Methodology of Model Building and Correction of Line-end Shortening Effects during OPC with an EDA tool
Original Publication Date: 2004-Aug-06
Included in the Prior Art Database: 2004-Aug-06
A Model Based OPC EDA tool is suggested that takes into account the line-end shortening effect in deep UV lithography by developing a separate line-end model that allows pre-correcting the line-end edges and then applying the OPC.
Methodology of Model Building and Correction of Line -end Shortening Effects during OPC with an EDA tool
Introduction: Model based OPC typically uses a model of the lithographic tool and process built using SEM measurements of patterns that mimic the features occurring in production designs. Most commonly found features are 1-dimensional such as lines, spaces or gratings but frequently enough 2-dimensional structures such are found and produce line-end shortening effects which effects are typical of deep UV lithography using chemically amplified resists. It is necessary to capture these effects in a model so that the EDA OPC tools may successfully apply corrections that account for the line-end shortening effects. Background: The EDA tools include tools for making necessary optical process corrections (OPC) to manage diffraction, resist and process effects for making sub-micron ICs. OPC techniques are generally classified into two categories, namely rules-based techniques and model-based techniques. The rules based techniques entail applying known corrections to known structures in the vicinity of known structures. The model-based OPC, on the other hand, requires a model of the tool and process which is going to be employed for the technology under consideration. The derivation of the model is followed by the application of corrections and their verification by simulation. While the process is well developed and understood for the 1 D structures, there is a need for an EDA tool that is able to account for the complexity of issues, such as line-end shortening, related to the 2 D structures being used in modern day ICs in conjunction with chemically amplified resists used in deep UV lithography. The end of a line is made up of two 90 degree corners which due to the lithographic process of patterning exhibit rounding. In most cases, depending on structures in the neighborhood, this rounding results in a shortening of the length of the line of widths in the vicinity of resolution limits of the process. This is known as line-end shortening. There is provided no special treatment in modern EDA OPC tools to account for line-end shortening effects...