TY - BOOK

T1 - Sputter Deposition of Multifunctional Thin Films

AU - Rausch, Martin

N1 - no embargo

PY - 2019

Y1 - 2019

N2 - Magnetron sputter deposited thin films show a wide variety of applications. In particular, Mo-based films are used in displays and microelectronics, whereas NiW-based electrochromic films are used for architectural glass. Nonetheless, from a scientific point of view there are still various questions to be answered, especially concerning the process-stability and deposition behavior of different coating systems on an industrial-scale. Therefore, one of the aims of the current thesis is adding substantial knowledge to the process stability of a planar industrial-scale Mo target. A systematic study of the influence of the depth of the target erosion groove on film properties revealed a non-linear evolution of film properties over target usage. The changes in film quality were attributed to the varying influence of reflected Ar neutrals to the overall energy input into the growing film. Argon atoms that are reflected from a new, uneroded target surface contribute to a large energy input into the growing film. With the evolution of an erosion groove, the reflecting angle of the Ar neutrals changes, which results in a decreasing energy input into the growing film. When the target erosion proceeds, the target surface gets closer to the magnet bars behind the target, leading to an increase of charge carriers in the plasma and a rise in deposition current. Therefore, a larger amount of Ar+ ions bombard the target, with a concomitant larger amount of Ar neutrals reflected from the target surface. This increases the energy input into the growing film again, revealing the importance of reflected Ar neutrals on film growth. Similar conclusions were drawn from the systematic study of the deposition behavior of MoAlTi and NiW films from rotatable targets on an industrial scale. In both cases, reflected Ar neutrals were identified as main source of selective re-sputtering of the film constituent with higher sputter yield. Since the amount of selective re-sputtering is pressure-dependent, changing the Ar pressure allows controlling the elemental composition of films grown from multi-element targets to a certain degree. However, the two studied multi-element systems MoAlTi and NiW showed an opposite trend concerning lateral elemental distribution, with “light” Al being depleted and “light” Ni being enriched opposite the target center. Mass-energy analyzer measurements and Monte-Carlo simulations led to the conclusion that during magnetron sputtering of multi-element targets two atomic-mass depended mechanisms exist, namely a scatter-dominated and an emission-dominated regime. When the mass of the target element is smaller than the mass of the background gas, the sputtered elements tend to be predominantly scattered. This leads to a depletion of the light element opposite the target center. On the contrary, when the mass of the target element is larger than the mass of the background gas, the emission characteristics of the sputtered elements are conserved throughout the deposition process. This leads to an enrichment of that element opposite the target that is preferentially emitted close to the target normal. To conclude, the current thesis underlines the importance of reflected Ar neutrals on the growth of both single-element and multi-element thin films. Not only microstructure and accompanying film properties like stress and electrical resistivity, but also the elemental composition can be influenced by this high-energetic particle bombardment. The findings reported within this thesis can therefore contribute to a wider understanding and improved process control of sputter processes in industry and academia.

AB - Magnetron sputter deposited thin films show a wide variety of applications. In particular, Mo-based films are used in displays and microelectronics, whereas NiW-based electrochromic films are used for architectural glass. Nonetheless, from a scientific point of view there are still various questions to be answered, especially concerning the process-stability and deposition behavior of different coating systems on an industrial-scale. Therefore, one of the aims of the current thesis is adding substantial knowledge to the process stability of a planar industrial-scale Mo target. A systematic study of the influence of the depth of the target erosion groove on film properties revealed a non-linear evolution of film properties over target usage. The changes in film quality were attributed to the varying influence of reflected Ar neutrals to the overall energy input into the growing film. Argon atoms that are reflected from a new, uneroded target surface contribute to a large energy input into the growing film. With the evolution of an erosion groove, the reflecting angle of the Ar neutrals changes, which results in a decreasing energy input into the growing film. When the target erosion proceeds, the target surface gets closer to the magnet bars behind the target, leading to an increase of charge carriers in the plasma and a rise in deposition current. Therefore, a larger amount of Ar+ ions bombard the target, with a concomitant larger amount of Ar neutrals reflected from the target surface. This increases the energy input into the growing film again, revealing the importance of reflected Ar neutrals on film growth. Similar conclusions were drawn from the systematic study of the deposition behavior of MoAlTi and NiW films from rotatable targets on an industrial scale. In both cases, reflected Ar neutrals were identified as main source of selective re-sputtering of the film constituent with higher sputter yield. Since the amount of selective re-sputtering is pressure-dependent, changing the Ar pressure allows controlling the elemental composition of films grown from multi-element targets to a certain degree. However, the two studied multi-element systems MoAlTi and NiW showed an opposite trend concerning lateral elemental distribution, with “light” Al being depleted and “light” Ni being enriched opposite the target center. Mass-energy analyzer measurements and Monte-Carlo simulations led to the conclusion that during magnetron sputtering of multi-element targets two atomic-mass depended mechanisms exist, namely a scatter-dominated and an emission-dominated regime. When the mass of the target element is smaller than the mass of the background gas, the sputtered elements tend to be predominantly scattered. This leads to a depletion of the light element opposite the target center. On the contrary, when the mass of the target element is larger than the mass of the background gas, the emission characteristics of the sputtered elements are conserved throughout the deposition process. This leads to an enrichment of that element opposite the target that is preferentially emitted close to the target normal. To conclude, the current thesis underlines the importance of reflected Ar neutrals on the growth of both single-element and multi-element thin films. Not only microstructure and accompanying film properties like stress and electrical resistivity, but also the elemental composition can be influenced by this high-energetic particle bombardment. The findings reported within this thesis can therefore contribute to a wider understanding and improved process control of sputter processes in industry and academia.

KW - Magnetron Dampfphasenabscheidung

KW - Dünnschichtabscheidung

KW - Schichtwachstum

KW - Plasma

KW - Massenspektrometer

KW - Multielement Target

KW - Magnetron Sputter Deposition

KW - Thin Film Deposition

KW - Thin Film Growth

KW - Plasma

KW - Mass-Energy Analyzer

KW - Multi-Element Target

M3 - Doctoral Thesis

ER -