The effect of Phosphorous implant in converting the Enhancement Mode Transistor into Depletion Mode Transistor

Abstract

Metal-Oxide-Semiconductor field effect transistor (MOSFET) forms the basis in most of electronic applications. In certain part of electronic circuitry, there is a requirement to use depletion mode of MOSFET which delivers current at Vg=0V. This type of transistor is normally on unless reverse-polarity Vg is applied to turn it off. In this research, thorough investigations on process parameters that affect the performance of depletion mode transistor have been studied. The study was emphasized on the ion implantation to forms the depletion channel. It is a very crucial process step in creating a successful depletion type MOSFET. To support the study, Design of Experiment (DOE) for ion implantation dose and energy has been implemented in MIMOS fabrication facility. The 0.5um CMOS process technology was used as a baseline to produce n-type depletion mode MOSFET. Besides running the experiment, simulation software (ATHENA and ATLAS) were used in this study to reduce the cost and time of producing experiment wafers. Comparison of experiment test results and simulation output was also discussed in details in this thesis. On the other hand, problems and observations from the experiment were highlighted and discussed too. One of the main issues is on the two-peak point of transconductance curve. According to the experimental results, it can found that phosphorus ion with dose 3.3e12 cm-2 and energy 60 keV used in depletion channel implant should produce good characteristics of depletion mode MOSFET with threshold voltage -0.7 V.