Date of Award
Doctor of Philosophy (PhD)
Mool C. Gupta
A novel high power 121.6 nm radiation source based on dielectric barrier discharge (DBD) has been developed for advanced lithography applications. The discharge unit consists basically of a hollow tube made of a dielectric material with two loop-electrodes wrapped on the outside of the tube. The discharge is generated inside the tube by means of a 13.56 MHz RF power system. The discharge unit is located in a vacuum chamber that provides a dynamic gas flow and windows for radiation transmission.
A very intense and spectrally clean Lyman-α line at 121.6 nm was observed by operating the DBD discharge in a mixture of high-pressure Ne (200--800 Torr) with a small admixture of hydrogen (less than 0.1%). The hydrogen Lyman-α line at 121.6 nm was emitted via near-resonant energy transfer between Ne excimer and H2, which leads to the dissociation of H2 and the excitation of atomic hydrogen. The Lyman-α emission intensity depends on the operating parameters of the discharge, such as gas pressure, gas mixture, gas flow rate and discharge geometry. By optimizing these parameters, the radiation power at 121.6 nm was maximized. A radiation source with 8 watts of optical power at 121.6 nm wavelength with a narrow line width (Δλ < 0.03 nm) and stable operation was achieved. Since the lamp operation is based on RF driven plasma, one method to increase the power was to couple more RF power in discharge. By applying a proper RF network and optimizing the electrode area and gap, the RF reflection losses were reduced to less than 2%. With the water-cooling circuit, the temperature of discharge unit was maintained at room temperature and the lamp operation was able to maintain over 100 hours of continuous use.
The discharge was optimized by simulation using XOOPIC software, which models the plasma as discrete macroparticles interacting with EM field. Some plasma parameters, such as the spatial distribution of electrons and ions, electron energy and density, were calculated from simulation. The results from simulation were in agreement with our experimental measurements. By modeling the operating parameters of the discharge, such as pressure, discharge tube diameter, electrode area and gap, high radiation power at 121.6 nm was achieved.
The lamp source was sent to MIT-Lincoln Lab for 121.6 nm lithography applications. From the initial results of the experiments, patterns with 63 nm feature size lines were obtained. One other application of lamp was explored where direct metal pattern writing by VUV photodissociation of a palladium acetate (Pd(OCOCH3)2, Pdac) was achieved. Palladium metal pattern was directly written on glass substrate by using a MgF2 mask, which has feature linewidth of 1 μm.
A stable, high power, and narrow spectral width radiation source has been developed. It is suitable for photolithography and nanofabrication applications.
"High Power 121.6 NM Radiation Source for Advanced Lithography"
(2005). Doctor of Philosophy (PhD), dissertation, Electrical/Computer Engineering, Old Dominion University, DOI: 10.25777/z99w-ny77