Arieh Aviram

Recent progress in electron-beam resists for advanced mask-making

Resists for advanced mask-making with high-voltage electron-beam writing tools have undergone dramatic changes over the last three decades. From PMMA and the other early chain-scission resists for micron dimensions to the aqueous-base-developable, dry-etchable chemically amplified systems being developed today, careful tuning of the chemistry and processing conditions of these resist systems has allowed the patterning of photomasks of increasing complexity containing increasingly finer features. Most recently, our research efforts have been focused on a low-activation-energy chemically amplified resist based on ketal-protected poly(hydroxystyrene). These ketal resist systems, or KRSs, have undergone a series of optimization and evaluation cycles in order to fine-tune their performance for advanced mask-fabrication applications using the 75-kV IBM EL4+ vector scan e-beam exposure system. The experiments have led to an optimized formulation, KRS-XE, that exhibits superior lithographic performance and has a high level of processing robustness. In addition, we describe advanced formulations of KRS-XE incorporating organometallic species, which have shown superior dry-etch resistance to novolak-based resists in the Cr etch process while maintaining excellent lithographic performance. Finally, current challenges facing the implementation of a chemically amplified resist in the photomask manufacturing process are outlined, along with current approaches being pursued to extend the capabilities of KRS technology.

Preparation and thermodynamics of Some Homologous Nitrones, a New Group of Liquid Crystals

Abstract To investigate the mesomorphic behavior of aldonitrones, a series of 13 homologs of N-(p-alkoxyphenyl)-α-anisylnitrones was prepared and characterized. Although most of these substances exhibit normal nematic or smectic mesophases, the trend in nematic-isotropic transition temperatures to increase as a function of alkoxy chain length is an exceptional occurrence. Comparison of our data with that of analogous compounds previously reported indicates that thermal persistence of the nematic phase of these compounds increases in the following order : 4, 4′-dialkoxybenzylideneaniline, 4, 4′-dialkoxyazobenzene, N,α-di-(4-alkoxyphenyl)-nitrone, 4, 4′-dialkoxyazoxybenzene. In addition, the phase transitions were investigated by means of differential scanning calorimetry. The entropies of the mesophase-isotropic transitions of the nitrones imply that the long alkoxy chains, in contrast to a widely held belief, are not restricted to a single conformation in the mesophase.

Mesomorphism in the 4,4′-Dialkoxy-trans-Stilbenes

Abstract In order to ascertain the effect of linkage groups (X[dbnd]Y) in mesomorphic substances of the general formula a homologus series of stilbenes has been prepared, where R[dbnd]Cn, H2n+1O—, X[dbnd]Y[dbnd]CH. The lower members of the series (1 ≤ n ≤ 10) are monotropic nematic, while the higher members (12 ≤ n ≤ 16) are monotropic smectic substances. The mesophase-isotropic transition temperatures are higher than those reported for the related nitrones (X[dbnd]CH, Y[dbnd]N → O) and Schiff Bases (X[dbnd]CH, Y[dbnd]N). Also the entropies of the nematic-isotropic transitions, as measured by differential scanning calorimetry, are nearly the same in the stilbenes and the nitrones. These results suggest that the permanenet dipole associated with the linkage group plays a relatively unimportant role in enhancing the intermolecular attractions which are responsible for mesomorphic alignment.

Scanning Calorimetry of Mesophase Transitions: Marker’s Acid

Marker’s acid (MA), first reported by Marker, Oakwood and Crookes in 1936 (1), contains a 3β-carboxylic acid group in the place of a 3β-hydroxyl found in cholesterol. The structure of MA has been rigorously demonstrated by both Roberts, Shoppee and Stephenson (2) and Corey and Sneen (3) to be cholest-5-ene-3β-carboxylic acid (alternatively named 3β-carboxy-∆5-cholestene). This configuration makes MA an isomeric form of cholesteryl formate. As such, it might be expected to exhibit a cholesteric mesophase at some temperature.