Dimensional Metrology for Nanomanufacturing

Our goal is to develop measurements that quantify the shape, size, orientation, and fidelity of nanoscale patterns as a platform to quantitatively evaluate nanofabrication and assembly processes. NIST will provide stakeholders in these fields with measurement technology that provides potential solutions to several of the Grand Challenges identified in the 2007 International Technology Roadmap for Semiconductors (ITRS) for metrology in emerging technologies that currently have no apparent solution.

Small Angle Scattering techniques are employed to measure, with sub-nm precision, pattern shape, dimensions, and orientation for structures created in periodic arrays. Critical Dimension Small Angle X-ray Scattering (CD-SAXS) utilizes the transmission scattering from a small beam size (100 x 100 mm) to provide detailed shape and dimensional data for 10 to 500 nm structures placed with high uniformity in pitch. A lab scale prototype at NIST complements current optical scatterometry, CD-AFM, and CD-SEM methods. It can easily quantify the pattern shape in arrays of nanostructures with periodicities in the range of (10 to 500) nm with sub-nm precision, is non-destructive, is capable of quantifying buried or free-standing patterns, and is straight-forward to interpret via scattering theory. Rotational Small Angle Neutron Scattering (R-SANS) is a complementary technique capable of measuring the distribution in orientation for patterning methods based on directed self-assembly. These unique dimensional measurements are applied to evaluate emerging nanofabrication processes including extreme ultraviolet lithography, electron beam lithography, and directed self-assembly.

Non-Planar Electronics: In order to meet future challenges from thermal and power efficiency requirements of sub 32nm technology nodes, transistor architecture is migrating from planar to non-planar structures. These structures, such as the tri-gate and FinFET products, feature increased complexity in pattern shape and nanoscale conformal coatings. Current measurement platforms are challenged by the small dimensions inherent in these structures, where diminishingly small variations in composition and dimensions will reduce or eliminate device functionality. Critical Dimension Small Angle X-ray Scattering (CD-SAXS) is a metrology platform with the potential capability to quantify 3-dimensional non-planar structure with sub-nm precision. Specifically, CD-SAXS has the potential to non-destructively characterize the thickness and, to a limited extent the uniformity of the thickness, of the conformal high-k dielectric layer.

In FY08, we have demonstrated this capability of X-ray based scatterometry by measuring high-k dielectric layers deposited from 0 to 10nm in thickness over grating patterns with a nominal critical dimension of 20 nm. For these patterns, CD-SAXS provides high precision data on average high-k dielectric thickness, line width (CD), and pitch. In addition, the measurement has the capability to measure the average top layer thickness and the dielectric thickness on the pattern sidewall independently, providing a measure of uniformity.

Orientation in Directed Assembly: Di-block copolymers are polymeric chains composed of two sub-chains covalently linked that can assemble into nanoscale domains. Morphologies achieved to date include spherical, cylindrical, lamellar, and bicontinuous phases. The capability to assemble these polymers within a thin coating to achieve phases with narrow size disparity makes them attractive as sacrificial resists as well as functional materials. However, control over orientation requires external guides and control over processing conditions. A wide array of strategies have been employed to date to create large area films with nearly single crystalline order including solvent annealing, chemical pattern templates, topological templates, and electric fields. Challenges still exist in the precise measurement of block copolymer orientation, particularly in thick films and during early stages of processing, where electron microscopy is frequently destructive and x-ray contrast is often low.

To address this challenge for BCP films, and other nanoscale soft matter systems, we are developing Rotational Small Angle Neutron Scattering. Rotation Small Angle Neutron Scattering, in conjunction with specular neutron reflectivity, can provide the relative fractions of perpendicular and parallel components. Shown are data from a “mixed” state film, where the one phase is perdeuterated, measured along the Qx-Qz plane. The hexagonal diffraction spots are indicative of several layers of ordered cylinders parallel to the substrate. Neutron reflectivity reveals these cylinders as located near the bottom substrate. These data indicate the perpendicular cylinders become more dominant as film thickness increases, providing a detailed picture of coexisting orientations with the relative fractions varying with thickness and annealing temperature.

• The “Grand Challenges” of the International Technology Roadmap for Semiconductors demonstrate the lack of measurement solutions for pattern uniformity and pattern placement in dense arrays of sub-50 nm structures which are the foundation of next generation electronics and data storage.
• Critical Dimension Small Angle X-ray Scattering (CD-SAXS) achieves the first example of 3D metrology for interconnects. Preliminary measurements on FINFET structures demonstrate the feasibility on these buried structures. Such measurements are not possible with current methods.
• A NIST collaboration with IBM and Hitachi Global Data Storage has provided the distribution of orientation of self-assembled structures, a key indicator of pattern quality necessary for technology development, using Rotational Small Angle Neutron Scattering (R-SANS).