Negative hybrid solgel resist as hard etching mask for pattern transfer with dry etching
Hybrid organicinorganic (HOI) solgel systems are emerging as a flexible class of materials in micro-fabrication, since they can be directly structured by different lithographic techniques (UV, EBL, hard and soft X-ray). In this work, we explored a new solgel system to be used as a sacrificial layer, highly resistant as an etch mask in fluorine containing plasmas. Commonly, the etch selectivity for hard materials (e.g. Si, W, SiC among others) with respect to most common resists is less or much less than 10:1, depending also on the plasma chemistry and details of the process and of the reactor. A previous contribution demonstrated how the selectivity of a plasma etching process for silicon masked by a hybrid solgel system containing a high concentration of boehmite nano-particles (Al2O3/AlO(OH)) could reach values as high as 60, in a continuous process (i.e. non-switched) in ICP reactor with SF6, C4F8, Ar gas mixture. In order to improve the performance as a resist of such a HOI, we present a novel system which avoids loading the material with a solid fraction. The target of the synthesis is to condense in situ an alumina based network, starting from an aluminum-containing precursor. The alumina content in the final material is up to 80%. By means of soft X-ray lithography (XRL), high resolution pattern were produced in a film that after development resulted having a thickness of 30nm. The new synthesized system shows extremely high etch selectivity even after mild thermal treatments ( 3?m tall structures without appreciable loss in the critical dimension (CD) and almost vertical sidewalls. The resist showed thus a selectivity exceeding 60:1, on structures with details at the 200nm scale.
hybrid solgel patterning dry etching x-ray lithography new resist