Sol-Gel Thin Film Electronic Properties
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SOL-GEL THIN FILM ELECTRONIC PROPERTIES W. L. Warren, P. M. Lenahan, C. J. Brinker*, G. R. Shaffer, C. S. Ashley* and S. T. Reed*. The Pennsylvania State University, University Park, PA 16802 *Sandia National Laboratories, Albuquerque, NM 87185
ABSTRACT We have explored the effects of various processing parameters on the dielectric and electronic integrity of sol-gel derived silicate thin films and have identified several factors that strongly affect the thin film electronic properties. We find that sol-gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown Si0 2 film on Si. INTRODUCTION Silicon dioxide thin films are extensively used in microelectronic devices as the gate and field oxides in metal-oxide- semiconductor-field-effect-transistors (MOSFET's), passivation layers, diffusion and oxidation barriers, and scratch resistant coatings. Currently, thermally grown silicon dioxide films on silicon (typical growth temperatures range from 800 0C to 1100*C) are the best insulators and exhibit the lowest interface trap densities; they are the heart and soul of modem day microelectronic devices and are the standard by which other dielectrics are judged. In recent years; however, there has been a considerable amount of interest in the development of lower temperature/shorter time dielectric deposition schemes.[1-4] Some applications include III-V compound semiconductor MOSFET processing as well as primary dielectrics for thin film transistors. In this study we have explored the electronic and physical properties of sol-gelderived silicate thin films on silicon. We have investigated how various processing parameters affect the dielectric integrity of the silicate films on silicon and have identified several factors that affect the electronic properties of the silicate gel thin films. We find that (1) the water to silicon alkoxide ratio strongly affects both the film's electronic and physical properties; (2) the film's properties are relatively independent of the annealing ambient; and (3) a rather short (5 min.) anneal time at T>8000 C is necessary to obtain sufficient insulating properties. Our results illustrate that sol-gel thin films on silicon can be of high quality; they exhibit low interface trap densities and fairly good insulating properties, indicating that sol-gel oxides may be potentially useful to the microelectronics community.
Mat. Res. Soc. Symp. Proc. Vol. 180.
@1990
Materials Research Society
414
EXPERIMENTAL DETAILS The solutions used in this study were prepared using silicon alkoxides, Si(OC 2 H 5)4 , as molecular precursors to Si02 . In alcohol/water solutions the alkoxide is hydrolyzed and condensed to form Si-O-Si bonds as shown by the following net reaction. n Si(OC 2 H5 )4 + 2n H2 0 -4 n Si0 2 + 4n (C 2 H5 OH) Many factors influence the structure of the inorganic polymers. The most important are the water to alkoxide ratio, pH, and aging conditions [5-9] of the initial solut
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