Annealing apparatus using two wavelengths of laser radiation
A thermal processing apparatus and method in which a first laser source, for example, a CO 2 emitting at 10.6 μm is focused onto a silicon wafer as a line beam and a second laser source, for example, a GaAs laser bar emitting at 808 nm is focused onto the wafer as a larger beam surrounding the line beam. The two beams are scanned in synchronism in the direction of the narrow dimension of the line beam to create a narrow heating pulse from the line beam when activated by the larger beam. The energy of GaAs radiation is greater than the silicon bandgap energy and creates free carriers. The energy of the CO 2 radiation is less than the silicon bandgap energy so silicon is otherwise transparent to it, but the long wavelength radiation is absorbed by the free carriers.
1. A thermal treatment apparatus, comprising:
a stage;
a source of continuous-wave visible light energy;
a source of continuous-wave infrared energy;
a first optical assembly comprising a reflector disposed along an optical axis of the source of continuous-wave visible light energy and having a reflection axis that intersects the stage; and
a second optical assembly comprising a homogenizer and a polarizer disposed along an optical axis of the source of continuous-wave infrared energy.
2. The thermal treatment apparatus of claim 1 , wherein the second optical assembly further comprises a beam expander.
3. The thermal treatment apparatus of claim 2 , wherein the second optical assembly further comprises an anamorphic optic.
4. The thermal treatment apparatus of claim 3 , wherein the first optical assembly further comprises a pyrometer oriented along the reflection axis.
5. The thermal treatment apparatus of claim 1 , wherein the first optical assembly produces a first beam of the continuous-wave visible light energy, the second optical assembly produces a second beam of the continuous-wave infrared energy, and the first beam surrounds the second beam.
6. The thermal treatment apparatus of claim 5 , further comprising a translation mechanism to scan the first beam and the second beam with respect to the stage while maintaining the first beam surrounding the second beam.
7. The thermal treatment apparatus of claim 6 , wherein the translation mechanism is coupled to the stage.
8. The thermal treatment apparatus of claim 6 , wherein the translation mechanism is coupled to the first and second optical assemblies.
9. A thermal treatment apparatus, comprising:
a stage;
a source of activating energy;
a source of heating energy;
a first optical assembly comprising a reflector disposed along an optical axis of the source of activating energy and having a reflection axis that intersects the stage; and
a second optical assembly comprising a homogenizer, a beam expander, and a polarizer disposed along an optical axis of the source of heating energy, wherein the beam expander comprises two cylindrical lenses and the homogenizer comprises a one-axis light pipe between the two cylindrical lenses.
10. The thermal treatment apparatus of claim 9 , wherein the first optical assembly further comprises a pyrometer disposed along the reflection axis.
11. The thermal treatment apparatus of claim 10 , wherein the activating energy comprises a continuous-wave source of activating energy, the heating energy comprises a continuous-wave source of heating energy, the first optical assembly shapes the activating energy emitted by the continuous-wave source of activating energy into a first beam and directs the first beam to a first area adjacent the stage, the second optical assembly shapes the heating energy emitted by the continuous-wave source of heating energy into a second beam and directs the second beam to a second area adjacent the stage, and the first area surrounds and encompasses the second area.
12. The thermal treatment apparatus of claim 11 , further comprising a translation mechanism to translate the stage or the first and second beams while maintaining the first area surrounding and encompassing the second area.
13. The thermal treatment apparatus of claim 11 , wherein the continuous-wave source of activating energy is visible light and the continuous-wave source of heating energy is infrared light.
14. The thermal treatment apparatus of claim 13 , wherein the continuous-wave source of activating energy comprises a laser diode and the continuous-wave source of heating energy comprises a CO 2 laser.
15. A thermal treatment apparatus, comprising:
a stage;
a CO 2 laser;
a plurality of diode lasers;
a first optical assembly optically coupled to the CO 2 laser, the first optical assembly comprising a homogenizer, a polarizer, an anamorphic optic, and a reflector to direct a continuous-wave beam from the CO 2 laser to a first area adjacent the stage;
a second optical assembly optically coupled to the plurality of diode lasers, the second optical assembly comprising a reflector to direct a continuous-wave beam from the plurality of diode lasers to a second area adjacent the stage, wherein the second area surrounds the first area; and
a translation mechanism coupled to the stage or to the first and second optical assemblies.
16. The thermal treatment apparatus of claim 15 , wherein the plurality of diode lasers comprises at least one GaAs diode laser.
17. The thermal treatment apparatus of claim 15 , further comprising a pyrometer disposed opposite the reflector from the stage and on an optical axis of the reflector.