Henry Thomas Pearce-Percy

Dynamic corrections in MEBES 4500

Some systematic errors of the mebes raster scan lithography system are examined and how significant accuracy improvements can be achieved is demonstrated. The accuracy improvements result from error compensation hardware and software applying corrections that are either a function of time (write scan position) or of position on the substrate. Error analysis shows the following correctable errors to be among the largest error sources in the mebes iv: electronic noise, stage z runout, deflection alignment drift, mask flatness, and clamping distortion, and scan nonlinearity. These errors contribute to placement/overlay accuracy and to butting accuracy. The dynamic corrections implemented are automatic write scan correction, which reduces deflection alignment errors, scan linearity measurement and correction, grid correction, and height detection and correction, which reduce cassette height and mask flatness errors. With these corrections implemented, system performance improves dramatically.

Extension of graybeam writing for the 130-nm technology node

This paper describes improvements in column design and writing strategy that, together, enable mask production for the 130 nm technology node. The MEBESR 5500 system employs a new high-dose electron gun and column design. We summarize experiments relating lithographic quality to increased dose and the effects of spot size and input address on lithography. These experiments are performed with ZEP 7000 resist and dry etch. A new graybeam writing strategy, Multipass Gray-II (MPG- II), is described in detail. This strategy creates eight dosed gray levels and provides increased writing throughput (up to 8X, compared to single-pass printing) without loss of lithographic quality. Significantly, critical dimension (CD) uniformity, butting, and other important specifications are improved with MPG-II. Lithographic results and throughput data are reviewed. A consequence of the improvement in CD control and throughput is greater productivity for 180 nm devices.

Optimization of field-emission columns for next-generation MEBES® systems

To support device generations below 250 nm mask writing systems must improve productivity for smaller design address grids and simultaneously provide higher dose to support high resolution processes. Combining multipass writing techniques with higher pixel rate provides improved productivity and increased dose; however, many high resolution processes require even higher dose delivery. The optimization of field-emission systems for maximum effective brightness has been discussed previously, but the inclusion of electron-electron (e-e) interactions in the optimization process is a significant complication. There is little discussion in the general literature, except for Brodie and Meisburger [A. D. Brodie and W. D. Meisburger, Microelectron. Eng. 17, 399 (1992)] about the impact of e-e interactions on the design of columns for electron-beam lithography systems. This article discusses several formulations of the problem and the solutions. Closed-form solutions for particular special cases (spherical- and chr...

Evaluation of a high-dose extended multipass gray writing system for 130-nm pattern generation

Recent developments in electron-beam (e-beam) systems and mask-writing strategies facilitate pattern generation for the 130-nm IC generation. The MEBESR 5500 pattern generation system incorporates a high-dose electron optical system and a high-throughput writing strategy, Multipass Gray-II (MPG-II). We evaluate the effectiveness of these innovations by three criteria: improved resolution, improved critical dimension (CD) control, and increased throughput. The conclusions of this paper are based on results from extensive modeling, test masks, and factory acceptance masks. Mask resist choice and processing have been optimized for the MEBES 5500 system. A consequence of these improvements is greater productivity for 150 nm devices and early development of 130 nm devices. The MEBES 5500 system uses a high-dose gun and electron optical system. The maximum current density that can be delivered to the mask is 800 A/cm2, twice the value of previous MEBES systems. Without loss of throughput, it is possible to increase the dose deposited in the resist, while using smaller e-beam sizes. These capabilities are exploited to improve printing of submicrometer features, including 200 nm-scale optical proximity correction (OPC) patterns. At small data addresses (<17.1 nm), the MPG-II writing strategy provides twice the throughput of the existing multipass gray (MPG) strategy with the same instrument, and 16X the throughput of traditional single-pass printing (SPP) with the MEBES 4500 system. The fundamentals of the MPG-II strategy are described, as well as throughput and lithographic results.

Advanced electron-beam pattern generation technology for 180-nm masks

Optical lithography will be the dominant technique used for 180 nm generation production devices. With a reduced feature size on the wafer, 4X optical reduction, optical proximity correction (OPC), and phase shift lithography techniques, mask-related errors become even more critical to wafer yield. In addition, small feature sizes and lithography enhancement techniques require finer edge resolution. Clearly, new patten generation tools are needed for this generation of maskmaking requirements. Multipass gray (MPG) writing strategy was introduced with the MEBESR 4500S. The ability to deliver a 4X improvement in dose while improving throughput is a significant advantage over previous MEBES systems. Since MPG is used in conjunction with offset scan voting, reduction in butting of over 50% has been demonstrated with MPG. Higher doses are now possible with use of a multipass writing strategy and a brighter source. As a result, resists with higher contrast and process robustness can be used. A significant improvement in uniformity is noted with the new process, an essential step needed in meeting 180 nm requirements. Dry etch is essential to meet these new requirements and with sufficient process margin to be manufacturable. This paper describes the key electron-beam pattern generation technology necessary to meet the requirement of 180 nm masks, including a high dose field- emission gun and column capable of delivering 800 A/cm2; complete dynamic beam correction; a digital stage servo to provide stable, reproducible stage control under high acceleration conditions; a high speed data path to support 320 MHz beam blanking and a 10 nm data address. This paper also examines the improvements made to the MEBES platform and documents the resulting improvements and compares these results to the requirements for 180 nm masks.

Raster Shaped Beam Pattern Generation for 70 nm Photomask Production

Photomask complexity is rapidly increasing as feature sizes are scaled down and as optical proximity correction (OPC) methods become widespread. The growing data content of critical mask levels requires that pattern generator solutions be adapted to maintain productivity. Raster shaped beam (RSB) technology has been developed to enable the production of 70 nm photomasks and the development of 50 nm masks. RSB is built on and extends the capability of the 50 kV MEBES platform. The beam is shaped as it is scanned, printing the mask pattern on a calibrated flash grid. Complex OPC patterns are efficiently tiled by combining a relatively small maximum shape size with a high flash rate of 100 MHz. The maximum shape size and the current density can be adjusted to match a wide set of mask applications. Proximity effects are corrected with dose modulation using a real-time computation.

Lithography and CD performance of advanced MEBES mask pattern generators

As optical lithography is extended to the 130 nm generation and beyond, demanding requirements are placed on mask pattern generators to produce quartz substrate masks. This paper reports on the lithography and critical dimension (CD) performance of the MEBES 5500 mask pattern generator. Compared to previous MEBES tools, this system employs a new high-dose electron gun and column design. We summarize experiments relating lithographic quality to increased dose and the effects of spot size on lithography. Methods to reduce beam-induced pattern placement errors are reviewed. A new graybeam writing strategy, Multipass Gray-II, is described in detail. This strategy creates eight dosed gray levels and provides increased writing throughput (up to 8X compared to single-pass printing) without loss of lithographic quality. These experiments are performed with ZEP 7000 resist and dry etch process; improvements in CD control have been achieved by optimizing the process. A consequence of the improvement in CD control and throughput is improved productivity in generating 180 nm devices.

Electron-optical optimization for Gaussian, high-current, high-dose columns

This article demonstrates the electron-optical optimization of a high-current, high-dose column operating at 10 keV. The goal is to increase the available dose to the resist, which requires increasing the current density to more than 800 A/cm2. Our calculations use the MEBS Ltd. BOERSCH program. We model the complete column as a set of thin lenses, separated by field-free drift spaces. Monte Carlo simulation propagates discrete bunches of electrons through the column, taking into account the mutual repulsion between pairs of electrons. Gaussian spot size and current density in the column were calculated for three beam currents: 314, 75, and 35 nA. The results show that to achieve a higher current density, it is necessary to change the electron gun and the column. Specifically, a low aberration gun and a significantly shorter column are required. At 10 keV, the column performance at high beam currents (∼300 nA) is almost entirely dominated by electron–electron interactions. Major improvements in gun perfor...