Abstract:
An extreme ultraviolet lithography mask may be heated locally to change its reflectivity and to adjust for proximity and other optical disturbances. The localized heating may result in the formation of silicide at the molybdenum silicon interface in the multilayer stack that makes up the extreme ultraviolet lithography mask.

Description:
BACKGROUND  
       [0001]     This invention relates generally to lithography.  
         [0002]     In extreme ultraviolet lithography, a multilayer mask blank exhibits localized reflectivity to define features which may be transferred from the mask to a semiconductor wafer in repeatable fashion. The use of extreme ultraviolet lithography enables relatively smaller feature sizes to be transferred.  
         [0003]     Mask aerial images may be subject to the so-called proximity effect associated with the limitations of the exposure projection lens. The proximity effect is an optical effect that causes features at different pitches to be printed at different critical dimensions for the same exposure dose. The distortion of the mask image may also include line end shorting, due to the resolution limit of the projection lens.  
         [0004]     Proximity correction and mask pattern distortion correction may be accomplished by modifying the mask design. For example, in order to adjust the pitch dependent feature&#39;s critical dimension, lines on the mask may be designed either larger or smaller than the size desired to be transferred, to compensate for the proximity effect. In the case of line end shorting, additional chromium absorber may be added to that end. These modifications, in many cases, push the mask fabrication to its limit. The problems include not only a huge amount of data handling, but also the resolution limitation in mask patterning due to small correction features, very long inspection time, and possible data confusion.  
         [0005]     Thus, there is a need for a better way to correct the proximity effect in extreme ultraviolet lithography masks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a cross-sectional view of one embodiment of the present invention;  
         [0007]      FIG. 2  is a top plan view of a schematic embodiment of the present invention;  
         [0008]      FIG. 3  is a schematic depiction of one embodiment of the present invention; and  
         [0009]      FIG. 4  is a simulation of critical dimensions in nanometers versus pitch in nanometers for lines at different pitch. 
     
    
     DETAILED DESCRIPTION  
       [0010]     Referring to  FIG. 1 , an extreme ultraviolet lithography multilayer blank may include a stack  12  made up of a plurality of pairs of molybdenum and silicon layers. In one embodiment, forty such pairs may be included. These pairs may be deposited one after the other. A substrate  14  may be provided underneath the stack  12 . In some embodiments, apertures may be made through the stack  12  to define features to be transferred.  
         [0011]     The reflectivity of the blank  10  may be locally modified by local heating. The heating pattern depends on the mask data design and the need for proximity correction. Once the mask design is known, the heating patterning and dose can be designed and provided to a heating tool. The heating tool can be, for example, an electron beam tool, an ion beam tool, or a laser. The heating pattern and dose may then be controlled by software in the heating tool, for example. In the case of electron beam heating, the heating pattern generation may be similar to that of standard resist electron beam writing.  
         [0012]     Referring to  FIG. 2 , in a simple case, a first plurality of dense lines  22  with one spacing are juxtaposed across from an isolated line  20  with a different spacing. The isolated line  20  and the dense lines  22  are printed together. With a given exposure dose, the isolated line  20  may print smaller than the dense lines  22 . This indicates that a lower dose is needed for the isolated line  20 .  
         [0013]     The modification of dose can be achieved by locally heating the dotted line region R in  FIG. 2 . By controlling the heat intensity, the desired reflectivity reduction can be achieved. Basically, the peak reflectivity is reduced and is shifted to shorter wavelengths in response to heating due to some silicide formation at the molybdenum and silicon interfacing layers in the stack  12 . The reflectivity reduction at the exposure is achieved via both directly reducing the blank peak reflectivity and shifting the reflectivity spectrum away from the exposure wavelength.  
         [0014]     After the blank reflectivity modification is done, the mask pattern may be aligned to the blank modified reflectivity region. The alignment requirement for general proximity correction can be relatively loose. Where more sophisticated pattern correction is involved, such as in line end shorting, the alignment may become more important.  
         [0015]     The same concept of reflectivity correction can also be applied after the mask is patterned. In this case, alignment can be done by directly using the mask pattern.  
         [0016]     Referring to  FIG. 4 , simulation results show the printed line critical dimension on the wafer versus pitch with or without dose correction. The targeted line width is  27  nanometers. The reflectivity corrected mask in this case has four different reflectivity regions with corresponding dose ranges from a nominal −7.1%, −21.4%, and −42.8%, respectively.  
         [0017]     Referring to  FIG. 3 , in one embodiment of the present invention, the mask  10  may be exposed to localized heating from an irradiation source  24 . The source  24  generates a beam L which is directed by a micromirror device  26  towards the mask  10  and, particularly, at the region desired to be corrected. A controller  28  may run software which controls the positioning of either or both of the micromirror  26  and the irradiation source  24  to direct the local heating as desired. The intensity of the irradiation source  24  may also be adjusted by the controller  28  to achieve the desired results.  
         [0018]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.