臺灣博碩士論文加值系統

摘 要
在現今ＩＣ製程朝向體積減少以及速度更快的前提下，銅製程以及化學機械平坦化（ＣＭＰ）的運用已變得不可或缺。銅在金屬化學機械平坦化中的化學反應特性與其他金屬如︰鈦，鋁，鎢及鉭不同，銅不會在金屬表面形成一層穩定的氧化物，取而代之的是一種偏向溶解的反應，也因此難以控制金屬化學機械平坦化的研磨速率以及造成淺盤凹陷（dishing）的效應。
在本實驗中，藉由即時電化學的量測，我們可以得到完整的直流極化曲線及交流阻抗曲線，再藉由合理的假設及等效電路的模擬，就能清楚的了解銅在硝酸系統及其添加劑中的電化學反應:
1. 銅在硝酸溶液中形成電雙層結構（ＥＤＬ）及不穩定的表面氧化物，研磨時電雙層被壓縮且氧化物層被磨除。
2. 在硝酸溶液中添加檸檬酸（Citric acid），則抑制了陰極反應，造成整體反應變慢，但主要反應機制與銅在硝酸溶液中相同；研磨時不穩定的表面氧化物被拋去，加上檸檬酸很難擴散到研磨墊與金屬中抑制陰極反應，使抑制效果變得輕微。
3. 在硝酸溶液中添加抑制劑（1H-BTA），則ＢＴＡ會與Cu+在銅表面形成穩定且緻密的Cu-BTA結構，因此大幅的抑制了表面反應進而減緩整體的反應速率。研磨時Cu-BTA層會被拋去，但仍會形成動態的Cu-BTA層且對減緩反應速率有一些效果。
若對金屬化學機械研磨中的機械參數進行調變，則會有以下結果︰
1. 壓力增加對反應無大改變，主要是因為反應已經達成動態平衡了。
2. 反應速率隨著轉速增加而增加，代表轉速使整體擴散速率提升，進而加速反應速率。
3. 添加劑濃度也會反應在抑制效率上，但在研磨時濃度影響就會變得較不明顯。

Abstract
Chemical mechanical polishing (CMP) has long been recognized as a viable technique for global planarization to delineate metal patterns for sub-micron integrated circuit (IC) processing. Copper (Cu) has been used as multilevel interconnects and have emerged as the most important material for such applications. But, unlike Al, Ti, Ta and W, the oxides layer of Cu can be porous or not stable on the copper surface and can easily dissolute from the surface.
In this study, in-situ electrochemical measurements were used to investigate the influences of nitric acid concentrations and additives on the copper corrosion mechanism.
1.There formed electrochemical double layer (EDL) and unstable oxide passivation while copper immunity in 3% nitric acid slurry. The EDL becomes dense and oxide polished in abrasion.
2.In adding of citric acid, it inhibits the reduction of NO3- and reduces total reaction rate, but main reaction mechanisms are still the same as that in 3% nitric acid slurry. In abrasion, the inhibit effects becomes slightly because citric acid becomes hard to diffuse into the interface between polishing pad and metal surface and inhibits cathode reactions and unstable oxide is polished.
3.In adding of BTA, Cu+ will complex with BTA and formed a stable Cu-BTA film that inhibits the dissolution reaction rates. In abrasion, the effect of BTA also becomes slightly because Cu-BTA will be polished and formed another kind of dynamic equilibrium and thinner Cu-BTA film.
In changing of mechanism conditions in CMP:
1.Because all reactions achieve to dynamic equilibrium in abrasion, and the influence of changing pressure conditions seems slightly.
2.In different rotation rates the impedance decreases as the sequence of rotation rate increases.
3.In different additive concentrations, it shows inhibit effective increases with the additives concentrations increase without abrasion, but it seems slightly in abrasion

Content
摘要
Abstract
Acknowledgements
Content…………………………………………………………………..i
Figure captions…………………………………………………………iv
Table captions………………………………………………………….viii
Chapter 1 Introduction………………………………...……………..1
1.1Planarization in IC manufacture………………………………1
1.2Electrochemical measurements to investigate metal CMP…....4
1.3Motivation………………………………………………….....5
Chapter 2 Fundamental Concepts………………………………..….8
2.1 Chemical Mechanical Planarization……………………….….8
2.1.1 Chemical Mechanical Planarization Process……...…….8
2.1.2 Chemical reactions of CMP……………………...……10
2.1.3 Chemical Mechanical Planarization Issue………..……14
2.2 Physical properties of copper……………………………..…15
2.2.1 Copper corrosion………………………………………16
2.2.2 Protection of copper…………………………………...17
2.2.3 Copper Chemical Mechanical Planarization………..…18
2.2.4 Copper CMP issue…………………………………..…19
2.3 Electrochemical thesis…………………………………….…21
2.3.1 Mixed-Potential Theory……………………………….21
2.3.2 Electrochemical Impedance Spectroscopy…………….27
Chapter 3 Experimental……………………………………………….41
3.1 Electrochemical instrument…………………….……………41
3.2 Chemicals prepare……………………………...……………41
3.3 DC measurements……………………………….…………...43
3.4 AC measurements……………………………….…………...44
Chapter 4 DC measurements…………………………….……………46
4.1 The potentiodynamic curves of copper in nitric acid base slurry……………………………………………..…….……46
4.2 Nitric acid with abrasion and without abrasion……...………48
4.3 Addotion of inhibitor…………………………………...……48
4.4 Addition of complex agent……………………………..……49
Chapter 5 EIS measurement technologies……………………....……54
5.1 Nyquist plots of copper in nitric acid system…………..……54
5.2 Simulation of Electrochemical Impedance Spectroscopy…...59
5.2.1 Nitric Acid System…………………………………….59
5.2.2 Nitric acid with Citric acid…………………………….63
5.2.3 Nitric acid with BTA…………………………………..67
5.2.4 Comparison of influences of additives………………...71
5.3 Chemical and Mechanical Effects………………………...…74
5.3.1 Pressure effect…………………………………………74
5.3.2 Rotation rate effect………………………………….…75
5.3.3 Concentration effect…………………………………...75
5.3.4 Discussion……………………………………………..76
5.4 Summary……………………………………………………..84
5.4.1 General conclusion of the nitric acid system……….…84
5.4.2 The potentiodynamic curves of copper in the nitric acid system………………………………………………...84
5.4.3 Electrochemical impedance spectroscopy (EIS) plots of copper in the nitric acid system………………………85
5.4.4 Comparison of various abrasion pressures and rotation rates…………………………………………………..85
5.5 Auger Electron Spectroscopy Measurements (AES) …….…88
Chapter 6 Conclusions and Future work………………………….…91
References……………………………………………………………....93
Figure Caption
Figure 1.1 Degree of Surface Planarization………………….………..3
Figure 1.2 Comparison of planarization distance for various planarization technologies………………………...………3
Figure 2.1 A multilevel interconnect structure which using CMP technology………………………………………………...9
Figure 2.2 Schematic Diagram of Chemical Mechanical Planarization Polisher…………………………………………………..10
Figure 2.3 The schematic of CMP configuration………..…………..10
Figure 2.4 Wafer surface topography and Polishing Pad deformation During CMP Process…………….………………………11
Figure 2.5 Proposed mechanism of planarization of patterned metal feature by CMP………………………………………….11
Figure 2.6 The balance between the rate of polishing and the rate of passivation formation…………………………………...12
Figure 2.7 Pourbaix diagram of copper-water system……………..13
Figure 2.8 Domains of corrosion, immunity and passivation of copper………………………………………….………...13
Figure 2.9 Comparison of intrinsic gate delay and interconnect delay (RC) as a function of feature size……………………….16
Figure 2.10 Metal dishing and oxide erosion after multi-step CMP process…………………………………………………..20
Figure 2.11 Polarization of anodic and cathodic half-cell reactions for copper in acid solution to give a mixed potential, Ecorr., and a corrosion rate (current density), icorr………………….26
Figure 2.12 Determination of the mixed potential Ecorr. for a corroding metal M exposed to acid solution with a second oxidizer, Fe3+/Fe2+, present………………………………………...26
Figure 2.13Combined polarization: sum of activation, hact, and concentration, hconc, polarization………………………..27
Figure 2.14Cyclic nature of AC voltage……………………………30
Figure 2.15 Electrical behavior of an electric double layer………..30
Figure 2.16 AC voltage-current phase angle……………………….31
Figure 2.17 Vector nature of voltage and current…………………..31
Figure 2.18Electrical double layer for an uncoated, oxide-free corroding metal………………………………………….34
Figure 2.19 Electrified interface structure for a corroding, coated metal...34
Figure 2.20 Single time constant complex plane plot………..……….37
Figure 2.21 Single time constant Bode magnitude plot……..………37
Figure 2.22 Single time constant Bode phase plot……………….….38
Figure 3.1 Schematic of the in-situ electrochemical measurement system…………………………………………………...42
Figure 4.1 The polarization curves for 3 % nitric acid with BTA and citric acid in non-abrasion………………………………50
Figure 4.2 The polarization curves of nitric acid system within additives in abrasion……………………………………50
Figure 4.3 The typical polarization curves for the abraded and non-abraded copper surface in nitric acid base slurry….51
Figure 4.4 The polarization curves at various BTA concentrations in nitric acid slurry. ( non-abrasion )………………………51
Figure 4.5 The polarization curves at various BTA concentrations in nitric acid slurry. (abrasion)……………………………..52
Figure 4.6 The polarization curves at various citric acid concentrations in nitric acid slurry. ( non-abrasion )……………………52
Figure 4.7 The polarization curves at various citric acid concentrations in nitric acid slurry. (abrasion)…………………………..53
Figure 5.1 The Nyquist plots for non-abraded Cu in 3% nitric acid aqueous solution…………………………………………56
Figure 5.2 The Nyquist plots in nitric acid system indicate two impedance semicircles dropped down and compressed in abrasion……………………………………………….…56
Figure 5.3 It shows slightly flatten and similar shape of two semicircles in Nyquist plots with the addition of complex agent in non-abrasion……………………………………57
Figure 5.4 It shows two similar semicircles separate clearly in Nyquist plots with the addition of complex agent in abrasion…...57
Figure 5.5 In Nyquist plots, a depressed and much larger semicircle is shown while adds inhibitor into electrolyte in non-abrasion……………………………………………58
Figure 5.6 In abrasion, a depressed semicircle with decreasing of impedance is smaller than that in non-abrasion and keeps the same shape………………………………………….58
Figure 5.7 Electrochemical reaction mechanisms of nitric acid system…………………………………………………...61
Figure 5.8 Equivalent circuit of nitric acid system…..………………61
Figure 5.9 Fitting of nitric acid system (non-abrasion)…..………….62
Figure 5.10 Fitting of nitric acid system (abrasion)…………………..62
Figure 5.11 Comparison of fitting impedance size of nitric acid only system…………………………………………………...63
Figure 5.12 Electrochemical reaction mechanisms of nitric acid system within citric acid………………………………………...65
Figure 5.13 Equivalent circuit of citric acid in nitric acid system…….65
Figure 5.14 Fitting of nitric acid system with adding citric acid (non-abrasion)…………………………………………...66
Figure 5.15 Fitting of nitric acid system with adding citric acid (abrasion)………………………………………………..66
Figure 5.16 Comparison of fitting impedance size of citric-nitric acid system…………………………………………………...67
Figure 5.17 Electrochemical reaction mechanisms of nitric acid system within BTA……………………………………………...69
Figure 5.18 Equivalent circuit of BTA in nitric acid system………….69
Figure 5.19 Fitting of nitric acid system within adding BTA (non-abrasion)…………………………………………...70
Figure 5.20 Fitting of nitric acid system within adding BTA (abrasion)………………………………………………..70
Figure 5.21 Comparison of fitting impedance size of BTA-nitric acid system…………………………………………………...71
Figure 5.22 The impedance plots of two semicircles seen lessened while the polishing pressure increased in nitric acid system…..78
Figure 5.23 In the presence of BTA, the impedance of copper without abrasion is higher than that in abrasion…………………78
Figure 5.24 In the presence of citric acid, the impedance of copper without abrasion is higher than that in abrasion………...79
Figure 5.25 The impedance plots reduce while rotation rate rises……79
Figure 5.26 The impedance plots diminish while rotation rate rises and keeps its style in abrasion situation……………………..80
Figure 5.27 Two impedance semicircles decrease with rotation rate rise and keep their shapes in abrasion……………………….80
Figure 5.28 The impedance of semicircle decreased while concentration in nitric acid increased…………………………..……….81
Figure 5.29 The two impedance semicircles decreased in abrasion…..81
Figure 5.30 Different complex concentrations only influent the whole impedance which represent…………………………….82
Figure 5.31 Different complex concentrations only influent slightly in the impedance represent…………………………………82
Figure 5.32 Concentration differences reflect to Nyquist plot in adding BTA and no abrasion situation…………………………83
Figure 5.33 Affects of BTA concentration seem slightly in abrasion...83
Figure 5.34 The electrochemical impedance spectroscopy (EIS) plots of copper in various nitric acid systems……………………86
Figure 5.35 The impedance plots of copper in abrasion in various nitric acid systems…………………………………………..87
Figure 5.36 Comparison of fitting impedance size of citric-nitric acid and nitric acid only system……………………………...87
Figure 5.37 Comparison of fitting impedance size of BTA-nitric acid and nitric acid only system……………………………...88
Figure 5.38 Auger Electron Spectroscopy (AES) survey spectra determining elements that present on the copper surface after exposure to the nitric acid based slurry……………90
Table Caption
Table 1.1 Processes and features of kinds of planarization methods.....2
Table 1.2 Various planarity on surface topography could be obtained by some planarization methods……………………………….4
Table 3.1 Chemical represents of experimental slurries……………...42
Table 3.2 Electrochemical set-up and mechanical factors in experiment……………………………………………..….45
Table 5.1 Capacitance and Resistance value of above Equivalent……61
Table 5.2 Capacitance and Resistance value of above Equivalent……65
Table 5.3 Capacitance and Resistance value of above Equivalent……69

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