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SEMI M49-0704 © SEMI 2001, 2004 5 6.5.10 In ad dition two levels of systematic off-set between di fferent t ools are defined: 6.5.10.1 matching tolerance (di fference o f means ∆ m ) 6.5.10.2 correlat io n (reg ression c…
SEMI M49-0704 © SEMI 2001, 2004 4
Otherwise matching tolerance tests are performed under
the conditions of σ
3
tests.
NOTE 4: In the absence of certified or standard reference
materials matching may be tested by using appropriate wafers
complying with 130 nm technology node specifications. It is
recommended to test for matching with a set of samples
covering the parameter range of interest.
5.2.9 precision over tolerance (P/T) ratio — the ratio
of the precision of measurement equipment and a
product’s tolerance. (SEMI M27)
5.2.10 sorting — real and virtual separation of test
specimens in different categories specified by one or
multiple parameters.
5.2.11 tolerance — the absolute magnitude of the
range of the product specification. (SEMI M27)
6 Specification for Geometry Measurement
Equipment for Silicon Wafers
6.1 The specification is structured in three sections
(Tables 1–3):
• Generic Equipment Characteristics (Table 1)
• Materials to be measured (Table 2)
• Metrology Specific Equipment Characteristics
(Table 3)
6.2 Tables 1–3 contain the specifications, referenced
documents, test methods, and comments. Additional
explanations and discussions are provided in this
section.
6.3 Generic Equipment Characteristics (Table 1)
6.3.1 The section “Generic Equipment Characteristics”
consists of five subsections:
• Wafer handling
• Reliability
• Procedural
• Documentation
• Computer/User Interface/Connectivity
6.3.2 Subsections covering “Facilities Requirements”
and “Safety/Legal/Regulatory” are not included in the
present document as these issues are highly user
specific and dependent on national regulations.
6.4 Materials to be measured (Table 2)
6.4.1 Table 2 specifies the parameters of Si wafers that
the measurement equipment must be capable to handle
and to measure.
6.5 Metrology Specific Equipment Characteristics
(Table 3)
6.5.1 This section specifies the dimensional parameters
of Si wafers to be measured and to be reported by
equipment for measuring the geometry and flatness of
wafers as well as the required spatial resolution,
precision and accuracy of the measurement equipment.
6.5.2 The ability of a metrology tool to properly
measure surface features of different spatial
wavelengths is affected by the spatial bandwidth of the
tool's response function. Spatial bandwidth can be
defined in many ways and is influenced by many
factors beyond the scope of this document. Some of
these need to be standardized.
6.5.3 Spatial resolution is defined by the high spatial
frequency limit of the bandwidth of the tool's response
function.
6.5.4 Low and high cut-off frequency f
min
and f
max
define the bandwidth of the response function of
measurement equipment. The cut-off frequencies
correspond to an attenuation of 0.5 for the amplitude of
a sinusoidal surface feature with the exception of a low
pass filter (f
min
= 0) for which the attenuation remains 1
at f
min
.
6.5.5 The rate of change of the attenuation approaching
the cut-off frequencies has to be larger than the rate of a
Gaussian filter with the corresponding cut-off
frequency.
6.5.6 The present document recommends f
max
and f
min
that must be measured by the instrument.
6.5.7 Any variations in filtering procedures applied
near the FQA boundary must be described by the
supplier of the equipment.
6.5.8 The bandwidth as specified in Table 3 is a
nominal value.
6.5.9 In the present document a hierarchy of variability
levels is used to describe the performance of
measurement equipment which is calibrated and
adjusted/aligned according to the supplier's procedures.
The various terms are defined in section 5. These
variability levels are consistent with terms defined in
SEMI E89 but not fully interchangeable. Their relation
is indicated in parentheses.
6.5.9.1 Level 1 variability: standard deviation σ
1
(SEMI E89 static repeatability)
6.5.9.2 Level 2 variability: standard deviation σ
2
(SEMI E89 dynamic repeatability)
6.5.9.3 Level 3 variability: standard deviation σ
3
(SEMI E89 reproducibility)
SEMI M49-0704 © SEMI 2001, 2004
5
6.5.10 In addition two levels of systematic off-set
between different tools are defined:
6.5.10.1 matching tolerance (difference of means ∆
m
)
6.5.10.2 correlation (regression curve)
6.5.11 Explicitly specified in the present document are
only level 3 variability σ
3
and matching tolerance ∆
m
as
they correspond to the utilization of measurement
equipment for wafer manufacturing most closely. The
supplier of a specific tool may optionally provide
specifications for level 1 and/or level 2 variability,
respectively.
6.5.12 Level 3 variability σ
3
and matching tolerance ∆
m
are specified with respect to anticipated specifications
for wafer geometry and flatness as given in Table 3 for
a reference wafer.
6.5.13 In the present document P/T-ratios are used for
specifying level 3 variability σ
3.
6.5.13.1 A precision-to-tolerance ration P/T less than
10% at 6σ is recommended in SEMI M27 for
metrology equipment. This would be an extremely
demanding specification for flatness and geometry
measurement tools. In addition, flatness characterisitics
of Si wafers are typically described by a single sided
distribution with the median approaching zero, the
lower specification boundary. Therefore two grades that
are based on 3σ criteria, instead on 6σ, are
recommended for such tools in the present document:
• grade A: P/T < 10%, 3σ
3
• grade B: P/T < 20%, 3σ
3
6.5.13.2 The individual measurement features a tool
provides may be graded differently, e.g. SFQR might
meet grade A, but SBIR only grade B. This has to be
indicated appropriately in the tools’ technical
specifications.
6.5.14 Matching tolerance is specified to be less or
equal to 1.5σ
3
of level 3 variability. This corresponds to
a greater than 99% probability that the difference of any
individual measurement results obtained with two
different tools is smaller or equal to 5σ
3
.
6.5.15 The target for bias is a range of ± 1.5σ
3
with
respect to a certified value provided appropriate
reference materials are available. This corresponds to a
greater than 99% probability that any individual
measurement is in the range of ± 4σ
3
around the
certified value when a reference material is tested.
6.5.16 Reference material with a series of surface
features with appropriate height and half width is
required to verify bandwidth of a measurement tool.
The height of the features corresponds to the wafer
specification as outlined in Table 3.
6.5.17 The specifications of the measurement
equipment are verified by using wafers the parameters
of which are in a range, the upper limit of which
corresponds to 1.5 times anticipated wafer
specification, the lower limit to 0.5 of anticipated wafer
specification. These are listed in Table 3 as Reference
Wafer Specifications.
NOTE 5: The edge region of wafers represents the most
challenging area for meeting the desired performance
characteristics. This is because of the larger surface geometry
variations in the region near the edge, e.g. from polishing roll-
off.
6.5.18 Reference Wafers — The specifications of the
measurement equipment are verified by using reference
wafers with properties covering the range given in
Section 1 of Table 3. All reference wafers shall meet
the thickness and warp requirements listed in the table
but different wafers may be used to meet the flatness
and nanotopography requirements. For site related
specifications not all sites must fall within the range,
but the appropriate sites to be tested should be
indicated. In all cases, at least three wafers in the range
of values for each property shall be employed in the
testing.
6.5.19 Verification of bias, matching tolerance and the
various levels of variability are performed with
equipment which is calibrated according to the
supplier's procedures and which is under statistical
process control.
6.5.20 Compatibility of two tools is considered to be
satisfactory when the specifications of the older tool are
met with the newer tool operating in the emulation
mode.
6.5.21 The quality of a correlation between different
measurement equipment is not specified in the present
document.
7 Related Documents
7.1 ASTM Documents
E 177 — Standard Practice for Use of the Terms
Precision and Bias in ASTM Test Methods
E 456 — Standard Terminology for Relating to Quality
and Statistics
SEMI M49-0704 © SEMI 2001, 2004 6
7.2 Other Documents
Evaluating Automated Wafer Measurement Instruments, SEMATECH
6
, Technology Transfer 94112638A-XFR
Metrology Tool Gauge Study Procedure for the International 300 mm Initiative (I300I), International 300 mm
Initiative
6
, Technology Transfer #97063295A-XFR
International Technology Roadmap for Semiconductors: 1999 edition
7
,
8
ISO 3274: 1996 — Geometrical Product Specifications (GPS) – Surface Texture: Profile method – Nominal
characteristic of contact (stylus) instruments
1
Table 1 Generic Equipment Characteristics
Item Recommended Specification Comment References
1 WAFER HANDLING
1.1 Robot End-Effector optional wafer edge or backside contact edge as defined
by SEMI M1
1.2 Scan Stage optional wafer edge or backside contact edge as defined
by SEMI M1
1.3 Wafer Contact Materials contact materials to leave metals and
organics on wafers < as defined in ITRS 99
1.4 Wafer Detection protection of accidental contact due to e.g.,
cross-slotting double slotting, protrusions,
etc.
1.5 Wafer Rotational Alignment random in, aligned out
1.6 Number of Cassette Stations 2–4, arbitrary sender/receiver assignment
1.7 Type of Cassettes open, FOUP/SMIF, FOSB to be specified
alternatively
1.8 Cassette Loading manual/guided vehicle, conveyor belt
1.9 Automatic Cassette ID user specific
1.10 Wafer Seating vertical or off-horizontal during setting
cassette on
station by
operator
1.11 Cassette Filling Modes random access and loading, programmable
empty slot filling
1.12 Automatic Wafer ID
reading
user specific
1.13 Particulate Contamination < 0.001 PWP per cm
2
, > 90 nm LSE front,
and > 120 nm LSE backside (See NOTE 1.)
verify with
mirror polished
wafer surfaces
SEMI E14
2 RELIABILITY
2.1 MTBF > 2000 h SEMI E10
2.2 MTTA > 4 h SEMI E10
2.3 MTTR according to service contract SEMI E10
2.4 Availability > 98% per year
2.5 Uptime > 160 h/w
2.6 Response Time according to service contract
2.7 Statistical Process Control
(SPC) performance
automated
6 International Sematech, 2706 Montopolis Drive, Austin, Tx. 78741-6499, USA
7 SEMATECH, 3101 Industrial Terrace Suite 106, Austin TX 78758
8 More recent versions of the ITRS are available from the homepage of International Sematech: www.sematech.org