METHOD FOR PRODUCING DOPING REGIONS IN A SEMICONDUCTOR LAYER OF A SEMICONDUCTOR COMPONENT

Abstract

The invention relates to a method for producing doping regions in a semiconductor layer of a semiconductor component, wherein the method includes the following steps: A) implanting a first dopant of a first doping type into at least one implantation region in the semiconductor layer, which implantation region adjoins a first side of the semiconductor layer; B) applying a doping layer, which contains a second dopant of a second doping type, indirectly or directly at least to the first side of the semiconductor layer, wherein the first and the second doping type are opposite; C) by the effect of heat, simultaneously driving the second dopant from the doping layer into the semiconductor layer and performing one or more of the processes of at least partially activating the implanted dopant in the implantation region and/or performing at least partial recovery of crystal damage in the semiconductor layer, which crystal damage was produced by the implantation, and/or driving in the first dopant from the implantation region.

Claims

1. A method for generating doping regions in a semiconductor layer (1) of a semiconductor component, comprising generating at least one doping region of a first doping type by introducing a first dopant of the first doping type and generating at least one doping region of the second doping type by introducing a second dopant of the second doping type, with the first and the second doping type being opposite, the method further comprises: A implanting the first dopant into at least one implantation region in the semiconductor layer, with the implantation region abutting to a first side of the semiconductor layer (1), B applying a doping layer which comprises the second dopant indirectly or directly at least on the first side of the semiconductor layer (1); C driving the second dopant by the effect of heat out of the doping layer (3) into the semiconductor layer (1) for generating at least the second doping region and carrying out one or more of the processes of at least partially activating the implanted dopant in the implantation region, at least partially curing crystal damage generated in the semiconductor layer (1) by the implantation process, or driving the first dopant out of the implantation region to generate the first doping region, with the processing step A of the implantation region providing a diffusion barrier for the second dopant.

2. The method according to claim 1, wherein the implantation region is embodied as the diffusion barrier for the second dopant, in which the first dopant is implanted with a concentration which is greater than a solubility limit of the first dopant in the semiconductor layer (1).

3. The method according to claim 1, wherein in the processing step A the dopant in the implantation region is implanted with a doping concentration exceeding 1×10.sup.20 cm.sup.−3.

4. The method according to claim 1, wherein the first doping type is of an n-doping type and the second doping type is of a p-doping type.

5. The method according to claim 1, wherein in the processing step B the doping layer (3) overlaps the implantation region.

6. The method according to claim 1, wherein the implantation region only extends over a portion of the first side of the semiconductor layer (1).

7. The method according to claim 6, wherein in the processing step A the implantation occurs via a mask.

8. The method according to claim 1, wherein the implantation region extends over an entire first side of the semiconductor layer (1).

9. The method according to claim 1, wherein the processing steps B and C are performed in-situ in a processing chamber.

10. The method according to claim 1, wherein in the processing step C, heating occurs to a temperature exceeding 700° C.

11. The method according to claim 1, further comprising after the processing step C in a processing step D directly applying a metallic contacting layer is directly applied on the semiconductor layer (1).

12. The method according to claim 1, further comprising after the processing step C, in a processing step D′ applying a dielectric layer on the semiconductor layer (1), and in a processing step D″ applying a metallic contacting layer on the dielectric layer.

13. The method according to claim 1, wherein the semiconductor layer (1) is a silicon layer.

14. The method according to claim 1, wherein a generation of the doping region of the first doping type occurs exclusively via ion implantation in the processing step A.

15. The method according to claim 1, further comprising that producing a photovoltaic solar cell using the method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following additional preferred features and preferred embodiments are explained based on exemplary embodiments and figures. Here it shows:

[0058] FIGS. 1A-1C in the left column I), partial steps of a first exemplary embodiment of a method according to the invention in which an implantation region extends completely over a first side of a semiconductor layer and in the right column II), partial steps of a second exemplary embodiment of a method according to the invention, in which an implantation region extends only over a partial region of a first side of the semiconductor layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] All illustrations in FIGS. 1A-1C show schematic cross-sections of details of the production process of a photovoltaic solar cell, not shown in a manner true to scale. In particular, the solar cell and/or its precursor continue to extend during the production process towards the right and the left and further details are not shown for reasons of clarity.

[0060] In FIGS. 1A-1C identical reference characters indicate the same elements or any elements with identical effects.

[0061] Sub-steps of a first exemplary embodiment of a method for generating doping regions in a semiconductor layer 1 are shown in the left column I) of FIGS. 1A-1C. The semiconductor layer 1 is embodied as a n-doped silicon wafer with a base doping of 0.5 to 10 Ohm cm. The method serves for the production of a photovoltaic solar cell.

[0062] A processing step A is shown in the detail of FIG. 1A in which an implanting occurs of a doping substance phosphorus, which therefore shows the n-doping type, in an implantation region 2 in the semiconductor layer 1. The implantation region 2 abuts at a first side of the semiconductor layer, which in the present case represents the front side VS of the semiconductor layer 1.

[0063] As discernible from FIG. 1A at I) the implantation region 2 is generated over the entire surface at the first side of the semiconductor layer 1.

[0064] The implantation occurs in a manner known per se at a few thousand electron-volt ion energy at a dose ranging from 1e14 to 1e16 cm.sup.−2.

[0065] An application of a doping layer 3 occurs in a processing step B at both sides and over the entire surface directly on the semiconductor layer 1. The doping layer 3 therefore covers the entire surface of the front side VS, as well as the rear side RS of the semiconductor layer 1.

[0066] The doping layer comprises boron as the second dopant and thus has the p-doping type.

[0067] The doping layer 3 is embodied as a boron silicate glass known per se and is produced in a tube furnace process known from prior art. Such a process is also called a two-side coating of the semiconductor layer 1 with boron-silicate glass (BSG).

[0068] In this tube furnace process, at temperatures from 700° C. to 950° C., in the present case approximately 900° C., boron atoms are introduced from the BSG, i.e. the doping layer 3, into the semiconductor layer 1 for a period from 30 to 60 minutes via the application of heat in order to produce a second doping region 4. Thus, at the back side RS a boron doped region develops over the entire surface, which represents the second doping region 4. Simultaneously an activation occurs of the first dopant phosphorus, a curing process, which corrects crystal damages in the semiconductor layer 1 generated by the implantation of phosphorus as well as the introduction of the implanted dopant phosphorus for the formation of the first doping region 2a. The first, phosphorus-doped doping region 2a extends therefore over the entire surface at the front side VS of the semiconductor layer 1. Furthermore, by the temperature treatment here a curing process occurs of the implantation region 2. During the implantation process here glass is formed in the implantation region 2, at least partially. In the above-mentioned temperature treatment however a recrystallization of the amorphous region occurs to a crystalline region, so that furthermore potential defects are cured.

[0069] The result is shown in FIG. 1B at I).

[0070] Although the doping layer 3 also covers the implantation region 2 over the entire surface, here essentially no diffusion occurs of boron into the implantation region 2, though, because the implanted phosphorus acts in the implantation region as a diffusion barrier in reference to boron. The implantation region 2 is therefore embodied as a diffusion barrier for the second dopant boron. Here it is actually possible that minor quantities of boron penetrate into the implantation region 2, however it is essential that in the entire implantation region and the entire first doping region 2a formed such a low volume of the second dopant diffuses therein that the electric features are completely or at least essentially determined by the first dopant phosphorus.

[0071] Accordingly there is a considerable difference to methods of the prior art using overcompensation: The doping concentration of the second dopant boron in the second doping region 4 is considerably greater, typically by at least one dimension, than the doping concentration of the second dopant boron in the first doping region 2a, due to potentially minor diffusion from the doping layer 3 into the implantation region 2. With regards to the electronic features the implantation region 2 therefore acts as a (complete) diffusion barrier for the second dopant, regardless of minor quantities of the second dopant boron penetrating into the implantation region 2 on the atomic level.

[0072] Subsequently, the boron-silicate glass is removed with hydrofluoric acid. The result is shown in FIG. 1C at I). Here, in a simple fashion, a phosphorus-doped first doping region 2a was produced at the front side VS of the semiconductor layer 1 and a boron-doped second doping region 4 at the back side RS of the semiconductor layer 1.

[0073] The front side VS represents here the side facing the irradiation when used as a solar cell.

[0074] A second exemplary embodiment is shown at the right column of FIGS. 1A-1C at II), in which at the back side RS of the semiconductor layer 1 several local first doping regions 2a are produced. For reasons of clarity only one local first doping region 2a is shown.

[0075] In a processing step A, a local implanting occurs of the first dopant phosphorus into the implantation region 2. The local implanting process occurs such that via the shadow mask M the implantation of the first dopant is prevented over partial areas. This is shown in FIG. 1A at II).

[0076] Accordingly, after the processing step A, several spatially spaced apart local implantation regions 2 are given at the back side RS of the semiconductor layer 1. For this purpose the shadow mask M shows accordingly several openings, which for reasons of clarity are not shown in FIGS. 1A-C as explained above.

[0077] In a processing step B, as already described in the first exemplary embodiment, a coating of both sides occurs of the semiconductor layer 1 with the doping layer 3, which is formed as a boron-silicate glass and thus comprises boron as the second dopant.

[0078] Subsequently, in a processing step C, similar to the way described for the first exemplary embodiment, simultaneously the activation of the first dopant occurs, the introduction of the second dopant out of the doping layer 3 into the semiconductor layer 1, the introduction of the first dopant out of the implantation region 2 to generate the first doping region 2a, and the curing of defects in the implantation region 2.

[0079] An essential difference to the first exemplary embodiment is here that due to the local embodiment of the implantation region 2, which therefore fails to completely cover the back side RS of the semiconductor layer 1, at the back RS of the semiconductor layer 1 in an alternating fashion second doping regions 4 and first doping regions 2a are present. However, at the front side VS of the semiconductor layer 1, over the entire surface, a second doping region 4 is formed, which is therefore also boron-doped.

[0080] The result is shown in FIG. 1B at II).

[0081] Subsequently, as described above, the boron-silicate glass is removed. The result is shown in FIG. 1C at II).

[0082] Therefore, in a simple fashion via the second exemplary embodiment of the method according to the invention the production of a photovoltaic solar cell is provided, which at the front side VS has over the entire surface a boron-doped doping region and at the back side alternating boron-doped and phosphorus-doped doping regions. This way, on the one side in a simple fashion, the boron-doped second doping region 4 can be contacted at the back side via a metal contacting structure, and on the other side, the phosphorus-doped first doping region 2a can be contacted via another metal contacting structure such that a photovoltaic solar cell is generated contacted at the back side. The boron-doping formed at the front side VS can here serve as a so-called “floating emitter” at the front side, without any separate electric contacting, in order to allow the use of other passivation layers and/or to improve the lateral one of minority charge carriers.

[0083] Additionally, (not shown) an electrically conductive connection of the doping region 4 at the front VS can occur to the doping region 4 at the back side RS, for example by forming a EWT-solar cell, by providing another local boron-diffusion which penetrates the semiconductor layer perpendicularly in reference to the front and thus connects the front doping region 4 to the rear doping region 4, and/or by the formation of a MWT-solar cell by providing an additional metallization of the doping region 4, which is guided through the semiconductor layer 1 to a rear contacting.