Laser Enhanced Electroless Plating of Micron-Scale Copper Wires

Abstract

Laser "direct writing" (LDW) or maskless pattern deposition has been extensively studied for more than a decade. 1,2 LDW is potentially attractive in semiconductor device customization, repair, prototyping, and packaging applications. [3][4][5] Copper is an important metallization material in microelectronic circuits 6,7 and multichip module interconnections, 8,9 largely because of its low electrical resistivity. A major limitation of LDW technologies for device metallization applications using laser chemical vapor deposition (LCVD) techniques has been the lack of Cu precursors with sufficiently high vapor pressure. The most common precursors used for the large area CVD of copper are copper(II) and ligand-stabilized copper(I) ␤-diketonate compounds. 10 While the vapor pressures of these precursors are, in general, sufficient for conventional CVD (deposition rates greater than or equal to a micrometer per hour), they are too low to allow the fast deposition rates (mm/s) required for LCVD applications. Advanced technologies making direct use of liquidphase delivery of precursors to the reaction zone have been developed. Solid-phase precursors can be dissolved into selected solvents such as 2-propanol or ethanol to provide highly controllable flow rates to the reaction zone. 11 Liquid precursors can be dissolved in solvents, 12 made into a paste layer, 13 or used as neat compounds. 14,15 The mechanism of deposition using liquid precursors has been proposed to be either a photochemical 16,17 or thermal decomposition reaction involving one or more precursors. 18,19 Laser-enhanced electroplating 20,21 and electroless plating 22 were first reported by von Gutfeld et al. They reported local plating enhancement rates as high as ϳ10 3 utilizing highly localized heating caused by the absorption of a focused laser beam at the substrate. Self-induced repair (SIR) of microelectronic circuits using joule heating induced local electrodeposition demonstrated by Chen is analogous to laser enhanced electroless plating. 23 The electrochemical conditions necessary for an electroless plating process to take place are (i) the reducing potential of the reductant must be less than that of the reducing potential of the metal and (ii) the metal must have enough catalytic activity for the anodic oxidation to take place at a reasonable rate. In a laser-enhanced electroless plating (LEEP) process the laser-induced temperature rise in the substrate enhances the local chemical reaction, causing the redox reaction to take place and metal to be deposited. The reducing agent needs to be chosen such that reduction takes place at an elevated temperature but not at ambient so that spatially selective laser deposition can take place. The redox potentials of selected reducing agents are listed in Table I. ExperimentalThe experimental setup is shown in Fig. 1. An Ar ion laser delivering a linearly polarized transmission electron microscopy (TEM 00 ) beam was used as the driving energy source. The laser was operated at a single wavelength of 514.5 nm whi...

Deposition of Durable Micro Copper Patterns into Glass by Combining Laser-Induced Backside Wet Etching and Laser-Induced Chemical Liquid Phase Deposition Methods

“…When the dissolved copper ions meets a reducing agent, such as formaldehyde (HCOH), a copper redox reaction may occur uncontrollably [ 31 ]; to prevent reckless and uncontrollable redox reactions, ligands need to be added to function as stabilizers for the copper ions [ 30 ], and potassium sodium tartrate tetrahydrate (KNaC 4 H 4 O 6 ·4H 2 O; Rochelle salt) and ethylenediaminetetraacetic acid (C 10 H 16 N 2 O 8 ; EDTA) are well-known ligands [ 19 ]. Lastly, the copper reduction reaction can occur in a high-pH alkaline surrounding, and the pH is controlled by NaOH in many cases [ 18 ].…”

“…Microfluidic devices, sensors, smart glasses, microelectronics, and components of micromechanics are possible applications if glass possesses conductivity [ 4 , 5 , 6 , 7 ]. Several methods have been studied for combining conductive materials with glass, such as using indium tin oxide (ITO) [ 8 , 9 ], femtosecond laser deposition [ 10 , 11 ], electroless copper plating [ 12 , 13 , 14 , 15 ], and laser-induced chemical liquid phase deposition (LCLD) [ 16 , 17 , 18 , 19 ].…”

“…LCLD is, therefore, an easy, simple way to make copper circuits on glass, but the copper deposited by the LCLD method has an issue with durability because of its weak adhesion with glass. Although the LCLD method has been studied for several years, few studies were found on how to ensure the durability of deposited copper on a glass material [ 18 , 19 ].…”

Surface modification of silicon by laser surface treatment: Improvement of adhesion and copper deposition

“…5,6 Through a copper deposition on the silicon substrate using a focused Ar ϩ laser (λ ϭ 514.5 nm, continuous wave (CW)) beam, it is possible to realize microscale line width and selective, fine shape lines. 7 Micropatterned copper films were obtained on the silicon substrate by laser-induced deposition using copper formate (Cu(HCOO) 2 ·4H 2 O) as a precursor.…”

Surface modification of silicon and PTFE by laser surface treatment: improvement of wettability

“…A direct laser writing using thin solid films of metalorganic precursors offers some unique advantages in terms of materials design, process control, and solution processes [8,9]. For copper deposition on the surface.…”