Mask CD compensation method using diffraction intensity for lithography equivalent metrology

In 45nm node and beyond, since mask topography effect is not ignorable, 3D simulation is required for precise printing performance evaluation and mask CD bias optimization. Therefore, the difference between real mask and 3D mask model on simulation needs to be clarified. Verification of 3D mask model by diffraction intensity measurement with AIMSTM45-193i was discussed in our previous works. In various conditions (mask materials, pattern dimensions and CD-SEMs), the diffraction intensity measured on actual masks were agreed to 3D simulations by introducing constant CD offset. The cause of the CD difference was explained to be mainly due to electron beam size by using simple SEM image simulation. In this work, we introduce the new procedure to measure diffraction intensity by AIMSTM in order to confirm the CD difference between 3D mask model and CD-SEM more accurately because the agreement of diffraction intensity between AIMSTM and simulation was not perfect especially for 1st order's diffraction. As a result, the value of CD difference was slightly changed on the same mask by using the same CD-SEM. Measured diffraction intensity showed better matching to 3D simulation results with the constant CD offset on all evaluated conditions. Secondary, to confirm how accurately printing performance could be predicted by CD-SEM measurement results, MEEF difference calculated from diffraction intensity between 3D simulation and CD-SEM with the offset was confirmed. Additionally, this method was extended to hole patterns. Measured diffraction intensity was matched to simulation result with the same CD offset with line/space patterns and appropriate corner rounding.