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SEMI M6-1000 © SEMI 1981, 2000 4 6.4 W afe r defect limits — See T ab l e 1 . Table 1 Waf er Defect Limit s Item Characteristics* Max Defect Limits Notes 1S a w M a r k s 20 µ m TIR 1 2A r e a Contam ination To be de ter…
SEMI M6-1000 © SEMI 1981, 20003
5.1.7 Lot acceptance procedures (see Section 6.4),
5.1.8 Certification (if required) (see Section 8),
5.1.9 Packing and marking (see Section 9),
5.1.10 Selection of test method to be used in
evaluating those items for which alternate tests exist
(see Section 7), and
5.1.11 Carbon and oxygen content.
5.2 Optional criteria. The followin g items may be
specified optionally in addition to those listed above:
NOTE 4: Items in Paragraph 5.2 are less commonly specified
than the others, but are included for completeness as
parameters for which methods of evaluation have been
developed.
5.2.1 Impurities other than common doping elements,
5.2.2 Diffusion length, and
5.2.3 Minority carrier lifetime.
NOTE 5: Up to now diffusion length and minority carrier
lifetime cannot be measured with sufficient inter-laboratory
accuracy. Subsequent recommendations, following lifetime
round robin experiments, will be available in the future and
will be presented in an addendum to this standard.
Even in the case of comparable and reproducible lifetime and
diffusion length measurements, the measured characteristics
must be regarded as an indication for solar cell efficiency.
There is no general relation between initial minority carrier
lifetime and solar cell efficiency as other parameters such as
carbon or oxygen content will also influence the wafer in the
solar cell process. However, in practical cases a dependence
between minority carrier lifetime and solar cell efficiency can
be found for a fixed solar cell process and a certain silicon
wafer material. If one of them is changed the relation between
them is suspect to change too.
6 Requirements
6.1 Dimensions and Permissible Variations
6.1.1 Wafer Thickness and Variation
6.1.1.1 Wafer thickness is typically 330 micrometer in
1999. In the future wafers should be specified in 50
micrometer intervals in the range between 150 and 400
micrometers.
6.1.1.2 The variation of wafer thickne ss in a lot as
measured according to 7.2 at the center point of each
wafer will be less than 15% of the specified wafer
thickness.
6.1.2 Rectangular Mainly Square Wafer Dimensions
— Depending upon the wafer type, one of the sections
6.1.2.1, 6.1.2.2 or 6.1.2.3 applies.
6.1.2.1 Square Crystalline Silicon Wafer Dimensions
6.1.2.1.1 Physical dimensions — See Figure 1, Table
2
Rectangular cells are permitted as long as the measures
of A and B are according to the nominal size measures
in Table 2.
Example: A = 100 mm, B = 150 mm.
Dimension D (identical for all sizes) min = 0.5 mm,
max = 2.0 mm. By bilateral agreement, one corner can
be of different angle and size to indicate the orientation
of the wafer.
Squareness: The wafer will fit inside a square of the
maximum dimension A and contain a square of the
minimum dimension A.
6.1.2.1.2 TTV: 50 micrometer.
6.1.2.2 Circular Monocrystalline Photovoltaic Solar
Cell Silicon Wafers
6.1.2.2.1 Diameters (mm): 100, 125, 150, 175, 200:
Variation in diameter: ± 1 mm all sizes
6.1.2.2.2 TTV: 30 micrometer.
6.1.2.2.3 Warp: 75 micrometer.
6.1.2.3 Pseudo-Square Monocrystalline Photovoltaic
Solar Cell Silicon Wafers
6.1.2.3.1 Physical dimensions: See Figure 2, Table 3
6.1.2.3.2 TTV: 30 micrometer.
6.1.2.3.3 Warp: 75 micrometer.
6.2 Materials and Manufacture
6.2.1 The material shall consist of wafers conforming
to the structural class specified in the purchase order or
contract.
6.3 Physical Parameters
6.3.1 The material shall conform to the
crystallographic orientation details as specified in the
purchase order or contract.
6.3.2 The material shall conform to the details
specified in the purchase order or contract, as follows:
6.3.2.1 Conductivity type and dopant (see Note 3),
6.3.2.2 Resistivity,
6.3.2.3 Amounts of impurities other th an common
dopants (such as phosphorous, boron), especially
oxygen and carbon content (optional),
6.3.2.4 Diffusion length (optional), and
6.3.2.5 Minority-carrier lifetime (optional).
SEMI M6-1000 © SEMI 1981, 2000 4
6.4 Wafer defect limits — See Tab le 1.
Table 1 Wafer Defect Limits
Item Characteristics* Max Defect Limits Notes
1Saw Marks
20 µm TIR
1
2Area
Contamination
To be determined
3Edge
Chips/Indents
2 per wafer max
up to l mm wide
and l mm deep
2
4 Cracks/crow's feet None
* Characteristics are defined in SEMI M1, Section 10.
NOTE 1: The outer l mm (0.040") is excluded from these criteria.
NOTE 2: Excluding conchoidal chips.
6.5 Sampling
6.5.1 Unless otherwise specified, Practice E 122 shall
be used.
6.5.1.1 When so specified, appropriate sample sizes
shall be selected from each lot in accordance with
ANSI/ASQC Z1.4. Each quality characteristic shall be
assigned an acceptable quality level (AQL) and lot
tolerance percent defective (LTPD) value in accordance
with ANSI/ASQC Z1.4 definitions for critical, major,
and minor classifications. If desired and so specified in
the contract or order, each of these classifications may
alternatively be assigned cumulative AQL and LTPD
values. Inspection levels shall be agreed upon between
the supplier and the purchaser.
7 Test Methods
NOTE 6: Silicon wafers are extremely fragile. While the
mechanical dimensions of a wafer can be measured by use of
tools such as micrometer calipers and other conventional
techniques, the wafer may be damaged physically in ways that
are not immediately evident. Special care must therefore be
used in the selection and execution of measurement methods.
7.1 Length, Width, or Diameter — Determine the
diameter of circular wafers in accordance with ASTM
Test Method F 613. Determine the side length of square
wafers by a method agreed upon between the supplier
and the purchaser.
7.2 Thickness, Center Point — Determine in
accordance with ASTM Test Methods F 533 or DIN
50441-1.
7.3 Thickness Variation — Determ ine in accordance
with ASTM Test Methods F 533 or F 657.
7.4 Structural Class — Determine the structural class
by a method agreed upon between the supplier and the
purchaser.
7.5 Surface Orientation — Determine in accordance
with ASTM Test Methods F 26 or DIN 50433-1, DIN
50433-2 and DIN 50433-3.
7.6 Conductivity Type — Determine in accordance
with ASTM Test Methods F 42 or DIN 50432.
7.7 Resistivity — Determine by methods agreed upon
between the supplier and the purchaser.
NOTE 7: Resistivity of wafers is most appropriately
determined for referee purposes by ASTM Method F 84 or
DIN 50431. Reliable measurements with these methods can
only be made in regions of a wafer which contain no grain
boundaries; these methods are therefore not appropriate for
multicrystalline material. Under some circumstances these
tests may be considered destructive, and an alternative means
may be required. One non-destructive test is ASTM Test
method F 673, having a range from 0.001 to 100 Ω-cm. This
method is relatively insensitive to the presence of grain
boundaries and is recommended for all material types.
Another nondestructive test is ASTM Test Method F 398.
This method is limited to carrier concentrations in the ranges
from 1.5 × 10
18
cm
-3
to 1.5 × 10
21
cm
-3
for n-type silicon and
from 3 × 10
18
cm
-3
to 5 × 10
20
cm
-3
for p-type, and has only
moderate inter-laboratory precision. Other available methods
include ASTM Test methods F 43 or DIN 50430 (referee
methods requiring a bar-shaped sample).
7.8 Other Impurities — Determine by methods agreed
upon between the supplier and the purchaser.
NOTE 8: ASTM Test Methods F 1188, F 1619 and DIN
50438-1 are specific tests for oxygen. ASTM F 1391 and DIN
50438-2 are specific tests for carbon; special thick test
specimens are necessary.
7.9 Minority Carrier Diffusion Length — Determine
by methods agreed upon between the supplier and the
purchaser.
NOTE 9: Methods for minority carrier diffusion length are
listed in ASTM F 391.
7.10 Minority Carrier Lifetime — D etermine by
methods agreed upon between the supplier and the
purchaser.
NOTE 10: Methods for minority carrier lifetime
measurements are given in ASTM F 28 (bulk material),
ASTM F 1535 (wafers) and JEIDA-53 (wafers). As the wafer
methods measure an effective lifetime, the sample preparation
(surface passivation) and measurement conditions will
influence the results and must be considered.
8 Certification
8.1 Upon request of the purchaser in the contract or
order, a manufacturer’s or supplier’s certification that
the material was manufactured and tested in accordance
with this specification, together with a report of the test
results, shall be furnished at the time of shipment.
SEMI M6-1000 © SEMI 1981, 20005
8.2 In the interest of controlling in spection costs, the
supplier and the purchaser may agree that the material
shall be certified as ‘capable of meeting’ certain
requirements. In this context, ‘capable of meeting’ shall
signify that the supplier is not required to perform the
appropriate tests in Section 7. However, if the purchaser
performs the test and the material fails to meet the
requirement, the material may be subject to rejection.
9 Packing and Package Lab eling
9.1 Special packing requirements shall be subject to
agreement between the supplier and the purchaser.
Otherwise all wafers shall be handled, inspected, and
packed in such a manner as to avoid chipping,
scratches, and contamination, and in accordance with
the best industry practices to provide ample protection
against damage during shipment.
9.2 The wafers supplied under these specifications
shall be identified by appropriately labeling the outside
of each box or other container and each subdivision
thereof in which it may reasonably be expected that the
wafers will be stored prior to further processing.
Identification shall include as a minimum the nominal
diameter, conductivity type, dopant, orientation,
resistivity range, and lot number. The lot number, either
(1) assigned by the original manufacturer of the wafers,
or (2) assigned subsequent to wafer manufacture but
providing reference to the original lot number, shall
provide easy access to information concerning the
fabrication history of the particular wafers in that lot.
Such information shall be retained on file at the
manufacturer’s facility for at least one year after that
particular lot has been accepted by the purchaser.