Wafer Bonding Facilitates the Fabrication of Micro- & Nano-Electrical Devices

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Micro- and nano-sized electrical and electromechanical devices are everywhere, from the smartphones in our pockets to the credit card swipers in retail stores to various systems in cars and airplanes. Because these devices are so small, they require incredibly small parts—parts so small that they cannot readily be handled by human hands. Fabricating and processing the “brains” of small-scale electrical and electromechanical systems—tiny silicon wafers onto which semiconductor circuitry has been grafted—necessitates a specialized process called “wafer bonding.”

What is Wafer Bonding?

The silicon wafers in question are both very small (they’re usually some of the smallest components of products that fit in our pockets, after all) and extremely thin—they’re often measured in micrometers (millionths of a meter). They generally don’t start out so small or so thin, however, and must be cut and ground, or sanded, down to those miniscule dimensions.

Photo credit: Stratageme.com via Foter.com / CC BY-NC-SA

Photo credit: Stratageme.com via Foter.com / CC BY-NC-SA

Wafer bonding is technically a packaging process for these wafers. During wafer bonding, the wafers are coated in a special adhesive compound that protects them against damage during cutting and thinning procedures. The compound flows between the topography of the circuitry and creates a rigid, uniform, and level surface that is then adhered to glass carrier plates. The adhesive can be cured and hardened through various means, depending on the chemical makeup of the adhesive itself, including heating cycles or via exposure to UV light.

These carriers allow the wafers to be handled more easily and provide support that prevents damage caused by the pressure applied by cutting and grinding tools. The wafers remain attached to the glass carrier throughout any additional processing, such as etching or CMP (chemical-mechanical planarization).

After processing, the carrier plates are detached. In most cases, the now-tiny wafers are then peeled off the adhesive compound; some variations of the process see the compound used as a protective coating against moisture or other environmental hazards.

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