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SEMI P19-92 © SEM I 1992, 1996 2 isolated line — a clearfield, dark line as shown in Figure 2 (SYN: is land). Figure 2 Isolate d Line isolated s pace — A dark field, clear line as shown in Figure 3 (SYN: window, tren ch,…

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SEMI P19-92 © SEMI 1992, 19961
SEMI P19-92
SPECIFICATION FOR METROLOGY PATTERN CELLS FOR
INTEGRATED CIRCUIT MANUFACTURE
Purpose
This document defines several standard test patterns to
provide consistent industrywide evaluation and testing
of micropatterning equipment, metrology instruments,
and processes used in integrated circuit manufacturing.
1 General Specification
1.1 Scope
1.1.1 This specification defines the s hape, general
size, and recommended placement and design rules
(where appropriate) of several basic pattern cells for
linewidth metrology, resolution testing, and proximity
testing. These standard patterns include cells that can be
used for optical microscopy, electron microscopy, and
electrical probe testing.
1.1.2 This document does not attempt to specify the
measurement techniques to be used in verifying critical
dimensions for these test patterns on the reticle.
Similarly, this document does not attempt to specify
how the printed patterns are to be measured on the
wafer. This document specifies only what the patterns
are supposed to be; it is left to the user to ensure that
the actual pattern conforms to this specification, subject
to all other applicable SEMI specifications. A separate
SEMI document will specify CD measurement
conditions (see Section 1.2.1).
1.2 Applicable Documents
1.2.1 SEMI Standards
SEMI P24 — CD Metrology Procedures
1.3 Definitions
linewidth — In semiconductor technology, at a given
cross-section of the line, the distance between the
airline material boundaries at some specified height
above the interface between the patterned layer in
which the line is formed and the underlying layer (see
Figure 1).
Figure 1
Linewidth (X
0
, Z
0
) = Y
2
- Y
1
NOTE: The physical basis for various methods of measuring
linewidth may result in the measurements being carried out at
differing heights for the same line at the same cross-section.
For this reason, substantial method-dependent differences in
measurement results may be expected and it is convenient to
identify the method used in expressions such as “SEM
linewidth,” “optical linewidth,” or “electrical linewidth”
(ASTM F 127). Furthermore, the height at which the
measurement is taken shall be qualitatively stated, even if it
cannot be quantitively determined.
feature — areas within a single, continuous boundary
(for example, an aggregate image) that have an optical-
density value (gray-level range), that is distinct from
the background area outside the feature (ASTM D
3849, D 24) (e.g., the simplest element of a pattern,
such as a single line, space, or L-bar).
feature group — a small assembly of one or more
similar features arranged together, such as three nested
L-bars.
nominal feature dimension — the linear dimension of
interest, such as the linewidth or contact hole width.
basic cell — an arrangement of features or groups, as
defined by this document, based upon a specific,
nominal-feature dimension.
composite cell — an arrangement of several basic cells.
SEMI P19-92 © SEMI 1992, 1996 2
isolated line — a clearfield, dark line as shown in
Figure 2 (SYN: island).
Figure 2
Isolated Line
isolated space — A darkfield, clear line as shown in
Figure 3 (SYN: window, trench, contact, opening).
Figure 3
Isolated Space
2 Detail Specification
2.1 Introduction
2.1.1 This specification describes th e pattern cells,
which are illustrated in the figures at the end of this
document. These cells are to be placed
photolithographically or by other direct patterning
methods onto wafer substrates at different masking
levels during the IC manufacturing process.
2.1.2 Many details of the pattern cel ls, such as the
orientation, magnitude, range of the linewidths, and
polarity of tone (clearfield vs. darkfield) will be defined
by the user, unless otherwise noted. When reporting
results based on tests using these cells, details such as
field polarity, orientation, and topographic
considerations must be indicated.
2.1.3 All critical dimensions given i n this document
are the actual CAD values at 1X. For a given
magnification, M, the target dimensions on the reticle
should be exactly M times the dimension given in this
specification. The reticle dimensions must not be sized
to compensate for any wafer process-induced bias.
2.2 Applications
2.2.1 These cells are intended to be used in several
applications. The following applications list some of the
intended uses for the pattern cells.
2.2.1.1 in-line process monitoring — To establish
patterns to determine if the layer has been processed to
design specifications.
2.2.1.2 process transfer — To standardize the patterns
for process monitoring within manufacturing
fabrication sites and to facilitate process and technology
transfers between sites.
2.2.1.3 equipment evaluation — To standardize the
patterns used to evaluate semiconductor equipment.
2.2.1.4 equipment characterization — To standardize
the patterns for the characterization process of different
metrology equipment.
3 Guidelines for Application s
3.1 General
3.1.1 The cells described here repres ent a primary
metrology set from which composite patterns may be
constructed.
3.1.2 A composite pattern set meets this standard if it
consists of any number of the basic cells described
herein, provided all design rules for each cell are
obeyed.
3.1.3 Each basic cell contains a fundamental design
feature. This feature may be repeated at different (user-
defined) dimensions within a modified metrology cell.
The user will determine all appropriate dimensions for
the feature as they apply to specific
processing/equipment situations.
3.1.4 The figures provided within th is document are
intended to illustrate the proper layout of each pattern
cell and to define the appropriate design elements used
within each basic cell. The pattern cell dimensions are
provided when appropriate.
3.1.5 All feature groups must be separated by at least
five times the largest feature width. This proximity rule
is defined in order to ensure that patterns intended to be
independent are indeed non-coupled.
SEMI P19-92 © SEMI 1992, 19963
3.1.6 Labels, border lines, indicator marks, or any
other adjacent feature will be separated by a minimum
of 5 µm.
3.1.7 A label to indicate the nomina l feature width
must be placed near each basic cell, except the linearity
cell, which has no user-defined features. The units of
the CD labels must be micrometers and at least two
significant figures must be used. The labels must be of
a clearly printable size. Decimal points are optional. If
decimal points are eliminated, digits to the left of the
imaginary decimal point must be slightly larger than
those digits to the right. Characters to the left of the
decimal are optional. All CD labels that are printed with
one size only will correspond to numbers less than 1.0
µm, and any number greater than 1.0 µm must contain
at least one character to the right of the decimal place.
If the cell includes a bias, a label to indicate this bias,
including a “+” sign, must be placed near the basic cell.
One significant figure may be used for bias labels if the
bias is less than 1.0 µm and a multiple of 0.1 µm. (e.g.,
+ 4 = + 0.4 µm).
3.1.8 It is recognized that there are design limitations
dictated by the equipment used to generate the pattern
(e.g., CAD grids, PG rectangles, E-beam spot sizes). It
is permitted within this standard to modify these cells in
order to meet these equipment limitations (e.g., stay on
grid).
3.2 Specific
3.2.1 L-Bar Cell — (See Figure 4.)
3.2.1.1 The L-bar cell is designed to b e a measurement
site for isolated features as well as line and space
groups in orthogonal axes. The cell can be used to
measure the quality of pattern transfer and metrology of
imaged features. The cell is also a qualitative visual test
site for resolution of straight lines and lines bent at right
angles.
3.2.1.2 The design elements are the no minal feature
width, the inter-feature spacing, the minimum feature
length, and the intergrouping linewidth difference
(bias).
3.2.1.3 The basic cell consists of one o r more groups
of nested L-shaped lines at a specific pitch. The pitch is
defined at twice the nominal feature width. (See Figure
5.)
W
0
= Nominal feature width
S = Interfeature spacing
L = Nominal feature length
W
0
-W
1
= Intergrouping linewidth difference (bias)
Figure 5
Table 1
Nominal Feature
Width
Number of Nested
L-bars Minimum Length
>1 µm 3 10 W
0
≤1 µm 5 10 µm
The center L-bar of each group shall extend beyond the
ends of the other L-bars by at least 10 µm. If these
cells are to be used for cross-section analysis, the length
of the L-bars may be designed considerably longer than
the minimum length.
3.2.1.4 The L-bar basic cell consists o f one, three,
five, or seven feature groups. If the basic cell only
consists of a single feature group, then the lines and
spaces must both be equal to the nominal feature width.
If the basic cell consists of three, five, or seven groups,
then the groups are nested. For the middle group, the
lines and spaces must both be equal to the nominal
feature width. The feature widths in each successive
feature group nested outside the middle group are
incrementally increased by the bias. The feature widths
in each successive feature group inside the middle
group are incrementally decreased by the bias. The
pitch for all L-bar groups within a basic cell must be
held constant and equal to twice the nominal feature
width.
3.2.2 Straight-Line Cell — (See Figure 6.)
3.2.2.1 The straight-line cell is a versi on of the L-bar
cell, modified for tilted SEM inspection by removing
the elbows.