Determination of the effect of processing steps on the CMOS compatibility of a surface micromachined pressure sensor

Abstract

A surface micromachining process for the fabrication of a pressure sensitive field effect transistor (FET), compatible with complementary metal oxide semiconductor (CMOS) processing, has been established in which residual membrane stress can be tuned without changing the underlying CMOS operation. The residual membrane stress must be controlled at a low tensile value for optimum operation of the pressure FET. Controlling this residual stress involves the development of suitable processing conditions, and the effect of alteration from standard CMOS processing on the underlying circuitry must be evaluated. The effects of different processing conditions for a surface micromachined polysilicon pressure sensing membrane on the CMOS characteristics are presented. Variations in the polysilicon sensor layer deposition and implant conditions in the surface micromachining process and back-end CMOS interlayer dielectric reflow were examined as these strongly influence the residual stress in the membrane. The electrical characteristics for devices that had only CMOS processing did not vary significantly from the electrical characteristics of devices that had the pressure sensor surface micromachining layer processing.

Integrated micromachined thermopile IR detectors with an XeF2dry-etching process

“…Both n-type and p-type MOS transistors with different ratios of channel width to channel length (W/L) were tested (14 transistors on each chip) to determine the threshold voltages V TH . The threshold voltage V TH of a MOS structure is given by [23,24]…”

Alternative Post-Processing on a CMOS Chip to Fabricate a Planar Microelectrode Array

“…The microstructures designed on a CMOS chip can be released using a post-processing of the chip [ 12 – 16 ], which generally includes some surface or bulk micromachining process. The surface micromachining process can be used to deposit and remove additional layers on the CMOS chip surface, but it is expensive [ 17 , 18 ]. On the order hand, the backside of a silicon wafer can be etched through a bulk micromachining process [ 19 ], using either dry or wet etching.…”

A maskless post-CMOS bulk micromachining process and its application

“…The standard CMOS (complementary metal-oxide semiconductor) process is an integrated circuit (IC) process that can fabricate memory circuits and microprocessors. Many studies have recently been developed to use the standard CMOS process to fabricate MEMS (micro electro mechanical system) devices, such as pressure sensors [1], tactile sensors [2], accelerometers [3], thermal sensors [4], gas sensors [5], fluid density sensors [6], pH sensors [7], gyroscopes [8], humidity sensors [9], micromirrors [10], resonators [11], microwave switches [12], inkjet heads [13], optical switches [14], optical modulators [15] and others. This technique that uses the CMOS process to manufacture MEMS devices is called CMOS-MEMS [16].…”