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Combined Optical and Electron Beam means to Produce 50 Nanometer Integrated Circuit Patterns

IP.com Disclosure Number: IPCOM000087213D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 66K

Publishing Venue

IBM

Related People

Lin, BJ: AUTHOR

Abstract

Electron scattering limits electron-beam lithography to 250 nm images in less than 100 nm of electron resist, despite the resolution capability in the range of nanometers (nm) of electron microscopes. Optical beam scattering is relatively insignificant, but it is difficult to focus and scan an optical beam to less than 500 nm. Here, a proper combination of the advantages of the two types of exposure system makes it possible to produce 50 nm images with high aspect ratio for fabrication of integrated circuit masks or devices.

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Combined Optical and Electron Beam means to Produce 50 Nanometer Integrated Circuit Patterns

Electron scattering limits electron-beam lithography to 250 nm images in less than 100 nm of electron resist, despite the resolution capability in the range of nanometers (nm) of electron microscopes. Optical beam scattering is relatively insignificant, but it is difficult to focus and scan an optical beam to less than 500 nm. Here, a proper combination of the advantages of the two types of exposure system makes it possible to produce 50 nm images with high aspect ratio for fabrication of integrated circuit masks or devices.

First, a grating mask of 50 nm lines and 100 nm periodicity is required. This grating mask can be produced holographically by interference of two coherent light beams with wavelength ranges from 100 to 150 nm. Given the laser wavelength and refractive index of the photoresist, the angle of the interfering beams is varied to produce exact 50 nm fringes. There are three ways to obtain the VUV (vacuum ultraviolet) coherent light beams.

1) High-order harmonics are obtained from commercially available lasers. For example, 354.7 nm as a peak power of 1.3x10/7/ W can be obtained from a Nd:YAG laser operating at 1064 nm mixed with its second harmonics. The 354.7 nm line is then frequency tripled and quadrupled to yield 118.2 nm and 88.7 nm, respectively [1]. Experiments to generate 40 nm radiation are in progress [2].

2) The fundamental frequency of VUV lasers can be used. Presently, a 116.1 nm electron-beam pumped hydrogen laser has been reported [3].

3) Select a narrow frequency band from a synchrotron light source.

X-ray is used to shadow-expose this grating mask through a convenient thickness of photoresist, generally 500 nm to 1000 nm. Presently, a 100 nm resolution by X-ray through such thickness of photoresist has already been reported [4]. Then the substrate is rotated 90 degrees and re-exposed with the same grating mask to a different exposure level. The photoresist now consists of closely packed squares in four different levels of exposure. After a controlled development, four different thicknesses of photoresist are produced. Let the exposure level of the bright part of the vertically oriented grating be a, and the level of the dark part, a small fraction of a, i.e., p(a). Similarly, let the exposure level of the bright and dark part of the horizontally oriented grating be b and p(b), respectively. Then the four levels of exposure are a+b, a+p(b), b+p(a), and p(a)+p(b), as shown in Fig. 1C. Fig. 1C shows the four exposure levels obtained by double exposing a grating mask with different intensities. The grating mask is rotated by 90 degrees after the first exposure of Fig. 1A, and then the exposure of Fig. 1B is made, yielding the result illustrated in Fig. 1C. By manipulating a, b, p(a), and p(b), an optimum separation of the four levels can be obtained.

Four electron-beam exposure steps intermixed with development...