Notch-free etching of high aspect SOI structures using alternating deposition and etching and pulsed plasma
View Patent ↗A method of preventing notching during a cyclical etching and deposition of a substrate with an inductively coupled plasma source is provided by the present invention. In accordance with the method, the inductively coupled plasma source is pulsed to prevent charge build up on the substrate. The off state of the inductively coupled plasma source is selected to be long enough that charge bleed off can occur, but not so long that reduced etch rates result due to a low duty cycle. The pulsing may be controlled such that it only occurs when the substrate is etched such that an insulating layer is exposed. A bias voltage may also be provided to the insulating layer and the bias voltage may be pulsed in phase or out of phase with the pulsing of the inductively coupled plasma source.
1. A method for etching a feature in a substrate comprising the steps of:
placing the substrate in a vacuum chamber;
introducing at least one process gas into the vacuum chamber;
generating a high density plasma using a high density plasma source;
subjecting the substrate to a cyclic process having an etching step and a deposition step;
applying a bias voltage in at least one step of the cyclic process to the substrate;
pulsing the high density plasma source in at least one step of the cyclic process; thereby reducing notching on the substrate; and
removing the substrate from the vacuum chamber.
2. The method of claim 1 wherein the bias voltage is D.C.
3. The method of claim 1 wherein the bias voltage is RF.
4. The method of claim 3 wherein the RF bias voltage frequency is less than about 500 kHz.
5. The method of claim 1 wherein the bias voltage is pulsed.
6. The method of claim 5 wherein the RF bias is pulsed in-phase with the pulsing of the high density plasma source.
7. The method of claim 5 wherein the RF bias is pulsed out of phase with the pulsing of the high density plasma source.
8. The method of claim 1 wherein the high density plasma source is an inductively coupled plasma source.
9. The method of claim 1 wherein the high density plasma source is pulsed during the etch step.
10. The method of claim 9 wherein the high density plasma source has a pulse duration of less than the time required for substrate charge to reach steady state.
11. The method of claim 1 wherein the pulsed high density plasma source has a pulse period of less than about 5 ms.
12. The method of claim 1 wherein the pulsed high density plasma source has a pulse period of about 200 μs.
13. The method of claim 1 wherein the pulsed high density plasma source has a duty cycle of less than about 50%.
14. The method of claim 1 wherein the pulsed high density plasma source has a duty cycle of about 10%.
15. The method of claim 1 wherein the substrate contains an insulating layer.
16. The method of claim 15 wherein the high density plasma source is pulsed when said insulating layer is exposed.