L. Nánai

Laser-assisted metal deposition from liquid-phase precursors on polymers

Abstract In this work, a short review is presented for results utilizing the technique of laser-assisted metallization of dielectrics. Experimental efforts and results related to the metal (palladium (Pd), copper (Cu) and silver (Ag)) deposition on polymeric materials (polyimide (PI), mylar) are reported. These polymers and metals are chosen due to their growing importance in the rapidly-developing microelectronics packaging industry. The method of laser-induced chemical liquid-phase deposition (LCLD) offers many advantages compared to other techniques such as laser-induced forward transfer (LIFT), pulsed-laser deposition (PLD) and laser-assisted chemical vapor-phase deposition (LCVD). The LCLD is time and cost effective because vacuum tools and special pre-treatments are not required. The consumed chemicals used in precursors are non-harmful and easy to handle due to the liquid phase. For the optimal physical and chemical properties of deposits, the laser and solution parameters are varied. XeCl and KrF excimer and Ar + lasers are employed for executing the palladium, Ag and/or Cu formation on the polymer substrates. Chemical and physical analyses of the formed metal patterns are performed by EDX, XRD, FESEM, SEM, resistance and adhesion measurements.

Laser direct writing of copper on polyimide surfaces from solution

Conductive copper patterns were deposited on polyimide (PI) substrates by using a focused, scanned continuous wave (cw) Ar+ laser beam at 488 nm wavelength. The deposition process was initiated by a photothermal reaction of a tartarate-complex solution of Cu2+ ions in an alkaline and reducing environment. Deposits were characterised by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray (EDX) Spectrometry, DEKTAK profilometer and resistance measurements. The dependence of the characteristics of laser direct written patterns on the scanning speed of the laser beam, number of scans and laser power was examined. Uniform copper lines covered with copper-oxide (line width from 30 to 60 μm and height from 2 to 20 μm) with high conductivity and adhesion were achieved under optimised conditions.

Enhancement of exciton emission from ZnO nanocrystalline films by pulsed laser annealing

Pulsed ArF laser annealing in air and in hydrogen atmosphere improves the optical properties of ZnO nanostructured films. Independently on the ambient atmosphere, laser annealing produces two major effects on the photoluminescence (PL) spectra: first, the efficiency of the exciton PL increases due to the decrease of the number of non-radiative recombination centers; second, the intensity of the defect-related orange band decreases because of the removing of excessive oxygen trapped into the films during deposition. However, annealing in the ambient air also increases the intensity of the green band related to oxygen vacancies. We show that the combination of laser annealing and passivation of oxygen vacancies by hydrogen results in films free of defect-related emission and keeps intact their nanostructural character.

Laser-induced oxidation of metals: state of the art

Abstract The general features of laser-induced metal oxidation and laser-assisted oxide deposition are discussed. The mechanisms of isothermal and laser-induced oxidation processes are compared. The peculiarities of the laser-assisted processes, e.g. non-linearities and non-equilibriums feedback effects, are emphasized. Instabilities connected with the appearance of positive feedback between the laser and thermal parameters, as well as the optical properties of the system, are considered. Absorptivity changes and variations of the metal oxidation constant, such as due to changes in temperature and wavelength, are presented by using vanadium as an example. Experimental data of laser-assisted metal oxidation of different metals are presented in tabulated form. Some morphological irregularities as a result of laser irradiation are shown. Trends of theoretical and experimental investigations are indicated.

Laser‐induced metal deposition on semiconductors from liquid electrolytes

Maskless deposition of gold and copper from electrolyte solutions onto n‐doped semiconductors (GaAs, Si) is investigated. The metal deposits are found to have lateral dimensions of about 1 μm and are in barrier contact with the semiconductor. The proposed deposition mechanism is governed by the electric fields resulting from the Dember effect, the p‐n junction, and the thermal emf.

Reaction dynamics of CW Ar+ laser induced copper direct writing from liquid electrolyte on polyimide substrates

Abstract Conductive copper patterns were deposited on polyimide (PI) surfaces using a focused, scanned CW Ar + laser beam at 488-nm wavelength. The deposition process was initiated by a photothermal reaction of a tartarate–complex solution of Cu 2+ ions in an alkaline and reducing medium. Deposits were characterised by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectrometry (EDS) and resistance measurements. The mass of the deposited copper ( m Cu ) and also the rate of the deposition (d m Cu /d t ) were calculated from the resistance measurements. The dependence of the copper deposition rate on the scanning speed of the laser beam, number of scans, laser power and the temperature of the solution were examined. It was found that more chemical reactions were running parallel during the direct writing process yielding metallic copper and copper(II)-oxide on the PI surface.

Laser direct writing of palladium on polyimide surfaces from solution

Abstract Conductive palladium (Pd) patterns were generated by laser-induced chemical liquid-phase deposition (LCLD) on polyimide (PI) substrates using a continuous Ar + laser beam. The deposition process was executed from the amine complex solution of Pd 2+ ions. Dependence of the characteristics of the laser direct written patterns on scanning speed of the laser beam, number of scans and laser power was examined. Deposits were characterised by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectrometry (EDS), and profilometric measurements. The resistance of the patterns was also measured. It was found that good quality lines — narrow, homogeneous, and with high conductivity and adhesion — were achieved under optimized conditions.

Laser-assisted formation of metallic oxide microtubes

The fabrication of metallic oxide microtubes is possible directly, without any support structure, by continuous wave infrared laser-assisted oxidation of the metal in air. The particular case presented is the growth of tube-like vanadium pentoxide microcrystals grown in our laboratories. {copyright} {ital 1997 Materials Research Society.}

Palladium thin film deposition from liquid precursors on polymers by projected excimer beams

Abstract Palladium thin films are deposited on polyimide (PI) and mylar (PET) surfaces from a solution by employing XeCl and KrF excimer lasers. The substrates are plunged in a [Pd(NH 3 ) 4 ] 2+ /HCOH system, and an illuminated diaphragm is projected onto the polymers through the precursor layer. Due to the incident laser beam, chemical reactions take place at the solution/polymer interface, yielding thin Pd films on the surface. The formation and thickness of the Pd layer depend on the numbers of pulses, laser fluence and wavelength of the laser. The formed metallic, adhesive, and homogeneous Pd deposits are found to be suitable for further electroless copper deposition. Techniques such as DEKTAK profilometry, optical microscopy, FESEM (equipped with EDX) and XRD are involved in the determination of morphological, structural and compositional characteristics of the deposited layers.

Nickel deposition on porous silicon utilizing lasers

Thin metallic nickel deposits on porous silicon (PS) surfaces from electroless nickel plating bath have been obtained by the laser-induced photochemical metallization method. Lasers such as XeCl (λ = 308 nm, τ ∼ 15 ns), KrF (λ = 248 nm, τ ∼ 500 fs). Ti:sapphire (λ = 745.5 nm. τ ∼ 120 fs) and Q-switched Nd:YAG (λ = 1064 nm, τ ∼ 150 ns) were utilized in order to achieve direct deposition of Ni. Depending on the laser parameters, the thickness of the deposits varies from a few up to several tens of nanometers when excimer pulses are applied Investigations using Ti:sapphire and Q-switched Nd:YAG have failed; however, no Ni deposition occurred. The high lateral resolution of the patterns (<5 μm) makes the fabricated metal structures suitable for direct applications (i.e. electrical contacts, mechanical structures as well as contact masks). The deposits were analyzed using SEM, EDX and resistance measurements. FIB and profilometry were involved to characterize the cross-section of the formed metal layers.