Chemically amplified resist materials are now available to reach critical dimensions of the pattern close to 32 nm values.
Pattern collapse is a very serious problem in fine patterning less than 32 nm critical dimension, because it decreases the
yield. The pattern collapse is the pattern response to unbalanced capillary forces acting on the pattern walls during the
spinning drying step after development process. Centrifugal force has not considered for pattern collapse modeling up to
now, so that pattern collapse due to spinning is studied. In this study we investigate the 32 nm node pattern collapse
mechanism with radial distance and rinse speed of dense patterns. In the process of creating the simulation tool, the
rotating model is used. As rinse speed and radial distance are increased, critical aspect ratio is decreased. As a result,
pattern collapse is increased.
Resist reflow is a simple and cost effective technique by which the resist is baked above the glass transition temperature (Tg) after the typical contact hole pattern has been exposed, baked and developed. Resist reflow method can obtain very high resolution without the loss of process margin than any other resolution enhancement techniques that can make the same linewidth. But it is difficult to predict the results of the thermal flow and the process optimization. If the results of reflow process can be exactly predicted, we can save great time and cost. In order to optimize the layout design and process parameters, we develop the resist flow model which can predict the resist reflow tendency as a function of the contact hole size, initial shape and reflow temperature for the normal and elongated contact hole. The basic fluid equation is used to express the flow of resist and the variation of viscosity and density as a function of reflow temperature and time are considered. Moreover surface tension and gravity effects are also considered. In order to build a basic algorism, we assume that the fluid is incompressible, irrotational and Newtonian. First, we consider the boundary movement of side wall and we think the basic equations for free surface flow of fluid as 2-dimensional time-dependent Navier-Stokes equations with the mass conservation equation. Surface tension acting on the interface pressure difference and gravity force that enable the resist flow are also included.
Extreme Ultraviolet Lithography (EUVL) is one of the patterning technologies proposed for the next generation lithography (NGL) which makes pattern less than 50 nm critical dimension (CD). And EUVL uses a very short exposure wavelength of 13.4 nm. So it has many characteristic in common with optical lithography, but EUVL are different from the conventional mask applied to the projection optical lithography. Specially, industry experts generally agree that the biggest challenges and risks for the next generation of lithography systems involve the mask. In EUVL, a mask is produced by applying multilayers of molybdenum and silicon to a flat substrate. The circuit pattern is produced by applying a final EUV-absorbing metal layer and then etching away the metal to form the image of the circuit. Also, the light shining with 6 degrees oblique to mask can not get target CD easily because the shadow effect is influenced on pattern. Therefore we must understand this kind of effect before doing real process. We tried to change the structure of the mask in order to decrease this effect and to have enough process latitude for the 32 nm node. EUV mask is affected by the thickness and kind of absorber and buffer material. First, we changed the absorber material such as Cr, TaN and Ge etc. without changing the buffer material. Second, we changed the thickness of the absorber materials. We tried to minimize the shadow effect by adjusting the side wall angle of the absorber layer parallel to the oblique incidence. Additionally we considered different shapes and depth of the etched multilayer binary mask and the refilled multilayer binary mask such as the inclined side wall of the etched multilayer. In this paper, we will describe the optimized EUV mask structure for 32 nm node by studying not only the aerial image, but also the resist profile. Solid-EUV simulator of Sigma-C is used to calculate the aerial image, resist pattern profile, and the process latitude with the optimized process parameters.
Selectivity of extreme ultra-violet lithography mask's material and thickness significantly influences on pattern formation. Since the reflectance changes periodically depending on absorber thickness, we investigated the absorber thickness effect on to near field and aerial image for 32 nm line/space and isolated pattern. We chose germanium and chromium as absorber materials. We also investigated the line width variation by absorber thickness change with different duty ratios. SOLID-EUV of sigma-C was used for this study.