Image sensor comprising microlens array, and manufacturing method thereof

Abstract

The present invention relates to an image sensor comprising a microlens array, and to a manufacturing method thereof. The method of the present invention includes gradually increasing the aluminum composition ratio of a compound semiconductor as the latter gradually gets farther from a substrate, to enable a microlens-forming layer to grow, and making the oxidation rate of the region adjacent to the substrate slower and the oxidation rate of the region farther from the substrate faster, making the interface between the oxidized region and the unoxidized region into a lens shape after the completion of oxidation. The thus-made lens is integrated into an image sensor. The present invention reduces costs for manufacturing image sensors in which a microlens is integrated, increases the signal-to-noise ratio and resolution of the image sensor, and achieves improved sensitivity.

1 . An image sensor including a microlens array, comprising:
 a substrate having one side on which a plurality of photo-detectors configured to sense light are formed; and   a plurality of microlenses disposed on the other side of the substrate and spaced a predetermined distance apart from one another, the plurality of microlenses respectively corresponding to the plurality of photo-detectors and configured to focus external light and allow the light to be incident to the photo-detectors,   wherein each of the microlenses includes a lens-shaped semiconductor material layer stacked such that an oxidation rate of the semiconductor material layer gradually increases as the semiconductor material layer becomes farther from the substrate, and wherein each of the microlenses includes a plurality of different layers, the each of the plurality of layers includes a digital alloy formed by stacking at least two semiconductor material layers having different oxidation rates.   
     
     
         2 . The image sensor of  claim 1 , wherein each of the microlenses is formed by selectively oxidizing the semiconductor material layer. 
     
     
         3 . The image sensor of  claim 1 , wherein the oxidation rate of each of the plurality of layers is gradually increased by controlling the thickness of a layer having a highest oxidation rate out of the at least two semiconductor material layers having the different oxidation rates. 
     
     
         4 . The image sensor of  claim 3 , wherein the semiconductor material layer includes a combination of an aluminum (Al)-containing ternary or quaternary compound and is formed by stacking an Al-containing binary or ternary compound and an Al-free binary or ternary compound. 
     
     
         5 . The image sensor of  claim 1 , wherein the semiconductor material layer includes any one compound combination selected from aluminum gallium arsenide (AlGaAs), aluminum gallium nitride (AlGaN), indium gallium aluminum nitride (INGaAlN), indium gallium aluminum arsenide (InGaAlAs) or indium gallium aluminum phosphide (InGaAlP). 
     
     
         6 . The image sensor of  claim 1 , wherein a horizontal section of each of the microlenses has a circular or polygonal shape. 
     
     
         7 . The image sensor of  claim 1 , wherein each of the microlenses is a spheric or aspheric lens. 
     
     
         8 . The image sensor of  claim 1 , wherein a central portion of each of the microlenses has a height of about 1 to about 2 μm. 
     
     
         9 . An image sensor including a microlens array, comprising:
 a microbolometer disposed on a first substrate and including a plurality of thermal detectors configured to sense heat generated by infrared (IR) light; and   a microlens array including a plurality of microlenses formed on one side of a second substrate, the plurality of microlenses configured to focus external light incident from the other side of the second substrate and allow the external light to be incident to each of the thermal detectors,   wherein the microbolometer and the microlens array are hybrid-integrated with each other such that the microlenses are respectively spaced a predetermined distance apart from and opposite to the corresponding thermal detectors.   
     
     
         10 . The image sensor of  claim 9 , wherein each of the microlenses includes a lens-shaped semiconductor material layer stacked such that an oxidation rate of the semiconductor material layer gradually increases as the semiconductor material layer becomes farther from the second substrate. 
     
     
         11 . A method of manufacturing an image sensor including a microlens array, the method comprising:
 (a) forming a microlens-forming layer on one side of a substrate by stacking a semiconductor material layer whose oxidation rate is gradually increased as the semiconductor material layer becomes farther from the substrate;   (b) forming a plurality of mesa structures by etching a predetermined region of the microlens-forming layer until the substrate is exposed, the plurality of mesa structures spaced a predetermined distance apart from one another and having exposed lateral surfaces, respectively;   (c) oxidizing a lateral surface of each of the mesa structures while increasing an oxidation rate as each of the mesa structures becomes farther from the substrate to make an interface between an oxidized region and an unoxidized region into a lens shape after completion of oxidation to form microlenses having a radius of curvature in the centers of the respective mesa structures, and selectively removing oxidized regions other than the microlenses; and   (d) forming a plurality of photo-detectors on the other side of the substrate to respectively correspond to the microlenses.   
     
     
         12 . The method of  claim 11 , further comprising, after step (a), forming an oxidation barrier layer on a top surface of the microlens-forming layer to a predetermined thickness. 
     
     
         13 . The method of  claim 11 , wherein, in step (a), the microlens-forming layer is formed using a plurality of different layers,
 wherein each of the plurality of layers includes a digital alloy formed by stacking at least two semiconductor material layers having different oxidation rates, and an oxidation rate of each of the plurality of layers is gradually increased by controlling the thickness of a layer having a highest oxidation rate out of the at least two semiconductor material layers having the different oxidation rates.   
     
     
         14 . The method of  claim 11 , wherein, in step (a), the microlens-forming layer includes a combination of an Al-containing ternary or quaternary compound and is formed by alternately stacking an Al-containing binary or ternary compound and an Al-free binary or ternary compound. 
     
     
         15 . The method of  claim 11 , wherein, in step (b), each of the mesa structures is formed as a circular or polygonal mesa structure. 
     
     
         16 . The method of  claim 11 , wherein, in step (c), each of the microlenses is formed in a lens shape having a radius of curvature by exponentially oxidizing the microlens-forming layer according to the oxidation rate of the semiconductor material layer stacked by gradually increasing the oxidation rate in the microlens-forming layer. 
     
     
         17 . The method of  claim 11 , wherein, in step (c), the oxidizing of the lateral surface of each of the mesa structures is performed using a wet oxidation process at a temperature of about 300 to about 500° C. for about 30 to about 200 minutes. 
     
     
         18 . A method of manufacturing an image sensor including a microlens array, the method comprising:
 (a′) manufacturing a microbolometer on a first substrate, the microbolometer including a plurality of thermal detectors configured to sense heat generated by IR light;   (b′) manufacturing a microlens array including a plurality of microlenses on one side of a second substrate, the plurality of microlenses configured to focus external light incident from the other side of the second substrate and allow the external light to be incident to each of the thermal detectors; and   (c′) hybrid-integrating the separately manufactured microbolometer and microlens array such that the thermal detectors are respectively disposed a predetermined distance apart from and opposite to the corresponding microlenses.   
     
     
         19 . The method of  claim 18 , wherein step (b′) comprises:
 (b′-1) forming a microlens-forming layer on one side of the second substrate by stacking a semiconductor material layer whose oxidation rate is gradually increased as the semiconductor material layer becomes farther from the second substrate; 
 (b′-2) etching a predetermined region of the microlens-forming layer until the second substrate is exposed to form a plurality of mesa structures spaced a predetermined distance apart from one another and having exposed lateral surfaces; and 
 (b′-3) oxidizing a lateral surface of each of the mesa structures while increasing an oxidation rate as each of the mesa structures becomes farther from the second substrate to make an interface between an oxidized region and an unoxidized region into a lens shape after completion of oxidation to form microlenses having a radius of curvature in the centers of the respective mesa structures, and selectively removing other oxidized regions than the microlenses.