Towards 200mm 2D Materials Transfer—Wafer Scale Characterizations During 2D Materials Transfer Onto Temporary Substrate

Microelectronics companies always go further in the more Moore and more than Moore law trying to achieve smaller and smaller devices. However, at low dimensions, the mobility in silicon is drastically hampered. To overcome the limits of the silicon at low dimension, 2D materials are seen as a good candidate as their mobility is not affected by size.[1] This explains why 2D materials and more specifically TMDs are emerging in all industrial roadmap as the silicon successor. However, a considerable challenge needs to be taken into account as good crystalline quality 2D material’s growth is reached only at a high temperature (900°C - 1100°C). This value is not compatible with BEOL (&lt; 400°C) integration and up to now a critical transfer step is mandatory, to bring the 2D from its growth substrate to the final substrate.<br/>During this step, all the intrinsic properties have to be preserved for integration into 2D material-based devices [2]. The transfer process can be split into two steps.<br/>The 2D separation from its growth substrate and then bonding or fishing on the appropriate substrate. There is no easy solution involving a direct transfer from the growth substrate to final substrate, and, all the time, the use of temporary substrate is required. The latter can be, polymer,[3] thermal release tape [4] or glass substrate [5], [6]. The main difficulty remains to collect it on the temporary substrate without generating cracks, folds or any other damages. Once the material on the temporary substrate, another transfer from the temporary substrate to the final substrate is needed. Finally, all additional layers or handle used for the transfer are removed.<br/>A lot of effort was made on 2D material characterization of MoS₂ grown by Atomic Layer Deposition (ALD) process.[7] As most of the time, characterizations are performed on a small area, and the data are not fully representative of the overall quality of the transferred 2D layer across the whole surface. Thus, a comprehensive wafer-scale characterization is essential to monitor the quality and uniformity of the transferred 2D material. Automation and statistics across the whole wafer acquired with several characterization tools, such as Raman spectroscopy, photoluminescence (PL), Atomic Force Microscopy (AFM), Wavelength Dispersive X-ray Fluorescence (WDXRF), scanning electron microscopy (SEM) were used to get growth information i.e. the thickness of the 2D, defects, homogeneity.<br/>In this presentation, we detailed the first step, consisting of the 200 mm transfer of 2D material from the growth substrate to a temporary substrate. Our method is based on direct bonding. The main advantage relies on the possibility to avoid any additional layer to be deposited on top of the 2D. This prevents any contamination and the 2D material is directly transferred from one wafer to another, preventing wrinkles or cracks generation. We show here that thanks to a 200 mm wafer scale characterization we are able to optimize the MoS2 growth such as the quality of the transfer.