Process for etching trenches in an integrated optical device

Abstract

The described process allows trenches to be etched in a structure comprising a support substrate and a multilayer, formed on the substrate, for the definition of wave guides of an integrated optical device and comprises a selective plasma attack in the multilayer through a masking structure that leaves uncovered areas of the multilayer corresponding to the trenches to be etched. Such a masking structure is obtained by forming a mask of metallic material on the multilayer that leaves uncovered the areas corresponding to the trenches to be etched and forming a mask of non-metallic material, for example photoresist, on it that leaves uncovered regions comprising at least part of the areas and an edge portion of the mask of metallic material.

1 . Process for etching trenches in a structure comprising a support substrate and a multilayer, formed on the substrate, comprising a core layer and coating layers for the definition of wave guides of an integrated optical device, the process comprising a selective plasma attack in the multilayer through a masking structure that leaves uncovered areas of the multilayer corresponding to the trenches to be etched and being 
 wherein the masking structure is obtained with the following successive operations:    forming a mask of metallic material on the multilayer that leaves uncovered the areas corresponding to the trenches to be etched and    forming a mask of non-metallic material that leaves uncovered regions comprising at least part of the areas corresponding to the trenches to be etched and an edge portion of the mask of metallic material.    
   
   
       2 . Process for etching trenches according to  claim 1 , wherein the operation of forming the mask of non-metallic material leaves uncovered regions comprising the areas corresponding to the trenches to be etched and an edge portion of the mask of metallic material.  
   
   
       3 . Process for etching trenches according to  claim 1 , wherein the mask of metallic material leaves uncovered further areas of the multilayer not corresponding to the trenches to be etched.  
   
   
       4 . Process for etching trenches according to  claim 1 , wherein the operation of formation of the mask of non-metallic material is preceded by operations for the formation of other structures of the integrated optical device.  
   
   
       5 . Process for etching trenches according to  claim 1 , wherein the non-metallic material comprises a photoresist.  
   
   
       6 . Process for etching trenches according to  claim 1 , wherein the attack comprises a low-density plasma attack.  
   
   
       7 . Process for etching trenches according to  claim 1 , wherein the attack comprises a high-density plasma attack.  
   
   
       8 . A method, comprising: 
 forming on a material a metallic first mask that exposes a region of the material;    forming on the first mask a second mask that exposes a section of the region and a portion of the first mask that is contiguous with the section of the region; and    forming a trench in the exposed section of the material.    
   
   
       9 . The method of  claim 8 , further comprising: 
 forming on a substrate a first optical layer having a first index of refraction;    forming on the first layer a second optical layer having a second index of refraction; and    forming on the second layer a third optical layer having a third index of refraction, the first, second, and third layers composing the material.    
   
   
       10 . The method of  claim 8 , further comprising removing the first and second masks after forming the trench.  
   
   
       11 . The method of  claim 8  wherein forming the first mask comprises forming the first mask only within predetermined distance from a perimeter of the region.  
   
   
       12 . The method of  claim 8  wherein forming the second mask comprises forming the second mask such that the second mask exposes the entire region of the material and exposes a portion of the first mask that is contiguous with multiple sides of the region.  
   
   
       13 . The method of  claim 8  wherein forming the second mask comprises forming the second mask such that the second mask exposes a section that is smaller than the entire region of the material and exposes only a portion of the first mask that is contiguous with fewer than all sides of the section.  
   
   
       14 . The method of  claim 8  wherein forming the second mask comprises forming the second mask such that the second mask exposes a section that is smaller than the entire region of the material and exposes only a portion of the first mask that is contiguous with a single side of the section.  
   
   
       15 . The method of  claim 8  wherein forming the trench comprises anisotropically etching the exposed section of the material.  
   
   
       16 . The method of  claim 8  wherein forming the trench comprises plasma etching the exposed section of the material.  
   
   
       17 . The method of  claim 8  wherein forming the second mask comprises forming the second mask from a non-metallic material.  
   
   
       18 . A structure, comprising: 
 an optical path having a surface and through which an optical signal can propagate; and    a trench disposed in the path, having a first side wall that is substantially perpendicular to the surface, and having a bottom that is substantially flat and substantially parallel to the surface.    
   
   
       19 . The structure of  claim 18  wherein the trench further comprises a second side wall that is substantially perpendicular to the surface of the optical path.  
   
   
       20 . The processor of  claim 18  wherein the trench further comprises a second side wall that forms an angle other than 90° with the surface of the optical path.  
   
   
       21 . The structure of  claim 18  wherein the trench further comprises a second side wall that is substantially perpendicular to the surface of the optical path and that is substantially parallel to the first side wall.  
   
   
       22 . The structure of  claim 18  wherein the optical path comprises: 
 a first optical layer having a first index of refraction;    a second optical layer disposed on the first optical layer and having a second index of refraction; and    a third optical layer disposed on the second optical layer, having a third index of refraction, and having a surface that forms the surface of optical path.    
   
   
       23 . The structure of  claim 22  wherein the first index of refraction substantially equals the third index of refraction.  
   
   
       24 . The structure of  claim 22  wherein: 
 the first index of refraction substantially equals the third index of refraction; and    the second index of refraction is greater than the first and third indices of refraction.    
   
   
       25 . The structure of  claim 22  wherein the trench is disposed at an end of the optical path.  
   
   
       26 . An integrated circuit, comprising: 
 an optical path having a surface and through which an optical signal can propagate; and    a trench disposed in the path, having a first side wall that is substantially perpendicular to the surface, and having a bottom that is substantially flat and substantially parallel to the surface.    
   
   
       27 . An electronic system, comprising: 
 an integrated circuit having, 
 an optical path having a surface and through which an optical signal can propagate, and  
 a trench disposed in the path, having a first side wall that is substantially perpendicular to the surface, and having a bottom that is substantially flat and substantially parallel to the surface.