Atomic Layer Deposition of Al[sub 2]O[sub 3] Thin Films Using Trimethylaluminum and Isopropyl Alcohol

Abstract

Al 2 O 3 thin films were deposited on Si substrates by atomic layer deposition ͑ALD͒ using Al(CH 3 ) 3 ͑trimethylaluminum, TMA͒ as a metal source and (CH 3 ) 2 CHOH ͑isopropyl alcohol, IPA͒ as an oxygen source at 250°C. The film growth rate is saturated at 0.8 Å/cycle, and it is slightly lower than that for the procedure which uses water vapor instead of IPA. The as-deposited film has a stoichiometry close to Al 2 O 3 ͑Al/O ratio ϳ2:3.1͒ and the residual carbon content of the films is below the detection limit of secondary ion mass spectroscopy. An interface oxide between the Al 2 O 3 film and Si-substrate was not detectable on the asdeposited film by transmission electron microscopy. However, after annealing at 800°C for 5 min, an interface oxide is newly formed even under the neutral ambient of Ar, and it grows thicker under the oxidizing ambient of O 2 . That is, oxygen, which is needed for forming the interface oxide during the annealing process is supplied from both of the ambient oxygen and the excess oxygen in the films. Thus, although the loss of dielectric constant is inevitable during the annealing process, it can be minimized by using IPA in Al 2 O 3 ALD.As the size of microelectronic devices is scaled down, oxide films with high dielectric constants are required for gate and capacitor dielectrics. Even though SiO 2 is an excellent dielectric material in many features, the preparation of reliable SiO 2 films thinner than 30 Å is difficult, because of the quantum mechanical tunneling of electrons, which generates a large leakage current across the films. 1 Thus, an alternative oxide film with higher dielectric constant than SiO 2 is needed. 2 In this respect, Al 2 O 3 has been considered as a possible candidate for gate oxides as well as Ta 2 O 5 , HfO 2 , and ZrO 2 . 3-5 Also, Al 2 O 3 is considered as a promising capacitor dielectric, which can replace silicon oxynitride ͑SiON͒ in future dynamic random access memories ͑DRAM͒. 6 In addition, Al 2 O 3 has been recently regarded as a good passivation layer, which can prevent hydrogen penetration into the active region of semiconductor devices. 7 In preparing high-dielectric metal oxides with a thickness in the subhundred angstrom range, atomic layer deposition ͑ALD͒ attracts considerable interest owing to its inherent merits in thin film depositions, such as a digital controllability of film thickness on an atomic scale, a superior conformal deposition on three-dimensional structures, and no particle generation, etc. 8-10 In typical ALD of metal oxide thin films, H 2 O has been most widely used as the oxygen source. [11][12][13][14][15][16] However, by using H 2 O an unwanted interface oxide may be formed between the metal oxides and Si substrates, and it is thought that the interface oxide is composed mainly of SiO x , as the result of the reaction between H 2 O and the Si substrates during the initial stage of the ALD. Hence, the interfusion of the interface oxide would be expected to reduce the dielectric constant of the deposited thin films. 17-19 Th...

Characterisation of metal oxide films deposited by non‐hydrolytic ALD

“…The amounts detected were comparable to those found in TiO 2 films deposited with TiCl 4 C H 2 O under similar conditions. This result is in general agreement with the earlier study by Jeon et al 5 who reported growth of nearly carbon-free alu- mina films from the reaction of TMA with isopropyl alcohol at 250°C. XRD analysis (not presented here) was performed on films deposited with both precursor combinations at temperatures of 200, 250 and 300°C.…”

Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al2O3 with a Series of Alcohol Oxidants

“…However, in early studies, ALD Al 2 O 3 processes with H 2 O oxidants have shown undesirable substrate oxidation issues. Specifically, an unwanted silicate of interfacial layers between the ALD-deposited Al 2 O 3 film and the Si substrate has been observed. , Because the interfacial oxide can deteriorate the electrical properties, it is desirable to reduce the interlayer formation. Furthermore, the use of stronger oxidants such as O 2 plasma led to a much thicker interlayer compared to the H 2 O case, indicating that the reactivity of oxidants during ALD is a key role for substrate oxidation .…”

“…In previous reports, attempts have been made to deposit Al 2 O 3 films using oxidants other than H 2 O, such as acetic acid and alcohols. ,− However, acetic acid has limitations, such as its narrow ALD window and high carbon impurities. In particular, the process temperature is limited to temperatures lower than 120 °C due to the decomposition of acetic acid, which is a critical barrier for practical applications in semiconductor production …”

A Review of Atomic Layer Deposition for Nanoscale Devices

“…It has been applied in the numerous advanced technologies for the fabrication of nanoscale thin films such as microelectronics, Complementary Metal oxide Semiconductor (CMOS) transistors, DRAM memory, MEMS/NEMS, energy conversion, photovoltaics, and display devices [8][9][10][11][12] that require precise control of film properties in thickness, uniformity, and conformability.…”