Microneedles

1. A method of manufacturing a plurality of silicon microneedles which have a bevelled tip, the method comprising the steps of:

providing a silicon substrate having a front face and a rear face;

forming a first mask arrangement on the front face of the substrate, the first mask arrangement defining one or more gaps;

performing a SF 6 based plasma etch of the front face through the gaps in the first mask arrangement to provide one or more etch features having a sloping face, wherein the SF 6 based plasma etch undercuts the first mask arrangement with an undercut that is at least 10% of the depth of a corresponding etch feature;

forming a second mask arrangement on the etch features to define locations of the microneedles, in which the second mask arrangement is located entirely on sloping faces of the etch features; and

performing a DRIE (deep reactive ion etch) anisotropic plasma etch of the etched front face of the substrate to form a plurality of microneedles which have a bevelled tip, wherein the sloping faces of the etch features at least in part give rise to the bevelled tips of the microneedles.

2. A method according to claim 1 in which the DRIE plasma etch of the etched front face is an anisotropic cyclical etch and deposition process.

3. A method according to claim 1 in which the first mask arrangement is an oxide mask.

4. A method according to claim 1 in which the second mask arrangement is deposited onto the etch features by PE-CVD (plasma enhanced chemical vapour deposition).

5. A method according to claim 1 in which the bevelled tips of the microneedles are formed as single bevel structures.

6. A method according to claim 1 in which the bevelled tips of the microneedles have a bevel angle of at least 60°.

7. A method according to claim 1 in which: the gaps defined by the first mask arrangement each have a width; the etch features each have a base width; and the base width of each etch feature is substantially equal to the width of its corresponding gap in the first mask arrangement.

8. A method according to claim 1 in which the SF 6 based plasma etch is formed in a gaseous mixture comprising SF 6 and an inert diluent.

9. A method according to claim 8 in which the gaseous mixture consists essentially of SF 6 , O 2 , C 4 F 8 and Ar.

10. A method according to claim 1 further comprising the step of performing a DRIE plasma etch of the rear face to form plurality of channels in the silicon substrate which are positioned so that, after the plurality of microneedles are formed, the channels act as bore passages extending through the microneedles.

11. A method according to claim 10 in which the step of performing a DRIE plasma etch of the rear face is performed prior to the step of performing a DRIE plasma etch of the etched front face.

12. A method according to claim 1 in which the DRIE plasma etch of the etched front face forms one or more ridge structures which are spaced apart from the microneedles.

13. A method according to claim 12 in which a plurality of interconnected ridge structures are formed to provide a plurality of microneedle surrounding fence structures each of which surround and are spaced apart from a microneedle.

14. A method according to claim 12 in which:

the SF 6 based plasma etch etches through a gap in the first mask arrangement to provide one or more etch features which have a pair of opposed sloping faces, and

the DRIE plasma etch of the etched front face is performed so that one of the pair of opposed sloping faces at least in part gives rise to the bevelled tip of a microneedle and the other of the pair of opposed sloping faces at least in part gives rise to a ridge which is spaced apart from the microneedle.

15. A method according to claim 1 in which the bevelled tips of the microneedles are formed as double bevel structures.

16. A method according to claim 15 in which the double bevel structures are formed by controlling etch conditions during the step of performing a SF 6 based plasma etch of the front face.

17. A method according to claim 15 in which the step of performing a SF 6 based plasma etch of the front face produces single bevel structures, and the double bevel structures are produced during the step of performing a DRIE plasma etch of the etched front face.

18. A method according to claim 17 in which the second mask arrangement comprises oxide masks having a thickness in the range 3 to 5 microns.

19. A method according to claim 1 in which the SF 6 based plasma etch is formed in a gaseous mixture comprising SF 6 and a sidewall passivation precursor.

20. A method according to claim 19 in which the sidewall passivation precursor is at least one of C 4 F 8 and CHF 3 .

21. A method according to claim 20 in which the gaseous mixture consists essentially of SF 6 , CHF 3 and C 4 F 8 .

22. A method according to claim 19 in which the gaseous mixture further comprises O 2 .

23. A method according to claim 22 in which the gaseous mixture consists essentially of SF 6 , O 2 and C 4 F 8 .