Product specifications

7
Compensation Using Agilent
IBASIC Program
Capacitance compensation routine
is available as a sample program
on a diskette furnished with Agilent
E5250A Switch Mainframe.
You can use the routine as a subpro-
gram of Agilent BASIC or Agilent
Instrument BASIC. By specifying
cable lengths, measurement frequency,
and raw capacitance and conductance
data as parameters to the subprogram,
you can obtain compensated data.
An advantage of using this routine is
that you can modify the cable param-
eters used in compensation calcula-
tion so that you can use cables other
than Agilent 16494A or P/N 8120-4461.
Measure your cable parameters and
modify the parameter values in com-
pensation routine.
Tips for More Accurate
Capacitance Measurements
• Wafer Chuck Capacitance
In general, wafer chuck should be
isolated from circuit common and
ground. This means it should have
higher impedance at the measure-
ment frequency. A common problem
is measurement error due to large
capacitance between wafer chuck
and circuit common. Thermal chuck
(or so called hot chuck) has larger
capacitance. As the wafer size
became larger, the wafer chuck
sizes increased, so the chuck capac-
itance became larger too. This error
cannot be compensated by open/
short calibration or E5250A com-
pensation. The error is in propor-
tion to w
2
L
cable
C
chuck
,
where:
w is defined as 2πƒ,
ƒ is measurement frequency,
L
cable
is inductance in cables between
matrix switch and device,
and C
chuck
is capacitance between
wafer chuck and circuit common.
To minimize the error, use well isolated
wafer chuck and make the measure-
ment cables shorter. Using lower fre-
quency is most effective. If you use
ICS, set the frequency value in 4284
Setup dialog box shown in Figure 10.
• Device Structure
Figure 19 shows typical device
structures for oxide capacitance
measurements. In general, most
accurate capacitance measure-
ment can be done on structure A
because measurement device is
isolated from wafer chuck by NP
junction. Structure B is better than
C because structure B has higher
impedance (R
contact
and C
chuck
) at
wafer chuck. Measurement data
of structure A also includes error
due to series resistance. If possible,
change device structure so that
wafer chuck does not affect the
device measurement.
Figure 18. Automated test example
Case A Case B Case C
CM H
CM L
CM H
CM L
CM L
CM H
N+
N well
P substrate P substrate P substrate
Hot Chuck Hot Chuck
Hot Chuck
Circuit Structure
CM H
CM L
C dut
R contact
C chuck
CM H
CM L
C dut
R contact
C chuck
CM H
CM L
C dut
R contact
C chuck
Figure 19. Device connection
Figure 17. Sequence setup