Wafer Level Hermetic Bonding Using Sn/In and Cu/Ti/Au Metallization

Abstract

temperature storage, we introduced a thin buffer layer into the A low temperature hermetic wafer bonding using In/Sn under bump metallization (UBM). The buffer layer plays two interlayer and Cu/Ti/Au metallization was investigated for roles. Firstly it is used to prevent diffusion during materials MEMS and sensor packaging application. Bonding was evaporation, room temperature storage, and at the initial stage performed in a vacuum wafer bonder at 1800C and 1500C for of bonding between SnIn and Cu, which will allow the solder 20min under 5.5MPa. It is found that bonding at 1800C, voids materials on each die has chance to wet the metallization and free joints composed of high temperature intermetallic to form a good seal. Then, since buffer layer is thinner, it can compounds (IMCs) were obtained with good hermeticity and be dissolved or broken out, which allow the diffusion reliability. However, bonding at 1500C, voids were generated happened between solder and high temperature component to along the seal joint which caused poor hermeticity comparing form IMCs. with that bonded at 1800C. After four kinds of reliability tests, By introducing thin Ni buffer layer, we have successfully i. e., Pressure cooker test, high humidity storage, high achieved high yield hermetic wafer level bonding using In/Sn temperature storage, temperature cycling test, dies bonded at with respect to Cu metallization system at 1800C. In this case, 1800C showed good reliability properties by hermeticity test Ni was resolved into solder alloy and was incorporated into and shear tests. Present results proved that high yield and low CuSnIn high temperature compounds [9-10]. From the point temperature hermetic bonding can be achieved by using of view of reliability, we would like to get a thinner IMC Sn/In/Cu metallization with thin Ti as a buffer layer.layers. Then a more effective buffer layer is preferred. In Introduction addition, since thin Au layer is employed upon the solder surface to prevent oxidation, AuIn phase is formed inside Low temperature fluxless solder bonding process is a CuSnIn IMCs during bonding. We hope the buffer layer can promising MEMS packaging technology demanded by promisng MES pacagingtechnlogy emandd by mprove the adhesion between different IMCs. It iS known that industrial users because it offers comparative advantages such imrvthadeonbwenifrntIC.tiskwnht Ti has a good wetting property with various solders and at the as low residual stress [1-2]. Wafer level bonding is a cost-same time, it is a more effective barrier layer comparing with effective method for MEMS packaging. Low-cost vacuum Ni to these solders [11]. Further, it is difficult to be resolved packaging of MEMS has become one of the most important into liquid Sn-In solder. The effect of such kind of buffer layer challenges [1][2]. For eutectic wafer bonding, researchers have '~~~on the wafer level bonding needs to be studied and investigated several systems of low temperature solders and understood. In present research, we try to use Ti as a buffer hig...

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

“…At room temperature, the stable phases in Cu-In binary system are Cu, , and In. Based on the previous experimental results and the Cu-In binary phase diagram, various IMCs (Cu7In3 (δ), Cu2In (η), Cu11In9, CuIn2, Cu16In9, and CuIn ) can appear during bonding [2], [3], [10]- [13], [16], [17], and phase transformation can occur during aging. Voids with different sizes appear after aging due to the volume shrinkage between different phases [15].…”

“…Combining two binary systems to a ternary or higher order SLID systems can benefit wafer-level packaging of MEMS/MOEMS devices such as lower bonding temperature, and better physical properties for higher functional performance and long-term reliability [1]. The ternary Cu-Sn-In system establishes a promising low-temperature bonding system as the eutectic temperature of Sn-In is almost 40° below the melting point of In [1], [13]. Utilizing low-melting temperature Sn-In (either alloy or layered structure) for SLID systems instead of using pure Sn or In offers several advantages: 1) a higher solubility of the HT metal (Cu) into the LT liquid phase (which is a critical parameter in reaction kinetics), 2) lower bonding temperature, 3) higher re-melting temperature, 4) decreasing the complexity of the IMCs form in the bond area compared to Cu-In, and 5) stabilizing Cu6Sn5 and hindering the Cu3Sn phase formation (which is followed by void formation) [1].…”

“…Various studies have investigated the microstructural evolution and bond reliability of the Cu-Sn-In system. D-Q Yu [13] et al obtained a reliable bond (analyzed by hermeticity and shear tests) via Cu-Sn-In wafer-level bonding at 180°C. According to V. Vuo-rinen [2], Cu-Sn-In SLID bonding, even at a low bonding temperature of 170 °C for one hour, can show high strength bonds with low defect content.…”

Development of 3D Wafer Level Hermetic Packaging with Through Glass Vias (TGVs) and Transient Liquid Phase Bonding Technology for RF Filter

“…TLP bonding provides a low bonding temperature and a higher remelting temperature, beneficial for RF or MEMS device packaging. Some research groups have demonstrated TLP wafer-level bonding using Cu-Sn, Au-Sn, and Cu-Sn-In material systems [ 9 , 16 , 17 , 18 ]. The Au-Sn material system provides low-cost TLP bonding, widely applied in electronic encapsulation.…”