Vishal Garg

DUV laser lithography for photomask fabrication

In the recent past significant work has been done to isolate and characterize suitable single layer Chemically Amplified Resist (CAR) systems for DUV printing applicable to photomask fabrication. This work is complicated by the inherent instability of most DUV CAR systems, particularly in air, showing unacceptable CD degradation over the normal photomask write time in today’s DUV mask pattern generators. The high reflectivity of most photomask substrates at DUV wavelengths, creating unacceptable standing waves in the photo resist profile, further compounds this problem. A single layer CAR system suitable for 90nm technology node mask fabrication with DUV printing has been characterized and optimized. Results of this optimization in terms of relevant mask making parameters will be detailed. Furthermore, comparison of the properties of this resist system to other commercially available systems, including FEP-171, will be shown. The pattern fidelity of DUV laser generated masks has been studied in considerable detail. A demonstration of the capabilities of the Etec Systems ALTA 4300 will be shown. The pattern fidelity achieved will be compared/contrasted to that achieved with today’s leading edge 50KeV vector scan e-beam systems. Advanced methods for modulating the DUV printed patterns’ fidelity will be detailed. Finally, the cost and cycle time implications of inserting the DUV laser pattern generator into the mask manufacturing flow will be discussed.

Imaging properties of a leading-edge DUV laser generated photomask

In the recent past Deep Ultra Violet (DUV) Laser generated photomasks have gained widespread acceptance for critical and semi-critical applications in semi-conductor lithography. The advent of stable, highly capable, single-layer Chemically Amplified Resist (CAR) processes has made fabrication of this type of mask very robust in todays mask manufacturing environment. This platform affords mask makers benefits of the highly parallel architecture available in todays DUV Laser pattern generators - providing excellent cost and cycle time advantages when compared with alternative leading-edge processes using 50 KeV VSB e-beam systems. To date literature on this topic has focused mostly on characterization and optimization of DUV mask making processes. Meanwhile treatment of the resultant aerial image for critical litho applications has been largely ignored. In this paper details of the aerial image produced using DUV Laser generated photomasks will be detailed. Both 248nm and 193nm source printing with multiple types of illumination will be discussed. Details of a print test comparison performed on photomasks from two popular mask lithography platforms in use today; DUV, and 50 KeV VSB, will be documented. Finally, the most recent process improvements achieved in DUV Laser mask fabrication will be detailed. Special attention will be given to the impact of these enhancements on image quality.

Integration of the Micronic Omega6500 into the mask manufacturing environment

The Micronic Omega6500, a new high performance scanned laser mask lithography system, has been installed in a production mask facility of DuPont Photomasks, Inc. (DPI) The Omega6500 is a 5-beam system with an exposure wavelength of 413 nm, acousto-optic modulation beam intensity control and acousto-optic deflection.1 The use of a fast expandable datapath architecture along with a hierarchical data format allows extremely dense files to be printed at the full area coverage rate. Due to the differences between this tool and existing tools within DPI, and since this tool is completely new to the photomask industry, a cooperative project was initiated between DPI and Micronic to characterize the performance of the Omega6500 in a mask production environment. In specific we examined the optimization of the resist process, evaluated data handling capability and procedures, and determined changes required to job planning and manufacturing flow. Performance test procedures were created and used to evaluate the precision performance of the system. A production emulation plate suite was used to characterize pattern integrity and precision on real masks.

Improved throughput in 0.6-NA laser reticle writers

New writing strategies have been developed to meet the demand for high-volume mask manufacturing. The ALTA® 3000HT system enables users to meet their performance requirements at increased production capacity. The write time of an ALTA 3000HT mask writer has been observed to be substantially shorter than that of the ALTA 3000 system. The ability to change between eight and four averaging passes, as well as the addition of key hardware improvements, give users increased flexibility in meeting the throughput and print quality requirements for volume production mask manufacturing. Observed throughput and print performance data are presented.

Extending analog design scaling to sub-wavelength lithography: co-optimization of RET and photomasks

The mask requirements for 110nm half-node BiCMOS process were analyzed with the goal to meet customer needs at lower cost and shorter cycle times. The key differentiating features for this technology were high density CMOS libraries along with high-power Bipolar, LDMOS and DECMOS components. The high voltage components were characterized by transistors that formed cylindrical junctions. The presence of curved features in the data is particularly detrimental to the write time on a 50KeV vector mask writer. The mask write times have a direct impact on both mask cost and cycle time. Design rules also permit rectangular or stretched contacts to allow conductance of high currents. To meet customer needs but still manage the computational lithography overhead as well as the patterning process performance, this process was evaluated in terms of computational lithography and photomask co-optimization for the base-line 50KeV vector and laser mask-writers. Due to the differences in imaging and processing of the different mask writing systems, comparative analysis of critical dimension (CD) performance both in terms of linearity and pitch was done. Differences in imaging on silicon due to mask fidelity were also expected and characterized. The required changes in OPC necessary to switch to the new mask process were analyzed.

Pattern fidelity performance from next-generation DUV laser lithography on 65nm masks and wafers

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.

Print characterization of photomasks from next-generation deep-ultra-violet laser pattern generator

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.

Enhancement of the image fidelity and pattern accuracy of a DUV laser generated photomask through next-generation hardware

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 tools 33x, 0.8NA objective lens has been replaced with a 42x, 0.9NA objective lens. Finally, the tools datapath has been enhanced to maintain the ALTA systems 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.

Improved throughput in the ALTA 3000 IC mask writing system

The write time of an ALTA 3000HT mask writer has been observed to be up to 36% better than that of the ALTA 3000 system. The ALTA 3000HT system enables users to meet their performance requirements at increased production capacity with the use of new writing strategies. The ability to change between eight and four averaging passes, as well as the addition of key hardware improvements, gives users increased flexibility in meeting the throughput and print quality requirements for high-volume mask manufacturing. Observed throughput and print performance data, as well as benefits analysis and cost of ownership data, are presented.