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Keynote Speakers

Oct. 5th

Hong-Xing Wang

Xi’an Jiaotong University, China
Professor of Institute of Wide Bandgap Semiconductors

Progress of diamond substrate development

Diamond has many excellent properties, such as wide bandgap, high carrier mobility, high breakdown voltage, high thermal conductivity, superior mechanical strength, and chemical stability among the well-known materials. In this talk, large size diamond development and application will be presented. For heteroepitaxial single crystal diamond growth, preferred orientation Ir (001) film was deposited on sapphire substrate. Then bias enhanced CVD method was used to form diamond nucleation, on which a microwave plasma CVD(MPCVD) system was used to grow single crystal diamond. Then, tungsten atoms were introduced into MPCVD to grow high quality single crystal diamond on this sample. Thereafter, a laser machining technique was used to produce patterned trenches in diamond substrate, on which microchannels were achieved by epitaxial lateral overgrowth of diamond layer by MPCVD. In addition, we studied the enhanced heat spreading due to conduction followed by convective dissipation of a locally heated resistor mimicking a linear hot spot within electronic chips. The combined effect of conductive spreading and convective dissipation exhibited a significant cooling enhancement, which could be useful for GaN/diamond Composite Devices.

Hong-Xing Wang is a professor of Institute of Wide Bandgap Semiconductors, School of Electronic and Information Engineering at Xi'an Jiaotong University. He received his Ph.D from The University of Tokushima, Japan(2001). He joined Nitride Semiconductor Co. Ltd., Tokushima, Japan. As the senior researcher, he was engaged in research and development of GaN LED growth. 2003-2008, he was the executive director of Dialight Japan Co. Ltd. , Osaka, Japan. 2008-2013, he was the R&D manager in Seki Technotron Corp., Tokyo, Japan. In 2013, he moved from Japan to China and joined Xi'an Jiaotong University. His research interests focus on developing wide bandgap semiconductor materials and devices, (1) Development of MOCVD and MPCVD, (2) III-Nitride LEDs and power devices, (3) Single crystal diamond and devices, (4) Quantum sensing devices based on NV centers in diamond, (5) GaN and diamond composite devices . He has more than 120 papers and 100 patents.

Martin Kuball

University of Bristol, United Kingdom

Heat Transport across Interfaces for the Optimization of Heat Sinking in Device Applications

Heterogenous integration of materials is a powerful approach to overcome drawbacks of individual materials while benefiting from their “good” material properties. A simple example is the recent integration of GaN with diamond, where GaN has excellent electronic properties but only medium-high thermal conductivity, while diamond has the highest bulk thermal conductivity (TC) known to mankind, but limited electronic properties. Integration of both materials therefore allows equally excellent electronic and excellent thermal properties for device applications. When two materials are integrated e.g. via bonding or direct growth of one material on the other, interfaces are created, which may contain microstructure. These interfaces are typically amorphous or in other cases separate interface layers need to be included to enable the two different materials to mechanically adhere. These interfaces create thermal boundary resistances (TBR), which is a material property describing how difficult it is for heat to transfer from one material to the other. Factors such as microstructure, but also mismatch of phonon properties (in the case of semiconductors) or electronic properties in the case of metals come into play for TBR. It is therefore critically important to assess heat transfer across their interfaces to avoid thermal bottlenecks resulting in excessive device temperatures though. Experimental techniques to assess thermal conductivity of materials and TBR between materials are reviewed in this presentation, with examples from GaN-on-Diamond, diamond to metal diamond composites.

Prof. Martin Kuball is Royal Academy of Engineering Chair in Emerging Technologies and Director of the Center for Device Thermography and Reliability at the University of Bristol, UK. He holds a PhD from the Max Planck Institute for Solid State Physics, Stuttgart, Germany. He is Fellow of IEEE, MRS, SPIE, IET and IoP. He co-founded TherMap Solutions, a start-up commercializing thermal conductivity measurement tools.

Keynote Speakers

Oct. 6th

Roy Knechtel

Schmalkalden University of Applied Sciences, Germany
Professor for Autonomous Intelligent Sensors

Anodic Bonding a Low Temperature Bonding Method for Processed MEMS and CMOS Wafers

Wafer bonding is the process step to realize real three-dimensional microsystems with freely defined layer structures, free standing mechanical elements, hermetically sealed cavities and other 3D elements. There are various bonding technologies available with advantages and drawbacks in application and process integration. Out of this variety, anodic bonding is in general a very attractive low temperature bonding method. It is a direct joining process of glass containing mobile ions to various substrates like silicon (even coated with functional materials like oxide or Aluminum) or metals. Utilizing the progress in glass structuring and with adapted bonding conditions it can be used for CMOS-MEMS integrated wafers enabling very complex, multifunctional chip solutions especially for sensor, microfluidic and optical applications. Anodic bonding is characterized by a very good process stability and complete process control. This makes it very attractive for industrial production processes. However also this bonding process has its own challenges, which need to be addressed.

Roy Knechtel is since 2019 Professor for Autonomous Intelligent Sensors at Schmalkalden University of Applied Sciences / Germany. His research interests are about sensors principles, multi-sensor-integration and sensor applications with focus on the sensor and especially MEMS Technologies. Here Wafer Bonding processes plays an important role to realize and improve complex sensor systems. Before following the call to become a professor he was from 1998 until 1999 with X-FAB MEMS Foundry Technologies Erfurt. Here developed in different positions Wafer Bonding processes and MEMS technologies such as for pressure and inertial sensors and microphones. Roy Knechtel holds an PhD in Micro-System-technologies. He authored more than 80 wafer bonding related publications and more than 10 patents. He is technical Chair and lead organizer of WaferBond – Conference on Wafer Bonding for Microsystems, 3D- and Wafer level Integration.

Serena Iacovo

imec, Belgium

The unique properties of SiCN as bonding material for hybrid bonding

Direct Cu-SiCN hybrid bonding is successfully realized by using a thermal budget of 250 °C. The excellent results should be attributed to the tight control on the different processing steps but also to the properties of the SiCN dielectric used as bonding material.

Serena Iacovo is currently working as a senior R&D wafer bonding engineer at IMEC, Belgium. She joined imec in February 2017 and she is currently responsible of wafer-to-wafer permanent bonding activities such as Hybrid, Backside PDN and 3D sequential integration. Her research is focusing on the physical mechanism behind direct bonding, void formation mechanisms and wafer-to-wafer overlay optimization. She received a Ph.D degree in Physics from KULeuven, Belgium, working on defects characterization in materials by using as main characterization technique electron spin resonance. Her research as a PhD student contributed to the identification of the important role of dangling bond defects, during direct bonding at room temperature, in enhancing bond strength between bonded dielectrics. She obtained a master and a bachelor’s degree from the University of Calabria, Italy, in electronic engineering.

Keynote Speakers <Satellite Session>

Oct. 11th

Mark Goorsky


Interface reactions and thermal transport in heterogeneous heterostructures

Low temperature bonding has been leveraged to produce a wide array of materials combinations. One relatively unstudied aspect of this technique is the modification of surfaces prior to bonding. These modified surfaces become buried interfaces and can impact the electrical or thermal transport across such interfaces. One form of surface modification is amorphization. Amorphous interfaces reduce electrical transport but recent reports have indicated that amorphous interfaces across a heterogeneous junction can improve thermal transport properties. Another form of modification is the introduction to a thin (few nm) metal film at an interface. The stability of the amorphous and / or metallic interface layers after annealing is not well known. We provide a few examples in semiconductor-based systems to address the stability of different, technologically important, interface combinations as a function of annealing. Our main goal is to be able to exploit these surface preparation conditions to engineer the interface properties to optimize device performance. The understanding of the evolution of the interface structure is described through homogeneous bonded materials (Si-Si) in which annealing leads to the epitaxial recrystallization of the interface with the recrystallization front dependent on different growth planes. A dramatic change in electrical properties is likewise observed. For heterogeneous bonded materials, the interfacial reconstruction is more complicated with the formation of more stable phases and interdiffusion observed. This is observed in GaN/Si interfacial structure with world record thermal boundary conductance highest for the un-annealed interface. In other systems in which the two phases are thermodynamically stable, the crystallization of the amorphous layer dominates. When a metal layer is present, this is similar to deposition of a metal layer. In these cases, the interface reaction will be based on free energies of formation of the metal and semiconductor. If a reaction is favorable – as is the case for Al/β-Ga2O3 – then reaction kinetics control the transformation which means that the β-Ga2O3 orientation determine the extent of the reaction.

Professor Mark Goorsky is a leader in wafer bonding, layer exfoliation and transfer, and chemical mechanical polishing of semiconductors and optical materials. Goorsky also provides expertise in materials characterization of semiconductor materials and devices, with emphasis on structural (x-ray scattering and electron microscopy) and chemical (electron energy loss spectroscopy, energy dispersive elemental analysis) techniques. He received the university-wide 2016 UCLA Distinguished Teaching Award, was a member (2011-2015) of the US Air Force Science Advisory Board, was (2002-2019) associate editor for the Journal of Crystal Growth, was awarded the T.S. Walton Award from the Science Foundation of Ireland in 2010 (where he participated in projects to understand the integration of germanium and III-Vs with silicon) and received (1995-2000) a National Science Foundation CAREER AWARD.

Tadatomo Suga

Meisei University, Japan

Low temperature bonding by extension of the SAB concept

Loïc Sanchez

LETI, France

Die to wafer for photonic and 3D applications

Integrated transmitters incorporating lasers and modulators on silicon are of primary importance for all communication applications, and at the same time are the most challenging to manufacture due to the need of hybrid III-V integration. In order to introduce III-V materials in low cost silicon platform manufacturing, direct bonding approach could present a great interest due to the growth limitation of III-V hetero-epitaxial layers directly onto silicon. Furthermore, by using a 100 nm silicon dioxide layer between the silicon wave guide and the III-V active stack, direct bonding allows the optical coupling necessary to build active optical device. Nevertheless, the potential low cost model of silicon photonic is based only on the hypothesis that we are able to work on the full surface of the 200/300 mm SOI photonic wafer. III-V wafer direct bonding is not suitable to fulfill this requirement for two main reasons. First, the maximum diameter available for III-V wafers is limited to 150 mm up to now. Secondly, the III-V material is necessary only on the emitter and receiver areas which represent only a very little part of the device area. Therefore, the most part of the reported full III-V wafer is lost by the layer patterning on required areas. To overcome this limitation in term of wafer diameter and to limit the loss of a very expensive starting material we have developed at LETI a collective die direct bonding process. By replacing the initial die silicon holder by a more conventional tape on a dicing frame, our bonding process keep similar results in term of throughput, die placement accuracy and bonding rate. In addition, tape using has highly improved the bonding process in term of non-device design dependency, die thickness variability tolerance and simplicity of execution.

Sanchez Loïc is 41 years old. He graduated with an engineering degree from the «POLYTEC CLERMONT-FERRANT». He joined the CEA in 2005 in a common CEA-SOITEC team to develop the Smart-cut® Process on Germanium. Beside this, he has been driven projects with CEA industrial partners (ST, SOITEC,…) on high mobility substrates, 3D monolithic integration and die to wafer self-assembly. He is now responsible of die to wafer direct bonding developments in the Surface and Interface department for 3D integration and photonics applications.

Frank Fournel

LETI, France

From Hot SAB bonding to organic hydrophilic bonding

Direct bonding is now a wild sprayed bonding technology with mass production for some applications. However, research studies are still mandatory in order to understand or optimize its chemical physical mechanism. For example, interesting new developments have been recently obtained on the link between direct bonding and organic compounds. Even if organic contamination is one of the main detrimental surface contamination, specific organic molecule types are shown to enhance drastically the bonding energy at low temperature. More than the adherence enforcement, this effect highlights the silica hydrolysis as a key phenomenon in silicon direct bonding mechanism. And even more than just a little amount of organic compound at the bonding interface, direct bonding can even appear between one or two full organic surfaces. This opens a large window for direct bonding applications keeping some direct bonding advantages, as bonding throughput for instance. Other interesting direct bonding developments allow now direct bonding to appear above room temperature. Indeed recent results, using SAB technology, allow us to bond materials with important dissimilar thermal expansion coefficients. This opens interesting leverage arms for internal stress control. Even if direct bonding is now a well-established technology, interesting developments still appear, widening always and always its application field.

Frank Fournel is 48 years old. He graduated from the "Ecole Supérieure de Physique et de Chimie Industrielle" de la ville de Paris (ESPCI) with a master in “Materials science” (thin layer option). He got his PhD in 2001 for his work in CEA Grenoble during collaboration between CEA and INAC on the use of molecular bonding to elaborate twisted substrate in order to drive a self-positioning nanostructure growth. Just after this, he has been employed by CEA in the thin film and circuit layers transfer laboratory. His main focus is on the fundamental understanding of the direct bonding and its application in thin layer transfer technique and substrate engineering. Beside this, he has been involved or driven many international project with CEA industrial partners (ST, Alcatel, SOITEC, Tracit technology, Fresnel optic…) which gave him the advantage to drive simultaneously academic research and applicative one. He is now the head of the bonding technology engineering in LETI. He is now also involved in metallic bonding (direct, eutectic or thermo-compression), in anodic bonding and in polymer bonding (permanent or temporary) and covalent bonding (SAB). His focus concerns now also all the 3D applications including temporary bonding for instance for Si interposer or including Cu/Cu hybrid bonding for high pitch interconnexions. He was involved in the SOI conference board for 3 years and he is now a board member of the international ECS Wafer Bonding Symposium conference as well as the International Wafer’Bond conference. He has 185 international publications, 115 deposited patents and participated to two book chapters.