An investigation of the electronic properties of aluminum-nitride MIS structures

Jeffrey Allen Shields, Purdue University

Abstract

Aluminum nitride films having (0002) orientation were deposited onto silicon substrates using reactive rf diode sputtering of an aluminum target with an argon:nitrogen plasma, resulting in $\rho$ = 4.6-7.6 $\times$ 10$\sp9$ ohm-cm, K$\sb{\rm N}$ = 9.3-12.3, and ${\cal E}\sb{\rm max}$ = 1.8-2.8 $\times$ 10$\sp6$ volts/cm. X-ray diffraction measurements indicated that the (0002) orientation grows more readily on SiO$\sb2$ and silicon than on aluminum, thought due to the presence of a thin Al$\sb2$O$\sb3$ layer at the AlN/Al interface. A pre-deposition sputter etch of the silicon substrate with an argon plasma produced AlN films having improved crystalline quality. However, severe radiation damage resulted at the AlN/Si interface. A 30 minute anneal at 500$\sp\circ$C in forming gas led to a partial removal of the radiation damage, with the anneal being more effective when the aluminum gates were present. A hydrogen-releasing mechanism similar to that of a standard Al/SiO$\sb2$/Si Post Metallization Anneal was indicated, with hydrogen diffusing along the polycrystalline grain boundaries. Under stationary state conditions, the injected charge in Al/AlN/SiO$\sb2$/Si structures establishes a dc virtual gate at or near the AlN/SiO$\sb2$ interface. The charge trapping and detrapping time constants are much shorter than those of comparable ZnO device structures, indicating that the charge storage process is not dominated by deep-level traps at the AlN/SiO$\sb2$ interface. Small signal admittance measurements made upon Al/AlN/SiO$\sb2$/Si and Al/AlN/Al structures indicated a general 1/$\omega$ dependency. In strong accumulation and inversion the data was independent of bias, indicating that the charge storage process is not dominated by shallow upper band-gap bulk traps. Based upon the data obtained from the Al/AlN/Al structures, it appeared that the small signal properties of these films were being dominated by the contacts. Current vs. Voltage measurements revealed that there are at least two distinct conduction mechanisms which dominate at different electric fields, thought to consist of an Ohmic mechanism at low fields, and a Schottky emission mechanism at high fields.

Degree

Ph.D.

Advisors

Pierret, Purdue University.

Subject Area

Electrical engineering

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