Time of flight secondary ion mass spectroscopy investigation of ultralow-k dielectric modifications in hydrogen and deuterium plasmas

Abstract

Photoresist stripping processes based on hydrogen reductive chemistry have emerged as attractive replacements of the conventional treatments performed using O2 plasma. H2 discharges and plasma processes based on gas mixtures containing H2 provide, in fact, adequate stripping rates while reducing the chemical modifications of the porous ultralow-k (ULK) dielectric materials employed in interconnect technology. In this work the authors investigate the chemical modification of a number of organosilicate low-k dielectrics interacting with remote H2 plasma. The materials include both spin-on and plasma-enhanced chemical vapor deposited dielectrics with k, porosity, and chemical composition spanning on a broad range of values. The mechanisms of plasma∕dielectric reaction and the depth of interaction are evaluated by means of time of flight secondary ion mass spectrometry. In order to study the nature of the plasma∕dielectric interactions and the chemical modifications introduced in the ULK materials, deuterium (D2) is used to substitute for H2 in the discharge. Although the plasma-generated radicals interact strongly with the materials, negligible stoichiometry modifications are observed during exposure of silica-rich ULK materials. On the other hand, the dielectrics with higher carbon content undergo major compositional changes. The chemical damage introduced by H2-based discharges depends strongly on the formulation of the organosilicate material. The substrate temperature is also seen to affect the influx of plasma species. This acts on the extent of material modifications. Nevertheless, the nature of plasma∕dielectric interactions does not vary for processes performed in the temperature range of 200–300°C.