Sidewall smoothing in high aspect ratio/deep etching using a discrete gas switching method

• US 6,924,235 B2
• Filed: 08/12/2003
• Issued: 08/02/2005
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Plasma-Therm Corporation
• Original Assignee: Unaxis USA Incorporated (Unaxis)
• Inventors: Johnson, David, Westerman, Russell, Lai, Shouliang
• Primary Examiner(s): Le, Thao P.
• Application Number:
  US10/640,469
• Publication Number:
  US 20040092118A1
• Time in Patent Office: 721 Days
• Field of Search: 438/689, 438/712
• US Class Current: 438/689
• CPC Class Codes: H01J 37/3244 Gas supply means
• CPC Class Codes: H01L 21/67017 Apparatus for fluid treatment H01L21/67126, H01L21/6715 take precedence
• CPC Class Codes: H01L 21/67069 for drying etching

Abstract

An improved method for introducing gases into an alternating plasma etching/deposition chamber is provided by the present invention. To minimize the introduction of pressure pulses into the alternating etching/deposition chamber when the deposition and etchant gas supplies are switched on and off, a mass flow controller is used to provide a relatively constant flow of gas. A gas bypass or a gas exhaust is provided such that when a gas inlet to the alternating etching/deposition chamber is closed an alternative path is provided for the flow of gas from the mass flow controller. The provision of a bypass or exhaust maintains the pressure of the gas received from the mass flow controller at a substantially constant level. The elimination or minimization of a pressure pulse of the gas helps increase the smoothness of the walls of high aspect ratio features etched in a silicon substrate in the alternating etching/deposition chamber.

Claims

1. An apparatus for improved gas switching, said apparatus comprising:

a plasma chamber;

at least one plasma source for producing a plasma within said plasma chamber;

a substrate holder positioned within said plasma chamber;

an exhaust in fluid communication with said plasma chamber;

an etchant gas supply having an associated gas inlet for providing an etchant gas to said plasma chamber and an associated gas bypass in fluid communication with said etchant gas supply and said exhaust of said plasma chamber for exhausting said etchant gas;

a deposition gas supply having an associated gas inlet for providing a deposition gas to said plasma chamber and an associated gas bypass in fluid communication with said deposition gas supply and said exhaust of said plasma chamber for exhausting said deposition gas; and

a gas control switch, said gas control switch controlling at least one of said etchant gas supply and said deposition gas supply such that said gas inlet and said gas bypass of said at least one gas supply are configured such that the respective gas flows bypass said plasma chamber directly to said exhaust of said plasma chamber when the respective gas inlet is closed.

2. A gas supply system for providing gas to an alternating deposition/etching chamber used to manufacture semiconductors, said gas supply system comprising:

a mass flow controller for providing a flow of gas;

an exhaust in fluid communication with said deposition/etching chamber;

a gas inlet in fluid communication with said mass flow controller, said gas inlet allowing the flow of gas into said deposition/etching chamber; and

a gas bypass in fluid communication with said mass flow controller and said exhaust, said gas bypass allowing the flow of gas directly from said mass flow controller to said exhaust when said gas inlet is closed.

3. The gas supply system of claim 2 wherein the gas further comprises an etchant gas.

4. The gas supply system of claim 2 wherein the gas further comprises a deposition gas.

5. The gas supply of claim 2 further comprising a discrete gas switch, said gas switch controlling the flow of gas from the mass flow controller such that the flow of gas from the mass flow controller is alternatively switched between the gas inlet and the gas bypass.

6. A method of controlling a flow of gas from a mass flow controller to a semiconductor manufacturing chamber to maximize a smoothness of sidewalls of etched trenches in a silicon substrate, said method comprising:

providing a specified flow of gas from the mass flow controller;

providing the flow of gas from the mass flow controller directly to the semiconductor manufacturing chamber during a gas on state; and

diverting the flow of gas from the mass flow controller directly to an exhaust of the semiconductor manufacturing chamber through a gas bypass during a gas off state.

7. The method of claim 6 wherein the flow of gas is diverted from the chamber during the gas off state such that the pressure of the gas at the outlet of the mass flow controller remains relatively constant.

8. A method of anisotropic plasma etching of silicon in a chamber to provide laterally defined recess structures therein with smooth sidewalls, the method comprising:

providing directly to said chamber during a first gas on state pulses of a reactive etchant gas for etching silicon alternated by providing directly to said chamber during a second gas on state pulses of a reactive polymerizing gas for depositing a polymer layer;

diverting said reactive etchant gas directly to an exhaust in fluid communication with said chamber through a reactive gas bypass during a first gas off state and diverting said reactive polymerizing gas directly to said exhaust of said chamber through a polymerizing gas bypass during a second gas off state;

plasma etching in at least one etching step a surface of the silicon by contact with said reactive etching gas during said first gas on state to remove material from the surface of the silicon and provide exposed surfaces;

polymerizing in at least one polymerizing step at least one polymer onto the surface of the silicon by contact with said reactive polymerizing gas during said second gas on state which the surfaces that were exposed in said preceding etching step are covered by a polymer layer thereby forming a temporary etching stop; and

alternatingly repeating the etching step and the polymerizing step.

9. The method of claim 8 wherein the pulses of reactive etchant gas are discretely pulsed within the etching step.

10. The method of claim 8 wherein the pulses of reactive polymerizing gas are discretely pulsed within the deposition step.

11. The method of claim 8 further comprising maintaining said reactive etchant gas at a substantially constant pressure at an outlet of a reactive etchant MFC during said first gas on state and said first gas off state.

12. The method of claim 8 further comprising maintaining said reactive polymerizing gas at a substantially constant pressure at an outlet of a reactive polymerizing MFC during said second gas on state and said second gas off state.

13. The method of claim 8 wherein the anisotropic plasma etching of silicon in the chamber further comprises the varying of one or more of the following parameters:

gas flow rates, chamber pressure, plasma power, substrate bias, etch rate, deposition rate, cycle time, and etching/deposition ratio over time.

14. The method of claim 13 wherein the varying of one or more of the parameters is from process cycle to process cycle.

15. The method of claim 13 wherein the varying of one or more of the parameters is within the process cycle.

16. The method of claim 8 further comprising the step of delivering the reactive etchant gas at a substantially constant rate from a mass flow controller.

17. The method of claim 8 further comprising the step of delivering the reactive polymerizing gas at a substantially constant rate from a mass flow controller.