Richard G. Morton

Behavior of fused silica irradiated by low level 193 nm excimer laser for tens of billions of pulses

Abstract Fused silica samples from seven suppliers have been irradiated with low-level (0.1 mJ/cm2) 193 nm irradiation using an ArF excimer laser. At high pulse counts of tens of billions of pulses, a decrease of the optical path length is observed in the irradiated area. Two of the samples were irradiated with a higher fluence source of 3 mJ/cm2 for 100 million pulses in a separate area. That higher level exposure produced an increase in the optical path length as expected due to compaction. Birefringence measurements were also made which show that the character of birefringence is different for the high fluence and low fluence irradiated areas. A description of the test and measurements is presented along with data covering pulse counts to 40 billion pulses.

Behavior of fused silica irradiated by a low-level 193-nm excimer laser for tens of billions of pulses

Fused silica samples from six suppliers were irradiated with a range of fluences (0.004 mJ/cm2 to 0.2 mJ/cm2) using an ArF 193-nm excimer laser. The test was performed in an effort to determine fluence level dependency of induced wavefront distortion and birefringence. Each sample was irradiated with four beams of different fluence levels for 22 billion pulses over a period of 133 days. Wavefront distortion in the irradiated areas was observed for all samples. The sign and magnitude of the distortion were dependent upon the fluence level and the particular sample under irradiation. Birefringence measurements were also made. The birefringence characteristic varied among the samples, possibly as a function of fluence level and material. FTIR spectrum measurements were made and were correlated with wavefront distortion measurements. A description of the test and measurements is presented along with data covering a pulse count of 22 billion pulses.

Long-term reliable operation of a MOPA-based ArF light source for microlithography

Since the introduction of the XLA-100 in January 2003, we have built, tested, and shipped a large number of XLA-100 MOPA lasers to microlithography scanner manufacturers. Some systems have already been installed at chip fabrication lines. To ensure product design robustness, we have been performing a long-term system performance test of an XLA-100 laser at Cymer. In this paper, we will report optical performance of the XLA-100 we see during manufacturing final tests, and a summary of the long term testing.

ArF lasers for production of semiconductor devices with CD < 0.15 μm

The present day notion of the extensibility of KrF laser technology to ArF is revisited. We show that a robust solution to ArF requirements can be met by significantly altering the lasers core technology-discharge chamber, pulsed power and optics. With these changes, a practical ArF tool can be developed. Some of the laser specifications are: Bandwidth: 0.6 pm (FWHM) 1.75 pm (95% Included Energy); Average Power: 5 W; Repetition Rate: 1000 Hz; Energy Stability (3(sigma) ): 20% (burst mode) 8% (continuous); Pulse Width: 25 ns.

Design considerations and performance of 1-kHz KrF excimer lasers for DUV lithography

The operation of 1 kHz KrF lasers for DUV lithography applications requires a design which minimizes perturbations to the optical and electrical properties of the gas present, at one millisecond intervals in the lasing region and vicinity. The optimum design results from a compromise between electrical and fluid dynamic requirements, since these cannot be simultaneously fully satisfied. Other constraints on a commercially viable design are those rooted in issues such as manufacturability, safety, cost, compatibility with fluorine, and service lifetime of the resulting structure. CYMER has successfully engineered a laser which produces linear average power output scaling with pulse repetition rates to 1 kHz at a line- narrowed bandwidth of less than 0.8 pm. The stabilized pulse energy is 10 mJ with a FWHM of approximately 15 nS, producing an average power of 10W at 1 kHz pulse repetition rate. The 3(sigma) value of pulse energy stability is 5 percent. In addition, the chamber exhibits low fluorine consumption and a lifetime in excess of 2 billion shots. Measured performance data are presented along with a general system layout and facilities requirements.

Dependence of compaction in fused silica on laser pulsewidth at 248 nm (Abstract Only)

Designers of DUV lithographic lenses are faced with serious materials problems relating to compaction and color-center formation in fused silica, especially at 193 nm. However, these problems, while less sever, are not negligible at 248 nm. Compaction appears to be the more serious, since it degrades imaging performance and effectively sets the lifetime limit for the lens. Previous damage studies have clearly shown that fused silica compacts as a function of the parameter grouping (NI2/(tau) ), where (tau) is the pulsewidth. This fact has strongly influenced the design of the excimer laser light source by stressing repetition rate over pulse energy as a way of achieving high average power, and by driving the optical pulsewidth to be as long as possible. These studies, however, have emphasized the dependence of damage rates on the energy density I(mJ/cm2), whereas the optical pulsewidth (tau) has been given only cursory attention and has not been well controlled during the damage experiments. In this paper we report the results of an experiment to more clearly establish the functional dependency of compaction on laser pulsewidth.

Optical damage testing of materials for use in 157-nm photolithographic systems

As photolithographic processes utilize ever shorter wavelengths to produce more densely packed circuitry on silicon chips, the choice of materials suitable for use in the DUV spectral region becomes severely limited. We report here on preliminary life test results for calcium fluoride irradiated at 157 nm by F2 laser beams. The sample housing and beam delivery tubes were purged continuously with high purity nitrogen to keep the background oxygen level as low as possible and to sweep away any potential organic gases liberated from the sample mounting hardware and overall experimental apparatus. Data were collected to evaluate induced changes in transmission, wavefront distortion and birefringence over the course of billions of shots at a nominal fluence of 0.1 mJ/cm2.

Performance of 1-kHz KrF excimer laser for DUV lithography

In response to the requirement for higher wafer throughput and increased dosage accuracy in DUV lithography steppers and scanners, Cymer has developed a 1 kHz KrF laser optimized for this application. We shall describe its performance and design features.