High-temperature degradation in plasma-enhanced chemical vapor deposition Al2O3 surface passivation layers on crystalline silicon

Abstract

In this publication, the activation and degradation of the passivation quality of plasma-enhanced chemical vapor deposited aluminum oxide (Al2O3) layers with different thicknesses (10 nm, 20 nm, and 110 nm) on crystalline silicon (c-Si) during long and high temperature treatments are investigated. As indicated by Fourier Transform Infrared Spectroscopy, the concentration of tetrahedral and octahedral sites within the Al2O3 layer changes during temperature treatments and correlates with the amount of negative fixed charges at the Si/Al2O3 interface, which was detected by Corona Oxide Characterization of Semiconductors. Furthermore, during a temperature treatment at 820 °C for 30 min, the initial amorphous Al2O3 layer crystallize into the γ-Al2O3 structure and was enhanced by additional oxygen as was proven by x-ray diffraction measurements and underlined by Density Functional Theory simulations. The crystallization correlates with the increase of the optical density up to 20% while the final Al2O3 layer thickness decreases at the same time up to 26%. All observations described above were detected to be Al2O3 layer thickness dependent. These observations reveal novel aspects to explain the temperature induced passivation and degradation mechanisms of Al2O3 layers at a molecular level like the origin of the negative fixe charges at the Si/SiOx/Al2O3 interface or the phenomena of blistering. Moreover, the crystal phase of Al2O3 does not deliver good surface passivation due to a high concentration of octahedral sites leading to a lower concentration of negative fixed charges at the interface.

A study on Si/Al2O3 paramagnetic point defects

“…13 Moreover, an enhanced concentration of tetrahedral AlO 4 sites compared to octahedral AlO 6 sites was reported for Si=Al 2 O 3 interfaces, which might also correlate with the appearance of negative fixed charges. 9,[14][15][16] Interestingly, Q tot is lower with the addition of a thermally grown interfacial SiO 2 layer, as was published by Dingemans et al and Mack et al 17,18 To explain this, Mack et al suggested an electron transfer mechanism from Si via interface defects, leading to Q tot . Thus, at least a part of D it might deliver defects for electron transport.…”

“…[54][55][56][57][58] The feature at 3000 cm À1 À 3800 cm À1 can be assigned to Si-OH and O-H stretching modes. 16,44 In Figure 3(b), the strong peak from the additional interfacial SiO 2 layer can be seen in the range of 900 cm À1 À 1300 cm À1 . 48,50 In Figure 3(c), an FTIR spectrum of a single thermally grown SiO 2 layer is shown; the feature around 600 cm À1 À 900 cm…”

“…64 Further, a correlation between void density and layer stress release in carbon films on Si was shown by Puchert et al 65 In this context, it might be interesting to connect these observations to other thickness dependent phenomena known from Al 2 O 3 layers like blistering. 16,66,67 Here, the density of temperature-induced bubbles within Al 2 O 3 layers was observed to increase dramatically with increasing Al 2 O 3 layer thickness. 16,66,67 Thus, the higher void density observed in this contribution for thick Al 2 O 3 layers might lead to a higher capture probability for hydrogen components.…”

“…16,66,67 Here, the density of temperature-induced bubbles within Al 2 O 3 layers was observed to increase dramatically with increasing Al 2 O 3 layer thickness. 16,66,67 Thus, the higher void density observed in this contribution for thick Al 2 O 3 layers might lead to a higher capture probability for hydrogen components. With increasing temperature, the gas pressure might increase within these voids until they are destroyed.…”

“…In Figures 3(a) and 3(b), the known peaks from Al 2 O 3 were observed and summarized briefly (see also Table II). 16,44 The broad peak at a maximum wavenumber of around 670 cm À1 consists of O-Al-O bending modes (650 cm À1 À 700 cm À1 ), Al-O stretching modes for Al-O in octahedral matrices (400 cm À1 À530 cm À1 ), and Al-O stretching modes in tetrahedral and octahedral matrices (750 cm À1 À 850 cm À1 ). [45][46][47][48][49][50] The peak around 900 cm À1 À 1300 cm À1 is assigned to Si-O and O-Si-O stretching modes and optical phonon modes.…”