Dynamic Measurements of MEMS-Based Field Effect Transistors Using Scanning Capacitance Microscopy
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0910-A20-03
Dynamic Measurements of MEMS-Based Field Effect Transistors Using Scanning Capacitance Microscopy M.L. Anderson, R.W. Young, and C.Y. Nakakura Microelectronics Development Laboratory, Sandia National Laboratories, Albuquerque, NM, 87112 ABSTRACT In this research, we have employed scanning capacitance microscopy (SCM) to image 2D carrier profiles of a MEMS device. Multiple device states were examined for changes in carrier response as a function of applied bias. First, experimental and simulated dopant profiles of the source and drain pn junctions were measured with device contacts grounded. Their comparison revealed good agreement. Scanning capacitance microscopy was then used to image changes in carrier distribution within the channel of the device while independent bias voltages were applied to the source, gate, drain, and well regions. Device operation was confirmed by simultaneously measuring the drain current. The SCM image contrast directly beneath the gate was observed to change as a function of applied gate bias voltage. INTRODUCTION As the critical dimensions of new semiconductor technologies continue to decrease into the deep submicron regime, the ability to tailor the fabrication of Si-based metaloxide-semiconductor field-effect transistors (MOSFETs) becomes increasingly important. Straightforward techniques for characterizing 2D dopant distributions could significantly aid in device design, processing, and failure analysis. As a result, SCM has received considerable attention as a means to quantitatively measure device parameters (e.g., effective channel length and pn junction delineation) and to calibrate and verify process models [1, 2]. Although MOSFETs are inherently dynamic, the vast majority of these studies have focused on devices that are “off”, or grounded. In this paper, we present SCM measurements coupled with MEDICI [3] simulations of a MEMS device in the “off” and “on” states (non-conducting and conducting, respectively). By turning the transistor “on” while imaging, we explore the physics of device operation. In addition, this MEMS device serves as a model system because of its large feature dimensions. Scanning capacitance microscopy images of the device cross section were acquired while the sample was in a non-conducting state and compared to simulation. Experimental and simulated measurements of the pn junction location were in good agreement, indicating that the SCM alone can be employed to quantify device parameters of this MEMS-based MOSFET. In addition, channel formation beneath the gate was confirmed by applying independent bias voltages to the source, gate, drain, and well regions, while measuring changes in carrier distribution with the SCM. Device operation was confirmed by simultaneously measuring the drain current. The static measurements demonstrate that the SCM can be used as a simple dopant profiler, whereas active device imaging provides the means to monitor device functionality and validate theories of dynamic processes.
EXPERIMENTS The n-channel SUMMiTTM [4
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