Electron beam lithography in thick negative tone chemically amplified resist: Controlling sidewall profile in deep trenches and channels

Controlled Nanoscale Cracking of Graphene Ribbons by Polymer Shrinkage

“…Commercially available SU8 contains an octaglycidylic ether of a condensation product derived from bisphenol A, , and an acidic photoinitiator, which is responsive to both UV light and e-beam. It has been suggested that an e-beam could lead to the protolysis of the photoinitiator, which leads to the formation of carbonium ions, and consequently, the protonation of the oxygen atom of the epoxy group . Electron beam lithography at low intensities is accompanied by proximity effect, in which the incident, as well as the backscattered, electrons affect the absorbed radiation at a certain resist depth.…”

“…proposed a reaction–diffusion model to characterize the proximity effect of an e-beam, wherein the diffusion coefficient corresponding to the diffusion of the photoinitiator in the polymer was found to be a decreasing function of the resist depth . Sarkar et al demonstrated that the interplay of the diffusion coefficient and the gradient of the photoinitiator concentration results in the broadening of the sidewalls for isolated SU8 lines . Elsewhere, Denning et al demonstrated that the holographic exposure of SU8 could lead to the removal of loosely held oligomers in the crosslinked network, which results in shrinkage of SU8 structures …”

“…It has been suggested that an e-beam could lead to the protolysis of the photoinitiator, which leads to the formation of carbonium ions, 57 and consequently, the protonation of the oxygen atom of the epoxy group. 60 Electron beam lithography at low intensities is accompanied by proximity effect, 61 in which the incident, as well as the backscattered, electrons affect the absorbed radiation at a certain resist depth. Glezos et al proposed a reaction− diffusion model to characterize the proximity effect of an ebeam, wherein the diffusion coefficient corresponding to the diffusion of the photoinitiator in the polymer was found to be a decreasing function of the resist depth.…”

Adjustable sidewall slopes by electron-beam exposure layout

“…However, in EBL, the depth dependent intensity is usually not considered even though it has a large impact on resist profiles due to lateral resist erosion. 5 In this paper, we show that the z-dependency of the deposited energy can be used to adjust sidewall slopes easily by modifying the exposure layout within a single lithographic step. This enables adjacent features with variable positive or negative sidewall slopes on the same substrate.…”

“…Therefore, not all kinds of above discussed sidewall profiles, in particular an undercut in a single-resist-layer-system, can be explained. 5 To additionally consider the inhomogeneous distribution of the deposited energy along the resist depth, a 3D model of the PSF was introduced. More specifically, the energy deposition is calculated for discrete resist depths by convolving the pattern with a z-dependent PSF.…”