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HOMEDiscover MHIA Story of Innovating ChallengersRoom-temperature Wafer Bonder. Taking a Dreamlike Bonding Technology to the Forefront of ManufacturingA Tale of Development [1] How Development Began

Room-temperature Wafer Bonder. Taking a Dreamlike Bonding Technology to the Forefront of Manufacturing. Seven Supreme Engineers Who Rewrote the Book on Semiconductor Manufacturing Processes. Room-temperature bonding is a technology that enables powerful adhesion of two materials without using glue or heat. At MHI, our aspiration is to apply this almost magical technology in actual manufacturing. And thus began the story - the challenge - of a team of top engineers to develop the world's first room-temperature bonding device for industrial applications.

  • A Tale of Development
  • Introducing Products and Technologies
  1. 1. How Development Began
  2. 2. The Quest for Technological Perfection
  3. 3. Unique Support and Future Outlook

Research and Design Engineers Joined Forces to Commercialize Room-temperature Bonding and Apply it inside the Manufacturing Plant

"Room-temperature bonding" is a technology that, as its name suggests, enables two materials to stick firmly together, at normal room temperature, without use of an adhesive agent, heat or water. It takes advantage of one of the inherent properties of atoms: their predisposed quest, at all times, to bond with something. The surface of all materials is covered by an invisible oxide film, and when that film is removed, the underlying dangling bonds become exposed, which induces them to try to bond with something again. This property of atoms was first discovered when scientists were working to unravel the mystery as to why the component parts of a man-made satellite stick firmly to each other in space, and research in this field proceeded to be taken up in Japan.
At MHI's Advanced Technology Research Center, research into room-temperature bonding was undertaken jointly with the National Institute of Advanced Industrial Science and Technology (AIST)1, and working together with the Machine Tool business division R&D got under way toward commercializing this technology. This development program bore fruit in 2005 with the development of the world's first room-temperature wafer bonder for use by semiconductor device manufacturers. Here, we spoke with the seven members of the project team to learn the main features of these wafer bonders and to hear what technological challenges they faced in pursuing their development.

(Note1) Research into room-temperature bonding has been aggressively pursued for many years by the AIST as well as at The University of Tokyo.

The Development Team

Photo: The Development Team
KENSUKE IDE Deputy Chief Engineer, Project Manager of Wafer Bonder Engineering Department, Machine Tool Division. TAKAYUKI GOTO Research Manager, Advanced Technology Research Center, Technology and Innovation Headquarters. JUN UTSUMI Research Manager, Advanced Technology Research Center, Technology and Innovation Headquarters. TAKESHI TSUNO Acting manager, Advanced Technology Research Center, Technology and Innovation Headquarters. MASATO KINOUCHI Acting manager, Advanced Technology Research Center, Technology and Innovation Headquarters. KEIICHIRO TSUTSUMI Advanced Technology Research Center, Technology and Innovation Headquarters. TAKENORI SUZUKI Acting manager, Engineering Department, Machine Tool Division

How Development Began

Development of Room-temperature Wafer Bonders Resolved the Problem of Thermal Damage to Devices

A room-temperature bonder is a machine used by semiconductor device manufacturers who produce the memories, sensors and other devices built into electronic system equipment. With devices such as acceleration or pressure sensors, for example, anywhere between several thousand and several ten-thousand units are manufactured at one time on a round wafer: a semiconductor substrate 100-300 millimeters in diameter and about 0.5 millimeters thick. A wafer bonder is used to bond an encapsulation wafer onto a wafer to form a package, or to bond a wafer made of a different material in order to give the other wafer a certain function. At MHI, room-temperature technology was incorporated into such wafer bonders, resulting in the development of a new kind of machine that has completely changed the common perception of a wafer bonder in the market.


Photo: Wafer

Wafer Packaging Image.

Wafer Packaging Image. Sealing wafer, MEMS device wafer, Bond (seal), Shearing (chip formation)

"Conventional wafer bonders have all bonded one wafer to another using heat in a temperature range of 200-500 degree C," says Kensuke Ide, Deputy Chief Engineer, Project Manager of Wafer Bonder, Engineering Department of MHI's Machine Tool business Division. "But semiconductor devices are only several millimeters in size, and internally they are extremely minute in detail and complex in structure. Because of this inherent sensitivity, when bonding has been performed using a conventional wafer bonder, the heat has caused the wafers to expand or warp, resulting in defective devices and therefore lower yields."
Room-temperature wafer bonders were born from the mutually complementary aspirations of device development engineers working at manufacturers of microelectromechanical systems (MEMS)2, who sought to bond wafers without relying on heat, and engineers at MHI, who were eager to apply room-temperature bonding technology to actual manufacturing processes. "A variety of benefits result from use of a room-temperature bonder," explains Ide. "First, since wafers can be bonded at room temperature, there's no impact from heat, so device quality remains stable. Second, because there's no thermal stress, devices can be designed on even smaller scale, which means that more devices can be manufactured per wafer, which translates to cost reduction per device. Third, as there's no need for heating and cooling, production time can be reduced substantially and the technology can be applied to a wide range of materials. In fact, a room-temperature wafer bonder can be applied to nearly all materials used in semiconductors – silicon, quartz, metals, compound semiconductors, oxide single crystals and so on – so this enables considerably greater freedom in device development and design."

(Note2) Devices that include machine elements: for example, acceleration sensors, pressure sensors, inkjet printheads, gyroscopes, biodevices, etc.

Photo: interview with Ide
Photo: interview with Goto

"With a prototype bonder, it's conceivable there will be bonding errors, but with an industrial system to be used on a customer's production line, errors simply can't be allowed. Bonding has to be precisely on the mark, each and every time." So describes Takayuki Goto, Research Manager of the Advanced Technology Research Center. But outstanding precision isn't the only requirement faced by engineers developing a bonding machine: it also has to be operable automatically. "Quite an array of factors had to be incorporated into the bonder's development," he elaborates. "For example, an alignment mechanism had to be developed that's capable of lining up, with exact precision, the positions of the two wafers to be bonded. And a robot had to be provided to transfer the wafers automatically. To develop the world's first bonding machine for industrial use, we therefore called together the very best engineers in their fields - each and every one of them not only a specialist in specific technology areas such as nanoprocessing or optical devices, but also multitalented when it comes to mechanics and electronics. It was only after we assembled this collection of supremely talented players that, as a team, we were ready to begin the task of developing our product."

Designing the room-temperature wafer bonder got under way, with Ide and Goto in the leading roles, in June 2004. And thanks to the persistent and steady efforts made by each team member as well as to their collective teamwork, they succeeded in developing the world's first room-temperature wafer bonder in February 2005, i.e. within the phenomenally short span of just eight months. After that, the size of applicable wafers was expanded and a product was developed for 3-dimensional stacked devices.
Thus were born MHI's room-temperature wafer bonders - systems a world apart from those offered by other manufacturers, systems featuring numerous technologies to enhance the reliability of all devices.

Picture of Room-temperature Wafer Bonder

NEXT: The Quest for Technological Perfection
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