ASTM F1404-92(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F1404 − 92(Reapproved 2007)
Test Method for
Crystallographic Perfection of Gallium Arsenide by Molten
Potassium Hydroxide (KOH) Etch Technique
This standard is issued under the fixed designation F1404; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Semiconductive Single Crystal (Withdrawn 2003)
F47Test Method for Crystallographic Perfection of Silicon
1.1 This test method is used to determine whether an ingot
by Preferential Etch Techniques
or wafer of gallium arsenide is monocrystalline and, if so, to
measure the etch pit density and to judge the nature of crystal
3. Summary of Test Method
imperfections. To the extent possible, it follows the corre-
3.1 The determination of the etch pit density is only
sponding test method for silicon, Test Method F47. Test
meaningfulformonocrystallinematerial.Afteramechanicalor
Method F47 also presents the definition of many crystallo-
chemical polish, or both, of the sample surface, the sample is
graphic terms, applicable to this test method.
etched in molten KOH. This agent preferentially attacks the
1.2 This procedure is suitable for gallium arsenide crystals
gallium arsenide surface in regions of crystal imperfections,
with etch pit densities between 0 and 200000/cm .
suchaslowanglegrainboundaries,twinlamellae,precipitates,
1.3 Gallium arsenide, either doped or undoped, and with slip lines, and dislocations. The etched surface is examined
various electrical properties, may be evaluated by this test
microscopically to characterize these imperfections, and deter-
method.The front surface normal direction of the sample must mine their density.
be parallel to the <001> within 6 5° and must be suitably
3.2 Viewed through an optical microscope, etch pits appear
preparedbypolishingoretching,orboth.Unremovedprocess-
asdarkelongatedhexagonalpits.Theetchpitdensity(EPD)is
ing damage may lead to etch pits, obscuring the quality of the
determinedbycountingthesepitsatninedifferentstandardized
bulk crystal.
locationsacrossthesamplealong<011>and<001>directions.
1.4 This standard does not purport to address all of the
Alens micrometer or a grid installed in the microscope is used
safety problems, if any, associated with its use. It is the
to define the sampling area. The reported EPD is obtained by
responsibility of the user of this standard to establish appro-
averaging the EPD values in the nine counted areas.
priate safety and health practices and to determine the
3.2.1 The orientation of the elongated KOH etch pits may
applicability of regulatory limitations prior to use. Specific
also be used to determine the crystal orientation prior to the
hazard statements are given in Section 8.
addition of flats to gallium arsenide (GaAs) wafers or crystals.
4. Significance and Use
2. Referenced Documents
4.1 The use of GaAs for semiconductor devices requires a
2.1 ASTM Standards:
consistent atomic lattice structure. However, lattice or crystal
D1125Test Methods for Electrical Conductivity and Resis-
line defects of various types and quantities are always present,
tivity of Water
and rarely homogeneously distributed. It is important to
E177Practice for Use of the Terms Precision and Bias in
determine the mean value and the spatial distribution of the
ASTM Test Methods
etch pit density.
F26Test Methods for Determining the Orientation of a
5. Characteristics of Revealed Imperfections
5.1 The KOH etch of the specimen surface reveals patterns
This test method is under the jurisdiction of ASTM Committee F01 on
Electronics and is the direct responsibility of Subcommittee F01.15 on Compound that are characteristic for several of the crystalline defects
Semiconductors.
described in detail in Test Method F47.
Current edition approved Dec. 1, 2007. Published January 2008. Originally
5.1.1 Dislocations on {100} GaAs surfaces are character-
approvedin1992.Lastpreviouseditionapprovedin1999asF1404-92(1999).DOI:
izedbymicroscopicanisotropicsix-sidedetchpits.Thesizeof
10.1520/F1404-92R07.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F1404 − 92 (2007)
the pits depends on the consistency of the etch and the etching the American Chemical Society. Other grades may be used,
time and will be typically 25 to 50 µm for the procedure provided it is first ascertained that the reagent is of sufficiently
described in Section 9. Because the sides of these pits are not high purity that it will not reduce the accuracy of the test.
normal to the incident light, they appear dark under vertical
7.2 Purity of Water— Reference to water shall be under-
field illumination. The use of a Nomarski microscope is
stood to mean either distilled or deionized water with a
optional.
resistivitygreaterthan2MΩ·cmat25°C,asdeterminedbythe
5.1.2 Lineage, a precursor to a low-angle boundary, appears
nonreferee method of Test Methods D1125.
as a linear array of etch pits with a density greater than 25
7.3 Chemical Polish— One of the following:
pits/mm.Forthistestmethod,lineararrayslessthan0.5mmin
7.3.1 PolishingEtch,(suchasbromine/methanol,orsulfuric
length are not considered lineage. The individual etch pits are
acid/hydrogen peroxide).
aligned end to end, or side to side. The lineage does not
7.3.2 Sodium Hypochlorite.
necessarily follow a <110> direction.
7.4 Lapping Abrasive— Alumina, Size 5 (0.06 to 0.3 µm).
5.1.3 Slip is evidenced by a pattern of one or more straight
lines of etch pits that do not necessarily touch each other. The
7.5 Degreasing Chemicals—As required according to pre-
endsoftheanisotropicetchpitswillbeonacommonline.This
vious process such as:
line of etch pits will be in a <110> direction.
7.5.1 1,1,1–trichloroethane (TCA 1-1-1),
7.5.2 Acetone,
5.1.4 A grain boundary appears as a grooved line of any
length in which individual etch pits cannot be resolved 7.5.3 Isopropanol (2-propanol), and
7.5.4 Other Wax-Removing Solvent.
microscopically at 200× magnification.The grooved lines may
encloseanareaoftheetchedsurfaceorextendtotheperiphery
7.6 Defect Etch:
of the specimen.
7.6.1 Potassium Hydroxide (KOH), anhydrous.
5.1.5 A twin boundary appears as a straight line at the
intersectionofacrystallographicplane(usuallya<111>plane) 8. Hazards
and the etched surface under examination. Two parallel twin
8.1 The chemicals used in this evaluation procedure are
boundaries that are separated by only a few crystal lattice
potentially harmful and must be handled with the utmost care
planes form a twin lamella that appears as a straight grooved
at all times. Read the most current copy of the Material Safety
line.
Data Sheet (MSDS) for each chemical used. Wear protective
gloves and a safety mask so that molten KOH cannot contact
6. Apparatus
your skin. Safety glasses must be worn at all times. Observe
common laboratory safety precautions. Dispose of all chemi-
6.1 Slicing Equipment—Typically an inside diameter (ID)
cals properly.
saw. Such a saw produces a minimum amount of cutting
damage.
9. Sample
6.2 Wafer Preparation Equipment —This equipment in-
9.1 The wafer to be measured must be free of inclusions,
cludes lapping and polishing facilities capable of removing a
large grains and twins. Those would interfere with the deter-
minimum of 12µ m from the surface to be characterized. A
mination of the average EPD value.
polishing etch may be used in place of the wafer polisher, but
9.2 Theprocedureappliestocrystalsgrownbyanymethod,
will require substantially more stock removal (50 µm mini-
such as Liquid Encapsulated Czochralski (LEC), Horizontal
mum).
Bridgman (HB), and Vertical Gradient Freeze (VGF). The
6.3 Laboratory Equipment—Nickel crucibles and tweezers
sample surface must be oriented within 5° parallel to a <100>
are necessary to work with molten KOH. Platinum or zirco-
plane.
nium have also been used successfully and can be substituted
for the nickel tools.
10. Procedure
6.4 Device,capableofheatingthecruciblewiththesamples
10.1 Orient the ingot so that the front surface normal
to 500°C.
direction of the sample is parallel to the <001> within 5°.
EithertheX-rayortheopticalmethodofTestMethodsF26can
6.5 Microscope, provided with 10× and 20× magnification
beapplied.Cutawaferatleast0.025in.-thickfromthecrystal.
objectivelenses,a10×magnificationeyepiece,a0.5-mmpitch
Ifthecrystalhasnoflats,notcha{110}edgeofthewafer.This
micrometer, and a metric stage micrometer.
7. Reagents and Materials
“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-
cal Soc., Washington, DC. For suggestions on the testing of reagents not listed by
7.1 Purity of Reagents—Reagent grade chemicals shall be
theAmericanChemicalSociety,see“ReagentChemicalsandStandards,”byJoseph
used in all tests.Where available, all reagents shall conform to
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
the specifications of the Committee onAnalytical Reagents of Pharmacopeia.”
F1404 − 92 (2007)
will later permit locating areas for etch pit counting. LEC 10.12.1 Iflargeandovercrowdedpitsarepresentthesample
crystalsgrownon<100>resultinroundwafers.HBwafersare may have been etched too long, or at too high a temperature.
D-shaped, unless processed into round wafers. 10.12.2 Change the objective lens to 20× magnification and
check again. If the pits are still too difficult to count, repeat
10.2 Polish the wafer. Afterwards, the wafer must be
10.1 to 10.11 for a shorter etch time, for example, to a total
cleanedanddried.Makesurethataminimumof0.0015in.has
time of 7 min.
been removed from each side. If the wafer appears contami-
nated or not fully polished, repeat the polishing process. 10.13 Foretchpitdensitieslessthan500/cm ,chooseafield
of view that results in a minimum of 20 pits and a maximum
10.3 If the wafer was exposed to wax during previous
of 150 pits in each counting area. The field selection should
processes, it must be fully degreased. Immerse the wafer for
remain as representative as possible.
five min in hot (60°C) 1,1,1–trichloroethane, followed by 5
min in cold 1,1,1–trichloroethane, followed by an acetone dip 10.14 Theetchpitdensityistobeestablishedin9locations.
TheselocationsaredefinedinTable1forroundwaferssuchas
and by an isopropanol dip. Finally, immerse the wafer for five
min in hot (60°C) isopropanol; remove the wafer and allow to produced by the LEC process and in Table 2 for D-shaped
air dry. wafers produced by the HB method. Table 2 has been taken
from Table 1 of Test Method F47.
10.4 Place the wafer in the center of the bottom of a nickel
10.14.1 For LEC GaAs the EPD distribution does not have
crucible. If several wafers are treated simultaneously, the
circular symmetry. The average EPD does not fully describe
wafersshouldnottoucheachotherorthewallsofthecrucible.
the condition of the entire wafer.
A large, flat crucible may be necessary.
10.14.2 For specimens with EPD greater than 500/cm ,a
10.5 Cover the wafers with KOH completely. Use KOH
10× objective lens is recommended.A20× objective is recom-
sparingly and avoid skin contact; remember to wear eye
mended when counting EPDs in the range of 30000 to
protection.
200000/cm .
10.6 Preheat the heating device to 450°C. Place the lid on
10.15 Round LEC Wafers— To count the EPD, place the
the crucible. Place the crucible on the heating device. Check
etched specimen on the microscope stage so that the major flat
after 3 min to verify that KOH is completely molten; if not,
faces towards the operator. If the sample has no flats, orient it
increase the heat-up time. Leave the crucible on the heating
so that the long axis of the pits point toward the operator. Note
device for additional 7 min.
the location of the reference notch from 10.1 for test records.
10.15.1 MeasurethediameterofthewaferusingtheVernier
10.7 Usinglongtongs,removethecruciblefromtheheating
scale of the microscope stage. Determine the nine counting
device and place it on a hot pad nearby. Remove the lid.
positions according to Table 1 and Fig. 1.
10.8 Pour the molten KOH into a second nickel crucible.
The molten KOH can be used once more for a second batch of NOTE 1—The order of the counting locations differs from Test Method
F47 to avoid interference with the flats on GaAs wafers.
wafers.
10.15.2 With the wafer flat facing the operator, move the
10.9 Using the nickel tweezers, place the wafer(s) nearly
wafer so that the 0.5-mm micrometre disk is centered in
uprightalongthewallofthecruciblesothatmostofthemolten
Position 1. Count the etch pits and record the results as well as
KOH drips off. This will also allow for easy wafer removal
the microscope objective magnification. Repeat the procedure
once the KOH freezes. Allow the wafers to cool for 5 min.
for Position 2 etc. Upon reaching Position 5, rotate the wafer
10.10 Place the wafer(s) under running dionized water until
45° clockwise and continue for Positions 6 through 9. In
the remaining solid KOH is fully removed.Any KOH remain-
calculating the average EPD, be sure to count Position 3 only
ing in the crucible may be removed the same way.
once.
10.11 Examine the wafer. The previously polished surface
10.16 {100} Oriented D-Shaped Wafers From Boules
shouldnowhaveadull,matteappearance.Itmayexhibitsome
Grown by the Bridgman Method:
cellularstructures.Examineitunderthemicroscopewitha10×
10.16.1 The etch pit density of these wafers will be counted
objective lens to determine if the proper development of etch
at9locationsthataredifferentfromthelocationsusedforLEC
pits has occurred. If no pits have developed, repeat 10.4
wafers. Because of the wafer shape asymmetry, and because
through 10.11 with an adjustment of the heating period, for
the KOH etch pits on D-shaped wafers have a more uniform
example, to a total time of 15 min.
distribution, the two counting axes are chosen at 90° to one
10.12 Adjustments for Overetched Wafers: another as shown in Fig. 2.
TABLE 1 Test Locations for Round GaAs Wafers
NOTE 1—Reference point is the wafer edge opposite to the major flat.
Wafer Diameter Positions 1 and 6 Positions 2 and 7 Position 3 Positions 4 and 8 Positions 5 and 9
2in.(50.8mm) 4mm 15mm 26mm 37mm 48mm
3 in. (76.2 mm) 5 mm 21.5 mm 38 mm 54.5 m
...