Bismaleimide (BMI) polymer as a sacrificial material for an integrated circuit air gap dielectric

• US 20040124495A1
• Filed: 12/26/2002
• Published: 07/01/2004
• Est. Priority Date: 12/26/2002
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Chen, Tian-An, OʼBrien, Kevin P.
• Granted Patent: US 6,872,654 B2
• Time in Patent Office: Days
• US Class Current: 257/522
• CPC Class Codes: H01L 21/02118 carbon based polymeric organic or inorganic material, e.g. polyimides, poly cyclobutene or PVC polymers per se C08G, photoresist per se G03F
• CPC Class Codes: H01L 21/02203 the layer being porous
• CPC Class Codes: H01L 21/02282 liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating
• CPC Class Codes: H01L 21/02348 treatment by exposure to UV light
• CPC Class Codes: H01L 21/312 Organic layers, e.g. photoresist H01L21/3105, H01L21/32 take precedence; photoresists per se G03C
• CPC Class Codes: H01L 21/7682 the dielectric comprising air gaps

Abstract

A method for implementing a bismaleimide (BMI) polymer as a sacrificial material for an integrated circuit air gap dielectric. The method of one embodiment comprises forming a first and second metal interconnect lines on a substrate, wherein at least a portion of the first and second metal interconnect lines extend parallel to one another and wherein a trough is located between the parallel portion of said first and second metal interconnect lines. A layer of bismaleimide is spin coated over the substrate. The layer of bismaleimide is polished with a chemical mechanical polish, wherein the trough remains filled with the bismaleimide. A diffusion layer is formed over the substrate. The substrate is heated to activate a pyrolysis of the bismaleimide. An air gap is formed in the trough in the space vacated by the bismaleimide.

Claims

1. A method comprising:

forming a first and second metal interconnect lines on a substrate, wherein at least a portion of said first and second metal interconnect lines extend parallel to one another and wherein a trough is located between said parallel portion of said first and second metal interconnect lines;

spin coating a layer of bismaleimide over said substrate;

polishing said layer of bismaleimide with a chemical mechanical polish, wherein said trough remains filled with said bismaleimide;

forming a diffusion layer over said substrate;

heating said substrate to activate a pyrolysis of said bismaleimide; and

forming an air gap in said trough in space vacated by said bismaleimide.

2. The method of claim 1 wherein said pyrolysis causes said bismaleimide to transition physical states from a solid form to a gaseous form.

3. The method of claim 2 further comprising diffusing gas molecules of said bismaleimide through said diffusion layer, said diffusion layer sufficiently porous to allow said gas molecules to pass through.

4. The method of claim 3 wherein substantially all of said bismaleimide in said trough is removed.

5. The method of claim 4 further comprising forming a support layer over said diffusion layer to prevent said air gap in said trough from being collapsed upon.

6. The method of claim 5 wherein said bismaleimide has a thermal stability property wherein less than 1% weight loss occurs in said bismaleimide below 300°

C.

7. The method of claim 6 wherein said bismaleimide further comprises a decomposition temperature of between 350°

C. to 450°

C.

8. The method of claim 7 wherein said bismaleimide further comprises a decomposition residue property wherein less than 5% residue is left after complete decomposition from said pyrolysis at above 400°

C.

9. The method of claim 8 wherein decomposition of said bismaleimide during said pyrolysis occurs in a nitrogen purge atmosphere.

10. The method of claim 8 wherein decomposition of said bismaleimide during said pyrolysis occurs in a air purge atmosphere.

11. The method of claim 9 wherein said air gap serves as a dielectric between said first and second metal lines, said air gap having a dielectric constant k of approximately equal to 1.

12. A method comprising:

forming a plurality of signal lines on a substrate, said signal lines to be separated with a dielectric material to prevent errors that can result from signal transitions in nearby signal lines;

forming troughs in locations where said dielectric material is be located;

spin coating a thin film of bismaleimide over said substrate, wherein said troughs are filled with said bismaleimide;

planarizing and polishing said thin film of bismaleimide, wherein said troughs remain filled with said bismaleimide;

forming a diffusion layer over said substrate;

applying heat to cause a pyrolysis and decomposition of said bismaleimide; and

forming air gaps in space vacated by said bismaleimide in said troughs, said air gaps to function as a dielectric between said plurality of signal lines.

13. The method of claim 12 further comprising transforming said physical state of bismaleimide from a solid state to a gaseous state.

14. The method of claim 13 further comprising diffusing gas molecules of said bismaleimide through said diffusion layer.

15. The method of claim 14 wherein said signal lines are metal routing lines.

16. The method of claim 15 wherein said pyrolysis and diffusion causes substantially all of said bismaleimide to be removed from said troughs.

17. The method of claim 16 wherein said bismaleimide includes physical properties comprising:

a film process ability wherein said bismaleimide can be spun onto a surface;

film uniformity wherein said bismaleimide is amorphous;

thermal stability wherein said bismaleimide maintains a solid state and has minimal weight loss up to at least 300°

C.;

a decomposition temperature above 350°

C.; and

low residue level after decomposition.

18. The method of claim 16 wherein said bismaleimide is decomposed in a nitrogen purge atmosphere.

19. The method of claim 15 wherein said troughs are formed with a dry etch process.

20. A semiconductor apparatus comprising:

a first metal interconnect line on a first support layer;

a second metal interconnect line on said first support layer and located adjacent to said first metal line; and

a separation region between said first and second metal interconnect lines to contain an air gap dielectric, wherein a trough is formed with said first and second metal interconnect lines and said first support layer, said air gap dielectric comprising an air gap region formed by a method comprising;

coating said separation region and said first and second metal interconnect lines with a thin film of bismaleimide, wherein said trough is filled with said bismaleimide;

planarizing said bismaleimide, wherein said thin film of bismaleimide is leveled with an upper surface of said first and second metal interconnect lines;

forming a diffusion layer over said separation region and said first and second metal interconnect lines, wherein said trough is capped with said diffusion layer; and

applying heat to cause a pyrolysis and decomposition of said bismaleimide, wherein said bismaleimide is evacuated from said trough, forming an air gap between said first and second metal interconnect lines.

21. The semiconductor apparatus of claim 20 further comprising transforming said physical state of bismaleimide from a solid state to a gaseous state.

22. The semiconductor apparatus of claim 21 further comprising diffusing gas molecules of said bismaleimide through said diffusion layer.

23. The semiconductor apparatus of claim 22 wherein said air gap serves as a dielectric between said first and second metal interconnect lines, said air gap having a dielectric constant k of approximately equal to 1.

24. The semiconductor apparatus of claim 23 wherein substantially all of said bismaleimide in said trough is removed.

25. The semiconductor apparatus of claim 24 wherein said bismaleimide has a thermal stability property wherein less than 1% weight loss occurs in said bismaleimide below 300°

C.

26. The semiconductor apparatus of claim 25 wherein said bismaleimide further comprises a decomposition temperature of between 350°

C. to 450°

C.

27. The semiconductor apparatus of claim 26 wherein said bismaleimide further comprises a decomposition residue property wherein less than 5% residue is left after complete decomposition from said pyrolysis at above 400°

C.