Thin film membrane structure

• US 20030100136A1
• Filed: 11/26/2001
• Published: 05/29/2003
• Est. Priority Date: 11/26/2001
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Dougherty, George M.
• Granted Patent: US 6,780,786 B2
• Time in Patent Office: Days
• US Class Current: 438/50
• CPC Class Codes: B01D 2323/10 Specific pressure applied
• CPC Class Codes: B01D 2325/02 Details relating to pores or porosity of the membranes
• CPC Class Codes: B01D 2325/02833 more than 10 and up to 100 nm
• CPC Class Codes: B01D 2325/04 Characteristic thickness
• CPC Class Codes: B01D 67/0072 by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
• CPC Class Codes: B01D 71/02 Inorganic material
• CPC Class Codes: B01D 71/0215 Silicon carbide; Silicon nitride; Silicon oxycarbide
• CPC Class Codes: B81B 2201/10 Microfilters, e.g. for gas or fluids
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 2201/0115 Porous silicon
• CPC Class Codes: B81C 2201/017 Methods for controlling internal stress of deposited layers not provided for in B81C2201/0164 - B81C2201/0169
• CPC Class Codes: H01L 21/28525 the conductive layers comprising semiconducting material H01L21/28518, H01L21/28537 take precedence
• CPC Class Codes: H01L 29/16 including, apart from doping materials or other impurities, only elements of Group IV of the Periodic Table

Abstract

A membrane structure comprising a silicon film having a grain structure including grains defining pores therebetween.

Claims

1. A membrane structure comprising a silicon film having a grain structure including grains defining pores therebetween.

2. A membrane structure comprising a silicon film including grains having gaps formed therebetween to define individual pores, the maximum cross-sectional dimension of any one grain approximately equal to the thickness of the film.

3. The structure of claim 2 wherein a lateral dimension of any pore is less than that of any grain.

4. The structure of claim 2 wherein a lateral dimension of the pores is between about 10 and 50 nanometers.

5. The structure of claim 2 wherein the thickness of the film is less than or equal to about 150 nanometers.

6. The structure of claim 2 wherein the thickness of the film is between about 50 and 150 nanometers.

7. The structure of claim 2 wherein the roughness of the film is approximately equal to its thickness.

8. The structure of claim 2 wherein the film forms a filter.

9. The structure of claim 2 wherein the film is conformal to an underlying surface.

10. The structure of claim 2 further including a structural layer to support the film.

11. The structure of claim 2 further including a conformal layer formed on the film to provide a selected chemical or biological function.

12. A membrane filter structure comprising a silicon film having a grain structure including grains defining pores therebetween, a lateral dimension of the pores being between about 10 and 50 nanometers and the maximum diameter of any one grain not exceeding the thickness of the film.

13. A method of fabricating a membrane structure comprising:

forming a sacrificial layer over a first surface of a substrate;

forming a silicon layer over the sacrificial layer such that the silicon layer has a grain structure including grains defining pores therebetween wherein the maximum diameter of any one grain does not exceed the thickness of the membrane structure; and

removing the sacrificial layer.

14. The method of claim 13 further including forming a passageway through the substrate.

15. The method of claim 13 further including forming a conformal layer over the silicon layer to provide a selected chemical or biological function.

16. A method of fabricating a membrane structure comprising:

forming a sacrificial layer over a surface of a substrate;

forming a structural layer over the sacrificial layer;

forming a silicon layer over the structural layer such that the silicon layer has a grain structure including grains defining pores therebetween wherein the maximum diameter of any one grain does not exceed the thickness of the membrane structure; and

removing the sacrificial layer.

17. A method of fabricating a membrane filter structure comprising:

forming a sacrificial layer over a first surface of a substrate;

growing a silicon film over the sacrificial layer at a temperature near the tensile-to-compressive transition temperature of the silicon film such that the silicon film has a grain structure including grains defining pores therebetween wherein the maximum diameter of any one grain does not exceed the thickness of the membrane filter structure; and

removing the sacrificial layer

18. The method of claim 17 wherein the silicon film is formed under a near zero-stress condition.

19. The method of claim 17 wherein the silicon film has a residual stress within a range of about −

50 to 50 mega-Pascals.

20. The method of claim 17 wherein the silicon film has a residual stress within a range of about −

100 to 100 mega-Pascals.

21. The method of claim 17 wherein the silicon film is grown such that a lateral dimension of any pore is less than that of any grain.

22. The method of claim 17 wherein the silicon film is grown such that a lateral dimension of the pores is between about 10 and 50 nanometers.

23. The method of claim 17 wherein the silicon film is grown such that the thickness of the film is between about 50 and 150 nanometers.

24. The method of claim 17 wherein the silicon film is grown such that the roughness of the film is approximately equal to its thickness.

25. The method of claim 17 further including forming a conformal layer on the silicon film to provide a selected chemical or biological function.

26. The method of claim 17 further including monitoring the residual stress of the silicon film.