Vacuum sealing using atomic layer deposition of Al2O3 at 250 °C

This paper describes the use of low-temperature atomic layer deposition (ALD) of Al2O3, for vacuum seals in wafer-level vacuum packaging and other applications. The conformal coverage provided by ALD Al2O3 is shown to seal circular micromachined cavities. The cavities are 0.8 μm in height, 400 μm in diameter, and are capped by porous plasma-enhanced chemical vapor deposited dielectrics that form a membrane. The ALD Al2O3 film, of thickness ≈0.2 μm, is deposited at a temperature of 250 °C on this membrane. The retention of vacuum is indicated by the deflection of the membrane. Lifetime tests extending out to 19 months are reported.