Comparison of interfaces, band alignments, and tunneling currents between crystalline and amorphous silica in Si/SiO2/Si structures

Abstract

Recently, to improve the performance of an integrated metal-oxide-semiconductor (MOS) device, an attempt has been made in the industry to replace the amorphous oxide with a crystalline oxide. However, various characteristics caused by the difference between amorphous and crystalline oxide in the MOS structure have not been systematically investigated. Therefore, we demonstrate the difference in atomic interface structures, electronic structures, and tunneling properties concerning varied oxide phases in a representative system, Si/SiO _2 /Si structures, with sub-3 nm-thick silica from first-principles. We investigate two oxide phases of amorphous ( a -) and crystalline ( c -) SiO _2 with and without H passivation at the interface. Si/ a -SiO _2 exhibits a smooth interface layer, whereas Si/ c -SiO _2 exhibits an abrupt interface layer, resulting in the thicker interface layer of Si/ a -SiO _2 than Si/ c -SiO _2 . Thus for a given total silica thickness, the adequate tunneling-blocking thickness, where all the Si atoms form four Si–O bonds, is thinner in a -SiO _2 than c -SiO _2 , originating more tunneling current through a -SiO _2 than c -SiO _2 . However, the effects of dangling bonds at Si/ c -SiO _2 rather than Si/ a -SiO _2 on tunneling currents are crucial, particularly in valence bands. Furthermore, when the dangling bonds are excluded by H atoms at Si/ c -SiO _2 , the tunneling current dramatically reduces, whereas the H-passivation effect on the tunneling blocking at Si/ a -SiO _2 is insignificant. Our study contributes systematic knowledge regarding oxide phases and interfaces to promote for high performance of MOS devices.

Keywords

• Si/SiO2/Si structures
• interface structures
• bandgaps and band offsets
• leakage-tunneling currents
• MOS structures
• interface engineering