Advanced Mask Facility Research Articles

Chrome on glass mask writing at 75 kV with the IBM EL4+electron-beam system

The IBM EL4+mask writer, located in the Advanced Mask Facility in Burlington, Vermont has recently been used to investigate chrome on glass lithography at 75 kV with a current density of 60 A/cm2. One of the main concerns with doing lithography at high beam voltages on a quartz substrate is the effect of beam heating on the resist. Using ZEP7000 resist on both quartz glass and silicon wafer substrates, we have characterized image size control from 0.1 to 3 μm for a large range of pattern geometries.

EL5: One tool for advanced x-ray and chrome on glass mask making

The state-of-the-art for mask making continues to be driven by 1× x-ray masks. The IBM EL4+ e-beam mask writer at the Advanced Mask Facility in Burlington, Vermont, was originally designed for 0.35 μm ground rules (GRs) direct write at 50 kV, but delivered at 75 kV operation to achieve 0.25 μm GR performance for 1× mask making. Over the next 2 years, with optimization and improvements in each of the subsystems, its performance was enhanced beyond the 0.18 μm GR requirements. It is clear, however, that for 0.13 and 0.1 μm GR mask manufacturing, a new tool is required. It has also become apparent that because of the very high development and tool build costs, and small number of required x-ray mask makers, the same technology must be applicable for chrome on glass (COG) mask making. Based on the experience with EL4+, IBM is designing an EL5 tool which will provide the 0.13/0.1 μm GR performance for 1×, and easily convert to 4× COG exposure for 9 in. glass as well as 300 mm wafer direct write operation. As with previous IBM EL series e-beam systems, it is anticipated that EL5 performance will be extendable beyond 0.1 μm GR.

Parallel and hierarchical postprocessing for variable spot electron beam lithography

Chip designs, for both logic and memory, are becoming increasingly large and complex. It is not unusual for the postprocessing of these designs to be one of the biggest bottlenecks in the mask order processing pipeline. To address this bottleneck a parallel postprocessing system was developed. It was named P5 for practically perfect parallel postprocessor. This system is in use for production processing of designs to be written on IBM’s EL4+ electron beam lithography tool located in the Advanced Mask Facility in Essex Junction, VT. In addition the system is being enhanced with the addition of hierarchical data handling capability. Early results of this enhancement work are presented in this article.

Performance enhancements on IBM’s EL-4 electron-beam lithography system

IBM’s latest electron-beam mask maker, EL-4, is installed at IBM’s Advanced Mask Facility in Essex Junction, Vermont. The EL-4 system is a 75 kV variable-shaped-beam lithography system designed to produce 1X or NX masks for 0.25 μm lithography ground rules, extendable to 0.13 μm. It is currently producing NIST-style x-ray membrane masks with pattern sizes up to 50×50 mm2. After a brief description of the EL-4 tool and its operating features, the article describes the recently implemented new writing subsystem, provides an overview of the tool software structure, and presents measurement data from masks recently produced on the tool.

Performance of the EL-3+ maskmaker

IBM’s new e-beam maskmaker, designated EL-3+, is installed and operating in the IBM Advanced Mask Facility in Burlington, Vermont. This tool represents a significant extension in the state of the art in the manufacture of masks, particularly in the areas of minimum feature size and overlay. The tool routinely operates with 0.35 μm ground rules at 70 nm (3σ) registration to grid. The tool has demonstrated the ability to work at 0.25 μm ground rules as well. The primary mission of the tool is the production of 1X x-ray masks. Some of the tool parameters include a 50 keV electron beam operating at a current density of 20 A/cm2. The system uses a shaped spot with a maximum size of 2×2 μm2. Exposures are made over areas with dimensions of up to 80 by 80 mm with a 2.1 mm field size. Deflection within a field is done through a combination of magnetic and electric deflection in a variable axis immersion lens (VAIL) configuration. During exposure the pattern data is stored on-line in a 1 G-byte buffer. The pattern buffers are loaded directly from a host IBM 4381. The system automatically corrects for any field distortions to a level of 6.25 nm using a calibrated reference grid.