Temporary Wafer Bonding and Debonding

Temporary wafer bonding fixes a device wafer to a carrier with an adhesive, so it can be thinned and processed on the back side without breaking. Once that work is done, the pair is debonded and the device wafer carries on to dicing and packaging. SiSTEM supplies the Cost Effective Equipment range for both steps, the Apogee Temporary Wafer Bonder and two Apogee debonders, to research labs and production lines across the UK and Europe.

Why wafers are bonded to a carrier

Below about 100 µm a wafer is too thin to handle on its own. It bows and cracks easily, and a vacuum chuck can’t hold it flat. Bonded to a rigid carrier such as silicon or glass, it behaves like a full-thickness wafer through grinding, polishing, etching, metallisation and through-silicon via formation. Temporary bonding is routine in compound semiconductor manufacturing, where SiC, GaN, GaAs and InP wafers are thinned for power and RF devices, and in MEMS and 3D integration.

How temporary bonding works

An adhesive, typically a wax or a thermoplastic, is coated onto the device wafer or the carrier. The two wafers are aligned and pressed together under heat and vacuum, and the adhesive fills the gap between them. The bonded pair then goes through its downstream steps as one substrate. Finally a debonder separates the pair, the adhesive residue is cleaned off, and the thinned device wafer continues on a film frame or carrier.

What makes a good bond

A few things decide whether the bonded pair survives thinning and releases cleanly afterwards.

Voids. Air trapped in the bond line leaves an unsupported spot that can crack during grinding. Bonding in vacuum, with the wafers kept apart until the air is out, prevents it.

Flatness and total thickness variation. Any variation in the bond line thickness shows up in the thinned wafer. Platens that level against each other and even force across the wafer keep it low.

Temperature. The adhesive has to reach its flow temperature evenly across the wafer. Heating both platens keeps the device wafer and the carrier at the same temperature.

Force. Too little leaves gaps in the bond line, and too much can damage a fragile substrate. It needs to be set per recipe for each adhesive and wafer size.

The carrier and adhesive also need to match the device wafer’s thermal expansion closely enough to survive any hot steps downstream without bowing or delaminating.

Choosing a debonding method

The adhesive mostly decides the debonding route. Waxes and thermoplastics soften with heat, so the pair can be heated and slid apart. Adhesives chosen to survive high temperatures, or devices that can’t take heat, suit a mechanical peel at room temperature. Some adhesive systems release in solvent instead, and CEE’s tools cover the thermal and mechanical routes. If you’re not sure which fits your stack, tell us the adhesive and wafer sizes and we’ll check the process with CEE.

Temporary bonding and debonding tools from CEE

Apogee Temporary Wafer Bonder. The bonder takes substrates from 2″ to 300 mm and works with a wide range of temporary adhesives on SiC, GaN, GaAs, InP, sapphire, silicon and glass. Separator flags hold the carrier above the device wafer while the chamber pumps down, and the carrier only settles once the air is out, which keeps voids out of the bond line. Both platens are heated to 300°C with independent control and level themselves against each other. Bond force runs from 550 to 12,000 N, and DataStream logs every bond cycle.

Apogee Thermal Slide Debonder. For wax and thermoplastic adhesives, the thermal slide debonder heats the bonded pair between two platens and holds the device wafer on the upper platen by vacuum. The lower platen then slides the carrier away at a programmed force and speed. It takes substrates from 2″ to 200 mm and runs the debond automatically, so every wafer sees the same recipe. The device wafer comes out on a Gel-Pak. It replaces CEE’s earlier 1300CSX slide debonder.

Apogee Mechanical Debonder. The mechanical debonder peels the carrier away at room temperature, with the device wafer held on tape in a film frame throughout. It suits devices with a low thermal budget and adhesives built to survive high-temperature processing, and it uses no solvents. It takes substrates from 50 mm to 200 mm with peel force set by recipe from 1 to 75 N, at up to 20 wafers an hour.

All three are CE marked, and CEE builds them in the United States. CEE bond and debond tools are already part of compound semiconductor production in the UK and Europe.

Temporary bonding and debonding questions

What is temporary wafer bonding?
Bonding a device wafer to a carrier with an adhesive that can be released later, so a wafer too thin to handle alone can be thinned and processed on the back side.

What is thermal slide debonding?
Heating a bonded pair until a wax or thermoplastic adhesive softens, then sliding the carrier off the device wafer at a controlled force and speed.

Which wafer materials can be bonded?
CEE’s tools are qualified on SiC, GaN, GaAs, InP, sapphire, silicon and glass, among others. Send us your stack and we’ll confirm it with CEE.

Can one bonder serve two debonders?
Yes. The bonder works with both debonders, so a line can run wax or thermoplastic bonds through the thermal slide debonder and high-temperature adhesives through the mechanical debonder.

Buying through SiSTEM

SiSTEM quotes and supplies CEE’s bond and debond tools across the UK and Europe and handles the warranty in territory. If a tool goes down, we stay on the fault with the manufacturer until you confirm it’s working properly again. Get a quote, or contact us with your adhesive and wafer sizes to talk through your process.