Abstract:
A method for fabricating a half-tone mask having a main chip region and a guard-board region, in which a deposition on entire surface by electrolytic process is made possible to simplify the fabricating process, including the steps of providing a transparent substrate, forming a half-tone mask on the transparent substrate, and selectively forming light shielding layers in the guard-board region of the half-tone mask.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a half-tone mask, and more particularly to a method for fabricating a half-tone mask using, an electrolytic process which makes it possible to simplify the fabricating process. 
     In general, in order to fabricate chips, a plurality of chip regions are defined on a wafer using a stepping process. Then the chip regions are subjected to processes for many times. 
     However, in the stepping process in which a half-tone mask of a semitransparent material with a transmissivity of 4-10% is used, regions that have been multiply exposed can happen through the many times of exposure processes. 
     That is, even though the half-tone mask has a transmissivity of 4-10%, a light transmission through the mask having the transmissivity of, 8-20% for doubly exposed regions and 16-40% for four times exposed regions may expose the photoresist, resulting in the form of undesired patterns on the wafer. 
     Accordingly, to solve the aforementioned problem, a region that is not transmissive to lights is required on the half-tone mask, for which a guard-board is provided on at the periphery of a main chip with which multiple exposure can be prevented. 
     The guard-board of the conventional half-tone mask will be explained with reference to the attached drawing. 
     FIG. 1 illustrates a guard-board in the conventional half-tone mask, FIG. 2a is an enlarged sectional view of part &#34;A&#34; the guard-board of FIG. 7, FIG. 2b is an enlarged plan view of the guard-board of FIG. 1, and FIG. 2c is a detail view of part &#34;B&#34; of FIG. 2b. 
     As shown in FIG. 1, a conventional half-tone mask has the main chip 12 at the center, around which a guard-board region 13 is formed. 
     The region excluding the main chip 12 and the guard-board region 13 is an unnecessary region 11 in the mask. 
     The guard-board occupies an area of about 2×10 8  μm 2  in the half-tone mask. As shown in FIG. 2a-2c, the guard-board has a shape of a checker board with a plurality of phase shift layers 20 each having a size of 1.0 μm×1.0 μm. That is, the guard-board is formed by using a method including the steps of forming a phased shift layer 20 of silicon oxide film(SiO 2 ) or SOG(Spin On Glass) on a quartz substrate and forming a plurality of contact holes 20a each having a size of 1.0 μm×1.0 μm with a pitch of 1:1 in the phase shift layer 20. 
     However, the guard-board of the conventional half-tone mask has the following problems. 
     In general masks, contact holes of about 2.0 μm×2.0 μm size are used in fabrication of semiconductor devices. 
     However, the formation of the guard-board of the conventional half-tone mask requires formation of a plurality of contact holes each having a size of 1.0 μm×1.0 μm with a pitch of 1:1. The contact holes have to be formed an area of about 2×10 8  μm 2  maintaining a size error within ±10%, which is a difficult process to carry out. As a result, productivity in mass production drops, causing mask costs to increase. 
     SUMMARY OF THE INVENTION 
     The object of this invention, designed to solve the aforementioned problems, is to provide a method for fabricating a half-tone mask, in which the fabricating process is simplified for improving mass productivity and reducing mask production cost. 
     To achieve the objects of this invention, there is provided a method for fabricating a phase shift mask which has a main chip region and a guard-board region, the method including the steps of providing a transparent substrate, forming a half-tone mask on the transparent substrate, and selectively forming light shielding layers in the guard-board region of the half-tone mask. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 illustrates a guard-board in a conventional half-tone mask; 
     FIG. 2a is an enlarged sectional view of the guard-board of FIG. 1. 
     FIG. 2b is an enlarged plan view of the guard-board of FIG. 1. 
     FIG. 2c is a detail view of a part of FIG. 2b. 
     FIGS. 3a-3e illustrate sectional views of a half-tone mask showing a method for fabricating the half-tone mask in accordance with a preferred embodiment of this invention; 
     FIG. 4 shows an electrolytic system in accordance with this invention; and 
     FIGS. 5a-5b illustrate sectional views of a half-tone mask showing a method for fabricating the half-tone mask in accordance with another embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring the drawings, the method of fabricating a half-tone mask of this invention will be described in detail hereinafter. 
     FIGS. 3a-3e illustrate sectional views of a half-tone mask showing a method for fabricating the half-tone mask in accordance with a preferred embodiment of this invention, and FIG. 4 shows an electrolytic system in accordance with this invention. 
     First, as shown in FIG. 3a, a phase shift layer 22 and a thin metal film 23 are formed successively on a transparent substrate 21, such as quartz. 
     In this time, the phase shift layer 22 is formed of chromium nitride(CrON) or molybdenum silicon nitride(MoSiON) and the metal film 23 is formed of chrome. This metal film 23 used, not as a light shielding layer, but as a semitransparent layer, is very thin. 
     Then, a photoresist film 24 is deposited on the metal film 23. 
     As shown in FIG. 3b, the photoresist film 24 is subjected to photolithography or selective projection of an electron beam to form a photoresist pattern 24a. 
     As shown in FIG. 3c, a chip mask pattern is formed in a main chip region 12 by selectively removing portions of metal film 23 and the phase shift layer 22 by etching process. Then, the photoresist film pattern 24a is removed. 
     In this time, the main chip region 12 and the guard-board region 13 may or may not be separated (FIG. 3b shows they are separated). 
     As shown in FIG. 3d, a photoresist film is deposited again on the entire surface, which is subjected to exposure and development so as to form a photoresist pattern 25 exposing the metal film 23 only in the guard-board region 13. 
     Then as shown in FIG. 3e, a metal is plated in the guard-board region 13 to form a light shielding layer 26 using a selective electrolytic process. Then the photoresist pattern 25 is removed. 
     In this time, the electrolytic process is performed using a system as shown in FIG. 4. 
     That is, the electrolytic process is carried out with an electrolytic solution filled electrolysis tank 18 having the substrate shown in FIG. 3d submerged therein, together with the metal film 23 connected to a cathode, and a metal 19 to be consumed (i.e., a consumer metal, material of the light shielding layer), e.g., chrome(Cr) or molybdenum(Mo). submerged and connected to an anode. 
     Then, the consumer metal 19 is selectively plated on an exposed part of the metal film 23, i.e., on the guard-board region 13. 
     Here, as the electrolytic solution, a sulfuric acid water solution containing chromium oxide is used in case the consumer metal 19 is chrome, and a sulfuric acid water solution containing molybdenum oxide(MoO 2 ) is used in case the consumer metal 19 is molybdenum(Mo). 
     In the meantime, the light shielding layer 26 can be selectively formed in the guard-board region 13 in accordance with another embodiment. 
     FIGS. 5a-5b illustrate sectional views of a half-tone mask showing a method for fabricating the half-tone mask in accordance with another embodiment of this invention. 
     As, as shown in FIG. 5a, a light shielding layer 26 can be formed in the guard-board region 13 using a method including the steps of, depositing a light shielding material 27, such as chrome or molybdenum, on the entire surface under the condition that the substrate having the pattern 25 thereon has been formed using the method explained in FIGS. 3a-3d, and the step of, selectively removing the light shielding material 27 formed on the photoresist pattern 25 and the photoresist pattern 25 using with a lift-off process, as shown in FIG. 5b. 
     The method for fabricating the half-tone mask in accordance with this invention as explained hereinabove has the following advantages. 
     For example, since the light shielding layer can be formed in the guard-board region using an electrolytic process or a lift-off process, the fabricating process is simplified the productivity is improved, and the low cost production of the half-tone mask can be accomplished. 
     Although the invention has been described in conjunction with specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the spirit and scope of the appended claims.