電鍍銅於薄膜電晶體陣列線路金屬化之研究

Pattern Metallization by Cu Electrodeposition for Thin-Film Transistors Array

鄭湘寧(Shrane-Ning Jenq)

指導教授 ： 萬其超 ； 王詠雲

國立清華大學/工學院/化學工程學系/博士(2006年)

摘要

本論文主要目的為發展一種憑藉光阻進行選擇性電沉積的加成方式，來製作非晶系薄膜電晶體的銅閘極。對非晶系薄膜電晶體的銅閘極而言，所沉積銅導線的邊緣形狀必須是錐形(tapered) 。此需求可利用在基本的電鍍溶液中添加有機添加劑-聚乙二醇(PEG)與二硫二丙烷磺酸鈉(SPS)來達成。本論文並且釐清個別有機添加劑對在銅晶種層上所沉積銅導線邊緣形狀的影響。在不添加任何有機添加劑的情形下，電沉積銅薄膜呈現粗糙的表面並且導線的形狀是由光阻形狀所定義的。PEG添加劑可以使得銅膜表面形貌變得細緻，但是導線的形狀仍由光阻形狀所定義。令人感興趣的是SPS添加劑使位於銅導線邊緣的沉積銅往遠離光阻側壁的傾斜方向成長，而產生與光阻形狀無關的錐形導線。當銅鍍液中含有PEG和SPS時，能產生兼具有細緻形貌、光滑表面及低片電阻可應用電晶體陣列的錐形導線。當銅鍍液中含有PEG與SPS時，對形成錐形導線而言，SPS扮演一個相當重要的角色。
SPS如何在電鍍過程中造成錐形導線的原因，可由自我組裝薄膜(SAMs)的行為來做解釋。錐形銅導線可再一次藉由在銅晶種層預吸附SPS後，於不含SPS銅鍍液中進行電沉積來產生。此外，SPS與氯離子對銅導線側壁形狀的影響被確認。而自我組裝雙硫化合物與相關具有不同末端官能基的硫醇化合物對銅導線側壁形狀的影響亦被探討。當氯離子未出現在含SPS的銅鍍液中時，錐形的導線形狀消失。硫醇化合物的末端磺酸官能基亦對形成傾斜側壁的銅導線而言，扮演一個關鍵的角色。因此，我們就SAMs與SPS及氯離子間電化學行為的角度提出一個機制，用來說明SPS與氯離子在電鍍溶液內，如何在電鍍過程中於相鄰光阻的位置產生傾斜側壁的沉積銅。
此外，本論文亦針對不同分子量的PEG在電化學特性、表面形貌及對銅導線側壁形狀的影響作研究。在添加分子量200的PEG於鍍液中後，產生低極化、大晶粒與錐形邊緣的銅導線。相對地，在添加分子量2000、4000與10000的PEG於鍍液中後，產生高極化、小晶粒與被光阻形狀所定義的導線形狀等現象。
並且，經過適當的酸性處理，錐形銅導線亦能沉積在鎳晶種層上，就像前文所述在銅晶種層上所形成的一樣。經由選擇性蝕刻將所露出鎳層去除掉，多層結構的銅閘極便形成了。這種新方法提供一種替代的濕製程方式，來製作非晶系薄膜電晶體銅閘極。

關鍵字

電鍍銅 ； 薄膜電晶體 ； 銅閘極 ； 線路金屬化 ； 加成法

並列摘要

We have developed an additive process fabricating copper gate of amorphous thin-film transistor (α-Si-TFT) by selective electrodeposition through mask. A tapered edge shape of Cu deposit is a key requirement for gate electrode of α-Si-TFT, which can be achieved by the addition of organic additives (e.g. polyethylene glycol (PEG), bis-3-sodiumsulfopropyl disulfide (SPS)) in basic Cu bath. The influence of individual organic additive on edge shape of Cu deposit on Cu seed was also clarified. It was found that Cu electrodeposition without organic additive results in rough deposit and a pattern shape defined by the mask shape. PEG additive can refine the deposit morphology but the pattern shape is still defined by the mask shape. It is interesting that the deposit with SPS alone grows in an oblique direction away from the mask sidewall on the edge of deposited pattern and produces a tapered pattern independent of the mask sidewall. When the Cu bath contains both PEG and SPS, the combined effect results in a tapered pattern with fine morphology, smooth surface and low sheet-resistance, which is suitable for TFT array. And, SPS plays a key role in creating a tapered Cu deposit when the bath contains PEG and SPS.
How SPS causes the tapered pattern during electrodeposition could be explained in terms of its self-assembled monolayers (SAMs) behavior. A tapered shape of Cu deposit could also form on copper seed pre-adsorbed with SPS although the copper bath itself did not contain SPS. The influence of SPS and Cl- on the sidewall shape of Cu pattern was identified. The influence of self-assembled disulfide and related thiolates with various end-groups on the edge shape of Cu pattern was also explored. A tapered pattern disappears during electrodeposition through mask when a Cu bath contains SPS in the absence of Cl-. Sulfonate end-group of thiolate also plays a key role in forming sloped sidewall of Cu pattern. Therefore, mechanism illustrating sloped sidewall of Cu deposit adjacent to photoresist mask during electrodeposition in a Cu bath containing SPS and Cl- was proposed in terms of SAMs and electrochemical behavior of SPS and Cl-.
Besides, the influence of PEG with various molecular weights on the electrochemical behavior, surface morphology and edge shape of Cu deposit was studied. Low polarization, deposit with big grain and tapered edge shape of Cu pattern were typical for a Cu bath containing PEG with MW 200. In contrast, high polarization, deposit with fine grain and shape of Cu deposit defined by the shape of P/R mask represent for a Cu bath containing PEG with MW 2000, 4000 and 10000.
Furthermore, after suitable acid pretreatment, the tapered Cu deposit could also be achieved on Ni seed layer as well as on Cu seed. The multilayer copper gate was fabricated after selectively etching of exposed nickel layer. The new method provides an alternative wet process for fabricating Cu gate of α-Si-TFT.

並列關鍵字

Cu electrodeposition ； TFTs ； Cu gate ； Pattern metallization ； Additive process

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