Abstract:
A method includes performing a chemical-mechanical planarization (CMP) on an article, providing a polishing fluid including luminescent particles capable of generating a fluorescent light in response to a light incident on the article, and detecting an intensity of the fluorescent light. An apparatus that is capable of performing the method and a system that includes the apparatus are also disclosed.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 14/097,363, filed Dec. 5, 2013, which is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The technology described in this disclosure relates generally to material processing and more particularly to planarization. 
       BACKGROUND 
       [0003]    Chemical-mechanical polishing/planarization (CMP) is often implemented in semiconductor devices fabrication. A CMP process can be used for planarizing surfaces of a wafer with a combination of chemical and mechanical forces. Mechanical grinding alone may cause surface damages, while wet etching alone cannot attain good planarization. The CMP process involves both the mechanical grinding and the wet etching to generate a smooth surface on a wafer, and prepare the wafer for subsequent processes (e.g., photolithography) in the fabrication of semiconductor devices. 
       SUMMARY 
       [0004]    In accordance with one aspect of the teachings described herein, an apparatus configured to perform a chemical-mechanical planarization (CMP) on an article comprises a polishing head and a fluorescence detector. The polishing head is configured to hold the article. The fluorescence detector is configured to detect an intensity of a fluorescent light generated in response to a light incident on the article. 
         [0005]    In accordance with another aspect of the teachings described herein, a system configured to perform a chemical-mechanical planarization (CMP) on an article comprises a polishing head, a polishing fluid, and a fluorescence detector. The polishing head is configured to hold an article. The polishing fluid includes luminescent particles capable of generating a fluorescent light in response to a light incident on the article. The fluorescence detector is configured to detect an intensity of the fluorescent light. 
         [0006]    In accordance with yet another aspect of the teachings described herein, a method comprises performing a chemical-mechanical planarization (CMP) on an article, providing a polishing fluid including luminescent particles capable of generating a fluorescent light in response to a light incident on the article, and detecting an intensity of the fluorescent light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1(   a )- FIG. 1(   b ) depict an example diagram showing a CMP system. 
           [0008]      FIG. 2(   a ) and  FIG. 2(   b ) depict an example diagram showing a polishing fluid including luminescent particles used in the CMP system as shown in  FIG. 1(   a ) and  FIG. 1(   b ). 
           [0009]      FIG. 3(   a ) and  FIG. 3(   b ) depict another example diagram showing a polishing fluid including luminescent particles used in the CMP system as shown in  FIG. 1(   a ) and  FIG. 1(   b ). 
           [0010]      FIG. 4  depicts an example band diagram showing electrons being transferred from a luminescent particle to a CMP stop layer. 
           [0011]      FIG. 5  depicts an example flow chart for performing CMP on an article. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    In semiconductor device fabrication, usually a thin material layer (e.g., titanium nitride, titanium oxide) is used as a CMP stop layer for a CMP process and/or an etching hard mask for an etching process that follows the CMP process. Oftentimes, it is hard to control the CMP process with accuracy when the CMP process is to be stopped. The CMP process is usually supposed to stop when material layers on top of the CMP stop layer are removed and the CMP stop layer (e.g., titanium nitride, titanium oxide) is exposed. If the CMP process is not stopped in time, the thin CMP stop layer may be removed and it cannot serve as the etching hard mask. Material layers under the CMP stop layer cannot be protected during the subsequent etching process. 
         [0013]      FIG. 1(   a )- FIG. 1(   b ) depict an example diagram showing a CMP system. The CMP system  100  is configured to perform a CMP process with fluorescence detection so that the CMP process stops with accuracy when a CMP stop layer (e.g., nitrides) is exposed. 
         [0014]    As shown in  FIG. 1(   a ) and  FIG. 1(   b ), the CMP system  100  includes a polishing head  102 , a polishing pad  104 , a platen  106 , and a fluorescence detector  108 . A polishing fluid (not shown) used for the CMP process includes luminescent particles that are capable of generating a fluorescent light  116  in response to an incident light  112  (e.g., from a light source  118 ) and transferring charges (e.g., electrons or holes) to a CMP stop layer included in a wafer  114 . One or more small windows  110  in the polishing pad  104  allows the incident light  112  to pass through and fall on the wafer  114  that includes the CMP stop layer (e.g., a nitride layer), and allows the fluorescent light  116  to pass through to the fluorescence detector  108 . The intensity of the fluorescent light  116  is changed when the CMP stop layer is exposed during the CMP process. The fluorescence detector  108  is configured to detect the change of the intensity of the fluorescent light  116  so as to stop the CMP process when the CMP stop layer is exposed after material layers on top of the CMP stop layer are removed. 
         [0015]    For example, the windows  110  are fabricated using one or more materials that are approximately transparent to the incident light  112  and the fluorescent light  116 . In some embodiments, a first window is used to allow the incident light  112  to pass through, and a second window is used to allow the fluorescent light  116  to pass through. The two windows are fabricated with different materials which are approximately transparent to the incident light  112  and the fluorescent light  116  respectively. 
         [0016]    The CMP system  100  further includes a polish-head-rotation controller  120  and a computer  122 . For example, the polish-head-rotation controller  120  is configured to control the polishing head  102  to rotate and oscillate to bring the wafer  114  into contact with the polishing pad  104  that moves in the plane of the wafer surface to be planarized (e.g., together with the platen  106 ). The computer  122  is configured to control the light source  118  and/or the fluorescence detector  108 . As an example, the computer  122  compares the detected intensity of the fluorescent light  116  with a predetermined threshold, and causes the polish-head-rotation controller  120  to stop the polishing head  102  if the detected intensity of the fluorescent light  116  is smaller than the predetermined threshold. In certain embodiments, the polishing pad  104  is made of stacks of soft and hard materials (e.g., porous polymeric materials). 
         [0017]      FIG. 2(   a ) and  FIG. 2(   b ) depict an example diagram showing a polishing fluid including luminescent particles used in the CMP system  100 . The polishing fluid  202  includes an abrasive and corrosive chemical slurry (e.g., a colloid). For example, the polishing fluid  202  includes one or more abrasive materials  204 , and a plurality of luminescent particles  206  capable of generating the fluorescent light  116  in response to the incident light  112 . The luminescent particles  206  each include one or more surfactant particles  208  capable of attaching to a CMP stop layer  214  included in the wafer  114 . The wafer  114  includes multiple layers on a substrate  210 . One or more material layers  212  (e.g., silicon oxide) are formed on the CMP stop layer  214 . For example, the CMP stop layer  214  includes a nitride layer (e.g., titanium oxide, titanium nitride) and does not generate a fluorescent light in response to the incident light  112 . 
         [0018]    At the beginning of the CMP process, the surfactant particles  208  are attached to the luminescent particles  206  and the fluorescent light  116  has a high intensity. As the CMP process continues, the material layers  212  formed on the CMP stop layer  214  are removed, and at least part of the CMP stop layer  214  is exposed. The surfactant particles  208  begin to attach to the CMP stop layer  214 , as shown in  FIG. 2(   b ). Charges (e.g., electrons or holes) are transferred from the luminescent particles  206  to the CMP stop layer  214 . In response, the intensity of the fluorescent light  116  begins to decrease. The fluorescence detector  108  detects such changes in the intensity of the fluorescent light  116 , and the CMP process is stopped when the intensity of the fluorescent light  116  drops below a threshold. For example, the luminescent particles  206  include CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, InAs, InN, InP, GaN, GaP, GaAs, AlP, or other suitable materials. The abrasive materials  204  include silica or other suitable materials. The surfactant particles  208  include organic molecules that contain one or more hydroxyl-based (e.g., —OH) functional groups, one or more carboxyl-based (e.g., —COOH) functional groups, one or more ammonium-ion-based (e.g., —NH + ) functional groups, one or more sulfonic-acid-based (e.g., —SO 3 H) functional groups, or other suitable functional groups. 
         [0019]      FIG. 3(   a ) and  FIG. 3(   b ) depict another example diagram showing a polishing fluid including luminescent particles used in the CMP system  100 . The polishing fluid  302  includes one or more abrasive materials  304 , and a plurality of luminescent particles  306  capable of generating the fluorescent light  116  in response to the incident light  112  and attaching to a CMP stop layer  314  (e.g., titanium oxide, titanium nitride) included in the wafer  114 . In some embodiments, one or more material layers  312  (e.g., silicon oxide) are formed on the CMP stop layer  314 . 
         [0020]    During the CMP process, the material layers  312  formed on the CMP stop layer  314  are removed, and at least part of the CMP stop layer  314  is exposed. The luminescent particles  306  begin to attach to the CMP stop layer  314 , as shown in  FIG. 3(   b ). Charges (e.g., electrons or holes) are transferred from the luminescent particles  306  to the CMP stop layer  314 . In response, the intensity of the fluorescent light  116  begins to decrease. When most of the luminescent particles  306  attach to the surface of the CMP stop layer  314 , the intensity of the fluorescent light  116  is very low. The fluorescence detector  108  detects such changes in the intensity of the fluorescent light  116 , and the CMP process is stopped when the intensity of the fluorescent light  116  drops below a threshold. For example, the luminescent particles  306  include certain dye materials, such as EBFP, Azunite, GFPuv, and T-sapphire. In another example, the luminescent particles  306  include certain fluorescence conducting polymer materials, such as MEHPPV and P3HT. The luminescent particles  306  include organic molecules that contain one or more hydroxyl-based (e.g., —OH) functional groups, one or more carboxyl-based (e.g., —COOH) functional groups, one or more ammonium-ion-based (e.g., —NH + ) functional groups, one or more sulfonic-acid-based (e.g., —SO 3 H) functional groups, or other suitable functional groups. The abrasive materials  304  include silica or other suitable materials. 
         [0021]      FIG. 4  depicts an example band diagram showing electrons being transferred from a luminescent particle to a CMP stop layer. As shown in  FIG. 4 , a luminescent particle is in contact with a CMP stop layer. In response to an incident light  402 , one or more electrons  404  of the luminescent particle are excited from a first energy level  408  to a second energy level  410 , leaving behind one or more holes  406  at the first energy level  408 . The second energy level  410  is higher than an energy level  412  corresponding to a conduction band of the CMP stop layer, and the one or more electrons  404  flow from the luminescent particle to the CMP stop layer. In some embodiments, the energy of the incident light is larger than a difference between the first energy level  408  and the second energy level  410  which corresponds to a band gap of the luminescent particle (e.g., Eg). For example, the first energy level  408  is at about −6.0 eV, and the second energy level  410  is at about −4.0 eV. The energy level  412  of the CMP stop layer is at about −4.5 eV. 
         [0022]      FIG. 5  depicts an example flow chart for performing CMP on an article. At  502 , the CMP process begins on an article (e.g., a wafer) including a CMP stop layer. A polishing fluid that is used for the CMP process includes a plurality of luminescent particles capable of generating a fluorescent light in response to an incident light and attaching to the CMP stop layer included in the article. Once the luminescent particles attach to the CMP stop layer, electric charges (e.g., electrons, holes) transfer from the luminescent particles to the CMP stop layer and as a result an intensity of the fluorescent light decreases. At  504 , the intensity of the fluorescent light is detected. At  506 , a determination whether the intensity of the fluorescent light is decreasing (e.g., becoming smaller than a threshold) is made. If the intensity of the fluorescent light is decreasing (e.g., becoming smaller than a threshold), it indicates that at least a large part of the CMP stop layer is exposed. The CMP process ends to avoid removing the CMP stop layer, at  508 . Otherwise, the CMP process continues. 
         [0023]    For example, the luminescent particles include CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, InAs, InN, InP, GaN, GaP, GaAs, AlP, EBFP, Azunite, GFPuv, T-sapphire, MEHPPV, P3HT, or other suitable materials. In some embodiments, the luminescent particles include surfactant particles capable of attaching to the stop layer. As an example, the surfactant particles include organic molecules that contain one or more hydroxyl-based functional groups, one or more carboxyl-based functional groups, one or more ammonium-ion-based functional groups, one or more sulfonic-acid-based functional groups, or other suitable functional groups. 
         [0024]    This written description uses examples to disclose embodiments of the disclosure, include the best mode, and also to enable a person of ordinary skill in the art to make and use various embodiments of the disclosure. The patentable scope of the disclosure may include other examples that occur to those of ordinary skill in the art. One of ordinary skill in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. Further, persons of ordinary skill in the art will recognize various equivalent combinations and substitutions for various components shown in the figures. 
         [0025]    Well-known structures, materials, or operations may not be shown or described in detail to avoid obscuring aspects of various embodiments of the disclosure. Various embodiments shown in the figures are illustrative example representations and are not necessarily drawn to scale. Particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. The present disclosure may repeat reference numerals and/or letters in the various examples, and 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. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments. For example, a particular layer described herein may include multiple components which are not necessarily connected physically or electrically. Various operations may be described as multiple discrete operations in turn, in a manner that is most helpful in understanding the disclosure. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Operations described herein may be performed in a different order, in series or in parallel, than the described embodiments. Various additional operations may be performed and/or described. Operations may be omitted in additional embodiments. 
         [0026]    This written description and the following claims may include terms, such as top, on, under, etc. that are used for descriptive purposes only and are not to be construed as limiting. The embodiments of a device or article described herein can be manufactured, used, or shipped in a number of positions and orientations. For example, terms designating relative vertical position may refer to a situation where a device side (or active surface) of a substrate or integrated circuit is the “top” surface of that substrate; the substrate may actually be in any orientation so that a “top” side of a substrate may be lower than the “bottom” side in a standard terrestrial frame of reference and may still fall within the meaning of the term “top.” The term “on” as used herein (including in the claims) may not necessarily indicate that a first layer/structure “on” a second layer/structure is directly on or over and in immediate contact with the second layer/structure unless such is specifically stated; there may be one or more third layers/structures between the first layer/structure and the second layer/structure. The term “under” as used herein (including in the claims) may not indicate that a first layer/structure “under” a second layer/structure is directly under and in immediate contact with the second layer/structure unless such is specifically stated; there may be one or more third layers/structures between the first layer/structure and the second layer/structure. The term “substrate” used herein (including in the claims) may refer to any construction comprising one or more semiconductive materials, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials).