The benefits of automatic classification of microlithography defects include fast and reliable rework decisions, improved root-cause analysis, and more consistent SPC data that significantly enhances yield in the lithography cell. An adaptive knowledge-based system has demonstrated the ability to accurately classify defects more than 85% of the time and is sufficiently versatile to classify new defect modes that will accompany advanced lithography processes. The knowledge-based system defines each class of defects with mathematical descriptors that include categories such as size, intensity, edge sharpness, color, etc. New defect classes can be defined with as few as three to five images of the specific defect. All defect classes are stored in the knowledge-base as rule vectors consisting of values for each descriptor. Different defect classes can share many common descriptors. However, as long as there is at least one descriptor that differentiates them, the defect class can be deemed unique. This method provides manufacturers the ability to define defects according to their existing rules and to define new defect types as they occur.
SiOXNYARCs are critical for maintaining CD control in current and future generations of designs. However, even minor fluctuations in t, n, and k across the wafer, or from wafer to wafer, can have a significant impact on ARC performance. For process control of ARC deposition, metrology tools must be able to reproducibly measure thickness and optical properties to 6 σ, translating into 1.5 Å for a nominally 500 Å SiOXNYARC and 0.0015 for index. A combination of laser ellipsometry and DUV reflectometry has demonstrated the ability to meet these requirements, with two tool-matching results of 0.8 Å for thickness and 0.001 for index. The accuracy of the thickness measurements was further tested at SiOXNYARC films were etched to clear. TEM confirmation of thickness measurements demonstrated the metrology was accurate with films as thin as 75 Å. The metrology method was subsequently used to monitor both the thickness and reflectivity at 49-points across a wafer at various etch times until the film was thinner than 25 Å.