Correlating Coefficient of Friction and Shear Force to Platen Motor Current in Tungsten and Interlayer Dielectric Chemical Mechanical Planarization at Steady-State Conditions

Abstract

Following up our earlier work that highlighted the relationship between shear force (SF) and platen motor current (PMC), in parallel with the relationship between coefficient of friction (COF) and PMC for various tungsten and interlayer dielectric (ILD) chemical mechanical planarization (CMP) cases at non-steady-state conditions, we explored whether or not PMC could be used as a reliable indicator instead of SF and COF at steady-state conditions. For the 12 cases studied, 72 distinct steps were analyzed. It was determined that PMC somewhat mirrored SF and PMC for long time (i.e. 10 s or longer) intervals after data averaging and applying a trend matching algorithm. SF and PMC trends matched only about 64% of the time (ranges between 45% to 85%) for all 72 steps, while PMC and COF trends matched 62% of the time ranging between 42% and 85%. PMC-SF and PMC-COF correlations were fairly poor at 1-sec time intervals as evidenced by much lower percent match values. Such poor correlations proved that at small time intervals, PMC was not sensitive enough to capture important information regarding myriad fluid dynamics and tribological phenomena and the instantaneous stick-slip occurrences encountered in CMP.

Real-Time Prediction of Removal Rate and Friction Coefficient During Chemical Mechanical Polishing Using Motor Load Currents with a Polisher

“…However, there is a strong correlation between the friction coefficient and the removal rate, which is similar to the results of previous reports. 18,19,32,33 Multiple regression analysis 34 was conducted using the platen load current (C p ) and head load current (C h ) as explanatory variables, and the removal rate (R R ) and friction coefficient (F c ) as objective variables. In both cases, the platen load current and head load current satisfied the significance level, and Eqs.…”

“…The relationship between the friction coefficient and the platen load current for various substrates has been discussed in references 18 and. 19 The percent match between the experimental and predicted values with the friction coefficient using platen load currents was also evaluated. A match of 64.0% was realized for values ranging from 44.7 to 85.2.…”

“…[11][12][13][14] The majority of the process is automated, and most polishers for semiconductor devices are equipped with a variety of sensors, including a film thickness meter, to enable various realtime measurements while polishing. 15,16 In particular, endpoint methodologies for adjusting film thickness play a key role in semiconductor CMP, and endpoint methodologies using optical, 17 platen load current (torque sensor), [18][19][20] and piezo electronic sensor 21 methods are commonly employed.…”

“…26 Other studies have considered the singlecorrelation between the friction coefficient and platen load current associated with the CMP of copper, cobalt, and STI (shallow trench isolation) 18 and CMP of tungsten and interlayer dielectrics. 19 In double-sided polishing, motors are often installed for the lower and upper platens, and in single-sided polishing (Fig. 1), motors are often installed for the platen and substrate.…”

“…Therefore, the real-time prediction of the removal rate and friction coefficient between the pad and substrate using only the information from these motors would be effective for process monitoring and automation methods associated with mass production. In particular, focusing on multiple load currents of the motor, rather than just the platen load current, 18,19 may enable highly accurate prediction or clarification of the relationship between these parameters.…”