Evaluating Electrical Characteristics of the CMOS Devices
Figure 1. Mask set design. Shown is a single “mask unit cell” and its contents. Each completed 2 inch wafer contains roughly forty whole mask cells.
ECE 4752 Wafer Test Procedures
In order to evaluate the electrical characteristics of the CMOS devices fabricated in ECE/ChBE 4752, a probe station is used to connect test equipment to the devices on-wafer. This is accomplished by positioning probes with mechanical manipulators such that their tips rest on metal pads on the wafer.
Care must be taken while manipulating the probes to avoid damaging the probe tips or the devices under test. The probes and wires used in the 4752 lab are suitable for relatively low-frequency and low-power measurements. The general procedure for testing a device involves connecting suitable test equipment to probes using the banana-plug wires, landing probes on the appropriate metal pads using the microscope and probe positioners, and performing the desired measurements. If unexpected results are obtained, incorrect equipment setup or poor contact between probes and pads could be at fault. However, sometimes the device itself may be deficient due to defects in materials and processing. All relative directions described are with reference to the main unit cell orientation showed in Figure 1.
Figure 2. Layout of one of the resistor types on the mask cell.
Resistors
Resistors are the simplest components on the wafer to be tested. For DC considerations, the only figure of merit of interest is the resistance, from which the resistor material resistivity can be approximated given the device dimensions. Two probes are required to test a resistor, one for each of the metal pads, which show up as large squares on either end of Figure 2. For simplicity, an ohmmeter should be used for testing the resistance, though a curve tracer could also be used. Each pad should be connected to one of the ohmmeter plugs so that a resistance measurement can be made. Each leg of the serpentine
ECE 4752 Wafer Test Procedures
In order to evaluate the electrical characteristics of the CMOS devices fabricated in ECE/ChBE 4752, a probe station is used to connect test equipment to the devices on-wafer. This is accomplished by positioning probes with mechanical manipulators such that their tips rest on metal pads on the wafer.
Care must be taken while manipulating the probes to avoid damaging the probe tips or the devices under test. The probes and wires used in the 4752 lab are suitable for relatively low-frequency and low-power measurements. The general procedure for testing a device involves connecting suitable test equipment to probes using the banana-plug wires, landing probes on the appropriate metal pads using the microscope and probe positioners, and performing the desired measurements. If unexpected results are obtained, incorrect equipment setup or poor contact between probes and pads could be at fault. However, sometimes the device itself may be deficient due to defects in materials and processing. All relative directions described are with reference to the main unit cell orientation showed in Figure 1.
Figure 2. Layout of one of the resistor types on the mask cell.
Resistors
Resistors are the simplest components on the wafer to be tested. For DC considerations, the only figure of merit of interest is the resistance, from which the resistor material resistivity can be approximated given the device dimensions. Two probes are required to test a resistor, one for each of the metal pads, which show up as large squares on either end of Figure 2. For simplicity, an ohmmeter should be used for testing the resistance, though a curve tracer could also be used. Each pad should be connected to one of the ohmmeter plugs so that a resistance measurement can be made. Each leg of the serpentine