High-Precision Alignment and Bonding System for the Fabrication of 3-D Nanostructures

Abstract

We successfully developed a high-precision wafer alignment and bonding system for the fabrication of a variety of 3-D nanostructures. To control the wafer positions with high accuracy during the wafer-bonding process, we improved upon a design of the conventional mask-alignment stage. A stress sensor was incorporated to measure the load between the two wafers. In addition, the parallelism of the wafers was monitored by an optical interferometry system. To determine alignment errors in both the x and y directions simultaneously, we devised an alignment method consisting of crossed vernier scales. We demonstrated that the new alignment and bonding system allowed us to realize precise 3-D photonic crystals with the alignment inaccuracy of < 100 nm at most, and we show that the best experimental error achieved to date was < 25 nm. As this system has the benefit of more readily and intuitively determining the absolute positions of the two wafers, it can be applied to the fabrication of a wide variety of nanoscale multilayer devices.

Fabrication of 3D Photonic Crystals toward Arbitrary Manipulation of Photons in Three Dimensions

“…In this procedure, one of the most important processes is the alignment of stacking positions. From our numerical calculations, we found that the accuracy of the stacking position should be better than 0.1 periods of the parallel rods in the stacked-stripe structure to obtain a photonic-badgap effect close to that in perfect structure [30,31]. This requires a stacking accuracy of several tens of nanometers when considering operation in the optical-communications wavelength range, where the lattice constant is designed to be approximately 500-700 nm.…”

A tunable waveguide-coupled cavity design for scalable interfaces to solid-state quantum emitters

“…x alignment must be within ±30 nm to maintain an enhancement ≥90% of the maximum. Various pick-and-placement techniques have already been demonstrated with excellent in-plane alignment, including optical microscopy with better than 200 nm in-plane tolerance 32,49 and scanning-electron microscope based alignment with 25 nm tolerance, [50][51][52][53] aided by lithographically defined alignment structures as indicated in Figure 1(a). Finally, any remaining error is correctable in situ using AlN NEMS actuators in x and y directions.…”

Effects of Anisotropy and Supporting Configuration on Silicon Wafer Profile Measurements for Pattern Overlay Estimation

“…5,17,18 For wafer level 3-D approaches, more complex problems, (such as differences in profiles, device structures, device densities, residual stress, effective coefficients of thermal expansion (CTEs) of the two wafers) are associated. When foreign substrates are introduced, the problem gets even more complex.…”

“…4 New wafer-to-wafer alignment and bonding techniques are continuously being developed for high precision and accuracy. 5,17,18 If no PIWGC exists, the pattern overlay problem would be a lot easier to understand and to address. PIWGC often distorts a 300 mm Si wafer to a convex or concave shape component.…”