Properties of epitaxial SrTiO3 thin films grown on silicon by molecular beam epitaxy

Single crystalline perovskite oxides such as SrTiO3 (STO) are highly desirable for future generation ULSI applications. Over the past three decades, development of crystalline oxides on silicon has been a great technological challenge as an amorphous silicon oxide layer forms readily on the Si surface when exposed to oxygen preventing the intended oxide heteroepitaxy on Si substrate. Recently, we have successfully grown epitaxial STO thin films on Si(001) surface by using molecular beam epitaxy (MBE) method. Properties of the STO films on Si have been characterized using a variety of techniques including in-situ reflection high energy electron diffraction (RHEED), ex-situ X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). The STO films grown on Si(001) substrate show bright and streaky RHEED patterns indicating coherent two-dimensional epitaxial oxide film growth with its unit cell rotated 45 degrees with respect to the underlying Si unit cell. RHEED and XRD data confirm the single crystalline nature and (001) orientation of the STO films. An X-ray pole figure indicates the in-plane orientation relationship as STO[100]//Si[110] and STO(001)//NSi(001). The STO surface is atomically smooth with AFM rms roughness of 1.2 Angstrom. The leakage current density is measured to be in the low 10(-9) A/cm(2) range at 1 V, after a brief post-growth anneal in O-2. An interface state density D-it = 4.6 x 10(11) eV(-1) cm(-2) is inferred from the high-frequency and quasi-static C-V characteristics. The effective oxide thickness for a 200 Angstrom STO him is around 30 Angstrom and is not sensitive to post-growth anneal in O-2 at 500-700 degrees C. These STO films are also robust against forming gas anneal. Finally, STO MOSFET structures have been fabricated and tested. An extrinsic carrier mobility value of 66 cm(2) V-1 s(-1) is obtained for an STO PMOS device with a 2 mu m effective gate length.