Wafer Fabrication

Crystalline defects in epitaxial thin films may cause problems when producing high-performance semiconductor devices. For example, epitaxially grown thin films may inherit crystal defects from the single crystal substrate. To ensure optimum device performance, it is important to evaluate the grains and crystal defects within the single crystal substrate prior to film growth.

Wafer Processing
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Crystal defect imaging in the wafer by X-ray topography

Transmission X-ray topography of 4H-SiC wafer

Silicon-carbide (SiC) is one of the next-generation materials used for power semiconductor devices. The topography image, below, of a 3-inch SiC wafer was obtained using a dedicated topography system, XRTmicron. Using a synergistic combination of high-resolution X-ray optics and a 2D detector system, dislocations in the wafer are clearly observed.

Wafer Processing - Transmission topography image

Transmission topography image of 4H-SiC 22-40 reflection

Dislocation types identification for SiC wafer

It is known that several types of dislocations, threading screw dislocation (TSD), threading edge dislocation (TED), and basal plane dislocation, may be present in 4H-SiC wafers. From the image obtained by transmission X-ray topography using Mo Kα1 X-rays, these types of dislocations can be clearly identified within the wafer.

Wafer Processing - Types of dislocations

Types of dislocations in transmission topography image for 4H-SiC -2202 reflection

3-dimensional computed image of 4H-SiC using X-ray transmission topography

The 3-dimensional computed images shown below are generated by a technique call 3D section topography. The data were collected using high-resolution transmission topography followed by digital processing to construct the final images. From 3D section topography, dislocations and defects within highly perfect single crystal substrates can be visualized and quantified. With high-brilliance X-ray sources and high-definition cameras, information on the depth and direction of extended dislocations can be obtained through rapid measurements (~10 sec/image). For a more detailed investigation, 2D slices can be taken through the computed 3D volume at any point within the volume.

Wafer Processing - 3D section topography

3D section topography (4H-SiC Epi-sub)

Crystal defect analysis of a single crystal substrate by X-ray reflection topography

A 10 mm × 10 mm magnesium oxide single crystal substrate was observed by X-ray reflection topography (MgO 024 reflection, incident angle ω= 28.3˚, diffraction angle 2θ= 109.8˚, exposure time =120 sec.). The SmartLab automated multipurpose X-ray diffractometer, equipped with an XTOP high-sensitivity and high-resolution X-ray camera, is capable of obtaining high-resolution topographic images that are similar in quality to those collected on dedicated equipment. In the figure below, grains are seen separated by white lines, crystal defects show up as white spots or fine mesh patterns. Surface scratches are also clearly visible.

Wafer Processing - Mg oxide single substrate

Magnesium oxide single substrate

Wafer Processing - Topgraph of a Mg oxide single crystal substrate

Topograph of a magnesium oxide single crystal substrate

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Related application notes

X-ray topography, crystal quality and lattice constants

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