Contrast Enhanced Lithography Research Articles

Design of high-resolution positive-working photoresist

Factors which improve the resolution of a positive-working photoresist composed of a naphthoquinonediazide and a novolac resin are discussed. Control of the dissolution rate of the resist film into the developer is essential to improve the resolution. The relationship between the dissolution rate and the chemical structures of the matrix resin and the photoactive compound is discussed. It is also shown that the photobleaching phenomenon of the photoactive compound helps to increase the resolution and the term “internal contrast-enhanced lithography (CEL) effect” is introduced.

The simulation of contrast-enhanced lithography

The Dill's parameters of nonlinear photobleaching materials of p-diazo-dimethylaniline chloride zinc chloride (DZC) and poly(di-n-hexylsilane) (PDHS) are irregularly dependent on their film thickness, and also their refractive indexes change during exposure. These difficulties make Dill's model inadequate for the simulation of nonlinear photobleaching materials used in contrast-enhanced lithography. A direct approach was proposed to solve these difficulties. Equations with four parameters were derived to simulate the nonlinear photobleaching curves of DZC, PDHS and other nonlinear photobleaching curves reported in literature. The equations correlated very well with these curves by using best-fit parameters. Linearity was found with these four parameters in these equations as a function of film thicknesses of DZC and PDHS. Based on this linearity, the modelling and simulation of these nonlinear photobleaching materials as contrast-enhancement layers are more convenient and accurate than those using Dill's model.

A new contrast enhanced lithography (cel) process using “chinese rosin” as a binder

AbstractA new contrast enhanced lithography (CEL) process using Chinese rosin as a binder is described. This binder is soluble in both non‐polar organic solvent and aqueous alkaline solution. Good coatability with organic solvent, no formation of mixing layer, and direct development without removing the CEL layer are the major advantages of this process. Among the three different kinds of photobleachable dyes, DZ‐2 (diazonium salt) has the best optical property and the resist profile is improved on g‐line reduction projection printing at the smallest dose. Moreover, this DZ‐2—Chinese rosin system is also effective at 365 nm, and the resist profile and the focus margin are improved on i‐line reduction projection printing by using this system.

Water‐Soluble contrast enhancing materials—new photobleachable dyes

AbstractMany styrylpyridinium compounds (SPC), which are very stable in the dark, were prepared and evaluated as photobleachable dyes for contrast enhanced lithography (CEL). The photobleaching characteristics of water‐soluble contrast enhancing materials composed of SPC and water‐soluble polymer depend on the structure of the SPC and the kind of polymers used. The technique using SPC‐based CEL proved to be very effective for the resist pattern profiles.

Study of half-micron photolithography by means of contrast enhanced lithography process

A simple, but efficient, analysis method has been developed to evaluate material properties, process conditions, and effectiveness of contrast enhanced lithography (CEL). The method, realized as a result of the systematic calculation and concept, is based on the evaluation of the energy transmittance of the contrast enhancing material (CEM). In practical applications of the new method to the design and evaluation of both CEM characteristics and half‐micron contrast enhanced photolithography, the method has been proved to be useful in the precise design as it shows good agreement with experimental results. The study has brought us pieces of important information on such design as the optimum exposure conditions, the ideal CEM characteristics, etc. Based on the information, we have developed a new CEM, water soluble photopolymer (WSP) for i and g lines. Through the simulation, it has been confirmed that the ultimate resolution can be improved by 20% to 30%.

0.4-µm gate-length devices fabricated by contrast-enhanced lithography

This letter describes the fabrication of submicrometer polysilicon-gate MOS devices by an advanced optical process called contrast enhancement. Functional devices having gate lengths as small as 0.4 µm were fabricated with this process. Contrast-enhanced lithography (CEL) allows usable photoresist patterns to be fabricated at smaller dimensions than is possible with conventional resist. The simultaneous replication of mask dimensions for isolated lines at 0.35 µm and above was achieved in this work using a single exposure on an Optimetrix 10:1 DSW system. Contrast enhancement has been applied to the fabrication of n-channel MOS devices having gate lengths from 0.4 to 1.5 µm in steps of 0.1 µm. Long-channel devices were also fabricated. The transconductance of the 0.4-µm devices is 40 mS/mm at V ds = 5 V. Threshold voltages (V ds = 0) are nearly independent of gate length, ranging from 1.21 to 1.31 V over the 7.5- to 0.4-µm range in gate length. The effective mobility for long-channel devices is 430 cm2/V.s.