BARC (bottom anti-reflective coating) for immersion process

Abstract

193nm immersion Lithography will be installed at 45nm and beyond. For severe CD control, BARC (Bottom Antireflective Coating) has been used and this material must be used for immersion lithography.So far, we have developed several BARCs with various advantages (fast etch rate, broad resist compatibility, high adhesion, conformal…etc). Especially in an immersion process, development of BARC has to satisfy for the optical control and defectivity.The reflectivity control at Hyper NA is not same as the lower NA, because optical pass length in the BARC is not the same between low NA and High NA. In order to achieve enough etch selectivity to the substrate, hard mask materials are necessary. These under layers have absorption at 193nm. As a result of simulation, target optical parameters of next BARC should be low k value (k = ~0.25) for multi BARC stack.On the other hand, the defect issue must be decreased in the immersion process. However, the generation of many kinds of defects is suspected in the immersion process (water mark, blob defect, sublimation defect…etc). Regarding the BARC, there are also several specific defects in this process. Especially, after edge bead rinse, film peeling at edge area is one of the concerns. We researched the root cause of edge peeling and a solution for this defect.In this paper, we will discuss the detail of our BARC approach for litho performance, optical parameter, leaching, sublimation, edge peel defects and etch selectivity, and introduce new BARC for 193nm immersion lithography.

Low out-gassing organic spin-on hardmask

“…For the evaluation of out-gas, a QCM system was employed. [3,4] The OHM film was prepared on a silicon wafer without bake. It was then baked at several temperatures.…”

Wafer Edge Process Integration and Defect Inspection with the Immersion Lithography Process

“…The immersion lithography photo resist stack composite with BARC, resist and topcoat films. The bottom anti-reflective coatings are essential for achieving the resolution target by minimizing the substrate reflectivity, and it's must be for immersion lithography [1]. The topcoats allow more flexibility in managing the contact angle, which affects numerous aspects of patterning quality; topcoats chosen for a higher contact angle reduce the number of defects as compared to no topcoat or a topcoat with a lower contact angle [2].Since the wafer edge contacts with water from the immersion hood, many patterning defects are caused by particles transport back to scanner wafer stage from wafer edge.…”