Shinji Wakamoto

Double-patterning requirements for optical lithography and prospects for optical extension without double patterning

Double patterning (DP) has now become a fixture on the development roadmaps of many device manufacturers for half pitches of 32 nm and beyond. Depending on the device feature, different types of DP and double exposure (DE) are being considered. This paper focuses on the requirements of the most complex forms of DP, pitch-splitting (where line density is doubled through two exposures) and spacer processes (where a deposition process is used to achieve the final pattern). Budgets for critical dimension uniformity and overlay are presented along with tool and process requirements to achieve these budgets. Experimental results showing 45-nm lines and spaces using dry ArF lithography with a k1 factor of 0.20 are presented to highlight some of the challenges. Finally, alternatives to DP are presented.

Immersion lithography extension to sub-10nm nodes with multiple patterning

This paper investigates the possibility of 193 nm immersion lithography extensions to sub-10 nm technology nodes using the patterning scheme of unidirectional (1D) grating lines and cuttings. Technological feasibility down to 5 nm nodes is examined with experimental data of self-aligned multiple patterning method (SAxP) and Litho-Etch (LE) cuttings. For the cutting by LE repetition, relationship between node definition and the repetition number n (LE^n) is discussed. Cost is evaluated for SADP, SAQP and SAOP to generate unidirectional grating formation, and the following LE^n cutting process. Finally, schemes of gridded cutting and trim are introduced, and found to be advantageous to keep the scaling merit of transistor cost at 7 and 5 nm technology nodes.

Double patterning requirements for optical lithography and prospects for optical extension without double patterning

Double patterning (DP) has now become a fixture on the development roadmaps of many device manufacturers for half pitches of 32 nm and beyond. Depending on the device feature, different types of DP and double exposure (DE) are being considered. This paper focuses on the requirements of the most complex forms of DP, pitch splitting, where line density is doubled through two exposures, and sidewall processes, where a deposition process is used to achieve the final pattern. Budgets for CD uniformity and overlay are presented along with tool and process requirements to achieve these budgets. Experimental results showing 45 nm lines and spaces using dry ArF lithography with a k1 factor of 0.20 are presented to highlight some of the challenges. Finally, alternatives to double patterning are presented.

KrF step-and-scan exposure system using higher-NA projection lens

A KrF step and scan exposure system using a projection lens has been developed. The exposure field is 25mm by 33mm which is large enough to fit two 256Mbit DRAM chips. The maximum numerical aperture is 0.6 and the maximum coherence factor of the illumination system is 0.75 for the maximum numerical aperture. Original design concepts for scanning technologies are introduced. Actual data of the system indicate the sufficient performance for 250nm design rule device production.

Recent performance results of Nikon immersion lithography tools

Nikons production immersion scanners, including the NSR-S609B and the NSR-S610C, have now been in the field for over 2 years. With these tools, 55 nm NAND Flash processes became the first immersion production chips in the world, and 45 nm NAND Flash process development and early production has begun. Several logic processes have also been developed on these tools. This paper discusses the technical features of Nikons immersion tools, and their results in production.

Overlay improvement by using new framework of grid compensation for matching

Overlay accuracy is a key issue in the semiconductor manufacturing process. To achieve overlay requirements, we developed compensation functions, i.e. Enhanced Global Alignment (EGA), Super Distortion Matching (SDM), and Grid Compensation for Matching (GCM). These functions are capable to reduce all the components except local linear components caused by a wafer global deformation. In this paper we introduce a novel correction framework which includes new compensation function called Shot Correction by Grid Parameter; thereby enabling further enhancements to overlay. Using this novel framework, we show both simulation and experimental data demonstrating improved overlay accuracy.

New advanced lithography tools with mix-and-match strategy

Nikon has developed cutting-edge lithography tools, and its product lineup encompasses all exposure wavelengths. They are: the NSR-S307E ArF scanner for the 90nm node; the NSR-S207D KrF scanner for the 110nm node; the NSR-SF130 i-line stepper for the middle layer and the new concept NSR-SF200 KrF stepper, which offers unparalleled productivity and cost performance. In addition, a powerful support system is provided, the Lithography Equipment Engineering System, which will allow its customers to use all of these exposure tools simultaneously and derive the maximum benefit of the mix-and-match strategy. The use of this system will increase the uptime and enable their combined performance to exceed that of a stand-alone tool.Latest actual performance data from each of the tools and the result of the optimization performed using application software will be reported.

Mix-and-match overlay performance of the NSR-S622D immersion scanner

Current technology nodes, as well as subsequent generations necessitate ongoing improvements to the mix-and-match overlay (MMO) capabilities of lithography scanners. This work will introduce newly developed scanner solutions to address this requirement, and performance data from the latest generation immersion scanner, the NSR-S622D, will be introduced. Enhanced MMO accuracy is imperative for the 22 nm half-pitch and future technology nodes. In order for the matched overlay accuracy to approach single machine overlay (SMO) capabilities, MMO errors must be reduced further. The dominant MMO error sources can be divided into three main areas: SMO, lens distortion matching and wafer grid matching. Nikon continues to decrease these matching error contributors over time, and the latest generation NSRS622D immersion scanner provides a number of innovative solutions to satisfy the most demanding overlay matching requirements ; as a result MMO performance within 3nm is achieved on S622D. Moreover, overlay master system is developed for further product overlay accuracy and stability improvement.

Stability and calibration of overlay and focus control for a double patterning immersion scanner

To achieve the 2 nm overlay accuracy required for double patterning, we have introduced the NSR-S620D immersion scanner that employs an encoder metrology system. The key challenges for an encoder metrology system include its stability as well as the methods of calibration. The S620D has a hybrid metrology system consisting of encoders and interferometers, in XY and Z. The advantage of a hybrid metrology system is that we can continuously monitor the position of the stage using both encoders and interferometers for optimal positioning control, without any additional metrology requirements or throughput loss. To support this technology, the S620D has various encoder calibration functions that make and maintain the ideal grid, and control focus. In this paper we will introduce some of the encoder calibration functions based on the interferometer. We also provide the latest performance of the tool, with an emphasis on overlay and focus control, validating that the NSR-S620D delivers the necessary levels of accuracy and stability for the production phase of double patterning.

Achieving overlay budgets for double patterning

The problem of the alignment tree for double patterning (DP) is presented. When the 2nd DP exposure is aligned to the underlying zero layer, the space CD uniformity is shown to be well outside the budget for the 32 nm HP node. Aligning the 2nd DP layer to the zero layer gives better overlay results, but aligning the 2nd DP pattern to the 1st DP pattern gives results well within the overlay requirements for the 32 nm HP. Aligning the 2nd DP layer to the 1st DP layer is recommended to give the best CD uniformity and overlay results. Experimental results show, qualitatively, the CD uniformity is significantly worse when the 2nd pattern is aligned to the zero layer, but the overlay for both alignment trees could be corrected to roughly the same levels. The raw overlay data shows a significantly different signature for the two alignment trees, possibly caused by alignment mark signal differences between the marks on the zero and 1st layers, or distortion of the zero layer after the first etch. The requirements for a DP exposure tool were reviewed and can be summarized as improved dose control, improved overlay performance, and significantly higher throughput.