The miniaturization of pattern size on photomask is advanced year by year. It becomes more important to improve Line
Edge Roughness (LER) and resolution because of their impacts on lithography performances. When miniaturization is
advanced, high sensitivity inspection is also indispensable. Therefore, LER becomes the key factor to reduce the
nuisance defect for high sensitivity mask inspection. Basically, LER originates from resist materials and EB writer. If
resist pattern LER is good, final pattern LER can be good too. One of the easiest solutions for LER is using thick resist.
Thick resist can vertically smooth down the LER. However, it deteriorates resolution due to the high aspect-ratio.
Another solution for LER is using low sensitivity resist. Low sensitivity resist needs many electron exposures by EB
writer. Therefore, electronic density of EB pattern increases and pattern edge becomes clear. However, it deteriorates
throughput, which is essential to production. Only by mask resist, it is difficult to satisfy all items, that is mask LER,
resolution and throughput.
In this study, the improvement of LER without deterioration of resolution is tried by dry etching process. It is found that
remaining resist after Cr etching has its limitation for mask LER. And Cr over etching and source power of Cr and MoSi
etching are effective factors for mask LER. On the basis of these results, the optimal etching process is determined. It is
confirmed that mask LER can be improved without deterioration of resolution by the optimal etching process.