為了配合體積更小、效能更高的積體電路，內連線的製作必須要能達到深次微米的要求。然而因電阻及電遷移阻抗等性質，在傳統製程中所使用的鋁金屬已不再具有絕對的優勢。相對的，銅金屬則具有低電阻、較高的融點及較佳的電遷移阻抗等優點，而原先無法使用乾式蝕刻製程的缺點及擴散到氧化層的問題也已藉由金屬鑲嵌技術的開發及擋層材料的研究發展而克服，可說已被視為下一世代IC內連線的最佳物質。
而在以電鍍方式沈積銅層之前，必須先在矽晶圓上先以濺鍍或化學氣相沈積的方式沈積上一層擴散阻障層及銅金屬的晶種層薄膜。擴散阻障層的材料目前多以氮化鈦或是氮化鉭為主，其目的主要在阻止銅金屬與介電層二氧化矽之間的擴散作用。而銅晶種層則是作為電鍍時導電之用。我們在實驗中發現，阻障層材料會與溶液中的金屬離子發生接觸置換反應，而使得基材表面沈積上一層金屬層。我們一方面希望能藉此研究確認各種阻障層材料的可靠性，以期能夠對於現有的積體電路銅製程發展上有所助益。另一方面更可藉由此置換反應直接沈積上金屬作為電鍍時的晶種層，以減少為沈積銅晶種層在PVD或CVD真空設備上的花費。

目前初步的實驗結果發現，銅、銀及鈀三種金屬離子都能在含有BHF的溶液中與氮化鈦薄膜進行接觸置換的反應，而氮化鉭薄膜則僅在同時含有鈀離子及氟離子的溶液中反應。對於擴散阻障層的材料功用而言，氮化鉭較之氮化鈦要來的更為穩定。下表為各種不同溶液組成中，金屬離子與基材間的反應情形。

Solution Si TiN film TiN powder TaN film Ti

F- / Cu2+ ○ ○ × × ○

F- / Ag+ ○ ○ ○ × ○

F- / Pd2+ ○ ○ ○ ○ ○

BHF ※ × × × ※

Cu2+ × × × × ○

Ag+ × × × × ○

Pd2+ × × × × ○

反應時間：15分鐘 反應溫度：20℃

○ 表示金屬離子還原並沈積於基材上

×表示無任何反應發生

※ 表示基材表面遭到溶液之腐蝕

由上表可發現矽基材亦只在氟離子存在下與各金屬離子發生置換反應，可知氟離子在各置換反應中均扮演極為關鍵的角色且此類反應將不同於鈦與金屬離子間單純的氧化還原反應。因此，我們藉由各種分析儀器來探討有關此一反應可能之反應機構。在本篇研究中，我們提出三種有關氮化鈦薄膜置換反應可能的反應機構並藉由實驗結果探討各機構的合理性，並分別對矽基材，氮化鉭及氮化鈦之置換反應提出一最有可能之反應方程式。此外，我們也發現KI及NaI可取代BHF來驅動鈀離子與氮化鈦間之置換反應且不會如氟離子般造成基材之腐蝕。

在置換反應的應用方面，我們發現經由置換反應，可在適當的溶液組成及溫度條件下沈積一層緻密的鈀金屬層在氮化鉭表面。此一鈀層可作為後續銅電鍍製程中導電所需的晶種層，相對於未處理之氮化鉭基材並可增加鍍銅層在氮化鉭表面之鍍著面積。

The fabrication of interconnect has become an essential part of IC industry in recent years. In order to improve the function and efficiency of a chip, the dimension of interconnect must be shrunk to deep submicron. Copper is regarded as the best conducting material for interconnect in the next generation by virtue of its lower resistivity, higher melting point, and better electromigration endurance. Moreover, some drawbacks in the application of copper have already been overcome, e.g., the development of barrier layer material which solves the problem of thermal diffusion between copper and silicon oxide.
Before the electrodeposition of copper, a diffusion barrier layer and copper seed layer must be deposited on top of the silicon wafer by PVD or CVD process. Titanium nitride and tantalum nitride are majorly used as the material for barrier layer in order to prevent the whole structure from thermal diffusion. Besides, seed layer was used to conduct electricity in electrodeposition process.

It was found that nitride barrier material could react with some metal ions by contact displacement and deposit metal upon silicon substrate. The research of contact displacement reaction is therefore useful for evaluating the reliabilty of titanium nitride and tantalum nitride as barrier layer. Additionally, if copper can be deposited directly through this reaction or other electrochemical methods without seed layer, the cost of vaccum facilities accompanied with PVD or CVD process can be saved. The following table shows the results of different solutions in contact with various substrates.

Solution Si TiN film TiN powder TaN film Ti

F- / Cu2+ ○ ○ × × ○

F- / Ag+ ○ ○ ○ × ○

F- / Pd2+ ○ ○ ○ ○ ○

BHF ※ × × × ※

Cu2+ × × × × ○

Ag+ × × × × ○

Pd2+ × × × × ○

Time: 15 minutes. Temp: 20℃.

Symbol ○ represents that the deposition of metal was observed.

Symbol ×represents that no reaction was observed.

Symbol ※ represents that the corrosion of substrate was observed.

It can be seen that TiN film can react with Cu2+, Ag+, and Pd2+ in the presence of fluoride ion, while TaN film reacts with Pd2+ and F- only. Further more, metal deposition on silicon sample also takes place only when the fluoride ion exists. Thus, we concluded that fluoride ion should play an essential role in displacement reaction in all cases, which is not a simple redox reaction like the Mz+-Ti couple. In addition, the details of contact displacement reaction can be studied with the aid of some instruments, such as XRD, ESCA, SEM, and IR Spectroscopy. Three possible mechanisms of TiN displacement reaction were proposed in this study based on the results of experiments. Besides, KI and NaI were found to activate the palladium displacement without corrosion on TiN, which is superior to BHF if Pd is applied to serve as seed layer for subsequent copper deposition. Furthermore, palladium deposition atop TaN by contact displacement was found to serve as a platform or seed layer for subsequent copper electrodeposition.

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