The overall process, from the pre-treatment of aluminum substrates to the eco-friendly neutral electroless Ni-P plating process, was observed, compared, and analysed. To remove the surface oxide layer on the aluminum substrate and aid Ni-P plating, a zincation process was carried out. After the second zincation treatment, it was confirmed that a mostly uniform Zn layer was formed and the surface oxide of aluminum was also removed. The Ni-P electroless plating films were formed on the secondary zincated aluminum substrate using electroless plating solutions of pH 4.5 and neutral pH 7.0, respectively, while changing the plating bath temperature. When a neutral pH7.0 electroless solution was used, the Ni-P plating layer was uniformly formed even at the plating bath temperature of 50 oC, and the plating speed was remarkably increased as the bath temperature was increased. On the other hand, when a pH 4.5 Ni-P electroless solution was used, a Ni-P plating film was not formed at a plating bath temperature of 50 oC, and the plating speed was very slow compared to pH 7.0, although plating speed increased with increasing bath temperature. In the P contents, the P concentration of the neutral pH 7.0 Ni-P electroless plating layer was reduced by ~ 42.3 % compared to pH 4.5. Structurally, all of the Ni-P electroless plating layers formed in the pH 4.5 solution and the neutral (pH 7.0) solution had an amorphous crystal structure, as a Ni-P compound, regardless of the plating bath temperature.

We used an etching process to control the line-width of screen printed Ag paste patterns. Ag paste was printed on anodized Al substrate to produce a high power LED. In general, Ag paste spreads or diffuses on anodized Al substrate in the process of screen printing; therefore, the line-width of the printed Ag paste pattern increases in contrast with the ideal line-width of the pattern. Smudges of Ag paste on anodized Al substrate were removed by neutral etching process without surface damage of the anodized Al substrate. Accordingly, the line-width of the printed Ag paste pattern was controlled as close as possible to the ideal line-width. When the etched Ag paste pattern was used as a seed layer for electroless Ni plating, the line width of the plated Ni film was similar to the line-width of the etched Ag paste pattern. Finally, in pattern formation by Ag paste screen printing, we found that the accuracy of the line-width of the pattern can be effectively improved by using an etching process before electroless Ni plating.

We investigated the effects of DMAB (Borane dimethylamine complex, C2H10BN) in electroless Ni-B film with addition of DMAB as reducing agent for electroless Ni plating. The electroless Ni-B films were formed by electroless plating of near neutral pH (pH 6.5 and pH 7) at 50˚C. The electroless plated Ni-B films were coated on screen printed Ag pattern/PET (polyethylene terephthalate). According to the increase of DMAB (from 0 to 1 mole), the deposition rate and the grain size of electroless Ni-B film increased and the boron (B) content also increased. In crystallinity of electroless Ni-B films, an amorphization reaction was enhanced in the formation of Ni-B film with an increasing content of DMAB; the Ni-B film with< 1 B at.% had a weak fcc structure with a nano crystalline size, and the Ni-B films with > 5 B at.% had an amorphous structure. In addition, the Ni-B film was selectively grown on the printed Ag paste layer without damage to the PET surface. From this result, we concluded that formation of electroless Ni-B film is possible by a neutral process (~green process) at a low temperature of 50˚C.

We investigated the characteristics of electroless plated Cu films on screen printed Ag/Anodized Al substrate. Cu plating was attempted using neutral electroless plating processes to minimize damage of the anodized Al substrate; this method used sodium hypophosphite instead of formaldehyde as a reducing agent. The basic electroless solution consisted of CuSO4·5H2O as the main metal source, NaH2PO2·H2O as the reducing agent, C6H5Na3O7·2H2O and NH4Cl as the complex agents, and NiSO4·6H2O as the catalyser for the oxidation of the reducing agent, dissolved in deionized water. The pH of the Cu plating solutions was adjusted using NH4OH. According to the variation of pH in the range of 6.5~8, the electroless plated Cu films were coated on screen printed Ag pattern/anodized Al/Al at 70˚C. We investigated the surface morphology change of the Cu films using FE-SEM (Field Emission Scanning Electron Microscopy). The chemical composition of the Cu film was determined using XPS (X-ray Photoelectron Spectroscopy). The crystal structures of the Cu films were investigated using XRD (X-ray Diffraction). Using electroless plating at pH 7, the structures of the plated Cu-rich films were typical fcc-Cu; however, a slight Ni component was co-deposited. Finally, we found that the formation of Cu film plated selectively on PCB without any lithography is possible using a neutral electroless plating process.

We investigated cleaning effects using NH4OH solution on the surface of Cu film. A 20 nm Cu film was deposited on Ti / p-Si (100) by sputter deposition and was exposed to air for growth of the native Cu oxide. In order to remove the Cu native oxide, an NH4OH cleaning process with and without TS-40A pre-treatment was carried out. After the NH4OH cleaning without TS-40A pretreatment, the sheet resistance Rs of the Cu film and the surface morphology changed slightly(δRs:~10mΩ/sq.). On the other hand, after NH4OH cleaning with TS-40A pretreatment, the Rs of the Cu film changed abruptly (δRs:till~700mΩ/sq.); in addition, cracks showed on the surface of the Cu film. According to XPS results, Si ingredient was detected on the surface of all Cu films pretreated with TS-40A. This Si ingredient(a kind of silicate) may result from the TS-40A solution, because sodium metasilicate is included in TS-40A as an alkaline degreasing agent. Finally, we found that the NH4OH cleaning process without pretreatment using an alkaline cleanser containing a silicate ingredient is more useful at removing Cu oxides on Cu film. In addition, we found that in the NH4OH cleaning process, an alkaline cleanser like Metex TS-40A, containing sodium metasilicate, can cause cracks on the surface of Cu film.

In an effort to overcome the problems which arise when fabricating high-aspect-ratio TSV(through silicon via), we performed experiments involving the void-free Cu filling of a TSV(10~20 μm in diameter with an aspect ratio of 5~7) by controlling the plating DC current density and the additive SPS concentration. Initially, the copper deposit growth mode in and around the trench and the TSV was estimated by the change in the plating DC current density. According to the variation of the plating current density, the deposition rate during Cu electroplating differed at the top and the bottom of the trench. Specifically, at a current density 2.5 mA/cm2, the deposition rate in the corner of the trench was lower than that at the top and on the bottom sides. From this result, we confirmed that a plating current density 2.5 mA/cm2 is very useful for void-free Cu filling of a TSV. In order to reduce the plating time, we attempted TSV Cu filling by controlling the accelerator SPS concentration at a plating current density of 2.5 mA/cm2. A TSV with a diameter 10 μm and an aspect ratio of 7 was filled completely with Cu plating material in 90 min at a current density 2.5 mA/cm2 with an addition of SPS at 50 mg/L. Finally, we found that TSV can be filled rapidly with plated Cu without voids by controlling the SPS concentration at the optimized plating current density.

The electrolyte effects of the electroplating solution in Cu films grown by ElectroPlating Deposition(EPD) were investigated. The electroplated Cu films were deposited on the Cu(20 nm)/Ti (20 nm)/p-type Si(100) substrate. Potentiostatic electrodeposition was carried out using three terminal methods: 1) an Ag/AgCl reference electrode, 2) a platinum plate as a counter electrode, and 3) a seed layer as a working electrode. In this study, we changed the concentration of a plating electrolyte that was composed of CuSO4, H2SO4 and HCl. The resistivity was measured with a four-point probe and the material properties were investigated by using XRD(X-ray Diffraction), an AFM(Atomic Force Microscope), a FE-SEM(Field Emission Scanning Electron Microscope) and an XPS(X-ray Photoelectron Spectroscopy). From the results, we concluded that the increase of the concentration of electrolytes led to the increase of the film density and the decrease of the electrical resistivity of the electroplated Cu film.

Underlayer의 종류 및 두께가 Al 박막의 배향성 및 면저항 변화에 미치는 영향을 연구하였다. Al의 underlayer로서 sputtering 방식으로 증착되는 Ti와 TiN이 적층된 구조인 Ti/TiN이 사용되었으며, 각각에 대해 두께를 변화시키면서 Al 박막의 배향성, 면저항을 조사하였고, 400˚C, N2 분위기에서 열처리하면서 면저항의 변화를 조사하였다. Ti만을 Al의 underlayer로 사용한 경우, Ti두께가 10nm 이상이면 우수한 Al<111> 배향성을 나타냈으며 Al-Ti 반응 때문에 열처리 후 Al 배선의 면저항이 크게 상승하였다. Ti와 Al사이에 TiN을 적용함에 의해 Al<111> 배향성은 나빠지나 Al-Ti 반응에 의한 면저항의 증가는 억제할 수 있었다. Ti/TiN underlayer의 경우, 우수한 Al<111> 배향성을 확보하기 위한 Ti의 최소두께는 20nm이었고, Al-Ti 반응을 억제하기 위한 TiN의 최소두께는 20nm이었다.