Abstract:
A method of applying a fluorescent material to a surface includes providing a substrate, providing a semiconductor light-emitting stack on the substrate, bonding the substrate to the semiconductor light-emitting stack, and overlaying top and side surfaces of the semiconductor light-emitting stack with the fluorescent material, wherein the fluorescent material contains no binding material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 13/045,202, filed on Mar. 10, 2011, which is a Divisional of co-pending application Ser. No. 11/160,588, filed on Jun. 29, 2005, which is a Continuation-in-Part of application Ser. No. 10/604,245, filed on Jul. 4, 2003, and for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 091114688 filed in Taiwan on Jul. 15, 2002 under 35 U.S.C. §119; the entire contents of all of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor light-emitting device, and more particularly, to a semiconductor light-emitting device having a fluorescent material structure. 
     2. Description of the Prior Art 
     Semiconductor light-emitting devices, such as light-emitting diodes (LEDs) and laser diodes (LDs), are characterized by small size, good emitting efficiency, long life-span, high reaction speed, good reliability, and excellent monochromaticity, and have been used widely in electronic devices, cars, signages, and traffic lights. With the achievement of full color LEDs, LEDs have gradually replaced traditional illumination devices, such as fluorescent lamps and incandescent bulbs. 
     In the past, the white light is usually achieved by using the structure of light-emitting diode chip and fluorescent material, such as fluorescent powder. The fluorescent material is excited by blue light and then emits yellow, or green and red light. The mixture of blue and yellow light; or of blue, green, and red light may generate white light. Nowadays the substrate of a white light-emitting diode is generally made of sapphire (Al 2 O 3 ), SiC, or other transparent substrate. In order to ensure that the light emitted by the light-emitting diode will pass through the fluorescent material (fluorescent powder) and blend into the required color, the fluorescent material must entirely cover all the possible light emitted by the light-emitting diode. 
     However, it is difficult to evenly overlay the fluorescent material around the transparent substrate or the light-emitting diode chip. When the light generated by the light-emitting diode travels through the uneven fluorescent material, the thicker portion of the fluorescent material absorbs more light than the thinner one does. Therefore, the light-emitting diode will display different colors in different directions corresponding to different thicknesses of the fluorescent material. U.S. Pat. No. 6,642,652, which is included herein by reference, discloses a flip-chip light-emitting device having fluorescent material. The patent teaches complicated methods, such as electrophoresis, for evenly covering the light-emitting device with fluorescent material. However, the disclosed methods involve increases in the cost and decreases in the yield of the light-emitting device. Furthermore, the patent cannot achieve a simple solution to the problem of uneven thickness of the fluorescent material over an LED chip. 
     To avoid the above-mentioned problems, the present invention provides a semiconductor light-emitting device and manufacturing method thereof. Before chip packaging, a fluorescent material structure is formed over the wafer or the chip to avoid color variation caused by uneven thickness of the fluorescent material over the chip. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a method of applying a fluorescent material to a surface to avoid the above-mentioned problems. 
     The method of applying a fluorescent material to a surface of the claimed invention includes providing a substrate, providing a semiconductor light-emitting stack on the substrate, bonding the substrate to the semiconductor light-emitting stack; and overlaying top and side surfaces of the semiconductor light-emitting stack with the fluorescent material, wherein the fluorescent material contains no binding material. 
     The method for forming a semiconductor light-emitting device comprises steps of separating a semiconductor light-emitting stack from a growth substrate, bonding the semiconductor light-emitting stack to the light-impervious substrate, and form a fluorescent material structure over the semiconductor light-emitting stack. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 3  show front views of an embodiment of the semiconductor light-emitting device according to the present invention. 
         FIGS. 4 and 5  show front views of another embodiment of the semiconductor light-emitting device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 1 
     Referring to  FIGS. 1 to 3 , a semiconductor light-emitting device  10  includes a light-impervious substrate  11 , a bonding structure  12 , a semiconductor light-emitting stack  13 , and a fluorescent material structure  14 . The semiconductor light-emitting stack  13  can be subject to a biased current to emit original light, such as the blue light for GaN based light-emitting diode. Since light cannot penetrate the light-impervious substrate  11 , the light will move towards the side opposite to the light-impervious substrate  11 , i.e., the side of the fluorescent material structure  14 . When the original light enters the fluorescent material structure  14 , a fluorescent material  1401  inside the fluorescent material structure  14  absorbs original light and is excited to generate converted light which has a wavelength different from that of the original light. The original light and the converted light may mix up to white light preferably. The semiconductor light-emitting stack  13  of the present invention may be a vertical structure (with electrical connections at the opposite sides), or a horizontal structure (with electrical connections at the same side). 
     The light-impervious substrate  11  of present invention is a semiconductor substrate, a metal substrate, a combination of above materials, or other light-impervious materials. Preferably, the light-impervious substrate  11  comprises a material selected from a group consisting of Si, GaN/Si, GaAs, and any combination thereof. Otherwise, as shown in  FIG. 2 , the light-impervious substrate  11  is a wafer having a trench  1302  for partitioning more than two semiconductor light-emitting stacks  13 . A suitable way is to dice the semiconductor light-emitting stack  13  after the fluorescent material structure  14  is formed. 
     As shown in  FIG. 3 , the light-impervious substrate  11  further has a transparent substrate  1101  and a reflective layer  16 . The reflective layer  16  is used for reflecting light moving towards the transparent substrate  1101 , such that the original light and/or the converted light will be guided to the fluorescent material structure  14  instead of penetrating the transparent substrate  1101 . The transparent substrate  1101  comprises a material selected from a group consisting of GaP, SiC, ZnO, GaAsP, AlGaAs, Al 2 O 3 , glass, and any combination of such. 
     The bonding structure  12  is used for bonding the light-impervious substrate  11  and the semiconductor light-emitting stack  13 . The bonding structure  12  can be metal, such as In, Au, Al, and Ag etc. The metal is formed between the light-impervious substrate  11  and the semiconductor light-emitting stack  13  at a predetermined temperature, such as 200° C.˜600° C., and serves as a mirror to reflect light moving towards the light-impervious substrate  11 . The bonding structure  12  can also form an ohmic contact between the light-impervious substrate  11  and the semiconductor light-emitting stack  13 , so that the light-impervious substrate  11  is electrically connected to the semiconductor light-emitting stack  13 . 
     In other way, the bonding structure  12  can be a region adjacent to an interface where the light-impervious substrate  11  directly contacts the semiconductor light-emitting stack  13 . The light-impervious substrate  11  and the semiconductor light-emitting stack  13  are bonded together under an appropriate pressure, such as 200 g/cm 2 ˜400 g/cm 2 , and a higher temperature, such as 500° C.˜1000° C., preferably 550° C.˜650° C. 
     The light-impervious substrate  11  and the semiconductor light-emitting stack  13  are preferably glued together by the bonding structure  12 . The gluing process is performed at lower temperature, such as 150° C.˜600° C., preferably 200° C.˜300° C., and a predetermined pressure, such as 328 g/cm 2 ˜658 g/cm 2 , preferably about 505 g/cm 2 , and thereby reduces high-temperature damage to the semiconductor light-emitting stack  13  and achieves a proper bonding effect. The bonding structure  12  comprises a material such as metal, epoxy, PI, BCB, and PFCB, or other substitutes. Moreover, the bonding structure  12  is a transparent material, such as BCB. 
     When the light-impervious substrate  11  is electrically connected to the semiconductor light-emitting stack  13 , an electrical channel is vertically formed. An electrical connection  1301  of the semiconductor light-emitting device  10  can be disposed over the semiconductor light-emitting stack  13 , and the light-impervious substrate  11  serves as another electrical connection. Alternatively, another electrical connection can be formed on the light-impervious substrate  11 . 
     The fluorescent material structure  14  is composed of one or more fluorescent materials  1401  capable of absorbing original light generated by the semiconductor light-emitting stack  13  to generate converted light that has a wavelength different from that of the original light. The converted light may have multiple hues by using multiple fluorescent materials  1401 . Moreover, the fluorescent material structure  14  is formed over the semiconductor light-emitting device  10  and is substantially in contour conformity with the semiconductor light-emitting stack  13  and thereby simplifies the chip packaging procedure. The fluorescent material  1401  can be formed over the semiconductor light-emitting stack  13  via a binder (not shown). The binder and the fluorescent material  1401  are mixed up and then put over the semiconductor light-emitting stack  13 . In other way, the binder is applied to the semiconductor light-emitting stack  13 , and then the fluorescent material  1401  is deposited over the binder. Furthermore, other structures (not shown), such as a cup or container, over the semiconductor light-emitting stack  13  may be formed to carry, fill, or package the fluorescent material  1401 . 
     Preferably, the fluorescent material structure  14  only includes the fluorescent material  1401 , or is a non-glued fluorescent material structure. The non-glued fluorescent material structure  14  here is defined as a lumped fluorescent material containing no binder, epoxy, or other binding material. The method to lump the fluorescent material  1401  together can be used such as sedimentation or other physical deposition process. The bonding strength between the semiconductor light-emitting stack  13  and fluorescent material structure  14  can be further increased by heating and/or compressing the fluorescent material  1401 . The use of the non-glued fluorescent material structure  14  avoids light-absorbing by binder or epoxy and thereby provides better light transformation and color performance. 
     Although the fluorescent material structure  14  of the above embodiment is formed over the semiconductor light-emitting stack  13 , it is not necessary that the fluorescent material structure  14  must directly contact the semiconductor light-emitting stack  13 . Instead, another structure, such as a protection layer or optical layer, can be formed between the semiconductor light-emitting stack  13  and the fluorescent material structure  14 . Additionally, the fluorescent material structure  14  is in a form of powder, like sulfide powder. Preferably, an average diameter of the powder is between 0.1˜100 micrometers. 
     Embodiment 2 
       FIGS. 4 and 5  are front views of second embodiment of the present invention. Elements in the second embodiment that are the same as those in the first embodiment have the same denotations, and repeated description of these elements are omitted herein. 
     As described in the first embodiment, the bonding structure  12  is used for bonding the light-impervious substrate  11  and the semiconductor light-emitting stack  13 . In this embodiment, the bonding structure  12  further comprises a first intermediate layer  1201 , an adhesive layer  1202  and a second intermediate layer  1203 . The first intermediate layer  1201  and the second intermediate layer  1203  are respectively formed over the light-impervious substrate  11  and semiconductor light-emitting stack  13 . The adhesive layer  1202  is used to bond the first and second intermediate layers  1201  and  1203 . The two intermediate layers  1201  and  1203  are used to increase bonding strength between the adhesive layer  1202  and the light-impervious substrate  11 , and between the adhesive layer  1202  and the semiconductor light-emitting stack  13 . 
     The adhesive layer  1202  of the bonding structure  12  is such as epoxy, PI, BCB, PFCB, or other organic adhesive material. The first and second intermediate layers  1201  and  1203  are SiN x , Ti, Cr, or other materials for increasing the bonding strength between the adhesive layer  1202  and the light-impervious substrate  11 , and/or between the adhesive layer  1202  and the semiconductor light-emitting stack  13 . 
     As shown in  FIGS. 4 and 5 , the semiconductor light-emitting device  10  further has a protection structure  15  formed over the fluorescent material structure  14  for protecting the fluorescent material structure  14  and other structures below the fluorescent material structure  14  from humidity, shock, etc. The protection structure  15  comprises a material such as Su8, BCB, PFCB, epoxy, acrylic resin, COC, PMMA, PET, PC, polyetherimide, fluorocarbon polymer, silicone, glass, any combination of above materials, or other materials pervious to light. 
     The protection structure  15  further includes a plurality of optical layers  1501  and  1502 , each optical layer having a different thickness. Each thickness of the optical layers  1501  and  1502  preferably increases with a distance from the semiconductor light-emitting stack  13 , i.e. the thickness of the outer layer is thicker than that of the inner layer. In this embodiment, the thickness of the optical layer  1502  is thicker than that of the optical layer  1501 . The thickness variation of the optical layers  1501  and  1502  can release the thermal stress caused by the semiconductor light-emitting device  10  on the protection structure  15  so as to prevent the protection structure  15  from cracking. The plurality of optical layers  1501  and  1502  can be diffuser, light-gathering layer, i.e. lens, or other structure capable of adjusting light emitting properties of the semiconductor light-emitting device  10 . 
     The semiconductor light-emitting device  10  further has a reflective layer  16  for reflecting light moving towards the light-impervious layer  11  and guiding light to the fluorescent material structure  14 . The reflective layer  16  can be disposed between the bonding structure  12  and the light-impervious layer  11 , and therefore the bonding structure  12  is transparent, as show in  FIG. 4 . In other hand, the reflective layer  16  can be disposed between the bonding structure  12  and the semiconductor light-emitting stack  13 , as shown in  FIG. 5 . Moreover, the reflective layer  16 , such as a Bragg reflector, can be formed within the semiconductor light-emitting stack  13  (not shown). 
     The material of the reflective layer  16  is such as metal, oxide, a combination of above materials, or other materials for reflecting light. Preferably, the reflective layer  16  comprises a material selected from a group consisting of In, Sn, Al, Au, Pt, Zn, Ag, Ti, Pb, Ge, Cu, Ni, AuBe, AuGe, AuZn, PbSn, SiN x , SiO 2 , Al 2 O 3 , TiO 2 , and MgO. 
     The semiconductor light-emitting stack  13  of the present invention further comprises a transparent conductive layer (not shown) for spreading current, or for forming an ohmic contact with other layers, such as p type semiconductor layer or n type semiconductor layer. The material of the transparent conductive layer is indium tin oxide (ITO), cadmium tin oxide (CTO), antimony tin oxide, zinc oxide, zinc tin oxide, Ni/Au, NiO/Au, TiWN, or transparent metal layer. 
     Embodiment 3 
     Please refer to  FIGS. 1 to 5  again. The method for manufacturing the semiconductor light-emitting device  10  of the present invention comprises steps for separating the semiconductor light-emitting stack  13  from a growth substrate (not shown), bonding the semiconductor light-emitting stack  13  to the light-impervious substrate  11 , and forming the fluorescent material structure  14  over the semiconductor light-emitting stack  13 . The bonding step is to form a bonding structure between the semiconductor light-emitting stack  13  and the light-impervious substrate  11 . Alternatively, the bonding step is to directly bond the semiconductor light-emitting stack  13  to the light-impervious layer  11  at a predetermined temperature and pressure, such as 500° C.˜1000° C., preferably 550° C.˜650° C., and 200 g/cm 2 ˜400 g/cm 2 . The bonding structure  12  can be an adhesive layer (not shown) for gluing the semiconductor light-emitting stack  13  and the light-impervious layer  11  under a predetermined temperature, such as 150° C.˜600° C., preferably 200° C.˜300° C., and a predetermined pressure, such as 328 g/cm 2 ˜658 g/cm 2 , preferably about 505 g/cm 2 . The bonding structure  12  can also be a metal layer (not shown), which is bonded with the semiconductor light-emitting stack  13  and the light-impervious layer  11  at an appropriate temperature, such as 200° C.˜600° C., and pressure. The metal layer can also serve as a mirror for reflecting light. 
     Preferably, the bonding step comprises forming the first intermediate layer  1201  over the light-impervious layer  11 , forming the second intermediate layer  1203  over the semiconductor light-emitting stack  13 , and bonding the semiconductor light-emitting stack  13  and the light-impervious layer  11  via the adhesive layer  1202 . The adhesive layer  1202  is formed between the first and second intermediate layers  1201  and  1203 . The first and second intermediate layers  1201  and  1203  can enhance the bonding strength between the adhesive layer  1202  and the semiconductor light-emitting stack  13 , and between the adhesive layer  1202  and the light-impervious layer  11 . 
     The fluorescent material structure  14  is preferably formed over the semiconductor light-emitting stack  13  by sedimentation of the fluorescent material  1401 , or by the mixture of the fluorescent material  1401  and a binder, such as epoxy. 
     A protection structure  15  can also be formed over the fluorescent material structure  14 . The protection structure  15  can include a plurality of layers  1501  and  1502  so as to protect other structures below the protection structure  15  from the humidity and shock, or release the thermal stress occurred at high temperature. 
     Moreover, the present invention forms the reflective layer  16  between the light-impervious substrate  11  and the bonding structure  12 , or between the bonding structure  12  and the semiconductor light-emitting stack  13 . Alternatively, the reflective layer  16 , such as a Bragg reflective layer, is formed within the semiconductor light-emitting stack  13  to reflect light. 
     Additionally, the fluorescent material structure  14  can be formed on a wafer or a chip. If the fluorescent material structure  14  is formed on the wafer, a trench  1302  is designed on the semiconductor light-emitting stack  13 , and then the fluorescent material structure  14  is formed over the semiconductor light-emitting stack  13 . Then, the wafer is diced by the trench  1302  after the formation of the fluorescent material structure  14  or the protection structure  15 , such that the chips of the semiconductor light-emitting devices  10  are made. 
     It will be obvious to those skilled in the art that changes and modifications may be made to the embodiments of the present invention without departing from the invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the spirit and scope of this invention.