Device Design And Technology Research Of Vertical Multi-Gate MOSFETs

As a new-type semiconductor device, multi-gate MOSFETs have many advantages compared with traditional MOSFETs, such as the nearly ideal subthreshold slope, higher carrier mobility, higher transconductance and higher driven-current, and stronger ability against short-channel effects. So multi-gate MOSFETs are considered as one of the most promising new-type devices when CMOS is scaled to the ultimate limit of 50nm gate length.In the thesis, after the demonstrating and researching the fundamental principles and models of multi-gate MOSFETs, we design the structure, layout and process-flow of a vertical multi-gate MOSFET whose process is based on bipolar technology. Then our design is verified by the fabricating experiments, and the various characteristics of the vertical multi-gate MOSFETs are deeply analyzed by testing. And some critical processes and device parameters are also carefully researched, after that some improving methods are presented.Firstly, we introduce the research background, profile and necessity of the multi-gate MOSFETs in the thesis. Then, the two unique characteristics, volume inversion and constant voltage assumption, are discussed and analyzed. Besides these, the conception of inversion-layer centroid is successfully used to formulate the current and inversion layer charges for the thin-film double-gate MOSFET in subthreshold region.Next, we design the vertical multi-gate MOSFET based on bipolar process including structure, layout, process flow and parameters which are compatible with the process condition of the 24th Institute. Through three fabricating experiments and testing, lots of characteristics of the device are obtained. Besides analyzing the reasons and results of these characteristics, we also pay attention to carrier mobility and the research method of non-uniformly doped channel device.Finally, we discuss the trench-etch and post-etch treatment which are the most important step in the whole process. And some improving ways about device structure and process are also provided.