| 초록 |
In recent years, the Fan-out Wafer Level Package (FoWLP) technology has being drawn attention due to reducing packaging cost and increasing I/O for high performance. Redistribution layers (RDL), one of the important parts for FoWLP process, are formed using seed deposition, patterning, and Cu electrodeposition to rearrange I/O connections on the die. During Cu electrodeposition for the RDL process, overburdens were formed on top surfaces patterned submicrometer trenches. The Chemical Mechanical Polishing (CMP) has been used to remove these overburdens in semiconductor industry, however, this CMP process caused an increase in process cost. To minimize these overburdens, microcontact printing (µ CP) that transfers the self-assembled monolayers (SAMs) on the top surface of trenches can be one of the solutions suppressing the Cu deposition on these top surfaces. These transferred SAMs on the top surface of trenches by the µ CP act as an electrochemical barrier leading to selective electrodeposition of Cu films. Development of the µ CP process can reduce the cost removing the Cu overburdens. In this study, microcontact printing (µ CP) process was proceeded by forming nanometer thickness of the SAMs of alkanethiol on a flat polydimethylsiloxane (PDMS) stamp and transferring these SAMs using the SAMs-formed PDMS stamp on a patterned substrate (structure of 100 nm Cu/20 nm Ti/SiO2, line depth of 5 µm). Cu electrodeposition under various sizes of trench pattern in Cu/H2SO4 electrolyte was proceeded. Electrochemical properties such as desorption behavior of SAMs depending on the carbon chain length were investigated. The SAMs on the top surfaces, surface morphology, and cross-sectional view of Cu filled trenches were observed. Consequently, SAMs on printed area inhibited Cu electrodeposition. This result reveals the feasibility of Cu trench-selective deposition in various dimensions. The µ CP method shows the possibility of replacing CMP which removes overburdens of Cu for the RDL process. |
