Extreme Ultraviolet Lithography
MD JAWWAD REZANOOR (113001040); AMLAN SEN(092100040); MIZANUR RAHMAN(093052040) Azimur Rahman School of Engineering, Presidency University, Dhaka
Abstract- Extreme Ultraviolet lithography (EUVL) is the leading technology, widely believed to take semiconductor lithography to the next generation. EUVL is the technology being considered for printing circuits at the 32nm node and below in a high volume manufacturing (HVM) environment fab. Compared to the traditional optical lithography technique, in EUVL a 13.5nm wavelength radiation is used. This paper discusses the techniques involved in EUVL, prospects it holds and the challenges in its implementation.
years, following the so called Moore’s law. To keep up the progression rate of shrinking size, a new technology is required for which EUVL is currently the front runner. The drastically smaller light wavelength of 13.5 nm used in EUVL as opposed to 193-248nm used in the conventional methods is the main distinguishing factor between these methods.
LIMITATIONS OF OPTICAL LITHOGRAPHY
Optical projection lithography is an optical system that transfers the image from the mask to the photoresist layer coated on the silicon wafer. In optical lithography the intricate patterns of integrated circuits are scaled at a ratio of 4:1 through a mask and then carved on the wafer. Currently, the most advanced lithographic tool used in HVM employ ArF immersion lithography and double patterning with a light wavelength of 193nm to print features that have half-pitch as small as 32nm. In the past 40 years, the minimum dimension of integrated circuits (ICs) has been shrinking at a rate of 30% smaller feature size every three
Fundamentally, there are no major limitations to optical lithography; however there are process, implementation and cost limits. There exists the Rayleigh limitation on the pitch, not on the critical dimensions (CDs). The following equations describe two of the most fundamental characteristics of an imaging system: its resolution (RES) and depth of focus (DOF). These equations are usually expressed as
Where is the wavelength of the radiation used to carry out the imaging, and NA is the numerical aperture of the imaging system. These equations show that better resolution can be achieved by reducing and increasing NA. The penalty for doing this, however, is that
the DOF is decreased. Until recently, the DOF used in manufacturing exceeded 0.5 µm, which provided for sufficient process control. A couple of cases can be considered regarding the values of k1 and k2 ; usually k1 = k2 = ½ corresponds to the usual definition of diffraction limited imaging. However, the exact values will be always determined through experimenting. Camera performance has a major impact on determining these values; other factors that have nothing to do with the camera also play a role. The comfort zone for manufacturer corresponds to the region for which k1 > 0.6 and DOF > 0.5 µm. This is shown in the figure below
However for smaller node size we look forward to EUVL and other NGLs (New Generation Lithography). These methods have their pros and cons. In comparison with EUVL, they mostly fall short because of their low throughput and implementation difficulties. i) Electron beam Lithography: This is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film. It has its advantage in beating the diffraction limit of light and hence making features in the nanometer regime, also higher resolution is easily achievable. The problem with E-beam lithography is its low throughput. Also, because electrons are charged particles, E-beam lithography must be performed in a vacuum.
ii) X-Ray Lithography: X-ray lithography (XRL) has a choice of a large range of wavelengths, from about 0.4 to 100 nm. In its first incarnation, proximity printing was used with a wavelength of about 1 nm and...
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