US 5,563,702 A · Automated photomask inspection apparatus and method

Abstract

A method and apparatus for inspecting patterned transmissive substrates, such as photomasks, for unwanted particles and features occurring on the transmissive, opaque portions and at the transition regions of the opaque and transmissive portions of the substrate. A transmissive substrate is illuminated by a laser through an optical system comprised of a laser scanning system, individual transmitted and reflected light collection optics and detectors collect and generate signals representative of the light transmitted and reflected by the substrate as the substrate is scanned repeatedly in one axis in a serpentine pattern by a laser beam which is focused on the patterned substrate surface. The defect identification of the substrate is performed using only those transmitted and reflected light signals, and other signals derived from them, such as the second derivative of each of them. The actual defect identification is then performed by comparing combinations of at least two of those measured and derived signals. Simultaneously, defect and particle inspection using the same measured transmitted and reflected light signals. Additionally, phase shift and line widths on the substrate can also be performed simultaneously using the same transmitted light signal that is collected for defect analysis.

Claims41

Dependent claims

An inspection system to inspect a substrate for unwanted particles and features, said substrate having a top and a bottom surface with a pattern of opaque material on said top surface, said inspection system comprising:

an illumination system to provide an illumination beam through a path to a point on said top surface of said substrate and said pattern thereon;
a transmission detector coaxially aligned with said path to detect a transmitted portion of said illumination beam through said substrate from an illuminated point on said top of said substrate and to provide a signal representative of said detected transmitted portion of said illumination beam;
a reflection detector to detect a portion of said illumination beam reflected from said illuminated point on said substrate and said pattern thereon coaxially along said path of said illumination beam and to provide a signal representative of said detected reflected portion of said illumination beam;
a comparator to compare said signals, with each other, from said transmission and reflection detectors developed by illumination of the same point on said top surface of said substrate and said pattern thereon to provide a comparison value of those signals;
a first memory to store expected values of comparison values from said comparator;
and
a processor coupled to said comparator and said first memory to determine if said comparison value is an expected value and to generate a report when an unexpected value is determined.

4 more elements

A method for inspecting a substrate for unwanted particles and features, said substrate having a top and a bottom surface with a pattern of a opaque material on said top surface, said method including the steps of:

a. directing an illumination beam through a path to a point on the top surface of said substrate and said pattern thereon;
b. detecting, in coaxial alignment with said illumination beam of step a., a transmitted portion of said illumination beam through said substrate;
c. generating a signal representative of said detected transmitted portion of said illumination beam of step b.;
d. detecting, coaxially along said path of step a., a reflected portion of said illumination beam from said top surface of said substrate and said pattern thereon;
e. generating a signal representative of said detected reflected portion of said illumination beam of step d.;
f. generating a comparison value of said signals, with respect to each other, from steps c. and e.;
g. storing expected comparison values;
and
h. generating a report when the comparison value of step f. does not correspond to an expected comparison value stored in step g.

6 more elements

A method for inspecting a substrate for unwanted particles and features, said substrate having a top and a bottom surface with a pattern of opaque material on said top surface, said method including the steps of:

a. selecting a substrate of the type to be inspected;
b. directing an illumination beam through a path to a point on the top surface of said substrate and said pattern thereon;
c. detecting, in coaxial alignment with said illumination beam of step b., a transmitted portion of said illumination beam through said substrate;
d. generating a signal representative of said detected transmitted portion of said illumination beam of step c.;
e. detecting, coaxially along said path of step b., a reflected portion of said illumination beam from said top surface of said substrate;
f. generating a signal representative of said detected reflected portion of said illumination beam of step e.;
g. generating an expected comparison value of said signals from steps d. and f. with respect to each other;
h. storing said expected comparison value of step g.;
i. repeating steps a. through h. for a selected number of different substrates of the type to be inspected;
j. selecting a particular substrate to be inspected;
k. directing an illumination beam through a path substantially normal to a point on the top surface of said substrate of step j.;
l. detecting, in coaxial alignment with said illumination beam of step k., a transmitted portion of said illumination beam through said substrate of step j.;
m. generating a signal representative of said detected transmitted portion of said illumination beam of step l.;
n. detecting, coaxially along said path of step k., a reflected portion of said illumination beam from said top surface of said substrate of step j. and said pattern thereon;
o. generating a signal representative of said detected reflected portion of said illumination beam of step n.;
p. generating a comparison value of said signals, with respect to each other, from steps m. and o.;
and
q. generating a report when the comparison value of step p. does not correspond to an expected comparison value stored in step h.

15 more elements

a. selecting a substrate of the type to be inspected;
b. directing an illumination beam through a path to a point on the top surface of said substrate and said pattern thereon;
c. detecting, in coaxial alignment with said illumination beam of step b., a transmitted portion of said illumination beam through said substrate;
d. generating a signal representative of said detected transmitted portion of said illumination beam of step c.;
e. detecting, coaxially along said path of step b., a reflected portion of said illumination beam from said top surface of said substrate and said pattern thereon;
f. generating a signal representative of said detected reflected portion of said illumination beam of step e.;
g. generating an expected comparison value of said signals from steps d. and f. with respect to each other;
h. storing said expected comparison value of step g.;
i. translating said substrate to a next position;
and
j. repeating steps a. through i. for each point of interest on said substrate of step a.;
k. repeating steps a. through j. for a selected number of different substrates of the type to be inspected;
l. selecting a particular substrate to be inspected;
m. directing an illumination beam through a path substantially normal to a point on the top surface of said substrate of step l. and said pattern thereon;
n. detecting, in coaxial alignment with said illumination beam of step m., a transmitted portion of said illumination beam through said substrate of step l.;
o. generating a signal representative of said detected transmitted portion of said illumination beam of step n.;
p. detecting, coaxially along said path of step m., a reflected portion of said illumination beam from said top surface of said substrate of step l. and said pattern thereon;
q. generating a signal representative of said detected reflected portion of said illumination beam of step p.;
r. generating a comparison value of said signals, with respect to each other, from steps o. and q.;
s. storing said comparison value of step r.;
t. translating said substrate to a next position;
u. repeating steps m. through s. for each point of interest on said substrate of step l.;
v. generating a report when any comparison value for a particular point on said substrate of step l. stored by of step s. does not correspond to an expected comparison value stored in step h. for the same point on substrates of the same type.

20 more elements

a. directing an illumination beam through a path to a point on the top surface of said substrate and said pattern thereon;
b. detecting, in coaxial alignment with said illumination beam of step a., a transmitted portion of said illumination beam through said substrate;
c. generating a signal representative of said detected transmitted portion of said illumination beam of step b.;
d. detecting, coaxially along said path of step a., a reflected portion of said illumination beam from said top surface of said substrate and said pattern thereon;
e. generating a signal representative of said detected reflected portion of said illumination beam of step d.;
f. storing the generated signals of steps c. and e. together with the location of the point illuminated in step a.;
g. translating said substrate to a next position;
and
h. repeating steps a. through f. for each point of interest on said substrate and said pattern thereon;
i. generating a signal corresponding to a first selected function value of the signal values for one of the stored transmission and reflection signals of step f. for each point of interest on the substrate being inspected;
j. storing the signal values generated in step i. together with the corresponding point on the surface of said substrate;
k. generating expected comparison values for each combination of the three values stored in steps f. and j. for each point of interest on a substrate of the type being inspected;
l. generating a comparison values of two or more of said signal values from steps f. and j., with respect to each other, for each point of interest on the substrate being inspected;
m. generating a report when the comparison value of step
l. for any point of interest on the substrate being inspected does not correspond to an expected comparison values stored in step l. for that point on the surface of substrates of the same type.

12 more elements

An inspection system to simultaneously inspect a substrate for defects, and unwanted particles and features, said substrate having a top and a bottom surface with a pattern of opaque material on said top surface, said inspection system comprising:

an illumination system to provide an illumination beam through a path to a point on said top surface of said substrate and said pattern thereon;
a transmission detector coaxially aligned with said path to detect a transmitted portion of said illumination beam through said substrate from an illuminated point on said top of said substrate and to provide a signal representative of said detected transmitted portion of said illumination beam;
a reflection detector adjacent said top surface of said substrate to detect a portion of said illumination beam reflected from said illuminated point on said substrate coaxially along said path of said illumination beam and to provide a signal representative of said detected reflected portion of said illumination beam;
a first comparator coupled to each of said transmission and reflection detectors to compare said signals from each of said detectors, with each other, developed by illumination of the same point on said top surface of said substrate to provide a first comparison value of those signals;
a memory having expected values of said first comparison value from said first comparator stored therein;
a database containing the value of a pair of expected signals from said transmission and reflection detectors for a point being inspected for the particular type of substrate being inspected;
a second comparator coupled to each of said transmission and reflection detectors and said database to compare a value of each of said signals from said transmission and reflection detectors with the values of the expected pair of transmission and reflection detector signals from said database to identify the presence of a defect at the point of inspection on said substrate;
and
a processor coupled to said first and second comparators and said first memory to determine when said first comparison value is an unexpected value and to identify the type of unwanted particle or feature when an unexpected value is determined.

6 more elements

A method for simultaneously inspecting a substrate for defects, and unwanted particles and features, said substrate having a top and a bottom surface with a pattern of opaque material on said top surface, said method including the steps of:

a. directing an illumination beam through a path to a point on the top surface of said substrate;
b. detecting, in coaxial alignment with said illumination beam of step a., a transmitted portion of said illumination beam through said substrate;
c. generating a signal value representative of said detected transmitted portion of said illumination beam of step b.;
d. detecting, coaxially along said path of step a., a reflected portion of said illumination beam from said top surface of said substrate and said pattern thereon;
e. generating a signal value representative of said detected reflected portion of said illumination beam of step d.;
f. generating a first comparison value of said signal values, with respect to each other, from steps c. and e.;
g. storing expected first comparison values;
h. storing a pair of expected values of said signal values representative of said detected transmission and reflected portions of said illumination for the particular type of substrate being inspected;
i. individually comparing each of said signal values of steps c. and e. to the expected value of each of said signal values of step h.;
j. generating a report when the comparison value of step f. does not correspond to an expected comparison value stored in step g. and also if either of the signals does not agree with an expected value in step i.

7 more elements

Dependencies are inferred from the claim text.

Automated photomask inspection apparatus and method

Life of this patent

Automated photomask inspection apparatus and method

Life of this patent

Abstract

Claims41