Kevin J. Stewart

Simple negative resist for deep ultraviolet, electron beam, and x‐ray lithography

Negative resists using photo‐acid initiated cationic polymerization of epoxy resins were reported in the early 1980s with the advent of onium salts. An efficient, stable onium salt, triphenylsulfonium hexafluoroantimonate produces acid upon exposure to radiation, for example, deep ultraviolet (UV) light, electron beam, and x rays. Combining this onium salt with commercial glycidyl ether epoxy resins provides an inexpensive resist capable of submicron imaging in deep UV, electron beam, and x‐ray lithography. Lithographic investigations have concentrated on o‐cresol epoxy novolac resin–onium salt resist formulations. Resist contrasts are high, >3 in the deep UV, ≥2 with electron beam, and ≥3 for x ray. Submicron resolution is obtained without solvent swelling. Swelling affects resolution below 0.5 μm, although high aspect ratio sub‐half‐micron images have been obtained. Epoxide equivalent weight and molecular weight distribution are significant resin properties which influence resist formulating and lithogr...

A simplified silylation process

This paper discusses a simplified ‘‘silylation’’ process, which converts typical diazo‐type photoresists into oxygen plasma etch barriers that are insoluble and thermally stable. Previous workers have reported on a silylation process that incorporates silicon in the resist in the gas phase. This paper reports on the use of a bifunctional silylation agent, which when diffused into the patterned resist using a solvent carrier, crosslinks the novolac resin, incorporating silicon in the matrix. The mechanism and the properties of the resist film after silylation such as thermal stability, reactive ion etch (RIE) resistance, silicon content, and solubility will be discussed.

A simple bilayer lift-off process

Abstract This paper discusses a simplified “lift-off” process, which consists of two layers. This consists of an underlayer of soluble, thermally stable polyimide, and a new process, “silylation”, which converts typical positive photoresists into oxygen RIE barriers. The uses of this new material and process for chip and packaging applications are described in this paper.

New high resolution and high sensitivity deep UV, X-ray, and electron beam resists

Abstract A new family of highly sensitive negative resists for Deep UV, X-ray and electron beam exposure capable of better than 100 nm resolution and very high pattern aspect ration has been investigated. The resists are based epoxidized novolac resins sensitized with acid generating compounds.

X-ray photoelectron spectroscopy and infrared study of the processing of a silylated positive photoresist

Liftoff processes are being used in microelectronics technology for various metallization steps. In a typical application, a photoresist is spun on top of a soluble polymer, exposed, developed, silylated, and cured. Subsequently, the silylated resist acts as a stencil mask for O2 reactive ion etching (RIE) pattern transfer into the underlying polymer. The generation of debris, leading to etch residues (‘‘grass’’), is a major concern during this process step. The goal of this work is to follow the various process steps that the resist is subjected to, and in particular to determine the effect of ultraviolet (uv) hardening on the silylated resist. We used the complementary techniques of x‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrophotometry (FTIR) to obtain information on the chemical composition in the surface region and in the bulk of the film. In contrast to conventional baking, uv hardening appears to induce a substantial carbon depletion in the top layer. The aromatic s...

Electron impact reactions of triphenylsulfonium salt resist sensitizers in the solid state

To elucidate the mechanism of electron beam exposure of triphenylsulfonium salt sensitized resists, films of triphenylsulfonium hexafluoroantimonate or triflate in various polymers and in the pure solid state were exposed to pulses of electrons. The composition of the resulting pulses of gaseous products was analyzed by Fourier transform mass spectrometry. Components of product mixtures were identified by using both electron impact and chemical ionization techniques. The main volatile products of triphenylsulfonium under electron impact are diphenyl sulfide, benzene, and biphenyl. The yield of benzene is much larger from triphenylsulfonium salts dissolved in polymer than in the pure solid state. This implies rapid hydrogen‐abstraction reactions by the intermediate phenyl radicals from matrices with available aliphatic hydrogens. The product distributions observed from several polymer solvents, and their dependence on electron energy, show few other rapid reactions between the matrix and the primary produc...