H. Pepin

Extreme-ultraviolet Mo/Si multilayer mirrors deposited by radio-frequency-magnetron sputtering.

Mo/Si multilayer mirrors with a high reflectance at normal incidence in the 130-135-Å spectral region have been deposited by rf magnetron sputtering. A new and quick technique was used to calibrate the deposition rates. Characterization by transmission electron microscopy (TEM) and grazing-incidence x-ray diffraction (XRD) indicated good thickness control of the deposition process and low interface roughness. However, the TEM and, indirectly, the XRD reflectance measurements, indicated that the interfaces are asymmetric. A brief review discussing the origin of the modulation of the Bragg peak intensities in the XRD reflectance is given. An analytical formula was derived for periodic multilayers that describes the effect of asymmetric interfaces on the amplitude of the Bragg peak modulation. Theoretically, in XRD reflectance measurements, any asymmetry in the interdiffusion of the Mo-Si interfaces results in a decrease of the usual amplitude modulation of the Bragg peaks. Extreme-ultraviolet (XUV) reflectance measurements were also made with synchrotron radiation on a new high-resolution reflectometer. The near-normal-incidence peak reflectances measured at λ = 134 Å were ~ 59% for the best multilayer mirrors. Good fits to both XRD and XUV reflectance measurements have been obtained with a model that allows for interface asymmetry.

Monochromatic x-ray imaging of a laser produced plasma

We show that high quality monochromatic x-ray images of an extended laser produced plasma can be obtained with a Johann spectrometer. Monochromatic x-ray shadowgraphy is also demonstrated with such a configuration. The versatility of this diagnostic is illustrated with measurements (spectroscopic and imaging) of some resonance transitions of neonlike copper.

keV x-ray emission produced by a sub-picosecond laser interacting with a controlled preformed plasma

The efficiency of the conversion from laser energy into aluminium K-shell line energy has been measured for different interaction regimes of a sub-picosecond laser pulse with controlled preformed plasmas. We compare the cases of thermal plasmas for which transient ionization effects are dominant to non-thermal plasmas in which both transient and non-Maxwellian effects are present. In a first experiment, a low-intensity green laser pulse (400 fs, ) is normally incident on a preformed plasma previously generated by a similar laser pulse. In a second experiment a high-intensity p-polarized green pulse (400 fs, ) is sent with a large incidence angle on the preformed plasma. We have observed in these experiments that the conversion efficiency (He- or Li-like lines from aluminium) scales as , where is the duration of the x-ray emission measured at the full width half maximum, and that this scaling was not affected by non-Maxwellian effects.

Study And Application Of Soft X-Ray Emission From Laser-Produced Plasmas

Laser created X-ray sources have been investigated both theoretically and experimentally using X = 1.06 pi and X = 0.26 wm and short pulses (T = 0.5 nsec). We also report the first detailed X-ray measurements using a low energy commercially available KrF laser (τ = 25 nsec). The conversion efficiency is given for various target atomic numbers and a large range of laser intensities. Finally, we introduce lithographic considerations and examine the laser requirements for an X-ray lithography source acceptable for industrial applications.

Microlithography Using A Laser Plasma Created X-Ray Source

Laser produced plasmas are investigated both theoretically and experimentally with respect to their suitability as X-ray lithography sources. We find that a minimum of 100 W average laser power is required for an acceptable wafer throughput (36 6 in. wafer/h). In addition, the optimization of the X-ray conversion efficiency in the keV range (0.75-2 keV) necessitates a laser intensity greater than 1 x 1013 W cm-2 and a judicious choice of target atomic number. We also describe a simulation program called XLIMLAS which can be used, for instance, to determine the laser conditions which maximize the energy deposited in the resist by matching the X-ray spectrum to the wavelength dependent mask substrate transmission and to the resist absorption. Moreover, this optimisation must ensure a high quality of the resist line edge profiles. Finally, we present some experimental results on sensitivity and patternability of FBM120 resist.

Picosecond time resolved spectroscopy of a controlled preformed plasma heated by an intense sub‐ps laser pulse

The time history of the Al Li‐like spectrum has been measured on the picosecond time scale in different regimes of interaction of a sub‐ps laser pulse with controlled preformed plasmas. The a‐d/k,j line intensity ratio is constant as a function of time, with a value close to the LTE value, for solid density plasmas obtained by radiation pressure confinement. For the cases of an interaction with a longer density gradient scale length the core excited lines are strongly enhanced by transient effects in thermal plasmas and by both transient and non‐Maxwellian effects in non‐thermal plasmas.

Ultrafast laser-based thermal X-ray sources

Abstract The effects of hot electrons on the thermal radiative properties (brightness, duration and spectral shape) and dynamics of solid density plasmas, generated during the interaction of a femtosecond laser and a solid target, are assessed. Line and broadband thermal emissions with duration between 500 fs and 700 fs, have been successfully produced with peak power between 1 and 10 MW, when the fraction of laser energy in the hot electron population was less than 2%, and when the hot electron energy density at the target surface was less than 1 KJ / cm 2 .