Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Divisional Application of U.S. patent application Ser. No. 13/013,960, filed on Jan. 26, 2011, which claims priority from U.S. patent application Ser. No. 11/984,775 (issued as U.S. Pat. No. 7,910,387), filed on Nov. 21, 2007 and claiming priority from Taiwan Patent Application No. 096132098, filed on Aug. 29, 2007, which applications are hereby incorporated in their entirety by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a method for fabricating light emitting semiconductor device and applications thereof, and particularly relates to a wafer level light emitting semiconductor device and applications thereof. 
     2. Background of the Present Disclosure 
     Light emitting semiconductor devices having advantages of low power consumption, less heat generation, long life, small size, impact tolerance, high speed, free of mercury and good optical performance have been applied as a light source with steady wavelength in various electronic devices. The brightness and operational life of a light emitting diode (LED) device have been tremendously improved along with the development of the optical technology, and so LED devices may serve as the primary light source of electronic devices in the future. 
     An LED device with white light is typically made by a LED die encapsulated by a phosphor compound mixed with at least one phosphor, whereby the phosphor is activated by a portion of the blue light emitting from the LED die to derive the blue light into yellow light, and the yellow light is then mixed with the other portion of the blue light to produce white light which in turn emits from the LED device. 
     Conventionally, the steps for coating the phosphor compound onto the LED die are conducted in the device packaging process. During the packaging process, a die should be mounted onto a substrate prior to the phosphor compound being coated thereon. However, since the phosphor compound is directly blanketed over the LED die, the phosphor mixed in the fluid compound may be precipitated to the periphery of the LED die during the compound coating process. Furthermore, the fluid compound may be aggregated on the lateral side of the LED die, so the resulting LED package may have a horizontal thickness greater than the vertical thickness thereof. Thus the initial blue light provide by the LED die and the yellow light derived from the phosphor cannot be mixed adequately, resulting in the light emitted laterally from the LED package having a color temperature different from light emitted vertically form the LED package. In addition, the brightness of the LED package may be decreased. 
     To resolve these problems, an advanced method has been applied.  FIGS. 1A to 1F  illustrate cross-sectional views of a LED packaging process in accordance with a conventional packaging method. First pluralities of LED die units  100  are flipped and mounted on a substrate, such as a silicon substrate  101 . A conformal coating process, such as screen painting or a thick film process, is then conducted to form a photoresist layer  103  over the substrate  101  and the LED die units  100 , and a plurality of openings  104  are formed in the photoresist layer  103  by a patterning process to expose the LED die units  100 . Subsequently, a compound  105  mixed with phosphor is filled into the openings  104 . A backing process is then conducted prior to the photoresist layer  103  being peeled. The packaged LED die units are then separated from the substrate  101 ; and each of the die units  100  is bonded with wires to from a LED device. 
     However, the mounting steps may affect the accuracy for aligning LED die units  100  mounted on the substrate  101  with the openings  104  formed in the photoresist  104  during the LED device batch manufacturing process. The phosphor compound may not encapsulate the LED die in equilibrium. Thus light provided by the resulting LED device may have an undesired color temperature, and the brightness of the LED device may be decreased. Also, the heat-dispersing efficiency of the LED device may be reduced by the disequilibrium of phosphor compound coated on the LED die. 
     SUMMARY 
     Therefore, it is desirable to provide an improved method for coating a LED die a phosphor compound to form a LED device with high brightness and heat-dispersing efficiency by lower cost. 
     In accordance with one aspect of the present disclosure, a phosphor coating method for fabricating a light-emitting semiconductor is provided. The phosphor coating method comprises the steps as follows: First a light emitting semiconductor wafer having a plurality of die units formed thereon is provided, and a photoresist is then formed on the light emitting semiconductor wafer to cover the die units. A pattern process is conducted to form a plurality of openings associated with the die units, whereby each die can be exposed via one of the openings. Subsequently, a compound mixed with phosphor is filled into the openings. 
     In accordance with another aspect of the present disclosure, a method for fabricating a light emitting semiconductor device is provided, wherein the fabricating method comprises the steps as follows: First a light emitting semiconductor wafer having a plurality of die units formed thereon is provided, and a photoresist is then formed on the light emitting semiconductor to cover the die units. A pattern process is conducted to form a plurality of openings associated with the die units, whereby each die can be exposed via one of the openings. Subsequently, a compound mixed with phosphor is filled into the openings. A dicing process is then conducted to separate the die units from the light-emitting semiconductor wafer after the photoresist is removed. 
     In accordance with yet another aspect of the present disclosure, a light emitting semiconductor wafer coated with phosphor is provided, wherein the light emitting semiconductor wafer comprises a plurality of light emitting die units defined by at least one trench. Each light emitting die unit comprises a first semiconductor epitaxy layer with a first electric property, an active layer, a second semiconductor epitaxy layer with a second electric property, a first electrode, a second electrode and a patterned phosphor coating layer, wherein the active layer, the second semiconductor epitaxy layer and the first electrode are sequentially piled on the first semiconductor epitaxy layer, And the second electrode is electrically connected to the first electrode via the second semiconductor epitaxy layer, the active layer and the first semiconductor epitaxy layer. The patterned phosphor-coating layer is deposited on the second semiconductor epitaxy layer to encapsulate a portion of the second semiconductor epitaxy layer, the active layer, and the first semiconductor epitaxy layer that are exposed by the trench. The patterned phosphor coating layer also includes at least opening to expose the first electrode of the light emitting die unit. 
     In accordance with the above embodiments, the features of the present disclosure are to conduct the phosphor coating process on the semiconductor wafer, wherein a photolithography process rather than a conventional die attachment or bonding process is applied to fabricate a plurality of light emitting semiconductor devices. A conformal photoresist layer having a plurality of openings is form over the light emitting semiconductor wafer to surround a plurality of light emitting semiconductor die units. The openings are associated with the light emitting die units. Subsequently, a compound mixed with phosphor is filled into the openings. Since a reticle technology is applied to form the openings associated with the light emitting die units, each of the openings can precisely align one of the light emitting die units, and the patterned photoresist (the revetment surrounding each die unit) can have an accurate predetermined level. Thus the phosphor compound that is filled into each of the opening can be accurately controlled in a predetermined volume, so as to avoid additional waste of phosphor compound. Accordingly light emitting die unit can be encapsulated in equilibrium to improve the brightness of the light emitting die units. 
     In one embodiment of the present disclosure, a light emitting unit comprising a first semiconductor layer, a second semiconductor layer, an active layer, a first electrode, a second electrode and a phosphor layer is provided. The first semiconductor layer has a first electric property. The second semiconductor layer has a second electric property and is disposed above the first semiconductor layer. The active layer is disposed between the first semiconductor layer and the second semiconductor layer. The first electrode is disposed on the second semiconductor layer. The second electrode is disposed under the first semiconductor layer. The phosphor layer is disposed on the first semiconductor layer. The phosphor layer covers the active layer and the second semiconductor layer. The first electrode is exposed out of the phosphor layer. 
     In one embodiment of the present disclosure, the first semiconductor layer includes a top surface and a bottom surface opposite to the top surface. The top surface includes a central portion and a peripheral portion lower than the central portion. The active layer is disposed on the central portion. The second electrode is disposed on the bottom surface. The central portion and part of the peripheral portion are covered by the phosphor layer. 
     In one embodiment of the present disclosure, the first semiconductor layer includes a top surface and a bottom surface opposite to the top surface. The top surface includes a first portion and a second portion lower than the first portion. The active layer is disposed on the first portion. The second electrode is disposed on the bottom surface. The first portion and part of the second portion are covered by the phosphor layer. 
     In one embodiment of the present disclosure, the first electric property and the second electric property are n type and p type, respectively. 
     In one embodiment of the present disclosure, the first electric property and the second electric property are p type and n type, respectively. 
     In one embodiment of the present disclosure, a carrier is disposed under the second electrode. 
     In another one embodiment of the present disclosure, a light emitting unit comprising a first semiconductor layer, a second semiconductor layer, an active layer, a first electrode, a second electrode and a phosphor layer is provided. The first semiconductor layer has a first electric property. The second semiconductor layer has a second electric property and is disposed above the first semiconductor layer. The active layer is disposed between the first semiconductor layer and the second semiconductor layer. The first electrode is disposed on the second semiconductor layer. The second electrode is disposed on the first semiconductor layer. The phosphor layer is disposed on the first semiconductor layer. The phosphor layer covers the active layer and the second semiconductor layer. The first electrode and the second electrode are exposed out of the phosphor layer. 
     In another one embodiment of the present disclosure, the first semiconductor layer includes a top surface and a bottom surface opposite to the top surface. The top surface includes a first portion, a second portion lower than the first portion and a third portion lower than the second portion. The active layer is disposed on the first portion. The second electrode is disposed on the second portion. The first portion, part of the second portion and part of the third portion are covered by the phosphor layer. 
     In another one embodiment of the present disclosure, the first semiconductor layer includes a top surface and a bottom surface opposite to the top surface. The top surface includes a first central portion, a second central portion lower than the first central portion and a peripheral portion lower than the second central portion. The active layer is disposed on the first central portion. The second electrode is disposed on the second central portion. The first central portion, part of the second central portion and part of the peripheral portion are covered by the phosphor layer. 
     In another one embodiment of the present disclosure, the first electric property and the second electric property are p type and n type, respectively. 
     In another one embodiment of the present disclosure, a carrier is disposed under the second electrode. 
     In another one embodiment of the present disclosure, a carrier is disposed under the first semiconductor layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this present disclosure will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIGS. 1A to 1F  illustrate cross-sectional views of a LED packaging process in accordance with a conventional packaging method. 
         FIG. 2A  illustrates a vertical view of a light emitting semiconductor wafer and partial magnitude in accordance with a preferred embodiment of the present disclosure. 
         FIG. 2B  illustrates a cross-sectional view of a portion of a light emitting semiconductor wafer  200  in accordance with a preferred embodiment of the present disclosure. 
         FIG. 2C  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  200  shown in  FIG. 2B , after a photoresist  210  is formed thereon. 
         FIG. 2D  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  200 , after the pattern process is conducted on the photoresist  210 . 
         FIG. 2E  illustrates a vertical view of a portion of the light emitting semiconductor wafer  200 , after the pattern process is conducted on the photoresist  210 . 
         FIG. 2F  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  200 , after a phosphor-encapsulating layer  214  in each of the opening  211 . 
         FIG. 2G  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  200 , after the patterned photoresist is removed. 
         FIG. 2H  illustrates a cross-sectional view of a packaged die unit  201  in accordance with a preferred embodiment of the present disclosure. 
         FIGS. 3A to 3E  illustrate a series of partial cross-sectional views of a manufacture process for fabricating a light emitting semiconductor device in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The foregoing aspects and many of the attendant advantages of this present disclosure will become more readily appreciated and better understood by reference to the following detailed description of preferred embodiment as a method for fabricating a LED device, when taken in conjunction with the accompanying drawings. It should be appreciated that the features and present disclosure concepts may be applied on other light emitting semiconductor device, such as an ultra-high efficiency LED or a laser diode. 
       FIG. 2A  illustrates a vertical view of a light emitting semiconductor wafer and partial magnitude in accordance with a preferred embodiment of the present disclosure.  FIGS. 2B to 2H  illustrate a series of partial cross-sectional views of a manufacture process for fabricating a light emitting semiconductor device along the line S shown in  FIG. 2A . 
     First a light emitting semiconductor wafer  200  having a plurality of die units  201  is provided (referring to  FIG. 2B ). In the preferred embodiment of the present disclosure, the light emitting semiconductor wafer  200  comprises a p type semiconductor epitaxy layer  203 , an active layer  204  and an n type semiconductor epitaxy layer  205  piled in sequence to form a semiconductor epitaxy structure  206 . At least one trench  207  that is formed in the light emitting semiconductor wafer  200  vertically extending from the top surface of the p type semiconductor epitaxy layer  203  into the active layer  204  and the n type semiconductor epitaxy layer  205  is used to identify the die units  201  on the light emitting semiconductor wafer  200 . 
     In the preferred embodiment of the present disclosure, each of the die units  201  further comprises a first electrode  208 , formed on the n type semiconductor epitaxy layer  205 , and a second electrode  209  that is consisted of a portion of a conductive substrate  202  used to grow the semiconductor epitaxy structure  206 . The first electrode  208  is electrically connected to the second electrode  209  via the p type semiconductor epitaxy layer  203 , the active layer  204 , and the p type semiconductor epitaxy layer  205 . 
       FIG. 2C  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  200  shown in  FIG. 2B , after a photoresist  210  is formed thereon. A screen-printing or a thick film process is applied to form the photoresist layer  210  for blanketing over the die units  201 . A mask (not shown) is then applied to conduct an exposure and developing process for forming a plurality of openings  211  in the photoresist layer  210  associated with the die units  201 .  FIG. 2D  and  FIG. 2E  respectively illustrate a cross-sectional view and a vertical view of a portion of the light emitting semiconductor wafer  200 , after the pattern process is conducted on the photoresist  210 , wherein each opening  211  aligns with one of the die units  201 , and each opening  211  has a size greater than the size of the corresponding die unit  201  for exposing thereof. Thus the portion of the patterned photoresist  210  used to identify the openings  211  may be remained on a portion of the trench  207  to serve as a plurality of revetments (hereinafter referred to as revetments  210   a ), and each opening  211  can expose a corresponding die unit  201  and the other portion of the trench  207  so as to separate the die unit  201  from the revetments  210   a . In some embodiments of the present disclosure, each of the revetments  210   a  has a level higher than or equal to the level of the corresponding die unit  201 . In the embodiments of the present disclosure, the shape and size of each opening  211  may be designed according to the predetermined shape and size of the corresponding die unit  201 . 
     In some embodiments of the present disclosure, another portion of the patterned photoresist  210 , denoted as  210   b , may be remained in each of the openings  211  to cover the first electrode  208  of each corresponding die unit  201 . 
     After the photoresist  210  is patterned, a compound  212  mixed with phosphor is filled into the openings  211  via a compound filler  213 . Since the size of each opening  211  is greater than the size of the corresponding die unit  201 , and each of the revetments  210   a  has a level higher than or equal to the level of the corresponding die unit  201 . The phosphor compound  212  filled in these openings  211  not only blankets over the top surface of the n type semiconductor epitaxy layer  205  of each die unit  201 , but also fills in the gap between the revetment  210   a  and the side wall  201   a  of the die unit  201  perpendicular with the top surface of the n type semiconductor epitaxy layer  205 . Thus the phosphor compound  212  can be accurately filled into each of the opening  211  in a predetermined volume. 
     In some embodiments of the present disclosure, the phosphor compound  212  is consisted of organic polymers mixed by phosphoric materials. Light emitting from the die units  201  can activate the phosphoric materials from which some visible light with red, yellow, green, blue or other colors may be derived. In the preferred embodiment of the present disclosure, the phosphor compound  212  is consisted of organic polymers or silica gel mixed by phosphoric materials. The openings  211  are filled with phosphor compound  212  by a continuous filling step or by a discontinuous filling step adjusted according to the design of the patterned photoresist  210   a  to entirely encapsulate the die units  201  without causing any voids. 
     Subsequently, a baking process is conducted to solidify the phosphor compound  212  so as to form a phosphor-encapsulating layer  214  in each of the openings  211  (referring to  FIG. 2F ). The remaining portions of the photoresist  210   a  and  210   b  are then removed to form the structure shown in  FIG. 2G  to complete the phosphor coating process. In some embodiments of the present disclosure, an exposure-development process or a plasma-etching process is applied to remove the remaining portions of the photoresist  210   a  and  210   b . After the remaining portions of the photoresist  210   a  are removed, the resultant trench  207   a  can be exposed to separate each of the die units  201  by a certain distance D and serve as a cutting street during a subsequent dicing process. After the remaining portions of the photoresist  210   b  are removed, a plurality of openings  216  are formed in each of the phosphor encapsulating layers  214  used to encapsulate one of the die unites  211 , so as to expose a portion of the corresponding first electrode  208  and to provide a bonding area for a subsequent wire bonding process. 
     Subsequently, a dicing process is conducted to separate the die units  201  from the light emitting semiconductor wafer  200  coated with phosphor along the cutting street. Each of the separated die units  201  having a phosphor-encapsulating layer  214  thereon is then subjected to a bonding process and a packaging process to form a light emitting semiconductor device having a die unit  201  electrically connected to a chip carrier  215  (referring to  FIG. 2H ). 
       FIGS. 3A to 3E  illustrate a series of partial cross-sectional views of a manufacturing process for fabricating a light emitting semiconductor device in accordance with another embodiment of the present disclosure. 
     First a light emitting semiconductor wafer  300  having a plurality of die units  301  is provided (referring to  FIG. 3A ). In the preferred embodiment of the present disclosure, the light emitting semiconductor wafer  300  comprises a p type semiconductor epitaxy layer  303 , an active layer  304  and an n type semiconductor epitaxy layer  305  piled in sequence to form a semiconductor epitaxy structure  306 . At least one trench  307  that is formed in the light emitting semiconductor wafer  300  vertically extending from the top surface of the p type semiconductor epitaxy layer  303  into the active layer  304  and the n type semiconductor epitaxy layer  305  is used to identify the die units  301  on the light emitting semiconductor wafer  300 . In the preferred embodiment of the present disclosure, each of the die units  301  further comprises a first electrode  308 , formed on the n type semiconductor epitaxy layer  305 , and a second electrode  309 , formed on the p type semiconductor epitaxy layer  303 . The first electrode  308  is electrically connected to the second electrode  309  via the p type semiconductor epitaxy layer  303 , the active layer  304 , and the p type semiconductor epitaxy layer  305 . 
       FIG. 3B  illustrates a cross-sectional view of a portion of the light emitting semiconductor wafer  300  shown in  FIG. 3A , after a photoresist  310  is formed thereon. A screen-printing or a spin-coating process is applied to form the photoresist layer  310  for blanketing over the die units  301 . A mask (not shown) is then applied to conduct an exposure and developing process for forming a plurality of openings  311  in the photoresist layer  310  in associate with the die units  301 , wherein each opening  311  aligns with a corresponding die units  301 , and each opening  311  has a size greater than the size of the corresponding die unit  301  for exposing thereof. Thus the portions of the patterned photoresist  310  used to identify the openings  311  may be remained on a portion of the trench  307  to serve as a plurality of revetments (hereinafter referred to as revetments  310   a ), and each opening  311  exposes a corresponding die unit  301  and the other portion of the trench  307  so as to separate the die unit  301  from the revetments  310   a . In some embodiments of the present disclosure, each of the revetments  310   a  has a level higher than or equal to the level of the corresponding die unit  301 . In the embodiments of the present disclosure, the shape and size of each opening  311  may be designed according to the predetermined shape and size of the corresponding die unit  301 . 
     In some embodiments of the present disclosure, other portions of the patterned photoresist, such as portions  310   b  and  310   c , may be remained in each of the openings  311  to cover the first electrode  308  and the second electrode  309  of each corresponding die unit  301 . 
     After the photoresist  310  is patterned, a compound  312  mixed with phosphor is filled into the openings  311  via a compound filler  313 . Since the size of each opening  311  is greater than the size of the corresponding die unit  301 , and each of the revetments  310   a  has a level higher than or equal to the level of the corresponding die unit  301 . The phosphor compound  312  filled in these openings  311  not only blankets over the top surface of the n type semiconductor epitaxy layer  305  of each die unit  301 , but also fills in the gap between the revetment  310   a  and the side wall  301   a  of the die unit  301  perpendicular with the top surface of the top surface of the n type semiconductor epitaxy layer  305 . Thus the phosphor compound  312  can be accurately filled into each of the opening  311  with a predetermined volume. 
     In some embodiments of the present disclosure, the phosphor compound  312  is consisted of organic polymers mixed by phosphoric materials. Light emitting from the die units  301  can activate the phosphoric materials, from which some visible light with red, yellow, green, blue or other colors may be derived. In the preferred embodiment of the present disclosure, the phosphor compound  312  is consisted of organic polymers or silica gel mixed by phosphoric materials. The openings  311  are filled with phosphor compound  312  by a continuous filling step or by a discontinuous filling step by the compound filler  313 , and the volume of the phosphor compound  312  can be adjusted according to the design of the patterned photoresist  210   a  to entirely encapsulate the die units  301  without causing any voids. 
     Subsequently, a baking process is conducted to solidify the phosphor compound  312  so as to form a phosphor-encapsulating layer  314  in each of the opening  211  (referring to  FIG. 3C ). The remaining portions of the photoresist  310   a ,  310   b  and  310   c  are then removed to form the structure shown as  FIG. 3D  to complete the phosphor coating process. In some embodiments of the present disclosure, an exposure-development process or a plasma etching process is applied to remove the remaining portions of the photoresist  310   a ,  310   b  and  310   c . After the portions of the photoresist  310   a  are removed, the resultant trench  307   a  can be exposed to separate each of the die units  201  for a certain distance D and serve as a cutting street during a subsequent dicing process. After the portions of the photoresist  312   b  and  312   c  are removed, a plurality of openings  316  and opening  317  are formed respectively in each of the phosphor-encapsulating layers  314  used to encapsulate one of the die unites  311 , so as to expose a portion of the corresponding first electrode  308  and a portion of the corresponding second electrode  309  to provide bonding areas for a subsequent wire bonding process. 
     Subsequently, a dicing process is conducted to separate the die units  301  from the light emitting semiconductor wafer  300  coated with phosphor along the cutting street. Each of the separated die units  301  having a phosphor-encapsulating layer  314  thereon is then subjected to a bonding process and a packaging process respectively to form a light emitting semiconductor device having a die unit  301  electrically connected to a chip carrier  315  (not shown). 
     In accordance with the above embodiments, embodiments of the present disclosure conduct the phosphor coating process on the semiconductor wafer, wherein a photolithography process rather than a conventional die attachment or bonding process is applied to fabricate a plurality of light emitting semiconductor devices. A conformal photoresist layer having a plurality of openings is formed over the light emitting semiconductor wafer to surround a plurality of light emitting semiconductor die units. The openings are associated with the light emitting die units. Subsequently, a compound mixed with phosphor is filled into the openings. Since a reticle technology is applied to form the openings associated with the light emitting die units, each of the openings can precisely align one of the light emitting die units, and the patterned photoresist (the revetment surrounding each die unit) can have an accurate predetermined level. Thus the phosphor compound that is filled into each of the openings can be accurately controlled in a predetermined volume, so as to avoid additional waste of phosphor compound. Accordingly, light emitting die units can be encapsulated in equilibrium to improve the brightness of the light emitting die units. 
     As is understood by a person skilled in the art, the foregoing preferred embodiments of the present disclosure are illustrative of the present disclosure rather than limitations of the present disclosure. The disclosed embodiments are intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.

Technology Category: h