Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Patent
1993-06-24
1995-10-17
Rosasco, Steve
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
430321, G03F 900
Patent
active
054589991
ABSTRACT:
A phase shifting method uses a special interferometer in which the illuminating beam is divided into two or more components and the mask is irradiated from both sides. The pattern to be transferred onto the wafer (the mask) is generated on an optically transmissive substrate by appropriately combining reflective, transparent and absorptive areas. The optical paths of the beams illuminating the back side and the front side of the mask (that will be called transmitted and reflected beams respectively) are chosen so that the phase of the two beams is different by approximately an odd multiple of .pi. radians at the surface of the mask. The combined beams are projected onto the target wafer by suitable optics. The phase difference between the illuminating beams reduces the edge blurring that results from diffraction effects. This steepens the slope of the intensity profile at the edge of the features making it possible to achieve smaller feature sizes in the microlithographic replication without using those phase shifting elements of the conventional phase shifting method which made mask fabrication difficult. As a consequence of the lack of the phase shifting layers, the wavelength range of the method of this invention can easily be extended towards shorter wavelengths, and, further, the new mask is less vulnerable to optical damage. The additional freedom that the phase relation and intensity of the beams can be varied continuously allows for optimization that can lead to improved resolution, compared to conventional phase shifting techniques.
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Newmark et al, "Phase-shifting mask design tool", SPIE vol. 1604 11th Annual BACUS Symp. on Photomask Technology (1991), pp. 226-235.
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Liu, "Systematic design of phase.gtoreq.shifting masks with extended depth of focus and/or shifted focus plane", IEEE Trans. on Semicond. Mfgr, Feb. 93, pp. 1-21.
Cavallaro Joseph R.
Kido Motoi
Szabo Gabor
Tittel Frank K.
Graham John G.
Rosasco Steve
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