Mechanisms for sealing of porous low-k SiOCH by combined He and NH3 plasma treatment

Abstract

Porous dielectric materials, such as SiOCH, are used as the insulator in interconnect wiring in microelectronics devices to lower the dielectric constant and so decrease the RC time delay. Sealing of the pores (up to a few nm in diameter) is necessary to prevent degradation of the low-k properties during subsequent processing steps by diffusion of reactants through the pores into the material. Sequential treatment of porous SiOCH by He and NH3 plasmas is potentially a means of sealing pores while maintaining the low-k of the dielectric. The He plasma activates surface sites to accelerate the reactions responsible for pore sealing. NH3 plasma treatment completes the sealing through one of two mechanisms resulting from the adsorption of NHx radicals — catalyzing the formation of a densified surface layer or formation of Si-N, C-N and N-N bonds to bridge over the pore. In this paper, we discuss mechanisms for pore sealing bridging bonds based on results from an integrated computational investigation of the etching, cleaning, activation and sealing of porous SiOCH in sequential Ar/C4F8/O2, Ar/O2, He and Ar/NH3 plasmas. The authors found that pores in excess of 1 nm in radius are difficult to seal due to the inability of N-bonding to bridge the pore opening. Factors affecting the sealing efficiency, such as treatment time, average pore radius and aspect ratio are discussed.