US 5,825,670 A · High precison calibration and feature measurement system for a scanning probe microscope

Abstract

The present invention allows for calibration of a scanning probe microscope under computer control. The present invention comprehends either the removal of nonlinear artifacts in the microscope output data after measurement has been taken (a off-line process), or the correction of nonlinear movements in the microscope scanner such that the scanner moves in a linear fashion during measurement (a realtime process). The realtime process may be operated in both an open-loop and a closed-loop process. The processes of the present invention uses an average cross-section of the scan in order to simplify the calculation and to improve the signal-to-noise ratio. Interpolation methods and centroid calculations are used to locate features on the scanned sample to subpixel precision. Comparison of the measured scan feature positions with the known topography of the scanned calibration specimen enable the present invention to assemble a calibrated length scale which may be used to correct individual feature positions in a full two-dimensional scan, each scan line in a two-dimensional image, or an average cross-section of the two-dimensional scan.

Claims69

Dependent claims

A method for high precision calibration by removing artifacts due to nonlinear motion in a scanning probe microscope, comprising the steps of:

a) scanning a calibration specimen in order to create a calibration data array;
b) mapping the calibration data array into a one-dimensional calibration profile;
c) creating a calibrated length scale by comparing the calibration profile to a known topography of the calibration specimen;
d) scanning a measurement specimen in order to create a measurement data array;
e) applying the calibrated length scale to the measurement data array in order to correct nonlinearities in the measurement data array in at least one direction;
and
f) displaying the corrected measurement data array to a user.

4 more elements

A method for realtime open-loop control of a scanning probe microscope, comprising the steps of:

a) performing a coarse adjustment of the microscope by determining a nonlinear voltage drive function which corrects some, but not all, artifacts due to nonlinear motion of the microscope;
b) scanning a calibration specimen in order to create a calibration data array;
c) mapping the calibration data array into a one-dimensional calibration profile;
d) measuring feature locations in the calibration profile;
e) calculating a pitch value for each consecutive pair of feature locations;
f) creating a processed profile comprising the pitch values as a function of position;
g) adjusting the nonlinear voltage drive function to order to reduce any nonlinearities in the processed profile;
and
h) scanning a measurement specimen in order to create a measurement data array.

6 more elements

A method for realtime open-loop control of a scanning probe microscope executing a scan of any size, comprising the steps of:

a) selecting a first scan size;
b) scanning a calibration specimen using the first scan size in order to create a two-dimensional first calibration data array;
c) generating a one-dimensional first calibration profile by calculating an average cross-section of the first calibration data array;
d) measuring first feature locations in the first calibration profile;
e) calculating a pitch value for each consecutive pair of first feature locations;
f) creating a first processed profile comprising the pitch values as a function of position;
g) determining a first nonlinear voltage drive function .DELTA.v.sub.1 (t) including a term Mag.sub.1 *e.sup.(-Arg.sbsp.i.sup.)t, where Mag.sub.1 and Arg.sub.1 are selected in order to reduce nonlinearities in the first processed profile;
h) selecting a second scan size;
i) scanning a calibration specimen using the second scan size in order to create a two-dimensional second calibration data array;
j) generating a one-dimensional second calibration profile by calculating an average cross-section of the second calibration data array;
k) measuring second feature locations in the second calibration profile;
l) calculating a pitch value for each consecutive pair of second feature locations;
m) creating a second processed profile comprising the pitch values as a function of position;
n) determining a second nonlinear voltage drive function .DELTA.v.sub.2 (t) including a term Mag.sub.2 *e.sup.(-Arg.sbsp.2.sup.)t, where Mag.sub.2 and Arg.sub.2 are selected in order to reduce nonlinearities in the second processed profile;
o) fitting Mag.sub.1 and Mag.sub.2 to a first derating function in order to create a first fit function;
p) fitting Arg.sub.1 and Arg.sub.2 to a second derating function in order to create a second fit function;
q) selecting a measurement scan size;
r) determining a measurement nonlinear voltage drive function .DELTA.v.sub.m (t) including a term Mag.sub.m *e.sup.(-Arg.sbsp.m.sup.)t, where Mag.sub.m is interpolated/extrapolated from the first fit function and Arg.sub.m is interpolated/extrapolated from the second fit function;
and
s) applying the measurement nonlinear voltage drive function to the microscope in order to execute a measurement scan.

17 more elements

A method for high precision calibration by removing artifacts due to nonlinear motion in a scanning probe microscope executing a scan of any size, comprising the steps of:

a) selecting a first scan size;
b) scanning a calibration specimen using the first scan size in order to create a first calibration data array;
c) mapping the first calibration data array into a one-dimensional first calibration profile;
d) creating a first calibrated length scale by comparing the first calibration profile to a known topography of the calibration specimen;
e) selecting a second scan size;
f) scanning a calibration specimen using the second scan size in order to create a second calibration data array;
g) mapping the second calibration data array into a one-dimensional second calibration profile;
h) creating a second calibrated length scale by comparing the second calibration profile to a known topography of the calibration specimen;
i) selecting a measurement scan size;
and
j) creating a measurement calibrated length scale L(X) applicable to the measurement scan size by interpolating/extrapolating parameters from the first and second calibrated length scales.

8 more elements

A method for high precision calibration by removing artifacts due to nonlinear motion in a scanning probe microscope, comprising the steps of:

a) scanning a calibration specimen comprising an array of multi-level structures, wherein each structure includes a feature on each level, in order to create a two-dimensional calibration data array;
b) for each level, locating each feature in the calibration data array;
c) for each level, calculating a z-coordinate of each feature as an average of z-coordinate values associated with each feature;
d) for each level, calculating an x-coordinate and a y-coordinate of each feature as a centroid of each feature;
e) for each level, generating a two-dimensional pitch array calculated as an observed separation between adjacent features, wherein each pitch value is associated with an (x, y) coordinate of a midpoint between the adjacent features;
f) calculating a three-dimensional x-coordinate differential nonlinearity array;
g) calculating a three-dimensional y-coordinate differential nonlinearity array;
h) calculating a three-dimensional z-coordinate differential nonlinearity array;
i) fitting the x-coordinate differential nonlinearity array to a first nonlinear function;
j) fitting the y-coordinate differential nonlinearity array to a second nonlinear function;
k) fitting the z-coordinate differential nonlinearity array to a third nonlinear function;
l) creating an x-coordinate calibrated length scale Lx(x,y,z) as an integral of the x-coordinate differential nonlinearity array;
m) creating a y-coordinate calibrated length scale Ly(x,y,z) as an integral of the y-coordinate differential nonlinearity array;
n) creating a z-coordinate calibrated length scale Lz(x,y,z) as an integral of the z-coordinate differential nonlinearity array.

11 more elements

A method for high precision calibration of a scanning probe microscope executing a scan of any size, comprising the step of:

a) selecting a scan size;
b) scanning a calibration specimen in order to create a calibration data array;
c) mapping the calibration data array into a one-dimensional calibration profile;
d) measuring feature locations in the calibration profile;
e) calculating a pitch value for each consecutive pair of feature locations;
f) creating a processed profile comprising the pitch values as a function of position;
g) calculating a normalized voltage drive function from a current scan size of the microscope and the current nonlinear voltage drive function;
h) calculating normalized pitch values from the processed profile, wherein each of the normalized pitch values is defined as an observed pitch value divided by a mean of the observed pitch values;
i) generating a composite function by multiplying the normalized voltage drive function by the normalized pitch values;
j) calculating a piecewise continuous approximation (PCA) of the composite function;
k) calculating a new nonlinear voltage drive function as an N-element array consisting of values of the PCA at N equally spaced points, where N is an integer;
l) repeating steps (a) through (k) for M different scan sizes, where M is an integer;
m) forming an N.times.M two dimensional array from the arrays calculated at step (k), arranged in order of scan size, where N is a number of steps in each scan;
n) associating each element D.sub.ij of the two-dimensional array with its scan size V.sub.j, where 1.ltoreq.i.ltoreq.N and 1.ltoreq.j.ltoreq.M;
o) calculating a piecewise continuous approximation (PCA.sub.i (V)) to D.sub.i (V) for each column i in the two dimensional array;
p) selecting a measurement scan size V.sub.k ;
q) determining a drive array for the scanner by retrieving the values PCA.sub.i (V.sub.k) for 1.ltoreq.i.ltoreq.N;
and
r) applying the drive array of step (q) to the microscope in order to execute a measurement scan.

16 more elements

A method for high precision calibration of a scanning probe microscope executing a scan of any size, comprising the steps of:

a) selecting a scan size;
b) scanning a calibration specimen in order to create a calibration data array;
c) mapping the calibration data array into a one-dimensional calibration profile;
d) measuring feature locations in the calibration profile;
e) calculating a pitch value for each consecutive pair of feature locations;
f) creating a processed profile comprising the pitch values as a function of position;
g) calculating a normalized voltage drive function from a current scan size of the microscope and the current nonlinear voltage drive function;
h) calculating normalized pitch values from the processed profile, wherein each of the normalized pitch values is defined as an observed pitch value divided by a mean of the observed pitch values;
i) generating a composite function by multiplying the normalized voltage drive function by the normalized pitch values;
j) fitting the composite function to a first continuous function;
k) if the composite function fit is inadequate in view of predetermined criteria, fitting the composite function to a more complex continuous function;
l) repeating step (k) until the predetermined criteria are satisfied;
m) repeating steps (a) through (1) for M different scan sizes, where M is an integer;
n) tabulating the results of steps (a) through (m) in an array consisting of scan size, function identification number, and values of the function parameters;
o) establishing an applicable scan voltage range for each identified function in the array;
p) calculating a piecewise continuous approximation PCA(V) of each function parameter within each voltage range;
q) selecting a measurement scan size V.sub.k ;
r) determining the fitted composite function parameters PCA(V.sub.k) for the measurement scan size;
s) determining a nonlinear drive function for the measurement scan size from the fitted composite function;
and
t) applying the nonlinear drive function to the microscope in order to execute a measurement scan.

18 more elements

A method for high precision calibration of a scanning probe microscope executing a scan of any size, comprising the steps of:

a) selecting a scan size;
b) scanning a calibration specimen in order to create a calibration data array;
c) mapping the calibration data array into a one-dimensional calibration profile;
d) measuring feature locations in the calibration profile;
e) calculating a pitch value for each consecutive pair of feature locations;
f) creating a processed profile comprising the pitch values as a function of position;
g) calculating a normalized voltage drive function from a current scan size of the microscope and the current nonlinear voltage drive function;
h) calculating normalized pitch values from the processed profile, wherein each of the normalized pitch values is defined as an observed pitch value divided by a mean of the observed pitch values;
i) generating a composite function by multiplying the normalized voltage drive function by the normalized pitch values;
j) fitting the composite function to a first continuous function;
k) if the composite function fit is inadequate in view of predetermined criteria, fitting the composite function to a more complex continuous function;
l) repeating step (k) until the predetermined criteria are satisfied;
m) repeating steps (a) through (1) for M different scan sizes, where M is an integer;
n) tabulating the results of steps (a) through (m) in an array consisting of scan size, function identification number, and values of the function parameters;
o) establishing an applicable scan voltage range for each identified function in the array;
p) fitting the values of the function parameters to a continuous function within each voltage range;
q) selecting a measurement scan size V.sub.k ;
r) determining the fitted composite function parameters for the measurement scan size from the appropriate continuous function from step (p);
s) determining a non linear drive function for the measurement scan size from the fitted composite function;
and
t) applying the nonlinear drive function to the microscope in order to execute a measurement scan.

18 more elements

Dependencies are inferred from the claim text.

High precison calibration and feature measurement system for a scanning probe microscope

Life of this patent

High precison calibration and feature measurement system for a scanning probe microscope

Life of this patent

Abstract

Claims69