Thick Germanium-on-Nothing Structures by Annealing Microscale Hole Arrays With Straight Sidewall Profiles

Thick (
$>4~\mu \text{m}$
) germanium-on-nothing (GON) structures are fabricated by high-temperature annealing of microscale hole arrays under vacuum condition (830 to 910°C and
$2\times 10 ^{-6}$
Torr). From annealing results obtained at various temperatures and durations, the annealing temperature of 890°C where practical annealing duration (< 60 min) is achieved is determined to be the optimum due to the surface detects noticeably found at 910°C. A prediction model for annealing duration is also proposed as a function of temperature from analysis of the annealing results. Interestingly, either single or double-stack GON structures result from hole arrays with the same aspect ratio of 12 but straight or curvy sidewalls. Key factors for realizing thick GON structures include the initial microscale hole array pattern, optimum annealing temperature, and relatively straight sidewall profiles (i.e., small arc angle,
$\theta _{arc} < 1^{\circ }$
) of hole arrays. [2021-0230]