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Development and studies of plasma EUV sources for lithography
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Type
Thesis
Author
Syed Murtaza Hassan
Supervisor
Lee, Paul Choon Keat
Abstract
Extreme-ultraviolet (EUV) lithography is the next generation lithographic techniques under development for the fabrication of semiconductor feature sizes smaller than 32 nm. The generation of EUV needs a hot-dense plasma source at wavelength of 13.5 nm, which can be created either by a discharge produced plasma (DPP) or a laser produced plasma (LPP). This study concentrates on low current (< 80 kA) DPP sources, i.e. miniature plasma focus as a gas discharge, X-pinch as a vacuum discharge and also, laser generated plasma at intensity of ~ 1011 W/cm2 as a LPP source.
For the case of the miniature plasma focus (MPF), the variation in EUV yield at different filling gas pressures indicates that the plasma dynamics play an important role in the compression of plasma to reach a necessary temperature of about 20 eV for the EUV emission. The EUV radiation increases significantly at discharge currents beyond 25 kA. Due to the complex nature and extreme conditions produced in the plasma based EUV sources, several diagnostic tools are developed. These include the current probe, high voltage capacitive probe, EUV and x-ray detectors to obtain not only the electrical signals but to show the evidences of pinching in DPP devices. Different EUV emitting zones are found and correlated with the discharge parameters by employing several optical imaging systems based on the time integrated photography, gated photography, laser-probing, a streak camera and EUV pinhole imaging. The increase of 60-80% in EUV yields by using the solid anode can be attributed to the electrons bombardment on the solid metal part and the uniform compression in the absence of hole in anode. In the region of 3-4 mbar gas (hydrogen) pressure in a tin-insert case, the plasma pinch diameter in the EUV band is recorded of about 3.5 mm full-width (FW 1/e2) and 1.15 mm full-width at half maximum (FWHM). The length of plasma pinch is determined as 2.9 mm (FW 1/e2).
In the X-pinch experiment, a high EUV and enhanced x-ray radiation yields (10%-30%) have been attributed to the formation of high-density plasma at the peak of the current for a wire material with a thickness less than 10 µm. The highest intensity EUV radiation is achieved by using the phosphor bronze wires (an alloy composed of 6% Sn and 94% Cu) due to the presence of tin (Sn) atoms. The measured source size is approximately 0.9 mm × 1.1 mm (FWHM), which is much smaller than the other typical pinch plasma devices and comparable with the LPP source. Due to the highly directed plasma jets towards the electrodes in the pinch device, the debris is the least in the direction perpendicular to the mid-plane of an X-pinch, i.e. the main collection region for the EUV radiation. Encouraging results have been achieved in various configurations of the X-pinch loads in an effort to generate EUV radiation without the elongated jets formation and the production of x-rays.
For the LPP source, the utilization of dual nanosecond laser pulses enhances the EUV conversion efficiency at 13.5 nm in 2 sr by 10% its value for a single laser pulse. The highest conversion efficiency is achieved in case of the laser produced plasma. However, it is found that the discharge produced plasma is the most efficient means of producing high-energy-density radiation system. To find the optimal parameters for the EUV emission under complicated conditions, 2D magnetohydrodynamics (MHD) code has been developed for the DPP sources.
For the case of the miniature plasma focus (MPF), the variation in EUV yield at different filling gas pressures indicates that the plasma dynamics play an important role in the compression of plasma to reach a necessary temperature of about 20 eV for the EUV emission. The EUV radiation increases significantly at discharge currents beyond 25 kA. Due to the complex nature and extreme conditions produced in the plasma based EUV sources, several diagnostic tools are developed. These include the current probe, high voltage capacitive probe, EUV and x-ray detectors to obtain not only the electrical signals but to show the evidences of pinching in DPP devices. Different EUV emitting zones are found and correlated with the discharge parameters by employing several optical imaging systems based on the time integrated photography, gated photography, laser-probing, a streak camera and EUV pinhole imaging. The increase of 60-80% in EUV yields by using the solid anode can be attributed to the electrons bombardment on the solid metal part and the uniform compression in the absence of hole in anode. In the region of 3-4 mbar gas (hydrogen) pressure in a tin-insert case, the plasma pinch diameter in the EUV band is recorded of about 3.5 mm full-width (FW 1/e2) and 1.15 mm full-width at half maximum (FWHM). The length of plasma pinch is determined as 2.9 mm (FW 1/e2).
In the X-pinch experiment, a high EUV and enhanced x-ray radiation yields (10%-30%) have been attributed to the formation of high-density plasma at the peak of the current for a wire material with a thickness less than 10 µm. The highest intensity EUV radiation is achieved by using the phosphor bronze wires (an alloy composed of 6% Sn and 94% Cu) due to the presence of tin (Sn) atoms. The measured source size is approximately 0.9 mm × 1.1 mm (FWHM), which is much smaller than the other typical pinch plasma devices and comparable with the LPP source. Due to the highly directed plasma jets towards the electrodes in the pinch device, the debris is the least in the direction perpendicular to the mid-plane of an X-pinch, i.e. the main collection region for the EUV radiation. Encouraging results have been achieved in various configurations of the X-pinch loads in an effort to generate EUV radiation without the elongated jets formation and the production of x-rays.
For the LPP source, the utilization of dual nanosecond laser pulses enhances the EUV conversion efficiency at 13.5 nm in 2 sr by 10% its value for a single laser pulse. The highest conversion efficiency is achieved in case of the laser produced plasma. However, it is found that the discharge produced plasma is the most efficient means of producing high-energy-density radiation system. To find the optimal parameters for the EUV emission under complicated conditions, 2D magnetohydrodynamics (MHD) code has been developed for the DPP sources.
Date Issued
2010
Call Number
TK7872.M3 Sye
Date Submitted
2010