Cattien V. Nguyen

Aerial image contrast using interferometric lithography: effect on line-edge roughness

Interferometric lithography affords the unique ability to independently control dose, pitch and aerial image contrast during photolithographic exposure. In this report, we describe the use of a deep-UV interferometric lithography exposure tool to study the impact of aerial image contrast on resists imaging properties. A wide range of high resolution resists materials was surveyed, including positive- and negative-tone systems, chemically amplified and conventional diazonaphthoquinone imagining chemistries, and aqueous- and solvent-developed systems. In all cases, resist line- edge roughness was observed to increase as aerial image contrast was decreased, though the precise behavior varied with resist material. Polymer molecular weight was systematically varied with resists materia. Polymer molecular weight was systematically varied in a negative- tone chemically amplified resist formulation. The results indicate that molecular weight is a significant factor influencing the magnitude and type of line-edge roughness at low aerial image contrast.

Templating Nanopores Into Poly(MethylSilsesquioxane): New Lowdielectric Coatings Suitable for MicroElectronic Applications

Thin films of nanoporous poly(methylsilsesquioxane) have been prepared from organic/inorganic polymer hybrids. Low molecular weight 6-arm star poly(caprolactone)s are incorporated into partially pre-condensed methylsilsesquioxane resin. Upon heating, the glass resin cross-links around the organic polymer templates. Thermal decomposition of the orgainc polymer produces nanoporous thin films which show tunable dielectric constants as low as 1.9 and exhibit properties suitable for use in interconnect devices. Experimental data including porosity, morphology, and dielectric constants are presented.

Tolane oligomers: Model thermotropic liquid crystals

Abstract The liquid crystalline phases of several rigid-rod, non-polar tolane oligomers are characterized by differential scanning calorimetry and transmitted polarized light microscopy. We determine that a stable nematic phase can be formed at ambient pressure if the molecular axial ratio (length-to-width ratio) is greater than 4.5. A smectic phase forms in addition to the nematic phase if the axial ratio exceeds 6.1. Symmetrical fluorination of the terminal phenyl groups reveals that the liquid crystalline phase behaviour of these rigid rods is highly sensitive to perturbations of the charge distribution along the molecules. Nematic tolane oligomers can exhibit high stregth disclinations (s = ±3/2 and ±2) in their schlieren textures, and we discuss conditions that promote the stability of these defects.

Force Microscopy of Chiral Liquid-Crystal Surfaces

The free surface of chiral liquid crystals has been observed by optical and scanning force microscopy. In a narrow temperature region near the smectic A* to cholesteric (or isotropic) transition, a unique periodic surface undulation is observed. Both the period and depth are seen to be temperature dependent, though their ratio is approximately constant. This structure appears to be related to the chiral nature of the molecules and may be a result of competing alignment forces, analogous to that predicted by de Gennes and Bouligand.

Smectic liquid crystals modified by tail and core fluorination

The systematic substitution of fluorine for hydrogen in mesogenic materials has proved to be of great value for the modification of a wide range of physical properties. This is especially true in the case of ferroelectric liquid crystals in which the fluorine has been strategically introduced into the aromatic core (k), at or near the chiral center (Z) or in the achiral tail (n) in the generic liquid crystal (with X equals O, S and Z equals Me, halogen): H/F(CF2)n(CH2)mOC6H(4 - k)FkCOXPhOCOC*HZR. In this system the fluorine can be introduced in any of these three specific locations, or any combinations thereof, with the intent of enhancing performance such as broadening of the ferroelectric Sc* phase temperature range, enhancement of the magnitude of spontaneous polarization Ps and a variety of more subtle yet important modifications such as viscosity and dielectric and optical anisotropy. The ramifications of the incorporation of fluorine on these physical properties are discussed with a variety of examples.

Remarkable Influence of Fluorination in Smectic and Ferroelectric Liquid Crystals

Abstract Liquid crystals possess a wide variety of interesting and useful properties which are strongly correlated to their structure. In order to modify and enhance certain useful properties we have examined the effects of systematic introduction of fluorine. Especially interesting examples are the influences on the phase range and type including ferroelectric properties and on miscibility leading to phase separation via spinodal decomposition of the anisotropic LC phase.

Silyl‐protected hydroxystyrenes: Living anionic polymerization at room temperature and selective desilylation

Both 4- and 3-(tert-butyldimethylsilyl)oxystyrene (MSOST) undergo living anionic polymerization at room temperature with sec-butyllithium (sBuLi) in cyclohexane or methylcyclohexane upon injection of a small amount of tetrahydrofuran. Desilylation can be conveniently afforded with hydrogen chloride or tetra(alkyl)ammonium fluoride to provide poly(hydroxystyrene) (PHOST) with a narrow molecular weight distribution, which could be further transformed to other polystyrene derivatives. 13C NMR spectra of poly(tert-butyldimethylsilyloxystyrene) (PMSOST) and PHOST prepared under different conditions (tetrahydrofuran vs. cyclohexane, −78 °C vs. 20 °C) have indicated that the room temperature living polymerization in the hydrocarbon-rich solvent produces polymers with high syndiotacticity. Similarly, 4-(tert-butyldiphenylsilyl)oxystyrene (PhSOST), a new monomer, provides living anionic polymerization at room temperature. Desilylation of this polymer can be achieved using tetra(n-butyl)ammonium or tetraethylammonium fluoride. Inertness of the phenylsilyl ether to HCl allows selective desilylation of the dimethylsilyl ether with HCl in the presence of the phenylsilyl ether group, providing a new route to interesting macromolecules. Application of the selective desilylation technique to the synthesis of a block copolymer of HOST and 4-tert-butoxycarbonyloxystyrene (BOCST) is described.

Carbon Nanotube Scanning Probe for Surface Profiling of DUV and 193 nm Photoresist Pattern

The continental scaling down of CMOS feature size to 100 nm and below necessitates a characterization technique to resolve high aspect ratio features in the nanoscale regime. This paper reports the use of atomic force microscopy coupled with high aspect ratio multi-walled carbon nanotube scanning probe tip for the purpose of imaging surface profile of photoresists. Multi-walled carbon-nanotube scanning probe tip for the purpose of imaging surface profile of photoresists. Multi-walled carbon-nanotube tips used in this work are 5-10 nm in diameter and about a micron long. Their exceptional mechanical strength and ability to reversibly buckle enable resolution of steep, deep nanometer-scale features. Images of photoresist patterns generated by 257 nm interference lithography as well as 193 nm lithography are presented to demonstrate multi-walled carbon nanotube scanning probe tip for applications in metrology.