Abstract:
A light transmissive cover for a device comprising: a cover member of light transmissive material; and a junction member joined to the cover member, the junction member being a member used to be joined to the body of the device and having a light interrupting film on the inner surface thereof. A device provided with a light transmissive cover, the device being provided with a cover member of light transmissive material joined to the body of device via a junction member so as to cover at least a part of the device, and having a light interrupting film on the inner surface of the junction member is also disclosed. In addition, methods for manufacturing them disclosed.

Description:
This is divisional of application Ser. No. 10/970,342, filed Oct. 21, 2004, now U.S. Pat. No. 7,274,096 which claims priority to Japanese application no. 2003-362080 filed Oct. 22, 2003, is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device provided with a light transmissive cover. 
     2. Description of Prior Art 
     In a digital mirror device that utilizes a device having, on a silicon substrate, a plurality of micro-mirrors, capable of being driven mechanically, and an electronic circuit, for controlling the motion of the micro-mirrors and that projects an image by digitally controlling the motion of the micro-mirrors so as to reflect light from a light source, a light transmissive cover is attached to the device. 
     As shown in  FIG. 5 , a conventional digital mirror device  100  provided with a light transmissive cover is manufactured by positioning a separately fabricated light transmissive cover  106  to cover a device  104  mounted on a mounting substrate  102 . The cover is composed of a case  110  formed of metallic material such as kovar (Fe—Ni—Co alloy with coefficient of thermal expansion similar to that of a glass material) and a glass sheet  112  fitted thereinto, and is provided inside with a light interrupting film  114  of CrO 2 . 
     Such a cover is fabricated as follows. As shown in  FIG. 6(   a ), a metal material such as kovar is mechanically processed, such as by machining, to form a case  110  having an opening  111 . Then, as shown in  FIG. 6(   b ), a glass material  112  is fitted into the opening  111  of the case  110 . Subsequently, as shown in  FIG. 6(   c ), the glass material  112  is ground to a thickness corresponding to that of the case. Then, after a CrO 2  film is formed on the inside of the case  110  by a process such as sputtering or evaporation, patterning is performed to form a light interrupting film  114 , as shown in  FIG. 6(   d ). The cover  106  thus fabricated is subsequently joined to a substrate having a device mounted thereon so as to cover the device to complete a device  100  provided with a light transmissive cover as shown in  FIG. 5 . 
     In the conventional device  100  provided with the light transmissive cover manufactured as described above, it was necessary that each case  110 , for fixing the light transmissive glass member  112 , and each cover glass  112 , was processed separately. Therefore, the manufacture required not only much time and labor but also large cost. In addition, as the case  110  was fabricated by machining process, the cover became very large relative to the device  104  when it was assembled into a light transmissive cover  106 . It was also disadvantageous that the product precision (quality) was not uniform. 
     As a prior art, for manufacturing a device provided with a cover, a method is described in JP 2002-43463 A in which a first semiconductor substrate having a semiconductor element formed thereon is joined to a second substrate (a lid substrate) comprising a glass or ceramic cover. In this case, the cover is fabricated by filling the recessed portion of the second substrate for cover with powder material such as glass or the like so as to become flat, and then also making the opposite side of the second substrate flat. 
     A method is described in JP 2002-246489 A in which, as a wafer level hermetic sealing method, a wafer having a semiconductor element formed thereon and a lid substrate having a lid for cover collectively formed thereon are separately fabricated, and a junction part consisting of solder is formed on the wafer or the lid wafer, and after the two wafers are joined by the junction part, the wafer is diced into chips. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to resolve the problems described above, and to provide a device, provided with a light transmissive cover which is manufactured easily and which permits the assembled device to be reduced in size, and a method for manufacturing the device. 
     It is also an object of the present invention to provide a light transmissive cover used therefor and a method for manufacturing it. 
     A light transmissive cover for a device of the present invention is characterized in that it comprises a cover member of light transmissive material and a junction member connected thereto which is a member used to be joined to the body of the device and which has a light interrupting film on its inner surface. 
     A device provided with a light transmissive cover in accordance with the present invention is characterized in that it is provided with a cover member, of a light transmissive material, joined to the body of the device via a junction member so as to cover at least a part of the device, and has a light interrupting film on the inner surface of the junction member. 
     A light transmissive cover for a device in accordance with the present invention can be manufactured by a method comprising the steps of patterning a sheet of a junction member material, such as a silicon wafer, having a wafer-size or a larger size to form an opening in the region which covers the device, joining the junction member material sheet with a sheet of light transmissive material such as a glass sheet, and forming a light interrupting film on the inner surface of the opening of the junction member material sheet. 
     A device provided with a light transmissive cover in accordance with the present invention can be manufactured, after a light interrupting film has been formed according to the method as described above, by a method comprising the steps of joining the junction member material sheet to a wafer at prescribed position, the wafer having a semiconductor element formed thereon, and dicing the wafer having a semiconductor element formed thereon together with the light transmissive material sheet and the junction member material sheet into separate chips. 
     Alternatively, a light transmissive cover for a device in accordance with the present invention can be manufactured by a method comprising the steps of joining a junction member material sheet to a light transmissive material sheet, patterning the junction member material sheet to form an opening in a region which covers the device later and to form grooves for subsequent dicing, and forming a light interrupting film on the inner surface of the opening of the junction member material sheet. 
     A device provided with a light transmissive cover in accordance with the present invention can also be manufactured, after a light interrupting film has been formed according to the method as described above, by a method comprising the steps of joining the junction member material sheet to a prescribed position of the wafer having semiconductor element formed thereon, and dicing the wafer having semiconductor elements formed thereon, together with the light transmissive material sheet and the junction member material sheet, into separate chips. 
     When using light transmissive covers, irrespective of a method employed for manufacturing the covers, the respective covers having light interrupting films formed thereon may be diced into separate chips, and each diced chip may then be joined to the wafer having semiconductor element formed thereon, at the prescribed position or, on the contrary, chips each diced in advance and comprising an element may be joined to respective covers having been fabricated integrally before the dicing into chips, and the respective covers may then be diced into chips. Further, it is also possible to join a diced cover to a diced chip. 
     Thus, the present invention further includes following methods of manufacturing a device provided with a light transmissive cover: 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: patterning a junction member material sheet of wafer size or of a larger size to form openings in the regions destined to cover the devices, joining the junction member material sheet to a light transmissive material sheet, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, cutting the joined light transmissive material sheet and junction member material sheet to form individual light transmissive covers each having one above-mentioned opening, joining each of the individual light transmissive covers to a prescribed position of a wafer having elements formed thereon, and dicing the wafer having the elements formed thereon into separate chips. 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: joining a junction member material sheet to a light transmissive material sheet, patterning the junction member material sheet to form openings in the regions destined to cover the devices later, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, cutting the joined light transmissive material sheet and junction member material sheet to form individual light transmissive covers each having one above-mentioned opening, joining each of the individual light transmissive covers to a prescribed position of a wafer having elements formed thereon, and dicing the wafer having the elements formed thereon into separate chips. 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: patterning a junction member material sheet of wafer size or of a larger size to form openings in the regions destined to cover the devices later, joining the junction member material sheet to a light transmissive material sheet, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, joining individual chips each having an element formed thereon to the sections of individual light transmissive covers of the junction member material sheet each having one above-mentioned opening, and obtaining, by dicing, separate chips each comprising the section of individual light transmissive cover having the device joined thereto. 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: joining a junction member material sheet to a light transmissive material sheet, patterning the junction member material sheet to form openings in the regions destined to cover the devices later, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, joining individual chips each having an element formed thereon to the sections of individual light transmissive covers of the junction member material sheet having the light interrupting film formed each having one above-mentioned opening, and obtaining, by dicing, separate chips each comprising the section of individual light transmissive cover having the device joined thereto. 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: patterning a junction member material sheet of wafer size or of a larger size to form openings in the regions destined to cover the devices later, joining the junction member material sheet to a light transmissive material sheet, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, cutting the joined light transmissive material sheet and junction member material sheet to form individual light transmissive covers each having one above-mentioned opening, and joining the individual light transmissive cover to an individual chip having an element formed thereon. 
     A method of manufacturing a device provided with a light transmissive cover, the light transmissive cover being provided with a cover member of a light transmissive material joined to the body of the device via a junction member so as to cover at least a part of the device and having a light interrupting film on the inner surface of the junction member, said method comprising the steps of: joining a junction member material sheet to a light transmissive material sheet, patterning the junction member material sheet to form openings in the regions destined to cover the devices later, forming a light interrupting film on the inner surface of the opening of the junction member material sheet, cutting the joined light transmissive material sheet and junction member material sheet to form individual light transmissive covers each having one above-mentioned opening, and joining the individual light transmissive cover to an individual chip having an element formed thereon. 
     In accordance with the present invention, light transmissive covers can be manufactured collectively using a wafer-sized material, or in some cases, a larger-sized material, so that manufacturing process may be simplified as compared to prior art methods wherein light transmissive covers are manufactured separately. Product precision (quality) of covers can be improved as the covers are manufactured collectively before being separated from each other. 
     In addition, integrating collectively manufactured light transmissive covers with a wafer having elements formed thereon for subsequent processing has an advantage that the need of forming grooves in a cover case for wiring extension from the device within the cover to a mounting substrate is eliminated. In general, when a brittle material such as silicon is used as a case member (junction member) for a cover, there is a problem that the case is liable to breakage during processing. When, however, a silicon wafer is used as a junction member material sheet according to the invention, it can be integrated with a material such as a glass sheet and be then processed, and it is possible to eliminate the problem. Moreover, in this case, when through-holes (openings) are to be formed in the junction member material sheet by etching or the like, the etching is stopped at the interface with the glass sheet, thereby permitting through-holes with good shapes to be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1F  illustrate the manufacture of a light transmissive cover according to an embodiment of the present invention, and the manufacture of a device with a light transmissive cover using the resultant cover; 
         FIG. 2  shows an example of a device provided with a light transmissive cover according to the present invention mounted on a substrate; 
         FIGS. 3A to 3C  illustrate the manufacture of a light transmissive cover according to another embodiment of the present invention, and the manufacture of a device with a light transmissive cover using the resultant cover; 
         FIGS. 4A and 4B  illustrate an alternative method of forming a light interrupting film; 
         FIG. 5  illustrates a conventional device provided with a light transmissive cover; and 
         FIGS. 6A to 6D  illustrate a conventional method of manufacturing a device provided with a light transmissive cover. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described in detail with reference to drawings. It is to be understood that the present invention is by no means limited by the embodiments described below. 
     First, manufacture of a light transmissive cover according to an embodiment of the present invention and manufacture of a device with a light transmissive cover using the resultant cover will be described with reference to  FIGS. 1A to 1F . 
     As shown in  FIG. 1A , a silicon wafer  11  is patterned to form openings  12 . The patterning may be performed by etching (for example, wet etching using an alkaline etching solution such as KOH or TMAH, or dry etching such as reactive ion etching (RIE)). The size of the opening  12  formed is determined by taking into consideration the size of the device to be joined to a cover. Then, as shown in  FIG. 1B , the silicon wafer  11  is joined to a glass sheet  13  to be integrated therewith. The joining may be performed using methods such as anodic bonding or the like. An adhesive may also be used to perform the joining. 
     Next, as shown in  FIG. 1C , a light interrupting film  14  is formed on the inner surface of the opening  12  of the silicon wafer  11 . Alternatively, a light interrupting film  14  may be formed after the step of  FIG. 1A , i.e., the formation of the openings  12  in the silicon wafer  11 . The light interrupting film  14  may be formed by, for example, depositing a CrO 2 /Cr thin film by sputtering or evaporation and patterning the deposited film. Film thickness of the CrO 2 /Cr thin film formed may be generally of the order of 0.2 μm. The light interrupting film  14  may be formed by patterning it so as to cover a part of glass sheet surface in the region of the opening  12 , as shown in the drawing. 
     After the light interrupting film  14  has been formed, grooves  15  are formed by machining or the like in the silicon wafer  11  integrated with the glass sheet  13  for dicing to be performed later, as shown in  FIG. 1D . Then, as shown in  FIG. 1E , the wafer  11  having the grooves  15  formed therein is joined to a prescribed position of another wafer  16  having elements such as digital mirror devices (not shown) formed thereon. Ultrasonic bonding, for example, may be used to perform this joining. In some cases, it is possible to use an adhesive to join the silicon wafer  11  integrated with the glass sheet  13  to the wafer  16  having, in advance, elements formed thereon. 
     After the two wafers have been joined, the wafer  16 , having elements formed thereon in advance, is cut together with the glass sheet  13  to individual pieces to obtain devices  17  as chips each having a light transmissive glass cover member  18  fixed thereto, as shown in  FIG. 1F . In this device  17 , the light transmissive glass cover  18  is fixed via the silicon junction member  20  to the body  19  of the device comprising the element. 
     As shown in  FIG. 2 , in the region seen at the left of the device  17  and not covered with the cover member  18 , a pad  23  or the like is provided for mounting the device  17  on a substrate  21  by wire bonding to electrically connect the device  17  with a wire  25  to a pad  24  of the substrate  21 . Depending upon a method for mounting the device on a substrate, such a region need not be provided in the device  17 . 
     Next, a method of manufacturing a light transmissive cover in accordance with another embodiment of the present invention and a method of manufacturing a device provided with a light transmissive cover using the resultant cover will be described. 
     As shown in  FIG. 3A , a silicon wafer  31  is joined to a glass sheet  32  to be integrated therewith. The joining may be performed using a method such as anodic bonding as in the previous embodiment. Then, the silicon wafer  31  is patterned to simultaneously form openings  33  in regions destined to cover devices later, and grooves  34  for later dicing, by a method such as machining as shown in  FIG. 3B . Next, a light interrupting film  35  is formed by deposition and patterning of CrO 2  thin film or the like, as shown in  FIG. 3C . Then, as has been described with reference to  FIGS. 1E and 1F , the silicon wafer  31  having the openings  33  and the grooves  34  formed therein may be joined to a prescribed position of another wafer having elements formed thereon beforehand, and the wafer containing the elements may be cut together with the glass sheet  32  into individual pieces to obtain devices as chips each having a light transmissive glass cover member fixed thereto via a junction member. 
     Although, in the method as described above, a light interrupting film is formed using a CrO 2  thin film, another method can also be used to form a light interrupting film. For example, the dry etching method used for forming openings in a silicon wafer may also be used to form a light interrupting film. Next, the method of forming a light interrupting film by means of dry etching of a silicon wafer will be described. 
     When silicon is dry-etched under certain conditions, a vapor-like material of silicon compound is produced and deposits on the etched silicon surface, in the form of islands. Silicon cannot be etched at the locations where the silicon compound deposits and, thus, the silicon surface after dry etching is in a state of being covered with a large number of needle-shaped protrusions (like the ceiling of a limestone cave covered with a large number of stalactites). Light incident upon the etching surface in such a state is not reflected back, and the surface appears black to the naked eye. In the present invention, such an etched silicon surface may be formed and the resultant black surface may be utilized as a light interrupting film. 
     An example of light interrupting film formed by dry etching of silicon will be described with reference to  FIGS. 4A to 4B . First, as shown in  FIG. 4A , a silicon wafer  41  having openings  42  formed as has been described with reference to  FIGS. 1A to 1B  is joined to a glass sheet  43  to be integrated therewith. Then, the silicon wafer  41  is subjected to dry etching to form a light interrupting film  44  on the inner surface of the openings  42  as shown in  FIG. 4B . 
     Dry etching in this case is performed using the Bosch process in which etching and deposition of silicon are alternately repeated. The Bosch process is a dry etching process developed by Bosch GmbH in Germany, and is generally used for deep etching of silicon. In this process, SF 6  is used as an etching gas and C 4 F 8  is used as a gas for deposition. Thus, a supply of SF 6  at 700 sccm, 15 Pa, and for 7 seconds and a supply of C 4 F 8  at 100 sccm, 5 Pa, and for 3 seconds are alternately repeated, and silicon is subjected to dry etching at the conditions of wafer temperature of −10° C., source power of 2000 W, and bias power of 100 W. The sizes of needle-shaped protrusions formed etc. can be controlled by varying the etching conditions. 
     Then, as has been described before with reference to  FIGS. 1D to 1F , grooves for later dicing are formed in the silicon wafer, and the wafer having the openings and grooves formed thereon is joined to a prescribed position of another wafer having elements formed thereon beforehand. Then, the wafer comprising the elements can be cut together with the glass sheet into individual pieces to obtain devices as chips each provided with the light transmissive cover. 
     Although, in the embodiments described above, as seen in  FIG. 1F , the light transmissive film  14  is joined to the body of the device without removing part of the film that has been deposited on the end of the junction member  20 , this part of the light interrupting film may be removed before the joining. 
     Although, in the foregoing description of the embodiments of the present invention, a glass sheet is used as a light transmissive material sheet, and a silicon wafer is used as a junction member material sheet, the present invention is not limited to these examples. Any sheet material other than a glass sheet may be used as a light transmissive material sheet as long as it has appropriate light transmissivity and can be integrated with a junction member material sheet to be processed in the integrated body. Likewise, any sheet material other than a silicon wafer may be used as a junction member material sheet as long as it can be integrated with a light transmissive material sheet and can be subjected to a process such as patterning by means of etching or the like. 
     The light transmissive cover according to the present invention can be applied to any device which uses a light transmissive member, including a digital mirror device.