Abstract:
Image sensor devices and methods for fabricating the same are provided. An exemplary embodiment of an image sensor device comprises a support substrate. A passivation structure is formed over the support substrate. An interconnect structure is formed over the passivation structure. A first semiconductor layer is formed over the interconnect structure, having a first and second surfaces, wherein the first and second surfaces are opposing surfaces. At least one light-sensing device is formed over/in the first semiconductor layer from a first surface thereof. A color filter layer is formed over the first semiconductor layer from a second surface thereof. At least one micro lens is formed over the color filter layer.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to image sensor device fabrication, and more particularly relates to a method for fabricating an image sensor device capable of light illumination from a back side of a substrate therein. 
   2. Description of the Related Art 
   An image sensor includes a grid of pixels comprising elements such as photodiodes, reset transistors, source follower transistors, pinned layer photodiodes, and/or transfer transistors for recording an intensity or brightness of an incident light. Each of the pixels responds to the incident light by accumulating a charge. The more incident light, the higher the charge. The charge can then be used by another circuit so that a color and brightness can be used for a suitable application, such as a digital camera. Common types of pixel grids include a charge couple device (CCD) or complimentary metal oxide semiconductor (CMOS) image sensor. 
   Typically, an image sensor is a semiconductor device converting an optical image to an electrical signal. Among the above mentioned image sensors, the CCD image sensor comprises a plurality of metal-oxide-silicon (MOS) capacitors for storage and transfer of charge carriers. The CMOS image sensor, a product of CMOS manufacturing technology, is a semiconductor device that converts an optical image to an electrical signal using a switching scheme of a MOS transistor for transportation of photo-electric charges from a photodiode to an output node as well as detection of an output signal at the output node. 
     FIG. 1  is a cross section showing a CMOS image sensor having a plurality of microlenses therein as disclosed in U.S. Pat. No. 6,979,588 (issued to Jeong et al.). As shown in  FIG. 1 , the CMOS image sensor includes a semiconductor substrate  10  with a plurality of isolation regions  12  formed therein, defining a plurality of pixel regions. A photodiode  14  for converting an incident light to photo-charges is formed in a corresponding pixel region. For the sake of convenience, transistors required for the unit pixel is not depicted in the drawings. An interlayer dielectric (ILD)  16  is formed on the semiconductor substrate  10 , thereby metal interconnects  18  are provided at predetermined locations of the ILD  16  to prevent shielding of incident light on the underlying photodiodes  14 . A passivation layer  20  is formed over the metal interconnects  18  for protecting a device from moisture and scratching during post-manufacturing processes. In addition, color filter array  22  having red, green and blue color filters are formed directly on the passivation layer  20 . An over-coating layer (OCL)  24  is providing on the color filter array  22 , thereby providing a planarized surface. A plurality of dome shaped microlens  26  is formed on the OCL  24 , substantially corresponding to each of the pixel regions. Therefore, incident light  30  projected onto the photodiodes  14  can pass through the internal structures formed between the photodiodes  14  and the microlenses  26  along an optical path L 1 . 
   Nevertheless, with the trend toward size reduction of pixel units formed on a substrate, optical interference such as refraction, reflection, diffraction and light absorption may occur during the progress of the incident light  30  along the optical path L 1  by the metal interconnect structures and the materials formed therein, thereby affecting the quantum efficiency of the photodiodes  14  and cross-talk may thus occur between adjacent pixel units. 
   BRIEF SUMMARY OF THE INVENTION 
   Therefore, image sensor devices of better performance with reduced-size are desired. 
   Image sensor devices and methods for fabricating the same are provided. An exemplary embodiment of an image sensor device comprises a support substrate. A passivation structure is formed over the support substrate. An interconnect structure is formed over the passivation structure. A first semiconductor layer is formed over the interconnect structure, having a first and second surfaces, wherein the first and second surfaces are opposing surfaces. At least one light-sensing device is formed over/in the first semiconductor layer from a first surface thereof. A color filter layer is formed over the first semiconductor layer from a second surface thereof. At least one micro lens is formed over the color filter layer. 
   An exemplary embodiment of a method for fabricating an image sensor device comprises providing a first substrate having a first semiconductor layer thereon, wherein the first substrate and the first semiconductor layer are formed with same conductivity but different doping concentrations and the first semiconductor layer has a first surface not contacting the first substrate and a second surface contacting the first substrate, wherein the first and second surfaces are opposing surfaces and the first surface contacts the interconnect structure. At least one light-sensing device is formed over/in the first semiconductor layer from the first surface thereof. An interconnect structure is formed over of the first semiconductor layer, covering the light-sensing device. A passivation structure is formed over the interconnect structure, covering the interconnect structure. A second substrate is bonded with the passivation structure. The first substrate is thinned, exposing the second surface of the first semiconductor layer. A color filter layer is formed over the first semiconductor layer from the second surface thereof. At least one micro lens is formed over the color filter layer. 
   Another exemplary embodiment of a method for fabricating an image sensor device comprises providing a first substrate having a first and second semiconductor layers sequentially stacked on the substrate, wherein the first substrate, and the first and second semiconductor layers are formed with same conductivity but different doping concentrations and the first semiconductor layer has a first surface contacting the second semiconductor layer and a second surface contacting the first substrate. At least one light-sensing device is formed over/in the second semiconductor layer. An interconnect structure is formed over the first substrate, covering and the light-sensing device. A passivation structure is formed over the interconnect structure. A second substrate is bonded with the passivation structure. The first substrate is thinned and exposes the second surface of the first semiconductor layer. A color filter layer is formed over the first semiconductor layer from the second surface thereof. At least one microlens is formed over the color filter layer. 
   Yet another exemplary embodiment of a method for fabricating an image sensor device comprises providing a semiconductor on insulator (SOI) substrate having a first semiconductor layer formed thereon, wherein the SOI substrate comprises a stack of a bulk substrate with an insulating layer and a second semiconductor layer sequentially formed thereon, the first semiconductor layer is formed over the second semiconductor layer, the first and second semiconductor layers are formed with same conductivity but different doping concentrations, and the insulating layer has a first surface contacting the second semiconductor layer and a second surface contacting the bulk substrate. At least one light-sensing device is formed over/in the first semiconductor layer. An interconnect structure is formed over the first semiconductor layer, covering the light-sensing device. A passivation structure is formed over the interconnect structure. A second substrate is bonded with the passivation structure. The bulk substrate is removed, exposing the second surface of the insulating layer. A color filter layer is formed over the insulating layer from the second surface thereof. At least one microlens is formed over the color filter layer. 
   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. 1  is a cross section view showing a related art CMOS image sensor; 
       FIGS. 2   a - 2   c  are schematic cross sections showing an embodiment of a method for fabricating an image sensor device; 
       FIGS. 3   a - 3   c  are schematic cross sections showing another embodiment of a method for fabricating an image sensor device; and 
       FIGS. 4   a - 4   c  are schematic cross sections showing yet another embodiment of a method for fabricating an image sensor device. 
   

   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. 
   Methods for fabricating image sensor devices will now be described in greater detail in the following. Some embodiments of the invention, such as the exemplary embodiments described, can potentially reduce optical interference and improve quantum efficiency of the light-sensing device formed within an image sensor device, especially when a size thereof is further reduced. In some embodiments, this can be accomplished by thinning a backside of a semiconductor substrate thereof, comprising light-sensing devices, and forming a color filter layer and micro lenses on the thinned semiconductor substrate. 
     FIGS. 2   a - 2   c  are schematic cross sections showing an embodiment of a method for fabricating an image sensor device. 
   As shown in  FIG. 2   a , a nearly fabricated image sensor device is first provided, including a substrate  100  with a semiconductor layer  101  formed thereon, having a plurality of isolation regions  102  formed in the semiconductor layer  101  and defining a plurality of pixel regions thereon. A light-sensing device  104  for converting an incident light to photo-charges or light-sensing is formed in the semiconductor layer  101  in a corresponding pixel region but is not limited thereto. The light-sensing device  104  can also be formed over the semiconductor layer  100   c  of a corresponding pixel region (not shown). Examples of the light-sensing device  104  can be charge-coupled devices (CCD), CMOS image sensors (CIS) and/or optical microelectromechanical systems (MEMS), incorporating photodiodes in active or passive arrangements. Herein, the substrate  100  is a semiconductor on insulator (SOI) substrate, including a semiconductor layer  100   c  overlying an insulating layer  100   b  formed on a bulk substrate  100   a , the bulk substrate  100   a  is a semiconductor substrate such as a silicon substrate. The insulating layer can be, for example, a silicon oxide layer. Herein, the semiconductor layer  100   c  can comprise, for example, silicon or silicon germanium, and the semiconductor layer  101  can comprise, for example, silicon of monocrystal. The semiconductor layer  101  can be formed by, for example, conventional epitaxial processes. In addition, the semiconductor layer  100   c  and the semiconductor layer  101  are further doped with the same conductivity type dopants, such as well known N or P type dopants, but have different doping concentrations therein. The semiconductor layer  100   c  preferably comprises a doping concentration greater than that of the semiconductor layer  101 . For example, the semiconductor layer  100   c  has a doping concentration of about 1E16˜1.5E20 atoms/cm 2  and the semiconductor layer  101  has a doping concentration of about 1E13˜1E16 atoms/cm 2 . The semiconductor layer  101  is formed at a thickness T 2  of about 2˜8 μm and the semiconductor layer  100   c  is formed with a thickness of about 500˜10,000 Å. Typically, an overall thickness T 1  of the SOI wafer  100  and the semiconductor layer  101  is about 500˜900 μm. 
   Moreover, as shown in  FIG. 2   a , an interlayer dielectric (ILD) layer  106  is formed on the semiconductor layer  101  and covers the light-sensing device  104  thereon. An interconnect structure comprising dielectric layers  108 ,  112 ,  116 ,  118  and conductive elements  110 ,  114 ,  120  respectively provided on or between at predetermined locations of above dielectric layers in consideration of the underlying light-sensing devices  104  is provided over the ILD layer  106  so that the incident light projected on the light-sensing devices is not shielded by the existence of the conductive segments formed therein. The dielectric layer  122  here at a topmost place of the interconnecting structure may function as a passivation for protecting a device from moisture and scratching during post-manufacturing processes. Fabrication of the interconnect structure can be achieved by, for example, damascene process incorporating copper metal and low dielectric constant (low-k) dielectric materials and is well known by those skilled in the art. 
   Moreover, as shown in  FIG. 2   a , another substrate  200  is provided with or without a bond layer  202  formed thereon and the bond layer  202  is arranged to face the dielectric layer  122  formed over the substrate  100 . The substrate  200  and the substrate  100  are next pushed toward each other to bond into a composite structure. 
   As shown in  FIG. 2   b , the composite structure comprising the substrates  200  and  100  is then inverted. The substrate  100  is then thinned by removing the bulk substrate  100   a  of the substrate  100 , stopping on the insulating layer  100   b  by methods such as mechanical grinding, chemical mechanical polishing (CMP), dry etching and/or wet etching, thereby exposing the insulating layer  100   b  far from a back side of the semiconductor layer,  101  having devices or structures formed thereon, leaving a slightly thinned insulating layer  100   b ′. Herein, an overall thickness T 1 ′ including of the slightly thinned_insulating layer  100   b ′, the semiconductor layer  100   c  and the semiconductor layer  101  is about 2˜10 μm. 
   The slightly thinned semiconductor layer  100   b ′ is formed by first thinning the bulk substrate  100   a  by a method such as, mechanical grinding, to a thickness of about 25˜100 μm from a back side thereof. Next, an etching (not shown) such as a plasma etching or chemical etchant is performed to further reduce the bulk substrate  100   a  to remove the remaining bulk substrate  100   a ′ and automatically stopping on and exposing a back side of the insulating layer, thereby leaving a slightly thinned insulating layer  100   b ′, The chemical etchant used to removed the remaining bulk substrate is a mixture comprising acidic solution such as HF, HNO 3 , H 2 O 2 , H 3 PO 4 , CH 3 COOH, or H 2 SO 4  and alkaline solution such as NaOH, KOH, NH 3 , TMAH, showing a great etching selectivity difference of about 10˜5000 between the bulk substrate  100   a  and insulating layer  100   b  since a material difference does exist therebetween. 
   Next, as shown in  FIG. 2   c , an anti-reflection layer  600  is formed directly on the back side of the slightly thinned insulating layer  100   b ′, having a thickness of about 100˜5000 Å. The anti-reflection layer  600  may comprise dielectric materials formed by PVD or CVD methods, such as SiONx, SiNy or organic materials by spin coating, such as acrylic polymers, polyester, polystyrene, or polyimide. Preferably, the anti-reflection layer  600  has a refractive index (n) between 1.0 (in air) and 3.5 (in silicon substrate). Next, color filter array  300  having red, green and blue color filters is formed on the anti-reflection layer  600  and an optional over-coating layer (OCL)  302  is next provided on color filter array  300 , thereby providing a planarized surface. A plurality of dome shaped microlens  304  is next formed on the OCL  302 , substantially corresponding to each of the pixel regions from a back side thereof. Therefore, incident light  400  can be projected onto the light-sensing devices  104  via passing along an optical path L 2  which is relatively shorter than that in the CMOS image sensor illustrated in  FIG. 1  since fewer structures and no metal interconnects are now formed between the light-sensing devices  104  and the microlenses  304 . Therefore, an image sensor device having such structures can be formed with reduced optical interference and improved quantum efficiency. 
     FIGS. 3   a - 3   c  are schematic cross sections showing another embodiment of a method for fabricating an image sensor device similar to that illustrated in  FIGS. 2   a - 2   c . Herein, the same numerals represent same elements and only the differences are described in the following. 
   As shown in  FIG. 3   a , a nearly fabricated image sensor device is first provided. It is noted that a substrate  100  is now provided with two semiconductor layers  101   a  and  101   b  sequentially formed thereon. The light-sensing device  104  for converting an incident light to photo-charges or light-sensing is now formed in the semiconductor layer  101   b  in a corresponding pixel region but is not limited thereto. The light-sensing device  104  can also be formed over the semiconductor layer  101   a  of corresponding pixel region (not shown). Examples of the light-sensing device  104  can be charge-coupled devices (CCD), CMOS image sensors (CIS) and/or optical microelectromechanical systems (MEMS), incorporating photodiodes in active or passive arrangements. Herein, the substrate  100  is a bulk substrate comprising, for example, silicon and the semiconductor layers  101   a ,  101   b  can comprise, for example, silicon germanium or silicon formed by conventional epitaxial processes. Also, the substrate  100  and semiconductor layers  101   a ,  101   b  are doped with same conductivity type dopants, such as well known N or P type dopants, but have different doping concentrations therein. Herein, the substrate  100  preferably comprises a doping concentration less than that of the semiconductor layers  101   a , and semiconductor layers  101   a  comprises a doping concentration greater than that of the semiconductor layers  101   b . For example, the substrate  100  has a doping concentration of about 1E13˜1E16 atoms/cm 2 , the semiconductor layer  101   a  has a doping concentration of about 1E16˜1.5E20 atoms/cm 2 , and the semiconductor layer  101   b  has a doping concentration of about 1E13˜1E16 atoms/cm 2 . Also, as shown in  FIG. 3   a , the semiconductor layer  101   b  is formed at a thickness T 2  of about 2˜8 μm, the semiconductor layer  101   a  is formed at a thickness T 3  of about 1,000˜50,000 Å. Typically, an overall thickness T 1  including the substrate  100  and the semiconductor layers  101   a ,  101   b  is about 500˜900 μm. 
   Moreover, as shown in  FIG. 3   a , an interlayer dielectric (ILD) layer  106  is formed on the semiconductor layer  101   b  and covers the light-sensing device  104  thereon. An interconnect structure comprising dielectric layers  108 ,  112 ,  116 ,  118  and conductive elements  110 ,  114 ,  120  respectively provided on or between at predetermined locations of above dielectric layers in consideration of the underlying light-sensing devices  104  is provided over the ILD layer  106  so that the incident light projected on the light-sensing devices is not shielded by the existence of the conductive segments formed therein. The dielectric layer  122  here at a topmost place of the interconnecting structure may function as a passivation for protecting a device from moisture and scratching during post-manufacturing processes. Fabrication of the interconnect structure can be achieved by, for example, damascene process incorporating copper metal and low dielectric constant (low-k) dielectric materials and is well known by those skilled in the art. 
   Moreover, as shown in  FIG. 3   a , another substrate  200  is provided with or without a bond layer  202  formed thereon and the bond layer  202  is arranged to face the passivation layer  122  formed over the substrate  100 . The substrate  200  and the substrate  100  is next push toward each other to bond into a composite structure. 
   As shown in  FIG. 3   b , the composite structure comprising the substrates  200  and  100 , and the semiconductor layers  101   a  and  101   b  illustrated in  FIG. 3   a  is inverted. The substrate  100  (shown in  FIG. 3   a ) is then removed by methods such as mechanical grinding, chemical mechanical polishing (CMP) dry etching and/or wet etching, thereby exposing a back side of the semiconductor layer  101   a , where no device or structures formed thereon, leaving a slightly thinned semiconductor layer  101   a′.    
   The slightly thinned semiconductor layer  101   a ′ is formed by first thinning the substrate  100  by a method such as, mechanical grinding, to a thickness of about 25˜100 μm. Next, an etching (not shown) such as a plasma etching or wet chemicals is performed to further reduce the substrate  100  to a thickness of about 5˜10 μm. Next, another etching (not shown) is performed, incorporating etchant such as alkaline solution, to remove the remaining substrate and automatically stopping on and exposing a back side of the semiconductor layer  101   a , thereby leaving a slightly thinned semiconductor layer  101   a ′. The alkaline solution used to removed the remaining substrate is a mixture comprising NaOH, KOH, NH3, TMAH, etc. and showing a great etching selectivity difference of about 1.5˜50 between the semiconductor layer  101   a  and the substrate  100  since a doping concentration difference does exist therebetween. 
   Next, as shown in  FIG. 3   c , a buffer layer  700  and an anti-reflection layer  600  are sequentially formed on the back side of the slight thinned semiconductor layer  101   a ′, having a thickness of about 100˜1000 Å and 100˜5000 Å, respectively. The anti-reflection layer  600  may comprise dielectric materials formed by PVD or CVD methods, such as SiNx, SiONy or organic materials by spin coating, such as acrylic polymers, polyester, polystyrene, polyimide, and the buffer layer  700  may comprise SiO 2  or SiONz for releasing stresses formed between the semiconductor layer  101   a ′ and the anti-reflection layer  600 . Preferably, the anti-reflection layer  600  has a refractive index (n) between 1.0 (in air)˜3.5 (in silicon substrate). Next, color filter array  300  having red, green and blue color filters is formed on the anti-reflection layer  600  and an optional over-coating layer (OCL)  302  is next provided on color filter array  300 , thereby providing a planarized surface. A plurality of dome shaped micro lenses  304  are next formed on the OCL  302 , substantially corresponding to each of the pixel regions from a backside thereof. Therefore, incident light  400  can be projected onto the light-sensing device  104  via passing along an optical path L 2 ′ which is still relatively shorter than that in the CMOS image sensor illustrated in  FIG. 1  since fewer internal structures and no metal interconnects are now formed between the light-sensing device  104  and the microlens  304 . Therefore, an image sensor device having such structures can be formed with reduced optical interferences and improved quantum efficiency. 
     FIGS. 4   a - 4   c  are schematic cross sections showing yet another embodiment of a method for fabricating an image sensor device similar to that illustrated in  FIGS. 2   a - 2   c . Herein, the same numerals represent same elements and only the differences are described in the following. 
   As shown in  FIG. 4   a , a nearly fabricated image sensor device is first provided, including a substrate  100  with a semiconductor layer  101  formed thereon, having a plurality of isolation regions  102  formed therein and defining a plurality of pixel regions thereon. A light-sensing device  104  for converting an incident light to photo-charges or light-sensing is formed in the substrate  101  in a corresponding pixel region but is not limited thereto. The light-sensing device  104  can also be formed over the substrate  100  of a corresponding pixel region (not shown). Examples of the light-sensing device  104  can be charge-coupled devices (CCD), CMOS image sensors (CIS) and/or optical microelectromechanical systems (MEMS), incorporating photodiodes in active or passive arrangements. Herein, the substrate  100  is a bulk substrate comprising, for example, silicon, and the semiconductor layer  101  can comprise, for example, silicon of monocrystal formed by conventional epitaxial processes. In addition, the substrate  100  and the semiconductor layer  101  are further doped with the same conductivity type dopants, such as well known N or P type dopants, but have different doping concentrations therein. The substrate  100  preferably comprises a doping concentration greater than that of the semiconductor layer  101 . For example, the substrate  100  has a doping concentration of about 1E16˜1.5E20 atoms/cm 2  and the semiconductor layer  101  has a doping concentration of about 1E13˜1E16 atoms/cm 2 . The semiconductor layer  101  is formed at a thickness T 2  of about 2˜10 μm. Typically, an overall thickness T 1  including of the substrate  100  and the semiconductor layer  101  is about 500˜900 μm. 
   Moreover, as shown in  FIG. 4   a , an interlayer dielectric (ILD) layer  106  is formed on the semiconductor layer  101  and covers the light-sensing device  104  thereon. An interconnect structure comprising dielectric layers  108 ,  112 ,  116 ,  118  and conductive elements  110 ,  114 ,  120  respectively provided on or between at predetermined locations of above dielectric layers in consideration of the underlying light-sensing devices  104  is provided over the ILD layer  106  so that the incident light projected on the light-sensing devices is not shielded by the existence of the conductive segments formed therein. The dielectric layer  122  here at a topmost place of the interconnecting structure may function as a passivation for protecting a device from moisture and scratching during post-manufacturing processes. Fabrication of the interconnect structure can be achieved by, for example, damascene process incorporating copper metal and low dielectric constant (low-k) dielectric materials and is well known by those skilled in the art. 
   Moreover, as shown in  FIG. 4   a , another substrate  200  is provided with or without a bond layer  202  formed thereon and the bond layer  202  is arranged to face the passivation layer  122  formed over the substrate  100 . The substrate  200  and the substrate  100  are next pushed toward each other to bond into a composite structure. 
   As shown in  FIG. 4   b , the composite structure comprising the substrates  200  and  100  is then inverted. The substrate  100  is then removed, thereby exposing a backside of the semiconductor layer  101 , leaving a slightly thinned semiconductor layer  101 ′. The slightly thinned semiconductor layer  101 ′ is formed by first thinning the substrate  100  by a method such as mechanical grinding, to a thickness of about 25˜100 μm from a back side thereof. Next, an etching (not shown) such as a plasma etching or wet chemicals is performed to further reduce the substrate  100  to a thickness of about 5-10 nm. Next, another etching (not shown) is performed, incorporating etchant such as acidic solution, to remove the remaining substrate and automatically stopping on and exposing a back side of the semiconductor layer  101 , thereby leaving a slightly thinned semiconductor layer  101 ′. The acidic solution used to removed the remaining substrate is a mixture comprising HF, HNO 3 , H 2 O 2 , H 3 PO 4 , CH 3 COOH, H 2 SO 4  and showing a great etching selectivity difference of about 5˜300 between the semiconductor layer  101  and the substrate  100  since a doping concentration difference does exist therebetween. Next, an ion implantation and thermal anneal (both not shown) are sequentially performed on the back side surface of the slightly thinned semiconductor layer  101 ′, thereby forming a well region  500  near the back side surface of the slightly thinned semiconductor layer  101 ′. Typically, the well region  500  is formed with a depth of about 200-5000 Å from the back side surface of the slightly thinned semiconductor layer  101 ′, having a doping concentration of about 1E16˜5E19 atoms/cm 2 , which is greater than that of the semiconductor layer  101 ′. 
   Next, as shown in  FIG. 4   c , a buffer layer  700  and an anti-reflection layer  600  are sequentially formed on the back side of the slight thinned semiconductor layer  101   a ′, overlying the well region  500  thereof and having a thickness of about 100˜1000 Å and 100˜5000 Å, respectively. The anti-reflection layer  600  may comprise dielectric materials formed by PVD or CVD methods, such as SiONx, SiNy or organic materials by spin coating, such as acrylic polymers, polyester, polystyrene, polyimide, and the buffer layer  700  may comprise SiO2, SiONz, for releasing stresses formed between the semiconductor layer  101   a ′ and the anti-reflection layer  600 . Preferably, the anti-reflection layer  600  has a refractive index (n) between 1.0 (in air)˜3.5 (in silicon substrate). Next, color filter array  300  having red, green and blue color filters is formed on the anti-reflection layer  600  and an optional over-coating layer (OCL)  302  is next provided on color filter array  300 , thereby providing a planarized surface. A plurality of dome shaped microlens  304  is next formed on the OCL  302 , substantially corresponding to each of the pixel regions from a backside thereof. Therefore, incident light  400  can be projected onto the light-sensing devices  104  via passing along an optical path L 2  which is relatively shorter than that in the CMOS image sensor illustrated in  FIG. 1  since fewer structures and no metal interconnects are now formed between the light-sensing devices  104  and the microlenses  304 . Therefore, an image sensor device having such structures can be formed with reduced optical interference and improved quantum efficiency. 
   Referring to the image sensor device respectively illustrated in  FIGS. 2   c ,  3   c  and  4   c , since a backside of a semiconductor substrate/layer where comprising the light-sensing devices are exposed and a color filter layer and microlenses are formed thereon, incident light can be projected onto the light-sensing devices via passing along an optical path relatively shorter than that of the conventional light-sensing devices. Therefore, reduced optical interference and improved quantum efficiency of the light-sensing device formed within such image sensor device can be achieved. This is desired especially when a size of the light-sensing device is further reduced. 
   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.