Cyclopentadienyl Precursors for the Atomic Layer Deposition of Erbium Oxide Thin Films

Abstract

In this article, three novel cyclopentadienyl precursors are evaluated for the atomic layer deposition (ALD) of erbium oxide, with either ozone or water as the oxygen source. The erbium precursors evaluated are Er(iPrCp)3, Er(MeCp)2(iPr‐amd), and Er(nBuCp)3. The films are deposited on silicon within the temperature range 200–400°C. Self‐limiting growth is achieved with all three precursors, with both ozone and water. It is found that the water processes of all three precursors present significantly higher growth rates when compared to the ozone processes. An up to three‐fold increase in the growth rate is observed for the water processes of Er(iPrCp)3 and Er(MeCp)2(iPr‐amd) (amd: amidinate) when compared to their ozone processes. The films are smooth and uniform, as determined by atomic force microscopy (AFM) (rms roughness < 3% of film thickness). The composition of the films is investigated by means of X‐ray photoelectron spectroscopy (XPS). It is found that the films contain small amounts of carbon as an impurity, especially in the case of ozone‐processed films. Using Er(nBuCp)3 together with ozone as the oxygen source, a highly conformal Er2O3 thin film is deposited on a 1:60 high‐aspect‐ratio substrate. This is the first report of the conformal growth of Er2O3 thin films by ALD on a high‐aspect‐ratio structure.

Evaluation of Volatility and Thermal Stability in Monomeric and Dimeric Lanthanide(III) Complexes Containing Enaminolate Ligands

“…Lanthanide complexes of the formula Ln­(β-diketonate) 3 have very high thermal stabilities and can exhibit self-limited growth of oxides up to 400 °C. ,− However, Ln­(β-diketonate) 3 precursors are unreactive toward water and require ozone as a coreactant for oxide growth. ,− Ozone is highly reactive and causes oxidation of silicon substrates. Lanthanide cyclopentadienyl complexes also have very high thermal stabilities and water can be used as a coreactant for the growth of oxide films. ,− For example, the growth of Er 2 O 3 films with Er­(C 5 H 4 Me) 3 and water exhibits an ALD window from about 250 to 350 °C on Si(100) substrates . The growth of PrAlO 3 films using Pr­(C 5 H 4 iPr) 3 , AlMe 3 , and water shows an ALD window from about 275 to 325 °C .…”

“…ALD requires chemical precursors that are volatile, thermally stable at the deposition temperatures, and highly reactive toward a second reagent. , Many different ligands have been employed to create volatile and thermally stable lanthanide precursors for film growth by ALD . Ligands in previously reported precursors have included β-diketonate, − cyclopentadienyl and substituted cyclopentadienyl, ,− bis­(trimethylsilyl)­amide, alkoxide, , and amidinates and guanidinates. ,− Additionally, volatile lanthanide complexes containing N , N -dimethylaminodiboranate ligands have been recently reported but have not been tested in ALD growth. − Currently available lanthanide precursors have exhibited several problems in ALD growth, including the low reactivity of β-diketonate precursors toward water as a coreactant, substrate oxidation when ozone is used as a coreactant, low thermal stability, and lack of true self-limited growth. As a result, there is an ongoing need for volatile, thermally stable lanthanide precursors for ALD that address these issues.…”

Photofragmentation Pathways for Gas-Phase Lanthanide Tris(isopropylcyclopentadienyl) Complexes

“…12−15 For example, Kondo et al deposited Pr 2 O 3 films on silicon substrates with a high dielectric constant of 26 ± 3 using praseodymium tris (ethylcyclopentadienyl) [Pr(EtCp) 3 ] precursors, and Blanquart et al used erbium cyclopentadienyl complexes to deposit Er 2 O 3 thin films by ALD. 11,14 The high volatility of lanthanide cyclopentadienyl complexes also makes them potential precursors for photolytic laser-assisted metal−organic chemical vapor deposition (LCVD), allowing lower deposition temperatures. It is our goal to better understand the photofragmentation pathways of gas-phase lanthanide cyclopentadienyl complexes in order to better control the purity of thin-film deposition using LCVD.…”

“…Lanthanide oxide thin films have applications in metal-oxide semiconductor field-effect transistors (MOSFETs), − protective coatings, , luminescent materials, − and waveguides. , Lanthanide cyclopentadienyl complexes have been frequently employed to prepare lanthanide oxide thin films by both metal–organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) techniques. − For example, Kondo et al deposited Pr 2 O 3 films on silicon substrates with a high dielectric constant of 26 ± 3 using praseodymium tris­(ethylcyclopentadienyl) [Pr­(EtCp) 3 ] precursors, and Blanquart et al used erbium cyclopentadienyl complexes to deposit Er 2 O 3 thin films by ALD. , The high volatility of lanthanide cyclopentadienyl complexes also makes them potential precursors for photolytic laser-assisted metal–organic chemical vapor deposition (LCVD), allowing lower deposition temperatures. It is our goal to better understand the photofragmentation pathways of gas-phase lanthanide cyclopentadienyl complexes in order to better control the purity of thin-film deposition using LCVD.…”

Atomic Layer Deposition of TiO2 and ZrO2 Thin Films Using Heteroleptic Guanidinate Precursors

“…Ideally, a heteroleptic precursor should display the best properties of its different ligands, while simultaneously the downsides of these ligands, e.g., poor thermal stability, should be suppressed. The molecular properties one tries to affect by substituting one or more ligands of a homoleptic precursor are most commonly volatility, thermal stability and reactivity …”