Large stage system for scanning probe microscopes and other instruments

A large scale horizontal translation stage for a microscope or other instrument particularly a scanning probe microscope is disclosed. The translation stage is provided with air bearings which allow it to float over a planar surface. The translation stage is kinematically mounted on a guiding member such that the horizontal position of the translation stage is defined by the guiding member but the translation stage is free to move in a direction perpendicular to the planar surface. To position a sample, the air bearings are actuated and the guiding member moves the translation stage to a desired position. An attractive force, preferably suction in the air bearings, is then applied to hold the translation stage firmly against the supporting surface while the sample is analyzed. The preferred embodiment includes two optical microscopes. The first optical microscope is directed substantially perpendicular to the plane of the sample and has a focal point which coincides with the surface of the sample when it is being positioned by the translation stage. The second optical microscope is directed obliquely and focused on the probe.

FIELD OF THE INVENTION 
The present invention pertains to systems and methods for microscopically 
examining the surface of objects. More specifically, it pertains to the 
examination of large objects such as intact semiconductor wafers and 
lithographic photo-masks, using scanning probe microscopes such as 
scanning tunneling microscopes and atomic force microscopes. 
BACKGROUND OF THE INVENTION 
1. Definitions 
"Scanning probe microscope" (SPM) means an instrument which provides a 
microscopic analysis of the topographical features or other 
characteristics of a surface by causing a probe to scan the surface. It 
refers to a class of instruments which employ a technique of mapping the 
spatial distribution of a surface property, by localizing the influence of 
the property to a small probe. The probe moves relative to the sample and 
measures the change in the property or follows constant contours of the 
property. Depending on the type of SPM, the probe either contacts or rides 
slightly (up to a few hundred Angstroms) above the surface to be analyzed. 
Scanning probe microscopes include devices such as scanning force 
microscopes (SFMs), scanning tunneling microscopes (STMs), scanning 
acoustic microscopes, scanning capacitance microscopes, magnetic force 
microscopes, scanning thermal microscopes, scanning optical microscopes, 
and scanning ion-conductive microscopes. 
"Probe" means the element of an SPM which rides on or over the surface of 
the sample and acts as the sensing point for surface interactions and may 
include the cantilever and tip, a chip from which the cantilever projects, 
and a plate on which the chip is mounted. In an SFM the probe includes a 
flexible cantilever and a microscopic tip which projects from an end of 
the cantilever. In an STM the probe includes a sharp metallic tip which is 
capable of sustaining a tunneling current with the surface of the sample. 
This current can be measured and maintained by means of sensitive 
actuators and amplifying electronics. In a combined SFM/STM the probe 
includes a cantilever and tip which are conductive, and the cantilever 
deflection and the tunneling current are measured simultaneously. 
"Cantilever" means the portion of the probe of an SFM which deflects 
slightly in response to forces acting on the tip, allowing a deflection 
sensor to generate an error signal as the probe scans the surface of the 
sample. 
"Tip" in an SFM means the microscopic projection from one end of the 
cantilever which rides on or slightly above the surface of the sample. In 
an STM, "tip" refers to the metallic tip. 
"Scanning Force Microscope" SFM (sometimes referred to as Atomic Force 
Microscope) means an SPM which senses the topography of a surface by 
detecting the deflection of a cantilever as the sample is scanned. An SFM 
may operate in a contacting mode, in which the tip of the probe is in 
contact with the sample surface, or a non-contacting mode, in which the 
tip is maintained at a spacing of about 50 .ANG. or greater above the 
sample surface. The cantilever deflects in response to electrostatic, 
magnetic, van der Waals or other forces between the tip and surface. In 
these cases, the deflection of the cantilever from which the tip projects 
is measured. 
"Scanning Tunneling Microscope" (STM) means an SPM in which a tunneling 
current flows between the probe and the sample surface, from which it is 
separated by approximately 1-10 .ANG.. The magnitude of the tunneling 
current is highly sensitive to changes in the spacing between the probe 
and sample. STMs are normally operated in a constant current mode, wherein 
changes in the tunneling current are detected as an error signal. A 
feedback loop uses this signal to send a correction signal to a transducer 
element to adjust the spacing between the probe and sample and thereby 
maintain a constant tunneling current. An STM may also be operated in a 
constant height mode, wherein the probe is maintained at a constant height 
so that the probe-sample gap is not controlled, and variations in the 
tunneling current are detected. 
"Kinematic mounting" means a technique of removably mounting a rigid object 
relative to another rigid object so as to yield a very accurate, 
reproducible positioning of the objects with respect to each other. The 
position of the first object is defined by six points of contact on the 
second. These six points must not over or under constrain the position of 
the first object. In one common form of kinematic mounting, three balls on 
the first object contact a conical depression, a slot (or groove) and a 
flat contact zone, respectively, on the second object. Alternatively, the 
three balls fit snugly within three slots formed at 120.degree. angles to 
one another on the second object. The foregoing are only examples; 
numerous other kinematic mounting arrangements are possible. According to 
the principles of kinematic mounting, which are well known in the 
mechanical arts, six points of contact between the two objects are 
required to establish a kinematic mounting arrangement. For example, in 
the first illustration given above, the first ball makes contact at three 
points on the conical surface (because of inherent surface imperfections, 
a continuous contact around the cone will not occur), two points in the 
slot, and one point on the flat surface, giving it a total of six contact 
points. In the second illustration, each ball contacts points on either 
side of the slot into which it fits. 
2. The Prior Art 
The introduction of scanning probe microscopes, including the scanning 
tunneling microscope and atomic force microscope, has provided a 
substantially improved capability for inspection of surface and near 
surface structures. Such microscopes can, in certain circumstances, 
resolve individual atoms on a surface and can map topographic variations 
on the sample with 0.1 nm vertical sensitivity or better. These 
microscopes have found widespread application in academic and industrial 
research laboratories. The majority of systems constructed have been used 
for the examination of samples smaller than 25 mm in any one dimension. 
Samples of this size may conveniently be prepared and handled, and are 
commonly used in other types of optical and electron microscopes. In the 
semiconductor industry, for example, it is routine practice to fracture a 
wafer in order to microscopically examine a small fragment of it. The 
process is destructive and so the material examined is wasted. Furthermore 
it is not possible to continue processing the wafer in order to directly 
correlate the state of the surface at the time of inspection with the 
properties or the performance of the part after subsequent processing 
stages; thus valuable information is inaccessible. However, as the 
significance and value of the images and data from scanning probe 
microscopes have become better appreciated, a need has arisen for tools 
which can inspect intact samples at various stages of a production 
process. In the semiconductor industry it is desirable to inspect 
semiconductor wafers which may be 200 mm in diameter or more, and 
photomasks and other materials which may be 250 mm square and as much at 7 
mm in thickness. In other industries, and in scientific research, there 
are also many applications where the inspection of such large objects is 
desirable, especially if the inspection process is non-destructive. 
Large sample inspection systems have been constructed embodying many 
microscope types, including optical microscopes and scanning electron 
microscopes and scanning probe microscopes. Typically such prior art 
systems include dual motorized translation stages which provide linear or 
rotational relative motion between the sample and the microscope in a 
plane parallel to the sample surface and approximately orthogonal to the 
direction of imaging. Where rectilinear motion is desired, two linear 
motion stages are commonly stacked in orthogonal directions to provide the 
desired motion. Either the sample or the microscope is attached to the 
stages and a support structure couples the three elements mechanically. An 
example of such an arrangement for optical microscopy is given in Lindow 
et al., U.S. Pat. No. 4,748,335. Although in some systems one stage may be 
attached to the microscope and the other to the sample, it is important to 
note that the mechanical linkage path between the microscope and the 
sample is comprised of two separate bearing assemblies in the two 
translation stages assembled in series; vibrational or thermal 
instabilities or non-planarities or non-linearities of motion are additive 
for the two stages and produce a composite positioning error which can 
substantially degrade the performance or positioning accuracy of the 
microscope. It is the stability of this mechanical support path which 
determines the mechanical stability of the microscope and its ability to 
resolve fine structures as well as to image the same point on the object 
even when the instrument is subject to external physical sources of 
interference such as vibrations, temperature fluctuations, and the like. 
Thus, in the design of high resolution instruments such as the scanning 
probe microscope, a key goal is to minimize the number of bearing stages 
between the sample and the microscope and to maximize the mechanical 
stability and strength of the complete support path whilst providing a 
means of precisely and accurately positioning the sample relative to the 
microscope. 
Furthermore, in the early research versions of the scanning probe 
microscope, speed and ease of imaging were not major factors in the design 
of instruments. For example, the speed at which the sample could be 
translated from inspection site to site was not a major factor since the 
inspection process was in any case manually controlled by an operator. As 
systems for fully automated inspection have been developed, the 
translational speed and accuracy of the sample positioning system have 
become of greater importance, and it is a goal in the design of large 
sample systems to provide a high-speed, accurate method of positioning the 
microscope with respect to the sample. 
Along with the drive for imaging speed and efficiency, the use of an 
auxiliary optical microscope has become important. Such microscopes are 
employed to locate the desired imaging location visually in the first 
place, so that the probe microscope tip can be correctly positioned over 
the sample. Such a system is disclosed in application Ser. No. 07/850,677, 
filed Mar. 13, 1992, now U.S. Pat. No. 5,448,399. Video optical 
microscopes can scan images much faster than typical probe microscopes of 
the present generation, and so overall throughput is increased by this 
combination of techniques. Furthermore the video image may be digitized so 
that the site selection process can be fully automatic using pattern 
recognition and other image analysis techniques. 
Application Ser. No. 07/850,669, filed Mar. 13, 1992, and now U.S. Pat. No. 
5,376,790, describes a probe microscope system in which biaxial 
translation is accomplished using a kinematic stage mount in which two 
adjustable kinematic translation elements combine to select the position 
of the probe microscope with respect to the sample. This provides a very 
efficient and compact translation mechanism for small samples. In that 
system the sample is mounted on the scanner, however, which is less 
practical with large samples since, as the mass of the sample increases, 
the resonant frequency of the scanner becomes lower and the system is more 
susceptible to external sources of vibration and interference. U.S. Pat. 
No. 5,448,399 also teaches how an auxiliary optical microscope may be 
incorporated in a scanning probe microscope. 
U.S. Pat. No. 4,999,494 to Elings describes a scanning tunneling microscope 
system in which the microscope head is supported by feet which bear on the 
surface of the sample or on another surface which supports the sample. The 
probe microscope is attached to motorized stage means which position the 
microscope head in a plane roughly parallel to the sample surface. The 
head is unconstrained in the vertical direction and can thus accommodate 
variations in the flatness of the support surface whilst remaining in 
contact with the surface. A limitation of this approach is that the 
translation speed of the stage and the ability of the stage to make the 
smallest incremental motions is limited by friction and stiction effects 
between the support feet and the translation surface, which effects are 
always present since the support feet are permanently in contact and 
supporting the weight of the probe microscope. A further limitation of the 
approach is that there may be wear to either the feet or to the sample or 
support surface as the sample is translated, since the surfaces are 
rubbing. For semiconductor applications, this is particularly undesirable 
since the particles thus generated can cause defects to appear on the 
circuits being inspected. 
Other prior art large sample probe microscope systems have been described, 
and these are essentially similar to systems developed for optical and 
electron microscopy. That is to say they achieve relative motion of the 
sample and probe by mounting either the sample or probe on a stacked 
combination of two linear translation units. Such systems consequently 
suffer from the mechanical instabilities of the bearings and structure of 
such translation means, and are also limited in translation speed and 
accuracy by the friction of such translation means. 
As described in U.S. Pat. No. 4,723,086 to Leibovich et al., it is known to 
use an air bearing to provide support for a translation stage in a stacked 
configuration. Although an air bearing performs satisfactorily while the 
stage is being moved, it does not provide adequate stability when a 
desired position is reached and it is desired, for example, to scan the 
surface of a sample. U.S. Pat. No. 4,778,143 to Koshiba describes the use 
of an elastic member to lock a floating movable stage onto a stationary 
base, but elastic structures do not come close to providing the stability 
and rigidity required during the sample scanning operation in a scanning 
probe microscope. A scanning probe microscope must be rigidly constrained 
so that it is not affected by mechanical or thermal variations. This high 
degree of rigidity is necessary to enable the probe to accurately sense 
features on the scale of individual atoms. The Koshiba arrangement is 
specifically designed to provide an elastic coupling between the movable 
stage and the base and to allow tilting of the movable stage. This is 
entirely unsuitable for an SPM. 
Another desirable feature for the examination of large objects using 
scanning probe microscopes is the development of means for accurately 
scanning with the probe rather than the sample. In this way, the 
mechanical design is considerably simplified since the probe head, 
including a scanner, detector and probe are normally much lighter than a 
large sample; inertial effects due to scanning the more massive sample are 
therefore eliminated. U.S. Pat. No. 4,871,938 to Elings as well as many 
others have described systems for scanning the tip of a scanning tunneling 
microscope and U.S. Pat. No. 5,025,658 to Elings has also described a 
system for forming atomic force microscope images with a scanning tip, 
cantilever and optical detector. Optical detection as disclosed by Elings, 
however, requires precise alignment of the cantilever with the 
illuminating laser beam; furthermore, the optical arrangement is bulky and 
reduces scanning fidelity. Finally the optical interferometer arrangement 
requires that the cantilever be deformed in order to satisfy an optical 
interference condition for correct operation, and this means that the 
force exerted by the tip on the sample may not be precisely selected in 
order to optimize imaging conditions. An article by G. L. Miller et al. in 
Rev. Scientific Instruments 62(3), March 1991, and an article by D. A. 
Grigg in Ultramicroscopy, May 1992, describe an atomic force microscope in 
which capacitance displacement sensors are incorporated in order to detect 
tip deflections due to sample topography as well as to detect lateral 
deflections of the scanner. This has the distinct advantage that the 
detection system is purely electronic in nature, although the capacitance 
detector is bulky and complex; it may not be easily batch fabricated but 
requires external electronics in order to energize and process the 
detector signals. 
U.S. application Ser. No. 638,163 filed Jan. 4, 1991, and abandoned Nov. 5, 
1992, in favor of file wrapper continuation application U.S. application 
Ser. No. 07/954,695, and now U.S. Pat. No. 5,345,815, describes the use of 
a piezo-resistive cantilever assembly which detects height fluctuations on 
the sample surface and converts them into electrical signals, which 
arrangement is used in a preferred embodiment according to this invention. 
The advantage of this scheme is the inherent simplicity and low mass of 
the detection system. A number of problems exist with the system described 
in application Ser. No. 638,163 which relate to the present disclosure: 
1) One limitation is that the cantilever does not have a monolithic probe 
tip mounted on the cantilever for scanning the surface of the sample. The 
tip must be glued to the cantilever before use. Thus the process described 
does not achieve the economy of fabrication or simplicity of operation 
that is desired. 
2) No means is provided for conveniently making electrical and mechanical 
contact with the micro-fabricated piezo-cantilever assembly. 
SUMMARY OF THE INVENTION 
According to the present invention a method and apparatus for inspecting 
large intact objects is provided, including inspection of samples such as 
200 mm or more diameter semiconductor wafers and photomasks and the like. 
A specific object of the invention is to provide a translation stage 
coupled to a microscope and sample which links the two in a stable 
kinematic configuration whilst imaging is in progress, but which permits 
lateral translation of the microscope relative to the sample using a very 
low friction air bearing whilst the parts are in relative motion. In this 
way very high mechanical stability and immunity to external vibrations is 
achieved whilst the translation means is static, but whilst it is moving 
the reduced friction of the air bearing permits high speed motion, thereby 
reducing the effects of backlash and stiction which can limit positioning 
accuracy and precision with conventional stage systems. 
It is a further object of this invention to provide a very precise planar 
motion of the sample relative to the probe microscope head using a planar 
reference surface and a sample stage which is positioned parallel to this 
surface with good precision; such motion permits the probe to be 
maintained close to the sample surface even whilst the stage is in motion 
and so reduces the time spent in relocating the sample surface with the 
probe microscope after a motion cycle. 
It is a further object of the invention to provide an efficient method for 
optically viewing the sample surface, including a microscope for examining 
the probe and the sample separately, in an arrangement which minimizes the 
risk of collision between the probe and the sample and the optical 
microscope and the sample as the coarse motion stage is in motion. This is 
accomplished by optimizing the relative heights of the probe and the 
optical microscope components. 
It is a further object of the invention to provide a bright-field oblique 
optical view of the probe and sample, by means of a reflector mounted near 
the probe. A bright-field oblique optical view receives a much greater 
amount of reflected light from the imaged object than a dark-field view, 
which receives mainly scattered light from the imaged object in the 
oblique optical view. 
It is an object of the invention to provide a complete scanning probe 
microscope system for the examination and measurement of large objects, 
including a scanning force microscope system in which the probe itself 
rather than the sample is scanned, in a system which includes three 
position sensors which are used to correct the scanning motion of the tip. 
It is a further object of the invention to provide a means of imaging the 
sample using a piezo-resistive, batch-fabricated cantilever and tip 
assembly and a mounting structure which facilitates insertion and changing 
of the cantilever and tip assembly. 
In an embodiment according to this invention, a single translation stage 
moves laterally on air bearings over a smoothly polished, highly planar 
base. The translation stage is free to move in any horizontal direction. 
When a desired position is reached, the air bearings are de-energized and 
a source of vacuum may be connected to the air bearings, thereby holding 
the translation stage tightly against the base. Since the air bearings are 
formed of rigid materials, the translation stage is held firmly in place 
so that highly delicate operations, such as the scanning of a sample with 
a scanning probe microscope, can be performed. When it is desired to 
analyze a different region of the sample, pressurized air is supplied to 
the air bearings. The translation stage may then be moved easily and 
precisely to a new position, which may be far removed from the original 
position, without countering the effects of stiction and friction. 
In a preferred embodiment, the scanner (e.g., a piezoelectric tube) is 
mounted in the head of a scanning probe microscope. Accordingly, the 
scanner is forced to move only the fixed, limited mass of the probe and 
detection system, rather than the variable mass of the sample. This 
arrangement is particularly suitable for examining large samples.

DESCRIPTION OF THE INVENTION 
Many features pertinent to the microscopic inspection system and method of 
the present invention are specifically described in U.S. patent 
application Ser. Nos. 07/850,677, filed Mar. 13, 1992, 07/850,669, filed 
Mar. 13, 1992, and 07/851,560, filed Mar. 13, 1992, each of which is 
incorporated herein by reference in its entirety. 
FIGS. 1A and 1B illustrate the overall system schematically. A computer 
control unit 110 and a video display screen 111 are used to control the 
operation of a microscope head unit 100 and to record and analyze data and 
images therefrom. Computer control unit 110 includes interfacing circuitry 
for generating scanning and positioning signals to a probe microscope head 
106, for controlling stage translation units 108 and 109, for controlling 
a sample stage 105 and a TV system 113, and for recording data from these 
various units. Images and data are displayed on video display screen 111, 
and a graphical user interface permits selection and control of the 
overall microscope operation. Details of the software control structure 
are specifically disclosed in U.S. application Ser. No. 07/851,560, now 
abandoned, and details the function of the controller are disclosed in 
U.S. Pat. No. 5,376,790. 
Microscope head unit 100 includes an external enclosure 103 which is 
designed to reflect or absorb external sources of vibrational or acoustic 
energy, as well as to maintain a uniform temperature within the enclosure. 
Typically, it may be fabricated from steel or polymer materials, and sound 
deadening materials may be laminated to its surfaces in order to optimize 
microscope performance. FIG. 1C shows a top view of microscope head unit 
100 in which external enclosure 103 has been omitted for clarity. A sample 
104 is introduced to the microscope head through an entry door 112 (FIG. 
1B), either automatically by a robot or manually by an operator. Sample 
104 is positioned on sample stage 105 and is captured thereon by holding 
means incorporated in stage 105, which holding means may be based upon 
mechanical fixtures, or by electrostatic magnetic or vacuum chucking, or 
by other means according to the type of sample and other considerations. 
Sample stage 105 rests in static configuration on a surface 115 of a 
reference block 102 which has been ground to a precise contour. For the 
examination of planar objects, surface 115 is ground flat to high 
precision, such that translation of sample stage 105 over surface 115 
provides minimal motion of sample 104 with respect to probe microscope 
head 106 and TV system 113 in a direction perpendicular to surface 115. 
Typically reference block 102 may be fabricated from granite, which has 
excellent mechanical strength and thermal inertia, whilst it provides high 
damping of any vibrational energy coupled into it. Reference block 102 may 
be 100 mm in thickness or more. Reference block 102 is mounted on 
servo-vibration isolating units 101 which are mounted on a floor standing 
support table, 114. Combined servo-vibration isolation units 101 and 
floor-standing support table 114 are available for example from the 
Technical Manufacturing Company, Peabody, Mass. 
Sample stage 105 may be translated in two axes by motor translation units 
108 and 109 which operate under command from computer control unit 110. 
During translation, sample stage 105 may be partially or fully supported 
by an integral air-bearing mechanism such that there is negligible 
friction between sample stage 105 and surface 115. Probe microscope head 
106 and TV system 113 are rigidly mounted to a support structure 107, 
which is itself mounted rigidly on reference block 102. 
Support structure 107 is designed to minimize the motion of the microscope 
head 106 and the TV system 113 with respect to reference support block 
102. Typically, it may be constructed of materials which combine high 
strength with a low coefficient of thermal expansion as well as good 
acoustic damping characteristics. Materials such as granite or steel are 
suitable for this application. Support structure 107 is mounted to 
reference block 102 at three points around the perimeter of block 102 in 
order to ensure that the structure is optimally stable and has a high 
mechanical resonant frequency. For a system which attains very high 
stability, support structure 107 may be built from a steel I-beam girder 
of cross-sectional dimensions 100 mm.times.100 mm with a web thickness of 
2 cm and may be coupled to reference block 102 along its length by an 
additional structure welded to it, as illustrated in FIGS. 1B and 1C. 
Design of support structure 107 follows conventional mechanical design 
principles. 
FIG. 2 illustrates top view of reference block 102 and sample translation 
systems 108 and 109. Probe microscope 106, TV system 113, sample 104, 
sample stage 105 and support structure 107, which overlay this structure, 
have been omitted from FIG. 2 for clarity. Lateral motion of a sample 
stage guide 219 is guided by two linear track bearings, numbered 211 and 
218, which are mounted orthogonal to one another. Bearings 211 and 218 are 
selected for offering good linearity of motion coupled with a high 
resistance to mechanical and thermal fluctuations. Bearings 211 and 218 
also provide high resistance to forces which could cause rotation, pitch 
and yaw or other deviations relative to the desired motion axis. Such 
bearings utilize a recirculating ball mechanism. Bearing 218 is rigidly 
mounted to reference block 102. A slider 212 is attached to two 
recirculating ball heads 231 and 232 which are freely movable along the 
length of bearing 218 with low friction. Two heads are used for this 
purpose since they provide enhanced stiffness against rotation of slider 
212 about an axis perpendicular to surface 115. The position of slider 212 
along bearing 218 is controlled by a leadscrew 215 acting on a lead nut 
214, which is in turn rigidly attached to slider 212. Leadscrew 215 passes 
through a clearance hole bored in slider 212. Rotation of leadscrew 215 is 
accomplished by a motor 216 driving through a coupler 213 and a thrust 
bearing 223, under instruction from computer control unit 110. Motor 216 
is rigidly attached to a support member 217, which is in turn rigidly 
attached to reference block 102. 
Bearing 211 is rigidly attached to slider 212 at one end, whilst the other 
end of bearing 211 is cantilevered above reference surface 115. Means for 
stiffening bearing 211 in the vertical axis may be provided in order to 
increase the resonance frequency of the bearing to vertical oscillations 
and so minimize vibrational sensitivity. Alternatively bearing 211 may be 
coupled to reference block 102 in a manner which constrains motion of 
bearing 211 in a direction perpendicular to reference surface 115 yet 
leaves bearing 211 free to move in a direction parallel to the surface of 
reference block 102. Such may be accomplished by the addition of an extra 
roller or track bearing assembly placed at the free end of bearing 211, 
running parallel to and equivalent to bearing 218, or by equivalent means. 
Sample stage guide 219 is attached to two or more of recirculating ball 
sliders 233 and 234, which are freely slidable along the length of bearing 
211. As with slider 212, sample stage guide 219 is positioned along the 
length of bearing 211 by a leadscrew 210 and a lead nut 220, which is 
rigidly attached to sample stage guide 219. A clearance hole for leadscrew 
210 is bored through sample stage guide 219. Leadscrew 210 is driven by a 
motor 209 acting through a coupler 221 and a thrust bearing 222. Motor 209 
is rigidly mounted to slider 212 and receives drive signals from computer 
control unit 110. 
Motors 216 and 209 may be chosen for desirable torque and speed 
characteristics and may be DC or stepping motors. Stepping motors are 
preferred since they provide an economical means of precisely positioning 
the sample stage 105 without the use of additional position sensors which 
would be required if DC motors were used. Motor drive circuitry and 
software must be properly designed such that the motors can perform at 
high frequency, in order to give the high translation speeds made possible 
by the low friction air-bearings employed in this design, yet provide a 
sufficiently small minimum step size for precise translational motion of 
the Sample. In particular the drive amplifier impedances and the 
acceleration and deceleration software routines must be carefully 
optimized, as will be evident to those skilled in the art. Also viscous 
damping systems may be coupled to the motor spindle such that transient 
performance is improved. Micro-stepping drives may provide a reduced 
minimum step size whilst permitting higher speed translation. Typically 
motors 209 and 216 translate at two inches per second maximum speed, with 
a minimum step size of 6microns. 
Limit switches 205, 206, 207 and 208 serve to signal to computer control 
unit 110 when slider 212 or stage guide 219 has reached the limits of its 
travel in either direction and may be of mechanical or optical types. 
Leadscrews 215 and 210 may be of ground steel with lead chosen to provide 
suitable speed of motion and step size of motion. Lead nuts 214 and 220 
are of the anti-backlash type and may use either spring preloading or be 
of the recirculating ball type for increased accuracy of motion. 
The position of sample stage guide 219 may thus be accurately controlled in 
two orthogonal directions by computer control unit 110. Sample stage 105 
is placed over sample stage guide 219 and is mechanically coupled to it 
such that the horizontal position of sample stage guide 219 kinematically 
defines the position of sample stage 105 on reference surface 115, whilst 
permitting free motion of sample stage 105 in a direction perpendicular to 
reference surface 115. FIG. 2 illustrates five roller bearing assemblies 
224, 225, 226, 227 and 228 whose centre elements are rigidly mounted, with 
outside elements freely rotatable, at five points around the edges of 
sample stage guide 219, with their rotational axes oriented horizontally. 
Bearings 224-228 are of a ball race roller type with planar or radiused 
outer bearing surfaces. Bearings 226 and 228 are rigidly coupled to sample 
stage guide 219 via adjustment hinge mechanisms 229 and 230 respectively. 
These mechanisms permit fine translational adjustment of the centre of 
rotation of the roller bearings in a direction parallel to surface 115 and 
orthogonal to the rotational axes of the respective roller bearings. 
FIG. 5 illustrates the design of adjustment hinge mechanisms 229 and 230, 
which are identical. Hinge block 500 is machined to be rigidly attached to 
sample stage guide 219 along rear surface 503. Roller bearing 226 or 228 
is mounted onto hinge block 500 as shown and is free to rotate. Hinge 
block 501 is machined to a thin flexible hinge point along its length, 
point 501, such that the separation of bearing 226 from rear surface 503 
can be adjusted by set screw 502 which is threaded into hinged portion 504 
of hinged block 500. Other mechanisms for translation adjustment of roller 
bearings 226 and 228 with different force/displacement characteristics 
will be clear to those skilled in the art and may be substituted for 
adjustment hinge mechanisms 229 and 230 where more constant preloading 
forces are desired. 
FIG. 3 is a cross-sectional view of sample stage 105 and stage guide 219 
through a section parallel to surface 115 at the height of the axles of 
roller bearings 224-228 and shows the manner in which sample stage guide 
219 engages sample stage 105. Bearings 224, 225, 226, 227 and 228 engage 
corresponding bearing surfaces 300, 301, 302, 303 and 304 respectively. 
These bearing surfaces should ideally be cylindrical, such that a cross 
section parallel to surface 115 is circular and so that there is a single 
point of contact between the bearings and their corresponding bearing 
surfaces. In some applications, it may be sufficient to provide flat 
bearing surfaces. Bearing surfaces 300-304 are embedded into an interior 
surface of sample stage 105 such that sample stage 105 can freely 
translate in the vertical direction. Bearings 224, 225 and 226 serve to 
constrain the motion of sample stage 105 in a horizontal direction 
orthogonal to bearing 211 as well as preventing rotation of sample stage 
105 about an axis perpendicular to surface 115. Bearing 226 may be 
adjusted in order to minimize play in this direction and establish 
appropriate loading on bearings 224, 225 and 226. Bearings 227 and 228 
constrain the motion of sample stage in a direction parallel to bearing 
211, and the location of bearing 228 may be adjusted by hinge mechanism 
230 in order to establish minimal play and appropriate loading on bearings 
227 and 228. Thus the location of sample stage 105 with respect to sample 
stage guide 219 is kinematically defined in a plane parallel to reference 
surface 115. 
Further details of sample stage 105 are illustrated in FIG. 4, which is a 
perspective view of the general configuration of three air bearings 401, 
402 and 403, which rest on surface 115 when the air supply is switched 
off, but which raise the stage a few microns above the surface when 
compressed air is supplied to the three jets through fittings 404, 405 and 
406 respectively; pipes bored into stage 105 conduct compressed air to the 
three air bearings. The air supply to fittings 404, 405 and 406 is 
separately adjusted by air pressure regulators 407, 408 and 409, 
respectively, so that the stage floats evenly above surface 115, even if 
the mass loading of sample 104 and sample stage 105 is not evenly 
distributed on the three air bearings. The air supply to the regulators 
407, 408 and 409 is switched by a solenoid-driven switch valve 410 which 
operates under command from computer control unit 110. A typical motion 
sequence involves first turning on the air bearings through valve 410 and 
waiting for the air bearings to rise. Then the motors 209 and 216 are used 
to translate the sample stage 105 to the required location. At that point, 
the air bearings are disengaged using valve 410. Servo-mechanisms for 
automatically regulating the height and tilt of stage 105, incorporating 
pressure or other types of proximity sensors and pressure controllers will 
be apparent to those ordinarily skilled in the art. It is a specific 
advantage of this design that perfect stability and strength of air 
bearings 401-403 is not required since, when stage 105 is in motion, air 
bearings 401-403 need simply provide low-friction support, whilst, when 
the stage is at rest, stability and rigidity are provided by the kinematic 
mechanical contact between the stage 105 and the support surface 115. In 
accordance with this invention, the stability of the sample stage 105, 
whilst it is at rest in contact with surface 115, is enhanced by 
connecting a vacuum pump 411 to each of air bearings 401-403 via a switch 
valve 410, thus creating an additional compressive force between sample 
stage 105 and reference surface block 102. Alternative means for creating 
an additional compressive force might include use of electro-magnetic or 
electrostatic forces which could be easily turned on and off according to 
whether the stage was in static or moving configuration, or a mechanical 
clamping means. Other means of providing this enhanced stability mount 
will be obvious to those skilled in the art. 
FIGS. 6A and 6B show a cross-sectional view through sample stage 105 and 
stage guide 219, illustrating the relationship of the various components 
which interact with sample stage 105, stage guide 219 and reference block 
102. Air supply ducting which is bored into sample stage 105 in order to 
connect supply pipes is not shown for clarity. It is seen that the stage 
105 is free to move in the vertical direction guided by bearings 227 and 
228 as well as the bearings 224, 225 and 226. 
Air bearings 401, 402 and 403 are machined separately to fit into sample 
stage 105 and are inset to their respective locations using a press. The 
top surface of sample stage 105 is ground and polished precisely parallel 
to the contact plane of air bearings 401, 402 and 403, such that when the 
stage is translated on surface 115 the height of the top surface of stage 
105 is invariant. This is advantageous since the surface height of a 
parallel-sided sample 104 thus remains constant even as it is translated, 
and a probe can be maintained in close proximity to the surface of sample 
104 so the time spent recontacting the surface can be shortened. 
A typical air bearing is illustrated in FIG. 4B as a cross section through 
air bearing 402 in a plane orthogonal to surface 115. An air bearing 
aperture 451 provides a reactive force to sample stage 105 in a direction 
away from surface 115 roughly equal to the surface area of the aperture 
multiplied by the air pressure supplied to it via a bored pipe 452 and 
pipe fitting 405. Different sized apertures for the air bearings can be 
employed to provide different degrees of floatation force according to the 
mass of sample 104 and sample stage 105. For example, if sample stage 105 
is built from a dense material, such as stainless steel, it is 
advantageous to machine a large air bearing area in order to exert the 
necessary lifting force at modest air supply pressure; when the combined 
mass of sample 104 and stage 105 is small then a smaller air emission 
surface area may be acceptable. A diameter of 1 cm for aperture 451 may be 
suitable for a sample stage 105 made from stainless steel, whereas a 
diameter of only 5 mm may be suitable where the sample stage is 
constructed from aluminum; in both cases the stage floats with air inlet 
pressures of approximately 20-30 pounds per square inch. The design of air 
bearings follows conventional principles which are known to those skilled 
in the art. Air bearings 401, 402 and 403 may be machined from stainless 
steel or other materials, and may have a single or multiple orifices in 
order to distribute the load. Furthermore, air bearings 401, 402 and 403 
may have a pointed or spherical lower surfaces which contact surface 115 
when the air bearings are de-energized, such that there are only three 
points of contact between sample stage 105 and surface 115, one at each 
air bearing. In this way, the mechanical stability of sample stage 105 
with respect to tilt is assured since the three contact paints provide 
optimum stability and, combined with the kinematic interaction with stage 
guide 219, sample stage 105 is uniquely positioned with very high 
stability. 
FIG. 4A also shows surface details of sample stage 105. Sample stage 105 
includes a milled surface pattern 12 which is connected through internal 
ductwork and external piping 413 to a vacuum pump 411, such that when a 
sample 104 is placed on the stage 105, the vacuum thus created holds the 
sample to the stage with excellent stability. Vacuum vents of various 
shapes are provided such that semiconductor wafers and the like of 
different diameters can be so attached to sample stage 105. Vacuum valve 
414 controls the vacuum supply and may be either manually controlled or 
may receive computer control signals from controller 110. 
FIG. 7A shows the disposition of probe microscope head 106 on support 
structure 107 with respect to sample 104. The microscope head 106 includes 
a probe 701 and means for scanning the probe over the sample surface, 
comprising a scanner assembly 703. Probe 701 is kinematically, removably 
mounted on a probe mount 702, which in turn secured to scanner assembly 
703. Microscope head 106 also includes two optical microscopes, described 
below, for providing an on-axis view of the sample surface and an oblique 
view of the probe and the sample. TV system 113 is also described below. 
A portion of microscope head 106 is raised or lowered relative to both 
support structure 107 and sample translation stage 105 by means of a 
motor-driven, vertical translation stage 705. Vertical translation stage 
705 comprises a plate 761 mounted on a vertical slide rail 760. Slide rail 
760 is rigidly fixed to a vertical plate 762 which in turn is rigidly 
fixed to support structure 107. Stage 705 thus can be raised or lowered 
relative to support structure 107. 
A bracket 704 is rigidly fixed to vertical stage 705. Scanner assembly 703 
is kinematically, removably mounted onto this bracket. In addition, an 
objective lens 709, a lens 710, and mirrors 711 and 712 are attached to 
bracket 704. 
The motion of vertical translation stage 705 is controlled by a stepping 
motor 706 and a micrometer 707, under control of computer control unit 
110. The drive shaft of stepping motor 706 is axially connected via a 
flexible coupler to a pushing screw 706a which is threaded through a fixed 
nut 706b mounted on plate 762. Stepping motor 706 slides on a slide rail 
706c also mounted on plate 762 as pushing screw 706a advances or retreats 
through fixed nut 706b. 
Stage 705 is biased against the tip of the pushing screw by a pair of 
springs 766 as well as by a fixture 767 rigidly fixed to stage 705. 
Springs 766 are connected between stage 705 and plate 762. Fixture 767 
rigidly connects the body of stepping motor 706 to stage 705. Fixture 767 
also makes contact with the tip of pushing screw 706a, as shown in FIG. 
7A. Springs 766 in combination with fixture 767 provide means to maintain 
contact between the tip of the pushing screw and stage 705 at all times. 
In addition, springs 766 provide means to reduce significantly backlash 
between pushing screw 706a and fixed nut 706b. 
As pushing screw 706a advances or retreats through fixed nut 706b stage 705 
is lowered or raised, respectively, relative to both support structure 107 
and sample stage 105. Micrometer 707 has a resolution of 80 turns per inch 
of travel. Limit switches 718 and 719 are attached to plate 762 and signal 
to control unit 110 when stage 705 is at the limits of its travel. Stage 
705 thus provides for motion of probe 701 along an axis perpendicular to 
sample 104. Stage 705 also provides for adjustment of the focus of 
objective lens 709, by lowering or raising the focal plane of lens 709 
with respect to an imaged object. 
In combination with TV system 113, the components shown in FIG. 7A also 
form a video microscope system which selectively permits viewing of sample 
104 at high magnification from a perpendicular direction above the sample 
using lens 709, or viewing of probe 701 and sample 104 at lower 
magnification at an oblique angle through lens 710. This dual facility is 
very valuable in controlling the probe microscope since both the integrity 
of probe 701 and the location to be examined on sample 104 can 
conveniently be selected. 
A top view of TV system 113 is illustrated in FIG. 7B. TV system 113 
includes a color video camera 750, and a motorized zoom lens 751 as well 
as two mirrors 752 and 753 for directing light from an optical beam 
splitter 715 along a beam path 754. Motorized zoom lens 751 may be a 60 
mm-300 mm focal length motorized zoom lens, or other zoom lens combined 
with a motor, such as has been disclosed in application Ser. No. 
07/850,677. Video camera 750, zoom lens 751 and mirrors 752 and 753 are 
mounted on flat plates which are attached to support structure 107. 
Referring again to FIG. 7A, high magnification microscope objective lens 
709 is attached to bracket 704, and provides a view of the surface of 
sample 104 from a roughly perpendicular direction. An image of sample 104 
is reflected by a beam splitter 715 towards TV system 113 such that an 
image of the sample may be viewed on monitor 111. 
Low magnification lens 710 and mirrors 711 and 712 are attached to bracket 
704 and thus can be raised or lowered via vertical translation stage 705. 
Lens 710 is focused obliquely onto probe 701 and may be a 50 mm focal 
length bi-convex lens. Thus the surface of sample 104 comes into focus 
when probe 701 is in the proximity of sample 104. A mirror 713 and optical 
beam splitter 715 are mounted on a vertical plate 770 attached to support 
structure 107. Mirrors 713,712 and 711 serve to direct light from beam 
splitter 715 to lens 710 along a beam path 720 and to direct the image 
back along the same path, through beam splitter 715 and thus to TV system 
113, causing an image to be seen on monitor 111 (FIG. 1). It is a specific 
design objective that the probe 701 should remain in focus over the entire 
travel of stage 705 since this permits visualization of the integrity of 
probe 701 at all times. This is accomplished by arranging that the lens 
710 operate at infinite conjugate i.e., the lens 710 forms an image of the 
probe at infinity, by placing the imaged object one focal length in front 
of the lens, and also by ensuring that beam path 720 between mirrors 712 
(mounted on bracket 704) and 713 (rigidly fixed to support structure 107) 
is parallel to the direction of motion of stage 705. Other equivalent 
means for ensuring that the probe remains in focus will be obvious to 
those skilled in the art, including the provision of a second focusing 
mechanism to accomplish this task. 
Illumination for the two viewing systems is provided from a single 
illuminating light bulb 717 via a condenser lens 716 and beam splitter 
715. Beam splitter 715 splits the illuminating light into two beams of 
roughly equal intensity. The first beam illuminates sample 104 through 
lens 709, in an arrangement commonly known in microscopy as Kohler 
illumination, which provides uniform spatial illumination. An on-axis 
image of sample 104 is formed by lens 709 and directed towards TV system 
113 by reflection from plate glass beam splitter 715. Thus the video image 
of sample 104 may be visualized on monitor 111. The second beam of 
illuminating light is reflected by beam splitter 715 towards mirror 713, 
and serves to illuminate the oblique view through lens 710 via mirrors 
713, 712 and 711. A shutter 722 is mounted on the spindle of a motor 721 
such that it may be rotated. Which view (on-axis or oblique) is visualized 
on monitor 111 is determined by the position of shutter 722, which 
selectively obscures one of the two images according to control signals 
from computer 110. Thus only one image is visualized at a time. FIG. 7A 
illustrates the shutter 722 in position to block the on-axis view (through 
lens 709) such that the oblique view is visualized; if shutter 722 is 
rotated to position 714 (dashed lines) then the oblique view (through lens 
710) is obscured and the on-axis view is visualized. Intermediate 
positions for shutter 714, or other arrangements, would permit 
simultaneous viewing of parts of both images. Bulb 717, lens 716 and motor 
721 are mounted on vertical plate 770 which is attached to support 
structure 107. 
A detailed view of shutter 722 and motor 721 is shown in FIG. 9. Shutter 
722 is a bracket which is preferably coated to be optically absorbent, 
either by painting or anodizing it black, or by the use of black velvet 
material, as is commonly known in the art. Shutter 722 may also be angled 
with respect to the light beam in order to reflect energy away from beam 
splitter 715. Motor 721 may be any type of stepping motor for positioning 
objects rotationally, or the like. 
One potential limitation of the oblique viewing system formed by lens 710 
is that the system normally operates in dark-field mode, which is to say 
that only a fraction of scattered light from sample 104 and probe 701 is 
visualized in the oblique image. For example, a perfectly reflecting 
sample would appear dark in the image, since the illumination from bulb 
717 would be reflected from the surface away from lens 710 and be lost. To 
overcome the problem, a mirror 723 is attached to probe mount 702. Mirror 
723 is positioned and angled such that it reflects the lost illumination 
reflected by the sample and probe back along a reverse path so that the 
sample and probe are now illuminated in bright field conditions and the 
oblique view optical image is substantially improved. Mirror 723 may be 
planar or may be curved for improved efficiency or to accommodate a wider 
range of probe and sample surface gradients. The angle, position, shape 
and size of mirror 723 are dictated by the angle of the oblique view, and 
by the slope of the sample surface and by other factors, as will be clear 
to those skilled in the art. 
There are other alternative embodiments of this design of the oblique 
viewing system that provide for bright field viewing conditions. For 
example, the direction of light from bulb 717 incident on the probe (and 
the sample when the probe is in close proximity to the sample surface) can 
be altered, using lenses and mirrors, so that the probe is illuminated 
from the opposite side of scanner assembly 703. In this configuration, the 
direction of illumination is angled in such a way that specularly 
reflected light from the probe and sample follows the reciprocal path 720. 
A possible disadvantage of this configuration, however, is that scanner 
assembly 703 may at least partially block this path of direct 
illumination. Means for overcoming this obstruction, for instance by 
directing light through an opening in the side of scanner assembly 703 and 
past the probe mount 702, may be somewhat cumbersome. 
Another alternative embodiment uses a light source positioned substantially 
beneath scanner assembly 703 so that sample and probe are illuminated from 
close range, for instance by an LED (light-emitting diode) or a fiber 
optic light source. 
One aspect of the design of this probe microscope system concerns 
minimizing the risk of collisions when inspecting objects with undulating 
topography. When moving the sample stage 105 it is possible for some 
raised portion of the sample 104 to contact either probe 701 or objective 
lens 709 with the attendant risk of damage to those elements. With probe 
701 close to the surface of the sample 104, lens 709 may be struck by some 
raised portion of sample 104 distant from the probe location whilst the 
stage is in motion. Equally, whilst lens 709 is focussed on the surface of 
sample 104, probe 701 may be struck by some raised portion of sample 104 
when stage 105 is in motion. In order to minimize the risk of such 
collisions, it is advantageous to position probe 701 so that it is 
approximately at the mid-point of the working distance of objective lens 
709, which is to say that when lens 709 is focused on a flat sample, probe 
701 is separated from the sample 104 by half the distance that lens 709 is 
separated from the sample. In this case, a sample with a protrusion of 
height equal to the working distance divided by 2 can only just strike 
probe 701 when the stage is in motion. Equally, when probe 701 is close to 
the sample surface, the same size of sample protrusion (working distance 
divided by 2) can just strike lens 709. Thus the risk of damage to either 
probe or lens is minimized by this placement height. In applications where 
the sample is flat, the height separation between probe 701 and the focal 
plane of lens 709 may be reduced such that minimal time is spent in 
adjusting stage 705 when changing imaging mode from probe to optical 
viewing, and vice-versa. 
The benefits of this arrangement may be illustrated by considering the 
normal operational sequence for this type of microscope system. First, the 
sample 104 must be loaded into the instrument. This is accomplished by 
first raising vertical translation stage 705 so that probe 701 is clear of 
any protrusions on sample stage 105, energizing the stage 105 air bearings 
and translating the stage to some convenient loading location under 
computer control. Having loaded the sample and secured it using the vacuum 
chuck or by other means, the stage may then be translated to place some 
portion of the sample beneath lens 709. Motor 706 is commanded to position 
vertical translation stage 705 such that lens 709 is focused onto the 
surface of the sample. At this time, probe 701 is clear of the sample 
surface since it is mounted above the focal plane of lens 709. In routine 
operation it is normal to first select a desired field of view to examine 
with the probe using the high magnification optical microscope. Sample 104 
can be translated laterally over surface 115 to select the field of view. 
At any time the integrity of probe 701 can be viewed using oblique lens 
710. When it is desired to scan a probe image of the region selected using 
the optical view from lens 709, the stage 105 can be commanded to 
translate a pre-programmed lateral displacement which causes the probe 701 
to be above the selected region of sample 105. Air supply to air bearings 
401-403 of stage 105 can then be disconnected by valve 410 and vacuum pump 
411 can be connected to air bearings 401-403 so that stage 105 is drawn 
firmly to surface 115 of block 102. Probe 701 can then be lowered towards 
the sample surface for scanning, under computer control of vertical 
translation stage 705 through motor 706. During this sequence, probe 701 
may be continuously examined using oblique viewing lens 710 since the 
image through this lens remains in focus on probe 701 as probe 701 
approaches the sample. When probe 701 is in proximity of the sample an 
in-focus view of the sample 104 may also be visualized through lens 710. 
When probe imaging is complete the probe may be withdrawn, air bearings 
401-403 re-energized, and the sample moved to some new location for 
imaging. 
FIG. 8C illustrates the mounting arrangement for scanner 703 on bracket 
704. Bracket 704 has three ball bearings 882, 883,884 mounted on it. 
Scanner 703 has corresponding contact regions 885, 886 and 887 which 
engage the three ball bearings and kinematically locate scanner 703 on 
bracket 704. Contact region 885 is flat and engages ball bearing 882. 
Contact region 886 is conical and engages ball bearing 883 whilst contact 
region 887 is in the form of a slot and engages ball bearing 884. A clamp 
888 serves to force the scanner 703 tightly onto the ball bearing mounts. 
An electrical connector 813 is mounted on the rear of scanner 703 and 
mates with a corresponding electrical connector 880 which is mounted 
loosely on bracket 704, such that whilst connectors 813 and 880 make 
reliable electrical contact they do not affect the positioning of scanner 
703 on bracket 704, which is solely dictated by the kinematic mounting 
arrangement formed by the ball bearings and contact points described 
above. 
FIG. 8A shows the internal structure of scanner 703, which is identical to 
that of application Ser. No. 07/850,669, with some notable exceptions. 
Scanner 703 consists of a body 815 in which is mounted a piezoelectric 
tube scanner 870. Mounting points 885, 886 and 887 are machined in body 
815 at the fixed end of tube scanner 870. In application Ser. No. 
07/850,669, the scanner was used to translate the sample in the 
microscope, which was mounted on the free end of the tube scanner, whilst 
the probe and optical deflection detection system were static relative to 
the scanner body. For a large sample system it is advantageous to scan the 
probe rather than the sample since the mass of the probe is generally 
smaller and is relatively constant. It is also advantageous to use a 
piezo-resistive probe since the mass of the deflection detection system is 
then much smaller and the need for precise optical alignment is 
eliminated. Therefore, in the present invention probe 701 is a 
piezo-electric probe with batch-fabricated integral tip and is used to 
sense the surface topography of sample 104. Probe 701 is kinematically 
mounted onto probe mount 702, which makes electrical contact with probe 
701. Probe mount 702 is attached to the free end of tube scanner 870 which 
incorporates a fixture 830, similar to the similarly numbered fixture in 
application Ser. No. 07/850,669. Position sensing photodiodes 808, 814 and 
816 are identical to the similarly numbered photodiodes described in 
application Ser. No. 07/850,669, as are the many systems and methods in 
which these photodiodes are interfaced and utilized to improve accuracy of 
imaging. FIG. 8B illustrates the mounting of fixture 830, which, for 
example, may be glued to the free end of tube 870 leaving exposed regions 
to which probe mount 702 may also be attached. 
FIG. 8D illustrates probe 701. A piezo-cantilever chip 891 includes a 
piezo-resistive cantilever 893 and is glued to an alumina plate 892 using 
glue and standard IC mounting techniques or other alignment methods. Plate 
892 includes three rectangular slots 849, 850 and 851 which are precisely 
laser machined in alumina plate 892 and are oriented at an angle of 120 
degrees with respect to each other. Slots 849, 850 and 851 form kinematic 
mounting points which align probe 701 precisely in probe mount 702 with a 
precision of less than 1 micron, using principles outlined in application 
Ser. No. 07/850,669. 
Piezo-resistive cantilever 893 and substrate chip 891 are microfabricated 
monolithically from a silicon wafer, using processes described in 
application Ser. No. 638,163. The piezo-resistive cantilever 893 includes 
two flexure arms 841 and 854 which are attached to cantilever end part 
855, all of which are highly doped, using standard semiconductor 
fabrication methods, to make them electrically conductive. Also fabricated 
on the end part 855 is a high aspect-ratio tip 840 which is used to probe 
the surface of the sample 104. As tip 840 is scanned over the surface of 
sample 104 interatomic forces cause the tip to rise and fall with height 
variations of the surface of sample 104. Thus the deflection of cantilever 
893 is a direct measure of the surface height of sample 104 in the region 
of the tip. The electrical resistance of flexure arms 841 and 854 is 
modified as the cantilever is deflected because of the piezo-resistive 
effect. Thus an electrical current may be passed from a metallic contact 
pad 848 on plate 892 through wire 846 onto a contact pad 844, along a 
conductive track 852, through flexure arm 854, across end part 855, along 
flexure arm 841, along a conductive track 853, through a contact pad 843, 
and finally through a wire 845 to contact pad 847, and the resistance to 
current flow is proportional to the cantilever deflection. This change in 
resistance may be converted into a voltage variation using a bridge 
amplifier circuit, as is well known in the art. Conductive tracks 852 and 
853 may be fabricated by depositing and patterning a metal film using 
standard semiconductor techniques. Similarly, contact pads 848 and 847 may 
be silk screened onto alumina substrate 892. In accordance with this 
invention, other types of probes used in scanning probe microscopes, such 
as STM probes or conducting cantilevers or tips, may be substituted for 
piezo-resistive cantilever 893. 
FIG. 8E illustrates probe 701 and probe mount 702, including mirror 723. 
Probe mount 702 includes three ball bearings 895, 896 and 899 which are 
attached to its surface. Ball bearings 895, 896 and 899 are arranged in 
the same pattern as slots 850, 851 and 849, and serve to kinematically 
locate probe 701 in probe mount 702, such that tip 840 can be reliably 
positioned relative to scanner body 815 within an error of 20 microns. 
Springs 897 serve to force probe 701 against the three ball mounts and 
also make electrical contact to contact pads 848 and 847. A flexible 
circuit board 898 connects springs 897 independently to the bridge 
amplifier circuit in order to complete the cantilever connection. 
Amplification and processing of the signal from probe 701 are carried out 
by methods well known in the art and may advantageously be performed with 
the apparatus described in application Ser. No. 07/850,669. 
There are alternative embodiments of this invention, including 
configurations in which the sample is static and the probe is mounted on 
the translation stage, and also configurations in which the sample is 
mounted on the probe. 
For example, in one alternative embodiment, illustrated in FIG. 10A, probe 
701 is attached to a horizontal translation stage 1000 for coarse 
translation of the probe over a static sample 104. In such a 
configuration, stage 1000 may ride on air bearings 1001 over the surface 
of the sample or over a surface 1002 which supports the sample. 
Another alternative embodiment is illustrated in FIG. 10B. In this 
configuration, sample 104 is mounted on the underside of a horizontal 
translation stage 1003 and faces a static probe 701. This configuration 
has an advantage over the configuration shown in FIG. 10A in that the 
mechanical path of the translation stage is smaller. For example, air 
bearings 1001 for the configuration shown in FIG. 10A must be spaced 
further apart than those of the configuration shown in FIG. 10B to provide 
for the full range of translation over the sample. The mechanical path of 
the configuration shown in FIG. 10B is therefore much smaller, providing 
increased positioning stability of probe 701 relative to the sample 104. 
A further alternative embodiment is illustrated in FIG. 10C. In such a 
configuration, probe 701 is mounted on a horizontal translation stage 1004 
and faces a static sample 104 which is mounted above it. This embodiment 
has the same advantage as that shown in FIG. 10B, that is, it has a 
smaller mechanical path than the embodiment shown in FIG. 10A. 
The description of the above embodiments is intended to be illustrative and 
not limiting. Many alternative embodiments in accordance with the broad 
principles of this invention will be apparent to those skilled in the art.