10. September 2021, 11:15 Uhr | Heinz Arnold
This is how the Micro Transfer Printing (MPT) process works, which X-Fab has licensed from X-Celeprint and integrated into its own manufacturing environment.
X-Fab now offers the possibility to combine different semiconductor technologies in one chip via Micro-Transfer-Printing and to manufacture them in high volumes.
To this end, X-Fab has signed a licensing agreement with X-Celeprint, which has developed the micro transfer printing (MTP) process. With the help of MPT, dies produced by different processes can be combined on one wafer and then processed together as one device. This method is known as heterogeneous integration or chiplets. These include, for example, SOI, GaN, GaAs and InP components, as well as MEMS. Both companies had collaborated in the EU project "Pilot Line for Micro-Transfer-Printing of Functional Components on Wafer Level" (MICROPRINCE), launched in 2017 and coordinated by X-FAB.
To include MPT-based Heterogeneous Integration in its foundry service offering, X-FAB has made significant investments over the past five years, purchasing new machines and introducing new workflows and cleanroom protocols. Now, customers can benefit from being able to use the scalable process for heterogeneous integration at low risk - all the way up to high-volume manufacturing. "We have brought the process to mass production and can now process thousands of wafers at a yield of over 95 percent while maintaining the quality we stand for," said Volker Herbig, VP of X-Fab's MEMS business unit. The first customers are already using the process, he adds.
An example of an MPT process as developed by X-FAB based on the license from X-Celeprint: It starts with a wafer containing CMOS drive ICs. A partner company supplies wafers with GaN switches (power transistors). With the help of a stamp, 7 to 8 µm thin GaN switches can be taken from this source wafer and placed four at a time on a CMOS IC on the target wafer for a bridge circuit. This process is called transfer printing. Hundreds or thousands of GaN switches can be printed on the CMOS ICs per step. Therefore, this process only needs to be repeated ten to twenty times to place chiplets on all the CMOS ICs in a full 200-mm wafer - that's of many thousands or tens of thousands of components. "So it's a massively parallel process," Herbig explains. "In the future, we'll try to do as many steps as possible at the wafer level."
However, X-FAB can also expose the ICs on the wafers it produces itself to prepare the wafer for removal and transfer printing. Third-party companies can then remove the ICs from the wafer assembly and place them on panels for further panel-level processing. X-FAB itself works exclusively at the wafer level.
In general, X-Celeprint's MPT process allows 7 to 18 µm thin dies to be printed from a source wafer onto the target wafer using completely different process technologies. Externally, these combined chips behave almost like monolithically integrated ICs. Because each die is fabricated using the optimal process technology, the chips can achieve higher overall performance and lower power consumption than is possible with current methods. They also take up less space and development to production readiness is faster, significantly shortening time-to-market.
"Based on X-Celeprint's breakthrough MPT technology, we are now in the unique position of being able to combine different semiconductor technologies. And we can offer capacities that will definitely cover customers' future needs," says a delighted Volker Herbig. "Now X-FAB customers can have complete, highly complex subsystems manufactured at wafer level." Functions that can be combined include signal conditioning, power semiconductors, RF components, MEMS, CMOS sensors, optoelectronic components and optical filters.
As a next step, X-Fab plans to "print" photonic ICs based on MPT. "Here the big challenge is the precise alignment of the various components, so some development work is still needed," Herbig said.
Kyle Benkendorfer, CEO of X-Celeprint, sees the licensing agreement with X-FAB as a milestone in commercializing MPT technology: "Now dies from wafers from different manufacturers can be combined in one package. This opens up new possibilities for the entire semiconductor industry to produce chips with higher functional density and performance than before - and with high yield, at lower cost and in shorter times."