Jane M. Shaw

Micromachining applications of a high resolution ultrathick photoresist

This article describes a new negative‐tone photoresist, SU‐8, for ultrathick layer applications. An aspect ratio of 10:1 has been achieved using near‐ultraviolet lithography in a 200‐μm‐thick layer. The use of this resist for building tall micromechanical structures by deep silicon reactive‐ion etching and electroplating is demonstrated. Using SU‐8 stencils, etched depths of ≳200 μm in Si and electroplated 130‐μm‐thick Au structures with near‐vertical sidewalls have been achieved.

Conducting polyanilines: Discharge layers for electron‐beam lithography

This paper describes the use of electrically conducting polyanilines as discharge layers for electron‐beam (e‐beam) lithography. The emeraldine oxidation state polyaniline is a soluble material which can be doped by various cationic reagents, most commonly protonic acids, to afford conductivity on the order of 10° Ω−1 cm−1. The conducting polyanilines are incorporated as thin interlayers (2000 A) in a multilayer resist system consisting of a planarizing underlayer (2.8 μm) and the imaging resist (1.2 μm) on top. We find that various acid‐treated polyanilines eliminate charging during e‐beam patterning of the resist, i.e., zero pattern displacements are observed as compared to the case where a conducting interlayer is not incorporated into the resist system. In the latter case placement errors greater than 5 μm are observed as a result of charging. A minimum conductivity of 10−4 Ω−1 cm−1 is required for the polyaniline interlayers in order to observe zero pattern displacement. In addition, we have simplifi...

Water soluble conducting polyanilines: Applications in lithography

A new class of water soluble conducting polyanilines has been developed. This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid. The resulting polyanilines readily dissolve in water. These materials can be applied as removable discharge layers for electron‐beam lithography and for mask inspection by scanning electron microscopy. They can be spin‐applied directly on top of resists without any interfacial problems. Image distortion as a result of charging during resist exposure is not observed with these materials. After exposure the polyaniline is readily and cleanly removed during the resist develop. By incorporating cross‐linkable functionality on the polyaniline backbone, water soluble polyanilines that are radiation curable are attained. Upon irradiation these materials cross‐link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge applications. In addition, the cross‐linkable polyanilines can be us...

In-Situ Radiation Induced Doping

Abstract In this paper we describe a novel method of inducing conductivity in polyaniline photochemically or by electron-beam exposure. This is accomplished with the use of onium salts which are a class of materials that decompose upon irradiation generating protonic acids. We find that the onium salt may be blended with the polyaniline and upon irradiation, the generated acid acts as an in situ dopant for the polymer. Conductivity on the order of ⋍0.1 S/cm has been attained. This system has significant applications in lithography since it allows patterns of conducting lines to be generated. The polyaniline/onium system represents the first electrically conducting photo and electron-beam resist. In addition, we find that this radiation induced doping technique is applicable to polythiophene systems as well.

Water Soluble Polyanilines: Properties and Applications

A new class of water soluble conducting polyanilines have been developed. This is accomplished by oxidatively polymerizing aniline monomers on a template such as a polymeric acid. The resulting polyanilines readily dissolve in water. These Materials can be applied as removable discharge layers for electron-beam (e-beam) lithography and for SEM Mask Metrology. Cross-linkable functionality can be incorporated on the polyanilinc backbone resulting in water soluble polyanilines that are radiation curable. Upon irradiation these materials cross-link and become insoluble and thus can be utilized as permanent conducting coatings for electrostatic discharge (ESD) applications. In addition, the cross-linkable polyanilines can be made into water developable conducting resists. 1.0μm conducting lines have been patterned with e-beam irradiation.

Lithographic applications of conducting polymers

Electrically conducting polyaniline is found to be suitable for several lithographic applications. Because the polyaniline is not significantly soluble in the conducting state, the material has generally been processed by first applying the soluble, nonconducting version of the material, and in a second step externally doping the polymer film with aqueous acids. We have eliminated the need for this type of external doping by developing methods of inducing the doping in a dry fashion in situ in the polymer. This is accomplished by incorporating onium salts or amine triflate salts in the polyaniline which decompose upon radiation or thermal treatment, respectively, to generate the active dopant species, i.e., protonic acids. The use of these in situ dopants simplifies the processing of the conducting polyaniline and makes the material more convenient for lithographic applications. With the use of onium salts, the polyaniline is made into a high resolution negative conducting resist. 0.25 μm conducting lines...

Optical properties of hydrogenated amorphous‐carbon film for attenuated phase‐shift mask applications

The optical properties of a plasma‐deposited amorphous‐carbon film have been investigated in the ultraviolet (365 nm) and deep ultraviolet range (248 nm). By varying process conditions, the optical transmission through the films was tuned from 4% to 20% at 365 nm and from 3% to 9% at 248 nm. This tuneability was related to the hydrogen content of the film as affected by the process parameters. The index of refraction n measured by spectroscopic ellipsometry is ∼2 at the wavelengths used. These optical properties make this film attractive for use in single layer attenuated phase‐shift masks for potential application in 0.25 μm lithography at 365 and 248 nm.

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.