Paper PS-MoA9
Mitigation of Plasma-induced Damage of Advanced 2.0 Porous Dielectrics by the Pore Stuffing Approach

Monday, October 28, 2013, 4:40 pm, Room 104 C

Plasma-induced damage is a major hurdle for the integration of 2.0 dielectrics in advanced interconnects targeting sub-10 nm nodes. State-of-the-art low-k dielectrics are porous organo-silicate glass (p-OSG) films, with high carbon content and interconnected porosities up to 50 %, making the material sensitive to modifications by plasma reactive radicals and VUV photons. A possible solution is the so-called pore stuffing approach: after porogen burnout, a sacrificial polymer is introduced into the porous matrix, hampering diffusion of radicals in the bulk material and attenuating VUV light propagation.

PECVD ultra-low-k dielectric films with k = 2.0 and porosity of 40 – 50 % were stuffed with PMMA. The protection efficiency was evaluated against fluorocarbon-based, oxygen-based plasmas and 147 nm VUV light generated in industrially relevant 300 mm CCP chambers. The material damage was determined by FTIR, spectroscopic ellipsometry, ellipsometric porosimetry, TOF-SIMS, water contact angle measurements, and capacitance measurements. Plasma damage was significantly reduced in PMMA protected samples, resulting in lower hydrophilicity, smaller carbon loss, smaller fluorine penetration, and lower dielectric constants in comparison to unprotected material. PMMAs of molecular weights between 2000 and 7000 g/mol influenced the filling conditions and filling process window, but gave similar level of plasma protection. Plasma-induced VUV light led to significant PMMA degradation, through carbonyl bonds depletion and formation of other polymer by-products, resulting in only a short-term protection of the dielectric against 147 nm radiation. Pattern transfer for 40 nm lines required small changes in discharge parameters, and resulted in lowered sidewall damage when compared to non-stuffed samples.

After the etching, the polymer is usually removed from the pores by a thermal burn-out above 400°C, which is not compatible with BEOL processing. An alternative approach is proposed, using a non-damaging He/H₂ downstream plasma at 280°C, allowing a full CMOS process compatibility.

Pore stuffing is a promising approach to mitigate the plasma damage in porous ultra-low-k material by using a temporary hybrid material approach. In contrast to former hybrid solutions, this one is not suffering from shrinkage or material interaction and therefore, might allow one further step to k_eff ≤ 2.0 interconnect systems.