Abstract:
A photo mask blank structure for transferring a mask to an integrated circuit includes a transparent substrate, which has a surface region. The photo mask structure further includes an opaque film overlying the surface region, a negative photoresist material overlying the opaque film, a stop layer overlying the negative photoresist material, and a positive photoresist material overlying the stop layer. The positive photoresist material includes a first opening pattern, and the stop layer includes a second opening pattern that is associated with the first opening pattern of the positive photoresist material. The negative photoresist material includes a third opening pattern that is associated with the first and second opening patterns. The stop layer provides a separation between the negative photoresist material and the positive photoresist material.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 12/163,533, filed Jun. 27, 2008, entitled “Method and Structure for Fabricating Dark-Periphery Mask for the Manufacture of Semiconductor Wafers”, the entire content of which is herein incorporated by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to integrated circuits and their processing for manufacture of semiconductor devices. More particularly, the invention provides a method for manufacturing a photolithography mask for the manufacture of advanced integrated circuits such as dynamic random access memory devices, static random access memory devices (SRAMs), application specific integrated circuit devices (ASICs), microprocessors and microcontrollers, Flash memory devices, and others. 
     Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Conventional ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across. 
     Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of U.S. dollars to build. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. 
     An example of such a limit is an ability to manufacture the masks that are used in performing lithography for the manufacture of integrated circuits. A commonly used mask is called a phase shift mask. Phase shift masks have been used to print feature sizes of few microns using interference patterns from illumination sources and positive photoresists. Unfortunately, conventional processes to manufacture phase shift masks have become difficult to perform in an efficient and accurate manner. For example, negative photoresists have been employed for making masks for devices of feature sizes of less than 0.18 microns. Although such negative photoresists perform better than positive photoresists, processing time is much longer. Often times, thirty to sixty percent of the negative photoresist should be exposed, which further adds to processing time. Additionally, conventional processes seem to be cumbersome and cause quality problems in the masks themselves. These and other limitations are described throughout the present specification and more particularly below. 
     From the above, it is seen that an improved technique for processing semiconductor devices is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, techniques for the manufacture of semiconductor devices are provided. More particularly, the invention provides a method for manufacturing a photolithography mask for the manufacture of advanced integrated circuits such as dynamic random access memory devices, static random access memory devices (SRAMs), application specific integrated circuit devices (ASICs), microprocessors and microcontrollers, Flash memory devices, and others. 
     In a specific embodiment, the invention provides a method for manufacturing a mask for integrated circuit devices. The method includes providing a substrate, e.g., glass plate. The substrate includes an opaque film overlying the substrate, an overlying negative photoresist layer, a stop layer (e.g., insulating layer) overlying the negative photoresist layer, and a positive photoresist layer overlying the stop layer. These layers form a sandwich structure. The method then patterns the positive resist layer to form one or more window openings in the positive photoresist layer, while maintaining protection of the underlying negative photoresist via etch stop layer. Preferably, the exposure time for the positive resist is opened up within a predetermined window. The method removes the exposed stop layer within the one or more window openings to expose a portion of the negative photoresist layer and patterns the exposed portion of the negative photoresist layer. The method includes a step of developing the exposed portion of the negative photoresist layer and removing exposed portions of the opaque layer to expose an underlying portion of the substrate. The method includes removing any remaining portions of the negative photoresist layer, stop layer, and positive photoresist layer to provide a patterned mask using a portion of the opaque layer. Alternatively, the patterned positive photoresist film is removed before patterning the negative photoresist film. 
     In an alternative specific embodiment, the invention provides a method for manufacturing integrated circuit devices. The method includes providing a substrate, which includes an opaque film overlying the substrate. The system also has an overlying negative photoresist layer, a stop layer overlying the negative photoresist layer, and a positive photoresist layer overlying the stop layer. The method includes patterning the positive resist layer to form one or more window openings in the positive photoresist layer. The method also includes removing the exposed stop layer within the one or more window openings to expose a portion of the negative photoresist layer and patterning the exposed portion of the negative photoresist layer. The method includes developing the exposed portion of the negative photoresist layer and removing exposed portions of the opaque layer to expose an underlying portion of the substrate. The method further includes removing any remaining portions of the negative photoresist layer, stop layer, and positive photoresist layer to provide a patterned mask. The patterned mask is used for a manufacture of integrated circuits. Alternatively, the patterned positive photoresist film is removed before patterning the negative photoresist film. 
     In yet an alternative specific embodiment, the invention provides a photo mask blank structure for integrated circuit device. The photo mask blank structure has a transparent substrate having a surface region and an opaque film overlying the surface region. A negative photoresist material is overlying the surface region. A stop layer is overlying the negative photoresist material. Preferably, portions of the stop layer and/or portions of the positive photoresist layer prevent any possibility of the negative photoresist from being exposed and damaged before patterning. The structure also has a positive photoresist material overlying the stop layer. Preferably, the structure is for the manufacture of a phase shift mask but can also be for other mask structures. 
     Many benefits are achieved by way of the present invention over conventional techniques. For example, the present technique provides an easy to use process that relies upon conventional technology. In some embodiments, the method provides higher device yields in dies per wafer. Additionally, the method provides a process that is compatible with conventional process technology without substantial modifications to conventional equipment and processes. Preferably, the invention can be applied to a variety of applications such as memory, ASIC, microprocessor, and other devices. Preferably, the invention provides a way to manufacture a half tone phase shift mask using fewer steps, which result in a more efficient process. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more throughout the present specification and more particularly below. 
     Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 through 8  are simplified cross-sectional view diagrams illustrating a method of fabricating a phase shift mask according to an embodiment of the present invention; and 
         FIGS. 9 through 17  are simplified cross-sectional view diagrams illustrating an alternative method of fabricating a phase shift mask according to an alternative embodiment of the present invention 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention, techniques for the manufacture of semiconductor devices are provided. More particularly, the invention provides a method for manufacturing a photolithography mask for the manufacture of advanced integrated circuits such as dynamic random access memory devices, static random access memory devices (SRAM), application specific integrated circuit devices (ASIC), microprocessors and microcontrollers, Flash memory devices, and others. 
     A method for fabricating a mask structure according to an embodiment of the present invention is outlined as follows: 
     1. Provide a substrate, e.g., glass plate; 
     2. Form an opaque film (e.g., chrome) overlying the substrate; 
     3. Form a negative photoresist layer overlying the opaque film; 
     4. Form a stop layer overlying the negative photoresist layer; 
     5. Form a positive photoresist layer overlying the stop layer; 
     6. Pattern the positive resist layer to form one or more window openings in the positive photoresist layer without exposing the negative photoresist layer that is covered by the positive photoresist; 
     7. Remove the exposed stop layer within the one or more window openings to expose a portion of the negative photoresist layer; 
     8. Pattern the exposed portion of the negative photoresist layer, which has covered portions that are free from any damage from preceding processes; 
     9. Develop the exposed portion of the negative photoresist layer; 
     10. Remove the exposed portions of the opaque layer to expose an underlying portion of the substrate; 
     11. Remove any remaining portions of the negative photoresist layer, stop layer, and positive photoresist layer to provide a patterned mask using a portion of the opaque layer; 
     12. Use the patterned mask for the manufacture of integrated circuits; and 
     13. Perform other steps, as desired. 
     The above sequence of steps provides a method for fabricating a photolithography mask according to an embodiment of the present invention. As shown, such steps include use of both positive and negative photoresist films. Preferably, covered portions of the negative photoresist protect such portions of the negative photoresist to form a dark periphery mask. Further details of the present invention can be found throughout the present specification and more particularly according to the Figures described below. 
       FIGS. 1 through 8  are simplified cross-sectional view diagrams illustrating a method of fabricating a phase shift mask according to an embodiment of the present invention. These diagrams are merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown, the method provides a quartz substrate  100 . The quartz substrate includes a chromium film  103  overlying the substrate. Other films can also be used. The method forms a negative photoresist layer  105  formed overlying the chromium film. An insulating layer  107  and positive photoresist layer  109  are formed overlying the negative photoresist film. Depending upon the application various types of materials may be used for the insulating layer  107 . Referring to  FIG. 2 , the method exposes  201  the positive photoresist layer. As shown, exposed regions  203  will be removed via development as illustrated in  FIG. 3 . Openings are formed in the photoresist layer for a mask pattern  301  as also illustrated. 
     The method then etches exposed regions  405  of the insulating film through openings in the photoresist layer, as illustrated by  FIG. 4 . Preferably, dry etching techniques can be used. As merely an example, such dry etching techniques include, among others, plasma etching, reactive ion etching, etc. Plasma etching selectively removes the insulating film from the negative photoresist film. Here, the negative photoresist film acts as an etch stop layer. Alternatively, wet etching techniques can also be used. Referring to  FIG. 5 , the method exposes  501  the negative photoresist to form patterns. The patterns are developed and removed  601  as illustrated by  FIG. 6 . Preferably, the unpatterned portion of the positive photoresist film and/or etch stop layer protects unexposed regions of the negative photoresist. The method etches  701  the chromium film, which has been exposed, as illustrated by  FIG. 7 . Etching occurs without damaging the quartz substrate. The quartz substrate acts as an etch stop in the etching process of the chromium film. The etched chromium film is now patterned to form the mask pattern, which will be used in the manufacture of integrated circuits. Referring to  FIG. 8 , the method then strips  801  the photoresist films and insulating layer. Stripping often occurs using ashers employing an oxygen bearing plasma, which can be mixed with water. Of course, the particular stripping technique depends upon other factors. Depending upon the embodiment, there can be other variations, modifications, and alternatives. Further details of other methods and structures according to the present invention can be found throughout the present specification and more particularly below. 
     A method for fabricating a mask structure according to an embodiment of the present invention is outlined as follows: 
     1. Provide a substrate, e.g., glass plate; 
     2. Form an opaque film (e.g., chrome) overlying the substrate; 
     3. Form a negative photoresist layer overlying the opaque film; 
     4. Form a stop layer overlying the negative photoresist layer, 
     5. Form a positive photoresist layer overlying the stop layer; 
     6. Pattern the positive resist layer to form one or more window openings in the positive photoresist layer; 
     7. Remove the exposed stop layer within the one or more window openings to expose a portion of the positive resist layer; 
     8. Strip the positive resist layer; 
     9. Pattern the exposed portion of the negative photoresist layer; 
     10. Develop the exposed portion of the negative photoresist layer; 
     11. Remove the exposed portions of the opaque layer to expose an underlying portion of the substrate; 
     12. Remove any remaining portions of the negative photoresist layer, stop layer, and positive photoresist layer to provide a patterned mask using a portion of the opaque layer; and 
     13. Perform other steps, as desired. 
     The above sequence of steps provides a method for fabricating a photolithography mask according to an embodiment of the present invention. As shown, such steps include use of both positive and negative photoresist films. Preferably, covered portions of the negative photoresist protect such portions of the negative photoresist to form a dark periphery mask. Further details of the present invention can be found throughout the present specification and more particularly according to the Figures described below. 
       FIGS. 9 through 17  are simplified cross-sectional view diagrams illustrating a method of fabricating a phase shift mask according to an alternative embodiment of the present invention. These diagrams are merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown, the method provides a quartz substrate  900 . The quartz substrate includes a chromium film  901  or other like films overlying the substrate. The method forms a negative photoresist layer  903  formed overlying the chromium film. An insulating layer  905  and positive photoresist layer  907  are formed overlying the negative photoresist film. Depending upon the application, various types of material for the insulating layer. Referring to  FIG. 10 , the method exposes  1101  the positive photoresist layer. As shown, exposed regions will be removed via development as illustrated in  FIG. 11 . Openings are formed in the photoresist layer for a mask pattern  1103  as shown in  FIG. 11 . 
     The method then etches exposed regions  1105  of the insulating film through openings in the photoresist layer, as illustrated by  FIG. 12 . Preferably, dry etching techniques can be used. As merely an example, such dry etching techniques include, among others, plasma etching, reactive ion etching, etc. Plasma etching selectively removes the insulating film from the negative photoresist film. Alternatively, wet etching techniques can also be used. Here, the negative photoresist film acts as an etch stop layer. The method then removes  1301  the positive photoresist using a stripping process or the like (See  FIG. 13 ). As shown, the surface of the patterned layer is free from positive photoresist material. Referring to  FIG. 14 , the method exposes  1401  the negative photoresist to form patterns. Other portions of the negative photoresist layer have been protected via etch stop layer or the like. The patterns are developed and removed  1501  as illustrated by  FIG. 15 . The method etches  1601  the chromium film, which has been exposed, as illustrated by  FIG. 16 . Etching occurs without damaging the quartz substrate. The quartz substrate acts as an etch stop in the etching process of the chromium film. The etched chromium film is now patterned to form the mask pattern, which will be used in the manufacture of integrated circuits. Referring to  FIG. 17 , the method then strips  1701  the photoresist film and insulating layer. Stripping often occurs using ashers employing an oxygen bearing plasma, which can be mixed with water. Of course, the particular stripping technique depends upon other factors. Depending upon the embodiment, there can be other variations, modifications, and alternatives. 
     Although the above has been illustrated according to a specific embodiment, there can be other modifications, alternatives, and variations. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.