Ro o m -t e m p e r a t u r e Wa f e r
Bonder for Various Applications

SALES DEPARTMENT, MACHINE TOOL DIVISION

Fully automatic wafer bonder

There is an increasing demand for wafer-level packaging of micro electro mechanical systems (MEMS). Our equipment is the
only industrial-level equipment capable of bonding wafers at room temperature. Because of the high-quality bonding results, it isalready used in the manufacture of various devices.

1. Principles and characteristics of room-temperaturebonding

2. Product specifications
Mitsubishi Heavy Industries, Ltd. (MHI) can provide twomodels of room-temperature wafer bonders. The first is asemiautomatic model suitable for research and development
purposes or the trial production of devices. The second is afully automatic model suitable for mass production of devices.
The semiautomatic model (Fig. 1) bonds one set of wafers(one top and one bottom wafer) semiautomatically under thecontrol of the operator, enabling flexible operation. The fully
automatic model, shown in the photograph next to the title, canconsecutively and automatically bond 25 sets of wafers (25 topand bottom wafers in total) in cassette-to-cassette operation,resulting in increased productivity. Table 1 shows the general
specifications of these models.
Both models have all the components necessar y forbonding, including a wafer transfer unit and high accuracyalignment unit (bonded wafer positioning unit), and both offer
low-cost performance. The equipment has been designed withfull consideration of operability and maintainability.

Room-temperature bonding is a technology for bonding
activated surfaces by removing an oxide film and absorbed
substance on the bonded surface (wafer surface) under highvacuum conditions by means of ion irradiation. This process
has the following features:(1) Since the process requires no heating, neither thermal
stress nor bonding strain is generated. This solves theproblem of reduced yield rate caused by the differencein the coefficients of thermal expansion of the bondedmaterials.
(2) The process can produce a bonding strength comparable
to that of the base material.
(3) High throughput is possible because there is no requirement
for a heating/cooling cycle.
(4) The process is applicable to a wide range of materials
including silicon, silicon oxide, metals, oxide single
crystals, and compound semiconductors. Heterogeneous
bonding is also possible.

Table 1 General specifications
Semiautomatic model

Fully automatic model

Applications

Research and development
or trial device manufacture

Mass-production of devices

Process

Semiautomatic operationfor 1 set (2 wafers) each

Cassette-to-cassette
operation for 25 sets(50 wafers)*The bonding conditions
can be assigned for each set.

Wafer diameter4 or 6 inches (selectable)

Applicable toSilicon, silicon oxide, metals, oxide single crystal,compound semiconductors

Automation Transfer Semiautomaticlevel
Alignment ManualFig. 1 Semiautomatic wafer bonder

Degree of vacuum

Automatic
Automatic

10-6 Pa (process chamber)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)

45

Oxide single crystal (lithium niobate)wafer (3 inches)

Sealing wafer

Silicon wafer (4 inches)

Devicewafer
Sealing wafer
Bonding of 3 wafers

4 inches

Fig. 2 Example of wafer-level MEMS packaging(acceleration sensor)
With the cooperation of MEMS Core Corporation.

TSV
Bonded interface
AI50 mFig. 5 Example of heterogeneous bonding(oxide single crystal and silicon)

Bondedsections

Gallium arsenide wafer (2 inches)

Fig. 3 Example and schematic drawing of through-silicon via(TSV) bonding for three-dimensional stacked devices

Base material failed on substrate

Tension test jig

Fig. 4 Bonding of metal film (gold) to metal film
Base material failure was verified by a tension test.

Fig. 6 Example of compound semiconductor bonding

high frequency devices for cell phones on oxide single crystals(Fig. 5), and various light-emitting diodes for compound
semiconductors (Fig. 6). Furthermore, as well as supplying
the equipment, MHI also offers process support for trial
production of client devices using room temperature bonding.
MHI is dedicated to the manufacture of new devices in terms ofboth equipment and process support.

3. Application areas
The primary feature of this equipment is the ability toperform high-quality bonding of a wide range of bonding
materials. The application areas cover a wide range, including
MEMS wafer-level packaging for silicon and silicon oxide (Fig. 2),
electrode bonding of three-dimensional stacked devices formetals (Fig. 3), bonding between two metal films (Fig. 4),

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 45 No. 3 (Sep. 2008)46