Nicholas J. Clecak

Airborne chemical contamination of a chemically amplified resist

We have found that the performance of the t-BOC/onium salt resist system is severely degraded by vapor from organic bases. This effect is very pronounced and can be observed when the coated wafers stand for 15 minutes in air containing as little as 15 parts per billion (ppb) of an organic base. The observed effect, caused by this chemical contamination, depends on the tone of the resist system. For negative tone systems the UV exposure dose, required to obtain the correct linewidth, increases. While for the positive tone system, one observes the generation of a skin at the resist-air interface. Both effects are caused by the photogenerated acid being neutralized by the airborne organic base. There are a wide variety of commonly used materials which can liberate trace amounts of volatile amines and degrade resist performance. For example, fresh paint on a laboratory wall can exhibit this detrimental effect. These effects can be minimized by storing and processing the resist coated wafers in air that has passed through a specially designed, high efficiency carbon filter. The implementation of localized air filtration, to bathe the resist in chemically pure air, enabled this resist system to operate in a manufacturing environment at a rate of 100 wafers/hour.

Novel Liquid Crystalline Materials: Synthesis and preliminary characterization of new 4,4′-disubstituted diphenyldiacetylene, tolane and stilbene derivatives

Abstract The synthesis and mesomorphic properties of several new series of liquid crystalline materials are described. These include two novel diacetylenic structures, 4,4′-di-n-acyloxydiphenyldi-acetylene and the unsymmetrical 4-n-alkoxy, 4′-cyanodiphenyldiacetylene, and the analogous 4-n-alkoxy,4′-cyanotolanes and stilbenes. A discussion of the effect of structure on transition temperatures is included.

Influence of polymer properties on airborne chemical contamination of chemically amplified resists

We describe here an extensive study of the relation between polymer structure and rates of NMP uptake for a set of polymer films with a very broad range of properties. NMP labeled using radioactive 14C was introduced at a concentration of 12 ppb into a stream of purified air. The film of interest was then immersed in the airstream for a predetermined time under controlled conditions. The radionuclide serves as a tag which allows precise quantitation of NMP absorbed by the polymer film. NMP uptake rates measured using this method are shown to correlate with polymer physical properties in a straightforward manner. The observed trends are in accord with those expected on the basis of the solution diffusion model of polymer permeation. These data provide a basis for the rational design of polymers for chemically amplified resists which are insensitive to airborne contaminants.

Molecular design for stabilization of chemical amplification resist toward airborne contamination

This paper describes the first logical approach to the design of chemical amplification resists that are stable toward airborne contamination. This molecular design is based on the observation that uptake of N-methylpyrrolidone (NMP) by thin polymer films is primarily governed by glass transition temperatures (Tg) of the polymers. This concept has led to the design of environmentally very robust chemical amplification resists that provide positive images upon development with aqueous base.

Novolac Based Deep-UV Resists

This paper describes the results obtained from studies of deep-UV lithographic properties of resists which utilize chemical amplification in novolac resins. These studies have shown that three-component novolac-based systems are surprisingly effective as deep-UV resists despite the high opacity of novolac at 254 nm. Analytical results are described which have measured the amount of Bronsted acid produced in chemical amplification resist films. The minimum acid concentration necessary for acceptable dissolution rates is far less than the corresponding active species content necessary for the proper functioning of diazoketone-novolac deep-UV resists.

Highly etch resistant, negative resist for deep-UV and electron beam lithography

I lighly sensitive resists have been developed from a combination of silsesquioxanes, acid photogenerators, and phenolic resins. The resist forms negative images and is developable with aqueous base. Both electron beam and deep-uv optical sensitivity was observed. The films displayed exceptionally high oxygen reactive ion etch resistance. Bilayer systems were developed with this resist as the imaging layer with either polyimide or hard baked novolac as the planarizing layer. Improved optical resists for single layer application have been obtained by using poly(4-hydroxystyrene) derivatives as the matrix resin.

Thermal properties of 4-alkyl-4′-cyanotolanes: a new series of liquid crystals☆☆☆

Abstract The thermal properties of a new series of liquid crystals, the 4-alkyl-4′-cyanotolanes, were measured. The DuPont 990 thermal analyser was used to measure the temperatures and heats of the transitions. The entropy changes in both the crystal to mesophase and mesophase to isotropic liquid transitions are found to be a function of the length of the alkyl chain on the molecules.

Polysilanes for microlithography

We have recently reported the formation of scum-free micron images in a bilayer composed of a thin (1500 angstrom) imaging layer of poly(cyclohexylmethylsilane) coated over a thick planarizing layer of a hardbaked diazoquinone-novalac type photoresist using deep UV exposure. Although excellent resolution was achieved (< 0.5 micrometers ) in this process, the exposure doses required (125-150 mJ/cm2) were higher than desirable for commercial DUV imaging tools. We have addressed this problem using two approaches: (i) the synthesis of new polysilanes which are intrinsically more sensitive to photodegradation in the solid state and (ii) the incorporation of additives which enhance the photosensitivity. Regarding the former, a number of aryl substituted polysilane homopolymers which are significantly more photolabile than the standard poly (methylphenylsilane), as assayed by the rate of spectral photobleaching upon exposure to DUV radiation, have been prepared and tested. In addition, a number of small molecule additives which quantitatively quench the polymer fluorescence in the solid state have been identified. Some of the additives which efficiently quench the polymer fluorescence in the solid state also accelerate the rate of photodegradation. The combination of the new polysilane materials with sensitizing additives has allowed submicron DUV imaging at exposure doses as low as 20 mJ/cm2 or less in a bilayer configuration employing O2-RIE for image transfer of the wet-developed images.

Thermal properties of 4-alkyl-4′-cyanostilbenes: a new series of liquid crystal compounds

Abstract The transition heats and temperatures of a series of 4-alkyl-4′-cyanostilbenes were measured with the DuPont 990 thermal analyzer. The entropies of both the solid-to-mesophase and the mesophase-to-isotropic liquid was found to be dependent on the number of carbons in the alkyl on the molecule. The entropy change in the nematic-to-smectic transition found in the C 7 member of the series was found to be extremely small.

Positive-tone dry-develop resist based on crosslinking a phenolic resin

We have previously shown that a copolymer of p-hydroxstyrene and p-acetoxymethylstyrene can be used as a sensitive deep UV resist. In that study we demonstrated that a formulation of this copolymer and an onium salt could be exposed, baked and developed in aqueous base to yield a high resolution negative tone relief image. In this paper we discuss a gas phase silylation process that converts this negative tone solvent-developable resist system into a positive tone dry-developable resist system. We have used an FT-IR microscope, coupled to a motorized X-Y stage, to study the silylation process as a function of UV exposure dose and silylation processing parameters. By altering the copolymer ratio, we found that resist contrast increased when the amount of acetoxymethylstyrene increased. This resist system and dry develop process were used to print 0.35 micrometers images at a DUV dose of approximately 25 mJ/cm2.