Process optimization and interface cotrol in chemical vapor deposition of high dielectric constant thin films

Abstract

As metal-oxide semiconductor (MOS) devices continue to scale downward, conventional SiO2 MOS gate dielectrics are reaching their physical limits because SiO2 films of and < 30 A have high direct tunneling current. Thus a thicker film of high-k dielectric materials is needed to reduce the associated problems of excessive leakage current while keeping the same equivalent thickness. In another application, the use of high-k dielectrics is considered as one of the best alternatives to conventional dielectrics in DRAM capacitors. In this respect, considerable investigations have recently been made on high-k dielectric materials including Ta2O5, TiO2, and (Ba,Sr)TiO3(BST). This paper reports our recent studies in MOCVD growth of TiO2 and BST thin films, focusing on interface control of the dielectric thin films, precursor chemistry, and process optimization. For interface control of TiO2 films on Si(100), a buffer layer was first deposited to prevent interfacial carbon contamination during low temperature film growth. Growth of BST thin films was studied using surface science techniques in conjunction with a MOCVD study. A molecular-level approach using surface science techniques probed individual precursor reaction pathways and ligand substitution. Several mechanistic questions have been addressed using isotopic labeling experiments both in a surface science apparatus and undermore » real MOCVD processing conditions. In addition, we have found that the dielectric properties and the step coverage of BST films are strongly affected by the precursor properties.« less