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Fundamentals of Microfabrication Technologies
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
Direct-wafer bonding or fusion bonding generally means any joining of two materials without an intermediate layer or external force, including an electrical field. In principle, most materials bond together if their surfaces are flat, smooth, and clean. The principle of this method is simple: two flat, clean, and smooth wafer surfaces are brought into contact and form a weak bonding based on physical forces (Gösele and Tong 1998; Tong and Gösele 1999). The physical forces can be van der Waals forces, capillary forces, or electrostatic forces. The wafer pair is then annealed at high temperature (in the case of hydrophilic Si at >1000°C), and the physical forces are converted to chemical bonds. In the case of silicon, high-temperature bonding falls into two categories: hydrophilic bonding, in which the bonded surfaces are silicon dioxide, and hydrophobic bonding, in which the surfaces are silicon.
Wafer-Level Three-Dimensional Integration for Advanced CMOS Systems
Published in Krzysztof Iniewski, Circuits at the Nanoscale, 2018
Ronald J. Gutmann, Jian-Qiang Lu
BEOL platforms, the focus of the remainder of this section, can be classified in many ways. Wafer bonding is either oxide-to-oxide, metal-to-metal (mostly copper-to-copper or Cu-to-Cu), or with dielectric adhesives (such as polyimides or BCB). The wafers to be bonded can be either fully interconnected (with ~ four to ten interconnect layers) or include only local interconnect (silicide, salicide, or tungsten) with extensive interconnect levels after wafer bonding. The bonding process can form the interwafer via directly such as with Cu-to-Cu bonding (via-first process flow) or wafer bonding can occur with blanket films on each wafer surface, such as bonding oxide-to-oxide or with dielectric adhesives, followed by a damascene process for interstrata interconnect (via-last process flow). A handling wafer can be used to enable a back-to-front bond with wafer thinning occurring on the handling wafer or the wafers can be directly bonded to simplify the process flow and form a face-to-face bond. These alternative process flows and the enabling unit processes are described elsewhere.
Wafer-Level Three-Dimensional ICs for Advanced CMOS Integration
Published in Rohit Sharma, Krzysztof Iniewski, Sung Kyu Lim, Design of 3D Integrated Circuits and Systems, 2018
Ronald J. Gutmann, Jian-Qiang Lu
BEOL platforms, the focus of the remainder of this section, can be classified in many ways. Wafer bonding is either oxide-to-oxide, metal-to-metal (mostly copper-to-copper or Cu-to-Cu), or with dielectric adhesives (such as polyimides or BCB). The wafers to be bonded can be either fully interconnected (with 4–10 interconnect layers) or include only a local interconnect (silicide, salicide, or tungsten) with extensive interconnect levels after wafer bonding. The bonding process can form the interwafer via directly, such as with Cu-to-Cu bonding (via-first process flow), or wafer bonding can occur with blanket films on each wafer surface, such as bonding oxide-to-oxide or with dielectric adhesives, followed by a damascene process for an interstrata interconnect (via-last process flow). A handling wafer can be used to enable a back-to-front bond, with wafer thinning occurring on the handling wafer, or the wafers can be directly bonded to simplify the process flow and form a face-to-face bond. These alternative process flows and the enabling unit processes are described elsewhere.
Room temperature direct bonding of diamond and InGaP in atmospheric air
Published in Functional Diamond, 2022
Jianbo Liang, Yuji Nakamura, Yutaka Ohno, Yasuo Shimizu, Yasuyoshi Nagai, Hongxing Wang, Naoteru Shigekawa
Diamond is attracting a wide attention as a heat spreader because of its critically high thermal conductivity of 18–22 W/cm K, which is one of the most potential materials for suppressing the rise in the device temperature [1,2]. A low-defect epitaxial growth of diamond on semiconductor substrates such as Si, GaN, Ga2O3 is difficult because of the large mismatch in the lattice constants and thermal expansion coefficients of diamond and the semiconductor substrates. GaN-on-diamond structures are being extensively studied by depositing an intermediate layer such as SiN on the backside of GaN and then depositing diamond [3–6]. However, the crystal quality of the deposited diamond is very low, which largely lowers the thermal conductivity. As an alternative technique, the wafer bonding technique allows materials with different lattice constants and thermal expansion coefficients to be seamless bonded.
Progress in wafer bonding technology towards MEMS, high-power electronics, optoelectronics, and optofluidics
Published in International Journal of Optomechatronics, 2020
Jikai Xu, Yu Du, Yanhong Tian, Chenxi Wang
Wafer bonding technology which can integrate multiple kinds of active and passive devices into a system is popular in the device packaging for the integrated circuit (IC) and micro-electro-mechanical system (MEMS).[1–6] Many bonding methods have been developed for joining homo/heterogeneous materials.[7–9] According to the intermediate layer is introduced or not during the bonding procedure, the bonding technology can be divided into two categories. The schematic illustration of categorization for wafer bonding technology is shown in Figure 1. One is intermediate-layer bonding, the other one is direct bonding. Among all kinds of intermediate layers, polymer, glass frit, eutectic alloys, and noble metals are commonly used. However, the polymer usually has the problem of gas leakage, which can not meet the strict hermetic requirements for MEMS devices. Due to the high accuracy of MEMS devices, they need better protection via the packaging to make devices work normally.[10–13] For example, the high vacuum is used to reduce the frictional resistance, while high isolation is important to prevent the signal crosstalk. Glass frit has a high bonding temperature up to 400 °C, which is harmful to the temperature-sensitive device and suspended structures. MEMS devices can be used for energy harvesting and tunable sensing, an isolated environment is very important.[14–22] Compared with polymer and glass frit, eutectic alloys and noble metals have the advantages of strong interfaces and excellent sealing ability. Therefore, they are widely used in MEMS packaging.