Keithley 707B User Manual

Tips, Tools and Techniques that

Simplify I-V and C-V Characterization

A GREATER MEASURE OF CONFIDENCE

TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Tools, Tips, and Techniques that Simplify I-V and C-V Characterization

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Introduction

Semiconductor characterization presents a wide range of test challenges. This e-Guide offers
an overview of advanced tools, tips, and techniques that you can use to simplify the I-V and C-V
measurements that are essential to characterizing emerging semiconductor materials, devices,
and processes.

Table of Contents

Making Accurate I-V and C-V Measurements ............................................................................................... 3

Ensuring C-V Measurement Integrity ....................................................................................................... 4-5

Preventing C-V Measurement Errors While Reducing Test Times .................................................................. 6

New C-V Measurement Techniques for High Impedance Devices ................................................................. 7

Measuring Sub-Picoamp Currents Accurately .............................................................................................. 8

Combining I-V, C-V, and Pulse I-V Measurements in One System ................................................................. 9

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Making Accurate I-V and C-V Measurements for Semiconductor Research,

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Design, Development, and Test

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I-V Measurements

Making low current measurements presents a variety of measurement challenges. Error sources such
as leakage currents, noise, offset currents, piezoelectric currents, and environmental conditions can
have a serious impact on measurement accuracy. Precision DC I-V measurements are the foundation
of electrical characterization for cutting-edge devices, materials, and semiconductors. With proper
measurement techniques and practices, these critical measurement challenges can be met.

Ultra-Fast Pulsed I-V Measurements

Today, many parametric measurements require a fast, pulsed I-V measurement. Using pulsed I-V
signals to characterize devices rather than DC signals makes it possible to study or reduce the
effects of self-heating (joule heating) or to minimize current drift/degradation in measurements. Many
applications require pulsed I-V along with C-V and DC I-V measurements. Learn how to combine all
three measurement types into one test system while maintaining the measurement performance.

Capacitance-Voltage (C-V) Measurements

Capacitance measurements have been used to determine a variety of semiconductor parameters
on many different devices and structures. Three measurement techniques are used to derive critical
parameters from a wide range of new materials, processes, devices. Multi-frequency capacitance
provides capacitance vs. voltage (C-V), capacitance vs. frequency (C-f), and capacitance vs. time
(C-t) measurements to evaluate at frequencies ranging from 10-MHz down to 1-kHz. Sometimes
even lower frequency capacitance measurements are necessary to evaluate test parameters of thin
film transistors, MEMS structures, and other high impedance devices. Called very low frequency
(VLF) C-V, this newer technique performs C-V measurements in the range of 10-mHz to 10-Hz.
To characterize slow trapping and de-trapping phenomenon in some materials, a capacitance
measurement technique called quasistatic (or almost DC) measurements can be used.

Want to learn more about Keithley’s
powerful characterization solutions?

Download our Applicaton Guies for DC I-V

Testing, Pulsed I-V Testing, and C-V Testing.

Get advice on optimizing your I-V/C-V characterization applications.

Send us your question or join the discussion on our application forum.

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Ensuring C-V Measurement Integrity

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Capacitance measurements at the wafer level are often plagued by preventable measurement errors. Ensuring
the accuracy of capacitance measurements can be challenging due to parasitic capacitance from cable,
switch matrix, and fixturing combined with small capacitance values, often in the picofarad or femtofarad
range. These values are typically far lower than most LCR meters can resolve. Additionally, measuring
capacitance on a semiconductor wafer is very different from measuring a packaged device due to the effects

of the probe station’s chuck.

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Interconnect Capatitance

To ensure measurement integrity, it’s important to
understand how a capacitance measurement is made.
A typical capacitance meter will apply a DC bias
voltage across the device under test while measuring
the AC signal at a frequency between 1-kHz to 10­MHz. For MOScap structures, the DC voltage is swept,
which causes the device under test to pass through
accumulation into the depletion region and then into the
inversion region.

Keithley’s Model 4200-SCS Parameter Analyzer
includes an extensive set of sample programs,
test libraries, and built-in parameter extraction
examples to simplify C-V measurements.

The optional Model 4210-CVU C-V Meter plugs
directly into the Model 4200-SCS chassis for
measuring capacitances from femtofarads to
microfarads at frequencies from 1kHz to 10MHz.
Users can quickly configure linear or custom C-V,
C-f, and C-t sweeps with up to 4096 data points.

Get advice on optimizing your I-V/C-V characterization applications.

Send us your question or join the discussion on our application forum.

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

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Source

0VDC

Measure

ACI

+

–

+

–

Source

DCV

Simplified Test Circuit

DUT

A B

Source

ACV

+

–

+

–

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Ensuring C-V Measurement Integrity

Most capacitance measurements are performed on a probe station, which is the source of many errors. A probe
station’s chuck can act as a large antenna that collects random noise. Since a wafer’s substrate is connected
electrically to the prober’s noisy ground, the AC ammeter circuitry used in the capacitance meter can pick up
this noise, which adds errors to measurements. Therefore, it’s essential to connect the terminals of your meter to
the DUT terminal with the least noise, which generally means the terminal with the least amount of capacitance
to ground. Unfortunately, stopping a test and changing the setup to do this is time-consuming and increases
the opportunity for reconnection errors. To ensure your C-V measurements, the Model 4200-SCS Parameter
Analyzer software allows switching the AC ammeter with a simple mouse click, without the need to change
the test setup.

The DC bias required to make a C-V measurement creates an electric field that pushes or pulls the mobile carriers
closer to or farther away from the DUT’s oxide layer. Precise control over that electrical field requires the ability
to switch the DC bias from one device terminal to another. Similarly. the Model 4200-SCS Parameter Analyzer
software makes switching the DC bias to the desired DUT terminal fast and easy. There’s no need to change the
test setup, which saves time and eliminates inadvertent misconnections, that can cause errors and require extra

H

CUR

H

POT

C

DUT

V

L

POT

L

CUR

A

C

CHUCK

When measuring capacitance on a wafer and probe station, it is essential to connect AC ammeter circuitry to the least
noisy DUT terminal.

Simplified Test Circuit

troubleshooting time.

ACI

+

–

+

–

+

Source

ACV

–

+

Source

DCV

–

Simplified Test Circuit

A B

DUT

Source

0VDC

Measure

Want to learn more about increasing
your C-V measurement accuracy?

Watch our “Four Things you Might Not

Know about Making C-V Measurements”

webinar or download our C-V Measurement

Tips, Tricks, and Traps white paper.

+

–

Measure

ACI

+

–

Source

DCV

A B

DUT

Source

0VDC

Source

ACV

+

–

Model 4200-SCS Parameter Analyzer software enables easy AC ammeter and DC bias switching to DUT terminals.

+

–

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Preventing C-V Measurement Errors While Reducing Test Times

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HGCHGC HGCHGC HGCHGC HGCHGC HGCHGC HGCHGC

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User

connections

and backplane

expansion

H
G
C

H
G
C

H
G
C

H
G
C

H
G
C

H
G
C

H
G
C

H
G
C

When making C-V measurements, it is important to minimize the effects
of stray capacitance, including steps like the use of offset compensation

Low I

and making the proper connections. C-V instruments are designed to be

Paths

connected to the prober via interconnect cables and adaptors and may
be routed through a switch matrix, which can add stray capacitance to

General
Purpose
Paths

the measurements.

Keithley’s Model 4200-SCS Parameter Analyzer incorporates

C-V
Paths

Confidence Check, a unique diagnostic tool that simplifies checking

the integrity of open and short connections and connections to a DUT.
When the Model 4210-CVU instrument is connected to the DUT, Confidence Check displays the measured readings
in real time, so it can be used to perform quick and accurate C

-V measurements without the need to run a

pre-programmed test.

The Model 4210-CVU Confidence Check tool helps correct for stray capacitance that can interfere with test integrity
when test signals are routed through a switching matrix such as those designed for use with Keithley’s Model 707B
Six-Slot Switch Mainframe or Model 708B Single-Slot Switch Mainframe. To verify switch matrix connections,

Ready-to-use C-V application tests in the Model 4200-SCS Parameter Analyzer.

perform real-time capacitance measurements using the Confidence Check tool. When the Model 4210-CVU is
connected to a DUT, the Confidence Check tool displays the measured readings in real time.

Want to learn more about how to
ensure C-V measurement integrity?

View our “Tips, Tricks, and Traps of Semiconductor

Capacitance-Voltage (C-V) Testing” webinar

or download the Model 4200-SCS brochure.

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Keithley’s Confidence Check confirms the integrity of the connections to your DUT.

TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

New C-V Measurement Techniques for High Impedance Devices

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C-V measurement instruments typically measure capacitance and impedance at frequencies ranging from megahertz
down to tens of hertz. However, even lower frequency capacitance measurements are often necessary to derive
specific test parameters of devices such as MOScaps, thin film transistors, and MEMS structures. A low frequency
C-V measurement is essential for characterizing the slow trapping and de-trapping phenomenon in some materials.

Keithley’s Very Low Frequency (VLF) C-V technique allows measuring very small capacitances at a precise low test
frequency. This patent-pending, narrow-band sinusoidal technique allows for low frequency C-V measurements of

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MOSCaps on wafer

Force HI Force HI

PreAmp PreAmp

SMU1

smu_src

smr.src is connected

to the chuck. This SMU
applies the DC and AC

voltage and measures

the volta

Prober Chuck

A

Force LO

(Internally Connected)

connected to the gate

of the MOScap and

measures the current.

e.

A

smu_sense is

SMU2
smu_sense

The VLF C-V technique uses a Model 4200-SCS with two SMU
instruments and two remote preamplifiers connected to
either side of the device under test.

very high impedance devices, up to >1E15 ohms. Other AC impedance
instruments are usually limited to impedances up to about 1E6 to 1E9
ohms. The VLF C-V approach also reduces the noise that may occur
when making traditional quasistatic C-V measurements.

The VLF C-V technique is well-suited for both MOS device applications and emerging technologies like organic
electronics, including organic LEDs, organic FETs, and organic photovoltaic cells, thin film transistors, and
microelectromechanical systems.

Want to learn more?

Download our Performing Very Low Frequency Capacitance-Voltage

Measurements on High Impedance Devices application note.

Get advice on optimizing your I-V/C-V characterization applications.

Send us your question or join the discussion on our application forum.

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Measuring Sub-Picoamp Currents Accurately

Typical Current Generated (A)

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Determining the gate leakage current of FETs, testing sensitive nanoelectronic devices, and measuring leakage cur­rent of insulators and capacitors demand the ability to measure currents of picoamps or less. And making accurate
low current measurements like these depend not only on choosing a test system with a very sensitive ammeter, but on
selecting the proper settings in the system’s software, using low noise fixtures and cabling, allowing sufficient settling
time, and using techniques that prevent unwanted currents from reducing measurement accuracy.

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Standard

cable

Low
noise
cable

Triboelectric

Effects

Teflon

Ceramics

Mechanical

Stress

Effects

Current-Generating Phenomena

Dirty

surface

Epoxy

board

Clean

surface

Electrochemical

Effects

9

Ω

10

12

Ω

10

Resistor

noise in 1Hz

bandwidth

Unwanted currents in your test setup reduce measurement
accuracy. Sources of error include triboelectric effects,
piezoelectric effects, contamination, humidity, ground loops,
light, and source impedance. These sources of measure­ment error can be reduced by using techniques such as
shielding, guarding, proper grounding of instruments, and
choosing the appropriate settings in the Model 4200-SCS
Parameter Analyzer software.

Want to learn more?

Download our Optimizing Low Current Measurements

with the Model 4200-SCS Semiconductor Characterization

The Model 4200-SCS’s DC PreAmps can be mounted on the back of the parameter analyzer or on the probe station.
By reducing the signal path between the DUT and the PreAmp, the Model 4200-SCS can reduce cable effects like parasitic
capacitance and leakage currents, which provides for more accurate low-level measurements.

System application note.

Get advice on optimizing your I-V/C-V characterization applications.

Send us your question or join the discussion on our application forum.

8

TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Combining I-V, C-V, and Pulse I-V Measurements in One System

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Electrical characterization requires the ability to make three types of measurements: precision DC I-V measurements, AC impedance
(capacitance) measurements, and ultra-fast I-V or transient I-V measurements. Since the cabling required for each measurement type
is fundamentally different, combining all three measurement capabilities into a single test system is challenging. Poor-quality connec­tions to the device under test can compromise the measurement integrity of even the most powerful and sophisticated test system.
Matching cabling and grounding requirements for each measurement type enhances measurement integrity. However, changing cables
for each measurement type is so time-consuming that many users simply tolerate the sub-optimal results.

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To address these challenges, Keithley has developed the Model 4225-RPM Remote Amplifier Switch and the Model 4210-MMPC
High-performance, Multi-measurement Cabling System. All three measurement types maintain their signal fidelity, cabling errors are
reduced, and time is saved when integrated into the test setup with the remote amplifier switch and cabling kit.

Want to learn more about integrating
multiple measurement types in a
single characterization system?

Download our White Papers:

n

Labs’ Demands for Greater Measurement

Model 4225-RPM Remote Amplifer Switch with multi-measurement Performance Cabling System.

Flexibility Require Cabling Systems Capable of
Accommodating Multiple Measurement Types

n

The Challenge of Integrating Three Critical Semiconductor

Measurement Types into a Single Instrument Chassis

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

Want to learn more?

Contact us by phone, fax, mail, or email:

Keithley Instruments hosts an online applications forum to encourage idea exchange,
discussions among users. Join the discussion today.

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TOOLS, TIPS, AND TECHNIQUES THAT SIMPLIF Y I-V AND C-V CHARACTERIZ ATION

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