Surface-normal optical path length for infrared photodetection

Abstract

A SiGe surface-normal optical path photodetector structure and a method for forming the SiGe optical path normal structure are provided. The method comprises: forming a Si substrate with a surface; forming a Si feature, normal with respect to the Si substrate surface, such as a via, trench, or pillar; depositing SiGe overlying the Si normal feature to a thickness in the range of 5 to 1000 nanometers (nm); and, forming a SiGe optical path normal structure having an optical path length in the range of 0.1 to 10 microns. Typically, the SiGe has a Ge concentration in the range from 5 to 100%. The Ge concentration may be graded to increase with respect to the deposition thickness. For example, the SiGe may have a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.

1 . A method for forming a silicon-germanium (SiGe) optical path length, normal to a silicon (Si) substrate surface, for infrared (IR) photodetection, the method comprising: 
 forming a Si substrate with a surface;    forming a Si feature, normal with respect to the Si substrate surface;    depositing SiGe overlying the Si normal feature; and,    forming a SiGe optical path overlying the normal feature having an optical path length perpendicular to the substrate surface.    
   
   
       2 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a feature selected from the group including a via, trench, and pillar.  
   
   
       3 . The method of  claim 1  wherein depositing SiGe overlying the Si normal feature includes depositing SiGe to a thickness in the range of 5 to 1000 nanometers (nm).  
   
   
       4 . The method of  claim 1  wherein forming a SiGe optical path includes forming an optical path length in the range of 0.1 to 10 microns.  
   
   
       5 . The method of  claim 1  wherein depositing SiGe overlying the Si normal feature includes depositing SiGe with a Ge concentration in the range from 5 to 100%.  
   
   
       6 . The method of  claim 1  wherein depositing SiGe overlying the Si normal feature includes depositing SiGe with a graded Ge concentration that increases with respect to the deposition thickness.  
   
   
       7 . The method of  claim 6  wherein the SiGe has a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.  
   
   
       8 . The method of  claim 1  further comprising: 
 depositing a Si layer overlying the SiGe;    depositing SiGe overlying the Si layer; and,    wherein forming a SiGe optical path includes forming an optical path with a plurality of SiGe layers.    
   
   
       9 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a trench with a pair of sidewalls; 
 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe sidewalls overlying the trench sidewalls; and,    wherein forming a SiGe optical path normal structure includes forming an optical path pair-structure.    
   
   
       10 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a trench; 
 wherein depositing SiGe overlying the Si normal feature includes filling the trench with SiGe; and,    wherein forming a SiGe optical path includes forming an optical path uni-structure.    
   
   
       11 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a pillar with two pairs of sidewalls; 
 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe sidewalls overlying the two pairs of pillar sidewalls; and,    wherein forming a SiGe optical path includes forming an optical path array-structure adjacent the corresponding pillar sidewall pairs.    
   
   
       12 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a via with two pairs of sidewalls; 
 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe sidewalls overlying the two pairs of via sidewalls; and,    wherein forming a SiGe optical path includes forming an optical path array-structure adjacent the corresponding via sidewall pairs.    
   
   
       13 . The method of  claim 1  wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a via; 
 wherein depositing SiGe overlying the Si normal feature includes filling the via with SiGe; and,    wherein forming a SiGe optical path includes forming an optical path uni-structure.    
   
   
       14 . The method of  claim 1  further comprising: 
 forming an interlayer dielectric overlying the SiGe optical path; and,    forming a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path.    
   
   
       16 . A method for forming an infrared (IR) photodetector with a silicon-germanium (SiGe) optical path length, perpendicular to a silicon (Si) substrate surface, the method comprising: 
 forming a Si substrate with a surface;    forming an interconnect in electrical communication with a CMOS active region selected from the group including a source, drain, gate, and a diode region;    forming a Si feature, normal with respect to the Si substrate surface;    depositing SiGe overlying the Si normal feature; and,    forming a SiGe optical path with a path length perpendicular to the substrate surface and in electrical communication with the active region, through the interconnect.    
   
   
       16 . The method of claim  15  further comprising: 
 forming an interlayer dielectric overlying the SiGe optical path; and,    forming a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path.    
   
   
       17 - 20 . (canceled)  
   
   
       21 . A silicon-germanium (SiGe) optical path with a path length normal to a silicon (Si) substrate surface, for infrared (IR) photodetection, the structure comprising: 
 a Si substrate with a surface;    a Si feature, normal with respect to the Si substrate surface; and,    a SiGe optical path overlying the Si feature, having an optical path length perpendicular to the substrate surface.    
   
   
       22 . The structure of  claim 21  wherein the Si feature is selected from the group including a via, trench, and pillar.  
   
   
       23 . The structure of  claim 21  wherein the Si substrate surface is formed in a first plane; and, 
 wherein the SiGe optical path is formed in a second plane, normal to the first plane, with a thickness in the range of 5 to 1000 nanometers (nm).    
   
   
       24 . The structure of  claim 21  wherein the SiGe optical path has an optical path length in the range of 0.1 to 10 microns, in the second plane.  
   
   
       25 . The structure of  claim 21  wherein the SiGe optical path includes a Ge concentration in the range from 5 to 100%.  
   
   
       26 . The structure of  claim 21  wherein the SiGe optical path includes graded Ge concentration that increases with respect to the deposition thickness.  
   
   
       27 . The structure of  claim 26  wherein the SiGe optical path has a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.  
   
   
       28 . The structure of  claim 21  further comprising: 
 at least one Si layer overlying SiGe; and,    wherein the SiGe optical path includes a plurality of SiGe layers overlying Si.    
   
   
       29 . The structure of  claim 21  wherein the Si feature is a trench with a pair of sidewalls; and, 
 wherein SiGe optical path is an optical path pair-structure adjacent the trench sidewalls.    
   
   
       30 . The structure of  claim 21  wherein the Si feature is a trench; and, 
 wherein the SiGe optical path is an optical path uni-structure filling the trench.    
   
   
       31 . The structure of  claim 21 , wherein the Si feature is a pillar with two pairs of sidewalls; and, 
 wherein the SiGe optical path is an optical path array-structure adjacent the corresponding pillar sidewall pairs.    
   
   
       32 . The structure of  claim 21  wherein the Si normal feature is a via with two pairs of sidewalls; and, 
 wherein the SiGe optical path is an optical path array-structure adjacent the corresponding via sidewall pairs.    
   
   
       33 . The structure of  claim 21  wherein the Si normal feature is a via; and, 
 wherein the SiGe optical path is a optical path uni-structure filing the via.    
   
   
       34 . An infrared (IR) photodetector comprising: 
 a CMOS active region formed in a silicon (Si) substrate with a surface, the active region selected from the group including a transistor source, drain, gate, and a diode region;    an interconnect in electrical communication with the active region;    a Si feature, normal with respect to the Si substrate surface, and in electrical communication with the interconnect; and,    a SiGe optical path overlying the Si feature having an optical path length perpendicular to the substrate surface.    
   
   
       35 . The photodetector of  claim 34  further comprising: 
 an interlayer dielectric overlying the surface-normal SiGe optical path; and,    a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path.