Correlation between conductivity and ph measurements for koh texturing solutions and additives

Abstract

The variability of an etchant concentration in an immersion processes for treatment of semiconductor devices can be significantly lowered by continuously measuring the conductivity of an etchant solution and comparing against predetermined thresholds. The etchant concentration can be maintained by a feed and bleed process based on conductivity measurements of the etchant solution and the conductivity measurements being correlated with premeasured pH values of an etchant solution.

What is claimed is: 
     
         1 . A system for etching at least one substrate comprising:
 a closed-loop circulation system having a process chamber and a recirculation line fluidly coupled to the process chamber, the closed-loop circulation system configured to circulate a circulation volume of an etchant solution;   means for bleeding contaminated etchant solution from the circulation volume of the etchant solution;   means for adding fresh etchant solution to the circulation volume of the etchant solution;   a conductivity sensor operably coupled to the closed-loop circulation system and configured to repetitively measure conductivity of the circulation volume of the etchant solution; and   a controller configured so that upon detecting that the circulation volume of the etchant solution has an average measured conductivity over a predetermined period of time that is at or below a lower threshold of conductivity, the controller automatically: (1) activates the means for the bleeding contaminated etchant solution to bleed a volume of the contaminated etchant solution from the circulation volume of the etchant solution; and (2) activates the means for adding fresh etchant solution to add fresh etchant solution to the circulation volume of the etchant solution to increase the conductivity of the circulation volume of the etchant solution to a value that is greater than the lower threshold of conductivity but less than or equal to an upper threshold of conductivity.   
     
     
         2 . The system of  claim 1 , further comprising a temperature sensor operably coupled to the closed-loop circulation system and configured to repetitively measure temperature of the circulation volume of the etchant solution. 
     
     
         3 . The system of  claim 2 , wherein the temperature of the etchant solution is between 25° C. to 90° C. 
     
     
         4 . The system of  claim 1 , further comprising a heater operably coupled to the closed-loop circulation system and configured to heat the circulation volume of the etchant solution. 
     
     
         5 . The system of  claim 4 , wherein the heater is operably coupled to the controller. 
     
     
         6 . The system of  claim 1 , further comprising a pH sensor operably coupled to the closed-loop circulation system and configured to repetitively measure pH of the circulation volume of the etchant solution. 
     
     
         7 . The system of  claim 1 , wherein the etchant solution comprises etchant at a concentration from 0.5 wt. % to 20 wt. % based on the total weight of the etchant solution. 
     
     
         8 . The system of  claim 7 , wherein the etchant solution comprises an etchant selected from the group consisting of KOH, NaOH, TMAH, HF, HNO 3 , and combinations thereof. 
     
     
         9 . The system of  claim 8 , wherein etchant solution further comprises one or more of deionized water, additives, isopropyl alcohol, and organic surfactants. 
     
     
         10 . The system of  claim 1 , wherein the repetitively measured conductivity of the circulation volume of the etchant solution is utilized to determine the average measured conductivity. 
     
     
         11 . The system of  claim 1 , wherein the etchant solution is maintained at a substantially constant temperature; and wherein the upper and lower thresholds of conductivity are based, at least in part, on the substantially constant temperature. 
     
     
         12 . The system of  claim 1 , further comprising a means for adding a second etchant solution. 
     
     
         13 . The system of  claim 12 , wherein the means for adding a second etchant solution comprises a valve. 
     
     
         14 . The system of  claim 1 , wherein the controller is operatively coupled to a bleed valve. 
     
     
         15 . The system of  claim 1 , wherein the conductivity sensor is coupled to the controller. 
     
     
         16 . The system of  claim 1 , wherein the controller  50  can store a predetermined conductivity value that has an assigned relationship to the corresponding pH value and etchant concentration. 
     
     
         17 . The system of  claim 1 , wherein the lower threshold of conductivity may be a predetermined value that is stored or calculated by the controller. 
     
     
         18 . The system of  claim 1 , wherein the substrate comprises silicon. 
     
     
         19 . The system of  claim 18 , wherein the substrate comprises silicon dioxide or silicon nitride. 
     
     
         20 . The system of  claim 1 , wherein system further comprises a means for immersing the substrate in etchant solution.