Metalorganic Deposition of Oxide Films

Debra L. Kaiser and Joseph J. Ritter

Metalorganic deposition by spin coating is a relatively simple, low-cost approach for fabricating thin films. This technique has been used to deposit barium strontium titanate (BST) and zirconium oxide (ZrO₂) films on Si (100) substrates. These films are being used to study crystallization, interfacial reactions, compositional homogeneity and electrical behavior.

For BST, the liquid coating solution was composed of a barium strontium titanium actetate lactate (BSTAL) solution, glacial acetic acid (GAA), isopropanol (ISP), and either ethylene glycol methyl ether (EGME) or propylene glycol methyl ether (PGME). Processing variables were the composition of the coating solution (precursor:solvent ratio), the acceleration rate, and the spin rate. After spinning, the liquid coating was heated to temperatures in the range 90 °C to 580 °C in air to dry and pyrolyze the films.

For ZrO₂, the coating solution was a mixture of zirconium acetate, GAA, ISP, and PGME. Processing variables and heat treatment conditions were the same as for the BST films.

Films with thicknesses down to 2.5 nm as measured by x-ray reflectivity and high resolution transmission electron microscopy (HRTEM) have been fabricated. Figure 1 shows a HRTEM image of a 4.2 nm ZrO₂ film on a Si (100) substrate, with an interfacial SiO_x layer.

Fig. 1. HRTEM image of a spin-coated ZrO₂ film

Figure 2 shows an atomic force microscopy (AFM) image of a 10 nm thick BST film with an RMS surface roughness of less than 1 nm.

Fig. 2. AFM image of a spin-coated BST film