Kazui Mizuno

Development of an electron-beam lithography system for high accuracy masks

A mask electron-beam writer for production lines beyond 100 nm was developed. The system HL-7000M is equipped with cell projection function for high critical dimension accuracy. The newly developed technologies are a cell projection optics, objective lens optics, a low distortion stage, a highly accurate control electronics, and high accuracy proximity effect correction hardware. This article describes the details of the electron optics and its performances.

Advanced e-beam reticle writing system for next-generation reticle fabrication

A new advanced e-beam reticle writing system HL-950M has been developed to meet requirements for the production of 130 nm node reticles as well as development of 100 nm node reticles. In order to improve the critical dimension (CD) accuracy and pattern positioning accuracy, several new technologies have been introduced on the basis of the field-proven technologies of the previous system HL-900M. Fine address size is realized by a newly developed control electronics2 that enables the system to handle address unit of 2.5 nm, providing four times higher resolution than HL-900M. Reconstruction of sub-sub-field (SSF) pattern data has been developed so that the same pattern is exposed twice with reconstructed SSF pattern data sets with different SSF boundaries, realizing better stitching and positioning accuracy. High accuracy proximity effect correction has been developed with a new second order proximity effect calculation scheme, providing better CD uniformity particularly against drastic change of the pattern density. As main results of the system evaluation, the global CD accuracy of 9 nm (3(sigma) ) and the global pattern positioning accuracy of 15 nm (3(sigma) ) have been obtained. The overall performance of the HL-950M system has satisfied the specifications required for the 130 nm node reticle production and 100nm node reticle development.

Continuous writing method for high speed electron‐beam direct writing system HL‐800D

Hitachi has developed a new e‐beam direct writing system named HL‐800D [Y. Sakitani, H. Yoda, Y. Shibata, T. Yamazaki, and K. Ohbitu, J. Vac. Sci. Technol. B 10, 2759 (1992)]. This system has been developed for mass production of ultra‐large scale integrated circuits such as a 256M‐DRAM manufactured with high accuracy and high throughput. To achieve a productive level of throughput, this system employs a continuous writing method with variable stage speed. In the method, an e‐beam traces a moving wafer stage accurately using deflections during continuous writing, and the wafer stage moves with the most suitable speed depending on the writing pattern density. The continuous writing method makes considerable improvement in throughput compared with a conventional ‘‘step and repeat’’ stage moving method. Stitching accuracy is confirmed by test writing.

Performance improvement in e-beam reticle writer HL-800M

An advanced e-beam mask-writing system HL-800M has been developed for the 0.25-micrometer rule-devices. To meet the design-rule, the targets of this system specifications are critical dimension (CD) control of 30 nm, positioning accuracy of 40 nm, and throughput over 0.5 plate per hour. To achieve CD control, we judged that it was inevitable to increase the acceleration voltage up to 50 kV for patterns smaller than 2 micrometer. However, for patterns larger than 5 micrometer, the e-beam proximity-effect causes the pattern-width linearity to be worse. To achieve the sufficient linearity, proximity correction on the hardware module of the systems was performed. This hardware module executes proximity effect correction for each patterns over the area on the plate, so that total throughput was improved compared with that of the correction by software. Besides, a noise cancellation module was introduced to reduce the errors in the e-beam shot positions. This module detects the vibration noise caused by with the power-supply frequency and feeds the correction signal back to the e-beam deflectors. For positioning accuracy, in addition to the mirror correction using hardware for the stage interferometer, a new positioning-correction function depending on the coordinates of the system was developed. In the results of the exposure evaluations, CD uniformity on a 6025 plate showed width-deviations of 3 sigma were 31 nm (X) and 18 nm (Y). Pattern-width linearities for various kinds of patterns were within plus or minus 50 nm. Furthermore, the noise cancellation module was made the amplitude of the e-beam vibration reduced from 33 nm to less than 8 nm. For positioning accuracy, evaluation patterns measured by the LMS2020 (Leica) showed sufficient results for our target. For throughput, the average of the writing time per 6-inch plate for ten patterns is shorter than our targeted throughput with a dosage of 4 (mu) C/cm2. The HL-800M system is capable of producing reticles for 0.25-micrometer design-rule.

Technological capability and future enhanced performance of HL-7000M

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.

New electron-beam mask writing system for 0.25-um lithography

A new electron beam (EB) mask writing system based on both the Hitachi HL-700MIII and HL-800D systems is developed. The target of the system is a 0.25 micrometers design rule in semiconductor mass-production. To improve critical dimensions (CD) to better than 0.03 micrometers , an acceleration voltage of 50 kV is used with a variable shaped beam method. Further, EB proximity correction using a pattern area density map which is the same as that of HL-800D has been adopted for the improvement of pattern width linearities. This correction system, which consists of hardware only, covers the entire mask area. In the mechanical system, continuously moving stage with constant velocity and three-axis active vibration- isolation are used to improve positioning accuracy to better than 0.04 micrometers . In addition, a new mask handling system in which a robot carries the mask realizes automatic transportation without human assistance. Some experiments to evaluate the new system have been performed. In particular, the characteristics of masks written with an EB accelerated to 50 kV have been investigated. The results of CD pattern uniformity for a 1 micrometers line pattern over the entire mask area are better that 0.025 micrometers . In addition, pattern linearity using EB proximity correction is within +/- 0.03 micrometers . A stitching accuracy of 0.037 micrometers is obtained.

Recent CD accuracy improvements for HL-7000M

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.

Advantage in using the combination of HL-800M and CAR process

The advanced 50 kV e-beam mask writing system HL-800M (Hitachi Co. Ltd.) was developed for 0.25 - 0.18 micrometer design-rule mask fabrication and widely applied. The combination of 50 kV e-beam writing system (EB) and Chemically Amplified Resist (CAR) is one of the solutions to improve accuracy for the fabrication of further high-end masks. The purpose of this study is to show the advantages of Critical Dimension (CD) accuracy in using the combination of 50 kV EB;HL-800M and positive-CAR; RE-5120P (Hitachi Chemical Co. Ltd.). In order to control CD, Proximity Effect Correction (PEC) is indispensable for the high acceleration voltage EB. Therefore, HL-800M has a high-speed-PEC system with hardware circuits. In this study, the PEC condition of HL-800M was optimized to improve CD accuracy. As a result, CD linearity of 18 nm was obtained in the pattern width from 0.7 micrometer to 3 micrometer. Besides, we evaluated the CD variation due to resist heating in using this combination. And, in the experiment of the resist heating effect, the CD variation was less than plus or minus 7 nm in the range of dosage ratio from 100% (11 (mu) C/cm2) to 500%. In other words, the CD variation due to resist heating is not so much serious problem for practical use in using the combination of the 50 kV EB and CAR.

Improvement of CD accuracy for next-generation reticles using HL-800M and CA resists

The 50 kV electron-beam (EB) writing system HL-800M (Hitachi Co. Ltd.) was developed for 0.25 - 0.18 micrometer design-rule mask fabrication and widely applied. Chemically Amplified Resist (CAR) has merits of high sensitivity, high resolution and dry-etching durability. The combination of 50 kV EB and CAR is one of the best solutions to improve accuracy and throughput of next generation reticles such as 0.18 micrometer design-rule mask and beyond. The purpose of this study is to optimize the exposure and process conditions of the combination of 50 kV EB and CAR for improving Critical Dimension (CD) accuracy. At first, new positive-type CAR; RE515OP (Hitachi Chemical Co. Ltd.) has been evaluated. This resist shows the high resolution of 0.25 micrometer. Because of the vector-scanning EB such as HL-800M, the use of negative-type resist improves throughput of exposure. Negative-type CAR; NEB-22A (Sumitomo Chemical Co. Ltd.) has been also evaluated. This resist shows also the high resolution of 0.14 micrometer. It is clarified that both resists have the characteristic to meet the 0.18 - 0.15 micrometer design-rule mask fabrication. Besides, in order to improve CD accuracy with HL-800M, Proximity Effect Correction (PEC) condition has been optimized. Especially, as parameters of mesh-size and times of smoothing area-density, CD errors are investigated. As a result, CD linearity of 18 nm is obtained in the pattern-widths from 0.7 micrometer to 3 micrometer.

High-performance and stability reticle writing system HL-800M

HL-800M has been developed as electron beam reticle writing system (EB) for advanced reticle production. It is very important for EB to keep high performance constantly in the actual advanced reticle production. To meet such a requirement, this system adopts accelerated voltage of 50kV, variable shaped beam, continuous moving stage and 3-stage deflector. Especially, to improve the positioning accuracy, this system has temperature control system, active vibration-isolation system and the new software for position error correction. The proximity effect correction which changes exposure shot time depending on the pattern density and the multi-exposure function are also installed. As a result, the positing accuracy of 32nm and the long term placement of 28 nm are obtained. The line-width linearity from 1 micrometers to 10 micrometers is within the range of 70 nm, and 40 nm form 1 micrometers to 3 micrometers . The stitching accuracy at the stripe boundary is 26nm, and 20nm in case of the 3-path exposure.