Publications

The authors have developed an atomic-force-microscopy-based technique to measure intrinsic material roughness after base development. This method involves performing an interrupted development of the resist film and measuring the resulting film roughness after a certain fixed film loss. Employing this technique, the authors previously established that the photoacid generator (PAG) is a major material contributor of film roughness and that PAG segregation in the resist is likely responsible for nanoscale dissolution inhomogeneities. The additional roughness imparted on a test polymer by incorporation of a series of iodonium, sulfonium, diazo, and imido PAGs was measured. The roughness was then correlated to the inhibition properties of the various PAGs. This was accomplished both through a NMR technique that measures interaction of the PAG with the polymer and by evaluating the dissolution inhibition properties of the PAG through a percolation model. Several PAGs that result in significantly lower material roughness and thus the potential for significantly reduced linewidth roughness in resist imaging have been identified.

The rise of low- k1 optical lithography in integrated circuit manufacturing has introduced new questions concerning the physical and practical limits of particular subwavelength resolution-enhanced imaging approaches. For a given application, trade-offs between mask complexity, design cycle time, process latitude and process throughput must be well understood. It has recently been shown that a dense-only phase shifting mask (PSM) approach can be applied to technology nodes approaching the physical limits of strong PSM with no proximity effects. Such an approach offers the benefits of reduced mask complexity and design cycle time, at the expense of decreased process throughput and limited design flexibility. In particular, dense-only methods offer k1,0.3, thus enabling 90 nm node lithography with high-numerical aperture 248 nm exposure systems. We present the results of experiments, simulations, and analysis designed to explore the trade-offs inherent in dense-only phase shift lithography. Gate and contact patterns corresponding to various fully scaled circuits are presented, and the relationship between process complexity and design latitude is discussed. Particular attention is given to approaches for obtaining gate features in both the horizontal and vertical orientation. Since semiconductor investment is dependent on cost amortization, the applicability of these methods is also considered in terms of production volume.

A frequency selective surface (FSS) structure has been fabricated for use in a thermophotovoltaic system. The FSS provides a means for reflecting the unusable light below the band gap of the thermophotovoltaic cell while transmitting the usable light above the band gap. This behavior is relatively independent of the light's incident angle. The fabrication of the FSS was done using optical lithography and a phase-shift mask. The FSS cell consisted of circular slits spaced by 1100 nm. The diameter and width of the circular slits were 870 and 120 nm, respectively. The FSS was predicted to pass wavelengths near 7 um and reflect wavelengths outside of this pass band. The FSSs fabricated performed as expected with a pass band centered near 5 um.