Impact of Al<inf>2</inf>O<inf>3</inf> position on performances and reliability in high-k metal gated DRAM periphery transistors

Abstract

The impact of the Al 2 O 3 position with respect to HfO 2 in the process flow, is investigated. It is shown that Al 2 O 3 incorporation in order to increase the pMOS threshold voltage, slightly degrades the mobility, slightly increases NBTI and increases the EOT with respect to the reference without Al 2 O 3 . Moreover, the trap density profiles depend on the Al 2 O 3 position: higher in the interfacial layer when Al 2 O 3 is below and higher in the HfO 2 when Al 2 O 3 is above HfO 2 . Furthermore, Al 2 O 3 below HfO 2 shows higher gate leakage, reduced LF noise but marginal NBTI difference compared to AL 2 O 3 above HfO 2 .

Low-Frequency Noise Assessment of Work Function Engineering Cap Layers in High-k Gate Stacks

“…For most of the high-κ devices, CNF is dominating over mobility fluctuations. 19,[25][26][27][28] Trap density profile.-If pure elastic tunneling is assumed then the frequency f can be translated into a trap depth z in the oxide according to…”

“…Compared to Al 2 O 3 below the HfO 2 layer there is a reduction in the leakage current and increase in low frequency noise, while the NBTI reliability is not compromised. 25…”

Increase in Oxide Trap Density Due to the Implementation of High-k and Al2O3 Cap Layers in Thick-Oxide Input-Output Transistors for DRAM Applications

“…7. These trap densities are about one decade lower than typically found in high-κ materials [8], [9], [12], [13], so that the present gate stacks are somewhere intermediate pure SiO 2 and pure HfO 2 from a viewpoint of oxide trap density. The blue HKMG curve in Fig.…”

“…To that aim, low-frequency (LF) noise is used as a tool to probe the border trap profile in the thick oxide gate stack [6], [7]. It has been shown previously for thin-oxide DRAM periphery transistors that marked changes can be observed for HKMG pMOSFETs with an Al 2 O 3 cap [8], [9] or for nMOSFETs with a La or a Mg cap/shifter. Evidence will be given here for a strong increase of the oxide trap density in the 5 nm SiO 2 , derived from the 1/f-like noise spectra, when a high-κ and/or Al 2 O 3 cap layer is implemented.…”