Excimer Laser Etching of Cupric Oxide
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EXCIMER LASER ETCHING OF CUPRIC OXIDE G.N.A. van Veen, W. Vrijmoeth*, T.S. Baller and J. Dieleman The NetherPhilips Research Laboratories, 5600 JA Eindhoven, lands *State University of Utrecht, Dept. of Experimental Physics, P.B. 80.000, 3508 TA Utrecht, The Netherlands. ABSTRACT Polycrystalline CuO samples are irradiated in UHV by excimer laser pulses at 308nm. Mass spectrometry combined with time-of-flight measurements is used to determine the composition of the desorbing particles and the desorption mechanisms. Additional information is provided by Scanning-Electron-Microscopy of the etched surfaces. At fluences below 1.8 J cm- 2 the products Cu, 0 and 02 are desorbed by a purely thermal mechanism at temperatures up to 6000 K and a copper rich surface mask is formed. At higher power densities an additional ablative contribution is monitored which increases with power density, and much less surface area is covered by a Cu-rich mask. INTRODUCTION In the continuous search for new processing techniques to fulfill the ever increasing demands posed by, in particular, the microelectronics industry, the research on laser and laserchemical etching has been initiated[l]. In this context also the etching behaviour of Cu and its binary compounds has recently attracted attention. Thus far studies have focused on laserchemical etching of Cu exposed to a C12 flux in (U)HV[2-4] and on laser etching of CuCl[5]. Mass spectroscopy combined with time-of-flight studies on the desorbed products have revealed that, depending on the choice of values of experimental parameters and of the solid studied, the etching mechanism may vary from purely thermal to thermal with an increasing nonthermal contribution at higher energies (e.g. ablation). The present paper reports the results of similar studies on the laser etching in UHV of an other binary copper compound, viz. CuO. EXPERIMENTAL An extended description of the set-up and the experimental methods used in the experiments has been given previously [3], therefore only the essentials, er quadrupole mass needed to interprete the present spectrometer investigations, will be treated. differential CuO, L / A disc of polycristalline pump unit 225.7 pressed from CuO powder under 4 kbar, with a surface roughness target interaction of typically 5lgm is situated in chamber the centre of an UHV interaction chamber with a base pressure iii the 10-8 Pa range (figure 1). This target is irradiated by 28 Fig 1. Experimental set-up
Mat. Res. Soc. Symp. Proc. Vol. 100. 91988 Materials Research Society
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nsec.(FWHM) excimer laser pulses at 308 nm along the surface normal with a repetition rate of 4 Hz. Neutral particles ejected from the CuO target at an angle of 22.5" to the incident laser beam are ionized by electron impact after having travelled over a fixed flight path of 276 mm. The resulting ions are extracted from the ionisation chamber, mass selected by a quadrupole mass spectrometer (MS) and detected by a particle counter. With this equipment it is possible to measure the time-of-flight (TOF)
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