Hints & Tips

Q. How can I measure and extract Area (CJ) and Sidewall (CJSW)capacitances using UTMOST?

A. The CJ/CJSW routine(Routine#72) in UTMOST can be used to extract area and sidewall capacitances. CJ and CJSW parameter extraction requires measuring two different diodes. One of the diodes should have relatively large area compare to its periphery (Area structure; Typical size: W=200 um L=200um) and the second structure should have long periphery which is comparable to its area (Periphery or Finger structure; Typical size: W= minimum design rule width L= 200 um and 50 fingers).

The extraction of CJ and CJSW requires that both diodes should be measured and the two unknowns (CJ and CJSW) should be solved from the two equations:

C1 = CJ * A1 + CJSW * P1
C2 = CJ * A2 + CJSW * P2

where; C1: Measured capacitance value for the area diode.

C2: Measured capacitance value for the periphery diode.

 

The CJ/CJSW routine utilizes the above equations and automatically extracts and updates parameters CJ, PB, MJ, CJSW, PBSW and MJSW in the parameter screen.

The Kelvin measurement method should be used for capacitance measurements.The LCR meters have High Voltage, High Current, Low Voltage and Low Current terminals. The cables which are coming from the high Voltage and Current terminals should be connected together using a "T" connector and the T connector should be connected to the "High" probe. The Low Current and Low Voltage terminals should be connected to the "Low " probe.

The parasitic capacitances associated with the metal lines and pads should be compensated prior to the actual measurement. The Capacitance Calibration in the "Hardware Configuration" screen should be executed for proper parasitic capacitance compensation. To calibrate, the High-Terminal probe should contact the pad which is connected to the bottom junction and the Low-Terminal probe should stay just above the pad (no contact!) which is connected to the top junction. After the hardware connection is completed press the "Calibrate" button in the "Capacitance Calibration" screen to start the calibration.

After the calibration is completed follow these steps to complete the CJ/CJSW measurement:

1. Calculate the Area and Periphery of both structures.
2. In the main UTMOST screen Press the "Hardware" followed by the "Probing"
buttons to open the "Hardware Probing" screen and select the "Devices". This will
open the "Device Pads" screen
3. Enter the Area and Periphery values for the Device#1 (area) and Device#2
(periphery). (Figure 1.).

 

Figure1. Device Pads Screen.

 

4. Open the "Strategy" screen delete the "Width" and "Length" values for
Device#1 and Device#2.
5. Open the Measurement Setup screen for the CJ/CJSW routine and enter
the measurement variables "start_bias" and "stop_bias".
(Typical values:start=-0.1, stop=3 or 5 ). Toggle the "Auto Polarity"
button to "Enable".
6. Contact both pads of Area diode using the high and low probes.
7. Open the "Extraction" screen, select the "CJ/CJSW" routine and press the
"Measure" button. UTMOST will prompt a message: "Connect AREA
diode Press ENTER to continue"
8. After the measurement is completed UTMOST will prompt the second
message:"Connect SIDEWALL diode Press ENTER to continue"
9. Move the probes to the periphery structure and press ENTER to complete
the measurement.
10. After the periphery structure is measured UTMOST will display both
junction capacitance curves on the "Graphics" screen.

In order to extract the initial values for CJ, PB, MJ, CJSW, PBSW and MJSW select the "Fit" option from the Graphics screen. The extracted values will be copied into the parameters screen and the simulation with these initial parameters will be overlayed with the measured data.

The Junction capacitance parameters can be selected for global optimization and by using the internal simulator all six parameters can be optimized together.