Abstract:
A semiconductor optical sensor includes a plurality of sensing units and to senses an incident optical signal to generate an electrical signal. One of the sensing units includes a substrate, an optical sensing element, a lens and an optical shielding element. The optical sensing element, whose material is different from that of the substrate, converts the incident optical signal into the electrical signal. The lens, whose material includes the same as that of the substrate, guides the incident optical signal to the optical sensing element by changing the propagation path of the incident optical signal. The optical shielding element, which surrounds the optical sensing element, alters the propagation path or propagation distance of the incident optical signal after the incident optical signal passes through the lens such that the incident optical signal will not reach an optical sensing element of an adjacent sensing unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 62/074,102, filed Nov. 3, 2014, which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present disclosure relates to a semiconductor optical sensor, especially to a semiconductor optical sensor with optical shielding element. 
         [0004]    2. Description of Prior Art 
         [0005]    The optical sensor system generally includes lens, photo sensitive element, metal routing. The incident optical signal is first focused by the lens and then converted into electric signal by the photo sensitive element. The converted electric signal is sent, through the metal routing, to other elements for further analyzing and processing. However, the performance of the optical sensor system may be degraded by the unabsorbed part of the incident optical signal after the incident optical signal passes through the photo sensitive element. In the optical sensor constituted by an array of photo sensitive elements, crosstalk among the photo sensitive elements caused by leaked optical signal (unabsorbed part of the incident optical signal) will influence the measurement result. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present disclosure to provide a semiconductor optical sensor with better light focusing and reduced optical crosstalk. 
         [0007]    According to one aspect of the present disclosure, a semiconductor optical sensor includes a plurality of sensing units, the semiconductor optical sensor converting an incident optical signal into an electric signal and one of the sensing units comprising: a substrate; an optical sensing element using a different material with that of the substrate and converting the incident optical signal into the electric signal; a lens using a same material with that of the substrate and changing a propagation path of the incident optical signal to guide the incident optical signal to the optical sensing element; and an optical shielding element surrounding the optical sensing element and changing the propagation path of the incident optical signal or a propagation distance of the incident optical signal such that the incident optical signal does not further propagate to another sensing unit adjacent to the sensing unit impinged by the incident optical signal. 
         [0008]    According to another aspect of the present disclosure, a semiconductor optical sensor converts an incident optical signal into an electric signal and comprises: a substrate; an optical sensing element using a different material with that of the substrate and converting the incident optical signal into the electric signal; a lens using a same material with that of the substrate and changing a propagation path of the incident optical signal to guide the incident optical signal to the optical sensing element; an optical confinement element arranged at a lateral side of the optical sensing element and coplanar with the optical sensing element, the optical confinement element absorbing or reflecting a portion of the incident optical signal after the incident optical signal passing the lens; and an optical reflection element arranged atop the optical sensing element and reflecting an unabsorbed component of the incident optical signal after the incident optical signal passing the optical sensing element. 
         [0009]    The semiconductor optical sensor according to the present disclosure can prevent the unabsorbed incident optical signal from leaking to adjacent sensing units, thus reducing optical cross talk and dark current. 
     
    
     
       BRIEF DESCRIPTION OF DRAWING 
         [0010]    The present disclosed example itself, however, may be best understood by reference to the following detailed description of the present disclosed example, which describes an exemplary embodiment of the present disclosed example, taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1A  shows a perspective view of the semiconductor optical sensor according to the present disclosure. 
           [0012]      FIG. 1B  is a sectional view of the semiconductor optical sensor shown in  FIG. 1A . 
           [0013]      FIG. 2  shows a sectional view of the semiconductor optical sensor according to another embodiment of the present disclosure. 
           [0014]      FIG. 3A  shows a perspective view of the semiconductor optical sensor according to still another embodiment of the present disclosure. 
           [0015]      FIG. 3B  is a sectional view of the semiconductor optical sensor shown in  FIG. 3A . 
           [0016]      FIG. 4  shows a sectional view of the semiconductor optical sensor according to still another embodiment of the present disclosure. 
           [0017]      FIG. 5  shows a sectional view of the semiconductor optical sensor according to still another embodiment of the present disclosure. 
           [0018]      FIG. 6A  shows a perspective view of the semiconductor optical sensor according to still another embodiment of the present disclosure. 
           [0019]      FIG. 6B  is a sectional view of the semiconductor optical sensor shown in  FIG. 6A . 
           [0020]      FIG. 7  shows the exemplary process flow for manufacturing the semiconductor optical sensor of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The present disclosure will be described in greater detail by referring to the following discussion and drawings that accompany the present disclosure. It is noted that the drawings of the present disclosure are provided for illustrative purposes and, as such, they are not drawn to scale. In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide a thorough understanding of the present disclosure. However, it will be appreciated by one of ordinary skill in the art that the present disclosure may be practiced with viable alternative process options without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the various embodiments of the present disclosure. 
         [0022]      FIG. 1A  shows a perspective view of the semiconductor optical sensor according to the present disclosure, and  FIG. 1B  is a sectional view of the semiconductor optical sensor shown in  FIG. 1A . The semiconductor optical sensor  10  comprises a plurality of sensing units  100  and the plurality of sensing units  100  can be arranged in an array.  FIGS. 1A and 1B  only depict the partial structures (or the complete structures) of three adjacent sensing units  100  along one row of the sensor array. The semiconductor optical sensor  10  comprises a substrate  120 , a plurality of hemispheric lens  110  arranged on a lower face of the substrate  120 . The lens  110  can be fabricated with the same material as that of the substrate  120 . The material of the substrate can be, but not limited to, silicon (Si), silicon on insulator, (SOI), InP, or SiC. The lens  110  can be fabricated on the substrate  120  by semiconductor manufacture process such as, but not limited to, etching, imprinting, or pattern transferring. The lens  110  can be fabricated with lower cost because they are fabricated from the same material as the substrate  120  and with semiconductor manufacture process. The alignment between the substrate  120  and the lens  110  can be achieved by the standard photolithography in semiconductor manufacture process and becomes simpler and more precise. In some embodiments of the present disclosure, the lens  110  can be fabricated with material different from that of the substrate  120 . The semiconductor optical sensor  10  further comprises a plurality of optical sensing elements  130  on an upper face of the substrate  120 . The incident optical signal as indicated by the arrow shown in  FIG. 1A  is from the bottom of this depiction, getting focused on the optical sensing elements  130  by the lens  130  and then converted into electric signal by the optical sensing elements  130 . 
         [0023]    The semiconductor optical sensor  10  further comprises a plurality of optical confinement elements  140 ; each of the optical confinement elements  140  is arranged between adjacent optical sensing elements  130 . The optical confinement element  140  is such constructed to prevent the unabsorbed component of an optical signal, which impinged to an optical sensing element  130 , from propagating to adjacent optical sensing elements  130 . In the shown embodiment, the adjacent optical sensing elements  130  share one optical confinement elements  140  place therebetween. The optical confinement elements  140  and the optical sensing elements  130  are fabricated on the upper face of the substrate  120 . The optical confinement elements  140  can be fabricated with the same material as that of the optical sensing element  130  such that the optical confinement elements  140  can absorb the unabsorbed component (leaked components) of the optical signal impinged to the sensing unit  100  to trap the incident optical signal within the sensor unit  100  surrounded by the optical confinement elements  140 , thus reducing optical crosstalk. In one embodiment shown in  FIG. 1B , the optical confinement element  140  has the same height as that of the optical sensing element  130  such that the optical confinement element  140  and the optical sensing element  130  can be made with the same semiconductor manufacture steps (for example, the same deposition step followed by respective lithography patterns). In other embodiments, the optical confinement element  140  can be higher than or lower than the optical sensing element  130  to achieve different optical confinement effects. 
         [0024]    Each of the sensing units  100  further comprises an optical reflection element  150  arranged atop the optical sensing element  130 , namely, opposite to the lens  110 . More particularly, the optical reflection element  150  is atop the dielectric layer  160  (the dielectric layer  160  is omitted in  FIG. 1A  to more clearly show the relative positions of other elements). The dielectric layer  160  can adopt well-known dielectric material, such as silicon oxide (SiO 2 ), in semiconductor manufacture process. The optical reflection element  150  allows unabsorbed components of the incident optical signal passing through the optical sensing element  130  to be reflected back toward the optical sensing element  130  (namely, changing the propagation direction of the unabsorbed components of the incident optical signal to allow the unabsorbed components to be absorbed again) for increasing optical-electrical conversion efficiency for the optical sensing element  130 . The thickness of the dielectric layer  160  can be adjusted according to the wavelength of the incident optical signal, the dielectric constant of the dielectric layer  160  and the material of the optical reflection element  150  to achieve optimal reflection. In one embodiment of the present disclosure, the optical reflection element  150  may be made out of conductive material, dielectric, semiconductor or their combinations. When conductive material is selected as the material for the optical reflection element  150 , the optical reflection element  150  can be electrically connected to the optical sensing element  130  through conductive wires (not shown) such that the optical reflection element  150  can serve as both the optical reflector and the electrical contact for connecting with other electrical devices such as capacitor, resistor, inductor and transistor. The other electrical devices can be fabricated on the surface of the substrate  120  or within the substrate  120 . 
         [0025]    As shown in  FIG. 2 , the optical sensing element  130  and the optical confinement element  140  can be fabricated within (embedded within) the substrate  120 , while the optical reflection element  150  can be directly fabricated on the upper face of the substrate  120 . The lens  110  is arranged on the lower face of the substrate  120  and can be integrally formed with the substrate  120  as well as can have the same material as that of the substrate  120 . In the shown embodiment, the heights of the optical sensing element  130  and the optical confinement element  140  are smaller than the thickness of the substrate  120 . In other embodiments, the heights of the optical sensing element  130  and the optical confinement element  140  can be equal to the thickness of the substrate  120 , namely the optical sensing element  130  is exposed out of the upper face of the substrate  120  and in direct contact with the optical reflection element  150  to prevent the incident optical signal from leaking. The optical reflection element  150  can be made out of conductive material to achieve the electric connection between the optical sensing element  130  and the optical reflection element  150  as well. 
         [0026]      FIG. 3A  shows a perspective view of the semiconductor optical sensor according to another embodiment of the present disclosure, and  FIG. 3B  is a sectional view of the semiconductor optical sensor shown in  FIG. 3A . The semiconductor optical sensor  30  comprises a plurality of sensing units  300  and the plurality of sensing units  300  can be arranged in an array.  FIGS. 3A and 3B  only depict the partial structures (or the complete structures) of three adjacent sensing units  300  along one row of the array. The semiconductor optical sensor  30  comprises a substrate  320 , a plurality of hemispheric lens  310  arranged on a lower face of the substrate  320 . The lens  310  can be fabricated with the same material as that of the substrate  320 , or material different with that of the substrate  320 . The semiconductor optical sensor  30  further comprises a plurality of optical sensing elements  330  on an upper face of the substrate  320 . The incident optical signal is focused on the optical sensing elements  330  by the lens  330  and then converted into electric signal by the optical sensing elements  330 . 
         [0027]    The semiconductor optical sensor  30  further comprises a plurality of optical confinement elements  340  to separate adjacent optical sensing elements  330 . In the shown embodiment, the optical confinement element  340  surrounds the optical sensing element  330  to prevent the optical signal incident to the optical sensing element  330  from leaking. Each of the optical confinement elements  340  is exclusive for one sensing unit  300 , namely, the adjacent sensing units  300  do not share a common optical confinement element  340 . In above mentioned semiconductor optical sensors  10  and  20 , the adjacent of sensor units  300  share one optical confinement element  140 . The optical confinement elements  340  can be fabricated with the same material as that of the optical sensing element  330 , or can be fabricated with material different from that of the optical sensing element  330 . In one embodiment, the optical confinement element  340  is made out of conductive material to confine optical signal within the sensing unit  300  by light reflection. When the optical confinement element  340  is made of conductive material, the optical confinement element  340  also serves as electric contact for the sensing unit  300  to electrically connect the sensing unit  300  with external circuit. The optical sensing element  330  can be electrically connected to the optical confinement element  340  through metal routing or through doped area on the substrate and between the optical sensing element  330  and the optical confinement element  340 . 
         [0028]    Each of the sensing units  300  further comprises an optical reflection element  350  arranged atop the optical sensing element  330 , namely, opposite to the lens  310 . More particularly, the optical reflection element  350  is atop the dielectric layer  360  (the dielectric layer  160  is omitted in  FIG. 3A  to more clearly show the relative positions of other elements). The dielectric layer  360  can adopt well-known dielectric material in semiconductor process such as silicon oxide (SiO2). The optical reflection element  350  allows unabsorbed components of the incident optical signal passing through the optical sensing element  330  to be reflected back toward the optical sensing element  330  (namely, changing the propagation direction of the unabsorbed components of the incident optical signal to allow the unabsorbed components to be absorbed again) for increasing optical-electrical conversion efficiency for the optical sensing element  330 . The thickness of the dielectric layer  360  can be adjusted according to the wavelength of the incident optical signal, the dielectric constant of the dielectric layer  360  and the material of the optical reflection element  350  to achieve optimal reflection. In one embodiment of the present disclosure, the optical reflection element  350  may be made out of conductive material, dielectric, semiconductor or their combinations. When conductive material is selected as the material for the optical reflection element  350 , the optical reflection element  350  can be electrically connected to the optical sensing element  330  through conductive wires (not shown) such that the optical reflection element  350  can serve as both the optical reflector and the electrical contact for connecting with other electrical. The optical confinement elements  340  and the optical reflection element  350  can be fabricated in the same step or different steps of semiconductor manufacture process. 
         [0029]    In this embodiment, the height of the optical confinement elements  340  is larger than or equal to the sum of the thicknesses of the optical sensing element  330  and the optical reflection element  350 . Namely, for an imaginary plane on the top face of the optical confinement elements  340  and parallel with the top face of the substrate  320 , the optical sensing element  330  and the optical reflection element  350  are covered by the imaginary plane. In other embodiments, as the semiconductor optical sensor  40  shown in  FIG. 4 , the optical reflection element  350  covers both the optical sensing element  330  and the optical confinement element  340 . In other embodiments, as the semiconductor optical sensor  50  shown in  FIG. 5 , the optical reflection element  350  does not cover the optical confinement element  340 , and the optical confinement element  340  is not high enough to enclose the optical reflection element  350 . 
         [0030]    In other embodiments, the semiconductor optical sensors  10 ,  30 ,  40 , or  50 , and the optical reflection element  150  (or the optical reflection element  350 ) can be directly fabricated on the upper face of the optical sensing element  130  (or the optical sensing element  330 ) as long as material and process permit. Namely, the optical reflection element  150  (or the optical reflection element  350 ) is in direct contact with the optical sensing element  130  (or the optical sensing element  330 ) and no dielectric layer  160  (or dielectric layer  360 ) is present. In the semiconductor optical sensor  40 , the optical reflection element  350  can be in direct contact with both the optical sensing element  330  and the optical confinement element  340 . Similar to the optical sensor  20  shown in  FIG. 2 , the optical sensing element  330  and the optical confinement element  340  of the semiconductor optical sensors  10 ,  30 ,  40 , or  50   
         [0031]    In the embodiments shown in  FIGS. 1 to 5 , the optical sensing element  130  (or the optical sensing element  330 ) and the optical confinement element  140  (or the optical confinement element  340 ) are substantially arranged on the same plane to provide good optical confinement. 
         [0032]      FIG. 6A  shows a perspective view of the semiconductor optical sensor according to another embodiment of the present disclosure, and  FIG. 6B  is a sectional view of the semiconductor optical sensor shown in  FIG. 6A . The semiconductor optical sensor  60  comprises a plurality of sensing units  600  and the plurality of sensing units  600  can be arranged in an array.  FIGS. 6A and 6B  only depict the partial structures (or the complete structures) of three adjacent sensing units  600  along one row of the array. The semiconductor optical sensor  60  comprises a substrate  620 , and a plurality of hemispheric lens  610  arranged on a lower face of the substrate  620 . The lens  610  can be fabricated with the same material as that of the substrate  620 , or material different with that of the substrate  320 . The semiconductor optical sensor  30  further comprises a plurality of optical sensing elements  630  on an upper face of the substrate  620 . The incident optical signal is focused on the optical sensing elements  360  by the lens  630  and then converted into electric signal by the optical sensing elements  630 . 
         [0033]    The semiconductor optical sensor  60  further comprises a plurality of optical shielding elements  640  to prevent crosstalk among the sensing units  600 . The optical shielding element  640  encapsulates a plurality of sides of the optical sensing element  630  except the side of the optical sensing element  630 , which is in contact with the substrate  620 . The encapsulating way of the optical shielding element  640  can be such that the optical shielding element  640  is in full contact with the upper side and lateral sides of the optical sensing element  630  as shown in  FIGS. 6A and 6B . Alternatively, the optical shielding element  640  can be in partial contact or separated with the upper side and lateral sides of the optical sensing element  630 . The optical shielding element  640  confines light propagation from the upper side and lateral sides of the optical sensing element  630 . Namely the optical shielding element  640  substantially achieve the function of the optical confinement element  140  (or the optical confinement element  340 ) in combination with the optical reflection element  150  (or the optical reflection element  350 ). The optical shielding element  640  reflects or absorbs the unabsorbed components of the incident optical signal, which passes through the optical sensing element  630  and emits from the upper side and lateral sides of the optical sensing element  630 , to prevent the unabsorbed components from leaking. Each of the sensing units  600  has exclusive optical shielding element  640 , namely, two adjacent sensing units  600  do not share a common optical shielding element  640 . The optical shielding element  640  can be made out of conductive material, dielectric, semiconductor or their combinations. In one embodiment, the optical shielding element  640  is made out of conductive material to confine optical signal within the sensing unit  600  by light reflection. When the optical shielding element  640  is made out of conductive material, the optical shielding element  640  also serves as electric contact for the sensing unit  600  to electrically connect the sensing unit  300  with external circuit. Similarly, the optical sensing element  630  and the optical shielding element  640  can be completely or partially formed within (embedded within) the substrate  620 . 
         [0034]    The shapes of the above mentioned lens  110 ,  310 ,  610  are not limited to spherical or hemispheric and can be any shape (such as aspheric shape) or structure (such as photonic crystal) capable of providing optical perturbation. Purposes for optical perturbation may be, but not limited to, reflecting, transmitting, focusing, collimating or diffracting the incident optical signal. The surface of the lens can be additional treated to enhance the ability for optical perturbation. Moreover, the structure of the optical confinement element  340  and the optical shielding element  640  is not limited to circular and can be elliptical or rectangular etc. 
         [0035]    The optical confinement element  140  and the optical reflection element  150  of the semiconductor optical sensors  10  can constitute an optical shielding element encapsulating the optical sensing element  130 . Similarly, the optical confinement element  340  and the optical reflection element  350  of the semiconductor optical sensors  30  can constitute an optical shielding element encapsulating the optical sensing element  330 . The optical shielding element constituted by the optical confinement element  140  and the optical reflection element  150  also confines the incident optical signal passing the lens  110  and/or the optical sensing element  130  and prevents the unabsorbed components of the incident optical signal from leaking to the adjacent sensing unit  100 , thus reducing optical crosstalk. 
         [0036]    The criterions of selecting material for the substrate and the optical sensing element (such as the substrate  120  and the optical sensing element  130 , the substrate  320  and the optical sensing element  330 , and the substrate  620  and the optical sensing element  630 ) depend on optical signal to be sensed by the semiconductor optical sensor. For example, the refractive index of the substrate should be compatible with the wavelength of the optical signal and the material of the substrate should be compatible with the material of the optical sensing element. In one embodiment, the bandgap of the substrate should be larger than the bandgap of the optical sensing element. For example, the substrate is primarily made out of silicon (Si) and the optical sensing element is primarily made out of germanium (Ge). The semiconductor optical sensors use this kind of material combination can be used to sense optical signal in near infrared region (0.75-1.4 um). In other embodiments, the optical sensing element is made out of a material with different physical characteristics from that of the substrate material. Difference in physical characteristics may be induced by, but not limited to chemical element composition, material bandgap modification, extrinsic doping, defect introduction, and etc. 
         [0037]    The exemplary process flow can be described as following. First the optical sensing element and the optical confinement element are formed (step  701 ). In some implementations, the optical sensing element is formed by selectively growing Germanium based absorption material within an area on top of the substrate, or by blanket epitaxial growth of Germanium based absorption material on top of the substrate. The optical confinement can be formed during the same steps of forming the absorption material by intentionally leaving the some of the absorption material surrounding the optical sensor element. In some implementations, the optical confinement can be formed either before or after the formation of optical sensing element by depositing a reflective or absorptive material. In some implementations, after forming the Germanium based absorption material, a dielectric or semiconductor can be deposited enclosing the optical sensing element, and followed by depositing either an absorptive material such as Germanium or reflective material such as Aluminum. After forming the optical sensing and confinement element, the optical reflection material can be formed by depositing a reflective material atop the optical sensing element (step  702 ). Then, this structure is bonded to another host substrate by attaching the top surface near the optical reflection element onto the surface of the host substrate (step  703 ). The host substrate can include multiple metal routing or CMOS devices for further signal processing. The bonding can be done by metal to metal bonding, oxide to oxide bonding or other mechanisms. After the wafer bonding process, the optical device is flipped, and a large portion of the original substrate is removed and shaped into a curved structure as the lens structure by using methods such as a grey scale mask or nanoimprinting (step  704 ). In some implementations, the lens can be formed by deposition or attachment after a large portion of the original substrate is removed. 
         [0038]    The foregoing descriptions of embodiments of the disclosed example have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosed example to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the disclosed example. The scope of the disclosed example is defined by the appended.