Abstract
ArF-resist-shrinkage and line-edge roughness-induced CD errors are the two main challenges for CD SEM. The requirement of measurement precision for the 65-nm node is less than 0.5 nm. The current CD SEM ADI precision is between 0.7 to 0.9 nm after shrinkage curve correction. Optical CD (OCD) has provided three major advantages. That is more sampling (> 2500:1), insensitivity to line edge roughness, and less resist damage. These advantages facilitate much better measurement precision (< 0.3 nm) than CD SEM and make OCD a potential APC metrology candidate. However, the recipe and library generation of OCD is more complicated and time consuming than CD SEM. Any thin-film variation will disturb the CD accuracy and recipe coverage range of OCD. For different pitches and film combinations, new OCD libraries need to be generated. Matching through all pitches between CD SEM and OCD is also very difficult. We propose a new concept on optical-CD-like CD SEM measurement, i.e. average line width (ALW) and contact hole diameter (ACD) measurement at high resolution and low magnification (HRLM) CD SEM. The resolution chosen is below 2nm and the magnification is 50KX. The low magnification CD measurement can average the e-beam dosage and reduce the ArF shrinkage. Several repeated patterns such as line/space and hole arrays are measured to get an averaged CD under lower magnification condition. These low magnification average CDs increase the sampling size and they are insensitive to the line edge roughness. The CD linearity of ALW/ACD and the CD matching to current CD SEM methodology will be presented. Small step FEM CD by low magnification and high magnification CD measurement will be studied. The difference between low/high magnification SEM and optical CD will be also studied.