A Sensitive Novolac‐Based Positive Electron Resist

Abstract

A positive electron resist has been developed which appears to operate on a different mechanism from conventional positive electron resists. Resists in the latter category such as PBS or PMMA achieve differential solubility primarily as a result of scission of the main chain. In the case of the new resist, differential solubility appears to be achieved by the removal of a polymeric dissolution inhibitor. The resist is a composite system consisting of a novolac resin similar to that used in most positive photoresists in solid solution with poly(2-methyl-l-pentene sulfone) which functions as a dissolution inhibitor of the novolac resin in aqueous base. The process operates by spontaneous depolymerization of the polymeric dissolution inhibitor, a process which is initiated by electron irradiation. The sensitivity of this resist (called NPR) is 3 #C cm -2 at 20 kV and the contrast is 1.0. Submicron features have been delineated in 1.0 #m resist films. The resist withstands A1, poly-Si, SIO2, doped SiO~, and SixNu plasma etching environments and has been used as a plasma etch mask to transfer submicron features into these film substrates.

Determination of the Radiation Efficiency, Contrast and Sensitivity in Electron and Ion Lithography

“…The effect of the developer and the development conditions on these parameter values are discussed. A similar effect of the used developer on the contrast value yd for electron lithography of Amil Acetate layers is shown in [4] and in the case of PMPS & Novolak in [ 5 ] . In addition in the ref.…”

Understanding nonlinear dissolution rates in photoresists

“…In their resist, slower dissolution rates and a longer induction period are clearly linked to the presence of oxygen during the PAB. 10 Empirical evidence for the oxidation theory is that the bake temperature has a large effect on the shape and extent of surface inhibition, a result reported by many researchers. 10,17,27 In this work, the oxidation theory was examined by confirming the effect of bake temperature on dissolution rate and estimating the sorption/concentration gradient of oxygen at various bake temperatures.…”

“…This is by far the weakest theory for surface inhibition, since surface inhibition is known to occur in pure novolac resin with no added PAC. 10 Also, if PAC segregated to the surface causing surface inhibition in unexposed areas, heavily exposed areas would inevitably show surface enhancement. To the knowledge of the authors, that effect has never been observed.…”

“…A tacit assumption of this theory is that oxygen is more highly concentrated at the surface of the resist, resulting in a higher MW at the surface of the resist as the polymer chains undergo crosslinking. Bowden et al 10 report that for N64C novolac resin, considerable surface inhibition is observed with a PAB open to air, whereas a PAB under vacuum resulted in very little surface inhibition and faster bulk dissolution rates. An IR study confirmed the growth of the carbonyl peak (indicating crosslinking) in the open air bake, whereas crosslinking was not observed during the vacuum bake.…”

The Photopolymer Science and Technology Award

“…His group developed a positive electron beam resist NPR [2]. NPR represented an entirely new approach to electron resist design.…”