In:
Journal of Applied Physics, AIP Publishing, Vol. 94, No. 11 ( 2003-12-01), p. 7328-7335
Abstract:
Ultrathin silicon dioxide (SiO2) layers with excellent electrical characteristics can be formed using the nitric acid oxidation of Si (NAOS) method, i.e., by immersion of Si in nitric acid (HNO3) solutions. The SiO2 layer formed with 61 wt % HNO3 at its boiling temperature of 113 °C has a 1.3 nm thickness with a considerably high density leakage current. When the SiO2 layer is formed in 68 wt % HNO3 (i.e., azeotropic mixture with water), on the other hand, the leakage current density (e.g., 1.5 A/cm2 at the forward gate bias, VG, of 1 V) becomes as low as that of thermally grown SiO2 layers, in spite of the nearly identical SiO2 thickness of 1.4 nm. Due to the relatively low leakage current density of the NAOS oxide layer, capacitance–voltage (C–V) curves can be measured in spite of the ultrathin oxide thickness. However, a hump is present in the C–V curve, indicating the presence of high-density interface states. Fourier transformed infrared absorption measurements show that the atomic density of the SiO2 layers increases by 7% with an increase in the HNO3 concentration from 61 to 68 wt %. Measurements of valence band spectra clarify that this concentration increase causes the enhancement of the valence band discontinuity at the Si/SiO2 interface from 4.1 to 4.3 eV. When postmetallization annealing (PMA) treatment is performed at 400 °C in hydrogen on 〈aluminum (Al)/chemical SiO2/Si(100)〉 metal–oxide–semiconductor diodes, the leakage current density markedly increases, and this increase is attributed to a reaction between the Al electrode and the chemical SiO2 layer, resulting in a decrease in the SiO2 thickness. With PMA at 200 °C in hydrogen, on the other hand, the SiO2 thickness decreases only slightly to 1.3 nm. In this case, the leakage current density greatly decreases (e.g., 0.4 A/cm2 at VG=1 V and 5×10−3 A/cm2 at VG=−1 V), and consequently it becomes 1/3–1/10 of those for thermally grown SiO2 layers with the same thickness. The hump in the C–V curves disappears after PMA at 200 °C, indicating the elimination of interface states, and the interface state passivation is attributed to one of the reasons for the decrease in the leakage current density. Measurements of the valence band spectra show that another reason for the decrease in the leakage current density by PMA are an increase in the band discontinuity at the Si/SiO2 interface, and the elimination of SiO2 gap states.
Type of Medium:
Online Resource
ISSN:
0021-8979
,
1089-7550
Language:
English
Publisher:
AIP Publishing
Publication Date:
2003
detail.hit.zdb_id:
220641-9
detail.hit.zdb_id:
3112-4
detail.hit.zdb_id:
1476463-5
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