Resolution limits of metal assisted chemical etching of polysilicon
Creators: name: Barrera, Crystal
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: MACE
Polysilicon
Imprint lithography
Metal
Assisted
Chemical
Etch
Wet

description: Patterning and etching high aspect ratio, sub-50 nanometer structures for 3D device architectures is becoming a critical challenge in advanced semiconductor device fabrication. Metal assisted chemical etching (MACE) is a wet etch process that has demonstrated very high aspect ratio structures in single crystal silicon at sub-50 nanometer scale. The capabilities of this process can be applied to etching of gate structures made in bulk or epitaxially grown single crystal silicon, however, it is important to extend MACE to other materials for a range of semiconductor device architectures. In this research, we build on preliminary results published in the literature showing MACE for polycrystalline silicon. If it can be demonstrated that MACE of polysilicon can retain the sub-50 nanometer resolution and high aspect ratio produced with MACE of single crystal silicon, process techniques can be developed around polysilicon MACE to fabricate critical structures needed in advanced Dynamic RAM, 3D Flash and vias for logic devices. It is also important to demonstrate that atomically precise side walls that are near-perfect in maintaining 90-degree wall angle, as demonstrated with MACE applied to single crystal silicon, can also be achieved in polycrystalline silicon. Metal assisted chemical etching (MACE) is a promising approach that addresses many issues that arise from underperforming reactive ion etching (RIE) methods that have limitations in fabricating high aspect ratio sub-50 nanometer nanostructures due to presence of tapered profiles and high side wall roughness. However, MACE is extremely limited in the types of materials for which it has been demonstrated. MACE has shown reliable etching only in single crystal silicon which limits its applications to a small number of front-end semiconductor device layers. This work extends the capabilities of MACE to polysilicon which when combined with additional process steps has the potential to create patterns for metal vias and deep trench capacitors, both of which are important in the semiconductor industry. Much of the existing literature on MACE for polysilicon builds an underlying hypothesis; etch quality of polysilicon is compromised by the inherent crystalline structure of the material. There is an especial lack in understanding how MACE works at crystal grain boundaries, which presents risk in reduced atomic precision due to sidewall roughness induced by these boundaries –limiting the value of MACE for sub-50 nanometer structures. In this work, we present a MACE wet etch of polysilicon that produces structure arrays with sub-50nm resolution and anisotropic profile. The three demonstrated structures are pillars of 6:1 aspect ratio and 50nm spacing for comparison to MACE literature, pillars of 30nm spacing to establish resolution limitations of polysilicon etch, and a diamond pillar array with potential to fabricate holes with as low as 15nm spacing