Shuji Ding

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.

Development of 193-nm B.A.R.C.s for dual damascene applications

Full and/or partial filling of 193 nm antireflective materials in contact holes is required for dual damascene applications. One of the major challenges for via filling is to minimize various fill bias associated with via size, via pitches and wafer size to an acceptable level. Toward this aim, various formulations were prepared and tested on different types of wafers using different processing conditions. It has been found that both the properties of the filling materials (e.g., molecular weights, glass transition temperatures, etc.) and processing conditions (e.g., spinning speed, dispense modes, baking temperatures, etc.) affect the filling behaviors. This paper presents our recent progress in the development of 193 nm B.A.R.C. materials designed for the dual damascene process. Through screening of the B.A.R.C. materials and optimization of the processing parameters, we have successfully developed two types of B.A.R.C. materials, namely, AZ EXP ArF-2P1 and AZ EXP ArF-2P5A, both of which show good filling performance.

Characterization and improvement of resist pattern collapse on ArF (193 nm) organic B.A.R.C.

Due to miniaturization of semiconductor devices, ArF (193nm) lithography is likely expected to be used for sub 100nm regime. For sub 100nm devices, high NA (>=0.70) exposure tools and various strong off-axis illumination (OAI) conditions should be used. But unlike KrF (248nm) lithography, resist pattern collapse becomes one of the most serious problems in ArF lithography. In order to solve pattern collapse problem, thin resist process is generally introduced but its poor etch resistance is an obstacle for being applied in real production process. Due to this reason, new kinds of organic BARC materials are investigated and optimized to avoid pattern collapse. As mentioned, the most important issue in ArF organic BARC is believed to be the pattern collapse problem. A number of organic BARCs were made by varying polymer, cross-linker, thermal acid generator, and additive. We tried to analyze the key factor in terms of pattern collapse. This paper is to compare the various elements of the organic BARC formulation and to discuss what brings and causes pattern collapse.

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.

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.