Srinivasan Chakrapani

Radiation sensitive developable bottom anti-reflective coatings (DBARC): recent results

Second generation, radiation sensitive, developable 193 Bottom Antireflective coatings (DBARCs) are made solvent resistant through a crosslinking mechanism activated during post apply bake (PAB) that is reversible by acid catalyzed reaction upon exposure of the DBARC/resist stack. This allows coating the resists on the DBARC, after PAB, without dissolution of the antireflective coating. This DBARC approach avoids the plasma etch breakthrough needed for conventional bottom antireflective coatings which are irreversibly crosslinked, while maintaining excellent reflectivity control, typically lower than 1% on bare Si. We will give an update on the performance our latest 193 nm DBARC prototype materials used with different conventional alicyclic based 193 nm resists. For instance, using a binary mask with conventional illumination several of our prototype DBARC formulations were able to resolve 120 nm trench features with a 250 nm pitch.

Some non-resist component contributions to LER and LWR in 193-nm lithography

Improvement of line edge roughness (LER) and line width roughness (LWR) is required for integration of semiconductor devices. This paper describes various process factors affecting LER/LWR of 193 nm resists such as mask layout (bright field/dark field), pitches, optical settings, substrates, film thickness, baking temperature and development condition. The origins of line roughness are discussed in view of aerial image contrast, transmittance of resists and pattern profiles. Bright field mask exhibited lower LER/LWR values than dark field mask, LER/LWR deteriorated as larger pitches and illumination condition affected roughness and these results are explained using normalized image log-slope (NILS). BARC dependence of line roughness is explained by pattern profile difference due to interactions between resist and BARC and in some cases BARC reflectivity. Contributions of film thickness, SB & PEB temperature and development condition to line roughness are also reported.

Process optimization consideration for 193nm developable bottom anti-reflective coatings (DBARCs)

Developable BARCs (DBARCs) are useful for implant layers because they eliminate the plasma etch step avoiding damage to the plasma sensitive layers during implantation. It is expected that DBARC will also be used for non-implant layers and double exposure technology. AZ has pioneered DBARC based on photosensitive cleave as well as crosslink/decrosslink mechanisms. In this paper, we focus on various processing factors for 193nm DBARC and discuss the influences of prewet, thickness, topography and substrates on lithographic performance. Prewet of DBARC before resist coating deteriorated performance, however, it was resolved by modifying DBARC formulations. The optimized DBARC showed both optical and lithographic performance comparable to conventional BARCs. DBARCs minimized reflection from the substrates and notching of patterns was improved observed on silicon oxide topography. This paper includes simulation, DBARC contrast curve analyses, and recent dry and immersion exposure results of DBARC.

Latest developments in photosensitive developable bottom anti-reflective coating (DBARC)

Developable bottom anti-reflective coatings (DBARC) are an emerging litho material technology. The biggest advantage of DBARC is that it eliminates the plasma etch step, avoiding damage to plasma sensitive layers during implantation. AZ has pioneered developable BARC based on photosensitive cleave as well as crosslink/decrosslink mechanisms. In this paper, we focus on the crosslink/decrosslink concept. DBARC/resist mismatching was corrected both from process and formulation sides. The optimized DBARC showed comparable lithographic performance as conventional BARCs. This paper provides the chemical concept of the photosensitive developable DBARCs, approaches for DBARC/resist matching and performance of photosensitive DBARCs for 248 nm and 193 nm exposures. Recent 193 nm immersion exposure results are also presented.

Comparison of thermal flow and chemical shrink processes for 193 nm contact hole patterning

This paper compares thermal shrink properties of contact holes and chemical shrink performance for 193 nm lithography. Pitch dependence, shrink properties, contact hole circularity, sidewall roughness, and process window are also discussed. Thermal flow process exhibited more pitch dependence than chemical shrink process. Thermal shrink rate increased substantially at higher bake temperatures. Contact holes in defocused area shrunk non-evenly and DOF deteriorated upon heating. In chemical shrink process, shrink rate was hardly influenced by mixing bake temperature, contact holes from center focus to defocus area shrunk evenly preserving effective DOF and MEF became smaller at smaller CD. Chemical shrink has clear advantages over thermal flow process and sub-70 nm contact holes were obtained with iso-dense overlap DOF 0.25 μm by optimizing resist formulations and process conditions. Application of shrink processes will pave the way for the next generation LSI production.

Novel diamantane polymer platform for enhanced etch resistance

The dominant current 193 nm photoresist platform is based on adamantane derivatives. This paper reports on the use of derivatives of diamantane, the next higher homolog of adamantane, in the diamondoid series, as monomers in photoresists. Due to their low Ohnishi number and incremental structural parameter (ISP), such molecules are expected to enhance dry etch stability when incorporated into polymers for resist applications. Starting from the diamantane parent, cleavable and non-cleavable acrylate/methacrylate derivatives of diamantane were obtained using similar chemical steps as for adamantane derivatization. This paper reports on the lithographic and etch performance obtained with a number of diamantane-containing monomers, such as 9-hydroxy-4-diamantyl methacrylate (HDiMA), 2-ethyl-2- diamantyl methacrylate (EDiMA), and 2-methyl-2-diamantyl methacrylate (MDiMA). The etch advantage, dry and wet lithographic performance of some of the polymers obtained from these diamantane-containing polymers are discussed.

Performance of a dry 193nm resist under wet conditions

193 nm immersion lithography is rapidly moving towards industrial application, and an increasing number of tools are being installed worldwide, all of which will require immersion-capable photoresists to be available. At the same time, existing 193 nm processes are being ramped up using dry lithography. In this situation, it would be highly advantageous to have a single 193 nm resist that can be used under both dry and wet conditions, at least in the initial stages of 45nm node process development. It has been shown by a number of studies that the dominant (meth)acrylate platform of 193 nm dry lithography is in principle capable of being ported to immersion lithography, however, it has been an open question whether a single resist formulation can be optimized for dry and wet exposures simultaneously. For such a dry/wet crossover resist to be successful, it will need to make very few compromises in terms of performance. In particular, the resist should have similar LER/LWR, acceptable process window and controlled defects under wet and dry exposure conditions. Additionally, leaching should be at or below specifications, preferably without but at very least with the use of a top protective coat. In this paper, we will present the performance of resists under wet and dry conditions and report on the feasibility of such crossover resists. Available results so far indicate that it is possible to design such resists at least for L/S applications. Detailed data on lithographic performance under wet and dry conditions will be presented for a prototype dry/wet crossover L/S resist.