Nobutoshi Mizusawa

Critical Dimension Control in Synchrotron Radiation Lithography Using a Negative-Tone Chemical Amplification Resist

Total critical dimension (CD) controllability for 0.14 µ m line-and-space in SR lithography was evaluated for all wafer levels. The evaluation was carried out for the CD accuracy between the wafers, in the wafer and in the exposure field. The influence of the exposure process instability to the CD accuracy was also evaluated. The instability of the post exposure baking (PEB) temperature and the post exposure delay (PED) time affects the CD accuracy, and they were estimated to be less than 5 nm, respectively. The CD accuracy at the same point on the X-ray mask was 5.4 nm in the wafer and 10.5 nm between the wafers. It was found that the CD accuracy between the wafers was degraded by the inaccurate exposure dosage caused by the daily change of the SR beam distribution in the vertical direction. In the exposure field, the CD instability due to SR beam nonuniformity was 4.1 nm and that due to the X-ray mask was 15 nm. Consequently, the total CD controllability is presently estimated to be 19.5 nm for all wafer levels and the improvement of the dose repeatability and X-ray mask CD control is required to achieve the CD accuracy of less than 11 nm.

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.

Technology and performance of the Canon XRA-1000 production x-ray stepper

In order to introduce next generation lithography (NGL) into practical use, developing a production-worthy exposure tool is as important as developing a proof-of-concept system and mask technology. The progress of the exposure tool can be used as a measure of the status of each NGL choice. Canon has been focusing on the development of a proximity x-ray lithography (PXL) system for volume production use since the start of development. This has included development of magnification correction, development of a high-seed wafer stage, improvement of illumination intensity, extension of process latitude in the alignment system design, and development of an accurate environment control system. For example, we introduced a new method, using mechanical deformation of the mask, for magnification correction. We also developed a new wafer stage based on a field proven-high-speed wafer stage from our current optical lithography systems. A stepping time (including settling time) of less than 400 ms for a 50 mm step in...

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.

Technology and performance of X-ray stepper for volume production

Proximity X-ray lithography (PXL) has finished the demonstration stage of device fabrication and has started to be applied for volume production. We started the development of X-ray lithography tool in the middle of 1980s, and in 1992 we have installed our prototype machine in the SR facility of Mitsubishi Electric Corporation (MELCO) and we have evaluated the machine in collaboration with MELCO. In the collaboration study, we have confirmed the system concept of X-ray stepper and clarified subjects for volume production tool development.

Overlay accuracy of Canon synchrotron radiation stepper XFPA for 0.15 μm process

Canon has been developing a synchrotron radiation stepper system for x‐ray lithography feasibility studies. We have developed a novel accurate alignment system using the dual grating lens (DGLs) method. In this article, we explain the principle of the DGL, and the results of the alignment accuracy and process applicability tests. We have evaluated alignment performance for translation (X,Y) and rotation (θ) at the center of every exposure area. We obtained the alignment accuracy 3σ of 19 nm (X), 15 nm (Y) and 0.8 μrad (θ), using etched SiN patterns on Si substrates, and the overlay accuracy in an actual dynamic random access memory fabrication process 3σ of 34 nm (X), 31 nm (Y), and 2.1 μrad (θ). After eliminating the alignment offset in each shot, the values (3σ) are 18 nm, 21 nm, 1.4 μrad, respectively. These results show that the alignment method is promising for 0.15 μm level device fabrication.