Vacuum measurement in wafer level encapsulations by interference microscopy

Abstract

Vacuum encapsulation is required for various microsensors to improve their performances. In the case of wafer level vacuum encapsulation, dedicated techniques must be developed to measure the background pressure in the bonded cavities. In this paper we investigated ex situ measurement techniques based on the measurement by interference microscopy of the deformation and vibrations of the caps as function of an external pressure. Because these techniques detect the equality between external and internal pressure, they do not require any modelling nor prior calibration. Application to wafer level encapsulations fabricated by goldsilicon eutectic wafer bonding demonstrates that a detection limit in the 10 À2 -10 À1 mbar range can be reached for millimetre size caps.

Vacuum quality evaluation for uncooled micro bolometer thermal imager sensors

“…Other methods like measuring the vacuum related lid deformation changes [10,11] are theoretically possible but not practicable as it is a stationary, complex, slow and inaccurate measurement. Therefore measuring the pressure via integrated pressure sensors is the only applicable method.…”

“…Therefore measuring the pressure via integrated pressure sensors is the only applicable method. As resonant sensors do not have suitable measuring range [11] only sensors based on the Pirani effect [10,12] can be used. In principle Pirani sensors are consisting of thermally sensitive structures in form of a plate, a cantilever beam or a bridge, which are thermally isolated to the substrate material.…”

Wafer-Level Packaged MEMS Resonators with a Highly Vacuum-Sensitive Quality Factor

“…One is the membrane deflection method, which evaluates the deflection of the thin packaging lid resulting from the difference between the inner and outer pressure of the package [1]. This is a rather simple method, but the resolution of the pressure prediction is low.…”

“…Eq. (1) shows the relationship between the ambient pressure p and the quality factor Q, one of the resonance characteristics:…”

On the determination of Poisson’s ratio of stressed monolayer and bilayer submicron thick films

“…Mechanical properties like Young's modulus E, the residual stress r 0 and the Poisson's ratio t can be determined from (Bonnotte et al 1997;Bosseboeuf et al 2006;Timoshenko and Woinowsky-Krieger 1959):…”