Diana Convey

Mesoscale modeling for SFIL simulating polymerization kinetics and densification

Step and Flash Imprint Lithography (SFIL) is a revolutionary next generation lithography option that has become increasingly attractive in recent years. Elimination of the costly optics of current step and scan imaging tools makes SFIL a serious candidate for large-scale commercial patterning of critical dimensions below ~50 nm. This work focuses on the kinetics of the UV curing of the liquid etch barrier and the resulting densification/contraction of the etch barrier as it solidifies during this step. Previous experimental work in our group has measured the bulk densification of several etch barrier formulations, typically about 9 % (v/v). It remains unknown, however, how much etch barrier contraction occurs during the formation of nano-scale features. Furthermore, it is of interest to examine how changes in monomer pendant group size impact imprinted feature profiles. This work provides answers to these questions through a combination of modeling and experimental efforts. Densification due to the photopolymerization reaction and the resulting shift from Van der Waals’ to covalent interactions is modeled using Monte-Carlo techniques. The model allows for determination of extent of reaction, degree of polymerization, and local density changes as a function of the etch barrier formulation and the interaction energies between molecules (including the quartz template). Experimental efforts focus on a new technique to examine trench profiles in the quartz template using TEM characterization. Additionally, SEM images of imprinted images from various etch barrier formulations were examined to determine local contraction of the etch barrier. Over a large range of etch barrier formulations, which range from 10 - 20 % volumetric contraction as bulk materials, it was found that dense 100 nm lines printed approximately the same size and shape.

Effects of etch barrier densification on step and flash imprint lithography

Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height.

Step and flash imprint lithography template characterization, from an etch perspective

As a means of studying process windows with short turnaround time while avoiding substrate-to-substrate repeatability issues, Step and Flash Imprint Lithography templates were fabricated with physical masking of quadrants during dry etching used to introduce process perturbations. For every 20 s of descum (Ar/O2 etch) time, critical dimensions (CD) were observed to change approximately 2.6 nm on sub-100 nm features. Similarly, increasing Cr overetch time by 20% resulted in a positive CD change of 3.8 nm. Line edge roughness decreased with increasing descum and Cr overetch times. Best overall performance was observed for a 20 s descum used in conjunction with a 110% Cr overetch. Of four tip types studied, sharpened silicon atomic force microscopy tips were able to accurately measure etch depth of 80 nm trenches, but geometrical considerations limited sidewall angle determination to greater than 100°. Cross-sectioning of features on 6×6×0.25 in. quartz plates was successfully accomplished using a focused io...

Spectroscopic ellipsometry measurements of thin metal films

Optical methods are used to determine the thickness of thin metal films, with emphasis on spectroscopic ellipsometry and transmission. We discuss the conditions where this is possible and how to determine the optical constants for the material. The determination of the thickness of each of two metals in a bimetallic stack is discussed. Finally, by measuring thickness with these methods and measuring weight gain, we determine the density of platinum deposited by evaporation and deposited by a simple sputter deposition method. Explicitly, one of the results is that the determined optical constants depend on the deposition method. This implies that, with only a few exceptions, one must determine the optical constants of the material of interest, and that it is inappropriate to use values from another source such as a handbook or from another investigator. The resulting optical constants in this work suggest that the microstructure of the platinum films from the two different methods will not be the same, and x-ray diffraction and sheet resistance measurements verify that this is the case. Specifically, the significantly lower extinction coefficient of the sputter-deposited films correlates with a higher sheet resistance.

Optimizing the ellipsometric analysis of a transparent layer on glass

In this work we show how to choose optimum analysis conditions to analyze a transparent film on a transparent substrate where the index of refraction for the film is not very different from that of the substrate. We show that there are three ‘zones’ from which to choose the angle of incidence and that one should choose one angle in each zone. We discuss theoretically the basis of these three zones and how to determine the boundaries. Oxynitride on glass and polymer on glass are used as examples and the data and analysis are shown. Copyright

32.5L: Late-News Paper: Multitouch Pixilated Force Sensing Touch Screen

In this paper we discuss the advantages of direct touch detection with pixilated force sensing in eliminating false readings and improving accuracy in locating touch centers. We also show the properties of the transparent force sensing layer and demonstrate a 3.5 inch prototype touch panel that senses both location and force of touch actions and is multitouch capable.

Effect of process parameters on the optical constants of thin metal films

In this study, we show that the optical constants of sputter-deposited chromium depend on the argon pressure used for the deposition. Higher argon pressure gives lower extinction coefficients. Sheet resistance measurements show that those materials with lower extinction coefficients also have lower conductivity. Whereas the argon pressure strongly affects the resulting optical constants of the film material, the choice of substrate material does not affect the resulting optical constants of the film.

Effect of annealing temperature on physical properties of thin epitaxial PZT films on STO/Si substrates

In this work, we report the effect of annealing temperature on the properties of epitaxial PbZr0.52Ti0.48O3 (PZT) films deposited using sol-gel techniques on (001) Si substrates with a thin, epitaxial SrTiO3 (STO) interlayer. The STO is grown on silicon using molecular beam epitaxy (MBE) and acts as the template for PZT growth. We report the values for stress, density, thickness, and refractive index vs. anneal temperatures for a thin PZT film. AFM surface roughness values of less than 0.4 nm are typical for this film. XRD patterns show the film to be c-axis orientated, with PHI scans demonstrating that the [100] PZT is orientated along the [110] Si direction. SEM cross-sections show the film morphology is free of gain boundaries and are clear of interfacial layers from the multiple spin/bake/anneal deposition technique, thereby making this material an excellent candidate for electro-optic applications.

Recovery of Mo/Si multilayers coated LTEM substrate

Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor that is coated with Mo/Si multilayers. One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. The starting substrates, due to the required tight specifications of flatness and defects, might have a very high manufacturing cost and hence a method to recover these substrates for reuse without compromising the properties will enable a lower cost for the masks. This paper details a potential approach to remove the damaged multilayers from the substrates without compromising the morphology and characteristics of the starting substrate. Furthermore, the process is applicable to optical elements of the EUV projection optics system that have reflective Mo/Si mirrors of various shapes.

Fabrication of a monolithically integrated multiple wavelength Fabry-Perot filter array using transparent etch stop layers for accurate wavelength determination

In this paper we describe a method of fabricating a Fabry-Perot filter array consisting of four distinct wavelengths using a stopping layer, which in turn is discriminately measured. Precise control of the oxide thickness is demonstrated by using reflectance to measure center wavelengths (CWL) between 645nm-822nm with full width half maximum (FWHM) values of 15 nm. These parameters are used to confirm good narrow band filter characteristics. The physical and chemical properties of an oxide layer converted from a silicon-carbon-nitride (SiCN) etch stop layer (ESL) is reported for both as-deposited and the resultant oxidized film. The filter array can be fabricated directly on top of silicon photo diodes, to form a complete multi-wavelength sensor system. Fabricating a multi-wavelength filter array using etch-stop layers can provide better thickness control and across wafer uniformity compared to a timed-etch approach.