Y. S. Liu

Optical absorption of some polymers in the region 240–170 nm

Absorption coefficients for some technologically important polymer materials are given in the wavelength range ∼240–170 nm. Absorption coefficients at 193 nm for these polymers show a wide range of values from ∼2×102 cm−1 for polytetrafluoroethylene (Teflon) to ∼4×105 cm−1 for polyimide. The general nature of the optical properties of polymers in the vacuum ultraviolet is also discussed.

Laser-induced selective copper deposition on polyimide

Laser irradiation of organometallic palladium compounds with an argon ion laser at 351 nm is used to selectively deposit catalytic amounts of palladium on polyimide. Subsequent immersion of the irradiated samples in an electroless copper solution results in copper deposition. Since a few monolayers of palladium are sufficient to catalyze the electroless copper process, fast writing speeds of several centimeters per second are obtained.

Dependence of photoetching rates of polymers at 193 nm on optical absorption depth

Mixtures of poly(methyl methacrylate) and poly(α‐methyl styrene) were prepared and their optical absorption coefficients at 193 nm were measured. A study of photoetching rate of these polymeric materials using an ArF excimer laser at 193 nm shows two regions of distinctly different etching characteristics. At relatively high fluences (>300 mJ/cm2) the photoetch rate decreased with increasing absorption in the polymer films, while at lower fluences, an optimum range of absorption coefficients was found to give the maximum photoetching rate.

Oxidation of silicon by ion implantation and laser irradiation

Q‐switched laser irradiation has been used to anneal O+‐implanted silicon to form SiO2 layers. Results of differential Fourier‐transformed infrared spectroscopy and transmission electron microscopy confirm the formation of oxide layers. Segregation of oxygen toward the surface was observed by secondary ion mass spectroscopy and correlated with resolidification velocities, which vary as a function of laser energy densities.

Laser ablation of polymers for high-density interconnect

Abstract Fabrication of micro-vias with a diameter of less than 100 μm in polymeric materials is a key processing technology for high-density interconnect applications. This paper discusses material properties that are relevant to laser ablation and describes several laser techniques (e.g. excimer, UV YAG and CW argon ions lasers) for micro-via fabrication in a thin-film multilayer structure for high-density interconnect applications.

Photoetching Of Polymers With Excimer Lasers

Photoetching with excimer lasers has been studied in a variety of polymeric materials. Photoetching rates of polymers irradiated were measured at various laser wavelengths and fluences. The relationship of these results to the polymer absorption coefficient is examined. We propose that different mechanisms of photoetching may prevail, which depend on the absorption coefficient of the polymer. Potential use of this dry-etching process for lithography applications is evaluated.

Laser Processing For Interconnect Technology

Laser processing of polyimide dielectric layers for use in high-density interconnect structures was studied. A pulsed excimer laser was used to photoetch via holes and a CW argon ion laser operating at 351 nm was used to selectively deposit catalytic amounts of palladium on polyimide. Subsequent immersion of the irradiated samples in an electroless copper solution resulted in selective copper deposition.

Interactions of excimer lasers with polymers

Interactions of high photon energy (hν≳5 eV) radiation from an excimer laser with polymeric materials has been studied. Photo‐etching rates at both 193 nm and 248 nm were measured. These results, considered together with our recent measurements of the VUV optical properties of these polymers, give new insights into the mechanisms of the ablative photo‐etching process.