Contact Hole Position Shift Behavior with Resist Reflow Process in Random Array

Abstract

Contact Hole (CH) patterning, especially for sub-40 nm node, is one of the most difficult techniques in optical lithography. Resist reflow process (RRP) can be used to obtain smaller CH. RRP is a simple technique that the resist is baked at the temperature above the glass transition temperature after the develop process. Heating causes the resist to flow, and result in smaller dimension of CHs. However, RRP is unmanageable method because CH offset caused by pattern position shift in random array CH. Uniformed hole width can be obtained with decreasing the bulk effect through the whole CH array with stronger adhesion force and optical proximity correction. However, we still have CH position shift problem. Because of a difference in an amount of resist that flow into the hole in random array during the reflow process, position shift occurs. This position shift makes overlay error, and it may exceed the overlay error limit suggested by ITRS roadmap. And it is hard to make an accurate estimate of CH position shift because PR is fluid. Thus, in this work, we tried to find a trend of CH position shift with RRP through the several CH pattern layouts. Consequently, we confirmed that CH moved to approaching direction from each other, and the degree and direction of position shift depend on RRP time and obtained sub-40 nm CHs in random array by considering the position shift through the simulation.