EUV lithography

Fabrication of nanostructures with ever decreasing dimensions is a key challenge faced in many areas of nanotechnology. Projection photolithography, which has been the main enabling force behind the success of the semiconductor industry, is not the answer to the fabrication challenge of new applications such as patterned magnetic media because of its limited resolution and high cost. E-beam lithography is an alternative fabrication technique that provides ample resolution but it severely lacks in throughput. EULITHA's Extreme Ultraviolet Interference Lithography (EUV-IL) is a revolutionary technology for the high-throughput fabrication of periodic nano-patterns with half pitch below 50 nm.

In EUV-IL two or more coherent EUV beams are brought together to form an interference pattern, which is recorded in a photoresist film. Interference of two beams leads to the formation of linear gratings while interference of three or more beams creates 2D patterns such as a grid or an array of dots. The interfering beams are obtained from a single EUV beam by transmission diffraction gratings. The period (pitch) of the obtained pattern is related to the period of the diffraction gratings through a certain relation depending on the number and arrangement of diffraction gratings on the mask. For example, when two beams, created by two diffraction gratings positioned parallel to each other (Figure 1) interfere, the obtained grating period is equal to the half of the period of the diffraction gratings. This de-magnification factor of two between the mask and the printed pattern is one of the great advantages of the EUV-IL technique as it significantly eases the fabrication of the required diffraction gratings (masks).

The ultimate resolution available from the EUV-IL technique is equal to a quarter of the wavelength in terms of the half-pitch of the produced patterns. This corresponds to a limit of less than 4 nm for the common wavelength of 13 nm used in EUV-IL. The highest resolution obtained to date with EUV-IL stands at 12.5 nm. We expect to push this number towards the ultimate limit through developments in photoresists, masks and exposure tools used in EUV-IL.