Takayuki Yabe

Variable cell projection as an advance in electron-beam cell projection system

As an advance in the electron-beam cell projection system, we have developed a deflection control and correction unit of the variable cell projection (VCP) system, which can increase the variety of projected images through a block of patterns on a CP mask. We estimate the extent of the minimum spacing between two patterns distinguished by partial illumination to be 58 nm on a wafer, which is due to the beam blur of 28 nm and the illuminating beam edge rotation of 6 mrad relative to the CP mask patterns. Exposure results show that the VCP can actually distinguish the patterns separated by 80 nm on a wafer. We also show that the VCP can improve the uniformity of linewidths of exposed patterns by about 5 nm compared with the simple VSB method.

Correcting deviations in the shape of projected images in the electron beam block exposure column

The block exposure column has a mask with one hundred stencils in a deflection area. Each mask pattern projected by electron beams is reduced in size to 1/60th and imaged onto a wafer. Deviations in image shapes are dependent on deflected beam trajectories and imaging beam currents. We show techniques to measure the image shapes using reflected electron signals. Correction methods are proposed to reduce the deviations. After the corrections, the block exposure can expose images of every mask pattern of the size 5×5 μm with the image size deviation less than 11 nm, which includes 5.8 nm of an isotropic expansion and 9.6 nm of distortions.