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.

Description

FIELD OF THE INVENTION[0001]In chemical mechanical planarization, one area that can potentially impact inter-layer dielectric removal rates is the coefficient of friction associated with the pad, wafer, and slurry abrasive particles. To understand the dominant tribological mechanism present when polishing interlayer dielectrics, Stribeck curves are presented using a dimensionless grouping of CMP specific parameters, called the Sommerfeld number.So=μU / pδeff where μ is the slurry viscosity, U is the relative pad-wafer velocity, p is the applied wafer pressure, and δeff is the effective fluid thickness. Determination of μ and U are fairly straightforward as can be measured experimentally for a given slurry and U depends upon tool geometry and the relative angular velocity of the platen and wafer.[0002]Wafer pressure is the applied downforce divided by the contact area between the wafer and the pad. Each pad type consist of a different surface area due to different grooving configuratio...

AI Technical Summary

Benefits of technology

[0025]The number of measurements taken using the method of the present invention during a single CMP polishing procedure is not limited. However, a number of between 3 and 15 is preferred and between 5 and 10 is more preferred. If the number is too large, the time period for measurement between changes becomes too short and since force and COF measurements tend to show a short period of adjustment of a second or less, it is desirable to have a long enough test period to yield reliable data. A time period that is too long is wasteful in that the advantage of the present invention is to allow multiple measurements of the same system under the same conditions except for pressure and relative velocity and a long period means fewer runs. The length of the period for each measurement may be the same or may vary, but equal periods of measurement for each set of process conditions is preferred. Time periods of between 5 and 70 seconds are preferred and between 10 and 40 seconds are more preferred. Measurement of shear and down forces itself may be done at high frequency for example, cases, above 500 hz. And more preferably 1000 Hz or

[0026]Sequences of changes in measurements are not particularly limited. Measurements may proceed by ascending or descending value of either relative velocity or pressure with the other variable maintained constant, or they may both be increased or decreased at the same time. One may be increased and the other decreased at the same time or one may be increased or decreased while the other is kept constant and then the other increased or decreased while the former is kept constant. The change may also be entirely random. Specific measurement conditions may also be repeated within a single CMP polishing procedure as a way of verifying whether there is any difference at one point in a CMP polishing procedure as compared with another point later on.

[0027]The minimum difference in pressure conditions between measurements is not particularly limited but variations of greater than ¼th psi are preferred. The minimum difference in relative velocity conditions between measurements is not particularly limited but differences greater than 0.2 meters per second are preferred.EXAMPLES

Problems solved by technology

However, change in load and consequently changes of pressure in the apparatuses and methods of the prior art could only be accomplished by stopping the CMP polishing process and manually changing the load on the wafer or the apparatus and there was no means by which to directly measure the normal force which then had to be estimated.

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