Investigations of thermocompression bonding with thin metal layers

Abstract

In this study we successfully bonded silicon wafer substrates with metal based thermocompression technology. This technology has the advantage of inherent possibility of hermetic sealing and electrical contact. We used three different kinds of metals: gold, copper and aluminum. We will show the hermeticity, bonding strength and reliability of the different processes and compare the results

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

“…Various metal-based wafer-level hermetic packaging methods have been proposed, including solder bonding [11]- [14], eutectic bonding [15]- [18], solid-liquid inter-diffusion (SLID) bonding [13], [19], [20], surface activated bonding (SAB) [21], and thermo-compression bonding [22]- [27]. All these technologies have individual advantages and disadvantages.…”

“…• C [22]- [27], [31] and high bonding pressures, and has been demonstrated with metals such as gold (Au) [22]- [24], aluminum (Al) [25], [26], and copper (Cu) [27], [31]. However, low bonding temperatures during vacuum packaging are desired to avoid thermally induced damages of MEMS devices and CMOS circuits.…”

AlAl thermocompression bonding for wafer-level MEMS sealing

“…Thermocompression bonding using deposited metal films as bonding material is promising for wafer-level encapsulation. Metals such as Au [3,4], Cu [4,5] and Al [4,[6][7][8][9] have been demonstrated as bonding layer between two silicon wafers. Bonding with an intermediate metallic layer is an attractive choice for MEMS devices.…”

“…In thermocompression bonding, metallic bonds are formed between metal deposited substrates by bringing them into intimate contact and simultaneously applying temperature and pressure [4]. The applied pressure must be high enough to bring the surfaces into atomic contact despite any surface roughness.…”

Low-Temperature Aluminum-Aluminum Wafer Bonding

“…As a calculation shows (4), the elastic energy is too low to influence the bonding between atoms directly, but the applied stress and the resulting strain breaks up the surface layer. The wafers are bonded at high temperatures, usually in the range of 400°C to 550°C (1)(2)(3)(5)(6)(7). In recent experiments, Malik et al were able to reduce the required bonding temperature to about 300°C by depositing the Al metallization layer onto an intermediate SiO2 layer (3).…”