New Vertex application note

Ion energy and ion flux measurements through high-aspect ratio holes using the Vertex system

Vertex Multi Sensor
The Vertex Multi Sensor measures the ion energy distribution as a function of aspect ratio hitting a surface inside a plasma reactor from multiple locations to analyse the uniformity of ion interactions across a substrate.

Abstract

High aspect ratio (AR) etching is a key process in integrated circuit (IC) fabrication. The manufacture of a 3D NAND memory stack requires structures with an AR > 50 to be created. The key challenge is to create bow-free, straight profiles with minimal twisting. Transport of ions and neutrals to the bottom of these structures can be limited by sidewall shadowing. In particular, ion bombardment of feature sidewalls complicates etching profile control while ion loss to the sidewall reduces ion flux to the bottom of the feature. Only ions with a relatively narrow angular spread, relative to normal incidence, will reach the bottom of high AR features. Ions are accelerated toward the substrate by the sheath electric field perpendicular to the substrate surface. However, ions have some thermal velocity when entering the sheath and therefore have an energy component parallel to the substrate surface. The ratio of the perpendicular to parallel components of the ion energy vector determines the angular distribution.

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