Operating instructions

Process Description

2 Process Description

The following chapters describe processes that can be performed on

EV Group wafer bonding equipment.

2.1 Direct Wafer Bonding

This is a wafer bonding method in which the adhesion between two

surfaces occurs as a result of chemical bonds established between

molecules from the two surfaces. Typically the adhesion is weak at

room temperature (mediated by Van der Waals forces) and maximum

bond strength is reached by transforming the weak bonds into covalent

bonds through a high temperature thermal annealing (process flow

shown in fig. 1).

Figure 8 - Direct wafer bonding process flow

For Si-Si direct bonding the annealing temperature is >600°C for

hydrophobic bonding (SiO2 removed from Si prior bonding by 1-2% HF)

or >900°C for hydrophilic bonding (with native, thermally grown or

deposited oxides). After correct thermal annealing the bond strength

reaches same range as Si bulk fracture strength.

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