Abstract:
An apparatus and method of analyzing a sample to be scanned within a hermetically sealed housing of an atomic force microscope (AFM) while the interior of the housing is maintained at one of a number of various environmental conditions. The AFM includes an XYZ stage assembly on which a sample holder supporting the sample may be releasably positioned. The stage assembly allows for the manipulation of the sample and sample holder in the X, Y and Z axes without disturbing any environmental condition present within the chamber due to the hermetic seal maintained between the stage assembly and the AFM during the motion of the stage assembly. The ability of the stage assembly to manipulate the sample in each of the three directions while the sample is enclosed within the AFM also allows the AFM to compensate for non-parallel scanning planes and for drift in all three directions occurring in the sample because of the different environmental conditions in which the sample may be scanned. The scan is performed by the AFM using a scanning tube sealingly disposed within the housing and capable of moving small distances in the X, Y and Z axes. Fine adjustments to the position of the tube in order to accurately scan the sample are accomplished by the inclusion of sectioned piezoelectric elements within the tube which are capable of adjusting the position of a probe or cantilever attached to the end of the tube in small, highly accurate distances in each of the X, Y and Z directions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to scanning probe microscopes (SPMs) including atomic force microscopes (AFMs) and, particularly, to an AFM that has a hermetically sealed superstructure that allows analyzation of a sample under different environmental conditions.  
           [0003]    2. Description of the Related Art  
           [0004]    An Atomic Force Microscope (“AFM”), as described for example, in U.S. Pat. No. RE34,489 to Hansma et al. (“Hansma”), is a type of scanning probe microscope (“SPM”). AFMs are high-resolution surface measuring instruments. Two general types of AFMs include contact mode (also known as repulsive mode) AFMs, and cyclical mode AFMs (periodically referred to herein as TappingMode.TM. AFMs). (Note that TappingMode.TM. is a registered trademark of the present assignee.)  
           [0005]    The contact mode AFM is described in detail in Hansma. Generally, the contact mode AFM is characterized by a probe having a bendable cantilever and a tip. The AFM operates by placing the tip directly on a sample surface and then scanning the surface laterally. When scanning, the cantilever bends in response to sample surface height variations, which are then monitored by an AFM deflection detection system to map the sample surface. The deflection detection system of such contact mode AFMs is typically an optical beam system, as described in Hansma.  
           [0006]    Typically, the height of the fixed end of the cantilever relative to the sample surface is adjusted with feedback signals that operate to maintain a predetermined amount of cantilever bending during lateral scanning. This predetermined amount of cantilever bending has a desired value, called the set-point. Typically, a reference signal for producing the set-point amount of cantilever bending is applied to one input of a feedback loop. By applying the feedback signals generated by the feedback loop to an actuator within the system, and therefore adjusting the relative height between the cantilever and the sample, cantilever deflection can be kept constant at the set-point value. By plotting the adjustment amount (as obtained by monitoring the feedback signals applied to maintain cantilever bending at the set-point value) versus lateral position of the cantilever tip, a map of the sample surface can be created.  
           [0007]    The second general category of AFMs, i.e., cyclical mode or TappingMode.TM. AFMs, utilize oscillation of a cantilever to, among other things, reduce the forces exerted on a sample during scanning so as to minimize tip and/or sample damage, for example. In contrast to contact mode AFMs, the probe tip in cyclical mode makes contact with the sample surface or otherwise interacts with it only intermittently as the tip is scanned across the surface. Cyclical mode AFMs are described in U.S. Pat. Nos. Re 36,488, 5,226,801, 5,412,980 and 5,415,027 to Elings et al.  
           [0008]    In U.S. Pat. No. 5,412,980, a cyclical mode AFM is disclosed in which a probe is oscillated at or near a resonant frequency of the cantilever. When imaging in cyclical mode, there is a desired tip oscillation amplitude associated with the particular cantilever used, similar to the desired amount of cantilever deflection in contact mode. This desired amplitude of cantilever oscillation is typically kept constant at a desired set-point value. In operation, this is accomplished through the use of a feedback loop having a set-point input for receiving a signal corresponding to the desired amplitude of oscillation. The feedback circuit adjusts the vertical position of either the cantilever mount or the sample by applying a feedback control signal to a Z axis actuator so as to cause the probe to follow the topography of the sample surface.  
           [0009]    Typically, the tip&#39;s oscillation amplitude is set to be greater than 20 nm peak-to-peak to maintain the energy in the cantilever arm at a much higher value than the energy that the cantilever loses in each cycle by striking or otherwise interacting with the sample surface. This provides the added benefit of preventing the probe tip from sticking to the sample surface. Ultimately, to obtain sample height data, cyclical mode AFMs monitor the Z actuator feedback control signal that is produced to maintain the established set-point. A detected change in the oscillation amplitude of the tip and the resulting feedback control signal are indicative of a particular surface topography characteristic. By plotting these changes versus the lateral position of the cantilever, a map of the surface of the sample can be generated.  
           [0010]    Notably, AFMs have become accepted as a useful metrology tool in manufacturing environments in the integrated circuit and data storage industries. A limiting factor to the more extensive use of the AFM was the inability to change the environmental conditions in which a particular sample positioned within the AFM is analyzed. For example, due to various operating conditions, it is desirable to determine the effects that these conditions will have upon various samples, such as elevated or reduced temperatures and pressures. However, because most AFMs are constructed to be utilized only at ambient temperatures and pressures, such AFMs are not sealed as environmental conditions experienced by the sample do need to be altered from the ambient. Although attempts have been made to offer environmental capability, there are significant drawbacks associated with performing tests under varying environmental conditions with existing AFMs.  
           [0011]    More particularly, some recent AFM designs have been adapted to enable samples to be tested under varying environmental conditions. Examples of AFMs having this capability are described herein. In one known system, a cover is releasably and sealingly engaged with a chamber containing the sample to be scanned. The cover also includes resilient seals disposed around the moving parts of the AFM that extend into the chamber, such as the screws or Z actuator(s) and the cantilever tube. The sealing engagement of the cover with the moving parts and the chamber enables the sample contained within the chamber to be placed within a number of different environmental conditions, such as under a protective fluid, in the presence of a particular gas, or the like.  
           [0012]    However, due to the imperfect seal created between the cover and the chamber, it is difficult to obtain stable variations in the environment surrounding the sample. For example, any gases discharged to the chamber may slowly escape overtime from the AFM past the seals created between the chamber and the cover if the seal is not formed correctly when the cover is engaged with the chamber, or when the seals surrounding the moving parts are disturbed when those parts are moving. Further, because the seal between the cover and the instruments and chamber is not hermetic, the seal can only withstand a certain pressure differential before failure, such that very low pressure environmental conditions, such as a vacuum, cannot be established within the AFM environment.  
           [0013]    In another system, all of the components of the AFM are contained within a sealed chamber such as a bell jar. The AFM components are monitored by a controller connected to the components by feed throughs extending through the base of the bell jar in order to operate the AFM as needed. Further, gas inlets and outlets can be extended through the bell jar base to enable the environmental conditions within the bell jar to be altered, such as by introducing a specific gas, or removing all gases present within the jar to form a vacuum.  
           [0014]    In another similar AFM, each of the components of the AFM are disposed within a bell jar that is sealingly connected to a base to completely enclose the interior of the jar. The AFM components are controlled using feed throughs extending through the base and connected to an exterior controller in order to conduct the analysis of the sample located inside the bell jar. Using the feed throughs, various environmental conditions can be created within the bell jar such that a sample can be evaluated in each of the different conditions.  
           [0015]    Because each of the above-mentioned AFM is constructed using a sealed bell jar, they are capable of changing the environmental conditions present within the AFM. However, the construction of these types of AFMs makes it highly difficult to either change or alter the position of a sample being analyzed within the AFM that is undergoing analysis, such as to measure different selected areas of the sample surface or to compensate for sample drift. This is because the construction of the prior art bell jar AFMs requires that the seal between the cover and the bell jar be broken in order to access the sample disposed within the AFM. In doing so, the environmental conditions formed within the AFM are necessarily dissipated, such that once the sample is either changed or repositioned, the AFM must be resealed and the desired environmental conditions must be regenerated within the AFM. Thus, much time and effort is exhausted in simply duplicating the environmental conditions within the AFM.  
           [0016]    Also, with regard to the positioning of the probe or cantilever tip with respect to the sample, most prior art AFMs utilize a piezoelectric element in order to move the cantilever closer to or away from the sample. Piezoelectric elements are normally used for this purpose due to the fact that the elements can be actuated by the application of a voltage to the element in order to move the cantilever very small distances, on the order of around one micron, in order to engage the sample as needed.  
           [0017]    However, based on the inherent construction of the piezoelectric elements used, the elements are subject to a certain amount of error with regard to the distance that the cantilever is moved by the element. For example, if an element is sent a specific voltage differential in order to actuate the element and move the cantilever a specified distance, the actuation of the element may be accompanied by noise which causes the element to move the cantilever a distance slightly greater or less than that specified. When the distance the cantilever is to be moved is significantly greater than the error factor, the error factor does not significantly effect the position of the cantilever. However, when the cantilever is only to be moved a very short distance, the error factor can greatly effect the positioning of the cantilever. This can cause inaccurate or even worthless data. This problem is of particular concern when the environmental conditions associated with the experiment are altered from the ambient; for example, thermal drift can exacerbate positioning errors.  
           [0018]    In sum, one significant drawback of prior art AFMs is that the sample cannot be readily manipulated within the AFM when a non-ambient environmental condition, such as reduced pressure or temperature is present within the AFM. As a result, the metrology field was in need of an AFM having the capability of altering the position of the sample within the AFM without interrupting the environment created within the AFM.  
           [0019]    Another drawback of prior art AFMs is that the piezoelectric elements utilized to move the cantilever with respect to the sample when scanning the sample are greatly affected by noise in the voltage differentials applied to the elements to move the cantilever only a small distance. Therefore, it is also desirable to provide an improved piezoelectric actuator which greatly reduces the effect of the noise of the system on the movement of the cantilever by the actuator over a short distance.  
         SUMMARY OF THE INVENTION  
         [0020]    A preferred embodiment of this invention overcomes the drawbacks of prior art AFMs by providing a scanning probe microscope that enables a sample to be moved in all three axes within the AFM without disturbing a non-ambient environment created within the AFM. Each of the components of the AFM is sealingly engaged with the superstructure to provide an enclosed, hermetically sealed environment in which the sample can be analyzed.  
           [0021]    According to a first aspect of the invention, the AFM includes an XYZ stage assembly sealingly engaged with the bottom of the superstructure for positioning and moving the sample within the superstructure. The stage assembly includes a pair of sliding or translation plates for moving the sample in the X and Y axes, and a number of vertical actuators to move the sample in the Z axis, all of which are connected to an interface or sample support stage disposed inside the superstructure. The stage assembly can be manipulated by controls located on the exterior of the AFM in order to manually or automatically position the sample as desired within the AFM.  
           [0022]    According to another aspect of the preferred embodiment, the AFM also includes a head assembly hermetically sealed to the superstructure opposite the stage assembly. The head assembly includes a scanning tube including a number of piezoelectric elements and having a probe or cantilever disposed at one end within the superstructure adjacent the stage assembly. The tube is sealingly engaged with the superstructure opposite the cantilever within a tube mount plate that can be releasably secured to the superstructure. The engagement between the tube and the mount plate allows the tube to move freely along the X, Y and Z axes because the engagement of the tube with the mount plate is spaced from the mobile portions of the tube.  
           [0023]    According to still another aspect of the preferred embodiment, the scanning tube includes sectioned piezoelectric elements which are used to move the tube sections and position the probe where desired with respect to the sample. The sectioned piezoelectric elements include a larger section that is actuated when relatively large cantilever movements are necessary, and a small section that is used when fine adjustments in the position of the cantilever are made. The small section enhances the fine positioning of the cantilever by reducing the effect of the noise contained in the voltage differential used to actuate the small section of the piezo element. The piezoelectric elements can be sectioned either physically or by an conductive metallic coating placed on the exterior of the element in order to enable incoming voltage signals to activate the desired section of the element.  
           [0024]    In another aspect of this embodiment, the XYZ stage assembly of the AFM incorporates a sample holder locating pin attached to the interface stage of the assembly. The locating pin operates to help ensure that a sample holder positioned on the interface stage assembly will remain aligned with the probe regardless of any drift occurring in the sample or the sample holder based on the changing environmental conditions within the AFM.  
           [0025]    According to still a further aspect of the preferred embodiment, the AFM can be operated in a manner that is capable of initially determining whether the sample to be scanned is positioned on a plane parallel to the scan plane of the cantilever. If the sample is not positioned parallel to the probe, the AFM can automatically adjust the position of the sample utilizing the Z actuators connected to the stage assembly disposed within the superstructure to tilt the stage assembly on which the sample is positioned such that the sample is disposed parallel to the scan plane of the probe.  
           [0026]    In yet another aspect of the preferred embodiment, a scanning probe microscope includes a superstructure defining a hermetically sealed interior within which a probe and a sample are disposed such that the SPM can image the sample under a non-ambient condition. The SPM also includes a stage assembly hermetically sealed to the superstructure and configured to support the sample. In operation, the stage assembly can translate the sample without disturbing the non-ambient condition.  
           [0027]    In another aspect of this embodiment, the SPM includes a tube actuator having opposed ends. The opposed ends include a first end that is generally fixed and a second end that translates the probe. Moreover, the actuator is sealed to the superstructure at the fixed end to allow movement of the tube actuator, and thus the probe, under any environmental condition without compromising the hermetic seal provided by the superstructure.  
           [0028]    According to a still further aspect of this embodiment, the stage assembly includes a sample support stage for receiving a sample holder. Preferably, the sample support stage includes an indexing element to position the sample holder at a preselected position relative to the probe. And, the indexing element is preferably a pin extending outwardly from the sample support stage and operates to minimize adverse expansion/contraction effects due to changed environmental conditions.  
           [0029]    These and other objects, features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:  
         [0031]    [0031]FIG. 1 is a cross-sectional view of a prior art sealed atomic force microscope illustrating the vertical movement of a sample disposed within the AFM;  
         [0032]    [0032]FIG. 2 is an isometric view of the hermetically sealed AFM constructed according to the preferred embodiment;  
         [0033]    [0033]FIG. 3 is a cross-sectional view along line  3 - 3  of FIG. 2;  
         [0034]    [0034]FIG. 4 is an exploded cross-sectional view of a scanning tube mount shown in FIG. 3;  
         [0035]    [0035]FIG. 5 is an exploded view of the sliding translation plates and plate support of an x, y, z stage assembly shown in FIG. 3;  
         [0036]    [0036]FIG. 6 is a partially broken away cross-sectional view of the x, y, z stage assembly of FIG. 3;  
         [0037]    [0037]FIG. 7 is a top plan view of the plate support for the x and y sliding translation plates;  
         [0038]    [0038]FIG. 8 is an isometric view of a prior art piezoelectric element utilized with a scanning tube;  
         [0039]    [0039]FIG. 9 is an isometric view of a sectioned piezoelectric element utilized with the scanning tube of the present invention;  
         [0040]    [0040]FIG. 10 is a flow chart illustrating the steps of a Z axis drift correction method using the AFM of FIG. 2;  
         [0041]    FIGS.  11 - 13  are schematic views illustrating the sample plane tilt control method performed by the AFM for a sample being scanned; and  
         [0042]    [0042]FIG. 14 is a flow chart illustrating the steps of a tip/sample engage method using the AFM of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0043]    Turning initially to FIG. 1, an example of a conventional AFM structure  20  for performing environmental AFM measurements is illustrated. The conventional AFM  20  includes a chamber  22  defining an open interior  24  in which a sample  26  can be positioned. The sample  26  is supported on a platform  28  that is vertically movable within the chamber  22  by the actuation of a pair of screws  30  secured to opposite sides of the platform  28 . The screws  30  extend upwardly through openings  31  in a cover  32  positioned over the chamber  22  in order to completely enclose the chamber  22 . The cover  32  includes a pair of first sealing members  33  disposed within the openings  31  that surround and sealingly engage the screws  30  and a peripheral sealing member  34 , such as a rubber gasket. The sealing member  34  is positioned around the periphery of the cover  32  and engages the chamber  22  in order to provide a seal between the chamber  22  and the cover  32  that effectively encloses the interior  24  of the chamber  22 . The cover  32  also includes a central opening  36  disposed between the openings  31  in which the lower end of a scanning tube  38  can be disposed. The exterior of the tube  38  is engaged with a second sealing member  40  (e.g., an O-ring) extending along the periphery of the opening  36  in order to provide a sealed engagement between the tube  38  and the cover  32 . The positioning of the second sealing member  40  also allows the scanning tube  38  to be moved vertically with respect to the interior  24  of the chamber  22 , such that a probe  37  coupled to the scanning tube  38  can selectively engage the sample  26  located on the platform  28 .  
         [0044]    To use the conventional AFM  20 , initially the sample  26  is positioned on the platform  28 . The cover  32  can then be sealingly engaged over the interior  24  of the chamber  22 . The screws  30  can then be adjusted relative to the scanning tube  38  in order to position the tube  38 , and thus the probe  37 , adjacent the sample  26  prior to scanning the sample  26 . The environment within the chamber  22  can then be altered by heating or cooling the gas within the chamber  22 , or by removing or changing the gas present within the chamber  22 . After the environmental conditions within the chamber  22  have been altered as desired, the tube  38  and platform  28  can be vertically adjusted with respect to one another to engage the tube  38  with the sample  26  in order to perform the analysis.  
         [0045]    However, on many occasions the sample  26  will need to be adjusted on the platform  28  along the X or Y axis in order to properly align the sample  26  with the tube  38 . This may be due to the user&#39;s desire to analyze different portions of the sample  26 , or because changed environmental conditions caused a certain degree of drift within the AFM  20 . In order for the position of the sample  26  to be adjusted on the platform  28  along the X or Y axis, the cover  32  must be removed from the chamber  22 , allowing any environmental condition created within the chamber  22  to be disrupted. Once the sample  26  is properly repositioned, the cover  32  and chamber  22  must be resealed and environmental condition previously generated within the chamber  22  must be recreated in order to perform the desired scan on the sample  26 .  
         [0046]    Moreover, after adjusting the position of the platform  28  and tube  38  with respect to one another, it may also be necessary to adjust the environmental conditions within the chamber  22  to the previous levels, although typically not.  
         [0047]    Referring now to FIGS. 2 and 3, a sealed AFM  120  constructed according to the preferred embodiment is illustrated which overcomes the deficiencies of the conventional AFM  20  and other similar AFMs. The AFM  120  includes a hermetically sealed superstructure  122  that is formed from a body  124  integrally formed of a rigid material, such as a metal, and preferably a stainless steel such as INVAR®. The body  124  defines an interior chamber  125  and includes an upper wall  126  and a lower wall  128  that defines a central opening  129 , joined by a pair of opposed side walls  130 . The body  124  also includes a front wall  132  including a window  134 . The window  134  in the front wall  132  is hermetically sealed by a sheet of transparent material  142  that is fixedly and sealingly engaged with the front wall  132  by bolts  135 . The sheet  142  allows a sample  144  positioned within the AFM  120  to be viewed, for example during positioning a scanning of the sample  144 . The rear of the body  124  is generally open and is covered by a removable back panel  136  that is sealingly engageable with the body  124 . The back panel  136  allows access to the chamber  125  and includes a vacuum flange  138  and a first hermetic feed through  140  to enable gases to pass into and out of the superstructure  122  when the AFM  120  is in operation. A second feed through  145  is located on one side wall  130 , as shown in FIG. 3. The first and second feed throughs  140  and  145  allow static connections, such as electric leads, to be made between components inside the AFM  120  and a controller  141  outside the AFM  120  without comprising the hermetic sealing of the AFM  120 .  
         [0048]    With continued reference to FIGS.  2 - 4 , the body  124  includes an integral pedestal  146  extending upwardly from the upper wall  126  of the body  124 . The pedestal  146  includes a throughbore  148  extending downwardly into the interior chamber  125  of the body  124 . In the interior chamber  125 , the throughbore  148  is aligned with a tube housing  150  that is secure to and extends downwardly from the upper wall  126 .  
         [0049]    A head assembly  151  including a piezoelectric scanning tube  152 , a mount plate  166 , a window  174 , and a light source (e.g., a laser)  182  is releasably fixed to the pedestal  146 . The head assembly  151  can be removed from the pedestal  146  such that, if any of the components of the head assembly  151  become damaged or are not functioning properly, the entire head assembly  151  can be removed for repair from the pedestal  146  and replaced without having to disassemble the parts of the head assembly  151  from one another. Piezoelectric scanning tube  152  is positioned within and extends downwardly through the throughbore  148  and housing  150 . The scanning tube  152  is formed of a piezoelectric material and includes an upper section or actuator  154  and a lower section or actuator  156 . The lower section  156  is joined to the upper section  154  by a coupling  160 , which is preferably made of an insulative material.  
         [0050]    Electrodes (not shown) disposed on the elongated piezoelectric tube sections are each connected to the exterior controller  141  by leads  163   a  and  163   b , respectively, that are capable of transmitting a voltage differential across the electrodes coupled to actuators  154 ,  156 . When a voltage is applied to the electrodes the sections  154 ,  156  are caused to contract or expand and consequently move the scanning tube  152  a specified distance depending upon the magnitude of the voltage applied to the elements  154  and  156 . Based on their particular construction and/or configuration, each of the sections  154 ,  156  will move a specific distance based upon the voltage applied to the elements. In the preferred embodiment, piezoelectric section  154  is designed to provide tube movement, and then translation of the probe coupled to the distal or free end  153  of tube  152 , along the X and Y axes, illustrated by the axis reference  155  in FIG. 2, while section  156  provides tube movement in response to appropriately applied voltages. In this manner, the position of the lower end  153  of the scanning tube  152  can be adjusted within the body  124  over the range of movement for element  156 , which is approximately five (5) microns, and element  154 , which is about 100 μm. Notably, by positioning the X-Y section  154  of tube  152  further from the probe, the movement of the probe in X and Y is amplified (lever effect) which is desirable due to limited scan ranges associated with piezoelectric tubes.  
         [0051]    Referring now to FIGS. 8 and 9, in a conventional AFM  20 , piezoelectric sections  154  and  156  are formed as unitary elements  400  having electrodes  402 ,  404  disposed thereon that are operably connected to a pair of lead wires  406 ,  408  so that a voltage differential can be applied thereto. As stated previously, the amount of movement of the tube  152  generated by the activation of the specific element  154  or  156  is completely controlled by the voltage supplied to the piezoelectric element  400 . The voltage applied to the piezoelectric section  154  or  156  necessarily has a certain amount of noise present within the voltage signal. Depending upon the particular sensitivity of the element  400 , the noise present within the voltage signal can cause the element  400  to move the scanning tube  152  a distance greater or less than desired. For example, if the sensitivity of element  400  is one hundred (100) nanometers per volt, if ten (10) millivolts of noise are present in the voltage signal, the piezoelectric element  400  will move the scanning tube  152  an additional one (1) nanometer when this voltage is applied. Thus, noise, depending upon the size of the voltage signal, the sensitivity of the element  400 , and the amount of movement desired for the tube  152 , can seriously affect the accuracy of the movement of the tube  152  in response to the actuation of the element  400 .  
         [0052]    Referring now to FIG. 9, in one preferred embodiment the electrodes  402 ,  404  of one or both of sections  154 ,  156  are segmented into a first pair of upper electrodes  410 ,  412 , and a second pair of lower electrodes  414 ,  416 ,  418 . Notably, either or both piezoelectric actuators  154  and  156  can have electrodes segmented in this fashion. Preferably, the segmented electrodes are disposed on the piezoelectric actuators  154 ,  156  ( 154  in FIG. 9) by plating the outer surface areas of actuators  154 ,  156  with a metallic, conductive coating  418 . A strip of the coating is then removed from the exterior of the actuator  154  in conventional fashion such that a nonconductive strip  420  is positioned around the perimeter of the actuator dividing the actuator into an upper section  422  and a lower section  424  having corresponding electrodes sized according to a selected sensitivity. Each section  422  and  424  is connected to a pair of leads  426 ,  428  and  430 ,  432 , respectively, such that a voltage signal passed to the upper section  422  will not actuate the lower section  424 , and vice versa. By segmenting either or both of the piezoelectric actuators  154  and  156 , the tube system sensitivity can be modified. In particular, when a voltage differential is applied across section  422 , which now has, for example, a sensitivity often (10) nanometers per volt due to its reduced size (i.e., the voltage differential is applied over a smaller surface area of the piezoelectric), and ten (10) millivolts of noise is present within the signal, the upper section  422  of scanning tube  152  only causes an additional {fraction (1/10)} th  of a nanometer of movement due to the noise. Thus, by segmenting actuators  154  and  156 , it is possible to generate much more accurate movement of the probe with scanning tube  152 . Again, small movements of tube  152  may be required based on a number of reasons, including for example noise within the applied voltage signal, so that a much more accurate scan of the sample  144  can be achieved.  
         [0053]    Referring once again to FIGS. 2, 3 and  4 , the free end of lower section  156  supports a probe assembly  162  including a probe holder  164  configured to receive an AFM probe  166 . The holder  164  and probe  166  are similar to those disclosed in the above-noted references, such as those shown in U.S. Pat. Nos. Re34,489 and Re36,488, hereby incorporated by reference, and is used to generate a signal corresponding to, for example, the various topographical features of the sample  144  using one of the previously discussed methods of operation. Upon the activation of the piezoelectric actuators  154  and  156 , the probe  166  can be moved along with the tube  152  with respect to the sample  144  in order to scan the surface of the sample  144 .  
         [0054]    Opposite the probe  166 , the scanning tube  152  is sealingly secured to the pedestal  146 . This is accomplished by providing a mount plate  167  that is releasably fixed to the pedestal  146 . The plate  167  includes an opening  168  coaxially aligned with the throughbore  148  in the pedestal  146  through which the upper section  154  of the scanning tube  152  can be positioned. A circumferential recess  170  is disposed around the opening  168  opposite the pedestal  146  that is dimensioned to receive an O-ring sealing element  172  therein. The O-ring  172  is compressed against the plate  167  by a circular first window  174 , formed of an optically transparent material, such as glass, in order to provide a hermetic seal between the window  174  and the mount plate  167 . The window  174  also includes a downwardly extending collar  176  which has a diameter slightly larger than the exterior diameter of the scanning tube  152 . The collar  176  extends downwardly into the opening  168  and is positioned around the upper section  154  of the tube  152 . The collar  176  and upper section  154  are adhesively secured to one another in order to maintain the scanning tube  152  in position with respect to the mount plate  167  and the superstructure  122 . Optionally, the mount plate  167  may also include a second recess  178  disposed about the opening  168  opposite the first recess  170  and in which is positioned another O-ring sealing member (not shown) in order to create the hermetic seal achieved between the mount plate  167  and the pedestal  146 .  
         [0055]    The window  174  is optically transparent in order to allow a collimated light beam to pass therethrough. The beam is supplied from a laser source  182  positioned on the mount plate  167  opposite the pedestal  146 . The laser source  182  can be a conventional source utilized in AFM technology, such as a laser diode. The laser beam emitted by the source  182  is directed downwardly through the window  174  and into the scanning tube  152 . The beam passes through the scanner  152  and strikes a reflective surface (not shown) located on the probe  166  opposite the sample  144 .  
         [0056]    Based upon the movement of the probe  166  due to its engagement with the topographical features of the surface of the sample  144 , the laser beam is reflected upwardly at an angle through a second throughbore  184  disposed in the upper wall  126  adjacent the pedestal  146 . A recess  186  is disposed around the second throughbore  184  on the exterior of the body  124  and receives an O-ring  188  therein. The O-ring  188  is sandwiched between a second transparent window  190 , formed similarly to window  174 , and the recess  186  to provide a hermetic seal around the second throughbore  184 .  
         [0057]    The beam passes through the transparent window  190  and out of the superstructure  122  to contact a laser detection unit  192 , preferably mounted to the upper wall  126  of the superstructure  122 . The structure of the detection unit  192  can be any conventional device utilized in AFM technology, and preferably is a quad-photodetector implemented as part of an optical lever detection scheme. Generally, the detection device  192  receives the reflected laser beam and detects the position of the beam.  
         [0058]    In operation, probe  166  scans the surface of sample  144  at a selected set-point (e.g., a selected set-point oscillation amplitude in an oscillating mode, which the AFM maintains during scanning via feedback. The signals generated by maintaining AFM operation at the set point are indicative of surface characteristics. This data is then transmitted to a computer and stored, e.g., to generate a topography map.  
         [0059]    More particularly, as probe  166  scans across various topographical features of sample  144 , probe  166  deflects to an extent greater or less than specified by the set point, such that the laser beam striking the reflective surface on the probe  166  is reflected to a different portion of the detector  192 . The position where the laser beam strikes the detector  192  is transmitted to the controller  141 . The controller  141  then determines the amount of deflection represented by the laser beam position and ascertains the difference between the amount of deflection of the probe  166  registered by the detector  192  and the set point of deflection. The controller  141  then transmits appropriate signals to the scanner  152  to reposition the probe  166  at a position where the set point of deflection is reestablished, until the probe  166  again encounters a surface feature of the sample  144 . The controller  141  continuously receives and utilizes the data from the detector  192  regarding the position of the laser beam in a feedback loop to continually reposition the probe  166  with respect to the sample  144  and obtain deflection measurements for the entire surface of the sample  144 . This data is then analyzed by the controller  141  in order to generate an image of the scanned surface of the sample  144  to thereby determine surface characteristics of the sample  144 . Notably, there are other feedback modes. For example, although an amplitude-based feedback scheme is discussed above (e.g., in an oscillation mode), all modes of AFM operation, including, for example, using the phase of the oscillating mode output as the control parameter, can be implemented in the preferred embodiment.  
         [0060]    As best shown in FIGS. 2 and 3, the side wall  130  disposed adjacent the detection unit  192  also includes an opening  194  extending through the side wall  130 . The opening  194  is encircled by a recess  196  in which is received an O-ring sealing member  198 . The O-ring  198  is compressed within the recess  196  by a third transparent window  200 , formed similarly to the first window  174 , in order to hermetically seal the opening  194 .  
         [0061]    Opposite the interior chamber  125  of superstructure  122 , an optics assembly  202  is disposed adjacent to the opening  194  in alignment with the window  200 . The optics assembly  202  extends outwardly from the side wall  130  and provides a visual image to the user of the position of the sample  144  and probe  166  within the chamber  125 . This image can be utilized to initially position the probe  166  at the region of interest of the sample  144  to ensure proper alignment  
         [0062]    More generally, the optics assembly  202  can be moved in the X, Y and Z directions in order to properly align the probe  166  and sample  144  to provide an accurate image of the positioning of the probe  166  with respect to the sample  144 . For example, after the sample  144  is positioned in the chamber  125 , the probe  166  and sample  144  can be engaged automatically by the controller  141  utilizing images provided by the assembly  202 . The optics assembly  202  can be any conventional assembly, such as a high resolution camera, and will normally include a compression collar  204  disposed within the opening  194  that is secured to an optics assembly mount (not shown) which supports the camera (not shown). The compression collar  204  provides an additional sealing element within the opening  194  to enhance the hermetic seal within the opening  194 .  
         [0063]    Referring now to FIGS. 2, 3 and  5 - 7 , the lower wall  128  of the body  124  is fixedly and sealingly secured to a base  206  by bolts  207 , or similar fasteners, inserted through openings  208  in the superstructure  122 . The base  206  includes an upper positioning member  209  and a lower support member  210  fixed to one another. The upper member  209  and lower member  210  are each configured similarly to the lower wall  128  of the body  124  and each include a central opening  212  and  214 , respectively, that is aligned with the other and with the opening  129  in the lower wall  128 . The lower support member  210  is further connected opposite the upper member  209  to a number of downwardly extending legs  216  which serve to support the AFM  120  above a surface (not shown) on which the legs  216  are positioned.  
         [0064]    The base  206  encloses and supports an XYZ stage assembly  217  that is used to adjust the position of the sample  144  within the interior chamber  125  of the AFM  120  when the chamber  125  is maintained in a non-ambient environmental condition. The stage assembly  217  includes an upper glide plate  218 , a lower slide plate  220 , a support plate  258  disposed beneath the slide plates  218  and  220 , a number of linear Z-actuators  274  (the function of which will become apparent below) that extend past the support plate  258  and through the slide plates  218  and  220 , and an interface or sample support stage  288  for receiving a sample holder and which is disposed within the interior chamber  125  of the AFM  120  above the slide plates  218  and  220 .  
         [0065]    The area of the central opening  214  in the lower member  210  is smaller than the opening  212  in the upper member  209  such that the lower member  210  can retain the stacked slide plates  218  and  220  above the lower member  210  within the opening  212  in the upper member  209 . The slide plates  218  and  220  have a length and width, and a combined height slightly less than that of the opening  212  so that the plates  218  and  220  can slide within the opening  212 .  
         [0066]    The upper slide plate  218 , formed of a rigid material, such as a metal or plastic, is positioned against the lower wall  128  of the body  124  and is preferably generally square in shape. The plate  218  includes a recess  222  facing the lower wall  128  that is preferably circular and receives a sealing member  224  (e.g., an O-ring) therein. When the plate  218  is positioned in the opening  212  against the lower wall  128 , the sealing member  224  slidingly and sealingly engages the lower wall  128  to provide a hermetic seal between the plate  218  and the lower wall  128 .  
         [0067]    The upper plate  218  also includes a number of depressions  226  spaced from one another and located adjacent the recess  222 . The depressions  226  can be formed directly within the material forming the upper slide plate  218 , or can be formed as inserts  232  releasably positioned within a number of pockets  234  formed in the slide plate  218 . The depressions  226  receive and retain ball bearings  228  which are capable of rotating with respect to the depressions  226 . The bearings  228  are formed of a very hard, rigid material, such as a ceramic, and are engaged opposite the slide plate  218  with a bearing plate  230  disposed in a recess  231  within the lower wall  128 . The rolling engagement of the bearings  228  with the bearing plates  230  allows the plate  218  to slide with respect to the lower wall  128  in order to move the slide plate  218  along, as shown in this embodiment by the axis reference  155  in FIG. 2, the Y axis. Also, as the slide plate  218  moves with respect to the lower wall  128 , the sealing member  224  continually engages the lower wall  128  to maintain the hermetic seal between the slide plate  218  and the body  124 .  
         [0068]    The slide plate  218  also includes a number of bores  236  positioned adjacent the center of the slide plate  218  which extend completely through the plate  218 . The bores  236  are spaced equidistant from one another and are disposed in a generally triangular configuration on the slide plate  218 .  
         [0069]    In order to move the slide plate  218  along the Y axis with respect to the lower wall  128 , an actuating rod  238  engages one side of the slide plate  218 . The rod  238  frictionally abuts one side of the slide plate  218  such that the plate  218  can slide with respect to the rod  238 . Opposite the slide plate  218 , the rod  238  extends outwardly through a first bore  241  in the positioning member  209  and terminates in a handle  242 . The rod  238  is preferably threaded along its exterior such that the rod  238  can be threadedly engaged within the bore  241 . By grasping the handle and rotating the rod  238  with respect to the bore  241  into the central opening  212  of the upper member  208 , the rod  238  urges the slide plate  218  along the Y axis with respect to the interior chamber  125  of the superstructure  122  against the bias of a first spring member (not shown) disposed opposite the rod  238 . Alternatively, rather than biasing the plate  218  with a spring member, a similar threaded rod configuration may be employed opposite rod  238  in surface  211  to translate plate  218  in the negative Y direction.  
         [0070]    The lower slide plate  220  is formed of a material similar to the material forming the slide plate  218  and is also generally square in shape. The side of the slide plate  220  opposite the optics assembly  202  includes an upwardly extending flange  244 . The flange  244  has a height slightly less than the height of the central opening  212  in the upper member  208  such that the flange  244  defines an abutment capable of engaging the adjacent end of the upper slide plate  218 . Slide plate  220  also includes a central, preferably circular, opening  246  having a circumference greater than the circumference of a circle encompassing each of the bores  236  located in the upper slide plate  218 .  
         [0071]    Adjacent the opening  246  and opposite the flange  244 , the upper plate  218  further includes a bearing  250 , formed similar to bearings  228 , disposed within a depression  252  disposed in the upper slide plate  218  opposite the lower wall  128 . The bearing  250  rolls along the lower plate  220  within the depression  252  to enable the upper plate  218  to slide smoothly with respect to the lower plate  220 .  
         [0072]    The lower plate  220  also includes a number of depressions  254  formed similarly to depressions  226  and spaced equidistant from one another about the circumference of the central opening  246  in alignment with the depressions  226  in the upper plate  218 . Each depression  254  receives and retains a bearing  256  formed similarly to the bearings  228  disposed in the upper plate  218 . The bearings  256  are each rollingly engaged with a bearing plate  232  located in each spaced end of the support plate  258  disposed beneath the lower plate  220 , such that the lower plate  220  can slide with respect to the support plate  258 .  
         [0073]    In order to slide the lower plate  220  with respect to the chamber  125  along the X axis, an elongate rod  262 , formed similarly to the rod  238 , slidably contacts one side of the lower plate  220 . The rod  262  extends outwardly through a second bore  264  in the upper positioning member  208  and terminates in a handle  266  disposed on the exterior of the AFM  120 . Most preferably, the rod  262  is threadedly engaged with the second bore  264  so that the position of the lower plate  220  is altered by rotating the rod  262  with respect to the aperture  264  to move the lower plate  220  against the bias of, for example, a second spring member (not shown) disposed between the plate  220  and the body  124 , similarly to the adjustment of the upper plate  218 . Also, due to the presence of the flange  244 , the adjustment of the lower plate  220  can also move the upper plate  218  when necessary to properly position the plates  218  and  220 . When the flange  244  causes the upper plate  218  to move with the lower plate  220 , the rod  238  slides along the side of the upper plate  218  so as not to restrict the movement of the plate  218 .  
         [0074]    The support plate  258  is formed of a material similar to the slide plates  218  and  220  and is fixedly positioned within a number of slots  268  disposed around the periphery of the central opening  214  in the lower support member  210 . The support plate  258  is generally Y-shaped, including a central portion  270  and a number of arms  272  extending radially outwardly from the central portion  270 . As best shown in FIGS. 5 and 7, the support plate  258  is preferably formed with three equidistant and equal length arms  272  which each rest within one slot  268  disposed around the central opening  214 . Each arm  272  includes a recess  273  opposite the central portion  270  in which is disposed a bearing plate  230  that rollingly engages one of the bearings  256  disposed within the depressions  254  on the lower plate  220 .  
         [0075]    Looking now at FIGS. 3 and 6, the vertical, or Z-axis linear actuators  274  extend upwardly from beneath the base  206  into the interior chamber  125  of the superstructure  122 . The actuators  274  each include a lower housing  276  disposed and supported beneath the superstructure  122  by connection to the lower member  210  that extends upwardly between adjacent arms  272  of the support plate  258 . A vertically movable shaft  278  extends upwardly out of each housing  276  through the central opening  246  in the lower slide plate  220  and through one of the bores  236  in the upper slide plate  218 . The housings  276  each incorporate a suitable lift mechanism, such as an electric or hydraulic mechanism, that is connected to the shaft  278  and to the controller  141  in order to enable the controller  141  to automatically raise and lower the shafts  278 .  
         [0076]    Each shaft  278  is maintained in alignment within the bores  236  by a guide member  279  frictionally engaged within the bore  236  that is attached to the housing  276  and surrounds the shaft  278 , and a collar  280  positioned around the guide member  279  in abutment with the upper slide plate  218  beneath the bore  236 . The guide member  279  enables the shaft  278  to move with the upper plate  218  when the upper plate  218  is moved.  
         [0077]    Above the upper plate  218 , each shaft  278  extends through a lower collar  282  fixedly secured to the upper plate  218  around the associated bore  236 . Each collar  282  is formed of a rigid material and includes a circumferential groove positioned against the upper plate  218 . The groove  284  retains a sealing member  286  (e.g., an O-ring) that is compressed between the collar  282  and upper plate  218  to provide a hermetic seal around the bore  236 .  
         [0078]    The shafts  278  extend upwardly through the lower collar  282  into the chamber  125  to contact the lower surface of the interface stage  288 . The interface stage  288  is a piece of a rigid material, such as a metal, and preferably a stainless steel such as INVAR®, that is generally rectangular in shape, having a flat upper surface  290  and a generally flat lower surface  292 . Each of the shafts  278  terminates in a rounded upper end  294  that is rotatably engaged within one of a number of cavities  296  disposed in the lower surface  292  of the stage  288  to form a kinematic mount  297  between the shaft  278  and the stage  288 . Each cavity  296  includes a peripheral sealing member  298  that sealingly engages the upper end  294  of the shaft  278 , while also allowing the upper end  294  to slide with respect to the sealing member  298  when the shaft  278  moves with respect to the stage  288 . The stage  288  also includes a number of upper collars  300  attached to the lower surface  292  around the cavities  296 . Each upper collar  300  is formed identically to the lower collar  282 , including a circumferential groove  302  facing the lower surface  292  of the interface stage  288  and containing a sealing member  304  that is compressed between the collar  300  and the stage  288 .  
         [0079]    The upper collar  300  and lower collar  282  are interconnected by a flexible bellows  306  formed of a relatively flexible, gas-impervious material, such as a hard plastic, or preferably a ribbed sleeve of stainless steel. The bellows  306  is fixedly connected to the lower collar  282  and the upper collar  300  such that an air tight, hermetic seal is formed between the bellows  306  and each of the collars  282  and  300 . The upper collar  300  is additionally sealed to the interface stage  288  by a securing collar  308  that is fixed to the lower surface  292  of the stage  288  around the upper collar  300 . In this manner, an air-tight, hermetic seal is achieved by the stage assembly  217  with the superstructure  122  between the exterior, ambient environment and the environment within the chamber  125 .  
         [0080]    Based upon the hermetic seal achieved between the superstructure  122  and the various components of the stage assembly  217 , with the AFM  120  of the present invention it is possible to manipulate the position of a sample  144  positioned on the stage  288  along the X, Y and/or Z axis while the chamber  125  is under environmental control, i.e., while the chamber  125  is maintained at a temperature or pressure that is elevated or reduced from the ambient. For example, an operator can cause the sample to be moved in the X or Y directions by using the rods  238  and  262  to slide the plates  218  and  220  and stage  288  operably engaged to the plates  218  and  220  with respect to the superstructure  122 . Because the upper plate  218  includes the sealing member  224  that is engaged with the superstructure  122  throughout the entire range of motion of the plate  218 , the environment within the chamber  125  can be maintained while the sample  144  is moved. Further, because of the collars  282  and  300  and the bellows  306  disposed around the Z-actuator shaft  278 , when the stage  288  is raised, lowered or tilted using the actuators  274 , the hermetic seal is maintained between the chamber environment and the exterior environment.  
         [0081]    Referring now to FIG. 6, the interface stage  288  includes a pin  310  disposed in the center of the stage  288  and spaced from a slot  312 . The pin  310  and slot  312  are used to align or register a sample holder  314 , best shown in FIG. 2, to which the sample  144  is fixedly attached on the interface stage  288  directly beneath the probe  166 . The sample holder  314  can be fixed to the pin  310  and slot  312  by any suitable releasable securing means, such as a magnet, or simply by pressing the holder  314  onto the pin  310  and slot  312  to form a registration or interference fit with the slot  312  and pin  310 .  
         [0082]    In addition to fixedly holding the sample  144  on the stage  288 , the sample holder  314  also enables the environment within the chamber  125  to be altered as desired using one or more components incorporated onto the sample holder  314 . For example, the sample holder  314  can incorporate a heating element (not shown) or a cooling element (not shown) used to change the temperature within the chamber  125 . The particular element(s) disposed on the holder  314  can be connected to a separate power supply (not shown) or the controller  141  through the hermetic feed throughs  140  or  145  on the body  124  in order to allow the environment within the chamber  125  to be altered during the scanning of the sample  144  disposed on the sample holder  314 . Also, the interior environment of the chamber  125  can be altered to create a vacuum, a low pressure environment or a high pressure environment within the chamber  125  by withdrawing the air contained within the chamber  125  through the vacuum flange  138  disposed on the back panel  136 . The flange  138  can also be used to introduce an amount of a specific gas into the chamber  125 .  
         [0083]    When using the AFM  120 , when the sample  144  encounters the environmental changes within the chamber  125 , often the sample  144  will experience drift in the X, Y and/or Z directions. In order to obtain an accurate measurement of the surface of the sample  144  when drift occurs, the design of the AFM  120  of the present invention greatly reduces the amount of drift that must be compensated for and also enables the controller  141  to automatically compensate for drift. First, by positioning the pin  310  in the center of the interface stage  288  in alignment with the probe  166  , the amount of drift occurring in the X and Y directions is minimized with respect to the sample  144  on the holder  314  due to the fact that any drift occurring in the sample  144  in these directions will not move the center of the sample  144  away from the point of alignment between the pin  310  and the probe  166 . Thus, any drift which occurs in the sample  144  can be accommodated for by increasing or decreasing the scan area of the cantilever  164  from the center of the sample  144  as necessary to focus on the portion of the sample  144  of interest. Because the pin is placed symmetric about the probe location, the effects of the lateral drift component are minimized.  
         [0084]    Further, when the area of interest in the sample  144  has drifted significantly in the X and/or Y directions due to the changing environmental conditions within the chamber  125 , the controller  141  enables the AFM  120  to automatically compensate for this drift when scanning the surface of the sample  144 . In the method discussed in Elings et al. U.S. Pat. Nos. 5,077,473 and 5,081,390, which are incorporated herein by reference, the controller  141  can record an image of the surface of the sample  144  under a first environmental condition and record one or more features of the surface of the sample  144  as reference points. When the environmental conditions within the chamber  125  of the AFM  120  containing the sample  144  are subsequently changed, the probe  166  will not be located over the same point on the sample  144  when the first scan was initiated should a certain degree of sample/probe drift occur. In this situation, to ensure that the second scan performed under the changed environmental conditions is conducted over the same scan area of the sample  144 , the controller  141  will initiate a quick scan of a large region of the sample  144  in order to locate the reference points recorded from the previous scan. This scan may require that the sample  144  be moved with respect to the probe  166  . Once the reference points are located, the controller  141  will compare the location of the reference points in the previous scan to the present location of the reference points in order to compute a correction factor for the drift which has occurred in the sample  144 . The controller  141  can then cause the components of the AFM  120  to adjust the position of the sample  144  and conduct a normal scan over the area of interest of the surface of the sample  144 . To arrive at an accurate image of that portion of the sample  144 , the controller  141  will then apply the calculated drift correction factor to the values obtained by the AFM  120  from the scan.  
         [0085]    While the AFM  120  of the present invention is capable of compensating for drift in the X and Y directions, as discussed previously, the AFM  120  is also capable of automatically compensating for drift in the Z direction as well. More specifically, as illustrated in FIG. 10, after the completion of a scan, the controller  141  preferably will activate the tube  152  to move the probe  166  a known distance away from the surface of the sample  144  before changing the environmental conditions within the chamber  125 . Once the conditions have stabilized, the controller  141  will move the scanning tube  152  to reposition the probe  166  in the last recorded scanning position on the sample  144  as shown in block  324 . At this position, in block  326  the controller  141  will measure the deflection of the probe  166  . Next, in decision block  328 , the controller  141  will then compare the measured deflection to a stored deflection value for that point on the sample obtained during the previous scan. If the values are equal, the controller  141  will proceed to perform a scan of the sample  144  in block  330 .  
         [0086]    However, if the deflection values are not equal because the probe  166  does not engage the sample  144  at this position, or because the amount of deflection of the probe  166  exceeds the previously measured amount, meaning that the sample  144  has experienced drift in the Z direction based upon the changed environmental conditions, the controller  141  will determine whether the measured deflection value is greater or less than the stored value in decision block  332 . After determining this, the controller  141  will actuate the scanning tube  152 , and/or the Z-actuators  274  to lower in block  334  or elevate in block  336  the position of the stage  288  with respect to the probe  166  . Once the probe  166  and sample  144  are vertically repositioned to create the proper deflection value in block  338 , the controller  141  will calculate a drift correction factor for the Z direction and will proceed to block  330  and initiate a second scan, after correcting for any drift in the X and Y direction as well, as described previously. The Z direction correction factor can then be used to arrive at an accurate image of the sample surface once the scan is complete. Notably, a primary goal of the Z drift correction of the present invention is to maintain the position of the sample being analyzed within the Z range of the Z piezo of the tube actuator. Because the typical Z range of a Z piezo used in AFM is approximately 6 microns, it is preferred to keep the sample in the middle of that Z range so the Z tube maintains 3 microns of up/down symmetry.  
         [0087]    Referring now to FIGS.  11 - 14 , the controller  141  can also utilize the Z-actuators  274  to perform a tip-sample engage operation including, for example, correcting for any tilt in the surface of the sample  144  to be scanned (and more particularly, the scan region of interest) with respect to the known scan plane of the probe  166 . FIGS.  11 - 13  illustrate this correction process. Notably, prior to conducting a scan, the controller  141  of the AFM  120  knows the scan plane for the tip of the probe  166  coupled to the scanning tube  152 . To perform a scan, the controller  141  in block  340  first moves the sample  144  toward the probe  166  using the Z-actuators  274  at a known speed and in block  342  stops the movement when a specified amount of deflection of the probe  166  is registered, e.g., the set point of deflection. In block  344  the controller  141  will then initiate a quick scan of the sample  144  in the X and Y directions and then disengage the probe  166  from the sample  144  in block  346 . The controller  141  uses the results of this scan in decision block  348  to ascertain what the plane of the scan area of the sample  144  is relative to the scan plane of the probe  166  If the controller  141  determines that the scan plane on the sample  144  is parallel to the scan plane of the probe  166  (as in FIG. 1), the controller  141  will proceed in block  350  to scan the sample  144  with the probe  166 . However, if the sample plane is not parallel to the scan plane, as shown in FIG. 12, the controller  141  can actuate the Z actuators  274  in block  352  as necessary to tilt the stage  288  and alter the scan plane of the sample  144  in a manner which makes the sample scan plane parallel to the scan plane of the probe  166 . This is graphically represented in FIG. 13 where the scan plane of FIG. 12 has been shifted by tilting the stage  288  with the Z-actuators  274  such that the cantilever scan plane is now parallel to the sample scan plane. After aligning the sample plane with the scan plane, the controller  141  can move to block  340  to again check the alignment of the sample plane with the scan plane, or to block  350  to begin a scanning operation of the sample  144 .  
         [0088]    Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifested various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and scope of the underlying inventive concept.