The diagnostics of 13.56 MHz planar radio-frequency (rf) plasma were c
arried out using spatially resolved optical emission spectroscopy betw
een the parallel electrodes. Plasma sheath thickness d evaluated from
the optical emission profiles depends on gas pressure P, and a relatio
nship of P(n)d=const. was obtained for CH4, CF4, and O-2 plasmas with
n greater than or equal to 1/3, and for He and Ar plasmas with n great
er than or equal to 1/2. The etching rate and the etching profile of s
ilicon in CF4 plasma were also examined as a function of gas pressure.
A novel technique for controlling rf plasmas using the optical sheath
thickness and maximum optical emission intensity is presented. This t
echnique was applied to dry etching of silicon in CF4 plasma. When thi
s novel control technique was used, the deviation in the etched depth
for a constant etching time became smaller than that obtained using co
nventional power control methods.