Atomic layer deposition of ZrO2/La2O3 high-k dielectrics on germanium reaching 0.5 nm equivalent oxide thickness

Abstract

We investigate ultrathin ZrO2/La2O3 high-k dielectric stacks on germanium grown by atomic layer deposition. La2O3 is deposited from tris(N,N′-diisopropylformamidinate)-lanthanum and oxygen. Interfacial layer-free oxide stacks with a relative dielectric constant of 21 and equivalent oxide thickness values as low as 0.5 nm are obtained. Metal oxide semiconductor capacitors with platinum as the gate electrode exhibit well-behaved capacitance-voltage characteristics, gate leakage current densities in the range of 0.01–1 A/cm2, and interface trap densities in the range of ∼3×1012 eV−1 cm−2.

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

“…4͑a͒, thus suggesting the presence of a SiO x -like component which coexists with the La-based profile ͑i.e., LaO 2 ͒ in the region at the film/ substrate interface. In addition, in the as-grown film, the SiO 3 and 30 Si signals detected at the surface reveal a moderate Si diffusion occurring through the La 2 O 3 film during the ALD growth. Finally, the depth profile of the OH signal in Fig.…”

“…4͑d͔͒, the thin La͑OH͒ 3 layer vanishes and no further reduction in the OH signal intensity is detected. Moreover, the 30 Si signal in Fig. 4͑d͒ assumes a flat profile along the whole stack thickness indicating that, with a high temperature thermal treatment, Si diffusion from the substrate throughout the entire stack thickness is promoted.…”

“…A clear reduction in the intensity of the OH signal is observed, in accordance with the structural analysis, hence supporting the hypothesis of the La͑OH͒ 3 conversion into h-La 2 O 3 upon annealing at 600°C. The 30 Si signal indicates that Si atoms diffusion, from the substrate through the film, occurred during the thermal treatment. According to all the above results, the stack order atop the Si substrate after RTA at 600°C can be roughly approximated by a trilayer structure composed by an amorphous IL ͑most likely LaSiO species͒, a crystalline layer characterized by a decreasing Si content and a very thin La͑OH͒ 3 surface layer.…”

“…44 In fact, La͑ i PrCp͒ 3 has been previously utilized in combination with H 2 O for the ALD growth of La 2 O 3 / Si stacks. 45 Recently, ALD growth by using La͑ i PrfAMD͒ 3 +O 2 has also been reported 30 10,15,40,43 and La x Zr 1−x O 2−␦ ͑Ref. 49͔͒ and Ge substrates ͓e.g., HfO 2 and ZrO 2 ͑Ref.…”

“…Recently, lan-thanum germanate La x Ge y O z ͑LaGeO͒, which is almost unavoidably formed due to a strong and spontaneous reaction when La 2 O 3 comes in contact with the Ge surface, 24 has emerged as an attractive choice for high-k / Ge interfaces because of its beneficial role in defects passivation [24][25][26] and band offset enhancement. 27 Indeed, an intense effort within the Ge-based CMOS community is currently underway to optimize the properties of the ZrO 2 / La 2 O 3 stacks because preliminary work [27][28][29][30][31] has demonstrated encouraging electrical characteristics including a large potential for stack EOT scalability below 1 nm.…”