The effect of the slurry thickness on the chemical mechanical polishing (CMP) of the silicon oxide thin films was investigated. During CMP, the slurry thickness between the wafer to be polished and the pad was measured from the sheet resistance by a 4-point probe embedded on the pad. By increasing the slurry thickness at a constant download, the friction force continuously decreased due to the reduction of the effective contact area between the wafer and the pad. However, the polishing rate of the silicon oxide film increased at first stage with the slurry thickness, reaching a maximum value and then decreased. The critical slurry thickness, at which the polishing rate shows a peak, was not found to vary with the download. These results show that the limiting steps that govern the polishing rate of the silicon oxide can be divided into two distinct regions at the critical slurry film thickness. One is the chemical reaction rate limited region at the thinner slurry film than the critical thickness and the other is the mechanical polishing rate limited region at the thicker slurry film. In order to obtain high selectivity and a smooth surface after the polishing of stacked films, CMP should be performed with a slurry layer that is thicker than the critical slurry film thickness. These results should be valuable when considering the process of a STI (Shallow Trench Isolation) for device isolation. In addition, we have investigated a process monitoring of CMP by in-situ measuring the friction force. The monitor enabled us to accurately detect the polishing end point in the polishing of stacked films
Slurry thickness를 독립변수로 조절할 수 있는 연마 장치를 사용하여, slurry thickness가 oxide CMP에 미치는 영향을 조사하였다. 먼저, 패드에 장착된 4-point probe를 이용하여 웨이퍼와 패드사이에 형성되는 slurry thickness를 실시간으로 측정하였다. Download, 상대속도, slurry의 pH와 abrasive 농도를 변화시키면서 slurry thickness에 따른 마찰력을 측정하여, slurry thickness에 따른 패드asperity와 웨이퍼 간의 effective contact area의 수학적인 관계를 조사하였다. Oxide의 연마속도 결정단계는 slurry thickness에 따라 표면화학반응속도영역과 기계연마속도영역으로 구분되었다. Critical thickness보다 얇은 slurry film인 경우, 연마속도는 slurry와 웨이퍼 간의 화학반응속도에 의해 결정되며, 연마속도와 마찰력은 반비례한다. Critical thickness보다 두꺼운 경우 연마속도는 웨이퍼와 abrasive간의 기계연마속도에 의해 결정되며, 연마속도와 마찰력은 비례한다. 적층구조에서 높은 선택비와 연마 후 매끈한 표면를 얻기 위해서는 critical thickness보다 두꺼운 slurry film을 형성시킬 수 있는 공정조건에서 CMP를 수행하여야 한다. 이러한 결과는 소자분리 공정으로 STI를 고려한다면 효과적이다. 또한, 실시간 마찰력 측정법을 공정 모니터링에 적용하여 신뢰할만한 결과를 얻을 수 있었다.
