Femtosecond laser-induced formation of submicrometer spikes on a semiconductor substrate

• US 7,442,629 B2
• Filed: 08/04/2005
• Issued: 10/28/2008
• Est. Priority Date: 09/24/2004
• Status: Active Grant

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Mazur, Eric, Shen, Mengyan
• Primary Examiner(s): NGO, NGAN V
• Application Number:
  US11/196,929
• Publication Number:
  US 20060079062A1
• Time in Patent Office: 1,181 Days
• Field of Search: 438/487, 438/940, 257/E21.347, 257/E21.475
• US Class Current: 438/487
• CPC Class Codes: B23K 26/1224 in vacuum
• CPC Class Codes: H01L 21/02381 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/02532 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/0259 Microstructure
• CPC Class Codes: H01L 21/02686 Pulsed laser beam
• CPC Class Codes: H01L 21/2252 using predeposition of impurities into the semiconductor surface, e.g. from a gaseous phase
• CPC Class Codes: H01L 21/268 using electromagnetic radiation, e.g. laser radiation
• CPC Class Codes: H01L 21/302 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
• CPC Class Codes: H01L 21/67075 for wet etching
• CPC Class Codes: H01L 29/30 characterised by physical imperfections; having polished or roughened surface
• CPC Class Codes: H01L 29/34 the imperfections being on the surface
• CPC Class Codes: Y10S 438/94 Laser ablative material removal

Abstract

The present invention generally provides semiconductor substrates having submicron-sized surface features generated by irradiating the surface with ultra short laser pulses. In one aspect, a method of processing a semiconductor substrate is disclosed that includes placing at least a portion of a surface of the substrate in contact with a fluid, and exposing that surface portion to one or more femtosecond pulses so as to modify the topography of that portion. The modification can include, e.g., generating a plurality of submicron-sized spikes in an upper layer of the surface.

Claims

1. A method of processing a semiconductor substrate, comprising

placing at least a portion of a surface of the semiconductor substrate in contact with a liquid, and

exposing said surface portion to one or more short laser pulses so as to modify surface topography of that portion to generate surface features having heights less than about 1 micrometer.

2. The method of claim 1, further comprising selecting said laser pulses to have pulse widths in a range of about 100 fs to about a few ns.

3. The method of claim 2, further comprising selecting said laser pulses to have pulse widths in a range of about 100 fs to about 500 fs.

4. The method of claim 1, further comprising selecting said liquid to be any of a polar or a non-polar liquid.

5. The method of claim 4, further comprising selecting said liquid to be water.

6. The method of claim 1, further comprising selecting said liquid to be silicon oil.

7. The method of claim 1, further comprising selecting said liquid to be an alcohol.

8. The method of claim 1, further comprising selecting the semiconductor substrate to be a silicon wafer.

9. The method of claim 2, further comprising selecting said laser pulses to have wavelengths in a rang of about 400 nm to less than about 800 nm.

10. The method of claim 9, further comprising selecting said laser pulses to have an energy ranging from about 10 microjoules to about 400 microjoules.

11. The method of claim 1, further comprising controlling said laser pulses so as to generate a plurality of surface spikes having an average height less than about 1 micrometer and average widths in a range of about 100 nm to about 500 nm.

12. The method of claim 11, wherein said surface spikes have an average height in a range of about 200 nm to about 1 micrometer.

13. The method of claim 10, wherein the step of exposing the surface to laser pulses further comprises applying the pulses to the substrate surface at a rate in a range of about 1-kHz to about 1 Hz.

14. The method of claim 1, further comprising selecting the number of laser pulses applied to the surface to be in a range of about 1 to about 2500 pulses.

15. A method of processing a substrate, comprising

disposing a layer of a liquid over at least a portion of a surface of a substrate,

applying a plurality of radiation pulses having pulse widths in a range of about 50 femtoseconds to about 500 femtoseconds to said portion so as to generate a plurality of surface features having heights less than about 1 micrometer.

16. The method of claim 15, wherein said radiation pulses have pulse widths in a range of about 100 fs to about 500 femtoseconds.

17. The method of claim 15, further comprising selecting said liquid to be any of a polar or a non-polar liquid.

18. The method of claim 15, further comprising selecting said semiconductor substrate to be a silicon wafer.

19. The method of claim 15, further comprising selecting said laser pulses to have wavelengths in a range of about 400 nm to about less than about 800 nm.

20. The method of claim 15, further comprising selecting said laser pulses to have an energy ranging from about 10 microjoules to about 400 microjoules.

21. The method of claim 15, wherein said surface features comprise surface spikes having heights in a range of about 100 nm to about 500 nm.