Molecular Caulking

Abstract

Porosity has been introduced in existing low-k interlayer dielectrics to further reduce their dielectric constant. It is desirable to deposit a metallic layer on top of the porous dielectric by chemical vapor deposition ͑CVD͒. However this presents the challenge of preventing the precursor from penetrating into the porous dielectric and depositing metal within this insulating layer. In the present paper a low-k CVD polymer capping ͑Molecular Caulking™͒ is deposited at room temperature onto the porous ultralow k dielectric methyl silsesquioxane. Experiments show that the Molecular Caulking prevents precursor penetration during subsequent metallorganic CVD. In addition, while the Molecular Caulking itself slightly penetrates into the methyl silsesquioxane, it does not appreciably increase surface roughness or film dielectric constant.In future gigascale integrated circuits ͑ICS͒ resistive-capacitive ͑RC͒ delay is an increasingly important issue. 1 Carbon-doped oxides and aromatic polymers are examples of materials being investigated to replace SiO 2 as the interlayer dielectric ͑ILD͒. 2 Both materials possess lower dielectric constants and will lower the contribution to RC delay. In order to reduce the dielectric constant further, it is generally accepted that the ILD will contain some amount of porosity. The introduction of porosity results in a number of other undesirable properties such as a reduction in mechanical strength and susceptibility to penetration of chemicals. Most importantly, during chemical vapor deposition ͑CVD͒ exposure of the porous dielectric to gaseous precursors that are expected to infiltrate an open pore film or even a closed pore film if the pore wall thickness in the nanoscale dimensions 3-6 cause degradation of film properties. CVD will typically have a reactive sticking coefficient much less than one in order to have good conformal coverage. Indeed, one way to reduce this penetration would be to increase the reactive sticking coefficient, e.g., by increasing the deposition temperature. However, this would reduce the conformality of the deposition. Clearly porosity and conformal CVD on high aspect ratio substrates are fundamentally at odds.Several methods have been studied recently to solve this problem. A recent review details some of the currently proposed strategies to seal porous dielectrics. 7 A new sealing layer, Molecular Caulking, is presented here. MC films are deposited by CVD at room temperature using a free radical polymerization process. Preliminary results are promising. The approach taken was to measure the new sealant's ability to prevent penetration of metal precursors ͑copper, cobalt͒ during CVD. The depth distribution of deposited metals were measured by Rutherford backscattering spectrometry ͑RBS͒. In addition, changes in the dielectric constant as a result of MC, were determined by metal insulator semiconductor ͑MIS͒ capacitance measurements. Deposited film thickness was determined by both ellipsometry and ion beam backscattering using the 5.75 MeV 4 He elastic nucle...

Plasma‐Enhanced Atomic Layer Deposition of Palladium on a Polymer Substrate

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Dehydrohalogenation in Alpha-Functionalized Poly-p-xylylenes

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