EUV/DUV mask blanks and reflectors

Rigaku's multilayer coating technology is one of several enabling technologies for extreme Ultra-Violet (EUV) lithography, a prime candidate for making the next generation of computer chips.

Multilayer coated condenser optics serve to collect, shape and filter the EUV light to achieve a highly intense uniform beam. This beam then illuminates a reflection mask, which consists of a patterned multilayer. The pattern is further reduced through multilayer coated imaging optics to achieve a previously unobtainable feature size within a computer chip.

Condenser optics

Sophisticated optics consisting of several multilayer coated optics filter and shape the beam from the X-ray source. The optical system is designed to collect the largest possible solid angle from a point source such as a laser produced plasma X-ray source. The optics must be robust as the source creates some debris which could impinge on the optical surface. This debris will eventually damage the multilayer coating. Rigaku is developing technology to remove and replace multilayer coatings to salvage the expensive condenser optical system.

Reflection masks

Masks consist of a Si wafer coated with a highly reflective Mo/Si multilayer and covered by a non-reflective layer. The non-reflective layer is patterned in the image of a single layer or segment of a layer of a computer chip. Each layer or segment must be individually exposed, requiring several masks to create a single chip. The multilayer must have no defects larger than 30 nm over the entire surface of the mask. Such defects would be imaged into the chip, resulting in a defective device. Rigaku is working to develop production processes which will achieve the required defect dimension and density.

Imaging optics

Three or more aspheric optics are used to reduce the final image by a factor of four. These optics must have nearly perfect coating uniformity with no distortion. The wave-front reflected from these optics should create no shift in phase of the reflected wavelength.  A phase shift would result in destructive interference yielding lower intensity light impinging on the chip's photoresist.