Low-pressure deposition of high-quality SiO2 films by pyrolysis of tetraethylorthosilicate

Abstract

The deposition of SiO2 by pyrolysis of tetraethylorthosilicate (TEOS) at pressures below 1 Torr was investigated at temperatures between 650 and 800 °C. We found oxide thickness variations of <±5% for suitable process conditions (PD ≤500 mTorr, wafer spacing ≥4.7 mm, TD <730 °C, deposition rate 16 nm min−1). Tests with 150-mm wafers showed that uniformities of ±2% can be achieved if the wafer spacing is increased to 10 mm. Raising the deposition pressure improves the step coverage in deep trenches but degrades the thickness uniformity across the wafer. The investigations of etch rates in different media show strong dependences on the anneal temperature for etchants containing HF but only a slight dependence for plasma etching. The dielectric breakdown strength of the oxides was 8 MV cm−1 and the failure rate after 500-ms current stress at 1 mA cm−2 lower than 20%. We found values for the interface state density of 1×1010 eV−1 cm−2 and for the oxide charge density in the range 3×1010 cm−2 to 2.5×1011 cm−2, depending on the oxide thickness. The hysteresis of C–V scans was <2 mV. No substantial shift of the C–V curve was found after temperature–bias stress. Our I–V investigations showed that the carrier transport is governed by the Poole–Frenkel mechanism. These results as well as secondary ion mass spectroscopy investigations of the layers confirm that Merck TEOS can be used to grow oxide films of sufficient electrical quality for microelectronic applications.