矽晶圓上高附著性無電鍍鎳磷層之研究

The Study of Highly Adhesive Electroless Nickel Plating Film on Silicon Wafer

許晉偉(Hsu, Chin Wei)

指導教授 ： 衛子健

國立清華大學/工學院/化學工程學系/碩士(2016年)

摘要

本研究為改善矽晶圓上無電鍍鎳磷層附著力的方法，首先以末端具有胺基官能團(NH2)的矽烷化合物對矽基板表面進行改質，藉由矽烷化合物的水解端與氫氧化的矽基板表面進行脫水反應，使矽烷化合物以共價鍵結構連結在矽基板上。經矽烷改質後的矽基板搭配自行開發的聚乙烯醇包覆奈米鈀粒子(Polyvinyl alcohol capped palladium, PVA-Pd)作為無電鍍鎳反應之觸媒，利用矽烷化合物中胺基官能團與PVA-Pd進行交互作用，增強觸媒對基板的吸附能力以利於後續無電鍍鎳磷層附著力之增強。
材料分析方面，以穿透式電子顯微鏡(Transmission electron microscope, TEM)鑑定PVA-Pd的粒徑大小及微結構分析; 利用X射線光電子能譜儀(X-ray photoelectron spectroscopy, XPS)，水滴接觸角量測儀(Water contact angle measurement)觀察矽烷化合物在矽基板表面改質的效果與變化; 接著以原子力顯微鏡(Atomic force microscope, AFM)觀察觸媒在基板上的分佈情形; 並以掃描式電子顯微鏡(Scanning electron microscopy, SEM)分析無電鍍鎳磷層之表面形貌及厚度變化; 最後利用附著力測試分析無電鍍鎳磷層與矽基板表面的垂直拉升附著力，藉由附著力測試的結果，發現以矽烷改質的矽基板表面搭配PVA-Pd的無電鍍鎳層相較於僅利用商業錫鈀膠體觸媒的無電鍍鎳磷層，其平均附著力可由原先的4.63MPa提升到10.83MPa; 並藉由XPS分析氮原子及鈀原子交互作用的機制，以了解附著力顯著提升的原因。
將以此方法製作的高附著性無電鍍鎳磷層進行退火，為了能有效瞭解高溫退火下無電鍍鎳磷層之附著力變化的原因，我們利用25-1部分因素實驗設計法探討影響附著力變化的因子。經由控制五個變因，分別為退火溫度、退火時間、矽烷化合物浸泡時間、觸媒濃度及觸媒浸泡時間可以得到不同附著力的無電鍍鎳磷層。經由變異數分析，可以得知附著力受退火溫度及矽烷化合物浸泡時間顯著的影響，此外退火溫度、退火時間及矽烷化合物浸泡時間的交互作用亦會影響無電鍍鎳磷層附著力之大小。
為了更深入瞭解矽烷化合物的浸泡時間以及退火製程如何影響附著力，先分別在不同的ETAS浸泡時間下分析附著力數值的變化，再藉由AFM及水滴接觸角分析不同時間下矽烷化合物的結構，並建立矽烷化合物改質層的可能型態與其上無電鍍鎳磷層附著力數值的關係，最後推論在30分鐘的浸泡時間下能得接近於單層吸附的矽烷化合物層，該層以Si-O-Si的共價鍵結構搭配胺基官能團與觸媒的交互作用，因此具有最佳的無電鍍附著力；而在低於30分鐘的浸泡時間(1及15分鐘)，尚未形成單層吸附狀態的矽烷化合物，因胺基官能團的數目較少，觸媒與矽烷上胺基的交互作用力不足，導致無電鍍鎳磷層的附著力較差；而在大於30分鐘的浸泡時間(60及90分鐘)下為多層吸附的矽烷層結構，其層跟層之間多以氫鍵鍵結，而氫鍵的強度遠低於Si-O-Si共價鍵，導致無電鍍鎳磷層的附著力亦較差。
將上述不同矽烷浸泡時間的無電鍍鎳磷層進快速熱退火程序後，行為卻天差地別。在ETAS浸泡時間在30及30分鐘以上(60及90分鐘)時，經退火後因ETAS在高溫下形成碳的殘餘物使得ETAS與鈀原子間的交互作用消失又無任何鎳矽化合物的生成導致無電鍍鎳磷層附著力快速下降；而在ETAS浸泡時間改為30分鐘以下(1及15分鐘)，其退火後之無電鍍鎳磷層與矽基板反而可藉由不完整的矽烷改質層產生鎳矽化合物使附著力大幅上升。

關鍵字

無電鍍鎳磷層 ； 矽烷化合物 ； 奈米鈀粒子 ； 附著力

並列摘要

Electroless deposition of nickel-phosphorus (Ni-P) film is a promising skill for the preparation of diffusing barrier layer in silicon and circuit board industry. Typically, Sn/Pd colloid is the most common catalyst for electroless deposition. However, lacking of distinct adsorbing mechanism, the mechanical adhesion of Ni-P film catalyzed by Sn/Pd colloids on bare silicon surface is usually not satisfactory, particularly in the smooth surface such as silicon wafer and glass. Therefore, we devote to develop alternative to replace Sn/Pd colloids. In this study, the development of above-mentioned new catalyst is systematically discussed, including catalyst synthesis, interaction with silanized substrate and the improvement of mechanical adhesion of subsequent electroless Ni-P film.
Using polyvinyl alcohol (PVA, molecular weight 9000-10000) as the protective agent, palladium nitrate as the precursor and formaldehyde as the reductant, we successfully synthesized PVA-capped palladium colloids (PVA-Pd) aqueous dispersion. Transmission electron microscopy (TEM) analysis reveals the well-defined nano-particle of PVA-Pd is a face centered cubic nano-crystal with the size of 2-5 nm.
This novel PVA-Pd is then applied as the catalyst for electroless plating of nickel-phosphorous (Ni-P) layer on a 3- 2-(2-aminoethylamino) ethylamino propyl trimethoxysilane (ETAS)-modified silicon surface. The ETAS modification of substrate is evaluated by X-ray photoelectron spectroscopy (XPS) and water contact angle. In addition, evidenced by XPS, the binding energy of both Pd center of PVA-Pd and nitrogen of ETAS are both chemically shifted due to the interaction between Pd center and long pair electrons of the amino group on ETAS. Unlike commercial Sn/Pd colloids which are physically adsorbed on the substrate, our PVA-Pd is found to chemically adsorb on the substrate so that the adhesion of subsequent Ni-P film is enhanced.
A 200 nm-thick Ni-P layer is then electroless deposited on the PVA-Pd adsorbed silicon surface by using a commercial Ni-P bath at 80oC for 1 minute. Compared with the mechanical adhesion of Ni/P layer made by commercial Sn/Pd colloids on bare silicon surface, the mechanical adhesion of Ni/P layer made by our PVA-Pd and ETAS surface modification is significantly improved from 4.63MPa to 10.83MPa without the need of post annealing.
However, in our previous study or even in searching all relevant literatures, the control of ETAS modification and its relation to the adhesion of ELP film has never been explored. Most studies either directly utilize silane-compound to improve adhesion of deposited film or aim to control, explain or tune the morphology of ETAS modification but without conducting ELP. Very few reports went into details of how different levels of silane-compound modification influence the interfacial properties and most importantly, how these different interfacial properties connect to the adhesion of subsequent ELP layer. In this report, we aim to elaborate how microscopic ETAS modification affects macroscopic ELP film adhesion. In particular, several levels of ETAS modification on Si wafer were created by controlling the immersion time of ETAS stock solution; then these samples were carefully characterized by means of atomic force microscopy (AFM), water contact angle (WCA) and X-ray photoelectron spectroscopy (XPS) to verify the configurations of ETAS layer. Finally a scenario of ETAS modification on Si wafer versus immersion time is proposed accordingly and the relation between ELP Ni-P film adhesion and ETAS configuration with or without a post rapid thermal annealing (RTA) treatment is discussed. To the best of our knowledge, this is the first report trying to connect the effect of molecular silane-compound modification with macroscopic film adhesion in the field of surface modification.

並列關鍵字

Electroless deposition ； Nickel-phosphorus film ； Silane-compound ； Adhesion

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