Photolithographic mask fabrication

#This invention relates to fabrication of photolithographic masks for semiconductor processing.

#Photolithography uses an imaging system that directs radiation onto a patterned mask to form an image that then is projected onto a semiconductor wafer covered with light-sensitive photoresist.

#FIG. 1 is a block diagram of a photolithography imaging system that uses a mask in processing a wafer.

#FIGS. 2A-2G are cross-sectional representations of a mask being fabricated using a fabrication process.

#FIG. 3 is a flow chart of a procedure for fabricating the mask of FIG. 2G.

#Like reference symbols in the various drawings indicate like elements.

#Photolithography uses an imaging system that directs radiation onto a mask to form a pattern and then projects the image of that pattern with a reduction, for example, of 4:1, onto a semiconductor wafer covered with light-sensitive photoresist. The pattern is formed from absorptive features or lines etched into the mask, as discussed below. The radiation used in photolithography may be at any suitable wavelength, with the resolution of the system increasing with decreasing wavelength. The ability to print smaller features onto the semiconductor wafer improves as the resolution increases.

#One type of photolithography system uses radiation in the extreme ultraviolet (EUV) wavelength range. In general, EUV radiation has wavelengths in the range of 1 to 40 nanometers (nm), and the EUV radiation used in photolithography has wavelengths in the range of 10 to 15 nm. Photolithography carried out with radiation in this region has come to be known as EUV lithography (EUVL).