Modification of Ultra Low-k Dielectric Films by O2 and CO2 Plasmas

Teju Tunde Olawumi,Mikhail Krishtab,Kaidong Xu,Mikhail R Baklanov,Johann W Bartha,Christophe Detavernier,Elisabeth Levrau,Frederic Lazzarino

doi:10.1149/2.0061501jss

Teju Tunde Olawumi, Mikhail Krishtab + Show 6 more

Open Access

https://doi.org/10.1149/2.0061501jss

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Abstract

Low-k materials developed for ULSI interconnects should have sufficient resistance to processing plasma. CO2 plasma is being considered as a promising candidate for low damage photoresist ash and as a surface activation chemistry for self-assembled monolayers and atomic layer deposition on low-k materials. This article explores the interaction of two organosilicate (OSG) based low-k materials with different k-values (OSG2.4 and OSG2.2) with CO2 plasma in both CCP and ICP-remote plasma chambers. Time dependent exposure of the materials to CO2 plasma revealed quick and effective sealing of OSG2.4 surface whereas it takes longer time for OSG2.2. The sealing reduces further plasma damage and leads to accumulation of CO2 in the pores of both materials. The same behavior occurs in ICP–remote plasma but without a complete sealing of the surface. This suggests the important role of ion bombardment. Damage to low-k by conventional O2 plasma was studied alongside and it was found that for t < 60 s, O2 plasma exerts more damage on OSG2.2 than CO2. This trend is reversed at t > 60 s. Furthermore, lesser time exposure to CO2 plasma was investigated with respect to source power at constant pressure and it was discovered that damage although small, increases with varying source power.

Highlights

Exposure in Capacitively-Coupled Reactive Ion Etching (CCP-RIE) plasma chamber.— The low-k films deposited on Si were cleaved into 35 mm × 35 mm sized coupons and glued with a thin layer of thermal joint paste (Wakefield 120) on to TiN wafers which served as both carrier and to observe the effects of the plasma conditions
Low-k modification: FTIR data.—Several samples of the two low-k films have been exposed to different plasma exposure times from 2 s up to 150 s of CO2 plasma in a CCP-RIE chamber on the TEL Tactras
In consistence with previous research,[5,6,7,8,9,10,11,12] O2 plasma was found to be more damaging compared to CO2 at short treatment times the total carbon depletion is not so pronounced in both cases (Figure 4)

Summary

Introduction

Low-k modification: FTIR data.—Several samples of the two low-k films have been exposed to different plasma exposure times from 2 s up to 150 s of CO2 plasma in a CCP-RIE chamber on the TEL Tactras. The vibration absorption peak assigned to SiCH3 (1275 cm−1) shows a substantial intensity decrease with increasing plasma exposure indicating appreciable damage to the low-k film by the O2 plasma treatment.

Results

Conclusion