# Presentation: 860109

## Materials Integration of III-V Compounds for Electronic Device Applications	 

- The funding for this project has provided us with the means to understand the basic materials issues associated with wafer bonding and layer transfer.  This research enables advancements in the performance of III-V semiconductor devices through the development of wafer bonded template substrates – those with high resistivity and with an appropriate lattice constant for large lattice parameter materials, and with compatible thermal expansion coefficients.

***GOALI – DMR -0408715  ***

***Mark Goorsky, PI  ***

- Representative schematic of wafer transfer process.  a) wafers are coated with silicon nitride; b) transfer wafer is implanted with hydrogen to facilitate exfoliation; c) Nitride surfaces are treated to increase bond strength, bonded at room temperature, and annealed to increase bond strength.  The structure can then be heated to higher temperature to cause exfoliation, otherwise, etching and polishing can reduce thickness of the InP (or any layer from a substrate or graded buffer layer to be transferred).

- Flow chart showing experimental sequences conducted during this research program.  The color-coded arrows represent each technology.  For example, InAs on InP structures will be subjected to annealing, MBE (InAs and pHEMT) and MOCVD (InAs and InAlAs layer deposition)

## Materials Integration of III-V Compounds for Electronic Device Applications	 

-  Our publications and continuing research have elucidated key materials issues in the transfer, adhesion mechanisms, chemical-mechanical polishing and thermal stability of III-V semiconductor layers.  With this knowledge, we have pioneered the use of layer transfer via hydrogen implantation for a variety of III-V (and IV and II-VI) materials.  The broader impact of these advances is now being implemented in on-going SBIR and STTR collaborations.

***GOALI – DMR -0408715  ***

***Mark Goorsky, PI  ***

- Our transferred InP layers on SiN / GaAs substrates are suitable for MOVPE growth of quantum well (QW) structures as demonstrated with the cross-section TEM image.

- PL (and HRXRD) confirms that the QW structures exhibit comparably strong luminescence and high structural quality as those grown on standard InP substrates and IR transmission measurements confirm that large areas of 3” wafers are successfully bonded.

- X-ray reflectivity measurements proved an important technique to assess the interfacial bonding mechanisms and high resolution x-ray diffraction represents an ideal means to monitor the exfoliation process in all semiconductor materials.

- Our most recent efforts have extended this technology to InAs layer transfer and the transfer of In0.9Al0.1As graded buffer layers to InP substrates. These achievements resulted from a better understanding of how the hydrogen exfoliation process depends on the mechanical and thermal properties of the host material, the hydrogen gettering effect of strained regions and on the diffusivity of hydrogen within the host material. The AFM images on the right show InAs transferred from a bulk substrate and from a graded buffer layer prior to the CMP step.

**Notes:**
The funding for this project has provided us with the means to understand the basic materials issues associated with wafer bonding and layer transfer of semiconductors layers. For a variety of III-V applications, conventional epitaxial techniques are not adequate due to large lattice mismatch.  However, wafer bonding offers a suitable alternative. Wafer bonding may be used to integrate high quality materials without the restraints of epitaxy.  Additionally, hydrogen ion implantation and exfoliation techniques can be used to separate a thin, uniform, high quality layer from the bulk.  In this process a high dose (~1016 – 1017 cm-2) of hydrogen is implanted into the substrate, and upon subsequent annealing, hydrogen platelets form at in the implanted region and coalesce to induce exfoliation of a thin layer.  The bulk of the substrate is virtually unaffected and may be recycled to produce multiple exfoliation layers. 

The transferred layer requires chemical-mechanical polishing to reduce the roughness and we have developed CMP to promote low removal rates and no detectable levels   of polishing damage.  Our transferred structures are stable to temperatures as high as 800 °C and can withstand the MOVPE growth environment (provided by R. Hicks in Chime at UCLA). Our collaboration with NGST has been very fruitful for both processing expertise and the opportunities for our students to work in an advanced development and manufacturing facility.  The publications and invited talks that stemmed from this funded project brought these ideas to the wider scientific community.  Based on knowledge gained from this NSF: GOALI grant, we have agreed to collaborate with two different small companies to develop the exfoliation techniques for II-VI materials (UES – MeV implantation for CdZnTe) and GaAs (Srico – Orientation patterned GaAs for non-linear optics applications).

The funding for this project has provided us with the means to understand the basic materials issues associated with wafer bonding and layer transfer such that we now have the capability to transfer layers of everything from GaN to InSb and to bond both dielectric and bare semiconductor surfaces.

## Educational and Outreach Activities
In conjunction with the Center for Excellence in Engineering and Diversity at UCLA, we have sponsored undergraduate students to gain research experience in our laboratories.  In addition, we have, through CEED, participated in outreach programs through Science and Engineering Days at UCLA.  Our demonstrations examining wafer bonding by comparing wafers bonded together in the open air and those bonded within a PMMA “bonding box” provides students with insight into several components of science and engineering:  The strength of van der Waals bonds is surprisingly high to the students and discussion of the flatness of the semiconductor wafers helps them appreciate the state-of-the-art in semiconductor processing technology. 

Our efforts have continued with the American Indian Science and Engineering Society.  In these demonstrations to high school students from throughout the southwest, we demonstrate the issues of thermal expansion coefficients by examining the strength of bonded materials (using adhesives and bonded wafers) at both low (cryogenic) and high temperatures.  

- In conjunction with the Center for Excellence in Engineering and Diversity at UCLA, we have sponsored undergraduate students to gain research experience in our laboratories.  In addition, we have, through CEED, participated in outreach programs through Science and Engineering Days at UCLA.  Our demonstrations examining wafer bonding by comparing wafers bonded together in the open air and those bonded within a PMMA “bonding box” provides students with insight into several components of science and engineering:  The strength of van der Waals bonds is surprisingly high to the students and discussion of the flatness of the semiconductor wafers helps them appreciate the state-of-the-art in semiconductor processing technology.
- Our efforts have continued with the American Indian Science and Engineering Society.  In these demonstrations to high school students from throughout the southwest, we demonstrate the issues of thermal expansion coefficients by examining the strength of bonded materials (using adhesives and bonded wafers) at both low (cryogenic) and high temperatures.

***Materials Integration of III-V Compounds for Electronic Device Applications******	****** ***

***GOALI – DMR -0408715  ***

***Mark Goorsky, PI  ***