Hidemitsu Hakii

CD-Metrology of EUV masks in the presence of charging: measurement and simulation

The required measurement precision for multilayered EUV mask metrology is set below 0.4 nm three sigma. In addition to limited precision of CD-SEM, there are fundamental physical factors that deteriorate the accuracy of the measurements, the most important of which is charging. It is widely believed that EUV masks are conductive. However, experiments have revealed noticeable charging in CD-SEM measurements of EUV masks that cannot be ignored. In this work, the results of the experiments and simulations of the SEM signals are presented. It was shown that charging affects the metrology in a few ways. The SEM signal shifts at each frame, changes with beam current and also depends on the wall angle of the absorber. The results of the simulations are compared to experimental results.

Influence of the charging effect on the precision of measuring EUV mask features

Influence of the prominent charging effect on the precision of measuring EUV mask features using CD-SEM was studied. The dimensions of EUV mask features continuously measured by CD-SEM gradually varied because of the charging. The charging effect on the measured CD variation mainly consists of three factors: 1) shift of the incident points of primary electrons deflected by the surface charge, 2) distortions of the profiles of secondary electron signal intensity caused by the deflection of the secondary electrons, 3) deviation of the maximum slope points of the secondary electron signal intensity due to the variation of the image contrast. For those three factors described above, how the material constant affect the CD variation measured by CD-SEM is discussed.

A study of phase defect measurement on EUV mask by multiple detectors CD-SEM

We have studied MVM (Multi Vision Metrology) -SEM® E3630 to measure 3D shape of defects. The four detectors (Detector A, B, C and D) are independently set up in symmetry for the primary electron beam axis. Signal processing of four direction images enables not only 2D (width) measurement but also 3D (height) measurement. At last PMJ, we have investigated the relation between the E3630’s signal of programmed defect on MoSi-HT and defect height measured by AFM (Atomic Force Microscope). It was confirmed that height of integral profile by this tool is correlated with AFM. It was tested that E3630 has capability of observing multilayer defect on EUV. We have investigated correlation with AFM of width and depth or height of multilayer defect. As the result of observing programmed defects, it was confirmed that measurement result by E3630 is well correlated with AFM. And the function of 3D view image enables to show nm order defect.

A study of precision performance and scan damage of EUV masks with the LWM9000 SEM

EUV mask is a reflection-type-mask, of which film and structure are very different from those of existing masks (e.g. Cr and MoSi). LWM9000 SEM of Vistec/Advantest was used for measurement of EUV masks. Two types of EUV masks were used to investigate static and dynamic measurement precision and the impact of charge-up by e-beam irradiation during measurement. An optional function of LWM9000 SEM was used to improve static precision. Because the LWM9000 SEM uses ozone for in-situ cleaning of the work chamber, the interaction between the electron beam and ozone presence was also investigated. The EUV mask was evaluated at the EUV wavelength before and after e-beam scanning and measurements to determine any changes in reflectance.

New CD-SEM metrology method for the side wall angle measurement using multiple detectors

A new metrology method for CD-SEM has been developed to measure the side wall angle of a pattern on photomask. The height and edge width of pattern can be measured by the analysis of the signal intensity profile of each channel from multiple detectors in CD-SEM. The edge width is measured by the peak width of the signal intensity profile. But it is not possible to measure the accurate edge width of the pattern, if the edge width is smaller than the primary electron beam diameter. Using four detectors, the edge width can be measured by the peak width which appears on the subtracting signal profile of two detectors in opposition to each other. Therefore, the side wall angle can be calculated if the pattern height is known. The shadow of the side wall appears in the signal profile from the detector of the opposite side of the side wall. Furthermore, we found that there was the proportional relation between pattern height and the shadow length of the signal on one side. This paper describes a method of measuring the side wall width of a pattern and experimental results of the side wall angle measurements.

Study of the three-dimensional shape measurement for mask patterns using Multiple Detector CD-SEM

The Multiple Detector CD-SEM acquires the secondary electron from pattern surface at each detector. The 3D shape and height of mask patterns are generated by adding or subtracting signal profile of each detector. In signal profile of the differential image formed in difference between left and right detector signal, including concavo-convex information of mask patterns. Therefore, the 3D shape of mask patterns can be obtained by integrating differential signal profile. This time, we found that proportional relation between pattern height and shadow length on one side of pattern edge. In this paper, we will report experimental results of pattern height measurement. The accuracy of measurement and side wall angle dependency are studied. The proposal method is applied to OMOG masks.

Addressing 3D metrology challenges by using a multiple detector CDSEM

In next generation lithography (NGL) for the 22nm node and beyond, the three dimensional (3D) shape measurements of side wall angle (SWA) and height of the photomask pattern will become critical for controlling the exposure characteristics and wafer printability. Until today, cross-section SEM (X-SEM) and Atomic Force Microscope (AFM) methods are used to make 3D measurements, however, these techniques require time consuming preparation and observation. This paper presents an innovative technology for 3D measurement using a multiple detector CDSEM and reports its accuracy and precision.

An evaluation of a new side-wall-angle measurement technique for mask patterns by CD-SEM

The verification of not only two-dimensional feature but also three-dimensional feature, sidewall angle (SWA), has been becoming increasingly important in NGL mask fabrication. The OMOG (Opaque MoSi on Glass) mask for ArF immersion lithography with double patterning and the reflective type mask for EUV (Extreme Ultra- Violet) lithography are especially in need of it. There are several metrology tools e.g. SEM, AFM, and Scatterometry for sidewall angle (SWA) measurement. We evaluated a new SWA measurement method using white-band width (WBW), which is equivalent to mask pattern edge width, by CD-SEM. In general, WBW correlates with SWA. It narrows as SWA becomes steeper. However, the correlation deteriorates when SWA is vertically near. This is due to the resolution limit of electron beam diameter used for measurement. We analyzed the new approach to measure SWA by CD-SEM to solve this problem. And the analysis revealed that WBW changes proportionately electron beam current value. The amount of width change depends on SWA. In this paper, we will describe the new SWA measurement method and its evaluation results as well as SWA measurement results of OMOG and EUV masks.

A study of contour image comparison measurement for photomask patterns of 32 nm and beyond

In order to analyze small reticle defects quantitatively, we have developed a function to measure differences in two patterns using contour data extracted from SEM images. This function employs sub-pixel contour data extracted with high accuracy to quantify a slight difference by ΔCD and ΔArea. We assessed the measurement uncertainty of the function with a test mask and compared the sizes of programmed defects by each of conventional and proposed methods. We have also investigated a correlation between measured minute defects in high MEEF (Mask Error Enhancement Factor) regions and aerial images obtained by AIMS (Aerial Image Measurement System) tool. In this paper, we will explain the Contour Comparison Measurement function jointly developed by Toppan and Advantest and will show its effectiveness for photomask defect analyses.