The AVS 22nd International Conference on Atomic Layer Deposition (ALD 2022) will be dedicated to the science and technology of atomic layer controlled deposition of thin films. It will be held in Ghent (Belgium) from 26 to 29 June.
In the frame of StorAIge, the Université Grenoble Alpes (CNRS-LTM) will present their latest results on « Sub 10-nm Ferroelectric HfO2 Capacitors Doped with Gd. » Evgeniy Skopin‚ Nicolas Guillaume‚ Liliane Alrifai‚ Ahmad Bsiesy
Session on 29/06/2022 at 10:45am: AA2-WeM2: ALD for Memory Applications I
Recent discoveries of the ferroelectric properties of doped HfO2 opens the possibilities of its integration in Ferroelectric-based non-volatile Random-Access Memories (FeRAMs). Replacing memories based on perovskites materials by ferroelectric HfO2 has many decisive advantages. Indeed‚ HfO2 is readily used in CMOS back end of the line‚ and its use opens the possibility to grow thinner layers of around 10 nm vs 70-100 nm for the conventional ferroelectric perovskites. Thinner layers are mandatory for integration in advanced sub 100 nm CMOS technology nodes.
Plasma Enhanced Atomic Layer Deposition (PEALD) allows the synthesis of a different range of materials such as oxides and metals with low surface roughness and precise thickness control. TiN metal (M) layers and Gd doped HfO2 insulator (I) layer were grown in the same PEALD chamber without contact with the air between depositions to synthesize ferroelectric MIM capacitors. Changing ratios between Hf and Gd PEALD cycles inside one supercycle allows choosing an appropriate Gd doping concentration. In its order‚ during annealing‚ Gd doping in HfO2 (Gd:HfO2) leads to a crystallization of HfO2 in a metastable non-centrosymmetric orthorhombic phase‚ which induces the HfO2 ferroelectric properties. A decrease of the ferroelectric oxide thickness can allow operating lower switching voltages for the low power circuits.
Continuing our previous work [SB]‚ by using the growth of MIM capacitor by PEALD in one batch (i.e. without air break between metal‚ insulator‚ and metal layers)‚ we recently demonstrated the ferroelectricity of sub-10 Gd:HfO2 layers (8.8nm-‚ 6.6nm‚ and 4.4nm-thick layers) in TiN / Gd:HfO2 / TiN stacks and studied the remnant polarization amplitude change with the Gd:HfO2 layer thickness. Structural measurements (X-ray diffraction and reflectometry) confirmed a HfO2 transformation to the orthorhombic (ferroelectric) phase. Electrical measurements showed that switching voltage can be decreased for the thinner Gd:HfO2 layers (hysteresis loop measurements and Positive Up Negative Down measurements). Polarization switching cycling measurements demonstrate ferroelectric endurance of at least up to 108 cycles. This work opens the possibilities for the integration of sub-10nm Gd:HfO2 in the memory device circuits thanks to the unique PEALD deposition capabilities.
More information on ALD 2022 : https://ald2022.avs.org/