Dinesh N. Khanna

Lithographic performance of a dry-etch stable methacrylate resist at 193 nm

High resolution performance down to the 0.13 micrometers level is demonstrated in a methacrylate resist with pendent polycyclic side groups. The best performance is achieved with a bottom coat although interactions with the resist were still observed which led to the presence of scum in fine lines and to a large dose change relative to silicon. The demonstrated dry etch rate of the resist was found to be about 10% higher than APEX-E; predictions based on the ring parameter would have led us to expect a more favorable etch rate. The observed discrepancy has led us to speculate on possible exposure of the resist by the plasma environment and loss of the etch resistance polycyclic unit through evaporation.

Bottom antireflective coatings for ArF, KrF, and i-line applications: a comparison of theory, design, and lithographic aspects

The present paper discusses theory, design and properties of bottom anti-reflective coatings (BARCs) for deep UV and i- line applications. All BARCs are interference devices, and as such their optical constants are optimal only for certain combinations of thickness and the real and imaginary parts of the refractive index. Maps of the optimality conditions in the parameter space will be provided. The design of BARCs for various exposure wavelengths involves choosing the right dye molecules capable of highly absorbing at the particular wavelengths and optimizing the etch rates of the resulting film sand fine tuning the formations for best lithographic performance. At an exposure wavelength of 365 nm, dye compounds such as amino aromatic or azo type compounds can be used, for 248 nm it is necessary to use fused rings such as anthracene to have sufficient absorption, and in the case of 193 nm exposures simple benzene or phenolic compounds exhibit the required d absorbance. Since the dye molecules are invariably aromatic or fused rings, it is necessary to balance the absorption property versus the etch rate by incorporating non-aromatic moieties. Further, the BARC formulations need to be free from intermixing, formation of foot or undercut in order to obtain fine resist patterns. Our development efforts on BARCs have led to the AZ EXP ArF, KrF and BARLi series of BARCs designed for 193, 248 and 365 nm wavelength exposures, respectively. Lithographic data of some of these products will also be presented with the emphasis on the AZ EXP ArF-1 material designed for 193 nm exposure.

Effect of cresol monomers in three-component novolak resin on photolithographic performance

In our previous publication we reported an improved process for isolation of novolak resins form phenol-formaldehyde condensation mixtures. The process results in resins having low polydispersity and slow photospeed. Novolak resins were prepared by the same process, employing different ratios of the cresol components. This paper will discuss an experimental design analyzing relationship between cresol component ratios and properties of the resins. The characteristics of the resins and their effect on the lithographic performances as an i-line photoresist composition will also be discussed.

Novolak resin for ultrafast high-resolution positive i-line photoresist compositions

An improved process for isolation of novolak resins from phenol-formaldehyde condensation products has been developed. The process results in resins having low polydispersity and higher photospeed while typical phenol/formaldehyde resin syntheses generate a broad distribution of molecular weight fragments with a wide polydispersity. The novolak resins were characterized by NMR and GPC and were formulated to obtain ultra fast high resolution i-line photoresists. The characteristics of the resins and their effect on lithographic properties as i-line photoresist compositions will be discussed in this paper.

Performance impact of novel polymeric dyes in photoresist applications

Dye compounds are commonly used in photoresists as a low cost and effective way to control swing and/or standing wave effect caused by thin film interference as well as reflective notching by reflective light from highly reflective substrate and topography. Convention dyes are typically a monomeric compound with high absorptivity at the wavelength of exposure light and compatible with the resist system selected. Because of the monomeric nature, conventional dyes are relatively low in molecular weight hence their thermal stability and sublimination propensity has always been an issue of concern. We recently synthesize several highly thermal stable diazotized polymeric dyes. Their thermal properties as well as compatibility with resist system were investigated. The impact of polymeric dyes on the resists lithographic performance, swing reduction and reflective notching control are discussed.

Performance of 193-nm resists based on alicyclic methacrylate and cyclo-olefin systems

Among the chemistries/polymers reported for the 193nm photoresist applications, methacrylate copolymers consisting of 2-methyl-2-adamantane methacrylate and mevalonic lactone methacrylate and cycloolefin polymers derived from derivatives of norbornene have shown promising results. We have studied the lithographic properties of these two but different promising chemistries. Both system offer linear resolutions down to 0.13 micrometers using conventional 193 nm illumination and high sensitivity at standard developer conditions. While the methacrylate based system shows best performance on substrates with bottom coats, the cycloolefin-Maleic anhydride alternate copolymer based resists performs well on bare silicon as well as substrates with bottom coats. The etch rates of the methacrylate and cycloolefin based resists were found to be 1.4 and 1.3 times relative to that of KrF resist APEX-E. Further, new polymers consisting of isobornyl and alkyl ether chains on the ester groups of norbornene carboxylate were made in order to decrease the glass-transition temperatures of the norbornene-maleic anhydride type polymers. These results will be included and discussed in detail.

Process and performance optimization of bottom antireflective coatings: II

The newly developed AZ BARLi II coating material is a photoresist solvent-based bottom antireflective coating (BARC) for i-line lithographic application. The coating material has good compatibility with common edge bead removal solvents such as ethyl lactate, PGME, or PGMEA mixed with ethyl lactate or PGME. To evaluate the BARC material, its chemical compatibility with common EBR solvents has been tested by several analytical techniques including liquid particle counts and surface defect studies. Both top and bottom EBR dispense processes have been investigated and optimized. Improvements on edge roughness, visual cleanliness, and the BARC coating buildup at the edge will be discussed in this paper.

Process effects resulting from conversion to a safe-solvent organic BARC

The use of bottom antireflective coatings (BARCs) as a means for controlling substrate reflectivity and thin film effects, has become commonplace in todays wafer fabs. In an effort to simplify process integration, reduce environmental impact, and reduce processing costs, some next generation organic BARC materials have recently been introduced which are formulated with photoresist compatible solvent systems. This study examines the process effects of converting from the cyclohexanone based AZTM BARLiTM anti-reflective coating, to the recently introduced PGME/Ethyl Lactate based AZTM BARLiTM II anti-reflective coating. We will present a comparison of the optical properties of the two products, and examine i-line lithographic process effects including process latitudes, CD distributions, and coat defects, as well as post etch CD distributions, and dye sublimation during cure.

Monitoring and controlling synthesis of bottom antireflective coating materials by in-situ FT-IR technique

A number of polymeric azo dyes was synthesized in our laboratories in the course of developing and studying i-line bottom antireflective coating materials. The key step in the synthesis involved formation of a diazonium salt intermediate which is a highly energetic species and can quickly convert to a couple of by-products, depending on the reaction medium such as solvent, temperature, time, and acidity. It is important to understand the mechanistic insight and compositional changes during the course of the reaction. ASi ReactIRTM 1000 reaction analysis system was used as the on-line monitor to follow such complicate process. By using this technique, we were able to obtain high quality kinetic data for thermal stability study of the intermediate, gained good understanding of reaction mechanism, optimized the synthesis process effectively, and achieved good control of reaction yield. The in-situ FT-IR technique proved to be a powerful tool for monitoring and controlling such a process. The highly absorptive polymers synthesized by the optimized process showed good consistency of the overall lithographic performance.