Amorphous Mixed TiO 2 and SiO 2 Films on Si(100) by Chemical Vapor Deposition
- PDF / 51,434 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 57 Downloads / 215 Views
Amorphous Mixed TiO2 and SiO2 Films on Si(100) by Chemical Vapor Deposition Ryan C. Smith a, Charles J. Taylor a, Jeffrey Roberts a, Noel Hoilienb, Stephen A. Campbell b, and Wayne L. Gladfelter a,* a Departments of Chemistry and b Computer and Electrical Engineering, University of Minnesota, Minneapolis, MN 55455. ABSTRACT Amorphous thin films of composition TixSi1-xO2 have been grown by low pressure chemical vapor deposition on silicon (100) substrates using Si(O-Et)4 and either Ti(O-iPr)4 or anhydrous Ti(NO3)4 as the sources of SiO2 and TiO2, respectively. The substrate temperature was varied between 300 and 535ºC, and the precursor flow rates ranged from 5 to 100 sccm. Under these conditions growth rates ranging from 0.6 to 90.0 nm/min were observed. Asdeposited films were amorphous to X-rays and SEM micrographs showed smooth, featureless film surfaces. Cross-sectional TEM showed no compositional inhomogeneity. RBS revealed that x (from the formula TixSi1-xO2) was dependent upon the choice of TiO2 precursor. For films grown using TTIP-TEOS x could be varied by systematic variation of the deposition conditions. For the case of TN-TEOS x remained close to 0.5 under all conditions studied. One explanation is the existence of a specific chemical reaction between TN and TEOS prior to film deposition. TEOS was mixed with a CCl4 solution of TN at room temperature to produce an amorphous white powder (Ti/Si = 1.09) and 1HNMR of the CCl4 solution indicated resonances attributable to ethyl nitrate. INTRODUCTION As the thickness of the gate oxide in field effect transistors approaches 2 nm, direct tunneling will lead to unacceptable leakage currents making it necessary to replace the silicon dioxide layer with a material possessing a higher dielectric constant. In our investigations into the chemical vapor deposition of TiO2 (κ = 19-30) polycrystalline films were produced.[1-3] For the thin films necessary in microelectronics, surface roughness and grain boundaries resulting from polycrystalline films can have an undesirable effect on properties such as the dielectric breakdown and leakage current. The high κ material can be made amorphous, thus eliminating grain boundaries, by combining it with a low κ, glass forming oxide such as SiO2. Titanium silicon oxide films have been produced by sol-gel,[4, 5] flame hydrolysis,[6, 7] and plasma enhanced CVD[8, 9] for optical applications and some reports of their electrical properties have also appeared.[8, 10] In this paper we describe the deposition of titanium silicon oxide films onto Si(100) by the simultaneous chemical vapor deposition of TiO2 and SiO2 and note the dramatic effect that the precursor structure plays in determining the film composition. EXPERIMENTAL DETAILS Tetraethylorthosilicate (TEOS) was used as the source of silicon dioxide while titanium tetraisopropoxide (TTIP) or anhydrous titanium tetranitrate (TN) was used to deposit the TiO2 component. Precursors were purchased from Aldrich, and TEOS and TTIP were distilled under vacuum prior to use. All precursors w
