Reactive ion etching of high-aspect-ratio 100 nm linewidth features in tungsten

Abstract

The subtractive patterning of fine-linewidth (sub-250-nm) tungsten absorbers for x-ray masks requires the ability to etch features with high aspect ratios and vertical sidewalls. In this letter, a reactive-ion-etching process which meets these requirements is described. The etch gases used are SF6 and H2. It is further shown that an intermittent etch process, whereby the sample is vented to atmosphere in between etches results in an etch profile with vertical tungsten sidewalls. This interrupted etching is compared with the results from continuous etching. The straighter sidewalls in the case of the interrupted etch suggests a passivation of the sidewalls which occurs during the venting process. Results are presented to show etching of 100 nm gratings and 200 nm dot arrays. An in situ endpoint detection method developed for the reactive-ion-etching system is presented.