@inproceedings{FursenkoLukosiusLupinaetal.2017, author = {Fursenko, Oksana and Lukosius, Mindaugas and Lupina, G. and Bauer, Joachim and Villringer, Claus and Mai, Andreas}, title = {Development of graphene process control by industrial optical spectroscopy setup}, publisher = {SPIE}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15319}, pages = {250 -- 259}, year = {2017}, abstract = {The successful integration of graphene into microelectronic devices depends strongly on the availability of fast and nondestructive characterization methods of graphene grown by CVD on large diameter production wafers [1-3] which are in the interest of the semiconductor industry. Here, a high-throughput optical metrology method for measuring the thickness and uniformity of large-area graphene sheets is demonstrated. The method is based on the combination of spectroscopic ellipsometry and normal incidence reflectometry in UV-Vis wavelength range (200-800 nm) with small light spots (~ 30 μm2) realized in wafer optical metrology tool. In the first step graphene layers were transferred on a SiO2/Si substrate in order to determine the optical constants of graphene by the combination of multi-angle ellipsometry and reflectometry. Then these data were used for the development of a process control recipe of CVD graphene on 200 mm Ge(100)/Si(100) wafers. The graphene layer quality was additionally monitored by Raman spectroscopy. Atomic force microscopy measurements were performed for micro topography evaluation. In consequence, a robust recipe for unambiguous thickness monitoring of all components of a multilayer film stack, including graphene, surface residuals or interface layer underneath graphene and surface roughness is developed. Optical monitoring of graphene thickness uniformity over a wafer has shown an excellent long term stability (s=0.004 nm) regardless of the growth of interfacial GeO2 and surface roughness. The sensitivity of the optical identification of graphene during microelectronic processing was evaluated. This optical metrology technique with combined data collection exhibit a fast and highly precise method allowing one an unambiguous detection of graphene after transferring as well as after the CVD deposition process on a Ge(100)/Si(100) wafer. This approach is well suited for industrial applications due to its repeatability and flexibility.}, language = {en} } @article{FursenkoLukosiusBaueretal.2019, author = {Fursenko, Oksana and Lukosius, Mindaugas and Bauer, Joachim and Villringer, Claus and Lux, Helge and B{\"a}rwolf, Florian and Lisker, Marco and Mai, Andreas}, title = {Diagnostic of graphene on Ge(100)/Si(100) in a 200 mm wafer Si technology environment by spectroscopic ellipsometry/reflectometry}, series = {Journal of Vacuum Science \& Technology B}, volume = {37}, journal = {Journal of Vacuum Science \& Technology B}, number = {6}, publisher = {American Vacuum Society (AVS)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-16083}, year = {2019}, abstract = {Comprehensive diagnostics is a prerequisite for the application of graphene in semiconductor technologies. Here, the authors present long-term investigations of graphene on 200-mm Ge(100)/Si(100) wafers under clean room environmental conditions. Diagnostic of graphene was performed by a fast and nondestructive metrology method based on the combination of spectroscopic ellipsometry and reflectometry (SE/R), realized within a wafer optical metrology tool. A robust procedure for unambiguous thickness monitoring of a multilayer film stack, including graphene, interface layer GeOx underneath graphene, and surface roughness is developed and applied for process control. The authors found a relationship between the quality of graphene and the growth of GeOx beneath graphene. Enhanced oxidation of Ge beneath graphene was registered as a long-term process. SE/R measurements were validated and complemented using atomic force microscopy, scanning electron microscopy, Raman spectroscopy, and secondary ion mass spectrometry. This comparative study shows a high potential for optical metrology of graphene deposited on Ge/Si structures, due to its great sensitivity, repeatability, and flexibility, realized in a nondestructive way.}, language = {en} } @article{LukoseLiskerAkhtaretal.2021, author = {Lukose, Rasuole and Lisker, Marco and Akhtar, Fatima and Fraschke, Mirko and Grabolla, T. and Mai, Andreas and Lukosius, Mindaugas}, title = {Influence of plasma treatment on SiO2/Si and Si3N4/Si substrates for large-scale transfer of graphene}, series = {Scientific Reports}, volume = {11}, journal = {Scientific Reports}, issn = {2045-2322}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14179}, year = {2021}, abstract = {One of the limiting factors of graphene integration into electronic, photonic, or sensing devices is the unavailability of large-scale graphene directly grown on the isolators. Therefore, it is necessary to transfer graphene from the donor growth wafers onto the isolating target wafers. In the present research, graphene was transferred from the chemical vapor deposited 200 mm Germanium/Silicon (Ge/Si) wafers onto isolating (SiO2/Si and Si3N4/Si) wafers by electrochemical delamination procedure, employing poly(methylmethacrylate) as an intermediate support layer. In order to influence the adhesion properties of graphene, the wettability properties of the target substrates were investigated in this study. To increase the adhesion of the graphene on the isolating surfaces, they were pre-treated with oxygen plasma prior the transfer process of graphene. The wetting contact angle measurements revealed the increase of the hydrophilicity after surface interaction with oxygen plasma, leading to improved adhesion of the graphene on 200 mm target wafers and possible proof-of-concept development of graphene-based devices in standard Si technologies.}, language = {en} } @article{ElvirettiLiskerLukoseetal.2022, author = {Elviretti, M. and Lisker, Marco and Lukose, Rasuole and Lukosius, Mindaugas and Akhtar, Fatima and Mai, Andreas}, title = {Reliable metal-graphene contact formation process flows in a CMOS-compatible environment}, series = {Nanoscale Advances}, volume = {4}, journal = {Nanoscale Advances}, publisher = {Royal Society of Chemistry (RSC)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-16581}, pages = {4373 -- 4380}, year = {2022}, abstract = {The possibility of exploiting the enormous potential of graphene for microelectronics and photonics must go through the optimization of the graphene-metal contact. Achieving low contact resistance is essential for the consideration of graphene as a candidate material for electronic and photonic devices. This work has been carried out in an 8′′ wafer pilot-line for the integration of graphene into a CMOS environment. The main focus is to study the impact of the patterning of graphene and passivation on metal-graphene contact resistance. The latter is measured by means of transmission line measurement (TLM) with several contact designs. The presented approaches enable reproducible formation of contact resistivity as low as 660 Ω μm with a sheet resistance of 1.8 kΩ/□ by proper graphene patterning, passivation of the channel and a post-processing treatment such as annealing.}, language = {en} } @article{RajuDubeyLukoseetal.2025, author = {Raju, Ashraful Islam and Dubey, Pawan Kumar and Lukose, Rasuole and Wenger, Christian and Mai, Andreas and Lukosius, Mindaugas}, title = {Optimized silicon nitride-spaced graphene electro-optic modulator with high efficiency and bandwidth}, series = {Optical and Quantum Electronics}, volume = {57}, journal = {Optical and Quantum Electronics}, number = {7}, publisher = {Springer Nature}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-20597}, year = {2025}, abstract = {Optical modulators with high modulation efficiency, large operational bandwidth, high-speed and low energy consumption is essential for the advancement of on-chip optical signal processing. To overcome the bandwidth-efficiency trade-off in graphene optical modulators, a buried silicon nitride waveguide-coupled double-layer graphene electro-absorption (EA) optical modulator has been proposed. In the proposed design, silicon nitride layer is also embedded between the two graphene layers as a dielectric spacer to enhance the graphene-light interaction. An extensive simulation has been performed to optimize the dielectric spacing layers between the two graphene for optimal device performance including the waveguide dimensions and optical modes profile. The simulated results show a high modulation efficiency of 1.1 dB/V and a modulation depth of 0.16 dB/µm, corresponding to a 15-dB extinction ratio for a 100 µm device at 1550 nm, with a 30 nm spacer and 12 V driving voltage. The proposed modulator achieves a 14 GHz bandwidth and operates over a 1050 nm broadband operation spectral range. The concurrent presence of high modulation bandwidth and efficiency renders these modulator designs highly viable for on-chip optical communication applications.}, language = {en} }