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Electron projection lithography (EPL) is a realistic technology for the 65nm node and below, as a complementary technology of optical lithography especially for contacts and gate layers because of its high resolution and large process margin. Nikon has developed an EPL exposure tool as an electron-beam (EB) stepper and the first generation EB stepper; NSR-EB1A is now almost completed as an R&D tool for the 65nm technology node. Using a ϕ200mm reticle, a 20mm×25mm exposure field is realized. Full-field exposure performance of NSR-EB1A is shown. A 70nm isolated line and 1:1 nested lines are simultaneously resolved, as are 50nm 1:2 nested lines. 60nm contact holes are resolved with a depth of focus over a 10μm range and dosage window over ±6%. Stitching accuracy is about 20nm (3σ) and the single machine overlay is about 30nm (mean + 3σ). These data mean sufficient performance for device manufacturing of the 65nm technology node. The concept of a large subfield is one candidate for resolution and throughput e...

PREVAIL is the high throughput e-beam projection approach to NGL, which IBM is pursuing in cooperation with Nikon as alliance partner. Key lithographic building blocks of the technology have been demonstrated experimentally with a proof-of-concept (POC) system and results have been reported earlier at MNE 99 and elsewhere. This paper reports on the implementation of the PREVAIL technology in a production-level e-beam stepper. The architecture and writing strategy of the tool together with design features of the various tool subsystems are described.

The IBM/Nikon alliance is developing an EPL stepper alpha tool based on the PREVAIL technology. This article provides a status report on the alliance activity with particular focus on the electron optical subsystem developed at IBM. We have previously described design features of the PREVAIL Alpha system. The state-of-the-art e-beam lithography concepts have since been reduced to practice and turned into functional building blocks of a production level lithography tool. The electron optical subsystem has been designed, built, assembled, and tested at IBM’s Semiconductor Research and Development Center (SRDC) in East Fishkill, NY. After demonstrating subsystem functionality, the column, an interim mechanical system and all associated control electronics hardware and software have been shipped during January 2001 to Nikon’s facility in Kumagaya, Japan, for integration into the Nikon commercial e-beam stepper Alpha tool. Postshipment activity has been directed primarily toward demonstrating subfield stitching, a task which exercises system architecture, calibration, stability, and noise performance.

Electron Projection Lithography (EPL) is considered one of promising technologies below 45nm node, especially for contact/via holes and gate layers. EPL has some nice features such as very high resolution to be applied for two device nodes, large process margin associated with large depth of focus and an expected lower CoO. Nikon has been developing an EPL tool, so-called EB Stepper. NSR-EB1A is the first EB Stepper that was designed as R&D tool for 65nm technology node and that was already delivered for Selete (Semiconductor Leading Edge Technologies, Inc.) at Tsukuba in Japan. Nikon has developed two NSR-EB1A tools so far, one system for Selete as a 300mm wafer system and the other for Nikon's development and evaluation as a 200mm wafer system. Both tools have already started to show full performance data and good stability characteristics. The latest EB1A tool performance shows very good results in such data as the resolution of 50nm 2:1 L/S and 60nm 1:1 dense contact holes patterns, stitching accuracy of around 18nm, and overlay accuracy of around 20nm(X+3sigma).

As Next Generation Lithography (NGL) systems, several systems are proposed. EPL (Electron Beam Projection Lithography) system, which is one of NGL systems using electron beam (EB), is expected to be a most promising candidate, which has a high throughput (>20 wph of a 300 mm wafer) and a high resolution (

Silicon stencil reticle has been developing for the EB stepper, which is the electron beam projection lithography system for 70nm node generation and beyond. The reticle distortion is affected by stress such as silicon membrane stress and resist stress on a reticle in their fabrication. To analyze pattern distortion using finite element method (FEM), the image placement (IP) and the critical dimension (CD) errors of the stencil reticle were measured at every step of reticle fabrication processes. It was found that the resist stress is the key factor of IP error in the membrane process. In the wafer process, the IP errors are mainly related to silicon membrane stress. IP and CD errors of 200mm stencil reticle in both processes are discussed using FEM. The calculation results show CD errors are caused by the stress of silicon membrane. Moreover, it is discussed that CD error depends on pattern shape and density even on the stress-controlled reticle blanks.

Nikon, in collaboration with IBM, has been developing EB stepper, which is the electron beam projection lithography (EPL) system for 70 nm node generation and below. As the standard reticle for EB stepper, the scattering silicon stencil type is used to obtain highest performance. The EB reticle has thin silicon membranes of thickness 2 micrometers and membrane size 1.13 mm square with stencil opening patterns, which are supported by a grid-grillage structure. The development of the EB reticle is one of key issues in the EB stepper development. We had accomplished 76nm reticle development using silicon-on-insulator wafer with a stress- controlled membrane. Now we are in the 200 mm reticle development phase. We have curried out experiments in cleaning, inspection and repair for the EB reticle, which are very important issues for the EB reticle fabrication. We showed possibilities of Ar aerosol cleaning, a reticle repair using Focused Ion Beam, pattern defect inspection with DUV microscope and so on.

The latest development status of EB Stepper is reported. The experimental data include the latest resist image data exposed by 100keV electron beam, mask error factors and dosage margins at several backscattered electron levels, transmission data of continuous membrane reticles, and recommended structures for alignment marks, etc. The basic studies related to system design are also explained, those are the strategy for the management of reticle deformation and the stitching accuracy in overlaid layers, etc. Through these data, the resolution capability down to 50nm technology node is clearly shown and alignment/stitching capability is also described. The requirement to a continuous membrane reticle is indicated from experimental data.

The imaging concept of electron projection lithography (EPL) with silicon stencil reticle is explained. A silicon membrane thickness of 1 - 4 micrometer is suitable for the reticle. A scattering contrast of greater than 99% is expected. Nikon EB stepper's dynamic writing strategy of discrete exposure on a sub-field by sub-field basis with deflection control of the electron beam is explained. The basic system configuration of EB stepper is introduced. Examples of error budget for CD variation and Overlay/Stitching are shown. Nikon's policy for countermeasures for critical issues such as proximity effect correction, sub-field/complementary stitching and wafer heating influence are explained. For extensibility down to 70 nm and below, both exposure tool and reticle should be improved.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Nikon is developing an Electron Beam (EB) stepper as one of the next-generation lithography systems for feature sizes of less than 100 nm. As a reticle for the EB stepper using a high power EB (acceleration voltage: 100 kV, current on reticle: 100 (mu) A), a scattering stencil reticle with a grid-grillage structure has been investigated, EB projection experimental column which operates a high power EB was constructed. Some experimental data of scattered electron characteristics using the EB projection experimental column are given as follows: (1) Scattering contrast of 99.9% can be obtained using 100 kV electron beam (membrane thickness; 2 micrometer, aperture half angle onto reticle; 2 mrad). (2) Changes of resist pattern width of 1:1 and 1:2 lines and spaces are around 40% and around 20% respectively due to the proximity effects by backscattered electrons form the silicon substrate. (3) Contrast of EB mark detection for the system calibration, the reticle alignment, and the wafer registration is obtained. Comparing with the values that be obtained by theoretical calculation, some of experimental data gave good agreement.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electron projection lithography (EPL) is one of the promising technologies below the 65 nm node, especially for contact hole and gate layers. Nikon is developing an EPL exposure tool as an electron beam (EB) stepper and the first generation EB stepper is now being manufactured. The voltage of 100 kV is adopted for electron beam acceleration. The subfield size is 0.25 mm×0.25 mm on the wafer and the deflection width of the electron beam is 5 mm on the wafer. The magnification of the projection optics is 1/4. A 5 mm×25 mm area from the φ200 mm reticle can be exposed by the combination of beam deflection and stage scanning motion (dynamic exposure). This area is called “a mechanical stripe.” After one mechanical stripe exposure, the reticle and wafer stages turn around and the next exposure of the adjacent mechanical stripe starts as a scan and stitch stage motion. Finally, a 20 mm×25 mm exposure field from the φ200 mm reticle is exposed. We report the first dynamic exposure in the history of EPL although only a φ100 mm reticle was used. A 5 mm×10 mm area was used as the mechanical stripe and 10 mm×10 mm exposure fields were exposed. 100 nm nested lines were resolved in the entire exposure field and stitching accuracies of 17–18 nm (3σ) are obtained. There remain systematic errors, and stitching accuracy less than 15 nm will be achieved after fine adjustment of the subfield positions. We feel the reality of EPL is now sufficiently proven.

We have fabricated Si stencil reticles that are employed by a new type of e-beam projection lithography system (EB stepper). We applied a stress reduction technique to the Si membrane to improve the pattern placement accuracy. The residual stress of Si membranes which were fabricated by anisotropic etching of B-doped Si wafers in KOH aqueous solution was reduced by annealing at 1150 °C. We carried out pattern-displacement measurements for a Si stencil reticle made of a Si membrane where the residual stress was reduced to 10 MPa, and we observed that the pattern displacement error was reduced to less than 20 nm. Furthermore, the pattern displacement in the stencil reticle had a high correlation with the displacement determined from a simulation based on a finite element model. However in the same reticle, we discovered additional, comparatively small displacements in random directions, which was not expected in a membrane that had a homogeneous tensile stress. As a cause of the pattern displacement in rand...

An illumination system suitable for an excimer laser stepper has been investigated. Unnecessary interference pattern(speckel) is reduced effectively by scanning the laser beam. We report spatial coherence of the lasers with different spectral line width, illumination system of the stepper, appearance of the interference pattern,its spacing and contrust and their relation to the illumination system and to the coherence of the laser. Then we report reduction of this pattern together with a simple method to measure its contrast.