Paper PS2-TuA5
Frequency and Pressure Effects in Plasma Etching of High Aspect Ratio Features in Dielectric Films

Tuesday, October 16, 2007, 3:00 pm, Room 607

Microelectronics processing requires etching of many different dielectric films and structures. Among these applications, some of the most challenging are the etching of high aspect ratio contacts and memory cells. Dual-frequency capacitively-coupled discharges at high power are widely used for these applications. Typically a lower excitation frequency provides the capability for high energy ion bombardment while a higher frequency allows decoupled control of plasma density. This paper examines the effect of applying three different excitation frequencies at the wafer electrode to access this process regime, using a mechanically confined plasma in a narrow-gap etch reactor. The effects of process pressure and 27MHz vs 60MHz, in combination with 2MHz, were characterized by plasma diagnostic measurements of ion flux and radical densities. Dense arrays of high aspect ratio holes were etched to measure the feature-level influence of these process control parameters. Results indicate that the combination of 60MHz and lower pressure allows operation at higher ion:radical flux ratios, which may help to prevent early etch stop. Additionally the radical chemistry is controlled by the ratio of 27MHz to 60MHZ power. Therefore the combined use of three frequencies improves the tuning of feature profiles and the control of striations.