Low-rate electrochemical etch of thin film metals and alloys
View Patent ↗Embodiments of the present invention include systems and methods for low-rate electrochemical (wet) etch that use a net cathodic current or potential. In particular, some embodiments achieve controlled etch rates of less than 0.1 nm/s by applying a small net cathodic current to a substrate as the substrate is submerged in an aqueous electrolyte. Depending on the embodiment, the aqueous electrolyte utilized may comprise the same type of cations as the material being etched from the substrate. Some embodiments are useful in etching thin film metals and alloys and fabrication of magnetic head transducer wafers.
1. A method for electrochemical etching, the method comprising:
providing a substrate comprising a metal or alloy of a first material;
providing an etching solution comprising an electrolyte of a second material; and
immersing the substrate in the etching solution while applying a cathodic current to the substrate, wherein the cathodic current is applied such that the etching solution causes the first material of the substrate to etch and the etching solution causes a reduction reaction to take place and wherein applying the cathodic current to the substrate comprises increasing a current density through the substrate from a zero net current through the substrate to a first net current through the substrate, wherein the first net current is more cathodic than the zero net current.
2. The method of claim 1 , wherein the cathodic current comprises an anodic current component that causes the first material of the substrate to etch and a cathodic current component that causes the reduction reaction to take place.
3. The method of claim 1 , wherein applying the cathodic current to the substrate comprises applying a first potential to the substrate, wherein the first potential is more negative than an open-circuit potential of a couple comprising the first material and the etching solution.
4. The method of claim 3 , wherein the first potential is less negative than a second potential of the first material, wherein the second potential is a second open-circuit potential of a couple comprising the first material and an ion of the first material.
5. The method of claim 1 , wherein the current density through the substrate is increased such that: the first net current has a larger anodic component than, or equal anodic component as, a net current through the substrate having a zero anodic component, and the first net current has a smaller anodic component than the zero net current.
6. The method of claim 1 , further comprising adjusting the cathodic current in order to adjust an etch rate of the first material of the substrate.
7. The method of claim 6 , wherein controlling the cathodic current such that the first material of the substrate is etched at an etch rate that provides nanometer-level or angstrom-level etch precision.
8. The method of claim 1 , wherein the cathodic current is controlled by way of a galvanostatic method or a potentiostatic method.
9. The method of claim 1 , further comprising maintaining a temperature, pH, electrolyte concentration, and mixing rate of the etching solution at or close to a specified value.
10. The method of claim 1 , wherein the second material contains a same or similar element to that found in the first material.
11. The method of claim 1 , wherein the method is used to etch plated or sputtered structures.
12. The method of claim 1 , wherein the method is used to fabricate a magnetic recording head.
13. The method of claim 1 , wherein the method is used to remove an oxide from the substrate.
14. The method of claim 13 , wherein subsequent to the oxide being removed using the method, the cathodic current is increased such that while the substrate is immersed in the etching solution, the first material or a second material is electrodeposited onto the substrate.