Low-Temperature PETEOS-to-PETEOS Wafer Bonding Using Titanium as Bonding Intermediate
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0914-F03-15
Low-Temperature PETEOS-to-PETEOS Wafer Bonding Using Titanium as Bonding Intermediate Jian Yu1, Richard L. Moore2, Sang Hwui Lee1, J. Jay McMahon1, Jian-Qiang Lu1, and Ronald J. Gutmann1 1 Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, NY, 12180 2 College of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, NY, 12203 Abstract Bonding of pre-processed silicon wafers at back-end-of-the-line (BEOL) compatible conditions is one of the attractive approaches for three-dimensional (3D) integration. Among various technologies being evaluated, bonding of low temperature oxides (e.g., plasma-enhanced tetraethylorthosilicate (PETEOS)) is of great interest. In this work, we report low-temperature PETEOS-to-PETEOS wafer bonding, using a thin layer of titanium (Ti) as bonding intermediate. The bonding strength is evaluated qualitatively, while the bonding interface is examined by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). Preliminary results of PETEOS/Ti/PETEOS bonding on patterned wafers with single-level Cu damascene structures are also discussed. INTRODUCTION Wafer-level monolithic three-dimensional (3D) integration holds great promise to enhance performance and functionality while reducing form-factor and manufacturing cost for future generation integrated circuits (ICs). In this approach, functional components are fabricated on separate wafers, followed by face-to-face alignment, bonding at back-end-of-the-line (BEOL) compatible conditions, backside thinning and vertical inter-wafer interconnection [1-3]. Since post-metallization Si device wafers are often encapsulated in passivation films formed at low temperatures (e.g., plasma-enhanced tetraethylorthosilicate (PETEOS)), bonding of those low temperature oxides (LTO) is of great interest [2-6]. Two common methods for LTO deposition are low-pressure-chemical-vapor-deposition (LPCVD) and plasma-enhanced-CVD (PECVD). Compared to thermally grown oxide (SiO2), those CVD oxides are usually porous, with trapped air, gaseous byproducts and hydrocarbon species incorporated; therefore, severe bubble formation is often observed at the interface after bonding of CVD oxides [2, 5]. The conventional oxide wafer bonding involves an initial spontaneous attraction between two hydrophilic mating surfaces covered with hydroxyl groups (-OH), and a subsequent hightemperature anneal (up to 1000°C) to form covalent bonds via siloxane groups (Si-O-Si) [7]. To lower the bonding temperature, various surface modifications (e.g., plasma activation [6] and chemical mechanical polishing (CMP) [3-5]) have been investigated prior to bonding of LTO. In this work, we explore the feasibility of BEOL-compatible PETEOS-to-PETEOS wafer bonding, assisted with a thin layer of titanium (Ti) as bonding intermediate. Ti is known to have excellent adhesion with SiO2 [8-9] and effective gettering of oxygen and nitrogen [10]. In addition, Ti is an IC-compatible material commonly used in very-large-scale-integration (VLSI) fabric
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