Slurry Testing on  CETR Bench-Top CMP Machine

Instrumentation

The bench-top CMP machine with controlled polishing mod. CP-4 accommodates polishing pads (or their coupons) of 1” to 8”, slurry, conditioning discs of 0.25” to 4.25” and wafers (or their coupons) of 0.5” to 4”. It performs a CMP process with crucial micro-tribological parameters real-time monitored and processed at the total sampling rate of 20 kHz:
- normal loads and friction forces (torques) via CETR proprietary sensors, in-situ, 
- contact high-frequency acoustic noise via CETR proprietary sensors and amplifiers, in-situ,
- electrical surface and contact resistance, ex-situ.

This novel multi-sensing technology allows for in-situ monitoring of polishing processes on any wafer layers, which provides the means for effective slurry testing. 

Slurry Control
Typical raw data is presented below to illustrate differences between colloidal-silica and fumed-silica slurries.

For the quantitative process control, we utilize time of material removal from wafers. An example is presented below for tungsten slurries. Based on the end-user fab experience, three parameters were monitored for incoming inspection of slurries:
- maximum time of complete tungsten removal from the reference wafers,
- maximum time of complete under-layer removal from the reference wafers,
- minimum level of acoustic emission corresponding to the minimum intensity of polishing.
As observed, most of the batches of the slurry were good and fit all three criteria, while one batch (blue lines) was unacceptable due to both longer-than-critical time for material removal and lower-than-critical level of polish intensity.

Conclusion

The bench-top CMP Machine with Control Polish is an effective tool for development, optimization and quality control of polishing slurries and other consumables.