Eva E. Simonyi

Effects of processing history on the modulus of silica xerogel films

Sintered xerogel films (porous SiO2) show a higher elastic modulus than other amorphous low dielectric constant (K) materials available for the same value of K. By comparing xerogels that were sintered, templated or made with ethylene glycol or ethanol as solvents, we show that process history is at least as important as the chemistry of the solid matrix or the porosity. The modulus extrapolated to zero porosity for the porous sintered and templated films is the same as those of the dense films made by chemical vapor deposition of SiO2. This suggests that the solid matrix for sintered xerogel films is close to ideal and their modulus is better because of the ordered arrangement of pores and fusion of particles making up the matrix. The modulus measured by nanoindentation on thick xerogel films (>0.8 μm) is well explained by the open cell foam model.

Processing dependent thermal conductivity of nanoporous silica xerogel films

Sintered xerogel films (porous SiO2) show a much higher thermal conductivity than other low dielectric constant (low-K) materials available for the same value of K. The thermal conductivity of xerogels which we have processed using different methods is compared with that of other low-K materials such as silica hybrid (silsesquioxanes) and polymeric low-K materials. The methods used were: (1) single solvent (ethanol) method, (2) binary solvent (mixture of ethanol and ethylene glycol) method, (3) sintering. For the xerogel films, we show that process history is as important as the chemistry of the solid matrix or the porosity in determining the thermal conductivity. The thermal conductivity, measured by the 3-ω method or the photothermal deflection method, is affected by phonon scattering, which in turn is effected by the size and distribution of pores and particles and the presence of imperfections such as interfaces, substituted chemical species, impurities, microcracks, and microporosity. The thermal con...

An alternative low resistance MOL technology with electroplated rhodium as contact plugs for 32nm CMOS and beyond

This paper addresses a critical CMOS challenge of increasing parasitic resistance by introducing electroplated rhodium (Rh) as an alternative middle-of-line (MOL) metallurgy to replace the conventional CVD tungsten (W) processes for lower contact resistance and better extendibility to 32 nm technology and beyond. Electroplating of Rh is shown to have similar to Cu superconformal filling capability, allowing us to successfully fill high aspect ratio vias (40 nm times 240 nm). Plating of 300 mm wafers with 60 nm times 290 nm vias was demonstrated using CVD or ALD ruthenium (Ru) as the seed layer. An annealing process was developed to obtain a thin Rh film resistivity of 6.5 muOmega-cm, which is 1.5 to 3X lower than the resistivity of CVD W films. Since Rh is stable in Si environment, when compared to a fast diffusing Cu, a very thin Ti/Ru layer can be implemented. Therefore we propose to use PVD Ti/ALD Ru/electroplated Rh as the alternative MOL metallurgy. With this simple liner/seed/fill stack, the overall MOL resistance is calculated to be 2x lower than the overall MOL resistance of the conventional W stacks, and slightly lower than Cu fill stacks. In addition, the ability to use a thinner liner layer than that used for Cu-base fill process, provides a greater potential for extendibility of Rh fill into future CMOS MOL generations.

Moisture-driven crack growth in blanket low dielectric constant and ultralow dielectric constant films

Moisture-driven crack growth was measured as a function of film thickness for a variety of low dielectric constant and ultralow dielectric constant films and a comparison of the crack driving force was made. By plotting the crack velocity versus the crack driving force, a series of universal curves was produced which showed that fracture resistance scales with the dielectric constant.

Low-k spacers for advanced low power CMOS devices with reduced parasitic capacitances

Integration of low-dielectric constant SiCOH dielectrics (k~3) adjacent to gate stacks is demonstrated using 65 nm technology. Substantial reductions in parasitic capacitances are achieved through reductions in the outer fringe component of the overlap capacitance and the capacitance between the gate stack and metal contacts. These results are consistent with modeling. Although this is demonstrated with 65 nm devices, low-k spacers can cut active power consumption and have the potential to improve performance through reductions in parasitic capacitances which will be of greater importance for future technology nodes.

Chemical and mechanical properties of UV-cured nanoimprint resists and release layer interactions

UV-curable nanoimprint resist characteristics and performance are key to controlling resist-related defects formed during template removal due to cohesive failure and strong resist-template adhesion. The debonding process is governed by both the chemical bonds that form between the template and the resist during cure, and by the structure of the resist itself which determines its elastic-plastic response under load. To gain insight to contributions from resist composition to the debonding process we examine the connection between mechanical and chemical properties of a family of methacrylate polyfunctionalized polyhedral oligomeric silsesquioxane (mPSS) containing resists to their adhesion to fluoroalkyl silane release layers. We also survey debonding of one of the mPSS formulations, an acrylate formulation and a vinyl ether formulation from as series of metal oxide and metal nitride release layers. The results show that while intrinsic storage modulus of a cured material is important, interfacial segregation of reactants in fluid resists can influence adhesive properties as well. The metal-containing release layers are shown to have generally much lower adhesion to cured resists than does a fluoroalkyl silane release layer. They present a useful alternative for template release treatments.

Mechanical Enhancement of Low-k Organosilicates by Laser Spike Annealing

Low-k organosilicate films are considered essential for meeting the material needs of interconnect dielectric layers in present and future semiconductor devices. These materials, whether deposited by chemical vapor deposition or spin-on processes, are mechanically inferior as compared to undoped silicate glass or fluorine doped silicate glass. The introduction of porosity to further lower the dielectric constant diminishes the mechanical properties even more. For this reason, post-porosity treatments such as E-beam and UV curing have been explored. In this paper, we describe the use of laser spike annealing (LSA) to achieve similar results. Infrared analysis coupled with Rutherford backscattering, forward recoil, and X-ray photoelectron spectroscopy were used to study the effect of varying laser power and dwell time on the structural changes of both a dense and porous organosilicate, indicating removal of hydrogen and some carbon from the samples. These changes were interpreted in terms of oxidative and bond redistribution transformations. As a result of the structural changes, significant increases in Youngs modulus were achieved. Properties such as k, refractive index, film shrinkage, and water contact angle were also correlated with laser power and dwell time. LSA compares favorably with both E-beam and UV curing and three times improvements in modulus without significantly affecting k were observed.

Laser Spike Annealing: A Novel Post-Porosity Treatment for Significant Toughening of Low-k Organosilicates

Laser thermal treatment of organosilicate coatings in a process characterized by extremely short dwell times and extremely high temperatures, generally referred to as laser spike anneal (LSA) appears to be a viable approach to post-porosity enhancement of mechanical properties. Exposure of organosilicates in both the dense and porous state to very high temperatures (500-1300 degC) for extremely short periods of time, ranging from 200 to 800 musecs, yielded increases in the modulus by a factor of 3-5times without adversely affecting the dielectric constant. Chemical analysis of the treated methyl silsesquioxane structure indicated significant changes in the chemical composition of the film as evidenced by the disappearance of the methyl infra-red absorption associated with methyl groups attached to silicon. However, this disappearance in the methyl absorption was not reflected by a concomitant decrease in the carbon content of the film as determined by Rutherford back scattering (RBS) measurements. RBS analysis yielded a chemical composition which could be represented empirically by SixOyCmHn, the exact composition depending on the exact processing conditions

Pore orientation and silylation effects on mesoporous silica film properties

Low dielectric permittivity mesoporous silica (MPS) films with high mechanical and chemical stability are attractive for electrically isolating multilevel wiring in future nanodevices. Here, we show that pore structure is a crucial determinant of chemically induced leakage currents in pristine and silylated MPS films and strongly influences film stiffness and hardness in silylated MPS films. Films with three-dimensional pore networks exhibit superior mechanical properties than films with cylindrical pores oriented exclusively parallel to the surface. The latter, however, exhibit a fourfold higher resilience to copper diffusion. These differences are attributed to the pore structure and its influence on silylation-induced bond-breaking and passivation.

Effects of silylation on fracture and mechanical properties of mesoporous silica films interfaced with copper

Mesoporous silica (MPS) films are attractive for isolating Cu wiring in nanodevices but are susceptible to pore wall collapse and water and metal uptake. Pore-sealing and chemical passivation with molecular surfactants are potential solutions that could address these challenges. Here, we show that silylated MPS films capped with a Cu overlayer fracture near the Cu/MPS interface at a distance that correlates with the Cu penetration depth into MPS. Pristine MPS films fracture farther from the MPS/Cu interface than silylated MPS, where silylation-induced pore passivation hinders Cu penetration. Silylation also lowers the tensile stress and the fracture toughness of MPS films, but the relative extent of the decreases in these properties decreases the overall driving force for cracking. Such effects of molecular passivation on metal penetration, film stress, and fracture toughness and pathways are important for engineering stable porous dielectrics for nanodevice wiring structures.