Method of fabricating microphone device and thermal oxide layer and low-stress structural layer thereof

[0016] Referring to FIG. 7 to FIG. 15, FIG. 7 to FIG. 15 are schematic diagrams illustrating a method of fabricating a microphone device in accordance with a preferred embodiment of the present invention. It is appreciated that FIG. 7 to FIG. 15 only illustrate one microphone device, and the fabrication of microphone device may be divided into three stages: the first stage is to form a thermal oxide layer (illustrated in FIG. 7 to FIG. 9); the second stage is to form a structural layer (illustrated in FIG. 10 to FIG. 13); and the third stage is to form a back chamber (illustrated in FIG. 14 and FIG. 15).

[0017] As shown in FIG. 7, a substrate 50 e.g. a silicon wafer or an SOI wafer is provided. Subsequently, a plurality of trenches 52 are formed in the front surface of the substrate 50 by deep etching techniques such as inductively coupled plasma reactive ion etching (ICPRIE), deep X ray lithography, or electron cyclotron resonance (ECR) plasma etching. In this embodiment, the line wid