Minimizing damage of porous SiCOH using He/H2 plasmas

Abstract

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 CFx polymers on the sidewalls of features and inside pores. The CFx 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.[1] 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.[2] 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.