近年來氮化鋁薄膜愈來愈受到重視，原因在於其具有光電及通訊方面的應用。除了可用來作為成長藍光二極體GaN的緩衝層(buffer layer)外，最主要的通訊應用就是用來製備高頻表面聲波元件(SAW)與薄膜體波共振器(FBAR)，其頻率可達GHz以上。氮化鋁為六方晶系結構 (hexagonal)，由於C軸指向具有較低能量，且有良好的壓電特性，因此對於C軸指向特性的好壞有一定的要求。
本研究的目的在使用雙離子束濺鍍法(Dual Ion Beam Sputtering, DIBS)在矽基板(100)上沉積氮化鋁薄膜。雙離子束濺鍍法結合Kaufman與End-Hall兩種不同形式作為薄膜沉積的離子源。由於離子濺鍍法具有實驗參數可獨立操作及高真空度等優點，因此可藉由改變離子束能量、氮氣含量比與基板溫度作為獲得C軸指向與表面平整的氮化鋁薄膜之參數條件。
本實驗成功利用雙離子束濺鍍法成長C軸氮化鋁薄膜。使用鋁靶作濺鍍來源時，在固定工作壓力為4X10 –4 torr且基板未加熱情況下，將離子束電壓控制在700ev，氮氣濃度與氬氣濃度比為5:4，可得到一高平整性的氮化鋁薄膜﹔若薄膜中含有相當成份的氧化鋁，會大大影響氮化鋁的成長。由於氧化鋁的成長速率較氮化鋁快，因此基板的加熱會導致氧化鋁抑制氮化鋁的成長，使得氮化鋁之C軸取向的結晶性變差。
本實驗在薄膜成長後利用X-Ray繞射儀(XRD)、掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)、二次離子質譜儀(SIMS)以及化學分析電子質譜儀 (ESCA)分析薄膜成長結果。

Aluminum nitride (AlN) thin film is a promising material as buffer layer in GaN-based optoelectronic and electronic devices or as a substrate to fabricate Surface Acoustic Wave (SAW) and Film Bulk Acoustic wave Resonant (FBAR) devices in high frequency in wireless (>1GHz) communication technology. Aluminum nitride, thin film with the c-axis normal to the film is favored in a low energy deposition condition because it places the packed hexagonal basal plane parallel to the substrate surface. Grains of this orientation have a low surface energy which favors rapid growth in a columnar structure.

In this experiment r.f. dual ion beam sputtering (DIBS) system is used to prepare the AlN films on Si (100) substrate. Various processing variable were tested to deposit AlN films with desirable properties. After systematic testing, a high quality film with preferred c-axis orientation was grown successfully on Si (100) substrate with Al target under the process parameters of 700 ev energy flux; 55% N2 / (N2+Ar) ratio; 4X10 - 4 torr working pressure with no heating of substrate. The AlN target is also used. The results show the great sensitivity of the films to oxygen-containing environments. Only under low residual oxygen pressure, could aluminum nitride be grown well.

The deposited AlN thin film characteristic were studied by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Electron Spectroscopy for Chemical Analysis (ESCA).

Contents

中文摘要 I

Abstract II

Contents III

Table caption V

Figure caption VI

Chapter 1 Introduction 1

Chapter 2 Theoretical background 3
2.1 The structure and properties of aluminum nitride 3
2.2 Deposition of thin films 4
2.3 Sputtering 5
2.3.1 Plasma and sputtering 5
2.3.2 Ion beam sputtering 7
2.3.3 Dual ion beam sputtering 9
2.4 Reference research 9

Chapter 3 Experiments 12
3.1 Substrate cleaning process 12
3.2 AlN thin film deposition 12
3.3 Characteristic methods of thin films 13
3.3.1 X-Ray diffraction 13
3.3.2 Field emission scanning electron microscopy 13
3.3.3 Transmission electron microscopy 13
3.3.4 Secondary ion mass spectrometry 14
3.3.5 Electron spectroscopy for chemical analysis 14

Chapter 4 Results and Discussion 15
4.1 Sputtering parameters for AlN films deposition 15

Experiments I 17
4.2 The effects of growth parameters on crystal structure 17
4.2.1 Effect of energy flux 17
4.2.2 Effect of substrate temperature 18
4.2.3 Effect of nitrogen concentration 19
4.3 The effects of growth parameters on microstructure by SEM 19
4.3.1 Plane-view 19
4.3.2 The effects of growth parameters on thickness 20
4.4 SIMS analysis 20
4.5 ESCA 21
4.6 TEM analysis 22

Experiments II 24
4.7 The effects of growth parameters on crystal structure 24
4.7.1 Effect of substrate temperature 24
4.7.2 Effect of energy flux 25
4.7.3 Effect of beam current 25
4.8 The effects of growth parameters on microstructure by SEM 25
4.9 TEM analysis 25

Chapter 4 Conclusions 27

References 28
Table caption

Table 2.1 The properties of aluminum nitride 33
Table 2.2 The materials of thin films commonly used in SAW devices 33
Table 2.3 The relationship between the AlN and different coating of substrates 34
Table 2.4 The visual appearance of the films changes with the variation of the composition and its microstructure 34
Table 2.5 The optical constants of AlN prepared by different deposition systems 35

Table 3.1 The sputtering conditions for preparing AlN films 36
Table 3.2 JCPDS dates of AlN with hexagonal structure 37
Table 3.3 JCPDs data of Al 37
Table 3.4 JCPDs data of Al2O3 38

Table 4.1 The relative to other references for effects of growth parameters 39
Table 4.2 The deposition parameter using Al target of experiments I 40
Table 4.3 The deposition parameter using AlN target of experiments I 41
Table 4.4 The deposition parameter using AlN target of experiments II 41

Figure caption

Fig. 2.1 The crystal structure of AlN: (a) the structure of distorted tetrahedron, (b) unit cell, (c) hexagonal wurtzite structure 42
Fig. 2.2 The stage of structure evolution in polycrystalline thin films: (a) nucleation, (b) grain growth, (c) coalescence, (d) filling of channels and (e) film growth 43
Fig. 2.3 The schematic diagram of free energy change and mean radius 43
Fig. 2.4 The layer growth the deposit wets the substrate 44
Fig. 2.5 Coalescence of islands due to (a) Ostwald ripening, (b) sintering, (c) cluster migration 44
Fig. 2.6 The voltage distribution and discharge characteristic across dc glow discharge 45
Fig. 2.7 The typical glow discharge appearance 45
Fig. 2.8 A schematic diagram of gridded, broad-beam ion source and its controller 46
Fig. 2.9 A broad beam ion source with power supplies 46
Fig. 2.10 The principle of plasma bridge neutralizer 47
Fig. 2.11 The relationship between the sputtering yield and incident beam 47
Fig. 2.12 The relationship between ion current densities and two grids 48
Fig. 2.13 The illustration of the aperture of two grids 48
Fig. 2.14 A schematic diagram of the End-Hall ion source 49

Fig. 3.1 The dual ion beam sputtering deposition system 50
Fig. 3.2 The flow chart of deposition process 50
Fig. 3.3 Experiments process of AlN films 51
Fig. 3.4 The principle of secondary ion mass spectrometry 52
Fig. 3.5 The principle of electron spectroscopy 53

Fig. 4.1 The XRD patterns of AlN films synthesized at various energy fluxes using Al target 54
Fig. 4.2 The XRD patterns of AlN films synthesized at various energy fluxes using AlN target 55
Fig. 4.3 The XRD patterns of AlN films synthesized at R.T and Tsub=300℃ using Al target 56
Fig. 4.4 The XRD patterns of AlN films synthesized at R.T and Tsub=300℃ using AlN target 57
Fig. 4.5 The XRD patterns of AlN films synthesized at various N2 % and R.T using Al target 58
Fig. 4.6 The XRD patterns of AlN films synthesized at various N2 % and Tsub=300℃ using Al target 59
Fig. 4.7 SEM micrograph of AlN films prepared at 55% N2, 700 ev and R.T using Al target 60
Fig. 4.8 SEM micrograph of AlN films prepared at 55% N2, 700 ev and Tsub=300℃ using Al target 60
Fig. 4.9 SEM micrograph of AlN films prepared at 700 ev and R.T using AlN target 61
Fig. 4.10 SEM micrograph of AlN films prepared at 700 ev and Tsub=300℃ using AlN target 61
Fig. 4.11 The relationship between deposition rate and energy flux at time=180 min 62
Fig. 4.12 The relationship between deposition rate and N2 % at time=180 min 62
Fig. 4.13 SIMS depth profile of AlN films formed at 55% N2, 700 ev and R.T using Al target 63
Fig. 4.14 SIMS depth profile of AlN films formed at 55% N2, 700 ev and Tsub=300℃ using Al target 63
Fig. 4.15 SIMS depth profile of AlN films formed at 700 ev and R.T using AlN target 64
Fig. 4.16 SIMS depth profile of AlN films formed at 700 ev and Tsub=300℃ using AlN target 64
Fig. 4.17 A typical ESCA spectrum of AlN films on Si (100) at R.T and Tsub=300℃ using Al target 65
Fig. 4.18a The binding energy of Al 2p AlN films formed at 55% N2, 700 ev and R.T using Al target 66
Fig. 4.18b The binding energy of N 1s AlN films formed at 55% N2, 700 ev and R.T using Al target 66
Fig. 4.19a The binding energy of Al 2p AlN films formed at 55% N2, 700 ev and Tsub=300℃ using Al target 67
Fig. 4.19b The binding energy of N 1s AlN films formed at 55% N2, 700 ev and Tsub=300℃ using Al target 67
Fig. 4.20 TEM micrograph of AlN films synthesized at 55% N2, 700 ev and R.T using Al target 68
Fig. 4.21 Cross-sectional TEM photograph of AlN films synthesized at 55% N2, 700 ev and R.T using Al target 71
Fig. 4.22 TEM micrograph of AlN films synthesized at 55% N2, 700 ev and Tsub=300℃ using Al target 75
Fig. 4.23 TEM micrograph of AlN films synthesized at 700 ev and R.T using AlN target 77
Fig. 4.24 The XRD patterns of AlN films synthesized at R.T and T=300℃as deposited Al layer using AlN target 79
Fig. 4.25 The XRD patterns of AlN films synthesized at various substrate temperatures using AlN target 80
Fig. 4.26 The XRD patterns of AlN films synthesized at various energy fluxes using AlN target 81
Fig. 4.27 The XRD patterns of AlN films synthesized at various beam current using AlN target 82
Fig. 4.28 SEM micrograph of AlN films prepared at 650 ev and R.T using AlN target 83
Fig. 4.29 SEM micrograph of AlN films prepared at 650 ev and Tsub=300℃ using AlN target 83
Fig. 4.30 SEM micrograph of AlN films prepared at 650 ev and Tsub=453℃ using AlN target 84
Fig. 4.31 TEM micrograph of AlN films synthesized at 650 ev and Tsub=453℃ using AlN target 85

Fig. 5.1 A schematic diagrams showing formation mechanism of the AlN films 87

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