Ta 2 O 5 is a candidate for use in metal-oxide-metal ͑MOM͒ capacitors in several areas of silicon device technology. Understanding and controlling leakage current is critical for successful implementation of this material. We have studied thermal and photoconductive charge transport processes in Ta 2 O 5 MOM capacitors fabricated by anodization, reactive sputtering, and chemical vapor deposition. We find that the results from each of these three methods are similar if one compares films that have the same thickness and electrodes. Two types of leakage current are identified: ͑a͒ a transient current that charges the bulk states of the films and ͑b͒ a steady state activated process involving electron transport via a defect band. The transient process involves either tunneling conductivity into states near the Fermi energy or ion motion. The steady state process, seen most commonly in films Ͻ300 Å thick, is dominated by a large number of defects, ϳ10 19-10 20 cm Ϫ3 , located near the metal-oxide interfaces. The interior of thick Ta 2 O 5 films has a substantially reduced number of defects. Modest heating ͑300-400°C͒ of Ta 2 O 5 in contact with a reactive metal electrode such as Al, Ti, or Ta results in interfacial reactions and the diffusion of defects across the thickness of the film. These experiments show that successful integration of Ta 2 O 5 into semiconductor processing requires a better understanding of the impact of defects on the electrical characteristics and a better control of the metal-Ta 2 O 5 interface.

The scanning photoacoustic microscope (SPAM) is used in both the conventional and phase-contrast modes to detect a well-characterized subsurface flaw in Al. The physical mechanism is that of thermal diffusion, with a subsurface probe depth and flaw resolution length of approximately one thermal-diffusion length. Comparison of the dependences of the photoacoustic signal upon chopping frequency from the different regions of the sample confirm that the differential signal from the flaw corresponds to a transition from thermally thick to thermally thin boundary conditions. Experimental results are in good agreement with calculations based upon a three-dimensional thermal-diffusion model.

A low temperature oxygen/nitrogen plasma process is reported that substantially reduces leakage currents in chemical vapor deposited (CVD) and physical vapor deposited (PVD) films of tantalum oxide. We show that a combination of nitrogen and oxygen in a remote downstream microwave plasma source reduces leakage currents in CVD films of tantalum oxide and also reduces trap densities as measured by charge pumping. The as deposited CVD films show a high level of photoluminescence that is substantially lowered by the plasma anneal due to a reduction in the density of midgap states. For films deposited by PVD in the thickness range of 100 nm we find low leakage currents with a substantial improvement from the introduction of nitrogen into the plasma. However, PVD films in the thickness range of 20 nm show larger relative leakage currents and less of an improvement from the addition of nitrogen. The role of nitrogen in lowering leakage currents and charge trapping is thought to occur from a reduction in the density of bulk trap states in the oxide due to partial incorporation of nitrogen in the oxide. Both of these low temperature deposition and annealing processes are compatible with integration into the upper levels of metallization for high density circuits.

Si/SiO2 Fabry–Pérot microcavities with rare-earth-doped SiO2 active regions are realized for the first time. Cavity-quality factors exceeding Q=300 are achieved with structures consisting of two Si/SiO2 distributed Bragg reflectors and an Er-implanted (λ/2) SiO2 active region. The room-temperature photoluminescence intensity of the on-axis emission is 1–2 orders of magnitude higher for resonant cavity structures as compared to structures without a cavity.

No abstract