Electrical and optical properties of MoO 3 -TeO 2 amorphous films prepared by vacuum deposition method were investigated. X-ray diffraction patterns show an amorphous structure. The dc conductivity of the films was measured in the temperature range 323-523 K and follows a non-adiabatic small polaron hopping conduction mechanism between Mo 4þ and Mo 5þ , confirmed by X-ray photoelectron spectroscopy measurements. Conductivity of the films increases with increase of MoO 3 content. The Seebeck coefficient indicates the films to be n-type semiconductor. Optical absorption edge analysis gave a band gap energy of 2.7-2.9 eV depending on composition. The Urbach tail analysis gave the width of localized states between 0.23 and 0.25 eV.

A diazonaphthoquinone/novolak resist on a 42-alloy substrate was irradiated by the second harmonic wave (532 nm) of a pulsed Nd3+YAG laser. The resist was removed, despite the existence of hexamethyldisilane (HMDS). There was no apparent damage to the substrate. In contrast, the resist on a Si wafer could not perfectly be removed. In some cases, there was damage to the substrate. The peeling strength of the resist with HMDS was about three times than that without HMDS. The width of the resist removed by laser irradiation without HMDS was 1.02–1.03 times larger than that with HMDS. The use of this process will benefit the environment, since expensive and toxic chemicals are not used.

ABSTRACT:This study revealed a promising method for removing positive-tone diazonaphthoquinone/novolak resist. The fourth harmonic of an Nd 3þ :YAG (Y 3 Al 5 O 12 ) pulsed laser (266 nm) was irradiated onto the resist. Resist was removed when laser power exceeded 35 mJ/cm 2 , and a 250 nm-thick resist was removed with a laser power of 94 mJ/cm 2 . X-ray Photoelectron Spectroscopy (XPS) proved that 1100 nm-thick resist could be completely removed from a Si surface when it was irradiated almost 700 mJ/cm 2 . The resist onto three inch Si wafer (45.58 mm 2 ) was removed in two minutes by laser. No damage to the processed Si wafer could be detected by optical microscopic observation. This method is good for environment.

We have developed a resist removal process that uses a laser. Laser irradiation far below the ablation threshold was useful to remove a resist that was strongly adhered to the substrate. We used the second harmonics of Nd:YAG ͑Y 3 Al 5 O 12 ͒ laser pulses ͑532 nm͒ to irradiate the polyacrylic-type resist for manufacturing printed circuit boards. At appropriate laser fluence, the resist, which transmits the laser light 80% at 532 nm, was detached from the substrate while retaining its original shape. This technique is not based on laser ablation. Therefore, no damage occurred to the substrate. It was a dry process: it used neither water nor chemicals. Compared to conventional chemical processing, environmental pollution is prevented. Power consumption and running costs can be reduced.

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