Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2001-01-25
2003-07-22
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S497000
Reexamination Certificate
active
06597460
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to non-contact techniques for determining the position in space of points on an object part, including sub-micron precision height measurements of a selected part surface. Example applications are surface profiling, the determination of the height of surface features, which may include dissimilar materials, and the measurement of surface features with respect to a fixed coordinate system or datum so as to determine part location and orientation.
Various optical sensing technologies are available for measuring surface profiles. Height scanning interferometry, as referred to herein, employs broadband light sources to determine 3-D surface height profiles without the fringe-order ambiguity normally associated with laser-based interferometry. In the visible, this height scanning is often referred to in the art as scanning white light interferometry (SWLI), coherence radar, correlation microscopy and vertical scanning interferometry.
SUMMARY OF THE INVENTION
The invention features methods and systems that extend the basic technique of height scanning interferometry by compensating for the phase change on reflection (PCOR) caused by the interferometer and the object part being measured, including the wavelength dependence (dispersion) of PCOR. Proper compensation of such effects improves the accuracy of scanning height measurements. For example, object parts having regions with different optical properties can be more accurately characterized.
Also, the invention extends height-scanning interferometry to those metrology problems for which the absolute position and orientation of the surface is as important as the surface texture and profile. Thus, in addition to providing the form and texture of the surface, the overall position (piston), tip and tilt of the object part can be determined with respect to a fixed point or plane of reference when constructing the surface profile.
In general, in one aspect, the invention features a surface profiling method for determining the relative positions of multiple points on an object surface including multiple surface materials. The method includes: collecting interferometric data related to the relative positions; and calculating the relative positions based on the collected interferometric data and at least one value indicative of dispersion in the phase change on reflection (PCOR) for each of the surface materials.
In general, in another aspect, the invention features a surface profiling method for determining the relative positions of multiple points on an object surface including multiple surface materials. The method includes: collecting interferometric data related to the relative positions; and calculating the relative positions based on the collected interferometric data and at least one value indicative of the phase change on reflection (PCOR) &ggr;
part
for each of the surface materials.
In general, in another aspect, the invention features a surface profiling method for determining the absolute position with respect to a common datum surface of each of multiple points on an object surface. The method includes: collecting interferometric data related to the absolute positions; and calculating the absolute positions based on the collected interferometric data and at least one value indicative of dispersion in the phase change on reflection (PCOR) of the object surface and dispersion in the phase change on reflection (PCOR) of an interferometry system used to collect the interferometric data.
In general, in another aspect, the invention features a surface profiling method for determining the absolute position with respect to a common datum surface of each of multiple points on an object surface. The method includes: collecting interferometric data related to the absolute positions; and calculating the absolute positions based on the collected interferometric data and at least one value indicative of the phase change on reflection (PCOR) of the object surface &ggr;
part
and the phase change on reflection (PCOR) of an interferometry system used to collect the interferometric data &ggr;
sys
.
In general, in another aspect, the invention features a surface profiling method including: collecting interferometric data related to a surface profile of a measurement object; and calculating the surface profile based on the collected interferometric data and at least one value indicative of dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object.
Embodiments of this aspect of the invention can include any of the following features.
The calculation of the surface profile can be based on the collected interferometric data and multiple values indicative of dispersion in the phase change on reflection (PCOR) of different regions of the profiled surface of the measurement object.
The calculation of the surface profile can be based on the collected interferometric data and at least one value indicative of dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object and dispersion in the phase change on reflection (PCOR) of an interferometry system used to collect the interferometric data.
The collection of interferometric data can include collecting scanning interferometric data related to the surface profile of the measurement object.
The collected interferometric data can include at least one phase value ø(k) at a wavevector k for each of multiple points on the profiled surface, and wherein the calculation of the surface profile is based on the relationship
ø(
k
)=2
nk
(
h−&zgr;
)+(&ggr;
part
+&ggr;
sys
)+(&tgr;
part
+&tgr;
sys
)(
k−k
0
)
where h is the surface height, &zgr; is a reference offset position, n is a refractive index, &ggr;
part
is the phase change on reflection (PCOR) of the profiled surface at the wavevector k, &ggr;
sys
is the phase change on reflection (PCOR) of an interferometry system used to collect the interferometric data at the wavevector k, &tgr;
part
is the linear dispersion of the phase change on reflection (PCOR) of the profiled surface with respect to a reference wavevector k
0
, and &tgr;
sys
is the linear dispersion of the phase change on reflection (PCOR) of the interferometer system with respect to wavevector k
0
.
The collected interferometric data can include multiple phase values ø(k) corresponding to multiple wavevector values k for each of multiple points on the profiled surface, and wherein the calculation of the surface profile is based on the relationship
∂
φ
(
k
)
∂
k
=
2
n
(
h
-
ζ
)
+
(
τ
part
+
τ
sys
)
where h is the surface height, &zgr; is a reference offset position, n is a refractive index, &tgr;
part
is the linear dispersion of the phase change on reflection (PCOR) of the profiled surface with respect to a reference wavevector k
0
, and &tgr;
sys
is the linear dispersion of the phase change on reflection (PCOR) of an interferometry system used to collect the interferometric data with respect to the reference wavevector k
0
.
The interferometric data can be scanning interferometric data including multiple phase values ø(&zgr;) corresponding to multiple positions &zgr; of a scanning reference mirror for each of multiple points on the profiled surface, and the calculation of the surface profile includes transforming the multiple phase values for each point into a wavevector domain, calculating a derivative of the transformed phase values for each point with respect to wavevector, and calculating the surface profile from the derivative for each point and the at least one value indicative of dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object.
In such embodiments, the at least one value can be indicative of the dispersion in the phase change on reflection (PCOR) of the profiled surface of the measurement object and the dispersion in the phase change on reflection (PCOR) of a scanning interferometry system used to collect the int
Colonna De Lega Xavier
De Groot Peter
Deck Leslie L.
Kramer James W.
Connolly Patrick J
Fish & Richardson P.C.
Turner Samuel A.
Zygo Corporation
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