892 Laser Physics, Vol. 14, No. 6, 2004, pp. 892–896. Original Text Copyright © 2004 by Astro, Ltd. Copyright © 2004 by MAIK “Nauka / Interperiodica” (Russia). 1. INTRODUCTION Much of the tremendous progress in integrated cir- cuit technology and performance over the past 30 years has been fueled by the progress in lithography [1]. The ability to print increasingly smaller features has enabled higher speed transistors, higher packing densi- ties, and lower power dissipation in CMOS circuits. The productivity of the integrated circuit industry has been on a very steep performance curve, historically improving the cost per function of integrated circuits by 30% per year over this period. Roughly half of this improvement in productivity can be attributed to con- tinuous improvements in lithography technology. The remainder is due to increases in wafer and chip size and circuit design and process innovations. Leading edge production lithography employs optical projection printing that operates in the conventional Rayleigh dif- fraction limit. Generally speaking, the smallest features that can be reliably printed are equal to the wavelength of the light being used. Historically, the wavelength of light used for production lithography has decreased exponentially. Light sources have evolved from mer- cury arc lamps when they were filtered for the g line (435 nm) and then the I line (365 nm). Recently, exci- mer lasers have been introduced as light sources. Krf excimer lasers produce light in the deep ultraviolet region at a wavelength of 248 nm. Resolution enhance- ment technologies (RET) allow subdiffraction printing by controlling the phase as well as the amplitude of light at the image plane in the printing system through the use of phase shifting masks and other tricks [1]. One other method uses predistorted amplitude patterns at the image plane to compensate for some diffraction effects. The limit of the improvements offered by RET is the ability to print a feature at roughly half the wave- length of the light being used. Now, there are four lead- ing candidates for the next generation lithography tech- nology currently under development. They are X-ray proximity, extreme ultraviolet lithography (EUV), ion projection lithography (IPL), and SCALPEL projection electron beam lithography. At present, research in these fields is being conducted in order to attain dominance in commercial and industrial technology [2]. Now, in this work, we will propose a suitable method for improving the optical lithography resolution without increasing the exposure light frequency. Therefore, we will use the optical limiter as an essential unit for the resolution improvement. Optical limiting action can be performed by some other methods [3]. But in this paper we will adopt reflective-type optical limiters using a nonlinear quarter-wave multilayer stack. Through suit- able design of the multilayer stack, the incident light, after passing through the mask, is selectively transmit- ted with constant amplitude. Now, by using our idea, one can design and implement the mask with two adja- cent lines much closer than in the traditional case. This paper is organized as follows. In Section 2, the optical limiter action based on a reflective nonlinear multilayer stack is discussed. We simulate the coupled wave equation for forward and backward traveling waves. We also obtain the characteristic curve (I out –I in ) and the limiter action. A suitable setup configuration for high-resolution optical lithography is proposed in Section 3. Results and a discussion of our proposal are considered in Section 4. The paper ends with conclu- sions in Section 5. 2. OPTICAL LIMITERS In our proposal, the optical limiter has a key role in decreasing the minimum linewidth. In this case, we will examine the Kerr-like nonlinear periodic media [4–6] as an optical limiter. For simplicity, we consider the one-dimensional structure shown in Fig. 1. In this structure, the index of refraction can be expressed as (1) n n 0 n L n NL , + + = NOVEL METHODS OF LASER TECHNOLOGIES A Proposal for High-Resolution Photolithography Using Optical Limiters A. Rostami and A. Rahmani OIC Design Lab., E. Eng. Dept., Faculty of Engineering, Tabriz University, Tabriz, 51664 Iran e-mail: rostami@tabrizu.ac.ir Received May 20, 2003 Abstract—The main problem of the traditional photolithography in microelectronics and photonics engineer- ing (minimum linewidth) can be reduced using optical limiters. In this work, nonlinear Bragg grating (Kerr-like nonlinearity) is used as an optical limiter. Also, a suitable setup configuration for high-resolution photolithog- raphy based on an optical limiter is proposed. The minimum linewidth for integrated systems with this config- uration can decrease depending on the grating parameters. We show that the linear and nonlinear index of refractions profile parts and the number of layers in the proposed grating determine the minimum linewidth.