Bi/In bimetallic thermal resists for microfabrication, photomasks, and micromachining applications
Bilayer Bi/In thin films form thermal resists with many new microfabrication and micromachining applications due to their changed physical, chemical and optical characteristics after the laser exposures. Wavelength invariance has been shown from the results of both experiment and Airy Summation optical modeling. The modeling projects bimetallic resist sensitivity to be nearly constant at about ~7 mJ/cm2 from 248 to 13.4 nm and is still very sensitive at 1 nm in X-ray range. Two kinds of acid solutions were effective in developing the exposed films by removing the unexposed area. Both nitric acid mixture (HNO3:CH3COOH:H2O=1:3:6) and hydrochloride acid mixture (HCl:H2O2:H2O=1:1:48) give etching selectivity of exposed to unexposed area of larger than 60:1. The etch rate of unexposed area is about 2.6 nm/sec. The Bi/In resist can be stripped away by an RCA2 clean. Bi/In resist was successfully used as a mask layer for KOH anisotropic silicon etching process. Due to the unusual conductive property of its exposed and developed films, Bi/In has demonstrated that it can be used as a direct laser write electroplating resist material. Copper and nickel plating was carried out on developed Bi/In layers on various substrates such as Si wafers, glass slides, wet-oxidized wafers. Large optical transmission changes (OD>3.5 before exposure and OD<0.3 after exposure at I-line) indicate that Bi/In can be used as a direct-write photomask material.
Prototype laser-activated bimetallic thermal resist for microfabrication
The Thermal Resist Enhanced Optical Lithography (TREOL) process models an optical system to double device resolution by exploiting non-reciprocal laser activated processes. A possible prototype thermal resist consists of stacked bismuth on indium layers sputter deposited on a glass/quartz substrate with thickness ratios matching the eutectic alloy (Bi 53%). Laser radiation locally melts the metals which alloy upon cooling. BiIn resist is relatively wavelength insensitive because its UV optical characteristics vary modestly. Reflection and energy absorption/cc calculations indicate the best arrangement is a 30-45-nm total thickness bilayer with bismuth on indium. Exposing the highly absorbing BiIn with CW argon (514/488 nm) or 4-ns Nd:YAG pulses at 533 nm (40 mJ/cm2 for 300-nm thick) and 266 nm transforms the resist to a weakly absorbing alloy with a visually identifiable pattern. 30-nm thick converted film transmission changes from 1.0OD to 0.35OD (830-350 nm) until a 350-nm absorption edge. Profilometry and SEM showed no signs of ablation or oxide growth in exposed areas. The resist was developed with HNO3:CH3COOH:H2O etch, preferentially removing unexposed areas, leaving written patterns of alloyed lines seen both in profilometry and SEM images. Thus BiIn forms a complete thermal alloying resist with selectively etched exposed patterns that can be stripped in an HCl:H2O2:H2O bath.
Aluminum oxides as imaging materials for 193‐nm excimer laser lithography
Aluminum oxide films deposited over amorphous carbon(a‐C:H) planarizing layers have been investigated as imaging layers for 193‐nm excimer laser lithography. The AlOx films were deposited by ion beam deposition, e‐beam evaporation, or sputter deposition. The films have been analyzed by Auger electron spectroscopy and x‐ray photoelectron spectroscopy. Depending on the deposition conditions, AlOx films with compositions varying from metallic to fully oxidized Al can be formed. The optical appearance of these films varies from highly reflective for metallic Al to highly transparent for fully oxidized layers. Using pulsed 193‐nm radiation from an ArF excimer laser, the single‐pulse self‐development threshold energy is similar for films with different compositions when the film reflectivity is taken into account. It was found that pure Al films and highly oxidized Al films do not provide good adhesion on a‐C:H layers and have a tendency to peel during laser exposure. In contrast, films with intermediate compos...