The influence of the e-beam aperture angle on the critical dimensions (CD)-scanning electron microscope measurements for a high aspect ratio (AR) structure is investigated. The Monte Carlo simulator JMONSEL is used for evaluating the measurement sensitivity to the variation in the bottom CD. The aperture angle of the primary electron greatly influences the measurement precision of the bottom CD in the high AR structure. Then, we applied an energy-angular selective detection technique to the Monte Carlo simulation results and found that the measurement sensitivity for the large aperture angle was improved. In addition, the experimental results are qualitatively consistent with the results of the Monte Carlo simulation. These results indicate that the energy-angular selective detection technique is effective for improving the measurement resolution of CD at trench bottom of a high AR structure and the technique is also useful for the overlay measurement during after-etch inspection.
The influence of e-beam aperture angle on CD-SEM measurements for a high aspect ratio (HAR) structure was investigated. The Monte-Carlo simulator JMONSEL was used to evaluate the measurement sensitivity to the variation in the bottom CD. The aperture angle of the primary electron greatly influences the measurement accuracy of the bottom CD in the HAR structure. Then, we utilized a technique for energy-angular selective detection to the Monte-Carlo simulation results and found that the measurement sensitivity for the large aperture angle was improved. In addition, the experimental results were qualitatively consistent with the results of the Monte-Carlo simulation. These results indicate that the detection is effective for the bottom CD measurement of a HAR structure.
Voltage contrast (VC) images obtained using an energy filter (EF) were used to measure the bottom surface of high-aspect-ratio structures. The VC images obtained using the conventional EF were sensitive to variations in wafer potential. Since CD-SEM metrology requires precise EF voltage control when using VC images, we developed an EF voltage correction method to be used at each measurement point. Consequently, bottom-edge measurement, independent of the wafer potential fluctuations, was achieved using the newly developed EF. Our developed technique is effective for CD-SEM metrology using VC images.
Voltage contrast (VC) images obtained using an energy filter (EF) were used to measure the bottom surface of high-aspect- ratio (HAR) structures. The VC images obtained using the conventional EF were sensitive to variations in wafer potential. Since CD-SEM metrology requires precise EF voltage control when using VC images, we developed an EF voltage correction method to be used at each measurement point. Consequently, bottom-edge measurement, independent of the wafer potential fluctuations, was achieved by using the newly developed EF. Our developed technique is effective for CD-SEM metrology using VC images.
Proc. SPIE. 10145, Metrology, Inspection, and Process Control for Microlithography XXXI
KEYWORDS: Semiconductors, Metrology, 3D acquisition, Sensors, Copper, Dielectrics, Electrons, Manufacturing, Inspection, Scanning electron microscopy, 3D metrology, Process control, Semiconductor manufacturing, Signal generators, Signal detection
In recent trend of semiconductor manufacturing, accurate critical dimension (CD) metrology is required to realize miniaturized three-dimensional (3D) structures. However, the conventional edge contrast of scanning electron microscopy (SEM) is often suppressed when imaging the deep bottom of the 3D structures. In this paper, we propose effective approaches realizing the improved SEM image contrast for such metrology targets. Our approach utilizes the principle of the SEM contrast, and optimizes the three major influencing factors of SEM contrast; signal generation, signal propagation inside the specimen, and signal detection by the detectors. We show the examples of improved image contrast including, embedded voids imaging by high landing beam energy, contact-hole bottom imaging by angular selective detections, and precise edge position extraction realized by energy-angular selective imaging.
With the rapid progress in the minimization in the device fabrication, it comes to be indispensable to reduce Critical Dimensional (CD) error in the mask production. The electron beam mask lithography system HL-7000M series has been developed, to meet the needs for mass production line below 90 nm node. A novel high-accuracy Proximity Effect Correction (PEC) method of exposure correction for pattern density variation is applied in this system. By using this high accuracy PEC method, CD error caused by proximity effects has been reduced to 4 nm, from 14 nm with the conventional PEC method.
A new electron beam mask writer, HL-7000M, has been developed for mass production of 90 nm node photomask and, research and development of 65 nm node mask. A series of adjustments to improve CD accuracy provides us a novel systematic solution for VSB system optimization. By applying a novel constant-gain method for linearity adjustment,
linearity range, for designed size ranging from 0.3 um to 1.0 um, has been improved to < 3 nm for line and space pattern, the maximum XY discrepancy is 2 nm. Both experimental and theoretical studies for shot-divided patterns, which are often generated in OPC pattern conversion, have been applied. By modification of the shift term in beam size correction, exposure results for such shot-divided patterns, for divided pattern size varied from 500 nm to 1 nm, are improved to be less than 5 nm in range.
HL-7000M electron beam (EB) lithography system has been developed as a leading edge mask writer for the generation of 90 nm node production and 65 nm node development. It is capable of handling large volume data files such as full Optical Proximity Correction (OPC) patterns and angled patterns for System on Chip (SoC). Aiming at the technological requirements of the International Technology Roadmap for Semiconductors (ITRS) 2002 Update, a newly designed electron optics column generating a vector-scan variable shaped beam and a digital disposition system with a storage area network technology have been implemented into HL-7000M. This new high-resolution column and other mechanical components have restrained the beam drift and fluctuation factors. The improved octapole electrostatic deflectors with new dynamic focus correction and gain alignment methods have been built into the object lens system of the column. These enhanced features are worth mentioning due to the achievement of HL-7000M's Image Placement (IP) performance. Its accuracy in 3σ of a 14 x 14 global grid matching result over an area of 135 mm x 135 mm measured by Leica LMS IPRO are X: 6.09 nm and Y: 7.85 nm. In addition, the shot astigmatism correction has been in the development and testing process and is expected to improve the local image placement accuracy dramatically.
HL-7000M electron beam lithography system has been developed as a state-of-the-art reticle writer for the generation of 90nm node production and 65nm node development. It is capable of handling relatively large volume data files such as full Optical Proximity Correction patterns and angled patterns for System on Chip. Aiming at technological requirements, a newly designed electron optics column generating a vector-scan variable shaped beam and a digital disposition system with a storage area network technology have been integrated into HL-7000M. Since the requirement on the critical dimension uniformity is extremely demanding on the ITRS roadmap, HL-7000M has also needed to improve its beam shaping performance. The ability relevant to shaping beam size has a great impact on its line width or critical dimension accuracy. To reduce an aberration caused within the shaping lens system, the dual quadrupole electrostatic shaping deflector has been utilized. By applying advanced technologies, HL-7000M with a result of critical dimension uniformity (2.5nm and 2.8nm in 3σ) has achieved meeting its target requirement of the 90nm generation for production. Additionally HL-7000M has proved its potential, allowing the industry to establish quickly the processes further beyond the requirements of the 65nm node for development.