Experimental Study On Extreme Ultraviolet Source Generation From CO₂ Laser-irradiated Tin

Along with the development of science and technology, semiconductor industry is unceasing progress, the super-large-scale integration requires the exposure light with shorter wavelength. The laser-produced plasma (LPP) source is one kind of promising soft x-ray and extreme ultraviolet (EUV) source which has been studied form the 1970's. The study of the LPP source has been advanced in order to meet the requirements of the extreme ultraviolet lithography and the semiconductor industry. This study aims at using CO₂ laser pulse irradiate the solid tin target to produce plasma and EUV source.We reviewed the background and current state of LPP EUV source. Generally speaking, tin-doped microscopic liquid target or solid target was irradiated with a CO₂ laser pulse or Nd: YAG laser pulse, changing the target or laser parameters to obtain a clean and efficient EUV source. The EUV source experimental platform is built, combining their research results with existing experiment condition.The soft X-ray flat-field grating spectrograph is used to diagnose the soft X-ray spectrum. Based on the imaging features of sagittal and meridional plane and principle of concave reflective grating, the spectrograph is designed to diagnose the EUV source, which central wavelength is 13.5 nm. And it works. A raw spectrum is acquired after simple operation. According to the zirconium (Zr) metal filter transmission curve, the spectrum is solved.The EUV spectrums are recorded at different laser pulse energy by charging the size of diaphragm. The intensity of the 13.5 nm spectral region is highly sensitive to the laser power density. As the laser power density decreases, the peak sharply drops. The peak may disappear when the laser power density is below 1.0×109W/cm2.