FLAT TOP LASER BEAM PROCESSING FOR MAKING A SOLAR CELL SUBSTRATE
Flat top beam laser processing schemes are disclosed for producing various types of hetero-junction and homo-junction solar cells. The methods include base and emitter contact opening, back surface field formation, selective doping, and metal ablation. Also, laser processing schemes are disclosed that are suitable for selective amorphous silicon ablation and selective doping for hetero-junction solar cells. These laser processing techniques may be applied to semiconductor substrates, including crystalline silicon substrates, and further including crystalline silicon substrates which are manufactured either through wire saw wafering methods or via epitaxial deposition processes, that are either planar or textured/three-dimensional. These techniques are highly suited to thin crystalline semiconductor, including thin crystalline silicon films.
1 . A method of processing a thin crystalline silicon substrate, said method comprising the steps of:
delineating emitter and base regions with pulsed laser ablation utilizing a flat top laser beam on a thin crystalline silicon substrate making openings defining emitter to base isolation regions, said substrate having a thickness in the range of approximately 1 micron to 100 microns suitable for use in a back-contact back-junction solar cell;
performing pulsed laser ablation with a flat top laser beam on said thin silicon substrate to form base openings;
irradiating said base region with a flat top laser beam to form doped base regions;
selectively doping said emitter regions;
performing pulsed laser ablation with a flat top laser beam to open contacts for base regions and emitter regions;
forming metallization on said base regions and said emitter regions; and
performing pulsed laser ablation with a flat top laser beam of said metallization to form an interdigitated pattern of metal lines connected to said base regions and metal lines connected to said emitter regions.
2 . The method of claim 1 , wherein said flat top laser beam is created according to an aperturing of the beam method.
3 . The method of claim 1 , wherein said flat top laser beam is created according to a beam integration method.
4 . The method of claim 1 , wherein said flat top laser beam is created according to a diffractive grating method.
5 . The method of claim 1 , wherein said step of delineating emitter and base regions with pulsed laser ablation utilizing a flat top laser beam on a thin crystalline silicon substrate further comprises delineating said emitter and said base regions in an interdigitated pattern.
6 . The method of claim 1 , wherein said step of performing pulsed laser ablation with a flat top laser beam of said metallization is carried out below an oxide ablation threshold for said thin crystalline silicon substrate.
7 . The method of claim 1 , delineating emitter and base regions with pulsed laser ablation utilizing a flat top laser beam on a thin crystalline silicon substrate is carried out via pulsed laser ablation of a deposited borosilicate glass layer.
8 . The method of claim 1 , wherein said step of irradiating said base region with a flat top laser beam to form doped base regions further comprises irradiating a phosphorus-doped silicon oxide layer to form doped base regions.
9 . The method of claim 1 , wherein said step of delineating emitter and base regions with pulsed laser ablation utilizing a flat top laser beam is carried out via a laser ablation process and using a pulsed laser having a wavelength of approximately 800 nm or less and a pulse width less than approximately 100 picoseconds.
10 . The method of claim 9 , wherein said wavelength is approximately 355 nm or less.
11 . The method of claim 9 , wherein said pulse width is less than approximately 20 picoseconds.
12 . The method of claim 1 , wherein said irradiating said base region with a flat top laser beam to form doped base regions further comprises irradiating said base region with a hybrid flat top laser beam to form doped base regions further.
13 . A method of processing a thin crystalline silicon substrate, said method comprising the steps of:
delineating emitter and base regions with pulsed laser ablation utilizing a flat top laser beam on a thin crystalline silicon substrate, said substrate having a thickness in the range of approximately 1 micron to 100 microns suitable for use in a back-contact back-junction solar cell;
performing pulsed laser ablation with a flat top laser beam on said thin silicon substrate to form base openings;
irradiating said base region with a hybrid flat top laser beam to form doped base regions;
selectively doping said emitter regions;
forming isolated contacts for base regions and emitter regions.