Resist residues and transistor gate fabrication

Abstract

In this article, the authors investigate the formation and removal of resist residues with the main objective to improve the reliability of transistor gate fabrication. Device performance is strongly dependent on the quality of metal contacts and the interface between gate metal and substrates. Reliable transistor fabrication becomes increasingly difficult as transistor dimensions shrink. Residual resist layers can become significant if wet or dry etching steps are required for gate recessing, e.g., for high electron mobility transistors or the removal of thin oxide layers in III-V metal oxide semiconductor field effect transistor fabrication. They observe two sorts of residual resist layers in polymethyl methacrylate (PMMA): exposed and nonexposed. Exposed residuals have been observed by many groups in electron beam exposed and developed regions of PMMA. In this article, they show that the observed granularity lies on top of a continuous residual film and consider this effect on gate fabrication. They also present evidence of a nonexposed residual layer observed in regions of unexposed resist which have been subject to a standard solvent based resist strip and cleaning procedure. They further demonstrate that CV measurement techniques can be used to detect the presence of residual layers of resist.

Controlled electromigration protocol revised

“…The observed contrast is due to PMMA leftovers used during fabrication of the nanodevices. 28 The final conductance of this device was zero and clearly indicated the formation of a large gap. In this case, no care was taken to gently electromigrate once the junction size is reduced to an atomic size.…”

Direct-write X-ray lithography using a hard X-ray Fresnel zone plate

“…Recent progress in advanced lithography systems have realised highresolution patterns with dimensions below a few nanometers, and there is on-going research to explore the fundamental limits of lithography on the atomic sub-nanometer scale (Chou et al, 1997;Macintyre & Thoms, 2011;Winston et al, 2011). Unlike mask-based lithography, whose resolution is critically limited by the dimensions of the masks (Suzuki & Smith, 2007), 'direct-write lithography' is free of masks and capable of creating arbitrary patterns.…”

“…Consequently, the focusing capability is a key factor in determining the resolution of a direct-write process, although the sensitivity of PR materials and parasitic exposure must also be considered carefully. Up to now, among various direct-write processes such as electronbeam lithography, ion beam lithography (Winston et al, 2011) and focused laser lithography (Gan et al, 2013), direct-write electron-beam lithography (e-beam writers) has been widely used for practical purposes, and patterns as small as 5 nm have been achieved with great success (Macintyre & Thoms, 2011).…”

A Novel Nanofabrication Damascene Lift-Off Technique

“…Either the surface of the exposed area of the substrate is/becomes contaminated prior to material deposition, or the deposited material does not strongly adhere to the substrate by virtue of its chemistry and surface conditions. It should be noted that while the former can be caused by resist Manuscript residuals, which can be eliminated by ashing the resist using oxygen plasma [6], [7], the latter can be overcome by using adhesion layers in some materials such as Cr for Au deposition.…”