Patent Publication Number: US-11378894-B2

Title: Lithography system with an embedded cleaning module

Description:
CROSS REFERENCE 
     The present application is a continuation of U.S. patent application Ser. No. 14/168,114, filed Jan. 30, 2014, now U.S. Pat. No. 10,459,353, issued Oct. 29, 2019, which is a utility application claiming the benefit of U.S. Provisional Application No. 61/793,838 entitled “AN EUV SCANNER WITH EMBEDDED CLEANING MODULE” filed Mar. 15, 2013, herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component or line that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In one example associated with lithography patterning, a photomask (or mask) to be used in a lithography process has a circuit pattern defined thereon and is to be transferred to wafers. In advanced lithography technologies, an extreme ultraviolet (EUV) lithography process is implemented with a reflective mask. The reflective mask needs to be cleaned to make the mask defect free. 
     The cleanliness of a lithography mask is essential in the yield of the lithography process. Operating or transporting a mask in a completely particle-free clean room and exposure tool is impossible. In other words, certain level of environmental nano-scale or macro-scale particles, which mainly are induced during transportation, could be directly adhered on back-side or front-side of the mask, thereby diminishing the cleanness of mask and mask stage. As a result, the yield of the lithography production is suffered due to non-cleaning mask. Therefore, how to effectively clean mask featuring closely damage-free is one major topic in the lithography process. In one example, the existing cleaning processes may cause various damages to the mask, or have high manufacturing cost. In another example, the existing cleaning processes could not effectively remove nano-scale particles. In yet another example, the existing cleaning method is complicated and is associated with high cost tool. In yet another example, additional particles could be further induced during the existing cleaning procedure. There are no effective clean method and system in the EUV lithography process. Vacuum technique cannot be used to clean inside the EUV lithography system. 
     Therefore, what is needed is a system and method to address the above issues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purpose only. In fact, the dimension of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a block diagram of a lithography system embedded with a cleaning module, constructed according to various embodiments. 
         FIG. 2  is a block diagram of the cleaning module, constructed according to various embodiments. 
         FIG. 3  is a schematic view of the cleaning module of  FIG. 2 , constructed according to one or more examples. 
         FIGS. 4A through 4C  illustrate schematic views of the cleaning module of  FIG. 2  at respective cleaning stages, constructed according to other examples. 
         FIG. 5  is a schematic view of the cleaning module of  FIG. 2 , constructed according to another example. 
         FIGS. 6A and 6B  are schematic views of the cleaning module of  FIG. 2 , constructed according to yet another example. 
         FIGS. 7A and 7B  are schematic views of the cleaning module of  FIG. 2 , constructed according to different examples. 
         FIGS. 8A and 8B  are block diagrams of the lithography system of  FIG. 1  embedded with the cleaning module, in portion, constructed according to respective embodiments. 
         FIG. 9  is a flowchart of a method for performing a lithography exposing process and cleaning a mask, constructed according to one or more embodiments. 
         FIG. 10  is a schematic view of a mask container, constructed according to one embodiment. 
         FIG. 11  is a flowchart of a method for cleaning a mask, constructed according to other embodiments. 
         FIG. 12  is a flowchart of a method for cleaning the mask stage of the lithography system, constructed according to some embodiments. 
         FIG. 13  is a flowchart of a method for cleaning the mask stage of the lithography system, constructed according to other embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
       FIG. 1  is a block diagram of a lithography system  10  constructed according to aspects of the present disclosure in one or more embodiments. The lithography system  10  may also be generically referred to as a scanner that is operable to perform lithography exposing processes with respective radiation source and exposure mode. In the present embodiment, the lithography system  10  is an extreme ultraviolet (EUV) lithography system designed to expose a resist layer by EUV light from the radiation source. The resist layer is a material sensitive to the EUV light. The EUV lithography system  10  employs a radiation source  12  to generate EUV light, such as EUV light having a wavelength ranging between about 1 nm and about 100 nm. In one particular example, the EUV radiation source  12  generates a EUV light with a wavelength centered at about 13.5 nm. 
     The lithography system  10  also employs an illuminator  14 . In various embodiments, the illuminator  14  includes various refractive optic components, such as a single lens or a lens system having multiple lenses (zone plates) or alternatively reflective optics (for EUV lithography system), such as a single mirror or a mirror system having multiple mirrors in order to direct light from the radiation source  12  onto a mask stage  16 , particularly to a mask  18  secured on the mask stage  16 . In the present embodiment where the radiation source  12  generates light in the EUV wavelength range, reflective optics is employed. 
     The lithography system  10  also includes the mask stage  16  configured to secure a mask  18 . In the present embodiment, the mask stage  16  includes an electrostatic chuck (e-chuck) to secure the mask  18 . This is because that gas molecules absorb EUV light and the lithography system for the EUV lithography patterning is maintained in a vacuum environment to avoid the EUV intensity loss. 
     In the disclosure, the terms of mask, photomask, and reticle are used to refer to the same item. In the present embodiment, the lithography system  10  is a EUV lithography system, and the mask  18  is a reflective mask. One exemplary structure of the mask  18  is provided for illustration. The mask  18  includes a substrate with a suitable material, such as a low thermal expansion material (LTEM) or fused quartz. In various examples, the LTEM includes TiO 2  doped SiO 2 , or other suitable materials with low thermal expansion. The mask  18  includes a multiple reflective layers (ML) deposited on the substrate. The ML includes a plurality of film pairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenum above or below a layer of silicon in each film pair). Alternatively, the ML may include molybdenum-beryllium (Mo/Be) film pairs, or other suitable materials that are configurable to highly reflect the EUV light. The mask  18  further includes an absorption layer, such as a tantalum boron nitride (TaBN) layer, deposited over the ML. The absorption layer is patterned to define a layer of an integrated circuit (IC). Alternatively, another reflective layer may be deposited over the ML and is patterned to define a layer of an integrated circuit, thereby forming a EUV phase shift mask. 
     The lithography system  10  also includes a projection optics module (or projection optics box (POB)  20  for imaging the pattern of the mask  18  on to a target  22  (such as a semiconductor wafer) secured on a substrate stage  24  of the lithography system  10 . The POB  20  has refractive optics (such as for UV lithography system) or alternatively reflective optics (such as for EUV lithography system) in various embodiments. The light directed from the mask  18 , carrying the image of the pattern defined on the mask, is collected by the POB  20 . 
     The lithography system  10  also includes the substrate stage  24  to secure a target  22 . In the present embodiment, the target  22  is a semiconductor wafer, such as a silicon wafer or other type of wafer to be patterned. The target is coated with the resist layer sensitive to the radiation beam, such as EUV light in the present embodiment. In the present embodiment, various components, described above, are integrated together to function as a lithography exposing module that is operable to perform lithography exposing processes. 
     Particularly, the lithography system  10  includes a cleaning module  26  designed to clean the mask  18 , the mask stage  16 , or the both in various embodiments. The cleaning module  26  is embedded in the lithography system  10  and integrated with the lithography exposing module to enable on-line cleaning operations. The cleaning module  26  is designed to have an attraction mechanism for effectively cleaning the mask and/or mask stage without additional contamination/damage to the mask (or the mask stage) to be cleaned. 
     The lithography system  10  with embedded cleaning module  26  provides a system and a method for effectively cleaning the mask and mask stages on line, especially when the lithography system  10  is a EUV lithography system. In the present embodiment, the mask  18  is a reflective mask used in a EUV lithography exposing process for patterning of the integrated circuits with less feature sizes. Since the mask is repeatedly used to pattern a plurality of semiconductor wafers, a defect on the mask may be transferred to the plurality of semiconductor substrates and causes a significant yield issue. Defects including contamination may be introduced to a mask (and further to the mask stage) through various mask handling operations. In some embodiments, the mask handling operations include mask inspection, mask shipping and handling, mask storing, mask transferring, and mask securing on a mask stage. In other embodiments for a reflective mask used in the EUV lithography system, the mask handling operations include manufacturing inspection, shipping and handling, mask cleaning, vacuum storage, transferring to vacuum mask library, pre-alignment and temperature stabilization, and securing on an electrostatic chuck. 
     In the present embodiment, the cleaning module  26  is operable to clean the mask  18  and/or the mask stage  16  (collectively referred to as to-be-cleaned object or targeted object) inside the lithography system  10 , thereby removing and eliminating the particles and other contaminations. 
     The cleaning module  26  is further illustrated in  FIG. 2  in a block diagrammatical view constructed according to some embodiments. The cleaning module  26  includes a cleaning structure  28  using an attraction mechanism to attract and remove particles and other contamination from the targeted object (such as mask or mask stage), therefore reducing or eliminating damage to the mask and/or the mask stage. In one embodiment, the cleaning structure  28  includes an attracting object (cleaning material)  28 A, such as a glue material, with a sticking surface  28 B such that the particles can be attached to the sticking surface when the sticking surface approaches close to the targeted object. Additionally, a pressure may be applied to the cleaning material to ensure the contact between the cleaning material and the targeted object. In another embodiment, the cleaning structure  28  may include a mechanism, such as electrostatic force, to generate an attracting force to the particles. 
     The cleaning structure  28  may further include a carrier component  28 C, such as a carrier substrate, to secure and support the cleaning material with enough mechanical strength. For example, the carrier substrate may be a suitable plate with the cleaning material attached thereon and with enough mechanical strength to hold the cleaning material for cleaning operations. The carrier substrate is designed to have certain geometry (shape and size) that match those of the targeted object. In one embodiment, the carrier substrate is designed to have a shape and dimensions of the mask  18 . 
     The cleaning module  26  may also include a handling mechanism  30  to secure, transfer, and manipulate (such as apply a pressure) the cleaning structure  28 , thereby enabling the cleaning structure  28  for cleaning function. In one embodiment, the handling mechanism  30  includes a robot  30 A that is integrated in the lithography system  10  and is configured to be operable to hold and move the cleaning structure  28 . The handling mechanism  30  may further include a fixture  30 B with a mechanism and a configuration to secure the robot  30 A to an apparatus. For example, the robot  30 A is secured in a cleaning system by the fixture  30 B. In another example, the robot  30 A is secured in a lithography exposure system by the fixture  30 B with proper configuration to enable the cleaning operations. In another embodiment, the handling mechanism  30  may further include a control unit  30 C that is operable to control the robot for various motions and cleaning operations. The control unit  30 C may be integrated with the robot  30 A or may be distributed in various locations. For example, the control unit  30 C is integrated in a lithography exposure system and is coupled with the robot  30 A to control cleaning operations. 
     The cleaning module  26  is further described according to various embodiments. In one embodiment illustrated in  FIG. 3 , the cleaning structure  28  includes a cleaning material layer  32  with a sticking surface for cleaning the surface of a targeted object  34 . The cleaning material layer with the sticking surface is also referred to as sticking material layer. In various examples, the targeting object  34  includes the mask  18 , or the mask stage  16 . The cleaning material layer  32  is applied to a surface of the targeted object  34  such that various particles  36  are attached to the sticking surface of the cleaning material layer  32 , thereby removing the particles  36  from the targeted object  34 . 
     The cleaning material layer  32  may include a suitable material with non-polar chains and polar compound, such as a material with —OH, —H and —O to easily attract particles from the surface of the targeted object  34 . The cleaning material is soft without scratch concern. In various embodiments, the cleaning material  32  includes a suitable adhesive tape, polysaccharide, polyvinyl alcohol (PVA) with —OH bond and high chemical polarity, and natural latex (such as gum) with surfactant to modify the stickiness. 
     One example is further illustrated in  FIGS. 4A, 4B and 4C  in schematic views. Referring to  FIG. 4A , the cleaning material layer  32  is transferred to the targeted object  34 . An additional pressure  38  may be further applied to the cleaning material layer  32  to ensure fully contact between the cleaning material layer  32  and the targeted object  34 . As noted above, the cleaning material layer  32  may be a portion of the cleaning structure attached to a carrier substrate to provide proper mechanical strength. 
     Referring to  FIG. 4B , the cleaning material layer  32  fully contacts the targeted object  34  in the surface to be cleaned. Especially, the cleaning material layer  32  is designed to be flexible such that the surface profile is changed in response to the surface profile of the targeted object  34 . When one or more particle is present on the targeted object  34 , the corresponding surface profile of the targeted object  34  is modified with local bumps. The surface profile of the cleaning material layer  32 , in response to the local bumps, is substantially complimentary to the surface profile of the targeted object  34 . This characteristic of the cleaning material layer  32  is referred to as surface morphological change. Thus, the surface profile of the targeted object  34  is flexible and changeable, and usually is not a smooth when being contacted with the targeted object  34  due to the particles  36  on the targeted object  34 . With the surface morphological change of the cleaning material layer  32 , the surface profile of the cleaning material layer  32  is changed (e.g., stretching and deforming) under the pressure  38  such that the sticking surface locally surrounds the respective particle, thereby maximizing the contact areas between the particles and the sticking surface. Accordingly the sticking force to the particles (the attaching strength of the particles to the sticking surface) is maximized. The attachment of the particles to the sticking surface may be optimized through tuning the applied pressure  38 , the contact duration, and the stickiness of the cleaning material layer  32 . 
     Referring to  FIG. 4C , the cleaning material layer  32  is then separated from the targeted object  34 . The particles  36  are removed from the targeted object  34  due to Van Der Waal force or Coulomb&#39;s force. The separation may be achieved through a liftoff process  40 . 
       FIG. 5  illustrates a schematic view of a cleaning structure  42  constructed according to another embodiment. The cleaning structure  42  includes an electro-static structure with a mechanism to generate electrostatic force. When the cleaning structure  42  approaches close to the targeted object  34 , the particles  36  are attracted from the targeted object  34  to the electro-static layer by the electro-static force. In the present example, the cleaning structure  42  includes a current-driven electrostatic mechanism to generate the electrostatic force. In one instance for illustration, the cleaning structure  42  may include a conductive component coupled to a power source and designed to generate electric field in a distribution to effectively attract the particles  36  on the targeted object  34 . 
       FIG. 6A  illustrates a schematic view of a cleaning structure  44  constructed according to another embodiment. The cleaning structure  44  includes a roller  46  having a cylinder shape and being operable to roll. The roller  46  has a sticking material formed on the surface to attract the particles when rolling on the targeted object  34 . The cleaning structure  44  further includes a handler  48  integrated with the roller  46  and enabling various operations (such as moving and rolling) of the roller  46 . 
       FIG. 6B  illustrates a schematic view of the cleaning process by the cleaning structure  44  according to one example. During the cleaning process, the particles are removed by the roller  46  with rubbing and sticking forces. 
       FIG. 7A  illustrates a schematic view of a cleaning module  50  constructed according to another embodiment. The cleaning module  50  includes a cleaning structure  28  (such as the cleaning material layer  32  or the cleaning structure  42 ) and may further include a carrier substrate to provide a mechanical strength. The cleaning module  50  also includes the handing mechanism  30 , such as robot, to secure, transfer, and move the cleaning structure  28  for cleaning operations. The handling mechanism  30  is further secured to a component  52  of the lithography system  10  with proper configuration to enable the cleaning operations. In another example, the targeted object  34  is the mask  18  secured on the mask stage  16 , as illustrated in  FIG. 7B . 
       FIG. 8A  illustrates a schematic view of a portion of the lithography system  10  constructed according to some embodiments. The lithography system  10  includes the mask stage  16  and a chamber  56  with an enclosed space designed to hold various components and features. 
     In the present embodiment, the chamber  56  includes a mask library  58  to hold various masks. The mask library  58  is also able to hold one or more cleaning structure  28 , such as the cleaning structure designed to clean the mask stage  16 . As described above, the cleaning structure to clean the mask stage  16  has shape and size to similar to those of the mask  18  and is able to be held in the mask library  58 . The chamber  56  includes a mask handler  60 , such as a robot, designed to secure and transfer masks. The chamber  56  further includes a cleaning module  62  configured next to the mask library  58  and the mask handler  60 . As one example, the cleaning module  62  is designed to clean one or more masks. 
     The lithography system  10  includes a load lock  64  designed and configured to transfer the mask into and out from the lithography system. The lithography system  10  may include another robot embedded in or integrated with the load lock  64  for mask (or mask container) transferring. This robot works in an atmospheric environment. 
     Back to the cleaning module  62 . The cleaning module  62  may be designed with respective cleaning mechanism, such as one of those described above, including a cleaning material layer, roller and electrostatic cleaning structure. 
     In one embodiment, the cleaning module  62  is operable to clean the mask before the mask being transferred to the mask stage  16  for a lithography exposing process or after being transferred out from the mask stage  16 . 
     In another embodiment, the mask stage  16  is cleaned during the idle time by the cleaning structure  28  held in the mask library  58  or alternatively the cleaning module  62 . In one example, the cleaning structure  28  held in the mask library  58  is used to clean the mask stage  16 . In furtherance of the example, the cleaning structure  28  is moved close to the mask stage  16  or is secured onto the mask stage  16 . Then a cleaning process is implemented to clean the mask stage  16  by the cleaning structure  28 . The cleaning structure  28  is transferred into the mask stage  16  from the mask library  58  and thereafter transferred back to the mask library  58  from the mask stage  16  similar to the way a mask is transferred between the mask stage and the mask library. In various examples, the cleaning structure  28  may be transferred by a robot associated with the mask stage  16 , the mask handler  60 , or the handling mechanism  30  of the cleaning module  62 . 
       FIG. 8B  is a schematic view of the lithography system  10  in portion, constructed according to some other embodiments. The lithography system  10  in  FIG. 8B  includes a robot chamber  56 . The robot chamber  56  further includes a mask library  58 , a mask handler  60 , and a cleaning module  62 . 
     The mask library  58  is configured to hold one or more masks  18  and a cleaning structure  66  designed to clean the mask stage  16 . The cleaning structure  66  has a shape and dimensions of the mask such that it can approach to and additionally be secured on the mask stage  16  for proper cleaning. Furthermore, the cleaning structure  66  has a sticking mechanism, such as one illustrated in  FIGS. 4A-4C . In one example, the cleaning structure  66  includes a mask substrate covered by a cleaning material layer with sticking surface. Accordingly, one or more cleaning structure  66  may be stored in the mask library  58 . 
     One embodiment of an operation to clean the mask stage  16  by the cleaning structure  66  is described. During an idle time of the mask stage  16 , a robot  68  transfers the cleaning structure  66  from the mask library to the mask stage  16 , similar to the transferring of a mask from the mask library to the mask stage. In one example, the cleaning structure  66  is pushed in contact with the mask stage  16 . The mask stage  16  is cleaned through a procedure similar to the procedure described in  FIGS. 4A through 4C . In another embodiment, the cleaning structure  66  is secured on the mask stage  16  similar to securing a mask. In the present example, the mask stage  16  is an electrostatic chuck designed to secure the cleaning structure  66  by the electrostatic force. The clamping force to the cleaning structure  66  by the mask stage  16  ensures proper contact between the mask stage  16  and the cleaning structure  66 . During the time when the cleaning structure  66  is secured on the mask stage  16 , the particles on the mask stage  16  is attached to the sticking surface of the cleaning structure  66 . Afterward, the robot  68  moves the cleaning structure  66  away from the mask stage  16 , the particles on the mask stage  16  are attached to the sticking surface of the cleaning structure  66  and are removed and cleaned from the mask stage  16 . Then the cleaning structure  66  is sent back to the mask library  58  by the robot  68 . 
     The mask handler  60  is designed to transfer a mask, such as transferring the mask from the load lock to the mask library  56 . The mask handler  60  may include a robot arm for motion and a component to hold the mask. 
     The cleaning module  62  is designed to clean the masks. The cleaning module  62  is one example of the cleaning module  26  in  FIG. 2  and includes the cleaning structure  28  and the handling mechanism  30  (such as a robot) integrated to enable the cleaning operations to the mask  18 . In one embodiment, the cleaning module  62  further includes another mask stage  69  configured for mask cleaning. In one example, the mask  18  is transferred from the mask library  56  to the mask stage  69  of the cleaning module  62  by the robot  60 . The mask  18  is secured on the mask stage  69  of the cleaning module  62 . Then the handling mechanism  30  moves the cleaning structure  28  to the mask  18  secured on the mask stage  69 . The cleaning procedure is similar to one of the cleaning mechanism described above, such as the cleaning procedure described in  FIGS. 4A through 4C . After the cleaning operation, the mask  18  may be sent back to the mask library  58  by the robot  60 . 
       FIG. 9  is a flowchart of a method  70  to perform a lithography exposing process including mask cleaning by the lithography system  10  constructed according to some embodiments. The method  70  is described with reference to  FIGS. 8B, 9  and other relevant figures. Other embodiments of the method  70  may include more or less operations. The method  70  includes an operation  72  by transferring a mask  18  from an outside environment to a mask container, such as a dual pod mask container  90  illustrated in  FIG. 10  in a schematic view. The dual pod mask container  90  includes an inner pod  92  and an outer pod  94  configured to hold the mask  18 . 
     The method  70  includes an operation  74  by transferring the mask  18  to the lithography system  10 . In the present embodiment, the operation  74  includes placing the mask  18  held in the mask container into the load lock  64  of the lithography system  10 , and transferring the mask  18  into the mask library  58 . During the operation, the outer pod  94  and the inner pod  92  are removed from the mask  18 . After the operation  74 , the mask  18  is stored in the mask library  58 . 
     The method  70  includes an operation  76  to clean the mask  18  by the cleaning module  26 , such as the cleaning module  62  in the present embodiment. In one example, the mask  18  is transferred out from the mask library  58 ; cleaned by the cleaning module  62 ; and thereafter transferred back to the mask library  58 . In another example, the mask  18  is transferred out from the mask library  58 ; cleaned by the cleaning module  62 ; and thereafter transferred to the mask stage  16  for a lithography exposing process. In this case, the following operation  78  is eliminated. 
     The method  70  may include an operation  78  by securing the mask  18  to the mask stage  16 . For example, the robot  60  may transfer the mask  18  from the mask library  58  to the mask stage  16 ; the mask  18  is secured on the mask stage  16  by a suitable clamping mechanism, such as electrostatic force. 
     The method  70  includes an operation  80  by performing a lithography exposing process by the lithography system  10  with the mask  18 . The lithography exposing process may further include mask alignment, overlay checking and exposing by the light (such as EUV light) from the radiation source  12 . The resist layer coated on the target  22  (that is secured on the substrate stage  24 ) is exposed to form the latent pattern of an IC pattern on the resist layer. 
     The method  70  includes an operation  82  to clean the mask  18  by the cleaning module  62 . In one example, when the mask  18  is secured on the mask stage  69 , the cleaning module  62  performs a cleaning process to the mask  18 , such as illustrated in  FIG. 8B . In other embodiments, one of the operations  76  and  82  may be eliminated according to the individual situation including the contamination level and criticality of the IC pattern defined on the mask  18 . 
     The method  70  includes an operation  84  by transfer the mask  18  back to the mask library  58  after the cleaning process at the operation  82 . In various embodiments, the operations  76  through  84  may be repeated during the processes to pattern various targets. In one example, the mask  18  is repeated through the operations  76 - 84  to pattern a plurality of semiconductor wafers (a batch of wafers in this example). In another example, a first mask goes through the operations  76 - 84  to a first batch of wafers; a second mask goes through the operations  76 - 84  to pattern a second batch of wafers; and so on. 
       FIG. 11  is a flowchart of a method  100  to perform a cleaning process constructed according to some other embodiments. The method  100  begins at  102  that a mask  18  is stored in a mask container, such as a dual pod mask container  90  in  FIG. 10 . 
     The method  100  includes an operation  104  by performing a mask inspection to the mask  18 . In one embodiment, the mask inspection includes inspecting the front side and the backside of the mask  18 . A mask inspection system, such as a metrology tool with light scattering mechanism, is used to inspect the mask for particles. In one embodiment, a previous inspection data may be used as a reference. For example, the inspection data to a defect-free mask  18  is used as a reference. The comparison between the inspection data and the reference data will provide particle information, such as particle locations and sizes. In one example, the mask  18  in the mask container is loaded to the mask inspection system, inspected and unloaded. 
     At  106 , the inspection result is evaluated according to a certain criteria, such as specification associated with the lithography system, which is used to perform the lithography exposing process with the mask  18 . An exemplary specification, associated with the lithography system, is provided for illustration. The exemplary specification includes: a number of particles with size greater than 50 micron is 0; a number of particles with size greater than 10 micron is less than 35; and a number of particles with size greater than 3 micron is less than 70. Here the numbers are counted per mask. 
     If the inspection result is out of the specification, the method  100  proceeds to operation  108  by performing a cleaning process to the mask  18 . The cleaning process utilizes the cleaning module  26  to remove the particles through a suitable mechanism, such as one illustrated in  FIGS. 4A  though  4 C. Thereafter, the mask  18  is back to the operation  104  for another mask inspection. In the present embodiment, the cleaning module  26  is a standalone module such that the cleaning process is implemented before the mask is loaded to the lithography system  10 . 
     When the inspection result is evaluated to be in the specification at  106 , the method  100  proceeds to an operation  110  by placing the mask  18  back in the mask container. By implementing various operations of the method  100 , the mask  18  is maintained in the mask container with reduced contamination and ensured mask quality. 
     The method  100  may further include an operation  112  by loading the mask  18  to a lithography system and performing a lithography exposing process to one or more wafers using the mask  18 . In the present embodiment, the lithography system is the lithography system  10 , as illustrated in  FIGS. 1 and 8 . In one example, the operation  112  includes placing the mask  18  held in the mask container into the load lock  64  of the lithography system  10 , transferring the mask  18  into the mask state  16 , and performing a lithography exposing process to image the IC pattern of the mask  18  to a resist layer coated on the semiconductor wafer. In another example, the procedure including the operations  74  through  84  in the method  70  may be implemented to perform one or more exposing processes with the mask  18 . 
       FIG. 12  is a flowchart of a method  120  for cleaning the mask stage  16  by the cleaning structure  66 , constructed according to some embodiments. The method  120  is described with reference to  FIG. 12 ,  FIG. 8B  and other figures. The method  120  begins at operation  122  by storing the cleaning structure  66  in the mask library  58 . The method  120  proceeds to an operation  124  by securing the cleaning structure  66  to the mask stage  16 . The operation  124  further includes transferring the cleaning structure  66  from the mask library  58  to the mask stage  16  before the cleaning structure  66  is secured on the mask stage  16 . The method  120  further includes an operation  126  to clean the mask stage  16  by the cleaning structure  66 . During the cleaning operation  126 , suitable pressure and cleaning duration are implemented. The pressure between the mask stage  16  and the cleaning structure  66  is maintained to ensure the contact and attachment of the particles to the sticking surface of the cleaning structure  66 . The cleaning duration is tuned to be sufficient for the articles to be attached to the sticking surface of the cleaning structure  66 . The method  120  may further include transferring the cleaning structure  66  back to the mask library  58 . 
       FIG. 13  is a flowchart of a method  130  for cleaning the mask stage  16  by the cleaning structure  66 , constructed according to some other embodiments. The method  130  is described with reference to  FIG. 13 ,  FIG. 8B  and other figures. The method  130  begins at operation  132  by storing the cleaning structure  66  in the mask library  58 . The method  130  proceeds to an operation  134  by transferring the cleaning structure  66  from the mask library  58  to the mask stage  16 . The method  130  further includes an operation  136  to clean the mask stage  16  by the cleaning structure  66 . In one embodiment, a suitable pressure is applied to the cleaning structure  66  to ensure the contact between the mask stage  16  and the cleaning structure  66 . In another embodiment where the cleaning structure  66  utilizes the electrostatic mechanism for cleaning, the cleaning structure  66  approaches close to the mask stage  16  but may not be in direct contact with the mask stage  16 . The method  130  may further include transferring the cleaning structure  66  back to the mask library  58 . 
     The lithography system with embedded cleaning module and the method for utilizing the lithography system to clean mask and/or mask stage are described in various embodiments. The cleaning module includes a cleaning structure and a handling mechanism to manipulate the cleaning structure for cleaning. In one embodiment, the cleaning module provides an attraction mechanism that manipulates an adhesive surface to touch the surface of mask (or mask stage), thereby attracting nano-particles or macro-particles from the mask (or mask stage). In another embodiment, the cleaning module includes a current-driven electrostatic mechanism to clean the mask (or the mask stage). In yet another embodiment, a cleaning structure includes a mask substrate (alternatively a plate similar to the mask in shape and dimensions) attached with a cleaning material layer such that the cleaning structure can be properly handled, like handling a mask, to clean the mask stage. 
     Other embodiments or alternatives may present without departure of the present disclosure. In one embodiment, the lithography system  10  includes two or more cleaning modules embedded in the lithography system: a first cleaning module designed to clean a mask and a second cleaning module designed to clean a mask stage of the lithography system. In furtherance of the embodiment, the first cleaning module includes a first cleaning structure and a handling mechanism to secure and manipulate the first cleaning structure. The second cleaning module includes a second cleaning structure that further includes a carrier substrate and an attracting material layer attached to the carrier substrate. Furthermore, the carrier substrate has a shape and dimensions of the mask such that the cleaning structure is able to approach the mask stage or be secured on the mask stage for cleaning operation. In another embodiment, the cleaning module  26  may alternatively stand alone, such as the cleaning module used in the method  100  of  FIG. 11 . 
     Various advantages may present in one or more different embodiments of the present disclosure. The advantages, in various embodiments, include low-cost, pattern damage free of the front-side of the mask, effectively removing particles, simple operation, embedded in scanner, superior capability to remove nano-scale particle compared to other traditional approach. Compared to wet-cleaning process, this approach allows exactly control over the cleaning sites on the mask; therefore, the unnecessary cleaning site like front-side with pattern can be avoided to eliminate the damage. Furthermore, the cleaning structure and the cleaning method can be tuned as effective as possible with optimized modification of adhesive surface. 
     Thus, the present disclosure provides a lithography system in some embodiments. The lithography system includes an exposing module configured to perform a lithography exposing process using a mask secured on a mask stage; and a cleaning module integrated in the exposing module and designed to clean at least one of the mask and the mask stage using an attraction mechanism. 
     The present disclosure provides a lithography system in other embodiments. The lithography system includes an exposing module designed to perform a lithography exposing process and configured in an enclosed chamber maintained in a vacuum environment; and a cleaning module integrated with the exposing module. The cleaning module includes a cleaning structure with an attraction mechanism to remove particles and a handling mechanism that is designed to secure and transfer the cleaning structure. 
     The present disclosure provides a method that includes loading a mask into a lithography system designed to perform a lithography exposing process, the lithography system being embedded with a cleaning module having an attraction mechanism; securing the mask to a mask stage; performing a lithography exposing process by the lithography system to a semiconductor wafer using the mask; and cleaning the mask by the cleaning module. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.