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Chapter 5
knowledge, the first systematic studies on the stability of (selenised) molybdenum are
described in references [7-9] and this thesis.
Additionally, in this chapter, we present two systematic studies about the impact of
deposition conditions on the stability of molybdenum under damp heat conditions. We
also present the reaction mechanisms involved in the degradation of molybdenum. The
first study (‘Selenisation and pressure experiment’) [8] has focussed on the identification
of the influence of film morphology and selenisation on molybdenum stability and the
relationship of these factors with changes in conductivity and reflectivity.
The aim of the second study ('Lift-off experiment') [9] was the identification of the
degradation mechanisms of a molybdenum layer which has the exact composition and
morphology as this film in an actual CIGS module. Therefore, molybdenum films were
produced by deposition and lifting off of a CIGS layer, on order to get the MoSe layer
2
(see Figure 5.1). Furthermore, the molybdenum film has a bilayer structure in order to
optimize adhesion and conduction.
The degradation behaviour of these films under damp heat conditions was monitored
and the changes in film properties were determined. In this paper, we use this
information to propose the chemical reactions that are occurring during molybdenum
degradation.
5.2 Experimental
5.2.1 Sample preparation
molybdenum thin films have been deposited on soda-lime glass (SLG) substrates by
direct current (DC) magnetron sputtering of a 99.95% pure molybdenum target. The
base pressure within the chamber before the deposition process was about 7.5x10 −4 m
Torr. The substrates used are 76 mm × 26 mm × 1 mm SLG microscope slides from RS
France Company. These substrates have been cleaned in an ultrasonic bath containing
detergent and were rinsed with de-ionised water.
5.2.1.1 Selenisation and pressure experiment
Before the deposition, the target was pre-sputtered for 5 minutes; the target-substrate
2
distance was 55 mm and the sputtering power was 1 kW (power density: 3.1 W/cm).
Films have been grown at three different argon sputtering pressures (2, 10 and 15
mTorr), while the deposition time was 24 minutes for all samples. For all deposition
processes, the substrate was not heated intentionally. The DC sputtering parameters
of molybdenum are summarised in Table 5.1 .
Samples were either used as-prepared or placed in a selenium containing atmosphere
128
knowledge, the first systematic studies on the stability of (selenised) molybdenum are
described in references [7-9] and this thesis.
Additionally, in this chapter, we present two systematic studies about the impact of
deposition conditions on the stability of molybdenum under damp heat conditions. We
also present the reaction mechanisms involved in the degradation of molybdenum. The
first study (‘Selenisation and pressure experiment’) [8] has focussed on the identification
of the influence of film morphology and selenisation on molybdenum stability and the
relationship of these factors with changes in conductivity and reflectivity.
The aim of the second study ('Lift-off experiment') [9] was the identification of the
degradation mechanisms of a molybdenum layer which has the exact composition and
morphology as this film in an actual CIGS module. Therefore, molybdenum films were
produced by deposition and lifting off of a CIGS layer, on order to get the MoSe layer
2
(see Figure 5.1). Furthermore, the molybdenum film has a bilayer structure in order to
optimize adhesion and conduction.
The degradation behaviour of these films under damp heat conditions was monitored
and the changes in film properties were determined. In this paper, we use this
information to propose the chemical reactions that are occurring during molybdenum
degradation.
5.2 Experimental
5.2.1 Sample preparation
molybdenum thin films have been deposited on soda-lime glass (SLG) substrates by
direct current (DC) magnetron sputtering of a 99.95% pure molybdenum target. The
base pressure within the chamber before the deposition process was about 7.5x10 −4 m
Torr. The substrates used are 76 mm × 26 mm × 1 mm SLG microscope slides from RS
France Company. These substrates have been cleaned in an ultrasonic bath containing
detergent and were rinsed with de-ionised water.
5.2.1.1 Selenisation and pressure experiment
Before the deposition, the target was pre-sputtered for 5 minutes; the target-substrate
2
distance was 55 mm and the sputtering power was 1 kW (power density: 3.1 W/cm).
Films have been grown at three different argon sputtering pressures (2, 10 and 15
mTorr), while the deposition time was 24 minutes for all samples. For all deposition
processes, the substrate was not heated intentionally. The DC sputtering parameters
of molybdenum are summarised in Table 5.1 .
Samples were either used as-prepared or placed in a selenium containing atmosphere
128
