Research On Characteristics Of Laser Induced Discharge Plasma And Its Extreme Ultraviolet Radiation

In semiconductor manufacturing industry,the exploitation of short wavelength extreme ultraviolet（EUV）radiation in the exposure process results in a dramatic decrease of the critical size of the printed elements in integrated circuit,laser produced plasma extreme ultraviolet source has been put into high volume manufacturing of integrated circuit,while laser induced discharge plasma（LDP）is found to have low cost and simple structure,which is more suitable in mask inspection,spectral metrology and other fields.Laser induced discharge plasma is a kind of technology which uses pulsed laser to trigger discharge between electrodes in vacuum to produce plasma and extreme ultraviolet radiatation.（1）The Sn-LDP souces are simulated.A collision radiation model based on atomic code is applied to calculate the distributions of ionized and excited states,the EUV spectra of 13.5 nm at different temperatures and densities are calculated.A radiational magneto-hydrodynamic program is used to analyze the expansion characteristics of plasma and the radiation characteristics of EUV in the process of laser-induced discharge.The plasma expansion and EUV radiation characteristics of tin target in different discharge conditions are compared.（2）A laser induced discharge produced plasma experimental device was built up.The voltage and current signals were recorded to analyse the voltage-ampere characteristics of laser-induced solid or liquid tin target discharge.The equivalent resistance and inductance of the whole discharge circuit,the laser and discharge delay were analyzed.The EUV emission was detected in different voltage and current rising rate with liquid/solid tin target in LDP.（3）The discharge plasma plume expansion was studied in plasma imaging method.ICCD camera was used to capture the plume of laser induced liquid/solid tin discharge producd plasma.The effects of different laser and discharge parameters on the formation time and position of pinch were compared.The difference of physical mechanism between Z-pinch and micro-pinch was emphasized.（4）The plasma characteristics were investigated by optical emsission spectroscopy.The time-resolved visible spectra of tin were obtained.The temperature and density of the plasma under different laser and discharge parameters were calculated by Boltzmann plot method and Stark broadening method.The EUV spectra of laser induced discharge tin plasma under different laser and discharge parameters were also measured by a grazing incidence flat field grating spectrometer,the EUV conversion efficiency was estimated.The spectral intensity and stability of liquid target and solid target were compared.The radiation characteristics of laser-induced gadolinium discharge plasma at 6.7 nm make it one of the important technical means to realize the next generation of beyond-extreme ultraviolet（BEUV）source.Finally,the radiation characteristics of laser-induced gadolinium（Gd）target discharge plasma source were studied using the EUV spectrometer.In the experiment,the discharge plasma was induced by the Nd:YAG and CO₂laser.The structures of BEUV spectra under different voltages were investigated and compared with the simulation results to estimate the electron temperature and density.