Control of etch profiles during extended overetch

• US 5,759,922 A
• Filed: 01/10/1997
• Issued: 06/02/1998
• Est. Priority Date: 08/25/1993
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Donohoe, Kevin
• Primary Examiner(s): ANGEBRANNDT, MARTIN J
• Application Number:
  US08/781,472
• Time in Patent Office: 508 Days
• Field of Search: 156/643.1, 156/345 C, 156/659.1, 156/662.1, 156/655.1, 204/192.32, 204/192.35, 204/192.37, 204/298.01, 204/298.31, 438/731, 438/719, 438/730, 438/733
• US Class Current: 438/731
• CPC Class Codes: H01L 21/32137 of silicon-containing layers

Abstract

An etch process to substantially eliminate notching in sub-micron features by exposing a wafer to a chlorine plasma; operating the plasma under conditions which reduce the relative role of ions in the etch (as compared to neutrals in the etch); and essentially eliminating the magnetic field confinement in the transition zone of the etcher, i.e., the zone between the high density source and the wafer.

Claims

1. A method for etching a wafer having an exposed polysilicon layer over an oxide layer, the method comprising the steps of:

providing a high density plasma, Mori source etcher having a source plasma chamber, the source plasma chamber having an antenna and having an inductive plasma source;

generating a plasma in the source plasma chamber with the inductive plasma source, the plasma generation comprising applying top power in a range of 500 to 3000 watts and pressure in a range of 1 to 4 mtorr;

providing a transition zone without magnetic confinement configured to receive the plasma and to provide a plasma effluent, the plasma effluent having ions and neutrals;

passing the ions and the neutrals through the transition zone to decrease the ions to the neutrals ratio of the plasma effluent;

directing ions of the plasma effluent to the wafer with a radio frequency bias in operational proximity to the wafer; and

anisotropically etching the polysilicon layer without substantially etching the oxide layer to form a functional structure.

2. A method, as in claim 1, wherein the plasma effluent comprises chlorine ions and chlorine atoms.

3. A process of etching a wafer having an exposed polysilicon layer over an oxide layer, the polysilicon layer and the oxide layer forming a junction at an intersection thereof, the process comprising the steps of:

providing a high density plasma, Mori source etcher having a source plasma chamber and a transition zone chamber, the source plasma chamber having an antenna and having an inductive plasma source;

generating a plasma in the source plasma chamber with the inductive plasma source the plasma generation comprising applying a top power in a range of 500 to 3000 watts and pressure in a range of 1 to 4 mtorr;

providing the transition zone chamber without magnetic confinement configured to receive the plasma and to provide a plasma effluent, the plasma effluent having ions and neutrals;

passing the ions and the neutrals through the transition zone chamber to decrease the ions to the neutrals ratio of the plasma effluent;

etching the wafer with the plasma effluent;

the plasma effluent selective to etch the polysilicon layer and to substantially not etch the oxide layer; and

the plasma effluent during the etching step having an ion concentration to reactive neutral concentration characterized by a substantial elimination of notching of the polysilicon layer at the junction.

4. A process, as in claim 3, wherein the plasma effluent includes chlorine.

5. A process, as in claim 4, wherein the plasma effluent includes an inert gas.

6. A process, as in claim 4, wherein the plasma effluent does not include oxygen.

7. A process, as in claim 4, wherein the plasma effluent does not include bromine.

8. A process, as in claim 4, wherein the plasma effluent does not include fluorine.

9. A process, as in claim 4, wherein the oxide layer comprises silicon dioxide.

10. A process of etching a wafer having an exposed selected layer of material over a non-selected layer of material, the non-selected layer and the selected layer forming a junction at an intersection thereof, the process comprising the steps of:

delivering only a single element gas to an inductive plasma source chamber of a high density plasma, Mori source etcher;

generating a plasma effluent having ions and neutrals from the single element gas the plasma generation comprising applying a top power in a range of 500 to 3000 watts and pressure in a range of 1 to 4 mtorr;

passing the ions and the neutrals through a region without magnetic confinement to decrease the ions to the neutrals ratio of the plasma effluent;

distributing the plasma effluent to the wafer;

etching the wafer with the plasma effluent; and

the plasma effluent selective to etch the selected layer without substantially etching the non-selected layer, and during the etching, the plasma effluent having a ratio of ion concentration to reactive neutral concentration characterized by a substantial elimination of notching of the selected layer at the junction.

11. A process, as in claim 10, wherein the single element gas consists of chlorine.

12. A process of etching a wafer having a non-selected layer below a selected layer forming a junction at an intersection thereof, the process comprising the steps of:

delivering gas to an inductive plasma source chamber of a high density plasma, Mori source etcher;

generating a plasma in the gas to provide a plasma effluent having ions and neutrals, the plasma generation comprising applying a pressure in a range of 1 to 4 mtorr and a top power in a range of 500 to 3000 watts;

passing the plasma effluent through a region without magnetic confinement to decrease the ions to the neutrals ratio; and

etching the wafer with the plasma effluent, the plasma effluent having an ion concentration to reactive neutral concentration characterized by a substantial elimination of notching of the selected layer at the junction;

the plasma effluent selective for etching the selected layer and substantially not etching the non-selected layer.

13. A process, as in claim 12, further comprising the step of using chlorine gas to generate the plasma.

14. A process, as in claim 13, further comprising the step of employing an inert gas to provide the plasma effluent.

15. A process, as in claim 13, wherein the gas does not include oxygen.

16. A process, as in claim 13, wherein the gas does not include bromine.

17. A process, as in claim 13, wherein the gas does not include fluorine.

18. A process, as in claim 12, wherein the selected layer is made of polysilicon, and the non-selected layer is made of silicon dioxide.