We combined functionalities of two diffractive optics with almost 100x
lateral and Vertical scale-length difference onto a single fused-sili
ca surface. Fine-scale (2-mu m-period) gratings for beam sampling were
printed in photoresist by interference Lithography and transferred to
the substrate by a hydrofluoric acid etch. Subsequently, 115-mu m-lin
ewidth stairstep gratings for color separation at focus were proximity
printed and wet etched in a two-mask process. Line shapes of the lame
llar sampling grating are remarkably preserved following etching of th
e much deeper color separation grating structures with this nominally
isotropic etch process. Model simulations of isotropic etching of topo
graphical features show good agreement with the measured shape evoluti
on of the sampling grating profiles, and the simulations reveal the se
nsitivity of the final feature shape to its initial aspect ratio. As a
rule of thumb, lamellar grating profiles can be etched approximately
0.08A(-2) times their modulation depth, where A is their initial aspec
t ratio (height/width), before they evolve into a cusplike shape and b
egin to lose height. (C) 1998 Optical Society of America.