Application of the generalized curvilinear variable axis lens to electron projection

Abstract

Variable axis lens of mixed electrostatic and magnetic fields and its application in electron-beam lithography systems J.Electron and ion optical design software for integrated circuit manufacturing equipmentThe concept of the curvilinear variable axis lens ͑CVAL͒ has been introduced for the optics of projection reduction exposure with variable axis immersion lenses, an approach to electron projection lithography reported elsewhere. In the proof-of-concept system the special case of a planar CVAL following the fundamental imaging ray of the lens system was implemented and next generation lithography-commensurate performance was demonstrated. The present work addresses the question of whether general types of CVAL with different configurations of the optical elements are practical and acceptable in performance. Specifically, an analysis is presented of the performance trends of such optics in terms of blur and distortion depending on configuration, number and position of the optical elements in the system, as well as their relative drive requirements.

Evolution of electron projection optics from variable axis immersion lenses to projection reduction exposure with variable axis immersion lenses

“…Three dynamically adjustable lenses ͑''focus coils''͒ are needed to maintain not only focus, but also subfield size and orientation over the entire deflection field. Although arrived at differently, it exhibits characteristics predicted as key by the above mentioned fundamental investigation, 18 namely a trajectory flatter than r b and with slight, but specific, deviation from planarity. A third stigmator can be used to compensate deflection astigmatism, in essence to linearize the deflection.…”

“…18 The precept was that first and third order deflection aberrations are to be eliminated, the remainder and the fifth order aberrations evaluated by varying number and positions only of the deflectors, identifying trends and correlations with performance. The concept was expanded to the ''generalized'' or ''3D''-CVAL, not only blurring the distinction between lens axis and beam shifting, but also between deflection and ͑dynamic͒ correction.…”

Electro-Optic Characteristics of a Cooled Deuterated Potassium Dihydrogen Phosphate Crystal

“…The CVAL is designed to minimize the deflection aberrations but the dynamic image correction which has to be performed is a key technology in EPL systems, particularly EB stepper. Aberrations should be corrected as follows: 7,8) -deflection field curvature, -deflection astigmatism, -linear shape errors (Magnification, rotation, orthogonality, anisotropic-magnification errors) -beam positioning error The EO system is required to have at least two sets of dynamic stigmators, three dynamic focus lenses, and a positioncorrection deflector. Moreover, fourfold distortion must be considered, which is nonlinear and influences the stitching accuracy.…”

Correcting deviations in the shape of projected images in the electron beam block exposure column

“…1,2 The electron beam projection lithography system ͑EPL͒ by Nikon and IBM provides larger subfield size of 250ϫ250 m exposed in a single shot with larger deflection field width of 5 mm than conventional electron beam lithography tools. 3 The EPL has two sets of stigmators, three dynamic focus coils and an additional deflector, which are combined to correct dynamically deviations in image qualities, shapes, and positions. But larger field size requires complete adjustments of electron beam trajectories to reduce aberrations of the image.…”