Laser mask pattern generators (MPGs) write the majority today’s masks. They are the tools of choice for the application spaces of legacy-node chip production and second-level writing for advanced masks. Increasingly, they are also being used to print masks with large data volumes resulting from optical proximity corrections. To improve throughput and print performance for these masks, a software-based data path has been implemented on the ALTA® multi-beam MPG platform. Running on a scalable multicore architecture, the new data path provides more than an order of magnitude increase in processing speed for data preparation and rasterization compared to the existing hardware solution. The programs performing the data preparation and rasterization, along with the general-purpose computers on which they run, are referred to as the raster engine (RE). The RE accepts MEBES®, OASIS®, and GDSIITM formats, optimizes the data on a 0.1-nm grid, and applies both system and user-defined critical dimension (CD) corrections prior to printing. During mask printing, the prepared data are rasterized out to a 0.5-nm writing grid while applying additional corrections required by the ALTA architecture. A beam engine (BE) converts the rasterized data to radio frequency (RF) signals that drive the 32-channel acousto-optical modulator. The edge-placement resolution in the scan direction is controlled using timing rather than grey level interpolation of a fixed pixel grid. The stripe-axis resolution is achieved using fixed beam spacing with 80 gray intensity levels. Significant improvements are observed in the scan-axis print performance and the consistency of corner rounding. This paper also examines the effects of the number of passes used in multi-pass printing on the tradeoff between print quality and mask write times. Finally, the capability to align to the fiducials defined by the SEMI P48 standard for EUV masks has been added to the ALTA system.
In this paper we present a 45-degree mirror created for optical applications utilizing CMOS high-volume manufacturing
processes with a gray-scale lithography technique. The process that is presented here was done by creating a 3D pattern
in the photoresist and then by transferring the photoresist profile to the Si/SiO2 substrate by specific dry etch processing.
We discuss the optimization of the half-tone pattern to achieve the desired resist profile. We achieved smooth sidewalls
with various sidewall angles and show that different 3D angles and profiles can be achieved and processed
simultaneously.
Emulation of phase-shift mask (PSM) imaging techniques through the use of acousto-optic interaction, rather than fixed photomasks, is demonstrated. The phasefront and irradiance profile of a uniform illumination beam are manipulated acousto-optically in two dimensions by controlling the phase and amplitude of the radio-frequency (RF) signals, which drive the acousto-optic modulators used as the basis for these investigations. Enhancements in aerial image resolution and edge slope are shown by contrasting image quality for nonphase-shifted features against features patterned using acousto-optic emulation of alternating phase-shift mask, attenuated phase-shift mask, and chromeless phase-shift mask imaging techniques. A demonstration of vortex via patterning is also shown to highlight the versatility of this technique in creating complex two dimensional patterns. An overview of the experimental method and hardware is presented along with the results.
The ALTA 4700 incorporates new optical subsystems to improve pattern quality performance and has added the capability to do variable multipass printing. The optical system changes are the addition of a 0.9-NA reduction lens and a new AOD subsystem to reduce beam placement and intensity errors. Variable multipass printing allows two-, four- or eight-pass printing, thereby enabling the user to optimize the pattern quality/throughput tradeoff. Local CDU 3σ performance for one pattern is reduced from 8.2 to 5.1 to 3.4 nm as the number of passes is increased from two to four to eight. Reduction of CDU performance is more pattern dependent going from four to eight passes than going from two to four passes. Pattern write times scale roughly linearly with the number of passes. Local pattern loading effects can limit global CDU performance. These effects can be reduced by optimizing resist selection and develop processes.
Currently, the ALTA 4300 generation Deep Ultra-Violet (DUV) Laser tool is capable of printing critical and semi-critical photomasks for the 130nm and 90nm IC technology nodes. With improved optical elements, an improved objective lens, and a higher bandwidth datapath the capability of the tool has been dramatically enhanced. Both the tools diffractive optic element (DOE) and acousto-optic modulator (AOM) have been refined. Additionally, the tools 33x, 0.8NA objective lens has been replaced with a 42x, 0.9NA objective lens. Finally, the tools datapath enhancement has allowed critical level write times to remain less than four hours.
Quantitative results of these enhancements will be detailed through reporting of critical feature resolution limits, CD uniformity control, and pattern placement accuracy on mask. Performance will be shown from masks printed pre- and post- hardware upgrade. Experimental results will show actual improvements.
In this paper details of the aerial image created when printing wafers with DUV Laser generated photomasks pre- and post-upgrade will be shown. Both 248nm and 193nm source printing with multiple illumination conditions will be discussed. Details of a print test comparison performed on photomasks from each tool configuration will be documented. The print test comparison will include process window characterization from each mask type. A study of the inspectability of the DUV Laser generated photomasks will also be highlighted.
Currently, the ALTA 4300 generation DUV Laser tool is capable of printing critical and semi-critical photomasks for the 130nm and 90nm IC technology nodes. With improved optical elements, an improved objective lens, and a higher bandwidth data-path the capability of the tool has been dramatically enhanced - culminating with the introduction of the ALTA 4700. Both the ALTA 4300 system’s diffractive optic element (DOE) and acousto-optic modulator (AOM) have been refined. Additionally, the ALTA 4300 system’s 33x, 0.8NA objective lens has been replaced with a 42x, 0.9NA objective lens. Finally, the tool’s data-path has been enhanced to maintain the ALTA system’s superior write time on critical mask layers.
Quantitative results of these enhancements will be detailed through reporting of critical feature resolution limits, CD uniformity control, and pattern placement accuracy on mask. Performance will be shown from masks printed pre- and post- hardware upgrade. Experimental results will be compared with theoretical calculations that show expected and actual improvements.
In this paper details of the aerial image created when printing wafers with DUV Laser generated photomasks pre- and post- upgrade will be shown. 193nm print results will be shown with multiple illumination conditions. Details of a print test comparison performed on photomasks from each tool configuration will be documented. The print test comparison will include process window characterization from each mask type.
KEYWORDS: Semiconducting wafers, Photomasks, Metals, Reticles, Deep ultraviolet, Optical proximity correction, Manufacturing, Electron beam lithography, Lithography, Control systems
The capability and performance of the production-proven DUV ALTA 4300 system has been extended by the development of two new optical subsystems: a 0.9 NA, 42X reduction lens and a high-bandwidth acousto-optic deflector based beam position and intensity correction servo. The PSM overlay performance has been improved by modifications to the software algorithms. The enhanced performance, delivered by these subsystem improvements, has been introduced as a new product-the ALTA 4700. Characterization data show improved resolution performance in line end shortening, through pitch CD bias and feature corner acuity. The AOD subsystem reduces stripe beam placement errors and random and systematic beam intensity errors. This has enabled local CD uniformity to be reduced to 4.3 nm (3σ) and global CD uniformity to be reduced to 6 nm (3σ). Second layer overlay performance is now 20 nm (max error). This paper also demonstrates superior X-Architecture performance delivered by the ALTA 4700. Characterization data show global CD uniformity in 0°, 45°, 90°, and 135° orientations better than 6.5nm (3σ); mean CD control in all 4
orientations less than 3.6nm; and smooth angled lines through a wide range of angles. A split lot wafer evaluation demonstrates the equivalence of wafers produced DUV ALTA system reticles vs. those produced with reticles from a 50kV electron beam system. The evaluation shows the interchangeability of these two systems for 90nm Metal 1 applications-with no changes to the wafer OPC (originally optimized for the 50kV system). Characterization data focus on final wafer electrical performance-the performance characteristic that determines ultimate integrated circuit device yield.
Currently, the ALTA® 4300 generation DUV Laser system is capable of printing critical and semi-critical photomasks for the 130nm and 90nm IC technology nodes. With improved optical elements, an improved objective lens, and a higher bandwidth datapath the capability of the tool has been dramatically enhanced. Both the tool’s diffractive optic element (DOE) and acousto-optic modulator (AOM) have been refined. Additionally, the tool's 33x, 0.8NA objective lens has been replaced with a 42x, 0.9NA objective lens. Finally, the tool's datapath has been enhanced to maintain the ALTA system's superior write times on the critical layers. Quantitative results of these enhancements will be detailed through reporting of critical feature resolution limits, CD uniformity control, and pattern placement accuracy. Performance will be shown from masks printed pre- and post- hardware upgrade. Experimental results will be compared with theoretical calculations that show the expected improvement for each relevant parameter.
The capability of the DUV ALTAÒ 4300 system has been extended by the development of two new optical subsystems: a 0.9 NA, 42X reduction lens and a high-bandwidth acousto-optic deflector based beam position and intensity correction servo. The PSM overlay performance has been improved by modifications to the software algorithms. Characterization data show improved resolution performance in line end shortening, through pitch CD bias and feature corner acuity. The AOD subsystem reduces stripe beam placement errors and random and systematic beam intensity errors. This has enabled local CD uniformity to be reduced to 4.3 nm (3σ) and global CD uniformity to be reduced to 5.8 nm (range/2). Second layer overlay performance is now 20 nm (max error). A split lot wafer evaluation has demonstrated the equivalence of unmodified ALTAÒ 4300 reticles to those printed on a 50 KeV electron beam system for a 130/110 nm device. Wafer lithography results show equivalent CD uniformity, depth of focus and pattern registration results.
The ALTA 4300 system has been used to successfully write many advanced designs previously only possible with 50kV VSB systems. In order to further enlarge the application space of this high productivity system, an aerial image enhancement technique has been developed to deliver mask patterns that more closely match the pattern data for corners and jogs. This image enhancement is done in real time in the ALTA system's rasterizer by modifying the gray level mapping of pixels near the corner vertexes. SEM measurements of corner rounding with standard rasterization and the enhanced rasterization show a 35% improvement of corner rounding radius from ~205 to ~132 nm. A direct comparison of SEM micrographs show little qualitative difference between vector scan mask features and those written with aerial image enhancement. This convincingly demonstrates that the ALTA 4300 system with the new image enhancement can write many layers requiring vector scan corner acuity.
The ALTA 4300 system has been used to successfully write many advanced design layers previously only feasible with 50kV vector shaped beam tools. In order to further enlarge the application space of this high productivity an aerial image enhancement technique has been developed to deliver mask patterns that more closely match pattern data for corners and jogs. This image enhancement is done in real time in the ALTA system’s rasterizer by modifying the gray level mapping of pixels near the corner vertexes. SEM measurements of corner rounding with standard rasterization and the enhanced rasterization show an improvement of corner rounding radius from ~205 to ~132 nm. A direct comparison of SEM micrographs show no qualitative difference between vector scan mask features and those written with aerial image enhancement. This convincingly demonstrates that the ALTA 4300 system with the new image enhancement can write many layers requiring vector scan corner acuity.
The projected rapid reduction in mask minimum feature size from the 250 nm to the 100 nm wafer generation will drive laser pattern generators to deep UV wavelengths. Commercially available sources exist in the 250 nm wavelength region using nonlinear optical materials to frequency double longer wavelength laser lines. Nonlinear optical materials, such as SBBO and KBBF, exist for wavelengths below 200 nm but they have not been commercialized. Second harmonic generation in intracavity or mode-locked, external resonant-ring laser configurations can be used to produce sub-200 nm radiation. Existing system architectures are shown to be easily modified to use pulsed sources with a high repetition rate. Advances in nonlinear optical materials, laser design, and system architecture will ensure that laser pattern generation will be an effective maskmaking technology for the next decade.
ATEQ has developed a high resolution laser scanning printing engine based on the 8 beam architecture of the CORE- 2000. This printing engine has been incorporated into two systems: the CORE-2500 for the production of advanced masks and reticles and a prototype system for direct write on wafers. The laser direct writer incorporates a through-the-lens alignment system and a rotary chuck for theta alignment. Its resolution performance is delivered by a 0. 60 NA laser scan lens and a novel air-jet focus system. The short focal length high resolution lens also reduces beam position errors thereby improving overall pattern accuracy. In order to take advantage of the high NA optics a high performance focus servo was developed capable of dynamic focus with a maximum error of 0. 15 tm. The focus system uses a hot wire anemometer to measure air flow through an orifice abutting the wafer providing a direct measurement to the top surface of resist independent of substrate properties. Lens specifications are presented and compared with the previous design. Bench data of spot size vs. entrance pupil filling show spot size performance down to 0. 35 m FWHM. The lens has a linearity specification of 0. 05 m system measurements of lens linearity indicate system performance substantially below this. The aerial image of the scanned beams is measured using resist as a threshold detector. An effective spot size is
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