Patent FR-2801726-A1 (FR)
Title: Method for manufacturing photovoltaic element and corresponding cell, in particular for solar cells
Inventor: BAJARD JEAN
IPC: H01L31/042
Filed: 1999-11-26
Abstract: Method for manufacturing photovoltaic device or cell on the basis of monocrystalline or polycrystalline silicon has two stages applied to silicon wafer (1) of sufficient quality and in specific order. First stage comprises obtaining a standard photovoltaic device or cell which is very strongly doped at the front. Second stage comprises ion implantation, heat treatment and hardening by quenching.  The first stage of manufacture comprises obtaining a standard photovoltaic device or cell which is very strongly doped at the front. The front face of silicon wafer (1) is intensively doped to a suitable depth in the standard manner to obtain the back field provision, the emitter layer (2) and the collector junction of low depth, in particular by the activation of atoms of dopants, the metallization of front and rear faces to form layers for contact, the formation of a passivation layer (4), and the formation of an anti-reflection cover (4'). The method includes a successive deposition of thin amorphous layers which are suitably doped, and other specified layers required for functioning. The second stage of manufacture comprises two supplementary operations which include a ionic implantation on the front face to make it amorphous, followed by the main cycle of thermal treatment which preserves a good homogeneity of thermal conditions on the surface of wafer, and comprises two phases: a phase of heating the wafer to a temperature in the range 450-600 deg.C, which is sufficient for a partial recrystallization of the zone made amorphous and the formation of an embedded sub-structure (5), which is substantially planar and constituted of silicon made uniformly amorphous; a quenching or equivalent rapid cooling phase having a congealing or solidifying effect at the level of interfaces (6,6') of the sub-structure (5). The useful crystalline configurations allow a strong secondary generation of pairs of current carriers. The two sequences of operations can partly overlap, the ionic implantation can be effected in the course of first sequence, and the main thermal treatment can be carried out at the end of procedure; or the two sequences can be reversed. The operation of tempering of metal-semiconductor contacts is carried out in the course of the main thermal treatment. The activation of atoms of dopants is carried out at least partly in the course of the main thermal treatment. The activation of atoms of dopants is carried out at least partly in the course of the main thermal treatment. The method can include several thermal cycles with heating to a temperature of about 500 degrees C, or slightly above 500 degrees C. The formation of passivation layer (4) is to reduce by a maximum the surface recombination and to minimize the quantity of introduced oxygen. The thickness of anti-reflection cover (4') is determined so that the properties of cover are optimized at the start of the main thermal treatment. The method prevents or strongly limits the diffusion of metallic contact layers and protects them against oxidation. In the second embodiment, the sub-structure (5) comprises the first zones of thickness which favor the generation and recuperation of primary and secondary carriers, and the second zones of lower thickness, possibly null, having lower opposition to the transport of minority carriers. The second zones are separated and extend under metallic strips of the gate forming the contact layer open for the extraction of carriers, and constitute a substantially similar pattern. A photovoltaic element for a photovoltaic cell, photopile, or analogous device having high output, is obtained by the proposed method. The sub-structure (5) demarcated by the interfaces (6,6') comprises a high density of centers for secondary generation by impact.