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SEMI MF2166-0304 © SEMI 2004 6 9.6.2.1 Run (–) Co rona sweeps to place − 1.2 V on t he special reference wafer while measurem ents are being taken. (Not e 2) 9.6.2.2 Run (–) CTS (2 m in at 170–200°C) on the special refer…

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SEMI MF2166-0304 © SEMI 2004 5
9.2.2 Program the NCDCS to measure the following
parameters of p-type wafers: initial V
surf
, T
ox
, Q
eff
, V
fb
,
D
it
, and Q
m
.
9.2.2.1 Program the CTS portion of the Q
m
mea-
surement to run for at least 4 min at a temperature from
170 to 200°C.
9.2.3 Align the point probe over position A, then
execute a dummy measurement to stabilize the mobile
ions. Repeat this procedure at two other locations. An
example would be the locations (0,0; −40,40; and 40,
−40), where the x and y locations are expressed in
millimeters, relative to the wafer center, using a
Cartesian wafer coordinate system as defined in SEMI
M20. (See Figure R1-1.)
9.2.4 Execute three additional, identical runs.
Determine and record the parameters listed in Section
9.2.2 .
9.2.5 Calculate and record the average, standard
deviation, and % standard deviation for each parameter
measured at each location in runs 2 through 4. Enter
the data on a data sheet such as the example in Figure 1.
9.2.6 To check the NCDCS over its full range of
operation, repeat Sections 9.2.1 –9.2.5 using at least
two additional special reference wafers with parameter
values that span the typical parameter ranges in Section
7.4 .
9.3 Method A, Short-cycle Modification
9.3.1 Execute the procedure in Section 9.2.1 .
9.3.2 Next, execure the procedure in Section 9.2.2 ,
except program the NCDCS to measure Q
m
first,
followed by the other listed measurements.
9.3.2.1 Run the CTS portion of the measurements for
at least 4 minutes at a temperature from 170–200°C.
9.3.3 Then, execute the procedure in Section 9.2.3 .
9.3.4 Enter the data on a data sheet such as the example
in Figure 1. Use the “Mean” columns, leaving the “Std
Dev” and “% Std Dev” columns blank.
9.4 Method B — for NCDCSs that employ a line
source corona and can be programmed to obtain a full
set of parameters:
9.4.1 Rinse a special reference wafer in a DI water bath
for 10 min then dry for 10 min to naturalize any
residual charge.
9.4.2 Place the special reference wafer in the NCDCS.
9.4.3 Measure the voltage on the wafer surface (V
cpd
).
9.4.4 Zero the voltage on the wafer (V
cpd
should be
between −0.3 V and +0.3 V). Use positive or negative
corona sweeps as appropriate to erase the wafer
voltage. Re-measure and record the voltage on the
wafer surface to verify it has been adjusted to zero.
NOTE 2: To determine the voltage change for one corona
sweep, measure the voltage on the wafer. Then sweep the
wafer with one positive sweep. Re-measure the voltage on
the wafer. The difference in voltage on the wafer is the
voltage change per corona sweep.
9.4.5 Program the NCDCS to measure the following
parameters of p-type wafers: T
ox,
Q
eff,
V
fb,
D
it,
and Q
m
.
9.4.5.1 Program the CTS portion of the Q
m
mea-
surement to run for at least 4 min at a temperature from
170 to 200°C.
9.4.6 Choose three test locations such as (0,0; −40,40;
and 40,−40). Execute a dummy measurement to
stabilize the mobile ions.
9.4.7 Execute three additional, identical runs.
Determine and record the parameters listed in Section
9.4.5 .
9.4.8 Calculate and record the average, standard
deviation, and % standard deviation for each parameter
measured at each location in runs 2 through 4. Enter
the data on a data sheet such as the example in Figure 1.
9.4.9 To check the NCDCS over its full range of
operation, repeat Sections 9.3.1–9.3.7 using at least two
additional special reference wafers with parameter
values that span the typical parameter ranges in Section
7.4 .
9.5 Method B, Short-cycle Modification
9.5.1 Execute the procedures in Sections 9.2.1 –9.4.4 .
9.5.2 Next, execute the the procedure in Section 9.4.5 ,
except program the NCDCS to measure Q
m
first,
followed by the other listed measurements.
9.5.2.1 Run the CTS portion of the measurement for at
least 4 minutes at a temperature from 170–200°C.
9.5.3 Execute the procedure in Section 9.4.6 .
9.5.4 Enter the data on a data sheet such as the example
in Figure 1. Use the “Mean” columns, leaving the “Std
Dev” and “% Std Dev” columns blank.
9.6 Method C — for NCDCSs that employ a line
source corona but can only determine mobile ion
density.
9.6.1 Execute the procedures in Sections 9.4.1 through
9.4.4 .
9.6.2 Perform four mobile ion runs as follows:
SEMI MF2166-0304 © SEMI 2004 6
9.6.2.1 Run (–) Corona sweeps to place −1.2 V on the
special reference wafer while measurements are being
taken. (Note 2)
9.6.2.2 Run (–) CTS (2 min at 170–200°C) on the
special reference wafer while measurements are being
taken.
9.6.2.3 Run (+) Corona sweeps to place +2.4 V on the
special reference wafer while measurements are being
taken.
9.6.2.4 Run (+) CTS (4 min at 170–200° C) on the
special reference wafer while measurements are being
taken.
9.6.2.5 Calculate mobile ion density (Q
m
).
9.6.2.6 Zero the voltage on the special reference wafer
using the method outlined in Section 9.4.4 .
9.6.3 Using the data from runs 2 through 4, calculate
and report on a data sheet such as the example in Figure
2 the average, standard deviation, minimum, and
maximum for each parameter tested. Record the
following:
• (+) Corona,
• (+) CTS,
• (–) Corona,
• (–) CTS,
• Corona Voltage/Sweep, and
• mobile charge density (Q
m
).
9.6.4 To check the NCDCS over its full range of
operation, repeat Sections 9.6.1 –9.6.3 using at least
two additional special reference wafers with parameter
values that span the typical parameter ranges in Section
7.4 .
9.7 Method C, Short-cycle Modification:
9.7.1 Carry out the procedures in Sections 9.4.1 –9.4.4
.
9.7.2 Perform one mobile ion run as follows:
9.7.2.1 Run (–) Corona sweeps to place −1.2 V on the
special reference wafer while measurements are being
taken. (Note 2)
9.7.2.2 Run (–) CTS (4 min at 170–200°C) on the
special reference wafer while measurements are being
taken.
9.7.2.3 Run (+) Corona sweeps to place +2.4 V on the
special reference wafer while measurements are being
taken.
9.7.2.4 Run (+) CTS (8 min at 170–200° C) on the
special reference wafer while measurements are being
taken.
9.7.2.5 Calculate mobile ion density (Q
m
).
9.7.2.6 Zero the voltage on the special reference wafer
using the method outlined in Section 9.4.4 .
9.7.3 Report the data listed in Section 9.6.3 in the
“Mean” column of a data sheet such as the example in
Figure 2. Ignore the columns labeled “Std Dev,”
“Minimum,” and “Maximum.”
10 Interpretation
10.1 Regardless of method used, compare the
measured results with the target values supplied with
the special reference wafer(s).
10.2 Record as “In tolerance”/“No repair required” any
NCDCS for which the results of all measured values are
within 10% of the target values.
10.3 Record as “Out of tolerance”/“Repair required”
any NCDCS for which any measured value differs from
the target value by more than 10%. Repair or
recalibrate the system before returning it to production
use.
11 Report
11.1 Report the following information for each test
carried out in accordance with Method A or Method B
(see Figure 1 for an example data sheet that contains all
the information to be reported):
11.1.1 Tester identification, including supplier, model
number, corona method, and software Rev number,
11.1.2 Date of test,
11.1.3 Test operator identification,
11.1.4 Temperature and relative humidity of the test
room,
11.1.5 Characteristics of the special reference wafer
used in the test, including serial number,
11.1.6 Three-run average, standard deviation, and
relative standard deviation for each parameter value in
the list below across all locations,
11.1.6.1 Initial value of surface voltage, V
surf
(or V
cpd
),
V,
11.1.6.2 Dielectric thickness, T
ox
, nm,
11.1.6.3 Flatband voltage, V
fb
, V,
11.1.6.4 Effective charge, Q
eff,
ions/cm
2
,
11.1.6.5 Density of traps, D
it
, ions/cm
2
, and
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11.1.6.6 Mobile ion density, Q
m
, ions/cm
2
.
11.2 Report the following information for each test
carried out in accordance with Method C (see Figure 2
for an example data sheet that contains all the
information to be reported):
11.2.1 Tester identification, including supplier, model
number, corona method, and software Rev number,
11.2.2 Date of test,
11.2.3 Test operator identification,
11.2.4 Temperature and relative humidity of the test
room,
11.2.5 Characteristics of the special reference wafer
used in the test, including serial number,
11.2.6 Stress voltages and temperature,
11.2.7 Duration of CTS, min, and
11.2.8 Three-run average, standard deviation, and
relative standard deviation of mobile ion density, Q
m
,
ions/cm
2
.
12 Key Words
12.1 dielectric tester; dielectric trap; effective charge;
electrical dielectric thickness; flatband voltage;
interface trap; line corona; mobile charge; point corona.