Polygon Fracture Method Considering Maximum Shot Size for Variable Shaped-beam Mask Writing

Effects of shot peening parameters on gradient microstructure and mechanical properties of TRC AZ31

The DIII-D tokamak began operation in February 1986. At that time, approximately 7 Mb of data was collected for each shot. The average shot size is now about 26 Mb, and over 1 Gb of data has been collected during some operation days. The computer systems were designed to handle a maximum shot size of 25 Mb. In order to meet the increased demands, changes to hardware and software are being made and each experiment reviewed before being added to a shot. The largest increase in data transfer is from small diagnostic DEC VAX systems to the main VAX cluster. Plans in this area include upgrading the VAX which receives data (possibly to a VAX 6310) to have more CPU power and a faster interface to the Network Systems Hyperchannel which transfers data to the VAX. The new machine will be more easily upgraded with additional CPUs, communication devices, and storage devices. Software changes are being incorporated on diagnostic VAXes so that subsets of data or calculated results are included with the shot data file, rather than the often large (6-20 Mb) amount of data collected locally. More careful examination is being given to all experiments added to the tokamak, and only necessary and useful data is being added to the system for permanent storage.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The high-throughput EBM-mask writer, EBM-8000P has been developed for mature node mask market. The EBM-8000P inherits basic architectures from the previous EBM-8000 system, i.e. electron optics with 50kV acceleration voltage, 400A/cm² current density, variable shaped beam (VSB), and also, user interface such as JOB control system, mask handling system, which are equivalent to our latest single electron beam mask writers. The EBM-8000P has two models, the EBM-8000P/H, which is equivalent to the conventional EBM-8000, and the EBM-8000P/M, which aims for high throughput. The mask-writing throughput depends largely on the beam shot size and the current density, based on the generation of mask nodes. The EBM-8000P/M achieves high throughput and enough accuracy for 45-20 node by enlarging the maximum shot size while maintaining a current density of 400A/cm². Therefore, it is possible to achieve throughput that is 1.5 to 2 times faster than the conventional 70A/cm² mask writer (such as EBM-6000) which is for 45-20nm node.

Heating effect was evaluated for EBM-6000 which is operated at high current density of 70A/cm² and acceleration voltage of 50kV. FEP171 as widely used for current productions and lower sensitivity resists are tested. Lower sensitivity resist is one of key items to achieve highly accurate Local critical dimension uniformity (LCDU) because of shot noise reduction. CD variations in experiment are compared with simulated temperature changes induced by heating effect. Then, the ratio, &#916;CD/&#916;T, is found mostly constant for every resist, 0.1 nm/C°. Writing conditions are estimated to meet CDU spec of hp45 generation for a worst case pattern, i.e. 100% density pattern. For FEP171, the maximum shot size of 0.85 &#956;m shot size at 2pass writing mode is sufficient. It should be reduced to 0.5 &#956;m at 2pass writing mode for every lower sensitivity resist. When 4pass writing mode is used, the maximum shot size of 0.85 &#956;m is available. Writing conditions and writing time for realistic patterns are also discussed.

Electron beam (EB) direct writing systems have often been used for fabricating sub-half-micron advanced devices because EB direct writing is the most practical method for making the required patterns. Recently, the cell projection (CP) method has become indispensable for increasing the writing throughput in the EB direct writing system. However, it is considered that resist heating may be seriously aggravated below the quarter-micron level when the CP method is used, because the total deposited energy, which is irradiated by one CP EB shot, is almost the same as that irradiated by one variably shaped (VS) EB maximum size shot. Resist heating in the case of the CP method is calculated by a finite element method using the ANSYS (Ver. 5.0A: ANSYS, Inc.) program. In particular, thermal diffusion calculation is mainly carried out under the conditions of 50 kV acceleration voltage and 10 A/cm2 current density for practical application to advanced device fabrication. The calculated results suggest that resist heating in the CP method is mainly caused by the horizontal thermal flux between plural EB shots within the area of one CP shot, by the same mechanism as proximity resist heating under the VS method. Therefore, CP EB writing causes horizontal-mode resist heating. In particular, when a low current density is used, this resist heating mode arises significantly. However, CP writing with high acceleration voltage causes a reduction in the rise of the resist temperature, which causes resist heating. When the EB irradiation time is longer than 1.0 µ s under practical EB writing conditions, the resist temperature increases proportionally to the decrease of writing pattern size in the case of the CP writing with a maximum shot size of 5.0×5.0 µ m. It is also shown that the larger the beam blur of an incident beam, the more serious is the resist heating. When a highly sensitive resist (10 µ C/cm2) is used under these practical conditions, however, resist heating in the CP method is prevented without writing throughput degradation regardless of the CP maximum shot size, because the resist temperature does not rise above the thermal denaturation temperature of standard EB resists. Accordingly, the maximum CP shot size, which affects the writing throughput, is determined by the proximity effect and the Coulomb interaction for fine pattern fabrication.

Electron-beam writer characterization is key to enable predictable product performance in a photomask shop. This is traditionally done by writing test patterns with one distinct tool on one blank. Within this article, we introduce a method that reduces uncertainty caused by variation of blanks and process parameters, by using multiple, subsequent electronbeam exposure steps with different same-of-a-kind tools. The method is demonstrated for the disentanglement of two of the most fundamental parameters in an e-beam tool, current density and blanker latency, which together determine the actual dose. Additional accuracy can be achieved by probing the same tool parameter with different methods, which is shown by comparing Critical Dimension Scanning Electron Microscopy of line-space patterns below the maximum shot size with Thin Film Optical Scatterometry of comparatively large pads. The multiple exposure method needs a proper correction of systematic effects caused by contact of exposed areas with air during mask transfer from one writer to another, which are presented and discussed.

An objective lens system for e-beam cell projection lithography

We newly developed the mask bias method in electron beam (EB) cell projection lithography to improve the resolution and to increase the throughput. In this method, the open slits of EB mask are shrunk to reduce the ratio of open area in EB mask. This shrinkage decreases the Coulomb interaction effect and the proximity effect. This results that 0.14 micrometer L/S pattern can be resolved even at the maximum shot size (25 micrometer 2 ) and so the writing time of 0.14 micrometer L/S pattern can be reduced by half.