Masaki Yamabe

Electron beams in individual column cells of multicolumn cell system

In the Mask D2I project at ASET, the authors designed a novel electron beam exposure system having the concepts of multicolumn cell (MCC), character projection, and variable shaped beam to improve the throughput of electron beam exposure systems. They presented the electron optical structure of an individual column cell in the MCC and have shown shaped beam performances in the column cell. They evaluated the impacts on beam position in one column cell caused by deflections of major and minor deflectors in other column cell, which were less than 2.5nm for both averaged and transitional impacts between +full and −full deflections. They will improve the evaluation accuracy to analyze the origin of the impacts and decrease the impacts from other column cell.

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...

Stress stabilization of β‐tantalum and its crystal structure

We studied the relationship between Ta crystal structures and the stress stability of Ta under heating. The stress in Ta which was sputter deposited on SiC was unstable and changed more than 2×109 dyn/cm2 to the compressive side during heating at 200 °C for 30 min in air. In contrast, the stress in Ta which was sputter deposited on SiC whose surface was modified by Ar sputtering was very stable, and the stress change was less than 1.5×108 dyn/cm2 even after 6 h of heating at 200 °C. The x‐ray diffraction patterns of the Ta revealed that stable Ta was strongly (002) oriented β‐Ta, and that unstable Ta was randomly oriented β‐Ta with some α‐Ta. We found that amorphizing the SiC surface or inserting a thin amorphous interlayer enhanced growth of strongly (002) oriented β‐Ta.

Precise stress control of Ta absorber using low stress alumina etching mask for X-ray mask fabrication

In the stress control of an X-ray mask absorber, the repeatability of control and stability are important. We found that the change in the stress in a Ta film resulting from annealing depends on the oxygen concentration in the film; the magnitude of the stress change is determined by the annealing temperature and time. Using this characteristic of Ta film, we have successfully controlled the stress in the Ta absorber to less than 5 MPa with good repeatability. In our mask fabrication process, Al 2 O 3 film was used as an etching mask. We found that the Al 2 O 3 film prevented the Ta absorber stress from changing in high-temperature atmospheres because the Al 2 O 3 film prevented oxygen diffusion into the Ta film. Utilizing Al 2 O 3 films, we succeeded in preventing changes in Ta absorber stress in the thermal processes after Ta stress control, such as frame bonding and resist baking. Consequently, we were able to precisely control the Ta absorber stress in X-ray masks with good repeatability and stability in a realistic X-ray mask fabrication process.

Multi column cell (MCC) e-beam exposure system for mask writing

Association of Super-Advanced Electronics Technologies (ASET) Mask Design, Drawing, and Inspection Technology Research Department (Mask D2I) started a 4-year development program for the total optimization of mask design, drawing, and inspection technologies to reduce photomask manufacturing costs in 2006. At the Mask Writing Equipment Technology Research Laboratory, we are developing an e-beam exposure system introducing concepts of MCC (multi column cell), CP (character projection), and VSB (variable shaped beam), which has several times higher throughput than currently commercially available e-beam writing systems.

Evaluation of Throughput Improvement by MCC and CP in Multicolumn E-beam Exposure System

In the Mask D2I project at ASET, the authors evaluated an e-beam multi column cell exposure system with character projection to expose photomask patterns of hp65nm and hp45nm devices. They prepared more than 2,000 characters in a deflection area of a character projection mask extracted from the hp65nm pattern. The character projection in the multi column cell system could expose patterns equivalent to those by the conventional variable shaped beams. In a typical pattern layout of photomasks for hp45nm devices, the four column cell system required an exposure time of about 1/3 of the time required by a single column system. The character projection can reduce the exposure time corresponding to the reduction of shot counts.

Optimization of MDP, mask writing, and mask inspection for mask manufacturing cost reduction

As the feature sizes of LSI become smaller, the increase in mask manufacturing time (TAT) and cost is becoming critical and posing challenges to the mask industry and device manufacturers. In May 2006, ASET Mask D2I launched a 4-year program for the reduction in mask manufacturing TAT and cost, and the program was completed in March 2010. The focus of the program was on the design and implementation of a synergetic strategy involving concurrent optimization of MDP, mask writing, and mask inspection. The strategy was based upon four key elements: a) common data format, b) pattern prioritization based on design intent, c) an improved approach in the use of repeating patterns, and d) parallel processing. In the program, various software and hardware tools were developed to realize the concurrent optimization. After evaluating the effectiveness of each item, we estimated the reduction in mask manufacturing TAT and cost by the application of results obtained from the Mask D2I programs. We found that mask manufacturing TAT and cost can be reduced to 50% (or less) and to about 60% respectively.

FIB mask repair technology for electron projection lithography

We have studied stencil mask repair technology with focused ion beam and developed an advanced mask repair tool for electron projection lithography. There were some challenges in the stencil mask repair, which were mainly due to its 3-dimensional structure with aspect ratio more than 10. In order to solve them, we developed some key technologies with focused ion beam (FIB). The transmitted FIB detection technique is a reliable imaging method for a 3-dimensional stencil mask. This technique makes it easy to observe deep patterns of the stencil mask and to detect the process endpoint. High-aspect processing can be achieved using gas-assisted etching (GAE) for a stencil mask. GAE enables us to repair mask patterns with aspect ratio more than 50 and very steep sidewall angle within 90±1°precisely. Edge placement accuracy of the developed tool is about 14nm by manual operation. This tool is capable to achieve less than 10nm by advanced software. It was found that FIB technology had capability to satisfy required specifications for EPL mask repair.

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.

PATTERN ETCHING OF TA X-RAY MASK ABSORBER ON SIC MEMBRANE BY INDUCTIVELY COUPLED PLASMA

Patterning of an X-ray mask absorber after Si back-etching is desirable from the viewpoint of the pattern placement accuracy. We investigated Ta X-ray absorber etching on an SiC membrane equipped on a mask frame using a low-stress CrN hard mask and an ICP etcher with a He cooling system. In this system, the membrane temperature and the self-bias voltage could be controlled. A 40-nm-thick CrN film was etched using a 200-nm-thick resist and Cl2 and O2 gases with a selectivity of 0.72 and a vertical sidewall. A 400-nm-thick Ta film was etched using Cl2 gas at an electrode temperature of -10°C and a low gas pressure of 0.1 Pa. A high selectivity of Ta to CrN, 42, was obtained, and lines and spaces patterns below 0.1 µm with vertical sidewalls could be fabricated.