Microplasma for Dry Etching: New Approaches for Micro and Nano Systems

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

0100366 Gianchandani Plasma processing is routinely used in semiconductor processing applications, and is the dominant technique for silicon etching. Conventional etchers aim to create a uniform plasma across the process chamber in which the silicon wafers are located. However, there are applications in micromachining and nanotechnology in which alternative paradigms may prove useful. For example, present fabrication techniques are not practical for manufacturing an array of trenches with 100 different depths, which would require 100 lithography steps. Such a array could be useful for applications like biological cell sorting. This proposal addresses questions pertaining to the science and technology of spatially confined reactive plasmas (microplasmas) and their application to the etching of silicon and other materials. In particular, it focuses on in-situ microplasmas, which are generated by electrodes patterned on the silicon wafer itself. The viability of this concept, which differs radically from other recent work in microplasmas, has been demonstrated by preliminary experiments in which in-situ DC microplasmas were used to etch completely through a silicon wafer in less than one hour. The proposed effort will explore the physics, technology, and diagnostics for reactive microplasmas for etching silicon and other materials. A number of etching configurations will be examined for their impact on plasma confinement, etch rates, anisotropy, mask selectivities, and electrode wear. Promising electrode structures will be explored, including options in which the ion flux is electrostatically controlled to locally adjust the etch rate and sidewall profile. Various electrode materials, powering schemes, and gas chemistries will be evaluated. Both in-situ and ex-situ diagnostic tools (including thin-film Langmuir probes) will be developed and used. Spectroscopic analysis will be performed. The dependencies of the Paschen breakdown curve, the molecular behavior of the ambient gas, the ionization rates and the electron energies, as well as the relationship of these parameters to the etch rates and profiles will be explored. Theoretical models will be developed for the reactive microplasmas by refining global plasma analysis. This includes the incorporation of realistic basic data and consideration of discharge geometry and electrode material. The theoretical models will be used for scaling studies to determine if the plasmas can be reduced to nanometer dimensions. Supporting experiments will be carried out to explore the scaling limits and validate the theory. The proposed reactive microplasmas have the potential not only for making a contribution to traditional etching applications, but also facilitating the fabrication of microstructures that were previously infeasible. Using microplasmas, an array of 100 trenches with different depths could be built with just two masking steps. In addition, if the proposed research is successful, not only will it be possible to individually specify the profile of every trench in the array, but also to skew the direction of the etch with the help of local electric fields controlled by secondary electrodes. In the longer term, the proposed research could lead to other avenues of research, including localized deposition by sputtering or plasma enhanced chemical vapor deposition (PECVD).