Paper PS-ThP1
An In-situ Diagnostic to Detect Charging during Plasma Etching

Thursday, October 18, 2007, 5:30 pm, Room 4C

In plasma etching processes, especially those with high aspect ratios, it is known that defects can occur such as trenching, bowing, and twisting. These defects are particularly noteworthy in the manufacture of DRAM deep-trench capacitors. In order to investigate the role of charging on these phenomena an in-situ diagnostic was fabricated using photolithographic and deposition techniques. The device consists of a base layer of titanium with alternating layers of SiO₂ and titanium. During the construction of the device, vias are integrated into the layout, extending all the way from the top surface to the substrate. The silicon dioxide layers act as insulators to create discrete measurement layers, provided by the titanium layers. The titanium layers are attached to voltage measurement leads and can then be used to measure the build up of sidewall charging at different heights along the via when exposed to a plasma. To determine the effect of geometry, if any, on charging, several aspect ratios were used by maintaining the same device thickness but varying the diameter of the vias. The entire stack is less than one micron thick, with vias ranging in diameter from 1 micron to only 20 nanometers, thereby producing aspect ratios of 1:1 to 30:1. Results from the diagnostic will be shown for various etching recipes.