The expected minimum critical dimension (CD) of optical lithography (KrF (248 nm) and ArF (193 nm) laser optical lithography) is about 70 nm.(1) Due to limits of non-optical lithography technologies, optical lithography technology for $F_2$ laser (157 nm) was considered to lead the nano-lithography technologies for below 70 nm CD. And with decrease of wavelength used in optical lithography, resolution enhancement technologies (RET`s) such as phase shift mask (PSM), off Axis Illumination (OAI), optical proximity correction (OPC) were developed to decrease CD.
Si-O-N-F was chosen as a High Transmittance attenuated phase shift mask (Ht-Att-PSMs) materials for 157 nm optical lithography. lito satisfy the requirements of transmittance and phase shift. The optical properties, composition and thickness of deposited Si-O-N-F films were analysed. Using the new mask structure of a-Si/Si-O-N-F/quart, the condition satisfying the requirements of transmittance and phase shift was confirmed.
The optical properties of a-Si films and Si-O-N films in Deep Ultraviolet (DUV) region were analyzed using Spectroscopy Ellipsometry(SE) analysis.
a-Si thin films having thickness of less 25 nm were deposited. From spectroscopic ellipsometry(SE) and AES analysis, it was analyzed that a-Si film consisted of two layers of SiOx(8 nm) and a-Si(824 nm). Using SE and UV spectroscopy analysis, Transmittance variation of a-Si films having different thickness in DUV region was researched and explained using SE analysis. And the blue shift of optical band gap was analyzed and explained using size effect of thickness. From analysis of optical properties, it was confirmed that a-Si film with high transmittance in DUV could be used as a passivation layer of Si-O-N-F film.
In order to analyze the effects of composition on the optical properties of Si-O-N films, Si-O-N films having the same thickness (80 nm) and different composition were deposited. From SE analysis, it was analyzed that transmittance slope decreased and the refractive index increased with increase of N concentration.