Method of forming shallow trench isolation structure

Abstract

A method for forming a shallow trench isolation (STI) structure with a predetermined target height is provided. A substrate having a pad oxide layer formed on the substrate is provided. A nitride-containing layer with a thickness is formed on the pad oxide. A STI structure is formed and extends through the nitride-containing layer, the pad oxide layer, into the substrate. The thickness of the nitride-containing layer is measured to calculate the height of STI structure according to a correlation between the thickness of the nitride-containing layer and the height of STI structure. A thickness of the top portion STI structure to be removed is determined according to the difference between the height of the STI structure and the predetermined target height and is removed in a first etching process. The nitride-containing layer is removed without etching the STI structure or the pad oxide layer in a second etching process.

1 . A method of forming a shallow trench isolation structure with a target height above a pad oxide layer on a substrate, the method comprising:
 forming a nitride-containing layer on a top surface of the pad oxide layer, the nitride-containing layer having a thickness;   forming a shallow trench isolation (STI) structure extending through the nitride-containing layer, the pad oxide layer, and into the substrate, wherein the STI structure has a top surface and a height above the top surface of the pad oxide layer;   establishing a correlation between the thickness of the nitride-containing layer and the height of the STI structure;   measuring the thickness of the nitride-containing layer to calculate the height of the STI structure according to the correlation;   determining a thickness of the STI structure to be removed according to a difference between the height of the STI and a predetermined target height of the STI structure above the top surface of the pad oxide;   selectively removing the thickness of the STI structure in a first etch process, and   selectively removing the nitride-containing layer without substantially etching the STI structure or the pad oxide layer in a second etch process, whereby the resulting STI structure has the predetermined target height.   
     
     
         2 . The method of  claim 1 , wherein said establishing comprises polishing the STI structure to the nitride-containing layer until the top surfaces of the nitride-containing layer and the STI structure are substantially coplanar. 
     
     
         3 . The method of  claim 1 , wherein said establishing comprises polishing the STI structure to the nitride-containing layer, while leaving a step height difference between the top surfaces of the nitride-containing layer and the STI structure. 
     
     
         4 . The method of  claim 3 , further comprising:
 measuring the step height difference between top surfaces of the nitride-containing layer and the STI structure to calculate the height of the STI structure according to the correlation.   
     
     
         5 . The method of  claim 1 , wherein said forming the STI structure comprises:
 etching a trench extending through the nitride-containing layer, the pad oxide layer, and into the substrate; and   depositing an isolation oxide layer to overfill the trench.   
     
     
         6 . The method of  claim 1 , wherein the first etch process comprises dipping the substrate in a HF solution. 
     
     
         7 . The method of  claim 1 , wherein the second etch process comprises dipping the substrate in a phosphoric acid solution. 
     
     
         8 . The method of  claim 7 , further comprising:
 controlling a silicon concentration in the phosphoric acid solution within a range of about 57 to 110 parts per million (ppm).   
     
     
         9 . The method of  claim 7 , further comprising:
 controlling a silicon concentration in the phosphoric acid solution to be under an aggregate silicon concentration, whereby the STI structure is not removed.   
     
     
         10 . The method of  claim 7 , further comprising:
 during said dipping, maintaining the phosphoric acid solution at a predetermined temperature.   
     
     
         11 . A method of forming a shallow trench isolation structure with a target height above a pad oxide layer on a substrate, the method comprising:
 forming a nitride-containing layer on the pad oxide layer, wherein the nitride-containing layer has a thickness;   forming a shallow trench isolation (STI) structure extending through the nitride-containing layer, the pad oxide layer and into the substrate, wherein top surfaces of the STI structure and the nitride-containing layer are substantially coplanar;   measuring the thickness of the nitride-containing layer to determine a height of the STI structure above the pad oxide;   calculating an etching time to selectively etch a thickness of the STI structure in a HF solution, wherein the thickness of the STI structure is a difference between the determined height of the STI structure and a predetermined target height of the STI structure above the pad oxide;   selectively etching the thickness of the STI structure in the HF solution for the etching time; and   thereafter selectively etching the nitride-containing layer with a phosphoric acid solution without removing the STI structure, whereby the resulting STI structure has the predetermined target height.   
     
     
         12 . The method of  claim 11 , wherein said forming the STI structure comprises:
 etching a trench extending through the nitride-containing layer, the pad oxide, and into the substrate;   depositing an isolation oxide layer to overfill the trench; and   polishing the overfilled isolation oxide layer to be substantially coplanar to the nitride-containing layer.   
     
     
         13 . The method of  claim 11 , wherein said selectively etching the nitride-containing layer with the phosphoric acid solution comprises:
 controlling a silicon concentration in the phosphoric acid solution to be under an aggregate silicon concentration, whereby the STI structure is not removed.   
     
     
         14 . The method of  claim 11 , wherein said selectively etching the nitride-containing layer with the phosphoric acid solution comprises:
 controlling a silicon concentration in the phosphoric acid solution within a range of about 57 to 110 parts per million (ppm).   
     
     
         15 . A method of forming a shallow trench isolation structure with a predetermined target height above a pad oxide layer on each of a plurality of substrates in a processing lot, the method comprising:
 forming a nitride-containing layer on the pad oxide layer on each substrate, wherein the nitride-containing layer has a thickness;   forming a shallow trench isolation (STI) structure on each substrate to extend through the nitride-containing layer, the pad oxide layer and into the substrate, wherein a top surface of the STI structure and a top surface of the nitride-containing layer on each substrate are substantially coplanar;   measuring the thickness of the nitride-containing layer on at least one substrate in the processing lot to determine a height of the STI structure above the pad oxide on said at least one substrate;   calculating an etching time based on the measured thickness of the nitride-containing layer to selectively etch a thickness of the STI structure on each substrate in a first wet solution, wherein the thickness of the STI structure is a difference between the determined height and a predetermined target height of the STI structure above the pad oxide;   dipping the processing lot in the first wet solution to selectively etch the thickness of the STI structure for each substrate for the etching time; and   dipping the processing lot in a second wet solution to selectively etch the nitride-containing layer for each substrate without etching the STI structure or the pad oxide, whereby the resulting STI structure for each substrate is adjusted to the predetermined target height.   
     
     
         16 . The method of  claim 15 , wherein said forming the STI structure on each substrate comprises:
 etching a trench extending through the nitride-containing layer, the pad oxide, and into the substrate;   depositing an isolation oxide layer to overfill the trench; and   polishing the overfilled isolation oxide layer to be substantially coplanar with the nitride-containing layer.   
     
     
         17 . The method of  claim 15 , wherein the first wet solution comprises a HF solution 
     
     
         18 . The method of  claim 15 , wherein the second wet solution comprises a phosphoric acid solution. 
     
     
         19 . The method of  claim 18 , further comprising:
 controlling a silicon concentration in the phosphoric acid solution to be under an aggregate silicon concentration, whereby the STI structure is not removed.   
     
     
         20 . The method of  claim 18 , further comprising:
 maintaining a silicon concentration in the phosphoric acid solution within a range of about 57 to 110 parts per million (ppm).