Fumiaki Shigemitsu

Optimization of optical properties for single-layer halftone masks

An algorithm necessary to decide the optimum optical properties of a single-layer halftone (HT) mask has been established. This paper reveals the relations between the refractive index n and the extinction coefficient k, and thickness d, and describes how to select optimum films among various materials. It has been found that SiNx is a good material for a single-layer HT mask for I-line (365 nm) and KrF (248 nm). The lithographic performance of an I-line SiNx HT mask for grouped line and space (L&S) patterns under annular illumination has also been demonstrated.

Highly Sensitized Electron-Beam Resist By Means Of A Quenching Process

It was found that the sensitivity of poly(2,2,2-trifluoroethyl-a-chloroacrylate) (EBR-9) is greatly enhanced to around 0.1μC/ci when EBR-9 is quenched at 160°C/sec after baking. This sensitivity is about 27 times higher than that obtained by cooling at 65t/min in an atmosphere of still air. This result indicates that the sensitivity of an electron-beam resist depends on the cooling rate. In particular, a change in the cooling rate within the glass-transition region of EBR-9 leads to a drastic change in sensitivity. One method of thermal analysis, differential scanning calorimetry(DSC), made it clear that the slower the resist is cooled through the glass-transition region, the more enthalpy relaxation is produced. Furthermore, it was proved that a resist with much reduced enthalpy indicates a lower solubility rate, and that the annealing method was valid to estimate the reduced enthalpy using DSC. It is concluded that the quenched resist becomes more sensitive as a result of the enhanced solubility because of little enthalpy relaxation.

Performance Evaluation of Representative Figure Method for Proximity Effect Correction

The representative figure method has been proposed in previous papers to reduce the processing time for proximity effect correction. The Phantom, which is an application of the representative figure method to Ghost, assigns only one representative rectangle in each small area instead of the inverted original patterns, and the rectangles are exposed with a defocused beam. From the results of numerical calculation and experiment, there is little difference in correction effect between Phantom and Ghost, even if the small area size is nearly equal to the electron backscattering range. So, the small area size can be set as large as the backscattering range. It is shown that the same correction accuracy as Ghost can be obtained by Phantom. The correction exposure time can be reduced to 1/25~1/500 that of Ghost by Phantom.

Smart way to determine and guarantee mask specifications: tradeoff between cost and quality

Mask set price is soaring along with technology node advancement. One reason is that the number of masks per set is increasing with the geometry scaling. Another reason is that low k1 lithography with highly complex OPCs tightens dimensional mask specifications as to result in higher mask-making tool costs and lower production yield. Under these circumstances, tool cost reduction and production yield improvement are immensely required to reduce mask cost. Expensive quality-assured tools are indispensable to achieve the desired accuracy. Then, higher throughput and technical applicability of the same tool over multiple generations are definitely needed to improve total tool CoO. Meanwhile, not only such conventional basic approaches as improving field level and process performance but optimizing mask specifications efficiently is emerging as a key factor for keeping mask production yield high. Usually mask specifications are determined by the error budget allocated from the total lithography budget. In order to cope with the tighter specifications some sensible approaches have recently been proposed. Mask DFM is receiving particular attention as a new method being strongly linked to lithography and wafer fabrication technologies (1)(2)(3)(4). In this presentation, logical way to define the main mask specifications such as CD, defect and image placement accuracy is shown and sensible ways to sustain them are referred.

Photomask repeater strategy for high quality and low cost reticle fabrication

The severe mask specification makes mask cost increase drastically. Especially, the increase in the mask cost deals ASIC businesses a fatal blow due to its small chip volume per product. Pattern writing cost has always occupied the main part of the prime mask cost and the emphasis of this is still increasing. This paper reports on a Photomask Repeater strategy to be a solution for reducing mask cost in pattern writing, comparing with conventional EB system.

Mask cleaner innovation

A new clustered configurational photomask cleaning system has been developed. Accepting the clustered configuration, we can be free from the heavy tank photomask cleaner which has a large footprint and has no flexibility for designing a cleaning recipe. Provided we need to introduce a new cleaning process unit, we can substitute the unit by disassembling an old one in the system. We can always keep our photomask cleaner up-to date with the system, and, we can obtain most effective cleaning result by the least efforts and the smallest expense. Using this cleaning system with an optimized cleaning recipe, we have achieved the cleaning result of less than one particle, greater than 0.2 micrometers , detected by KLA Starlight.