Dry etching technique has been widely used for transferring pattern from resist to substrate. In this process, the energetic ions induce sputtering of the surface material because they have comparable mass to the surface atoms and enough kinetic energy to break the chemical bond. Focused Ion Beam (FIB) has thus been used as an effective tool for selective etching of surface material in making micro or even nanoscale structures. Electrons, however, possess much smaller mass than any atoms and do not cause sputtering when they collide with surface atoms. Therefore, dry etching with electron beams attracted almost no attention. In contrast, the wet process known as electron beam lithography, which utilize electron beam as the exposure source, has been extensively studied and become the major technique for deep sub-micron or nanometer scale fabrication.
In our recent experiments, we observed that electron beam irradiation on polyimide surface can directly break the chemical bonds between surface atoms and etch the surface with high resolution. The beam density used in the experiments is about 1 μA/cm2 at beam voltage of 5kV. Approximate estimation of the beam induced temperature increase in the beam spot region, as well as 3D image of the etched features obtained by using high resolution profiler, strongly suggest that the observed etching process is based on a non-thermal mechanism. The etched features on polyimide surface possess sharp edges and no evidence of surface melting was observed. An etching rate of about 2nm/min at the above beam density was observed and the resolution seems limited primarily by the size of the electron beam spot. Based on this results it is expected that the electron beam induced dry etching is capable of making nanoscale structures on polyimide surface and has potential to find its application in the upcoming nanofabrication technology.
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