Abstract:
A method of repairing a photomask with a depression defect includes providing a photomask including a depression defect on a transparent substrate, forming a protection layer which covers the depression defect, etching a predetermined depth of the transparent substrate of the photomask with the protection layer as the etch mask, and removing the protection layer and the transparent substrate under the unetched protection layer, wherein a defect free photomask is produced.

Description:
CROSS REFERENCE TO RELATED FOREIGN APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2006-0084251 filed on Sep. 1, 2006. in the Korean Intellectual Property Office, the contents of which are herein incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure is directed to a photomask-defect-repair method and a defect-free photomask. More particularly, the present disclosure is directed to methods of physically repairing defects in a photomask using a high-intensity tip of a repairer and the resulting defect-free photomask. 
     2. Description of the Related Art 
     Photolithography processes are used to implement basic patterns that are used to form various patterns that are the components of a semiconductor device. Thus, photolithography processes are the first processes used to form patterns of a semiconductor device, and can be considered among the most important processes. In photolithography, it is important to obtain a photomask that contains accurate pattern information. Inaccurate pattern information can be introduced by photomask manufacturing, as well as from defects that occur in normal conditions. In particular, a defect that occurs on the surface of the transparent substrate of a photomask can directly affect forming patterns on a semiconductor wafer. Since a transparent substrate of the photomask directly transfers light, the defect can appear on the surface of a wafer. Due to the challenges of obtaining a defect-free photomask, the majority of photomasks are used after performing a defect-repair process. 
     A transparent substrate can have two types of detects. An opaque defect that occurs on the surface of transparent substrate is called a dark defect, and a defect that produces a non-uniform surface of the transparent substrate is called a clear defect. The dark defect occurs when an unnecessary optical pattern remains on the surface of the transparent substrate due to inaccurate patterning or incomplete removal. The dark defect can also occur when an alien substance stays on the surface of the transparent substrate. The clear defect can result from defects of the transparent substrate. Types of clear defects include a depression defect and a protrusion defect. The depression defect is a defect that has a hollow surface. The protrusion defect is a defect that rises high or is protruded. 
     Photomask defects can be repaired using an ion beam or a laser. When using an ion beam, the defect portion is removed using a gallium ion beam or is covered with a carbon layer. When using a laser, the laser is focused on the defect portion for a period of time so that the defect portion is vaporized and therefore repaired. Also, the defect portion can be repaired by etching the transparent substrate to recess the defect portion. 
     The photomask defect repair process needs accurate control. Photomask repair processes, including methods using an ion beam, a laser, and substrate etching, leave repair marks on the transparent substrate. Since the contour of the dark defect is thinner, the repair mark remains after the dark defect is removed by the ion beam or the laser. A “river-bed” phenomenon is one such, repair mark. Repair processes using an ion beam or laser are well known in the art, and therefore detailed descriptions are omitted. 
     Previously, correction marks on the transparent substrate introduced by the ion beam or the laser correct process were negligible. However, due to the increased integration density of semiconductor devices, these subtle defects are no longer negligible. 
     Photomasks with defects are not used in the semiconductor manufacturing process, but are discarded. Since photomasks are expensive, discarding photomasks is costly. In addition, this can hinder the semiconductor manufacturing process since photomasks are not provided in a timely manner. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a defect-free photomask. 
     An embodiment of the present invention also provides a method of repairing defects of a photomask. 
     The above stated objects as well as other objects and features will become clear to those skilled in the art upon review of the following description. 
     According to an aspect of the present invention, there is provided method for repairing a photomask with a depression defect including forming a protection layer which covers the depression defect, etching a predetermined depth of a transparent substrate of the photomask with the protection layer as the etch mask, and removing the protection layer and the transparent substrate under the unetched protection layer. 
     According to another aspect of the present invention, there is provided a photomask-defect-repair method including etching a predetermined depth of a transparent substrate of a photomask including a protrusion defect, and physically removing the protrusion defect with a high-intensity tip of a defect repairer. 
     According to another aspect of the present invention, there is provided a method of repairing a dark defect on a photomask including removing the dark defect, forming a protection layer in an area where the dark defect is removed, etching a predetermined depth of the transparent substrate of the photomask with the protection layer as the etch mask, and removing the protection layer and the transparent substrate under the unetched protection layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A through 1E  are sectional views sequentially illustrating a photomask defect correction method according to an exemplary embodiment of the present invention. 
         FIG. 2A through 2D  are sectional views sequentially illustrating a photomask defect correction method according to another exemplary embodiment of the present invention. 
         FIG. 3A through 3G  are sectional views sequentially illustrating a photomask defect correction method according to another exemplary embodiment of the present invention. 
         FIG. 4A through 4C  are top view images captured during a process of correcting photomask defects according to the exemplary embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Features of embodiments of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. Embodiments of the present invention may, however, be embodied in many different forms and should not be constated as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. In the drawings, the shape and thickness of layers and regions are exaggerated or reduced for clarity. Like reference numerals refer to like elements throughout the specification. 
     Hereinafter, a photomask defect correct method according to an exemplary embodiment of the present invention will be described with reference to  FIGS. 1A through 1E . 
       FIG. 1A through 1E  are sectional views sequentially illustrating a photomask defect correction method according to an embodiment of the present invention. 
     Referring to  FIG. 1A , a depression defect  130  occurs on a transparent substrate  110   a  of a photomask  100  formed on an optical pattern  120 . 
     In this exemplary embodiment, the photomask  100  can be used in a photolithography process for manufacturing a semiconductor device or an LCD panel. A binary type photomask can be used in this exemplary embodiment, but it can also be a PSM (phase shift mask). In the case of the PSM, the PSM can include an optical pattern  120  that weakly transmits light and shifts the phase of the transmitted light, or the PSM can include an appropriate etched transparent substrate  110   a  which shifts the phase of the transmitted light. Thus, the transparent substrate  110   a  according to the present invention can include different kinds of the photomasks exposed to light. 
     The transparent substrate  110   a  is a material transparent to light, and can be made with high purity quartz such as glass or fused silica. 
     The optical pattern  120  is a material opaque to light, and makes an optical image using the transmitted light. The optical pattern  120  can be formed with chrome, or chrome oxide formed on the chrome according to the exemplary embodiment of the present invention. Besides chrome, the optical pattern  120  can be formed of another metal such as aluminum or molybdenum, or another metal oxide can be used instead of chrome oxide. Also, the optical pattern  120  can be a phase shift pattern. In case of the phase shift pattern, the phase shift pattern can be a molybdenum-silicon compound. Generally, this is called a MoSi series compound. That is, it can be various compounds such as MoSi, MoSiN, MoSiON, and others. 
     The depression defect  130  represents the type of defect where the surface of the transparent substrate  110   a  is lower than the surface of surrounding area. Examples of the depression defect  130  include a hole, a trench, a scratch, and a line cut into the surface. 
     Referring to  FIG. 1B , a protection layer  140  covers the depression defect  130 . The protection layer  140  can be a carbon layer. The carbon layer can be deposited with FIB (focused ion beam) equipment, which is equipment for repairing photomask defects. The carbon layer is deposited because the carbon layer has an etch tolerance to the etch gas used in the step that etches the transparent substrate  110   a  to an adequate depth, and carbon is generally used in the FIB equipment. Thus, the protection layer  140  can be made of another material other than carbon that has an appropriate etch tolerance. The thickness of the protection layer  140  is formed such that the thickness provides etching tolerance in the step that etches the transparent substrate  110   a  to an adequate depth. The etching depth of the transparent substrate  140  is not fixed, but can be varied according to light used, so a specific numerical value is not described. For example, the thickness of an exemplary protection layer is about 500 Å. 
     Referring to  FIG. 1C , the transparent substrate  110   a  is etched to a moderate depth, so a recessed transparent substrate  110   b  is formed. As the transparent substrate  110   b  is quartz, the transparent substrate  110   b  is etched by a combination of a main etch gas such as gas including F—, for example, CHF 3  or CxFy series gas (CF 4 , C 2 F 6 , C 3 F 6 , C 4 F 8 ), and an assistance gas such as Ar, Xe, Cl, Br, O, N, and others. The method of etching the transparent substrate  110   b  is well known, so a more detailed description is omitted. 
     At this time, because the optical pattern  120  has a tolerance to the etching gas for forming the transparent substrate  110   b , the optical pattern  120  is not etched and maintains its original shape. In order to avoid exposing the surface of the optical pattern  120  to the etching gas, an etch mask (not shown) is formed on the optical pattern  120 , and then the etching process can be performed. The etch mask can be, for example, a photoresist. 
     The adequate depth represents the depth that allows one who uses the completed photomask  100  to perform a photolithography process without difficulties. For example, if the phase shift function is not required, the depth would allow removing the depression defect  130  with stability. If the phase shift function is required, the depth would produce the phase shift of the light. Since the depth that produces the phase shift of the light can be set according to the wavelength of the light, a specific value is not provided. 
     When the transparent substrate  110   b  is etched to the depth of the recess, a substrate area where the protection layer  140  is formed is not etched and retains its original shape. Thus, a tower shaped defect  150  that has the protection layer  140  on top is formed. 
     Referring to  FIG. 1D , the tower shaped defect  150  is removed using a defect repairer M with high-intensity tip T. The tip T, for example, can be a high intensity material such as diamond. The defect repairer M provides impetus to tip T so that it can physically remove the tower shaped defect  150 . Impetus can make the tip T move in the direction of top, bottom, left, and right, and it can make the tip T vibrate. In a present exemplary embodiment, it is designed to make the tip T vibrate. Thus, in this exemplary embodiment the tip T performs carving, rubbing, polishing, or grinding the tower shaped defect  150 . In the drawing, the defect repairer M can make tip T remove the tower shaped defect  150  by moving from left to right. 
     Referring to  FIG. 1E , the photomask  100 , whose the depression defect  130  is repaired on the transparent substrate  110 , is completed. 
       FIG. 2A through 2D  are sectional views sequentially illustrating a photomask defect correct method according to another embodiment of the present invention. 
     Referring to  FIG. 2A , a protrusion defect  230  occurs on a transparent substrate  210   a  of a photomask  200  which has an optical pattern  220  on one side. The protrusion defect  230  represents all types of defects where the surface of the transparent substrate  210   a  is higher than the surrounding area of the surface. It can he understood as the opposite case of the depression defect  130  shown in  FIG. 1A . 
     Referring to  FIG. 2B , a recessed transparent substrate  210   b  is formed by etching the transparent substrate  210   a  to an adequate depth. In this step, the protrusion defect  230   a  is also recessed, however it is recessed such that it retains the original shape of the defect. A description of the recessing is similar to that of  FIG. 1C . 
     Referring to  FIG. 2C , the protrusion defect  230   b  on the surface of the transparent substrate  210 B is removed using a defect repairer M with the high-intensity tip T such as that described in connection with  FIG. 1D . 
     Referring to  FIG. 2D , the photomask  200 , whose protrusion defect  230  is repaired on the transparent substrate  210 , is completed. 
       FIG. 3A through 3G  are sectional views sequentially illustrating a photomask defect correction method according to another embodiment of the present invention. 
     Referring to  FIG. 3A , a dark defect  330   a  occurs on the surface of a transparent substrate  310   a  of a photomask  300 . The dark defect  330   a  represents all types of defects that are opaque to light on the surface of the transparent substrate  310   a . For example, it can be the defect due to incomplete removal of an optical pattern  320 , or it can be the defect due to the adhesion of an alien substance. In this exemplary embodiment the former case, which is a typical case, is used for illustration. In case of a defect due to the adhesion of an alien substance, it is common that cleaning process or shallow etching process is performed before applying method according to an embodiment of the present invention. If a defect occurs due to a malicious alien substance, it can be removed by applying method according to an embodiment of the present invention. 
     Referring to  FIG. 3B , the dark defect  330   b  present on the surface of the transparent substrate  310   a  is removed using an ion beam L. For example, the dark defect  330   b  can be physically removed by using a gallium ion beam. Another method is to use laser to remove the defect. In this case, the dark defect  330   b  is exposed to laser to be vaporized. The drawing reference index R can be understood as an ion beam gun or a laser gun, and the drawing reference index I can be understood as ion beam or laser. 
     Referring to  FIG. 3C , a river-bed defect  335  occurs after the dark defect  330   b  is removed. The river-bed defect  335  is a type of depression defect. The river-bed defect  335  typically occurs on the surface of the transparent substrate  310   a  after the dark defect  330   a  is removed by using ion beam or laser. Since the contour of the dark defect  330   a , that is the interface between the dark defect  330   a  and the transparent substrate  310   a , is weakly affected by the ion beam or laser, a defect remains on the surface of the transparent substrate  310   a  that is equivalent to the contour. 
     Referring to  FIG. 3D , a protection layer  340  to cover the river-bed defect  335  is formed, similar to the protection layer described in connection with  FIG. 1B . 
     Referring to  FIG. 3E , a recessed transparent substrate  310   b  is formed by etching the transparent substrate  310   a  to an adequate depth. In this step, the portion of river-bed defect  335  protected by the protection layer  340  becomes a stair-shaped defect  350 , similar to the tower defect  150  described in connection with  FIG. 1C . 
     Referring to  FIG. 3F , the stair-shaped defect  350   a  is removed by using a defect repairer M with a high-intensity tip T, similar to the defect repairer with high intensity tip described in connection with  FIG. 1D . 
     Referring to  FIG. 3G , the photomask  300 , in which the dark defect  330  is repaired on the transparent substrate  310 , is completed. 
       FIG. 4A through 4C  are top view images captured during a correction process of photomask defects according to exemplary embodiments of the present invention. 
     In  FIG. 4A , a dark defect  430  occurs on the surface of the transparent substrate  410   a  of photomask exposed between optical patterns  420 , as described in connection with  FIG. 3A . 
     In  FIG. 4B , a river-bed defect  435  remains on the surface of the transparent substrate  410   a  after removing the dark defect  430  using an ion beam and others, such as those described in connection with  FIG. 3C . 
     In  FIG. 4C , after forming a protection layer on top of the river-bed defect  435 , and creating a recess by etching the transparent substrate  410   a , the protection layer and the river-bed defect  435  formed under the protection layer are removed using a high-intensity tip. 
     While embodiments of the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be apparent to those skilled in the art that the scope of the invention is given by the appended claims, rather than the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein. Therefore, it should be understood that the above embodiments are not limitative, but illustrative in all aspects. 
     As described above, the photomask defect correction methods and the photomask created thereby according to exemplary embodiments of the present invention, since defect marks are not left, can increase product yield.