Agilent B1500A Semiconductor Device Analyzer Self-paced Training Manual Agilent Technologies
Notices © Agilent Technologies 2005 - 2008 Manual Part Number No part of this manual may be reproduced in any form or by any means (including electronic storage and retrieval or translation into a foreign language) without prior agreement and written consent from Agilent Technologies, Inc. as governed by United States and international copyright laws.
In This Manual This document is the self-paced training manual to help you to understand what is Agilent B1500A, what functions the B1500A has, how to use the B1500A, and what applications the B1500A contributes to. CAUTION The test setup data described in this manual are only examples. If these example data damage your devices, Agilent is NOT LIABLE for the damage. • Module 1. Introduction This module explains the product concept and the key features of the B1500A/ EasyEXPERT.
• Module 11. Advanced Definitions and Operations This module explains how to control external GPIB devices, how to call an execution file, how to perform a repeat measurement, and how to use the prober control script. • Module 12. Miscellaneous Operations This module explains what is the status indicator, what is the automatic data export function and the automatic data record function, how to perform selftest and calibration, how to perform SMU zero offset cancel, and such. • Module 13.
Class Exercises Class exercises use the test setup listed below. The test setup data are only examples and included in the Demo.xpg file stored in the Manual CD-ROM.
Module Exercise Device Test setup/definition/data Page Module 8 C-V sweep measurement MOSFET CV-1MHz 8-6 Module 9 Modifying application test definition MOSFET Trng IdVd Vth.xtd 9-14 Trng idvd idvg2.xtd 9-29 Trng idvd idvg3.xtd 9-32 Using auto analysys twice MOSFET Vth gmMax and Id 9-34 Using vector data MOSFET Trng Cgg-Vg 9-42 Module 10 Creating application test definition MOSFET Trng idvd idvg.
Test Setup for Class Exercises The Demo preset group contains the following test setup. The setup data are only examples for the class exercises. The following table lists the test setup name in alphabetical order. Test Setup Name Description ALWG monitor 511 kohm sampling measurement with SPGU ALWG output Charge Pumping 4T 0.
Test Setup Name Description Trng List MOSFET Vth-gmmax measurement using I/V List Sweep Trng Multi Multi Channel I/V Sweep (Bipolar transistor and LED) Trng Sampling 0.
Required Devices for Class Exercises To perform the class exercises, you need the device set (Agilent part number 04156-87001) which contains the following devices. Description Quantity N-channel MOSFET 2 ea. NPN Bipolar Transistor 1 ea. Red Miniature LED 1 ea. 0.1 μF Capacitor 50 V 1 ea. 1.0 Ω Resistor 1/8 W 1 ea. 1.1 kΩ Resistor 1/8 W 1 ea. 511 kΩ Resistor 1/8 W 1 ea. N-ch MOSFET NPN bipolar Transistor LED Brown Black Black Silver 1 ohm Resistor Brown Brown Black Brown 1.
Required Accessories for Class Exercises To perform the class exercises, you need the following accessories. Prepare the accessories shown below. Designation 1 Description Test Fixture Model No. Qty. 16442A/B a 1 ea. 28 pin socket module 1 ea. Connection wire 6 ea. 2 Triaxial Cable 16494A 4 ea. 3 Interlock Cable 16493J 1 ea. 4 Kelvin Triaxial Cable, for Module 5 16493K 1 ea. 5 CMU Cable, for Module 8 N1300A 1 ea. 6 Atto Sense/Switch Unit, for Module 6 E5288A 1 ea.
To perform the flash memory class exercise in Module 13 and if you use the ASU, you need the following accessories. Description Model No. Qty. E5288A Total 3sets 16494A or equivalent Total 7ea. BNC-SMA Cable 16493P 3 ea. SMA-SMA Cable, for synchronization of SPGU 16493Q 2 ea. ASU (Atto Sense/Switch Unit) with control cable Triaxial Cable To perform the flash memory class exercise in Module 13 and if you use the selector, you need the following accessories. Description Model No. Qty.
Contents Module 1. Introduction • New Features • EasyEXPERT • To Perform Easy Application Test • User Interface • Modular Mainframe • SCUU/GSWU • ASU • SMU/Pulse Generator Selector • B2200/E5250 Switch Control • Desktop EasyEXPERT Module 2.
Contents Module 3. Data Display and Management • Data Display window • Graph Analysis Tools • Data Status • To Change Graph/List/Display Setup • To See Print Preview • To Print Display Data • To Copy Graph Plot/List Data • To Save Analysis Result • To Use Preview Window Module 4.
Contents Module 5. Basic Measurement • SMU Fundamentals • Classic Test Environment • SMUs Connected in Series or Parallel • Cabling and Fixture Issues • Kelvin and Driven Guard • Probes and Prober Connections • Triax and Coax Adapters • Safety Interlock Issues Module 6.
Contents Module 7. Measurement Functions • SMU Pulsed Sweep Measurement • I/V-t Sampling Measurement • Negative Hold Time for High Speed Sampling • Auto Analysis • SMU Filter • SMU Series Resistor • Standby Function • Bias Hold Function Module 8.
Contents Module 9. Modifying Application Test Definitions • To Open Application Test Definition • To Modify Test Definition • To Use Debug Tools • To Use Built-in Functions • To Add Data Display • To Use Auto Analysis • To Use Test Setup Internal Variables • To Use Auto Analysis twice (as Class Exercise) • To Use Vector Data (as Class Exercise) Module 10.
Contents Module 11. Advanced Definitions and Operations • To Control External GPIB Devices • To Call Execution Files • To Perform Repeat Measurements • Prober Control Script Module 12.
Contents Module 13.
Contents Contents-8
5 Basic Measurement
Module 5 Basic Measurement In This Module • SMU Fundamentals • Classic Test Environment • SMUs Connected in Series or Parallel • Cabling and Fixture Issues • Kelvin and Driven Guard • Probes and Prober Connections • Triax and Coax Adapters • Safety Interlock Issues 5-2
Module 5 Basic Measurement SMU Block Diagram Three Modes A V Source Mode Output Switch Common Mode SMU FORCE I Source Mode COMMON - V + The source monitor unit (SMU) can function in three modes: - Voltage source while monitoring current - Current source while monitoring voltage - Source common with no monitor The SMUs on the B1500A can output V or I in constant, linear sweep, logarithmic sweep or pulsed modes. Constant V or I mode could be used for “spot” measurements or biases.
Module 5 Basic Measurement Basic Sweep Measurement VAR1 Single Sweep Double Sweep Linear Sweep Log Sweep The SMUs can now sweep up to a value and then back down (double sweep). This feature is useful when the device must be tested without abruptly removing the forcing condition. Log sweeps are required any time the measurement results span many decades, such as a MOS subthreshold curve. The variable used to set the SMU to a basic sweep is VAR1. It may be called the primary sweep.
Module 5 Basic Measurement Sweep Measurement Modes Combining VAR1, VAR1’, VAR2 VAR1 (primary sweep) Subordinate sweep Synchronous sweep VAR2 (secondary sweep) VAR1 (primary sweep) VAR1’ (synchronous sweep) A subordinate sweep variable (VAR2) may be combined with the basic sweep variable (VAR1). This corresponds to the step knob and sweep knob of a curve tracer. This produces a family of curves. VAR2 may be called the secondary sweep. Another useful combination is a synchronous sweep.
Module 5 Basic Measurement Why Four SMUs? z z z Four terminal MOS device Only one configuration required Speed up testing Drain Gate Substrate Source VAR1 SMU3 Common Constant SMU1 SMU2 VAR2 SMU4 The basic semiconductor device is the 4-terminal MOS transistor. By assigning an SMU to each terminal, you have complete flexibility to make any measurement without having to change the device hookup.
Module 5 Basic Measurement Class Exercise MOS Id vs Vd Basic Measurement z z z z z z You will connect the SMU cables and jumper leads You will then "properly" insert the MOS transistor You will learn how to load a setup data Observe Classic Test setup screen Click button to make a new measurement Observe Application Test setup screen To Get Started: z z z z Use the next several pages as you guide Verify that four triax cables are connected as shown Connect four jumper leads to the 28 pin socket as shown
Module 5 Basic Measurement SMU Triax Connection Force Lines to Fixture 1,2,3,4 Ports Force side Sense side CMU 16442A/B Fixture SMU4 SMU3 SMU2 SMU1 GNDU B1500A Rear View For the non-Kelvin connections, connect only the Force lines, leaving the Sense lines open. Connect corresponding numbers. On the 16442A/B fixture use the numbers labeled 1 - 6, not 1 - 3. Your B1500A may not match the SMU configuration shown in this figure. Note that SMU1 is the module top of the GNDU (ground unit).
Module 5 Basic Measurement Wrong Triaxial Hookup If you use the Sense lines … CMU SMU4 SMU3 SMU2 SMU1 GNDU Curves clamped at 10 mA level B1500A Rear View This picture shows the triax cables connected to the right set of connectors which is wrong. The 4 triax cables must be connected to the left set of connectors (FORCE). You will likely see this type of erroneous response with clamping at 10 mA (no trace above 10 mA even though compliance is set much higher).
Module 5 Basic Measurement Jumper Leads – MOS transistor F 1 G F F 2 1 1 PGU F VSU VMU SMU F 4 G G G 1 F 3 F 5 F G GNDU 6 F S G 2 2 2 4 5 6 9 10 11 12 14 15 16 17 18 20 21 22 23 24 1 2 7 8 13 19 28 3 15 25 26 27 28 14 1 S D G Sub 1: Substrate 2: Source 3: Gate 4: Drain For all class exercises, you need the 28-pin dual in line socket which comes standard with the 4145 fixture (16058A) or the newer fixture (16442A/B). Either fixture works fine.
Module 5 Basic Measurement To Import Demo Data 1. Prepare the Agilent B1500A Manual CD-ROM Edition 4 or later 2. Insert the CD-ROM into the B1500A built-in CD-ROM drive 3. Click My Favorite Setup button 4. Click Preset Group > Import Preset Group … 5. Import \data\Demo.xpg on the Manual CD-ROM The Agilent B1500A Manual CD-ROM stores demo data used for performing this class exercise. Insert the CD-ROM and import the demo data to the EasyEXPERT database. The demo.
Module 5 Basic Measurement To Get Setup Data To Get Classic Test Setup: 1. Highlight IDVD in My Favorite Setup 2. Click Recall button To Get Application Test Setup: 1. Highlight Id-Vd in My Favorite Setup 2. Click Recall button You can get the test setup data as shown. IDVD is a sample setup data for Classic Test. Id-Vd is a sample setup data for Application Test.
Module 5 Basic Measurement Classic Test – Channel Setup After you get the IDVD setup data, you will see the Classic Test setup screen as shown. The Channel Setup screen allows the user to assign a meaningful name to the force/meas functions of each SMU. These names may be used in the Function Setup screen to define algebraic expressions.
Module 5 Basic Measurement Classic Test – Measurement Setup Do not abort on compliance, oscillation, etc. The Measurement Setup screen is shown here. The variables VAR1 and VAR2 define the sweep parameters. In a case where two sweep parameters are defined, the second parameter (VAR2) is called the subordinate (secondary) sweep parameter. This means that the primary parameter will be swept once for each discrete value of the subordinate parameter.
Module 5 Basic Measurement Classic Test – Display Setup The Display Setup screen allows you to set the X-Y graph axes. The display setup is divorced from the measurement setup to allow the user to tailor the view to a particular region of interest. This screen also allows you to set data variable names to be displayed in the List Display and Parameters areas on the Data Display window which is opened when the measurement is started.
Module 5 Basic Measurement To Start Measurement 1. Click Single button This opens the Data Display window and starts measurement. The Data Display window shows measurement result data graph/list.
Module 5 Basic Measurement Data Display Window – Graph Analysis tools Graph Plot Parameters Auto Scale List Display This window displays measurement result graph, list, and parameter values. Markers are used to traverse the actual measurement data. Markers cannot be placed anywhere on the screen except on an actual measurement trace. They are denoted with a small circle. One moves the markers with the front panel rotary pulse generator (RPG) knob, mouse, or touch screen.
Module 5 Basic Measurement Data Display Window - List Analysis tools Graph Plot Parameters Marker position List Display The List Display corresponds exactly with the Graph Plot. Even the highlighted line of data corresponds to the marker position on the Graph Plot. Up to twenty columns of data can be set on the List Display. Note that the Graph Plot can only plot nine columns (X, Y1 to Y8). The list data can be copied to a spreadsheet software easily. Click Edit > Copy List.
Module 5 Basic Measurement To Copy List Data Paste to Notepad Open by a spreadsheet software 5-19
Module 5 Basic Measurement Application Test Recall Id-Vd application test setup data. After you get the Id-Vd setup data, you will see the Application Test setup screen as shown. Test Parameters area shows the device connection information and allows the user to set the SMU outputs. Device Parameters area allows the user to set device parameters. In the Id-Vd setup, the device parameters are polarity, gate length, gate width, temperature, and maximum drain current.
Module 5 Basic Measurement Application Test – Extended Setup Clicking the Extended Setup button opens … The Extended Setup dialog box allows the user to set the additional test setup parameters. In the IdVd setup, the additional parameters are source voltage, maximum gate current, maximum substrate current, integration time, hold time, and delay time.
Module 5 Basic Measurement SMUs May Be Connected In Series or Parallel z z z To Double the Output Voltage z from 100 V to 200 V for HRSMU and MPSMU z from 200 V to 400 V for HPSMU To Double the Output Current z from 100 mA to 200 mA for HRSMU and MPSMU z from 1 A to 2 A for HPSMU Use the VAR1’ mode to synchronize two SMUs You can double the voltage or current output by combining SMUs. The VAR1’ mode allows a second SMU to be swept in tandem with the first.
Module 5 Basic Measurement 200 Volt Sweep (400 Volt with 2 HPSMUs) Two SMUs in Series Base current = 0 or leave open WARNING Collector V2 V1 Base Const. SMU1 I=0 Emitter VAR1' VAR1 VAR1 SMU2 V=0 to -100 SMU3 V=0 to 100 200 V BVceo SMU1 V=0 to 100 VAR1' SMU2 V=0 to -100 200 V Resistor Sweep Higher voltages are necessary to observe breakdown conditions, such as BVceo. In the case of BVceo the base must be open (no SMU) or the SMU must be set as a current source with I=0.
Module 5 Basic Measurement Channel and User Function Pages Two SMUs in Series Voltage across resistor VR = V1-V2 The voltage across the resistor (VR) is the difference between V1 and V2. A simple user function can be used to plot VR.
Module 5 Basic Measurement Measurement and Display Pages Two SMUs in Series VAR1' Ratio = -1 The VAR1’ mode is used to synchronously sweep two SMUs. Setting Ratio = -1 forces one SMU to sweep in the opposite direction of the other.
Module 5 Basic Measurement Graphics Page 0 to 200 V Two SMUs in Series WARNING Use the interlock cable and observe safety precautions. 511K Resistor The result is a clean 200 V sweep. Remember that there is a serious shocking hazard. The interlock cable is necessary for any voltage sweep greater than 42 V.
Module 5 Basic Measurement 200 mA Output Two SMUs in Parallel V1 V2 1 ohm VAR1 SMU1 V=0 to 0.2 NOTE VAR1’ Ground Unit (GNDU) or Chassis Gnd Use Ground Unit or the chassis ground as the SMU return path. Shorting bar SMU2 V=0 to 0.2 Circuit Common Two SMUs can be operated in parallel. The trick is to not use any SMU as COMMON. HRSMU and MPSMU can only sink 100 mA. Use GNDU (ground unit) or the chassis to sink the 200 mA of current. Chassis noise level will not affect the measurement.
Module 5 Basic Measurement Channel and User Function Pages Two SMUs in Parallel Current in resistor Itotal = I1+I2 A user function totals the current in both SMUs.
Module 5 Basic Measurement Measurement and Display Pages Two SMUs in Parallel VAR1' Ratio = 1 The VAR1’ mode with Ratio = 1 forces two SMUs to sweep the same voltage.
Module 5 Basic Measurement Graphics Page 0 to 200 mA Two SMUs in Parallel 1 ohm Resistor The result is a clean sweep to 200 mV. It shows the current measurement data near 200 mA.
Module 5 Basic Measurement Cabling and Fixturing Issues z Guard connection z Kelvin connection z Prober interface z Triaxial Probes z RF Fixturing interface z Feedthru and triax to coax adapters z 16442A/B fixture interlock z 16058A fixture compatibility What? Where? Why? The B1500A is a precision instrument. However, the ability to make precise and reliable measurements may be compromised by your fixturing to the device.
Module 5 Basic Measurement Guard Connection for Non-Kelvin Connection Simplified Diagram Buffer x1 Rs 10K Guard SMU Force DUT V The guard connection is needed for measurement < 1 nA. Below 1 nA a regular coax cable's capacitance dominates over the DUT (device under test) capacitance. What you see is cable charging current. I = C(dv/dt) where dv/dt is the rate of change of SMU voltage from one step to the next of a coax cable with no guard. C is the total capacitance of the cable.
Module 5 Basic Measurement Triaxial Cable for Non-Kelvin connection Shield (Ground) Guard Force 16494A-001 (1.5 m) 16494A-002 (3.0 m) Shield Capacitance 900 pF 1800 pF Guard Capacitance 130 pF 240 pF Force Resistance 160m ohm 320m ohm Shown above are typical capacitance and series resistance of the force line. If cables are too long, high capacitance may cause the SMU to oscillate. Keep the force-guard cable capacitance less than 600 pF.
Module 5 Basic Measurement Why Use Guarded (Triax) Cables? Shield (Ground) Guard Leakage Shield (Ground) Force Force MOSFET Subthreshold MOSFET Subthreshold Id mA mA uA uA Id nA pA nA pA fA fA Vg Triax Cables Vg Coax Cables Eliminate cable low current errors. The triax cable is a special low dielectric loss, high impedance cable. This cable may be used down to fA levels when properly used with a guarded probe.
Module 5 Basic Measurement Guard Connection for Kelvin connection Simplified Diagram Buffer x1 Guard Rs 10K Sense Force SMU DUT V With the Kelvin connection, sensing is done at the DUT, eliminating the fraction of an ohm of cable resistance. The internal sensing resistor Rs is the only feedback path without the Kelvin connection. Note that the B1500A operates just fine without the sense cable. This is important to know because in general you do not need the sensing Kelvin connection.
Module 5 Basic Measurement Kelvin Triaxial Cable Ground Guard Force Sense The triaxial cables are good for low current measurements. However, two cables are necessary for low resistance Kelvin measurements. Agilent Technologies designed a special Kelvin triaxial cable for the precision semiconductor parameter analyzers. This cable is optimized for both low current and low resistance measurement. Both force and sense lines are held rigidly in the same Teflon cable.
Module 5 Basic Measurement Why Kelvin Measurements? VC monitor IB 20 Re = 735 mΩ Slope = 1/Re (Kelvin) Rcable = 214 mΩ Ib (mA) Slope = 1/(Re+Rcable) (Non-Kelvin) 0.1 0 Vc (mV) 50 In the example above, the device is connected with a SMU on the base sweeping current, a voltmeter on the collector, and the emitter is grounded with a Kelvin SMU. The base SMU does not have to be Kelvin since we are only forcing current and do not care about measuring the cable loss in the base.
Module 5 Basic Measurement Class Exercise Bipolar Re Using A Kelvin SMU z z z z You will connect a Kelvin triax cable to the B1500A You will then connect jumper leads and the bipolar device You will get the REKELV setup You will observe Re using Kelvin and Non-Kelvin connections.
Module 5 Basic Measurement Cable Connections z Triax to SMUs 1 and 2 z Kelvin Triax to SMU 3 CMU 16442A/B Fixture SMU4 SMU3 SMU2 SMU1 GNDU B1500A Rear View This class example requires a Kelvin triaxial cable. If the Kelvin cable is not available, substitute two standard triax cables. SMUs 1,2,3 can all be connected with Kelvin triaxial cables, but only SMU3 requires the Kelvin connection. Note If you use the 16058A fixture instead of the 16442A/B, connect the triaxial cables as shown below.
Module 5 Basic Measurement Class Example - Jumper Leads F 1 G F F 2 1 PGU F VSU SMU F 4 G G G 1 F 3 F 5 F G 1 F S G 2 2 4 5 6 9 10 11 12 14 15 16 17 18 20 21 22 23 1 2 7 8 13 19 28 3 15 25 VMU GNDU 6 24 26 EBC 2 27 28 14 1 E B C 17: Emitter 16: Base 15: Collector Connect jumper leads as shown. Where, the SMU4 F terminal is connected to the B1500A’s SMU3 Sense connector. So the couple of the SMU3 F and SMU4 F terminals makes a Kelvin terminal.
Module 5 Basic Measurement To Get Setup Data To Get REKELV Test Setup: 1. Highlight REKELV in My Favorite Setup 2.
Module 5 Basic Measurement Single Kelvin Measurement Click button to start measurement Click the Single button to make a new measurement. You should see a response similar to this, will the analysis line correctly overlaying the curve.
Module 5 Basic Measurement Non-Kelvin Measurement Click button to start append measurement You can switch the analysis line between the two curves with this softkey Remove the jumper lead connected between the terminal 17 and the SMU4 F terminal. And click the Append button to add another measurement to the graph. Now you see the very large difference between Kelvin and non-Kelvin measurements when the resistance is low. You can see that Re jumps from about 0.735 ohm in this example, to about 0.949 ohm.
Module 5 Basic Measurement Prober Kelvin Cable Connection To Kelvin Probe To Guarded Chuck Photo of SMU cable connection to a Cascade Microtech Summit probe station. The Kelvin triaxial cables mate directly to the probe station.
Module 5 Basic Measurement Connector Plate Non-Kelvin Connection Shielding Box Kelvin Triaxial Cable 16493K GUARD Line FORCE,SENSE Line COMMON GUARD FORCE Probe Cable (Coaxial) S M U F F S S Connector Plate 16495H-002 or 16495J-002 SENSE GUARD COMMON Insulator Prober DUT Jumper to eliminate cable resistance in force line This is a "hybrid" Kelvin connection. Cable resistance from SMU is eliminated by shorting FORCE and SENSE lines inside the prober.
Module 5 Basic Measurement Simplifying the Prober Connection z Use single triax for basic MOS FET measurements z One triax on each Force line z Leave the Sense lines open...no cable connected z Use triax bulkhead feedthru adapters on the prober z Use a probe holder with a triaxial connector z Use a probe holder than accommodates replaceable probe tips (inexpensive repair) The next section sheds light on the confusing topic of connection to the device under test.
Module 5 Basic Measurement Triaxial Probes Guarded to within 2mm of tip Single Triax Kelvin Triax These probes are guarded within 2mm of the probe tip, ideal for low current applications. The Kelvin triax probe is the ideal mate for the Kelvin triax cable. A third variation of these probes is a Kelvin triax probe with only one probe. The Kelvin connection is made inside the probe holder. This compromise eliminates most cable loss while making a single point contact.
Module 5 Basic Measurement Simplifying RF Connections z Triax is not necessary...bias currents are > 1 nA. Use triax to coax adapters with floating guard. Bias Network RF in Bias F DUT Bias Sensing SMU1 Bias Network RF out Bias Bias Sensing S F SMU2 S Above 1 nA guarding is of little use. Cable capacitance has a negligible effect on the bias port. Use the floating guard triax(m) to BNC(f) adapter at the B1500A rear panel. Then use standard coax BNC cables.
Module 5 Basic Measurement Interlock Connection z z For measurements above 42 Volts For program control using program memory 6 1 2 5 4 3 Short required View from B1500A rear panel To prevent shock hazard, the B1500A will not operate above 42 V, unless you connect the interlock circuit. The interlock connection is required when the voltage exceeds 42 V or when the program memory is used in a control program.
Module 5 Basic Measurement 16442A/B Fixture interlock cable 16493J-001 16493J-002 1.5 m cable 3.0 m cable The 16493J interlock cable is designed to be connected directly between the B1500A’s interlock connector and the 16442A/B. If the fixture lid is closed, internal switch is closed, and then the B1500A can perform measurement up to 100 volts; 200 V with the HPSMU.
Module 5 Basic Measurement 16058A Fixture Compatibility Use the 16058A with the B1500A 4 non-Kelvin SMU inputs 3 general purpose coaxial inputs Add the 16493A Adapter Cable Interlock connection 4 additional coaxial inputs Add the 16435A Adapter The 16058A has 4 non-Kelvin SMU inputs and 3 coaxial inputs for the other instrument connection. By adding the 16493A Adapter Cable, you get access to 5 more coaxial connections.
Module 5 Basic Measurement 5-52
6 Low Current Measurement
Module 6 Low Current Measurement In This Module • Low-Current Measurement Challenges • Calibration and Zero Cancel • Effect of Cable Movement • ASU for Ultra Low-Current Measurement • Low-Current Subthreshold • Trade-Off Speed Vs Accuracy • Low-Current Gummel Plot • Low-Current Gate Oxide Leakage This module is primarily written for the B1500A installed with the HRSMU (high resolution SMU) and covers sub pA measurement techniques. Course exercises are included which fully explore speed vs.
Module 6 Low Current Measurement Low Current Measurement What is possible? z Measurements below 10 fA at the wafer level z Repeatability within a few fA z Speeds less than 1 minute for subthreshold sweep Making wafer level measurements to fA levels is easy and routine using proper measurement procedures on a low noise probe station. This module explains how.
Module 6 Low Current Measurement Low Current Measurement Challenges z z z z NOISE FROM PROBER z Faraday enclosure required z Eliminate all electrical interference STRAY CAPACITANCE z Full guarding, including the probe z Guarded chuck to measure substrate current MEASUREMENT SETUP z Hold time, integration, auto ranging CALIBRATION & ZERO CANCEL Measurement below 1pA is not possible without special attention to the prober and cabling.
Module 6 Low Current Measurement Clean Probing Environment What is Required? 9 Low loss triaxial connection (no matrix card) 9 Guard to tip of probe (no bare needle or probe cards) 9 No air flowing near probe tip (including dry nitrogen) 9 No hot chuck 9 Chuck isolated from ground (10^13 ohms) 9 Chuck guarded for substrate measurements 9 Shielded probe station 9 No vibration; cables stationary 9 Microscope light, motors, etc. off This check list covers most sources of noise or stray capacitance.
Module 6 Low Current Measurement Debugging A Noisy Probe System Where to Start? z z Sweep 0 to 1 volt with no cables attached to SMU z Check that there is a +/- 3 fA base line Add prober cables but no prober z Wait several minutes z Still +/- 3 fA base line? z Add shielded prober but no probes z Add probes This is a systematic strategy for focusing in on the sources of noise and error. You can be very surprised. Some prober cable is not low loss.
Module 6 Low Current Measurement Low Current Calibration & Zero Cancel z z z WAIT 30 MINUTES AFTER TURN ON z Instrument must stabilize CAL & ZERO WITH PROBES UP z Prevent device damage ZERO EVERY 30 MINUTES z To get repeatable fA level measurements The SMU can be thought of as a sophisticated OP AMP. With any OP AMP there is an associated input offset error. This error is small and varies with ambient temperature shifts and other factors.
Module 6 Low Current Measurement Low Current Calibration & Zero Cancel Calibration Click Calibration button to open the Calibration window. SMU calibration is performed on the SMU Calibration tab screen. Specify the modules for calibration by checking the left check box and click Start Calibration button to start calibration. If ASU (atto sense/switch unit) is connected and 1 pA range is used for measurement, check Full Range Calibration check box before clicking Start Calibration button.
Module 6 Low Current Measurement Class Exercise Measurements Near Zero fA You will be able to answer the following questions: z What does a sweep into an open SMU port look like? z What is the time per meas using PLC integration? z Add a 1.5 m cable during a sweep...how long to settle? z Move and bend the cable...
Module 6 Low Current Measurement ZERO CHECK - No cable Using Default SMU Setup Cursor at the maximum point 3.17 fA Marker at the minimum point -1.84 fA +/- 3 fA variation typical, using 16 PLC integration time With slight modification of the default SMU settings of Classic Test I/V Sweep, you can check the conditions of your measurement system. This is a typical plot when no cable is attached to the SMU port.
Module 6 Low Current Measurement ZERO CHECK Channel Setup Change Mode to V and Function to VAR1 Delete SMU1 and SMU2 Click the Classic Test tab, I/V Sweep, and Select to display the Channel Setup screen. On this display, delete the rows of SMU1 and SMU2. Change the Mode of SMU4 to V. Change the Function of SMU4 to VAR1. This setup will be used for checking the zero measurement on SMU4.
Module 6 Low Current Measurement ZERO CHECK Measurement Setup Do not change this screen This default sweep setup is enough for the Zero Check measurement. The sweep steps are small (10 mV) and that is ideal for checking current at fA levels. Also the sweep starts at 0, so no big discontinuities on the first step of the sweep. There is no need to change anything on the Measurement Setup screen. But the ranging mode and the integration time settings must be changed. See the next page.
Module 6 Low Current Measurement ZERO CHECK Range and Integration Time Change SMU Range to AUTO or LIMITED 10 pA Change Integration Time to 16 PLC You must change the range setting from the default of LIMITED 1 nA to LIMITED 10 pA or to AUTO. Otherwise you will have 100 fA resolution instead of the best 1 fA resolution possible. Also change the High Resolution ADC Mode to PLC and Factor to 16. You will see +/- 3 fA variation measurement result as shown in the previous slide.
Module 6 Low Current Measurement ZERO CHECK Display Setup Linear, with zero set to mid scale The best check is done with a LINEAR scale which brackets either side of ZERO by 100 fA or less. A log scale is particularly unacceptable, Log plots of zero are not possible, and all readings of a log plot must be either all positive or all negative.
Module 6 Low Current Measurement ZERO CHECK Effect of connecting a triaxial cable Approx. 50 sec > +/- 3 fA < +/- 3 fA < +/- 3 fA If you change anything in your fixturing or cabling, wait at least 1 minute before making a measurement at low currents. Here we see the effect of connecting a cable to the open SMU port of the B1500A. The discontinuity lasted for 50 seconds of a 2 minute sweep from 0 to 1 volt in 10 mV steps.
Module 6 Low Current Measurement ZERO CHECK Effect of cable movement Bending Cable Bumping cable As you can see, your fixturing must be free from vibration. Bending cables during a test is another NO NO. The above measurements were made on a single triax cable for classic parameter analyzers. The Kelvin triax cable is less sensitive to movement (triboelectric effects). However, either cable works fine to fA level if the cables are reasonably still...i.e. not swinging, coiled up and moved, etc.
Module 6 Low Current Measurement ZERO CHECK Appendix: Using ASU For Ultra Low Current Measurement From HRSMU Force D-sub Sense (optional) Triax cable Force Control cable (control signal and Sense signal) For ultra low current measurement, use ASU (atto sense/switch unit). The HRSMU has an innate 1 fA measurement resolution. And the ASU extends it to 0.1 fA. Note that the ASU must be connected to the HRSMU before turning on the B1500A.
Module 6 Low Current Measurement ZERO CHECK Appendix: Using ASU Configuration You can check whether the ASU connection is correct or wrong. Open the Configuration window and look at the ASU tab screen. If the ASU Serial Number field shows its serial number, the HRSMU-ASU combination is correct. If the ASU Serial Number field shows *s/n mismatch, the combination is wrong. The B1500A can work with this wrong combination however it cannot satisfy its specifications.
Module 6 Low Current Measurement ZERO CHECK Appendix: Using ASU HRSMU+ASU HRSMU This slide shows the open measurement results with ASU and without ASU. The ASU provides the 1 pA measurement range and the stable measurement results as shown. The 1 pA range is disabled with the default setting. To enable the 1 pA range, set the ranging mode to LIMITED 1 pA (1 pA limited auto ranging) or FIXED 1 pA (1 pA fixed range).
Module 6 Low Current Measurement Class Exercise Low Current Subthreshold You will: z Check low level accuracy with fixture lid open/closed z Observe trade off between resolution and speed z Change resolution from LIMITED 1 nA to LIMITED 10 pA z Observe trade off between averaging and speed z Change integration from AUTO to PLC to MANUAL To Get Started: z z Use the next pages to setup the MOS FET correctly Get the IDVG setup in the Demo preset group The following pages show a typical plot of the subthres
Module 6 Low Current Measurement Jumper Leads – MOS transistor F 1 G F F 2 1 1 PGU F VSU VMU SMU F 4 G G G 1 F 3 F 5 F G GNDU 6 F S G 2 2 2 4 5 6 9 10 11 12 14 15 16 17 18 20 21 22 23 24 1 2 7 8 13 19 28 3 15 25 26 27 28 14 1 S D G Sub 1: Substrate 2: Source 3: Gate 4: Drain For all class exercises, you need the 28-pin dual in line socket which comes standard with the 4145 fixture (16058A) or the newer fixture (16442A/B).
Module 6 Low Current Measurement Class Exercise SD214DE MOS Subthreshold With lid closed, you should see this typical response using the IDVG setup data. If the subthreshold region is much higher, at the pA or nA level, the MOS device may be statically damaged. Replace the device using the handling procedure detailed on the previous page.
Module 6 Low Current Measurement Class Exercise Trade Off Speed vs Accuracy Change LIMITED range from 10 pA to 100 nA. Change Factor from 16 to 1. Change Mode from PLC to AUTO to NORMAL. You can trade off speed vs accuracy by varying the LIMITED range setting or the integration time setting. The 100 nA range will speed up the test but you will lose low-end resolution. Try setting LIMITED to 10 pA range or 100 pA range. Accuracy increases but speed slows considerably.
Module 6 Low Current Measurement Gummel Plot What is measured? z z Ve is swept while Vb and Vc are held at 0 V Ib and Ic are plotted on log scale Collector Base Emitter Constant SMU3 Constant VAR1 SMU2 SMU4 The "Gummel Plot" is an excellent low current measurement to make on a bipolar transistor. It plots log base current and log collector current against the same bias voltage. A good bipolar device has constant gain over a wide bias range (both curves are linear and parallel).
Module 6 Low Current Measurement Class Exercise Low Current Gummel Plot z You will notice that sub 10 fA measurements are possible To Get Started: z z z Set the jumper leads for the bipolar transistor Insert the device and perform a zero cancel offset Get the GUMMEL setup in the Demo preset group The following pages will lead you through the setup and measurement procedure for a low current Gummel measurement.
Module 6 Low Current Measurement Jumper Leads - Bipolar examples F 1 G F F 2 1 PGU F VSU SMU F 4 G G G 1 F 3 F 5 F G 1 F S G 2 2 4 5 6 9 10 11 12 14 15 16 17 18 20 21 22 23 1 2 7 8 13 19 28 3 15 25 VMU GNDU 6 24 26 EBC 2 27 28 14 1 E B C 17: Emitter 16: Base 15: Collector For all class exercises, you need the 28-pin dual in line socket which comes standard with the 4145 fixture (16058A) or the newer fixture (16442A/B).
Module 6 Low Current Measurement Gummel Plot Measurement Setup Small step size. Negative sweep values. Ve is swept below ground level to keep positive bias on the NPN device.
Module 6 Low Current Measurement Gummel Plot Range and Integration Time Maximum resolution 16 PLC Medium integration smoothes the plot at the ultra low levels.
Module 6 Low Current Measurement LOW CURRENT MEASUREMENT Gummel Plot This curve shows a normal gummel characteristic of the bipolar transistor. The collector current is linear when plotted on log scale from 10 mA down to fA levels. Keep the fixture lid closed and do not bump any part of the setup during the measurement.
Module 6 Low Current Measurement Gummel Plot With Base-Collector Self Oscillation Fix by isolating base-collector leads Fix by using ferrite bead on base lead This is a common occurrence when high frequency bipolar transistors are tested with jumper lead connections. When RF couples in the air to the base lead, there can be enough DC rectification to increase the base current bias. This causes positive feedback.
Module 6 Low Current Measurement ULTRA LOW CURRENT Subthreshold Curve This curve shows the high quality measurement that you would typically expect with the B1500A and a well guarded probe station. The MARKER is sitting at 5.3 fA near the subthreshold region. To get best ultra low current accuracy, zero the SMU offset error just prior to taking the measurement by using the Calibration window. See beginning of this module, before page 10 in this module. Do the ZEROing procedure with the probes up.
Module 6 Low Current Measurement ULTRA LOW CURRENT Measurement Setup Small STEP: 100 mV Large HOLD TIME: 3 sec To prevent charging current due to residual cable or probe capacitance, you should limit the STEP size to 100 mV. The B1500A has a built-in delay time on the low current ranges, and you do not need to add extra time. If the STEP is large, like the -500 mV for the first point in this sweep, simply add an initial hold time. 3 to 5 seconds should work fine.
Module 6 Low Current Measurement ULTRA LOW CURRENT Effect of Cable Charging Current Not part of the subthreshold characteristic You can see an initial high current that drops off after a few measurements. This is the effect when delay time is set to zero. Any residual capacitance due to un-guarded probes is the cause. This effect is minimal in this case due to the use of fully guarded probes to within 2 mm of the probe tip.
Module 6 Low Current Measurement ULTRA LOW CURRENT Range and Integration Time Lowest resolution: Auto or Limited 10 pA Set long integration time In this example we are measuring Id very accurately. The B1500A autoranges every decade of current down to 1 nA as a factory default. Change this to AUTO or LIMITED 10 pA to get two more ranges of low end resolution (1 fA resolution). The factory default of LIMITED 1 nA gives 100 fA resolution and is adequate for most measurements.
Module 6 Low Current Measurement Low Current Leakage Gate Oxide z z z Leakage to fA levels Electrical connection to wafer backside Chuck must be guarded Gate + Oxide Wafer backside Substrate Gate oxide leakage tests are complicated by the fact that there is an electrical connection to the back of the wafer. The chuck must be insulated and guarded to get meaningful low current results.
Module 6 Low Current Measurement Low Current Gate Oxide Measurement Fowler-Nordheim (FN) Plot The Fowler-Nordheim (FN) plot is a log plot of oxide leakage in accumulation mode breakdown. The plot shows a characteristic "arc" leading up to the rupture current. This plot is a measurement result example of a MOS capacitor on a wafer. You cannot get this kind of plot by measuring the class exercise MOS FET. The MARKER is set to -27.590 mA. This is the point at which rupture of the gate oxide occurred.
Module 6 Low Current Measurement FOWLER-NORDHEIM PLOT Measurement Page Negative sweep. Accumulation mode. Wait for 5 V initial step A 3 second delay at the beginning of the measurement will be required. The SMU must initially step from 0 to -5 V, a very large step. Fully guarded probes to within 2 mm of probe tip and fully guarded chuck eliminated the need for delays at every measurement point. The only wait will be the initial 3 second hold time.
Module 6 Low Current Measurement Low Current Gate Oxide Meas. Using Guarded Chuck SMU1 SMU2 Gate Oxide Capacitor Chuck Chuck Guard 10^13 ohms 10^13 ohms Shielding Box (Ground) This is a simplified block diagram of the prober requirements for a guarded chuck connection. When implemented properly, very fast low level sweeps are possible due to the elimination of stray capacitance at the probes (wafer top side) as well as in the chuck (wafer bottom side).
