SEM imaging and measurements of an p-channel MOSFET

Course: Laboratory Course Semiconductor Processing and Nanotechnology (MAS.301)
Group A3: Arthur Rönfeld, Christoph Huber & Fabian Gosdam
Period: Winter 2021
Date: 16.12.2021
Instructor: Karin Zojer

Measurement Setup

The goal of this exercise was to measure and characterize a p-Channel MOSFET within a Scanning Electron Microscope (SEM). The measurements were carried out using a sourcemeter which was connected with the SEM. We used the two channels SMU-A (Gate-Source Contact) and SMU-B (Drain-Source Contact) to power and measure the MOSFETs saturation and transfer characteristics.
After these two characteristics were measured the substrate and the Source were connected by the SEM measurement needle. The behavior of the resulting diode should now be measured.
The Output of the experiments were sent to the elab. The uploaded data contains the code, the diagram and the data as csv file.

Saturation and transfer characteristics

Saturation characteristics

The output/saturation characteristics for different Gate-Source Voltages are shown in Figure 1. The python code used to produce them is shown below.

Figure 1: Output/Saturation Characteristics P-type MOSFET
Source-Drain current plottet against the Source-Drain voltage for different Gate-voltages.

The output curves shown in Figure 1 should follow the output behavior as described by the gradual channal equations:

Figure 2: Formulas for the Output/Saturation Characteristics P-type MOSFET

The previous equations tell us about the three different operating regions of a MOSFET.
The first equation gives information about the cut-off region of an p-type MOSFET. In this region no current is flowing trough.
The second equation describes the characteristics of a p-type MOSFET in the linear region. The Drain Current ID in this zone depends on the dimensions (Width (W) and Length (L)) of the transistor, the mobility μp, the specific capacitance of the gate Cox in F/m², the difference of the gate-source voltage VGS and the threshold voltage VT but also on the drain-source voltage VDS.
The third equation gives information about the drain current ID in the saturation region. The drain current dependents on the mobility μp, the specific capacitance of the gate Cox in F/m², the length L, the width W and the difference of the gate-source voltage VGS and the threshold voltage VT squared.

Transfer/Input characteristics

Figure 2: Transfer/Input Characteristics
[MOSFET_p-type_Transfer characteristics.npy]
Drain-Source current plottet against the Gate-Source voltage for different Drain-voltages.

The Transfer/Input Characteristics define the change of the Drain-Source Voltage VDS with the change in the Drain Current ID and the Gate-Source Voltage.

Diode Measurement

After the saturation characteristics and the transfer characteristics were measured, the substrate was shorted to the source contact. This turned the p-type MOSFET into a diode. The characteristics of this diode should now be measured.

Figure 3: SEM Short between Substrate & Source

Figure 4: Diode Characteristics
[MOSFET_diode characteristics.npy]

Figure 3 shows the image of the MOSFET measurement. This was taken in the Scanning Electron Microscope and saved as an image. It can be clearly seen that the source contact was connected to the substrate. This results in a diode. A script to measure a diode was executed.
Figure 4 clearly shows the characteristic curves of a diode with a PN junction.