Elbert E. Huang

Nanoscopic Templates from Oriented Block Copolymer Films

cylindrical microdomains, an orientation normal to the substrate surface is desirable. Two different approaches are used to this end. In thin films, random copolymers anchored to a substrate can be used to produce a neutral surface. [5] For entropic reasons, the microdomains orient normal to the substrate surface. [6] In a second approach, electric fields were used to orient the cylindrical microdomains parallel to the field lines. [7‐10] The approach relies on the orientation-dependent polarization energy induced when an anisotropic body is placed in an electric field. An anisotropic microphase structure will orient such that the interfaces between the two blocks are aligned parallel to the electric field. In this article it is shown that cylindrical microdomains of a copolymer film can be used to generate an array of ordered nanoscopic pores with well-controlled size, orientation, and structure. To this end, selective etching procedures and a characterization of the samples by quantitative analysis of the X-ray scattering along with electron (EM) and atomic force microscopies (AFM) are described. The processes outlined are shown to be operative over a very large range in sample thickness ranging from 40 nm up to several micrometers. The resulting nanoporous films are promising candidates as membranes with specific transport properties and as templates for electronic and magnetic nanostructured materials. Figures 1A and 1B show AFM images obtained from a

Nanodomain control in copolymer thin films

Diblock copolymers are composed of two chemically distinct chains covalently bonded together at one end. We have discovered how to control the orientation of diblock copolymer microdomains (made up of nanoscopic cylinders, or lamellae) in thin films. To do this, we eliminated all preferential interfacial segregation of the components by anchoring random copolymers, composed of identical monomers to the diblock copolymer, to both interfaces of the film. The composition of the random copolymer is tailored to balance interactions between the segments of the copolymer and the interfaces.

Porosity in plasma enhanced chemical vapor deposited SiCOH dielectrics: A comparative study

The low dielectric constant (k) of plasma enhanced chemical vapor deposited SiCOH films has been attributed to porosity in the films. We have shown previously that the dielectric constant of such materials can be extended from the typical k values of 2.7–2.9 to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by enhancing the porosity in the films through the addition of an organic material to the SiCOH precursor and annealing the films to remove the thermally less-stable organic fractions. In order to confirm the relation between dielectric constant and film porosity the latter has been evaluated for SiCOH films with k values from 2.8 to 2.05 using positron annihilation spectroscopy, positron annihilation lifetime spectroscopy, small angle x-ray scattering, specular x-ray reflectivity, and ellipsometric porosimetry measurements. It has been found that the SiCOH films with k=2.8 had no detectable porosity, however the porosity increased with decreasing dielectric con...

Pore size distributions in nanoporous methyl silsesquioxane films as determined by small angle x-ray scattering

Small angle x-ray scattering (SAXS) measurements were performed on nanoporous methyl silsesquioxane films that were generated by the incorporation of a sacrificial polymeric component into the matrix and subsequently removed by thermolysis. The average pore radii ranged from 1 to 5 nm over a porosity range of ∼5–50%. The distribution in pore size was relatively broad and increases in breadth with porosity. The values and observations obtained by SAXS are in good agreement with field emission scanning electron microscopy.

Supercritical carbon dioxide extraction of porogens for the preparation of ultralow-dielectric-constant films

Supercritical carbon dioxide extraction of poly(propylene glycol) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen, is demonstrated to produce nanoporous, ultralow-dielectric-constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. 25 and 55 wt % porogen loads were investigated in the present work. Structural characterization of the samples conducted using transmission electron microscope, small angle x-ray scattering, and Fourier transform infrared spectroscopy, confirms the extraction of the porogen from the PMSSQ matrix at relatively low temperatures (⩽200 °C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 °C–450 °C). The values of dielectric constants and refractive indices measured are in good agreement with the stru...

Block copolymers as nanoscopic templates

Block copolymers self-assemble into well-ordered, microphase separated morphologies having dimensions on the molecular scale. The key to the use of these nanoscopic structures lies in controlling the spatial orientation of the morphology, particularly in thin films. The preferential interactions of the segments of the blocks with interfaces forces an alignment of the morphology parallel to the interface. Here we describe the use of controlled interfacial interactions and electric fields to manipulate the orientation of the morphology and subsequent steps towards the generation of nanoporous templates as scaffolds for nanoscopic structures.

Electromigration Challenges for Nanoscale Cu Wiring

Electromigration data and a theoretical model have shown that Cu lifetime in on‐chip Damascene interconnect structures has dropped for every new interconnect generation, even when tested at the same current density. In addition, a mixture of bamboo and polycrystalline grain structures instead of a bamboo‐like structure observed for <90 nm wide lines (65 nm technology node) resulted in further lifetime degradation by the addition of grain boundary diffusion. The techniques for improving EM lifetime either by modifying the interconnect structure by adding dummy vias on top of a Cu line, a Ru cap on the Cu top surface, or the formation of a thin CuSiN layer at the Cu/dielectric interface were investigated. The upper dummy vias, the Ru cap or CuSiN layer on the top surface of the Cu lines interrupted the Cu mass flow along the top surface interface which can improve lifetimes. The upper level dummy via structure was a powerful tool for helping to understand the Cu microstructure and to distinguish fast diffus...

Experimental study of nanoscale Co damascene BEOL interconnect structures

We characterize integrated dual damascene Co and Cu BEOL lines and vias, at 10 nm node dimensions. The Co to Cu line resistance ratios for 24 nm and 220 nm wide lines were 2.1 and 3.5, respectively. The Co via resistance was just 1.7 times that of Cu, with the smaller ratio attributed to the barrier layer series via resistance. Electrical continuity of Co via chain structures was good, while some chain-chain shorts and leakage suggests metal residuals from the Co polish process. The Co lines and vias, fabricated using conventional BEOL processes, exhibit good Co fill by TEM, with no visible evidence of Co in the dielectric. The relatively smaller resistance increase for Co vias suggests a potential via resistance benefit, a thinner or less resistive barrier can be employed. Co line resistance will likely not be competitive with Cu until after the next technology node.

Effect Of Impurity On Cu Electromigration

The impact of the existence of Cu grain boundaries on the degradation of Cu interconnect lifetime at the 45 nm technology node and beyond has suggested that improved electromigra‐tion in Cu grain boundaries has become increasingly important. In this paper, solute effects of non‐metallic (C, Cl, O and S) and metallic (Al, Co, In, Mg, Sn, and Ti) impurities on Cu elec‐tromigration were investigated. The Cu alloy interconnects were fabricated by adjusting Cu electroplating solutions or by depositing a Cu alloy seed, a thin film layer of impurity, an alloy liner, or a metal cap. A large variation of Cu grain structure in the samples was achieved by adjusting the wafer fabrication process steps. The non‐metallic impurities were found to be less than 0.1% in the electroplated Cu with no effect on Cu electromigration lifetimes. Most of the metallic impurities reduced Cu interface and grain boundary mass flows and enhanced Cu lifetime, but Al, Co, and Mg impurities did not mitigate Cu grain boundary diffusion.

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.