US 6,603,873 B1 · Defect detection using gray level signatures

Abstract

A method and apparatus for inspecting isolated features on a reticle is provided wherein the isolated features are analyzed for defects globally as individual, whole features, rather than locally, pixel-by-pixel. In one embodiment, the reticle is imaged to produce pixels having a gray level, and an isolated feature is identified. An energy value for the isolated feature to be inspected is calculated by summing the gray levels of its pixels. A plurality of scatter values for the feature in different directions in the feature is calculated based on the equilibrium center of the feature to produce a unique “signature” for the inspected feature. The energy and scatter values of the inspected feature's signature are then compared with energy and scatter values associated with a corresponding reference feature to determine whether a defect exists in the inspected feature.

Claims59

Dependent claims

A method of inspecting a target feature formed on a surface, which method comprises:

imaging the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
isolating the target feature;
calculating a value of a parameter of the isolated target feature;
identifying the target feature as corresponding to a target reference feature;
and
comparing the target feature parameter value with a corresponding parameter value associated with the target reference feature to determine whether a defect exists in the target feature;
wherein calculating the target feature parameter value comprises calculating an energy value for the target feature by summing the gray levels of the target data elements corresponding to the target feature, and calculating scatter values for the target feature in several directions, each scatter value based on a moment of inertia with respect to an equilibrium center of the target feature.

4 more elements

A method of inspecting a target feature formed on a surface, which method comprises:

imaging the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
isolating the target feature;
calculating a value of a parameter of the isolated target feature;
identifying the target feature as corresponding to a target reference feature;
and
comparing the target feature parameter value with a corresponding parameter value associated with the target reference feature to determine whether a defect exists in the target feature;
wherein calculating the target feature parameter value comprises calculating an energy value for the target feature by summing the gray levels of the target data elements corresponding to the target feature, and calculating a plurality of scatter values for the target feature based on an equilibrium center of the target feature, each scatter value calculated in a different predetermined direction in the target feature;
wherein calculating the scatter values comprises:
calculating the projection of each of the target data elements in the predetermined directions in the target feature;
calculating the center of equilibrium of the target feature with respect to the origin based on the projection of each of the target data elements;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the origin;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the center of equilibrium;
and
calculating the scatter values for the target feature about the axes in the predetermined directions that pass through the center of equilibrium.

11 more elements

A computer-readable medium bearing instructions for inspecting a target feature formed on a surface, said instructions, when executed, being arranged to cause one or more processors to perform the steps of:

controlling an imager to image the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
isolating the target feature;
calculating a value of a parameter of the isolated target feature;
identifying the target feature as corresponding to a target reference feature;
and
comparing the target feature parameter value with a corresponding parameter value associated with the target reference feature to determine whether a defect exists in the target feature;
wherein calculating the value of the parameter of the isolated target feature comprises calculating an energy value for the target feature by summing the gray levels of the target data elements corresponding to the target feature, and calculating scatter values for the target feature in several directions, each scatter value based on a moment of inertia with respect to an equilibrium center of the target feature.

4 more elements

controlling an imager to image the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
isolating the target feature;
calculating a value of a parameter of the isolated target feature;
identifying the target feature as corresponding to a target reference feature;
and
comparing the target feature parameter value with a corresponding parameter value associated with the target reference feature to determine whether a defect exists in the target feature;
wherein calculating the value of the parameter of the isolated target feature comprises summing the gray levels of the target data elements corresponding to the target feature, and calculating a plurality of scatter values for the target feature based on an equilibrium center of the target feature, each scatter value calculated in a different predetermined direction in the target feature;
and
the instructions, when executed, are arranged to cause the one or more processors to perform the step of calculating the scatter values by:
calculating the projection of each of the target data elements in the predetermined directions in the target feature;
calculating the center of equilibrium of the target feature with respect to the origin based on the projection of each of the target data elements;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the origin;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the center of equilibrium;
and
calculating the scatter values for the target feature about the axes in the predetermined directions that pass through the center of equilibrium.

12 more elements

An inspection tool for inspecting a target feature formed on a surface, the inspection tool comprising:

an imager for imaging the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
and
a processor for isolating the target feature, calculating a value of a parameter of the isolated target feature, and determining if a defect exists in the target feature responsive to the target feature parameter value;
wherein the processor is further configured to:
calculate an energy value for the target feature by summing the gray levels of the target data elements corresponding to the target feature;
and
calculate scatter values for the target feature in several directions, each scatter value based on a moment of inertia with respect to an equilibrium center of the target feature.

4 more elements

An inspection tool for inspecting a target feature formed on a surface, the inspection tool comprising:

an imager for imaging the target feature to produce one or more target data elements representative of the target feature, each target data element having a gray level and associated with a respective location on the surface;
and
a processor for isolating the target feature, calculating a value of a parameter of the isolated target feature, and determining if a defect exists in the target feature responsive to the target feature parameter value;
wherein the processor is further configured to calculate the target feature parameter value by calculating an energy value for the target feature by summing the gray levels of the target data elements corresponding to the target feature, and calculating a plurality of scatter values for the target feature based on an equilibrium center of the target feature, each scatter value calculated in a different predetermined direction in the target feature;
wherein the processor is further configured to calculate the scatter values by:
calculating the projection of each of the target data elements in the predetermined directions in the target feature;
calculating the center of equilibrium of the target feature with respect to the origin based on the projection of each of the target data elements;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the origin;
calculating moments of inertia of the target feature about axes in the predetermined directions that pass through the center of equilibrium;
and
calculating the scatter values for the target feature about the axes in the predetermined directions that pass through the center of equilibrium.

8 more elements

Dependencies are inferred from the claim text.

Defect detection using gray level signatures

Life of this patent

Defect detection using gray level signatures

Life of this patent

Abstract

Claims59