Shunichi Uzawa

Proposal for a 50 nm proximity x-ray lithography system and extension to 35 nm by resist material selection

In this article, a 50 nm generation proximity x-ray lithography (PXRL) system is proposed using shorter wavelengths of exposure light down to around 3 A. The illumination system uses a mirror at 1° incidence angle such as in the Canon stepper XRA-1000, which can be realized by coating with a fourth or fifth period metal such as Co or Rh. The resist containing chemical elements such as Cl, S, P, Si, and Br whose x-ray absorption edge lies in the wavelength band of the exposure light can yield a strong absorption using this system. Therefore, a resist material containing such elements is highly sensitive when applied to the 50 nm system. The average wavelength of power absorbed by the resist depends on the elements contained in the resist. This suggests that the resolution limits also depend on the resist material even for the same exposure system. Therefore, this system should be extendible down to the 35 nm generation by using such a resist and a thick diamond mask membrane. The system described assumes t...

Novel illumination system of synchrotron radiation stepper with full field exposure method

We estimate the pattern distortion and the critical dimension (CD) variation due to the thermal distortion under a large exposure field for the full field exposure method. We verify that the effect of the thermal distortion of the mask and wafer on the pattern distortion and the CD variation is small enough under the condition of mass production of devices of 0.1 μm design rule. We present a design of the novel two mirror illumination system which can improve the throughput both by exposing a field as large as 50 mm square and by condensing synchrotron radiation (SR) spread in the horizontal plane. The effects of the variation of the position of the SR source and the mirrors and the size of the SR source on the performance of the stepper are investigated.

X-ray stepper development for volume production at Canon

We describe some results of exposure experiments using the present prototype SR stepper which Canon has developed and the novel technology development which is necessary to establish the next generation SR stepper for volume production. Concerning the technology development, we have established (1) two mirror condensing system for full field exposure, (2) ADGL alignment method, (3) magnification correction method, (4) high speed stage stepping method. By adopting these technologies, we have been developing a beta- site machine for volume production and its features and preliminary specifications are described.

Current status of the SR stepper development

We describe some results of exposure experiments using the present prototype SR stepper which Canon has developed and also describe the novel technology development which is necessary to establish the next generation SR stepper for volume production. In the evaluation of the prototype machine, alignment performance, stage accuracy, and printing performance were examined, and we found the SR lithography can be applied to manufacturing devices beyond 0.15 micrometer level. In the technology development for the production machine, we have examined methods related to masks; they are reduction of thermal expansion, suppression out-of-plane displacement of mask membrane, and magnification correction. As a result of the examinations, we have a good perspective in development of a high-throughput SR stepper which is suitable for the production beyond 1 G-bit DRAM.

Application of SR lithography to 0.14-um device fabrication

The applicability of synchrotron radiation (SR) lithography to fabricate a giga bit scale dynamic random access memory (DRAM) cell array structure with minimum feature size of 0.14micrometers is demonstrated. Four lithography levels, isolation, transfer gate, bit line and storage node, were exposed by SR lithography. Exposure was carried out at Mitsubishi SR lithography facility using Canon x-ray stepper XFPA with a new negative tone resist and home-made x-ray mask set for each exposure level. These masks were composed of 2micrometers SiC membrane and 0.5micrometers W-Ti absorber. To minimize the mask-induced distortion, we applied the various techniques to the x-ray mask fabrication, changing the mask fabrication process flow, step annealing and electron beam multiple writing, and as the result, the pattern placement accuracy between two exposure level masks was about 50nm. Exposure latitude was about 22 percent for 0.15micrometers line and space pattern at the proximity gap of 30micrometers , and the critical dimension deviation for 0.14micrometers transfer gate pattern was 0.014micrometers at the almost same position in the mask in spite of the replication on the real DRAM topographic structure. The overlay accuracy was about 80nm for 20 X 20mm2 area. These results show SR lithography is the promising technique for giga bit level device fabrication.

New alignment system for submicron stepper

Recent rapid progress in the semiconductor industry requires much better accuracy for overlay. Today, the overlay accuracy of 0.1 pm is discussed in reality. To guarantee the 0.1 pm overlay for all processes is one target. In order to attain such requirements, the alignment system has been renewed. We have developed a new TV image processing system with high resolution, using real-time twodimentional image processing technology by multi-computer system. Together with TV system, the new alignment system by HeCd and HeNe laser bright field method is implemented, and they showed more extensive flexibility to various types of wafers.