Device Quality SiO₂ Films by Liquid Phase Deposition (LPD) AT 48°C

Abstract

We describe the preparation, properties and the comparison of SiO₂ films deposited by liquid phase deposition from supersaturated solutions with both silica powder and silicic acid. From each solution the resulting [Si (OH)₄]-rich supersaturated solution, when suitably diluted with De-Ionised (DI) water deposits SiO₂ onto silicon. Our work was motivated by the search for the optimum condition for device quality oxide growth within a low (<300°C) thermal budget, for large area device fabrication, on inexpensive substrates such as glass and plastic. The net growth of the LPD of the oxide layer is result of competition between deposition and etching; the balance and hence the rate of growth being controlled simply and reproducibly by the addition of de-ionised (DI) water. We have produced device grade SiO₂ from the solution at 48°C onto both n and p type Si substrates. Control of the oxide properties is achieved in the amount of DI water added to the super-saturated solution. Oxide layers of optimum quality being obtained by the titration of 60ml DI water to 100ml of supersaturated solution. FTIR, ellipsometery, and C-V/I-V measurements were used to characterise the films deposited from solutions of silica powder and silicic acid. The resistivity of the optimum layers from a saturated solution of silica powder was found to be of the order of ≈10¹¹ Ωcm with breakdown field strengths of the order of 3-5 x 10⁶ V/cm. The resistivity of the optimum layers prepared using silicic acid were much higher (10¹⁵ Ω-cm), with breakdown field strengths of the order of (9±1) x 10⁶ V/cm. The results approach those for thermally grown silicon dioxide, suggesting that LPD oxide have the potential of device quality insulator on large area substrate.