Abstract:
A method of manufacturing a semiconductor sensor includes a forming step, a preparing step, a fixing step and a separating step. In the forming step, a plurality of caps made of resin is formed on a supporting substrate through a separable agent. Each of the caps has a cavity therein. In the preparing step, a semiconductor wafer is prepared, on which a plurality of sensor elements are formed. In the fixing step, the caps are fixed to the semiconductor wafer. Each cavity of the caps corresponds to each of the sensor elements. In the separating step, the separable agent and the supporting substrate are separated from the caps so as to leave the caps on the semiconductor wafer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2005-333606 filed on Nov. 18, 2005, the disclosure of which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of manufacturing a semiconductor sensor. For example, the sensor is used for detecting a physical amount such as an acceleration, a yaw rate or an oscillation. 
   2. Description of Related Art 
   A movable portion is disposed in a semiconductor sensor for detecting a physical (dynamic) amount, e.g., acceleration sensor or gyro sensor. However, durability performance of the movable portion is low due to its structure. Then, in order to reduce generation of defects, e.g., breakage, in a process for manufacturing the sensors, a cap is attached to a surface of a sensor chip including the movable portion. 
   For example, a cap is formed by layering a glass substrate or silicon on a sensor chip, according to US 2004/0025589 A1 (corresponding to JP-T2-2004-506203). The cap is formed over an entire wafer without being divided, on which plural sensors will be formed. However, an electrode pad has to be made in an exposed state in order to be connected to a sensor circuit. Therefore, a complicated treatment such as an etching or a grinding has to be performed. Further, a cost for manufacturing sensors may be increased, because the glass substrate or the silicon is used. 
   By contrast, in JP-A-2004-101528, a temporary cap made of resin is used in a variety of processes for manufacturing a sensor, and the temporary cap is removed after the processes are completed. However, the temporary cap cannot be used as a permanent cap, because durability performance of the temporary cap is low. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing and other problems, it is an object of the present invention to provide a method of manufacturing a semiconductor sensor. According to the method, plural divided caps are formed on a wafer, from which plural sensor chips are formed. Further, the caps can be permanently used in the manufactured sensor. 
   According to an example of the present invention, a method of manufacturing a semiconductor sensor includes a forming step, a preparing step, a fixing step and a separating step. In the forming step, a plurality of caps made of resin is formed on a supporting substrate through a separable agent. Each of the caps has a cavity therein. In the preparing step, a semiconductor wafer is prepared, on which a plurality of sensor elements are formed. In the fixing step, the caps are fixed to the semiconductor wafer such that each cavity of the caps corresponds to each of the sensor elements. In the separating step, the separable agent and the supporting substrate are separated from the caps so as to leave the caps on the semiconductor wafer. 
   Accordingly, the caps are formed to be divided from each other on the wafer without a dicing, and the caps can be permanently used for the semiconductor sensor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIGS. 1A-1F  are cross-sectional views showing processes for manufacturing a semiconductor sensor according to a first embodiment of the present invention; 
       FIG. 2  is a plan view of  FIG. 1A ; 
       FIG. 3  is a plan view of  FIG. 1B ; and 
       FIGS. 4A-4G  are cross-sectional views showing processes for manufacturing a semiconductor physical quantity sensor according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   First Embodiment 
   A semiconductor sensor for detecting a physical quantity (dynamic amount), e.g., acceleration sensor or gyro sensor, including a movable portion is manufactured, as shown in  FIGS. 1A-1F , in a first embodiment. In the manufacturing process, a cap  3  for covering a sensor element  4   a  is formed, and the cap  3  is fixed to a semiconductor wafer  4 . The forming of the cap  3  and the fixing of the cap  3  are performed after the sensor element  4   a  is formed on the semiconductor wafer  4  by a common semiconductor process. Then, a dicing process is performed after the cap  3  is fixed to the wafer  4 . In the first embodiment, the manufacturing process will be described from the forming of the cap  3 . 
   First, a process for forming the cap  3  is performed. Specifically, as shown in  FIG. 1A , a supporting substrate  1  made of glass is prepared, and a thermal separable agent  2  (thermal separation layer) is coated on the substrate  1 . The thermal separable agent  2  can be easily separated, when an adhesive force of the thermal separable agent  2  is lowered at a specified temperature. The specified temperature is determined based on a material of the agent  2 , and the specified temperature is 150° C. or 170° C., for example. Thermoplastic polyimide or polyamide-imide is used for forming the thermal separable agent  2 . A commercial product, e.g., thermal release tape REVALPHA manufactured by NITTO DENKO Corp., is also used for forming the thermal separable agent  2 . 
   Then, plural cap portions (covers)  3   a  for covering the sensor elements  4   a  are formed on the thermal separable agent  2  by a printing method such as a screen-printing or an inkjet printing, for example. The cap portions  3   a  are made of resin, and have a pattern shown in  FIG. 2 . Each of the cap portions  3   a  corresponds to the sensor element  4   a  on the semiconductor wafer  4 , and the cap portions  3   a  are separated from each other. Each mask of the cap portions  3   a  is formed into a rectangular shape, as shown in  FIG. 2 . 
   Next, as shown in  FIG. 1B , supporting portions  3   b  made of resin are formed at four corners or on four sides of the mask of the cap portion  3   a . In this embodiment, the supporting portions  3   b  are formed on the four sides. The supporting portion  3   b  is used as a spacer for making a space between the cap portion  3   a  and the wafer  4 , and formed by a method similar to the above-described method for forming the masks of the cap portions  3   a . As shown in  FIG. 3 , the supporting portions  3   b  are formed on four sides of the mask of the cap portion  3   a . The supporting portions  3   b  are not formed on parts corresponding to the sensor elements  4   a , and the parts are left to form cavities. 
   Next, as shown in  FIG. 1C , an adhesive  3   c  is dispensed on the supporting portion  3   b , that is, the adhesive  3   c  is coated on the supporting portion  3   b . The adhesive  3   c  is optionally coated based on a material of the thermal separable agent  2 . For example, when thermoplastic polyimide is used for forming the thermal separable agent  2 , the coating for the adhesive  3   c  is not required. The supporting portions  3   b  are directly fixed to the wafer  4  with a temperature of about 250° C. Silicon adhesive or organic adhesive such as epoxy adhesive may be used as the adhesive  3   c , for example. 
   Thus, the cap  3  made of resin is completely constructed by the cap portion  3   a  and the supporting portion  3   b . Alternatively, the cap  3  is completely constructed by the cap portion  3   a , the supporting portion  3   b  and the adhesive  3   c . The cap  3  has a cavity, i.e., concave, in which the supporting portion  3   b  is not positioned. Next, the cap  3  will be fixed to the semiconductor wafer  4 . 
   Specifically, as shown in  FIG. 1D , the supporting substrate  1  having the caps  3  is positioned above the semiconductor wafer  4  including the sensor elements  4   a . At this time, a face of the supporting substrate  1 , on which the caps  3  are formed, and a face of the semiconductor wafer  4 , on which the sensor elements  4   a  are formed, face each other. Then, an alignment device  5  determines an alignment between the supporting substrate  1  and the semiconductor wafer  4 , such that each of the sensor elements  4   a  and each of the cap portions  3   a  are positioned to face each other by using alignment marks of the supporting substrate  1  and the semiconductor wafer  4 . 
   Next, as shown in  FIG. 1E , heat and pressure HP are applied on the supporting substrate  1  in the arrow direction by a wafer-integrating device. Thereby, the cap  3  is fixed to the wafer  4  through the supporting portion  3   b . The cap  3  covers the sensor element  4   a  such that the cap portion  3   a  and the sensor element  4   a  are not in contact with each other, because the cap  3  has the cavity formed by the supporting portions  3   b  as described above. At the same time, an adhesion force between the cap  3  and the thermal separable agent  2  is lowered, because the thermal separable agent  2  is heated so as to have a predetermined or more temperature. 
   Therefore, as shown in  FIG. 1F , the supporting substrate  1  and the thermal separable agent  2  are separated from the cap  3  in the arrow direction of  FIG. 1F . The supporting substrate  1  and the thermal separable agent  2  may be separated together from the cap  3 . However, in this case, much power is required compared with a case in which the thermal separable agent  2  is simply separated. Alternatively, after the supporting substrate  1  is separated from the thermal separable agent  2 , the thermal separable agent  2  may be separated from the cap  3 . In order to perform the respective separations in this order, materials for forming the thermal separable agent  2  and the supporting substrate  1  are determined such that an adhesion force at an interface between the thermal separable agent  2  and the supporting substrate  1  is lowered by heating. Thus, the supporting substrate  1  is easily separated from the thermal separable agent  2 . 
   Thus, a cap formed structure, in which the cap  3  covers the sensor element  4   a , is completed. Thereafter, processes may be performed to the cap formed structure, if required. Then, each of the sensor elements  4   a  is a chip unit divided by dicing. Thereby, a covered structure, in which each of the caps  3  covers the chip unit including the sensor element  4   a , is completed. At this time, a process for dividing the caps  3  after covering is not required, because each of the caps  3  is already formed to cover the corresponding sensor element  4   a.    
   According to the first embodiment, the caps  3  can be formed without a dividing process, and the number of the caps  3  corresponds to the number of the sensor elements  4   a . Therefore, a complicated process such as an etching or a grinding is not required in order to make an exposed electrode pad for being connected to a sensor circuit. Further, a cost for manufacturing the semiconductor physical quantity sensor can be reduced, because the caps  3  can be made of inexpensive resin. 
   Furthermore, the caps  3  are easily separated from the thermal separable agent  2  by heating, after the caps  3  are fixed to the semiconductor wafer  4 . Therefore, when a dicing process is performed, it is unnecessary to divide the caps  3  for the corresponding sensor elements  4   a . Afterward, the cap  3  can be used for a completed semiconductor sensor. Moreover, the cap  3  has a high durability performance, because the cap  3  is made of resin. Therefore, the cap  3  can be permanently used. 
   Second Embodiment 
   Caps  3  are formed by etching in a second embodiment, and the other parts may be made similar to the first embodiment. As shown in  FIG. 4A , a thermal separable agent  2  is coated on a supporting substrate  1 , and a cap layer  6  made of resin is formed on the thermal separable agent  2 . The caps  3  are formed by etching the layer  6 . For example, the cap layer  6  is made of thermosetting polyimide. A thickness of the layer  6  is the same as a thickness combining the cap portion  3   a  and the supporting portion  3   b  described in the first embodiment. 
   Then, as shown in  FIG. 4B , a resist (first mask)  7  is formed on the layer  6 , and a first aperture is formed in the resist  7  by an exposing treatment and a processing treatment, as shown in  FIG. 4C . A position of the first aperture corresponds to a position to be a cavity of the cap  3 . 
   Next, as shown in  FIG. 4D , the cavity is formed in the layer  6  by a wet etching, for example. The resist  7  is used as a mask, and the wet etching is performed such that the cavity has a depth in a thickness direction of the layer  6 . At this time, an etching selection ratio can be enhanced, because the layer  6  is made of the thermosetting polyimide. Accordingly, the etching can be accurately performed. 
   Then, after the resist  7  is removed by washing, another resist (second mask)  8  is formed on the layer  6 , as shown in  FIG. 4E . Next, as shown in  FIG. 4F , a second aperture is formed in the resist  8  by an exposing treatment and a processing treatment. A position of the second aperture corresponds to a position except for the cavity of the cap  3 , that is, the position of the second aperture corresponds to a position for dividing the caps  3 . Thereafter, as shown in  FIG. 4G , a part of the layer  6  corresponding to the second aperture is removed by a wet etching, for example. The resist  8  is used as a mask, when the wet etching is performed. Then, the resist  8  is removed. 
   Thus, the layer  6  is divided into the plural caps  3 , and the caps  3  have the cavities. Thereafter, the above-described processes shown in  FIGS. 1C-1F  are performed to the caps  3 . Thereby, a structure similar to that formed in the first embodiment can be formed, in which each cap  3  covers each sensor element  4   a . In addition, when the cap layer  6  is made of the thermosetting polyimide, an adhesive  3   c  is coated on the cap  3  as shown in  FIG. 1C , because an adhesion force is required. 
   According to the second embodiment, the cap  3  can be permanently used, because the cap  3  is made of resin having a high durability performance. Further, the same advantage can be obtained in the second embodiment as the first embodiment, because the caps  3  can be divided before the caps  3  are fixed to the semiconductor wafer  4 , although the process for dividing the caps  3  from the cap layer  6  is further required in the second embodiment. 
   Other Embodiments 
   The thermal separable agent  2  is heated through the supporting substrate  1  in the above embodiments. Alternatively, the semiconductor wafer  4  and the supporting substrate  1  may be totally heated in a heating chamber. 
   The thermal separable agent  2  is used in the first embodiment. Alternatively, an adhesive film having a small adhesion force may be used. Further, an UV hardened film may be used instead of the agent  2 . An adhesion force of the UV hardened film is lowered by radiating ultraviolet rays. A film, which is easily separated by a solvent, a chemical, a vapor of the solvent or the chemical or a water vapor, may be used. For example, when an organic adhesive is used as the adhesive  3   c , an organic solvent, e.g., isopropyl alcohol (IPA), acetone or xylene, can be used as the solvent. In this case, the supporting substrate  1  can be easily separated from the caps  3  by immersing the organic adhesive in the organic solvent. 
   Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.