Friday, March 28, 2014

SIMIT in Shanghai reports HfO2 growth directly on graphene by ALD

According to a fresh publication HfO2 can be grown directly on Graphene using a H2O/TEMAHf ALD process. reports from the team led by Xinhong Cheng at the Shanghai Institute of Microsystem and Information Technology (part of the Chinese Academy of Sciences), turned to a compound with a very unusual name: Tetrakis(ethylmethylamino)hafnium, or TEMAH. At 80 degrees Celsius (176 degrees Fahrenheit), TEMAH is a gas from which hafnium oxide (HfO2), a proven high-k dielectric can be derived. Unfortunately, getting the HfO2 to stick to graphene wasn't easy. "Using a traditional ALD techniques, we blew TEMAH into the deposition chamber with the hope that the HfO2 produced would be absorbed by the graphene substrate; but it would not stick," says Li Zheng, lead author on the JVSTA paper. "So, we pre-treated the substrate with water because we knew it would be absorbed onto the graphene and likely act as a nucleation [growth initiation] site. And that's what we found. TEMAH is attracted to the absorbed water, allowing a HfO2 layer to grow directly - and tightly - on the graphene surface."

Read more: Need your dielectric to stick to graphene? Just add water
Here is the abstract and link to the paper in JVSTA:

HfO2 dielectric film growth directly on graphene by H2O-based atomic layer deposition

J. Vac. Sci. Technol. A 32, 01A103 (2014);

"Due to its exceptionally high carrier mobility, International Technology Roadmap for Semiconductors considers graphene to be among the candidate materials for postsilicon electronics. In order to realize graphene-based devices, thin and uniform-coverage high-κ dielectrics without any pinholes on top of graphene is required. There are no dangling bonds on defect-free graphene surface; it is difficult to grow uniform-coverage high-κ dielectrics on graphene directly by atom layer deposition. Meanwhile, degradation of defects in graphene/high-κ structure is necessary for the optimization of high-κ dielectrics fabrication technology. Here the authors report on a H2O-based atom layer deposition method used for HfO2 growth, where physically adsorbed H2O molecules on graphene surface act as oxidant, and self-limit react with metal precursors to form HfO2 film onto graphene directly. Raman spectra reveal H2O-based atom layer deposition method will not introduce defects into graphene. The surface root mean square of HfO2 films is down to 0.9 nm and the capacitance of HfO2 films on graphene is up to 2.7 μF/cm2, which indicate high quality and compactness of HfO2 films. "