Application of silison plasma atching in microchannels.

Author(s)

Ronaldo Domingues Mansano

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 1998-02-17

Examining board members

Patrick Bernard Verdonck; Jose Augusto de Alencar Mendes Pereira; Ricardo Guerra Pereira; Antonio Carlos Seabra; Jacobus Willibrordus Swart

• Advisor: Patrick Bernard Verdonck

Abstract

Micromachining is becoming an increasingly important technology. Plasma etching of deep trenches in a silicon substrate is one of the most important processing steps in micromachining. In this work we studied several plasma etching processes, all based on fluorine containing gases, to obtain deep trenches with well controlled dimensions. Using the gas CBrF3, we were able to obtain trenches with vertical walls, relatively smooth surfaces until twenty micrometer deep. Addition of SF6 increases the etch rate, but also the undercut under the mask, resulting in less anisotropic processes. Etch depth has no limitation for these processes. Using pure SF6 and an aluminium electrode, very deep trenches can be etched with etch rates of several micrometers per minute, but the processes are isotropic. To obtain more vertical walls, a grafite electrode was used, and argon and hydrogen were added. In this way, polymerization inhibits lateral etching under the mask. Trenches of twenty seven micrometers deep with vertical walls were etched with such processes, but with a relativel low etch rate, approximately two hundred nanometers per minute. Inductively coupled plasmas are used to obtain relatively high etch rates at low pressures. In our modified Reactive Ion Etching reators the first tests showed that we are able to etch trenches with vertical walls at etch rates of approximately one micrometer per minute, using pure SF6. The roughness of the bottom of the trench is also reduced by these processes. For most of these processes we were able to determine the most important etch mechanisms. These processes are being used to manufacture such devices as pillars to form diamond sieves, fluidic amplifiers etc. (AU)