Isao Amemiya

High-performance membrane mask for electron projection lithography

A high-performance membrane mask for electron projection lithography (EPL) systems is proposed. The design and material selection of the mask described here were carefully executed by considering not only the lithographic performance but also various properties. The mask described in this article consists of a 600-nm-thick diamond-like carbon (DLC) scatter on a DLC membrane 30–60 nm thick. The optimum thicknesses are obtained by calculating angular distributions of the transmitted electrons by our in-house Monte Carlo simulator. It is expected to have an electron transmission of up to 80% and a beam contrast of 100% with an appropriate limiting aperture. A 1-mm-sq membrane of thickness of down to 30 nm could be successfully prepared. The high-performance membrane mask can obtain high resolution and high throughput of the EPL systems simultaneously.

Complementary mask pattern split for 8 in. stencil masks in electron projection lithography

We have improved the M-Split complementary mask pattern split program and our electron projection lithography (EPL) data conversion system to achieve a practical data processing time and data volume. The system was designed to rehierarchicalize the data, flattened after the subfield split, by extracting polygons that all have an identical shape as a cell. The M-Split stress check function was improved by using a normalized bending moment as a criterion. A clustered computing system was used to reduce the data processing time. The processing time for a complementary mask pattern split without rehierarchicalizing was reduced to 57 min by using the stress check function and a ten PC cluster system −3–10 times as fast as with commercially available EPL data conversion systems. We successfully fabricated a full-size 8 in. Si stencil mask consisting of 8000 subfields using the data for an actual 70 nm design-rule system on chip device to demonstrate the effectiveness of M-Split. With a higher performance PC clu...

Fabrication of a continuous diamondlike carbon membrane mask for electron projection lithography

Fabrication of 8 in. high-performance continuous diamondlike carbon (DLC) membrane masks for electron projection lithography is described. The mask substrate materials and structures were optimized by evaluating the lithographic performance of the mask. The optimum mask consists of a sandwich structure, consisting of a thicker DLC scatter/a CrNx etching stopper/and a thin DLC support membrane on a bulk silicon wafer. The internal stress of each film component can be controlled by adjusting the film deposition conditions. A DLC film can be easily etched by oxygen gas, and the CrNx etching stopper has a high etching durability. Highly accurate pattern properties can be obtained while also meeting performance requirements. The critical dimension accuracy of a DLC scatterer was less than ±5% with a 280-nm-feature size in a 135×43 mm field. The electron aperture transmittance of a 44-nm-thick DLC membrane, measured by energy and angular distribution analysis for membrane, was 13 times as high as the 150-nm-thi...

Fabrication of complete 8 in. stencil mask for electron projection lithography

We fabricated an 8 in. stencil mask having the complementary pattern of the 70 nm rule system-on-chip device. The 8 in. stencil mask was realized from the development of a mask substrate fabricated by using the sputtering method to form a scattering silicon membrane and an intermediate stopper layer. The intermediate layer material, which functions as an etching stopper, was CrNx. This material has demonstrated high performance in stencil mask fabrication, which is described in detail. The stress in the CrNx could be controlled within ±20 MPa by adjusting the deposition condition. The deposited silicon membrane stress could be easily adjusted in the range of 0–10 MPa. The etching selectivity, when the substrate backside etching was performed, was over 1000 under the low bias power. When the deep etching process was performed using SF6 and CHF3 etching gases for the mask pattern formation, the Si/CrNx etching selectivity was over 100 under the low bias power condition. The mask substrate, which is made up ...

Properties Of SiC Film As X-Ray Mask Membrane

Many properties of LPCVD SiC film as X-ray mask membrane have been investigated in detail. The film has an atomic ratio of 1.0 and negligible impurities, and was found to be damage-free to SR X-rays up to 500 KJ/cm 2 . An integrated transparency of 1.05 μm thick SiC membrane for SR X-rays was measured to be 76%. The interference peak at 633 nm of optical spectrum has given the membrane of around 1.0 μm in thickness the transmittance peak of 70% and increased to more than 80% after an AR coating or planarizations by polishing and etching-back. The attainable transmittance was found to be limited to about 84%, theoretically and experimentally, due to the absorption of the membrane. The peak transmittance of 87% is obtainable by the AR coating on the polished SiC membrane. The internal stress was found to be independent of thicknesses above 0.6 μm and the measured Youngs modulus is 4.5×10 11 Pa irrespective of the thickness and stress. Some extremely polished (0.1 nm Ra) and all the etched-back membranes studied withstood breakage at the pressure as high as the as-deposited ones. The stress uniformity in 30 mm square of the membrane was found to be ± 10 % by measuring five local stresses with a bulge method.

Complementary exposure of 70 nm SoC devices in electron projection lithography

We demonstrate complementary exposure of 70 nm system-on-a-chip (SoC) devices in electron projection lithography using Nikon’s EB stepper, NSR-EB1A, and a high-performance Si stencil mask (4×) fabricated by HOYA. A gate level of the SoC device pattern data called Anaheim was processed for mask fabrication using a 10 PC-clustered hierarchical data processing system in which complementary splitting was executed by the M-Split developed by Selete and ISS. Data processing times and output data volumes of the complementary split and of proximity effect correction were all drastically reduced by using our hierarchical data processing method. We optimized stitching features to compensate for the critical dimension (CD) changes that can occur with stitching errors caused by complementary exposures. The complementary stitching accuracy obtained was better than 20 nm and the CD accuracy was better than 10 nm for 100 nm line and space patterns because of the use of stitching features.

Lithographic performance of diamond-like carbon membrane mask in electron projection lithography

We have studied the lithographic performance of high-performance diamond-like carbon (DLC) membrane masks by demonstrating exposure experiments using Nikon’s electron beam stepper, NSR-EB1A. We estimated the inelastic mean free path of 100keV electrons in a membrane analytically using the measurement results of zero-loss electron transmittance and found it to be about 50nm. We then used this value to find the relationship between membrane thickness and zero-loss electron transmittance. The resolution for high-performance membrane masks is equivalent to that of a stencil mask and was not deteriorated by chromatic aberration due to inelastic electron scattering. Electrons undergoing inelastic scattering did not appear to affect resolution. The nominal exposure dose was proportional to the inverse of zero-loss electron transmittance. We also discussed the optimum membrane thickness in terms of throughput and electron inelastic scattering, focusing on plasmon excitation.

Performance improvement of diamondlike carbon membrane masks for electron projection lithography

This article describes the fabrication of eight-inch continuous membrane masks with a 15‐nm-thick support membrane for electron projection lithography (EPL). In order to develop an extremely thin support membrane with a tensional stress, two techniques were applied; one is a low pressure deposition process to improve the membrane bulk density, and the other is Si addition during the conventional carbon membrane deposition for improving the atomic distance mismatch between substrate and deposited film, and also to address the membrane volume strain cause by the rise in the tensional stress under the low pressure deposition condition. By using Si-additional techniques, an extremely thin membrane with a tensional stress was formed under the conditions of less than 0.5Pa chamber pressure. Long-term membrane stress stability of Si-added extremely thin membranes were particularly improved. It was less than 3MPa in elapsed times of 400h. The zero-loss electron transmittance for the fabricated 15‐nm-thick membran...

Stencil mask technology for electron-beam projection lithography

Some new electron-beam projection lithography techniques have been proposed after cell projection (CP) lithography. To make these lithography techniques practicable, development of the stencil mask is an indispensable key technology. Due to reduction in mask magnification, requirements for the stencil mask becomes sever in comparison with that for CP lithography. For example, the stress of the membrane with mask pattern must be controlled within 10 MPa in terms of the pattern image placement (IP) accuracy, and the membrane thickness must be 2 /spl mu/m or thinner from a viewpoint of the pattern aspect ratio. To solve these issues, we developed a new mask substrate with a CrNx intermediate etching stopper, and found that the CrNx material had an etching selectivity of over 1000 enough for the backside etch process. In addition, the internal stress of the CrNx layer can be easily controlled within /spl plusmn/20 MPa by deposition condition adjustment. Also, by using the CrNx stopper layer, membrane warping during the mask fabrication process did not occur. As a result, mask productivity was greatly improved.

Optical properties of polycrystalline β-SiC membrane for x-ray mask

Optical properties of poly-crystalline (beta) -SiC membrane deposited by LPCVD have been investigated in detail. The SiC films have a high refractive index value of 2.63 and a low extinction coefficient (k) of 0.0065 at wavelength of 633 nm. Optical transmittance increased as the SiC surface roughness decreased. Peak transmittance at 633 nm for 1.0 micrometers -thick polished SiC membrane with extremely smooth surface of 2 nm Rmax is limited to 83% due to the absorption of the membrane. The transmittance of the polished SiC membrane has increased up to 86% due to reduction in k after annealing at 1050 degree(s)C. Al2O3 film was the most suitable for the SiC film among anti-reflection (AR) materials studied. The attained transmittance values at 633 nm for the as-deposited, the polished and the annealed SiC membranes of 1.0 micrometers in thickness with Al2O3 AR films were, 83%, 88% and 91%, respectively.