In electron projection lithography (EPL), a proximity-effect was the most significant problem to critical dimension (CD) control. It was remarkable, especially when beam blur was as large as the minimum pattern size. We have developed proximity-effect correction software for EPL to solve this problem. First, this software made a correction table automatically. In this table, the optimum biases were given for various backward-scattering energy levels and beam blurs regarding all kinds of model patterns. Next, every pattern edge was classified in any of the model patterns. Then, the bias for each edge was determined taking certain proportion between the correction table bias and the previous bias. After that, pattern shape was modified. Those processes were iterated until every change in bias was less than 0.5 nm. Finally, stitching pattern features were added. This software was tested using actual 70-nm rule chip data. Errors in energy level for various kinds of patterns were better than 3 percent and line end shortening was successfully corrected. Data size expansion after the correction was about 10 percent. Processing time was about 10 hours on six PCs cluster system. In conclusion, this software provides enough CD uniformity and pattern fidelity for EPL practically. In addition, this software is applicable to not only EPL but also to EB-direct writing.
In electron-beam projection lithography (EPL), the proximity effect is more complicated than in conventional direct electron-beam writing. The correction of this effect uses pattern-shape modification because dose adjustment is not possible. Moreover, large sub-field transcription produces non-uniform beam blur due to optical aberration and local and global Coulomb effects. This large beam blur requires sophisticated correction depending on pattern features and layout over a very short range as well as pattern density over a backscattering range. In response to these issues, the authors have developed a flexible and precise correction method for the proximity effect under various conditions of beam blur, LSI process, and pattern arrangement. It features (1) multiple pattern-area-density maps, (2) look-up tables classified by pattern features and layout, and (3) a fast calculation algorithm for the iteration process of optimal bias. The developed method (running on four PCs with 2.4-GHz CPUs) attains a processing time of 55 min by using a bias map for 12-GB LSI flat data in 2000 sub-fields. An example of pattern classification by this method showed the usefulness of pattern bias for each individual pattern edge over a short range. It is concluded that the developed correction method is useful not only for proximity effects, including the Coulomb effect, but also for various process effects in mask making with precise CD control.
Electron-beam projection lithography (EPL) using stencil mask is one of the most promising candidates for next- generation lithography. However, the practical use of a stencil mask for fabricating ULSIs needs proximity effect correction (PEC) as well as complementary data to be prepared in order to solve the 'doughnut pattern problem'. We have developed a method for generating complementary data by using a pattern operation tool for design-rule checking and phase-shift-mask generation. The advantages of using these commercial DA tools war high processing speed as a result of maintenance of a hierarchical data structure, high reliability, and flexibility to allow the generation rules to be changed. Since beam blue, which varies according to pattern density in a sub-field, has to be estimated in PEC, sub-field division has to be performed prior to PEC. In the developed method, sub-field division is performed after the complementary-data generation. Sub-field division makes the chip dat almost flatten and enlarge the output data volume. If the sub-field division is performed prior to complementary decomposition, complementary-data generation cannot take advantage of high-speed processing resulting from the maintenance of a hierarchical data structure. We applied this method for metal layer dat of a 14 X 14-mm test chip that includes 300 million figures in flat form. For the complementary-data generation by the developed method CPU time was about 20 minutes using a 500-MHz PC with a 256-Mbyte memory. Maintenance of the hierarchical data structure made the volume of output GDSII data compact. The method can equalize the aperture densities of two complementary mask in a Coulomb-interaction range that is smaller than a sub-field. Although sub-field division using a DRC tool expands the output data volume in GDSII format, sub-field division using EB pattern data generator reduces output data in realistic size.
Electron projection lithography (EPL) is a promising tool for next-generation lithography. However, beam blur due to the Coulomb effect becomes significant and degrades resolution when a high beam current is used to improve throughput. Suppressing the impact of the Coulomb effect is thus necessary to make EPL a practical tool for fabricating ULSI devices. We discuss the influence of the Coulomb effect in EPL based on our experimental results obtained using a Nikon experimental EPL column. To investigate the influence of the Coulomb effect on exposure results, we prepared three kinds of mask with different opening rates to vary the beam current on a wafer over a wide rage without affecting the lens illumination. We found that the Coulomb effect decreased the dose and focus latitude, and that the optimum focus condition varied within a sub-field. Furthermore, we found that the beam blue caused by the Coulomb effect was increased by shrinkage of the rectangular pattern end. Such shrinkage is also a problem in optical lithography, and complex pattern reshaping is necessary to correct it. The shrinkage becomes greater as the beam current increased. We estimated the amount of beam blue caused by the Coulomb effect by fitting our results through an energy deposition simulation. Our overall conclusion s that pattern reshaping and low-Coulomb-effect optics will be necessary to overcome the Coulomb effect.
Electron beam projection lithography (EPL) using stencil masks is one of the most promising techniques in 50-70-nm- node lithography. However, in most real situations, stencil masks have to be divided into two complementary masks due to the 'doughnut pattern' problem as well as mechanical problems. This paper describes our complementary mask-data generation method that uses a pattern operation tool for conventional design-rule checking (DRC) and a phase-shift- mask (PSM) general tool, both of which are made by Mentor Graphics. Layout patterns are divided into pieces with the DRC tool and the pieces are alternately distributed between two layers with the PSM generation tool. The advantages of using these commercial DA tools include a high processing speed based on the maintenance of a hierarchical data structure, high reliability, and flexibility in changing generation rules. We used this method for metal-layer data of a 14 X 14-mm test chip. Although the original data included more than 3000 doughnut patterns, the obtained complementary data had no doughnut patterns. The aperture densities of the two complementary masks were almost equal. Because the CPU time required for data generation was about 20 minutes with a 500-MHz PC having 256-Mbyte memory, we believe that the proposed method is a valuable tool for complementary mask-data generation.
A high-contrast resist, called a contrast boosted resist (CBR), using a water-repellent compound that changes into hydrophilic compounds during aqueous base development has been developed for electron-beam (EB) lithography. TBAB, 1,3,5-tris(bromoacetyl)benzene, was identified as the best water-repellent compound for the CBR. A CBR composed of novolak resin, hexamethoxymethylmelamine, 1,3,5-tris(trichloromethyl)triazine as an efficient acid generator, and TBAB enables the definition of 0.225-micrometer line-and-space patterns with an exposure dose of only 2 (mu) C/cm2 using an EB writing system (acceleration voltage: 50 kV). The polarity change caused by the reaction of the TBAB with the base as well as crosslinking of the novolak resin by the TBAB are assumed to enhance the contrast in the CBR.
A new optical waveguide suitable for high-packing-density OEICs is proposed. The waveguides are embedded in trenches, with large depth/width ratios, in a silicon substrate. The spacing between the waveguides and their pitch were less than 2 micrometers and 4 micrometers , respectively. This structure enables ultra high density optical interconnections in a silicon substrate.
The multiple electron beam scattering effect is studied experimentally in an electron optical column. This effect causes a serious problem on the critical dimension of LSI pattern when the whole area of a wafer is exposed to an electron beam. This paper discusses the quantitative analysis and a method of reducing this effect.
The coherence length in Si is estimated by the measurements of the Nb-Si
bilayer superconducting transition temperature and the Nb-Si-Nb weak link
superconducting critical current. The coherence length is shown to increase
with an increase in the carrier concentration n as a function of n"3 . This
result agreed with the numerical result derived from the Seto-Van Duzer's
theory. The change in pair potential for the Al-Nb proximity system can be
reconstructed by measuring the dependence of differential resistance on incident
energy and the bound state levels using lithographic point-contact on Al-Nb
bilayer.
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