Die to wafer direct bonding of (100) single-crystal diamond thin films for quantum optoelectronics

TL;DR

This paper presents a scalable, semiconductor-compatible process for direct bonding of ultrathin single-crystal diamond films onto wafers, enabling advanced quantum optoelectronic device fabrication with high shear strength and stability.

Contribution

Introduces a novel surface-preparation and bonding method for ultrathin diamond films that surpasses previous shear strength records and is broadly transferable across wafer materials.

Findings

Record shear strength of 45.1 MPa for diamond bonding.

Bonding dominated by van der Waals interactions, not covalent bonds.

Bonded structures remain stable through nanofabrication processes.

Abstract

This work unlocks the manufacturing of nanophotonic quantum systems that exploit the unique material properties of single-crystal diamond (SCD). We achieve this by introducing a semiconductor-compatible process for the direct bonding of multiple high-quality, ultrathin diamond films onto a carrier wafer, enabling the subsequent parallel nanofabrication of optoelectronic integrated circuits. Central to this approach is a new diamond surface-preparation method that avoids boiling tri-acid mixtures while producing exceptionally clean 20 um thin single crystals. These platelets are bonded side-by-side to 100 mm silica wafers and exhibit a record shear strength of 45.1 MPa for (100)-oriented diamond, surpassing all previously reported bonding attempts. Evidence indicates that the bonding is dominated by van der Waals interactions, likely arising from mismatched protonation mechanisms between Si-OH and C-OH surface terminations, rather than from covalent-bond-driven mechanisms. Despite this non-molecular nature, the heterostructures remain stable through liquid immersions and standard nanofabrication steps. Because the method depends primarily on surface cleanliness and roughness rather than specific chemistries, it is broadly transferable across wafer materials. This capability to parallel-bond ultrathin SCD films onto large-area substrates provides a scalable route to high-performance platforms spanning nanophotonic quantum technologies, high-power electronics, MEMS, and biotechnology.