Minimizing damage of porous SiCOH using He/H2 plasmas

Summary form only given. The low dielectric constant (low-k) and low capacitance of porous materials used for the inter-layer dielectric reduces signal propagation delays in integrated circuits. Typical low-k materials include SiO₂ with methyl groups (CH₃) lining the pores - SiOCH. Generally, fluorocarbon plasmas are used to etch porous SiOCH, a process that deposits CF_x polymers on the sidewalls of features and inside pores. The CF_x polymer must be cleaned as these fluorocarbon compounds cause compatibility issues in future process steps. O₂ plasmas may be used for such cleaning due to the efficiency of oxidation of the polymer. However, O₂ plasma cleans can also remove hydrophobic methyl groups in the SiOCH, replacing them with hydrophilic groups (such as -OH) that increases the dielectric constant. Photons (777 nm and 130 nm) produced by plasma can also break Si-C bonds and speed the C depletion rate. It has been reported that the low-k SiOCH is relatively stable when H₂ plasmas are used for cleaning. The addition of He to the H₂ plasma also aids in preconditioning the surface to improve pore sealing in subsequent treatment using NH₃ containing plasmas. In this paper, we discuss results from a computational comparison of cleaning of porous SiOCH using Ar/O₂ and He/H₂ plasmas. The Hybrid Plasma Equipment Model was used to obtain the ion energy and angle distributions of reac tive fluxes from inductively and capacitively coupled plas mas. These were used as input to the Monte Carlo Feature Profile Model to predict profiles and composition of the low k materials. Damage of the porous SiOCH was characterized by the depth at which removal of -CH3 is observed. For pores which are not in the line-of-sight to the plasma, diffu sion of reactive species into the porous SiOCH is required for damage to occur. Results will be discussed, including valida ti- n, for the cleaning of pores as a function of treatment time, pore radius, interconnectivity and plasma power. Surface reaction mechanisms in Ar/O₂ and He/H₂ plasmas and pho ton generation (130 nm and 77 nm) in Ar/O₂ plasmas will be discussed.