Microstructure of oxidized layers formed by the low-temperature ultraviolet-assisted dry oxidation of strained Si0.8Ge0.2 layers on Si

Abstract

Ultraviolet-assisted low-temperature (550 °C) dry oxidation of Si0.8Ge0.2 strained layers on (100)Si has been studied. The oxidation rate of this material was found to be a factor of 2 greater than that of pure Si oxidation under identical irradiation conditions. Initially, the structure of the oxidized material consists of a SiO2 layer on top of a strained Si1−xGex layer with a Ge concentration significantly higher (x≳0.2) than the initial value. Increasing the oxidation time produces more SiO2 and a Si1−xGex layer further enriched with Ge. However, the oxidation rate is reduced and some of the Ge becomes trapped inside the growing SiO2 layer. For a prolonged irradiation time (≳5 h) SiGe oxidation still continues, unlike the case for pure Si, while the Ge trapped inside the SiO2 forms isolated microcrystalline regions.

Photonic effects during low-temperature ultraviolet-assisted oxidation of SiGe

“…19,20 For irradiation times longer than 90 min, there is a sudden increase in the size of the oxidized Ge peak simultaneous with a corresponding decrease of the unoxidized Ge peak. The sample oxidized for 122 min exhibits surface Si and Ge oxidized peaks located at 103.5 eV and 33.6 eV, which is very similar to those recorded for thick stoichiometric oxides, 3,8,10,[15][16][17] i.e., Si 4ϩ and Ge 4ϩ . The amount of Si and Ge atoms bound in suboxides was estimated to be ϳ5% and ϳ20% after 30-min oxidation and decreased for longer oxidation times.…”

“…It is, therefore, concluded that a VUV photon-irradiation enhancement effect on Si and Ge interdiffusion has been introduced, possibly involving either Si-Si or Si-Ge bond softening or even breaking. fluorine oxidation induces a high concentration of point defects (vacancies), perhaps the UV-assisted oxidation data [14][15][16][17] can be explained by a similar argument.…”

“…[14][15][16][17] These studies showed that there are two major differences between UV-assisted and conventional thermal oxidation. First, there is an enhancement of the SiGe dryoxidation rate over that of pure Si, which was previously observed only for thermal-wet oxidation.…”

Charging effects in Ge nanocrystals embedded in SiO2 matrix for non volatile memory applications

“…Indeed non volatile memories with implanted Ge nanocrystals have been demonstrated [3][4][5]. Isolated nc-Ge in SiO 2 layers can be obtained by various other techniques such as oxidation and reduction of Ge/Si islands [6], UV-assisted oxidation of Si 1Àx Ge x alloys [7], and rapid thermal oxidation (RTO) of ncGe [8][9][10][11] or (Ge + SiO 2 ) [12]. The fabrication of a non volatile memory cell requires a perfect control of 4 main parameters: (i) the tunnel oxide thickness, (ii) the nanocrystal density, (iii) the nanocrystal diameter, and (iv) the control oxide thickness.…”

“…For all the nc-Ge memory structures presented in Ref. [6][7][8][9][10][11][12], the formation of nanocrystals is obtained after oxidation steps. In most of these experiments, it appears quite difficult to control very thin tunnel oxide layers.…”