臺灣博碩士論文加值系統

中文摘要

由於通訊產業的蓬勃發展，GaAs 的應用變的日漸重要，整體而言砷化鎵較矽元件除了電子遷移速度高，在高頻使用的雜訊低，元件SIZE小，適合用於通訊之外，另外也具備抗輻射性，不易產生訊號錯誤情況，故產品穩定度高，特別是可應付用於衛星通訊時暴露於太空中所產生的輻射問題。
本文主要是以n型砷化鎵作為Substrate, 利用AuGeNi/Au針對各種不同濃度和氣體回火來做歐姆接觸並加以分析其特性及電性，同時進一步探討製程上的變異對電性之影響。
經由實驗結果的驗證，我們可以分別使用2×1018cm-3 和5×1017cm-3 不同濃度之GaAs出良好的歐姆接觸 ，在回火溫度400℃的條件下，以N2 回火作出之歐姆接觸點其最小特徵電阻為2.19×10-5 Ω-cm2 而在H2 回火400℃下其最小特徵電阻為3.78×10-5Ω-cm2。

Abstract
Gallium Arsenic（GaAs）device applications have become very critical due to the requirement for global communication industrial growth. In general, GaAs devices have the merit of the higher electric mobility speed than Si devices, As a result, the signal to noise ratio of GaAs devices is relatively low for high frequency applications. Also for artificial satellite communication application, the working devices have to expose in the outer space and face highly radiative environment.In other respect, GaAs related devices can present good performance due to their radiation.

The purpose of this study is to optimize the process for ohmic contact to N-type GaAs by comparing the characteristics of ohmic contacts fabricated to GaAs with different concentrations 5×1017cm-3 and 2×1018 cm-3. The influence of contact annealing temperature, time duration and gas ambient are also system actially investigated.

From this study, it is concluded that the ohmic contacts to n-GaAs can be successfully fabricated by alloying AuGeNi / Au to GaAs. The minimum specific resistances ρC of ohmic contract attained are 2.19×10-5Ω-cm2 and 3.78×10-5Ω-cm2 with annealing temperature 400°C, annealing time duration around 3 min, and in ambients of N2 and H2, respectively.

Contents
中文摘要….…….…………………………………………… i
Abstract…………………………...…………..……………… ii
Acknowledgments
Contents ........………………………….…………………… iii
Figure caption …………………………………...………... iv
Tale caption ……………………………………………...…x
中文簡介……………………………………...……………. xi
Chapter 1. Introduction ……………………..….………… 1
Chapter 2. Background …………………………………. 5
2.1 What is an ohmic contact and why is it important？…………………………...……… 5
2.2 Metal/semiconductor interfacial properties ...6
2.2.1 Definition and requirement of ohmic contact materials …………………………………… 6
2.2.2 Current transport mechanisms through M/S interface ………………………………………8
2.3 Limits of barrier height and doping level in GaAs. ……………………………………….. 11

Chapter 3. The measurement characteristics of ohmic contact.……………………………………….… 15
3.1 Judge the ohmic connects a standard of quality
…………………………………………………..15
3.2 Transmission Line Model (TLM) measurement
………………………………………………….……16
Chapter 4. Experimental arrangement……………..……...20
4.1 Metal-semiconductor junction processes……. 20
4.1.1 Wafer cleaning………………………..………20
4.1.2 Photolithography technique……….……….. 20
4.1.3 Wet Etch ……………………………...…...…. 21
4.1.4 Metal deposition………………………………. 22
4.2 Analysis tools…………………..………..……. ...22
4.2.1 HP 4155C current measurement……..…... .....22
4.2.2 Scanning electron microscopy（SEM）.…… 23
Chapter 5. Results and discussion ……………..…...…... 24
5.1 Surface morphology…………………………….24
5.2 Subsurface morphology……………….………..24
5.3 Contact resistivity analysis…..………...….….. 25
Chapter 6. Conclusions………….……….………....…….... 29
Reference …………………………………………………… 31
自傳 ……………………….…………………………….……….. 67


Figure caption
Fig 2.1 Ideal interfacial structure for low-resistance ohmic contact prepared by DA technique.……………………………… 35
Fig 2.2 Conduction mechanisms through metal/semiconductor interface with different donor levels……………………… 35
Fig 2.3 Specific contact resistances (ρc) for n-GaAs calculated as functions of Schottky barrier heights(фB) and doping concentrations(ND).………………………………………….…36
Fig 2.4 Schottky barrier heights(фB) of metals with various work functions for n- and p-GaAs.……………………………….36
Fig 3.1 Plot of total contact to contact resistance as a function of to obtain transfer length and contact resistance valve.……...37
Fig. 3.2 Experimental measurements for obtaining total resistance and contact end resistance values. . …………….………... 37
Fig. 3.3 Equivalent electrical circuit under the contact.…………... 38
Fig. 3.4 Extra resistance measurement (RE) used to derive contact end resistance………………………………………………….38
Fig 4.1 Flow chart for metal-semiconductor ohmic contact formation.………………………………………………………39
Fig 4.2 Flow chart of TLM pattern making procedures……………40
Fig. 4.3 Flow chart for metal evaporation processing………………41
Fig. 4.4 The principle of Electron beam evaporation………………..42
Fig 4.5 Electron beam evaporation system…………………………..42
Fig 4.6 HP 4155C current-voltage tracer……………………………43
Fig 4.7 SEM system , consisting of an electron optical column and a detection-amplification-display system………………………43
Fig. 5.1.1 Surface morphology of n-GaAs without annealing ………44
Fig. 5.1.2 Surface morphology of n-GaAs annealed at 300℃ for 3 min …………………………………………………………..44
Fig. 5.1.3 Surface morphology of n-GaAs annealed at 350℃ for 3 min………………………………………………………….45
Fig 5.1.4 Surface morphology of n-GaAs annealed at 400℃ for 3 min…… . …………………………………………………... 45
Fig 5.1.5 Surface morphology of n-GaAs annealed at 450℃ for 3 min. ……………………………………………………..46
Fig 5.1.6 Surface morphology of n-GaAs annealed at 500℃ for 3 min ………………………………………………………..46
Fig 5.1.7 Surface morphology of n-GaAs annealed at 400℃ for 1 min………………………………………………………..47
Fig 5.1.8 Surface morphology of n-GaAs annealed at 400℃ for 10 min …...………………………………………………….47
Fig 5.1.9 Surface morphology of n-GaAs annealed at 400℃ for 15 min……………………………………………………….48
Fig 5.2.1 SEM micrograph of AuGeNi alloy contact annealed at 300℃ （ND:2×1018cm-3 ）……………………………………… 49
Fig 5.2.2 SEM micrograph of AuGeNi alloy contact annealed at 350℃ （ND:2×1018 cm-3）…………………………………… 49
Fig 5.2.3 SEM micrograph of AuGeNi alloy contact annealed at 400℃ （ND:2×1018 cm-3）……………………………………… 50
Fig 5.2.4 SEM micrograph of AuGeNi alloy contact annealed at 450℃ （ND:2×1018 cm-3）……………………………………… 50
Fig 5.2.5 SEM micrograph of AuGeNi alloy contact annealed at 500℃ （ND:2×1018 cm-3）…………………………………..… 51
Fig.5.3.1 (a) The I-V characteristics of the ohmic contacts annealed at different temperatures.………………………………….… 52
Fig.5.3.1 (b) The relationship between the total resistance RT and the annealing temperature. …………………………………….……52
Fig.5.3.2(a) The I-V characteristics of the ohmic contacts annealed at different temperatures.……………………..………….. 53
Fig.5.3.2 (b) The relationship between the total resistance RT and the annealing temperature. …………………………………53
Fig.5.3.3(a) The I-V characteristics of the ohmic contacts annealed at different temperatures.…………………………...…….. 54
Fig.5.3.3 (b) The relationship between the total resistance RT and the annealing temperature.…. ………………………….. 54
Fig.5.3.4(a) The I-V characteristics of the ohmic contacts annealed at different temperatures.…………….……. ………..….... 55
Fig.5.3.4(b) The relationship between the total resistance RT and the annealing temperature.………………………………..... 55
Fig.5.3.5 (a) The I-V characteristics of the ohmic contacts annealed for different time durations..…. ………………. …….... 56
Fig.5.3.5 (b) The relationship between the total resistance RT and the annealing time duration………………………....…….... 56
Fig.5.3.6 (a) The I-V characteristics of the ohmic contacts annealed for different time durations.…. …………………...….... 57
Fig.5.3.6 (b) The relationship between the total resistance RT and the annealing time duration.………………………..……… 57
Fig.5.3.7 (a) The I-V characteristics of the ohmic contacts annealed for different time durations..………………………….… 58
Fig.5.3.7 (b) The relationship between the total resistance RT and the annealing time duration..………………………………..… 58
Fig.5.3.8 (a) The I-V characteristics of the ohmic contacts annealed for different time durations..………………………… 59
Fig.5.3.8 (b) The relationship between the total resistance RT and the annealing time duration.…………………………….. 59
Fig.5.3.9 (a) The I-V ch The I-V characteristics of the ohmic contact measured with different contact pad spacing...…….. 60
Fig.5.3.9 (b) The relationship between the total resistance RT and the contact pad spacing d during TLM measurement..…... 60
Fig.5.3.10 (a) The I-V ch The I-V characteristics of the ohmic contact measured with different contact pad spacing.………… 61
Fig.5.3.10(b) The relationship between the total resistance RT and the contact pad spacing d during TLM measurement.… 61
Fig.5.3.11 (a) The I-V ch The I-V characteristics of the ohmic contact measured with different contact pad spacing……… 62
Fig.5.3.11 (b) The relationship between the total resistance RT and the contact pad spacing d during TLM measurement.…...……………………….…………… 62
Fig.5.3.12 (a) The I-V ch The I-V characteristics of the ohmic contact measured with different contact pad spacing.....…… 63
Fig.5.3.12 (b) The relationship between the total resistance RT and the contact pad spacing d during TLM measurement....……………………………..……… 63
Fig.5.3.13(a) The specific resistance of ohmic contacts annealed at different temperatures treatment.……………………… 64
Fig.5.3.13(b) The relationship between the total resistance RT and the contact pad spacing d during TLM measurement..……………………………………..….…. 64
Fig.5.3.14 Specific ohmic resistance of AuGeNi/Au alloy contacts to n-type GaAs vs. ND………………………………….……65



Table caption

Table 5.1 The calculated specific ohmic contact resistance of AuGeNi/Au to n-GaAs based on themionic-emission model (paper) …………………………………………………………………66
Table 5.2 The calculated specific ohmic contact resistance of AuGeNi/Au to n-GaAs based on themionic-emission model (experiment) ……………………………………………………66

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