Patent Number: 051030950
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is depicted in its most basic form in FIG. 4 where it is incorporated into a scanning probe microscope 10'. As depicted therein, according to the improvement of this invention all three of the supports are moveable supports 16 which are independently movable by motor drives 24 which are controlled by the control computer 26. In tested versions of this embodiment, the supports 16 were designed to have much longer travel, higher speed, and finer resolution than the single motorized support of the prior art microscope 10 of FIG. 1. These features allow for substantial increase in the utility of SPMs. It should also be noted initially that while the primary illustrations contained hereinafter have the sample fixed, within the scope of the invention the probe can also be fixed with the sample being mounted on a device wherein the orientation between the sample and the probe is determined by three legs on the device. In the basic embodiment of FIG. 4, the movable supports 16 are mounted in the base 18 with the scanner 12 resting on the supports 16. A more versatile (and preferred) configuration is shown in FIG. 5. This embodiment is functionally equivalent to the embodiment of FIG. 4; but, has the advantage that the head design can be used in many SPM configurations, as will be illustrated. This embodiment is a free-standing head generally indicated as 28. The piezoelectric tube scanner 12 is mounted perpendicularly downward in the center of a support structure 30 (which may be, for example a cylindrical or triangular plate) which has three hollow legs 32 attached thereto and extending perpendicularly downward therefrom. While not completely necessary, it is preferred that the legs 32 be spaced radially at 120.degree. intervals about the scanner 12. Threadedly disposed within each leg 32 is an inner leg 34 having a ball 36 on the bottom end thereof. The legs 32 could also be replaced by a solid structure such as a cylinder with threaded holes to receive the three inner legs 34 and a central bore for the scanner as depicted in FIG. 7. The inner legs 34 are fine threaded screws (1/4-80 having been used in tested embodiments) which are rotated by individual small DC motors 38 that drive individual 1000:1 transmissions 40 which, in turn, rotate the screws 34. The motors 38 can have optical encoders on them to monitor their rotation, if desired; but, this is not considered as necessary and is, therefore, not preferred. The motors 38 are connected through an appropriate interface for the particular implementation (not shown and as will be readily determined by those skilled in the art without undue experimentation) to tilt control logic 42 which is most likely contained within the control computer 26 which controls the entire microscope. A separate tilt controller could, of course, be employed if desired and more applicable in certain applications. The head 28 in this particular illustration rests on a base 44 which holds the sample 22. The base 44 could be flat so that the head 28 could be moved around on it; or could have indexing marks (e.g., hole, groove, flat) to position the balls 36 to place the probe 20 over the sample 22 as shown in FIG. 5. The inventors herein have found that it may be useful to use magnetic balls or magnets behind ferromagnetic balls to hold the head 28 down snugly on the base 44. The DC motors 38 are energized by the tilt control logic 42 to rotate the threaded inner legs 34 and thereby move the legs 32 up and down which, in turn, moves the support structure 30 and scanner 12 up and down. When all of the legs 32 are driven simultaneously, the support structure 30 and scanner 12 move up and down without tilting. This type of motion would be used for approaching the tip of the probe 20 to the surface of a sample 22. The motion can be quite large (several millimeters) so that the tip would not need to be placed near the sample 22 by an operator before automatic approach is started. The tilt of the head 28 is varied by not energizing the motors 38 equally. Given the configuration depicted in FIG. 5 (i.e. one leg 32 in front of the probe 20 on the left side as the figure is viewed and two legs 32 spaced equally on either side of and behind the probe 20 on the right side as the figure is viewed), the scanner 12 can be tilted in the Y direction by raising/lowering the two right legs 32 an equal amount and/or lowering/raising the left leg 32. The scanner 12 can be tilted in X by a similar process, i.e., by raising/lowering the left leg 32 and one of the two right legs 32 an equal amount and/or lowering/raising the other right leg 32. The tilt can be monitored by the data taken from the scanning probe 20 and this data can be taken while the legs 32 are being raised and lowered so that the tilt can be set by the system even though the motorized screws do not have encoders. In this preferred approach, the feedback for the tilting comes from the scanning system itself by fitting to the plane of the vertical data instead of from positional readout devices on the motors 38. This preferred approach makes the scanning head 28 simpler and less expensive. After the tilt of the head 28 is set to a particular value, the head 28 can then be raised and lowered for changing the sample 22 by driving all three legs 32 at the same rate and in the same direction. As thus described, the improved scan head 28 of FIG. 5 allows for long distance probe approach or removal without operator participation. At the same time, it also allows for compensation for probe/sample tilt, or for the addition of controlled tilt. These abilities allow for several new SPM configurations that will be capable of automatic operation with accuracy and high throughput for large samples, multiple samples, and special applications such as integrated circuits which have steep cliffs or trenches. These various uses for the free-standing, tiltable scan head 28 of FIG. 5 will now be described in detail. FIG. 6 shows the scan head 28 resting directly on a large sample 22. The scan head 28 may be placed on an reasonably flat surface with the probe 20 withdrawn above the bottom of the supports. The approach and leveling operations can be accomplished automatically, making this configuration extremely convenient to use for suitable applications. This configuration would be useful for verifying surface structure or finish on large objects that would not be damaged by supporting the scan head 28. FIG. 7 shows an extremely useful SPM configuration employing the free-standing, tiltable scan head 28. The legs 32 of the scan head 28 rest on a rigid structure 46. The structure 46 has an opening 48 in the top thereof located under the scan head 28 allowing the scan head 28 to lower the probe 22 into the structure 46. Within the structure 46 is a sample positioning system 50 that can translate a large sample 22 (or several separate samples) attached thereon in two horizontal axes on perpendicular shafts 52 by drive 54 under the control of sample positioning logic 56, allowing for rapid and automatic probing of any part of the sample 22. The positioning also could be done with a rotary stage. This would be useful for multiple samples which could be rotated into position under the scan head. Standard commercial computer-controlled positioning products, for optical and other applications, can be employed for the system 50 and have several inches of travel as well as resolution and repeatability of 1 micron or less. Given a typical large scan head 28 that can cover up to 100 microns square or more scan size, this system can probe any section of a large sample automatically. The inventors herein have tested this configuration with structures 46 made of aluminum, and also of ceramics. The structure 46 must be rigid and isolated from vibration to maintain the stability required between probe and sample. The inventors herein have demonstrated adequate stability for sample sizes of up to eight inches, which is adequate for integrated circuit wafers and most magnetic or optical storage media. The translation stage of the system 50 can be either x, y or r, .theta. oriented, depending on the application. The scan head 28 of this invention is critical to making a large sample system accurate and versatile as it provides the abilities to compensate for local sample tilt, or to tilt the probe 22 relative to the sample 20, allowing for accurate mapping of steep structures. In this regard, the tilt can be determined from the data gathered by fitting the vertical scan information to a plane and then calculating the tilt required to level the plane relative to the scanner axes. Another potentially useful SPM configuration as depicted in FIGS. 8 and 9 employs the scan head 28 in an inverted orientation. A sample holding disk 58 is disposed horizontally for indexed rotation around a support shaft 60 by an indexing mechanism 62. The sample holding disk 58 has a plurality of shouldered bores 64 therein at sampling stations of the disk 58. This configuration facilitates the rapid changing of samples as an operator may attach the samples 22 to inserts 66 that may be dropped into the bores 64 from above to rest on the shoulders 68 thereof supported by gravity without conflict with the scan head 28. This system could support continuous sample cycling as the samples 22 in the sample holding disk 58 could be quickly changed without stopping the system. Preferably, the head 28 is mounted on a raise and lower mechanism 70 that works in combination with the indexing mechanism 62 under the joint control of the control computer 26. The raise and lower mechanism 70, when engaged, pushes the legs against the sample holder, thus maintaining the tilting capability. To index the sample holding disk 58 to a new sample scanning position, the head 28 is dropped slightly by the raise and lower mechanism 70 and the sample holding disk 58 is rotated to the next position with a bore 64 positioned under the probe 22. The head 28 is then raised by the raise and lower mechanism 70 until the balls 36 contact the bottom of the sample holding disk 58. The head 28 is then raised, lowered and tilted in the manner described above, as required to accomplish the scanning of the sample. As those skilled in the art will readily recognize and appreciate, this approach could also work well rotated 180.degree. to a "right side up" configuration and, in fact, such an orientation might be preferred in some instances as there would be no necessity of the positive upward force of the scanner mechanism against the sample mount.