Method of making dense, conformal, ultra-thin cap layers for nanoporous low-k ILD by plasma assisted atomic layer deposition
Barrier layers and methods for forming barrier layers on a porous layer are provided. The methods can include chemically adsorbing a plurality of first molecules on a surface of the porous layer in a chamber and forming a first layer of the first molecules on the surface of the porous layer. A plasma can then be used to react a plurality of second molecules with the first layer of first molecules to form a first layer of a barrier layer. The barrier layers can seal the pores of the porous material, function as a diffusion barrier, be conformal, and/or have a negligible impact on the overall ILD k value of the porous material.
1. A method for forming a barrier layer on a porous material comprising:
using a plasma defined ALD process wherein:
a) a plasma is used during the ALD process for localizing the barrier layer to an external surface of the porous material and without compromising porosity of the porous material;
b) ALD precursors are selected to be non-reactive to each other unless activated by plasma, ALD deposition cannot take place unless assisted by plasma, and takes place only in places irradiated by plasma;
c) plasma parameters comprise a Debye length and molecular mean free path each larger than a pore size of the porous material, wherein internal pores comprising the pores in the porous material are at least 5 nm below the external surface; and
d) deposition of the barrier layer inside internal pores of the porous material is avoided and deposition takes place only on the external surface of the porous material.
2. A semiconductor device formed by the method of claim 1 .
3. A method for forming a barrier layer on a porous material comprising:
in a vacuum chamber, chemically adsorbing a plurality of first molecules on the porous material in an initially plasma-free environment, the adsorption taking place on both an external surface of the porous material and internal pores of the porous material;
forming a first layer of the chemically adsorbed first molecules that is a monolayer or sub-monolayer on the porous material;
choosing second molecules that are non-reactive to the first molecules unless activated by plasma, and introducing a plurality of the second molecules to the vacuum chamber; and
generating a plasma in the vacuum chamber to activate a reaction between the first molecules and the second molecules, and converting the first layer to a first barrier layer, wherein plasma parameters comprise a Debye length and molecular mean free path each larger than a pore size of the porous material, to prevent plasma from penetrating into internal pores of the porous material, the barrier layer only formed on the external surface of the porous material, and forming the barrier layer inside internal pores of the porous material is avoided.
4. The method of claim 3 , wherein forming the first layer of the chemically adsorbed first molecules that is a monolayer or sub-monolayer on the surface of the porous layer comprises removing weakly bonded first molecules by one of purging the chamber with an inert gas and evacuating the chamber.
5. The method of claim 3 , further comprising:
chemically adsorbing a second plurality of first molecules on a surface of the first barrier layer in the chamber;
forming a second layer of the first molecules that is a monolayer or sub-monolayer on the surface of the first barrier layer; and
using a plasma to react a second plurality of second molecules with the second layer of first molecules to convert the second layer to a second barrier layer.
6. The method of claim 5 , further comprising repeating the steps of claim 4 to form additional layers of the barrier layer.
7. The method of claim 3 , wherein the first layer of the barrier layer is substantially a monolayer.
8. A semiconductor device formed by the method of claim 3 .