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SEMI M40-0200 © SE MI 2000 7 9.2.1.1 In terferometer a. Interferen ce microscope 9.2.1.2 Profilom eter a. AFM b. Other s canning probe m icroscopes c. Optical profilo meter d. Mechanical stylus 9.2.1.3 Scatterom eter a. …

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SEMI M40-0200 © SEMI 2000 6
other noise sources, such as background electronic
noise and Rayleigh air scatter, are not issues.
8 Roughness Measurement s
8.1 Parameters
8.1.1 R
q
and R
a
are generally used for silicon wafer
surfaces. Other roughness measurement parameters
may also prove useful. This guideline does not suggest
which parameters to use, rather it suggests how to
incorporate any parameter into a standardized
measurement specification.
8.2
Measurement Sites
8.2.1 Roughness can vary considerably across a wafer
surface. It may also have a preferential direction or
anisotropy, often called “lay” (ASME B46.1). Many
measurement techniques are limited to a very small
measurement area and to one or two scan directions.
Therefore specific measurement patterns must be
defined to obtain representative and reproducible
results. These patterns should correspond to effects
observed on wafers in different manufacturing steps.
These processing steps can generate features on a wafer
surface with rotational symmetries ranging from mirror
to infinite. The wafer slicing process may produce low
symmetry, while single-wafer polishing can produce
high symmetry.
8.2.2
In cases where only a small nu mber of spots is
measured, the spot pattern and the scan orientation have
to be identified. See Figure 1 for some patterns and
orientations; others may be agreed upon between
interested parties.
8.3
Site Patterns
8.3.1 One-point — This can be usef ul for rapidly
reviewing results of a quantity of wafers. This is often
at the wafer centerpoint.
8.3.2
In applications where only a small number of
locations are to be measured, the pattern and orientation
of the local scans have to be identified. Measurements
are performed at locations as outlined in Figure 1. For
each local scan, a representative roughness is
calculated. The wafer’s representative roughness is
then a function of the n individual representative scan
values. The roughness variation can be calculated by
the average, the standard deviation, the maximum or the
range (Max-Min) of the individual scan values. Other
statistical approaches may be employed.
8.3.3
Standard patterns include:
a. 1-point Wafer center,
b. 5-point Wafer Center plus four points at 2r/3
from the wafer center, and
c.
9-point Wafer Center plus four points at 2r/5
and four at 4r/5 from the wafer center.
NOTE 4: These patterns have been shown to be useful with a
range of symmetries and values. See Related Information.
8.3.4 Standard measurement orientation patterns
include:
a.
Type A - linear scans parallel and perpendicular
to the fiducial bisector, and
b. Type B - linear scans at 45
o
relative to the
fiducial bisector.
NOTE 5: Type A is generally used for all surfaces. Type B
has been reported to be useful for some surface conditions on
(111) wafers.
8.4 Bandwidth
8.4.1
Two issues affect the bandwidth of the
roughness results. The first is the bandwidth of the
roughness measuring tool, which is discussed in Section
7. The second bandwidth effect is from the analysis
software, which is user selected to emphasize certain
spatial frequencies. Both long and short spatial
wavelength (or frequency) limits must be defined in µm
(or µm
-1
). When entering this information into a
measurement, specification wavelength units shall be
used. Profiling instruments should have scan length
and bandwidth adjusted according to DIN 4768 and
4777 or ASME B46.1.
8.5
Precision
8.5.1 The precision of the roughness measuring
instrument (P) is important. The relationship between
P and the tolerance of the parts to be characterized (T)
is often called the P/T Ratio. SEMI M27 describes how
to determine and interpret the factors: “A test
instrument is usually deemed to be suitable for the
purpose if P/T lies below 10%. If P/T is greater than
30%, the test instrument is not likely to be suitable for
the purpose. Cases for which P/T lies between 10%
and 30% must be judged on an individual basis,
depending on the requirements being placed on the
measurement system.”
9 Roughness Measurement Specifications
9.1 The process of defining the me asurements to be
taken involves several distinct steps. The definition
sequence below represents one logical sequence; others
may be equally useful. See Table 1 for measurement
abbreviations.
9.2
First, select the type of instrument to be used,
including ALL of the following:
9.2.1 Generic instrument type
SEMI M40-0200 © SEMI 20007
9.2.1.1 Interferometer
a. Interference microscope
9.2.1.2
Profilometer
a. AFM
b. Other scanning probe microscopes
c. Optical profilometer
d. Mechanical stylus
9.2.1.3
Scatterometer
a. Total Integrating (TIS)
b. Angle-resolved light (ARLS)
c. Scanning Surface Inspection System (SSIS)
9.3
Next, select the roughness para meter to by
calculated.
9.4 Select the measurement pattern (Figure 1):
a. Center point
b. 5-point
c. 9-point
d. Full-FQA raster scan
e. Full-FQA R-theta scan
9.5
Select the pattern orientation ( Figure 1)
a. Type A
b. Type B
9.6
Select the local measuring condition
a. Point
b. Line
c. Area
9.7
Specify the measurement calculations to be
reported
a. Average (A)
b. Range (R)
c. Maximum (M)
d. Standard Deviation, 1 sigma (S
n-1
)
9.8 Specify the bandwidth and sca n length limits
within which data is to be gathered.
9.9 Lastly, record the abbreviations describing these
selections (see Appendix 1 for examples), separating
adjacent abbreviations with a comma and using periods
for decimal notation. This creates a seven-field
abbreviation. The field sequence described above
follows the order of elements in Table 1.
10 Measurement Reporting S equence
10.1 In general, one value is reported for a wafer.
Where more than one pattern is specified the calculated
values are reported in the order in which they are listed
in Table 1.
SEMI M40-0200 © SEMI 2000 8
Table 1 Roughness Measurement Codes
Element Abbreviation Item
A12 3 4
Profilometer AFM SPM OPR MPR
B1
Interferometer IM
C12 3
Instrument
Scatterometer TIS ARLS SSIS
159 R C SPattern
(See NOTE 1.)
Center 5-point 9-point FQA/Raster
scan
FQA/Concentric
R-theta scan
FQA/Spiral
R-theta scan
ABPattern
Orientation
AB
PLALocal
Measurement
Condition
Point Line Area
QAZ TKSParameter
(See NOTE 1.)
Rq Ra Rz Rt Kurtosis Skewness
ARM DCalculation
(See NOTE 1.)
Average Range Maximum Std. Deviation
(1 sigma
n-1
)
Bandwidth, µm [ __ ]/[ __ ]
(fill in blanks to two significant figures)
Long wavelength (µm)/Short wavelength (µm)
NOTE 1: If more than 1 element is specified, the representative letters are concatenated in the relevant field, in the order specified. See Appendix
1 for examples.