Keithley 6487 Reference Manual

Model 6487 Reference Manual Applications Guide G-23
Photodiode characterization prior to dicing
The Model 6487 can be used as part of a cost-effective semiconductor photodiode leakage
test system. This test characterizes the photo current under various illumination
conditions.
In addition to the Model 6487, specialized equipment is required. This equipment includes
a calibrated optical source in addition to semiconductor equipment (probe card or needle
mounts, etc.). Several Model 6487s can be connected to probe pads to provide leakage
current readings forced by the bias voltage source. As an alternative, one or more
Model 6487s could be switched through a switching mainframe and matrix switch card
arrangement to take current measurements from multiple pads.
Measuring photodiode leakage can be described in two steps:
1. V
sweep
, I
meas
in total darkness.
2. V
bias
, I
meas
in calibrated optical flux.
In the 1st step, voltage sweeps and the resulting current leakage is measured (see “Voltage
sweeps,” page 6-8). Then, a bias voltage is applied and resulting current leakage is mea-
sured while light is incrementally increased in calibrated steps. The results produce a
graph similar to Figure G-19.
Figure G-19
General photodiode leakage
I
V
0
General photodiode

Keithley 6487 Specifications

General

Type	Picoammeter/Voltage Source
Current Measurement Range	20 fA to 20 mA
Interfaces	GPIB, RS-232
Voltage Burden	< 200 µV
Input Impedance	>10^14 Ω
Power	100 V / 120 V / 220 V / 240 V
Basic Current Measurement Accuracy	0.4%