You will investigate the debonding behaviour as a function of interface characteristics of the growth wafer and will assess the defectivity generated during the transfer process.
An ever-increasing number of materials are grown at temperatures that are too high for direct material integration in CMOS production lines. Other materials are grown on substrates that are incompatible with CMOS processing (e.g., sapphire). Examples of these materials are 2D materials like graphene or h-BN grown on metal catalysts, or MX2 materials (e.g. MoS2, WS2, WSe2...) grown on SiO2 or sapphire at high temperatures (>>500oC). But the class of materials that can benefit from a layer transfer is much larger than only 2D materials. Other examples are topological insulators (e.g. Bi2Se3 grown by MBE on sapphire), or even III/V materials. A few commercial examples of film transfers exist today. An often-stated example is the laser lift off transfer of stacks like InGaN/GaN grown on sapphire for LED fabrication, but here, very thick (micron sized) layers are usually deposited.
To find a possible integration path for this class of new materials in the semiconductor industry based on layer transfer, it is essential to find pathways to overcome the adhesion between the deposited material and the growth substrate. This might be possible by using laser lift off layers, epitaxial lift off techniques, intercalation effects during or after growth or possibly by electrically changing the Van der Waals force between the deposited material and the growth substrate. Once the material is delaminated from the growth wafer, it needs to be laminated on a target (device) wafer. The interaction of the material with the target wafer often strongly changes the properties of the material itself. The material can become (un)intentionally doped and adhesion values will vary just by laminating it on a different surface. Therefore, it is of prime importance that the interaction between the material and the surrounding is understood. Furthermore, cleaning steps before and after transfer need to be developed in order to achieve the desired properties of the transferred layer (e.g., controlled doping level, specific bandgap, high mobility...). Such pre- and post-transfer cleans are essential to achieve the needed properties of the transferred layer.
What you will do
The transfer of a 2D material at Imec is implemented with a glass carrier wafer, a laser release layer, and a polymer support. A critical bottleneck remains the reliable delamination of the material from the growth wafer. You will investigate the debonding behaviour as a function of interface characteristics of the growth wafer (depending on the growth conditions, intercalation parameters and support layer characteristics) and will assess the defectivity generated during the transfer process. Low temperature (time resolved) photoluminescence might be a good metrology for fast defectivity analysis of MX2 layers. The measured defectivity values will depend on the surroundings of the 2D material, and fundamental understanding will be needed to enable the use of this technique for 2D material transfer quality assessment.
Who you are
To enable and to increase our fundamental understanding of the transfer process, we are looking for a postdoc with a deep knowledge of characterization techniques and a proven track record with thin film transfer.
You will be a member of the Bonding, Transfer and Assembly (BTA) group, but you will also work in close collaboration with the Materials, and Components Analysis (MCA) group to assess defectivity in 2D materials and the Lab team to assess transfer methodologies that are scalable.
This postdoctoral position is funded by imec through KU Leuven. Because of the specific financing statute which targets international mobility for postdocs, only candidates who did not stay or work/study in Belgium for more than 24 months in the past 3 years can be considered for the position (short stays such as holiday, participation in conferences, etc. are not taken into account)