Anodic Glass Bonding Thermal Expansion Strain Reduction Techniques
Anodic glass bonding strain is minimized by combining matched non-linear CTE glass selection, thin compliant interlayers, and controlled cool-down ramps.
Sputtered Aluminum
Conductive Film
Thin-film metallic layers deposited via physical vapor deposition provide electrical interconnects and reflective surfaces on semiconductor and micro-electro-mechanical wafers. Applying sputtered aluminum is standard for creating low-resistance electrical pathways and bond pads. Its deposition must be controlled to prevent microstructural defects.
Material Deposition
High-purity aluminum targets are bombarded with argon ions in a vacuum chamber to release metal atoms that deposit onto the substrate. In the case of sputtered aluminum, incorporating small percentages of silicon or copper prevents electromigration and silicon spiking at the contact windows. The film thickness is optimized based on the required electrical conductivity and etch resolution.
Residual Stress
The deposition process generates intrinsic stress in the metal film, which can cause substrate curvature or wafer warping. This mechanical stress is measured using wafer-curvature techniques before and after sputtering to ensure it remains within acceptable limits. Excessive stress in sputtered aluminum can cause film peeling or shift the calibration of thin-film strain gauges.
Metrological Quality
Sheet resistance and step coverage are verified using four-point probe measurements and scanning electron microscopy to guarantee uniform performance across the wafer. Variations in film thickness can lead to non-uniform resistance, which affects the thermal stability and bridge balance of sensor circuits. Maintaining tight control over sputter parameters is essential for achieving reproducible sensor characteristics, reducing calibration efforts, and increasing overall manufacturing yield.
This metrological control ensures that every batch of sensor wafers meets the strict performance requirements.