Ryusho Hirose

High precision binary optical element fabricated by novel self aligned process

Binary optical elements (BOE) tend to be used frequently in optical equipment because aspherical type BOE is easy to fabricate and the BOE can easily correct chromatic aberration. What makes this technology attractive to industry is that the BOE can be fabricated precisely by the semiconductor micro fabrication technique. However when it is used for more precise optics e.g. semiconductor exposure equipment, more precise BOE are necessary. In some manufacturing processes, we have confirmed that the alignment error between masks is the dominant factor to decrease diffraction efficiency by optical simulation. To study this problem, we have produced a BOE using a novel self-alignment method we have devised, then compared it to a BOE which has being made by a conventional method.

Application of large scale binary optical elements to high resolution projection optics used for microlithography

Binary optical elements (BOEs) are very attractive because of their compactness and high aberration correction abilities. However, in their application to high resolution optics, some critical issues such as the influence of fabrication errors and the behavior of spurious order diffraction beams must be carefully examined. An eight-level BOE, ideally giving 95 % diffraction efficiency, is fabricated by lithographic techniques using a stepper for pattern delineation. A large element exceeding the size of stepper exposure area can be obtained by pattern stitching in the radial and the tangential directions. The performance of these BOEs confirm that it is fundamentally possible to apply BOEs fabricated with currently available techniques to high resolution projection optics used for microlithography.

New g-Line Lens For Next Generation

In order to meet the production requirement for higher integration, g-line lenses of higher NA have been developed. It is generally believed that to enlarge both NA and image field is difficult. The maximum image field achieved with a high NA lens has so far been 15 mm square and the maximum NA of a wide image field lens has been 0.35. Canon has recently developed a new g-line lens of higher NA and larger image field. Results of evaluations so far show that the newly developed lens is the best-suited of any yet made for mass-production of 4M DRAMs. This is the 5x reduction lens with a numerical aperture of 0.45 and a field size of 20 mm square (28.2 mm dia.). In this paper, the performance of this lens is discussed, and SEM resist profiles produced by the new lens are shown. The last section gives an overview of progress in development of projection lenses in terms of the amount of information available, and also discusses the possibility of a lens for 16M DRAMs being developed.

Toward Submicron A New Phase Of Optical Stepper

According to the progress of the LSI design rule, optical lithography has steadily opened its new frontier. As the dimension of the LSI design rules becomes the same as that of the resolution limit, the required image quality becomes higher and higher. Optical lithography corresponded to such requirements by the development of the lens design and simulation technique. Some of the new results are shown in this paper, and the new submicron stepper of 0.8 μm shall be introduced as the fruit of such technique. In addition, some of the new developments which correspond to the submicron lithography are introduced. As a consequence, the future of optical lithography shall be discussed in view of the recent aim of 0.5 μm.