NOVELTY - Processing thin crystalline silicon substrate includes delineating emitter and base regions with pulsed laser ablation utilizing flat top laser beam on a thin crystalline silicon substrate making openings define emitter to base isolation regions; performing pulsed laser ablation with flat top laser beam on the thin silicon substrate to form base openings; irradiating the base region with flat top laser beam to form doped base regions; and performing pulsed laser ablation with flat top laser beam to open contacts for base regions and emitter regions.    USE - Processing thin crystalline silicon substrate for use in a back-contact back-junction solar cell (claimed) or all back-contact homojunction solar cell or heterojunction all back-contact solar cell.    ADVANTAGE - The method reduces damage of silicon substrate to a level acceptable for high efficiency solar cell manufacturing that does not require post-laser-processing wet cleaning, hence simplifying the process flow and reducing the manufacturing cost. Utilizing flat top beam achieves increased alignment window for back-surface field (BSF) opening inside the BSG opening and contact opening inside the BSF. Flat top laser processing method increases throughput for forming BSF.    DETAILED DESCRIPTION - Processing thin crystalline silicon substrate comprises:    (A) delineating emitter and base regions with pulsed laser ablation utilizing flat top laser beam on a thin crystalline silicon substrate making openings define emitter to base isolation regions, where substrate has a thickness of approximately 1-100 mu m suitable for use in a back-contact back-junction solar cell;    (B) performing pulsed laser ablation with flat top laser beam on the thin silicon substrate to form base openings;    (C) irradiating the base region with flat top laser beam to form doped base regions;    (D) selectively doping the emitter regions;    (E) performing pulsed laser ablation with flat top laser beam to open contacts for base regions and emitter regions;    (F) forming metallization on the base regions and the emitter regions; and    (G) performing pulsed laser ablation with flat top laser beam of the metallization to form an interdigitated pattern of metal lines connected to the base regions and metal lines connected to the emitter regions.