Removing aluminum nitride sections
View Patent ↗Approaches for substantially removing bulk aluminum nitride (AlN) from one or more layers epitaxially grown on the bulk AlN are discussed. The bulk AlN is exposed to an etchant during an etching process. During the etching process, the thickness of the bulk AlN can be measured and used to control etching.
1. An apparatus, comprising:
a chamber configured to expose a bulk aluminum nitride (AlN) substrate to an etchant during an etching process, the bulk AlN substrate being a substrate of a subassembly comprising one or more epitaxial layers grown on the bulk AlN substrate; and
a measurement unit configured to generate a signal indicative of a thickness of the bulk AlN substrate and a light source configured to generate output light at a wavelength that is substantially absorbed by the bulk AlN substrate and is not substantially absorbed by the one or more epitaxial layers, the measurement unit additionally comprising a detector arranged to detect the light transmitted through the subassembly, the detector being configured to characterize the spectral response of the subassembly over a wavelength range of the detected light.
2. The apparatus of claim 1 , wherein the measurement unit includes contacts configured to make electrical contact with the subassembly and the measurement unit is configured to measure one or more electrical characteristics of the subassembly through the electrical contacts.
3. The apparatus of claim 1 , wherein the measurement unit includes a chemical sensor configured to sense an ion concentration in the chamber near the subassembly and the measurement unit is configured to generate the signal based on the ion concentration.
4. The apparatus of claim 1 , wherein the signal is an analog signal that indicates the thickness of the aluminum nitride substrate over a thickness range.
5. The apparatus of claim 1 , wherein the signal indicates that the AN substrate has been substantially removed in a region of the subassembly.
6. The apparatus of claim 1 wherein the etchant comprises phosphoric acid at an elevated temperature.
7. The apparatus of claim 6 ,
wherein the phosphoric acid has a concentration in a range of about 87% to about 96% and having a temperature in a range of about 160° C. to 210° C.
8. The apparatus of claim 1 , wherein the light source emits light in a wavelength range from about 200 to about 365 nm.
9. An apparatus, comprising:
a chamber configured to expose a bulk aluminum nitride (AlN) substrate to an etchant during an etching process, the bulk AlN substrate being a substrate of a subassembly comprising one or more epitaxial layers grown on the bulk AlN substrate; and
a measurement unit configured to generate a signal indicative of a thickness of the bulk AlN substrate and comprising a detector arranged to detect light transmitted through the subassembly, wherein the light is generated by the subassembly and transmitted to the detector when the bulk AlN substrate becomes sufficiently thin.
10. The apparatus of claim 9 , further comprising a control unit configured to control the etching process based on the signal.
11. The apparatus of claim 10 , wherein the control unit is configured to reduce the etch rate when a change in the signal exceeds a predetermined limit.
12. The apparatus of claim 10 , wherein the control unit is configured to stop the etching process when a change in the signal exceeds a predetermined limit.
13. The apparatus of claim 10 , wherein the control unit is arranged to provide thermal energy to the etchant in the chamber.
14. The apparatus of claim 13 , wherein the control unit comprises one or both of a heater configured to heat the etchant and a cooler configured to cool the etchant.
15. The apparatus of claim 10 , wherein the control unit is configured to control a concentration of the etchant.