Orientation imaging of macro-sized polysilicon grains on wafers using spatially resolved acoustic spectroscopy

Rikesh Patel,Wenqi Li,Richard J Smith,Steve D Sharples,Matt Clark

doi:10.1016/j.scriptamat.2017.07.003

Rikesh Patel, Wenqi Li + Show 3 more

Open Access

https://doi.org/10.1016/j.scriptamat.2017.07.003

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Journal: Scripta materialia	Publication Date: Jul 14, 2017
Citations: 11	License type: cc-by

Affiliation: University of Nottingham

Abstract

Due to its economical production process polysilicon, or multicrystalline silicon, is widely used to produce solar cell wafers. However, the conversion efficiencies are often lower than equivalent monocrystalline or thin film cells, with the structure and orientation of the silicon grains strongly linked to the efficiency. We present a non-destructive laser ultrasonic inspection technique, capable of characterising large (52×76mm2) photocell's microstructure - measurement times, sample surface preparation and system upgrades for silicon scanning are discussed. This system, known as spatially resolved acoustic spectroscopy (SRAS) could be used to optimise the polysilicon wafer production process and potentially improve efficiency.

Highlights

Most manufactured crystalline silicon solar cells available can be categorised as either mono-crystalline or multicrystalline, known as polysilicon
The system used in this study was not designed for working on silicon - the commercially obtained silicon cells required preparation in order to be characterised
It is possible to redesign the spatially resolved acoustic spectroscopy (SRAS) system so that measurements could be made on silicon in-situ

Summary

Introduction

Most manufactured crystalline silicon solar cells available can be categorised as either mono-crystalline (i.e. single crystal) or multicrystalline (mc-Si), known as polysilicon. In order to optimise the quality of manufactured silicon cells, measuring the grain structure of the material becomes an integral part of the process control. Many methods exist to determine material grain sizes, including nanoscale measurements using scanning electron microscopy (SEM) [11] or X-ray based methods [12], and rapid optical imaging techniques [13,14]. The measured samples are subject to extreme restrictions on size and surface finishing Another well used method of grain characterisation is Xray diffraction (XRD), such as one based on Laue back scattered diffraction [18]. Patel et al / Scripta Materialia 140 (2017) 67–70 rapid scanning, and is an all-optical measurement system - we have adapted this technique to produce microstructure images on silicon

Spatially resolved acoustic spectroscopy

Finding the orientation

Methodology and results

Findings

Discussion