Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions
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= Adhesion layers = | = Adhesion layers = | ||
The deposition of metal thin-�lm structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications, including plasmonics, multilayer structures for photonic structures and metamaterials, organic transistors, substrates for graphene growth and �eld e�ect devices based on 2D materials and carbon nanotubes. | |||
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 �eld 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 di�erent 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 �lms. 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. | |||
Fig. 5.1 represents the simpli�ed 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-�lm thickness. Due to the continuous miniaturization of structures and devices, the total metal thin-�lm 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 simpli�ed model is still adequate. | |||
This chapter presents the characterization work carried out on two main thin-�lm systems: Cr/Au and Ti/Au stacks. | |||
= Adhesion layer effect on Au �thin films = | = Adhesion layer effect on Au �thin films = | ||
Revision as of 11:00, 14 August 2018
Adhesion layers
The deposition of metal thin-�lm structures on dielectric or semiconductor substrates is important in a wide range of micro/nanofabrication applications, including plasmonics, multilayer structures for photonic structures and metamaterials, organic transistors, substrates for graphene growth and �eld e�ect devices based on 2D materials and carbon nanotubes.
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 �eld 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 di�erent 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 �lms. 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.
Fig. 5.1 represents the simpli�ed 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-�lm thickness. Due to the continuous miniaturization of structures and devices, the total metal thin-�lm 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 simpli�ed model is still adequate.
This chapter presents the characterization work carried out on two main thin-�lm systems: Cr/Au and Ti/Au stacks.
Adhesion layer effect on Au �thin films
Adhesion layer model
Recommendations for nanodevice fabrication
Adhesion layer impact on Au �film stability with temperature
allic bond with gold. 5 nm to 10 nm thick of Cr or Ti is commonly used and it is important to deposit Cr or Ti and then immediately Au. If the vacuum chamber is opened in between, the surface of Cr or Ti will get oxidized and that will give a poor adhesion. If a gold layer needs to be deposited directly on Silicon, then native oxide has to be removed by deep in diluted HF and immediately load the evaporation chamber. And after the deposition, the wafer has to be heated op to get some Au-Si diffusion which improves the adhesion.