Tunable-wavelength optical filter and method of manufacturing the same

Abstract

A method of manufacturing a tunable wavelength optical filter. The method includes steps of forming a first sacrificial oxide film for floating a lower mirror on a semiconductor substrate; sequentially laminating conductive silicon films and oxide films for defining a mirror region on the first sacrificial oxide film in a multi-layer and laminating another conductive silicon film to form a lower mirror; sequentially laminating conductive silicon films and oxide films for defining the mirror region on a second sacrificial oxide film in a multi-layer and laminating another conductive silicon film to form an upper mirror and forming an optical tuning space between the lower mirror and the upper mirror and etching the first sacrificial oxide film and the second sacrificial oxide film such that the lower mirror is floated on the semiconductor substrate.

The invention claimed is: 
     
       1. A method of manufacturing a tunable wavelength optical filter, comprising the steps of:
 (a) forming a first sacrificial oxide film for floating a lower mirror on a semiconductor substrate; 
 (b) sequentially laminating conductive silicon films and oxide films for defining a mirror region on said first sacrificial oxide film in a multi-layer and laminating another conductive silicon film to form a lower mirror; 
 (c) forming a second sacrificial film on the resultant; 
 (d) sequentially laminating conductive silicon films and oxide films for defining the mirror region on said second sacrificial oxide film in a multi-layer and laminating another conductive silicon film to form an upper mirror; 
 (e) etching the rear side of said semiconductor substrate to form an opening for inserting an optical fiber thereinto; 
 (f) forming electrode pads for controlling the gap between said lower mirror and said upper mirror by an electrostatic force; 
 (g) etching the silicon film around said upper mirror in a dry etching method to expose said second sacrificial oxide film, such that said upper mirror is suspended by a connecting means; and 
 (h) forming an optical tuning space between said lower mirror and said upper mirror and etching said first sacrificial oxide film and said second sacrificial oxide film such that said lower mirror is floated on said semiconductor substrate. 
 
     
     
       2. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , further comprising the structure of lower mirror embedded type that only the upper mirror is suspended by the connecting means and the lower mirror is not floated on the semiconductor substrate, after the step (g) and before the step (h). 
     
     
       3. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , wherein said first and second sacrificial oxide films are etched by a wet etching method using a hydrogen fluoride solution or a gas phase etching method using anhydrous hydrogen fluoride which the etching speed of the sacrificial oxide film is quicker than that of the silicon film. 
     
     
       4. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , wherein said silicon film is formed so as to have a thickness of (2m+1)λ/4n (m=0, 1, 2, . . . ),
 wherein λ is the wavelength of the light source, and n is the optical refractive index of the silicon film. 
 
     
     
       5. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , wherein said oxide film is formed so as to have a thickness of (2m+1)λ/4n (m=0, 1, 2, . . . ),
 wherein λ is the wavelength of the light source, and n is the optical refractive index of the oxide film. 
 
     
     
       6. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , further comprising the step of forming thermal oxide films on the both sides of the semiconductor substrate, before forming said first sacrificial oxide film. 
     
     
       7. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , wherein said the step (b) comprises the steps of:
 depositing a first conductive silicon film on said first sacrificial oxide film, 
 depositing a first oxide film on said first silicon film and patterning the first oxide film to define the mirror region; 
 depositing a second silicon film on said first silicon film and said patterned first oxide film; 
 depositing a second oxide film on said second silicon film and patterning the second oxide film to define the mirror region; and 
 forming a third conductive silicon film on said second silicon film and said patterned second oxide film. 
 
     
     
       8. The method of manufacturing the tunable wavelength optical filter according to  claim 1 , wherein said the step (d) comprises the steps of:
 depositing a first conductive silicon film on said second sacrificial oxide film, 
 depositing a first oxide film on said first silicon film and patterning the first oxide film to define the mirror region; and 
 depositing a second silicon film on said first silicon film and said patterned first oxide film; 
 depositing a second oxide film on said second silicon film and patterning the second oxide film to define the mirror region; and 
 forming a third conductive silicon film on said second silicon film and said patterned second oxide film. 
 
     
     
       9. A method of manufacturing a tunable wavelength optical filter, comprising:
 forming a first sacrificial oxide film;   sequentially laminating silicon films and oxide films on the first sacrificial oxide film to form a lower mirror;   forming a second sacrificial film on the lower mirror;   sequentially laminating silicon films and oxide films on the second sacrificial oxide film to form an upper mirror;   etching the second sacrificial oxide film to form a gap between the lower minor and the upper minor; and   forming electrode pads for controlling the gap.   
     
     
       10. The method of claim 9, further comprising:
 etching the silicon film around the upper mirror to expose the second sacrificial oxide film; and   etching the second sacrificial oxide film, whereby floating the lower mirror on a semiconductor substrate.   
     
     
       11. The method of claim 9, wherein the electrode pad controls the gap by an electrostatic force. 
     
     
       12. The method of claim 9, wherein at least one of the upper mirror and the lower minor is suspended by a connecting means. 
     
     
       13. The method of claim 9, wherein the first sacrificial oxide film is formed on a semiconductor substrate. 
     
     
       14. The method of claim 13, further comprising etching the read side of the semiconductor substrate to form an opening for inserting an optical fiber therein.