According to the design rule shrinkage, more precise control of mask CD, including mean to target and uniformity, is
required in lithography process. Since dry etching is one of the most critical processes to determine CD qualities in
photomask, optical emission spectroscopy (OES) to monitor plasma status during dry etching process could be useful.
However, it is not possible to obtain distributional information of plasma with a conventional OES tool because the OES
acquires totally integrated signals of light from the chamber. To overcome the limit of OES, we set up a spatially
resolved (SR)-OES tool and measure the distribution of radicals in plasma during dry etch process. The SR-OES consists
of a series of lenses, apertures, and a pinhole as a spatial filter which enable us to focus on certain area in the chamber, to
extract the emitted light from plasma, and to perform the spectroscopic analysis. The Argon based actinometry combined
with SR-OES shows spatially distinguished peaks related to the etch rate of Chromium on photomask. In this paper, we
present experimental results of SR-OES installed on a commercial photomask dry etcher and discuss its practical
effectiveness by correlation of the results with chamber etch rate.