It has been reported that SiO x N y films with high positive fixed charge density (Q f) in the range of 1012 cm−2 is effective for field-effect passivation of n-type Si surfaces . So far, several methods have been applied to grow SiO x N y films. For example, high-temperature (>900°C) processes such as the direct thermal oxynitridation of Si in NO or N2O ambient [4, 5] and the annealing of SiO2 in nitrogen-containing ambient [6, 7] have been widely used. However, the high-temperature processes suffer a large thermal budget and a redistribution problem of dopant atoms. Plasma-enhanced chemical vapor deposition (PECVD) process is a low-temperature alternative below 400°C [8–10]. However, the PECVD method needs toxic precursor gases,
and it is also noted that the interfacial properties prepared by this method are usually inferior to those of thermal oxides , because the deposition method does not consume the substrate Si Selleckchem Ion Channel Ligand Library unlike thermal oxidation. Moreover, in the films prepared by low-temperature Tipifarnib PECVD, the concentration of hydrogen atoms in the form of Si-OH and Si-H bonds is high, which are responsible for poor dielectric properties . Nitridation of silicon oxide in low-pressure nitrogen plasma has also been investigated to fabricate SiO x N y at low temperatures [13, 14]. In the case of low-pressure nitrogen plasma, the ion bombardment of the film surface is a serious
problem to develop highly reliable ultra-large-scale integrated circuits . Recently, we have studied the plasma oxidation of Si wafers to C-X-C chemokine receptor type 7 (CXCR-7) grow SiO2 films using atmospheric-pressure (AP) plasma generated by a 150-MHz very-high-frequency (VHF) electric field and demonstrated that high-quality SiO2 films can be obtained using He/O2 or Ar/O2 plasma at 400°C [16, 17]. We have also
reported that the AP VHF plasma oxidation process at 400°C is capable of producing material quality of SiO2 films comparable to those of high-temperature (>1,000°C) thermal oxides. The SiO2/Si structure with low interface state density (D it) around the midgap of 1.4 × 1010 cm−2 eV−1 and moderately high Q f of 5.3 × 1011 cm−2 has been demonstrated . Therefore, addition of N into the SiO2 film by AP plasma oxidation-nitridation using O2 and N2 precursor gas mixture is an alternative approach for obtaining SiO x N y films at a low temperature of 400°C. The purpose of this work is to present a method for preparing SiO x N y films by AP VHF plasma oxidation-nitridation with a detailed analysis of interface properties of SiO x N y layer by capacitance-voltage (C-V) measurements on metal-SiO x N y -Si capacitors. Methods The details of the AP VHF plasma apparatus have been reported previously . A schematic illustration of an electrode for AP VHF plasma oxidation-nitridation is shown in Figure 1. In the gap between the substrate and parallel-plate electrode, stable plasma is generated at atmospheric pressure with 150-MHz VHF power using a gas mixture of 1% O2/He.