Corrosion-resistant internal coating method using a germanium-containing precursor and hollow cathode techniques
Enhanced corrosion resistance is achieved in a coating by using a germanium-containing precursor and hollow cathode techniques to form a first layer directly on the surface of a workpiece, prior to forming an outer layer, such as a layer of diamond-like carbon (DLC). The use of a germanium or germanium-carbide precursor reduces film stress and enables an increase in the thickness of the subsequently formed DLC. Germanium incorporation also reduces the porosity of the layer. In one embodiment, a cap layer containing germanium is added after the DLC in order to further reduce the susceptibility of the coating to chemical penetration from the top.
1. A method of coating an interior surface of a workpiece comprising:
connecting a biasing system such that said workpiece functions as an electrode;
controlling pressure within an interior of said workpiece such that a cooperation between said biasing system and said pressure establishes a hollow cathode effect within said interior;
forming a uniform, adhesion-promoting, corrosion-resistance layer on said interior surface, including repetitive cycling of deposition and exposure steps, wherein each deposition step includes introducing a germanium-containing precursor within said interior so as to deposit a portion of the uniform, adhesion-promoting, corrosion-resistance layer, and wherein each exposure step includes exposing said uniform, adhesion-promoting, corrosion-resistance layer to high energy bursts from a plasma that provides activation energy to form an interfacial compound, deposition of the uniform, adhesion-promoting, corrosion-resistance layer from each deposition step exceeding etchback from each exposure step;
forming a sequence of blend layers on the adhesion-promoting corrosion-resistance layer using an increasing relative concentration of hydrocarbon precursors for successive blend layers; and
forming a second layer on said blend layers, said second layer being a layer of diamond-like carbon (DLC), including utilizing a high intensity plasma available as a consequence of said hollow cathode effect during formation of said corrosion-resistance layer and said second layer.
2. The method of claim 1 further comprising forming a cap layer following said formation of said layer of DLC, including utilizing said hollow cathode effect in formation of said cap layer and including introducing germanium into said cap layer.
3. The method of claim 1 wherein said workpiece is metallic and said corrosion-resistance layer is formed directly on said workpiece.
4. The method of claim 3 wherein connecting said biasing system includes applying a pulsed DC voltage to said workpiece.
5. The method of claim 1 wherein introducing said germanium-containing precursor includes providing a flow of tetramethylgermane, such that said corrosion-resistance layer includes germanium carbide.
6. The method of claim 1 wherein introducing said germanium-containing precursor includes providing a flow of germane (GeH 4 ), such that said corrosion-resistance layer includes germanium and hydrogen.
7. The method of claim 1 wherein forming said corrosion-resistance layer further includes depositing one of silicon and silicon carbide.
8. The method of claim 1 wherein forming said corrosion-resistance and second layers include using Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques.
9. A method of coating an interior surface of a workpiece comprising:
establishing an environment within an interior of said workpiece such that formation of layers is by means of Plasma Enhanced Chemical Vapor Deposition (PECVD) utilizing hollow cathode effects, said workpiece being metallic and being biased to function as an electrode;
depositing a uniform, adhesion promoting, corrosion-resistance first layer directly on said interior surface, including cycling between (1) a deposition step introducing a germanium-containing precursor into said environment so as to deposit a portion of said first layer and (2) a step of exposing said first layer to high energy bursts from a plasma that provides activation energy to form an interfacial compound, deposition of the first layer from each cycle of said deposition step exceeding etchback from each cycle of said exposure step;
depositing a sequence of blend layers on the adhesion-promoting corrosion-resistance layer using an increasing relative concentration of hydrocarbon precursors for successive blend layers;
depositing a diamond-like carbon (DLC) layer on said blend layers; and
depositing a cap layer on said DLC layer, including introducing a germanium-containing gas into said environment.
10. The method of claim 9 wherein establishing said environment within said interior includes biasing said workpiece using a pulsed DC input and further includes establishing a pressure that is based upon factors which include a diameter of said interior.
11. The method of claim 9 wherein each of introducing said germanium-containing precursor and introducing said germanium-containing gas includes using one of tetramethylgermane and germane.
12. The method of claim 9 wherein said blend layers having decreasing concentrations of silicon within said sequence.
13. The method of claim 9 wherein depositing said first layer includes connecting a source of silicon-containing gas to said interior simultaneously with said germanium-containing precursor.
14. The method of claim 9 wherein depositing said DLC layer includes introducing germanium gas into said interior of said workpiece, such that germanium is introduced into said interior during deposition of each of said first layer, said DLC layer and said cap layer.