Improved resolution for DCOPA negative x-ray resist by exposure under a controlled atmosphere of nitrogen and oxygen

Abstract

A previous paper described the formulation of a negative x-ray resist with markedly improved adhesion that was capable of producing 2 μm minimum features in 0.5 μm final resist thickness. This work describes an exposure technique that further improves resolution so that 1 μm minimum features can be resolved in 0.5 μm of x-ray resist. The technique utilizes the fact that resist exposure is strongly influenced by the partial pressure of oxygen in the space separating the mask and the wafer. The interaction of x-ray photons and oxygen partial pressure produces an ideal exposure and developing profile for the resist. The result is greatly improved adhesion and high resolution of the resist feature. This technique may also be applicable to other resist types that are affected by the presence of O2 during exposure. Some experimental results show straighter edges and square corners as well as improved surface quality. Feature size control is ±0.1 μm for a 2 μm feature with a ±10% variation in exposure dose about the 50% exposure setting.