Abstract:
A method for forming a lens assembly is provided, including: providing a mold substrate, wherein at least a recess is formed from a surface of the mold substrate; providing a transparent substrate; disposing a lens precursor material on the surface of the mold substrate or on a first surface of the transparent substrate; disposing the mold substrate on the transparent substrate such that at least a portion of the lens precursor material is filled in the recess; disposing a mask on a second surface of the transparent substrate to partially cover the transparent substrate; after the mask is disposed, irradiating a light on the second surface of the transparent substrate to transform at least a portion of the lens precursor material on the first surface of the transparent substrate into a lens; and removing the mask and the mold substrate from the transparent substrate and the lens.

Description:
CROSS REFERENCE 
     This Application is a Divisional of U.S. application Ser. No. 13/017,445, filed on Jan. 31, 2011 now U.S. Pat. No. 8,072,685 and entitled “Lens assembly and method for forming the same”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens assembly and method for forming the same, and in particular relates to an island lens assembly. 
     2. Description of the Related Art 
     Electronic imaging devices are used in a wide range of applications, such as digital cameras, digital video recorders, image capture capable mobile phones and monitors. Electronic imaging devices, such as image sensor modules, typically convert light to electrical signals using a photodetector. Typically, an electronic imaging device includes an image sensor chip and a lens assembly, which is used to project an object onto the image sensor chip. Thus, the quality of the image projection of the lens assembly determines the quality of the image signal processed by the image sensor chip. Therefore, the quality and reliability of a lens assembly is important. 
     Accordingly, a lens assembly having high thermal stability, reliability, and strength is desired. In addition, fabrication time and cost of the manufacturing process of the lens assembly also need to be reduced. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an illustrative embodiment, a method for forming a lens assembly is provided, including: providing a mold substrate, wherein at least a recess is formed from a surface of the mold substrate; providing a transparent substrate; disposing a lens precursor material on the surface of the mold substrate or on a first surface of the transparent substrate; disposing the mold substrate on the transparent substrate such that at least a portion of the lens precursor material is filled in the recess; disposing a mask on a second surface of the transparent substrate to partially cover the transparent substrate; after the mask is disposed, irradiating a light on the second surface of the transparent substrate to transform at least a portion of the lens precursor material on the first surface of the transparent substrate into a lens; and removing the mask and the mold substrate from the transparent substrate and the lens. 
     According to an illustrative embodiment, a method for forming a lens assembly is provided, which includes: providing a mold substrate, wherein a plurality of recesses are formed from a surface of the mold substrate; providing a transparent substrate; disposing a lens precursor material on the surface of the mold substrate or on a first surface of the transparent substrate; disposing the transparent substrate on the mold substrate such that at least a portion of the lens precursor material is filled in the recesses; disposing a mask on a second surface of the transparent substrate to partially cover the transparent substrate; after the mask is disposed, irradiating a light on the second surface of the transparent substrate to transform at least a portion of the lens precursor material on the first surface of the transparent substrate into lenses; removing the mask and the mold substrate from the transparent substrate and the lenses; and dicing the transparent substrate along predetermined scribe lines between the lenses to form a plurality of separate lens assemblies. 
     According to an illustrative embodiment, a lens assembly is provided, which includes: a transparent substrate; and a plurality of separate lenses disposed on a surface of the transparent substrate, wherein a smallest distance between any two adjacent lenses of the lenses is less than about 900 μm. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1A  is a cross-sectional view showing the steps of forming a lens assembly known by the inventor; 
         FIGS. 1B and 1C  are cross-sectional views showing lens assemblies known by the inventor; 
         FIGS. 2A-2F  are cross-sectional views showing the steps of forming a lens assembly according to an embodiment of the present invention; 
         FIGS. 3A-3D  are cross-sectional views showing lens assemblies according to embodiments of the present invention; 
         FIGS. 4A-4B  are cross-sectional views showing the steps of forming a lens assembly according to an embodiment of the present invention; and 
         FIG. 5  is top view showing a lens assembly according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     It is understood, that the following disclosure provides many difference embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numbers and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Furthermore, descriptions of a first layer “on,” or “overlying,” (and like descriptions) a second layer include embodiments where the first and second layers are in direct contact and those where one or more layers are interposing the first and second layers. 
       FIG. 1A  is a cross-sectional view showing the steps of forming a lens assembly known by the inventor. A mold substrate is provided, which includes a base substrate  10  and a mold layer  12  formed thereon, wherein the mold layer  12  is usually formed of a polymer material such as PDMS. A recess  12   a  and a smaller recess  12   b  adjacent to the recess  12   a  are formed from a surface of the mold layer  12 . A lens precursor material is disposed on the recess  12   a . Typically, the disposed precursor material has a volume larger than the volume of the space in the recess  12   a . An excess portion of the lens precursor material may flow into the recess  12   b . A substrate  100  is then placed on the mold substrate, wherein a surface  100   a  of the substrate  100  faces the mold substrate and contacts with the lens precursor material filled in the recess  12   a . A light  14  is irradiated from a surface  100   b  of the substrate to harden the lens precursor material. In other words, the lens precursor material filled in the recess  12   a  is transformed into the lens  102 . Similarly, the lens precursor material filled in the recess  12   b  is transformed into the glue buffer area  104  at least partially surrounding the lens  102 . Because the recess  12   b  is formed adjacent to the recess  12   a  to contain the excess lens precursor material, the formed lens  102  can therefore have a predetermined thickness and predetermined profile. 
     Then, the mold substrate is removed from the substrate  100  and a lens assembly is formed.  FIG. 1B  is a cross-sectional view showing a lens assembly obtained by the method mentioned above. As shown in  FIG. 1B , the lens  102  is formed on the surface  100   a  of the substrate  100 . The glue buffer area  104  is formed adjacent to the lens  102 . In another case, when a large amount of lens precursor material is disposed on the mold substrate, the obtained lens assembly may have the structure shown in  FIG. 1C . As shown in  FIG. 1C , a base layer  106  is formed between the lens  102  and the substrate  100 . 
     However, the lens assemblies shown in  FIGS. 1B and 1C  may be deficient. For the lens assembly shown in  FIG. 1B , the pitches between the adjacent lenses  102  can not be reduced due to the constraint of the glue buffer area  104 . In addition, the glue buffer area  104  may cause resistance for thermal cycling of the lens assembly to be weak. For the lens assembly shown in  FIG. 1C , the problem where the entire film peels off the base layer  106  may occur. In addition, a strong stress may be induced due to shrinkage of the lens precursor material. 
     Therefore, a lens assembly having higher thermal stability and less stress is desired. Further, the pitches between adjacent lenses need to be reduced to improve lens assembly processing throughput. 
       FIGS. 2A-2F  are cross-sectional views showing the steps of forming a lens assembly according to an embodiment of the present invention. Referring to  FIG. 2A , a mold substrate is provided, which include a base substrate  20  and a mold layer  22  formed thereon. An adhesion layer  21  may be formed between the base substrate  20  and the mold layer  22 . At least a recess  22   a  is formed from a surface of the mold substrate. A lens will be formed in the recess  22   a  in a following process. In one embodiment, a recess  22   b  adjacent to the recess  22   a  and substantially surrounding the recess  22   a  where a lens will be formed may be optionally formed to enlarge the process window. 
     Next, a transparent substrate  200  having surfaces  200   a  and  200   b  is provided, which is going to be disposed on the surface of the mold substrate. A lens precursor material  23  is disposed between the mold substrate and the surface  200   a  of the transparent substrate  200 . In one embodiment, before the transparent substrate  200  is disposed, the lens precursor material  23  is disposed on the surface of the mold substrate. Typically, the lens precursor material  23  is disposed only on the recess  22   a  where a lens will be formed and the amount of the precursor material  23  is usually more than what is actually needed for forming the lens to ensure the recess  22   a  can be completely filled. It should be appreciated that embodiments of the invention are not limited thereto. For example, in another embodiment, the lens precursor material  23  is disposed on the surface  200   a  of the transparent substrate  200 . Then, the mold substrate is disposed on the transparent substrate  200  such that the lens precursor material  23  is filled in the recess  22   a.    
     As shown in  FIG. 2A , the transparent substrate  200  is disposed on the mold substrate to directly contact the lens precursor material  23  previously disposed in the recess  22   a . In on embodiment, the transparent substrate  100  may further include an adhesion promoter layer (not shown) on the surface of the transparent substrate  100 . The adhesion promoter layer is capable of improving adhesion between the transparent substrate  200  and the lens precursor material  23 . When the transparent substrate  200  is disposed on the mold substrate, an excess portion of the lens precursor material  23  may be forced to flow into the recess  22   b  adjacent to the recess  22   a . Therefore, the process window may be enlarged. 
     Referring to  FIG. 2B , a mask  26  is disposed on the surface  200   b  of the transparent substrate  200  to partially cover the transparent substrate  200 . In one embodiment, the mask  26  has at least an opening exposing a portion of the transparent substrate  200  and the portion of the lens precursor material  23  (see  FIG. 2A ) filled in the recess  22   a.    
     After the mask  26  is disposed, a light  24  which is suitable for hardening the lens precursor material  23  is irradiated to the surface  200   b  of the transparent substrate  200 . When the light  24  penetrates through the transparent substrate  200  and reaches the lens precursor material  23 , the lens precursor material  23  is transformed into a lens  202 , as shown in  FIG. 2B . Because the portion of the lens precursor material  23  filled in the recess  22   b  is covered under the mask  26  and is not irradiated by the light  24 , the lens precursor material  23  in the recess  22   b  is not hardened. The lens precursor material  23  in the recess  22   b  is referred to as a buffer area  204  hereinafter. 
     Next, the mask  26  and the mold substrate are removed from the transparent substrate  200  and the lens  202 , as shown in  FIG. 2C . In one embodiment, a plurality of lenses  202  are formed on the surface  200   a  of the transparent substrate  200 . A plurality of buffer areas  204  are also formed on the surface  200   a  of the transparent substrate  200 . Each of the lenses  202  is correspondingly surrounded by one of the buffer areas  204 . Because the buffer area  204  remains in the state of being a lens precursor material, the buffer area  204  may be removed easily from the transparent substrate  200 . There is no hardened glue buffer area remaining on the transparent substrate to cause the lens assembly to be formed having a weak resistance for thermal cycling. 
     Referring to  FIG. 2D , the remaining portion of the lens precursor material  23  (i.e., the buffer areas  204 ) is removed from the transparent substrate  200 . In one embodiment, a suitable solvent is used to remove the remaining portion of the lens precursor material (buffer areas  204 ). In one embodiment, the solvent used to remove the lens precursor material substantially does not remove or dissolve the formed lenses  202 . The material of the solvent may be varied according to the kind of material the lens precursor material uses. 
     As shown in  FIG. 2D , after the remaining portion of the lens precursor material is removed, a lens assembly is formed. Compared with the lens assembly shown in  FIG. 1B , no buffer area is formed. Thus, the thermal stability of the lens assembly according to an embodiment of the present invention is improved. Compared with the lens assembly shown in  FIG. 1C , no base layer linking all of the lenses is formed and the formed lenses  202  are separated from each other. Therefore, the problem where the entire film peels of the base layer is prevented. Reliability and strength of the lens assembly according to an embodiment of the present invention is improved. 
     Referring to  FIG. 2E , in one embodiment, at least a second lens  206  may be optionally formed on the surface  200   b  of the transparent substrate  200 . Processes similar to, but are not limited to, those shown in  FIGS. 2A-2D  may be performed again to form the second lens  206  on the surface  200   b  of the transparent substrate  200 . In one embodiment, a light shielding layer  205  may be optionally formed to enhance performance of the formed lens assembly. In one embodiment, each of the second lenses  206  correspondingly aligns with one of the lenses  202 . 
     Next, the transparent substrate  200  may be optionally diced along predetermined scribe lines SC defined on the transparent substrate  200  to form a plurality of separate lens assemblies. In one embodiment, the transparent substrate  200  may be diced by using a dicing blade. In another embodiment, the transparent substrate  200  may be diced by using an energy beam such as, but is not limited to, a laser beam, electron beam, ion beam, plasma beam, the like, or combinations thereof.  FIG. 2F  shows a cross-sectional view of one of the lens assemblies. Embodiments of the invention are not limited to the lens assembly shown in  FIG. 2F . Some variations and/or modifications may be made.  FIGS. 3A-3D  are cross-sectional views showing lens assemblies according to embodiments of the present invention, wherein similar or same reference numbers are used to designate similar or same elements. 
     Referring to  FIG. 3A , in one embodiment, a light shielding layer  208  may be optionally formed to cover a portion of the lens  202  to enhance optical characteristics of the lens assembly. Similarly, in a case where the second lens  206  is formed on the surface  200   b  of the transparent substrate, light shielding layers  208   a  and  208   b  may be optionally formed on the transparent substrate  200  to partially cover the lenses  202  and  206 , as shown in  FIG. 3B . 
     Referring to  FIG. 3C , in one embodiment, a light shielding layer  208  may be optionally formed on the transparent substrate  200  to enhance optical characteristics of the lens assembly, wherein a portion of the light shielding layer  208  is located between the lens  202  and the transparent substrate  200 . Similarly, in the case where the second lens  206  is formed on the surface  200   b  of the transparent substrate, light shielding layers  208   a  and  208   b  may be optionally formed on the transparent substrate  200  to enhance the optical characteristics of the lens assembly, as shown in  FIG. 3D . 
       FIGS. 4A-4B  are cross-sectional views showing the steps of forming a lens assembly according to an embodiment of the present invention, wherein similar or same reference numbers are used to designate similar or same elements. 
     Referring to  FIG. 4A , processes similar to those shown in  FIGS. 2A-2B  are performed to form lenses  202  on the surface  200   a  of the transparent substrate  200 . The main difference therebetween is that no recess for buffer area is formed from the surface of the mold substrate. Because a mask is used, the light  24  only transforms specific portions of the lens precursor material into the lenses  202 . Therefore, even if an excess portion of the lens precursor material other than that to be transformed into the lenses  202  flows to the surface  200   a  of the transparent substrate  200 , the excess portion of the lens precursor material will not be hardened. There is no base layer or buffer area formed on the surface  200   a  of the transparent substrate  200 . Therefore, the excess portion of the lens precursor material may be easily removed by using a suitable solvent. 
     After the mask  26  and the mold substrate are removed and the excess portion of the lens precursor material is removed, a lens assembly is formed, as shown in  FIG. 4B . Because there is no recess for the buffer area, the distance between adjacent recesses used for forming the lenses  202  may be reduced. Therefore, the smallest distance W 2  between the adjacent lenses  202  may be further reduced, compared with the distance W 1  of the lens assembly shown in  FIG. 2D . In one embodiment, the smallest distance W 2  between adjacent lenses  202  is less than about 900 μm. Because the smallest distance W 2  between adjacent lenses  202  is further reduced, a distribution density of the lenses  202  on the surface  200   a  of the transparent substrate  200  can be significantly increased. In one embodiment, the distribution density of the lenses  202  on the surface  200   a  of the transparent substrate  200  may be increased to be higher than about 20 lenses/cm 2 . 
       FIG. 5  is a top view showing a lens assembly according to an embodiment of the present invention, wherein similar reference numbers are used to designate similar or same elements. In this case, the transparent substrate  200  having a shape similar to a wafer is used. The wafer-like lens assembly may then be diced into a plurality of lenses, and the lenses may be stacked on a semiconductor wafer, respectively. 
     By using the method disclosed in the embodiments of the invention to form a lens assembly, more lenses can be formed in a single transparent substrate. Fabrication time and cost are significantly reduced. Because no buffer area or base layer will be formed in the lens assembly according to embodiments of the invention, thermal stability, reliability, and strength of the formed lens assembly are improved. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To 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.