Optical filter structure for arbitrary combination of rgb and ir wavelength ranges and its manufacturing method

Abstract

The present invention discloses an optical bandpass filter structure targeting an arbitrary combination of the spectral ranges of R (red), G (green), B (blue) and IR (infrared) light, which comprises a substrate that is a wafer-based semiconductor sensing element, and a filter layer that is formed on one side of the substrate. The filter layer includes a plurality of basic units organized as a two-dimensional array, in which each of the basic units is composed of a plurality of pixel filter films fabricated by a vacuum coating method.

What is claimed is: 
     
         1 . A method for manufacturing an optical filter structure for an arbitrary combination of R, G, B, and IR wavelength ranges, comprising the steps of:
 (a) providing a substrate;   (b) forming a photoresist mask having a plurality of hollowed out regions on a side of the substrate;   (c) conducting vacuum plasma coating formation on the plurality of hollowed out regions to deposit a plurality of pixel filter films, wherein each of the pixel filter films within the plurality of pixel filter films is formed by stacking, in alternation, a plurality of silver (Ag) layers of varied thickness, and a plurality of high-refractive-index material layers with refractive indices higher than that of silver;   (d) applying an additional layer of photoresist coating over the plurality of pixel filter films formed in step (c) so as to seal off the plurality of pixel filter films;   (e) etching another plurality of hollowed out regions in the photoresist mask where another plurality of pixel filter films will be coated, and returning to step (c) until all desired pixel filter films have been formed; and   (f) removing the photoresist mask.   
     
     
         2 . The method of  claim 1 , wherein steps (c) to (e) are repeated until an optical filter structure composed of at least three types of pixel filter films is produced. 
     
     
         3 . The method of  claim 1 , wherein step (b) further comprises the following fabrication sub-steps: (b1) spin coating a layer of photoresist; (b2) soft baking; (b3) exposure; (b4) soft baking; (b5) developing; (b6) soft baking; and (b7) cleaning. 
     
     
         4 . The method of  claim 1 , wherein step (c) is carried out in a vacuum reactive sputtering coating system, of which a sputtering target comprises silver (Ag) and oxide materials whose refractive indices are higher than that of silver, and wherein step (c) further comprises the following sub-steps: (c1) placing a clean substrate on a coating drum roller, with the side on which the photoresist mask is formed facing outwards; (c2) rotating the coating drum roller at a uniform speed in a coating chamber; (c3) releasing argon gas into the coating chamber, and activating a corresponding sputtering source when the coating chamber pressure reaches the range of 10 −3  Pa to 10 −5  Pa, such that the argon gas bombards and ionizes the sputtering target under the influence of an electric field; (c4) allowing ions originating from the sputtering target to attach to the substrate; (c5) bringing the substrate to a reaction source area, as the coating drum roller rotates; and (c6) introducing oxygen gas, argon gas, or a mixture thereof, into the reaction source area and, under the influence of the electric field, ionizing the oxygen or argon gas into plasma and driving the plasma toward the substrate at high speed such that silver layers or layers of other materials with refractive indices higher than that of silver are formed on the substrate. 
     
     
         5 . The method of  claim 4 , wherein the oxide materials with refractive indices higher than that of silver are materials selected from the group consisting of trititanium pentoxide (Ti3O5), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), lanthanum titanium oxide (La2O7Ti2 or H4), and mixtures thereof. 
     
     
         6 . The method of  claim 4 , wherein sub-step (c6) further comprises controlling a thickness of the silver layers or layers of other materials with refractive indices higher than that of silver formed in sub-step (c6) by controlling a duration of time spent in the reaction source area where the duration of time spent in the reaction source area is directly correlated with the thickness of each layer. 
     
     
         7 . The method of  claim 4 , wherein sub-step (c6) further comprises controlling the characteristics of the silver layers formed in sub-step (c6) by controlling the percentage of oxygen by volume in an argon-oxygen gas mixture, where the refractive index and extinction coefficient of the silver layers formed in sub-step (c6) ranges from 0.1 to 2 and 5.8 to 23, respectively, over the wavelength range of 350 nm to 4000 nm as the oxygen percentage by volume of the argon-oxygen gas mixture ranges from 10% to 90%. 
     
     
         8 . The method of  claim 4 , wherein sub-step (c6) further comprises controlling the characteristics of the layers of other materials with refractive indices higher than that of silver formed in sub-step (c6) by controlling the percentage of oxygen by volume in an argon-oxygen gas mixture, where the refractive index of the layers of other materials with refractive indices higher than that of silver formed in sub-step (c6) ranges from 1.3 to 2.5, with an extinction coefficient of close to 0, over the wavelength range of 350 nm to 4000 nm, as the oxygen percentage by volume of the argon-oxygen gas mixture ranges from 10% to 90%.