DE102009018653B4 - Method for the production of semiconductor devices using doping techniques - Google Patents

Abstract

Method for producing a silicon solar cell with selective emitter and metallization for contact finger generation, wherein the emitter regions below the contact fingers have a locally high doping concentration, wherein for adjusting the metallization for the generation of the contact fingers, the selectively doped structure by means of an IR-sensitive camera device (3) determined in their position in the wafer (1) and the metallization step is aligned using the visualized position, wherein the doped surface remains exactly limited to the area of the applied metallization.

Description

The invention relates to a method for the production of semiconductor devices using doping techniques, wherein during the processing a sequence of layers is generated, which are to be positioned exactly to each other, in particular a method for producing a silicon solar cell with selective emitter and metallization for contact finger generation, said the emitter regions below the contact fingers have a locally high doping concentration.

From the DE 10 2007 035 068 A1 For example, a method of fabricating a silicon solar cell with selective emitter is previously known. This method comprises the method steps of producing a planar emitter on an emitter surface of a solar cell substrate, applying an etching barrier to first portions of the emitter surface, etching the emitter surface in second portions of the emitter surface not covered by the etching barrier, removing the etching barrier and producing metal contacts the first subareas.

In this method, an emitter is firstly produced on at least one surface of a solar cell substrate having a homogeneous doping concentration which is high enough that it is suitable for contacting by the screen printing method. However, the problem is the exact positioning of the metal contacts on the above-mentioned first portions.

In a known manner, wafers are adjusted at different process steps in the respective production plant, so that the structures produced in the individual process steps can be aligned with each other. Here, it is possible either to align the wafers mechanically by stops or to determine the position of special reference points in the installation and to align the process with the aid of camera systems operating in the visual area.

The reference points used are usually the edges of the wafer or specially applied markings.

Exact positioning is crucial in the production of highly efficient solar cells, as the structures, which are only a few micrometers wide at certain process steps, have to be positioned exactly in order to achieve the desired function and high efficiency of the solar cell.

To solve the Justageproblems is according to the DE 699 15 317 T2 a self-adjusting method has been proposed for producing a selective emitter and metallization in a solar cell. In this method, so-called fired contacts are generated. In detail, an etching to remove Sägeschäden and an anisotropic texturing is first realized. This is followed by deposition of a dielectric containing n-type dopant onto the back surface of the wafer. In the next step, a p-type dopant is applied to the back surface and thermally treated to easily diffuse the n-type emitter and the p-type backside region. If necessary, the thermal process involves treating the dielectric, e.g. By oxidation to achieve sufficient resistance to plating solutions. In the next step, laser processing and the formation of patterns on the front dielectric as well as a laser processing of the rear dielectric as well as a simultaneous electroless metallization of the front and rear metal contacts takes place. Thus, the second heating is locally realized by passing a beam of a laser over the surface of the device where metallization is to be applied. In order to prevent excessive ablation during the heating step, it is necessary to defocus the laser.

In the method and apparatus for manufacturing a solar cell electrical contact structure on a substrate according to DE 10 2006 055 862 A1 the contact structure is realized by generating a metallic vapor in the region of the substrate, wherein a mask which partially shields the substrate from the metallic vapor is provided, which has a contact structure, ie corresponding openings. This mask is then moved in sections through the metallic vapor, with the movement of the mask through the metallic vapor relative to the substrate. Also in this method, the positioning accuracy between the substrate and the mask is limited, so that in the end, to reach contactable emitter, they must be sufficiently wide and have a locally strong doping.

Thus, the difficulty in positioning the metallization to make a front-side contact structure results in having to choose or choose the area of high doping wider, based on the actual metallization paths. This basically has a detrimental effect on the achievable efficiencies of manufactured solar cells, but ensures that the metallization actually comes to lie exclusively on the highly doped regions.

The publication US 2006/0 188 797 A1 describes a method for producing a Semiconductor device having a selective emitter and metallization, wherein the emitter regions have a locally high doping concentration, wherein the selectively doped structure is determined by means of an IR-sensitive camera device in its position in the wafer. From the above, it is therefore an object of the invention to provide a further developed method for the production of semiconductor devices using doping techniques, wherein during the processing a sequence of layers is generated, which are to be positioned exactly to each other. In particular, there is a further developed method for producing a silicon solar cell with selective emitter and metallization for contact finger generation, wherein the emitter regions below the contact fingers have a locally high doping concentration and it is necessary to increase the efficiency of the solar cell thus produced.

The object of the invention is achieved by a method according to the teaching of claim 1, wherein the dependent claims comprise at least expedient refinements and developments.

The core idea of the invention is to determine a selectively doped structure or a doping gradient generated in the semiconductor substrate by means of an infrared-sensitive camera device in its position in the substrate and to use the position thus found directly or indirectly for the adjustment of the following processing step.

According to the inventive method according to claim 1, the selectively doped emitter structure produced in a known manner is itself used to position the z. B. screen mask respectively the metal grid used. In contrast to methods of the prior art, therefore, a direct adjustment is made. To make the selectively doped structure visible, it is heated or exposed to an infrared, in particular NIR radiation. In this way it is possible to visualize the selectively doped structure, which can not be detected in the visible range of the light, for an IR-sensitive camera device. Thus, a referencing can take place directly on the recognized, visualized structure of the emitter regions. The prior art corresponding indirect adjustment to third features, eg. As wafer edges or alignment marks, which always entails a chain of tolerances, omitted in the inventive solution. It should be noted at this point that the Alignmentproblem is not limited to a metallization, but also occurs in other manufacturing steps, for. As in the processing of highly doped areas on the back of a back-side contact cell. Here can be used for the adjustment of the n-high doping on the existing p-high doping or vice versa.

The wafer can be subjected to IR transmitted light or IR incident light irradiation and the transmitted or emitted IR radiation can be used to visualize the selectively doped structure in order to adjust the z. B. screen print mask.

Using the principle according to the invention, it is then possible to carry out the selectively doped structure with reduced dimensions, ie. H. the doped surface remains exactly limited to the area of the subsequently applied metallization, which increases the efficiency and the efficiency of a solar cell produced in this way.

The invention will be explained below with reference to an embodiment and with the aid of figures.

Hereby show:

1 a principle arrangement for the realization of the method for producing a silicon solar cell, wherein for adjusting the screen mask for the generation of the contact fingers, the selectively doped emitter regions are visualized, and

2 Real images of a visualized doping structure of a wafer, it being understood that the highly doped region absorbs a greater proportion of IR radiation.

In one embodiment of the invention, a screen-printed solar cell with a selective emitter is assumed.

This is a cell structure in which the surface under the contact metallization highly doped and the remaining areas are weakly doped.

This doping can first be generated as a homogeneous weak doping by gas phase diffusion in a tube furnace. In a next step, those areas are then masked, which should remain weak doped. By a further gas phase diffusion then the non-masked areas are subjected to a high doping.

After removal of the masking, a full-area antireflection coating is produced. Then the metallization is applied by screen printing and made by sintering an electrical connection to the underlying emitter.

The screen mask is to be aligned exactly to the highly doped areas, so that the pressure of the contact fingers can be done with high accuracy.

For adjusting the screen-printing mask for the generation of the contact fingers, the selectively doped structure is determined by means of an IR-sensitive camera device in its position in the wafer and then aligned directly the screen printing mask using the visualized position.

Due to the much more accurate compared to the prior art adjustment, it is possible to subject less surface of a high doping, which improves the efficiency of the solar cell.

The visualization of the position of the selectively doped structure can be done with an arrangement according to 1 be made.

For this purpose, for example, below the doped silicon wafer 1 a radiation source 2 arranged, which emits the IR radiation.

Due to the dependence of the absorption coefficient in the silicon on the wavelength and the doping concentration is an IR-sensitive camera 3 capable of visualizing the selective emitter structure so that the positioning of the screen mask for the step of forming the metal contact fingers can be performed with high accuracy.

That from the IR camera 3 taken picture of the highly doped region of the emitter areas is in the representations after 2 shown. It becomes clear that the highly doped emitter area absorbs more infrared radiation, due to the IR camera 3 and a suitable display device can be visualized.

By the direct adjustment of the metal grid on the doping structure itself otherwise occurring positioning inaccuracies in the production of selective dopants can be avoided. As a result, the highly doped area can be more accurately limited to the area under the metallization, which entails the desired positive effects in terms of the efficiency of the solar cell. For the contact metallization can be used not only on the known screen printing technique, but also on a stencil printing or a so-called aerosol printing with a corresponding plating, without departing from the inventive concept.

In contrast to the known edge adjustment, the additional inaccuracy is eliminated by possibly rough or oblique edges.

Also compared to laser markings, there is another advantage, since the proposed technology of immediate adjustment excludes damage in the substrate from the outset by the laser marking.

Claims (5)

Method for producing a silicon solar cell with selective emitter and metallization for contact finger generation, wherein the emitter regions below the contact fingers have a locally high doping concentration, wherein for adjusting the metallization for the generation of the contact fingers, the selectively doped structure by means of an IR-sensitive camera device ( 3 ) in their position in the wafer ( 1 ) and aligning the metallization step using the visualized position, whereby the doped surface remains exactly confined to the area of the metallization to be applied. The method of claim 1 used in the manufacture of a back contact semiconductor solar cell. The method of claim 1, wherein the wafer is briefly subjected to a heat treatment for determining the position of the selectively doped structure. The method of claim 1 or 3, wherein the wafer is subjected to IR transmitted light or IR incident light irradiation and the transmitted or emitted infrared radiation is used to visualize the selectively doped structure, to directly carry out the adjustment of the metallization step. Method according to one of claims 1, 3 or 4, wherein the metallization is carried out by means of screen printing, stencil printing or aerosol printing.

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