Masami Yonekawa

Improved defectivity and particle control for nanoimprint lithography high-volume semiconductor manufacturing

Imprint lithography has been shown to be an effective technique for replication of nano-scale features. Jet and Flash* Imprint Lithography (J-FIL*) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is cross-linked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. Criteria specific to any lithographic process for the semiconductor industry include overlay, throughput and defectivity. The purpose of this paper is to describe the technology advancements made in the reduction of particle adders in an imprint tool. Hard particles on a wafer or mask create the possibility of creating a permanent defect on the mask that can impact device yield and mask life. By using material methods to reduce particle shedding and by introducing an air curtain system, test stand results demonstrate the potential for extending mask life to better than 1000 wafers.

Evaluation results of a new EUV reticle pod having reticle grounding paths

A new SEMI standard E152-0709 Mechanical Specification of EUV Pod for 150 mm EUVL Reticles has been published in July 2009. In the standard, reticle grounding requirements are mentioned as related information: an electrical connection between the front and back sides of EUVL reticles as well as the electrical connection to the reticle backside from outside the outer pod may be needed and specified in future. Reticle grounding is very important for reticle protection not only from electrostatic discharge (ESD) damage but also from particle contamination due to electrostatic attraction (ESA). Many past data suggested that EUV masks have to be grounded during shipping, storage and tool handling to prevent particle adhesion. Canon, Nikon and Entegris have jointly developed a new ESD-free EUV pod cnPod-ESD which has electrical connections to the reticle from outside the outer pod by modifying a SEMI compliant EUV pod cnPod. In order to have an electrical connection between the reticle backside and the outer pod, a cantilever is installed inside the inner pod cover. The cantilever touches the reticle backside just inside 146mm x 146mm which is specified as the minimum conductive layer area in SEMI P37 Specification for Extreme Ultraviolet Lithography Substrates and Blanks. In order to have an electrical connection between the reticle frontside and the outer pod, though it is not required in E152, an electrical conductive material is used for the reticle supports on the inner pod baseplate. We will show various evaluation data of the new ESD-free pods from particle contamination point of view and will discuss the necessity of the reticle grounding in this paper. We will also mention the necessity of modification of the SEMI standard P37 to make a universal EUV ESD-free pod.

Evaluation of transfer of particles from dual-pod base plate to EUV mask

Since 2005, Canon, Nikon, and Entegris have been jointly developing an EUV mask carrier based on the Dual Pod concept in place of a pellicle. By using our MIRAI-Selete Mask Protection Engineering (MPE) tool, a few prototypes were tested for performance of particle protection in the case of both mask shipping and its handling in vacuum. As a result, the fundamental mechanical specifications of the Dual pod were registered as those of SEMI E152 of an EUV Pod used in EUV mask. It is found that the latest pod named cnPod, which is based on the SEMI E152, performs almost satisfactorily. Although superior protection performance with respect to external particles has been confirmed, the performance with respect to internal particles laid on the base plate of an inner pod is still under investigation. Therefore, we evaluate the influence of the internal particles laid on the base-plate surface for the first time. In order to confirm whether the particles on the base plate are transferred to the mask-patterned surface, well-characterized particles are dispersed on the base-plate surface. By using this contaminated base plate and the MPE tool, mask handling experiments are conducted. Under our experimental conditions, it is found that the number of test particles transferred to the mask surface is very low compared to the total number of particles on the base-plate surface.

Evaluation results of a new EUV reticle pod based on SEMI E152

To protect the reticle during shipping, storage and tool handling, various reticle pod concepts have been proposed and evaluated in the last 10 years. MIRAI-Selete has been developing EUV reticle handling technology and evaluating EUV reticle pods designed using Dual Pod Concept for four years. The concept was jointly proposed by Canon and Nikon at the EUV mask technology and standards workshop at Miyazaki in November 2004; a mask is doubly protected by an inner pod and an outer pod and the mask is carried into an exposure tool with the inner pod. Canon, Nikon and Entegris have started collaboration in 2005 and developed three types of EUV pod prototypes, alpha, beta and gamma. The gamma pods were evaluated by MIRAI-Selete and the superiority of the dual pod concept has been verified with many experimental data on shipping, storage and tool handling. The dual pod concept was standardized as SEMI E152-0709 Mechanical Specification of EUV Pods for 150mm EUVL Reticles in 2009. Canon, Nikon and Entegris have developed a new pod design compatible with SEMI E152; it has a Type A inner baseplate for uses with EUV exposure tools. The baseplate has two alignment windows, a window for a data matrix symbol and five pockets as the front edge grip exclusion volumes. In addition to the new features, there are some differences between the new SEMI compliant pod design and the former design CNE-gamma, e.g. the material of the inner cover was changed to metal to reduce outgassing rate and the gap between the reticle and the side supports were widened to satisfy a requirement of the standard. MIRAI-Selete has evaluated the particle protective capability of the new SEMI compliant pods cnPod during shipping, storage and tool handling in vacuum and found the cnPod has the excellent particle protective capability and the dual pod concept can be used not only for EUVL pilot line but also for EUVL high volume manufacturing.

A short-pulsed laser cleaning system for EUVL tool

A traditional method of reticle protection, using a pellicle, is thought to be difficult to apply to EUVL tool. There is a possibility that some particles adhere to the surface of a reticle. In order to resolve this reticle issue, we are investigating in-situ short-pulsed laser cleaning system. In order to confirm whether it can be applied to EUVL tool or not, we have to verify experimentally that it is possible to remove particles in vacuum without any damage to a Mo/Si multilayer. In this work, as a short-pulsed laser, a Q-switched YAG Laser (wavelength: 266~1064 nm, pulse duration time: ~7 ns) has been used. As experimental results, at the pressure on the order of 10-3 Pa, around 100% removal rate to PSL (organic) particles can be achieved without particular damage using a DUV laser. And also, it is found that a laser cleaning method in vacuum is easier to remove particles on a surface than that in atmosphere and for SiO2 and Ni (inorganic) particles, this method is particularly effective. This reason can be explained that the drag force exerted to a particle by the surrounding gas molecules is neglected at the pressure on the order of 10-3 Pa because a gas is in free molecule regime.

Improved particle control for high volume semiconductor manufacturing for nanoimprint lithography

Nanoimprint Lithography (NIL) has been shown to be an effective technique for replication of nano-scale features. Jet and Flash Imprint Lithography* (J-FIL*) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. There are many criteria that determine whether a particular technology is ready for high volume semiconductor manufacturing. Included on the list are overlay, throughput and defectivity. Imprint lithography, like any lithographic approach requires that defect mechanisms be identified and eliminated in order to consistently yield a device. NIL has defect mechanisms unique to the technology, and they include liquid phase defects, solid phase defects and particle related defects. Especially more troublesome are hard particles on either the mask or wafer surface. Hard particles run the chance of creating a permanent defect in the mask, which cannot be corrected through a mask cleaning process. If Cost of Ownership (CoO) requirements are to be met, it is critical to minimize particle formation and extend mask life. To meet the CoO requirements, mask life must meet or exceed 1000 wafers. If, we make the conservative assumption that every particles causes damage to the mask pattern, the number of particle adders must be less than 0.001 pieces per wafer pass in the NIL tool. Therefore, aggressive strategies are needed to reduce particles in the tool. In this paper, we will report on the techniques required to meet this condition and will describe how the particle reduction techniques can be extended to our FPA-1200NZ2C system.