On the reliability of nanoindentation hardness of Al2O3 films grown on Si-wafer by atomic layer deposition

Xuwen Liu, Eero Haimi, Simo Pekka Hannula, Oili M.E. Ylivaara, Riikka L. Puurunen

Research output: Contribution to journalArticleScientificpeer-review

4 Citations (Scopus)

Abstract

The interest in applying thin films on Si-wafer substrate for microelectromechanical systems devices by using atomic layer deposition (ALD) has raised the demand on reliable mechanical property data of the films. This study aims to find a quick method for obtaining nanoindentation hardness of thin films on silicon with improved reliability. This is achieved by ensuring that the film hardness is determined under the condition that no plastic deformation occurs in the substrate. In the study, ALD Al2O3 films having thickness varying from 10 to 600 nm were deposited on a single-side polished silicon wafer at 300 °C. A sharp cube-corner indenter was used for the nanoindentation measurements. A thorough study on the Si-wafer reference revealed that at a specific contact depth of about 8 nm the wafer deformation in loading transferred from elastic to elastic-plastic state. Furthermore, the occurrence of this transition was associated with a sharp increase of the power-law exponent, m, when the unloading data were fitted to a power-law relation. Since m is only slightly material dependent and should fall between 1.2 and 1.6 for different indenter geometry having elastic contact to common materials, it is proposed that the high m values are the results from the inelastic events during unloading. This inelasticity is linked to phase transformations during pressure releasing, a unique phenomenon widely observed in single crystal silicon. Therefore, it is concluded that m could be used to monitor the mechanical state of the Si substrate when the whole coating system is loaded. A suggested indentation depth range can then be assigned to each film thickness to provide guidelines for obtaining reliable property data. The results show good consistence for films thicker than 20 nm and the nanoindentation hardness is about 11 GPa independent of film thickness.

Original languageEnglish
Article number01A116
JournalJournal of Vacuum Science and Technology A: Vacuum, Surfaces and Films
Volume32
Issue number1
Early online date11 Dec 2013
DOIs
Publication statusPublished - 2014
MoE publication typeA1 Journal article-refereed

Fingerprint

Atomic layer deposition
Nanoindentation
atomic layer epitaxy
nanoindentation
Film thickness
hardness
Hardness
wafers
Silicon
Unloading
film thickness
unloading
Substrates
Thin films
silicon
Silicon wafers
Indentation
Thick films
MEMS
Plastic deformation

Cite this

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title = "On the reliability of nanoindentation hardness of Al2O3 films grown on Si-wafer by atomic layer deposition",
abstract = "The interest in applying thin films on Si-wafer substrate for microelectromechanical systems devices by using atomic layer deposition (ALD) has raised the demand on reliable mechanical property data of the films. This study aims to find a quick method for obtaining nanoindentation hardness of thin films on silicon with improved reliability. This is achieved by ensuring that the film hardness is determined under the condition that no plastic deformation occurs in the substrate. In the study, ALD Al2O3 films having thickness varying from 10 to 600 nm were deposited on a single-side polished silicon wafer at 300 °C. A sharp cube-corner indenter was used for the nanoindentation measurements. A thorough study on the Si-wafer reference revealed that at a specific contact depth of about 8 nm the wafer deformation in loading transferred from elastic to elastic-plastic state. Furthermore, the occurrence of this transition was associated with a sharp increase of the power-law exponent, m, when the unloading data were fitted to a power-law relation. Since m is only slightly material dependent and should fall between 1.2 and 1.6 for different indenter geometry having elastic contact to common materials, it is proposed that the high m values are the results from the inelastic events during unloading. This inelasticity is linked to phase transformations during pressure releasing, a unique phenomenon widely observed in single crystal silicon. Therefore, it is concluded that m could be used to monitor the mechanical state of the Si substrate when the whole coating system is loaded. A suggested indentation depth range can then be assigned to each film thickness to provide guidelines for obtaining reliable property data. The results show good consistence for films thicker than 20 nm and the nanoindentation hardness is about 11 GPa independent of film thickness.",
author = "Xuwen Liu and Eero Haimi and Hannula, {Simo Pekka} and Ylivaara, {Oili M.E.} and Puurunen, {Riikka L.}",
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On the reliability of nanoindentation hardness of Al2O3 films grown on Si-wafer by atomic layer deposition. / Liu, Xuwen; Haimi, Eero; Hannula, Simo Pekka; Ylivaara, Oili M.E.; Puurunen, Riikka L.

In: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films, Vol. 32, No. 1, 01A116, 2014.

Research output: Contribution to journalArticleScientificpeer-review

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AU - Liu, Xuwen

AU - Haimi, Eero

AU - Hannula, Simo Pekka

AU - Ylivaara, Oili M.E.

AU - Puurunen, Riikka L.

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