Operating instructions

Process Description

2.7 Metal Thermo-compression Wafer bonding

Quite often people are wrongly considering that thermo-compression

and eutectic bonding are one single process. In thermo-compression

bonding process the two surfaces adhere to each other due to a metal

bond established between two metal surfaces pressed together under

heating. The bonding mechanism is enhanced by the deformation of the

two surfaces in contact in order to disrupt any intervening surface films

and enable metal-to-metal contact (fig. 7). By heating the two metal

surfaces the contact force applied for the bond process can be

minimized. High force uniformity across the bonding area results in high

yield.

Figure 14 - Metal thermo-compression wafer bonding process flow

There are several metals used for metal thermo-compression bonding,

as Au, Cu or Al. These are considered interesting for wafer bonded

MEMS applications mainly due to their availability in main

microelectronics applications. Their use for one or another type of

applications is conditioned by the type of substrates used (e.g. no Au-

containing substrates can be further processed in CMOS lines).

Typically the metals used for this process are evaporated, sputtered or

electroplated on the surface. In such process it is extremely important to

assure a proper diffusion barrier or adhesion layer between the metal

bonding layer and its substrate.

The surface microroughness of the metal bonding layers ranges from

<1nm and up to few tens of nm, depending on the metal used, on

deposition technique and on the wafer bonding process conditions.

Important:

The aim of this section of the operator manual is to offer a short overview of

the available wafer bonding processes which can be performed in EVG

permanent bonding equipment.

For detailed discussion regarding substrates or bonding layers specifications,

general process conditions or specific applications-related topics EVG

customers are advised to contact a qualified EVG process engineer.

151 of 370