US 4,926,489 AGranted

Reticle inspection system

AssigneeKLA Instruments Corporation

InventorsDonald L. Danielson, Mark J. Wihl, David A. Joseph

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Abstract

An automatic inspection system including an illuminator for illuminating a reticle or photomask to be inspected, while optically projecting a magnified image of the reticle or photomask onto a plurality of detector elements. A carriage assembly moves the object at a constant velocity to allow the detector elements to sequentially view the entire surface to be inspected. The detector elements are responsive to the intensity of light incident thereupon and are periodically scanned to obtain a two-dimensional measured representation of the object. A database adaptor formulates a two-dimensional representation from the design database description corresponding to the scanned object simultaneously and in synchronism with the scanning of the photomask or reticle. The measured and database adapted representation of the scanned object are input to a signal processor for alignment and defect detection. While the representations are shifted through a memory, an alignment circuit dynamically measures and corrects for misalignment between the representations, so that a defect detector can effectively compare the representations for defects. Additional correction of misalignment between the representations is obtained by modulating the size of the measured representation as detected by the detector elements. At the operator's option, a second measured image of a multi-cell reticle or photomask may be used for comparison as a substitute for the database representation.

Claims42

Dependent claims

Optical inspection apparatus for scanning a patterned object and comparing it to information contained in an electronic data base, comprising:

optical scanning means responsive to a first timing control signal and operative to scan the patterned object and to develop a first data signal including a sampled and quantitized electronic representation of the patterned object;
data base means responsive to a second timing control signal and operative to generate a second data signal corresponding to a design database description of the patterned object scanning by said scanning means, said second data signal having a variable time relationship to said first data signal;
data alignment means for comparing said first data signal to said second data signal and for developing an excess alignment signal which corresponds to any misalignment of said second data signal exceeding a predetermined limit, and for adjusting said time relationship between said first data signal and said second data signal to provided aligned first and second data signals which are time coincident with each other;
timing control means responsive to said excess alignment signal and operative to develop said first and second timing control signals, said first and second timing control signals being used to adjust the relative output data signal rates of said optical scanning means and said data base means for the purpose of maintaining the alignment of said first and second data signals within predetermined limits;
and
defect detector means for comparing said aligned first data signal and said aligned second data signal and for developing defect data signals corresponding to differences therebetween having predetermined characteristics.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/104,740Filed 5 Oct 1987 · continuation in part
Priority: 11 Mar 1983
Granted: 15 May 1990
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

G01N 21/95607
Inspecting patterns on the surface of objects: using a comparative method
G03F 1/84
Auxiliary processes, e.g. cleaning or inspecting: inspecting
G06T 7/001
Industrial image inspection: using an image reference approach
G06T 7/30
Image analysis: determination of transform parameters for the alignment of images, i.e. image registration