Simultaneous X-ray radiography and diffraction topography imaging applied to silicon for defect analysis during melting and crystallization

Abstract

One of the key issues to be resolved to improve the performance of silicon solar cells is to reduce crystalline defect formation and propagation during the growth‐process fabrication step. For this purpose, the generation of structural defects such as grain boundaries and dislocations in silicon must be understood and characterized. Here, in situ X‐ray diffraction imaging, historically named topography, is combined with radiography imaging to analyse the development of crystal defects before, during and after crystallization. Two individual indirect detector systems are implemented to record simultaneously the crystal structure (topographs) and the solid–liquid morphology evolution (radiographs) at high temperature. This allows for a complete synchronization of the images and for an increased image acquisition rate compared with previous studies that used X‐ray sensitive films to record the topographs. The experiments are performed with X‐ray synchrotron radiation at beamline ID19 at the European Synchrotron Radiation Facility. In situ observations of the heating, melting, solidification and holding stages of silicon samples are presented, to demonstrate that with the upgraded setup detailed investigations of time‐dependent phenomena are now possible. The motion of dislocations is recorded throughout the experiment, so that their interaction with grain boundaries and their multiplication through the activation of Frank–Read sources can be observed. Moreover, the capability to record with two camera‐based detectors allows for the study of the relationship between strain distribution, twinning and nucleation events. In conclusion, the simultaneous recording of topographs and radiographs has great potential for further detailed investigations of the interaction and generation of grains and defects that influence the growth process and the final crystalline structure in silicon and other crystalline materials.

X-ray Based in Situ Investigation of Silicon Growth Mechanism Dynamics—Application to Grain and Defect Formation

“…Indeed, diffraction imaging applied to silicon crystals have proven to give unique insights into the evolution of dislocations [64,65] and cracks [66]. As can be understood from the above, one of the main advantages of diffraction imaging is that it can reveal low scale structural defects like dislocations on wide field images encompassing complete crystals as shown for example for diamonds by Burns et al [61] and for Si [45,52,67].…”

“…In this new configuration, images recorded from both modes are fully synchronized. The image acquisition rate is of two frames per second in experiments reported in [52] which is sufficient to follow the solidification front of the samples. The choice of the diffraction vector of the recorded spots and the alignment of the camera with respect to the sample face is an important aspect because it influences the information that can be revealed from the recorded topographs.…”

“…Ideally a spot with a high intensity induced by the crystal plane structure factor should be chosen to better reveal defects. A detailed description of the equipment and imaging methods and configurations (alternate or simultaneous recording) can also be found in our previous publications [49,50,52].…”

“…The GaTSBI (Growth at high Temperature observed by Synchrotron Beam Imaging) tool was developed to fulfil this objective. This present paper is a review paper of our major results concerning the formation of grains, twinning, and competition [44][45][46][47][48][49][50][51][52][53] using advanced in situ and complementary ex situ characterization methods. In situ X-ray imaging and methods are described in detail.…”

X‐Ray Topography—More than Nice Pictures

“…[52] Very recently, the combination of in situ X-ray radiography and in situ X-ray topography allowed the defect analysis in photovoltaic silicon during melting and growth by recording simultaneously the solid-liquid morphology evolution and its interaction with the dislocations. [53] As far, the 3D distribution of defects inside the diffracting volume of a sample is projected into the 2D image plane. For a complex arrangement of dislocations the interpretation of the imaged pattern becomes difficult or impossible because of the loss of the 3D information.…”