Semiconductor device—Non-destructive recognition criteria of defects in silicon carbide homoepitaxial wafer for power devices—Part 3: Test method for defects using photoluminescence
Semiconductor device - Non-destructive recognition criteria of defects in silicon carbide homoepitaxial wafer for power devices - Part 3: Test method for defects using photoluminescence
1 Scope
This document provides definitions and guidance in use of photoluminescence for detecting as-grown defects in commercially available 4H-SiC (Silicon Carbide) epitaxial wafers. Additionally, this document exemplifies photoluminescence images and emission spectra to enable the detection and categorization of the defects in SiC homoepitaxial wafers.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
——IEC Electropedia: available at http://www.electropedia.org/
——ISO Online browsing platform: available at http://www.iso.org/obp
3.1
Photoluminescence; PL
emission of light from materials as a subsequence of electronic excitation by absorption of photons
3.2
photoluminescence imaging; PL imaging
technique for capturing, processing and analysing images of defects using light source for electronic excitation, focusing optics, optical filter, optical image sensor and computer systems
3.3
focusing optics
lens system used for magnifying and capturing optical images
3.4
optical filter
optical component designed to transmit only a specific wavelength region and to block other regions
3.5
optical image sensor
device to transform an optical image into digital data
3.6
image capturing
process of creating a two-dimensional original digital image of defects in the wafer
3.7
original digital image
digitized image acquired by an optical image sensor, without performing any image processing
Note: An original digital image consists of pixels divided by a grid, and each pixel has a grey level.
3.8
charge-coupled device image sensor; CCD image sensor
light-sensitive integrated circuit chip that converts detected optical information to electrical signals
Note: A CCD consists of fine elements, each of which corresponds to a pixel of original digital images.
3.9
pixel
smallest formative element of original digital images, to which a grey level is assigned
3.10
resolution
number of pixels per unit length (or area) of original digital images
Note: If resolutions in the X- and Y-directions are different, both values have to be recorded.
3.11
spatial resolution
ability to distinguish two closely spaced points as two independent points
3.12
grey level
degree of brightness defined in a greyscale
Note: Degree of brightness is usually represented as a positive integer taken from greyscale.
3.13
greyscale
range of grey shades from black to white
EXAMPLE 8-bit greyscale has two-to-the-eighth-power (= 256) grey levels. Grey level 0 (the 1st level) corresponds to black, grey level 255 (the 256th level) to white.
3.14
image processing
software manipulation of original digital images to prepare for subsequent image analysis
Note: For example, image processing can be used to eliminate mistakes generated during image capturing or to reduce image information to the essential.
3.15
binary image
image in which either 0 (black) or 1 (white) is assigned to each pixel
3.16
brightness
average grey level of a specified part of optical images
3.17
contrast
difference between the grey levels of two specified parts of optical images
3.18
shading correction
software method for correcting non-uniformity of the illumination over the wafer surface
3.19
thresholding
process of creating a binary image out of a greyscale image by setting exactly those pixels whose value is greater than a given threshold to white and setting the other pixels to black
Note: To make a binary image, the grey level of each pixel in the original greyscale image is replaced with 0 (black) or 1 (white), depending on whether the grey level is greater than or less than or equal to a given threshold.
3.20
edge detection
method of isolating and locating edges of defects and surface features in a given digital image
3.21
image analysis
extraction of imaging information from processed digital images by software
3.22
image evaluation
process of relating a series of values resulting from image analysis of one or more characteristic images via a classification scheme of defects
3.23
reference wafer
specified wafer used for parameter settings, which has already been evaluated for checking the reproducibility and repeatability of optical inspection process for defects
3.24
test wafer
semiconductor wafer under test to evaluate defects
3.25
crystal direction
direction, usually denoted as [uvw], representing a vector direction in multiples of the basis vectors describing the a, b and c crystal axes
Note 1: In 4H-SiC showing a hexagonal symmetry, four-digit indices [uvtw] are frequently used for crystal directions.
Note 2: For the equivalent crystal orientation families of cubic symmetry and hexagonal symmetry, they are represented by (UV) and (UUTW), respectively.
[SOURCE: ISO 24173:2009, 3.3, modified - The original note has been replaced by note 1 and note 2.]
3.26
defect
crystalline imperfection
3.27
micropipe
hollow tube extending approximately normal to the basal plane
3.28
threading screw dislocation; TSD
screw dislocation penetrating through the crystal approximately normal to the basal plane
3.29
threading edge dislocation; TED
edge dislocation penetrating through the crystal approximately normal to the basal plane
3.30
basal plane dislocation; BPD
dislocation lying on the basal plane
3.31
scratch trace
dense row of dislocations caused by mechanical damages on the substrate surface
3.32
stacking fault
planar crystallographic defect in monocrystalline material, characterized by an error in the stacking sequence of crystallographic planes
