Sputter deposition of cermet resistor films with low temperature coefficient of resistance
View Patent ↗A solution for producing nanoscale thickness resistor films with sheet resistances above 1000Ω/□ (ohm per square) and low temperature coefficients of resistance (TCR) from −50 ppm/° C. to near zero is disclosed. In a preferred embodiment, a silicon-chromium based compound material (cermet) is sputter deposited onto a substrate at elevated temperature with applied rf substrate bias. The substrate is then exposed to a process including exposure to a first in-situ anneal under vacuum, followed by exposure to air, and followed then by exposure to a second anneal under vacuum. This approach results in films that have thermally stable resistance properties and desirable TCR characteristics.
1. A method for forming a thin film resistor, comprising:
depositing a layer of cermet material on a substrate, the composition of the cermet material optimized to achieve a desired resistivity;
treating the cermet layer to achieve a desired thermal stability while maintaining the desired resistivity, the treatment comprising an anneal sequence of a plurality of anneal sandwiching a passivation process of lower temperature and longer time,
wherein the anneal is performed in a non oxidation ambient,
wherein the passivation process comprises an exposure to an oxidation ambient.
2. A method as in claim 1 wherein depositing the cermet material is performed by sputtering with a substrate bias at temperature below 400 C.
3. A method as in claim 1 wherein the anneal sequence comprises a first anneal and a second anneal sandwiching a passivation process.
4. A method as in claim 3 wherein the anneal sequence further comprises a second passivation process followed by a third anneal.
5. A method as in claim 1 wherein the anneal is performed in vacuum.
6. A method as in claim 1 wherein the first anneal is performed during the deposition.
7. A method as in claim 1 wherein the first anneal is performed at temperature below 450 C and less than 2 minutes.
8. A method as in claim 1 wherein the passivation process is performed in air ambient at atmospheric pressure and room temperature in less than 24 hours.
9. A method for forming a thin film resistor, comprising:
sputtering a layer of cermet material on a substrate;
performing an anneal sequence on the cermet layer, the anneal sequence comprising at least a first anneal, a passivation, and a second anneal,
wherein the passivation comprises lower temperature and longer time than the anneals,
wherein the anneal is performed in a non oxidation ambient,
wherein the passivation comprises an exposure to an oxidation ambient.
10. A method as in claim 9 wherein the cermet material comprises at least one of CrSi 2 —Cr—Sic, Cr—Si-0, and Si—Sic-CrB 2 compounds.
11. A method as in claim 9 wherein the anneal sequence further comprises a second passivation process followed by a third anneal.
12. A method as in claim 9 wherein at least one of the anneals is performed in reduced pressure at temperature below 450 C and less than 5 minutes.
13. A method as in claim 9 wherein at least one of the anneals is performed in non-oxygen-containing ambient.
14. A method as in claim 9 wherein the passivation process is performed in air ambient at atmospheric pressure and room temperature in less than 24 hours.
15. A method as in claim 9 wherein the passivation process is performed in reduced pressure having oxygen and nitrogen containing ambient.
16. A method for forming a thin film resistor, comprising:
sputtering a layer of cermet material on a substrate;
performing an anneal sequence on the cermet layer, the anneal sequence comprising at least a first anneal, a passivation process, and a second anneal,
wherein the anneal is performed in a non oxidation ambient at temperature between 400 and 500 C for between 1 and 5 minutes,
wherein the passivation comprises an exposure to an oxidation ambient at a temperature less than 100 C for between 1 and 48 hours.
17. A method as in claim 16 wherein the cermet material comprises at least one of CrSi 2 —Cr—Sic, Cr—Si-0, and Si—Sic-CrB 2 compounds.
18. A method as in claim 16 wherein the first or second anneal is performed in vacuum.
19. A method as in claim 16 wherein the passivation process is performed in air ambient at atmospheric pressure.
20. A method as in claim 16 wherein the anneal sequence further comprises a second passivation process followed by a third anneal.