以無電鍍為基礎之噴墨列印金屬化製程

Abstract

噴墨列印乃是一種可直接於基板上定義出圖案之技術，由於其具有低操作成本、高材料使用效率、不需微影製程、非接觸式、快速、大面積低溫沈與利於環保等諸多優點，因此近年來在電子產業上具有極大的應用潛力，特別是針對平面及軟性的基材。本實驗期望利用噴墨列印搭配已發展成熟之無電鍍技術，在低溫下直接形成銅與銀導線。 首先以混合電位理論來探討反應物濃度對於無電鍍銅與無電鍍銀系統的影響程度，在無電鍍銅系統中，銅離子濃度的改變對沈積電流密度的影響比甲醛來得大，而無電鍍銀的混合電位與銅相比較偏正值，表示銀系統比較容易有金屬沈積。銀離子還原的速率很快，反應幾乎是瞬間進行，因此非常適用於噴墨列印系統，噴印所得的銀導線厚度約為100 nm，電阻率為4.4 μΩ-cm；而無電鍍銅若將pH調高，添加KOH至1.0M，則銅金屬便能快速地在活性物質的表面還原析出。利用本實驗中所建立的數學模式預測噴印無電銅的反應大約可在12秒左右完成，而噴印所得的銅導線厚度約為25 nm，電阻率為11 μΩ-cm。銅離子的還原反應會伴隨著副產物氫氣的產生，當反應速率加快，氫氣產生的量也會變多，造成銅導線表面的不連續，進而影響導電性質；此外，強鹼的環境下亦會對噴墨頭造成腐蝕現象，縮短噴墨頭的使用壽命。 無電鍍噴印金屬講求快速反應，不同於傳統化鍍講求鍍槽的穩定性，而沈積金屬的厚度與反應時間及溫度無關，欲控制噴印金屬層的厚度可藉由調整噴墨溶液的反應物濃度，或是重覆噴印以使厚度增加。

Ink-jet printing, as a derivative of direct-write technology, offers the additional advantages of low cost, high material efficiency, elimination of photolithography, low temperature deposition, friendly environment and non-contact processing. Therefore, it has great potentials for applications on electronics fabrication processes, especially on plane and flexible substrate in recent years. In this study, ink-jet printing is combined with electroless plating which has been fully developed and direct writes cooper and silver lines at low temperature. First, the mixed-potential theory is applied to investigate the effects of reagents concentrations in both electroless copper and silver plating systems. In the electroless copper plating system, the change in copper concentrations has more effects on the deposition current density than formaldehyde. As compared with the silver system, the mixed potential is more negative, which means the occurrence of copper deposition is not as easy as silver. The reduction rate of silver ion is very fast and silver deposits almost immediately when the silver ion solution meets the reduction agent solution, hence it is suitable for applying to the ink-jet printing system. The thickness of ink-jet silver lines in this study is about 100 nm and the resistivity is 4.4 μΩ-cm. In the electroless copper plating system, copper can deposit very fast on a catalyzed surface by adding 1.0M KOH in the solution to adjust it to a high-pH condition. The reaction completes within about 12 seconds by the prediction of the mathematical model established in this study. The thickness of ink-jet copper lines is about 25 nm and the resistivity is 11 μΩ-cm. Hydrogen is a by-product in the reduction reaction of copper and it comes in a large amount when the copper reduction rate increases. The large amount of hydrogen would cause the discontinuity of surface of copper lines and hence affect the conductivity. Furthermore, the printing head would easily get corrosion in a strong-base environment and hence end its life. Metallization by ink-jet printing based on electroless plating, different from traditional electroless plating bath which calls for the stability of plating bath, needs high reduction rate of metals. The thickness of metal deposited has no relations with reaction time and temperature, but it can be controlled by adjusting the reagents concentration in ink solutions or by jetting multi-layers of metal to form a thicker conductive lines.