Analysis of tunneling magnetoresistance test structures by low energy electron nanoscale-luminescence spectroscopy

The performance of state-of-the-art tunneling magnetoresistive (TMR) heads depends on the thickness of insulating layers less than a few nanometers th ick that separate two magnetic films. We have used low energy electron nano scale-luminescence (LEEN) spectroscopy to observe optical emission from TMR test structures with buried insulating oxides less than a few nanometers t hick. TMR structures grown by metal evaporation consisted of a 0.8-3 nm Al oxide layer on a 2.4 nm CoFe alloy (84: 16) on a multilayer metal-on-Si sub strate, all capped with a 0.4 nm CoFe with Pt overlayer. LEEN studies with excitation energies ranging from 0.5 to 3 keV enabled emissions from the bu ried oxide layers versus the free surface to be distinguished. We used diff erent compositions, thicknesses, and oxidation exposures to separate At oxi de from transition metal oxide emissions, as well as from the ambient-expos ed Pt surface. A broad peak centered at 2.2-2.5 eV increased with O plasma exposure to At films on the CoFe alloy. Emission from oxidized CoFe without At consists of a broad emission centered at 2.5 eV. Common to all these sp ectra is emission at 1.8 eV, which energy-dependent LEEN demonstrates is du e to the ambient-exposed Pt. Spectral changes versus oxygen exposure reveal the regime separating oxidation of the magnetic and nonmagnetic layers. (C ) 2001 American Vacuum Society.