Low-Temperature SiO[sub 2] Layers Deposited by Combination of ECR Plasma and Supersonic Silane/Helium Jet

Abstract

As the semiconductor industry strives toward wafer postprocessing and three-dimensional integration, a demand has arisen for high-quality thin films deposited at temperatures below 400°C. In this work, we present SiO 2 films deposited at near room temperature, using a multipolar electron cyclotron resonance ͑ECR͒ plasma source, introducing the SiH 4 gas by using a highvelocity jet of silane diluted in helium. The electrical properties were studied under varying deposition parameters, such as gas flow rate, deposition pressure, and postdeposition and postmetallization annealing processes. At a low pressure, low SiH 4 flow and high helium flow, device-quality SiO 2 layers were obtained after a deposition combined with a 5 min postmetallization annealing at 400°C. These layers exhibited a refractive index of 1.46, an O/Si ratio of 2, an interface trap density in the order of 10 11 cm −2 eV −1 , an oxide charge density down to 10 10 cm −2 , and a breakdown field up to 11 MV/cm. They are thus suitable as a gate dielectric in a thin-film transistor.

Negative Charge in Plasma Oxidized SiO2 Layers

“…It can possibly exist in the lower-temperature materials. This is supported by our earlier study on plasma deposition of SiO 2 films at 100 o C, where we measured (by XPS) a correlation between the negative charge and the O/Si ratio slightly higher than 2 for thin films [10].This is also in agreement with the work of Afanas'ev and Stesmans, who mentioned the creation of O 3 {Si-OH centers (by irradiation with 10 eV photons) as neutral traps for electrons [17].…”

Plasma-enhanced chemical vapor deposition of silicon dioxide

“…It could however exist in our experiments because of the lower temperatures. This is supported by earlier data in our laboratory on plasma deposition of SiO 2 films at 100 • C, where the authors measured a correlation between the negative charge and the O/Si ratio (by XPS) [209]. Namely, the thin films mostly exhibited negative charge and the O/Si ratio was slightly higher than 2.…”

“…However, the charge for thinner layers remains negative. Negative effective charges were reported occasionally in PECVD silicon oxides when relatively thin layers (10-50 nm) were deposited in highly-diluted plasmas at low deposition rates [208][209][210]. Negative charges were also reported for silicon dioxide layers grown solely by plasma oxidation [211,212].…”

Low temperature pure boron layer deposition for Si diode and micromachining applications

“…As presented in Chapter 4, B-layers with excellent adhesion, conformality and etch selectivity (> 10 4 ) were achieved at SiNx-like stress levels: 490 MPa for 400℃ and -1250 MPa for 700℃ Bdeposition. As opposed to conventional PECVD SiO2 or SiNx masking layers that often require several micrometer thickness [38,39], low strain could be realized because a B-layer thickness as low as 2 nm was sufficient for masking purposes. Moreover, B-layer membranes of only 4 nm in thickness were fabricated.…”

“…In general, the lower the processing temperature of these materials the lower the etch selectivity and a thicker layer is needed as a hard mask. Much research has been dedicated to improving the quality of low temperature oxides and nitrides but still for wet etching of deep cavities the etch rates and/or the presence of pinholes can mean that micrometer-thick layers must be used [38,39]. This can in turn entail problems with mechanical stress, particularly if thin membranes are to be fabricated.…”