Anthony D. Lisi

Graded spin-on organic bottom antireflective coating for high NA lithography

Immersion lithography for the 32nm node and beyond requires advanced methods to control 193 nm radiation reflected at the resist/BARC interface, due to the high incident angles that are verified under high numerical aperture (NA) imaging conditions. Swing curve effects are exacerbated in the high NA regime, especially when highly reflective substrates are used, and lead to critical dimension (CD) control problems. BARC reflectivity control is also particularly critical when underlying surface topography is present in buried layers due to potential reflective notching problems. In this work, a graded spin-on organic BARC was developed to enable appropriate reflectivity control under those conditions. The graded BARC consists of two optically distinct polymers that are completely miscible in the casting solution. Upon film coating and post-apply baking, the two polymers vertically phase-separate to form an optically graded layer. Different characterization techniques have been applied to the study of the distribution of graded BARC components to reveal the internal and surface composition of the optically graded film, which includes Variable Angle Spectroscopic Ellipsometry (VASE) and Secondary Ion Mass Spectroscopy (SIMS). Also, optical constant optimization, substrate compatibility, patterning defectivity and etch feasibility for graded BARC layers are described. Superior 193 nm lithographic performance and reflectivity control of graded BARC beyond 1.20 NA compared to conventional BARCs is also demonstrated.

From Process Assumptions to Development to Manufacturing

A tool has been developed that can be used to characterize or validate a BEOL interconnect technology. It connects various process assumptions directly to electrical parameters including resistance. The resistance of narrow copper lines is becoming a challenging parameter, not only in terms of controlling its value but also understanding the underlying mechanisms. The resistance was measured for 45nm-node interconnects and compared to the theory of electron scattering. This work will demonstrate how valuable it is to directly link the electrical models to the physical on-wafer dimensions and in turn to the process assumptions. For example, one can generate a tolerance pareto for physical and or electrical parameters that immediately identifies those process sectors that have the largest contribution to the overall tolerance. It also can be used to easily generate resistance versus capacitance plots which provide a good BEOL performance gauge. Several examples for 45nm BEOL will be given to demonstrate the value of these tools.