Oxidation of HF-treated Si wafer surfaces in air

Abstract

The change in the chemical surface state of polished Si wafers [p-type, (100) oriented] during storage in air at room temperature was investigated for storage times up to half a year. Measurements were performed by x-ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectroscopy (HREELS). Immediately after the HF treatment (1 min 5% HF, 2 min water rinse) vibrational spectroscopy (HREELS) shows a predominant coverage of the surface with hydride groups (80%–90% of a ML), which can be inferred from the presence of the stretching (2100 cm−1), scissor (900 cm−1) and bending (640 cm−1) vibrations in the spectra. A slight additional coverage with oxygen is proved by XPS and originates from Si-OH groups (3670 cm−1) and oxygen-related hydrocarbon groups (XPS). These Si-OH groups result from an exchange reaction of Si-F with water during the two-minute water rinse. The development of an oxygen coverage during subsequent storage in air occurs extremely slowly and shows a logarithmic behavior. A monolayer coverage of oxygen (7×1014/cm2) is reached after approximately 7 days of storage in air. HREELS spectra exhibit the concurrent development of the asymmetric Si-O-Si vibration, which indicates that oxygen penetrates the lattice and breaks Si—Si bonds. During this period the Si-O-Si frequency shifts from about 1060 to 1100 cm−1. The penetration of backbonds of Si—H gets evident by broadening of the Si-H stretching vibration and finally by a shift to higher wavenumbers. Chemically shifted components of the Si 2p line (partially oxidized Si) are present with the SiO2−x component (chemical shift ≳3.4 eV) becoming dominant after roughly a week. Further oxidation proceeds essentially by an increase of the SiO2 peak in combination with a steeper slope of the logarithmic growth curve. The SiO2 thickness after half a year is about 8 Å. The frequency of the Si-O-Si vibration shifts up to 1120 cm−1, which can be related to a growing angle of the Si-O-Si bridge. Si—H groups are still present, the final peak position is about 2220 cm−1. The measurements show an extended induction period until the monolayer range of oxide coverage is attained. We ascribe this to the passivation of the surface by hydrogen and to a HF treatment according to Very-Large-Scale-Integration standards.

Freestanding silicon nanocrystals with extremely low defect content

“…For ambient-air oxidation of bulk-Si surfaces, values ranging from 3 to 170 h have been found, depending on the Si surface index, air humidity, and the initial amount of residual Si-OH groups at the surface. [37][38][39][40][41] According to the Cabrera-Mott mechanism of ambient-air oxidation of bulk-Si and Si-NC surfaces, 20,33,45 the oxidation is initiated by adsorption of water molecules at surface Si-OH groups followed by cleavage of Si-Si backbonds of Si-OH. This is followed by electron transfer from the broken bond to an adsorbed O 2 molecule, which drifts toward the cleaved bond, leading to the oxidation of this bond and of a neighboring Si-Si bond.…”

Photoreactivity of Si(111)−H in Ambient

“…24 Both the phase ∆ AB and the oxide thickness showed slow-fast-slow evolution with time, which has been described previously. [30][31][32][33][34][35] Graf et al investigated the oxidation of H-Si(100) under varying reaction conditions, e.g., immersed in water and in air. 30,31 They found that the oxygen coverage corresponding to the transition region between the slow and the fast growth kinetics is about the same in water (6 × 10 14 O atom/cm 2 ) and in air (4 × 10 14 O atom/cm 2 ).…”

“…30,31 They found that the oxygen coverage corresponding to the transition region between the slow and the fast growth kinetics is about the same in water (6 × 10 14 O atom/cm 2 ) and in air (4 × 10 14 O atom/cm 2 ). 30,31 The density of interface atoms at the Si(100) surface is 7 × 10 14 atom/cm 2 . 35 Therefore, it can be assumed that there is a critical coverage (∼0.7 ML) after which the oxide growth is accelerated.…”

“…35 Therefore, it can be assumed that there is a critical coverage (∼0.7 ML) after which the oxide growth is accelerated. 31 The rate of oxidation and photoreactive cross-section for oxidation can be determined by assuming that the onset of the fast increase of the SHG phase is actually characteristic of 0.7 ML oxide coverage surface. The rate of oxidation was calculated by dividing 0.7 ML by the duration of the slow phase of oxidation in seconds.…”

Seedless electroplating on patterned silicon

“…The wafers were cleaned using HNO 3 to remove organic contaminants and then etched in 1% HF, to remove the native oxide and inorganic particles from the wafer surface. It is known from the literature [6] that silicon surfaces etched in dilute HF solutions are highly resistant to oxidation in air due to the termination with hydrogen. After this the wafers were rinsed just for a few seconds with deionized water using a shower head in order to remove any acid left and then spin dried.…”