Ion Beam Treatment of Functional Layers in Thin-Film Silicon Solar ...

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5 Ion beam treatment of the glass surface Table 5.6: XPS measurement results on a reference and three different ion beam treated Corning glass. The values in the table are the atomic percentage (at%) normalized to 100 with Rel. error of ± 15%. The minimum measurable range was 1 at%. The four substrates were used for preparing ZnO:Al films as shown in Fig. 5.2. The rms roughness of the four ZnO:Al films are given in the last row. Glass Ref. Ar treated O 2 treated Ar/O 2 treated C 19.9 33 32.3 27.8 O 56 44 46.7 49.9 Fe - 3.8 - 5.0 Zn - 0.1 0.5 1.2 Si 18.7 8.1 14.6 7.5 Al 3.9 5.6 3.9 3.7 Ca 0.9 2.3 0.9 2.0 N 0.7 0.6 0.9 0.3 P - 1.1 - 0.8 Cl - 0.1 0.2 0.4 Ar - 1.2 - 1.3 rms roughness (nm) ZnO:Al films 4 12 34 44 the ion beam pretreated samples since the ion bombardment activated the surface. The percentage of O and Si were reduced, while Zn and Fe were added to the surface. Few Ar was implanted to the sample surface by Ar and Ar/O 2 bombardment. Additionally, slight changes were observed on Al, Ca, P, and Cl elements. On Ar ion beam treated glass surface, Fe contamination is severe (3.8 at%), but on O 2 ion beam treated glass surface, there is almost no Fe contamination (< 0.1 at%). Zn is observed on the three ion beam treated glass surface. However, on the Ar treated glass surface, the amount of Zn contamination is very low (0.1 at%), while on the Ar/O 2 treated glass, the Zn contamination is the highest (1.2 at%). Lower Fe contamination from O 2 ion beam treatment is a common phenomenon for this type of ion source: Fe is sputtered from the steel cathode because of the strike of argon ions, whereas the oxygen ions lightly passivate the surface of the steel cathode, resulting in a thin oxide film on the cathode. Since the etch rate for FeO is lower than Fe, less cathode erosion is enabled by the use of O 2 gas [149]. However, with mixed Ar/O 2 ions, the sputtering rate of steel cathode might becomes larger due to additional Ar ions, leading to more Fe contaminations (5.0 at%). The Zn contamination is supposed to be from the process chamber, since the ion source is installed in a same chamber with a rotatable ZnO:Al 2 O 3 target (See Fig. 3.1). The difference between Ar and O 2 treatment is that Ar is physically milling off materials from glass surface while O 2 ions can also react with the substrate atoms or contaminations as well as etching off the substrate materials. More FeO, Fe 2 O 3 , or ZnO might be formed on 118
5.4 X-Ray photoelectron spectroscopy of the glass substrate y XPS (b) Glass y Position [cm] x (a) Position [cm] (b) Glass x y AFM (a) ZnO:Al Glass Static Ion beam pretreatment Position [cm] Magnetron sputtering x (1) (2) Figure 5.35: Schematic experimental process of XPS overview scans on statically ion beam pretreated glass substrates. (1): a 10 × 10 cm 2 glass was treated by ion beam, (2): half of the substrate was measured by XPS, and the other half was sputtered with ZnO:Al films and then measured with AFM. The red dots indicate the points for measurement along x-direction. the glass surface by O 2 ion beam treatment. This could be an explanation of the higher Fe and Zn concentration on the glass surface after mixed Ar/O 2 ion beam treatment. The XPS measurements confirm that the compositions of glass substrates are changed by ion beam treatments. However, the changes are difficult to be related to the change of ZnO:Al film growth as shown in Fig. 5.2. 5.4.1.2 Static ion beam treatment In the previous subsection, the glass substrate was dynamically moved in front of the ion source in order to get homogeneous treatment. Therefore the measurements on the treated glass substrates is supposed not to be related to the position on the sample. In this section, the substrates are treated statically by ion source. As shown in Section 4.2, the ion density is not uniform in the chamber. As a result, the ion beam has highest intensity in front of the racetrack. Therefore, in one etching experiment, a series of etching points bombarded by different intensities of ions can be obtained. The schematic experimental process is shown in Fig. 5.35. Firstly one 30 × 30 cm 2 glass substrate was treated by ion beams statically. Then the glass substrate was cut into two halves (a) and (b). Part (a) was transfered to sputtering chamber to deposit standard ZnO:Al film. AFM measurements were performed at 30 points on the ZnO:Al films. The points are depicted in Fig. 5.35 (2) by the red dots on a red straight line along x-direction. The distance between each point is 1 cm. XPS survey scans were performed 119
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Ion Beam Treatment of Functional La
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Forschungszentrum Jülich GmbH Inst
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Contents Abstract 1 Zusammenfassung
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Contents 5.2 Reason of rough growth
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List of Figures 3.4 Schematic diagr
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List of Figures 6.1 2 s HCl etching
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List of Tables 4.1 Energy transfer
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Zusammenfassung In Dünnschichtsola
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1 Introduction Presently, the incre
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study and understanding of as-grown
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2 Fundamentals (a) (b) gas inlet an
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2 Fundamentals When pure Ar is used
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2 Fundamentals in this work was sup
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2 Fundamentals the process is then
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2 Fundamentals where f = 1 2 [(Z 1/
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2 Fundamentals large area. One of t
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2 Fundamentals where m ∗ is the e
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2 Fundamentals where k and T are th
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2 Fundamentals E g0 E g0 + E BM Fig
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2 Fundamentals Vacuum chamber Anode
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2 Fundamentals ation stage [72]. Ho
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2 Fundamentals Feature (Before etch
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2 Fundamentals 2.2.4.5 Surface evol
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2 Fundamentals Figure 2.14: Represe
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2 Fundamentals This paragraph expan
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2 Fundamentals Figure 2.17: Absorpt
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2 Fundamentals Figure 2.18: Schemat
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3 Experimental This chapter describ
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3.2 Ion beam treatment 3.1.1.3 Smal
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3.3 Characterization methods y Carr
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3.3 Characterization methods The va
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3.3 Characterization methods measur
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3.3 Characterization methods the ca
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3.3 Characterization methods the Mi
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3.3 Characterization methods One ch
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3.3 Characterization methods compou
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4 Characterization of the ion beam
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4.2 Static etching For Ar ion beams
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6 Ion beam treatment of the TCO sur
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7 Summary and Outlook Ion beam trea
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Bibliography [1] M. Pelliccione and
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Bibliography [23] A. Shabalin, M. A
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Bibliography [53] D. F. Mitchell, G
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Bibliography [79] J. Venables, G. S
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Bibliography [107] O. Kluth, Textur
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Bibliography [134] H. Sai, H. Fujiw
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Bibliography [158] H. Kato, K. Miya
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Bibliography [181] L. P. Schuler, M
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• Marek Warzecha, Hongbing Zhu, J
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Schriften des Forschungszentrums J
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