F. M. Houlihan

193 nm single layer resist strategies, concepts, and recent results

Matrix resins used in conventional resists are not suitable for use at 193 nm due to their opacity. Hence new materials that are functionally similar to but structurally different from novolac and poly(hydroxy styrene) are required for 193 nm lithography. We report on the use of alternating copolymers of cycloolefins with maleic anhydride as effective 193 nm matrix resins, with or without dissolution inhibitors based on polyfunctional cholates, for 193 nm lithography. Due to their structural diversity, the required high transparency and etch stability, compatibility with industry standard 0.262 N tetramethyl ammonium hydroxide (TMAH) can be built into the polymer by conventional free redical polymerization techniques. A correlation between the molecular properties of the resist components (matrix resin, dissolution inhibitor, photoacid generator, and base additive) and resist lithographic performance parameters is illustrated. The formulations containing dissolution inhibitors currently show 0.13 μm line/...

Resist design concepts for 193 nm lithography: Opportunities for innovation and invention

Photolithography using 193 nm radiation is the leading candidate for the manufacture of 0.18–0.13 μm design rule devices. The optical absorption of materials such as novolacs, and functionalized poly(hydroxystyrenes) and styrene-acrylate copolymers which are the matrix materials of choice for G line, I line, and 248 nm lithography is significantly higher than one at 193 nm making them too opaque to be useful at this shorter wavelength. The opacity of the current photoresists at 193 nm requires innovation in designing alternative materials and processes to realize the full potential of 193 nm (ArF) lithography. From a materials standpoint, this challenge must be addressed by new chemistries and process schemes capable of providing resists with the aqueous base solubility, etching resistance, resolution, photospeed, and process latitude required for large-scale manufacturing. In addition, regulatory constraints on volatile organic chemical emissions have spurred efforts to design revolutionary resist platfo...

Modeling influence of structural changes in photoacid generators on 193 nm single layer resist imaging

We present recent modeling work aimed at understanding the influence of structural changes in photoacid generators (PAGs) on acid generation efficiency, deprotection efficiency, and photoacid diffusion in 193 nm chemically amplified resists. An analytical model for the postexposure bake process is used to study the reaction and diffusion properties of the various acids generated by the PAGs. Fourier transfer infrared spectroscopy is used to monitor the generation of photoacid during exposure. Resist thickness loss after PEB as a function of exposure dose is related to the deprotection extent to extract the reaction rate parameters. The effects of the acid size and boiling point on process latitude, line end shortening, and line edge roughness are presented. Analytical model predictions of process latitude and line end shortening are also presented and compared to experimental data. In this study, the photogenerated acid with the smallest molar volume and highest boiling point temperature gave the best ove...

Revolutionary and evolutionary resist design concepts for 193 nm lithography

Abstract The intense absorption of aromatic molecules at 193 nm severely limits the use of conventional matrix aromatic resins such as novolac, poly vinyl phenol for 193 nm lithography. This paradigm shift in resist design provides opportunities for new chemistries and process schemes to provide the required aqueous base solubility, etch resistance, resolution, photospeed and process latitude. In addition, regulatory constraints on the volatile organic emissions (VOC) also provide opportunities to design revolutionary resist schemes that not only address the lithographic performance requirements but also alleviate the environmental safety and health (ES&H) aspects of resist technology. In this paper, we will analyze the several resist options available for 193 nm lithography and provide results for evolutionary single layer, bilayer and revolutionary “all-dry” plasma polymerized methyl silane (PPMS) resist schemes. For single layer schemes, we have synthesized several co- and terpolymers with cycloolefins, maleic anhydride and acrylates (acrylic, methacrylic acids and esters) and have used the protected polymers as matrix resins in three component systems with a photoacid generator (PAG) and dissolution inhibitor(s) (DI). Alternately, we have used the unprotected terpolymer with DIs and PAG in three component systems. The lithographic results for single layer and bilayer resist materials were obtained at 193 nm using a 0.55 NA Nikon or 0.56 NA ISI (Integrated Solutions Inc.) small field exposure systems. Single layer resist materials showed at least 0.16 μm l/s pair resolution and modulation down to 0.14 μm l/s pairs using a formulation and process optimized at 248 nm. We have also evaluated the performance of P(SI-CMS) (poly(trimethyl silyl methyl methacrylate-co-chloromethyl styrene), a negative e-beam resist, at 193 nm and have obtained 0.25 μm l/s pair resolution without much optimization. Structure-activity relationships between the polymer properties and lithographic performance for this system have been identified. The results obtained for PPMS, a plasma deposited all-dry resist technology, on the 193 nm Micrascan (0.50 NA) were also very encouraging. Again using a non-optimized process, we have obtained at least 0.15 μm l/s pair resolution in a bilayer scheme.

Retrospective of work at Bell Laboratories on the effect of fluorine substitution on the properties of photoacid generators

An overview is given on the work done at Bell Laboratories in which fluorine substitution was employed to tune the structure property relationships of chemically amplified resists. In particular, this paper will detail how structural changes in 2-nitrobenzyl photoacid generator (PAG) affect molecular properties such as quantum yield, thermal stability, and in turn also influence the lithographic characteristics of photoresist formulations such as sensitivity and post-exposure bake (PEB) and post-exposure delay (PED) latitude.

Fundamental studies of dissolution inhibition in poly(norbornene-alt-maleic anhydride) based resins

Abstract The dissolution inhibition mechanism for tert-butylcarboxylate (e.g. tert-butyl cholate) dissolution inhibitors and onium salt photoacid generators (PAGs) were examined in terpolymers of poly(norbornene-maleic anhydride-acrylic acid) (P(NB/MA/AA)). For tert-butyl carboxylates, increasing hydrophobicity increased the dissolution inhibition ability. Dissolution promotion tracked with the number of carboxylic acid moieties and the hydrophobicity of carboxylic acids moieties released upon acidolytic cleavage of the tert-butyl carboxylate. For onium salt PAGs, increasing the hydrophobicity and size of fluorinated anions decreased dissolution inhibition.

Characterization of novel sulfonic acid photogenerating 2‐nitrobenzyl ester derivatives

The thermal stability of 2‐nitrobenzyl sulfonate esters was dramatically increased by the introduction of an electron withdrawing, sterically bulky group (Br, CF3 ) at the ortho position of the benzyl moiety. This enhancement in thermal stability allowed synthetic access to thermally stable, photogenerators of acids based on more powerful organic acids which are useful in formulating deep‐UV resists having sensitivities approaching those of the more traditional onium salt‐based materials.

Probing the limits of optical lithography: The fabrication of sub-100nm devices with 193nm wavelength lithography

We discuss the fabrication of a FLASH EEPROM floating gate memory device with a cell size of 0.0896@mm. The floating gate level utilized an alternating aperture phase shift mask, a binary mask was used to expose the control gate level. Linewidth changes over topography, due to reflectivity variations, was controlled by an inorganic multilayer anti-reflective coating^1. All levels were exposed with a new generation of photoresists developed at Bell Laboratories with ARCH chemicals. Experiments were carried out to give some insight to the behavior of the materials and the viability of optical enhancement techniques. We have found that 193nm lithography with this new family of photoresists is reasonably proficient in the fabrication of devices with design rules of less than half the exposure wavelength.