Abstract:
A manufacturing method of microlenses includes providing a substrate; forming a microlens material on the substrate; disposing a mask over the microlens material; performing an exposure process by a radiant beam emitted to the microlens material via the mask; performing a developing process on the microlens material; and forming microlenses by performing a reflow process on the microlens material.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a manufacturing method for microlenses, and in particular, to a manufacturing method for microlenses using a mask. 
         [0003]    2. Description of the Related Art 
         [0004]    Image sensors for cameras usually have microlenses disposed thereon to increase the sensing efficacy of the image sensors. A conventional manufacturing method for microlenses utilizes a binary mask. However, the microlenses made by the conventional manufacturing method have spherical surfaces, which may decrease the image quality of the image sensor. 
         [0005]    In addition, side lobes may be caused on the microlenses made by the conventional manufacturing method, and the image quality of the image sensor may be decreased, too. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    To solve the problems of the prior art, the invention provides a mask for manufacturing microlenses with aspherical surfaces. 
         [0007]    The invention provides a manufacturing method for microlenses including: providing a substrate; forming a microlens material on the substrate; disposing a mask over the microlens material; performing an exposure process by a radiant beam emitted to the microlens material via the mask; performing a developing process on the microlens material; and performing a reflow process on the microlens material. 
         [0008]    The invention provides a manufacturing method for microlenses including: providing a microlens material; disposing a mask over the microlens material, wherein the mask comprises a plurality of phase shift layers and a plurality of shading layers respectively disposed on the phase shift layers; performing an exposure process by a radiant beam emitted to the microlens material via the mask, wherein the phase shift layers allow 3% to 5% radiation to the microlens material; performing a developing process on the microlens material; and performing a reflow process on the microlens material. 
         [0009]    The invention provides a mask for manufacturing microlenses including a transparent substrate, a plurality of phase shift layers, and a plurality of shading layers. The phase shift layers are arranged in an array on the transparent substrate. The shading layers are respectively disposed on the phase shift layers. An area of each of the phase shift layers is 1.2 to 2.5 times that of each of the shading layers. 
         [0010]    In conclusion, the microlenses made by the manufacturing method with mask have aspherical surfaces, and thus the image quality of an image sensor with the microlenses is improved. Moreover, side lobes caused on the microlenses may be prevented, and thus the image quality is further improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a bottom view of a mask according to the present disclosure; 
           [0013]      FIG. 2  is a cross-sectional view of the mask according to the present disclosure; 
           [0014]      FIG. 3  is a flow chart of a manufacturing method for microlenses according to the present disclosure; 
           [0015]      FIG. 4  is a cross-sectional view of a substrate and a microlens material before an exposure process of the manufacturing method for microlenses; 
           [0016]      FIG. 5  is a cross-sectional view of the manufacturing method for microlenses after the exposure process according to a first embodiment; 
           [0017]      FIG. 6  is a cross-sectional view of the substrate and the microlens material after a developing process of the manufacturing method for microlenses according to the first embodiment; 
           [0018]      FIG. 7  is a cross-sectional view of the substrate and microlenses according to the first embodiment of the present disclosure; 
           [0019]      FIG. 8  is a top view of the substrate and the microlenses according to the first embodiment of the present disclosure; 
           [0020]      FIG. 9  is a cross-sectional view of the substrate and a microlens material after a developing process of the manufacturing method for microlenses according to a second embodiment; 
           [0021]      FIG. 10  is a cross-sectional view of the substrate and microlenses according to the second embodiment of the present disclosure; and 
           [0022]      FIG. 11  is a top view of the substrate and the microlenses according to the second embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  is a bottom view of a mask  10  according to the present disclosure.  FIG. 2  is a cross-sectional view of the mask  10  according to the present disclosure. In this embodiment, the mask  10  is an attenuated-rim mask. The mask  10  includes a transparent substrate  11 , a plurality of phase shift layers  12 , and a plurality of shading layers  13 . The phase shift layers  12  are arranged in an array on the transparent substrate  11 . The shading layers  13  may include Cr, and are respectively disposed on the center of the phase shift layers  12 . 
         [0024]    The transmittance of the transparent substrate  11  is at least greater than 90%, and the transmittance of the shading layers  13  is 0% or lower than 1%. The phase shift layers allow 3% to 5% radiation to the microlens material. Each of the phase shift layers  12  and the shading layers  13  is square. 
         [0025]    An area S 1  of each of the phase shift layers  12  is 1 to 64 times that of the area S 2  of each of the shading layers  13 . In this embodiment, the area S 1  of each of the phase shift layers  12  is 1.2 to 2.5 times that of the area S 2  of each of the shading layers  13 . A width W1 of each of the phase shift layers  12  is 1 to 8 times the width W2 of each of the shading layers  13 . In this embodiment, the width W1 of each of the phase shift layers  12  is 1 to 1.6 times the width W2 of each of the shading layers  13 . 
         [0026]      FIG. 3  is a flow chart of a manufacturing method for microlenses according to the present disclosure.  FIG. 4  is a cross-sectional view of a substrate  20  and a microlens material  30  before an exposure process of the manufacturing method for microlenses. In step S 101 , the substrate  20  is provided. The substrate  20  includes a wafer  21  and an image sensor  22  disposed on the wafer  21 . In step S 103 , the microlens material  30  is formed on the image sensor  22  of the substrate  20 . In this embodiment, the microlens material  30  is photoresist. 
         [0027]      FIG. 5  is a cross-sectional view of the manufacturing method for microlenses after the exposure process according to a first embodiment. In step S 105 , the mask  10  is disposed over the microlens material  30 , and a light source  40  is disposed over the mask  10 . In step S 107 , an exposure process is performed. An exposure dose of the exposure process is between 7000 J/um and 9000J/um. 
         [0028]    The light source  40  emits a radiant beam L 1  along a direction D1 to the mask  10 , and the radiant beam L 1  may be an I-line (365 nm). The phase shift layers allow 3% to 5% radiation to the microlens material. After the light source  40  passes through the mask  10  and then emits to a part of the microlens material  30 , the microlens material  30  forms unexposed portions  31  and exposed portions  32 . The unexposed portions  31  are not emitted by the radiant beam L 1 , and the exposed portions  32  are emitted by the radiant beam L 1 . As shown in  FIG. 5 , the exposed portions  32  do not pass through the unexposed portion  31  along the direction Dl. 
         [0029]    In particular, the microlens material  30  has zones Z 1  under the shading layer  13 , zones Z 2  under an exposed part, facing the microlens material  30 , of the transparent substrate  11 , and zones Z 3  under an exposed part, facing the microlens material  30 , of the phase shift layer  12 . A part of the radiant beam L 1  is blocked by the shading layer  13 , and the zones Z 1  are not emitted by the radiant beam L 1 . When the radiant beam L 1  passes through the phase shift layer  12 , the phase of the radiant beam L 1  is changed. The radiant beam L 1  passing through the phase shift layer  12  may interfere with the radiant beam L 1  without passing through the phase shift layer  12 . Thus, the energy of the radiant beam L 1  emitted on the microlens material  30  is gradually decreased from zones Z 2  to zones Z 3 , and a cross-sectional surface of the exposed portion  32  is a V shape. 
         [0030]      FIG. 6  is a cross-sectional view of the substrate  20  and the microlens material  30  after a developing process of the manufacturing method for microlenses according to the first embodiment. In step S 109 , a developing process is performed on the microlens material  30 . The exposed portion  32  is removed by the developing process, and a groove g 1  is formed on the unexposed portion  31 . The unexposed portion  31  has flat planes P 1  on the top thereof. The groove g 1  is a V shape and has inclined walls P 2  adjacent to the flat planes P 1 . 
         [0031]    In the step  111 , a reflow process is performed on the microlens material  30 , and the microlens material  30  is to form the microlenses  50  as shown in  FIG. 7 . The temperature of the reflow process may be from 150° C. to 190° C.  FIG. 7  is a cross-sectional view of the substrate  20  and the microlenses  50  according to the first embodiment of the present disclosure.  FIG. 8  is a top view of the substrate  20  and the microlenses  50  according to the first embodiment of the present disclosure. In the embodiment, the microlenses  50  are aspherical microlenses. The microlenses  50  are arranged in an array on the image sensor  22 , and two adjacent microlenses  50  are connected to each other. Each of the microlenses  50  has an aspherical surface S 3 , and two adjacent aspherical surfaces S 3  are connected to each other. An inflection point C 1  is located between two adjacent and connected aspherical surfaces S 3 . 
         [0032]      FIG. 9  is a cross-sectional view of the substrate  20  and a microlens material  60  after a developing process of the manufacturing method for microlenses according to a second embodiment. In the second embodiment, the exposure dose of the exposure process is between 2000 J/um and 4000 J/um, which is lower than the first embodiment. After a developing process, a groove g 2  is formed on the microlens material  60  to make the microlens material  60  have main portions  61  and sub-portions  62 . A cross-sectional surface of the groove g 2  is a W shape. 
         [0033]    The sub-portions  62  are between two adjacent main portions  61 , and the main portions  61  are connected to adjacent sub-portions  62 . The thickness h1 of the main portion  61  is greater than the thickness h2 of the sub-portion  62 , and the width d1 of the main portion  61  is greater than the width d2 of the sub-portion  62 . 
         [0034]      FIG. 10  is a cross-sectional view of the substrate  20  and microlenses  70  according to the second embodiment of the present disclosure.  FIG. 11  is a top view of the substrate  20  and the microlenses  70  according to the second embodiment of the present disclosure. After a reflow process, the microlenses  70  comprise a plurality of first microlenses  71  and a plurality of second microlenses  72 , which may be aspherical microlenses. The first microlenses  71  are connected to adjacent second microlenses  72 . Each of the first microlenses  71  has a first aspherical surface S 4 , and each of the second microlenses  72  has a second aspherical surface S 5 . The first aspherical surface S 4  are connected to the second aspherical surface S 5 . An inflection point C 2  is located between the two adjacent and connected first aspherical surface S 4  and second aspherical surface S 5 . 
         [0035]    The diameter d3 of each of the first microlenses  71  is greater than the diameter d4 of each of the second microlenses  72 . In the embodiment, the diameter d3 of each of the first microlenses  71  is two times the diameter d4 of each of the second microlenses  72 . 
         [0036]    In conclusion, the microlenses made by the manufacturing method with mask have aspherical surfaces, and thus the image quality of the image sensor with the microlenses is improved. Moreover, side lobes caused on the microlenses may be prevented, and thus the image quality is further improved. 
         [0037]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.