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.
Wavelength invariant Bi/In thermal resist as a Si anisotropic etch masking layer and direct-write photomask material
Bilayer Bi/In thin film thermal resists are Bi and In films which form an etch resistant material at ~7 mJ/cm2 laser exposures with near wavelength invariance from visible to EUV. New simulations predicted that Bi/In film of 15/15nm absorbs substantially at 1 nm, which projects single pulse exposure sensitivity of ~16 mJ/cm2, hence suggesting good sensitivity to X-ray range. Thermal modeling has confirmed the exposure time/optical energy requirements for Bi/In. Exposed and developed Bi/In resist etches slower than silicon dioxide in alkaline-based silicon etchants TMAH, KOH, and EDP, making it a better masking layer for anisotropic Si etching. Also Bi/In has been used to create a direct-write photomask as its optical transmission changes from OD>2.9 before laser exposure to OD<0.26 after exposure. Both Bi/In anisotropic etching and direct write masks have been combined to successfully build test photocells with V-groove surface textures by using Bi/In masked silicon anisotropic etching and the other layers created using regular lithography but with Bi/In masks. These devices showed no operational differences from those created with regular resist processes. Investigation of resist interactions with Silicon after laser exposure and strip were done with Auger surface analysis which showed no detectable Bi or In contamination on substrates and no substrate sheet resistance change. X-ray diffraction and Rutherford back scattering tests suggest that the converted Bi/In may involve oxides.
X-Ray Lithography: Can It Be Justified
X-Ray lithography: Can it be justified? This is a question which is being asked in many circles today. The answer is, unfortunately, not black or white nor is it easy to determine. However, there are today more serious players in the x-ray field than there were a few years ago and maybe this is an important indicator. In this paper we will try to establish if x-ray lithography can or can not be soundly justified.