Femtosecond laser-induced formation of submicrometer spikes on a semiconductor substrate
The present invention generally provides semiconductor substrates having submicronsized 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.
1. A system for fabricating a radiation-absorbing semiconductor substrate, comprising:
a laser radiation system for generating laser pulses,
a vacuum chamber including a window for entry of said laser pulses into the chamber,
a translation stage disposed in said vacuum chamber and configured for supporting a sample, said stage allowing moving the sample relative to the laser pulses for exposing different portions of a surface of the sample to said laser pulses,
a liquid cell coupled to the stage so as to provide contact between a liquid contained therein and said surface of the sample,
wherein the vacuum chamber is configured to allow pumping out air bubbles in said liquid.
2. The system of claim 1 , further comprising a lens for focusing said laser radiation pulses through said window of the vacuum chamber onto said substrate surface.
3. The system of claim 1 , wherein said laser pulses have a pulsewidth in a range of 50 fs to a few ns.
4. The system of claim 1 , wherein said laser pulses have a pulsewidth in a range of 50 fs to about 500 fs.
5. The system of claim 1 , wherein said laser radiation system comprises a regenerative amplifier for amplifying said laser pulses.
6. The system of claim 5 , wherein said laser radiation system further comprises a harmonic generation system for receiving said amplified pulses and generating second-harmonic pulses.
7. The system of claim 6 , wherein said laser radiation system further comprises a dichroic mirror for directing said second-harmonic pulses via said window of the vacuum chamber onto said sample surface.
8. The system of claim 2 , wherein said focused radiation pulses exhibit a fluence in a range of about 1 kJ/cm 2 to about 8 kJ/cm 2 at said sample surface.
9. The system of claim 1 , wherein said laser radiation system comprises an amplified, Ti:Sapphire laser system.
10. The system of claim 1 , wherein said translation stage is a 3-D translation stage.
11. The system of claim 1 , further comprising an optical imaging system for monitoring said sample surface during irradiation by the laser pulses.
12. The system of claim 1 , wherein said liquid is transparent to radiation having wavelength components in a range of about 400 nm to about 800 nm.
13. The system of claim 1 , wherein said liquid presents a thickness in a range of 1 nm to about 20 nm to said laser pulses.
14. The system of claim 1 , wherein said liquid comprises any of water, alcohol or silicon oil.