Effect of Porogen Incorporation on Pore Morphology of Low-k SiC_xN_yFilms Prepared Using PECVD

Abstract

Low-k porous SiC x N y films were prepared through plasma-enhanced chemical vapor deposition, using 1,3,5-trimethyl-1,3,5-trivinylcyclotrisilazane (VSZ) as the matrix precursor and epoxycyclohexane (ECH) as a porogen. The effects of porogen loading and deposition temperature on porogen incorporation, pore morphology, and the properties of porous SiC x N y films were examined. In addition, the impact of film shrinkage and the corresponding nanopore structures after annealing were studied. The porosity of films deposited at 100 • C increased from 1.8% to 19.8% when ECH loading increased to 30%, above which the porosity remained nearly constant because of high film shrinkage. The pore size decreased slightly from 4.1 to 3.7 nm when ECH loading increased to 30%, above which the pores became larger and were broadly distributed. By contrast, increasing deposition temperature at 20% ECH loading decreased porogen incorporation and increased film density. The porosities and pore size of films decreased, respectively, when the deposition temperature increased. A short-range ordering of pores was observed only at low deposition temperatures because the N-Si-C cross-linked structures and organic phase were present. Optimized processing parameters facilitated the fabrication of low-k porous SiC x N y films exhibiting 19.8% porosity, 3.7-nm pores, a k value of 3.18, and an elastic modulus of 7. In CMOS backend interconnections, low-k etch-stop/dielectric barrier materials such as silicon carbonitride (SiC x N y ) (k = 4.5-5.5) and ultralow-dielectric-constant (ultralow-k, ULK) inter-layer dielectrics (ILDs) have been used to lower the effective capacitance (k eff ) in the 45 and 32 nm node and beyond.1 Silicon carbonitride films are typically prepared by performing plasma-enhanced chemical vapor deposition (PECVD) of multi-precursors such as silane/ammonia (or nitrogen)/methane 2,3 and trimethylsilane/amonia. 4 Recently, single source precursors such as hexamethyldisilazane 5 and BASICN 6 have been used for preparing dense low-k SiC x N y films by using PECVD because these films display low defects (i.e., low leakage current) and higher etch selectivity due to high C/Si ratio. 6 To further reduce the dielectric constant of silicon carbonitride film, incorporation of porosity is one of the primary approaches, in addition to continued addition of elements with lower polarizability such as more C atoms.A conservative approach was proposed by Nguyen et al., 7 who prepared a dielectric barrier bilayer of dense SiN y /porous SiC x N y , exhibiting 12% porosity, by performing plasma deposition of dimethylsilacyclopentane and NH 3 and then using UV to cure the samples. The dense films of the bilayer on top helped protect the underlying copper layer against plasma-induced damage and oxidation caused by the diffusion of oxygen, whereas the bottom porous film of the bilayer contributed to a reduction in the dielectric constant.8 Because they possess a bilayer (dense film/porous film) or sandwich (dense film/porous film/dense film) ...