Novolak‐Diazoquinone Resists: The Imaging Systems of the Computer Chip

Abstract

Si02 + 4 HF -+ SiF4 + 2H20S o m e of the fundamental steps of microlithography (coating, irradiation, development of the film with base, removal of the Si02 layer) and on the right the chemical processes involved. This year some twenty billion integrated circuits will be produced worldwide. Almost all (98%) of them will be made with a photosensitive varnish, the photo resist, that allows the transfer of a fine line-pattern from an original transparency onto a silicon wafer. This photoresist has two components: one is a novolak resin, a low molecular weight phenol-formaldehyde condensation polymer; the other is a diazonaphthoquinone derivative (DNQ), which is the photoactive part of the system. Novolak-diazoquinone resists have played a crucial role in the microminiaturization of electronics. They are photographic materials of extremely high resolution, able to define features as small as 0.25pm. Although they are now an indispensible ingredient of modern computer technology, until quite recently their molecular mechanism was not understood. We report here on work at Polytechnic University in New York aimed at solving the mystery of these important and intriguing systems. The solution, in so far as it has revealed itself to us, is rather unique and quite unexpected. Novolak-Diazoquinone Resists

On the Trigonometric Descriptions of Colors

“…This second effect is known qualitatively but was not tested quantitatively. E.g., Arnošt Reiser et al (1996) found that some molecules served as local heaters after their activation by light beam absorption and started to promote the following chemical reactions.…”

Photoimaging and Lithographic Processes in Polymers

“…Novolak is obtained through a polycondensation reaction between formaldehyde and cresols [4,14]. The novolak resin is photochemically inert at 436 and 365 nm, and is easily soluble in basic developers due to its phenolic OH groups, but upon addition of naphthoquinone the dissolution rate decreases dramatically [15,16].…”

“…After the novolak films containing DNQ are exposed to UV radiation, their solubility increases by a few orders of magnitude, the dissolution rate becoming even higher than in the case of novolak films without any dissolution inhibitor. The explanation of this phenomenon was sought in the photochemistry of DNQ, but no clear picture was offered until relatively recently [15,16]. When exposed to UV radiation, upon absorption of photons diazonaphthoquinone eliminates N 2 forming a reactive carbene biradical that undergoes Wolff rearrangement to form a ketene (Scheme 12.1).…”

Effects of solvent, excitation wavelength, and concentration on the photobehavior of some diazonaphthoquinones

“…Diazonaphthoquinones are compounds widely used in the fabrication of integrated circuits in microlithography [4][5][6][7] where they are embedded in a novolak matrix (a phenol-formaldehyde condensation polymer). Exposed to radiation the diazoquinones release molecular nitrogen undergoing a ring contraction, the so-called Wolff rearrangement.…”