Kenji Saitoh

Multilevel imaging system realizing k1=0.3 lithography

The pursuit of ultimate resolution by optical lithography has given rise to many new technologies, such as PSM, oblique illumination etc. In order to realize the benefit of these new technologies in practice, a new exposure technology IDEAL is proposed. First exposure is for fine patterns, which are imaged with high contrast and large depth of focus, while second exposure is done with multileveled light distribution. These two exposures collaborate each other to form fine patterns with reasonable focus margin and good 2D profile. Experimental result of logic gate patterns are shown and demonstrate the possibility of k1 equals 0.3 lithography. Using IDEAL, KrF lithography can be extended to 100-110 nm and ArF to 80 nm resolution.

Challenging the limit of single mask exposure

IDEALSmile is introduced as a new exposure technique. Since we have realized k1 equals 0.29, k1 equals 0.32 optical lithography is now achievable. In this paper IDEALSmile is targeted for contact hole patterns. The results validate that it is possible to simultaneously fabricate 110 nm (k1 0.32) half-pitch dense and isolated contact hole patterns using Canon FPA-5000ES3 (KrF, NA equals 0.73). Furthermore, our experimental results also show that it is possible to fabricate different half-pitch patterns at the same exposure dose, which is impossible by conventional methods. Since these results are obtained using binary mask and the modified illumination with single exposure, there are no concerns with regards to decrease in throughput and increase in cost of ownership. By attaining k1 equals 0.32 for contact hole patterns using binary mask with single exposure, printing 100 nm contact hole patterns can be achieved with single exposure using KrF lithography, such as the Canon FPA-5000ES4 (KrF, NA equals 0.80) scanner which will soon make its market debut. ArF or F2 lithography is effective as for contact hole patterns below the 100 nm node. There is no doubt that optical microlithography will continue for some time.

An innovative method for contact hole printing with binary mask and single exposure

In 2002, Canon introduced a new method for contact-hole printing, using a binary mask and single exposure, entitled IDEALSmile (Innovative Double Effective source Aided Lithography with Single Mask Implemented Lithographic Enhancement)). IDEALSmile demonstrated its significant potential for k/sub 1/=0.3 lithography of contact hole patterns. Since then, additional fundamental experiments, such as through-pitch performance, and process applications, were performed to verify the potential effects of IDEALSmile. We have now developed a new type of IDEALSmile by rearranging the dummy patterns and manipulating the diffracted light on the pupil plane. In this paper we will review the principle of IDEALSmile in detail and introduce the new IDEALSmile configuration.

Full-chip implementation of IDEALsmile on 90nm node devices with ArF lithography

Summary form only given. According to sizes dictated by ITRS roadmap, contact holes are one of the most challenging features to be printed in the semiconductor manufacturing process. To overcome this issue Canon, in 2002, introduced a new technology, entitled lDEALSmile1i2 (Innovative Double Effective source Aided Lithography with Single Mask Implemented Lithographic Enhancement), that was proven to be able to define contacts with high resolution and sufficiently large through pitch? process window using a binary mask, cheap and simple to be manufactured, modified illumination and single exposure, without any negative impact on throughput and no increase of cost of ownership, The technology was further improved in 2003 with the introduction of Enhanced-IDEALSmile4 that, in certain conditions, allows achieving even higher contrast, and increased DOF thanks to three beam interference obtained with special shifted arrangement of dummy patterns without modifying optimized illumination shape.

New resolution enhancement method realizing the limit of single mask exposure

IDEALSmile is introduced as a new exposure technique that realizes k1 equals 0.29. In this paper IDEALSmile is targeted for contact hole patterns (C/H). The results validate that it is possible to simultaneously expose not only k1 equals 0.32 half-pitch dense and isolated C/H patterns, but also different pitches using Canon FPA- 5000ES3, which is impossible by conventional methods. Since these results are obtained using a binary mask and modified illumination with single exposure, there are no concerns with regards to a decease in throughput and an increase in cost of ownership. However, one of the issues in fabricating C/H patterns is the mask error enhancement factor (MEEF). Our simulation ha shown that IDEALSmile exhibits good MEEF. Although there are questions regarding optical microlithography for critical C/H patterning, the IDEALSmile exposure method has the potential to be the solution. By attaining k1 equals 0.32, printing 100nm C/H patterns can be achieved with a single exposure using KrF lithography, such as the Canon FPA-5000ES4. Furthermore the IDEALSmile technique using ArF or F2 lithography will be effective for C/H patterns below the 100nm node. There is no doubt that optical microlithography will continue for some time.

Practical applications of IDEAL exposure method

IDEAL (Innovative Double Exposure by Advanced Lithography) has been introduced as a new double exposure technique to realize k1 equals 0.3 optical lithography. IDEAL uses a rough pattern mask with patterns close to the actual device design and a simple fine pattern PSM to resolve very high contrast images on a wafer. IDEAL can be applied to complicated two dimensional patterns for actual device such as double, rectangular or T-shaped gate patterns. Results of IDEAL on different pattern types are shown. IDEAL significantly reduces MEF (Mask Error enhancement Factor). At various rough and fine dose ratios, IDEAL demonstrates the advantage especially at fine linewidths below 150 nm where the MEF of single conventional exposures increase sharply. Our extensive calculation of MEF with various patterns and experiments on complicated two dimensional patterns further confirm that IDEAL is a practical method in advanced device manufacturing.

IDEAL double exposure method for polylevel structures

IDEAL has been proposed as a new double exposure technique to realize k1 equals 0.3 optical lithography. We have applied this technique to complicated 2D structures that can be found in a poly-level of a memory test pattern device. Experimental results showed that IDEAL has a quite large process window also on structured substrate such as SiN and poly-silicon. For the CD target of 0.13 micrometers , exposure latitude larger than 10 percent with a depth of focus larger than 0.5 micrometers was achieved by IDEAL exposure. The alignment latitude of the two reticles used to compose the final lithographic image was larger than +/- 40 nm, moreover line-end shortening effects are also improved by IDEAL exposure.

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.

Analysis of Overlay Accuracy in 0.14 µm Device Fabrication using Synchrotron Radiation Lithography

We applied synchrotron radiation lithography to the fabrication of a 0.14 µ m rule dynamic random access memory structure using high dielectric film capacitor and trench isolation techniques. An overlay accuracy of 80 nm was obtained. In order to clarify the contributions of the error causes to the overlay accuracy, we mathematically classified the overlay error into four components: rotation, translation, magnification and in-plane deformation (IPD). A rotation and translation error was estimated to be 38 nm. A wafer process-induced error such as a rotation and translation due to a degradation of the alignment mark worsens the overlay error by 33 nm. We have also found that the maximum magnification error including the mask magnification was 4 ppm and the magnification correction was necessary to achieve an overlay accuracy less than 50 nm. The IPD was estimated to be 60 nm, and the major cause was a mask overlay error. The analyzed results suggest that an IPD less than 30 nm and a rotation/translation component less than 30 nm are required to achieve an overlay error less than 50 nm.

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.