Multi-layer bottom antireflective coating structures for high NA ArF exposure system applications

In the recent ITRS roadmap, the ArF lithography combining with resolution enhancement techniques have great potential to lead IC technologies to the generation less than 100 nm. The problems of critical dimension control caused by highly reflective substrates are far more serious in the ArF regime than in the longer wavelengths. It is therefore important to find a high performance antireflective coating layer working in this spectral regime. For increasing resolution of optical lithography, expose systems with high numerical aperture (NA) are essential. The efficiency of conventional single layer BARC structure will degrade as the incident angle increased. It is due to the reflectance at resist/BARC interface increased in high incident angle regimes. Here we demonstrate a multi-layer bottom antireflective coating (BARC) layer for high NA ArF lithography. The multi-layer antireflective structure is composed of conventional SiON films. In a multi-layer BARC, the extinction coefficient of each BARC layer is gradually increased layer by layer, and is the highest at the bottom. By adding an optimized structure, the reflectance can be remained less than 2% at resist/silicon substrate interface as the incident angle from 0 to 60 degrees (i.e. NA similar to 0.85). The swing effect in the resist is also shown significantly reduced. It also has a great potential to be used as BARC layer on other highly reflectance substrate such as copper, aluminum silicon (Al-Si), poly-silicon, tungsten silicide (W-Si), which are commonly used in IC processe.