Evidence of low interface trap density in GeO2∕Ge metal-oxide-semiconductor structures fabricated by thermal oxidation

Abstract

We have fabricated GeO2∕Ge metal-oxide-semiconductor (MOS) structures by direct thermal oxidation of Ge substrates. The interface trap density (Dit) of Al∕GeO2∕Ge MOS structures, measured by the low temperature conductance method including the effect of the surface potential fluctuation, is found to be reduced as the oxidation temperature increases. The minimum values of Dit can be obtained for the oxidation around 575°C, which is in the maximum temperature range where GeO volatilization does not occur under atmospheric pressure of O2. It is also found that the hydrogen annealing before Al gate formation is effective for the passivation of GeO2∕Ge interface states. It is clarified, as a result, that the minimum Dit value lower than 1011cm−2eV−1 can be obtained for GeO2∕Ge MOS interfaces fabricated by direct oxidation of Ge substrates.

Effects of postgate dielectric treatment on germanium-based metal-oxide-semiconductor device by supercritical fluid technology

“…The incorporation of Ge in dielectric insulator is believed to act as defect traps and thereby causes an increased gate leakage current. 2,5,13 In this study, the implementation of SCF treatment after PDA process significantly reduces leakage current of gate insulator and recovers the C-V characteristic to a similar state as the initial Ge-MOS device without PDA process ͑control sample͒. This indicates again that oxidant ͑H 2 O molecule͒ is effectively transported into SiO 2 film by the high-pressure SCF and passivates the defect states generated in the Ge-MOS device during hightemperature thermal PDA process.…”

“…13 It was also reported that high-performance Ge MOSFET could be realized by careful control of interfacial GeO 2 formation. 2 In this study, a lowtemperature supercritical CO 2 ͑SCCO 2 ͒ fluid technology is proposed as a postgate dielectric treatment at 150°C to improve the SiO 2 / Ge interface after high-temperature PDA process. The SCCO 2 , which exists above its critical pressure ͑1170 psi͒ and temperature ͑30°C͒, provides good liquidlike solvency and high gaslike diffusivity, giving it excellent transport capacity.…”

“…The most critical issue hindering the application of Ge is lack of high-quality and stable Ge insulation oxide comparable to silicon dioxide ͑SiO 2 ͒ for silicon. 1,2 The poor native Ge oxide layer would be thermally decomposed at low temperature ͑about 420°C͒ and Ge diffuses into gate dielectric layer during the thermal deposition or postdielectric annealing ͑PDA͒ processes. Sequentially, poor interface properties and high gate leakage current will be exhibited in the Ge-MOS device.…”

Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

“…In spite of these physical instabilities of the bulk, the GeO 2 / Ge interface is still attractive because of its excellent electrical properties. 6 Researchers have developed a wide range of gate stack structures with a GeO 2 /Ge interface. One approach is to use thermal or plasma techniques such as nitridation to passivate a GeO 2 surface by forming a GeON layer on top of GeO 2 .…”

Processing of germanium for integrated circuits

“…They include approaches with various types of interfacial layers such as Si [40,41], GeO 2 [42][43][44][45], oxynitrides [46][47][48][49], and different high-k dielectric materials [50][51][52]. Novel processes have been investigated, i.e.…”