Bottom anti-reflective coatings (BARCs) are essential for achieving the 65-nm node resolution target by minimizing the substrate reflectivity to less than 1% and by planarizing substrates. We believe that the developments in 157-nm BARC products are on track to make them available for timely application in 157-nm lithography. We have made some significant improvements in resist compatibility and etch selectivity in relation to the latest available 157-nm resists.
Two chromophores having desired high light absorbance at the 157-nm wavelength have been identified. The prototype BARC formulations basically meet the critical requirements for workable 157-nm BARCs, including optical properties, thermal stability, photo-stability, etch rate and selectivity, and compatibility with photoresists. The BARCs also show good coating quality and stripping resistance. Another essential feature of the BARCs is that they are formulated in industry-accepted safe solvents. The lithographic profiles of a benchmarked 157-nm photoresist on our prototype BARC LH157B show straight 60-nm L/S patterns. LH157B also exhibited excellent lithography performance as an ArF BARC. Optimization of the BARC formulations is in progress.
The 70-nm technology node is projected to go into manufacturing production by late 2004. The most promising technology for the 70-nm technology node of semiconductor devices is 157-nm lithography. Although advances in developing 157-nm technology have been hampered by greater challenges than originally expected, considerable progress has been made. Great efforts have been made to improve the exposure tool, the laser, the resist materials, the resist processing, the mask materials, and bottom anti-reflective coatings (BARCs). BARCs are essential in achieving the 70-nm-node resolution target by minimizing the substrate reflectivity to less than 1% and planarizing substrates. This paper will describe the various design considerations for a workable 157-nm BARC, including optical constants, thermal stability, photo stability, etch rate and selectivity, resist compatibility, film conformality, coating quality, and lithography profile. It will demonstrate that to maintain less than 1% reflectance for a 157-nm BARC, the value of refractive index n (real) must be from 1.3 to 1.8 and that of k (imaginary) must be from 0.26 to 0.6, determined by Prolith modeling. The refractive index ranges are set as optical constant targets for the design of BARCs formulations. The photoresist profiles from 157-nm lithography utilizing our developed BARCs will also be presented.