No abstract

The 14 nm node is seeing the dominant use of three-dimensional FinFET architectures, local interconnects, multiple patterning processes and restricted design rules. With the adoption of these new process technologies and design styles, it becomes necessary to rethink the standard cell library design methodologies that proved successful in the past. In this paper, we compare the design efficiency and manufacturability of standard cell libraries that use either unidirectional or bidirectional Metal 1. In contrast to previous nodes, a 14 nm 9-track unidirectional standard cell layout results in up to 20% lower energy-delay-area product as compared to the 9-track bidirectional standard cell layout. Manufacturability assessment shows that the unidirectional standard cell layouts save one exposure on Metal 1, reduces process variability by 10% and layout construct count by 2-3X. As a result, the unidirectional standard cell layout could serve as a key enabler for affordable scaling.

The trend of ever decreasing feature sizes in subsequent lithography generations is paralleled by the need to reduce resist thickness to prevent pattern collapse. Thinner films limit the ability to transfer the pattern to the substrate during etch steps, obviating the need for a hardmask layer and thus increasing processing costs. For the 22 nm node, the critical aspect ratio will be less than 2:1, meaning 40-45 nm thick resists will be commonplace. To address this problem, we have developed new inorganic nanocomposite photoresists with significantly higher etch resistance than the usual polymer-based photoresists. Hafnium oxide nanoparticles are used as a core to build the inorganic nanocomposite into an imageable photoresist. During the sol-gel processing of nanoparticles, a variety of organic ligands can be used to control the surface chemistry of the final product. The different ligands on the surface of the nanoparticles give them unique properties, allowing these films to act as positive or negative tone photoresists for 193 nm or electron beam lithography. The development of such an inorganic resist can provide several advantages to conventional chemically amplified resist (CAR) systems. Beyond the etch resistance of the material, several other advantages exist, including improved depth of focus (DOF) and reduced line edge roughness (LER). This work will show etch data on a material that is ~3 times more etch-resistant than a PHOST standard. The refractive index of the resist at 193 nm is about 2.0, significantly improving the DOF. Imaging data, including cross-sections, will be shown for 60 nm lines/spaces (l/s) for 193 nm and e-beam lithography. Further, images and physical characteristics of the materials will be provided in both positive and negative tones for 193 nm and e-beam lithography.

The objective of this paper is to study the polarization induced by mask structures. Rigorous coupled-wave analysis (RCWA) was used to study the interaction of electromagnetic waves with mask features. RCWA allows the dependence of polarization effects of various wavelengths of radiation on grating pitch, profile, material, and thickness to be studied. The results show that for the five different mask materials examined, the material properties, mask pitch, and illumination all have a large influence on how the photomask polarizes radiation.

New applications of evanescent imaging for microlithography are introduced. The use of evanescent wave lithography (EWL) has been employed for 26nm resolution at 1.85NA using a 193nm ArF excimer laser wavelength to record images in a photoresist with a refractive index of 1.71. Additionally, a photomask enhancement effect is described using evanescent wave assist features (EWAF) to take advantage of the coupling of the evanescent energy bound at the substrate-absorber surface, enhancing the transmission of a mask opening through coupled interference.