We evaluated the requirements for 65-nm SRAM gate fabrication using attenuated phase shifting masks (att-PSM). Off-axis illumination (OAI) and att-PSM, together with optical proximity correction (OPC) were used as resolution enhancement techniques (RETs) for ultimate resolution. It was shown that the photolithographic parameters of the transmittance of the att-PSM and the illumination conditions for optimum conditions were a transmittance of between 15 and 20% and 3/4 annular illumination. The exposure latitude was simulated to be more than 10.9% at 300-nm defocus for a critical dimension (CD) specification of 10%. It has been demonstrated that a 65-nm SRAM-gate, with a line and space (L/S) ratio limited to 1:2 at the minimum pitch, could be fabricated with sufficient depth of focus (DOF). The pattern transfer was accomplished with a bi-layer process, in which the reactive ion etching (RIE) selectivity between a silicon-containing resist and an organic film is very high. This bi-layer process enabled the application of a very thin resist layer. The conditions described in this paper proved successful for the fabrication of a 65-nm SRAM gate with a good pattern profile despite the resist thickness of less than 120nm.
157-nm lithography is being investigated for the sub-65nm technology node of semiconductor devices. Many efforts have been reported on the exposure tool, the F2 laser, the resist materials, the resist processing and the mask materials. A critical component for the success of this 157-nm lithography is the availability of high numerical aperture (NA) lenses that lead to higher resolution capability and a larger process margin. It was reported in a previous article that a 0.85 high NA 157-nm microstepper has demonstrated a resolution capability of 55 nm dense line and space features in combination with an alternating phase shirting mask and using a 120nm thick fluoropolymer resist. The influence of the intrinsic birefringence of the CaF2 lens material on the wavefront aberrations of the projection optic was also experimentally confirmed. In this paper, the effect of the wavefront errors on the imaging performance will be discussed from an evaluation of the short-range flare and the local area flare present in the high numerical aperture (NA) lens.
157 nm lithography is being investigated for the sub-70 nm technology node of semiconductor devices. Many efforts have been reported on the exposure tool, the F2 laser, the resist materials, the resist processing and the mask materials. A critical component for the success of this 157 nm lithography is the availability of high numerical aperture (NA) lenses that lead to higher resolution capability and higher process margin. In this paper, we describe our recent evaluation results of a high precision 157 nm Microstepper with 0.85 NA lens combined with simulation analysis of the lithographic performance. The details of the evaluation results discussed here include the resolution limit of the high NA lens and the possible effects of intrinsic birefringence upon the lithographic performance.