Tektronix 82-WIN User manual

Model 82-WIN Simultaneous C-V Measurement

User’s Manual

A GREATER MEASURE OF CONFIDENCE

WARRANTY

Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a
period of 1 year from date of shipment.

Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables,
rechargeable batteries, diskettes, and documentation.

During the warranty period, we will, at our option, either repair or replace any product that proves to be defective.

To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in
Cleveland, Ohio. You will be given prompt assistance and return instructions. Send the product, transportation
prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation prepaid.
Repaired or replaced products are warranted for the balance of the original warranty period, or at least 90 days.

LIMITATION OF WARRANTY

This warranty does not apply to defects resulting from product modification without Keithley’s express written
consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-rechargeable
batteries, damage from battery leakage, or problems arising from normal wear or failure to follow instructions.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUD­ING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE.
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ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF
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1-888-KEITHLEY (534-8453) • www.keithley.com

2/03

Model 82-WIN Simultaneous C-V Measurement

User’s Manual

©1997, Keithley Instruments, Inc.

All rights reserved.

Cleveland, Ohio, U.S.A.

Second Printing, October 1999

Document Number: 82WIN-900-01 Rev. B

Manual Print History

The print history shown below lists the printing dates of all Re visions and Addenda created
for this manual. The Revision Le vel letter increases alphabetically as the manual undergoes
subsequent updates. Addenda, which are released between Revisions, contain important
change information that the user should incorporate immediately into the manual. Addenda
are numbered sequentially . When a ne w Revision is created, all Addenda associated with the
previous Revision of the manual are incorporated into the ne w Re vision of the manual. Each
new Revision includes a revised copy of this print history page.

Revision A (Document Number 82WIN-900-01)...............................................................April 1997

Revision B (Document Number 82WIN-900-01).................................................................October 1999

All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc.
Other brand names are trademarks or registered trademarks of their respective holders.

S

afety Precautions

The following safety precautions should be observed before using this product and any associated instrumentation. Although
some instruments and accessories would normally be used with non-hazardous voltages, there are situations where hazardous
conditions may be present.

This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions
required to avoid possible injury. Read and follow all installation, operation, and maintenance information carefully before us­ing the product. Refer to the manual for complete product specifications.

If the product is used in a manner not specified, the protection provided by the product may be impaired.

The types of product users are:

Responsible body

ment is operated within its specifications and operating limits, and for ensuring that operators are adequately trained.

Operators

instrument. They must be protected from electric shock and contact with hazardous live circuits.

Maintenance personnel

voltage or replacing consumable materials. Maintenance procedures are described in the manual. The procedures explicitly state
if the operator may perform them. Otherwise, they should be performed only by service personnel.

Service personnel

trained service personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that are rated Installation Category I and Installation Category II,
as described in the International Electrotechnical Commission (IEC) Standard IEC 60664. Most measurement, control, and data
I/O signals are Installation Category I and must not be directly connected to mains voltage or to voltage sources with high tran­sient over-voltages. Installation Category II connections require protection for high transient over-voltages often associated with
local AC mains connections. Assume all measurement, control, and data I/O connections are for connection to Category I sourc­es unless otherwise marked or described in the Manual.

Exercise extreme caution when a shock hazard is present. Lethal voltage may be present on cable connector jacks or test fixtures.
The American National Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 30V RMS,

42.4V peak, or 60VDC are present.

circuit before measuring.

Operators of this product must be protected from electric shock at all times. The responsible body must ensure that operators
are prevented access and/or insulated from every connection point. In some cases, connections must be exposed to potential
human contact. Product operators in these circumstances must be trained to protect themselves from the risk of electric shock.
If the circuit is capable of operating at or above 1000 volts,

Do not connect switching cards directly to unlimited power circuits. They are intended to be used with impedance limited sourc­es. NEVER connect switching cards directly to AC mains. When connecting sources to switching cards, install protective de­vices to limit fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connected to a properly grounded power receptacle. Inspect the con­necting cables, test leads, and jumpers for possible wear, cracks, or breaks before each use.

When installing equipment where access to the main power cord is restricted, such as rack mounting, a separate main input pow­er disconnect device must be provided, in close proximity to the equipment and within easy reach of the operator.

For maximum safety, do not touch the product, test cables, or any other instruments while power is applied to the circuit under
test. ALWAYS remove power from the entire test system and discharge any capacitors before: connecting or disconnecting ca-

is the individual or group responsible for the use and maintenance of equipment, for ensuring that the equip-

use the product for its intended function. They must be trained in electrical safety procedures and proper use of the

perform routine procedures on the product to keep it operating properly, for example, setting the line

are trained to work on live circuits, and perform safe installations and repairs of products. Only properly

A good safety practice is to expect that hazardous voltage is present in any unknown

no conductive part of the circuit may be exposed.

5/02

bles or jumpers, installing or removing switching cards, or making internal changes, such as installing or removing jumpers.

Do not touch any object that could provide a current path to the common side of the circuit under test or power line (earth) ground. Al­ways make measurements with dry hands while standing on a dry, insulated surface capable of withstanding the voltage being measured.

The instrument and accessories must be used in accordance with its specifications and operating instructions or the safety of the
equipment may be impaired.

Do not exceed the maximum signal levels of the instruments and accessories, as defined in the specifications and operating in­formation, and as shown on the instrument or test fixture panels, or switching card.

When fuses are used in a product, replace with same type and rating for continued protection against fire hazard.

Chassis connections must only be used as shield connections for measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is applied to the device under test. Safe operation requires the use
of a lid interlock.

If or is present, connect it to safety earth ground using the wire recommended in the user documentation.

!

The symbol on an instrument indicates that the user should refer to the operating instructions located in the manual.

The symbol on an instrument shows that it can source or measure 1000 volts or more, including the combined effect of
normal and common mode voltages. Use standard safety precautions to avoid personal contact with these voltages.

The

WARNING

information very carefully before performing the indicated procedure.

The

CAUTION

ranty.

Instrumentation and accessories shall not be connected to humans.

Before performing any maintenance, disconnect the line cord and all test cables.

To maintain protection from electric shock and fire, replacement components in mains circuits, including the power transformer,
test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses, with applicable national safety ap­provals, may be used if the rating and type are the same. Other components that are not safety related may be purchased from
other suppliers as long as they are equivalent to the original component. (Note that selected parts should be purchased only
through Keithley Instruments to maintain accuracy and functionality of the product.) If you are unsure about the applicability
of a replacement component, call a Keithley Instruments office for information.

To clean an instrument, use a damp cloth or mild, water based cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill on the instrument. Products that consist of a circuit board with
no case or chassis (e.g., data acquisition board for installation into a computer) should never require cleaning if handled accord­ing to instructions. If the board becomes contaminated and operation is affected, the board should be returned to the factory for
proper cleaning/servicing.

heading in a manual explains dangers that might result in personal injury or death. Always read the associated

heading in a manual explains hazards that could damage the instrument. Such damage may invalidate the war-

User’s Guide

Model 82~WIN

Simultaneous C-V

Measurement

Keithley instruments, Inc.

Release Date: April 1997

Accumulation

I-

Depletion

if-

\

ligh-Frequenqd .
he0 Deoletion

. .

V substrate

Inversion

Quasistatic

High Frequency

l

Contents

C-V Measurement

Introduction
Typical Measurement Sequence
First Time System Testing and

Measurement Procedures

Choose the Right Parameters .................................................................................................. .18

Additional C-V Measurement Features

Measurement Considerations

................................................................................................................................

Leakage Test

Cable Correction

GPIB Configuration
Instrument Selection
Instrument Setup
Making C-V Measurements
Analyzing Data

Optimal C-V Measurement Parameters

Determining the Optimal Delay Tie

Squarewave
Staircase
Capacitance vs. Delay Tie
Time Options

Potential Error Sources

...........................................................................................

1

1

.................................................................................................

Cable Correction

.....................................................................

................................................................................................................

Correcting for Excess Leakage Current

Correcting for Stray Capacitance

......................................................................

..............................................................................

..........................................................................................................

Performing Cable Correction

.....................................................................................

.........................................................................................................

...................................................................................................

.................................................................................................

........................................................................................................

.......................................................................................

..........................................................................................................

.....................................................................

Start, Stop, and Step Voltages..
Sweep Direction
Delay Time

.......................................................................................................

...............................................................................................................

...............................................................................

.......................................................................

Measurement Results
Determining Delay Tie with
Testing Slow Devices..

...............................................................................................

Leaky Devices .........................................................

............................................................................................

....................................................................................

................................................................................................................

.....................................................................................................................

......................................................................................

.............................................................................................................

...................................................................................................

.............................................................................................

Stray Capacitances

Leakage Resistances
High-frequency Effects

....................................................................................................

.................................................................................................

...........................................................................................

3

.5

5

6

-6

7

8
10
10

.l 1

11
13
15

18

.18

19

20

21

.23

24

.25

26
26
26
26
26
28

.28

28
31

.32

User’s Guide Model 82WN Simultaneous C-V

C-V Measurement l i

Avoiding

Capacitance

Cabling Considerations ...........................................................................................

Device Connections
Test Fixture

Correcting Residual

Offsets .....................................................................................................................

Errors..

Shielding .............................................................................................

Errors .......................................................................................

Gain and Nonlinearity

Voltage-dependent

Curve Misalignment.. .......................................

Noise .......................................................................................................................

Interpreting C-V Curves

Maintaining

Analyzing

Initial Equilibrium

Dynamic

Range Considerations.. ..............................................................................

Curves for

Equilibrium..

Equilibrium.. ..........................................................................

Series and Parallel Model

Example.. .................................................................................................................

Device Considerations

Series Resistance

Device
Test

Structure .......................................................................................................

Device Integrity..

Equipment Considerations

Light Leaks.. ............................................................................................................

Thermal Errors

...............................................................................................

.........................................................................................................

..................................................................................

..................................................................................................

.34

.34

35

.36

.36

.36

Errors

..................................................................................

Offset..

......................................................................................

.

......................................................

...........................................................................................

........................................................................................

.37

.37
.37
,38

.3 8

38

.40

....................................................................................................

41

.42

Equivalent Circuits.. ........................................................

......................................................................................................

.....................................................................................................

................................................................................

.42

.45

46

46

.46

.47

.47

.47

47

ii 0 C-V Measurement

User’s Guide Model 82-WIN Simultaneous C-V

C-V Measurement

Introduction

This chapter provides detailed information on using Metrics ICS

software with Keithley Model 82-WIN to set up C-V
measurements and acquire C-V data. A quicker and easier
approach is to use Keithley libraries, which contain typical
measurement setup parameters and analysis algorithms to
extract many parameters from basic C-V measurements. The
next chapter provides detailed information on how to use
Keithley libraries.

This chapter is organized as the following:

Typical Measurement Sequence: Outlines the basic
measurement sequence that should be followed to ensure
accurate measurements and analysis.

First Time System Testing and Cable Correction: Describes
the procedure to test the complete system for the presence of
unwanted characteristics such as leakage resistance, leakage
current, and stray capacitance. It also details the cable correction

procedure that must be performed in order to ensure accuracy of
high-frequency C-V measurement.

Measurement Procedures: Describes basic procedures for
making C-V measurement. A simultaneous C-V measurement
example is included to illustrate the procedures.

User’s Guide Model 82-WIN Simultaneous C-V

C-V Measurement l 1

Choosing the Right Parameters: Briefly discusses the
considerations in choosing right measurement parameters to
achieve accurate

C-V

measurements. It also describes a
procedure to determine the correct delay time to optimize C-V
measurements.

Additional C-V Measurement Features: Includes a
description of squarewave, single staircase, double staircase,
and capacitance vs. delay time measurements.

Measurement Considerations: Outlines numerous factors that
should be taken into account in order to maximize measurement
accuracy and minimize errors.

2 0 C-V Measurement User’s Guide Model 824MN Simultaneous C-V

Typical Measurement Sequence

Measurements should be carried out in the proper sequence in
order to ensure that the system is optimized and error terms are
minimized. The basic sequence is outlined below. If your
system is properly set up, tested, and calibrated, you may skip
Steps 1 and 2. Otherwise you must perform the testing and
calibration procedures.

Step 1: Test and

Correct for System Leakage and Strays

Initially, you should test and determine if any problems, such as
excessive leakage or unwanted stray capacitance, are present.
You should correct these problems before making C-V a
measurement. Refer to your system manuals for proper

installation and testing procedures. After initial testing, the
system need be tested only when you have changed some
aspects of its configuration, such as connecting cables or test
futures.

Probe-up suppression should be performed before each
measurement to ensure accuracy. This procedure is discussed in
the measurement section in detail.

Step 2: Correct for Cabling Effects

Cable correction is necessary to compensate for transmission
line effects through the connecting cables and remote input

coupler. Transmission line effects are more significant at higher

frequencies and with longer cables, or with switches in the
system. Failure to perform cable correction will result in
substantially reduced accuracy of high-f?equency C-V
measurement. In order to perform correction, you must connect
the Model 5909 calibration capacitors to the system, and
perform the correction procedure under Metrics ICS. Cable

correction must be performed the first time you use your

User’s Guide Model 82-WIN Simultaneous C-V

C-V Measurement * 3

system. After that, it needs to be performed only if the system

configuration

is

changed in

some

manner, or if the ambient

temperature changes by more than 5’C.

Step 3: Configure Your System with Metrics ICS

If you are not using the Keithley library setup to make C-V
measurement, it will be necessary for you to properly configure
your system under Metrics ICS, including GPIB, instrument,
switching matrices, measurement parameters, etc. You should
refer to the Metrics ICS and Keithley C-V Driver manuals for
detailed information regarding configuration of your system.

Step 4: Make a C-V Measurement

Before you can actually make measurements, you must select
measurement parameters such as sweep mode, range, frequency,
and voltage values. As the sweep is performed, measured values
are stored in data arrays for analysis and later retrieval.

Step 5: Analyze C-V Data

4. C-V Measurement

Besides Metrics ICS and Keithley C-V drivers, the Keithley
C-V system includes libraries for setup and data analysis.
Depending on the options you choose, you will be able to
extract a large amount of useful information from your C-V
measurement data. Available analysis features include doping
profile, flatband capacitance and voltage, interface trap density,
and mobile ion density, etc.

User’s Guide Model 82-WIN Simultaneous C-V

First Time System Testing and Cable Correction

Leakage Test

Before using the system, it is necessary to check system
leakage. Zero suppress in Metrics ICS is intended to correct for
small system leakage current and stray capacitance. Any
excessive leakage problem must be solved before attempting a

measurement. Procedures are outlined below.

You should run a probe-up test sweep to determine if there is

excessive system or voltage-dependent leakage and stray
capacitance. You may also load the Keithley standard system

leakage check library. Refer to the C-V Libraries and Analysis
chapter for information on using the leakage check library. Note
that setup parameters should be same as those used for your
measurement.

Once leakage check setup is loaded and properly configured,
click on Single on the Meas button. After the sweep, you may
view the capacitance and Q/t vs. voltage plots. There are two
key items to note when performing this procedure. For a typical
system, capacitance and Q/t values should be as small as

possible. Ideally, the stray capacitance should be less than 1%

of the expected capacitance values for optimal accuracy, and
leakage current should be very small as well. Typically, leakage
current should be less than 0.5 pA on the 200pF range, while on

the 2nP range, leakage current should be less than 2pA. In
addition, stray capacitance or leakage current should not display
any voltage-dependent features.

User’s Guide Model 824MN Simultaneous C-V C-V Measurement l 5

Make sure proper cables are installed in the correct

1.
places. Be certain you have not interchanged Model

4801 (low noise) cables with the Model 705 1 (50R)

cables or other regular cables.

Make sure all connecting jacks and connectors are f?ee

2.
of contamination. Clean any dirty connectors with
methanol, and allow them to dry thoroughly before
use.

Be certain that you are making a probe-up

3.
measurement.

Check to see that no leakage paths are present in the

4.
test future.

If necessary, tie down cables to avoid noise currents

5.
caused by cable flexing. Also avoid vibration during
testing.

6 l C-V Measurement

Verify that all cables are of the proper type and not of

1.
excessive length.

Verify the integrity of all cable shields, and that the

2.
shield connections are carried through to the
connectors.

Again, make sure the procedure is being performed in

3.

the probe-up configuration.

User’s Guide Model 824VlN Simultaneous C-V

Cable Correction

The Keithley library disk includes a standard cable calibration
file with typical cable compensation for the Keithley
simultaneous C-V system; the tile name is STANDARDCAL.
This file maybe be copied to the UCS sub directory of the hard
disk for initial use.

For optimal accuracy, system cables must be compensated, and
you should perform a new cable calibration on your system.
You may load the Keithley leakage check library for cable

calibration purposes. Click on the Setup Editor button, then

click on the Opts option button. If you have performed cable

calibration, you may load the calibration file. Otherwise, you

must perform cable calibration to assure measurement accuracy.

4. Use a test fixture of good, low capacitance design. Use
low-noise, coaxial, or triaxial probes.

5. Make certain the test fucture shield is in place when
characterizing the system. The same precaution holds
true when characterizing or measuring a device.

6. If problems persist, see Measurement Considerations at
the end of this chapter.

In order to perform cable calibration, you will need the Model
5909 calibration capacitors. Disconnect your test future and
connect each calibration capacitor in its place when prompted to
do so. Use the supplied female-to-female BNC adapters to

connect the sources to the cables. Calibration capacitors should
be connected to the end connecting to the probe station. When
making the connection, be sure not to handle the cables and

capacitors excessively, since the resulting temperature rise will

change the capacitance values. Refer to Figure 1 for

connections.

User’s Guide Model 82WlN Simultaneous C-V

C-V Measurement l 7

5951

Remote Input Coupler

to sa%rssmElNFvrauRER

Figure 1

Cable Correction Capacitor Connecfions

Performing Cable Correction

1.

Click on the Calibration button, and the cable
calibration window shown in Figure 2 will be
displayed.

2.

Select the frequency and range you want to calibrate,

then follow the prompts to connect the calibration

capacitors to the cable.

3.

Once calibration is finished, the screen should appear

as shown in Figure 3.

8 l C-V Measurement

User’s Guide Model 82-WIN Simultaneous C-V

4. Save this file as CABLE.CAL or the name you prefer.
Note that the file extension must be .CAL.

5. Now load the calibration file, then exit the Opts

window. You should now be in the Setup editor.

6. Click the Done button to exit SetuD.

Current calibration filename

Calibration file

Low CAP @f) :
High CAP

KO, Real

KO,

Kl, Real :
Kl, lmag :

hag

(~9 :

:

:

595 Display

Figure 2

1.

1 kHr -: rjl oakliz

fas1.933 I 1461.97 I 1462.4 1

Options Setup window

”

;,.,, I <..i^ ‘.:

I

,nlMht

Figure 3

User’s Guide Model 82-WIN Simultaneous C-V

System Cable Calibration window

C-V Measurement l 9

Measurement Procedures

Detailed information about properly configuring your system

can be found in Metrics ICS and Keithley Instruments C-V
driver manuals. Here, only a brief summary related to Keithley
C-V system is provided. An example of making a simultaneous
C-V measurement is outlined.

GPIB Configuration

Once the GPIE3 board is properly installed and tested, click on
the GPIB button on the menu strip. You should select the GPIB
card installed in your computer (see Figure 4). Note that the
GPIB Timeout option must be set to at least two times the

expected maximum sweep delay time, or a GPIB timeout error
may occur.

WPE

.

:

-“‘I

IO. C-V Measurement

Sub-Type

IKI KMCX38.2

Oj#i 0 ns:

Timeout

30 sect

Delay

No Delay

Figure 4

q

Iail

@!I

ED &ddr

]

I

Cl Show Messages

q

Show bog

Communicafions Setup Window

User’s Guide Model 824VlN Simultaneous C-V

Instrument Selection

You may have installed several Keithley instrument drivers with
your Metrics core. You can make a selection here, such as a
K182 Simultaneous C-V system. Alternatively, you can select
KI23x I-V, KU90 High Frequency C-V, and KI595 Quasistatic
C-V instruments.

Instrument Setup

1.

Click the Connect button to select the K182 driver.
GPIB bus address menu appears when you click the
Configuration button.

2.

Type in the corresponding primary address for each
instrument.

3.

Click the Verify button to test if instruments are
correctly configured. If they are not correctly
configured, an error message will appear. Otherwise,
the following message will be displayed: “The system
is correctly configured.”

4.

Once the system is correctly configured, ICS will
automatically store the configuration. After this
procedure, the configuration step need not be run again
unless the instrument configuration changes.

1. Click on the Setup button; the instrument setup editor
window will appear. (See Figure 5.)

The

2. Click on New, and the program will prompt you to
type in the Setup name.

User’s Guide Model 824MN Simultaneous C-V

C-V Measurement l 11

You may

select many different devices. For this

example, select the MOSFET icon.

Click on Source Unit, then click on K182 IN to select
the input.

Click on the G (gate) on the MOSFET symbol to
connect the input to the gate.

Similarly, click on KI82.OUT to select the output,
then click on the B (substrate) symbol of the MOSFET
to connect the output to the substrate.

Click on the W82 OUT icon; the measurement
parameter setup window will appear. (See Figure 6.)
You may now select the proper measurement
parameters. The parameter window should appear like
the one shown in the Figure 6. Refer to the Metrics ICS
and Keithley C-V driver manuals for full details on all
setup parameters.

12 * C-V Measurement

Before you make a measurement, be sure to load the

cable correction and calibration file. To do so, click on
the Opts. button in the Setup Editor, then click on
Load option to select the calibration file for your test
fucture.

Exit from the Opts. window and the Setup Editor
window.

User’s Guide Model 824VlN Simuttandous C-V

Figure 5 instrument Setup Editor Window

Stimulus

Bulkhbstrate voltage

Mode: -1

Start (V) :
stop [v] :
Step (VI :
No. Points
Delay (s) :

Time measurement bias

Bias voltage : 14

User’s Guide Model 82-WIN Simultaneous C-V

a
12

10.5 1

Figure 6

Measure

q cs:

q GorR:)G~

•I Vsub :

-

q t?/t:

i?iT:

Range
590: p-i@/

595: 12°F

1

lvsuB

r--l

I

Measurement Setup Parameter Window

Options

Model

@Parallel 0 Series

I

m

C-V Measurement l 13

Making C-V Measurements

. The zero cancel procedure described below will correct

system leakage and stray capacitance. Note that large

leakage current or stray capacitance should not be
suppressed. Determine the source of the problems, and
correct them before using your system.

!. Click on the Meas. button, and note there are several

options from which to choose. (See Figure 7.)

;. Before you make measurements, you should do a

probe-up zero suppress by clicking on the Zero Cancel
button and following the instructions.

C. After the zero cancel procedure, the message “Please

lower your probe” will be displayed on the screen.
During this period, the Model 590 C-V meter is in its

active reading mode, and you may lower your probe to
contact the DUT while at same time observing the
Model 590 display reading. Doing so ensures proper

electrical contact between the probe and DUT.

14 0 C-V Measurement

i. You are now ready to make a C-V measurement. For

this example, click on the Single button to make a

single-sweep measurement. You may observe that
when instrument finishes data taking, the data screen

will flicker a few times. This situation is normal while

ICS is updating the data. If the analysis package has
been loaded, it make take some time to perform the

calculations and display the data, depending on the

amount of data and the speed of your computer.

User’s Guide Model 824VlN Simultaneous C-V

Analyzing Data

Before you attempt to analyze data, you should plot raw dam
and determine if there are any obvious measurement problems.
Keep in mind that no analysis will compensate for substandard

system-related problems and select better measurement
parameters. If a large amotmt of noise is present, analysis results
will not be dependable and may even be meaningless. Repeat
the measurement procedure to determine the root cause of the
problems, and correct them before proceeding.

Figure 7

Measurement Selection Window

data caused by measurement problems. At this time, you may
find it necessary to make a few adjustments to compensate for

The first step is to transfer the analysis constants to
Metrics. Click on the Transform Editor button, then

the name, value, unit, and comments into the fields.

User’s Guide Model 82WlN Simultaneous C-V

C-V Measurement 0 15

2.

Click on the New Plot button to draw a new graph.
The Setup Plot window will pop up. (See Figure 8.)

3.

Select the data option you wish to plot. For our
example, select Vsm as the X-Axis data parameter. Fo:
a simultaneous C-V measurement, plot both Cn and Cc
on the y-axis.

t.

You may select one data set to plot on the y axis.

Select the data you wish to plot on the Y l-Axis

column. If you wish to plot another data set on a
different scale but on the same graph, select that data
set for the Y2-Axis column.

j.

If you wish to plot two sets of dam on the same scale
you may use the Build Group feature. Click on the
Build Group button, and add both Cu and Co to the
group, for example Sim-CV. (See Figure 9.) After you
close this window, you will notice a Sim-CV group is
available under the y-axis sub-menu selection. Choose
Sim-CV for the y-axis.

18

l C-V

Measurement

i.

Click on Apply and then Done. You should see both
Co and C, curves plotted on the graph. By using the
Build Group feature of Metrics ICS, you can put many
curves on the same graph. Also notice that you can set
up a second y-axis with different scale and different
data set.

User’s Guide Model 82WlN Simultaneous C-V

Plot Definition:
Axis Options:

Data Group:

Scale Type:

Min Value:

Max Value: 11.981

Setup Name: -1

Data Orientation:

Q Column Vectors
*

m-o]

-1

piz--l

Figure 8

Setup PIof View Mlindow

q

lAEpend data only to

View Vectors.

Data Vectors:

User’s Guide Model 82-WIN Simultaneous C-V

Figure 9

View Vectors:

Col 1: CH
Co12 CQ

Build Plot Group window

C-V Measurement. 17

Choose the Right Parameters

Optimal C-V Measurement Parameters

Simultaneous C-V measurement is a complicated matter.
Besides system considerations, you should carefully choose the
measurement parameters. Refer to the following discussion for
considerations when selecting these parameters.

Start, Stop, and Step Voltages

Most C-V data is derived from the steep transition, or depletion

region of the C-V curve. For that reason, start and stop voltages

should be chosen so that the depletion region makes up about

113 to 213 of the voltage range. (See Figure 10.)

Simultaneous CVvs. Vgs

18 l C-V Measurement

VGS (‘4)

Figure 10 Typical Simultaneous C-V Curve

User’s Guide Model 824MN Simultaneous C-V

The upper flat, or accumulation region of the high frequency
C-V curve defines the oxide capacitance, Cox. Since most

analysis relies on the ratio C/Cox, it is important that you
choose a start or stop voltage (depending on the sweep
direction) to bias the device into strong accumulation at the start
or the end of the sweep.

You should carefully consider the size of the step voltage. Start,
stop, and step size determine the total number of data points in
the sweep. Some compromise is necessary between having too
few data points in one situation, or too many data points in the
other.

For example, the complete doping profile is derived from data

taken in the depletion region of the curve by using a derivative

calculation. As the data point spacing decreases, the vertical

point scaling is increasingly caused by noise rather than changes

in the desired signal. Consequently, choosing too many points
in the sweep will result in increased noise rather than an

increased resolution in C-V measurement. It also takes more
time to perform a C-V sweep.

Many calculations depend on good measurements in the
depletion region, and too few dam points in this region will give
poor results. A good compromise results from choosing
parameters that will yield a capacitance change of
approximately ten times the percentage error in the signal.

Sweep Direction

For C-V sweeps, you can sweep either from accumulation to

inversion, or from inversion to accumulation. Sweeping from
accumulation to inversion will allow you to achieve deep
depletion-profiling deeper into the semiconductor than you
otherwise would obtain by maintaining equilibrium. When
sweeping from inversion to accumulation, you should use a
light pulse to achieve equilibrium more rapidly before the
sweep begins.

User’s Guide Model 82-WIN Simultaneous C-V

C-V Measurement l 19

Delay Time

For accurate measurement, delay time must be carefully chosen
to ensure that the device remains in equilibrium in the inversion
region during a sweep. With too fast a sweep the device will
remain in non-equilibrium, affecting Q/t (Figure 1 l), and also
resulting in skewed C-V curves (Figure 12).

Non-equilihrium Current Q-tvs.Vgs

20. C-V Measurement

Figure 11

Leakage Current Q/t 77mugh Device

User’s Guide Model 82WN Simultaneous C-V

Capacitance

T Delay T Delay

- Erroneous curve because - Erroneous curve because
maximum maximum delay time is delay time is

Figure 12 Figure 12

Choosing Optimum Delay Time Choosing Optimum Delay Time

Keithley Simultaneous C-V system has a built-in library to help
you determine optimal delay time quickly and easily. Refer to
the C-V Libraries and Analysis chapter for procedures, or use
the following procedure to determine optimal delay time.

Determining the Optimal Delay Time

For accurate interface trap density measurement, delay time
must be carefully chosen to ensure that the device remains in
equilibrium in the inversion region during a sweep.

1. Click on the Setup Editor button, then click on the
Source Units button.

2. Click on the IU82.OUT icon to open up the parameter
setup window. (See Figure 13.)

User’s Guide Model 82JMN Simultaneous C-V

C-V Measurement l 21