Plasma etching of porous substrates
The disclosed technology generally relates to semiconductor fabrication, and more particularly to plasma etching of dielectric materials having pores. In one aspect, a method for etching a porous material in an environment includes contacting the porous material with an organic gas at a pressure and a temperature. The organic gas is such that at the pressure and the temperature, the organic gas remains in a gas state when outside of the porous material, while the organic gas condenses into an organic liquid upon contacting the porous material. Upon contacting the porous material, the organic gas thereby fills the pores of the porous material with the organic liquid. Subsequent to contacting the porous material, the method additionally includes plasma etch-treating of the porous material having filled pores, thereby evaporating a fraction of the organic liquid filling the pores of the porous material.
1. A method of etching a porous material, comprising:
contacting a porous material with an organic gas in an environment having a pressure (P 1 ) and a temperature (T 1 ), wherein the organic gas is such that at the pressure (P 1 ) and the temperature (T 1 ), the organic gas remains in a gas state when outside of the porous material, while the organic gas condenses into an organic liquid when in contact with the porous material, wherein when in contact with the porous material, the organic liquid fills pores of the porous material;
subsequent to the contacting, plasma etch-treating the porous material having the pores filled with the organic liquid, thereby evaporating a fraction of the organic liquid filling the pores of the porous material; and
repeating contacting and plasma etch-treating n times, wherein n≧1.
2. The method according to claim 1 , wherein plasma etch-treating is performed for a duration greater than or equal to 3 seconds.
3. The method according to claim 1 , wherein contacting the porous material is performed for a duration greater than or equal to 1 second.
4. The method according to claim 1 , wherein the method is carried out in a gaseous environment comprising the organic gas and an etching gas.
5. The method according to claim 4 , wherein the organic gas is the etching gas.
6. The method according to claim 1 , wherein the pressure (P 1 ) is lower than an equilibrium vapor pressure (P 0 ) of the organic gas at the temperature (T 1 ) while being equal to or higher than a critical pressure (Pc) at the temperature (T 1 ), wherein the critical pressure (Pc) is the pressure at which the liquid phase and the vapor phase of the organic gas are at equilibrium within the porous material.
7. The method according to claim 1 , wherein a vaporization temperature of the organic liquid is below 250° C. at the pressure (P 1 ).
8. The method according to claim 1 , wherein the organic gas is a gas of an organic compound selected from the group consisting of hydrocarbons, fluorocarbons, hydrofluorocarbons, alcohols, aldehydes, ketones, metal-organic complexes, organosilicon compounds and mixture of at least two thereof.
9. The method according to claim 1 , wherein a condensation temperature of the organic gas in the pores is equal to or lower than −10° C. at the pressure (P 1 ).
10. The method according to claim 1 , wherein the porous material during contacting the porous material with the organic gas is at the temperature (T 1 ).
11. The method according to claim 1 , wherein the porous material is a nanoporous material.
12. The method according to claim 11 , wherein the nanoporous material is a silicon-containing porous material.
13. The method according to claim 1 , wherein the plasma etch-treating exposes the porous material directly to a vacuum ultraviolet (VUV) radiation generated by a direct plasma, and wherein the organic liquid comprises hydrocarbons that are substantially opaque to the VUV radiation.
14. The method according to claim 13 , wherein the pores of the porous material are interconnected within the porous material such that after the contacting, the organic liquid diffuses into the porous material below a surface of the porous material to a diffusion depth.
15. The method according to claim 14 , wherein plasma etch-treating further comprises etching the porous material to an etch depth equal to or less than the diffusion depth, such that the porous material that is exposed at the etch depth to the VUV radiation is protected from the VUV radiation by the organic liquid having the hydrocarbons.