As the design rule of the semiconductor shrinks, the CD MTT (Critical Dimension Mean-to-Target) specification for photomask becomes tighter. So, more precise control of CD MTT is required. We have investigated the CD MTT control and applied it to the attenuated PSM (Phase Shift Mask) successfully for several years. We can control the CD MTT of MoSi pattern by measuring Cr/MoSi pattern to estimate MoSi pattern CD and additional etch to shrink MoSi pattern as reported in previous study. At first, the MoSi pattern CD can be estimated with the Cr/MoSi pattern CD because the CD gap between MoSi pattern and Cr/MoSi pattern is relatively constant. Additional MoSi etch is performed to shrink the MoSi pattern CD after then. The CD gap alwasys exists and the variation of the CD gap is enough small to be not considered in conventional photomask production until now. However, the variation of the CD gap is not ignorable in case of sub-20 nm tech.
In this study, we investigated new method to measure MoSi pattern CD before Cr strip process to eliminate the CD gap between MoSi pattern and Cr/MoSi pattern. To eliminate the CD gap, we attempt three solutions – 1) Optimize etch process to perform perfect Cr/MoSi pattern profile without the CD gap, 2) Improve CD measurement accuracy by developing new SEM measuring mechanism, 3) Develop of new process to modify Cr/MoSi pattern profile to be measured without the CD gap. It was found that the CD gap can be eliminated and MoSi pattern CD can be measured perfectly. Finally, MoSi pattern CD control was improved because of CD gap elimination.
During EUV exposure, more frequent mask cleaning is essential for removing not only particles from lack
of pellicle but also the carbon contamination due to accumulative EUV exposure. Because of this reason,
process improvement for minimize corrosion and etching of the Ru capping layer is urgently needed. In this
work, the influence of TaBN absorber etch condition on Ru integrity followed by repetitive cleaning was
evaluated and the effects on long-term durability of Ru are compared under various cleaning conditions.
Consequently, it was shown that Ru durability was strongly influenced by the gas contents and over etch time
of absorber dry etch, not only as a function of cleaning conditions.
As technical advances continue, the pattern size of semiconductor circuit has been shrunk. So the field of the photomask needs the processing more strictly. It is critical to the photomask which contained considerably shrank circuit and ultra high density pattern for sub-20 nm tech device, although a small defect is negligible in the conventional process. Even if some defect can be repaired, it is not satisfied with a strict pattern specification. Stricter fabrication process and pattern specification increase the manufacture cost. Furthermore, EUV photomask manufacture cost is several times expensive than the conventional photomask. Therefore the effort to decrease defects is important for the photomask fabrication process. In addition, when defects are generated, it is obviously important that the repaired patterns have better pattern reliability. In this paper, we studied about advanced processes that control and remove hard defects minutely .on ArF attenuated phase-shift mask. This study was accomplished for 4 areas. First of all, we developed advanced Mosi etch process. Defects are generated under this etch process are not fatal. The thickness of hard defects were controlled thinner under this etch process compared with conventional etch process. Secondly, we studied cleaning process that has good performance on Cr : MoSi surface and a poor hydrophilic contrast to control side effect by etch process. Thirdly, we made inspection technique for detecting thin thickness hard defects. Lastly, we researched a repair technology that is effective in hard defects of thin thickness. The performance of the repaired pattern was verified by AIMS. In this study, it is researched that control shape, properties of defects to prepare a reliable repair and improved repaired photomask pattern reliability by 30% over.
We have investigated self-aligned resist patterning for a patterning accuracy of photo mask. Self-aligned resist
pattern can be formed by backside flood exposure on photo-mask. It had been already proved by the experiments with
248 nm light source exposure on binary (Cr on Quartz) and KrF attenuated phase shift masks. Attenuated phase shift
masks are generally composed of Cr/MoSiN/Quartz, MoSiN/Quartz, and Quartz layers. MoSiN layers of attenuated
phase shift mask have the optical property of 6% transmittance at 248 nm light source, and the interference of the 6%-
transmitted light makes the undesirable resist pattern profile on MoSiN-Quartz boundary. This paper shows the fresh
possibility of the self-aligned resist pattern fabrication on attenuated phase shift masks using backside flood exposure. To
solve the optical property of MoSiN layer, self-aligned resist patterns of KrF attenuated phase shift mask was fabricated
using 193 nm wavelength backside flood exposure and ArF attenuated phase shift mask used 172 nm wavelength. The
shorter wavelength than generally applied wavelength could minimize transmittance on MoSiN area. Besides we used
Negative PR to make the self-aligned resist pattern on exposed regions. These experimental concepts help to form the
selective PR patterning on only quartz regions of attenuated phase shift mask.
As the design rule of the semiconductor circuit shrinks, the specification for photomask becomes tighter. So, more
precise control of CD MTT (Critical Dimension Mean to Target) is required. We investigated the CD MTT control of the
attenuated PSM (Phase Shift Mask) by additional Cr dry etch. In conventional process, it is difficult to control CD MTT
precisely because about 5 factors - Blank Mask, E-beam writing, Resist develop, Cr dry etch, MoSiN dry etch - affect
CD MTT error. We designed the new process to control CD MTT precisely. The basic concept of the new process is to
reduce the number of factors which affect the CD MTT error. To correct CD MTT error in the new process, we
measured CD before MoSiN dry etch, and then additional corrective Cr dry etch and MoSiN dry etch was performed. So,
the factors affecting CD MTT error are reduced to 2 steps, which is additional corrective Cr dry etch and MoSiN dry
etch. The reliability of CD measurement before MoSiN dry etch was evaluated. The generable side-effect of the
additional corrective Cr dry etch was analyzed. The relationship between 'CD shift' and 'additional corrective Cr dry
etch time' was found for various patterns. As a result, accurate CD MTT control and significant decrease of CD MTT
error for attenuated PSM is achieved.