Method of determining the lubrication mechanism in cmp

Abstract

The present invention is a method for obtaining data easily, accurately and effectively that may be used in determination of Sommerfeld Numbers and COF for CMP polishing. Using the Sommerfeld Numbers and COF values thus obtained the lubrication mechanism of CMP polishing with particular materials and under particular conditions can easily and reliably be studied. The method of the present invention is accomplished by use of CMP polishing tools capable of simultaneously measuring shear force and normal force, and rendering a value for the COF while simultaneously enabling the operator to change pressure on and relative velocity of the CMP wafer and CMP polishing pad in real time. Using the said CMP tool, the pressure and relative velocity may be varied separately or together for the desired length of time according to the needs of the operator so that within one CMP process multiple measurements may be taken under the same process conditions.

1 . A method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad wherein the CMP polishing tool is capable of measuring the said shear force and normal force simultaneously and continuously by force measurement means during CMP polishing and of allowing the alteration during CMP polishing of the pressure applied to the CMP wafer and CMP polishing pad contact surface, the relative velocity between the CMP wafer and the CMP polishing pad or both simultaneously in determinable amounts. 
     
     
         2 . The method determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the shear force and normal force data are used to determine the coefficient of friction of the surface of the CMP wafer and the surface of the CMP polishing pad. 
     
     
         3 . The method determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 2  wherein the COF figure for a given time interval during the CMP polishing process thus obtained is used together with data reflecting the pressure applied to the CMP wafer surface and the CMP polishing pad as well as the relative velocity of the CMP wafer surface and CMP polishing pad corresponding to the same interval are used to calculate and plot a Sommerfeld number and together with the corresponding COF value a Stribeck Curve for the system created by said CMP wafer and CMP polishing pad. 
     
     
         4 . The method determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the CMP polishing tool determines and reports the shear force between the wafer head and the polishing pad by means of a plate positioned above the wafer head and from which the wafer head and its supporting apparatus hang, or upon which they rest, said plate connected to the framework of the CMP polishing tool by low friction motion means capable of sliding in a direction perpendicular to the line between the center of the polishing pad and the center of the wafer head, and a load cell sensor firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine the force from the leading edge of said plate when the CMP polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals thus obtained reporting the shear force and additionally in which load cells are attached to and support the bottom of the module of the polishing pad of the CMP polishing tool to determine the normal force, and the normal force and shear force thus obtained may be used to calculate the coefficient of friction between the wafer head and the polishing pad. 
     
     
         5 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 4  wherein the pressure and relative velocity may be varied separately or together for the desired length of time. 
     
     
         6 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the CMP polishing tool determines two perpendicular force components of shear force and the resulting shear force by means of two plates positioned above the wafer head from which the wafer head and its supporting apparatus hang, or upon which they rest, one plate connected to the framework of said CMP polishing tool by low friction rails, the other said plate connected to the first plate by low friction rails allowing the other said plate to slide in a direction perpendicular to the motion of the first said plate, load cells sensor firmly fixed to the framework of the CMP polishing tool or other immovable structure and positioned to contact and determine force from the leading edge of said plate when the CMP polishing tool is in operation and the wafer head is in contact with the polishing pad, the signals of the load cell sensors thus obtained reporting the components of shear force, and in which load cell sensors are attached to and support the bottom of the CMP polishing pad module of the CMP polishing tool to determine the normal force, and the shear force and the normal force thus obtained are delivered to a data processing means to calculate the coefficient of friction. 
     
     
         7 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 6  wherein the pressure and relative velocity may be varied separately or together for at the beginning or end of a fixed time period. 
     
     
         8 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the said length of the said time period is between 5 seconds and 70 seconds. 
     
     
         9 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the length of the said time period is between 10 and 40 seconds. 
     
     
         10 . The method of determining the shear force and normal force between a CMP wafer and a CMP polishing pad at multiple applied pressures and relative velocities of the CMP wafer and the CMP polishing pad according to  claim 1  wherein the said time periods are equal.