The notching and stiction problem, which widely exists in silicon on insulator (SOI) microstructure fabrication, were resolved in this study. In this paper, a new plasma trench technique that is based on the deep reactive ion etching (DRIE) process is proposed. In this modified process, the deep reactive ion etching (RIE) was divided into several steps, where conformal plasma enhanced chemical vapor deposition (PECVD) oxide coating, and directional oxide etch back were employed to prevent the notching effect and the reactive ion etching (RIE) lag effect is also improved. Therefore, the microstructures regardless of the feature sizes could be realized. The stiction problem is eliminated by using dry chemical release replacing wet release in this approach, where the notching effect is used. The notching or footing effect was exploited for attaining the lateral etch following the deployment of the anisotropic plasma etching of the inductively coupled plasma (ICP). This method was proven useful for both the uniform and non-uniform feature designs. With this novel process, the high aspect ratio beams can be obtained. The thickness of the silicon layer is 75 μm, while the depth of the beams is 70 μum where the 5 μm silicon was etched to suspend the movable beams. The aspect ratio is as high as 35. Trenches with very different widths of 2.5 μm and 35 μm are also achieved at the same time.
A tunable optical add/drop multiplexer (OADM) is demonstrated byu sing a micromachined 2 × 2 optical switch and a tunable fiber Bragg grating (FBG). The new hybrid OADM can be tuned to add/drop one of the multi input channels dynamically. The insertion loss of the dropped channel and added channel are 2.84 dB and 1.8 dB respectively. The transmission loss is 2.04 dB. These losses are all able to reduce greatlyi f the circulators are modified. The crosstalk between channels is less than -20 dB, and it can be further reduced byi mproving the reflectivityo f FBG. The tuning speed is on the order of millisecond. The tuning range is 3.0nm. The fabricated system is demonstrated by selectively adding/dropping one of the adjacent four channels with the spacing of 100GHz. Systems with multi channels being dropped and / or added can be achieved bycas cading the proposed structure.
This paper describes LISA (Lateral isolated Silicon Accelerometer) technology developed by IME< Singapore and its application on silicon vertical optical switch fabrication. Key processes in LISA technology for optical switch fabrication include deep trench etch and oxide refill to enable insulating anchors in silicon substrate, second deep trench etch to fabricate movable microstructures and metal layer covering for switch surface improvement. In this paper, deep trench (deeper than 35 um) oxide refill process is introduced, the dielectric characteristic of the isolation is evaluated, and more than 100V breakdown voltage is obtained, which is much higher that the requirement in optical switch driving voltage. Some process issues related to high aspect ratio trench etch and release such as notching on silicon beam top and sidewall are shown and discussed, a double spacer process is utilized accordingly to solve the issues. Besides, a mask free metal coating process is presented to improve the mirror surface and light reflectivity. The vertical optical mirrors fabricated by the LISA technology is 35um in height and um in width, the switch displacement is larger than 40um under 35V DC bias, the optical characteristics of the switch is under testing.