Zero-order diffraction efficiencies, in reflection, of short-pitch (pitch less than the incident wavelength), narrow-linewidth, photoresist gratings exhibit significant variations with angle of incidence. The intent of our effort was to explain these variations, which are characterized as resonance anomalies. At resonance we also have observed enhanced diffuse scattering. Modal analysis was applied to characterize the fields within the grating structure. A separate numerical method that combines effective-medium theory and waveguide mode computation was used to determine the lossy, guided-wave modes of the layered grating structure. We show that enhanced diffuse scattering is directly correlated with enhanced surface fields (order m = −1) that are associated with coupling of the incident field into guided-wave modes in the presence of the grating. Under certain conditions anti-guided-wave behavior in the grating is evident. Applications to scatterometry and surface characterization are suggested.
© 1999 Optical Society of America
(050.0050) Diffraction and gratings : Diffraction and gratings
(050.1950) Diffraction and gratings : Diffraction gratings
(050.1960) Diffraction and gratings : Diffraction theory
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
(120.5820) Instrumentation, measurement, and metrology : Scattering measurements
Stephen A. Coulombe and John R. McNeil, "Modal characteristics of short-pitch photoresist gratings exhibiting zero-order diffraction anomalies," J. Opt. Soc. Am. A 16, 2904-2913 (1999)