Qinghuang Lin

Small angle x-ray scattering metrology for sidewall angle and cross section of nanometer scale line gratings

High-volume fabrication of nanostructures requires nondestructive metrologies capable of measuring not only the pattern size but also the pattern shape profile. Measurement tool requirements will become more stringent as the feature size approaches 50nm and tolerances of pattern shape will reach a few nanometers. A small angle x-ray scattering (SAXS) based technique has been demonstrated to have the capability of characterizing the average pitch size and pattern width to subnanometer precision. In this study, we report a simple, modeling-free protocol to extract cross-section information such as the average sidewall angle and the pattern height of line grating patterns from the SAXS data. Diffraction peak intensities and reciprocal space positions are measured while the sample is rotated around the axis perpendicular to the grating direction. Linear extrapolations of peak positions in reciprocal space allow a precise determination of both the sidewall angle and the pattern height.

Small angle neutron scattering measurements of nanoscale lithographic features

State-of-the-art lithographic techniques are able to fabricate structures for the semiconductor and other nanofabrication industries with dimensions below 150 nm. The relentless drive to further miniaturize semiconductor devices has placed increasingly stringent demands on current microscopy-based techniques for precisely measuring the size and the quality (line-edge roughness) of lithographically produced features. Using newly developed neutron optics, we demonstrate the first application of small-angle neutron scattering to nondestructively and quantitatively measure both the dimension and the quality of 150 nm lines fabricated on single crystal silicon wafers.

When is bilayer thin-film imaging suitable: comparison with single-layer resists

Silicon-containing bilayer thin-film imaging resists versus single layer resists for a variety of different mask types, from both a focus-expose window, etch selectivity, and process integration perspective are examined. Comparable lithographic performance is found for 248 nm single layer and bilayer resists for several mask levels including: a 135 nm dense contact/deep trench mask level, a 150 and 125 nm equal line space mask printed over trench topography, and dual damascene mask levels with both vias and line levels. The bilayer scheme is shown to significantly relax the dielectric to resist etch selectivity constraint for the case of a dense contact or trench hardmask level, where high aspect ratio dielectric features are required. Only a bilayer resist scheme in combination with a transfer etch process enables the line/space pattern transfer from the imaging layer to the bottom of a trench with a combined aspect ratio > 10. When the single layer resist depth of focus window is limited by both the topography and variations in the underlying dielectric stack thickness, as is the case for the dual damascene via and line levels, bilayer resist is shown to be a practical alternative.

Integration of Photo-Patternable Low-κ Material into Advanced Cu Back-End-Of-The-Line

We report herein the demonstration of a simple, low-cost Cu back-end-of-the-line (BEOL) dual-damascene integration using a novel photo-patternable low-κ dielectric material concept that dramatically reduces Cu BEOL integration complexity. This κ=2.7 photo-patternable low-κ material is based on the SiCOH-based material platform and has sub-200 nm resolution capability with 248 nm optical lithography. Cu/photo-patternable low-κ dual-damascene integration at 45 nm node BEOL fatwire levels has been demonstrated with very high electrical yields using the current manufacturing infrastructure. The photo-patternable low-κ concept is, therefore, a promising technology for highly efficient semiconductor Cu BEOL manufacturing.

Characterization of thin and ultrathin polymer and resist films

The need for a better understanding of the physiochemical properties of radiation-sensitive thin polymer coatings for lithographic applications is driven by the trend of ever- shrinking pattern dimensions and film thickness, imposed by the semiconductor industry. In this work, we address the issue of film uniformity and moisture absorption for thin and ultrathin films (250nm to 50nm) of poly 4-hydroxystyrene (PHS). Using high resolution x-ray reflectivity, the roughness and density of spin coated films was found to remain constant within experimental error for the thickness range examined. Also, water uptake on PHS films was studied by neutron and x-ray reflectivity. Exposure of the polymer film to a controlled humidity level is shown to swell the polymer and be absorbed uniformly throughout the film. No preferential absorption of water at the interface was noticed, regardless of the hydrophilic or hydrophobic nature of the substrate surface. Overall density changes in the polymer matrix due to the moisture-induced increase in the film thickness are also discussed.

Building high-performance chemically amplified resists with polymer blends

The greatly compressed resist development cycle and the explosion of the number of resists at a specific lithographic wavelength have necessitated a hastened pace in developing high-performance resists. Traditionally, high- performance chemically amplified resists have been developed by copolymerization of monomers with various functionalities to achieve the desired properties. This approach, while immensely successful, however suffers from long lead times to deliver successful products to the markplace. In this paper, we report a more rapid approach to developing high- performance chemically amplified resists by blending different polymers with complementary properties. As a model system, a 248nm negative-tone bilayer resist has been demonstrated based on acid catalyzed cross-linking of blends of silicon-containing polymers with a non-silicon-containing polymer. The silicon-containing polymers and the non- silicon-containing polymer used were poly(p- hydroxybenzylsilesquioxane-co-p-methoxybenzylsilsesquioxane) (PHBS/MBS), poly(p-hydroxyphenylethylsilesquioxane-co-t- butylsilsesquioxane)(PHPES/BS) and poly(p- hydroxystyrene)(PHS), respectively. The resist based on this simple polymer blend approach has achieved lithographic performance comparable to that based on more elaborate copolymers that require time-consuming synthetic optimization. Differential scanning calorimetry (DSC), quartz crystal microbalance (QCM), and atomic force microscopy (AFM) were employed to probe the properties of the polymer blends and the resist. DSC results suggested that PHBS/MSB and PHS are miscible throughout the entire composition range. Addition of the phenolic polymer into the silicon-containing polymer dramatically improves the lithographic performance of the bilayer resist. This improvement in lithographic performance is attributed to the enhancement of thermal properties (i.e. glass transition temperature), the modulation of dissolution properties, and more cross-linkable sites for the acid catalyzed cross-linking. O2 RIE etch selectivity of the blends vs. and organic underlayer increases with increasing concentration of the silicon-containing polymer in the blends. The present approach could also be applied to developing other high-performance resists more swiftly at other lithographic wavelengths.

Feature-shape and line-edge roughness measurement of deep submicron lithographic structures using small-angle neutron scattering

We demonstrate the application of small angle neutron scattering (SANS) measurements for the quick, nondestructive, and quantitative measurement of the feature shape and size and line-edge roughness of lithographically prepared structures using a model photoresist pattern consisting of a periodic grating of 0.15micrometers lines. The measurements are performed directly on structures as fabricated on a silicon wafer with no other sample preparation. For well-defined patterns placed normal to the neutron beam, we easily observe up to six orders of diffraction peaks. Analytic expressions from standard small angle scattering formalism are sued to extract the average line structure, spacing, and line-edge roughness from the peak positions and intensities. Additional structural information is obtained by tilting the pattern relative to the incident beam. Changes in the observed scattering data as a function of the tilting angle are related to characteristics such as the height of the structures and the symmetry of the line shape.

Small-angle neutron scattering measurements for the characterization of lithographically prepared structures

The continuing decrease in feature sizes in the semiconductor and other nanofabrication industries has placed increasingly stringent demands on current microscopy-based techniques to precisely measure both the critical dimensions and the quality (i.e. line-edge roughness) of these structures. Small-angle neutron scattering (SANS) experiments provide a quick, non-destructive, and quantitative measurement of the three-dimensional shape and quality of lithographically prepared structures as fabricated on a silicon substrate. We demonstrate the application of SANS for the characterization of nanoscale structures using periodic 150 nm parallel lines prepared using standard 248 nm photolithographic processes.