Physical and Electrical Properties of Lanthanum Oxide Dielectrics with Al and Al∕TaN Metal Gates

Abstract

We report on a high-k lanthanum oxide ͑La 2 O 3 ͒ gate dielectric deposited on Si substrate by reactive radio-frequency sputtering for Al and Al/TaN metal gate electrode. The La 2 O 3 gate dielectric film with Al/TaN gate electrode exhibited excellent electrical properties such as low equivalent oxide thickness, high electric field breakdown, excellent reliability, and almost no hysteresis in C-V curves comparable to that with Al gate electrode. This indicates that Al/TaN metal gate can inhibit Si atoms outdiffusion from Si substrate and the diffusion of Al atoms in the oxide from secondary ion mass spectrometry data. Moreover, post-processing treatments can passivate a large amount of trapped charge at defect sites.Aggressive scaling of gate length and gate oxide thickness in complementary metal oxide semiconductor ͑CMOS͒ transistors gives rise to the problems of poly-Si gate depletion, high gate resistance, and boron penetration from the p + -doped poly-Si gate into the channel region. 1 To reduce the high gate resistance and gate depletion problems, the conventional poly-Si gate electrode must be substituted by metal gate electrode. A metal gate material not only eliminates the gate depletion and boron penetration problems, but also greatly reduces the gate sheet resistance. 2 In addition, high dielectric constant ͑high-k͒ materials have attracted much attention for future gate dielectrics, to reduce gate leakage current and power consumption that are unacceptably high. 3 The application of high-k gate dielectric and metal gate to CMOS transistors fabrication is an important issue in the sub-65 nm regime because the high-k gate dielectric and metal gate technology could realize low gate resistance ͑high speed device͒, no gate depletion ͑reduction of the electrical gate oxide thickness͒, no boron penetration from gate into the channel, and low gate leakage current, that is, the scaling down of transistor feature size and the improvement of device performance. [4][5][6] Recent research on high-k dielectrics has primarily focused on metal oxides. Among these, lanthanum oxide ͑La 2 O 3 ͒ seems to be a promising candidate that has attracted the attention of many research groups worldwide. 7,8 Note that La 2 O 3 films are considered not only for its high dielectric constant, but also because the large bandgap, the good thermodynamic stability in contact with silicon substrates and the compatibility with standard CMOS fabrication processes. 9 In this paper, a high-k lanthanum oxide gate dielectric grown by reactive radio-frequency ͑rf͒ sputtering for Al and Al/TaN metal gate on physical properties and electrical characteristics has been investigated. of an area of 3.14 ϫ 10 −4 cm 2 were fabricated on 4 in. p-type Si wafers with a resistivity of 7-11 ⍀-cm. After a standard RCA cleaning of the silicon wafer and a dilute 1% HF strip for 1 min, thin La 2 O 3 films ͑ϳ9 nm͒ were deposited by reactive rf sputtering at low pressure of about 10 −6 Torr in diluted O 2 ͑Ar/O 2 = 5/2͒ ambient, subsequent post-deposition annealin...

Silicon out-diffusion and aluminum in-diffusion in devices with atomic-layer deposited La2O3 thin films

“…Strikingly, the aluminum and silicon signals extend beyond their interface with the La 2 O 3 layer, which shows that aluminum diffuses into the La 2 O 3 layer and silicon diffuses from the substrate through La 2 O 3 towards the aluminum electrode. In contrast to the earlier observations by Pan et al, 6 the silicon atoms are not localized at the interface between Al and La 2 O 3 but dissolve in aluminum and reach even the top electrode, forming Si precipitates on the electrode. In addition, the Al 2 O + signal has a longer but steeper tail extending beyond the Al-La 2 O 3 interface, possibly indicating the formation of Al 2 O 3 at the interface.…”

“…Recent studies suggest that silicon atoms diffuse outwards from the substrate through La 2 O 3 towards the high-k electrode interface. 6 In this letter, we report on the extent of silicon out-diffusion and aluminum in-diffusion in MIS devices with La 2 O 3 as an intermediate dielectric.…”

Integrations and challenges of novel high-k gate stacks in advanced CMOS technology

“…Although Hf-based high-k gate dielectrics have been intensively investigated as candidate for conventional SiO 2 , recently much attention are also given to the rare earth oxides M 2 O 3 (M = La, Pr, Gd and Nd) due to their large band-gaps, high dielectric constants, small lattice mismatch with Si, and good thermodynamic stability in direct contact with Si [194][195][196][197]. Base on the observations from different groups, improved interface stability and reduced leakage currents can be achieved by forming the amorphous silicate as candidates.…”

O 3 -based atomic layer deposition of hexagonal La2O3 films on Si(100) and Ge(100) substrates

“…La 2 O 3 films have been grown on Si substrates by various techniques, namely, molecular beam deposition, 32,33 sputtering, 11,34 metal organic chemical vapor deposition, 35,36 and electron beam evaporation. 37,38 Conversely, the spread regarding the methods for La 2 O 3 deposition on Ge substrates is narrower since the majority of published work is predominantly concerned with La 2 O 3 growth by electron beam evaporation 20,21 and molecular beam deposition.…”