Hideki Suda

Swing effects in alternating phase shift mask lithography: Implications of low σ illumination

We develop sub-100-nm resist patterns with alternating phase shift mask (alt PSM) using 0.68 numerical aperture KrF lithography scanner at a partial coherence factor σ of 0.31, the lowest available in our tool—a need of alt PSM technique. Although we achieve resist lines down to 65nm, the standing wave and critical dimension (CD) swing effects are immense on big patterns. The 180nm lines show CD swings two times to that of 90nm lines. The sidewall profiles of 180nm lines are also more susceptible to swing inflection point selection than 90nm lines. The finding on the use of alt PSM is that the higher standing wave, larger CD swing, and more degradation of sidewall profiles on big patterns than small patterns are the implications of low σ illumination. We suggest the inclusion of big patterns for swing studies while setting up the lithography process using alt PSM.

Development of halftone phase-shift blank and mask fabrication for ArF lithography

The halftone phase-shift mask has been in practical use for i-line and KrF lithography. In ArF lithography, the HtPSM is also considered to be a promising resolution enhancement technique for its simple structure and fabrication process required. We in HOYA have attempted to expand the applicability of our MoSi-based HtPSM blank technology to ArF lithography, helping extend the life of the existing infrastructure for conventional HtPSM fabrication. We have completed tuning our new MoSi-based film for ArF application. The films optical properties, chemical durability and ArF laser irradiation durability meet industry requirements; and it is compatible with conventional mask-making process and repair techniques for the KrF HtPSM.

Alternating phase shifted scattering bars for low k1 trench pattering

This article studies the resolution enhancement for sub-120nm isolated trench patterns using alternating phase shifted scattering bars. Through simulation, we found that three sets of 40nm alternating phase shifted scattering bars with separation of 120nm are the best aerial image provider in terms of higher peak intensity, lower side lobe intensity, and smaller full width of half maxima. Simulation results are verified experimentally, and we achieved isolated trench at patterned critical dimension (CD) target of 120nm±10% with manufacturability process window for nominal design CD of 125nm. The patterned CD target 120nm corresponds to k1 factor of 0.33 for exposing wavelength of 248nm, sigma of 0.31, and maximum numerical aperture (NA) of 0.68. Three sets of alternating phase shifted scattering bars showed good mask linearity up to 115nm nominal design CD. We compared isolated trench process condition with dense patterns. Our experimental results show that both isolated and dense patterns can be printed ...

Development of deep-UV MoSi-based embedded phase-shifting mask (EPSM) blanks

Embedded phase-shift mask (EPSM) has an advantage in comparison with several other phase-shifting mask approaches because of its simple structure and fabrication process. We tried to modify MoSi-based EPSM blanks by re-examining the material and by optimizing sputtering condition in order to produce more useful EPSM blanks for Deep UV lithography technology. New MoSi-based EPSM blanks for which Nitrogen gas is used as the reactive sputtering gas has been developed. And it has been confirmed that the New MoSi-based EPSM (MoSi-N) blanks are superior to HOYA previously developed one (MoSi-ON) in chemical durability, manufacturing stability and Dry Etching property.

Intensity imbalance in phase shift masks and correction by multiple exposures

In this paper, the issue of intensity imbalance in an alternating phase shift mask has been studied for hole patterns with pitches 300 nm and below. A method of processing is developed, which would nullify the effects of phase errors that cause focus dependent difference in the sizes of holes belonging to opposite phases. This method uses two exposures with opposite foci. Using this method, the effect of the focus on the difference in the size of holes from opposite phases could be totally eliminated. It also changes the nature of the focus curve, bringing a significant improvement in the depth of focus without affecting exposure latitude and mask error enhancement factor. The method works quite effectively for all the via pitches, however, some constant size difference existed across focus, that is easily correctable by biasing one phase with respect to the other. It was also found that this technique could bring remarkable immunity against the lens aberrations such as defocus and astigmatism.

Key challenges in across-pitch 0.33-k1 trench patterning using hybrid mask

This paper studies the concept of and challenges in patterning trenches using hybrid phase shift mask. Our hybrid mask consists of alternating, chrome-less and 20% attenuated phase shift features on the same reticle. Using this mask, we could pattern across-pitch 120 nm trenches on 0.68-NA, KrF lithography scanner, which is equivalent to K1 of 0.33. However, many challenging issues like unequal best focus for different duty ratios of the same technique and same duty ratio of different techniques, variation in the dose requirements despite aerial image CD matching and the pitch dependent variation in the critical dimension imbalance of the zero and π phased trenches are observed. These issues, that are question marks on the viability of hybrid mask, are presented in this paper. Hybrid mask manufacturing and characterization data is also included to justify that the issues are not because of the mask manufacturing process.

Alignment in chromeless masks

One of the contributions to pattern placement/misalignment may come from the mask making process itself, in chromeless masks. This contribution will be important at 90 nm and smaller nodes. Hence it is necessary to estimate this contribution and find ways to minimize this. In this paper an effort has been made to measure this misalignment accurately. A series of box in box structures for overlay measurement, on KLA and CD SEM, were designed on the reticle. The structures had an outer box of etched chrome and an inner box with 180 degree phase. The edge of the chrome was used as the edge of the outer box. The line printed at the phase intersection was used as the edge of the inner box. Each of these structures were put in with a pre-determined value of X and Y misregistrations. The CD SEM structures were smaller in size but designed the same way as KLA structures. Such structures were put at 4 corners of the die. Overlay measurements were carried out using the optical overlay machine as well as CD SEM. An average misalignment of 11 nm and 1 nm were found in the X and Y directions respectively. When the results from each die corner was analyzed, it was found that the X misalignment had two different distributions. Also, exposure parameters such as focus and partial coherence for best misalignment measurement points were investigated. It is concluded that for obtaining accurate misalignment data, measurements should be conducted at a focus where the two opposite phase edges pattern at similar width. Also, a higher partial coherence is recommended as aberrations such a coma have more profound influence at lower partial coherence and this could contaminate the true misalignment data.

Development of MoSi-based halftone phase-shift blank and mask fabrication for ArF lithography (Photomask Japan 2000 Best Presentation Award)

The halftone phase-shift mask (HtPSM) has been in practical use for i-line and KrF lithography. In ArF lithography, the HtPSM is also considered to be a promising resolution enhancement technique for its simple structure and fabrication process required. We in HOYA have attempted to expand the applicability of our MoSi-based HtPSM blank technology to ArF lithography, helping extend the life of the existing infrastructure for conventional HtPSM fabrication. We have completed tuning our new MoSi-based film for ArF application. The film’s optical properties, chemical durability and ArF laser irradiation durability meet industry requirements; and it is compatible with conventional mask-making processes and repair techniques for the KrF HtPSM.

Development of novel W/Si materials for the single-layered attenuated phase-shifting mask

A novel material system of metal W corpuscles dispersed in silicon dioxides layer (W/Si film) has been developed for the single-layered attenuated phase-shifting mask (SAttPSM) for i-line. The W/Si film has been proved to have a wide flexibility in designing the optical transmittance and the film thickness by changing the sputtering conditions such as the O2 ratio to the sputtering gas (O2 and Ar) flow rate and the RF power supplied. The W/Si shifter film are also found to have some electric conductivity, which again depends on the sputtering conditions, tough chemical durability against both hard acid and basic solutions, and sufficient adhesion to quartz substrate SAttPSM, fabricated with the W/Si film and having the thickness of 1575 angstroms and the transmittance of 6.3%, showed the phase-shifting angle of 177.9 at i-line wavelength. The depth of focus around 0.35 micrometers hole pattern was widened from 0.6 micrometers to 1.4 micrometers .