Self-aligned well structures for low-noise chemical sensors
In one implementation, a chemical detection device is described. The device includes a chemically-sensitive field effect transistor including a floating gate conductor coupled to a gate dielectric and having an upper surface, and a sensing material on the upper surface. The device also includes a fill material defining a reaction region extending above the sensing material, the reaction region overlying and substantially aligned with the floating gate conductor.
1. A method for forming a chemical detection device, the method comprising:
forming a gate dielectric on a semiconductor substrate;
forming a floating gate structure on the gate dielectric, including:
forming a conductive material overlying the gate dielectric;
forming a sensing material on the conductive material;
forming a sacrificial material overlying the sensing material;
patterning the conductive material, the sensing material and the sacrificial material;
forming a fill material adjacent to the patterned sacrificial material and the patterned sensing material and the patterned conductive material; and
removing the patterned sacrificial material to expose the patterned sensing material and define a reaction region substantially aligned with the patterned conductive material.
2. The method of claim 1 , wherein removing the patterned sacrificial material comprises using a non-etching process.
3. The method of claim 1 , wherein removing the patterned sacrificial material comprises applying heat to thermally decompose at least some of the patterned sacrificial material.
4. The method of claim 3 , wherein the fill material has a decomposition temperature greater than that of the sacrificial material.
5. The method of claim 1 , wherein the sensing material comprises a metal-oxide.
6. The method of claim 1 , wherein the sensing material is sensitive to hydrogen ions.
7. The method of claim 1 , wherein the chemical detection device generates a sensor signal in response to a chemical reaction occurring within the reaction region.
8. The method of claim 7 , wherein the chemical reaction is a sequencing reaction.
9. The method of claim 1 , further comprising forming a source and drain in the semiconductor substrate.
10. The method of claim 1 , wherein the reaction region is configured to receive at least one reactant.
11. The method of claim 1 , wherein removing the patterned sacrificial material comprises using a wet etch process.