This paper describes techniques to determine the effective wavelength
of x-ray lithography sources. The experimental results give informatio
n on the actual x-ray absorption of the resist materials for the x-ray
source under test. Results for two beam lines of the HELIOS storage r
ing installed at the IBM Advanced Lithography Facility, and for one be
am line at the VUV ring at the Brookhaven National Laboratory are pres
ented, and compared to calculations.