Structural and electrical properties of electron beam gun evaporated Er2O3 insulator thin films

Abstract

We present a detailed study of the evolution with annealing temperature (in an oxygen environment) of the morphological and structural properties of thin erbium oxide (Er2O3) films evaporated in an electron beam gun system. The electrical characteristics of metal-oxide-semiconductor structures are also described. Atomic force microscope and x-ray difractometry were used to map out the morphology and crystalline nature of films ranging in thickness from 4.5 to 100 nm. High-resolution cross-sectional transmission electron microscopy imaging and Auger electron spectroscopy reveal three sublayers: an outer dense nanocrystalline Er2O3 layer, a middle transition layer and amorphous SiO2 film placed close to the Si substrate. The effective dielectric constant depends on the thickness and the annealing temperature. A 1–2.8 nm interfacial SiO2 layer as well as an ErO inclusion with low polarizability are formed during the deposition and the annealing process has a profound effect on the dielectric constant and the leakages. The minimum effective oxide thickness is 2.4–2.8 nm and in the thinnest films we obtained a leakage current density as low as 1–5×10−8 A/cm2 at an electric field of 1 MV/cm. We observe a shift of the flatband voltage to the positive side and significant lowering of the positive charge down to ∼1×1010 cm−2. For a 4.5 nm film, the maximum total breakdown electric field was approximately 1×107 V/cm.

Superior electrical properties of crystalline Er2O3 films epitaxially grown on Si substrates

“…Other researchers have reported the value of fixed charge density from 8 ϫ 10 13 to 1 ϫ 10 10 cm −2 . 8,10,19 Based on our measurements, we have obtained that the maximum fixed charge density in our Er 2 O 3 thin film is less than 10 12 cm −2 . Figure 3͑b͒ shows the I-V curve of the Er 2 O 3 thin film with the MOS structure.…”

“…In general, rare earth ͑RE͒ oxides have relatively high dielectric constants, larger band gaps ͑ϳ5.4 eV͒, 8 higher conduction band offset with Si ͑over 2 eV͒, 9 and a good thermodynamic stability. 10 18 In recent years, Er 2 O 3 thin films grown on Si substrates were achieved in several groups with different techniques. 10,19,20 For example, Mikhelashvili and Eisenstein 10 grew a series of Er 2 O 3 thin films with different thicknesses using electron-beam gun evaporation.…”

“…10 18 In recent years, Er 2 O 3 thin films grown on Si substrates were achieved in several groups with different techniques. 10,19,20 For example, Mikhelashvili and Eisenstein 10 grew a series of Er 2 O 3 thin films with different thicknesses using electron-beam gun evaporation. They measured k m = 9 for a 10 nm thick Er 2 O 3 thin film.…”

Thermal stability of Er2O3 thin films grown epitaxially on Si substrates

“…4 and 5͒ have been reported; an excellent review about this aspect has been given by de Almeida and Baumvol. 6 Because the theoretical studies show that they have high dielectric constant and good thermal stability, rare earth ͑RE͒ oxides such as Pr 2 [13][14][15] Among them, the Er 2 O 3 films grown epitaxially on Si substrate with an equivalent oxide thickness of 2 nm have been realized, which reveals a good electrical property. 16 To check whether epitaxially grown Er 2 O 3 is an ideal high-k material, the knowledge on its thermal stability is needed.…”

Optical properties of thin erbium oxide films formed by rapid thermal annealing on SiC substrates with different structures

“…Recently, oxides of rare-earth elements were often considered in the literature as alternative oxides used in oxide/silicon structures [4][5][6][7][8][9][10][11]. These oxides have high transparency in the visible spectral range, chemical and thermal stability and have an optimal refractive index for these purposes [4].…”