Characteristics of Atomic-Layer-Deposited Al[sub 2]O[sub 3] High-k Dielectric Films Grown on Ge Substrates

Abstract

This paper describes the structural and electrical properties of Al 2 O 3 thin films grown through atomic layer deposition onto Ge substrates over a wide deposition temperature range ͑50-300°C͒. From grazing-incidence X-ray reflectivity and X-ray photoelectron spectroscopy, we found that increasing the deposition temperature improved the Al 2 O 3 film density and its dielectric stoichiometry; nevertheless, dielectric intermixing between main Al 2 O 3 and interfacial GeO 2 appeared at temperatures above 200°C, along with degradation of the GeO 2 /Ge interface. Accordingly, a relatively large gate leakage current ͑J g ͒ and a high density of interfacial states D it ͑Ͼ10 13 cm −2 eV −1 ͒ were observed as a result of deterioration of the entire Al 2 O 3 /Ge structure at higher deposition temperatures. In addition, although subsequent high-temperature processing at 600°C in a N 2 ambient could relieve the oxygen-excessive behavior further, i.e., to provide a more stoichiometric film, the accompanying GeO x volatilization close to the dielectric interface caused greater damage to the electrical performance. Only forming gas annealing ͑H 2 /N 2 , 1:10͒ at low temperature ͑300°C͒ improved the capacitance-voltage characteristics of the Pt/Al 2 O 3 /Ge structure, in terms of providing a lower value of D it ͑ca. 6 ϫ 10 11 cm −2 eV −1 ͒, a lower value of J g , and a reduced hysteresis width.

Process temperature dependent high frequency capacitance-voltage response of ZrO2/GeO2/germanium capacitors

“…3͑a͒ inset͔ in case of T dep = 250°C most likely due to an increased outdiffusion of GeO x species from the interface. A similar observation has been reported in the case of ALD of Al 2 O 3 at T dep Ͼ 200°C, 11 which leads to defect generation and thus to a degradation of the electrical interface performance. 12 In general, the small ac voltage ͑30 mV͒ applied to the gate causes changes in the occupancy of interface trap levels around a few kT / q of the Fermi-level, which leads to losses at all frequencies, as shown in Fig.…”

Influence of growth temperature on dielectric strength of Al2O3 thin films prepared via atomic layer deposition at low temperature

“…Therefore, the density of the ALD Al 2 O 3 films is expected to decrease slightly when the growth temperature decreases. In other reports, the density of the film grown via ALD largely decreases with decreasing growth temperature due to severely increasing content of residual impurities in the film 14 , 17 . However, only a slight reduction in the refractive index of the film with decreasing temperature was observed, indicating a slight decrease in the density, which is confirmed by the XRR results plotted in the inset of Fig.…”

Thermally-driven H interaction with HfO2 films deposited on Ge(100) and Si(100)

“…The lower D incorporation observed for Ge samples may be related to the theoretically predicted resistance of Ge dangling bonds to H passivation 6 and/or instability of Ge-H bonds. 11 Nevertheless, previous reports showed that the use of FGA in the 300-400 C temperature range presented a reduction in the D it figures in structures like HfO 2 /GeO x N y /Ge, 3 Al 2 O 3 /Ge, 7 and GeO 2 /Ge. 8 These results, in conjunction with our observation that most of the D is incorporated near the HfO 2 /Ge interface region, point to a H-related passivation effect.…”

“…On the other hand, a significant reduction in D it figures is observed for gate stacks following FGA. 3,7,8 This apparent contradiction indicates the need for further understanding of the hydrogen (H) role in the electrical and physico-chemical properties of dielectric films on Ge. In view of this scenario, we investigated the thermally-induced interaction of H with HfO 2 films deposited on Ge and Si substrates.…”