Wafer-Level Packaging for Micro-Electro-Mechanical Systems Using Surface Activated Bonding

Abstract

Wafer-level packaging (WLP) is increasingly important for micro-electro-mechanical systems (MEMS) because of downsizing, cost reduction, and mechanical damage suppression during assembly. The diaphragms were fabricated using surface activated bonding (SAB), a room-temperature bonding, that realizes an accurate alignment, a low stress at a bonding interface, and a high throughput. Gaps and voids were not observed in acoustic microscopy images and in a transmission electron microscopy (TEM) cross-sectional image of the Si/Si interface. After dicing, the evaluations of the airtightness and stress of the interface were performed using a helium leak detector and a micro-Raman spectroscope, respectively. The stress was shown to be markedly lower than those of the anodic, and eutectic bonding. We demonstrated the low-stress and highairtightness diaphragms of WLP using SAB. We showed that these technologies are very suitable for MEMS that require a low stress and a high airtightness, such as biosensors and mechanical sensors.

Wafer-Level Vacuum Packaging Enabled by Plastic Deformation and Low-Temperature Welding of Copper Sealing Rings With a Small Footprint

“…For SLID bonding, voids can occur in the intermetallic compound layer, and special care has to be taken in designing the sealing layer thickness and in controlling the temperature ramping during bonding to get uniform and strong bonds [19], [20], [28]. Surface activated bonding enables room temperature sealing [21], [29], but the requirements on surface planarity and surface roughness of the substrates are very high [21], [30]. Thermo-compression bonding typically employs high temperatures of 300 -450…”

A Fluxless and Low-Temperature Flip Chip Process Based on Insertion Technique

“…Moreover, this configuration allows for a direct contact of the passivated surfaces between the chip and the substrate. This mechanical coupling can thus be obtained with low-temperature bonding methods such as the use of adhesives or surface activated bonding [21] for instance. Decoupling the mechanical contact function from the electrical contact leads to an improvement of yield and reliability of the interconnection.…”

Room-temperature wafer bonding using smooth gold thin films for wafer-level MEMS packaging

“…Among various low-temperature bonding techniques, surfaceactivated bonding (SAB) [15] and atomic diffusion bonding (ADB) [16] are promising candidates for achieving roomtemperature bonding. Several sealing systems have previously been reported using various materials (e.g., Si/Si [17], [18], Si/Cu [17], and Al/stainless steel [19]) based on SAB under ultra-high vacuum conditions. Since Au has several highly desirable properties, such as oxidation and corrosion resistance, Au-Au SAB has been demonstrated in ambient air [20], [21].…”