Homogeneous Al-Ti and Al-Ti-Si Thin Alloy Films
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Al-Ti-Si alloy films
are subject to intensive studies following Fischers report [3] on the excellent E/M behavior : see for instance Reference 4-6. EXPERIMENTAL Both e-beam evaporation and magnetron sputtering were used for the preparation of the alloy films. The Ti concentration of the magnetron sputtered films ranged up to 0.8 wt.%, whereas a second series of films contained 1 wt.% Si as well. The Ti concentration of the e-beam vapor deposited films was in the range 0-10 wt.%. (All alloy compositions mentioned further are in weight percent). The films were deposited onto thermally oxidized (25nm) silicon wafers to two different thicknesses of 0.5 and 1.0 pm. The magnetron sputter chamber was evacuated to a pressure of I0- 5 Pa and then back-filled with Ar to a pressure of 10-1 Pa. Homogeneous Al alloy targets were used to deposit the binary and ternary alloy films at a rate of 0.5 nm/s. Vapor deposition was performed in a high vacuum chamber with a background pressure of 10-6 Pa. The vapor flux of each element was monitored with quartz crystal oscillators0 to maintain a total deposition rate of 2 nm/s. Films were annealed at 450 C in a flowing 90%N2 /1OH 2 ambient for 35 minutes. Characterization of the films was performed with a variety of techniques, such as transmission electron microscopy (TEM), p measurements, E/M lifetime tests, X-ray diffraction, secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and surface profiling. A more detailed description of the experimental procedures can be found in Ref. 6.
Mat. Res. Soc, Symp. Proc. Vol. 54. 1986 Materials Research Society
182
RESULTS In this paragraph our results are arranged in four major sections (iii) electromigration, microstructure, electrical resistivity, (ii) chemical analysis and surface condition.
(i) (iv)
Electrical resistivity (0) The simultaneous deposition of two or more metals on substrates at room temperature usually results in the formation of metastable alloy films. These
films are highly supersaturated solid solutions and show an excess of lattice defects. They either consist of small crystallites, or are amorphous. Fig. 1 shows the p(x) relationship, where x is the weight percentage of Ti for magnetron sputtered Al-rich (Al+1%Si)-Ti alloy films. The electrical resistivity
Sas dep.
as deposited
dep>
T 1.50*c
66
2
2 -01
o
Al
0o.
Wt%Ti
08
12
--
FIG.1. f as a function of x for magnetron sputtered (Al+1%Si)-Ti alloy films.
0
1 t (mi n)
10
100
FIG.2. Typical p of magnetron sputtered Al+0.BTi+1%Si alloy films 0 after annealing at 450 C for various times, t.
increases dramatically with increasing concentration of Ti. This may be due to both the difference of scattering behavior between Al and Ti atoms, and Ian excess of lattice defects in the alloy films. The transition to an equilibrium two-phase alloy structure upon annealing is accompanied by a precipitous drop in p. For alloy films within the (AI+TiAI 3 ) phase region, the p values lie on a straight line. The intersection of both lines indicate
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