Tantalum Nitride Metal Film Dry Etching

TaN thin film has been widely applied in microelectronic process. It is used as barrier layer in Cu interconnect application in standard CMOS BEOL processes. Owing to its good compatibility with high-k materials, TaN is being studied as a substitute for metal gate material in sub 45nm CMOS processes. Further more, it can be used as absorber material in EUV lithography. And in recent application, it has been demonstrated that TaN thin film can be used as conductor material for MEMS micro bridge structure. But reports on TaN etching in MEMS application can seldom be found today.In this thesis, we will discuss about TaN dry etching process development applied in uncooled infrared bolometer arrays product. Amorphous silicon is chosen as the thermal sensitive material. Because of its high thermal-coefficient of resistance, the resistance will vary visibly while exposing to the infrared ray and the variance ratio of each cell will be transferred into image signal by the read-out ICs on the substrate. The electrode material which transfers the signals for such products must have good thermal reliability and low thermal-coefficient of resistance. TaN provides an ideal option for its properties meet both of the requirements.Being the electrode material, TaN is deposited onto the substrate after the etching of amorphous silicon and it defines the form of the resistors. Thus the etching of TaN is a critical step during the product development, which requires good control of the topography of sidewall and loss of the substrate as well. In this paper, we will talk about the TaN thin film etching development based Centura platform and with CHF3/CF4 to be the etching gas. The effects of such characteristics like radio-frequency power, pressure of the process chamber and gas flow are evaluated. The optimized recipe has good control of Si and SiO2 loss of the substrate. The residue was a serious issue during the development and has been overcome by optimization of the ash process. We created a model for the forming of residues and achieved good result after adding a CF4 treatment step into the tow-step ash processing. The effectivities of the recipes are demonstrated by e-test results of full-flow wafers. The effect of substrate's situation is also discussed. The optimized recipes are successfully implemented in the products finally.