Thermal and mechanical properties of hybrid methylsilsesquioxane/poly(styrene-b-4-vinylpyridine) low- k dielectrics usin
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A late porogen removal scheme was used to make low-k materials (k ¼ 2.72 to 2.02) using methylsilsesquioxane (MSQ) and a high-temperature porogen, poly(styrene-b-4vinylpyridine) (PS-b-P4VP), to circumvent the reliability issues related to as-deposited porous dielectric. Based on the nanoindentation and Fourier transform infrared spectroscopy (FTIR) analysis, the moduli of the hybrid films were found to be higher than their porous forms, and even better than the dense MSQ film, for porogen loading below a critical level (69.5 vol%). This could be attributed to their enhanced degree of crosslinking in MSQ as evidenced by the network/cage structural ratios. Besides, hightemperature porogen plays different roles during the cross-linking of MSQ depending on its loadings. In this study, with immediate loading at 16.7 vol%, PS-b-P4VP can serve as plasticizer to enhance the degree of cross-linking, but at a large loading >16.7 vol%, it becomes a steric hindrance reducing the degree of cross-linking.
I. INTRODUCTION
As the feature size in microelectronic devices is scaled down, the increase of propagation (RC) delay in the backend interconnect becomes the limiting factor of delay.1 To minimize the increase of RC delay, the industry first introduced copper metallization to reduce the resistance as well as improve the electromigration performance of wiring.2 To continually reduce the RC delay of interconnects, low dielectric constant (low-k) materials such as carbon-doped oxide (CDO)3 or SiLK,4 a polyphenylene polymer, with k ranging from 2.65 to 3.2, have been introduced primarily in 90 nm node to replace the interlayer dielectric (ILD), SiO2 (k 4.0) or fluorosilicate glass (k 3.7).5 Further reduction of the effective k in dual damascene interconnection involves the scaling of k value and the film thickness of the etchstop layer6 in addition to the traditional scaling of ILD materials in a 65 nm node. For 45 nm technology node and beyond, it is well recognized that the incorporation of porosity (kair ¼ 1) is critical to the search for viable low-k dielectrics ultralow-k materials with k < 2.4, according to the 2007 International Technology Roadmap for Semiconductors (ITRS).7 One practical approach for creating porous structure in spin-on low-k dielectrics is through a pore generator (porogen), which is removed at low temperatures, typically a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0136 J. Mater. Res., Vol. 25, No. 6, Jun 2010
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200 C immediately after the film deposition, using porogens such as norbornene-derivative,8 polyoxyethylene ether,9 and amphiphilic block copolymers (ABC) such as poly(methyl methacrylate-co-dimethylaminoethyl methacrylate) (PMMA-co-PDMAEMA) and poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (PEO-b-PPO-bPEO).10,11 Specifically, it has been demonstrated that the amphiphilic characteristic of ABCs with low decomposition temperature can significantly improve the miscibilit
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