Toru Tojo

Piezoelectrically Driven xyθ Table for Submicron Lithography Systems

A newly designed piezoelectrically driven XYθ table has been developed for submicron lithography systems. The XYθ table was fabricated using a monolithic plate structure, joined together with flexure hinges and driven by an inchworm function. This function involves the periodic clamping and unclamping of four blocks and the expansion and contraction of piezoelectric actuators. The XYθ table can travel a long distance with fine positioning in the X, Y, and θ directions. The velocities can be controlled up to 0.5 mm/s in the X and Y directions, and 0.3×10 −2 rad/s in the θ direction by changing the inchworm function stepping rate. Positioning accuracy of less than 1 μm in the X and Y directions, and 7.5×10−6 rad in the θ direction can easily be obtained using a servo system with a 0.5‐μm measuring resolution.

High-Accuracy Proximity Effect Correction for Mask Writing

A high-accuracy proximity effect correction method for high-precision masks has been developed to satisfy current and future requirements. In this paper, we explain the primary features of this method and the theories on which it is based. The developed formula for obtaining the optimum correction dose is expressed in the form of either iterations or an infinite series of functions. The advantage of this formula is that it quickly converges to the sought value, bringing about high-accuracy proximity effect correction with a high calculation speed. A coarse graining method (covering pattern density and representative figure methods) for reducing calculation time is explained. This method has been adopted for an EX-11 series and has been used for mask writing from the 180 nm design rule onward.

Advanced electron-beam writing system EX-11 for next-generation mask fabrication

Toshiba and Toshiba Machine have developed an advanced electron beam writing system EX-11 for next-generation mask fabrication. EX-11 is a 50 kV variable-shaped beam lithography system for manufacturing 4x masks for 0.15 - 0.18 micrometer technology generation. Many breakthroughs were studied and applied to EX-11 to meet future mask-fabrication requirements, such as critical dimension and positioning accuracy. We have verified the accuracy required for 0.15 - 0.18 micrometer generation.

New mask blank handling system for the advanced electron-beam writer

Meeting the latest requirements of aggressive users for advanced masks for optical lithography will be difficult. In addition, improving the productivity and throughput of advanced masks with high-density pattern data is necessary. To overcome these hurdles, Toshiba and Toshiba Machine have developed a new advanced mask writer, the EX-11, shown in Figure 1. The EX-11 takes measures against airborne contamination before drawing is started. It also employs a standard mechanical interface (SMIF) based on the concept of local cleaning technology. This paper describes the design concept of the new mask blank handling system for the EX-11, and the efficiency of these measures was confirmed by the experimental results.

Reduction of fogging effect caused by scattered electrons in an electron beam system

Background exposure of a resist caused by scattered electrons (the fogging effect) degrades critical dimension accuracy when the pattern density changes over the specimen. We measured the fogging effect in an electron beam optical column. In order to reduce the fogging effect, a scattered electron absorber plate having a converging holes structure was attached to the lower surface of the objective lens. When the most severe pattern for the fogging effect was applied, we achieved the size variation caused by the fogging effect less than 8 nm. The converging holes effectively trap the scattered electrons and greatly reduce the fogging effect.

Performance of novel 198.5-nm wavelength mask inspection system for 65-nm node and beyond optical lithography era

In 65nm node and some more technology node probably may go with current optical lithography and industry has predicted many challenges. In patterning point of view, quality and cost of mask became more and more important than ever. Particularly, mask defect engineering technology is key area not only inspect the defects but also mask process monitoring and improvements. In mask inspection technology there were a lot of new progresses to enhance the defect inspection sensitivity and stability. The key solution to achieve better sensitivity may be short inspection wavelength and adequate detection algorithm. In this paper, we will propose defect size specifications of 65nm and beyond optical mask with various OPC and RET environments. In addition, we will present initial data of newly developed 198.5nm inspection wavelength system. Through this study, we found future optical mask faces new challenges in defect inspection and to solve these problems, we need advanced mask inspection system and collaborations among patterning related fields.

Advanced mask inspection optical system (AMOS) using 198.5-nm wavelength for 65-nm (hp) node and beyond: system development and initial state D/D inspection performance

A novel high-resolution mask inspection platform using DUV wavelength has been developed. This platform is designed to enable the defect inspection of high quality masks for 65nm node used in 193nm lithography. In this paper, newly developed optical system and its performance are reported. The system is operated at wavelength of 198.5nm, which wavelength is nearly equal to 193nm-ArF laser exposure tool. Some defect image data and defect inspection sensitivity due to simulation-base die-to-die (D/D) inspection are shown on standard programmed defect test mask. As an initial state D/D inspection performance, 20-60 nm defects are certified. System capabilities for 65nm node inspection and beyond are also discussed.

High-Speed Convolution System For Real-Time Proximity Effect Correction

In order to realize a real-time proximity effect correction system, a high-speed, highly accurate hardware system for convolution calculation has been developed. The representative figure method is used in the system. Pipeline architecture and parallel processing architecture are also used. The calculation speed of the system is 500 s for a writing region of 10 ×10 cm. The optimum correction dose has been evaluated using the output data of the convolution system. The error in the correction dose caused by our system is found to be 0.5% at most. These results suggest that a real-time proximity effect correction system can be realized, which can be used for making reticles of Gbit-class dynamic ramdom access memories (DRAMs).

Reticle flexure influence on pattern positioning accuracy for reticle writing

This paper presents a method for estimating the influence of reticle flexure on pattern positioning accuracy, and evaluates the method by measuring patterned reticles. Reticle flexure causes the pattern shift which occurs by stretching or compression of the reticle surface. A height-mapping function of an electron beam (EB) writing system and a measuring machine are used to calculate the pattern shift due to reticle flexure. The bent shape of a reticle on the EB-writing system differs from that on the measuring machine, so that the patten shifts on the two machines are different. The pattern shifts caused by the bent shape difference were excluded from the measurement result of pattern positioning errors. The values of pattern positioning accuracy evaluation parameters, x, y-scaling and orthogonality, are calculated among several reticles (5 inches, 0.09 inches thick). The deviations of these three values are reduced to less than 50% of their uncompensated values.

Particle contamination control technology in electron beam mask writing system for next-generation mask fabrication

Electron beam mask writing is one of the most promising technologies for reliable fine mask patterning in present and future optical lithography. To establish a high performance mask writing system, not only the development of breakthrough technologies for improvement in mask accuracy of CD and image placement of the mask pattern but also the development of contamination control technologies should be pursued. To meet these requirements, the mask blanks upper surface scatter meter for EB writer (MUSE) system has been newly developed. MUSE can evaluate and measure the particles on the mask in vacuum environments and can be attached to the EB system. By using MUSE, not only the investigation of the origin of dust production in the EB system but also productive control of the EB system can be accomplished. This paper describes the MUSE system and the results of particle measurement in the EB mask writing system. The performance of the EB system with respect to particles is presented and discussed.