Automatic probe replacement in a scanning probe microscope

A scanning probe microscope having a probe attachment fixture, to which a probe assembly is removably attached during measurements, driven in an engagement direction, and a sample stage driven in scanning directions perpendicular to the engagement direction includes a buffer with a number of buffer stations within the sample stage. When the stage is driven so that one of the buffer stations is in alignment with the attachment fixture, and when the attachment fixture is driven in the engagement direction to be in proximity to the buffer station, the probe assembly is selectively transferred in either direction between the attachment fixture and the buffer station. In a preferred embodiment, probe assemblies are transferred on transfer pallets, and a stationary magazine is provided for storing these pallets, which are transferred in either direction between the magazine and the buffer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to scanning probe microscopy, and, more 
particularly, to providing means for automatically replacing probe tip 
assemblies within a scanning probe microscope without requiring manual 
intervention by the operator. 
2. Background Information 
In a scanning probe microscope, a scanning movement is established between 
a surface of a sample being investigated and a very sharp, very small 
probe tip. The phrase "scanning probe microscope" is meant herein to 
describe a device in which the scanning movement is derived from movement 
of the sample, from movement of the probe tip, or from a combination of 
these two types of movement, with movement of the sample being used to 
move between points at which measurements are made, while the scanning 
movement occurring within the probe itself is used to make measurements in 
the vicinity of each such point. This phrase is also meant to include an 
important group of devices known as "atomic force microscopes." 
The probe tip of a scanning probe microscope is typically mounted to a 
distal end of a cantilever, the proximal end of which is attached to an 
excitation actuator. The excitation actuator is a piezoelectric actuator 
driven to cause the cantilever, and thereby the probe, to vibrate 
vertically. The excitation actuator itself is additionally moved 
vertically by means of a Z-axis actuator, which is typically driven in 
response to changes in the amplitude of vibration of the probe tip. 
Changes in amplitude of vibration are caused by variations in the height 
of the sample surface, which change the level of engagement between the 
probe tip and the sample. The Z-axis actuator is driven, for example, to 
maintain the amplitude of vibrations at a constant level, with the level 
of the signal driving the Z-axis actuator being recorded to provide an 
indication of the height of the sample surface. 
As the scanning probe microscope moves from being a tool of basic research 
to more widespread use in the inspection of manufactured parts having 
critical surfaces, a number of limitations of the device and difficulties 
with its use become apparent. In particular, the probe tips themselves, 
being small and sharp, and being subject to high levels of stress, tend 
wear out or break quickly. A probe tip is typically changed as a probe 
assembly including the cantilever and the excitation actuator. Since such 
assemblies are particularly small and fragile, they are subject to 
handling damage whenever they are changed. Furthermore, the electrical 
connections to the excitation actuator present additional difficulties 
when a probe assembly has to be replaced. Also, since a scanning probe 
microscope used is an inspection tool is ideally operated almost 
continuously, the time required to change probes manually can have a 
significant effect on the throughput achieved in an inspection station. 
Furthermore, since there is a variety of types of tips for a scanning probe 
microscope, with individual types of tips being customized for different 
modes of measurement, there is typically a need to switch types to take 
different types of measurements, even on the same sample. In many 
applications of scanning probe microscopy, probe tips are changed more 
often because of a need to introduce n different type of tip than because 
tips become worn out or broken. 
Therefore, what is needed is a method for facilitating the process of 
changing the probe assemblies. In particular, such a method should allow 
such assemblies to be changed without manual intervention by the operator. 
DESCRIPTION OF THE PRIOR ART 
U.S. Pat. No. 4,992,660 describes a scanning tunneling microscope using a 
tip which can be easily replaced. Within the device, a tip holder is 
introduced into a transfer chamber, being carried in a chuck at an inner 
end of an introduction rod. Within the transfer chamber, a transfer rod 
carries a magazine with a number of externally threaded studs extending 
radially outward. The tip holder is placed on the magazine by driving the 
transfer rod inward, so that internal threads within the tip holder engage 
the external threads of a stud aligned with the introduction rod, and by 
rotating the introduction rod so that the tip holder screws onto the stud. 
A tip holder on the magazine is brought into the observation chamber, 
where measurements are taken, by first raising and rotating the transfer 
rod so that the tip holder is in alignment with a replacement rod within a 
chamber above the introduction rod. The replacement rod is then slid 
inward, so that a chuck at its end engages the tip holder, and is rotated 
to disengage the tip holder from the magazine. Then the magazine is moved 
downward, and the replacement rod is slid above the magazine and turned to 
engage the tip holder with a stud extending outward from the tip driver in 
the observation chamber. This process is reversed to remove the tip holder 
from the observation chamber. Both tip holders and sample holders are 
handled in this way, and the sample holder must be removed to the magazine 
before a tip holder can be replaced. 
Thus, the device of U.S. Pat. No. 4,992,660 includes a separate magazine 
structure, which must be slid and rotated to carry the tip holders. 
Precise rotational and translational drives are used on three rods--the 
introduction rod, the transfer rod, and the replacement rod. What is 
needed is a device using drive motions otherwise needed and generated in 
the device to move the tip holders around. Also, the multiple engagement 
of the tip holders from threaded studs, and the disengagement of the tip 
holders therefrom, can be expected to generate wear debris, causing 
problems in a clean room environment, or in the high vacuum environment of 
the device of this patent. What is needed is a method for minimizing 
relative movement between the tip holders and the surfaces they engage 
during the processes of engagement and disengagement. Also, what is needed 
for many scanning probe microscope applications, is an efficient way of 
making electrical connections, a way of identifying different types of tip 
holders in the apparatus, and a way of replacing a damaged or worn out tip 
holder without having to remove the sample holder from the observation 
chamber. 
U.S. Pat. No. Re 34,489 describes an atomic force microscope which is 
readily usable without extensive lost time for setup and repair. The probe 
is a cantilevered optical lever reflecting an incident laser beam. The 
probe is carried by a replaceable probe-carrying module which is factory 
set up and merely inserted and fine tuned by the user. The probe-carrying 
module also includes a provision for forming a fluid cell around the 
probe. Samples are easily mounted, replaced, and horizontally adjusted 
using a sample stage which is magnetically attached to the top of the scan 
tube. 
While a probe-carrying module is thus provided, a mechanism for 
automatically changing such modules is not addressed. The user is required 
to insert and fine-tune such modules. What is needed is a method for 
changing probe tips without manual operator intervention. 
U.S. Pat. No. 4,637,119, describes a receiver in the probe head of a 
multiple-coordinate measuring machine in which probe-pin combinations can 
be replaceably and precisely chucked. The receiver contains an isostatic 
three-point support against which the base of the probe-pin combination is 
drawn by an electrically operated camping device. The clamping device is 
coupled with the control computer of the measuring machine so that a probe 
change can be effected automatically. In a preferred embodiment, the 
clamping device consists of a permanent magnet and of an electromagnet by 
which the field of the permanent magnet can be selectively counteracted or 
increased to achieve pick-up and release functions. The permanent magnet 
is described as forming a core around which the coil of the electromagnet 
is wound. 
However, with the electromagnet coil would around the permanent magnet, it 
is particularly difficult to change the magnetic field extending to the 
device being clamped by means of the permanent magnet. This is because a 
permanent magnet by its nature is particularly difficult to magnetize or 
demagnetize, retaining the magnetic characteristics placed within it 
during its manufacture in the presence of varying external fields. What is 
needed is a way to separate the electromagnet from the permanent magnet, 
so that the coil of the electromagnet can change the flux within a soft 
iron material. Also, in a scanning probe microscope having a mechanism for 
moving the sample in a scanning motion relative to the probe, what is 
needed is a means to use this motion to bring the probe into position for 
placement on the probe drive of the device. Furthermore, what is needed is 
a means to identify different types of probes used in the device, and a 
built in compliance to establish a soft transfer of delicate probe 
mechanisms. 
U.S. Pat. No. 5,598,104 describes apparatus for positioning a probe in a 
flying-probe circuit tester. This apparatus includes a probe tip, a probe 
actuator connected to the probe tip, a probe plate coupled to the probe 
actuator, and a magnetic probe plate clamp that magnetically couples the 
probe plate, forming a slip plane that provides collision compliance for 
the probe positioning apparatus. One embodiment of the magnetic probe 
clamp uses a set of shoulder screws to provide quick attachment and 
release of the probe plate from the probe clamp. A second embodiment uses 
a magnetic shunt, activated by turning a lever, to disable the magnetic 
connection of the clamp from the probe plate. 
For use in an automatic system for changing tip assemblies, both 
embodiments of the attachment mechanism of U.S. Pat. 5,598,104 have a 
disadvantage of requiring a rotary motion, of shoulder screws or of the 
magnetic shunt, to disable the attachment force. Such rotary motion is 
relatively difficult to achieve, for example with a motor, in the small 
space adjacent to a scanning probe microscope, and poses a danger of the 
generation of debris from friction. Such debris can cause problems within 
the clean room environment in which a scanning probe microscope is 
typically operated. What is needed for an automatic tip changer is an 
attachment mechanism which does not require such motion. Furthermore, what 
is needed is a method for automatically making electrical connections when 
various assemblies are brought together by the apparatus, and for breaking 
these connections when these assemblies are separated by the apparatus. 
SUMMARY OF THE INVENTION 
It is a first objective of the present invention to provide a mechanism for 
removing and replacing the tip of a scanning probe microscope without a 
need for manual intervention by the operator. 
It is a second objective to provide a means for changing the tip of a 
scanning probe microscope in a manner minimizing the generation of wear 
debris. 
It is a third objective to provide a means for storing a number of 
different types of probes in a scanning probe microscope, in a manner 
allowing the probes to be easily accessed and used. 
It is a fourth objective to provide for the repeatable and precise location 
of a probe assembly in a scanning probe microscope. 
It is a fifth objective to provide for making and breaking electrical 
connections when a probe assembly is inserted within or removed from a 
scanning probe microscope. 
In accordance with a first aspect of the present invention, there is 
provided a scanning probe microscope including a probe assembly having a 
probe, a sample stage, an attachment fixture, a scanning drive mechanism, 
and an engagement actuator. The sample stage includes a chuck for holding 
a sample to be examined and a buffer including a number of buffer 
stations. Each buffer station includes a first mechanism for releasably 
holding the probe assembly. The attachment fixture, which holds the probe 
assembly during measurements made on a sample surface, includes a second 
mechanism for releasably holding the probe assembly. The scanning drive 
mechanism moves the sample stage in directions perpendicular to an 
engagement direction, moving the chuck adjacent the attachment fixture, 
and selectively moving each buffer station into alignment with the 
attachment fixture. The engagement actuator moves the attachment fixture 
in the engagement direction and opposite thereto. The engagement actuator 
moves the attachment fixture into proximity with a buffer station in 
alignment with the attachment fixture. The probe assembly is selectively 
moved in either direction between the attachment fixture and the buffer 
station when the buffer station is moved into alignment with the 
attachment fixture and when the attachment fixture is moved into proximity 
with the buffer station.

DETAILED DESCRIPTION 
FIGS. 1 and 2 show a probe tip assembly 10 removably engaged within an 
scanning probe microscope by means of an attachment fixture 12, with FIG. 
1 being a left elevation of the apparatus, while FIG. 2 is a bottom plan 
view of the apparatus. The probe tip assembly 10 includes a tip and 
cantilever 14 attached to a piezoelectric bimorph actuator 16 by means of 
a locator 18 which is used for tip alignment when a tip is replaced. The 
bimorph actuator 16 is in turn attached to an inclined surface 19 of an 
outward-extending tab 20 forming a portion of a probe support plate 22. 
The attachment fixture 12 is attached to a Z-axis piezoelectric actuator 
24. 
In operation to measure a sample surface, the tip 14 is moved into 
engagement with the sample to be examined (not shown) in the engagement 
(Z-axis) direction indicated by arrow 28. This movement, which occurs as 
the Z-axis piezoelectric actuator 24 expands in response to an applied 
signal voltage, is controlled through the use of an optical approach 
subsystem 30 held within an attachment ring portion 32 of the attachment 
fixture 12. The tip 14 is vibrated in the engagement direction of arrow 28 
by flexing the bimorph actuator 16 in response to an AC signal applied 
thereto. 
FIG. 3 is a vertical cross-sectional view of the scanning probe tip 
assembly 10 removably engaged with the attachment fixture 12 taken as 
indicated by section lines III--III in FIG. 2. The tip assembly 10 is held 
in engagement with the attachment fixture 12 by means of a permanent 
magnet 34 embedded within the attachment fixture 12. The probe support 
plate 22, being composed of a ferrous magnetic alloy, is attracted and 
held in place by magnetic flux extending from the permanent magnet 34. 
This support plate 22 is preferably composed of a material sold under the 
trade name SUPER INVAR for thermal stability as well as for magnetic 
properties. 
Continuing to refer to FIG. 3, and additionally referring again to FIG. 2, 
devices within the probe tip assembly 10 are electrically connected to 
circuits within the remaining portion of the atomic microscope by means of 
six spring contacts 36, each of which engages a contact post 37. The 
individual wires extending from these spring contacts 36 and contact posts 
37, which are not shown in FIGS. 1-3, form portions of a circuit which 
will be discussed in reference to FIG. 11. Each spring contact 36 includes 
a tip having limited axial motion, which is pushed against an end of the 
associated contact post 38 by means of a spring within the contact 36. 
Spring contacts and contact posts of this kind are supplied, for example, 
by Rika Denshi America, of Attleboro, Mass. Three spring contacts 36 are 
mounted in each of two insulating contact holders 38 embedded within the 
attachment fixture 12, and three contact posts 37 are mounted in each of 
two insulating contact holders 39, embedded within the probe support plate 
22. 
The tip assembly 10 includes three spherical locators 40, each of which has 
a spherical tip that extends into a corresponding indentation 42 within 
the attachment fixture 12. The three indentations are preferably 
configured in the shape of a kinematic mount, with a first of these 
indentations 42-1 being conical, with the second of these indentations 
42-2 being formed as a trough extending in alignment with the first of 
these indentations, and with the third of these indentations 42-3 
providing a flat surface on which the spherical tip of a corresponding set 
screw 40 rests. With this mounting arrangement, a point of the tip 
assembly 10 is located in alignment with the attachment fixture 12 at the 
first indentation 42-1. The angular relationship between the tip assembly 
10 and the attachment fixture 12 in the direction indicated by arrow 44 is 
determined by the relationship between the first indentation 42-1 and 
second indentation 42-2. The spherical locators 40 are preferably composed 
of two dowels 40-1 with spherical tips, and of a single setscrew 40-2 with 
a spherical tip. The setscrew 40-2, which is used to provide a leveling 
adjustment, is preferably placed within the indention 42-3 having a flat 
surface. Alignment of the tip assembly 10 about any axis perpendicular to 
the engagement direction indicated by arrow 28 is accomplished by 
engagement of the spherical tips of the three spherical locators 40 with 
the three indentations 42. 
This method provides a simple, accurate, and highly repeatable method for 
removably attaching the probe tip assembly 10 to the attachment fixture 
12. Since the attachment fixture 12 is moved straight downward, in the 
direction of arrow 28, onto the tip assembly 10, there is little sliding 
motion to cause the generation of debris, which could otherwise 
contaminate the clean room environment in which an scanning probe 
microscope is typically used. Nevertheless, the slopes of the indentations 
42 and of the spherical ends of spherical locators 40 accommodate small 
movements to correct the alignment of the probe tip assembly 10 on the 
attachment fixture 12. The tip assembly 10 is easily removed from the 
attachment fixture 12 by applying an external force capable of overcoming 
the attachment force between the probe support plate 22 and the adjacent 
permanent magnet 34. 
FIG. 4 is a fragmentary plan view of an scanning probe microscope using 
replaceable tips in the manner of the present invention. This microscope 
includes a sample stage 50, on which the sample to be inspected (not 
shown) is mounted, and a tip magazine 52 holding a number of tip 
assemblies 10. For example, the tip magazine 52 is configured to hold 
eight tip assemblies 10. When each tip assembly 10 is not attached to the 
attachment fixture 12 (shown in FIG. 1), it is mounted atop a transfer 
pallet 54. Each transfer pallet 54 can be held either within the tip 
magazine 52 on a pair of posts 56, or on a buffer 57, forming part of the 
sample stage 50, within a buffer station 58. The sample table 50 includes 
two buffer stations 58, while the tip magazine 52 includes, for example, 
eight tip magazine stations 59, each of which includes a pair of posts 56 
and a pneumatic cylinder 60, which is used to move a transfer pallet 54 in 
either direction between the tip magazine station 59 and one of the buffer 
stations 58. 
FIG. 5 is an isometric view of apparatus for moving the sample stage 50 in 
the horizontal X-direction indicated by arrow 61, and in the horizontal 
Y-direction indicated by arrow 62, while preventing movement of the sample 
stage 50 in the vertical direction indicated by arrow 28. This movement of 
the sample stage 50 is used both to scan the surface of a sample (not 
shown) being examined, relative to the tip 14 (shown in FIG. 1), during 
the process of scanning probe microscopy, and to move the transfer pallets 
54 held in the buffer stations 58 on the sample stage 50 into alignment 
directly under the attachment fixture 12 (also shown in FIG. 1) so that a 
tip assembly 10 can be transferred in either direction between the 
attachment fixture 12 and the transfer pallet 54. 
For operation of the apparatus as an scanning probe microscope, a sample 
(not shown) to be inspected is held to a vacuum chuck 64 on the top 
surface of the sample stage 50. While the vacuum chuck may be of various 
shapes, in this example it is round for accommodating circular disks to be 
measured. The sample stage 50 rides along upper surface 66 of a granite 
block 68, being supported by an air bearing 70 near each corner of a lower 
surface of the sample stage 50. The granite block 68 is manufactured with 
an extremely flat upper surface 66, so that vertical movement of the 
sample stage 50 is restricted. 
The sample stage 50 is mounted to move in the Y-direction of arrow 62 along 
a forward extending leg 72 of a "T"-shaped carriage 74, with the alignment 
of the sample stage being maintained by linear bearings 76, mounted within 
the sample stage 50, moving along guide rails 78 mounted within the 
carriage 74. This movement of the sample stage 50 is caused by the 
rotation of a leadscrew 80 by means of a drive motor 82. The leadscrew 80, 
which is rotatably mounted in the carriage 74 by means of bearings 84, 
engages the sample stage 50 by means of a drive nut 86 mounted in the 
sample stage 50. 
The carriage 74 is mounted to move in the X-direction, with linear bearings 
88 of the carriage 74 moving along a guide rail 90 extending between sides 
92 of a framework 94 bolted atop the granite block 68. This motion occurs 
with the rotation of a leadscrew 96, rotatably mounted within the 
framework 94 by bearings 98. The leadscrew 96, which is rotated by a drive 
motor 100, engages a nut 102 mounted within the carriage 74. Movement of 
the carriage 74 in the X-direction is imparted to the sample stage 50. An 
upper plate 104 of the framework 94 is used for mounting instrumentation, 
including the Z-axis actuator and approach subsystem 30 (shown in FIG. 1), 
for examining a surface of a sample fastened to the vacuum chuck 64. 
The transfer pallets 54 are mounted at a corner of the sample stage 50, so 
that the area of the vacuum chuck 64 is avoided. In this way, two probe 
tip assemblies 10 may be carried by the sample stage 50 without 
interfering with the sample (not shown) to be inspected, as it is carried 
on the vacuum chuck 64. Since the sample stage drive mechanisms, as 
described above, are configured particularly for moving a sample placed on 
the vacuum chuck 64 into precise locations beneath the probe 14 (shown in 
FIG. 1) used to examine the sample, these mechanisms are also used to move 
the sample stage 50 so that either of the transfer pallets 54 carried in a 
buffer station 58 of the sample stage 50 is moved directly under the 
attachment fixture 12 (also shown in FIG. 1). After this motion has 
occurred, a tip assembly 10 carried by the attachment fixture 12 is 
transferred to an empty transfer fixture 54, or a tip assembly 10 carried 
to a transfer pallet 54 is transferred to the attachment fixture 12, which 
must be empty before the transfer is made. 
FIG. 6 is a fragmentary, partially sectional, view of the sample table 50, 
taken as indicated by section line VI--VI in FIG. 4, showing particular 
details of transfer pallets 54 and buffer stations 58. Similarly, FIG. 7 
is a fragmentary, partially sectional, view of the sample table 50, taken 
as indicated by section line VII--VII in FIG. 4, showing additional 
details of transfer pallets 54 and buffer stations 58. 
Referring to FIGS. 4 and 6, each transfer pallet 54 includes an "L"-shaped 
lower portion 108 and a rectangular upstanding front portion 110. The 
lower portion 108 includes a pair of holes 112, allowing the transfer 
pallet 54 to be slid onto the posts 56 of each tip magazine station 59 
within tip magazine 52. A transfer plate 114, which is configured for the 
attachment of a tip assembly 10, is fastened atop the front portion 110. 
The transfer pallet 54 also includes magnetic means 115 for releasably 
holding a tip assembly 10 in place on the transfer plate 114. These 
magnetic means 115 include a permanent magnet 116, a pair of armature 
plates 118, between which the permanent magnet 116 extends, and a pair of 
bucking coils 120 with windings extending around an associated armature 
plate 118. 
Continuing to refer to FIG. 6, and referring again to FIG. 1, when a tip 
assembly 10 is to be held on the transfer pallet 54, the bucking coils 120 
are not electrically energized, and the magnetic circuit extending through 
the permanent magnet 116, the armature plates 118, and the probe support 
plate 22 provides a force holding the tip assembly 10 in place atop the 
transfer pallet 54. The permanent magnet 116 in the transfer pallet 54 is 
powerful enough to overcome the permanent magnet 34 (shown in FIG. 3) in 
the attachment fixture 12, so that a transfer of the tip assembly 10 from 
the attachment fixture 12 to the transfer pallet 54 occurs when the tip 
assembly 10 is brought downward, in the direction of arrow 28, by the 
motion of Z-axis actuator 24, into proximity with the transfer pallet 54, 
which has been aligned with the attachment fixture 12. The bucking coils 
120 are arranged so that the magnetic flux produced within the armature 
plates 118 by the application of a driving signal to these coils opposes 
the magnetic flux from permanent magnet 116. When a driving signal is 
applied to bucking coils 120, the magnetic force holding a tip assembly 10 
in place atop the transfer pallet 54 is sufficiently reduced that the tip 
assembly 10 is transferred from the transfer pallet 54 to the attachment 
fixture 12 if the attachment fixture 12 is in proximity with the tip 
assembly 10 and in alignment therewith. 
Referring to FIGS. 2, 4, and 6, the accurate alignment of the tip assembly 
10 as it is held atop the transfer pallet 54 is assured by a kinematic 
mount, of the type described above, for holding the tip assembly 10 in 
proper alignment with the attachment fixture 12. Thus, transfer pallet 54 
includes three set screws 122 extending upward through the transfer plate 
114. Each set screw 122 has a spherical end engaging a indentation 124 in 
the lower surface of probe support plate 22. A first indentation 124-1 is 
conical, a second indentation 124-2 is shaped as a trough aligned with the 
first indentation 124-1, and a third indentation 124-3 provides an 
enlarged flattened surface. The transfer pallet 54 also includes a pair of 
spring contacts 126, mounted within an insulating block 128, and aligned 
to engage a pair of contact posts 130 at the lower surface of the tip 
assembly 10. These contact posts 130 are connected by a resistor (not 
shown) within the tip assembly 10. The value of resistance of the resistor 
is used to identify the type of tip assembly, with various values of 
resistance being used to identify various different types of tip 
assemblies. 
Continuing to refer to FIGS. 4 and 6, and referring additionally to FIG. 7, 
each buffer station 58 includes a pair of forward extending legs 134,136, 
over which a transfer pallet 54 is slid for placement on the sample table 
50. The transfer pallet 54 is releasably secured to the buffer station 58 
by means of three spring-biased plungers assemblies 138, each of which 
includes a spherical tip 140 which is held outward, in engagement with a 
corresponding indentation 142 in the transfer plate 114 of a transfer 
pallet 54. These indentations 142 provide a kinematic mount as described 
above, with a first indentation 142-1 fitting tightly over the 
corresponding plunger tip 140, with a second indentation 142-2 extending 
as a trough in alignment with the first indentation 142-1, and with a 
third indentation 142-3 providing a flat surface in which the 
corresponding plunger tip 140 rests. 
After the transfer pallet 54 is installed within a buffer station 58, the 
transfer pallet is held upward, opposite the direction of arrow 28, with 
upper surfaces 144 of the "L"-shaped lower portion 108 of the transfer 
pallet 54 being held in contact with the heads 146, of pins 148, extending 
downward from the legs 134, 136 of the buffer station 58. These pins 148 
are mounted within insulating blocks 150 and are wired to provide an 
indication of electrical contact between each pin 148 and the transfer 
pallet 54. Such contact indicates both that a transfer pallet 54 is in 
place within the buffer station 58 and that the transfer pallet 54 has not 
been pushed downward by movement of a tip assembly 10 in contact with the 
transfer pallet 54 during an attempt to transfer the tip assembly in 
either direction between the attachment fixture 12 and the transfer pallet 
54. 
The transfer pallet 54 also includes four contact posts 154, each of which 
is in electrical contact with a spring connector 156 extending within a 
lower block portion 158 of buffer station 58, when the transfer pallet 54 
is fully inserted into the buffer station 58. These contact posts 154 are 
held within an insulating block 160, which is in turn adhesively attached 
within a slot 161 in the "L"-shaped lower portion 108. While this block 
160 extends within a hole 112 provided for engagement with a shaft 56 of 
the tip magazine 52, such a shaft 56 is not long enough to contact the 
block 160. Similarly, the contact fixture at the front section 110 of 
transfer pallet 54 includes four contact posts 162, each of which is in 
electrical contact with a spring connector in a tip magazine station 59 of 
the tip magazine 52, when the transfer pallet is held in place within the 
tip magazine station 59. 
Thus, electrical signals are carried between various circuits within the 
scanning probe microscope and any transfer pallet 54 which if fully 
engaged with either a tip magazine station 59 or a buffer station 58. 
These signals determine which type of probe tip assembly 10 is in place on 
the transfer pallet, by connection through contacts 130 to an identifying 
resistance. Furthermore, if no tip assembly 10 is in place on the transfer 
pallet 54, a measurement of this resistance will indicate an open circuit 
condition. These signals are also used to activate the bucking coils 120 
within the transfer pallet 54. With the transfer pallet 54 in place within 
a buffer station 58, the bucking coils 120 are activated to release the 
probe tip assembly 10, so that it can be transferred to the attachment 
fixture 12. With the transfer pallet 54 in place in a tip magazine station 
59, the bucking coils 120 are activated to release the probe tip assembly 
10 so that it may be replaced with another probe tip assembly. 
FIGS. 8-10 show a tip magazine station 59, with FIG. 8 being a partly 
sectional right side elevation of thereof, with FIG. 9 being a front 
elevation thereof, and with FIG. 10 being a bottom plan cross-sectional 
view thereof, taken as indicated by section lines X--X in FIG. 9. Of these 
drawings, only FIG. 8 shows a transfer pallet 54 in place on the tip 
magazine station 59, which provides both a position for holding a transfer 
pallet 54, which may in turn hold a tip fixture 10 (shown in FIG. 1), 
within the tip magazine 52 (shown in FIG. 4), and a means for moving the 
transfer pallet 54 in either direction between the tip magazine 52 and a 
buffer station 58 (shown in FIG 6) held in alignment with the tip magazine 
station 59. Since the tip magazine station 59 stays in the same position 
within the tip magazine 52, it may be considered a stage or element of the 
tip magazine 52. 
Referring to FIGS. 8-10, the tip magazine station 59 includes a pneumatic 
cylinder 60, which is mounted atop a stationary base 166. The pneumatic 
cylinder 60 moves an "L"-shaped transfer carriage 168 in the direction of 
arrow 62 to move a transfer pallet 54 from the tip magazine 52 (shown in 
FIG. 4) to a buffer station 58 (shown in FIG. 6), and then restores the 
transfer carriage 168 to its original position without the transfer pallet 
54. The two shafts 56, on which the transfer station is moved and held 
within the tip magazine, extend outward from the transfer carriage 168, 
being attached thereto. To move a transfer pallet 54 from a buffer station 
58 to the tip magazine 52, the pneumatic cylinder 60 first moves the 
transfer carriage 168 in the direction of arrow 62 into engagement with 
the transfer pallet 54, and then returns the transfer carriage 168 
opposite the direction of arrow 62, along with the transfer pallet 54. 
The pneumatic cylinder 60 acts in response to applied air pressure, as a 
single acting cylinder applying air pressure against a biasing spring, or 
as a double acting cylinder, applying air pressure to moved the transfer 
carriage 168 in either direction. This movement is constrained to be in 
the direction of arrow 62, and opposite thereto, by means of a bearing 
structure 170 forming a part of the transfer carriage 168 while moving 
within a slot 172 in the stationary base 166. Physical contact is made 
between the bearing structure 170 and the stationary base 166 through a 
number of rolling elements 174, which may be circulating balls, rollers 
operating in "V"-grooves having alternately perpendicular axes of 
revolution, or other rolling structures familiar to one who is skilled in 
the art of making such devices. 
As described above, operation of the pneumatic cylinder 60 is the same, 
regardless of the direction in which the transfer pallet 54 is being 
moved, with the transfer plate 168 being moved first in the direction of 
arrow 62, and then opposite this direction. However, when the transfer 
pallet 54 is being moved to a buffer station 58, the transfer plate 168 
must be conditioned to release the transfer pallet 54, while, when the 
transfer pallet 54 is being moved from a buffer station 58, the transfer 
carriage 168 must be conditioned to attract and retain the transfer pallet 
54. This conditioning is based on the presence of a transfer pallet 54 in 
the tip magazine station 59 before the pneumatic cylinder 60 is operated, 
indicating that this transfer pallet 54 is to be released, or on the 
absence of a transfer pallet 54 in the tip magazine station 59 before the 
pneumatic cylinder 60 is operated, indicating that a transfer pallet 54 is 
to be attracted and retained. 
The process of attracting and retaining or releasing a transfer pallet 54 
is dependent upon the movement of a permanent magnet 176 with the transfer 
carriage 168. When a transfer pallet 54 is in place within the tip 
magazine 52 on shafts 56 of the tip magazine station 59, as shown in FIG. 
8, a lower surface 178 of the transfer pallet 54 holds a roller 180 
downward, in the direction of arrow 182. This roller 180 is rotatably 
mounted on a lever 184, which is in turn pivotally mounted within the 
stationary base 166 at a pivot pin 186. A spring-biased plunger mechanism 
188, which is also disposed within the stationary base 166, presses 
downward on the other end of the lever 184, holding the roller 180 in 
contact with the lower surface 178. 
The magnet 176 is mounted at an end of a magnet bar 190, which is mounted 
to slide in and opposite to the direction of arrow 62 within a hole 192 
extending through a portion of stationary base 166. A pawl 194, pivotally 
mounted on the magnet bar 190 by a pin 196, is held by means of an 
extension spring 198 against a stopping surface 200 extending outward from 
the magnet bar 190. This spring 198 also acts to hold a flange portion 202 
of magnet bar 190 against an inner surface 204 of the transfer carriage 
168, so that the magnet bar 190 moves with the transfer carriage 168, with 
magnet 176 extending within a hole 206 in the carriage 168. When the 
magnet 176 is held in this position with the transfer pallet 54 in place 
on the shafts 56, the magnetic attraction occurring between the magnet 176 
and the front portion 110 of transfer pallet 54 holds the transfer pallet 
54 in place on the shafts 56. 
However, when the transfer carriage 168 is moved in the direction of arrow 
62 with a transfer pallet 54 in place as shown in FIG. 8, movement of the 
magnet bar 190 in the direction of arrow 62 is stopped when pawl 194 comes 
into contact with an interposer 208 extending upward as a portion of the 
lever 184. After this occurs, motion of the transfer carriage 168 in the 
direction of arrow 62 continues, with the carriage 56 being released from 
the attractive forces of magnet 176. The pawl-engaging surface 210 of 
interposer 208 and the interposer-engaging surface 212 of pawl 194 are 
inclined so that the pawl 194 and interposer 208 are held locked together 
by the force of extension spring 198 even when the transfer pallet 54 is 
moved, in the direction of arrow 62, out of contact with roller 180. 
Continuing to refer to FIG. 8, and referring again to FIGS. 4 and 6, when 
the transfer carriage 168 is moved to the limits of its motion in the 
direction of arrow 62, the transfer pallet 54 is moved into full 
engagement with a buffer station 58, so that three spring-biased plungers 
140 within the buffer station 58 are moved into corresponding indentations 
142 within the transfer plate 114 of the transfer pallet 54. A detenting 
action of these plungers 114 in indentations 142 is sufficient to hold the 
transfer pallet 54 in place on the buffer station 58, in the absence of a 
significant attractive force from magnet 176, as the shafts 56 are 
withdrawn from buffer station 58 with a return movement of the transfer 
carriage 168 in the direction opposite arrow 62. 
On the other hand, when a transfer pallet 54 is to be transferred from a 
buffer station 56 to the tip magazine 52, the buffer station 56 is first 
aligned with an empty tip magazine station 59 within the tip magazine 52. 
The lever 184 of the empty tip magazine station 59 is pivoted by means of 
plunger mechanism 188 so that the roller 180 is moved upward, opposite the 
direction of arrow 182, in the absence of a transfer pallet 54 on shafts 
56 of the tip magazine station 59. This pivoting of lever 184 moves the 
upward-extending interposer downward, out of the path of pawl 194, 
allowing extension spring 198 to move magnet bar 190 with flange 202 in 
contact with inner surface 204 of the transfer carriage 168 throughout the 
motion of this carriage 168 in the direction of arrow 62. As this motion 
is completed, an attractive force is established between the magnet 176 
and the upstanding block portion 110 of the transfer pallet 54 in place on 
a buffer station 58. As the reverse motion of the transfer carriage 168, 
opposite the direction of arrow 62, is begun, the attractive force from 
magnet 176 is sufficient to overcome the detent force holding the transfer 
fixture 54 in place on the buffer station 58, with plungers 114 from the 
buffer station 58 within the indentations 142 of the transfer pallet 54. 
Thus, during the reverse motion of the transfer carriage 168, the transfer 
pallet 54 is pulled off the buffer station 58 by means of the magnet 176 
moving with the transfer carriage 168. 
During this return motion of transfer carriage 168, opposite the direction 
of arrow 62, the lower surface 178 of the transfer pallet 54 comes into 
contact with roller 180. This contact moves the roller 180 downward, 
pivoting lever 184 so that interposer 208 is moved upward, into the path 
of pawl 194, which is returning opposite the direction of arrow 62. 
However, the reverse surfaces 214 and 216 of interposer 208 and pawl 194, 
respectively, are inclined so that continued movement of the magnet bar 
190 with these surfaces 214, 216 in contact causes the pawl 194 to rotate 
on pin 196 in the direction of arrow 216, moving over the interposer 208 
to rotate back into the position shown in FIG. 8. 
FIG. 11 is a schematic view showing electrical connections within and 
between the various components of the present invention. When the probe 
tip assembly 10 is held in engagement with the attachment fixture 12, six 
electrical connections between spring contacts 36 and contact posts 37 
connect up to six output lines from the attachment fixture 12 to the 
various electrodes of a piezoelectric actuator 218 within the probe tip 
assembly 10. The number of such connections actually required depends on 
the type of piezoelectric actuator being used. In the simplest case, a 
bimorph actuator providing only vertical vibration requires only 
connections to a drive electrode, vibration excitation and a grounding 
electrode. On the other hand, the piezoelectric actuator may provide 
scanning along the sample surface, in X- and Y-directions, along with 
vibration in the vertical direction, or Z-axis. Such an actuator requires 
connections to +X, -X, +Y, -Y, vibration excitation, and grounding 
electrodes, using the six electrical connections available from the 
attachment fixture 12. 
When the probe tip assembly 10 is in place on the transfer pallet 54, 
electrical connections are made through spring contacts 126 and contact 
posts 130 between the transfer pallet 54 an identification resistor 220 
within the probe tip assembly 10. The resistance value of this resistor 
220 indicates the particular type of probe tip assembly 10, 
differentiating among several different types of probe tip assemblies 
which may be used. This information indicates, for example, which of the 
electrical connections through contact posts 37 need to be driven, and how 
the should be driven. When the transfer pallet 54 is engaged with both the 
probe tip assembly 10 and a tip magazine station 59, the resistor 220 is 
further connected to the tip magazine station 59 through a pair contact 
posts 162 and associated spring contacts 222. In this way, the type of tip 
assembly in each tip magazine station 59 of the tip magazine 52 is known 
at all times. Alternately, when a transfer pallet 54 is engaged with both 
the tip magazine station 59 and with a buffer station 58, the resistor 220 
is further connected to the buffer station 58 through a pair of contact 
posts 154 and associated spring contacts 156. In this way, the type of tip 
assembly in each buffer station 58 of the sample stage 50 (shown in FIG. 
5) is also known. In either case, an open circuit in place of an expected 
level of resistance indicates the absence of a probe tip assembly 10. 
As previously described in reference to FIG. 6, the tip assembly 10 is 
normally held in place on the transfer pallet 54 by a permanent magnet 116 
within this fixture 54, being released for removal by the activation of a 
pair of bucking magnet coils 120. When the transfer pallet 54 is engaged 
with a tip magazine station 59, bucking magnet coils 120 are connected to 
circuits therewithin by means of the remaining spring contacts 222 and 
contact posts 162. This connection allows the attractive force holding the 
tip assembly 10 on a transfer pallet 54 to be overcome when a tip assembly 
is to be removed manually from the fixture 54. When the transfer pallet 54 
is engaged with a buffer station 58, bucking magnet coils 120 are 
connected to circuits therewithin by means of the remaining spring 
contacts 156 and contact posts 154. This connection allows the attractive 
force holding the tip assembly 10 on the transfer pallet 54 to be overcome 
so that the tip assembly 10 can be transferred from the transfer pallet 54 
to the attachment fixture 12. 
Also as previously described in reference to FIG. 6, the transfer pallet 54 
is normally held upward within a buffer station 58, so that a contact 
surface 144 of the transfer pallet 54 is held against three contact pins 
148. This contact surface 144 is electrically grounded through a spring 
contact 156 and a mating contact post 154. When the attachment fixture 12 
is moved downward to transfer a tip assembly 10 in either direction 
between the attachment fixture 12 and the transfer pallet 54, the 
connection between contact pins 148 and electrical ground is broken. This 
condition is measured using, for example, a pull-up resistor (not shown), 
in a manner well known to those skilled in the art, within the apparatus 
to provide a signal when the circuit is opened. When all three circuits 
through contact pins 148 are opened, the downward motion of attachment 
fixture 12 is stopped. 
Referring to FIGS. 1 and 4-6, operation of apparatus built in accordance 
with the present invention will now be described in terms of four transfer 
operations. In the first transfer operation, a probe assembly 10 is 
transferred from a buffer station 58, attached to the sample stage 50, to 
the attachment fixture 12. In the second transfer operation, a probe 
assembly 10 is transferred from the attachment fixture 12 to a buffer 
station 58. In the third transfer operation, a transfer pallet 54 is moved 
from a tip magazine station 59, within the tip magazine 52, to a buffer 
station 58 attached to the sample stage 50. In the fourth transfer 
operation, a transfer pallet 54 is moved from a buffer station 58 to a tip 
magazine station 59. 
The successful completion of the first transfer operation requires that the 
attachment fixture 12 must be initially empty to receive the probe 
assembly 10. This operation begins by moving the sample stage 50, using 
the drive motors 82, 100, into a position in which the probe assembly 10 
being transferred is directly below, and in alignment with, the attachment 
fixture 12. The attachment fixture 12 is next lowered, using the Z-axis 
piezoelectric actuator 24, until open circuit conditions at the pins 148 
indicate that the attachment fixture 12 has moved the probe assembly 10, 
and hence the transfer pallet 54 under it, downward within the buffer 
station 58. When this occurs, the downward motion of attachment fixture 12 
is stopped, and bucking coils 120 are energized to release the probe 
assembly 10 from transfer pallet 54. The attachment fixture 12 is then 
moved upward by means of the actuator 24, carrying the probe assembly 10 
through the attractive force of magnet 34. When the probe assembly 10 has 
been moved away from transfer pallet 54, the flow of current through 
bucking coils 120 is stopped. 
The successful completion of the second transfer operation requires that 
one of the buffer stations 58 of the sample stage 50 must initially hold a 
transfer pallet 54 which is empty for receiving the probe assembly 10. 
This operation begins by moving the sample stage 50, again using drive 
motors 82, 100, into a position in which the empty transfer pallet 54 is 
directly under, and in alignment with, the probe assembly 10 held by the 
attachment fixture 12. Next, the attachment fixture 12 is lowered, using 
the Z-axis actuator 24, again until open circuit conditions occur at the 
pins 148. When this occurs, the downward motion of the attachment fixture 
12 is stopped, and the probe assembly 10 is transferred from the 
attachment fixture 12, with the attractive force from permanent magnet 116 
overcoming the attractive force from magnet 34. Then, the attachment 
fixture 10 is returned upward using the actuator 24, with the probe 
assembly 10 remaining on the transfer pallet 54. 
Referring to FIGS. 4, 5, and 8, the third transfer operation begins with 
moving the sample stage 50, using motors 82, 100 as required, so that an 
empty buffer station 58 is adjacent to, and aligned with, the transfer 
pallet 54 to be moved onto the buffer station 58. Next, the pneumatic 
cylinder 60, of the tip magazine station 59 holding the transfer pallet 54 
to be moved, is actuated to move the transfer carriage 168 in the 
direction of arrow 62. Since the transfer pallet 54 is initially in place 
on the shafts 56 of the tip magazine station 59, the movement of magnet 
shaft 190 is restricted by contact between pawl 194 and interposer 208, 
releasing the magnetic force holding the transfer pallet 54 on the tip 
magazine station 59. Thus, as the movement of transfer carriage 168 is 
completed, the detent forces provided by pins 140 moving into indentations 
142 are sufficient to hold the transfer pallet 54 in place on the buffer 
station 58 as the pneumatic cylinder 60 returns the transfer carriage 168 
opposite the direction of arrow 62. 
The fourth transfer operation begins with moving the sample stage 50, using 
motors 82, 100 as required, so that the transfer pallet 54 to be moved to 
the tip magazine station 59 is adjacent to, and aligned with, this station 
59. Next, the pneumatic cylinder 60, of the tip magazine station 59, is 
actuated to move the transfer carriage 168 in the direction of arrow 62. 
Since the transfer pallet 54 is initially not in place on the shafts 56 of 
the tip magazine station 59, magnet shaft 190 moves with the transfer 
carriage 168. As the transfer carriage 168 reaches the end of its motion 
in the direction of arrow 62, an attractive force is established between 
magnet 176 and the transfer pallet 54. As the transfer carriage 168 is 
subsequently returned, opposite the direction of arrow 62, this attractive 
force overcomes the detent forces provided by pins 140 within indentations 
142, so that the transfer carriage 168 returns holding the transfer pallet 
54. 
These four transfer operations are combined in various ways to produce the 
required movements of tip assemblies 10 and transfer pallets 54. For 
example, with an empty transfer pallet 54 and a transfer pallet holding a 
tip assembly 10 in the two buffer stations 58 of the sample stage 50, the 
tip assembly 10 in one of the buffer stations 58 can be interchanged with 
a tip assembly 10 in the attachment fixture 12. This is done by using the 
second transfer operation to transfer one tip assembly 10 from the 
attachment fixture 12 to the empty transfer pallet 54, and by the using 
the first transfer operation to transfer the other tip assembly 10 from 
the other transfer pallet 54 to the attachment fixture 12. A tip assembly 
10 on the attachment fixture 12 is moved to the tip magazine 52 by first 
applying the second transfer operation to transfer to tip assembly 10 from 
the attachment fixture 12 to an empty transfer pallet 54 on a buffer 
station 58, and by then applying the fourth transfer operation to move the 
transfer pallet 54, with the tip assembly 10 attached thereto, to an empty 
tip magazine station 59. A tip assembly 10 is moved from the tip magazine 
52 to the attachment fixture 12 by first applying the third transfer 
operation to move the tip assembly 10 on a transfer pallet 54 from a tip 
magazine station 59 to a buffer station 58, and by then applying the first 
transfer operation to move the tip assembly 10 from the buffer station 58 
to the attachment fixture 12. 
While it is understood that there appears to be something of the old 
carnival "shell game" in all of this, the type of computing system 
generally used to control operations of this kind can easily keep track of 
where empty transfer pallets 54 are located, moving them where they are 
needed before transfer operations are begun. The feature of tip assembly 
type identification associated with the use of identification resistor 220 
can also help such a system identify where a particular type of probe is 
located. 
While the preferred embodiment described above includes a tip magazine 52 
to provide a large number of positions in which tip assemblies 10 may be 
stored for use in the scanning probe microscope, an alternative embodiment 
of the present invention, does not have the tip magazine 52. Instead, the 
number of buffer stations 59 is preferably increased beyond the two such 
fixtures shown in FIGS. 4 and 5, and only the first and second transfer 
operations are used. This embodiment is substantially less complex, at the 
expense of having fewer available tip assemblies 10. Preferably, this 
embodiment retains transfer pallets 54 which are moved vertically to break 
the electrical connections between pins 148 and surface 144, as described 
above in reference to FIG. 6. Also as described above, the opening of such 
electrical connections is preferably used to terminate downward motion of 
the attachment fixture 12. 
While the invention has been shown and described with reference to 
preferred embodiments, it is understood that this description is made to 
provide an example, and that various changes in form and arrangement of 
parts may be made therein without departing from the spirit and scope of 
the invention.