Proceedings Article | 28 September 2001
Proc. SPIE. 4557, Micromachining and Microfabrication Process Technology VII
KEYWORDS: Etching, Polymers, Germanium, Silicon, Coating, Low pressure chemical vapor deposition, Plasma enhanced chemical vapor deposition, Deposition processes, Semiconducting wafers, Plasma
The ability of various deposition processes and materials to fill and planarize topographical features (trenches deeper than 10 micrometers ) is investigated in this work. Three different deposition processes are considered: LPCVD (Ge), PECVD (Ge, Si3N4, SiO2) and spin coating (BCB, resist, polyimide). Comparing LPCVD and PECVD processes show that, for the same trench width, thick PECVD layers can close off trenches from the top, while thick LPCVD layers fill the trenches completely. The use of PECVD layers is thus advantageous for sealing applications, where a low bottom step coverage is desired. LPCVD layers on the other hand are very useful for planarization purposes where a low ratio between the deposited film thickness and the planarized trench width is desired. Also the deposition of polymers by spin coating yields excellent planarization results with a simpler process and lower thermal budget compared to LPCVD processes. All polymers investigated fill the trenches totally. If these planarization layers are used as sacrificial layers, they should be etched isotropically and selectively with respect to the structural layer. Ge can be etched in oxidizing solutions (H2O2/H2O) and the sacrificial etch of Ge is selective towards Si, SiO2 and many other layers. SiO2 can be removed by wet or vapor HF, and resist, polyimide and BCB can be removed by O2 or O2/SF6 plasma. Which layer should be used depends on the trench fill requirements, the thermal budget and the further processing needed.
