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Single Reticle Double Exposure

IP.com Disclosure Number: IPCOM000125702D
Original Publication Date: 2005-Jul-10
Included in the Prior Art Database: 2005-Jul-10
Document File: 5 page(s) / 228K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

For advanced technology nodes, the single reticle exposure of critical layers like Active Area layer (AA), Gate (Conducting) layer (GC), Metal Zero layer (M0) or Contact Hole (C/H) is inefficient. Usually used customized illumination modes need special apertures (stoppers) that take away a part of the exposure light, or extra exposure optics (Diffractive Optical Elements, DOEs). The DOEs are very expensive, and to get the desired illumination, sometimes they have to be combined with stoppers. A technical problem for this option is the limitation in the numbers of DOEs and stoppers which can be handled by an exposure tool. However, for sophisticated illumination modes it is advantageous to expose a customized aperture two times with different input lenses of the illuminator. Usual attempts to solve the printing requirements of complex DRAM (Dynamic Random Access Memory) layers, like AA or GC, are using not only one but two different reticles which are exposed in different illumination modes. Four items have to be changed mechanically in the exposure tool - i.e. reticle, lens NA (Numerical Aperture), illuminator NA (illuminator sigma) or the aperture and in most cases the illuminator input lens. The time loss due to all these changes makes the exposure slow and causes wear / costs for maintenance. As an example, the wafers of a lot are exposed in succession under one illumination. Then the exposure is restarted for the same wafers with the second reticle, so the double exposure of one litho layer is accumulating the sum of overlay errors of two exposures.

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Single Reticle Double Exposure

Idea: Dr. Andreas Jahnke, DE-Dresden; Dr. Christoph Noelscher, DE-Dresden

For advanced technology nodes, the single reticle exposure of critical layers like Active Area layer (AA), Gate (Conducting) layer (GC), Metal Zero layer (M0) or Contact Hole (C/H) is inefficient. Usually used customized illumination modes need special apertures (stoppers) that take away a part of the exposure light, or extra exposure optics (Diffractive Optical Elements, DOEs). The DOEs are very expensive, and to get the desired illumination, sometimes they have to be combined with stoppers. A technical problem for this option is the limitation in the numbers of DOEs and stoppers which can be handled by an exposure tool. However, for sophisticated illumination modes it is advantageous to expose a customized aperture two times with different input lenses of the illuminator.

Usual attempts to solve the printing requirements of complex DRAM (Dynamic Random Access Memory) layers, like AA or GC, are using not only one but two different reticles which are exposed in different illumination modes. Four items have to be changed mechanically in the exposure tool - i.e. reticle, lens NA (Numerical Aperture), illuminator NA (illuminator sigma) or the aperture and in most cases the illuminator input lens. The time loss due to all these changes makes the exposure slow and causes wear / costs for maintenance. As an example, the wafers of a lot are exposed in succession under one illumination. Then the exposure is restarted for the same wafers with the second reticle, so the double exposure of one litho layer is accumulating the sum of overlay errors of two exposures.

For low volume products a DOE is too expensive, and a development causes delay of use. Further on, the DOE is a compromise for needs of the array (high NA in combination with the dipole) and the support (lower NA with higher Depth of Focus (DoF) and more relaxed settings of Sub Resolution Assist Features (SRAFs)), but the same NA has to be used for both. The DOE or even the stopper may not deliver the expected results.

Other methods use contact holes with oblique illumination for dense patterns and low sigma circular illumination for isolated contacts (windmill illumination). The application of two illuming modes for the same reticle is already known, but one of them is customized and they are applied at the same NA. By the method described in the following optimized optical printing conditions for two different types of pattern in one layer can be obtained.

The core of the idea is to realize the double exposure of two sources with the same reticle or with the same stopper, and optionally with a change of the NA between the two exposures. Sources and NAs of the two exposures are adapted to different parts of the layout. This is provided by the sequential application of two standard illumination modes with the same reticle, where the first mode with a first NA is optimized for...