frame. In the frame of a read line  65  the tip was in contact with surface and hence the surface position  72  was measured. In a write line  61 , the tip was out of contact at a corresponding write height  71  and hence the corresponding write distance  81  was determined. This can be done on the left and on the right side of a write field  24  and for each line, meaning for all Y positions. As a consequence, if for example the sample plane is not perfectly parallel to the scan plane (which is almost always the case) or if a drift in Z occurs during the process, this is detected through the measured deviations of the distance  81  in X or Y direction. Such deviations can hence be compensated for to improve the control over the write process. In the example, the deviations have been corrected using the Z piezo stage  12 , so that the write distance  81  maintained constant during the whole write process and hence enabling a more accurate control of the patterning force over the whole write field  24 . 
         [0047]    The target depth and the measured depth can further be used as feed-forward input to determine the ideal reading position in Z for each line. If the reading Z position of the tip  31  is chosen is not deep enough the tip  31  might be getting out of contact with the sample  21  and hence not read the surface topography anymore. On the other hand, if the reading Z position of the tip  31  is chosen too deep then the tip  31  and the sample  21  can be harmed due to increased pressure between the tip  31  and sample  21  for shallow structures. In the example, the Z piezo was used during the read process to move the tip  31  to the programmed depth amplitude  75 , which is the expected maximum depth. This prevents the tip  31  from losing contact of the surface and hence insufficient reading and minimizes the degradation of the tip  31  and the sample  21  through the reading process. 
         [0048]      FIG. 2  shows on the left a written and imaged nano-relief of Richard Feynman. The square  22  around the image  24  illustrates the scan field of the XY positioning system  10  with and without the turnaround zone  23 . The graph  70  underneath the image displays a cross-section through one exemplary line of the topography image. The dashed line  74  is the programmed depth of the pattern and the solid line  73  measured/read depths. Feedback parameters like mean depth or depth amplitude are illustrated. The Z movement  12  between write and read (piezo travel  80 ) is also illustrated in the image. On the right portion the scan path is illustrated as a solid line with portions  61 ,  63 ,  65  and finally  64  in the sense of motion. The circles  62  and  66  illustrate the extensions of the write and read pixels (the write and read interaction volume); the size of the pixel at such can be quite different to the values mentioned in connection with the embodiment in  FIG. 2 . It is noted that it is also possible but not preferred that the reading of the written lines is performed in the same direction as the writing, then after cooling down tip  31 , it is returned at the starting point of the line and the switch to the next reading line either occurs at the end of the reading or tip  31  is again displaced at the beginning of the written and then read line. 
         [0049]    The example in  FIG. 2  uses thermally induced evaporation of resist material by a heated tip and an electrostatic force as the write/actuation mechanism  41  and a thermal sensor element integrated in the cantilever  30  as the sensor unit  40  to read with the same tip the topography as the specific property of the written nanostructure. 
         [0050]    Many combinations of different write and read processes using the same tip for writing and reading would be suitable for the presented invention: For example, Szoszkiewicz et al., (Nano Letters, 7(4):1064-1069, 2007) wrote hydrophilic nanostructures onto a hydrophobic polymer by local chemical modification using a heated tip and imaged the written nanostructures after the write process by measuring the friction on the sample surface using Lateral Force Microscopy. Nanostructures written by local anodic oxidation, as for example done by Martinez et al. (Nanotechnology, 21(24):245301, 2010), can be imaged by reading the topography or the electric potential using Kelvin Probe Microscopy. Dip Pen Lithography is a wide spread nanolithography technique and usually writes nanostructures by bringing a tip that is covered with an ink into contact with the sample surface and thereby deposit the ink onto the sample surface. Nelson et al. ( Applied physics letters,  88:033104, 2006) showed that they could write metal inks by thermal dip pen lithography and imaged the written structures with the same tip after writing of the nanostructure. Therefore, using the same tip for reading of the written ink nanostructures is possible, because it can be avoided that ink is deposited again during the reading process. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE SIGNS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 XYZ position system 
               
               
                 11 
                 xy displacement unit 
               
               
                 12 
                 z displacement unit 
               
               
                 20 
                 sample 
               
               
                 21 
                 surface to be nanostructured 
               
               
                 22 
                 central area 
               
               
                 23 
                 border area/turnaround zone 
               
               
                 24 
                 image of pattern 
               
               
                 30 
                 cantilever 
               
               
                 31 
                 tip 
               
               
                 40 
                 sensor unit 
               
               
                 41 
                 write/actuation mechanism 
               
               
                 50 
                 controller unit 
               
               
                 51 
                 read signal 
               
               
                 52 
                 control of xy motion 
               
               
                 53 
                 control of z motion 
               
               
                 54 
                 write signal 
               
               
                 60 
                 scan path 
               
               
                 61 
                 write path 
               
               
                 62 
                 write pixel extension 
               
               
                 63 
                 turn around portion 
               
               
                 64 
                 move to next line portion 
               
               
                 65 
                 read path 
               
               
                 66 
                 read pixel extension 
               
               
                 67 
                 write direction 
               
               
                 71 
                 write height 
               
               
                 72 
                 read height 
               
               
                 73 
                 measured depth (solid line) 
               
               
                 74 
                 programmed depth (dashed line) 
               
               
                 75 
                 depth amplitude 
               
               
                 80 
                 z piezo travel 
               
               
                 81 
                 write distance