Monolayer-mediated deposition of tantalum(V) oxide thin film structures from solution precursors

Integration of oxide thin films with semiconductor substrates is a critical technology for a variety of microelectronic memory and circuit applications. Patterned oxide thin film devices are typically formed by uniform deposition followed by postdeposition ion-beam or chemical etching in a controlled environment. This paper reports details of an ambient atmosphere technique which allows selective deposition of dielectric oxide thin layers without postdeposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers of octadecyltrichlorosilane by microcontact printing (micro-CP). Sol-gel deposition of ceramic oxides on these functionalized substrates, followed by mild, nonabrasive polishing, yields high-quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micrometer-scale dielectric oxide devices have been fabricated by this process, with lateral resolutions as fine as 4 microm. In this paper, the authors describe the solution chemistry, evolution of microstructure, and electrical properties of Ta2O5 thin films, as well as the stress-related mechanism which enables selective de-adhesion and resultant patterning. Selectively deposited, 80--120 nm thick Ta2O5 thin film capacitors were crystallized on platinized silicon at 700--800 C, and had dielectric constants of 18--25 depending upon the processing conditions, with 1 V leakage current densities as low as 2 x 10-8 A/cm2. The ability to selectively deposit Ta2O5 and other electrical ceramics (such as LiNbO3 and PbTiO3) on a variety of technologically important substrate materials suggests broad potential for integrated circuit and hybrid microelectronics applications