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.
EUV (Extreme Ultraviolet) Lithography has been delayed caused by several technical problems such as
EUV mask, source power and etc. So ArF immersion lithography has been continued with adopting new
technology. Especially, the wafer lithography tends to increase rapidly NTD(Negative Tone Develop) process
for overcoming high resolution such as small hole type patterns. For wafer NTD process, the pattern shape in
mask has changed from hole pattern to dot pattern. Also the local CD uniformity of aerial image is getting
more important. In this paper, we studied local CD uniformity with analyzing aerial images of high
transmittance HT-PSM (attenuated phase-shift mask) and conventional 6% HT-PSM from AIMS (Aerial Image
Measurement System) tool. Additionally, several cell sizes were analyzed to find an optimum target cell size
which has good wafer performance and AIMS aerial image. And we analyzed NILS(Normalized Image Log
Slope) factor which represent wafer photolithographic performance. Furthermore, we analyzed not only AIMS
NILS simulation, but also wafer lithographic performance.
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.