In situ Photoluminescence Study of Plasma Effects on Passivation of Crystalline Silicon Coated with Aluminum Oxide

Abstract

A degradation of crystalline silicon surface passivation provided by aluminum oxide (Al2O3) is generally observed after plasma processes, e.g., deposition of amorphous silicon nitride. To minimize such detrimental effect, a better understanding of the interaction between plasma species and the Al2O3 layer is required. Using in situ photoluminescence, the passivation quality of as‐deposited and annealed crystalline silicon wafers coated with Al2O3 grown by atomic layer deposition is characterized in real time during argon‐hydrogen plasma exposure. The photoluminescence intensity of as‐deposited samples instantly steps up after the plasma ignition, and then it gradually decreases as a function of plasma exposure time. However, only degradation of photoluminescence signal can be found if the samples are annealed prior to the plasma treatment. The interaction between vacuum UV light from plasma and different types of chemical bonds in the Al2O3 layer is proposed to explain the obtained results. Understanding the mechanisms and root cause leading to different behavior between as‐deposited and annealed samples under plasma exposure is a first step toward redesigning the process flow for better surface passivation.

In situ modulated photoluminescence study of the hydrogenation processes of tunnel oxide passivating contacts during plasma processes

“…This negative impact could be related to UV emissions from the NH 3 + H 2 plasma. [ 21 ] In 1985, Jaeger and Hezel [ 22 ] showed that UV light with energy greater than 3.7 eV leads to the breaking of Si–H or Si–OH chemical bonds at the surface of the solar cell, which significantly degrades the passivation properties. This would be consistent with the larger degradation on (p) nc‐SiO x :H because of its higher transparency, thus letting more high‐energy photons reach the c‐Si/SiO x interface.…”

Detection of stable positive fixed charges in AlOx activated during annealing with in situ modulated PhotoLuminescence

“…The setup developed in this study [15] is an evolution of an in situ photoluminescence (PL) system previously described by S. Abolmasov [16]. The PECVD reactor has a grounded electrode with a 9 mmdiameter hole in its center.…”

“…1. Schematic representation of the in situ MPL acquisition setup coupled with a PECVD reactor [15]. At a given laser power output with a modulation depth of 6%, modulation frequencies ranging from 225 Hz to 625 Hz are used in order to measure various phase shifts and thus get a more reliable fitting for the value of the lifetime in equation (1).…”

“…We can finally extrapolate a function for the evolution of with the excess minority carrier density (see Figure 2). Various measurements (blue dots) and extrapolation of the function (Δ-) to derive the minority carrier lifetime at a specific injection level of 1.10 15 cm -3 (green dot) [15].…”

“…Evolution with temperature of the minority carrier lifetime of an n-type FZ wafer (1-5 Ωcm) passivated with a SiOx/(n) poly-Si stack processed at high temperature (> 800°C) during the cooling phase of an annealing at 300°C for 1 minutes in H2. The green line is the fitting of the lifetime with a power low of coefficient Q = 1.0026 (adapted from [15]).…”