Tantalum Oxide and Niobium Oxide thin Films Grown by Pulsed Laser Deposition
- PDF / 331,906 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 71 Downloads / 282 Views
ABSTRACT Amorphous tantalum pentoxide (Ta 20 5 ) and niobium pentoxide (Nb 20 5 ) thin films were grown from both metal and oxide target by reactive pulsed laser deposition. Film structure and composition were studied as a function of substrate temperature and oxygen pressure. Good quality transparent films were obtained for substrate temperatures greater than 1400 C, and 02 pressures of 200 mTorr. Lower temperatures and pressures produced opaque films, associated with lower oxides. INTRODUCTION Tantalum oxide (Ta 2O 5) and niobium oxide (Nb20 5 ) thin films are of technological interest due to the high values of their dielectric constant and dielectric strength,1 which make them useful as dielectrics in capacitor structures for integrated circuits. These pentoxides are transparent up to the near UV, and have refractive indices n = 2 or greater in the visible,2' 3 which make them interesting for optical devices. In addition, these 46 pentoxides, or glasses containing them, have potential as nonlinear optical materials. Previous PVD growth of these materials has been mainly accomplished by reactive sputtering. There is also much recent work on CVD growth of tantalum oxide. Pulsed Laser Deposition (PLD) of tantalum pentoxide was initially explored by Sankur and Gunning. Recently, Nishimura et al. studied the growth by reactive PLD of this material in more detail. 8 These workers used a Ta 20, target and 02 pressures during growth from 15 to 100 mTorr, and reported good quality amorphous Ta oxide films. In this work we have attepted to extend the study of reactive PLD growth of tantalum oxide to include the possibility of growth directly from metal targets, and have explored the growth, under similar conditions, of niobium oxide. While it can be expected that PLD growth of the later material will proceed similarly to that of Ta oxide, this had not, to the best of our knowledge, been verified before. EXPERIMENT Pulsed Laser Deposition System The stainless steel chamber used for this work is evacuated by a 60 I/s turbomolecular pump. Pressures are measured with a Pirani gauge and an ionization gauge with a Bayard-Alpert tube. Substrates are heated by means of a PID-controlled substrate heater. A mass flow controller regulates gas admission for reactive PLD growth. A valve separating the TMP from the chamber permits pumping to be throttled, which allows for stable independent pressure control at a range of gas flow rates. The laser source is a Nd:YAG laser (Quantel 58 1c) with maximum repetition rate of 10 pulses per second. Beam incidence on the target is -45'. Targets are rotated in order to avoid crater formation. 205 Mat. Res. Soc. Symp. Proc. Vol. 397 01995 Materials Research Society
Sample Preparation Samples prepared for this work were grown on Si (100) wafers, float glass, and fused quartz substrates. One sample was grown on a pyrolythic graphite substrate for Rutherford Backscattering Spectrometry analysis. Except for the latter, substrates were cleaned in ultrasonic baths of trichloroethylene, acetone, and me
Data Loading...
