AES and XPS Studies of the Chemical Effects at the Magneto-Optic/Dielectric Interface
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Mat. Res. Soc. Symp. Proc. Vol. 54. c 1986 Materials Research Society
548
AUGER/XPS STRUCTURE (rim) MATERIAL/THICKNESS 35 SiO2, SiO, Si3N,
TOP DIELECTRIC MAGNETIC LAYER BOTTOM DIELECTRIC Si SUBSTRATE
TbF Co
70
SiOZ, SiO, Si3N4
40
Figure 1: The structure and composition of samples in Auger/XPS used interface studies.
I
Auger and XPS have been used to investigate interface chemistry as well as chemical and elemental composition of the films. All XPS data were taken on a PHI 5400 ESCA system using a 600im aperture with an Al anode and a 4kV argon ion beam for sputtering. In order to maximize the chemical information available from Auger electron spectroscopy, all Auger data were taken in the N(E) mode. To minimize electron and ion beam induced degradation of the dielectric layer, all Auger data were taken using a 3kV excitation beam at .25pA with sputtering from a differentially pumped ion gun operated at lkV with xenon gas. RBS with a glancing angle geometry for higher depth resolution was also used to confirm interface abruptness. The procedure used for calculating the atomic concentration in the depth profiles shown in Fig. 4 consisted of dividing the E*N(E) data by E and then subtracting off the background using a log-log plot. The atomic concentration was then determined using the peak to background height and sensitivity factors obtained from elemental standards. RESULTS A detailed investigation of the changes in the magnetic and optical properties of magneto-optic quadrilayers containing various dielectric layers has been reported elsewhere [3]. A brief summary of the results relevant to our investigation will be given here. A plot of the coercivity vs. annealing time at 200 C for all three dielectrics is shown in Fig. 2. It is apparent from this graph that the coercivity is dependent upon the particular dielectric being deposited. This is surprising since the coercivity depends primarily on the composition of the RETM film. These differences in coercivities were removed by increasing the thickness of the RETM film from 17 nm to 70 nm, thereby mitigating the effects of the chemical interactions at the dielectric/RETM interface. Upon annealing the coercivities of films having an oxide dielectric diverge from the nitride case, eventually going through the compensation point at room temperature. This behavior is quite similar to that observed when one intentionally varies the Tb concentration within the RETM film [4]. This strongly suggests that during annealing the RETM film is being depleted of magnetically active Tb. To clarify the effect of oxygen within the RETM film, a set of quadrilayer structures was sputtered under various partial pressures of oxygen. Thicker films (c300nm) of the RETM alloy were also sputter-deposited on Si substrates under various partial pressures of oxygen to vary the oxygen content. Figure 3 shows the change in coercivity as a function of the oxygen concentration within the TbFeCo alloy as determined by Auger and RBS. Increasing the oxygen content of the RETM film causes t
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