Utilizing Co as a contact metallization for wafer-level Cu-Sn-In SLID bonding used in MEMS and MOEMS packaging

Abstract

Many MEMS and MOEMS devices require hermetic packaging with preferably no postprocessing after the MEMS device's releasing. Wafer-level Solid-Liquid Interdiffusion (SLID) bonding can provide simultaneous hermetic packaging and better electrical interconnects. Moreover, employing a physically deposited contact metallization on the device wafer instead of chemically deposited layers (such as electrochemical Cu) is of utmost importance as far as reducing the complexity of the MEMS/MOEMS packaging process integration is concerned. The current work studied the possibility of utilizing Co as a contact metallization layer for the low-temperature Cu-Sn-Inbased SLID bonding. In order to guarantee the long-term reliability of the devices, a fundamental understanding of the formation and evolution of interconnection microstructures and mechanical characterization of the joint is of utmost importance. In this work, Cu-Sn-In electroplated Si chips were bonded to Co substrates at a temperature range 160-250°C. During the bonding process, a single intermetallic compound (IMC) (Cu,Co)6(Sn,In)5 formed at the bonding area, with no detectable Cu3Sn phase that causes voids formation. The Young's modulus and hardness of (Cu,Co)6(Sn,In)5 and Cu6Sn5, as a reference, were measured as 124.8±0.5 and 6.2±0.5, 114±1 and 6.7±0.5 MPa, respectively. Furthermore, the current study was able to produce a fully IMC joint of Cu-Sn-In/Co SLID system at 220°C for bonding time as short as 20 minutes.

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

“…Simultaneously, the low bonding temperature might not compromise the subsequent process steps, and therefore the newly formed interconnect areas should have a high remelting temperature [13], [14]. Additionally, the interconnect metallurgy must be designed such that unnecessary lithography processes and wet chemistry of device wafers can be avoided [15], [16], [17].…”

“…It has the potential to simultaneously enable hermetic sealing for MEMS and high-density, short signal path electrical interconnects for the integration of MEMS and integrated circuits (ICs) [3], [7], [18], [19], [20]. However, the process temperature of Cu-Sn SLID bonding exceeds 250 °C, and the typical procedure involves electroplating Cu and Sn on both wafers to be bonded [15], [16], [17]. Consequently, achieving optimal performance with Cu-Sn SLID interconnects in highperformance smart sensor systems requires ongoing improvements in bonding material design.…”

“…However, it is essential for further studies to design the metallization stack containing Co and to ensure the reliability of Cu-Sn-In/Co SLID interconnects. Taking this into consideration and drawing upon our previous studies [15], [40], [41], we have designed the SLID metallization stacks for Cu-Sn-In. In addition, we assessed the reliability of the Cu-Sn-In/Co SLID interconnects, using this novel SLID system, through a high-temperature storage (HTS) test, a thermal shock (TS) test, and tensile tests, comparing the results with Cu-Sn/Co SLID interconnects as a reference.…”