Dielectric Recovery of Plasma Damaged Organosilicate Low-k Films
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1079-N02-10
Dielectric Recovery of Plasma Damaged Organosilicate Low-k Films Hualiang Shi1, Junjing Bao1, Huai Huang1, Junjun Liu1, Ryan Scott Smith1, Yangming Sun1, Paul S. Ho1, Michael L. McSwiney2, Mansour Moinpour2, and Grant M Kloster2 1 Laboratory for Interconnect and Packaging, Microelectronics Research Center, Pickle Research Campus, The University of Texas at Austin, Austin, TX, 78758 2 Logic Technology Development, Intel Corporation, Hillsboro, OR, 97124 ABSTRACT Methyl depletion and subsequent moisture uptake have been found to be the primary plasma damages leading to dielectric loss in porous organosilicate (OSG) low-k dielectrics. A vacuum vapor silylation process was developed for dielectric recovery of plasma damaged OSG low-k dielectrics. The methyl or phenyl containing silylation agents were used to convert the hydrophilic -OH groups to hydrophobic groups. Compared with Trimethylchlorosilane (TMCS) and Phenyltrimethoxysilane (PTMOS), Dimethyldichlorosilane (DMDCS) was found to be more effective in recovering surface carbon concentration and surface hydrophobicity. But the carbon recovery effect was limited to the surface region. Alternatively, UV radiation with thermal activation was applied for dielectric recovery of plasma damaged OSG low-k dielectrics. The combined UV/thermal process was found to be efficient in reducing –OH, physisorbed water, and C=O bonds. The dielectric constant was recovered within 5% of the pristine sample and the leakage current was also much reduced. Aging test in air showed that no moisture retake was observed, indicating the repaired film was stable. INTRODUCTION Ultra low-k dielectrics with porosity are being incorporated to reduce the capacitance coupling in copper interconnects beyond 45 nm technology node [1, 2]. During plasma etching and ashing processes, carbon depletion, surface hydrophilisation, and surface densification have been observed, increasing the effective dielectric constant and leakage current [3-11]. These plasma damages limit the further scaling of low-k structures and have stimulated considerable interests in the study of dielectric recovery by silyation methods, using vapor-phase [12], liquidphase [13-14], and supercritical CO2 processes [15-17]. Since silylation agents are susceptible to water molecules, moisture should be removed before the silylation process. Otherwise, even a small amount of moisture will react with the silylation agents and form byproducts which can be adsorbed on the wafer surface to reduce the dielectric recovery and complicate the reaction mechanism. In the first part of this paper, the vapor-phase silylation process was first demonstrated under high vacuum with in-situ heating. This improved the control of moisture uptake, making the process easy to be integrated. To investigate the silylation mechanism, several key parameters were studied including substrate temperature, functionality of silylation agent, and the effect of chemical desorption. Three silylation agents were compared: Trimethylchlorosilane (TMCS), Dimethyl
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