Phase-shifting masks

Fig. 38. Diagram comparing the optical characteristics of a standard binary chrome mask with a phase-shift mask. The changes in the electric fields introduced by the phase-shift elements result in a sharper light intensity profile at the wafer surface.

Poster 16. Sung Kwan Kim, Yang-Soo Kim and Kwangsoo No (Korea Advanced Institute of Science and Technology) The Electronic Structures and Optical Properties of Hf-O-N Thin Films as a Phase Shift Mask for ArF Laser Lithography... 

Lithography In order to precisely resolve the nanometer structures in microelectronics, various enhancement techniques have been applied to the current optical exposure tools that are equipped with deep UV light (193 nm wavelength). These enhancement techniques include phase-shift masks and immersion lenses (putting a liquid between final lens of the stepper and the wafer). The trade-off for the high resolution of modern steppers is an extremely small depth of focus (DOF) that is around 0.5pm over a typical field size of... 

Using advanced photomask techniques such as phase-shift masks (PSMs,... 

Figure 4.32. The benefits of using phase-shift masks for photolithography. Reproduced with permission from Plummer, J. D. Deal, M. D. Griffin, P. B. Silicon VLSI Technology, Prentice-Hall New York, 2000.

FIGURE 11.14 The SEM image of two linear chains self-assembled from 150-nm polystyrene beads. These polymer beads represent the smallest bnUding blocks that have been snccessfully incorporated into the TASA process. The inset shows an SEM image of the template (a parallel array of trenches that were 150 and 150 nm in width and depth, respectively) that was fabricated using near-field optical lithography with a binary phase-shift mask. 

A number of optical techniques to enhance resolution have been proposed and have played an important role in extending the resolution and life of optical lithography, although they cannot be applied to any pattern sizes or shapes but are pattern-dependent. These techniques include annular and off-axis illumination, phase shift masks, multiple exposures, etc. [505]. 

Higher exposnre doses or longer developing times generate narrower lines (as small as 150 nm) positioned at the contact edges of the featnres on the mask. At these higher exposnre doses, the PDMS mask acts like a near-held phase-shift mask. 

Levenson, N.S. Viswanathan, and R. A. Simpson, Improving resolution in photolithography with phase shifting mask II. Imaging simulations and submicrometer resist exposures, IEEE Trans. Electron Dev. ED-36(6), 753 763 (1984). 

Pouty and A.R. Neureuther, Optical imaging with phase shift masks, Proc. SPIE 470, 228 232 (1984). 

B.J. Lin, The attenuated phase shifting mask, Solid State Technol. 35(1), 43 47 (1992) T. Terasawa, N. Hasegawa, and H. Fukuda, Imaging characteristics of multi phase shifting and half tone phase shifdng masks, Jpn. J. Appl. Phys. 30(1 IB), 2991 2997 (1991). 

Figure 13.9 Conventional and phase-shifting mask technology basics.

Nitayama, T. Sato, and K. Hashimoto, New phase shifting mask with self aligned phase shifters for a quarter micron photolithography, Tech. Digest Int. Electron Dev. Meet., pp. 3.2.1 3.2.4 (1989). 

Furthermore, because chromium has proven difficult to dry etch, there have been considerable efforts expended in finding alternative mask opaque absorber materials. Molybdenum silicide (MoSi) appears to be gaining traction in certain applications, particularly in attenuated phase-shifting mask (att-PSM) and EUV mask applications (see Section 14.3), and even for binary masks. ... 

Figure 13.55 Performance of Shipley s XP0589A resist on SiON BARC on Excitech 157-nm microexposure tool with NA 0.85 and u 0.3. Reticle phase-shifting mask. Soft bake 110°C/60 seconds. PEB 110°C/60 seconds. Resist thickness 200 nm. (Courtesy of the Shipley Corporation.)...

In general, the single-exposure techniques rely on the use of either hyper-NA >1.0 as implemented in immersion lithography (see Chapter 13) or exposure wavelength reduction as implemented in EUV lithography (see Chapter 14) and electron-beam lithography (see Chapter 15). These techniques may be complemented with reticle-based resolution-enhancement techniques such as phase-shifting masks and the like. 

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