Charles A. Sauer

180-nm mask fabrication process using ZEP 7000, multipass gray, GHOST, and dry etch for MEBES 5000

Advanced reticle specifications for resolution, critical dimension (CD) control and CD linearity of 180-nm generation devices require large-scale improvements to maskmaking processes. The approximately 200 nm of bias required with widely used wet etch processes will not meet these specifications. A solution to the high bias requirement of wet etch processing is to implement a plasma or dry etch process. Plasma etch processing has been shown to have little or no undercutting. However, some of the standard resists used with electron beam (e-beam) exposure of photomasks have poor dry etch characteristics. ZEP 7000 is an e-beam resist that has good dry etch resistance while exhibiting superior lithographic quality. In this paper, processes using ZEP 7000 resist and inductively coupled plasma (ICP) etching are described. The combination of these operations can result in zero bias or near zero bias process with e-beam exposure of photomasks. While the required dose for ZEP 7000 is higher than that of PBS, the higher beam current capability of newer e-beam systems, together with multipass writing strategies, enables the use of these slower resists without throughput penalty. Optimization of the development process was done using a two-component solvent developer. A puddle process was investigated for optimizing sensitivity, edge slope, resist loss, mean-to-target control, and CD uniformity. Dry etching with ICP has been shown to etch chromium films with good selectivity to the resist, give a highly anisotropic etch, and, most significantly, show insensitivity to loading effects. The net result of this effort is the development of a process that gives excellent CD control when meeting MEBES 5000 system requirements for 180-nm maskmaking. Data on resolution, CD control, and defects are presented using this process.

Electron-beam lithography simulation for maskmaking: IV. Effect of resist contrast on isofocal dose

There is a certain exposure dose at which variations in electron-beam (e-beam) spot size have virtually no impact on the resulting feature width. In optical lithography, this phenomenon is well characterized and is called the isofocal point. The exposure that produces a flat response of linewidth versus spot size is called the isofocal dose, and the resulting feature width is called the isofocal critical dimension (CD). It is intuitive that operating in the flat portion of the curve will have advantages from a process latitude perspective. Also, it is significant to note that the isofocal CD occurs at widths that are overexposed with respect to the target spacewidth. Typically, this difference is resolved by sizing data so that the dose to size approaches the amount needed to reach the isofocal point. As linewidths continue to shrink, sizing will become a point of contention, because resolution can be limited by the magnitude of data bias. In this paper, we examine the effect of resist contrast on the difference between dose to size and dose to isofocal. ZEP 7000, a resist from Nippon Zeon, is examined and compared to resists with other different dissolution rates. Included in the resist selection is a high gamma resist that is modeled on chemically amplified resists (CARs).

Lithographic performance results for a new 50-kV electron-beam mask writer

Current pattern generation tool designs will be inadequate to meet the advanced requirements for next-generation masks, particularly at the 100 nm node. Etec Systems, Inc. has developed a complete raster-based patterning solution to provide improved resolution, critical dimension (CD) uniformity, positional accuracy, and throughput. This solution meets the challenges of the 130-nm device generation with extendibility to at least 100 nm devices. Our complete patterning solution includes an electron-beam (e-beam) pattern generation system and a new 50 kV process. The e-beam system includes a column with 50 kV accelerating voltage and a new graybeam writing technique. To accomplish this technique, a pulse-width modulated blanking system, per-pixel deflection, retrograde scanning, and multiphase and multipass writing are used. This combination of features results in markedly improved lithographic performance and enables the use of conventional high-contrast resists for faster process implementation. Additional significant innovations of this pattern generation system include a novel stage design, an integrated automated material handling system (AMHS), on-board diagnostics, and improved environmental/thermal management. We believe this comprehensive patterning solution offers the best combination of benefits to the user in terms of versatility and extendibility.

Electron-beam lithography simulation for mask making: II. Comparison of the lithographic performance of PBS and EBR 900-M1

Development of a maskmaking process using a new resist consists of a number of steps that take a great deal of time, effort, and resources before a finished process can be qualified. It would be useful early in the development cycle to model the expected performance of a new resist material prior to determining its suitability. Extracting the modeling parameters and predicting their influence on lithographic performance can also guide the subsequent development work that needs to be done to complete a manufacturing process. This paper compares two different resists and models the expected lithographic performance as a function of its development rate parameters. Resist dissolution rate measurements were done using two methods -- an in situ development rate monitor (DRM) and the classical mechanical (Dektak) method. ProDRM was used to extract the development rate parameters from the data. ProBEAM/3D was used to simulate electron-beam (e-beam) lithography using a 2D model. This paper explores the relationship between dose, develop time, spot size, and lithographic parameters such as critical dimension control and wall angle. Two resists, EBR900-M1 and PBS, are examined and compared using MEBESR 4500 and MEBES 4500S exposure parameters.

Multipass gray printing for the new MEBES 4500S mask lithography system

Etec Systems, Inc. has developed a new e-beam mask lithography system, the MEBES 4500S, featuring a higher productivity writing strategy called multipass gray and a number of mechanical and electrical improvements. This new system, based on the proven technologies introduced in the MEBES 4500 system, provides improved throughput and accuracy. The MEBES 4500S system with multipass gray supports smaller mask design addresses needed for high resolution masks, while providing higher dose for high contrast processes with low sensitivity and improved CD linearity. Improved print performance is achieved by the introduction of several system design changes that work in conjunction with the multipass gray writing mode. These changes include improved column deflection system temperature control, enhanced TFE current control, improved work chamber thermal management, and improved stage drive vibration damping. Details of these features are presented along with first performance data for the new system.

Design considerations for an electron-beam pattern generator for the 130-nm generation of masks

The critical dimension (CD) requirements of the SIA roadmap require continued improvements in pattern generation (PG) tool technology. This includes electron-beam (e-beam) delivery, resist and process, writing strategy, and overall system throughput. In this paper, we discuss these interrelated topics and evaluate their impacts on the CD control, linearity, and uniformity performance of PG tools. By means of Monte Carlo simulations and experimental comparisons, we evaluate various parameters of e-beam delivery systems, including beam energy, spot size, writing strategy, and throughput. We also perform a thorough evaluation of mask heating effects due to e-beam exposure. Finally, we perform comparative studies of various resist and process combinations. The totality of our investigations allows us to conclude that a 50 kV raster scan e-beam system, using a high- contrast, high-sensitivity resist, such as SPR 700, with GHOST proximity effect correction (PEC), can meet the CD control, linearity, and uniformity requirements of the 130 nm technology node.

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.

Evaluation of the MEBES 4500 reticle writer to commercial requirements of 250-nm design rule IC devices

The design rule requirements and error budget allocation for maskmaking have made the mask a critical component in the fabrication of 250 nm design rule IC devices. The MEBES 4500 raster-scan reticle writer was designed to meet the mask requirements for pilot production of this generation of devices. In this paper, we will review the IC device and user requirements that drove the design criteria of the MEBES 4500 system. The architecture of the MEBES 4500 system is described and compared to these design criteria. MEBES 4500 perfonnance results during development, manufacture, and installation are also compared to the commercial requirements of 250 nm design rule ICs.

System architecture choices for an advanced mask writer (100 to 130 nm)

System architecture choices for an advanced mask writer (100 - 130 nm) have been evaluated. To compare and contrast variably shaped beam vector architecture with raster-based architecture, factors such as beam accelerating voltage and its effects on lithographic performance and system throughput for complex patterns have been studied. The results indicate that while both architectures have strengths and weaknesses, in the final analysis, raster-based systems offer the best combination of benefits to the user in terms of versatility and overall system throughput. Furthermore, other system requirements needed to support the challenges of the next generation mask writers are discussed. An architecture that includes a 50 kV raster graybeam (RGB), based architecture, a new writing strategy, a new stage system, an advanced environmental/thermal control management system, an automated material handling system, and a new resist and process is proposed.

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.