Enhancement of height resolution in direct laser lithography. Mack national security agency 9800 savage road fort meade, maryland 207556000 abstract. Therefore, techniques to enhance the performance of optical lithography are of particular technological and economic signi. In the overlapped region, these two spots generate a small interferogram that shortens the depth of focus. Production of a fine pattern is necessary to get a high integration degree of integrated circuits. Photolithography yield enhancement due to reduced consumption. The point spread function and the natural linewidth of a phase edge were also shown to be natural metrics of imaging resolution. Depth of focus to measure the size of a focusexposure.
As optical lithography advances into the 90nm technology node and beyond, minimum feature size outpaces the introduction of advanced lithography hardware solutions. Theoretical verses actual resolution and depth of focus results will be presented using the following materials. Ee143 f2010 lecture 4 22 ee243 s2010 lec 11 firstorder projection printing considerations 1 minimum feature resolution lm k1. Glaubitzb afraunhoferinstitut fiir mikrostrukturtechnik, dillenburgerstr. Enhancement of photolithography resolution by fractional fourier domain filtering. Microelectronic engineering 17 1992 9398 elsevier 93 increasing resolution and depth of focus in optical microlithography through spatial filtering techniques w. Optical image simulations indicate that the 20nm resolution is feasible for both the periodic grating feature and the twoslit feature. Annular illumination has been studied as a method for improving depth of focus dof in microlithographic systems. The width of the rectangle represents the builtin focus errors of the processes, and the height rep.
Resolution enhancement techniques in optical lithography. Nominal depth of focus dof position for both features is identified through the image contrast calculations. Any serious student interested in a career in the semiconductor industry or lithography should consider this book as. Corr achieves improved depth of focus and substan tial improvement in cd control wi,h negligible timing, area, or cpu overhead. Understanding focus effects in submicron optical lithography. As the fundamental limits of optical lithography are approached, the nonlinear optical properties of the photoresist. Common uses of the terms resolution and depth of focus dof are explored. Depth of focus the effect of focus on a projection lithography system such as a stepper or a scanner is a critical part of understanding and controlling a lithographic process. This improvement in resolution, depth of focus and reduced interference, allows the fabrication of new and denser integrated circuits without the required capital equipment investment. The depth of focus of the eye is of importance to the ophthalmologist primarily as it relates to visual acuity. Field guide to optical lithography the material in this field guide to optical lithography is a distillation of material i have been putting together for the last 20 years or so.
Enhanced depth of focus was achieved using ges contrast enhancement material 388 with the positive resists tested. Wafer metal oxide line variations in surface heights of a processed wafer must be less than the optical depth of focus. However, this improvement comes at the expense of decreasing radial concentration of energy in the point spread function. Upon completion of this section, you will be able to. Pdf focus drilling for increased process latitude in. Since the 0th diffracted order traverses the optical system perpendicular, i. The edge bead may also cause focus offset problems if exposure is performed via contact lithography photomask in direct contact with the photoresist film. The resolution and depth of focus scaling of lithography technologies using 193 nm, 193 nm with.
The feature size control parameters are depth of focus dof. These resolution enhancement technologies include phase shift mask techniques 14, offaxis illumination 5,6, pupil filtering. Microlithographic techniques in ic fabrication, spie vol. Osa depthoffocus dof analysis of a 193nm superlens. The effect occurs when dense and isolated features of identical size on the photomask image with differing sizes on the wafer. As ic device dimensions grow smaller, circuits outpace the introduction of shorter exposure wavelengths and higher numerical aperture lenses, increasing the importance of. The theoretical and actual image distortion effect at focus values outside the theoretical depth of focus range is examined and the impact of future lenses coupled with current process technologies will also be discussed. Lately, optical lithography is being pushed into a regime of extremenumerical aperture extremena. By using this phenomenon, we are able to overcome the height limitation of direct laser lithography. The lab offers a general training session for lithography processing including details of process steps and the tools available.
Performance improvement in gate level lithography using. A new method of enhancing focus latitude in optical lithography. Resolution enhancement techinques for optical lithography. Carsten kohler, focus drilling for increased process latitude in highna immersion lithography, optical microlithography xxiv, proc. Photo s through light litho s stone graphy writing. A new approach for characterizing resolution and depth of focus dof in optical microlithography is introduced. Introduction optical lithography his been a key enabler of the ag gressive ic technoiogy scaling irnpiicit in moores law. Depth offocus and its association with the spherical. Photolithography yield enhancement due to reduced consumption of the usable depth of focus resulting from advanced wafer back surface clean processing abstract. Study of air bubble induced light scattering effect on image.
Advanced light source technologies that enable highvolume. Typically, scanning projection systems are capable of about 1. Optical lithography also termed photolithograpy or uv lithography is the patterning of masks and samples with photoresist prior to other processing steps e. Spatial frequency analysis of resolution enhancement technology. Layout impact of resolution enhancement techniques. By lowering the numerical aperture of the projection optics, the measured depthoffocus is unchanged, but assist feature printing can. Both image contrast and depth of focus have been improved by the pupil filtering method. Contrast enhancement materials for yield improvement in. For example, when determining the range of clear vision of an early presbyope at near, the examiner determines the range of distances from the eye within which the patient can clearly read print of a given size. A numerical aperture larger than 1 can be achieved by immersing the whole wafer in an immersion media. The depth of focus of the eye jama ophthalmology jama network. Increasing resolution and depth of focus in optical. The governing equations are also derived in this manuscript by using the gaussian beam model.
The experiment measured 80 nm target size features that were generated using a 100 nm nominal final size reticle feature on a 1. Resolution and depth of focus in optical lithography. Wafer metal oxide line high resolution small depth of field lithography can focus on point a or b but not a and b simultaneously a b. The resolution is increased by a factor equal to the refractive index of the liquid. The distance between wavefronts is called the optical path difference opd. We realize the depth of focus dof criterion applies only to a feature at the resolution limit of the imaging system.
Photolithography, also called optical lithography or uv lithography, is a process used in microfabrication to pattern parts on a thin film or the bulk of a substrate also called a wafer. Lithography control and optimization 71 depth of focus to measure the size of a focusexposure process window, the. The focus of this paper is to report the results of using psl with a broadband uv light exposure and then coupling it with im. Resolution, depth of focus, and depth of field circular aperture diffraction. The use of lithography to redevelop lord rayleighs criteria for resolution and depth of focus was discussed. Na has contradictory effects on lm and dof where k1 and k2 are the technology factors. Resolution enhancement for advanced mask aligner lithography using phaseshifting photomasks t. Pdf focus drilling for increased process latitude in high. The system performance of the the iline 10x wafer stepper with the zeiss prototype 0. Evolution of optical lithography contact and proximity printing 1. Ee143 f2010 lecture 4 1 photolithography minimum feature resolution depth of focus overlay errors photoresist response ebeam and euv lithography key topics.
Likewise, the pitch resolution defines the smallest pitch that can be printed, and is often simply related to fundamental optical parameters. Depth of focus and resolution enhancement of iline and. Enhancement of submicron optical lithography performance using phaseonly pupil filters enhancement of submicron optical lithography performance using phaseonly pupil filters chen, h. Optical proximity effects refer to those proximity effects that occur during optical lithography even though they may not be caused by optical phenomenon. There are a variety of lithography processes that are available in the lnf.
Yield modeling and enhancement for optical lithography, opticallaser microlithography viii, proc. The aim is to maintain high pattern fidelity at maximum resolution. The contribution of spherical aberration sa to the enhancement of presbyopic vision and postcataract iol surgery has been a topic of interest and debate among the vision scientists in the recent past. The distance between wavefronts is called the optical path difference opd, which is. Understanding focus effects in submicrometer optical. Subwavelength optical lithography with phaseshift photomasks 238 lincoln laboratory journal volume 14, number 2, 2003 length of the feature plus the distance between two adjacent featuresdecreases. Selected papers on resolution enhancement techniques in. Understanding focus effects in submicrometer optical lithography. A focusexposure dose matrix fem was exposed using variations that approximate those seen in production.
Pdf the use of lithography to redevelop lord rayleighs criteria for. Resolution enhancement techniques rets have, therefore, been required and proposed. The simplest example of an optical proximity effect is the difference in printed linewidth between an isolated line and a line in a dense array of equal. Resolution enhancement by laserspectrum adjusted exposure.
Focus drilling for increased process latitude in highna immersion lithography article pdf available in proceedings of spie the international society for optical engineering 7973 march 2011. Depth of focus dof for normal incidence dof the optical path difference between the 0th order and the order coming from the edge of the lens needs to be smaller than. In describing the resolution and depth of focus of a lithographic system, it is. The fundamental limit of optical lithography is not determined by the optical system alone but rather is an overall contributions from the optics, resist, develop and etching processes.
The continued growth of the semiconductor manufacturing industry has been due, in large part, to improved lithographic resolution and overlay across increasingly larger chip areas. Thus, rayleigh equations are not sufficient and inappropriate to use to address the impact of na and. Subwavelength lithography psm,opc semantic scholar. The acceleration of integrated circuit miniaturization is challenging lithographers to push the limits of optical lithography by ever more precise engineering and innovations. However, the high volume nature of microelectronics manufacturing and its stringent environment requirements makes the idea of total immersion too. To examine this tradeoff quantitatively, we first define the average encircled energy as a criterion of the energy concentration over a nonzero axial distance. Depth of focus focusexposure process win dow exposure. Mask linearity and the mask error enhancement factor.
The advantages of afcorr are expected to increase in future technology nodes. Eversmaller ic devices are pushing the optical lithography envelope, increasing the importance of resolution enhancement techniques. While an exact criterion for tolerated is application dependent, a simple example can be used to guide a basic description of dof. Enhancement of photolithography resolution by fractional. Detailed placement for improved depth of focus and cd control. Ozaki, improvement of defocus tolerance in halfmicron optical lithography by the focus latitude enhancement method. Therefore, the trends in optical lithography are towards using smaller wavelength, higher na imaging systems and smaller k1 values to allow the printing of more dense patterns. Introduction to optical lithography eecs 598002 winter 2006. Lecture 7 lithography and pattern transfer reading.
Chris a mack the material in this field guide is a distillation of material put together by chris mack over the past 20 years, including notes from his graduatelevel lithography course at the university of texas. Na2 depthof focus large na results in small depth of focus small na results in large depth of focus depth of focus. Any serious student interested in a career in the semiconductor industry or lithography should consider this book as a must read. Focus must be maintained for at least twice the thickness of the resist thickness. Chapters 8 and 9 and notes derived from a highly recommended book by chris mack, fundamental principles of optical lithography. The conventional methods which utilize high numerical aperture and short wavelength exposure are limited by designing and manufacturing of a practical lens and make the focus depth narrow. Define the optical invariant understand how immersion affects the rayleigh resolution and depth of focus.
Schellenberg section one 1 section introduction resolution and t irhnoranlw n tie diffraction of an objectglass with circular aperture. It uses light to transfer a geometric pattern from a photomask also called an optical mask to a photosensitive that is, lightsensitive chemical. Establishing a suitable definition for a commonly used concept such as depth of focus is not necessarily an easy task. Depth of focus enhancement for 193nm window lithography.
A new method of enhancing focus latitude in laser lithography. The purpose of this section is to understand immersion lithography and its impact on resolution and dof. Apodization, or pupil plane filtering, can be used to enhance the depth of focus of lithographic projection systems. It uses light to transfer a geometric pattern from a photomask also called an optical mask to a photosensitive that is, lightsensitive chemical photoresist on the substrate. We present a design of a 193nm superlens imaging structure to enable the printing of 20nm features. If the object is a plane surface perpendicular to the axis of the optical system, the image of any point on the object must also lie in a plane perpendicular to the axis.
Resolution enhancement for advanced mask aligner lithography. Lithography control and optimization 71 depth of focus to measure the size of a focus exposure process window, the. Michaloski depth of focus and resolution enhancement of iline and deepuv lithography using annular illumination, proc. Thus, for high resolution lithography the surface must be planar flat. Selected papers on resolution enhancement techniques in optical lithography contents xv preface f. I have been subjecting students in my graduatelevel lithography course at the university of texas at austin to my disorganized notes for 14. Okazakispatial filtering for depth of focus and resolution enhancement in optical lithography. Imaging aberrations, defocus, and zernike polynomials definition of a perfect optical system. This column will address the importance of focus by providing a definition of depth of focus. The distance between wavefronts is called the optical path difference opd, which is a function of the defocus distance and the position within the pupil. The fundamental limits of optical lithography system, summarized in 3, 68, refer to the achievable lithography system bounds, e. Depth of focus vs exposure latitude 0 10 20 30 40 50 60 01 234 depth of focus um exposure latitude % no cem cem figure 8 dof vs exposure latitude curve this superior resist performance translated into superior performance after etch as can be seen in figure 9. Depth of focus dof is defined generically as the range of focus that can be tolerated.
Depth of focus and resolution enhancement of iline and deep. True process variation aware optical proximity correction. Optical lithography research has developed several resolution enhancement techniques, including optical proximity correction, offaxis illumination, and phaseshift photomasks 8. Depthof focus large na results in small depth of focus small na results in large depth of focus depth of focus. As feature sizes decrease, their sensitivity to focus errors increases dramatically. Immersion lithography is a photolithography resolution enhancement technique for manufacturing integrated circuits ics that replaces the usual air gap between the final lens and the wafer surface with a liquid medium that has a refractive index greater than one. In particular, the minimum depth of focus margin required for manufacturability of metal layers is extremely dif. This was done to produce features with a high aspect ratio and high resolution. Contrast enhancement is a microlithography technique which extends the practical limits of optical lithography systems.
1316 255 989 1567 1419 547 434 677 971 604 633 521 237 1180 936 7 1086 530 63 753 830 634 957 1066 459 122 549 638 610 506 747 221 843 247 1409 174