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SEMI M12-1103 © SEMI 1988, 2003 4 Figure 4 Character Window Location for Notched Wafers NOTE: The vertical center line r eferenced in Figure 4 is th e bisector of the primary fiducial (notch ). 8 Character Alignment 8.1 …

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SEMI M12-1103 © SEMI 1988, 2003 3
6.3 An example of the code is given in Figure 2.
6.4 SEMI-OCR Standard Character Set — This character set contains capital letters from A to Z, numerals from 0
to 9, a dash, and a period (see Appendix 1). The period is NOT used in the code symbols defined in this
specification (see Tables 2 and 3), although it is required for use in the code symbols defined in SEMI M13.
Table 3 SEMI OCR Character Set Modified for Use in this Specification
7 Character Window
7.1 The character window must be located on the front surface of the wafers.
7.2 All characters must be contained within the character window dimensions specified in Figures 3 (for flatted
wafers) or Figure 4 (for notched wafers).
7.3 The top of the characters is toward the side of the character window nearest to the flat or notch.
Figure 3
Character Window Location for Flatted Wafers
NOTE: The vertical center line referenced in Figure 3 is the bisector of the primary fiducial (flat).
SEMI M12-1103 © SEMI 1988, 2003 4
Figure 4
Character Window Location for Notched Wafers
NOTE: The vertical center line referenced in Figure 4 is the bisector of the primary fiducial (notch).
8 Character Alignment
8.1 Character Skew — the maximum allowable angle
between the character baseline and a line parallel with
the bottom of the character window shall be 3 degrees
(see Figure 5).
Figure 5
Character Skew
NOTE: This line is parallel to the bottom of the character
window.
8.2 Maximum Character Misalignment — the
maximum adjacent character misalignment, R
adj
shall
be 0.23 mm (see Figure 6), and the maximum line
character misalignment, R
line
, shall be 0.46 mm (see
Figure 7).
R
adj
Figure 6
Adjacent Character Misalignment
R
line
Figure 7
Line Character Misalignment
SEMI M12-1103 © SEMI 1988, 2003 5
9 Alphanumeric Error-Detecting Method
9.1 The alphanumeric check characters in character
locations 11 and 12 are a required part of the Code
defined in this specification.
9.2 All single-character substitution errors are detected.
9.3 All two-character transposition errors are detected
for any message up to 58 characters in length.
9.4 The character set may be expanded to include the
first 59 characters of the ASCII 64-character set.
9.5 There exist simple recursive algorithms for error
detection and check character generation that do not
require the use of multiplication or division.
9.6 Definition of the Error-Detecting Method
9.6.1 For the purpose of describing the error-detecting
method, we define the following symbols:
• A
i
represents the ith ASCII character.
• a
i
represents the numerical value assigned to A
i
.
9.6.2 The characters are numbered from left to right, so
that the message is given by
A
1
A
2
A
3
…A
12
9.6.3 A complete description of the error-detecting
method is given by the following seven rules:
9.6.3.1 The numerical value a
i
is found by subtracting
32 from the ASCII decimal representation of A
i
(refer
to Table 4 — Character Values).
9.6.3.2 An ASCII character A
i
is allowed only if its
numerical value a
i
is one of
0,1,2,…58.
9.6.3.3 The check character A
11
must be one of the
ASCII characters A,B,C,D,E,F,G,H.
9.6.3.4 The check character A
12
must be one of the
ASCII characters 0,1,2,3,4,5,6,7.
9.6.3.5 The check character pair A
11
A
12
may not be one
of the combinations H3, H4, H5, H6, H7.
9.6.3.6 When the message is written, the check
characters A
11
and A
12
are chosen such that 59 divides
the expression
8
11
a
1
+ 8
10
a
2
…+8
2
a
10
+ 8a
11
+ a
12
without a remainder.
9.6.3.7 If, on reading the message, 59 does not evenly
divide the expression given above, an error has
occurred.
Table 4 Character Values
ASCII Character ASCII Decimal Value Numerical Value
– 45 13
.(Note 1) 46 14
0 48 16
1 49 17
2 50 18
3 51 19
4 52 20
5 53 21
6 54 22
7 55 23
8 56 24
9 57 25
A 65 33
B 66 34
C 67 35
D 68 36
E 69 37
F 70 38
G 71 39
H 72 40
I 73 41
J 74 42
K 75 43
L 76 44
M 77 45
N 78 46
O 79 47
P 80 48
Q 81 49
R 82 50
S 83 51
T 84 52
U 85 53
V 86 54
W 87 55
X 88 56
Y 89 57
Z 90 58
Note 1: This character is not used in the code symbol covered
by this specification.
9.7 Suggestions for Implementation — The error-
detecting method can be implemented directly by
calculating the expression given above, and the check
characters can be found by exhaustive search.
However, this approach is unnecessarily complex; a
decrease in complexity can be made by taking
advantage of three simple observations.