Optical lithography using excimer lamps: 172 nm and beyond

Summary form only given. The Semiconductor Industry Association (SIA) has set 100 nm features as a goal in microelectronics by 2003. In order to achieve this goal, many research groups are studying lithography techniques such as DUV, direct write e-beam, synchrotron, excimers, and X-ray/EUV light sources. Excimer lamps as a photolithography light source offer many advantages that include high brightness, high efficiency, and tunability. Also, these lamps can be constructed without halogens, providing long lifetimes at high powers. At the College of William and Mary, we have designed and constructed two such novel excimer electrode-less lamps using Xe-Ar mixtures to produce UV light at selected wavelengths. One of the newly developed lamps uses a 1 kW 13.56 MHz capacitively coupled power source. The other lamp employs a multiple (6) magnetron power source to provide increments of 1.5 kW (up to 3 kW) of 2.45 GHz microwave power that is probe coupled to an over-moded cavity. On both lamps, experimental work was carried out to investigate the emissive output as a function of power, pressure, cooling, and gas composition. Theoretical models such as MAGIC and PSPICE were used to study the coupling of electrical energy into the plasma discharges. Further models were developed to interpret and compare the molecular emission spectra with that of other excimer lamps. The paper details the total emissive power in the <200 nm range and compare that to the total lamp output. In addition, we have shown that certain configurations have a 40% wall plug efficiency in accord with the predicted theoretical maximum.