We deposited compact W and W-Ta films by Pulsed laser Deposition (PLD), tailoring the crystalline domain size down two nanometers. W and W based films are extensively studied, mostly thanks to their high thermal stability, hardness and low resistivity. As an example, W films are used as barrier layer in the field of semiconductor integrated circuits and Al-W technology [1]. W films are also used as absorption layers in X-ray lithography and are a component of multi-layer X-ray mirrors [2]. Moreover, W coatings have been recently adopted to cover the plasma facing surfaces in Tokamaks [3]. A lot of efforts are currently devoted to the enhancement of non-permeation and resistance properties in hostile environment. These features have been generally achieved controlling film nanostructure [4]. The films we deposited are dense, non porous and exhibit different crystalline structures, ranging from highly crystallographic oriented to amorphous like structure with a high level of defects. They have been characterized by high resolution SEM, XRD, EDS, XPS and profilometry. We exposed the films to hydrogen flux and plasma in order to investigate their permeation/retention and erosion properties as a function of the crystalline structure. Permeation measurements on W and W-Ta films on 40 mm diameter steel substrate are presented, together with a precise determination of hydrogen interaction with films. Amorphous-like W films exhibit a Permeation Reduction Factor which is roughly two orders of magnitude higher if compared to other PVD W films [5]. Another unexpected property of these W films is a very high amount of retained hydrogen, which was as high as 0,1 H/W. Erosion effects have been exposing the films to an ion flux from plasma produced by capacitively coupled RF plasma (CCP) using hydrogen and noble gases. W crystalline oriented films show a higher sputtering resistance compared to the amorphous like ones, although the latter show lower surface degradation.
Permeation and Erosion Properties of Nanocrystalline and Amorphous-like W and W-Ta Coatings
ESPEDITO VASSALLO;
2012
Abstract
We deposited compact W and W-Ta films by Pulsed laser Deposition (PLD), tailoring the crystalline domain size down two nanometers. W and W based films are extensively studied, mostly thanks to their high thermal stability, hardness and low resistivity. As an example, W films are used as barrier layer in the field of semiconductor integrated circuits and Al-W technology [1]. W films are also used as absorption layers in X-ray lithography and are a component of multi-layer X-ray mirrors [2]. Moreover, W coatings have been recently adopted to cover the plasma facing surfaces in Tokamaks [3]. A lot of efforts are currently devoted to the enhancement of non-permeation and resistance properties in hostile environment. These features have been generally achieved controlling film nanostructure [4]. The films we deposited are dense, non porous and exhibit different crystalline structures, ranging from highly crystallographic oriented to amorphous like structure with a high level of defects. They have been characterized by high resolution SEM, XRD, EDS, XPS and profilometry. We exposed the films to hydrogen flux and plasma in order to investigate their permeation/retention and erosion properties as a function of the crystalline structure. Permeation measurements on W and W-Ta films on 40 mm diameter steel substrate are presented, together with a precise determination of hydrogen interaction with films. Amorphous-like W films exhibit a Permeation Reduction Factor which is roughly two orders of magnitude higher if compared to other PVD W films [5]. Another unexpected property of these W films is a very high amount of retained hydrogen, which was as high as 0,1 H/W. Erosion effects have been exposing the films to an ion flux from plasma produced by capacitively coupled RF plasma (CCP) using hydrogen and noble gases. W crystalline oriented films show a higher sputtering resistance compared to the amorphous like ones, although the latter show lower surface degradation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
