Real-time temperature monitoring of wafer and focus ring during plasma processing

As the demand for high performance and smaller devices, semiconductor technology has advanced. For example, the size of memory devices has shrunk. To increase the density and storage per unit space, the cell pitch scale down less than 40 nm in DRAM or 3D NAND devices and High Aspect Ratio(HAR), 3D structure has developed. For making these complex structures, advanced technologies of etching and deposition in atomic layer scale are needed. One of the advanced technologies, cryogenic etching is widely studied to make the HAR structure. Furthermore, to achieve excellent process uniformity across the wafer, precise control of temperature, plasma and other techniques is essential.

However, the etching and deposition characteristics at the center of wafer are different from the edge of wafer due to the un-uniformity of plasma and wafer temperature. The temperature difference of wafer and chamber parts such as focus ring can affect the temperature uniformity at wafer edge.

In this study, the temperature of wafer and alumina focus ring was monitored in 6 inch Inductively Coupled Plasma(ICP) chamber in real-time. The temperature of focus ring was measured with Fiber Bragg Grating(FBG) sensor and wafer temperature was measured with fiber optic probe. The wafer temperature was adjusted -60℃ to 20℃ by using a cryogenic chiller. The pressure was fixed at 10 mTorr. The RF power condition, 300 W to 700 W, was applied with 13.56 MHz RF generator.