Victor Joseph Silvestri

Some properties of chemically vapor deposited films of AlxOyNz on silicon

Transmission electron microscopy (TEM) studies of films prepared in the AlN-Al2O3 pseudobinary system by chemical vapor deposition (as described in a companion paper entitled, “Chemical Vapor Deposition of AlxOyNz Films”) indicates that four different phases can be obtained by altering the NH3/CO2 gas ratio and preparation temperature. Films prepared at 900°C yield three polycrystalline phases and an amorphous composition. From zero to 25 at. percent O an AlN phase is observed. Amorphous material is observed from 25 to 47 at. percent O. From 47 to 59 at. percent O an AlxOyNz spinel is observed. At 60 at. percent O (pure Al2O3) an alumina phase is observed (KI phase). For 770°C films the AlN phase is observed from zero to 8 at. percent 0; from 8 to 23 at. percent O the zeta-alumina phase is seen; and at 60 at. percent O the KI alumina phase is again observed. For both the 770 and 900°C films, the grain size of the AlN phase was found to decrease with increasing oxygen content.Direct current-voltage, dielectric breakdown and capacitance-voltage measurements were performed on the 900 and 770°C films with a variety of film compositions. For pure AlN and Al2O3, current-voltage and dielectric breakdown measurements correlate with the grain size observed by TEM. A maximum in breakdown field was observed for 900°C films at the composition which yielded minimum grain size of the AlN phase. A similar maximum is observed for the zeta-Al2O3 phase of the 770°C films. Positive flatband voltages and hysteresis of the capacitance-voltage trace was observed for most samples. Dielectric constants greater than 8 have been observed for some compositions.Several compositions appear to be attractive candidates for charge storage layers in MIOS devices.

Chemical vapor deposition of AlxOyNz films

A chemical vapor deposition process for depositing dielectric films of aluminum oxynitride is described. AlCl3, CO2 and NH3 were employed as the reactive gases in a nitrogen carrier. Films were grown from the mixed gases at 770 and 900°C in a resistively heated fused silica enclosure. The composition of the films could be varied over the entire range of the pseudobinary AlN-Al2O3 system by controlling the NH3/CO2 gas ratio with an appropriate flow of gaseous AlCl3. Growth rate and index of refraction for the films were obtained using ellipsometric techniques. The film compositions reported were determined by electron microprobe analysis. Film structure, evaluated using transmission electron microscopy, and the electrical properties of the dielectric films have been correlated and are discussed separately in a companion paper entitled, “Some Properties of CVD Films of AlxOyNz on Silicon”.