Advanced F2-lasers for microlithography

According to the SLA-Roadmap, the 157 nm wavelength of the F-2 laser emission will be used for chip production with critical dimensions of 100 nm down to the 70 MI node. Currently all basic technologies for 157 nm lithography are under investigation and development at material suppliers, coating manufacturers, laser suppliers, lens and tool manufacturers, mask houses, pellicle manufacturers, and resist suppliers. Based on 20 years of experience with 157 nm lasers in a variety of applications, Lambda Physik has developed a single-line 1 kHz Lithography Ft laser system, NovaLine F1020, which delivers 10 W stabilized output power at 157 nm. Laser discharge chamber, solid-state pulsed power module and laser resonator optics have been optimized for laser emission with spectral bandwidth of about 1 pm. The laser can be directly applied to catadioptric projection systems and is ready for system development, process development and pilot production. An on-board dose energy control has been developed yielding better than 0.5 % dose accuracy over 50 pulses in the slit. On a laboratory scale the laser could demonstrate a gas lifetime in excess of 600 million pulses. Optical modules and beam lines have been designed for lowest contamination. Long term and durability tests of the 157 nm lithography laser system have been carried out at Lambda Physik, comprising multi-ten billion exposure tests of individual components. Data from these tests as well as data obtained at several installations reveal lifetimes of the laser chamber in excess of 3 billion pulses and optics lifetimes above 2 billion pulses. According to these data and due to the minimum complexity of the optical resonator as a merit, the laser has an attractive cost of operation. Over the last year significant progress has been made in metrology for 157 nm. Energy sensors and power meters are available and have been extensively tested. Calibration of power meters is still an open issue, however. Spectral metrology as well as spatial beam profile and divergence metrology is available. Absolute wavelength calibration is still not finally solved. However, we have preliminary results of the absolute wavelength of the strong line of the 157 nm lithography laser. The correct wavelength is 157.63095 nm. This wavelength is 1.05 pm longer than earlier publications report. The exact knowledge of the emission wavelength has significant impact on the design of the 157 nm lens. in addition, four new lines have been discovered. The absolute wavelength of all lines is given as preliminary result. Under final development at Lambda Physik is the next 157 nm lithography laser generation which makes the step towards 2 kHz repetition rate and 20 W output power. The main architecture of the laser is the same as for the 1 kHz laser generation. Significantly improved and adapted to the higher repetition rate and output power are laser chamber, solid-state pulsed power module, high voltage power supply as well as thermal management of the laser system. Refractive designs of the projection lens based on CaF2 only or CaF2 in combination with a second material would require further line-narrowing of the F-2 laser to about 0.1 pm or 0.25-0.5 pm, respectively. In the frame of a feasibility study on further prospects on line-narrowing of the 157 nm radiation we could generate 1 mi pulses with a bandwidth of 0.39 pm after deconvolution. This corresponds to 0.9 W average power at 1 kHz repetition rate. To investigate possibilities to boost up the pulse energy, experiments to amplify 157 nm laser pulses have been carried out. Small signal gain of 6.5 %/cm has been measured with a non-optimized 157 nm amplifier module. Output pulse energies of 15 mi have been extracted from the amplifier at an input energy from the oscillator of 1 mi.