TECHNICAL FIELD

The present disclosure relates generally to extreme ultraviolet lithography, and more particularly extreme ultraviolet mask blanks with an alloy absorber and methods of manufacture.

BACKGROUND

Extreme ultraviolet (EUV) lithography, also known as soft x-ray projection lithography, can be used for the manufacture of 0.0135 micron and smaller minimum feature size semiconductor devices. However, extreme ultraviolet light, which is generally in the 5 to 100 nanometer wavelength range, is strongly absorbed in virtually all materials. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Through the use of a series of mirrors, or lens elements, and a reflective element, or mask blank, coated with a non-reflective absorber mask pattern, the patterned actinic light is reflected onto a resist-coated semiconductor substrate.

The lens elements and mask blanks of extreme ultraviolet lithography systems are coated with reflective multilayer coatings of materials such as molybdenum and silicon. Reflection values of approximately 65% per lens element, or mask blank, have been obtained by using substrates that are coated with multilayer coatings that strongly reflect light within an extremely narrow ultraviolet bandpass, for example, 12.5 to 14.5 nanometer bandpass for 13.5 nanometer ultraviolet light.

FIG. 1shows a conventional EUV reflective mask10, which is formed from an EUV mask blank, which includes a reflective multilayer stack12on a substrate14, which reflects EUV radiation at unmasked portions by Bragg interference. Masked (non-reflective) areas16of the conventional EUV reflective mask10are formed by etching buffer layer18and absorbing layer20. The absorbing layer typically has a thickness in a range of 51 nm to 77 nm. A capping layer22is formed over the reflective multilayer stack12and protects the reflective multilayer stack12during the etching process. As will be discussed further below, EUV mask blanks are made on a low thermal expansion material substrate coated with multilayers, a capping layer and an absorbing layer, which is then etched to provide the masked (non-reflective) areas16and reflective areas24.

The International Technology Roadmap for Semiconductors (ITRS) specifies a node's overlay requirement as some percentage of a technology's minimum half-pitch feature size. Due to the impact on image placement and overlay errors inherent in all reflective lithography systems, EUV reflective masks will need to adhere to more precise flatness specifications for future production. Additionally, EUV blanks have a very low tolerance to defects on the working area of the blank. Furthermore, while the absorbing layer's role is to absorb light, there is also a phase shift effect due to the difference between the absorber layer's index of refraction and vacuum's index of refraction (n=1), and this phase shift that accounts for the 3D mask effects. There is a need to provide EUV mask blanks having a thinner absorber to mitigate 3D mask effects.

SUMMARY

One or more embodiments of the disclosure are directed to a method of manufacturing an extreme ultraviolet (EUV) mask blank comprising forming on a substrate a multilayer stack which reflects EUV radiation, the multilayer stack comprising a plurality of reflective layer pairs; forming a capping layer on the multilayer stack; and forming an absorber layer on the capping layer, the absorber layer comprising an alloy of tellurium, germanium and antimony.

Additional embodiments of the disclosure are directed to an EUV mask blank comprising a substrate; a multilayer stack which reflects EUV radiation, the multilayer stack comprising a plurality of reflective layer; a capping layer on the multilayer stack of reflecting layers; and an absorber layer comprising an alloy of tellurium, germanium and antimony.

