Yasuhiro Someda

New detection method for the 2-dimensional beam shape

An accurate detection of the projected beam shape is the important issue in the electron beam lithography. A new detection system had been developed for obtaining the electron beam shape. The developed system consists of a transmittance mask with hole mark, an electron limiting aperture, and a faraday cup. The transmittance membrane, which has 0.2-micrometers size fine hole marks, was fabricated by double-sided etching. The limiting aperture cuts the scattered electrons that pass through the transmittance membrane. And high contrast can be obtained by the difference between the yields of the electron passing through the hole and that of electrons scattered in the transmittance membrane. Monte-Carlo simulation was performed to estimate the scattering contrast, validity of the system was thus proved. The cell projection beam, which has a 5-micrometers 2 are and a 0.2-micrometers line width, was applied for experiment. The detection contrast of the new method is 18 times higher than that of a conventional method with a dot mark. The detection resolution, which depends on the diameter of the dot or hole, was about 0.2-micrometer. We conclude that the new detection system is suitable for detecting a shaped beam such as cell projection method and electron projection lithography.

Performance improvement in e-beam reticle writer HL-800M

An advanced e-beam mask-writing system HL-800M has been developed for the 0.25-micrometer rule-devices. To meet the design-rule, the targets of this system specifications are critical dimension (CD) control of 30 nm, positioning accuracy of 40 nm, and throughput over 0.5 plate per hour. To achieve CD control, we judged that it was inevitable to increase the acceleration voltage up to 50 kV for patterns smaller than 2 micrometer. However, for patterns larger than 5 micrometer, the e-beam proximity-effect causes the pattern-width linearity to be worse. To achieve the sufficient linearity, proximity correction on the hardware module of the systems was performed. This hardware module executes proximity effect correction for each patterns over the area on the plate, so that total throughput was improved compared with that of the correction by software. Besides, a noise cancellation module was introduced to reduce the errors in the e-beam shot positions. This module detects the vibration noise caused by with the power-supply frequency and feeds the correction signal back to the e-beam deflectors. For positioning accuracy, in addition to the mirror correction using hardware for the stage interferometer, a new positioning-correction function depending on the coordinates of the system was developed. In the results of the exposure evaluations, CD uniformity on a 6025 plate showed width-deviations of 3 sigma were 31 nm (X) and 18 nm (Y). Pattern-width linearities for various kinds of patterns were within plus or minus 50 nm. Furthermore, the noise cancellation module was made the amplitude of the e-beam vibration reduced from 33 nm to less than 8 nm. For positioning accuracy, evaluation patterns measured by the LMS2020 (Leica) showed sufficient results for our target. For throughput, the average of the writing time per 6-inch plate for ten patterns is shorter than our targeted throughput with a dosage of 4 (mu) C/cm2. The HL-800M system is capable of producing reticles for 0.25-micrometer design-rule.

New electron-beam mask writing system for 0.25-um lithography

A new electron beam (EB) mask writing system based on both the Hitachi HL-700MIII and HL-800D systems is developed. The target of the system is a 0.25 micrometers design rule in semiconductor mass-production. To improve critical dimensions (CD) to better than 0.03 micrometers , an acceleration voltage of 50 kV is used with a variable shaped beam method. Further, EB proximity correction using a pattern area density map which is the same as that of HL-800D has been adopted for the improvement of pattern width linearities. This correction system, which consists of hardware only, covers the entire mask area. In the mechanical system, continuously moving stage with constant velocity and three-axis active vibration- isolation are used to improve positioning accuracy to better than 0.04 micrometers . In addition, a new mask handling system in which a robot carries the mask realizes automatic transportation without human assistance. Some experiments to evaluate the new system have been performed. In particular, the characteristics of masks written with an EB accelerated to 50 kV have been investigated. The results of CD pattern uniformity for a 1 micrometers line pattern over the entire mask area are better that 0.025 micrometers . In addition, pattern linearity using EB proximity correction is within +/- 0.03 micrometers . A stitching accuracy of 0.037 micrometers is obtained.

Dynamic space charge effect correction in cell projection lithography

Abstract A system of dynamic space charge effect correction for cell projection lithography has been developed. In cell projection lithography, higher currents are used than in conventional variable shaped beam lithography for very fine LSI patterns. Thus, beam blurring due to Coulomb effects is very important. The features of the correction system are as follows: (1) dynamic refocusing according to beam current through cell apertures, (2) dynamic deflection distortion correction according to beam current and (3) auto beam alignment through cell apertures. As a result, cell patterns are successfully delineated with dynamic space charge effect correction.

Double-shielded objective lens system for electron-beam lithography system

A double shielded objective lens has been developed for an electron beam lithography (EBL) system. The lens structure consists of outer magnetic circuit of permalloy and inner ferrite pole-piece, and the ferrite is isolated from the permalloy by a gap. This gap provides high magnetic resistance and reduces a magnetic flux from the permalloy to the ferrite. Therefore, this lens structure is expected to shield inside against outside magnetic field. Computer simulations showed that the magnetic field along the optical axis from the external magnetic field was reduced to less than 15% in the new lens compared with the previous lens. To evaluate the shielding effect experimentally, the change in the beam position on the stage was measured when an external magnetic field was applied. The shielding ability of the new lens was 50 times as large as the previous lens for the horizontal magnetic field. The double-shield structure was proven to be effective to shield the external magnetic field. Furthermore, in order to confirm shielding ability of the practical system, the positional vibration was measured as intensity fluctuation of a back-scattered electron signal from a tungsten mark edge. The beam vibration caused by an environmental field was reduced to 40% compared with the previous system. Thus, it is clarified that the double shielded objective lens is a valuable means of improving the positional accuracy.

Electron-beam mask writing system for 0.25-μm device generation

The new electron beam (EB) mask writing system based on both the HL-700MIII and HL-800D systems is developed. This system has been developed for semiconductor mass production of 0.25 μm design rule. To improve critical dimensions (CD), higher accelerated voltage of 50 kV is adopted with a variable shaped beam exposure method. Further, EB proximity correction hardware using a pattern area density map, which is the same as that of HL-800D, has been adopted for the improvement of pattern width linearity. In the mechanical system, continuously moving stage, three axis active vibration-isolation and three-point mask supporting are used to improve positioning accuracy and stitching accuracy. In addition, a new mask handling system using a robot realizes full-automatic mask loading. The results of CD uniformity for 1 .tm line pattern are better than 0.025 μm(3σ) and pattern linearity is within ± 0.03 μm. Positioning overlay accuracy among three masks is 0.038 μm(3σ). In addition, a stitching accuracy of 0.037 μm(mean + 3δ) is obtained.