By Dr. Phil Garrou, Contributing Editor

IFTLE has extensively discussed the applicability of the Ziptonix technologies (acquired and now owned by Xperi): ZiBond (oxide-oxide bonding) and DBI (copper-oxide to copper-oxide “hybrid bonding”) [for example see IFTLE 303, “Sony Introduces Ziptronix DBI Technology in Samsung Galaxy S7” and refs therein]

These technologies have now been commercialized in areas such as COS image sensors, Rf and MEMS. These are all wafer to wafer bonding applications. As of yet, a die-to-wafer process has not been developed for manufacturing, imposing W2W limitations such as the requirement that die sizes match and yields are high.

At the recent IMAPS Device Pkging Conf in March, Wang of Xperi discussed the “Design, characterization and testing of large area and high density 3D direct bond interconnect which discussed development of such a die to wafer technology.

DBI’s key attribute is the formation of electrical interconnects at low temperatures and pressures as shown below:

The technology requires highly polished (CMP’ed) surfaces (less than 1nm deviation across wafer surface topology is typical) .

The Xperi goal was expressed as developing a process for HBM memory stacks by stacking 4 double sided DBI memory die with the following attributes:

– throughput – 3000uph                       – no underfill

– no solder                                             – stack consecutively then batch anneal

For die to wafer bonding they followed he following process sequence:

The design that was evaluated for a HBM stack contained 10um pads on 40um pitch.

D2W vs W2W electrical test for their test vehicle is shown below:

Die to wafer reliability for a 31K daisy chain are shown below:

It will be interesting to see whether this data will extrapolate to the fabrication of real HBM die stack in the future.

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