Ion bonding glass1/28/2024 This is a wafer bonding process which uses as bonding layer an eutectic alloy formed during bond process.This process is very reliable and is used in high volume production by major MEMS devices manufacturers for applications where low vacuum encapsulation is required.Glass frit material can be deposited by screen printing or used as glass preformed sheets.Glass frit bonding has a high tolerance to surface roughness and can incorporate high topography of the substrates.The bond occurs by heating the substrates with applied contact force (fig.This type of bond is using as intermediate layer for bonding a low melting point glass.The main advantages of using this approach are: low temperature processing (maximum temperatures below 400☌), surface planarization and tolerance to particles (the intermediate layer can incorporate particles with the diameter in the layer thickness range).The choice of the material for intermediate layer is always made considering the substrate materials and topography.Polymers, spin-on glasses, resists and polyimides are some of the materials suitable for use as intermediate layers for bonding.Adhesive wafer bonding is a technique using an intermediate layer for bonding.In terms of equipment, it is important for the bond chamber to provide good temperature uniformity and ensure good electrical contacts.The resulting bond strength is very high and the process is irreversible. Oxygen ions are driven by the electric field to the silicon surface and produce oxidation of Si. At a certain temperature (depending on the glass composition), oxides dissociate and the mobile alkali ions are driven by the electric field into the glass, creating an oxygen rich layer at the silicon-glass interface. ![]() The bond occurs when the two wafers are heated after being brought in contact and an electric field is applied.The glass materials mostly used for anodic bonding are Borofloat from Schott Glass - Germany, and Pyrex7740 from Corning Inc., USA. ![]() Initially reported for joining a metal surface to a glass surface, the term “anodic bonding” is used today mainly to identify the bonding of silicon wafers to glass wafers with high content of alkali oxides (fig.Microroughness is typically defined as surface Rms measured by Atomic Force Microscope (AFM) on 2 x 2 μm² areas across the substrate.The general requirement of direct bonding is that surfaces have a microroughness Compound semiconductors (GaAs, InP, GaP, etc.).borofloat, BK7, special properties glasses) Si, silica, quartz, quartz glass, other glasses (e.g.Typical materials used for direct wafer bonding under various process conditions are:.The typical surface activation used for this process is a plasma activation using an EVG®800 series plasma chamber for accurate process control. The annealing temperature for this type of process ranges from room temperature to 400☌, depending on materials to be bonded. As a result, the annealing temperature and annealing time in this case are much lower than in a standard direct bonding process.After surface activation, higher energy bonds are formed at room temperature (even covalent) compared to the nonactivated surfaces and thus the energy required to reach the maximum bond strength by forming covalent bonds across the entire bonded interface is lower.Surface activated wafer bonding is also a direct bonding method which uses a special surface preparation process (surface activation) in order to change and control the bonding mechanism by controlling the surface chemistry.After correct thermal annealing, the bond strength reaches the same range as Si bulk fracture strength. For Si-Si direct bonding, the annealing temperature is >600☌ for hydrophobic bonding (SiO2 removed from Si prior bonding by 1-2% HF) or >900☌ for hydrophilic bonding (with native, thermally grown or deposited oxides). ![]()
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