Background Statement for SEMI Draft Document #5499
Revision to SEMI M83-1112, TEST METHOD FOR DETEMINATION OF
DISLOCATION ETCH PIT DENSITY IN MONOCRYSTALS OF III-V
COMPOUND SEMICONDUCTORS
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in
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latter case, only publicly available information on the contents of the patent application is to be provided.
Background Statement:
The Determination of Dislocation Etch Pit Density in Monocrystals of III-V-Compound Semiconductors TF
reviewed SEMI M83-1112 and made editorial changes to the document. The editorial changes were approved at
SEMICON Europa 2012. SEMI M83-1112 is then revised to incorporate those editorial changes.
Notice: Additions are indicated by underline and deletions are indicated by strikethrough.
Review and Adjudication Information
Task Force Review
Determination of Dislocation Etch Pit Density
in Monocrystals of III-V-Compound
Semiconductors TF
TBD*
Date:
Time & Timezone: TBD*
SEMICON Europa 2013*
Location:
City, State/Country: Dresden, Germany*
Ulrich Kretzer (ulrich.kretzer@fcmLeader(s):
germany.com)
Michael Tran (SEMI NA)
Standards Staff:
408.943.7019
mtran@semi.org
Group:
Committee Adjudication
Europe Compound Semiconductor Materials
Committee
TBD*
TBD*
SEMICON Europa 2013*
Dresden, Germany*
Arnd Weber (arnd.weber@sicrystal.de)
Michael Tran (SEMI NA)
408.943.7019
mtran@semi.org
*The meeting venue, time, and location are to be determined. The meeting will likely be in conjunction with
SEMICON Europa 2013. Any additional meeting information will be updated at the SEMI Standards Calendar of
Events: http://www.semi.org/en/Standards/CalendarEvents
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will
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SEMI Draft Document #5499
Revision to SEMI M83-1112, TEST METHOD FOR DETEMINATION OF
DISLOCATION ETCH PIT DENSITY IN MONOCRYSTALS OF III-V
COMPOUND SEMICONDUCTORS
1 Purpose
1.1 The purpose of this document is to specify a test method for determination of the dislocation etch pit density of
mono-crystals monocrystals and wafers of the III-V compound semiconductors GaAs, InP and GaP.
2 Scope
2.1 This standard test method covers the determination of dislocation etch pit density on round test slices and
commercial wafers of III-V compound semiconductors using optical microscopy for identification and registration
of dislocation etch pits.
2.2 The dislocation etch pit density is used as a measure for the dislocation density or the crystallographic
perfection of a crystal, respectively.
2.3 This test method describes methods for preparation of slices and wafers of the III-V compound semiconductors
GaAs, InP and GaP by structural etching. These etching procedures are performed to reveal dislocations by
formation of etch pits on the surface of the test specimens.
2.4 The described methods for identification and registration of etch pits as well as the procedures for evaluation
can be applied also to mono-crystalline monocrystalline semiconductor slices or wafers of other materials or
orientations, provided that there are suitable structural etching procedures available.
2.5 This test method is applicable to material with dislocation densities up to 200,000 cm-2. The resistivity and
conductivity type of the material is irrelevant.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Referenced Standards and Documents
3.1 SEMI Standards and Safety Guidelines
SEMI M10 — Standard Nomenclature for Identification of Structures and Features Seen on Gallium Arsenide
Wafers
SEMI M40 — Guide for Measurement of Roughness of Planar Surfaces on Silicon Wafers
SEMI M59 — Terminology for Silicon Technology
SEMI MF26 — Test Method for Determining the Orientation of a Semiconductive Single Crystal
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
4 Terminology
NOTE 1: Refer to SEMI’s Compilation of Terms (COTs) for a list of the most current terms and their definitions.
4.1 Terms, acronyms, and symbols realting to compound semiconductor material technology are defined in SEMI
M10 and SEMI M59.
4.2 Other Terms Used in this Standard
4.2.1 saucer pit — a shallow etch pit in a crystal surface with no clearly recognizable bottom point, indicating other
types of crystal lattice defect defects instead of dislocations
4.2.2 dislocation etch pit density (EPD) — the number of dislocation etch pits per unit area
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4.2.3 off-orientation — deviation of a crystal surface from a crystallographic plane, characterized by an angle ϕ (see
SEMI MF26) and a direction of tilt, which is given by the projection of a vector normal to the crystal surface onto
the referenced crystallographic plane
4.2.4 measurement field — a rectangular area of the surface of the test specimen for which a local value of the
dislocation etch pit density is determined
4.2.5 measurement location — the center of the measurement field specified by coordinates or an index which
refers to a measurement location plan
4.2.6 measurement location plan — list of measurement locations for which measurements of local EPD are
performed
5 Summary of Test Method
5.1 In this test method dislocation etch pit density in monocrystals of III-V compound semiconductors is
determined as a measure for the dislocation density.
5.2 Test specimens for this method are wafers or slices of monocrystals with surfaces with a deviation from the
{100} crystallographic plan of less than 15°.
5.3 Rough surfaces of etch specimens are flattened by polish-etching with specific etchants.
5.4 The test specimens are etched with an etchant specific for the semiconductor material. On the surfaces of test
specimens etch pits of characteristic shape are formed at the intersection points of dislocation lines with the surface.
5.5 The number of etch pits within certain measuring fields is determined by counting unsing an optical microscope.
The number and position of measuring positions is defined by a measurement location plan.
5.6 The etch pit density is calculated as the number of etch pits per area unit.
6 Physical Background
6.1 When the surface of a test specimen is treated by the etching techniques according to this standard, distinctive
etch pits of characteristic shapes will result at the intersections of dislocation lines with the surface. Etching of
{100} surfaces of GaAs generates elongated hexagonal etch pits (Fig. 1a), while on {100} surfaces of InP and GaP
approximately rectangular etch pits appear (Fig. 1b and 1c). The side-walls of etch pits correspond to low-index
planes of the crystal lattice. They converge towards a common bottom point. This bottom point is a characteristic
feature of dislocation etch pits and allows a discrimination from other etching features.
6.2 Besides dislocations other defects, such as point defects, precipitates and mechanical damage can cause the
formation of etch pits. The resulting etch pits can be distinguished from dislocation etch pits by the missing bottom
point (Fig. 2).
6.3 On surfaces deviating from the {100} crystallographic plane (off-orientated surfaces) the shape of dislocation
etch pits changes depending on angle and direction of off-orientation (Fig. 3).When the angle ϕ exceeds a value of
about 15° the distortion of the shape of etch pits prevents a reliable identification.
6.4 As demonstrated in Fig. 3 for GaAs, the distortion is stronger if the surface is tilted to towards a {111}As face
direction as compared to a tilt to towards a {111}Ga face direction. For other III-V semiconductors a similar
influence of tilt direction is observed. In the case of strong distortion of shape, as shown in Fig. 3d, a reliable
identification of etch pits is impossible. Because of the symmetry properties of the zinc blende structure of III-V
compound semiconductors the tilt direction changes from front to backside of a wafer in respect to the face
directions. Hence, it is possible to choose that side of a wafer for EPD measurement, which shows the better
developed etch pits.
6.5 Specific etchants are used which have a higher etching rate selectively at the intersection of the dislocation line
with the surface. The suitable etchants are specific for a particular semiconductor and a particular crystallographic
orientation of the surface (Table 1).
6.6 For a reliable identification of etch pits their lateral dimension must be within certain limits. The lower limit
depends on the magnification of the microscope used for inspection. The diameter of etch pits should be at least ten
times the optical resolution of the microscope. Overlapping of adjacent etch pits interferes with their reliable
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identification. Therefore their size should not exceed an upper limit which depends on dislocation density. For
material with dislocation density below 10,000 cm-2 suitable diameters of etch pits are 30 to 60 µm. For higher
dislocation densities between from 10,000 cm-2 and to 100,000 cm-2 their diameter should be 20 to 40 µm.
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a)
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Document Number: 5499
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b)
c)
Figure 1
Microscopical images of dislocation etch pits on {100} surfaces of different III-V compound semiconductor
materials: GaAs (a), InP (b) and GaP (c).
Figure 2
Dislocation etch pit (A) and saucer pit (B) on a {100} GaAs surface.
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a)
b)
c)
d)
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Figure 3
Microscopical images of dislocation etch pits on GaAs surfaces with an off-orientation from the {100}
crystallographic plane of 6° (a, b) and 15° (c, d). The off-orientation is directed to towards the {111}Ga face (a,
c) or the {111}As face (b, d). The distortion of the shape of etch pits due to off-orientation of the sample
surface is stronger in the case of tilt to towards the {111} As face. It is recommended to use that side of a
wafer for EPD measurement which shows etch pits as in a) and c).
7 Equipment and auxiliary materials
7.1 Etching equipment for molten potassium hydroxide (KOH)
7.1.1 All equipment must be fabricated from or sheathed by material chemically and thermally resistant against
molten KOH, e.g. silver, pure nickel of a purity of at least 99.5%, glassy carbon
7.1.2 Crucible, containing molten KOH
7.1.3 Carrier for samples
7.1.4 Tweezers for handling of samples
7.1.5 Temperature measurement instrument with type K thermocouple
7.1.6 Hot plate or furnace for temperatures up to 400°C
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7.2 Etching equipment for acidic etchants
7.2.1 All equipment must be fabricated from or sheathed by material chemically resistant against the used etchant,
e.g. PTFE (polytetrafluoroethylene), ETFE (ethylene-tetrafluoroethylene), PFA (perfluoroalkoxy), PMP
(polymethylpenten)
7.2.2 Beaker or etching basin, containing the etchant
7.2.3 Cooling basin or thermostat for controlling the temperature of etchant
7.2.4 Carrier for samples
7.2.5 Tweezers for handling of samples
7.3 Equipment for test specimen inspection
7.3.1 Incident light microscope with 50× to 200× magnification
7.3.2 Stage with sample holder or wafer chuck movable in the plane of sample surface. The range of motion has to
allow the positioning of each part of the sample surface within the measuring field of the microscope. For an
automatic execution of measurement a computer-controlled motor-driven stage is required.
7.3.3 CCD camera connected to the camera port of the microscope. For an automatic execution of measurement an
electronic image analysis system is required.
7.4 Auxiliary materials
7.4.1 The use of chemicals of grade 1 purity is recommended (for references to specifications and guidelines see §
3). The suitability of chemicals of lower purity has to be tested for the particular case by the user of this standard.
8 Procedure
8.1 Sample preparation
8.1.1 For a reliable identification and registration of etch pits a smooth surface is required, provided by a chemicalmechanical or etch-polishing process. Suitable etchants and conditions are listed in Table 2. After etching test
specimens are rinsed with deionized water and dry-blown with filtered air or nitrogen.
8.1.2 For polish-etching the surface of test specimens must have an average rms micro-roughness Rq (SEMI M40)
of Rq ≤ 15 µm and an off-orientation from the {100} crystallographic plane of ϕ ≤ 15°. If Rq > 15 µm or if the
surface shows sawing marks, the surface must be flattened by lapping or grinding.
8.1.3 The roughness of the chemo-mechanical or etch-polished surface of the test specimens should not exceed a
rms micro-roughness Rq of 100 nm within the area of the measuring fields. The etching time for etch-polishing time
is influenced by temperature and eventual depletion of the etching solution.
8.1.4 The polished test specimens are etched by the structural etchants to form dislocation etch pits. Suitable
etchants and conditions are listed in Table 2. The size of etch pits depends on etching time and temperature of the
etchant. Before inserting GaAs test specimens into the KOH melt they should be pre-heated to the temperature of the
melt to avoid breakage due to thermal shock. After etching test specimens are rinsed with deionized water and dryblown with filtered air or nitrogen.
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Table 1 Structural etchants of {100} surfaces of GaAs, InP and Ga
Material
Structural Etchant
Etching Time
{100} GaAs
Molten KOH at 370°C to 400°C1
4 to 15 min.
{100} InP
Mixture of aqueous solution of HBr (40%) and H2O2 (30%) in a ratio of
2:1 at room temperature
5 to 8 min.
{100} GaP
Mixture of aqueous solutions of HF (40%) and H2O2 (30%) in a ratio of
3:1 at 70°C to 80°C2
5 to 8 min.
Table 2 Polishing etchants for {100} surfaces of GaAs, InP and GaP
Material
Polishing etchant
Etching time
{100} GaAs
mixture of conc. H2SO4, aqueous solution of H2O2 (30%) and H2O in a
ratio of 5:1:1 at 50°C to 70°C
5 to 15 min.
{100} InP
mixture of aqueous solutions of HBr (40%), and H2O2 (30%) and H2O
in a ratio of 1:0.07:1 at 40°C to 60°C
2 to 8 min.
{100} GaP
mixture of aqueous solutions of HBr (40%), and H2O2 (30%) and H2O
in a ratio of 1:0.07:1 at 40°C to 60°C
2 to 8 min.
8.2 Measurement of dislocation density
8.2.1 General Remarks
8.2.1.1 In the considered compound semiconductors dislocations tend to form a three-dimensional cellular network.
This can be observed in particular in material with dislocation density above 2000 to 3000 cm -2 and low doping
levels. The surface of a test specimen represents a two dimensional cross section through this network. The
dislocation etch pits are arranged in linear structures forming cell boundaries; whereas the inner volume of the cells
is almost free of etch pits (Fig. 4). The typical cell size can vary from 50 to 200 µm in undoped LEC-grown GaAs to
0.5 to 3 mm in undoped VGF or VB-grown GaAs.
1
2
J.G. Grabmaier, C.B. Watson, Dislocation Etch Pits in Single Crystal GaAs, phys. stat. sol. (b) 32 (1969) K13 – K15
D.G. Hayes, A. Rasul, S.M. Davidson, A dislocation etchant for {100} gallium phosphide, Journal of Electronic Materials, 5 (1976) 351 - 361
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a)
b)
Figure 4
Dislocation etch pit structures on {100} surfaces of GaAs with different dislocation densities a) undoped LECgrown GaAs with EPD  100,000 cm-2 b) undoped VGF-grown GaAs with EPD  5000 cm-2
8.2.2 Measuring fields and measurement locations
8.2.2.1 A measuring field is an area of quadratic shape with a width aF on the surface of the test specimen of
diameter d for which a value of the etch pit density is determined. The measurement location is the geometrical
center of a measurement measuring field. The minimum distance of a measurement location from the edge of the
test specimen is given by the edge distance 𝑑 (see Table 3). All measurement locations are positioned within a
radius of (𝑑/2) − 𝑑 from the center of the test specimen.
8.2.3 Measurement location plans
8.2.3.1 Measurement location plan A
8.2.3.1.1 The measurement locations are arranged on a regular quadratic grid with spacing aG, aligned along the
<110> crystallographic directions. The center of the test specimen is a measurement location. The grid spacing aG
has to be smaller than 𝑑⁄10.
8.2.3.2 Measurement location plan B
8.2.3.2.1 The measurement locations are arranged symmetrically to the center of the test specimen on diameter lines
along the <110> and <100> crystallographic axes (see Fig. 5a). The center of the test specimen is a common
measurement location for both axes. On each axis a sufficient number of measurement locations are positioned with
equal spacing. The distance of two neighboring adjacent measurement locations must not exceed 25 mm (see Table
3).
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edge
distance
measuring field
<100>
45°
edge
distance
6
7
centre of
test specimen
<110>
<110>
1
2
3
4
5
8
9
measuring field
grid spacing aG
a)
b)
Figure 5
Measurement location plans for test slices or wafers with a diameter of 100 mm. a) measurement location
plan b) measurement location plan B
8.2.4 Application of measurement location plans
8.2.4.1 Measurement location plan A can be applied for all kind of material covered by this standard. Measurement
location plan B is provided for test specimens with etch pit densities between 10,000 cm-2 and 200,000 cm-2
particularly originating from LEC-grown mono-crystals monocrystals.
8.2.4.2 The width of measuring fields aF have to accommodate the typical cell size of the material to ensure an
adequate precision of measurement. For material with etch pit density between 10,000 cm-2 and 200,000 cm-2 aF
should be at least 500 µm. For material with etch pit density between 2000 cm-2 and 10 000 cm-2 and for material
exhibiting no cellular arrangement of etch pits aF should be at least 1 mm. The value of aF must not exceed the
distance between measurement locations to avoid overlapping of measuring fields.
8.2.4.3 For measurement location plan B the fraction Fe Fe of the evaluated test specimen surface is given by
equation (1):
Fe 
aF
2
aG
2
(1)
8.2.4.4 The value Fe Fe determines decisively the precision of the testing procedure (see § 9).
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Table 3 Edge distance, minimum number of measurement locations for measurement location
plan B for standard wafer diameters
Diameter d of Test Specimen (mm)
Edge Distance d (mm)
Minimum Number Of Measurement
Locations For Measurement
Location Plan B
50.8
3.0
9
76.2
4.5
9
100
6.0
9
125
7.5
13
150
9.0
13
200
12.0
17
9 Calculation
9.1 Local value of EPD
9.1.1 For each measurement location a local value of etch pit density EPD L is calculated from the number of etch
pits N within the measuring field according to equation (2):
EPDL 
N
2
aF
(2)
9.1.2 The value of aF must be given in cm to obtain the local EPD in cm-2.
9.2 Average value of EPD
9.2.1 The average EPD value for the test specimen has to be calculated from the EPD L values equally weighted by:
EPDav 
1
 EPDL
N
(3)
9.2.2 If for measurement location plan A the width of measurement fields aF is chosen equal to the grid spacing aG
fraction Fe Fe is 1, i.e. the complete surface of the test specimen except of the edge region is evaluated. This gives
the opportunity to determine the true value of EPDav of the test specimen.
9.3 Optional graphical data representation
9.3.1 Frequency distribution of etch pit density
9.3.1.1 For a test specimen measured using measurement location plan A the distribution of dislocation etch pit
density can be represented graphically by a histogram displaying the frequency of etch pit densities for the locations
measured (Fig. 6).
9.3.1.2 To obtain a reasonable representation of the data the interval limits of the frequency distribution have to be
set to integer multiples of 1⁄𝑎 2 1⁄𝑎𝐹2
𝐹
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0.08
1.0
0.9
0.07
0.8
cumulative frequency
relative frequency
0.06
0.05
0.04
0.03
0.02
0.7
0.6
0.5
0.4
0.3
0.2
0.01
0.1
0.00
0.0
4000
8000 12000 16000 20000
4000
-2
8000 12000 16000 20000
-2
etch pit density [cm ]
etch pit density [cm ]
Figure 6
Example for the graphical representation of frequency distribution of etch pit density
9.3.2 Etch pit density maps
For a test specimen measured using measurement location plan A the measured data can be plotted as a map using a
color or gray scale to code the values measured at the individual measurement locations (Fig. 7).
a)
b)
Figure 7
Examples for etch pit density maps: a) 150 mm undoped semi-insulating GaAs wafer, EPDav = 8410 cm-2,
measuring field width aF = 0.5 mm, evaluated fraction of surface Fe Fe = 100% b) 100 mm silicon-doped
GaAs wafer, EPDav = 54 cm-2, measuring field width aF = 0.5 mm, evaluated fraction of surface Fe Fe = 100%
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10 Precision of Measurement
10.1 The precision of measurement is influenced mainly by two factors: by the reliability of the etch pit detection
and by statistical effects resulting from the sampling procedure.
10.2 For measurement location plan A the evaluated fraction Fe Fe of the test specimen surface is decisive for the
precision of the measurement. Depending on the degree of inhomogeneity of the etch pit density distribution the
uncertainty of EPDav increases with decreasing Fe Fe.
10.3 To illustrate this relation Fig. 8 shows upper bounds of error for EPD av as a function of Fe Fe for test
specimens of three different ranges of average etch pit density. These curves have been determined empirically from
the analysis of measurements at 120 GaAs wafers with EPDav ranging from 30 cm-2 to 10,000 cm-2. Measurements
have been carried out using a measuring field width aF of 0.5 mm and a grid spacing aG of 0.5 mm resulting in
Fe Fe = 1. Measurements with lower Fe Fe have been simulated by omitting measuring fields in the calculation of
EPDav. By this means the grid spacing was enlarged incrementally to 20 × aF. Additionally, the measurement
measuring field width was increased to 1.0 mm, 1.5 mm and 2.0 mm by combination of 4, 9 and 16 neighboring
adjacent primary measuring fields. Based on the variation of both parameters the curves in Fig. 8 have been
calculated so that 95% of the simulated measurements showed a deviation of EPD av from the original value below
the bound.
10.4 In the case of use of measurement location plan B the relative uncertainty of EPDav is about 20%.
100
-2
upper error bound for EPDav (%)
EPDav < 200 cm
80
-2
60
EPDav = 200 ... 2000 cm
40
EPDav 2000 ... 10000 cm
-2
20
0
0.1
1
10
100
evaluated fraction Fe (%)
Figure 8
Upper error bounds for measurement on GaAs wafers. The curves give 95% limits for the relative
uncertainty of measurement in dependence of the evaluated fraction Fe Fe of the test specimen surface.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document
development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Doc. 5499  SEMI
LETTER (YELLOW) BALLOT
Document Number: 5499
Date: 2/6/2016
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DRAFT
11 Report
11.1 The test report must include the following.
11.1.1 Reference to this standard
11.1.2 Type of test specimen
11.1.3 Dimensions and shape of test specimen
11.1.4 Applied structure etching solution
11.1.5 Applied measurement location plan
11.1.5.1 In case of measurement plan A
11.1.5.1.1 Grid spacing aG
11.1.5.1.2 Width aF of measurement measuring fields
11.1.5.2 In case of measurement plan B
11.1.5.2.1 Number N of measurement locations
11.1.5.2.2 Width aF of measurement measuring fields
11.1.6 Average value of dislocation density EPDav
11.1.7 Optionally:
11.1.7.1 Dislocation density maps with the applied color or grey scale (measurement location plan A)
11.1.7.2 Frequency distribution of dislocation density (measurement location plan A)
11.1.7.3 Local etch pit density values EPDL (measurement location plan B)
11.1.8 Test date, test location, operator
12 Related documents
12.1 SEMI standards
SEMI C28 — Specifications for Hydrofluoric Acid
SEMI C30 — Specifications for Hydrogen Peroxide
SEMI C39 — Specifications for Potassium Hydroxide Pellets
SEMI C44 — Specifications and Guidelines for Sulfuric Acid
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This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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Doc. 5499  SEMI
LETTER (YELLOW) BALLOT
Document Number: 5499
Date: 2/6/2016