| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS-MoM |
| Session: | Advanced FEOL / Gate Etching I |
| Presenter: | Paul Bodart, CNRS-LTM, France |
| Authors: | P. Bodart, CNRS-LTM, France C. Petit-Etienne, CNRS-LTM, France G. Cunge, CNRS-LTM, France F. Boulard, CNRS-LTM, France M. Darnon, CNRS-LTM, France L. Vallier, CNRS-LTM, France E. Pargon, CNRS-LTM, France S. Banna, Applied Materials, Inc. T. Lill, Applied Materials, Inc. O. Joubert, CNRS-LTM, France |
| Correspondent: | Click to Email |
Plasma etching of high-k materials, including HfO2, has attracted much attention due to the necessity to integrate these materials in MOSFET transistor. After the metal gate patterning process, the high-k dielectric film must be removed from the source and drain regions of the transistor. It is today well established that HfO2 can be etched selectively towards SiO2 and Si in BCl3/Cl2 plasma. However, it remains difficult to minimize the plasma induced damages (Si amorphisation and recess) in the source/drain transistor regions in such processes. Since pulsed plasmas have shown a capability to minimize Si-recess in typical silicon gate oxide etching processes, we have investigated their potential for HfO2 etching.
The experiments are performed in a 300mm DPS tool from Applied Materials. The chamber is modified to allow plasma diagnostic like UV-broad band absorption spectroscopy. The reactor is also connected to an Angle-Resolved X Ray Photoelectron Spectroscopy analyzer by a robotized vacuum chamber. The etching rate of HfO2 sample (either 40 or 3.5nm-thick HfO2 films with 8 Å SiO2 interlayer deposited on Si substrates) and of SiO2 samples (10 nm thick) are measured in real time by in situ multi-wavelength ellipsométrie.
We have evaluated the capability of pulsed plasmas to minimize the plasma induced damage of silicon during the etching of HfO2 high-k gate dielectric. XPS analyses show that the perturbation of the bulk Si lattice is less pronounced with pulsed conditions, which is attributed to a lower ion bombarding energy. However, the formation of a BClx polymer selectively on the silicon (which is responsible for the HfO2 to Si etching selectivity) is reduced when the plasma is pulsed leading to a loss of selectivity. VUV absorption spectroscopy indicates that the fragmentation of BCl3 molecules, which leads to the formation of B-rich polymer precursors, decreases dramatically when the plasma is pulsed at low duty cycle. Therefore, as the duty cycle is reduced, the fluxes of B radicals to the wafer are reduced while the amount of Cl in the polymer increases. It follows that the polymer deposition rate drops, eventually leading to a loss of selectivity at the lowest duty cycles.
However, there are several ways to retrieve the process selectivity in pulsed plasma, such as reducing the BCl3 flow in the gas mixture or working at higher pulsing frequencies (up to 10 kHz) to enhance B formation in the gas phase. Pulsing the plasma is not a magic knob since it strongly changes the range of allows news physics and chemistry ranges plasma parameters.
However, plasma pulsing reduces significantly the plasma induced damages after process optimization.