Calibre Mask Process Correction
The next few IC technology nodes will be more challenging than any other transition since the first integrated circuit. Until the 32 nm node, distortions involved in making the masks using 193 nm lithography were small and had little impact since mask features are four times larger than the actual features on a die. Traditional OPC has mainly addressed the wafer image transfer and only included mask making effects as a part of the overall OPC model.
But at 32/22 nm, mask fabrication is subject to the same imaging limitations that have affected wafer lithography since the 130 nm node. Areas of particular sensitivity include narrow features and corners, residual proximity and linearity effects due to etch effects, and corner rounding in contact layers and on line ends. Accurate mask making for 32/22 nm now requires dedicated optical proximity correction for the mask making step. Instead of lumping mask errors into the overall OPC model, decoupling mask correction from the wafer correction simplifies the correction process and improves the quality of the overall result.
The Calibre® Mask Process Correction solution applies Mentor's model-based OPC technology with optimizations specifically developed for e-beam mask writers. New correction and modeling capabilities, including both density-based and Variable Etch Bias modeling, improve mask CD linearity and uniformity for advanced nodes. The solution also includes tools for mask model building and customization integrated with Calibre Workbench™. To round out Mentor's complete mask synthesis solution, the Calibre platform includes tools for mask rule-checking and sign-off, fracturing, and data conversion for the leading e-beam mask writing equipment.