Publisher Summary This chapter provides an overview of electron-beam ULSI applications. Electron-beam lithography is a technology for the transfer of computer aided design pattern data from a digitally stored format to a high-resolution spatial reality on a nominally flat substrate. Its main characteristics are high resolution, due in part to the short electron wavelength, and flexibility, due to the easily modified pattern source. The suitability of the overall lithographic process for the ultimate pattern transfer step is essential for a viable lithographic process. The most common application for electron-beam lithography is in the fabrication of masks and reticles used for projection optical lithography. For this application, the electron-beam lithography process generates the master mask primarily in a serial manner. This mask is subsequently used in projection optical lithography equipment (steppers) to replicate the mask pattern directly onto resist-coated substrates in a parallel manner. The electron-beam lithography process is highly suitable for mask fabrication and provides sufficient resolution for increasingly demanding mask requirements, such as optical proximity correction, phase shifting, and 1X magnification x-ray masks.

Electron-Beam ULSI Applications

Proposed high throughput electron beam systems require a large current, which intrinsically degrades the image quality due to Coulomb interaction effect. For that reason, the maximum achievable beam current is determined by the resolution required. Considerable efforts have been devoted to determine the beam blurs in electron beam systems. However, since measurement of the beam blur is highly difficult, we suggest three beam blur measurement methods in this paper: using process latitude, SEM resist figures and dot mark scan data. Although the results from these three methods do not agree exactly, it is possible to estimate beam blur, 90 nm 120 ran in mask writing system, EBM-3000 (Toshiba).

Effect of beam blur in mask fabrication

Proposed high throughput electron beam systems require a large current, which intrinsically degrades the image quality due to Coulomb interaction effect. For that reason, the maximum achievable beam current is determined by the resolution required. Considerable efforts have been devoted to determine the beam blurs in electron beam systems. However, since measurement of the beam blur is highly difficult, we suggest three beam blur measurement methods in this paper: using process latitude, SEM resist figures and dot mark scan data. Although the results from these three methods do not agree exactly, it is possible to estimate beam blur, 90 nm ∼ 120 nm in mask writing system, EBM-3000 (Toshiba).

A Study on the Effect of Beam Blur in Mask Fabrication

In this article, we introduce the constraints of cell projection mask (CPM) design for application to sub-0.13 μm patterning and the modified fabrication technology for the highly accurate CPM. First, we investigated the constraints of CPM design such as Coulomb interaction and proximity effect. Especially, in order to reduce beam blur effect, we applied mask bias and optimized shot size that could be obtained by calculated space margin and experiment. Second, we made highly accurate CPM using modified fabrication technology, which included deep trench etching process with oxide barrier, the stacked protection layer, and effective cleaning process. The minimum feature size achievable in this technology is 1 μm, corresponding to 0.04 μm on a wafer due to 1/25 reduction ratio of cell projection e-beam lithography system. Using CPM made by above process, we successfully defined 0.08 μm lines-and-spaces and 0.1 μm contact hole patterns with a standard deviation of 0.005 μm. In addition, we also compared the l...

Highly accurate cell projection mask for applications to sub-130 nm patterning

A study on the effect of beam blur in mask fabrication

In the electron beam (e-beam) block exposure lithography, the coulomb interaction effect is a critical problem. In this paper, impact of the coulomb interaction effect on delineating 0.1 micrometer/0.2 micrometer L/S patterns is investigated. We have delineated 0.1 micrometer/0.2 micrometer L/S patterns and have found that line widths and delineation conditions are greatly dependent on the shot current. Two methods for reducing the shot current were examined. By narrowing the line width of L/S patterns from 0.15 micrometer to 0.05 micrometer, the contrast of the e-beam profile increased from 16% to 87% and the dose latitude increased from 0 (mu) C/cm 2 to 18 (mu) C/cm 2 . On the other hand, by reducing the shot size from 4.5 micrometer multiplied by 4.5 micrometer to 1.5 micrometer multiplied by 4.5 micrometer, the contrast of the e-beam profile increased from 16% to 61% and the dose latitude increased from 0 (mu) C/cm 2 to 4 (mu) C/cm 2 . Even though both methods reduce the shot current 1/3, further resolution enhancement is obtained for the former method. We have found that reducing shot current by narrowing the line width is preferable in order to enhance the resolution of L/S patterns.

Impact of the Coulomb interaction effect on delineating densely repeated 0.1-μm patterns using electron-beam block exposure

In the electron beam (e-beam) block exposure lithography, the coulomb interaction effect is a critical problem. In this paper, impact of the coulomb interaction effect on delineating 0.1μm/0.2μm L/S patterns is investigated. We have delineated 0.1μm/0.2μm L/S patterns and have found that line widths and delineation conditions are greatly dependent on the shot current. Two methods for reducing the shot current were examined. By narrowing the line width of L/S patterns from 0.15μm to 0.05μm, the contrast of the e-beam profile increased from 16% to 87% and the dose latitude increased from 0μC/cm 2 to 18μC/cm 2 . On the other hand, by reducing the shot size from 4.5μm x 4.5μm to 1.5μm x 4.5μm, the the contrast of the e-beam profile increased from 16% to 61% and the dose latitude increased from 0μC/cm 2 to 4μC/cm 2 . Even though both methods reduce the shot current 1/3, further resolution enhancement is obtained for the former method. We have found that reducing shot current by narrowing the line width is preferable in order to enhance the resolution of L/S patterns.

Impact of the coulomb interaction effect on delineating densely repeated 0.1 μm patterns using electron beam block exposure

We fabricated 2.6 GHz surface acoustic wave (SAW) filters using an electron beam exposure system. The filter consists of an interdigital transducer of aluminum on piezoelectric material (LiTaO3). Since the LiTaO3 density was high, a large number of electrons were backscattered from the material when exposed by electron beams. When a conventional negative resist was used, the backscattered electrons degraded the image contrast so that resist residue remained on unexposed areas after development. The process margin, which indicates exposure tolerance, was calculated. The process margin was small for LiTaO3, indicating that it is difficult to suppress resist residue when negative resist is used and that a positive resist should be used. To obtain vertical walls of positive resist, we used a 0.4-micrometers double-layer configuration in which the upper layer had a lower sensitivity than the bottom layer. To prevent the piezoelectric substrate from breaking due to the pyroelectric effect, the resist pre- and post-baking temperature was raised gradually at a rate of 5 degrees/minute. The 0.4-micrometers line and space patterns required for a 2.6 GHz filter could be produced accurately. The fabricated SAW filter had a 2.58 GHz center frequency and an insertion loss of 5.0 dB.

Masami Satoh

Papers

Impact of the Coulomb interaction effect on delineating densely repeated 0.1-μm patterns using electron-beam block exposure

Impact of the coulomb interaction effect on delineating densely repeated 0.1 μm patterns using electron beam block exposure

EB lithography for fabricating a GHz SAW filter on LiTaO3 substrate (Poster Paper)