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Jul 16th, 2014
 
2.5/3DIC laser assisted debonding: a closer look
 
2.5/3D practitioners continue to search for the best solution to temporary bonding and debonding. All agree that rapid throughput and room temperature debonding are requirements for a low cost, commercial solution. During the last 12 months focus has shifted to laser assisted debonding solutions.
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The first company to introduce laser assisted debonding was  3M whose WSS (wafer support system) process has been described in detail previously [see “New temporary bonding solutions revealed at SUSS 3D Workshop”].

HD Micro has also developed a process based on their 3000 series polyimide  [ see, Itabashi & Zussman, Proceed. 60th IEEE ECTC, p. 1877-80].

At the recent Suss workshop at Semicon West the temporary bonding focus continued to be on laser assisted debonding.

Suss’s Stephan Luetter discussed their temporary bonding program. The Suss open platform program supports 10 materials suppliers and 4 laser assisted RT debonding processes (including Brewer, Dow and DuPont) .

SUSS laser assisted debond module


Suss compares the various temp bonding technologies below. The only downside for the laser debonding  is the requirement for a  glass carrier wafer to allow transmission of the laser light.

Suss assessment of various debonding technologies

The EDL300 is their eximer laser debond module which rasters the wafer with a 12x 4mm laser beam. Carrier is lifted of with a vacuum gripper with close to zero mechanical lift-off force. Suss has concluded that the new materials and simpler process flows allow cost of equipment reduction in the range of 1.5-3X.

Kim Arnold, program director for 3D system integration for Brewer Science, introduced their 3rd generation temporary bonding solution BrewerBondTM which makes use of the laser assisted room temperature debond process.  Brewer who has been supporting the 3DIC infrastructure for a decade has introduced several product families to meet their customer needs. Each generation has increased throughput and thermal stability, better allowing backside processing at higher temperatures.

Brewer has supplied 3 Generations of temporary bonding materials

Similar to previous processes, a light sensitive layer is decomposed during debonding with a 308nm excimer laser.

Gen 3 “BrewerBond” temporary adhesive process


Arnold indicated that development of a gen 4 product with higher throughput and higher thermal stability is underway.


Mark Oliver of Dow Chemical discussed their laser bond release adhesive and process. The Dow temporary adhesive shows excellent thermal stability at 300 C as shown by its isothermal weight loss.

Thermal stability of Dow temporary adhesive

Laser debonding  at 308nm is shown below. The adhesive ends up on the device wafer side and is removed with a simple tape peel.

 Laser assisted debonding with Dow temporary adhesive

All of these processes require the use of glass carrier wafers since laser light can penetrate glass but not silicon. At the  recent 16th symposium on Polymers for Microelectronics, Kai Zoschke of Fraunhoffer IZM pointed out that laser transmission requires both the proper glass  and the proper frequency laser.

Laser assisted debonding requires the correct glass / laser frequency combination

Temporary Bonding has recently been examined in detail ( > 50 ppg) by authors from Brewer, Suss, EVG, TOK, 3M and RTI in the newly released Wiley-VCH “Handbook of 3D Integration,  Volume 3: 3D Process Technology” Edited by P. Garrou, M. Koyanagi and P. Ramm.

 

 
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