Probe tip locator

Details Probe tip locator Probe tip locator

1998-11-20

2001-01-30

Fulton, Christopher W. (Department: 2859)

Geometrical instruments

Gauge

With support for gauged article

C033S502000, C033S706000

Reexamination Certificate

active

06178653

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a probe tip locator, and, in particular, to probe tip locator having a plurality of encoded bit fields for use with a scanning probe or stylus microscope.
BACKGROUND OF THE INVENTION
Before a probe can be used to scan a sample, its position relative to the x-y stage on which the sample is mounted must be known. The microscope generally knows the location of the probe tip within an initial level of uncertainty (a). In prior art microscopes, the initial level of uncertainty (a) can be large. The level of uncertainty (a) should, however, correspond to the precision of the stage, which is generally a few microns. A probe tip locator is used to more precisely determine the location of the probe tip, i.e., reduce the level of uncertainty (a) to an acceptable target value. The probe tip locator is placed at a predetermined location on the stage. The locator is designed so that a scan of the locator will provide information about the position of the probe over the locator. Using this information, the position of the probe tip relative to the microscope stage and scan actuator can be determined.
BACKGROUND OF THE INVENTION
The prior art probe tip locators typically use a single large locator. The prior art locator generally consists of a first reference line parallel to the y-axis and a second reference line which intersects the first reference line at an acute angle. A scan line which crosses the two reference lines is used to calculate the location of the probe tip. That is, by using a known offset vector, a scan of the first reference line is used to determine the x-axis location of the probe tip and the distance between the two scanned lines, along the scan line, is used to determine the y-axis location. That is, a scan line across the entire locator is needed to determine the location of the probe tip. The limits of the prior art locators is the scanning range (b). That is, in the prior art, a single scan of a distance b will reveal the location of the probe tip relative to the probe's coordinate system. One of skill in the art will recognize that when the scan range of the probe (b) is significantly smaller than the initial uncertainty of the probe position (a), the prior art locators are not useful because a scan across the entire area occupied by the locator is required in order to reveal the location of the probe tip.
SUMMARY OF THE INVENTION
The present invention is directed to a probe tip locator for use with a scanning probe or stylus microscope, and in particular, the present invention is directed at a probe tip locator for locating a probe tip when the microscope scan range is smaller than the needed capture range.
In a preferred embodiment, the locator generally includes an array of scannable structures. Each structure includes a first reference line parallel to the y-axis of the stage coordinate system and a second reference line which is angled from and intersects the first reference line at an acute angle. Each structure also includes an encoding scheme comprising a plurality of encoded bit fields which are parallel to the first reference line. Each encoding scheme comprises 4 neighboring lines forming a 4 bit field, allowing for the encoding and identification of 16 distinct first reference lines. A scan across just a portion of the locator, i.e., a scan which includes a first reference line, a second reference line, and at least four neighboring lines, whether from the same bit field or adjacent bit fields, is all that is needed to locate the probe tip. The microscope uses the encoded bit fields to determine which of the first reference lines has been scanned. If the scan includes neighboring lines from two adjacent bit fields, an algorithm is employed to determine which first reference line was scanned. By using this information, and a known offset vector, the x-axis location of the probe tip relative to the stage coordinate system can be determined. The y-axis location of the probe tip relative to the stage coordinate system is determined by measuring the distance between the first scanned reference line and the scanned second reference line.
In another preferred embodiment, the locator generally includes a plurality of reference lines parallel to the y-axis. Between each reference line is a first encoding scheme comprising 4 neighboring lines forming a 4 bit field, allowing for the identification of 16 distinct first reference lines. The locator also includes a second encoding scheme between the reference lines comprising 8 neighboring lines forming an 8 bit field, which encodes a total of 256 distinct positions along the y-axis between each reference line. A scan across just a portion of the locator, i.e., a scan which includes a reference line, at least four neighboring lines from a first encoding scheme, and at least eight neighboring lines from a second encoding scheme, whether the neighboring lines are from the same bit field or adjacent bit fields, is all that is needed to locate the probe tip. The microscope uses the encoded bit fields to determine which of the first reference lines has been scanned. Accordingly, a scan across just a portion of the locator is all that is required to reveal the location of the probe tip relative to the x-y stage.
Other objects and features of the present invention will become apparent from the following detailed description, considered in conjunction with the accompanying drawing figures. It is to be understood, however, that the drawings, which are not to scale, are designed solely for the purpose of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.


REFERENCES:
patent: 3600811 (1971-08-01), Weyrauch
patent: 3916528 (1975-11-01), Eisenkopf
patent: 4409479 (1983-10-01), Sprague et al.
patent: 4530159 (1985-07-01), Ernst

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