Abstract: A mask pattern for imaging a marker structure on a substrate with a lithographic apparatus, the marker structure being configured to determine optical alignment or overlay, includes constituent parts to define the marker structure. The constituent parts include a plurality of segments, each segment having substantially a size of a device feature and a segment shape. The mask pattern includes at least one assist feature located at a critical part of the segment shape. The at least one assist feature has substantially a size below a resolution of the lithographic projection and is configured to counteract optical aberrations or optical limitations generated in the lithographic projection at the critical part.

Abstract: A method of device inspection, the method comprising providing an asymmetric marker on a device to be inspected, the form of asymmetry of the marker being dependent upon the parameter to be inspected, directing light at the marker, obtaining a first measurement of the position of the marker via detection of diffracted light of a particular wavelength or diffraction angle, obtaining a second measurement of the position of the marker via detection of diffracted light of a different wavelength or diffraction angle, and comparing the first and second measured positions to determine a shift indicative of the degree of asymmetry of the marker.

Abstract: A method according to one embodiment of the invention may be applied to enhance scatterometry measurements made from a two-component test pattern. Reference patterns corresponding to each of the components of the two-component pattern are also printed. Scatterometry signals derived from the reference patterns, corresponding to the separate components of the test pattern, are used to enhance the signal from the test pattern to improve sensitivity and signal-to-noise ratios.

Abstract: In a method according to one embodiment of the invention, aberrations in a lithographic apparatus are detected by printing a test pattern having at least one degree of symmetry and being sensitive to a particular aberration in the apparatus, and using a scatterometer to derive information concerning the aberration. The test structure may comprise a two-bar grating, in which case the inner and outer duty ratios can be reconstructed to derive information indicative of comatic aberration. Alternatively, a hexagonal array of dots can be used, such that scatterometry data can be used to reconstruct dot diameters indicative of 3-wave aberration.

Abstract: In a process for measuring the CD of a mask pattern transferred to a semiconductor wafer, in which a series of dies are sequentially inspected by first locating a target area on the die and then vectoring to a CD measurement area, a technique is used whereby the stored image of an alignment target is used for pattern recognition in the process of acquiring each subsequent die's target. The stored image is updated with each new die inspected, using an image of the most recently acquired target area. In this manner, the stored target image always closely approximates the next target to be acquired. Thus, according to the invention, difficulties in recognizing and centering on the target are minimized, and CD measurements of much higher reliability can be effected.