Warning! This is the archived 1999 Fabweb site! Here is the latest site

ICCAP Tutorial

  1. Prelab
  2. Starting ICCAP
  3. Exploring IC-CAP
  4. Commercial Device Measurements
  5. Schottky Diode Fabrication
  6. Schottky Diode Measurement
  7. Schottky Diode Calculations
  8. Write-up
The purpose of this tutorial is to give you some experience with ICCAP (the Integrated Circuit Characterization and Analysis Program from HP) as well as an evaporator and a prober. Later in the semester you will be using these again without the 3:1 student teacher ratio you will have for this tutorial. You will, in fact, be graded on your preparedness when you use these items later with your IC wafer, so please make the most of this exercise and the lab instructor.

Three basic electronic devices will be tested. A commercial Bipolar Junction Transistor (BJT) and a commercial P-channel Metal-Oxide-Semiconductor Field Effect Transistor (P-MOSFET) will be measured, and some of their SPICE model parameters will be determined with IC-CAP. Schottky diodes will be fabricated, probed and measured as part of the tutorial, as well.

To avoid congestion in the wet lab, it will usually be best to start the Schottky diode fabrication about half way through the lab period. It will not matter if you finish the modeling and measurements since the write-up is not due for several weeks and they can serve as "filler" activities until then. "Filler" activities are needed when you are waiting for equipment, waiting for a diffusion to finish, or when it's too late in the period to start a photoresist operation. The Schottky diode fabrication must be completed during the lab period reserved for this tutorial.  

PRELAB

After reading through this IC-CAP Tutorial up to the "Commercial Device Measurements" section and following the links embedded in the World Wide Web version, answer the following questions. Note that you will want to go to an Engineering Workstation and work through the "Exploring IC-CAP" section found below before doing some of the following questions, which require you to use IC-CAP.
  1. Define what is meant by the term "cracking the oil". (See Appendix A in the printed version).
  2. What steps should you take if the foreline pressure exceeds 100 microns in a hot diffusion pump?
  3. In the context of a test instrument, "compliance" tells the instrument how far to go in order to comply with a measurement request. For example, if the instrument is told to sweep the voltage from 0 to 5 V, and the compliance is set at 100 mA, then the instrument will try to sweep the voltage up to 5V, but will limit the current to 100 mA.

    4. Suppose you tell an instrument to measure the I-V characteristic of a 1 Kohm resistor. You set the voltage sweep to go from 0 to 10 volts, and you set the compliance at 5 mA. Draw the current vs. voltage curve that would result. What is the significance of the 5 mA compliance on your plot?
  4. Familiarize yourself with the structure of ICCAP, by doing the following:
  5. The purpose of this question is to allow you to become familiar with the meanings of the various entries in the device setups, so that you can more efficiently utilize your time in the lab. You will need to ftp your Tutorial.mdl file to your Engineering Workstation account and run IC-CAP on an HP computer in an EWS lab. When you are finished, you will need to ftp the file back to your 344 account. You will be doing this on several occasions throughout the semester, so it is worth the small effort to become proficient at it now. IC-CAP calls the signals applied to the device under test "inputs," and the measured values "outputs." Edit the resistor/DC/I_vs_V setup in your Tutorial.mdl file as follows, in order to make it useful for measuring the IV characteristic of a resistor. Note: When you enter parameters into IC-CAP, you do not need to put the full units onto a number. For example, 5 mA is entered as 5m, and 10 V is entered as 10.
  6. Find the following entries in the your Tutorial.mdl model file. This may be accomplished by ftping the file to your Engineering Workstation account and running IC-CAP on an HP computer in an EWS lab.
  7. Check out the meanings of the parameters in the SPICE Manual (See pages 33 and 37).

    8. Did you complete this task? (yes or no)

INTRODUCTION TO ICCAP

The Integrated Circuit Characterization and Analysis Program from Hewlett- Packard will help you collect performance data and find optimized models for the devices you make "from scratch". These models will be useable by most implementations of SPICE, thus connecting design methods utilizing SPICE taught in several other courses with physical device fabrication. You will also use ICCAP to gather data without becoming bogged down in the details of operating the instruments. This should allow you to focus more on understanding the fabrication process and the devices themselves.

Since the overwhelming majority of ECE 344 students are ECE majors, testing will not be laid out in as much detail as the chemistry type procedures which are used to create the devices. We have prepared some basic, "safe" models and setups for you to use, but in almost every case, there are modifications which can, and therefore should, be made to the setups in order to exhibit as much useful information about your particular device as possible. The object will be to apply your knowledge of the devices to make these adjustments. For example, don't settle for plots in which all the "action" happens along one edge.  

THE STRUCTURE OF ICCAP

ICCAP was written in C++ and takes advantage of the power of object oriented programming. At the top of the hierarchy is the MODEL which is intended to be a collection of measurement setups, processing variables and equivalent circuit parameters. In short, everything necessary to determine a SPICE model for an integrated circuit. Several Devices Under Test (DUTs) with their own set of variables often make up a circuit. We will utilize the DUT level to separate fundamental device concepts or components. For example, a BJT has two distinct pn diodes within it which will be individually characterized as separate DUTs.

Each DUT level can have any number of measurement setups (for all practical purposes) since many instrument and probe configurations may be needed to determine each DUT's parameters (equivalent circuit). Each setup can also have its own variables and parameters. Equations can be used to EXTRACT equivalent circuit parameter values from measurements. Such calculations can come close to creating a good SPICE model, but they are inevitably based on approximations. SIMULATIONS (by SPICE) of the SPICE model based on the extraction results or default values can be compared to the real data for some or all of the measured data sets and OPTIMIZED for best "fit" by iterative techniques (Levenberg-Marquardt algorithm). SPICE will be used by ICCAP several times during an optimization to generate the predicted results from the measurement setup and current SPICE parameters. Iterative adjustment of the parameters between each SPICE call improves the "fit" with the actual measured data set. The user determines when the agreement between actual and simulated data (from the model) is good enough. The resulting model is called "optimized", as opposed to "optimal".

This program was designed to help the circuit designer take full advantage of ever improving IC processing capabilities. Interfaces to TCAD's implementations of Supreme and Pisces, processing and physical device simulation programs, can similarly provide the process engineer with feedback between simulation and real measurement results. Someday you may be working with versions of these programs, and so will ECE 344 students.

A vague new type of specialization has been forming within the broad scope of engineering. The kind of person likely to be in Electrical Engineering is often well suited to excel in this unnamed discipline. Skill at utilizing new computers, software and instruments in a minimal learning time, together with a solid understanding of the chemistry and physics involved in a marketable product can help one make significant contributions to the large team it takes to manufacture competitive products.

Modern software packages such as ICCAP trade off program size, complication, and speed for intuitive ease of use. Consequently, there are many ways you can accomplish a given task. Since navigating within menu driven software is quickly becoming an essential skill in and of itself for engineers, you will basically be turned loose on the software after a demonstration by your instructor. Below are some of the basics you will see in the demo. Excerpts from the ICCAP manual and training course viewgraphs are available to *.uiuc.edu machines. Complete documentation is available in the lab.  

Starting ICCAP

From an ECE 344 workstation:

Just use the root menu: Choose IC-CAP | load Tutorial . Answer yes to any questions about setting up your account if this is the first time you've started IC-CAP.

Note: The original Tutorial.mdl file can be found in your iccap/linked_models directory, so experiment with IC-CAP freely (until you've collected measured data of your own, that is.)

From an Engineering WorkStation(EWS) computer:

A separate Web page has been created for starting IC-CAP on an EWS machine.

From any X-Windows system:

A web page has been set up which tells you how to run IC-CAP on an ECE 344 computer, but display it on any computer running or emulating X-Windows. For security reasons this method is NOT recommended.  

Exploring IC-CAP

This section provides a brief "tour" of some of the IC-CAP features. Some of the prelab questions require knowledge which can be obtained by going through the following steps. You will need to ftp your Tutorial.mdl file to your Engineering Workstation account and run IC-CAP on an HP computer in an EWS lab.

Once you have started IC-CAP on an EWS (as described here), load your Tutorial.mdl file, if you did not load it on start-up.

To load the Tutorial.mdl file:

  1. Select "Read Model" from the "Model" icon in the "Model List" window.
  2. Choose "Tutorial.mdl", and click OK.
You should see four models (BJT2N2222, Schottky, MTP2955, and resistor) in the models list, and a separate window for each model may be open.
  1. If the BJT2N2222 model window is not open, open it now by double clicking the BJT2N2222 icon.
  2. To display the plot of the BJT2N2222/curvetracer/Ic_vs_Vce model, highlight the Ic_vs_Vce label under dc on the left.  Open the Plots folder and click Display Plot.
  3. The plot has no data in it yet, but notice how the path to the plot is presented just like a UNIX path in the plot window's title bar.
  4. Learn the features of IC-CAP plots.
  5. To see what conditions create the plot, choose the folder for the following information: 

       Measure/Simulate:    Inputs and outputs
       Plots:                         Plots
       Extract/Optimize:     Transforms

    Notice that this, like all setups, has four categories of tabular specifications. Inputs are the stimuli for the device, Outputs are the measurements, Transforms are calculations which generate named data sets (none are used in this setup though), and Plots are, of course, displays of data (or of equations referencing any named data sets.)

    6. Descriptions of some of the entry fields follow. If you highlight the Input/Output/Plot/Transform block under investigation and click the right mouse button, select Edit.  This will allow you to modify the entries, as well as see the options available for the field with pull down menus.
  6. Perform Close All (click on the Data  pull down menu, goto Close, then select DUT.)
  7. Next, to demonstrate the object oriented nature of IC-CAP, click on the Data pull down menu, goto Plots, goto Display All, and select Active DUT.  Several plots will appear, each from one of the four setups which are part of the DC DUT (Device Under Test). DUTs are usually collections of setups which share the same instrument connections.
  8. All the measurements for all the setups can be done at once by clicking on the Measure pull down menu, and selecting DUT.  It takes longer to complete than a single setup measurement so usually one wants to be sure the device is operational before doing multi-setup measurements.
  9. Take a look through the DUTs and setups. You are to modify the resistor/DC/I_vs_V setup for the prelab. The BJT characterization chapter of the IC-CAP manual and the MOSFET characterization chapter of the IC-CAP manual have extra details, if you are interested.  Some of the transforms use programs for which the source code is not available, but you can still learn a lot by studying them.
  10. That's it. Just click on Data pull down menu, goto Close All, and select DUT when you are finished studying the plots and setups.
  11. Storing changes: Whenever you complete new measurements or modify a setup, it's a good idea to save the information.
Note: If you wish to see examples of what the plots will look like, you may load bjt_npn.mdl from your linked_models directory on the ECE 344 machines. Setups of the same name are directly comparable. Please delete the resulting npn model before you save the Tutorial.mdl file.

You may also view the plots on the web.

Commercial Device Measurements

You will make some simple measurements on a 2N2222 general purpose BJT and a MTP2955 P-channel power FET. Some of the information here is the same as under "Exploring IC-CAP" above, but here you will actually be making measurements. Be sure that you don't accidentally skip over a measurement.

Initial startup

  1. Plug in the devices if they aren't already. The 2N2222 should be in the left socket and the MTP2955 on the right.
  2. Check that the HP 4145B cables labeled SMU1, SMU2 and SMU3 are connected to the test fixture's connectors of the same names.
  3. Turn on the HP4145B and HP4284A.
  4. Log into the UNIX workstation.
  5. Start ICCAP by selecting IC-CAP --> Load Tutorial.mdl from the root menu.
  6. Four Model windows will appear. Arbitrarily, we'll start with the BJT first. You will not be using the resistor model after the prelab.

BJT Measurements

A stripped down version of the model file bjt_npn.mdl (from your iccap/linked_models directory) is included in the Tutorial.mdl file and renamed BJT2N2222.
  1. Make sure the switch on the test fixture is in the left position to select the 2N2222.
  2. Open the BJT2N2222 model by double clicking on its icon.
  3. Click on Ic_vs_Vce (under curvetracer) to make it active.
  4. Open the Plots folder and select Display Plots.
  5. Open the Measure/Simulate folder and select Measure.
  6. When the measurement is finished, the plot will update with the new test data.
  7. If the plot doesn't look familiar to you, ask your lab instructor for help interpreting it or review the BJT plot screens. After ECE 342 (not a prerequisite) you will recognize this as what is commonly called the "family of curves" for a BJT. Instruments called curvetracers specialize in displaying such curves. The HP 4145B is far more flexible, especially under computer control.
  8. Learn the features of IC-CAP plots.
  9. To see what conditions created the plot choose the folder which contains the information you wish to inspect.
        Measure/Simulate:    Inputs and outputs
       Plots:                          Plots
       Extract/Optimize:      Transforms
    Notice that this, like all setups has four categories of tabular specifications. Inputs are the stimuli for the device, Outputs are the measurements, Transforms are calculations which generate named data sets (none are used in this setup though), and Plots are, of course, displays of data (or of equations referencing any named data sets.)
    You may need to edit the setups later for measurements, in order to get useful data.
  1. Close the BJT2N2222/curvetracer/Ic_vs_Vce setup window.
  2. For each of the BV (Breakdown Voltage) setups (i.e., BVcbo, BVebo, BVceo), display the plot and make the measurement. Note that you may not see a breakdown of the Collector-Base junction, even up to 100 V, so you will need to "Edit" the BVcbo Setup table to apply a higher voltage. The 4145B can only source from -100 to +100V. Hmmmmm..., how will you apply > 100V reverse voltage to the CB junction?
  3. Close all the windows by pulling down the Data menu, select Close All, and select DUT.
  4. Highlight dc on the left to make it the active DUT.  Goto the Data pull down menu, goto Display All, and select In Active DUT.  Several plots will appear, each from one of the four setups which are part of the DC DUT (Device Under Test). DUTs are usually collections of setups which share the same instrument connections.
  5. All the measurements for all the setups can be done at once by going to the Measure pull down menu and selecting Active DUT.  It takes longer to complete than a single setup measurement so usually one wants to be sure the device is operational before doing multi-setup measurements - you used the curvetracer/Ic_vs_Vc setup for that.
  6. That's it for making BJT measurements, just Close All on the DC DUT when you are finished studying the plots and setups.
  7. Store the data. Whenever you complete new measurements, it's a good idea to save the information.
  8. IC-CAP remembers which windows are open so, in general, you may wish to close a few now so the same screen clutter won't be present the next time you open the stored file. The "Close All" option of the Model menus are useful for this.
  9. Click the save icon and select the model to store in your Tutorial model in your iccap directory. IC-CAP will add a ".mdl" to the name to signify that it's a model.
  10. Remember to save often as you make changes to a Model file.
  11. It's always wise to occasionally store the data to a secondary filename. I usually add the letters "bu" for backup to this copy. For example, Tutorial.bu.mdl.
  12. Another good way to protect yourself from data loss is to submit your file occasionally.
  13. As always, it's a good idea to make a back-up copy of your data. You should not have to think about whether you need a backup, just do it and do it often.
Note: If you wish to see examples of what the plots will look like, you may load bjt_npn.mdl from your linked_models directory on the ECE 344 machines. Setups of the same name are directly comparable. Please delete the resulting npn model before you save the Tutorial.mdl file.

You may also view all of the commercial device plots on the web.  

MTP2955 P-Channel MOSFET measurements

The MTP2955 model is based on the iccap/linked_models/pmos2.mdl file. The SPICE models (pmos2 is the second of a series) for MOSFETs usually have geometric parameters based on the layout, so that the results from a new layout can be predicted from measurements made on three different sizes of MOSFETs. Since we only have one device and at the time of this writing and we don't know the geometry of it, we'll only determine the geometry independent SPICE model parameters.
  1. Make sure the switch in the test fixture is flipped to the right to select the MOSFET.
  2. Double click the MTP2955 icon to open.
  3. Highlight the idvg label to make it active.
  4. Open the Plots folder and select Display Plot.
  5. Open the Measure/Simulate folder and select Measure.
  6. The plot should vaguely resemble the curvetracer plot of the BJT2N2222, but note that the spacing between curves is not uniform. Review FET operation if this is a surprise to you.
  7. Collect the data for the other (idvg) setup in the same manner.
  8. Explore and understand the setups and MOSFET ICCAP plots. There is AT LEAST one entry in the tables in the setups that will have to be changed to get a "good" set of data. "Good" in this context means that most, if not all, the data points convey pertinent information about the device.
  9. Save your data to multiple places as before.

Schottky Diode Fabrication

Follow the Schottky diode recipe (found at the end of the ICCAP tutorial section) using wafers supplied by your instructor.

Be sure to record the wafer manufacturer's specs in your lab notebook along with any observations you make during the process. Employers often appreciate good record keeping by their engineers.  

Schottky Diode Measurements

  1. Area calculation:
  2. Start ICCAP with the Tutorial.mdl model file loaded if it isn't already running.
  3. Connect the instruments as follows:
  4. Make sure a jumper is in place of probe 4 so the wafer chuck is connected to an instrument instead.
  5. Turn on the instruments - the HP4145B and the HP4284A.
  6. Place the wafer onto the wafer chuck and turn on the chuck vacuum.
  7. Using the probing instructions, probe the device with probe 1. (Be sure to note the DOs and DON'Ts.
  8. Make sure the switches on the side of the prober are in the UP position, so that the probe station will be connected to the HP4145B for I-V measurements.
  9. Fill in the DC data sets as you did with the commercial devices, but this time you may find you will need to adjust some of the setup table inputs in order to maximize the meaningful data in the plots about the diodes (hint hint).
  10. Flip the switches on the side of the prober to the DOWN position, so that the probe station will be connected to the HP4284A for C-V measurements.
  11. Perform the CV/C_vs_V measurement. Note that the first time the capacitance meter is used, a calibration will be performed during which you will be prompted to disconnect the DUT. Just raise the probe tip when it asks, and then lower it back down when asked to reconnect.
  12. When the data looks like what you would expect from the knowledge you gained in ECE 340, save the model.
  13. In the ICCAP/Main window, highlight the the Shottky icon by left clicking once.  Goto the Edit pull down menu and select Copy.  Then goto the Edit menu and select Paste.
  14. Enter Schottky1 in the highlighted icon label box and press Enter. This will copy the Schottky model to a new model called Schottky1, which should now appear in the model list.
  15. Save all the models again.
  16. Probe another round diode and use the original Schottky model to gather new data. (Remember that you saved the previous data in the Schottky1 model.)
  17. When finished, copy the model to Schottky2 and save all the models again. Now you have saved data from one diode in the Schottky1 model, and data from another in the Schottky2 model. (The data from the Schottky2 diode is also still present in the Schottky model, since you just copied it to Schottky2.)
  18. Repeat for a third device, Schottky3.
  19. In addition to saving the models to a file, save them to an alternate filename as well - just in case something goes wrong.
  20. Don't forget to make sure you know the average diameter for your Schottky diodes. (You do not need to measure the diameters on the same dots that you tested using ICCAP.)

Schottky Diode Calculations

This may be done outside of lab. It should not take up any lab time until after all the device measurements are done.

For each of the schottky models:

  1. Create a plot of log10(C) vs. log10(Vo-V) in each of the schottky models. To do that:
  2. Fit a line to the data and note the slope. (Draw a diagonal line, or use the line fitting functions in ICCAP).
  3. Create another new plot called PowerLaw using the same basic process, but this time plot cap^(1//"slope") vs. v_al, where "slope" is the slope that you determined from the logC_vs_logV plot. The double slashes mean divide. IC-CAP would interpret a single slash as part of a path name. (An alternative is to use spaces on both sides of a single slash and IC-CAP will interpret it as divide.)
  4. Again fit a line to the data.
  5. Substitute the absolute value of the X intercept from this latest plot (PowerLaw) into the previous plot (logC_vs_logV) as Vo.
  6. Fit a line to the logC_vs_logV data again and, if necessary, plug it's slope back into the PowerLaw plot.
  7. Iterate as many times as necessary until the slope and intercept values differ by less than 5% between iterations.
  8. Now, you should have a pretty good measurement of Vo, and the slope should be close to -1/2.
  9. Next, add a transform by opening the Extract/Optimize folder.
  10. Add yet another plot to the setup and name it "DopingProfile".
  11. For the X Data enter 11.9*8.85E-14*Area*cap^-1 where Area is the area of the diode in cm^2.
  12. For the Y Data enter -2//(11.9*8.85E-14*1.6E-19)*YourTransform^-1, where "YourTransform" is the name of the derivative transform you created above.
  13. Now your plot will be of doping concentration versus distance into the wafer. That's the doping profile.
  14. Note that you can write plots and transforms to files and read them in from other setups. This can save a considerable amount of typing, but some numbers will still need to be changed in the target setups.
    1. Save often!

Write-Up

  1. Check the ECE 344 newsgroup for additions, deletions, or changes for this write-up.
  2. Do the Schottky Diode Calculations as described above.
  3. Electronically turn in your Tutorial.mdl file using "submit Tutorial.mdl to <instructor loginname>" while in your iccap directory. Please include all of the models (BJT, FET, Schottkys) in one file called "Tutorial.mdl" rather than in separate files.
  4. Show where the equations used in the Schottky Diode Calculations section for the determination of the doping concentration and built-in voltage of the Schottky diodes come from. (refer to your ECE 340 text.) Term by term discussion would be useful here. In other words, suppose that we did not tell you what equations to use in making the plots. 
    Derive using
  5. Find a value for Beta (Ic/Ib) for the transistor? Is it a constant (i.e. independent of bias)? Hint: You can add a plot of Ic/Ib vs Ic in the Ic_vs_Vce setup. You can also look at the fgummel plots.
  6. Find values of the threshold voltage (Vt) and the slope of the transconductance (gm) vs vg (in saturation) of your measured PMOSFET.

    7. To do that:

ECE 344 home page.

This screen was created by Mike Fitzimmons - U of Illinois ECE Dept. - mikef@uiuc.edu,
and is maintained by Kevin Beernink - U of Illinois ECE Dept. - beernink@uiuc.edu
E-mail comments and suggestions to ece344@uiuc.edu or use the FEEDBACK FORM.
Software/ICCAP/Tutorial.html updated 26-Aug-96

Warning! This is the archived 1999 Fabweb site! Here is the latest site