32 NM Logic patterning options with immersion lithography

Abstract

The semiconductor industry faces a lithographic scaling limit as the industry completes the transition to 1.35 NA immersion lithography. Both high-index immersion lithography and EUV lithography are facing technical challenges and commercial timing issues. Consequently, the industry has focused on enabling double patterning technology (DPT) as a means to circumvent the limitations of Rayleigh scaling. Here, the IBM development alliance demonstrate a series of double patterning solutions that enable scaling of logic constructs by decoupling the pattern spatially through mask design or temporally through innovative processes. These techniques have been successfully employed for early 32nm node development using 45nm generation tooling. Four different double patterning techniques were implemented. The first process illustrates local RET optimization through the use of a split reticle design. In this approach, a layout is decomposed into a series of regions with similar imaging properties and the illumination conditions for each are independently optimized. These regions are then printed separately into the same resist film in a multiple exposure process. The result is a singly developed pattern that could not be printed with a single illumination-mask combination. The second approach addresses 2D imaging with particular focus on both line-end dimension and linewidth control [1]. A double exposure-double etch (DE2) approach is used in conjunction with a pitch-filling sacrificial feature strategy. The third double exposure process, optimized for via patterns also utilizes DE2. In this method, a design is split between two separate masks such that the minimum pitch between any two vias is larger than the minimum metal pitch. This allows for final structures with vias at pitches beyond the capability of a single exposure. In the fourth method, dark field double dipole lithography (DDL) has been successfully applied to BEOL metal structures and has been shown to be overlay tolerant [6]. Collectively, the double patterning solutions developed for early learning activities at 32nm can be extended to 22nm applications.