Development of X-ray mask in Taiwan

This paper presents results of using silicon carbide (SiC) and silicon-rich silicon nitride (SiN_x) as membrane for X-ray masks in technology of X-ray lithography. Microcrystalline silicon carbide (β-SiC) film was deposited on silicon substrate by electron synchrotron resonance plasma-enhanced chemical vapor deposition (ECRPECVD) at 300 °C utilizing a SiH₄/CH₄/ H₂/Ar gas mixtures. Low tensile stress film which is suitable as x-ray membrane can be achieved by annealing after silicon carbide film deposition. The microwave power over 800 watts and the gas ratio (Methane:Silane) larger than 1.5 are needed for the stoichiometry of SiC film. On the other hand, we deposited silicon-rich silicon nitride film on silicon substrate by low pressure chemical vapor deposition (LPCVD) at 850 ° C to 900 ° C. In order to get low tensile stress film, different gas flow ratios (Dichlorosilane:Ammonia) were tested. The increased gas flow ratio (Dichlorosilane:Ammonia) and the increased deposition temperature are related to the decrease of tensile stress of film. Roughness, uniformity, optical transmittance and soft X-ray transmission of both films are reported. The absorption bands of both films were measured by FTIR spectroscopy. The surface morphology was monitored by AFM. The photon transmittion of both films was measured in the range of 400 to 800 nm for visible light and 800 to 1600 ev photon energy for SR-soft X-ray transmission was conducted in Synchrotron Radiation Research Center (SRRC), Hsinchu, Taiwan. The deposition rate of both films are 13 nm/min and 40 nm/min for silicon nitride and silicon carbide respectively.