Shih-Wei Chang

Fabrication of silicon nanopillar-based nanocapacitor arrays

We report the fabrication of silicon nanopillar-based nanocapacitor arrays using metal-assisted etching in conjunction with electrodeposition. The high aspect ratio made possible by the catalyzed etching provides for an increased effective electrode area and hence a significant improvement in the capacitance density. Electroplated Ni electrode forms a conformal layer over the silicon nanopillars. Capacitance measurements show the expected trend as a function of pillar height and array period. The fabrication approach is simple, compatible with integration into standard silicon technology, and easily scalable.

Process development and bonding quality investigations of silicon layer stacking based on copper wafer bonding

Process development of silicon layer stacking based on copper wafer bonding, grind-back, and etch-back was applied to demonstrate a strong four-layer-stack structure. Bonded copper layers in this structure became homogeneous layers and did not show original bonding interfaces. This process can be used in three-dimensional integrated circuit applications. Voids and total bonded area after each layer stacking were investigated for the bonding quality after each layer stacking. Large wafer bows from high residual stresses result in the structure failure at the stacking of a high number of layers.

Designing new materials and processes for directed self-assembly applications

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but this material has a relatively weak segregation strength that has limited its utility to patterns above 24 nm pitch. This paper reports on some of Dows efforts to develop new materials capable of extending DSA to smaller pitch by development of new BCP copolymer materials with stronger segregation strength. Some preliminary efforts are reported on new substrate treatments that stabilize perpendicular orientations in a high-χ block copolymer that also incorporate an etch-resistant block to facilitate patterning at small dimensions. In addition, development of new block copolymer materials that have a χ-parameter that is large enough to drive defect reduction and but not so high that it precludes thermal annealing are also presented. DSA of these new materials is demonstrated using thermal annealing processes at pitch ranging from 40 to 16 nm, and etch capability is also demonstrated on a material with 18 nm pitch. These technologies hold promise for the extension of DSA to sub 24 nm pitch.

New materials and processes for directed self-assembly

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. The most widely studied material for DSA is poly(styrene-block-methyl methacrylate) (PS-PMMA), but the relatively weak segregation strength of PSPMMA results in some limitations. This paper reports on these limitations for PS-PMMA and highlights a path to success through use of more strongly segregated “high-χ” block copolymers. In general, stronger segregation is predicted to lower defectivity at equilibrium, but unfortunately, kinetics of self assembly also becomes much slower as segregation strength increases. Recognizing diffusion is much faster for cylinder morphologies than lamellar ones, we have investigated new cylinder-forming BCPs that enable defect elimination with thermal annealing processes. In addition, a formulation strategy is presented that further improves the kinetics of the assembly process, enabling tremendous improvements in defectivity over simple BCP systems. Excitingly, successful chemoepitaxy DSA with a high-χ lamellar BCP is also demonstrated using a thermal annealing process and no top coat. These technologies hold promise to enable DSA with thermal annealing processing across pitches from 40 - 16 nm.

A comparison of the pattern transfer of line-space patterns from graphoepitaxial and chemoepitaxial block co-polymer directed self-assembly

Block co-polymer directed self-assembly (BCP DSA) has become an area of fervent research activity as a potential alternative or adjunct to EUV lithography or self-aligned pitch multiplication strategies. This presentation will evaluate two DSA strategies for patterning line-space arrays at 30nm pitch: graphoepitaxial DSA with surface-parallel cylinder BCPs and chemoepitaxial DSA with surface-normal lamellar BCPs. A comparison of pattern transfer into hard-mask and substrate films will be made by consideration of line and space CDs, line profile of cross-sectional SEM images, and comparison of relative LWR/SWR. The processes will be benchmarked against Micron’s process used in manufacturing its 16nm half-pitch NAND part.

Impact of materials selection on graphoepitaxial directed self-assembly for line-space patterning

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes, but significant hurdles remain for commercial implementation. While chemoepitaxy processes employing poly(styrene-block-methyl methacrylate) (PS-PMMA) are most widely studied for DSA line/space patterning, graphoepitaxy processes using more strongly segregated “high-X;” block copolymers have recently shown a lot of promise, with lower defectivity and line-width roughness (LWR) than comparative chemoepitaxy processes. This paper reports on some of the design considerations for optimizing line/space patterning with these materials. We have found that brush and block copolymer selection are critical to achieve high quality DSA. For example, brush thickness must be optimized to achieve matching space critical dimensions, and brush surface energy impacts kinetics of assembly. The X parameter of the block copolymer should be optimized to balance LWR, kinetics of assembly, and process window. Glass transition temperature (Tg) of the blocks showed little impact on performance. Overall, parameters of both BCP and brush must be simultaneously optimized to achieve high quality DSA.