Fast and extremely selective polyimide etching with a magnetically controlled reactive ion etching system

A dry etching technique using a newly proposed magnetically controlled reactive ion etching (MC-RIE) system to achieve fast and extremely selective polyimide etching is investigated. In this etching system, the etching parameters such as RF power, self-bias voltage, and gas pressure can be independently controlled by maintaining the plasma conditions. The self-bias voltage (ion accelerating energy) can be reduced to 30 V by using a plasma density (>1×10¹¹ cm³) ten times higher than that of the conventional magnetron enhanced reactive ion etching (M-RIE) system. Etching rates up to 5 μm/min are obtained under the following conditions: an oxygen gas pressure of 0.8 Pa, a self-bias voltage of about -60 V, and an RF power of 300 W. A Ti etching mask is found to have the highest selectivity of about 1000 from MC-RIE using O₂ gas. It is also found that increases in the selectivity (3000) and the etching rate are observed after 25% N₂ is added into the O₂ gas. Highly anisotropic etching with an aspect ratio of more than 10 in a 2 μm line pattern was achieved. The polyimide etched surface is smooth and the surface roughness is less than 0.1 μm