Ja. Gregus et al., REAL-TIME LATENT IMAGE MONITORING DURING HOLOGRAPHIC FABRICATION OF SUBMICRON DIFFRACTION GRATINGS, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 11(6), 1993, pp. 2468-2472
Real-time monitoring of latent images in photoresist during the hologr
aphic exposure of submicron period diffraction gratings is reported. T
he first-order diffraction efficiency is recorded as a function of tim
e for different resist thicknesses and polarizations. By monitoring th
e diffraction efficiency in real time, the process can be controlled t
o compensate for variations in exposure dose, resist thickness, and th
e optical properties of underlying materials. It is demonstrated that
latent image monitoring (LIM) can be performed in real time and that t
he diffraction efficiency correlates well with the linewidth. To inter
pret diffraction efficiencies with changes in resist thickness and pol
arization, rigorous coupled wave analysis combined with a commercial s
oftware package to simulate the real-time data was used. However, the
data show evidence for slow changes in the composition of the resist d
uring exposure that are consistent with chemical intermediates reactin
g with water in the film. The commercial exposure simulation tool cann
ot account for these phenomena, which complicate the application of LI
M to real-time exposure control.