Abstract:
The present invention relates to an optical converter and a manufacturing method thereof and a light emitting diode. An optical converter for a light emitting diode includes two substrates, in which, a annular first cavity wall is arranged between the two substrates, and an airtight space filled with an optical conversion substance is surrounded by the first cavity wall and the two substrates. The invention implements the encapsulation and manufacturing of the optical conversion substance for the LED. The structure and the manufacturing method according to the invention can be utilized to encapsulate an active optical conversion substance in the optical converter while avoiding the active optical conversion substance reacting to other active substance, e.g., oxygen, during manufacturing. Furthermore, the optical conversion substance is encapsulated with wafer level chip size packaging to thereby improve the efficiency of manufacturing the optical converter and reduce the cost.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of manufacturing a semiconductor device and in particular to an optical converter and a manufacturing method thereof and a light emitting diode. 
       BACKGROUND OF THE INVENTION 
       [0002]    Light Emitting Diodes (LED) have increasingly significantly improved their illumination performance indices along with the development and maturation of the technologies. Currently, a white-light LED lamp has gained a light emitting efficiency superior to that of a general incandescent lamp and approximate to that of a fluorescent lamp. Furthermore, the LED has increasingly wide applications in the illumination field due to its greatly improved luminous flux. Reference can be made to the disclosure of Chinese Patent Application No. 200810033327.3 for more information on an LED illumination device. 
         [0003]    The traditional LED can only emit light limited to basic colors such as red, blue, yellow and green, etc., despite its energy saving. Two technical approaches have been developed in the art to obtain a white LED illumination light source. One approach is to coat yellow/red fluorescent materials over a blue power-type GaN-LED, to excite yellow/red light by a blue LED pump and mix the light to obtain white light, and the other approach is to excite coated materials with the primary colors of red/green/blue by a purple, near-ultraviolet or royal purple power-type GaN-LED pump and to mix the light to obtain white light. Both of the technical approaches have the limiting factors of the operational lifetime of the coated fluorescent materials, the loss of photons during conversion by the pump, etc., which has hindered the further improvement of device performance. 
         [0004]    A technology of LED optical conversion with an optical conversion substance formed of nanometer quantum dots instead of a fluorescent material has become increasingly popular along with the development of the nanometer quantum dot technology. A nanometer quantum dot refers to particle cluster with extremely small sizes in three dimensions, and therefore the particles in the nanometer quantum dot may exhibit the quantum confinement effect. The quantum confinement effect refers to that when the size of material granules drops below a certain order of magnitude, e.g., from several tens of nanometers to several nanometers, the electron energy level near the metal fermi energy level changes from a quasi-continuous to a discrete energy level, and a gap between energy levels of the discrete highest occupied molecular orbital and lowest unoccupied molecular orbital where the particles constituting the nanometer quantum dot are present becomes larger, that is, the so-called widening energy gap. This effect of nanometer quantum dots is identical to what electrons and protons exhibit in atoms, and therefore the nanometer quantum dots are also referred to as “artificial atoms”. 
         [0005]    For semiconductor nanometer quantum dots formed of an element in the family of II-VIB or III-VB, electrons and holes are restricted in domain by quantum, a continuous energy band becomes a structure of discrete energy levels with the feature of molecules, and the nanometer quantum dots can emit light upon excitation. Excitation light of nanometer quantum dots has a very wide range of wavelengths, and nanometer quantum dots with different colors can be excited by light at the same wavelength. For example, red and green nanometer quantum dots are excited by a blue light LED to emit white light. Therefore, in the art, an LED optical converter has come to be formed of nanometer quantum dots instead of the existing fluorescent materials. Reference can be made to China Taiwan Patent Application No. 95107997 with Publication No. 287887 for more information on a technology of forming a white light LED from nanometer quantum dots. 
         [0006]    Due to the small size of a nanometer quantum dot and a large ratio of the number of atoms on the surface to the total number of atoms, i.e., large specific surface area, the nanometer quantum dot is highly chemically active, extremely instable and prone to combining with other atoms, and hence is more chemically active than in a normal status. 
         [0007]    Therefore, nanometer quantum dots have to be isolated from a relatively active substance such as oxygen and the like in a LED optical converter made of nanometer quantum dots, and a process of manufacturing the LED optical converter is essentially a process of encapsulating nanometer quantum dots in an inert material. Thus, the LED optical converter containing the nanometer quantum dots can be manufactured with semiconductor packaging technique. Furthermore, the nanometer quantum dots also have to be isolated from an active substance such as an adhesive and the like during the manufacture of the optical converter. 
         [0008]    Furthermore, an LED optical converter is manufactured in the prior art with a one-by-one packaging method, thereby resulting in inefficiency. No application has been available for the use of Wafer Level Chip Size Packaging (WLCSP) technology to manufacture any LED optical converter. Wafer level chip size packaging technology is referred to as the technology that packaging and testing are performed at a whole wafer and then the packaged wafer is singulated into individual finished chips with the same size in X and Y directions as original dies. The chips packaged with wafer level chip size packaging are highly miniaturized in size, and the cost of the chips is significantly reduced with the decreasing size of the chips and the increasing size of the wafer. An application of wafer level chip size packaging to manufacturing of an LED optical converter can be anticipated for a considerably improved efficiency and reduced cost of manufacturing. 
       SUMMARY OF THE INVENTION 
       [0009]    A technical problem to be solved with the invention is how to encapsulate an active optical conversion substance in an airtight environment to form an optical converter for an LED. 
         [0010]    To solve the above problem, the invention provides an optical converter for a light emitting diode, which includes two substrates, in which an annular first cavity wall is arranged between the two substrates, and an airtight space filled with an optical conversion substance is surrounded by the first cavity wall and the two substrates. 
         [0011]    Optionally, the optical conversion substance contains nanometer quantum dots. 
         [0012]    Optionally, the first cavity wall and one of the substrates are integral. 
         [0013]    Optionally, an adhesion layer is arranged between the first cavity wall and the other substrate. 
         [0014]    Optionally, the material of the adhesion layer is the optical conversion substance. 
         [0015]    Optionally, the optical conversion substance is a silica gel in which nanometer quantum dots are distributed evenly. 
         [0016]    Optionally, the silica gel has a viscosity of 5000 cp to 40000 cp. 
         [0017]    Optionally, the first cavity wall includes an upper cavity wall connected with one of the substrates and a lower cavity wall connected with the other substrate, which are superposed over one another. 
         [0018]    Optionally, an adhesion layer is arranged between the upper cavity wall and the lower cavity wall. 
         [0019]    Optionally, the first cavity wall is with a thickness of 40 μm to 200 μm. 
         [0020]    Optionally, an annular second cavity wall enclosing the first cavity wall is further arranged between the two substrates. 
         [0021]    Optionally, an adhesion layer is arranged between the second cavity wall and one of the substrates. 
         [0022]    Optionally, the first cavity wall is in the shape of a circular ring, and the second cavity wall is in the shape of a square ring. 
         [0023]    Optionally, the spacing between the first cavity wall and the second cavity wall is smaller than 200 μm. 
         [0024]    Optionally, the spacing between the first cavity wall and the second cavity wall is 80 μm to 100 μm. 
         [0025]    Optionally, the space between the first cavity wall and the second cavity wall is vacuum or filled with a rare gas or nitrogen. 
         [0026]    Optionally, the second cavity wall is with a thickness of 40 μm to 200 μm. 
         [0027]    Optionally, the two substrates are transparent substrates. 
         [0028]    Optionally, a material of which the two substrates are made includes glass or plastic. 
         [0029]    According to another aspect of the invention, there is provided a method of manufacturing an optical converter for a light emitting diode, which includes the steps of: forming a first cavity wall on a first substrate; filling an optical conversion substance within a space surrounded by the first cavity wall; and laminating the first cavity wall with a second substrate and the first substrate to seal the optical conversion substance. 
         [0030]    Optionally, the optical conversion substance contains nanometer quantum dots. 
         [0031]    Optionally, a way of forming the first cavity wall on the first substrate is to etch the first substrate to form the first cavity wall. 
         [0032]    Optionally, a way of forming the first cavity wall on the first substrate is to bond the first cavity wall on the first substrate. 
         [0033]    Optionally, the optical conversion substance with which the space surrounded by the first cavity wall is filled is with a height above a thickness of the first cavity wall; the lamination process extrudes the optical conversion substance to overflow between the second substrate and the first cavity wall; and the sealing is performed by bonding the second substrate and the first cavity wall with the optical conversion substance overflowing between the second substrate and the first cavity wall. 
         [0034]    Optionally, the optical conversion substance is a silica gel in which nanometer quantum dots are distributed evenly. 
         [0035]    Optionally, the silica gel has a viscosity of 5000 cp to 40000 cp. 
         [0036]    Optionally, the number of the first cavity wall formed on the first substrate is larger than two. 
         [0037]    Optionally, there are further included the steps of: forming a second cavity wall on the second substrate; forming an adhesion layer on the side of the second cavity wall away from the second substrate; and bonding the second cavity wall and the side of the first substrate on which the first cavity wall is arranged, so that the first cavity wall is enclosed by the second cavity wall. 
         [0038]    Optionally, a way of forming the second cavity wall on the second substrate is to etching the second substrate to form the second cavity wall. 
         [0039]    Optionally, a way of forming the second cavity wall on the second substrate is to bonding the second cavity wall on the second substrate. 
         [0040]    Optionally, the number of the first cavity wall formed on the first substrate is larger than two. 
         [0041]    Optionally, the first cavity wall is in the shape of a circular ring, and the second cavity wall is in the shape of a square ring. 
         [0042]    Optionally, the spacing between the first cavity wall and the second cavity wall is 80 μm to 100 μm. 
         [0043]    Optionally, the lamination is performed in an atmosphere of vacuum or a rare gas or nitrogen. 
         [0044]    Optionally, the first substrate and the second substrate are transparent substrates. 
         [0045]    Optionally, a material of which the first substrate and the second substrate are made includes glass or plastic. 
         [0046]    According to a further aspect of the invention, there is provided a method of manufacturing an optical converter for a light emitting diode, which includes the steps of: forming a lower cavity wall on a first substrate; filling an optical conversion substance within a space surrounded by the lower cavity wall; forming an upper cavity wall corresponding to the lower cavity wall on a second substrate; and laminating the upper cavity wall and the lower cavity wall to seal the optical conversion substance. 
         [0047]    Optionally, the optical conversion substance contains nanometer quantum dots. 
         [0048]    Optionally, a way of forming the lower cavity wall on the first substrate is to etch the first substrate to form the lower cavity wall. 
         [0049]    Optionally, a way of forming the lower cavity wall is formed on the first substrate is to bond the lower cavity wall on the first substrate. 
         [0050]    Optionally, a way of forming the upper cavity wall is formed on the second substrate is to etch the second substrate to form the upper cavity wall. 
         [0051]    Optionally, a way of forming the upper cavity wall is formed on the second substrate is to bond the upper cavity wall on the second substrate. 
         [0052]    Optionally, there is further included the step of forming an adhesion layer on the side of the upper cavity wall away from the second substrate. 
         [0053]    Optionally, the number of the lower cavity wall formed on the first substrate is larger than two. 
         [0054]    Optionally, the number of the upper cavity wall is the same as that of the lower cavity wall. 
         [0055]    Optionally, there are further included the steps of: forming a second cavity wall enclosing the upper cavity wall on the second substrate and with a thickness equal to the sum of those of the upper cavity wall and the lower cavity wall; forming an adhesion layer on the side of the second cavity wall away from the second substrate; and bonding the second cavity wall and the side of the first substrate on which the lower cavity wall is arranged, so that the lower cavity wall is enclosed by the second cavity wall. 
         [0056]    Optionally, a way of forming the second cavity wall on the second substrate is to etch the second substrate to form the second cavity wall. 
         [0057]    Optionally, a way of forming the second cavity wall on the second substrate is to bond the second cavity wall on the second substrate. 
         [0058]    Optionally, the number of the second cavity wall formed on the second substrate is the same as that of the upper cavity wall. 
         [0059]    Optionally, the spacing between the upper cavity wall and the second cavity wall is 80 μm to 100 μm. 
         [0060]    Optionally, there are further included the steps of: forming a second cavity wall enclosing the lower cavity wall on the first substrate and with a thickness equal to the sum of those of the upper cavity wall and the lower cavity wall; forming an adhesion layer on the side of the second cavity wall away from the first substrate; and bonding the second cavity wall and the side of the second substrate on which the upper cavity wall is arranged, so that the upper cavity wall is enclosed by the second cavity wall. 
         [0061]    Optionally, the number of the second cavity wall formed on the first substrate is the same as that of the lower cavity wall. 
         [0062]    Optionally, a way of forming the second cavity wall on the first substrate is to etch the first substrate to form the second cavity wall. 
         [0063]    Optionally, a way of forming the second cavity wall on the first substrate is to bond the second cavity wall on the first substrate. 
         [0064]    Optionally, the spacing between the lower cavity wall and the second cavity wall is 80 μm to 100 μm. 
         [0065]    Optionally, the upper cavity wall and the lower cavity wall are in the shape of a circular ring, and the second cavity wall is in the shape of a square ring. 
         [0066]    Optionally, the lamination is performed in an atmosphere of vacuum or a rare gas or nitrogen. 
         [0067]    Optionally, the first substrate and the second substrate are transparent substrates 
         [0068]    Optionally, a material of which the first substrate and the second substrate are made includes glass or plastic. 
         [0069]    According to still another aspect, there is provided a light emitting diode including any preceding optical converter and a PN junction, in which the PN junction is arranged on the side of either of the two substrates of the optical converter away from the other substrate. 
         [0070]    The invention implements the encapsulation and manufacturing of the optical conversion substance for the LED. 
         [0071]    The structure and the manufacturing method according to the invention can be utilized to encapsulate an active optical conversion substance in the optical converter while avoiding the active optical conversion substance reacting to other active substance, e.g., oxygen, during manufacturing. 
         [0072]    Furthermore, the optical conversion substance is encapsulated with wafer level chip size packaging to thereby improve the efficiency of manufacturing the optical converter and reduce the cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0073]      FIG. 1  is a schematic sectional view of an optical converter according to an embodiment of the invention; 
           [0074]      FIG. 2  is a top view of the optical converter illustrated in  FIG. 1 ; 
           [0075]      FIG. 3  is a flow chart of a method of manufacturing the optical converter illustrated in  FIG. 1 ; 
           [0076]      FIG. 4  to  FIG. 7  are schematic diagrams of manufacturing the optical converter in the flow illustrated in  FIG. 3 ; 
           [0077]      FIG. 8  is a schematic sectional view of an optical converter according to another embodiment of the invention; 
           [0078]      FIG. 9  is a top view of the optical converter illustrated in  FIG. 8 ; 
           [0079]      FIG. 10  is a flow chart of a method of manufacturing the optical converter illustrated in  FIG. 8 ; 
           [0080]      FIG. 11  to  FIG. 14  are schematic diagrams of manufacturing the optical converter in the flow illustrated in  FIG. 10 ; 
           [0081]      FIG. 15  is a schematic sectional view of an optical converter according to an embodiment of the invention; 
           [0082]      FIG. 16  is a top view of the optical converter illustrated in  FIG. 15 ; 
           [0083]      FIG. 17  is a flow chart of a method of manufacturing the optical converter illustrated in  FIG. 15 ; 
           [0084]      FIG. 18  to  FIG. 21  are schematic diagrams of manufacturing the optical converter in the flow illustrated in  FIG. 17 ; 
           [0085]      FIG. 22  is a schematic sectional view of an optical converter according to still another embodiment of the invention; and 
           [0086]      FIG. 23  is a schematic sectional view of an optical converter according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The First Embodiment 
       [0087]    There is provided in this embodiment an optical converter  101  for an LED, a sectional view of which is as illustrated in  FIG. 1  and a top view of which is as illustrated in  FIG. 2 . Referring to  FIG. 1  and  FIG. 2  together, the optical converter  101  includes a first substrate  102 , a second substrate  103  and an annular first cavity wall  104  sandwiched between the first substrate  102  and the second substrate  103 . An airtight space in which an optical conversion substance  105  is sealed is surrounded by the first cavity wall  104  together with the first substrate  102  and the second substrate  103 . 
         [0088]    The optical conversion substance  105  sealed in the optical converter  101  can be various, e.g., photoluminescence-type fluorescent materials or nanometer quantum dots, and since some of the photoluminescence-type fluorescent materials and the nanometer quantum dots are relatively active materials and hence prone to reaction to other substances, they need to be sealed for use. The optical converter  101  according to this embodiment can achieve this purpose. The nanometer quantum dots are typically not used separately but can be dispersed in an inert material, e.g., silica gel, and thus can be conveniently filled during manufacturing without influence upon the performance thereof. 
         [0089]    As illustrated in  FIG. 2 , the first cavity wall  104  is in the shape of a closed circular ring in the top view. Naturally, the circular ring is merely illustrative, and since the first cavity wall  104  serves to cooperate with the first substrate  102  and the second substrate  103  to form a airtight cavity, as long as the first cavity wall  104  is in the shape of a closed ring in the top view, e.g., a square ring, the object of this embodiment is also can be attained. The first cavity wall  104  can be with a thickness of approximately 40 μm to 200 μm. The thickness as referred to here can be defined as a distance from the top surface of the cavity wall to the substrate which is etched to form the cavity wall, and this definition will apply throughout the detailed descriptions of the invention. 
         [0090]    The first substrate  102  and the second substrate  103  can be in the shape of a square as illustrated in  FIG. 2  or in the shape, e.g., of a circle, accommodating the annular first cavity wall  104 . The first substrate  102  and the second substrate  103  can be shaped identically or differently as required for the shape of the finally formed LED. 
         [0091]    Since the first substrate  102  and the second substrate  103  serve to seal the optical conversion substance  105 , at least parts of the first substrate  102  and the second substrate  103  corresponding to the optical conversion substance  105  are transparent. Since the first substrate  102  and the second substrate  103  may contact with the optical conversion substance, and some optical conversion substances, e.g., those containing nanometer quantum dots, are relatively active substances, the first substrate  102  and the second substrate  103  shall be made of a chemically inert material. A preferred light-transmissive and inert material of which the first substrate  102  and the second substrate  103  are made may be silicate glass or a plastic material with a high light transmittance, for example. 
         [0092]    The first cavity wall  104  and the first substrate  102  are integral without adhesion layer therebetween, and an adhesion layer  106  is arranged between the first cavity wall  104  and the second substrate  103  to bond them together. The adhesion layer  106  is made of a material which does not react to the optical conversion substance  105 . Since some optical conversion substance  105  may have a certain viscosity, for example, when the optical conversion substance  105  is a silica gel with a viscosity of 5000 cp to 40000 cp in which nanometer quantum dots are distributed evenly, the optical conversion substance  105  can be used directly as the adhesion layer  106 . 
         [0093]    A method for forming the above optical converter  101  includes the following steps as illustrated in  FIG. 3 . 
         [0094]    Step S 101  is to etch the first substrate to form the first cavity wall on the first substrate; 
         [0095]    Step S 102  is to fill the optical conversion substance within the space surrounded by the first cavity wall; 
         [0096]    Step  103  is to laminate the first cavity wall with the second substrate and the first substrate to seal the optical conversion substance. 
         [0097]    The above method will be detailed below with reference to the drawings. 
         [0098]    As illustrated in  FIG. 4 , firstly the first substrate  101  made of transparent glass is prepared with a thickness of approximately 1000 μm. Then, the first substrate  102  is spin-coated with a photo-resist and etched by exposure, development and etching processes to form the first cavity wall  104  with a thickness of approximately 40 μm to 200 μm on the first substrate  102 , thereby forming the structure as illustrated in  FIG. 5  and thus finishing the step S 101 . 
         [0099]    Then, the step S 102  is executed in which the space surrounded by the first cavity wall  104  is filled with the optical conversion substance  105 , for example, through filling the optical conversion substance  105  within the space surrounded by the first cavity wall  104  by a dispensing machine or otherwise, e.g., silk screen printing or steel plate printing. The optical conversion substance  105  filled with here is a silica gel with a viscosity of 5000 cp to 40000 cp in which nanometer quantum dots are distributed evenly and with a height above the thickness of the first cavity wall  104 , thereby forming the structure as illustrated in  FIG. 6 . 
         [0100]    Then the step S 103  is executed in which the first cavity wall  104  is laminated with the second substrate  103  and first substrate  102  to seal the optical conversion substance  105 . Since the optical conversion substance  105  with which the space surrounded by the first cavity wall  104  is filled is of a height above that the thickness of the first cavity wall  104  in the step S 102 , the lamination process in the step S 103  may extrude the optical conversion substance  105  to overflow between the second substrate  103  and the first cavity wall  104 . Furthermore due to the high viscosity up to 5000 cp to 40000 cp of the optical conversion substance  105 , the optical conversion substance  105  overflowing between the second substrate  103  and the first cavity wall  104  bond the second substrate  103  and the first cavity wall  104  while lamination is in progress. Finally, the optical conversion substance  105  overflowing between the second substrate  103  and the first cavity wall  104  bond the first cavity wall  104  and the second substrate  103  together completely at the end of lamination to thereby seal the optical conversion substance  105  within the space surrounded by the first cavity wall  104 . 
         [0101]    Since the optical conversion substance  105  is active, the above manufacturing process can be conducted in an atmosphere of vacuum or rare gas or nitrogen. 
         [0102]    Naturally, in order to improve the efficiency of manufacturing the optical converter  101 , the first substrate  102  of a wafer level size can be etched to form thereon a plurality of first cavity walls  104  in the step S 101 , thereby forming the structure as illustrated in  FIG. 7 . Correspondingly, the second substrate  103  also adopts a glass substrate of the same size. Thus, a batch of optical converters  101  can be packaged and manufactured in one time to accomplish an application of wafer level chip size packaging to manufacturing of the optical converter  101  of the LED, thereby significantly improving the efficiency of manufacturing and reducing cost. 
       The Second Embodiment 
       [0103]    There is provided in this embodiment an optical converter  201  for an LED, a sectional view of which is as illustrated in  FIG. 8  and a top view of which is as illustrated in  FIG. 9 . Referring to  FIG. 8  and  FIG. 9  together, the optical converter  201  includes a first substrate  202  and a second substrate  203 . The first substrate  202  further includes an annular first cavity wall  204 , and the second substrate  203  further includes an annular second cavity wall  207 . The annular first cavity wall  204  and the annular second cavity wall  207  are sandwiched between the first substrate  202  and the second substrate  203 . An airtight space in which an optical conversion substance  205  is sealed is surrounded by the first cavity wall  204  together with the first substrate  202  and the second substrate  203 . An airtight space in which the first cavity wall  204  and the optical conversion substance  205  are sealed is surrounded by the second cavity wall  207  together with the first substrate  202  and the second substrate  203 . 
         [0104]    There is a distance of approximately 80 μm to 100 μm between the first cavity wall  204  and the second cavity wall  207  to thereby form a buffer space  209  isolated from the outside. The buffer space  209  is formed for the purpose of accommodating the optical conversion substance  205  overflowing from the first cavity wall  204 . The buffer space  209  is vacuumized or filled with a gas which does not react to the optical conversion substance  205 , e.g., a rare gas or nitrogen. 
         [0105]    Like the first embodiment, the optical conversion substance  205  sealed in the optical converter  201  can be various with a silica gel in which nanometer quantum dots are dispersed being preferred. 
         [0106]    As illustrated in  FIG. 9 , the first cavity wall  204  is in the shape of a closed circular ring in the top view, and the second cavity wall  207  is in the shape of a closed square ring enclosing the first cavity wall in the top view. Naturally, the circular and square rings here are merely illustrative, and since the first cavity wall  204  serves to cooperate with the first substrate  202  and the second substrate  203  to form the airtight cavity, and the second cavity wall  207  serves to cooperate with the first substrate  202 , the second substrate  203  and the first cavity wall  204  to form the buffer space  209  isolated from the outside, the first cavity wall  204  and the second cavity wall  207  also can be in another shape in the top view. The first cavity wall  204  can be with a thickness of approximately 40 μm to 200 μm. The second cavity wall  207  can be with the same or substantially the same thickness as that of the first cavity wall  204 . 
         [0107]    The first substrate  202  and the second substrate  203  can be in the shape of a square as illustrated in  FIG. 2  or in the shape, e.g., of a square, accommodating the annular second cavity wall  207 . Naturally like the first embodiment, the first substrate  202  and the second substrate  203  can be shaped identically or differently as required for the shape of the finally formed LED. 
         [0108]    At least parts of the first substrate  202  and the second substrate  203  corresponding to the optical conversion substance  205  are transparent, and the first substrate  202  and the second substrate  203  shall be made of a chemically inert material, for example, silicate glass or PMMA. 
         [0109]    It is different from the first embodiment that no adhesion layer is arranged between the first cavity wall  204  and the second substrate  203 , but an adhesion layer  208  is arranged between the second cavity wall  207  and the first substrate  202  to seal the space surrounded by the second cavity wall  207  and the first and second substrates  202  and  203 . Since the adhesion layer  208  will not contact the optical conversion substance in the second embodiment, the material of the adhesion layer  208  will not be limited in the second embodiment. 
         [0110]    A method for forming the above optical converter  201  includes the following steps as illustrated in  FIG. 10 . 
         [0111]    Step S 201  is to etch the first substrate to form the first cavity wall on the first substrate. 
         [0112]    Step S 202  is to fill the optical conversion substance within the space surrounded by the first cavity wall. 
         [0113]    Step S 203  is to etch the second substrate to form the second cavity wall on the second substrate. 
         [0114]    Step S 204  is to form the adhesion layer on the side of the second cavity wall away from the second substrate. 
         [0115]    Step S 205  is to bond the second cavity wall and the side of the first substrate on which the first cavity wall is arranged to make the first cavity wall to be enclosed by the second cavity wall, and to laminate the first cavity wall with the second substrate and the first substrate to seal the optical conversion substance. 
         [0116]    The above method will be detailed below with reference to the drawings. 
         [0117]    Firstly, the first substrate  202  made of transparent glass is prepared with a thickness of approximately 1000 μm. Then, the first substrate  202  is spin-coated with a photo-resist and etched by exposure, development and etching processes to form the first cavity wall  204  on the first substrate  202 , thereby forming the structure as illustrated in  FIG. 11 . 
         [0118]    Then, the step S 202  is executed in which the space surrounded by the first cavity wall  204  is filled with the optical conversion substance  205 , like the first embodiment, for example, through filling the optical conversion substance  205  within the space surrounded by the first cavity wall  204  by a dispensing machine or otherwise, e.g., silk screen printing or steel plate printing. The optical conversion substance  205  filled with here may be a silica gel in which nanometer quantum dots are distributed evenly and with a height at least equal to the thickness of the first cavity wall  204 . 
         [0119]    Next, the second substrate  203  made of transparent glass is prepared with a thickness of approximately 1000 μm. Then, the second substrate  203  is spin-coated with a photo-resist and etched by exposure, development and etching processes to form the second cavity wall  207  on the second substrate  203 , thereby forming the structure as illustrated in  FIG. 13  and thus finishing the step S 203 . The space surrounded by the second cavity wall  207  shall accommodate at least the entire first cavity wall  204 , so that the second cavity wall  207  can enclose the first cavity wall  204  in subsequent steps. Furthermore, the second cavity wall  207  shall also be with a thickness equivalent to that of the first cavity wall  204 . 
         [0120]    Next, the step S 204  is executed in which the adhesion layer  208  is formed on the side of the second cavity wall  207  away from the second substrate  203  as illustrated in  FIG. 14 . Since the adhesion layer  208  formed here will not contact the optical conversion substance  205 , its material will not be further limited, and the adhesion layer  208  can be attached on the side of the second cavity wall  207  away from the second substrate  203  directly with an adhesive rolling process. 
         [0121]    Then, the step S 205  is executed in which the first cavity wall  204  is enclosed in the second cavity wall  207 , and the second cavity wall  207  and the side of the first substrate on which the first cavity wall  204  is arranged are bonded with the adhesion layer  208 . During the process of bonding, the first cavity wall  207  is laminated with the second substrate  203  and the first substrate  202  to seal the optical conversion substance, thereby finally forming the structure as illustrated in  FIG. 8 . 
         [0122]    In the step S 202 , the optical conversion substance  205  with which the first cavity wall  204  is filled shall be with a height at least equal to the thickness of the first cavity wall  204  because the optical conversion substance  205  has a certain viscosity and surface tension. Therefore the optical conversion substance  205  may not take up the entire space surrounded by the first cavity wall  204  during being filled with dispensing process or the like. Therefore, the optical conversion substance  205  can be laminated with the second substrate  203  and the first substrate  202  to fill up the space surrounded by the first cavity wall  204 . Since the filled optical conversion substance  205  may be with a volume larger than that of the space surrounded by the first cavity wall  204 , a part of the optical conversion substance  205  may overflow from the space surrounded by the first cavity wall  204 . At this time, the buffer space  209  between the first cavity wall  204  and the second cavity wall  207  can serve to accommodate the overflowing optical conversion substance  205 . 
         [0123]    Also since the optical conversion substance  205  is active, the above manufacturing process can be conducted in an atmosphere of vacuum or rare gas or nitrogen. Accordingly, the buffer space  209  between the first cavity wall  204  and the second cavity wall  207  will also be vacuum or filled with a rare gas or nitrogen at the end of manufacturing. 
         [0124]    Naturally, in order to improve the efficiency of manufacturing the optical converter  201 , the first substrate  202  of a wafer level size can be etched to form thereon a plurality of first cavity walls  204  in the step S 201 . Correspondingly, the second substrate  203  also adopts a glass substrate of the same size and is etched to form thereon a plurality of second cavity walls  207  corresponding to the first cavity walls  204  in the step S 203 . Thus, a batch of optical converters  201  can be packaged and manufactured in one time to accomplish an application of WLCSP to manufacturing of the optical converter  201  of the LED. 
       The Third Embodiment 
       [0125]    There is provided in this embodiment an optical converter  301  for an LED, a sectional view of which is as illustrated in  FIG. 15  and a top view of which is as illustrated in  FIG. 16 . Referring to  FIG. 15  and  FIG. 16  together, the optical converter  301  includes a first substrate  302  and a second substrate  303 . The first substrate  302  further includes an annular lower cavity wall  307 , and the second substrate  303  further includes an annular upper cavity wall  308  in a shape corresponding to that of the lower cavity wall  307 . The lower cavity wall  307  and the upper cavity wall  308  are engaged, so that an airtight space in which an optical conversion substance  305  is sealed is surrounded by the lower cavity wall  307 , the upper cavity wall  308 , the first substrate  302  and the second substrate  303 . 
         [0126]    As mentioned in the first and second embodiments, the optical conversion substance  305  sealed in the optical converter  301  can be various, e.g., photoluminescence-type fluorescent materials or nanometer quantum dots. 
         [0127]    The lower cavity wall  307  and the upper cavity wall  308  can be in the shape of a closed circular ring in the top view and with a thickness of 40 μm to 200 μm. Widths of the lower cavity wall  307  and the upper cavity wall  308  may be identical or different and naturally preferably identical. The width of a cavity wall as referred to here is defined as a distance of the inner ring to the outer ring of the cavity wall, and this definition will apply hereinafter. The inner rings of the lower cavity wall  307  and the upper cavity wall  308  may or may not coincide and preferably coincide. Similarly, the outer rings of the lower cavity wall  307  and the upper cavity wall  308  may or may not coincide and preferably coincide. 
         [0128]    As mentioned in the first and second embodiments, the first substrate  302  and the second substrate  303  can be in the shape of a square or circle, for example. The first substrate  302  and the second substrate  303  can be shaped identically or differently as required for the shape of the finally formed LED. 
         [0129]    An adhesion layer  306  is arranged between the lower cavity wall  307  and the upper cavity wall  308  to bond them together. Since the adhesion layer  306  will not contact the active optical conversion substance  305  during manufacturing of this embodiment, the material of which the adhesion layer  306  is made will not be further limited, for example, be limited to an adhesive material which does not react to the optical conversion substance  305 . 
         [0130]    A method for forming the above optical converter  301  includes the following steps as illustrated in  FIG. 17 . 
         [0131]    Step S 301  is to etch the first substrate to form the lower cavity wall on the first substrate. 
         [0132]    Step S 302  is to fill the optical conversion substance within the space surrounded by the lower cavity wall. 
         [0133]    Step S 303  is to etch the second substrate to form the upper cavity wall on the second substrate. 
         [0134]    Step S 304  is to form the adhesion layer on the side of the upper cavity wall away from the second substrate. 
         [0135]    Step S 305  is to bond the upper cavity wall and the lower cavity wall to seal the optical conversion substance. 
         [0136]    As illustrated in  FIG. 18 , firstly the step S 301  is executed to etch the first substrate  302  to form the annular lower cavity wall  307  on the first substrate  302 , and the specific step of etching the first substrate  302  is the same as in the foregoing embodiments and detailed descriptions thereof will be omitted here. 
         [0137]    Then, the step S 302  is executed in which the space surrounded by the lower cavity wall  307  is filled with the optical conversion substance  305 . Like the foregoing embodiments, the filled optical conversion substance  305  shall be with a height above the thickness of the lower cavity wall  307 , thereby forming the structure as illustrated in  FIG. 19 . 
         [0138]    Next, the step S 303  is executed in which the second substrate  303  is etched to form the annular upper cavity wall  308 , thereby forming the structure as illustrated in  FIG. 20 . The upper cavity wall  308  is in the shape corresponding to that of the lower cavity wall  307  but may be with a width different from that of the lower cavity wall  307 . That is to say, the inner ring of the annular upper cavity wall  308  shall be smaller than the outer ring of the annular lower cavity wall  307 , and correspondingly the inner ring of the annular lower cavity wall  307  shall be smaller than the outer ring of the annular upper cavity wall  308 . 
         [0139]    Then, the step S 304  is executed in which the adhesion layer  306  is formed on the side of the upper cavity wall  308  away from the second substrate  303 , thereby forming the structure as illustrated in  FIG. 21 . Since the adhesion layer  306  formed here will not contact the optical conversion substance  305 , its material will not be further limited, and the adhesion layer  306  can be attached on the side of the upper cavity wall  308  away from the second substrate  303  directly with an adhesive rolling process. 
         [0140]    Finally, the step S 305  is executed in which the upper cavity wall  308  and the lower cavity wall  307  are bonded correspondingly to seal the optical conversion substance. The corresponding bonding as referred to here means that the inner ring of the annular upper cavity wall  308  falls inside the outer ring of the annular lower cavity wall  307  and the inner ring of the annular lower cavity wall  307  also falls inside the outer ring of the annular upper cavity wall  308 . Such bonding forms the airtight space in which the optical conversion substance  305  is sealed is surrounded by the lower cavity wall  307 , the upper cavity wall  308 , the first substrate  302  and the second substrate  303 . 
         [0141]    Also since the optical conversion substance  305  is active, the above manufacturing process can be conducted in an atmosphere of vacuum or rare gas or nitrogen. 
         [0142]    Like the foregoing embodiments, in order to improve the efficiency of manufacturing the optical converter  301 , the first substrate  302  of a wafer level size can be etched to form thereon a plurality of lower cavity walls  307  in the step S 301 . Correspondingly, the second substrate  303  also adopts a glass substrate of the same size and is etched to form thereon a plurality of upper cavity walls  308  corresponding to the lower cavity walls  307  in the step S 303 . Thus, a batch of optical converters  301  can be packaged and manufactured in one time to accomplish an application of WLCSP to manufacturing of the optical converter  301  of the LED. 
       The Fourth Embodiment 
       [0143]    Following the idea of the third embodiment, the first cavity wall  204  in the second embodiment can be divided into two upper and lower cavity walls made respectively on the first substrate and the second substrate, thereby forming the structure as illustrated in  FIG. 22 , in which,  401  denotes the optical converter,  402  denotes the first substrate,  403  denotes the second substrate,  406  denotes the adhesion layer,  407  denotes the lower cavity wall constituting the first cavity wall,  408  denotes the upper cavity wall constituting the first cavity wall,  409  denotes a buffer space formed of the spacing between the lower cavity wall  407  and upper cavity wall  408  engaged with each other and the second cavity wall  410 , the buffer space  409  functions in the same way as the buffer space  209  in the second embodiment, and  410  denotes the second cavity wall. 
         [0144]    Naturally in this embodiment, the second cavity wall  410  can be formed from etching on the second substrate  403  or the first substrate  402 . The object of this embodiment can be attained as long as the thickness of the second cavity wall  410  is the same or substantially the same as the sum of those of the lower cavity wall  407  and the upper cavity wall  408 . 
       The Fifth Embodiment 
       [0145]    Following the idea of the third embodiment, the second cavity wall  410  in the fourth embodiment can further be divided into a second lower cavity wall  511  formed from etching on the first substrate  502  and a second upper cavity wall  512  formed from etching on the second substrate  503 . An adhesion layer  506  for bonding the two upper and lower substrates is arranged between the second lower cavity wall  511  and the second upper cavity wall  512 , thereby forming the structure of an optical converter  501  as illustrated in  FIG. 23 . 
         [0146]    The manufacturing procedure is conducted firstly for the first substrate and then for the second substrate in the foregoing five embodiments. However, the scope of the invention will not be limited thereto, and the manufacturing steps for the first substrate and those for the second substrate can be reversed without influencing the implement of the invention. 
         [0147]    Furthermore, the first cavity wall, the second cavity wall, the upper cavity wall, the lower cavity wall and the like are formed by etching the substrates in the foregoing five embodiments. However, the scope of the invention will not be limited thereto, and the cavity walls also can be formed on the substrates by bonding the annular cavity walls on the corresponding substrates. 
         [0148]    A PN junction for light emission of the LED can further be arranged on the side of the first substrate of the optical converter away from the second substrate or the side of the second substrate away from the first substrate in the above embodiments to thereby form the general structure of the LED. Naturally, devices, e.g., light reflection plates, for improving the performance of the LED, can further be arranged on other sides of the PN junction than the side thereof close to the substrate to thereby form a complete LED with superior performance, and these devices are well known to those skilled in the art and detailed descriptions thereof will be omitted here. 
         [0149]    The preferred embodiments of the invention have been disclosed as above but are not intended to limit the claims of the invention. Any skilled in the art may make possible variations and modifications without departing from the spirit and scope of the invention, and accordingly the scope of the protection of the invention shall be defined in accordance with the claims of the invention.