To deliver a defect-free photomask, is an essential step of mask manufacturing. EB (Electron-beam) repair is widely applied to deal with defects on photomasks, and has to cover etch and deposition capabilities without any pattern damage. However, mask repair is facing more challenges, with the shrinkage of minimum feature resolution for advanced technology nodes. Especially for micro defects at the edge of wafer printability specifications, differences between defect and reference may be tiny and hard to distinguish in visual or by existing methods on repair tools, so that it was difficult to start.
In this paper, a new approach named Contour-based 2D Metrology will be introduced as assistance for the repair processes of such challenging micro defects. Both CDSEM images of defect and reference are input for extracting; then contour-based patterns are overlapped for each other and compared with GDS as well, to describe quantitative differences for each micro area. Assisted with such rigorous and comprehensive data analysis, micro defects can be accurately positioned according to Aims Results and repair processes would be proceeding.
As the process node becomes more advanced, the accuracy and precision in OPC pattern CD are required in mask
manufacturing. CD SEM is an essential tool to confirm the mask quality such as CD control, CD uniformity and CD
mean to target (MTT).
Unfortunately, in some cases of arbitrary enclosed patterns or aggressive OPC patterns, for instance, line with tiny
jogs and curvilinear SRAF, CD variation depending on region of interest (ROI) is a very serious problem in mask CD
control, even it decreases the wafer yield. For overcoming this situation, the 2-dimensional (2D) method by Holon is
adopted. In this paper, we summarize the comparisons of error budget between conventional (1D) and 2D data using CD
SEM and the CD performance between mask and wafer by complex OPC patterns including ILT features.
Contour extraction of complicated optical proximity correction (OPC) patterns for advanced photomasks is increasingly needed in addition to the conventional mask CD measurement. The lithography simulation based on contour extraction from the SEM images on photomasks is one of the efficient methods to assure adequacy of OPC patterns. In this paper, the function of the above-mentioned contour extraction, and the performance requirements for the CD-SEM for this function using Mask CD-SEM 'Z7', the latest product of HOLON, and the scheme to correct the distortion are explained. Furthermore, the perspectives of the application of our contour extraction method are outlined.
Recently, in Critical Dimension (CD) measurement on high-end masks, Optical Proximity Correction (OPC) pattern measurement is on increase and it has become important to measure angled lines. In CD searching on a CAD layout viewer, the exact CD values can be detected for the OPC patterns because they consist of a lot of rectangles. While, the CD values for angled lines have not been detected in it. Meanwhile the mask Critical Dimension Scanning Electron Microscope (CD-SEM) can measure angled lines, but measurement accuracy cannot be verified because there is no reference standard sample available for calibration of the CD values. In this study, we made the prototype of a standard sample for CD measurement with 0 degree and 45 degree angled lines by using VLSI Standards Inc. Nano Lattice Standard. The shape is the same as 6025 mask. We measured CDs of angled lines of the above sample using Holon EMU-260 and examined the calibration
method. We are going to discuss the CD marking method on a CAD layout viewer in order to automate measurement of angled lines in near future.
Rapid changes in the feature size of photo masks have made it clear that there is an obvious limitation to the use of optical measurement tools, and mask makers now have the necessity to use CD-SEMs as a measurement tool for forefront patterns. The level of measurement precision and accuracy required for mask CD metrology has reached a point at which magnification calibration using the standard scale becomes indispensable. Since CD-SEM measurements are heavily influenced by local pattern irregularities compared to optical measurements, however, proper statistical treatment of data is necessary to estimate accurate values. In this paper, the tool repeatability, sample dispersion, line edge roughness amount and tool's long-term precision will be determined by the treatment of numerous measurement data. The general calibration of the tool is done by line pitch measurement of JQA standard, in that case the disagreement between line width measured values and user's desired values could be appeared. In this case we propose the method to change threshold value of measurement, and in this paper the evaluation of this method will be shown.