Atomic Layer Deposition of HfO 2 : Recent Process Developments ROCESS
Authors : Aileen O’Mahony, Agnieszka Kurek, Harm Knoops, Tom Miller, Owain Thomas, and Robert Gunn, Oxford Instruments Plasma Technology
deposited by thermal ALD with H 2 O, or plasma enhanced ALD (PEALD) with O 2 plasma. A process optimisation study was undertaken with HfO 2 films deposited using tetrakis(dimethylamido)hafnium Hf(NMe 2 ) 4 , (TDMAH) as a comparison to the existing HfO 2 process of record which uses tetrakis(ethylmethylamido) hafnium Hf(EtMe) 4 , (TEMAH). TDMAH is widely available from precursor supply companies. It has a higher TDMAH to be delivered by vapour draw rather than requiring delivery assistance by argon bubbling (as required for TEMAH). A 0.4 s TDMAH dose was required for surface saturation (Figure 1) with significantly improved HfO 2 film uniformity across a 200 mm substrate (2.7%) for the TDMAH PEALD process compared to the TEMAH PEALD process. vapour pressure compared to TEMAH 5,10 which allowed the
layers or nanolaminate stacks on high aspect ratio structures. Metal alkylamides are widely used ALD precursors 5 as they are highly volatile, and reactive, with increased growth rates compared to halides (e.g. HfCl 4 , WF 6 ). Alkylamides do not generate corrosive by-products, such as HCl or HF, and are suitable for deposition at lower temperatures but are prone to decomposition at deposition temperatures ≥300°C 6 . Cyclopentadienylalkylamide 7,8 precursors have increased thermal stability allowing for deposition at higher temperatures but without the presence of a strongly oxidising co- reactant, lower GPC processes are reported. Improvements in HfO 2 ALD processing with alkylamide and cyclopentadienylalkylamide precursors was presented based on work completed at OIPT, and highlights from a recent publication by A. Sharma, Eindhoven University of Technology 9 . In these studies, Oxford Instruments’ FlexAL ALD systems were used with HfO 2 films
Oxford Instruments Plasma Technology (OIPT) is constantly innovating to help our customers get the best performance from their devices. Aileen O’Mahony discusses howwe are working with different pre-cursors for HfO 2 making sure the film quality and growth per cycle (GPC) are optimised. HfO 2 deposited by atomic layer deposition (ALD) is utilised in a number of key technological applications. In 2007, Intel introduced a hafnium-based high-k dielectric layer deposited by ALD into high-volume manufacturing for its 45 nm technology node transistors 1 . HfO 2 is used in memory devices such as DRAM 2 , and also ferroelectric-RAM technology due to the ferroelectric properties of both pure HfO 2 3 and doped HfO 2 layers 3,4 (e.g. HfO 2 doped with SiO 2 , Al 2 O 3 , ZrO 2 , La 2 O 3 ). ALD is the ideal method for the deposition of thin, conformal, high-quality layers, as well as allowing the processing flexibility for deposition of doped
Figure 1: Saturation of TDMAH precursor dose.
4 Summer 2018
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