Low-Temperature Deposition of Aluminum Oxide by Radical Enhanced Atomic Layer Deposition

Niskanen, Antti; Arstila, Kai; Ritala, Mikko; Leskelä, Markku

doi:10.1149/1.1931471

Cited by 72 publications

(61 citation statements)

References 34 publications

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“…[39] The same trend was observed earlier when comparing the growth rates obtained by RE-ALD and PE-ALD of aluminum oxide using trimethylaluminum (TMA) as the aluminum precursor. The processes utilizing oxygen radicals as the oxygen source produced higher growth rates, 0.23 nm per cycle [48] and 0.14 nm per cycle at 200°C, [49] than the 0.11 nm per cycle obtained with the thermally activated process using water as the oxygen source. [49,50] The crosssectional scanning electron microscope (SEM) image taken from a 30 nm thick titanium dioxide film deposited on a substrate with patterned trenches shows conformal coverage (Fig.…”

Section: Resultsmentioning

confidence: 73%

“…In this work, RE-ALD was used to deposit titanium dioxide from titanium isopropoxide and oxygen radicals with 152 a set-up described earlier. [47,48] RE-ALD circumvents the potentially harmful effects of plasmas, such as ion and electron bombardment, by locating the substrates outside and downstream of the plasma zone, exposing them only to radicals. The films were deposited near room temperature allowing deposition also on heat sensitive materials such as plastics and natural fibers.…”

Section: Introductionmentioning

confidence: 99%

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Radical Enhanced Atomic Layer Deposition of Titanium Dioxide

Niskanen

Arstila

Leskelä

et al. 2007

Chemical Vapor Deposition

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Titanium dioxide films are grown with radical-enhanced atomic layer deposition (RE-ALD) from titanium isopropoxide and oxygen radicals at between 50 and 300°C on silicon, glass, platinum, and RuO 2 surfaces. Additionally, the films are grown on polymers and natural fibers at 50°C. The oxygen radicals are produced by dissociating molecular oxygen with a remote microwave plasma discharge. Purified argon is used as the carrier and purge gas. Growth rate saturation and conformal growth are observed, and thus the film growth in the ALD mode was proven. The saturated growth rate is 0.19 nm per cycle at 50°C, with an overall cycle time of 11 s. The film grown at 50°C has a dielectric constant of 20, and undergoes catastrophic breakdown at 0.6 MV cm -1 electric field. It contains 13 at.-% hydrogen and 4 at.-% carbon. As the deposition temperature is increased to 250°C, the impurity contents decrease to 0.5 at.-% for hydrogen and 0.4 at.-% for carbon. The film density and refractive index are 3.2 g cm -3 and 2.2, respectively, for a film deposited at 50°C, and increases to 3.8 g cm -3 and 2.4, respectively, for a film deposited at 250°C. All the films grown below 250°C are amorphous according to X-ray diffraction (XRD).

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Section: Resultsmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Radical Enhanced Atomic Layer Deposition of Titanium Dioxide

Niskanen

Arstila

Leskelä

et al. 2007

Chemical Vapor Deposition

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“…This means that it is possible to deposit films with equivalent material properties at lower substrate temperatures than for thermal ALD. 40,56,65,87,187,233,243,249,254,320 The reactivity delivered by the plasma species is not only provided by reactive plasma radicals but is also determined by the kinetic energy of the ions accelerated in the plasma sheath, the surfacerecombination energy of the ions and other species, and the energy flux caused by the plasma radiation.…”

Section: B Deposition At Reduced Substrate Temperaturesmentioning

confidence: 99%

“…Consequently, this can lead to higher growth per cycle values. 31,32,40,58,60,134,154,187,207,208,229,233,254,259,261,274,294 Moreover, the plasma can be switched on and off very rapidly, which enables fast pulsing of the plasma reactant species 255,273,274,293,295 and reduced purge times (depending on the gas residence time in the reactor). 46,60 The latter is especially important for the ALD of metal oxides at low temperatures (room temperature up to 150 C), where purging of H 2 O, in the case of thermal ALD, requires excessively long purge times and, therefore, long cycle times.…”

Section: E Increased Growth Ratementioning

confidence: 99%

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

Profijt

Potts

Sanden

et al. 2011

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

729

537

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Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with Å-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications.

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“…5,49 A higher growth rate has been reported earlier for both remote and direct plasmas compared to thermal ALD for identical deposition temperature settings. 3,50,51 We would like to note that the H 2 O based process suffers from the so-called "soft saturation" behavior, especially at low temperatures. High doses of H 2 O have been found necessary to reach saturated film growth.…”

Section: A In Situ Thickness Monitoring By Sementioning

confidence: 99%

Reaction mechanisms during plasma-assisted atomic layer deposition of metal oxides: A case study for Al2O3

Heil

Hemmen

Sanden

et al. 2008

Journal of Applied Physics

110

111

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Plasma-assisted atomic layer deposition ͑ALD͒ of metal oxide films is increasingly gaining interest, however, the underlying reaction mechanisms have rarely been addressed. In this work, a case study is presented for the plasma-assisted ALD process of Al 2 O 3 based on Al͑CH 3 ͒ 3 dosing and O 2 plasma exposure. A complementary set of time-resolved in situ diagnostics was employed, including spectroscopic ellipsometry, quartz crystal microbalance, mass spectrometry, and optical emission spectroscopy. The saturation of the Al͑CH 3 ͒ 3 adsorption reactions was investigated, as well as the reaction products created during both the precursor dosing and the plasma exposure step. The generality of the observations was cross-checked on a second commercial ALD reactor. The main observations are as follows: ͑i͒ during the precursor dosing, the Al͑CH 3 ͒ 3 predominantly binds bifunctionally to the surface at 70°C through a reaction in which H is abstracted from the surface and CH 4 is released into the gas phase; ͑ii͒ during the plasma exposure, O radicals in the plasma are consumed at the surface by combustionlike reactions with the surface −CH 3 ligands, producing mainly H 2 O, CO 2 , and CO; ͑iii͒ small gas phase densities of CH 4 and higher hydrocarbons ͑C 2 H x ͒ are also present during the O 2 plasma exposure step indicating complementary surface reactions including a secondary thermal ALD-like reaction by the H 2 O produced at the surface; ͑iv͒ the plasma and its optical emission are strongly affected by the surface reaction products released in the plasma. In the latter respect, optical emission spectroscopy proved to be a valuable tool to study the surface reaction products during the plasma exposure as well as the saturation of the surface reactions. The implications of the experimental observations are addressed and it is discussed that the reaction mechanisms are generic for plasma-assisted ALD processes based on metal organic precursors and O 2 plasma as oxidant source.

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Low-Temperature Deposition of Aluminum Oxide by Radical Enhanced Atomic Layer Deposition

Cited by 72 publications

References 34 publications

Radical Enhanced Atomic Layer Deposition of Titanium Dioxide

Radical Enhanced Atomic Layer Deposition of Titanium Dioxide

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

Reaction mechanisms during plasma-assisted atomic layer deposition of metal oxides: A case study for Al2O3

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