LT5608B - Method for producing of solar cell selective emitter with self-aligned metallization - Google Patents

Abstract

The invention relates to methods for producing of semiconductor solar cell, especially, for forming of a selective emitter by one diffuse method and for opening self coincide with emitter n+ zone contact opening. A semiconductor plate (1) treated byfirst type additions is laid with dielectric layer (2). At future n+ zone in dielectric layer zone is opened an opening (3). Further a plate (1) is laid with glass containing additions type with contrary than plate conduction. After holding a plate at high temperature special time, zones (5) are formed in a plate at openings in a dielectric. Zones (5) are with larger quantity of additions and under a dielectric are zones (6) with smaller concentration of additions. After etching silicate glass, an opening, which self coincides with n+ zone, is opened. After immersing a plate in solution with Ni ions, on open n+ zone precipitates Ni layer. That method can be used at a plane as well textured surface of a semiconductor plate.

Description

Technical field

This method is directed to the production of a semiconductor solar cell, and more specifically to the formation of a selective emitter region (nln) by a single diffusion process and the opening of a contact opening adjacent to the emitter n ⁺ region.

State of the art

It is known that the parameters of the solar cell (SE) are improved by the use of a selective emitter, that is, in the n-region, by additionally forming an n ⁺ region (strongly doped) just under the metal contact, and by weaker doping. Strong alloying reduces the contact resistance at the silicon / metal interface (interface region). The weaker alloyed surface of the emitter has a lower surface charge recombination and is easier to passivate. In addition, there is never a dead layer on the weaker alloy, which reduces the lifetime of the charge.

Commercial solar cells with selective emitter has produced only one firm in the world (BPSolar), such as solar cell manufacturing process is more complicated and more expensive compared to J ^k

With conventional technology, in their developed [O. Schultz, SW Glunz, W. Warta, Proc. 21 st European Photovoltaic Solar Energy Conference, Dresden, 2006, p. 826-829]. In technology, a selective emitter is formed by two phosphorus diffusion processes and the necessary coating deposition [Prog. Photovolt: Res. Appl. 2004; 12: 253-281]. Both times the diffusion of phosphorus takes place from a gaseous source. After forming the n region on the surface of the whole plate and applying a protective layer, the opening for the nl region is opened by a mechanical or laser cut. This is followed again by the diffusion of phosphorus forming the n ~ region in the groove. Thus, the formation of a selective emitter requires three high-temperature processes («(1) and n ⁺ (2) diffusion, and formation of a protective layer (3)) and laser or mechanical cutting.

In another embodiment of selective emitter formation with crosslinking metallization [US Patent

6429037, S. R. Wenham, Self-alignment method for forming a selective emitter and metallization in a solar cell. M.A.

Green] used a layer of doped glass as the source of diffusion in the area, with a continuous layer covering the entire surface of the plate. The result of high temperature exposure is the n region of the whole surface of the plate. The laser then performs additional doping to create the m ⁺ region, affecting its glass only at specific locations. The laser surface treatment mode is chosen in such a way that not only additional diffusion occurs in the affected area, but also a layer of alloy glass is deposited. This opens the hole at the n ⁺ region where Ni is deposited from the corresponding solution containing Ni ions. At first sight, the method is simple and convenient, but the additional laser diffusion, which creates the n ⁺ region and at the same time opens the opening in the protective layer, creates undesirable defects in the existing emitter, worsening the parameters of the solar cell. In addition, additional doping is accompanied by etching, providing very little opportunity for stronger doping and deepening of the n ⁺ region, and the emitter diffusion must necessarily be made from solution.

The essence of the invention

The present invention is directed to forming a selective emitter and aperture for a metal contact in a solar cell, self-aligning with the n ⁺ region, in a single process of high temperature and selective etching. In our method, the increased number of defects in the emitter due to laser treatment and n ⁺ concentration limitation is avoided by opening the n ⁺ region in the barrier layer by laser or other imaging prior to emitter diffusion. Emitter diffusion reduces the number of laser-induced defects due to temperature effects. In addition, the concentration and depth of impurities in the rf region are no longer limited by the ability to etch the surface of this region as it is

In the invention of SRWenham and MA Green. The selective etching of phosphor glass, leaving the remainder of the barrier, allows the opening of the metal-contact opening to meet the n ⁺ region. In the proposed method:

(a) Apply a dielectric layer (barrier layer) of a certain thickness to the surface of the p-conductivity semiconductor wafer, the residue of which, after the process of emitter diffusion and selective removal of phosphorus silicate glass, remains as a passive duck and metal deposition limiting layer;

(b) One of the methods of image formation (photolithography, laser ablation, or mechanical engraving) is to open an opening in the dielectric layer for the diffusion of rf;

c) by placing the plate in a high temperature device with an atmosphere of phosphorus impurities or by coating the working surface of the plate with a continuous alloying layer containing sufficient amounts of phosphorus impurities to form a high alloy region, . At the orifice, the area with higher impurity rf is formed, and below the dielectric, a smaller area 3

d) Selective etching of phosphorus silicate glass opens the opening at the n ⁺ region, ie where the barrier layer has been etched during the imaging barrier. The remnant of the barrier layer protects the n-type region during contact metal deposition;

e) It is desirable that the residual barrier layer can play the role of a passive and anti-reflective layer after chemical deposition of the metal.

DESCRIPTION OF THE DRAWINGS

The attached Figures 1-7 of the solar cell show the essence of the invention:

FIG. 1 is a cross-sectional view of a semiconductor wafer (1) with a barrier dielectric layer (2) coated thereon;

FIG. 2 a cross-sectional view of a semiconductor wafer after the opening (3) in the barrier layer (2);

FIG. Case 3, when the plate is covered with a continuous layer of phosphorous silicate glass (4) after opening the opening in the barrier layer (2);

FIG. 4 cross-section of the semiconductor wafer after doping with a continuous layer of phosphorus silicate (4) with a n (6) and a n ⁺ (5) region under the barrier; FIG. 5 cross-section of the plate after alloying from a gas source, phosphorus silicate glass (4) formed at the orifice barrier, on and n ⁺ regions as in the case of diffusion from the phosphorus silicate glass layer;

• Figs. 6 cross-section of the plate after etching the phosphorus silica glass with the n ⁺ region (5) of the hole in the barrier residue (2);

FIG. 7 cross-section of the plate after the metal (7) is selectively deposited at the orifice barrier;

Detailed description of the method

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. The semiconductor wafer 1, doped with a first type of impurity, is coated with a dielectric layer 2 of a certain thickness (Fig. 1). The dielectric can be SiO ₂ , Si _x N _y , TiO ₂ , ABOs + SiCb, Ta ₂ O _5, and other layers that slow down the diffusion of phosphorus The dielectric layer can be formed thermally, plasmochemically or by coating. The thickness of the dielectric depends on the concentration of impurities in the future less doped emitter region, so that an opening 3 (Fig. 2) in the dielectric layer 2 is formed at the forward rf region as required by laser etching, photolithography or mechanical cutting. If the bavarian layer is coated with a solution, it is possible to form holes 3 (Fig. 2) immediately at the required locations by silk screening. The plate thus prepared is coated with phosphorus silicate glass 4 (Fig. 3) containing impurities of the opposite conductivity type and then placed in a high temperature inert atmosphere. After holding the plate under these conditions for a time, areas of higher diffusion depth 5 (Fig. 4) with higher impurity content (eg 10-40Ω / π) are formed at the openings in the dielectric, and areas of lower depth (6) with less impurity below the dielectric concentration (e.g. 50-3000Ω / π). The same can be done without covering the plate with a continuous layer of phosphorus silicate glass, and after forming the apertures 3 (Fig. 2) in the dielectric, place the plate in a high temperature inert atmosphere containing phosphorus atoms. In this case, phosphorus silicate glass 4 with a high concentration of phosphorus is formed to a considerable extent at the open surface of the semiconductor (Fig. 5) and diffusion occurs over the whole area as in the case described above. The result and the next steps are the same. By selectively etching the phosphorus silicate glass, we open the opening 3 to the Si surface, which spontaneously coincides with the n region 5 (Fig. 6). When the plate is immersed in the solution, a Ni ion 7 is deposited on the open surface of the semiconductor, forming a contact with the n ⁺ region of the semiconductor. Barrier layer remnant 2 (FIG. 7) protects the n-type region from metal plating.

This method can be applied to both a smooth and textured semiconductor wafer surface. As the nature of the surface changes, the optimal way to apply the barrier layer changes. This method of selective emitter formation combines well with various methods of forming the lower contact of a solar cell.

Examples of implementation of the invention

The following three examples are representative examples of the manufacture of a selective emitter for a solar cell according to the present invention, characterized by a barrier coating or the introduction of impurities.

First example

1.1 Corrosion of KOH in 20% solution removes the plate cutting lesions followed by texturing of the Si surface with a mixture of 2% KOH solution and isopropyl alcohol;

1.2 Plasmochemical SiO? plating - thickness 0.12-0.2u;

1.3 Photoresist coating;

1.4 Exposure of emitter metallization openings;

1.5 Sharpening;

1.6 Duplication;

1.7 Etching of plasma plasmic SiO ₂ to form openings corresponding to the emitter metallization image;

1.8 Removing the photoresist;

1.9 Dry cleaning

1.10 Coating of a continuous layer of phosphorus silicate glass with a solution containing 20-50% P ₂ O _{5 in} formed glass;

1.11 Drying of glass;

1.12. Thermal diffusion 800 to 1050 ° C in an inert atmosphere;

1.13 Corrosion of phosphorus silicate glass with the well-known P-corrosive;

1.14 Chemical Ni precipitation from alkaline solution (pH 8-10) for about 5 min.

1.15 Ni ignition at 350 - 450 ° C in an inert atmosphere;

1.16 Solder coating;

The second example

2.1 Corrosive treatment with hot KOH solution removes lesions caused by plate cutting;

2.2. A gel layer containing TiO ₂ with a thickness of 0.07 - 0.2μ in a centrifuge;

2.3 Gel layer thermodestruction at 115-800 ° C, Ar or O ₂ ;

2.4 laser ablation of TiO ₂ layer aperture corresponding to emitter contact image;

2.5 Removal of damage by etching with 2% KOH in water at 60 ° C;

2.6 Diffusion of phosphorus from a gas source 850-1050 ° C in an inert atmosphere;

2.7 P-etching of phosphorus silicate glass;

2.8 Ni chemical precipitation from alkaline (pH 8-10) solution for 4-5 min;

2.9 Ni ignition at 350-450 ° C in an inert atmosphere;

2.10 Coating of Cu on Ni;

The third example

3.1 Cutting through hot KOH removes cutting damage;

3.2 Apply a silk-screen gel layer to the face of the work plate with holes corresponding to the emitter contact image;

3.3 Gel thermodestruction at 450-800 ° C in a mixture of CO ₂ and Ar;

3.4 Coating a continuous layer of phosphorus silicate glass in a solution containing 20-50% P2O5 in formed glass;

3.5 Drying of the layer;

3.6 Thermal diffusion 800 - 1000 ° C in an inert environment;

3.7 Selective etching of phosphorus silicate glass;

3.8 Nickel plating of alkalis for 4-5 min.

3.9 Ni ignition at 350-450 ° C in an inert atmosphere;

3.10 Solder coating on Ni;

Three possible embodiments of the present invention are provided, characterized in that the barrier material is formed by its formation or by the formation of openings in the barrier. It is clear, however, that the aperture formation method may be chosen freely within the capabilities available, although laser aperture formation is the cheapest and most effective.

Claims (9)

DEFINITION OF INVENTION 1. A method of producing a selective emitter of a solar cell with self-adhesive metalization, including diffusion of the n region from the glass, formation of the n ⁺ region of the emitter, and contact opening by mechanical engraving and second diffusion process or laser diffusion and ablation precipitating Ni from a solution in one of the aforementioned methods in an open orifice, characterized in that: (a) Forms a backing layer of an electrician on the surface of a first type of semiconductor wafer b) Locally removes the barrier layer and opens an emitter metallization image corresponding to the aperture for the higher alloy degree emitter region (c) Coating with a high content (up to 50%) of the second type impurities on the surface so prepared at low temperatures d) Thermally treating the wafer at 800 - 1050 ° C in an inert atmosphere resulting in two areas of different alloying levels in the semiconductor - the lower alloy (50 - 3000Ω / ο) below the barrier and the high alloy (5-40Ω / Ο) at the aperture (e) a second type of impurity alloyed glass is abraded from the surface of said plate f) plate for 3-5 min. dip into a Ni-ion-rich hot alkaline solution (pH 7 - 10), resulting in a thin Ni layer on the open semiconductor, shaped like an emitter metallization 2. A process according to claim 1, wherein the bavarian layer is thermal SiO _x , plasmochemical. SiO _x , plasmochemical SiN _x , solution coated SiO _x , TiO ₂ , aluminosilicate glass or Ta ₂ Os; 3. The method of claim 1, wherein the barrier comprises two layers - SiO _x and TiO ₂ or aluminosilicate glass and SiO _x ; 4. The method of claim 1, wherein the opening in the barrier is formed by photolithography; 5. The method of claim 1, wherein the opening in the barrier is formed by laser ablation; 6. A method according to claim 1, characterized in that the opening in the barrier is mechanically incised and subsequently cleaned with hot alkaline solution; 7. The method of claim 1, wherein the step lc is not performed but heat-treated the plate in a stream of inert atmosphere which is also a carrier of the alloying material; 8. A process according to claim 2, characterized in that the barrier layer is coated with a solution in a centrifuge and formed at 100-800 ° C in an oxygen, inert atmosphere or a mixture of both: 9. The method of claim 2, wherein the solution in the coating layer of the barrier immediately forms an opening for a higher alloying emitter region corresponding to the emitter metallization image.