As the industry approaches to 45nm and below lithography, resolution and pattern collapse of SRAF (Sub Resolution Assistant Feature) on photoresist is becoming critical issues on photomask industry. The collapse of photoresist pattern has been become a serious problem in manufacturing of fine patterns in wafer and mask industries. The presumed causes of the resist pattern collapse are capillary forces acting on the patterns and adhesion property of the patterns. The use of thinner resist thickness has been known as one of the most effective method among reported literatures. However, etching resistance of present resist is still bad. Therefore it is difficult to reduce the photoresist thickness, though the pattern size is very small.In this paper, the available limits of resist thickness for FEP171 were calculated for several kinds of common absorber layers as considering current dry etch capability. We focused on pattern design and collapse window for SRAF. FEP171 resist performance especially for resolution and collapse window were evaluated for both 2000Å and 3000Å thickness with line, space, and length focused on sub 100nm features. Radial position effect and drying conditions were studied herein.

A lot of research has been carried on sulfate free cleaning process to minimize haze generating residual ions on mask surface. However sulfate free cleaned mask has been suffered from short life time of haze generation than we expected, because pellicle outgassing combines with ammonium residuals and formed haze near pellicle frame area and decrease yield. Therefore physical and PKL developed chemical surface modification treatment was studied and evaluated in term of near pellicle haze threshold energy, surface energy of mask substrate components (Qz/MoSi/Cr), AFM and AES depth profile. Dehydration bake treatment (physical surface modification treatment) and PKL developed chemical treatment increased near pellicle haze threshold energy by 2.5 and 4 times, respectively. Surface modification treatments didn't show negative effect on phase angle and transmittance losses of ArF EAPSM mask. The effect of illumination sources on surface modification treatment was also studied.

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Although sulfate free cleaning has reduced number of residual ions on mask surface drastically, the lifetime of photomask has improved marginally. New haze generation mechanism in sulfate free cleaning has been studied and evaluated based on surface properties of photomask thin film materials. It was found that haze generation is co-related with substrate surface properties as well as ionic re-combination under ArF illumination. Based on the haze generation study, the surface modification treatment has been studied and investigated in the view of surface energy. The surface modification treatment increases storage lifetime as well as cumulative haze threshold energy in wafer shops.

Progressive defect generation has been a serious issue in wafer lithography, as illumination wavelength becomes shorter with the introduction of the 248 and 193 nm wavelengths. Several research groups have reported that cleaning residues, mostly ammonium and sulfate ions, on a mask surface are critical sources of progressive defect generation. A new cleaning process has been developed and studied to minimize progressive defect generation sources. The new cleaning process consists of dehydration baking, dry etching, and H 2 O 2 treatment. Dehydration baking was proposed to reduce the concentration of sulfate residues while H 2 O 2 treatment and dry etching are proposed to control ammonium ions. Dehydration baking is employed at 230 C for 600 s to reduce the sulfate ion concentrations from 32 to 1.6 ppb on chrome on glass (COG) or binary intensity mask (BIM). ArF embedded attenuate phase shift mask (EAPSM) is associated with a high concentration of ammonium ions (>5000 ppb), and is easily susceptible to progressive defect generation under ArF illumination. More than 90% ammonium extraction (removal) efficiency was achieved by H 2 O 2 treatment for ArF EAPSM. Moreover, the optimized new cleaning process has reduced the concentration of ammonium ions up to 50 ppb compared with the 1500 ppb reported by conventional RCA cleaning in ArF EAPSM. In a strictly controlled sulfate environment (less than 6 ppb), threshold defect energy has improved from 25 to 100 kJ by reducing the concentration of ammonium ions down to 45 ppb and below. Therefore, the concentration of residual ammonium ions along with residual sulfate ions should be strictly controlled to improve wafer and photomask yields.