Premlatha Jagannathan

Environmentally stable chemically amplified DUV resist based on diazoketone chemistry

This paper describes a resist that uses a polymer bound diazoacetoacetate as a photoacid generator in a two component system. The diazoacetoacetate is not used merely as a photoactive component, but its utility is extended to function as a photoacid generator for deprotection chemistry. The carboxylic acid generated upon exposure deprotects carboxylic acid-labile groups bound to another polymer backbone. This scheme has led to a resist with excellent performance like lithographically useful photospeed, resolution, environmental stability and aqueous base solubility combined with wide process latitudes. The resist does not require a topcoat or additives for stabilization towards airborne contaminants. The photo acid is a weak acid and hence allows fairly high concentrations of the acid generator to be used which helps in reducing contamination effects. Furthermore, being bound to a polymer backbone, diffusion into unexposed regions is limited and therefore exhibits greater stability towards PEB delay effects. Loss from surface due to volatility is also reduced in a polymeric acid generator compared to low molecular weight, monomeric compounds.

Printing various feature types at low k factors with advanced i-line negative resists

Lithographic conditions are typically optimized for a specific feature type; while some levels expose lines and spaces, others target contacts and islands. In todays challenging lithographic environment, printing multiple feature types on the same reticle is being discussed. The overlapping process window must then be considered. It is well-established in the industry that, for DNQ systems, two dimensional structures print at different doses than one dimensional structures of the same nominal chrome or clear size on the reticle. In this paper, the overlapping or common process window for all of these features is examined using a state-of-the-art i-line negative photoresist. When evaluating depth of focus (DOF) and exposure latitude, a +/- 0.10 micrometers deviation from target was used. Contact holes consistently limited the common process window. Three illumination conditions were examined: 0.57 NA with 0.38 sigma, 0.57 NA with 0.67 sigma, and 0.60 NA with 0.38 sigma. For total common process window, the 0.57 NA and 0.38 sigma condition was found to be optimal. PROLITH/2 aerial image simulations were found to agree with experimental result regarding an increased common exposure latitude with high NA and low sigma. The nominal feature dimensions were: 0.44 micrometers isolated lines, 0.44 micrometers isolated spaces, 0.4 X 1.5 micrometers contact,s and 0.4 X 1.5 micrometers islands. The nominal dimensions for contacts and islands were chosen to maintain a 3:1 area rule should the minimum dimension be used for one side of the features. The importance of a minimum area rule is discussed. Some early work on a second i-line negative resist targeted to simultaneously print 0.30-0.40 micrometers lines and spaces with 0.35-0.50 micrometers 2 contacts and islands is mentioned.

Polymer-bound sensitizer in i-line resist formulations

An important component of a photoresist formulation is the photoactive compound. In conventional I-line resist, it is the DNQ molecule. In chemically amplified resists, it is the photoacid generator or the PAG. This component acts as the link between the exposure tool and the photoresist system. While PAGs for the 248 nm or DUV application are plenty, there is little effort in the arena of i-line PAGs. Typically, energy transfer in i-line lithography is achieved by using a DUV PAG in conjunction with an i-line energy transfer agent called sensitizer. This combination works very well, as described by workers before. This paper describes a polymer-bound sensitizer, which while maintaining the performance characteristics of a monomeric sensitizer, also enhances the solubility characteristics and the thermal stability of the resist.

New silicon-containing negative resist for bilayer lithography

The increasing use of high density integrated circuits has created a need for development of new resist materials and lithographic schemes involving process simplification in semiconductor device fabrication to lower defect levels and improve product reliability. Towards that goal, we have developed a new negative working photoresist applicable to a bilayer resist scheme using optical and E-beam exposures. In this paper, we discuss the synthesis and lithographic applications of the silicon containing resist PHBS-AZIDE. The resist comprises a single component in which the photoactive group, an azide moiety, is chemically bonded to the base polymer, poly(4-hydroxybenzylsilsesquioxane) via an esterification reaction. The new polymer is easily synthesized and has the advantageous properties of aqueous base developability, excellent oxygen RIE resistance and high sensitivity to DUV, i-line and E-beam exposures. Sub-half micron images have been demonstrated using PHBS-AZIDE as a thin top imaging layer in a bilayer mode.