Semiconductor devices - Non-destructive recognition criteria of defects in silicon carbide homoepitaxial wafer for power devices - Part 3: Test method for defects using photoluminescence

IEC 63068-3:2020 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.

Dispositifs à semiconducteurs - Critères de reconnaissance non destructifs des défauts au sein d’une plaquette homoépitaxiale de carbure de silicium pour des dispositifs d’alimentation - Partie 3 : Méthode d’essai pour les défauts à l’aide de la photoluminescence

L’IEC 63068-3:2020 décrit les définitions et les recommandations relatives à l’utilisation de la photoluminescence pour la détection de défauts bruts au sein de plaquettes homoépitaxiales en carbure de silicium (4H-SiC) disponibles dans le commerce. De plus, le présent document donne des exemples d’images de photoluminescence et de spectres d’émission, permettant la détection et la catégorisation des défauts au sein de plaquettes homoépitaxiales en SiC.

General Information

Status
Published
Publication Date
12-Jul-2020
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
13-Jul-2020
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IEC 63068-3
Edition 1.0 2020-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Non-destructive recognition criteria of defects in
silicon carbide homoepitaxial wafer for power devices –
Part 3: Test method for defects using photoluminescence
Dispositifs à semiconducteurs – Critères de reconnaissance non destructifs des
défauts au sein d’une plaquette homoépitaxiale de carbure de silicium pour des
dispositifs d’alimentation –
Partie 3: Méthode d’essai pour les défauts à l’aide de la photoluminescence
IEC 63068-3:2020-07(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 63068-3
Edition 1.0 2020-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Semiconductor devices – Non-destructive recognition criteria of defects in
silicon carbide homoepitaxial wafer for power devices –
Part 3: Test method for defects using photoluminescence
Dispositifs à semiconducteurs – Critères de reconnaissance non destructifs des
défauts au sein d’une plaquette homoépitaxiale de carbure de silicium pour des
dispositifs d’alimentation –
Partie 3: Méthode d’essai pour les défauts à l’aide de la photoluminescence
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.080.99 ISBN 978-2-8322-8614-2

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 63068-3:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Photoluminescence method ........................................................................................... 11

4.1 General ................................................................................................................. 11

4.2 Principle ............................................................................................................... 11

4.3 Requirements ....................................................................................................... 11

4.3.1 Measuring equipment .................................................................................... 11

4.3.2 Wafer positioning and focusing ...................................................................... 13

4.3.3 Image capturing ............................................................................................. 13

4.3.4 Image processing .......................................................................................... 13

4.3.5 Image analysis .............................................................................................. 13

4.3.6 Image evaluation ........................................................................................... 14

4.3.7 Documentation .............................................................................................. 14

4.4 Parameter settings ................................................................................................ 14

4.4.1 General ......................................................................................................... 14

4.4.2 Parameter setting process ............................................................................. 14

4.5 Procedure ............................................................................................................. 14

4.6 Evaluation ............................................................................................................. 14

4.6.1 General ......................................................................................................... 14

4.6.2 Mean width of planar and volume defects ...................................................... 14

4.6.3 Evaluation process ........................................................................................ 15

4.7 Precision ............................................................................................................... 15

4.8 Test report ............................................................................................................ 15

4.8.1 Mandatory elements ...................................................................................... 15

4.8.2 Optional elements .......................................................................................... 15

Annex A (informative) Photoluminescence images of defects .............................................. 16

A.1 General ................................................................................................................. 16

A.2 BPD ...................................................................................................................... 16

A.3 Stacking fault ........................................................................................................ 17

A.4 Propagated stacking fault ...................................................................................... 18

A.5 Stacking fault complex .......................................................................................... 19

A.6 Polytype inclusion ................................................................................................. 19

Annex B (informative) Photoluminescence spectra of defects ............................................. 21

B.1 General ................................................................................................................. 21

B.2 BPD ...................................................................................................................... 21

B.3 Stacking fault ........................................................................................................ 21

B.4 Propagated stacking fault ...................................................................................... 23

B.5 Stacking fault complex .......................................................................................... 23

B.6 Polytype inclusion ................................................................................................. 24

Bibliography .......................................................................................................................... 25

Figure 1 – Schematic diagram of PL imaging system ............................................................ 12

---------------------- Page: 4 ----------------------
IEC 63068-3:2020 © IEC 2020 – 3 –

Figure A.1 – BPD .................................................................................................................. 17

Figure A.2 – Stacking fault .................................................................................................... 18

Figure A.3 – Propagated stacking fault ................................................................................. 18

Figure A.4 – Stacking fault complex ...................................................................................... 19

Figure A.5 – Polytype inclusion ............................................................................................. 20

Figure B.1 – PL spectrum from BPD ..................................................................................... 21

Figure B.2 – PL spectra from Frank-type stacking faults ....................................................... 22

Figure B.3 – PL spectra from Shockley-type stacking faults .................................................. 22

Figure B.4 – PL spectra from various stacking faults in the wavelength range longer

than 650 nm .......................................................................................................................... 23

Figure B.5 – PL spectrum from stacking fault complex .......................................................... 24

Figure B.6 – PL spectrum from polytype inclusion ................................................................. 24

---------------------- Page: 5 ----------------------
– 4 – IEC 63068-3:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SEMICONDUCTOR DEVICES –
NON-DESTRUCTIVE RECOGNITION CRITERIA OF DEFECTS
IN SILICON CARBIDE HOMOEPITAXIAL WAFER FOR POWER DEVICES –
Part 3: Test method for defects using photoluminescence
FOREWORD

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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 63068-3 has been prepared by IEC technical committee 47:

Semiconductor devices.
The text of this International Standard is based on the following documents:
FDIS Report on voting
47/2628/FDIS 47/2638/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 6 ----------------------
IEC 63068-3:2020 © IEC 2020 – 5 –

A list of all parts in the IEC 63068 series, published under the general title Semiconductor

devices – Non-destructive recognition criteria of defects in silicon carbide homoepitaxial wafer

for power devices, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – IEC 63068-3:2020 © IEC 2020
INTRODUCTION

Silicon carbide (SiC) is widely used as a semiconductor material for next-generation power

semiconductor devices. SiC, as compared with silicon (Si), has superior physical properties

such as a higher breakdown electric field, higher thermal conductivity, lower thermal

generation rate, higher saturated electron drift velocity, and lower intrinsic carrier

concentration. These attributes realize SiC-based power semiconductor devices with faster

switching speeds, lower losses, higher blocking voltages, and higher temperature operation

relative to standard Si-based power semiconductor devices.

SiC-based power semiconductor devices are not fully realized due to some issues including

high costs, low yield, and low long-term reliability. In particular, one of the serious issues lies

in the defects existing in SiC homoepitaxial wafers. Although efforts of decreasing defects in

SiC homoepitaxial wafers are actively implemented, there are a number of defects in

commercially available SiC homoepitaxial wafers. Therefore, it is indispensable to establish

an international standard regarding the quality assessment of SiC homoepitaxial wafers.

The IEC 63068 series of standards is planned to comprise Part 1, Part 2, and Part 3, as

detailed below. This document provides definitions and guidance in use of photoluminescence

for detecting defects in commercially available silicon carbide (SiC) homoepitaxial wafers.

Part 1: Classification of defects
Part 2: Test method for defects using optical inspection
Part 3: Test method for defects using photoluminescence
---------------------- Page: 8 ----------------------
IEC 63068-3:2020 © IEC 2020 – 7 –
SEMICONDUCTOR DEVICES –
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 part of IEC 63068 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

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
---------------------- Page: 9 ----------------------
– 8 – IEC 63068-3:2020 © IEC 2020
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 1 to entry: 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 1 to entry: 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 1 to entry: 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 1 to entry: 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 1 to entry: 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
---------------------- Page: 10 ----------------------
IEC 63068-3:2020 © IEC 2020 – 9 –
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 1 to entry: 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 to entry: In 4H-SiC showing a hexagonal symmetry, four-digit indices [uvtw] are frequently used for crystal

directions.

[SOURCE: ISO 24173:2009 [1] , 3.3, modified – The original note has been replaced by a

new note to entry.]
3.26
defect
crystalline imperfection
____________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 11 ----------------------
– 10 – IEC 63068-3:2020 © IEC 2020
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
3.33
propagated stacking fault
stacking fault propagating from substrate toward the homoepitaxial layer surface
3.34
stacking fault complex

stacking fault complex consisting of a basal plane stacking fault and a prismatic fault

3.35
polytype inclusion

volume crystal defect showing different polytypes from that of the homoepitaxial layer

3.36
particle inclusion
macroscopic size particle existing in the homoepitaxial layer
3.37
bunched-step segment
surface morphological roughness consisting of bunched-steps
3.38
surface particle
particle deposited on the epitaxial layer surface after epitaxial growth
---------------------- Page: 12 ----------------------
IEC 63068-3:2020 © IEC 2020 – 11 –
4 Photoluminescence method
4.1 General

Defects with characteristic PL features shall be evaluated by PL 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 [11 2 0], where their PL images are obtained by detecting

emission wavelengths longer than 650 nm:
– individual linear defects exhibiting bright line images, e.g. BPDs;

– individual planar defects exhibiting dark contrast images, e.g. stacking faults, propagated

stacking faults, stacking fault complexes, and polytype inclusions.

When emission wavelengths from 400 nm to 500 nm are used for the defect detection,

stacking faults exhibit bright contrast images.

Defects without characteristic PL features or with weak PL contrasts against SiC area with no

defects should be evaluated by other test methods such as optical inspection and X-ray

topography. Those defects include micropipes, TSDs, TEDs, scratch traces, particle

inclusions, bunched-step segments, and surface particles.
4.2 Principle

PL images of defects are captured and transformed into a digital format. In the course of this

process, an SiC homoepitaxial wafer is irradiated with excitation light whose energy is greater

than the bandgap of 4H-SiC crystals, and the resulting PL is collected and recorded as a PL

image of a specified area of the wafer including defects. PL is detected using an optical image

sensor such as a CCD image sensor, and PL image is usually acquired using an optical filter

which transmits a specific range of PL appropriate for the detection of each type of defect.

Then, the obtained PL image (digital image) is processed by manipulating the grey levels of

the image. Through a specified scheme of image analysis, the image information is reduced

to a set of values which are specific to the detected defects.

A greyscale image is produced from the original digital image of defects in the wafer. This

image can be converted into a binary image (thresholding). The size and shape of defects are

measured, and the distribution and number of defects within a specified area of wafer are

calculated.

NOTE The size of planar and volume defects extending along the off-cut direction depends on the thickness of

homoepitaxial layer. Details of such defects and the method of estimating the size of their PL images are described

in Annex A and 4.6.2, respectively.
4.3 Requirements
4.3.1 Measuring equipment
4.3.1.1 PL imaging system

Measuring equipment for PL imaging of defects in 4H-SiC homoepitaxial wafers is shown in

Figure 1. The measuring equipment consists of light source, focusing optics, optical filter,

CCD
...

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