Amorphous silicon crystallization using combined beams from optically pumped semiconductor lasers
View Patent ↗An amorphous silicon layer on a glass substrate is crystallized by concentrating CW radiation from a number of OPS-lasers into a line of light on the layer. The layer is moved with respect to the line of light to control the dwell time of the line on any location on the layer and to crystallize an extended area of the layer.
1. Apparatus for crystallizing a silicon layer supported by substrate in a working plane, the apparatus comprising:
a plurality of external-cavity, optically pumped, surface-emitting semiconductor (OPS) lasers arranged to generate a corresponding plurality of continuous wave laser-beams;
a beam-homogenizer and line projector;
an arrangement for propagating the beams along parallel paths such that each beam at least partially overlaps an adjacent beam in an entrance plane of the beam homogenizer and line projector transverse to the parallel paths to form a combined beam; and
wherein the homogenizer and line projector is configured and arranged to divide the combined beam, in an axis transverse to the propagation direction, into a plurality of beam portions, and to project the beam portions into an elongated area in the working plane in a manner such that each of the beam portions essentially fills the elongated area and wherein the homogenizer and line projector have a longitudinal Z-axis and a Y-axis transverse to the Z-axis, and an X-axis transverse to the Z-axis and perpendicular to the Y-axis and wherein said arrangement propagates the beams along paths parallel to the Z axis of the homogenizer and line projector and wherein the homogenizer and line projector includes an array of elongated rectangular reflectors aligned parallel to the X axis and having a length in the X-axis, said homogenizer including a lens system and wherein the reflective surface array and the lens system are configured such that the reflective surface array divides the combined beam, in the Y-axis, into a plurality of beam portions and the lens system projects the beam portions into an elongated area in the working plane, with the elongated area having a length and width parallel to respective Y-axis and X-axis and with each of the beam portions essentially filling the elongated area.
2. The apparatus of claim 1 , wherein the elongated area has a length parallel to the transverse axis and has a length-to-width aspect-ratio greater than about 200:1.
3. The apparatus of claim 2 , wherein the elongated area has a width less than about 5 micrometers.
4. The apparatus of claim 3 , wherein the combined radiation of the projected beam-portions in the elongated area is uniform to within about 5% of a nominal value.
5. The method of claim 1 , wherein each of the laser beams has a wavelength less than about 575 nm.
6. The method of claim 5 , wherein each of the laser beams has a wavelength between about 450 nanometers and 575 nanometers.
7. The method of claim 6 , wherein the external-cavity, optically pumped, surface-emitting semiconductor lasers are external-cavity, intracavity frequency-doubled, optically pumped, surface-emitting, semiconductor lasers.
8. The apparatus of claim 5 , wherein any one of the OPS-laser beams has a wavelength different from the wavelength of the others.
9. The apparatus of claim 8 , wherein each of the OPS-laser beams has a wavelength different from the wavelength of each of the others.
10. The apparatus of claim 5 , wherein two of the OPS-laser beams have the same wavelength and are plane-polarized, with the polarization plane of one of the two beams being perpendicular to the polarization plane of the other.
11. The apparatus of claim 1 , wherein there are N OPS-lasers for generating N laser beams, and in the parallel paths the N laser beams are aligned in one row thereof parallel to the transverse axis.
12. The apparatus of claim 1 , wherein there are M×N OPS-lasers for generating M×N laser beams, and in the parallel paths the beams are arranged in M rows of N beams with the beams in the rows of beams being aligned parallel to the transverse axis.
13. The apparatus of claim 1 , wherein said lens system includes at least one cylindrical lens having optical power in the Y-axis only.
14. The apparatus of claim 13 , wherein longitudinal edges of the reflectors in the reflector array are about contiguous.
15. The apparatus of claim 13 , further including an optical element located in the parallel paths of the beams between the lasers and the homogenizer and line projector, the optical element having a plurality of rectangular sections aligned parallel to the Z-axis and parallel to the X-axis, having different lengths in the Z-axis, and arranged one on top of the other in the Y-axis with the thickness and number of sections selected such that the combined beam is intercepted by all of the sections.
16. The apparatus of claim 15 , wherein the optical element is a solid element in the form of a stepped prism.
17. The apparatus as recited in claim 13 , wherein said lens system includes a second lens having optical power in the Y-axis and in the X-axis.