We discovered the phenomena in scanning electron microscopy that the bottom of deep holes can be observed clearly when a high energy electron beam is irradiated. In order to utilize this phenomena, we developed a novel instrument that generates a scanning electron probe of 50 to 200 keVwith TV-scan rate that enables us to inspect maximum 8 inches diameter wafers.In the past, we could inspect deep holes by observing cross sectional view of a hole milled with a focused ion beam (FIB).1 Using the novel instrument, we can easily inspect such holes without destroying samples. This observation does not depend on the specimen conditions, such as aspect ratio of holes and specimen charging that often occurs in the case of observing insulators. This instrument enables us to observe inside structures of semiconductor devices. Irradiation damage on semiconductor devices, such as threshold voltage and sub-threshold coefficient deviation of MOS transistors can be recovered, except for the irradiated area by means of hydrogen annealing of 30 minutes with temperature of 450 degrees C.
The earliest semiconductor device manufacturing employed optical microscopes for measurement and control of the manufacturing process. The introduction of the Critical Dimension Scanning Electron Microscope (CD-SEM) in 1984 provided a tremendous increase in capability for process monitoring and has been the standard for in-line metrology for over 25 years. The advantages of the CD-SEM are highly accurate and stable measurement reproducibility at very specific locations throughout the device. The evolution of the CD-SEM in Metrology has included improved resolution, development of advanced measurement and pattern recognition algorithms, all required by performance improvement demands from the market.Current conventional metrology using the in-line CD-SEM involves measuring about ten points per wafer (one point per one chip). at a magnification of over x150k(Field of View is about 1μm 2 ). In contrast, the area of measurement pattern on chip is much larger than the area of CD-SEM measurement (mm 2 : (on chip) versus μm 2 : (CD-SEM measurement)). This would mean that the result of the CD-SEM measurement is influenced by local pattern variation.The very stringent requirements placed on in-line Metrology for the last couple of technology nodes has produced an additional metrology methodology, beyond the CD-SEM, that involves large area measurements with very high precision for the most critical levels. We will refer to this methodology as "Macro Area Measurements". We investigated the applicability of using a CD-SEM Macro Area Measurement methodology in this paper.The areas investigated focused on the following points: 1) Determining the optimum CD-SEM sampling plan for a macro area measurement. 2) Optimization of the measurement parameters.3) Optimization of the measurement condition. 4) Verification of Macro Area Measurement with an FEM (Focus Exposure Matrix) wafer.In the results, we are able to validate a new methodology that we called "Macro Area Measurement" which is demonstrated to successfully detect small process variations with the same throughput and reduced damage to the pattern.
As device feature size reduction continues, requirements for Critical Dimension (CD) metrology tools are becoming stricter. For sub-32 nm node, it is important to establish a CD-SEM tool management system with higher sensitivity for tool fluctuation and short Turn around Time (TAT). We have developed a new image sharpness monitoring method, PG monitor. The key feature of this monitoring method is the quantification of tool-induced image sharpness deterioration. The image sharpness index is calculated by a convolution method of image sharpness deterioration function caused by SEM optics feature. The sensitivity of this methodology was tested by the alteration of the beam diameter using astigmatism. PG monitor result can be related to the beam diameter variation that causes CD variation through image sharpness. PG monitor can detect the slight image sharpness change that cannot be noticed by engineer's visual check. Furthermore, PG monitor was applied to tool matching and long-term stability monitoring for multiple tools. As a result, PG monitor was found to have sufficient sensitivity to CD variation in tool matching and long-term stability assessment. The investigation showed that PG monitor can detect CD variation equivalent to ~ 0.1 nm. The CD-SEM tool management system using PG monitor is effective for CD metrology in production.
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