Paper PS2-FrM9
Novel Gases for Obtaining High Etch Selectivity of Oxide to Nitride for Contact Etch

Friday, November 14, 2014, 11:00 am, Room 308

Contact oxide etch is a critical process in developing the next generation integrated device fabrication. With the gate feature size scaling down, the aspect ratio of the features increases and contact oxide etch process becomes more challenging. Very high etch selectivities of Oxide to Nitride are required for contact etch, and there is an increasing need for finding new etch gases that can perform better than the traditional gases like C₄F₈ and additive mixtures used by the semiconductor industry. To this end, Air Liquide is actively working on finding novel etch gas chemistries and in this work, we present the performance of some of the promising etch molecules that offer high etch selectivity of oxide to nitride and mask for contact etch application.

From a new etch molecule design standpoint, there are key etch performance indicators for contact etch, the most important of which are the etch selectivity of oxide to nitride and the oxide etch rate. In this study, several novel fluorocarbons have been first tested systematically using dual CCP etch tool to find a correlation between the etch molecule (structure, and function), and its affect on the etch performance. The use of mass spectrometry as a diagnostic to qualitatively understand the plasma species, with a simple matrix analysis, is presented. Molecules are initially screened based on etch rate and selectivity of different planar films. Sidewall protection is important when etching these features, and so the polymerizing nature of etch gases is also investigated. Specifically, the role of ion energy and oxygen addition on controlling the rate of polymerization is studied in order to find the operating process window that yields high etch selectivity. The perfomance of the etch gases is finally tested on an oxide pattern structure with amorphous carbon as mask material. SEM cross-sections are presented to show the effect of etch gas on etch profile, mask selectivity and mask preservation. The new gases have demonstrated significant selectivity improvement in comparison to traditional etch gases.