Trench profile angle beveling

Abstract

A trench bevel etch process is developed as a method to produce trench profiles with a prerequired angle. This process depends on both surface reaction and gas conductance along the trench. To study the surface reaction probability, activation energies were measured for SF6 and CF4 chemistries and were found to be 6 and 140meV, respectively. It has been demonstrated that CF4 etch chemistry is in surface-reaction-rate-limited regime and contributes little to the trench beveling. SF6 chemistry with its low activation energy is in reactant-transport-rate-limited regime and contributes significantly to the bevel process. The dependences of bevel etch on trench aspect ratio was also investigated in detail. It has been found that high aspect ratio trench produces larger bevel angle than that does for small aspect ratio. A phenomenological model was constructed by introducing reactant conduction loss L and sidewall reaction loss S to quantitatively describe the effects of both reactant transport and surface reaction. Through comparison of theoretical modeling and experiment, an S value between 0.8 and 1 is reached to explain the experimental results from SF6 chemistry. This result demonstrates the SF6 is a spontaneous surface reaction and is consistent with our activation energy measurement.