METHOD FOR PRODUCING DOPED POLYCRYSTALLINE SEMICONDUCTOR LAYERS

Abstract

The present invention relates to a method for producing highly doped polycrystalline semiconductor layers on a semiconductor substrate, wherein a first Si precursor composition comprising at least one first dopant is applied to one or more regions of the surface of the semiconductor substrate; optionally a second Si precursor composition comprising at least one second dopant is applied to one or more other regions of the surface of the semiconductor substrate, where the first dopant is an n-type dopant and the second dopant is a p-type dopant or vice versa; and the coated regions of the surface of the semiconductor substrate are each converted, so as to form polycrystalline silicon from the Si precursor. The invention further relates to the semiconductor obtainable by the method and to the use thereof, especially in the production of solar cells.

Claims

1: A liquid-phase method for producing a doped polycrystalline semiconductor layer on a semiconductor substrate, said method comprising: applying a first precursor composition comprising: (i) a first dopant; and (ii) at least one silicon-containing precursor which is liquid under SATP conditions or at least one solvent and at least one silicon-containing precursor which is liquid or solid under SATP conditions; to one or more regions of the surface of the semiconductor substrate, in order to create one or more region(s) of the surface of the semiconductor substrate coated with the first precursor composition; optionally applying a second precursor composition comprising: (i) a second dopant; and (ii) at least one silicon-containing precursor which is liquid under SATP conditions or at least one solvent and at least one silicon-containing precursor which is liquid or solid under SATP conditions; to one or more regions of the surface of the semiconductor substrate, in order to create one or more region(s) of the surface of the semiconductor substrate coated with the second precursor composition, where the one or more region(s) coated with the first precursor composition and the one or more region(s) coated with the second precursor composition are different and do not overlap or essentially do not overlap, and where the first dopant is an n-type dopant and the second dopant is a p-type dopant or vice versa; and converting the silicon-containing precursor to polycrystalline silicon.

2: The method according to claim 1, wherein the first composition and/or optionally the second composition is applied to the semiconductor substrate by a printing or spraying method.

3: The method according to claim 1, wherein (a) the at least one n-type dopant is selected from phosphorus-containing dopants, antimony-containing dopants, and mixtures of the above, and/or (b) the at least one p-type dopant is selected from boron-containing dopants and mixtures thereof.

4: The method according to claim 1, wherein the precursor is a polysilane.

5: The method according to claim 4, wherein the precursor has the generic formula Si.sub.nX.sub.c with X=H, F, Cl, Br, I, C.sub.1-C.sub.10-alkyl, C.sub.1-C.sub.10-alkenyl, C.sub.5-C.sub.20-aryl, n≧4 and 2n≦c≦2n+2.

6: The method according to claim 4, wherein the precursor is a silicon-containing nanoparticle.

7: The method according to claim 4, wherein the precursor composition comprises at least two precursors of which at least one is a hydridosilane oligomer and at least one is an optionally branched hydridosilane of the generic formula Si.sub.nH.sub.2n+2 with n=3 to 20.

8: The method according to claim 7, wherein the hydridosilane oligomer (a) has a weight-average molecular weight of 200 to 10 000 g/mol; and/or (b) has been obtained by oligomerization of noncyclic hydridosilanes; and/or (c) is obtainable by thermal conversion of a composition comprising at least one noncyclic hydridosilane having not more than 20 silicon atoms in the absence of a catalyst at temperatures of less than 235° C.

9: The method according to claim 1, wherein the precursor is converted to polycrystalline silicon using electromagnetic radiation and/or electron or ion bombardment and/or by a thermal method.

10: The method according to claim 9, wherein the conversion to polycrystalline silicon is effected thermally at a temperature in the range of 300-1200° C.

11: The method according to claim 1, wherein the process further comprises the step of creating a dielectric layer on the semiconductor substrate, where the first and/or second precursor composition is subsequently applied to the dielectric layer.

12: The method according to claim 11, wherein the dielectric layer is SiO.sub.x or Al.sub.xO.sub.y.

13: The method according to claim 1, wherein the semiconductor substrate is a silicon wafer.

14: The method according to claim 1, wherein the first composition and the second composition are applied to the same side of the semiconductor substrate.

15: The method according to claim 1, wherein the first composition and the second composition are applied to the opposite sides of the semiconductor substrate.

16: A semiconductor substrate, produced by a method according to claim 1.

17: A method for producing a solar cell, said method comprising: forming a doped polycrystalline semiconductor layer on said semiconductor substrate of claim 16.

18: A solar cell or solar module, comprising: the semiconductor substrate according to claim 16.

19: The method according to claim 14, wherein the first composition and the second composition are applied to the same side of the semiconductor substrate in an interdigitated structure.

Description

EXAMPLES

Example 1

[0079] By means of spin-coating, phosphorus-doped formulations consisting of 30% neopentasilane with 1.5% phosphorus doping and 70% toluene and cyclooctane solvents were applied to both sides of an n-type silicon wafer having a resistivity of 5 ohmcm. Conversion was effected at 500° C. for 60 s to a 50 nm-thick amorphous silicon layer. In the course of thermal treatment of the phosphorus atoms at 1000° C. for 30 min, the deposited a-Si layer crystallized to crystalline silicon, as can be inferred from the diffraction image after outward diffusion in FIG. 1.

[0080] By means of spin-coating, boron-doped formulations consisting of 30% neopentasilane with 1.5% boron doping and 70% toluene and cyclooctane solvents were applied to both sides of an n-type silicon wafer having a resistivity of 5 ohm cm. Conversion was effected at 500° C. for 60 s to a 50 nm-thick amorphous silicon layer. In the course of thermal treatment of the boron atoms at 1050° C. for 60 min, the deposited a-Si layer crystallized to crystalline silicon.

Example 2

[0081] After the deposition of polysilanes and the conversion to amorphous silicon, it was possible to crystallize the latter by means of two different methods:

[0082] 1. solid-phase crystallization and

[0083] 2. liquid-phase crystallization.

[0084] 1: thermal annealing in a nitrogen atmosphere at temperatures above 600° C.

[0085] 2: melting of the a-Si and subsequent liquid-based crystallization by means of an E-beam or laser. FIG. 2A shows an electron backscatter diffraction map of samples processed by means of solid-phase crystallization. FIG. 2B shows samples of a liquid-phase crystallization.

Example 3: Production of a Back-Contact Solar Cell

[0086] A back-contact solar cell was produced as follows:

[0087] a. Single-sided patterning of a silicon wafer.

[0088] b. Deposition of a 2 nm-thick SiO film onto the planar side of the silicon wafer.

[0089] c. Inkjet printing of a liquid Si-based composition containing a p-type dopant in the form of a wet film in a finger structure to the planar side of the silicon wafer having the 2 nm-thick SiO layer. The composition contains 30% neopentasilane with 1%-10% boron doping and 70% toluene and cyclooctane solvents. The fingers typically have widths of 200 μm-1000 μm.

[0090] d. Simultaneous printing of a liquid Si-based composition containing an n-type dopant in the form of a wet film in a form complementary to the structure deposited in (a) onto the same side of the silicon wafer. The composition contains 30% neopentasilane with 1%-10% phosphorus doping and 70% toluene and cyclooctane solvents. The fingers typically have widths of 200 μm-1000 μm.

[0091] e. Converting the wet films to elemental silicon, especially amorphous silicon, by conversion. The conversion takes place under a nitrogen atmosphere at temperatures of 400-600° C. Duration: 1 s-2 minutes. Preferably 60 s at 500° C. The layer thickness of the amorphous silicon is 50-200 nm.

[0092] f. Deposition of an SiN film onto the planar reverse side.

[0093] g. Conversion of the doped a-Si layers to polycrystalline silicon at 850° C. for a duration of 30 minutes with addition of POCl.sub.3. This results in formation of an n+ region on the patterned silicon wafer side.

[0094] h. Removal of the phosphosilicate glass (PSG) from the front side and of the SiN from the reverse side by means of HF.

[0095] i. Deposition of an antireflection layer on the front side and

[0096] j. Contacting of the p+ and n+ regions on the reverse side by means of a metal.