semi合集-English.pdf - 第1502页

SEMI E30.5-0302 © SEMI 2001, 2002 30 metrology equipment f rom the host can be desirable. In some cases, t he amount of information required to define measurement site lo cations is less if a pattern-elem e nt-based f o …

100%1 / 7923
SEMI E30.5-0302 © SEMI 2001, 200229
M20 standard requires that the “M20” coordinate
system is fixed on the wafer, and is not affected by how
the wafer is loaded on equipment. Also, as stated in the
SEMI M20 standard, an orientation of “0” is for a wafer
loaded on equipment with the primary fiducial towards
the operator or “down”.
R1-2.2.1 Often, no other information is required for
measurements to be made on a wafer. However, the
“M20” coordinate system may not provide sufficient
accuracy to locate measurement sites on patterned
wafers. This is a result of any of a number of possible
reasons, all of which can be described as “experimental
errors”. For instance, wafers are not perfectly round,
fiducial dimensions may vary, and equipment (both
steppers that place patterns on wafers and metrology
equipment) capabilities to determine the location of the
wafer center and fiducial vary.
R1-2.2.2 In order to deal with these errors, metrology
equipment suppliers have developed various strategies,
as discussed in the introduction section. Perhaps
because the SEMI M20 standard's reference to
“origins” of “other coordinate systems” is in the same
sentence with “reference points”, many suppliers
adopted the location of one (or more) reference point(s)
as the origin for their pattern-based coordinate
system(s). Without a common reference site, multiple
coordinate systems resulted. More nefarious strategies
were developed to compensate for “stage errors” on
equipment. These usually entail a series of reference
points required to “zero in” on the measurement site,
and this made comparison of locations determined on
different equipment next to impossible.
R1-2.2.3 MSEM defines the “M20P” coordinate
system to be one which is identical to the “M20”
coordinate system, if there were no experimental errors.
In other words, the location of the origin and axes of the
“M20P” coordinate system are offset slightly from the
origin and axes of the “M20” coordinate system
because of experimental errors. If the location of
reference points, called “alignment sites” in MSEM, is
defined to be the "M20" coordinates where they are
“expected” to be, and equipment is designed to be able
to “find” the alignment sites, given the various possible
experimental errors, the “found” and “expected” SEMI
M20 coordinates can be used to determine the
“M20-to-M20P” coordinate system transformation, as
explained in appendix 1. Alignment site information is
specified through the use of the MSEM data items
named AlignList, the CPNAME CP-ALIGNLIST and,
the table type named ALIGN-DEF-LIST.
R1-2.2.4 Most metrology equipment cannot distinguish
whether patterned wafer site location errors are due to
the wafer, the layout on the wafer, or the equipment's
ability to locate the sites. However, information that is
available through the use of patterned-wafer alignment
sites can provide a means for identifying potential
metrology equipment problems. For instance, assume
that the only pattern-layout location error on a wafer is
that due to the establishment of the location of the
wafer center and fiducial. For many users and
metrology systems, this is a good assumption. If this is
the case, then the MSEM data item named XlateData
can be used to track this error. Although the error may
result from multiple sources, being able to track it on
various metrology equipment will enable users to apply
statistical process control techniques to identify the
specific sources.
R1-2.2.5 Sites specified for measurements or
additional alignments may be found by metrology
equipment at locations which deviate from their
expected locations through either pattern layout errors
or metrology equipment “stage” errors. Again, in a
controlled manufacturing process, these combined
errors should be normally distributed, and non-normal
deviations may indicate possible metrology equipment
problems. These types of errors shall be reported
through the use of the MSEM data item named Offset.
R1-2.2.6 A minimum of two alignment sites are
necessary to establish an “M20P” coordinate system on
a wafer. Additional sites are often used, as in the
example given in appendix 1. The system supplier shall
document the requirements for ALIGNLIST
information, and detail how any “site-by-site”
alignment sites (that is, those needed to obtain better
location accuracy in the neighborhood of measurement
site) are associated with the specific SITELIST
measurement sites.
R1-2.2.7 Alignment site location information may be
either provided to or by equipment. Some equipment
have the capability to find and report the locations of
“reference sites” without prior knowledge of their
locations on the wafer. In this case, the equipment shall
report the location of both alignment and measurement
sites in “M20” coordinates. When alignment site
information is provided to equipment to establish an
“M20P” coordinate, measurement site locations shall be
reported in the “M20P” coordinate system.
R1-2.2.8 MSEM encourages users to define “M20P”
locations in reference to the user's device layout design
within an ideal SEMI M20 wafer coordinate system.
An alternative is to define “M20P” locations by
“training” on a “benchmark” system.
R1-3 Layout of Rectangular Elements on a Silicon
Wafer
Equipment shall be capable of routine,
automated operation without needing wafer layout
information (e.g., field or die maps). However, having
the capability to provide wafer layout information to
SEMI E30.5-0302 © SEMI 2001, 2002 30
metrology equipment from the host can be desirable. In
some cases, the amount of information required to
define measurement site locations is less if a
pattern-element-based format is used. MSEM defines a
means to do this in this section, if desired, based on
SEMI standard SEMI M21.
R1-3.1 SEMI standard SEMI M21, “Specification for
assigning addresses to rectangular elements in a
Cartesian array”, is limited (for MSEM purposes) by
the fact that nothing is specified about how the
rectangular elements are located on the wafer. The
SEMI M21 standard details how to assign “addresses”
to elements and how to find the “array center” element.
In this section, MSEM defines how these elements are
located on a wafer, using the data item named
“M21Data”, and how to establish within-element
coordinate systems.
R1-3.2 There are users who want or require much more
layout information than is provided for by SEMI M21,
such as within-element structure details or element
attribute information. This additional layout
information is beyond the scope of MSEM, since it is
considered to be information which only is needed to
aid operator-interactive use of metrology systems.
R1-3.3 MSEM “M21” Layout
The first pattern
element layout issue to be addressed is that of
determining which SEMI M21 elements are to be
included in the MSEM “M21” layout. MSEM defines
the “M21” layout to include all elements which either
wholly or partially are within the circumference of the
wafer. Thus the MSEM “M21” element layout does not
correspond to the pattern layout exactly, since some
“M21” elements may not contain patterns.
R1-3.4 The second layout issue is that of how best to
specify the element locations on the wafer. The MSEM
approach is to specify the “M20P” coordinate for the
lower left corner of the minimum number of elements
needed to define the layout, along with the element
addresses. For a non-tiled layout, the location of a
single element is sufficient to establish the “M21”
layout. For tiled layouts, the location of one element in
each row or column is required. Note that the location
of the lower left corner of an element may be outside
the circumference of the wafer.
R1-3.5 Layout definition is supported only for
host-to-equipment communications. The user is
responsible for ensuring that the element addresses
provided to the equipment agree with the SEMI M21
specification. The equipment need not check this, other
than to ensure that there are not conflicts within the
provided layout, and shall report results with element
addresses as provided by the user.
R1-3.6 M21 layouts are established within the “M20P”
coordinate system, and need not require any additional
alignment site data than is needed to establish the
“M20P” coordinate system. However, as with “M20P”,
additional alignment may be necessary because of
errors in either the pattern layout or the equipment's
ability to locate features. OFFSET shall be used to
report the location corrections that result from any
within-element alignments.
R1-3.7 MSEM provides a means for element-based
coordinate systems, if required. This capability is
provided by the option of specifying “M21” as the
coordinate system for ALIGN-DEF-DATA and
SITEDEFDATA items. For element-based site
locations, MSEM requires that SEMI M21 element
coordinate systems have x and y axes parallel to the
respective M20-based coordinate system axes, with
their origins at the lower left corner of each element.
R1-4 An Example of How an M20P Coordinate System
is Established on a Silicon Wafer
R1-4.1 The following example is fairly basic. For this
example, the equipment does M20P alignment via a
repeated two-step process. The first step is done at a
low resolution, the second at a high resolution, and the
process is done at two positions on the wafer.
R1-4.2 The equipment documentation states that 4
alignment sites are required. These are defined to the
equipment via the table type named ALIGN-DEF-
LIST, as detailed below. The order of the sites in
ALIGN-DEF-LIST is not important. The sites are then
selected via the CPNAME item named
CP-ALIGNLIST, which is included in the PP-SELECT
command. The order of the sites listed in
CP-ALIGNLIST is important, and is as specified in the
equipment's documentation. The first site is the
alignment site for the first low resolution site, the
second item is for the first high resolution site, the third
item is the second low resolution site, and the fourth is
the second high resolution site.
SEMI E30.5-0302 © SEMI 2001, 200231
Table R1-1 ALIGN-DEF-LIST
Align-Name Coordx Coordy Coordsys Align- Attribute(n)
Coarse1 -60000 -200 M20P
Fine1 -60020 -205 M20P
Coarse 2 60000 200 M20P
Fine2 59980 195 M20P
R1-4.3 ALIGN-DEF-LIST
L,4
1. <Coarse1>
2. <Fine1>
3. <Coarse 2>
4. <Fine2>
R1-4.4 Using this information, the equipment will go to the nominal M20 location for Coarse, then “find” where it
actually is. The offset between the nominal M20 location and the actual M20 location is then used to “find” Fine1.
The actual M20 location of Fine1 is saved. The process is then repeated for Coarse 2 and Fine2. The equipment can
now determine the M20 to M20P offset from the nominal and actual coordinates.
First, a summary of the data:
xN1=-60020 yN1=-205 Nominal x and y data for the first fine site
xA1=-59800 yA1=-150 Actual x and y data for the first fine site
xN2= 59980 yN2= 195 Nominal x and y data for the second fine site
xA2= 60060 yA2= 175 Actual x and y data for the second fine site
R1-4.5 The equipment first calculates THETA ( Θ ), using, for example, the formula:
+
−
=Θ
−
MNMA
MNMA
1
tan
1
where MA and MN are, respectively, the slopes of the lines connecting the nominal and actual fine sites, in M20
coordinates, calculated as follows:
MA
yA yA
xA xA
MN
yN yN
xN xN
=
−
−
=
−
−
21
21
21
21
R1-4.6 The equipment then calculates DELTAX and DELTAY, using, for example, the formulas:
DELTAX
CD
=
+
+
sin ( ) cos ( )
(sin ( )) (cos ( ))
ΘΘ
ΘΘ
22
DELTAY
CD
=
−
+
sin ( ) cos ( )
(sin ( )) (cos ( ))
ΘΘ
ΘΘ
22