Operating instructions

Bond Module

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 surface activation, higher energy bonds are

formed at room temperature (even covalent) compared to the non-

activated surfaces and thus the energy required to reach the maximum

bond strength by forming covalent bonds across the entire bonded

interface is lower. As a result, the annealing temperature and annealing

time in this case are much lower than in a standard direct bonding

process. The annealing temperature for this type of process ranges

from room temperature to 400°C, depending on materials to be bonded.

The typical surface activation used for this process is a plasma

activation using an EVG®800 series plasma chamber for accurate

process control.

Typical materials used for direct wafer bonding under various process

conditions are:

- Si, silica, quartz, quartz glass (), other glasses (e.g. borofloat, BK7,

special properties glasses)

- Compound semiconductors (GaAs, InP, GaP, etc.)

- Oxide materials (LiNbO3, LiTaO3, etc.)

The general requirement of direct bonding is that surfaces have a

microroughness <0.5 nm (in some situations even higher values may be

acceptable, depending on process conditions boundaries).

Microroughness is typically defined as surface Rms measured by

Atomic Force Microscope (AFM) on 2 x 2 µm² areas across the

substrate.

144 of 370