Applications of a grating shearing interferometer at 157 nm

Abstract

Progress along the path towards smaller semiconductor feature sizes continually presents new challenges. 157nm technology is a promising new step along this path. The major challenges encountered to date include environmental purging for high transmission and beam alignment in a purged environment at this short wavelength. We present a simple shearing interferometer consisting of two Ronchi phase gratings in series, used on axis. The common path set-up and zero optical path difference between the interfering diffraction orders makes this device both robust and easy to align. Ease of alignment is an added benefit when working remotely in a purged environment with low light levels. If one grating is shifted relative to the other, a phase shift is introduced and phase measurement techniques can be employed for high accuracy characterization of the incident wavefront. Set-ups, measurements and characterization of wavefronts and spatial-coherence at 157nm made with this device are presented.

157-nm system test for high-NA lithographic lens systems

“…The grating shearing interferometer is attractive because it has advantages that include high spatial resolution, readily available substrates and pre-existing data evaluation techniques 11 . Because shearing interferometers measure wavefront slope rather than deviation, interferogram analysis is more complex than dual path interferometers.…”

“…To overcome this problem, the undesired shear of the source image that accompanies the lateral shear must be decoupled from the desired wavefront shear. Decoupling of desired wavefront shear from undesired source image shear is accomplished by introducing a shear of the source wavefront prior to injection to the system under test 11,21 . After passing twice through the system under test, the return beam is sheared a second time by the grating pair.…”

New-Type Shearing Interference Detection System Based on Double-Grating Structure for Suppressing the Skylight Background

“…Therefore, the interference detection technique can be used alone to suppress the skylight background, or it can also be combined with traditional methods to achieve better suppression ability. Due to the shortcomings of the low interference contrast of target light and the low aperture utilization of the early interference detection technique based on electro-optic modulation devices [ 7 ], a shearing interference detection technique based on the double-grating structure [ 11 , 12 , 13 , 14 ] was proposed [ 10 ], which can significantly improve the interference contrast of target light and increase the aperture utilization. However, the published scheme of the shearing interference detection technique [ 10 ] uses a beam-shrinking telescope to reduce the interference fringe area and improve the fringe contrast.…”