The importance of advanced e-beam writing system and chemically amplified resist (CAR) coated blank is increasing gradually in high-end grade photomask manufacture according to CD embodiment of 90 nm and beyond technology node requiring because of the shrinkage of design rule in the semiconductor industry. However, many studies have been reported that CAR has several troubles and especially, CAR sensitivity change is occurred by airborne molecular contamination (AMC). So, the storage life of CAR coated blank is shortened. This problem may cause the difficulty of high-end grade photomask manufacture because it is hard to secure stable mean to target (MTT) and CD uniformity by sensitivity change, T-top profile and footing profile. Therefore, the purpose of this paper is to investigate the storage life extension for high performance CAR coated blank through improvement of the packing materials.
Firstly, a variety of packing materials were collected and the selected packing materials were analyzed by Automatic Thermal Desorption Gas Chromatograph/Mass Spectrometer (ATD GC/MS) and Ion Chromatograph (IC) to examine AMC generated from the packing materials. As a result, molecular condensables such as alcohols, hydrocarbons and fatty acids were detected and molecular acids and molecular bases those are NH4+, Cl-, NOx- and SOx- were also detected from the packing materials, respectively. From the above results, we selected the best packing materials which generated the least AMC and the worst packing materials which generated the most AMC. Additionally, we verified photomask process with CAR coated blanks which were packed with those packing materials with post coating delay (PCD) by 50 kV e-beam writing system. In consequence, dose to clear (DTC) showed 4.6 μC/cm2 at 0 day PCD for both of the best and the worst packing materials of CAR coated blank. After 90 days PCD, DTC variation was only 0.4 μC/cm2 for the best packing materials, but DTC variation of 4.0 μC/cm2 showed in the worst packing materials. There was 10 times difference in DTC variation between the best and the worst packing materials. As well as, the CD variation at 0.5 μm dense line presented less than 5 nm movement for 90 days PCD.
As minimum feature size of device shrink down below 100 nm, the process margin for the mask fabrication reduced dramatically. Mask makers are enlisting equipment and material suppliers in their efforts to achieve wide process margin from existing processes. One of the most promising methods is thinning Cr thickness as low as possible. However, briging the thin Cr blank into mass production line could cuase some problem for advance photomask fabrication using 50 kV electron beam writing tools. In this paper, we verified the feasibility of Cr film ranged from 400 Å to 1000 Å. The results categorized into two sections. At first, we verified the writing property change with thinning Cr thickness and then investigated the etching characteristics. As a result, we found that Cr thickness don't affect writing properties regardless of Cr thickness. However, the thinner Cr blank represented superior etching characteristics to a conventional one. It showed low etching bias and loading effects. From these results, we concluded the thinner Cr blank could not only make the process wider but also improve the mask quality.