BS IEC 63068-2-2019 pdf free download – Semiconductor devices – Non-destructive recognition criteria of defects in silicon carbide homoepitaxial wafer for power devices Part 2: Test method for defects using optical inspection.
4 Optical inspection method
4.1 General Defects with surface morphological features shall be detected by optical inspection method. The following descriptions concern such defects in n/n+-type 4H-SiC homoepitaxial wafers with an off-cut angle of 4° along the direction of [1 1 2 0]:
– individual defects exhibiting hexagonal-shaped or round-shaped large holes on the wafer surface, e.g. micropipe (Figure A.1 );
– individual minute defects giving rise to a pit less than 50 µ m in diameter on the wafer surface, e.g. TSD (Figure A.2), TED (Figure A.3); – individual linear defects extending in various directions, e.g. scratch trace (Figure A.4);
– individual planar defects providing needle-shaped features on the wafer surface, which extend along the off-cut direction, e.g. stacking fault complex (Figure A.7);
individual planar defects providing faintly-outlined features on the wafer surface, which extend diagonally to the off-cut direction, e.g. stacking fault (Figure A.5), propagated stacking fault (Figure A.6);
– individual volume defects giving rise to triangle-shaped features on the wafer surface, which extend along the off-cut direction, e.g. polytype inclusion (Figure A.8);
– individual volume defects, e.g. particle inclusions (Figure A.9), surface particle;
– individual surface defects exhibiting obtuse triangle-shaped or trapezoid-shaped features on the wafer surface, e.g. bunched-step segment (Figure A.1 0). Defects without surface morphological features should be evaluated by other test methods such as photoluminescence and X-ray topography. Those defects include BPDs, TSDs without surface morphological features，TEDs without surface morphological features,stacking faults without surface morphological features, and propagated stacking faults withoutsurface morphological features.
4.2Principle
A grey scale image (or colour image) is produced from the original digital image of defects onthe wafer surface.This image is converted into a binary image (thresholding). The size andshape of defects are measured, and the distribution and number of defects within a specifiedarea of wafer are calculated.
First, an optical image of defects has to be captured and transformed into a digital format.Anoptical image is captured via an optical image sensor such as a charge-coupled device.Then,the obtained digital image is processed by manipulating the grey levels of the image.Througha specified scheme of image analysis， the image information is reduced to a set of valueswhich are specific to the application.
NOTE The size of planar and volume defects extending along the off-cut direction depends on the thickness ofhomoepitaxial layer.Details of such defects and the method of estimating the size of their optical images aredescribed in 4.6.2 and Annex A,respectively.
4.3Requirements
4.3.1 lllumination
4.3.1.1 Types of observations
Different wafer surface conditions and defect types will require an optimum setup of opticsand illumination to acquire distinct surface features in an image that are to be analysed.Therefore，a combination of optics and illumination for a specific application has to beprepared.Generally, the following types of lightings and observations are used.
a) Types of lightings are:
1) directional lighting;
2) diffused lighting;
3) mixture of directional and diffused lightings.
b) Types of observations are:
1) bright-field observation;
2) dark-field observation;
3) differential interference contrast observation;
4) polarized light observation.
All the types of observations can be done under reflective illumination. Influences from wafer backsides shall be eliminated in any observations.BS IEC 63068-2 pdf download.