臺灣博碩士論文加值系統

本論文的目的是研究以無電鍍法沈積銅薄膜於TiN、Ta、TaN及Ta2N擴散阻障層上，以作為ULSI元件導線的應用。由於擴散阻障層不具催化無電鍍銅反應的能力，因此，使用不同方法來活化擴散阻障層，乃成為本論文的研究重點之一。我們在實驗中所採用的活化方法為下：濺鍍銅晶種層法、敏化活化法及置換活化法。研究結果與討論分為五個部分。第一部分研究無電鍍銅沈積在帶有濺鍍銅晶種層的Ta、TaN上以及經過敏化活化後的TiN上，結果顯示，適當實驗條件下，在這三種阻障層上可以得到連續而均勻的銅膜；當銅膜厚度為1 m時，表面粗糙度Ra值為11 nm，電阻率為1.8  cm；銅膜沈積在TaN上具有強烈的(111)優選方向，與晶種層的方位直接相關；此外，配合此一濺鍍銅晶種層的活化方式，無電鍍銅可以填滿大小0.2 m、深寬比5之孔洞。第二部分研究無電鍍銅沈積在敏化活化後的TaN上，研究結果發現，連續的銅膜是藉由以下幾個步驟達成：(1)銅成核於催化位置上，(2)銅核的聚集而形成緻密的聚團，以及(3)聚團的合併；在最佳化的敏化活化條件下，無電鍍銅後可得到具有低表面粗糙度及電阻率的銅膜，且銅膜可以填滿小於0.2 m、深寬比5之孔洞。在第三部分，使用一種新的PdCl2/BOE/HNO3溶液來對Ta阻障層做置換活化，結果顯示，溶液中BOE與HNO3的相對含量比對於置換後Pd的型態與分佈有很大影響；當溶液中BOE：HNO3為3：2時，Pd的分佈較佳，且無電鍍後銅膜具有較好的連續性與較低的電阻率；銅膜沈積在置換活化後的Ta上表面粗糙度較大，主要是因為Pd活化位置無法達到很緻密的緣故。第四部分研究PdCl2/BOE/HNO3溶液對TaN及Ta2N的置換活化及活化結果對無電鍍銅膜的影響，結果發現，在TaN及Ta2N上置換結果差異頗大，主要與兩者不同的鍵結強度、電阻率以及Ta的氧化態相關；經過5% HF溶液預蝕刻後，由於原生氧化層被去除且表面粗糙度略為增加，因此置換活化後Pd分佈大為改善，且無電鍍後銅膜的表面粗糙度明顯降低。在最後一個部分，我們提出一個無電鍍銅的結晶機制，即：自我引發之重覆成核過程。根據此一機制，低角度晶界會存在於析出的銅核之間；此機制可以合理解釋實驗中所觀察到的無電鍍奈米銅晶粒的聚團；這些聚團在SEM電子束照射下，會再結晶成為大尺寸的晶粒，此一現象可以由奈米銅晶粒的旋轉使低角度邊界之差排消失來解釋。

The purpose of this research is to investigate electroless Cu deposition on various diffusion barriers such as TiN, Ta, TaN, and Ta2N, for the application of interconnects in ULSI devices. Since these diffusion barriers are not catalytic to electroless Cu deposition, an activation step should be carried out prior to the deposition of electroless Cu. Therefore, activation of barriers by different methods is a key point of this research.
The research is mainly divided into five sections. In the first section, Cu was electrolessly deposited on Ta and TaN with sputtered Cu as a seed layer, and on TiN which was activated by a two-step activation using SnCl2/HCl and PdCl2/HCl solutions, respectively. Continuous Cu films were electrolessly deposited on these substrates. The Cu film deposited on Cu seeded barrier showed a low Ra surface roughness of 11 nm and a resistivity of 1.8  cm, with a film thickness of 1 m. A strong (111) texture was obtained for the Cu film deposited on Cu seeded TaN because of the strong (111) texture of the seed layer. Besides, complete fill of Cu into 0.2 m vias with an aspect ratio of 5 was obtained.
In the second section, a two-step activation was used to catalyze electroless Cu deposition on TaN barrier. It was found that a continuous Cu film formed on the catalyzed TaN through these steps: nucleation on catalytic sites, coalescence of Cu nuclei into dense islands, and merging of the islands to form a continuous film. With proper control of the catalyzation solutions, Cu films were electrolessly deposited with a high purity, low surface roughness, and low resistivity. Besides, gap fill was achieved for vias with a size lower than 0.2 m and aspect ratio up to 5.
In the third section, a novel PdCl2/BOE/HNO3 solution was used to activate Ta barrier for deposition of electroless Cu film by displacement deposition of Pd. Composition of the activation solutions was modified to see the change in surface morphology of Pd catalytic sites. Experimental results showed that the optimized solution had a BOE/HNO3 ratio of 3:2, and electroless Cu deposited on Ta barrier activated by this solution had a low resistivity and continuous morphology. The surface roughness of electroless Cu film on Ta barrier was high due to the insufficient Pd catalytic sites.
In the fourth section, PdCl2/BOE/HNO3 solution was used to activate TaN and Ta2N barriers for electroless Cu deposition. It was found that with a pre-etching in a diluted HF solution, the activation of both TaN and Ta2N barriers by Pd displacement deposition was improved. The different phenomena between activation of TaN and Ta2N barriers were discussed.
In the final section, we propose a Cu crystallization process during electroless deposition: self-induced repeated nucleation. This mechanism explains the agglomerations of Cu nano-crystallites in electroless Cu deposition on Pd activated TaN barrier. With this mechanism, low-angle boundaries are formed between the Cu nano-crystallites. The in-situ recrystallization of nano-crystallites into large grains was observed as exposing the sample to the electron beam of SEM, and it can be explained by the elimination of boundary dislocations by rotation of the nano-crystallites.

Table of Contents
摘 要…………………………………………………………………i
Abstract………………………………….……………………………iii
誌 謝…………………………………………………………………v
Table of Contents..……………………..………………………………vi
List of Figures……………………………………………………….....xi
List of Tables………………………………………………………….xix
Chapter 1 Background………………………………………………….1
1-1 Metallization of Integrated Circuits……….……………………..1
1-1-1 Definition…………………….……………………………..1
1-1-2 Interconnect………….………………………………...........3
1-1-3 Diffusion Barrier Layer…………………….……...………..6
1-1-4 Multilevel Metallization……………..…...…………............7
1-2 Copper Metallization…………...………………………………10
1-2-1 Why Use Copper Metallization…………………….........10
1-2-2 Copper Deposition Techniques……………..……………..13
1-2-2-1 Physical Vapor Deposition……………………………13
1-2-2-2 Chemical Vapor Deposition…………….…….............15
1-2-2-3 Electrochemical Deposition…………………………..20
(A) Electrodeposition……………………………………….23
A-1 Fundamentals of Cu Electrodeposition……...............23
A-2 Cu Electrodeposition for Microelectronics……..…...25
(B) Electroless Deposition………………………………….29
B-1 Fundamentals of Electroless Cu deposition................30
B-1-1 Mixed Potential Theory…..………………….....30
B-1-2 Evans Diagram….……………………...............33
B-1-3 Interaction Between Partial Reactions……….....33
B-1-4 The Mechanism of Anode Partial Reaction…….35
B-1-5 The Mechanism of Cathodic Partial Reaction….36
B-1-6 Activation of Noncatalytic Surfaces……………38
B-1-6-1 Dry Activation……………………………..38
B-1-6-2 Wet Activation……………………………..38
(1) Two-Step Activation……………………….....38
(2) One-Step Activation……………………….....40
(3) Photochemical Activation……………………41
(4) Activation by Displacement Deposition……..43
B-1-7 Mechanism of Electroless Cu Crystallization.....47
B-2 Electroless Deposition of Cu in Microelectronics…..52
1-2-3 Comparison of Cu Deposition Techniques………………...55
1-2-4 Damascene and Dual Damascene………………………....55
1-2-5 Diffusion Barriers for Cu Metallization…………………...59
1-3 Purpose of This Study………………….……………………….61
References…………………………………………………………..63
Chapter 2 Electroless Cu Deposition on TiN, Cu seeded Ta, and Cu Seeded TaN Diffusion Barriers………………………….74
Abstract……………………………………………………………..73
2-1 Introduction…………………………………………………….75
2-2 Experimental Procedures……………………………………….77
2-3 Results and Discussion…………………………………………78
2-3-1 Surface Morphologies of Electrolessly deposited Cu films.78
2-3-1-1 Electroless Cu Deposition on TiN/SiO2/Si Substrate...78
2-3-1-2 Electroless Cu Deposition on Cuseed/Ta/SiO2/Si Substrate……………………………………………...82
2-3-1-3 Electroless Cu Deposition on Cuseed/TaN/SiO2/Si Substrate……………………………………………...85
2-3-2 Step Coverage and Gap Filling Capability………………..85
2-3-3 Crystallography of Electrolessly Deposited Cu Films……89
2-3-4 Electrical Resistivity of Electrolessly Deposited Cu Films.97
2-4 Summary….………..…………………………………………...99
References…………………………………………………………101
Chapter 3 Sn/Pd Catalyzation and Electroless Cu Deposition on TaN Diffusion Barrier Layer…………………………………..104
Abstract……………………………………………………………104
3-1 Introduction…………………………………………………...105
3-2 Experimental Procedures……………………………………...107
3-3 Results and Discussion………………………………………..110
3-3-1 Catalyzation of TaN Substrates…………………….......110
3-3-2 Electroless Cu Deposition on Catalyzed TaN Substrates.114
3-3-3 Electrical Resistivity of Electroless Cu Film……………121
3-3-4 Gap Filling Capability of Electroless Cu Deposition……125
3-3-5 Adhesion of Electroless Cu Film to TaN Layer…………127
3-4 Summary………………………………………………………127
References…………………………………………………………129
Chapter 4 Displacement Activation of Tantalum Diffusion Barrier Layer for Electroless Cu Deposition……………………..131
Abstract……………………………………………………………131
4-1 Introduction…………………………………………………...132
4-2 Experimental Procedures……………………………………...134
4-3 Results and Discussion………………………………………..136
4-3-1 SEM Analysis of Activated Substrates………………….136
4-3-2 AFM Analysis of Activated Substrates………………….139
4-3-3 Displacement Reaction Analysis in Activation Step……..139
4-3-4 AFM Analysis of Electroless Cu Deposition at the Early Stage……………………………………………………...144
4-3-5 Surface Morphologies of Long-Time Electrolessly Deposited Cu Films………………………………………………..146
4-3-6 XRD Analysis of the Electrolessly Deposited Cu Films…150
4-3-7 Film Continuity, Surface Roughness, and Electrical Resistivity of Electrolessly Deposited Cu Films………150
4-4 Summary………………………………………………………156
References………………………………………………………....158
Chapter 5 Electrochemical Deposition of Pd Nano Particles on TaN and Ta2N Diffusion Barriers and Its Application to Catalyzation of Electroless Cu Deposition………………161
Abstract……………………………………………………………161
5-1 Introduction…………………………………………………...162
5-2 Experimental Procedures……………………………………...164
5-3 Results and Discussion………………………………………..166
5-3-1 Characterization of As-Deposited Tantalum Nitride Barriers………………………………………………...166
5-3-2 Electrochemical Deposition of Pd Nano Particles on TaN and Ta2N Barriers…….…………………………………169
5-3-3 Electrochemical Deposition of Pd Nano Particles on HF Pre-Etched TaN and Ta2N barriers……………………..173
5-3-4 XPS Analysis of As-Deposited and Pd Deposited TaN and Ta2N Films………………………………...……………..176
5-3-5 Discussion on the Different Phenomena of Electrochemical Pd Deposition on TaN and Ta2N Barriers………………182
5-3-6 Characterization of Electroless Cu Films Deposited on TaN and Ta2N Barriers Activated by Electrochemical Pd Deposition………………………………………………..183
5-3-7 Comparison of Electrochemical Pd Deposition to the Two-Step Activation Method for Catalyzation of Electroless Cu Deposition on TaN Diffusion Barrier………………...187
5-4 Summary………………………………………………………190
References…………………………………………………………192
Chapter 6 The Nuclei Coalescence in Electroless Cu Deposition and Its Relation to the Repeated Three-Dimensional Nucleation………………………………………………..194
Abstract……………………………………………………………194
6-1 Introduction…………………………………………………...195
6-2 Experimental Procedures…………………………………….196
6-3 Results and Discussion………………………………………..197
6-4 Summary………………………………………………………204
References…………………………………………………………206
Chapter 7 Conclusions……………………………………………….207
Contributions of This Research………………………………………211
Future Works……………………………………………………….213

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