Attenuated embedded phase shift photomask blanks

#The present invention is directed to attenuated embedded phase shift photomask blanks and in particular to attenuated phase shift mask (APSM) materials and processes.

#Phase shift masks are gaining attention as the next generation lithographic technique for microelectronic fabrication due to their capability to produce higher resolution images compared to the conventional binary photomasks. Among the several phase shifting schemes, the attenuating embedded phase shifter proposed by Burn J. Lin, Solid State Technology, January issue, page 43 (1992), the teaching of which is incorporated herein by reference, is gaining wider acceptance because of its ease of fabrication and the associated cost savings. There have been a number of variations associated with this scheme to improve the optical properties of the photomask, i.e. tunability of the optical transmission and resistance against photon irradiation and chemical treatments.

#157 nm lithography is being considered as a post 193 nm lithography scheme. Currently, there are no mature APSM materials for 157 nm that exhibit appropriate optical properties, tunability, radiation and chemical durability, etch selectivity, low defects, and ease of manufacturability. Previously in U.S. appl. Ser. No. 9/793,646 filed on Feb. 26, 2001, we disclosed an APSM Material and process based on SiTiN,SiTiON system for 193 nm lithography—the teachings of which are incorporated herein by reference.

#These and other objects, features and advantages of the present invention will become apparent upon a consideration of the following detailed description and the invention when read in conjunction with the drawing Figures, in which:

#FIG. 1 shows two schematics of APSM. (a)single layer approach and (b)bi-layer approach.

#FIG. 2 is a Transmission curve as a function of wavelength for a single layer approach, in particular SiTiON.

#A composition of matter and process is invented for fabricating photomask blanks that produces phase shifting films having tunable optical characteristics (%T,n and k) (T is the transmission; n is the index of refraction; and k is the extinction coefficient) with 180° phase shift at 157 nm and with good stability against laser irradiation and chemical treatment, as well as a good etch selectivity. The phase shifting films comprise of a bi-layer structure. The layer adjacent to the substrate controls the %T and also acts as an etch stop layer while the other layer on top acts as the phase shifting layer. The first layer comprises a metal or metal based film. An example will be given for titanium and tantalum. The phase shifting films comprise silicon and a metal and nitrogen and/or oxygen. The metal can be an element from the groups II, IV, V, transition metals, lanthanides and actinides. An example will be given for titanium as the metal. The invention comprises a phase shifting layer (SiwTixNyOz, here w is in the range 0.1 to 0.6, x is in the range 0 to 0.2, y is in the range 0 to 0.6, z is in the range 0 to 0.7) on top of a etch stop layer (metal or metal based layer) which is deposited on a substrate (quartz, fluorinated quartz, CaF2, or Al2O3, etc), the methods for forming the layers.

#1. Deposition

#The thin film can be deposited by sputter deposition (RF, DC magnetron, AC magnetron, pulsed bipolar DC magnetron, RF diode sputtering, or other sputter deposition methods familiar to those skilled in the art) from either a single target of a composite material (for example, Si1−xMx, with x in the range 0 to 0.5 and M representing an element from either groups II,IV,V, transition metals, lanthanides and actinides) or two or more targets of different compositions (for example, SiO2 and M targets, or Si1−xMx and M targets). Variation in composition of the composite targets or individual variation of power and deposition time of the pure targets produces changes in film composition. Reactive sputtering with nitrogen and oxygen provides further capability to adjust the relative compositions of Si, M, and N and O, and thus the optical characteristics of the film. The substrate stage can be either stationary or planetary for the single target, and planetary for the multitarget with rotation speed adjusted accordingly.