Al2O3/GeOx gate stack on germanium substrate fabricated by in situ cycling ozone oxidation method

Abstract

Al2O3/GeOx/Ge gate stack fabricated by an in situ cycling ozone oxidation (COO) method in the atomic layer deposition (ALD) system at low temperature is systematically investigated. Excellent electrical characteristics such as minimum interface trap density as low as 1.9 × 1011 cm−2 eV−1 have been obtained by COO treatment. The impact of COO treatment against the band alignment of Al2O3 with respect to Ge is studied by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Based on both XPS and SE studies, the origin of gate leakage in the ALD-Al2O3 is attributed to the sub-gap states, which may be correlated to the OH-related groups in Al2O3 network. It is demonstrated that the COO method is effective in repairing the OH-related defects in high-k dielectrics as well as forming superior high-k/Ge interface for high performance Ge MOS devices.

Interface Engineering and Gate Dielectric Engineering for High Performance Ge MOSFETs

“…This COO method is proved to be effective in repairing the defects like OH-related groups to suppress the gate leakage current. The minimum it value of 1.9 × 10 11 cm −2 eV −1 is obtained by inserting GeO passivation layer with the COO treatment, as shown in Figure 14 [47].…”

“…For high-pressure oxidation and plasma postoxidation techniques, both of them can obtain a relatively low minimum value of it in the order of 10 11 cm −2 eV −1 even at a thin EOT of subnanometer [12,38]. For ozone postoxidation technique, a relatively low minimum value of it of 1.9 × 10 11 cm −2 eV −1 was also obtained under a relatively thick EOT (definite data not given in their report) [47]. Thus, these three techniques are all potential methods to improve the interfacial properties of Ge/dielectric gate stack in Ge MOSFETs.…”

“…Just recently, Yang et al have introduced the cycling ozone oxidation (COO) method into the ALD process to form a high quality Al 2 O 3 /GeO /Ge stack [47]. Figure 13 shows the process flow of COO method used in their work.…”

“…Schematic of fabrication procedure of Ge MOS gate stacks for samples with cycling ozone oxidation (COO) treatment[47].…”

Investigation on the Dominant Key to Achieve Superior Ge Surface Passivation by GeOx Based on the Ozone Oxidation

“…A high quality Ge MOS gate stacks with low interface state density (D it ) is imperative for the successful industrial application [2]. After about 15 years′ intensive studies [3][4][5], it has been demonstrated that Ge dioxide or sub-oxide (GeO x ) can provide excellent electrical properties with the D it in the range of 10 10 -10 11 cm -2 ·eV -1 [6][7][8][9][10][11][12][13][14][15][16][17]. And the GeO x can be grown by thermal oxidation in atmospheric pressure O 2 [6; 7], high pressure O 2 (~70 atm) [13; 14], oxygen plasma [9-12; 17], or ozone oxidation [8; 15; 16].…”