Microbolometer and method for forming

• US 6,690,014 B1
• Filed: 04/25/2000
• Issued: 02/10/2004
• Est. Priority Date: 04/25/2000
• Status: Expired due to Term

• Current Assignee: DRS Network & Imaging Systems, LLC (Leonardo S.p.A.)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Gooch, Roland W., Schimert, Thomas R., McCardel, William L., Ritchey, Bobbi A.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/557,748
• Time in Patent Office: 1,386 Days
• Field of Search: 250/338.4, 438/72, 438/96
• US Class Current: 250/338.4
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: H01L 27/14649 Infrared imagers

Abstract

A microbolometer is provided that includes an absorber element having material properties to change temperature in response to absorbing infrared radiation. An amorphous silicon detector is thermally coupled to the absorber element and is suspended above a silicon substrate at a height of one-quarter wavelength of the infrared radiation to be detected. The amorphous silicon detector changes electrical resistance in response to the absorber element changing temperature. The microbolometer also includes electrode arms coupled to the silicon substrate to provide structural support for the amorphous silicon detector above the surface of the silicon substrate. The electrode arms further provide electrical connectivity for the microbolometer.

Claims

1. A microstructure infrared radiation detector, comprising:

an absorber element having material properties to change temperature in response to absorbing infrared radiation;

an amorphous silicon detector thermally coupled to the absorber element and suspended above a silicon substrate at a height of one-quarter wavelength of the infrared radiation to be detected, the amorphous silicon detector changing electrical resistance in response to the absorber element changing temperature;

electrode arms coupled to the silicon substrate to suspend the amorphous silicon detector above the surface of the silicon substrate, the electrode arms further providing electrical connectivity for the microstructure infrared radiation detector; and

a thermal shunting layer deposited on the electrode arms, the thermal shunting layer providing predetermined degrees of thermal isolation depending on the area of the thermal shunting layer.

2. The detector of claim 1, wherein the electrode arms comprise a spiral configuration providing reduced space requirements for the electrode arms.

3. A microstructure infrared radiation detector, comprising:

a thin metal absorber film for absorbing heat when exposed to infrared radiation;

an amorphous silicon layer thermally coupled to the thin metal absorber film, the amorphous silicon layer absorbing heat from the thin metal absorber layer, the amorphous silicon layer changing electrical resistance in response to absorbing heat from the thin metal absorber layer;

electrode arms coupled to the amorphous silicon layer;

an antireflective structure between a substrate material and the amorphous silicon layer, the antireflective structure enhancing absorption of the infrared radiation by the thin metal absorber film; and

a thermal shunting layer deposited on the electrode arms, the thermal shunting layer providing predetermined degrees of thermal isolation depending on the area of the thermal shunting layer.

4. The detector of claim 3, further comprising:

the electrode arms coupled to the amorphous silicon layer and to a silicon substrate, the electrode arms suspending the amorphous silicon layer above the surface of the silicon substrate.

5. The detector of claim 4, wherein the electrode arms comprise a spiral configuration providing reduced space requirements for the electrode arms.

6. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

forming one or more connection pads and a reflector on a surface of a substrate;

forming a sacrificial spacer layer over the connection pads and the reflector;

forming a first low stress dielectric layer over the sacrificial spacer layer;

forming a detector layer over the first low stress dielectric layer, the detector layer having an electrical resistance that varies with a temperature of the detector layer, the detector layer formed above the reflector;

forming a second low stress dielectric layer over the detector layer;

forming an infrared absorber over the second low stress dielectric layer, the infrared absorber changing temperature in response to infrared radiation, the infrared absorber thermally transmitting energy from the infrared radiation to the detector layer, the infrared absorber formed over the detector layer;

forming electrode arms, the electrode arms providing electrical contact to the detector layer;

forming a third low stress dielectric layer over the structure;

forming post receptors in ends of the electrode arms by removing layers thereby exposing the connection pads;

forming a thermal shunting layer on the electrode arms;

forming posts in the post receptors; and

removing the sacrificial spacer layer.

7. The process according to claim 6, wherein forming one or more connection pads, comprises:

depositing a layer of aluminum; and

patterning the aluminum layer to form the one or more connection pads and the reflector.

8. The process according to claim 6, comprising:

depositing a polyimide layer to form the sacrificial spacer layer.

9. The process according to claim 6, comprising:

forming the sacrificial spacer layer to a depth of approximately one-quarter wavelength of the infrared radiation wavelength to be detected by the micro-sensor element.

10. The process according to claim 6, wherein forming, the first, second, and third low stress dielectric layers, comprises:

depositing a silicon nitride layer.

11. The process according to claim 6, comprising:

depositing an amorphous silicon layer to form the detector layer, the amorphous silicon layer doped with boron during deposition.

12. The process according to claim 6, comprising:

depositing a thick layer of aluminum in the post receptors.

13. The process according to claim 6, wherein removing the sacrificial spacer layer, comprises:

exposing the sacrificial layer to a dry etch to remove the sacrificial spacer layer.

14. The process according to claim 6, wherein removing the sacrificial spacer layer, comprises:

exposing the sacrificial layer to an oxygen plasma dry etch to remove the sacrificial spacer layer.

15. A process for fabricating a micro-sensor element for an infrared radiation detector element, comprising:

depositing a titanium layer on a surface of a silicon substrate wafer;

depositing an aluminum layer over the titanium layer;

patterning the aluminum and titanium layers to form a reflector element and a plurality of interconnects;

depositing a polyimide layer over the patterned aluminum and titanium layers, the polyimide layer having a depth of approximately one-quarter wavelength of the infrared radiation wavelength to be detected by the micro-sensor element;

removing a portion of the polyimide layer to form post receptors to receive aluminum posts for supporting the micro-sensor element above the reflector element and for providing electrical contact between the micro-sensor element and the interconnects;

depositing a first low stress dielectric layer over the polyimide layer;

depositing an amorphous silicon layer over the first low stress dielectric layer, the amorphous silicon layer doped with boron during deposition;

depositing a second low stress dielectric layer over the amorphous silicon layer;

depositing a thin film metal absorber layer over the second low stress dielectric layer;

patterning the thin film metal absorber layer to form an absorber element over the reflector element;

etching the second low stress dielectric layer to form electrode arms leaving amorphous silicon exposed in an area defined by the electrode arms;

forming a metal layer on the electrode arms;

depositing a third low stress dielectric layer over the structure;

removing layers down to the polyimide layer to form the micro-sensor element in the area surrounding the electrode arms and the absorber element;

removing the third low stress dielectric layer from a portion of the electrode arm ends;

depositing a titanium layer in post receptors and on the electrode arm ends where the third low stress dielectric layer has been removed;

depositing an aluminum layer over the titanium layer in post receptors and on the electrode arm ends; and

removing the polyimide layer by exposing the micro-sensor element to an oxygen plasma dry etch.

16. The process according to claim 15, further comprising:

an initial step of forming a layer of silicon dioxide on the surface of the silicon substrate wafer.

17. The process according to claim 15, wherein the first, second, and third low stress dielectric layers are formed by depositing a layer of silicon nitride.

18. An infrared radiation detector, comprising:

a first plurality of micro-structure infrared radiation detectors, each detector comprising;

a thin metal absorber film for absorbing heat when exposed to infrared radiation;

an amorphous silicon layer thermally coupled to the thin metal absorber film, the amorphous silicon layer absorbing heat from the thin metal absorber film, the amorphous silicon layer changing electrical resistance in response to absorbing heat from the thin metal absorber film;

an anti-reflective structure between a substrate material and the amorphous silicon layer, the anti-reflective structure enhancing absorption of the infrared radiation by the thin metal absorber film;

electrode arms coupled to the amorphous silicon layer and to a silicon substrate, the electrode arms suspending the amorphous silicon layer above the surface of the silicon substrate;

electrical conductors interconnecting the plurality of radiation detectors electrically in parallel as an array configuration functioning as a single detector;

a second plurality of micro-structure infrared radiation detectors, each radiation detector of the second plurality similar to the first plurality of radiation detectors;

electrical conductors interconnecting the second plurality of radiation detectors electrically in parallel as an array configuration; and

electrical conductors interconnecting individual radiation detectors of the second plurality electrically in series with a corresponding one of the radiation detectors of the first plurality.

19. The detector as set forth in claim 18, wherein the electrode arms comprise a spiral configuration providing reduced space requirements for the electrode arms.

20. A microstructure infrared radiation detector, comprising:

an absorber element having material properties to change temperature in response to absorbing infrared radiation;

an amorphous silicon detector thermally coupled to the absorber element and suspended above a silicon substrate thereby forming an open space between the amorphous silicon detector and the silicon substrate, the amorphous silicon detector changing electrical resistance in response to the absorber element changing temperature;

electrode arms positioned in the open space between the amorphous silicon detector and the silicon substrate and coupled to the silicon substrate and the amorphous silicon detector to suspend the amorphous silicon detector above the surface of the silicon substrate, the electrode arms further providing electrical connectivity for the microstructure infrared radiation detector; and

a thermal shunting layer deposited on the electrode arms, the thermal shunting layer providing predetermined degrees of thermal isolation depending on the area of the thermal shunting layer.

21. The detector of claim 20, further comprising:

an antireflective structure between the silicon substrate and the amorphous silicon detector, the antireflective structure enhancing absorption of the infrared radiation by the absorber element.

22. A microstructure infrared radiation detector, comprising:

an absorber element having material properties to change temperature in response to absorbing infrared radiation;

an amorphous silicon detector thermally coupled to the absorber element and suspended above a silicon substrate, the amorphous silicon detector changing electrical resistance in response to the absorber element changing temperature;

electrode arms positioned between the silicon detector and the silicon substrate, the electrode arms coupled to the silicon substrate to suspend the amorphous silicon detector above the surface of the silicon substrate, the electrode arms further providing electrical connectivity for the microstructure infrared radiation detector; and

a thermal shunting layer deposited on the electrode arms, the thermal shunting layer providing predetermined degrees of thermal isolation depending on the area of the thermal shunting layer.

23. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

forming one or more connection pads and a reflector on a surface of a substrate;

forming a sacrificial spacer layer over the connection pads and the reflector;

forming a first low stress dielectric layer over the sacrificial spacer layer;

forming a detector layer over the first low stress dielectric layer, the detector layer having an electrical resistance that varies with the temperature of the detector layer, the detector layer formed directly over the reflector;

forming a second low stress dielectric layer over the detector layer;

forming an infrared absorber over the second low stress dielectric layer, the infrared absorber changing temperature in response to infrared radiation, the infrared absorber thermally transmitting energy from the infrared radiation to the detector layer, the infrared absorber formed directly over the detector layer;

forming electrode arms, the electrode arms providing electrical contact to the detector layer;

forming a third low stress dielectric layer over the structure;

forming post receptors in the ends of the electrode arms by removing layers thereby exposing the connection pads;

forming posts in the post receptors; and

removing the sacrificial spacer layer.

24. The process of claim 23, wherein forming one or more connection pads comprises:

depositing a layer of aluminum; and

patterning the aluminum layer to form the one or more connection pads and the reflector.

25. The process according to claim 23, wherein forming a sacrificial spacer layer comprises:

depositing a polyimide layer to form the sacrificial spacer layer.

26. The process according to claim 23, wherein forming electrode arms, comprises:

depositing an electrode metal layer.

27. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

forming one or more connection pads and a reflector on a surface of a substrate;

forming a sacrificial spacer layer over the connection pads and the reflector;

forming a first low stress dielectric layer over the sacrificial spacer layer;

forming a detector layer over the first low stress dielectric layer, the detector layer having an electrical resistance that varies with a temperature of the detector layer, the detector layer formed above the reflector;

forming a second low stress dielectric layer over the detector layer;

patterning the second low stress dielectric layer to form openings defining electrode arms;

forming electrode arms in the patterned second low stress dielectric layer and an infrared absorber over the patterned second low stress dielectric layer, the electrode arms providing electrical contact to the detector layer, the infrared absorber changing temperature in response to absorbed infrared radiation, the infrared absorber thermally transmitting energy from the infrared radiation to the detector layer;

forming a third low stress dielectric layer over the structure;

removing the third low stress dielectric layer in ends of the electrode arms and removing the third low stress dielectric layer, the second low stress dielectric layer, the detector layer, and first low stress dielectric layer thereby to expose the connection pads to form post receptors, and also exposing the sacrificial spacer layer to form the micro-sensor element in the area surrounding the electrode arms and the absorber element;

forming a thermal shunting layer on the electrode arms;

forming posts in the post receptors; and

removing the sacrificial spacer layer.

28. The process according to claim 27, wherein forming one or more connection pads, comprising:

depositing a layer of aluminum; and

patterning the aluminum layer to form the one or more connection pads and the reflector.

29. The process according to claim 27 comprising:

forming the sacrificial spacer layer to a depth of approximately one-quarter wavelength of the infrared radiation wavelength to be detected by the micro-sensor element.

30. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

depositing a first metal layer on a surface of a silicon substrate wafer;

depositing a second metal layer over the first metal layer;

patterning the first and second metal layers to form a reflector element and a plurality of interconnects;

depositing a polyimide layer over the patterned first and second layers, the polyimide layer having a depth of approximately one-quarter wavelength of the infrared radiation wavelength to be detected by the micro-sensor element;

removing a portion of the polyimide layer to form post receptors to receive metal posts for supporting the micro-sensor element above the reflector element and for providing electrical contact between the micro-sensor element and the interconnects;

depositing a first low stress dielectric layer over the polyimide layer;

depositing an amorphous silicon layer over the first low stress dielectric layer, the amorphous silicon layer doped with boron during deposition;

depositing a second low stress dielectric layer over the amorphous silicon layer;

patterning the second low stress dielectric layer to form openings defining electrode arms;

depositing a thin film metal absorber layer over the patterned second low stress dielectric layer;

patterning the thin film metal absorber layer to form an absorber element and electrode arms;

depositing a third low stress dielectric layer over the structure;

removing the third low stress dielectric layer from a portion of the electrode arm ends and removing layers down to the post receptors and down to the polyimide layer to form the micro-sensor element in the area surrounding the electrode arms and the absorber element;

depositing a third metal layer on the electrode arm ends where the third low stress dielectric layer has been removed and in post receptors;

depositing a fourth metal layer over the third metal layer on the electrode arm ends and in post receptors; and

removing the polyimide layer by an oxygen plasma dry etch.

31. The process according to claim 30, further comprising:

an initial step of forming a layer of silicon dioxide on the surface of the silicon substrate wafer.

32. An infrared radiation detector, comprising:

a plurality of microstructure infrared radiation detectors, each detector comprising;

a thin metal absorber film for absorbing heat when exposed to infrared radiation;

an amorphous silicon layer thermally coupled to the think metal absorber film, the amorphous silicon layer absorbing heat from the think metal absorber layer, the amorphous silicon layer changing electrical resistance in response to absorbing heat from the thin metal absorber layer;

an anti-reflective structure between a substrate material and the amorphous silicon layer, the anti-reflective structure enhancing absorption of the infrared radiation by the thin metal absorber film;

electrode arms coupled to the amorphous silicon layer and to a silicon substrate, the electrode arms suspending the amorphous silicon layer above the surface of the silicon substrate; and

an infrared shield deposited on selected one of the plurality of infrared detectors to provide non-responsive reference detectors.

33. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

forming one or more connection pads and a reflector on a surface of a substrate;

forming a sacrificial space layer over the connection pads and the reflector;

forming a first low stress dielectric layer over the sacrificial space layer;

forming a detector layer over the first low stress dielectric layer, the detector layer having an electrical resistance that varies with the temperature of the detector layer, the detector layer formed directly over the reflector;

forming a second low stress dielectric layer over the detector layer;

patterning the second low stress dielectric layer to form openings defining electrode arms;

forming electrode arms in the patterned second low stress dielectric layer, the electrode arms providing electrical contact to the detector layer, and an infrared absorber over the second low stress dielectric layer, the infrared absorber changing temperature in response to absorbed infrared radiation, the infrared thermally transmitting energy from the infrared radiation to the detector layer;

forming a third low stress dielectric layer over the structure;

removing third low stress dielectric layer in ends of the electrode arms and removing the third low stress dielectric layer, the second low stress dielectric layer, the detector layer, and first low stress dielectric layer to expose the connection pads to form post receptors, and also exposing the sacrificial spacer layer to form the micro-sensor element in the area surrounding the electrode arms and the absorber element;

forming posts in the post receptors; and

removing the sacrificial spacer layer.

34. The process of claim 33, wherein forming one or more connection pads comprises:

depositing a layer of aluminum; and

patterning the aluminum layer to form the one or more connection pads and the reflector.

35. The process according to claim 33 further comprising forming an infrared shield on third low stress dielectric layer.

36. A process for fabricating a micro-sensor element for an infrared radiation detector, comprising:

forming one or more connection pads and a reflector on a surface of a substrate;

forming a sacrificial spacer layer over the connection pads and the reflector;

forming a first low stress dielectric layer over the sacrificial spacer layer;

forming a detector layer over the first low stress dielectric layer, the detector layer having an electrical resistance that varies with the temperatures of the detector layer, the detector layer formed directly over the reflector;

forming a second low stress dielectric layer over the detector layer;

removing the second low stress dielectric layer, the detector layer, and first low stress dielectric layer thereby exposing the connection pads to form post receptors;

patterning the second low stress dielectric layer to form openings defining electrode arms;

forming electrode arms in the patterned second low stress dielectric layer, the electrode arms providing electrical contact to the detector layer, and an infrared absorber over the second low stress dielectric layer, the infrared absorber changing temperature in response to absorbed infrared radiation, the infrared absorber thermally energy from the infrared radiation to the dielectric layer;

forming posts in the post receptors connecting electrode arm ends to connection pads;

forming a third low stress dielectric layer over the structure;

removing the third low stress dielectric layer, the second low stress dielectric layer, the detector layer, and first low stress dielectric layer exposing the sacrificial spacer layer to form the micro-sensor element in the area surrounding the electrode arms and the absorber element; and

removing the sacrificial spacer layer.

37. The process according to claim 36 further comprising forming an infrared shield on third low stress dielectric layer.

38. The process according to claim 36 wherein prior to patterning the second low stress dielectric layer to form openings defining electrode arms further comprising removing the second low stress dielectric layer, the detector layer, and first low stress dielectric layer to expose the connection pads to form the post receptors.