Mechanisms of porous dielectric film modification induced by reducing and oxidizing ash plasmas

Abstract

This work focuses on the impact of oxidizing and reducing ash chemistries on the modifications of two porous SiOCH films with varied porosities (8% [low porosity (lp)-SiOCH] and 45% [high porosity (hp)-SiOCH]). The ash processes have been performed on SiOCH blanket wafers in either reactive ion etching (RIE) or downstream (DS) reactors. The modifications of the remaining film after plasma exposures have been investigated using different analysis techniques such as x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray reflectometry, mercury probe capacitance measurement (C-V), and spectroscopic ellipsometry (SE). FTIR analyses show that the lp-SiOCH film is not significantly altered by any of the ash processes investigated (DS-H2∕He, RIE-O2, and RIE-NH3), except by downstream oxidizing plasmas (DS-O2 or DS-N2∕O2) which induce some carbon depletion and moisture uptake, resulting in a slight increase of the k value. The porosity amplifies the sensitivity of the material to plasma treatments. Indeed, hp-SiOCH is fully modified (moisture uptake and carbon depletion) under oxidizing downstream plasma exposures (DS-O2 and DS-N2∕O2), while it is partially altered with the formation of a denser and modified layer (40–60nm thick), which is carbon depleted, hydrophilic, and composed of SiOxNyHz with RIE-NH3 and DS-N2∕H2 plasmas and SiOxHy with RIE-O2 plasma. In all the cases, the k value increase is mainly attributed to the moisture uptake rather than methyl group consumption. hp-SiOCH material is not altered using reducing DS chemistries (H2∕He and H2∕Ar). The porous SiOCH film degradation is presented and discussed with respect to chemistry, plasma parameters, and plasma mode in terms of film modification mechanism.

Toward Successful Integration of Porous Low-k Materials: Strategies Addressing Plasma Damage

“…With oxygen-based plasmas, the highly reactive O radicals from the plasma can diffuse inside the pores and convert the Si-CH 3 terminal bonds into hydrophilic Si-OH terminal bonds. 38,43 This modification is larger for highly porous materials and is favored by a high oxygen radicals density in the plasma. 44 Hydrogen-based plasmas are much less damaging than oxidizing plasmas; nevertheless, hydrogen radicals can still partially damage porous low-k dielectrics, particularly when V-UV photons assist the breaking of chemical bonds.…”

“…44 Hydrogen-based plasmas are much less damaging than oxidizing plasmas; nevertheless, hydrogen radicals can still partially damage porous low-k dielectrics, particularly when V-UV photons assist the breaking of chemical bonds. 37,38,43,44 In addition to plasma related steps, porous low-k dielectrics may also be damaged during the other processing steps required for the integration. During the metallic barrier deposition, metallic precursors can diffuse inside the pores and modify the material.…”

The efficacy of post porosity plasma protection against vacuum-ultraviolet damage in porous low-k materials

“…[2][3][4][5][6][7][8][9] Second, highly porous low-k materials are a lot more prone to plasma damage due to a huge increase in accessible surface area. [10][11][12][13] Over the past 15 years, a lot of efforts have been devised to either prevent or mitigate plasma damage. 14 Among them, post-porosity plasma protection (P4) is the only strategy that takes advantage of the increasing porosity with decreasing dielectric constant in low-k materials.…”

Dielectric Recovery of Plasma Damaged Organosilicate Low-k Films

“…, and Si-OSi suboxide (1021cm -1 ) bonds were reduced [19][20][21][22]. Moreover, the dielectric constant at 1 MHz increased from 2.50 to 3.26.…”