Dept. of Materials Science and Engineering
Oregon Graduate Institute of Science & Technology
Metals deposited directly on thin gate oxide to test the quality of the oxide must be stable. This research tests the stability of metals for possible use in gate oxide monitor current flow tests (GOM) or as a gate electrode in sub-micron MOSFETs. Arrays of metallization disks with 5mm and 0.8mm diameters of Al-1wt%Si, Al-.5wt%Cu, Ti and Cr were magnetron sputter deposited directly on 7nm of thermally grown SiO [subscript 2] on (100) Si wafers and then heat treated at 40Â°C in N [subscript 2] to determine the effect of heat treatment on break-down voltage (BVG) for the MOS thin film devices. Al-1wt%Si and Al-.5wt%Cu were also deposited on poly-Si electrodes. BVG measurements were performed on as deposited and heat treated patterned wafers. Analytical electron microscopy was performed on transverse cross-sections and planar sections of the devices to correlate good and bad BVG performance with microstructural changes that occurred during heat treatment. A mechanism of oxide breakdown was proposed based on observed changes in microstructures and chemistries of the thin films. Metallizations that maintained a high BVG, Cr and Al-.5wt%Cu, were given extended heat treatments to test stability and to characterize their diffusion barriers, nanometer scale layers of Cr[subscript 2]O[subscript 3] and Al[subscript 2]Cu respectively, which limited diffusion of the substrate Si into the electrode. Al-1wt%Si, the electrode with the lowest as deposited BVG, was given an extended heat treatment to characterize the mechanisms of change in the metallization, silicon dioxide and Si which lead to SiO [subscript 2] breakdown. Structural changes in the oxide were detected with electron diffraction patterns following heat treatment. Nearest neighbor distances were reduced and nano-crystalline quartz appeared in the originally completely amorphous silica heat treated with an Al-1wt%Si electrode. The mechanisms of reduction of the BVG for oxides during heat treatment with a metallization is structural damage to the amorphous silica caused by the diffusion of Si from the substrate through the oxide into the electrode, the diffusion of metal into the oxide and reduction of oxide thickness by reaction with the metallization. The Al-1wt%Si as deposited directly on SiO[subscript 2] and heat treated, had the lowest BVG's and had sustained the greatest number of atomic displacements which resulted in quartz crystallites forming within the vitreous silica.
McCarthy, John M., "The microstructural effects of metallization and heat treatment on thin gate oxide for use in sub-micron MOSFETs" (1996). Scholar Archive. 12.