Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers - Revision history

Mmat at 10:00, 17 June 2025

2025-06-17T10:00:33Z

← Older revision		Revision as of 12:00, 17 June 2025
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	image:Picture7.png\|Fig. 4: TEM cross section images and 300x300 nm AFM images of the 2nm Cr/2nm Au sample (a-b) and of the 2nm Cr/20nm Au sample (c-d). </gallery>		image:Picture7.png\|Fig. 4: TEM cross section images and 300x300 nm AFM images of the 2nm Cr/2nm Au sample (a-b) and of the 2nm Cr/20nm Au sample (c-d). </gallery>

	To investigate the crystal orientation of the metal thin-films, tramsimission Kikuchi diffraction was used (Fig. 5a) (see [[LabAdviser/~~CEN~~/Nova ~~NanoSEM 600~~/Transmission Kikuchi diffraction\|Transmission Kikuchi diffraction]] for more information). The nanostructure of the 20nm Au film has a bimodal grain size distribution (Fig. 5b). While the smaller grains have different crystal orientations, the large grains (blue color) all have [111] orientation.		To investigate the crystal orientation of the metal thin-films, tramsimission Kikuchi diffraction was used (Fig. 5a) (see [[LabAdviser/314/Microscopy 314-307/SEM/Nova/Transmission Kikuchi diffraction\|Transmission Kikuchi diffraction]] for more information). The nanostructure of the 20nm Au film has a bimodal grain size distribution (Fig. 5b). While the smaller grains have different crystal orientations, the large grains (blue color) all have [111] orientation.

	Microstructural evolution and growth of metal thin-films deposited by physical vapor deposition on amorphous dielectric substrates follows island growth. The first thin-film growth step is the nucleation of small islands once the activation barrier and the critical nuclei size have been overcome. It is followed by a second step of island growth, during which the impinging atoms contribute to increase island size. The third step, usually happening simultaneously with step 2, is island coalescence, where a strong driving force is present for coarsening through surface atom diffusion and grain boundaries (GB) motion. During this process, the island growth is driven by the minimization of surface and interface energy.		Microstructural evolution and growth of metal thin-films deposited by physical vapor deposition on amorphous dielectric substrates follows island growth. The first thin-film growth step is the nucleation of small islands once the activation barrier and the critical nuclei size have been overcome. It is followed by a second step of island growth, during which the impinging atoms contribute to increase island size. The third step, usually happening simultaneously with step 2, is island coalescence, where a strong driving force is present for coarsening through surface atom diffusion and grain boundaries (GB) motion. During this process, the island growth is driven by the minimization of surface and interface energy.

Eves at 16:24, 9 January 2025

2025-01-09T16:24:02Z

← Older revision		Revision as of 18:24, 9 January 2025
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	The samples with the adhesion layers and 20 nm Au layer were also analyzed. The addition of the adhesion layer had in both cases a profound impact on grain size and orientation of the Au film, as visible in Fig. 7a and 7c. The image shows small grains mainly oriented in the [111] crystal direction, with an average grain size of 40 nm for Ti (Fig. 7b) and 36 nm for Cr (Fig. 7d). During the collection of the TKD maps, only the Kikuchi patterns produced by the electron scattering from the Au layer were recorded and indexed. Cr and Ti layers did not contribute to the pattern formation due to two main reasons: i) they are too thin to produce enough scattered electrons and ii) they are		The samples with the adhesion layers and 20 nm Au layer were also analyzed. The addition of the adhesion layer had in both cases a profound impact on grain size and orientation of the Au film, as visible in Fig. 7a and 7c. The image shows small grains mainly oriented in the [111] crystal direction, with an average grain size of 40 nm for Ti (Fig. 7b) and 36 nm for Cr (Fig. 7d). During the collection of the TKD maps, only the Kikuchi patterns produced by the electron scattering from the Au layer were recorded and indexed. Cr and Ti layers did not contribute to the pattern formation due to two main reasons: i) they are too thin to produce enough scattered electrons and ii) they are
	worse electron scattering centers ~~tahn~~ Au because they have a lower atomic number.		worse electron scattering centers than Au because they have a lower atomic number.

	[[File:Picture8.png\|300px\|center\|thumb\|Fig. 7: TKD IPFZ maps of the growth direction and grain size distributions of the 2-Ti/20-Au sample (a-b) and of the 2-Cr/20-Au sample (c-d).]]		[[File:Picture8.png\|300px\|center\|thumb\|Fig. 7: TKD IPFZ maps of the growth direction and grain size distributions of the 2-Ti/20-Au sample (a-b) and of the 2-Cr/20-Au sample (c-d).]]
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	= Adhesion layer model =		= Adhesion layer model =

	Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices		Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices.

	The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature.		The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature.

Eves at 16:22, 9 January 2025

2025-01-09T16:22:40Z

← Older revision		Revision as of 18:22, 9 January 2025
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	= Adhesion layer model =		= Adhesion layer model =

	Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices.		Based on the results obtained above, a revised adhesion layer model for Ti/Au and Cr/Au thin-film systems is proposed. The model is intended as an improvement in the description of the layer-layer interaction compared to the model described in Fig. 1, with the aim of helping the thin-film engineering of nanodevices

	The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature.		The adhesion layer model is shown in Fig. 14. The growth of both adhesion layers starts with the deposition of the atoms on the substrate (1) and the subsequent formation of an amorphous layer (2). During the deposition, both Ti and Cr get partially oxidized by oxygen and water molecules present on the substrate surface and in the deposition chamber. The adhesion layer acts as a wetting layer for Au, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to the case where Au is directly evaporated onto the SiO2 surface. The enhanced wetting is due to the formation of Ti-Au and Cr-Au chemical bonds. This leads to the formation of a continuous film having i) monodisperse grain size and ii) the energetically most favorable [111] crystal orientation for Au (3). For the Cr/Au system there is an extra step: the inter-diffusion between Cr and Au to form a Cr-Au alloy (4). Such diffusion is limited to a thickness of 2-3 nm for samples prepared at room temperature.

Eves: /* Adhesion layers */

2021-10-03T12:28:03Z

Adhesion layers

← Older revision		Revision as of 14:28, 3 October 2021
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	The deposition of metal thin-film structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications (plasmonics, metamaterials, organic transistors, substrates for graphene growth, field effect devices).		The deposition of metal thin-film structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications (plasmonics, metamaterials, organic transistors, substrates for graphene growth, field effect devices).

	Noble metals such as Au, Ag, and Pt are often used for the fabrication of these structures. Noble metals are preferred for their high thermal and electrical conductivities, strong and unique optical resonances in the visible and near-infrared (NIR) region of the electromagnetic spectrum due to the resonant response of their free electrons to the electric field of light, and chemical inertness. However, their chemical inertness is also a problem during the fabrication process, because the layers adhere poorly to the substrate, leading to different phenomena like delamination, peeling and deterioration of device performance over time		Noble metals such as Au, Ag, and Pt are often used for the fabrication of these structures. Noble metals are preferred for their high thermal and electrical conductivities, strong and unique optical resonances in the visible and near-infrared (NIR) region of the electromagnetic spectrum due to the resonant response of their free electrons to the electric field of light, and chemical inertness. However, their chemical inertness is also a problem during the fabrication process, because the layers adhere poorly to the substrate, leading to different phenomena like delamination, peeling and deterioration of device performance over time.

	An empiric approach has been applied to the adhesion enhancement, leading to the application of extremely thin adhesion layers between the substrate and the noble metal films. The most used of these adhesion layers are transition metals like Ti and Cr, but the advantages of using these materials as adhesion layers are poorly understood.		An empiric approach has been applied to the adhesion enhancement, leading to the application of extremely thin adhesion layers between the substrate and the noble metal films. The most used of these adhesion layers are transition metals like Ti and Cr, but the advantages of using these materials as adhesion layers are poorly understood.

Eves at 12:27, 3 October 2021

2021-10-03T12:27:56Z

← Older revision		Revision as of 14:27, 3 October 2021
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	The deposition of metal thin-film structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications (plasmonics, metamaterials, organic transistors, substrates for graphene growth, field effect devices).		The deposition of metal thin-film structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications (plasmonics, metamaterials, organic transistors, substrates for graphene growth, field effect devices).

	Noble metals such as Au, Ag, and Pt are often used for the fabrication of these structures. Noble metals are preferred for their high thermal and electrical conductivities, strong and unique optical resonances in the visible and near-infrared (NIR) region of the electromagnetic spectrum due to the resonant response of their free electrons to the electric field of light, and chemical inertness. However, their chemical inertness is also a problem during the fabrication process, because the layers adhere poorly to the substrate, leading to different phenomena like delamination, peeling and deterioration of device performance over time.		Noble metals such as Au, Ag, and Pt are often used for the fabrication of these structures. Noble metals are preferred for their high thermal and electrical conductivities, strong and unique optical resonances in the visible and near-infrared (NIR) region of the electromagnetic spectrum due to the resonant response of their free electrons to the electric field of light, and chemical inertness. However, their chemical inertness is also a problem during the fabrication process, because the layers adhere poorly to the substrate, leading to different phenomena like delamination, peeling and deterioration of device performance over time

	An empiric approach has been applied to the adhesion enhancement, leading to the application of extremely thin adhesion layers between the substrate and the noble metal films. The most used of these adhesion layers are transition metals like Ti and Cr, but the advantages of using these materials as adhesion layers are poorly understood.		An empiric approach has been applied to the adhesion enhancement, leading to the application of extremely thin adhesion layers between the substrate and the noble metal films. The most used of these adhesion layers are transition metals like Ti and Cr, but the advantages of using these materials as adhesion layers are poorly understood.

Mattod: /* Adhesion layer effect on Au thin films */

2018-08-30T11:45:07Z

Adhesion layer effect on Au thin films

← Older revision		Revision as of 13:45, 30 August 2018
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	To avoid oxidation of Ti or Cr that is in physical contact with the nano-electronic materials, one solution is to avoid these materials completely. Indeed, some of the best performing CNT devices are made without the use of adhesion layers, as e.g. Pd which is directly used. '''If an adhesion layer is required for mechanical stability, a less than 2nm thin Cr layer is recommended and Ti must be avoided'''. This is because the partially oxidized Ti might form a barrier between the nano-electronic material and the Au over-layer, with a consequent deterioration of the electron transport performances. Because of the single-layer morphology due to the Cr-Au alloy formation, the alloy will make electrical and physical contact to the nano-electronic material, despite the chrome oxide content. Furthermore, a low temperature annealing will enhance inter-diffusion of Au and Cr and improve electrical contact between the nano-electronic material and the Au over-layer.		To avoid oxidation of Ti or Cr that is in physical contact with the nano-electronic materials, one solution is to avoid these materials completely. Indeed, some of the best performing CNT devices are made without the use of adhesion layers, as e.g. Pd which is directly used. '''If an adhesion layer is required for mechanical stability, a less than 2nm thin Cr layer is recommended and Ti must be avoided'''. This is because the partially oxidized Ti might form a barrier between the nano-electronic material and the Au over-layer, with a consequent deterioration of the electron transport performances. Because of the single-layer morphology due to the Cr-Au alloy formation, the alloy will make electrical and physical contact to the nano-electronic material, despite the chrome oxide content. Furthermore, a low temperature annealing will enhance inter-diffusion of Au and Cr and improve electrical contact between the nano-electronic material and the Au over-layer.

	= ~~Adhesion~~ layer effect on Au thin films =		= Characterization of adhesion layer effect on Au thin films =

	== Effect on Au film morphology, grain size and texture ==		== Effect on Au film morphology, grain size and texture ==

Mattod at 11:44, 30 August 2018

2018-08-30T11:44:42Z

@@ Line 15: / Line 15: @@
 Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on two main thin-film systems, Cr/Au and Ti/Au stacks, to arrive at these recommendations is presented.
 = Adhesion layer effect on Au thin films =
@@ Line 93: / Line 113: @@
 [[File:Picture17.png|550px|center|thumb|Fig. 14. Revised adhesion layer model for Ti/Au and Cr/Au multilayer systems. (1) Adhesion layer nucleation; (2) growth of a partially oxidized adhesion layer; (3) growth of Au grains with [111] crystal orientation on top of the adhesion layer; (4) only for Cr: Cr/Au inter-diffusion and alloy formation during/after Au deposition.]]
 = Adhesion layer impact on Au film stability with temperature =

Mattod: /* Adhesion layers */

2018-08-30T11:43:50Z

Adhesion layers

← Older revision		Revision as of 13:43, 30 August 2018
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	[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate, adhesion layer and overlayer system. The substrate is either a dielectric or semiconductor material and the over-layer is a metal.]]		[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate, adhesion layer and overlayer system. The substrate is either a dielectric or semiconductor material and the over-layer is a metal.]]

	Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on on two main thin-film systems, Cr/Au and Ti/Au stacks, to arrive at these recommendations is presented.		Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on two main thin-film systems, Cr/Au and Ti/Au stacks, to arrive at these recommendations is presented.

	= Adhesion layer effect on Au thin films =		= Adhesion layer effect on Au thin films =

Mattod: /* Adhesion layers */

2018-08-30T11:43:29Z

Adhesion layers

← Older revision		Revision as of 13:43, 30 August 2018
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	[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate, adhesion layer and overlayer system. The substrate is either a dielectric or semiconductor material and the over-layer is a metal.]]		[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate, adhesion layer and overlayer system. The substrate is either a dielectric or semiconductor material and the over-layer is a metal.]]

	Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on on two main thin-film systems, Cr/Au and Ti/Au stacks to arrive at these recommendations is presented.		Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on on two main thin-film systems, Cr/Au and Ti/Au stacks, to arrive at these recommendations is presented.

	= Adhesion layer effect on Au thin films =		= Adhesion layer effect on Au thin films =

Mattod: /* Adhesion layers */

2018-08-30T11:42:50Z

Adhesion layers

← Older revision		Revision as of 13:42, 30 August 2018
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	Fig. 1 represents the simplified adhesion layer model usually used in the micro and nanofabrication community for a generic bilayer system. In this model, the adhesion layer and the noble metal over-layer are deposited sequentially by PVD and are considered to be completely uniform and in perfect contact. Ti and Cr are known to be more chemically reactive than noble metals and thereby increase the adhesion as they chemically bind to the substrate. However, the model does not include any layer-layer interaction. Moreover, it is considered to be independent of the thin-film thickness. Due to the continuous miniaturization of structures and devices, the total metal thin-film thicknesses have reached tens of nanometers, with the thickness of the over-layer approaching the one of the adhesion layer. In these conditions it is unclear if the simplified model is still adequate.		Fig. 1 represents the simplified adhesion layer model usually used in the micro and nanofabrication community for a generic bilayer system. In this model, the adhesion layer and the noble metal over-layer are deposited sequentially by PVD and are considered to be completely uniform and in perfect contact. Ti and Cr are known to be more chemically reactive than noble metals and thereby increase the adhesion as they chemically bind to the substrate. However, the model does not include any layer-layer interaction. Moreover, it is considered to be independent of the thin-film thickness. Due to the continuous miniaturization of structures and devices, the total metal thin-film thicknesses have reached tens of nanometers, with the thickness of the over-layer approaching the one of the adhesion layer. In these conditions it is unclear if the simplified model is still adequate.

	~~Here the first recommendations on the~~ adhesion ~~layers best suited for specific nanodevice applications are presented~~. ~~Below~~ the ~~background and characterization work carried out on on two main thin~~-~~film systems, Cr/Au and Ti/Au stacks to arrive at these recommendations~~ is ~~presented~~.”		[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate, adhesion layer and overlayer system. The substrate is either a dielectric or semiconductor material and the over-layer is a metal.]]

	~~[[File:Picture00.png\|650px\|center\|thumb\|Fig. 1: Schematic representation of a substrate,~~ adhesion ~~layer and overlayer system~~. ~~The substrate is either a dielectric or semiconductor material~~ and ~~the over~~-~~layer~~ is ~~a metal~~.]]		Here the first recommendations on the adhesion layers best suited for specific nanodevice applications are presented. Below the background and characterization work carried out on on two main thin-film systems, Cr/Au and Ti/Au stacks to arrive at these recommendations is presented.

	= Adhesion layer effect on Au thin films =		= Adhesion layer effect on Au thin films =