Infrared sensor design using an epoxy film as an infrared absorption layer

Abstract

A MEMS IR sensor, with a cavity in a substrate underlapping an overlying layer and a temperature sensing component disposed in the overlying layer over the cavity, may be formed by forming an IR-absorbing sealing layer on the overlying layer so as to cover access holes to the cavity. The sealing layer is may include a photosensitive material, and the sealing layer may be patterned using a photolithographic process to form an IR-absorbing seal. Alternately, the sealing layer may be patterned using a mask and etch process to form the IR-absorbing seal.

What is claimed is: 
     
         1 . A process of forming a MEMS IR sensor, comprising the steps of:
 providing a substrate;   forming an overlying dielectric layer over said substrate;   forming a temperature sensing component in said overlying dielectric layer;   forming access holes through said overlying dielectric layer proximate to said temperature sensing component;   forming a cavity in said substrate below said access holes by removing material from said substrate through said access holes;   forming an IR-absorbing sealing layer over said overlying dielectric layer so as to cover said access holes, said IR-absorbing sealing layer including an adhesive material, an IR absorbing material and a photosensitive material; and   performing a photolithographic operation which exposes a portion of said IR-absorbing sealing layer with ultraviolet light in an area defined for an IR-absorbing seal;   performing a develop operation which provides a developer fluid to said IR-absorbing sealing layer so that said developer fluid dissolves unexposed material in said IR-absorbing sealing layer so as to leave said IR-absorbing seal, said IR-absorbing seal absorbing at least 50 percent of infrared energy incident on said IR-absorbing seal in a wavelength band of 8 to 10 microns.   
     
     
         2 . The process  claim 1 , in which said step of forming said IR-absorbing sealing layer includes the steps of:
 providing said IR-absorbing sealing layer as a laminate between sheets of release film;   removing a first release film of said sheets of release film from a bottom surface of said IR-absorbing sealing layer;   applying said IR-absorbing sealing layer to said overlying dielectric layer so that said bottom surface of said IR-absorbing sealing layer adheres to said overlying dielectric layer; and   removing a second release film of said sheets of release film from a top surface of said IR-absorbing sealing layer.   
     
     
         3 . The process  claim 2 , in which said IR-absorbing seal has a homogenous structure, in which an adhesive material and an IR absorbing material are substantially uniformly distributed in the IR-absorbing seal. 
     
     
         4 . The process  claim 3 , in which said adhesive material and said IR absorbing material are a same epoxy material. 
     
     
         5 . The process  claim 3 , in which said IR-absorbing seal is 10 to 20 microns thick. 
     
     
         6 . The process  claim 1 , further including forming a plated I/O bump by a process including the steps of:
 forming an I/O opening in said overlying dielectric layer so as to expose an I/O pad disposed in said overlying dielectric layer;   forming a metal seed layer over said MEMS IR sensor by a sputtering process, said metal seed layer making electrical connection to said I/O pad through said I/O opening;   forming a plating mask over said metal seed layer so as to expose said seed layer in the I/O opening;   forming a plated copper bump on said metal seed layer by an electroplating operation;   forming a plated metal cap layer on said plated copper bump by an electroplating operation;   performing a plating mask strip operation which removes said plating mask from said MEMS IR sensor, such that said access holes remain covered by said IR-absorbing seal during said plating mask strip operation; and   performing a seed layer strip operation which removes said metal seed layer from said MEMS IR sensor outside of said plated I/O bump so as to leave a bump seed layer under said plated copper bump, such that said access holes remain covered by said IR-absorbing seal during said seed layer strip operation.   
     
     
         7 . The process  claim 1 , in which said temperature sensing component includes Seebeck junctions. 
     
     
         8 . The process  claim 1 , in which said substrate is silicon. 
     
     
         9 . A process of forming a MEMS IR sensor, comprising the steps of:
 providing a substrate;   forming an overlying dielectric layer over said substrate;   forming a temperature sensing component in said overlying dielectric layer;   forming access holes through said overlying dielectric layer proximate to said temperature sensing component;   forming a cavity in said substrate below said access holes by removing material from said substrate through said access holes;   forming an IR-absorbing sealing layer over said overlying dielectric layer so as to cover said access holes, said IR-absorbing sealing layer including an adhesive material and an IR absorbing material;   forming a seal etch mask over said IR-absorbing sealing layer so as to cover an area defined for an IR-absorbing seal;   performing a seal etch process which removes material from said IR-absorbing sealing layer exposed by said seal etch mask so as to form said IR-absorbing seal, said IR-absorbing seal absorbs at least 50 percent of infrared energy incident on said IR-absorbing seal in a wavelength band of 8 to 10 microns; and   performing a seal mask strip process which removes said seal etch mask from said MEMS IR sensor, such that said IR-absorbing seal continues to cover said access holes.   
     
     
         10 . The process  claim 9 , further including forming a plated I/O bump by a process including the steps of:
 forming an I/O opening in said overlying dielectric layer so as to expose an I/O pad disposed in said overlying dielectric layer;   forming a metal seed layer over said MEMS IR sensor by a sputtering process, said metal seed layer making electrical connection to said I/O pad through said I/O opening;   forming a plating mask over said metal seed layer so as to expose said seed layer in the I/O opening;   forming a plated copper bump on said metal seed layer by an electroplating operation;   forming a plated metal cap layer on said plated copper bump by an electroplating operation;   performing a plating mask strip operation which removes said plating mask from said MEMS IR sensor, such that said access holes remain covered by said IR-absorbing seal during said plating mask strip operation; and   performing a seed layer strip operation which removes said metal seed layer from said MEMS IR sensor outside of said plated I/O bump so as to leave a bump seed layer under said plated copper bump, such that said access holes remain covered by said IR-absorbing seal during said seed layer strip operation.   
     
     
         11 . The process  claim 9 , in which said temperature sensing component includes Seebeck junctions. 
     
     
         12 . The process  claim 9 , in which said substrate is silicon.