There has been a growing demand for more precise Mask CD MTT (Critical Dimension Mean to Target) control by
shrinking the semiconductor device. Generally, The CD MTT is determined by patterning process such as writing,
develop, and etch. But, additional CD MTT variation often occurs by cleaning process after patterning process. As a
result, it is important to preserve the CD MTT for minimizing CD variation by cleaning process. The cleaning process of
photomask is becoming more critical for 32nm node and below because the size of defect and SRAF pattern is in the
same range. In order to achieve high first cleaning pass yields, intensive cleaning method depending on media not
physical force is still essential to photomask manufacturing and these cleaning processes bring about considerable CD
MTT change. Therefore, it is necessary to increase the durability of MoSi material of attenuated HTPSM (Half Tone
Phase Shift Mask) by the new surface treatment method.
In this study, we presented the plasma etching technique for Cr strip etch in the 2nd process of the attenuated HTPSM for
minimizing CD variation by cleaning process. Diverse dry etching processes are investigated to improve the durability of
the MoSi patterns. In order to evaluate the surface modification of the MoSi film, surface compositions are analyzed by
XPS (X-ray Photoelectron Spectroscopy), TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry), and EELS
(Electron Energy Loss Spectroscopy). The variation of CD MTT and optical properties are also evaluated by CD SEM
and AIMS (Aerial Image Measurement System), respectively. The XPS analysis shows that sidewall passivation films
are formed during the main etch process and then modified at the over etch step and additional in-situ O2 plasma
treatment. The concentration of the MoO3 is increased when over etch step and in-situ O2 plasma treatment are added.
The difference of CD shift between initial measurement and 2nd measurement after cleaning process depends on plasma
etching conditions. Consequently, the increase in the peak intensity of MoO3 that is less soluble than that of MoO2 leads
to preserve CD by cleaning chemicals.