Selected Success Stories from Twenty Years of High-k Gate Dielectric Research

There are many success stories from the high-k gate dielectric research, carried out during the last two decades or so (say, 1996 to 2016), only a few of which could be accommodated in this paper. We plan to highlight four successful enterprises, namely, (1) Atomic Layer Deposition (ALD) of HfO 2 (including HfON, HfSiON), (2) Enhancement of the dielectric constant k through structural transformation and/or compound formation, (3) Role of the SiO 2 /high-k Interface Dipole and the Cap Layer at the high-k/metal interface in controlling the flat-band voltage, (4) Passivation of the Ge surface and Ge MOSFET with high channel mobility. These topics will be analyzed critically and the underlying physics will be presented. Atomic Layer Deposition scores over competitors (MOCVD, Magnetron Sputtering) in terms of better film uniformity and conformity (against uneven surfaces) with less pinhole. The alkyl-amide precursors: (TDMAH - Hf[N(CH3)2]4), (TEMAH - Hf[N(C2H5) (CH3)]4), (TDEAH - Hf[N(C2H5)2]4) were found to be suitable for low temperature deposition of smooth (RMS roughness ca. 1% of film thickness), uniform (thickness and composition wise), dense (ρ = 9.23 gcm -3 , i.e. 95% of the density of the monoclinic phase), low contamination (< 1% C and < 0.25% N), and conformal (100% site coverage on holes with > 35 aspect ration) films of HfO 2 with a deposition rate of ca. 0.093 nm per cycle.ALD is claimed to be a self-limiting process, but it was found that self limiting surface reaction occurred at a particular precursor temperature corresponding to a specific precursor dose; these precursor temperatures for the saturating dose were 75, 115, and 130 o C for TDMAH, TEMAH, and TDEAH, respectively. High deposition temperatures culminated in precursor decomposition followed by non-uniform films or no deposition on the substrate; moreover, HfO 2 film surface roughness increased due to growth of crystallites. One main concern is the contamination of the deposited high-k layer by the chemical reaction by-products – generally C, Cl, N, and H. Post-deposition O 3 treatment can reduce C, H contamination by producing H 2 O, CO or CO 2 followed by their out-diffusion. Higher deposition temperature results in lower C contamination. High temperature annealing between ALD stages has been found to lower the C contamination; likewise has been NH 3 /Ar plasma treatment. Typically, the value of the dielectric constant k for a high-k alloy varies in a monotonous (somewhat linear) fas