DE102010016992A1 - Manufacturing method of a semiconductor device - Google Patents

Abstract

The invention relates to a method of manufacturing a semiconductor device, comprising the following method steps: providing a substrate (3) with a semiconductor surface (31); Forming a first passivation layer (1) from a first dielectric material on the semiconductor surface (31); Applying a second passivation layer (2) made of a second dielectric material on the first passivation layer (1) and / or on a further semiconductor surface on the substrate (3) arranged opposite the semiconductor surface (31); and subjecting the substrate (3) to a layer-sacrificing treatment in which a layer thickness of the second passivation layer (2) is reduced essentially along the entire semiconductor surface (31) or the entire further semiconductor surface by a predominant part of the layer thickness.

Description

The invention relates to a manufacturing method of a semiconductor device.

One of the limiting factors for the efficiency of semiconductor devices and devices is the recombination of charge carriers on semiconductor surfaces that have surface states that favor recombination activity. This problem is particularly important in solar cells. Because in this case, the recombined charge carriers are no longer available for power generation. In order to reduce recombinations, the semiconductor surface must be passivated by lowering the recombination activity of carriers over surface states.

A very effective passivation system for semiconductor devices generally comprises a double layer of first and second passivation layers on a semiconductor surface. The two passivation layers are each formed from a different dielectric material. An example of such a double layer structure on a silicon substrate is a first passivation layer of thermally or wet-chemically grown silicon oxide and a second passivation layer of aluminum oxide deposited thereon. The reasoning underlying this passivation system is that the first passivation layer has a chemically passivating effect, while the second passivation layer is field-effect-passivating in that it displaces free charge carriers from the semiconductor surface due to a high solid area charge density.

Such double layers often have the disadvantage that the second passivation layer is sensitive to certain process steps of semiconductor device fabrication. In particular, in the manufacture of solar cells, after the application of the passivation layer, several further process steps are to be carried out which attack the second passivation layer and could at least partially destroy it. A similar problem arises in backside passivation of a solar cell and subsequent backside metallization by means of a metal paste followed by heat treatment (fire process). In particular, when the passivation underlying the metal paste is formed of alumina, it may be partially or completely destroyed or "eaten" during the heat treatment by the metal paste.

In order to circumvent this supposed problem, it is usually either an attempt to shift the second passivation layer as far as possible towards the end of the production process after layer of harmful treatment steps have been completed. Or a protective layer is deposited on the double layer system to protect the passivation. This can be done in particular in the case of the backside metallization described above prior to the application of the metal paste. However, these approaches have the disadvantage of requiring additional processing steps, thus increasing costs and reducing throughput.

It is an object of the invention to provide a manufacturing method of a semiconductor device in which an effective surface passivation of the semiconductor device is achieved inexpensively and with the least possible additional outlay.

The object is achieved according to the invention by a manufacturing method having the features of claim 1. Advantageous developments of the invention are listed in the subclaims.

The semiconductor device to be fabricated is preferably a solar cell in which improved surface passivation of the semiconductor substrate surface results in more efficient conversion of incident light into electrical current. However, good surface passivation may also be important in other areas of semiconductor technology. The surface passivation described here can be applied to solar cells on the front side, that is to say on the light incidence side of the solar cell, on the rear side, that is to say on the side of the solar cell facing away from the light, or on both sides. Advantageously, the semiconductor substrate is formed of silicon. The semiconductor substrate may include a semiconductor wafer.

The invention is based on the surprising finding that the application of a second passivation layer to a first passivation layer can lead to a lasting improvement in the passivation quality of the first passivation layer, even in the event that the second passivation layer is subsequently at least partially removed or damaged. The reduction of the layer thickness of the second passivation layer may intentionally occur in the manufacturing process, for example by means of an additional etching step. Alternatively, the treatment sacrificing the layer may be a process step which is necessary for the production and which inevitably leads to a reduction of the layer thickness of the second passivation layer by a predominant part.

In certain configurations, an improvement in the passivation quality of the first passivation layer may occur even if the second passivation layer does not respond to the first passivation layer Passivierschicht itself is applied, but on the first passivation layer opposite side of the substrate. In other words, the first passivation layer is first applied to one semiconductor surface of the substrate, and then the second passivation layer is deposited on the opposite further semiconductor surface, which is reduced by a predominant part of its layer thickness in a subsequent treatment of the substrate.

One explanation for this is that the second passivation layer does not or not only acts as a field-effect-passivating layer, as previously thought, but gives an improved passivation effect solely or predominantly through its unique presence of the first passivation layer. For example, the second passivation layer may act as a hydrogen donor for the first passivation layer. After the hydrogen has diffused into the first passivation layer, further maintenance of the second passivation layer is no longer necessary in this case.

In both embodiments, the layer thickness reduction takes place essentially along the entire semiconductor surface or the entire further semiconductor surface. This essentially means that, due to the process, areas of insignificant size can be present, which are not influenced by the treatment sacrificing the layer, for example edge areas of the substrate protected by retaining devices.

In a preferred embodiment, it is provided that the second passivation layer substantially completely loses its layer thickness during the treatment sacrificing the layer. In other words, the second passivation layer of the second dielectric material no longer exists after the sacrificial treatment layer. Essentially means here that not functional as a passivation layer, in particular non-contiguous layer residues can remain on the substrate.

Instead of dissolving or removing the first passivation layer during the sacrificial treatment, the first dielectric material can also be converted into another material. All that is essential is that the first passivation layer made of the first dielectric material no longer has an original layer thickness or no longer exists after the layer sacrificial treatment.

Even if a layer-sacrificing treatment should not normally be provided in a particular method for producing the solar cell, the deliberate removal of the second passivation layer may entail advantages. In certain embodiments, unwanted effects at the edge of the solar cell can thereby be avoided. If, for example, the first passivation layer is incomplete or incomplete on the substrate edge, as is often the case, when the second passivation layer is applied, this second passivation layer comes into direct contact there with the semiconductor surface. Due to surface charges of the second passivation layer, unwanted effects may occur at the substrate edge, for example a parasitic current flow due to an inversion or accumulation channel (shunting).

In an advantageous development, it is provided that the second passivation layer is dissolved at least partially during the treatment sacrificing the layer in a functional layer arranged above the second passivation layer. By this is meant that the layer thickness of the second passivation layer decreases due to an interaction with the functional layer. It is thus not necessary for the second dielectric material to be in a dissolved form in the functional layer. Rather, conversion of the entire second passivation layer or a portion thereof may occur as a result of a chemical reaction between the material of the functional layer and the second dielectric material.

The functional layer may be, for example, a metal paste. By means of a heat treatment (a so-called fire step), a contact layer for the solar cell is usually formed from the metal paste. Due to the heat treatment, the material of the metal paste reacts with the second dielectric material of the second passivation layer. The resulting reaction products can be present in solid form or else in gaseous form (for example nitrogen). The second passivation layer thus undergoes partial or complete chemical conversion. In this sense, in the present case, the heat treatment is a layer-sacrificing treatment. The contact layer formed by the firing step of the metal paste may have improved adhesion to the substrate due to this reaction between the paste material and the second dielectric material.

According to an expedient embodiment, it is provided that the second passivation layer is at least partially removed during the treatment sacrificing the layer. The second passivation layer can hereby be partially or completely mechanically removed or etched away. For example, the sacrificial layer treatment may be a texture etching treatment that optimizes the light incident surface of the solar cell for light absorption. Alternatively, it may be an etching step, in which certain layers are structured during solar cell production.

Preferably, it is provided that the first passivation layer are formed directly on the semiconductor surface and / or the second passivation layer is formed directly on the first passivation layer. Immediately means that there are no further intermediate layers between the respective layers. In particular, when the first passivation layer is a passivation layer which chemically passivates, it makes sense if it is arranged directly on the semiconductor surface to be passivated.

In an expedient embodiment, it is provided that the first passivation layer is formed on an n-type and / or p-type doped semiconductor surface. If no further, in particular no field effect passivating, second passivation layer is present on the frequently passively chemically passivated first passivation layer, the passivation can be used both for p-type and for n-type doped semiconductor surfaces. In contrast, in the case of a passivation layer which is predominantly field-effect-passivating, it depends on the sign of its fixed surface charge density, which doping type can be effectively passivated. The passivations described here can be used in particular on n ⁺ -doped high-efficiency solar cells made of silicon.

In addition, for the reasons stated above, with the present method it is also possible to effectively and inexpensively passivate a semiconductor surface which has differently doped regions, ie with regions of n or n ⁺ type adjacent to regions of p or p ⁺ type. Thus, different passivation systems for the individual doping regions are not necessary. Substantially all of the semiconductor surface can be passivated with one pass of the manufacturing process.

In an advantageous embodiment, it is provided that the first passivation layer is patterned before the application of the second passivation layer. Thus, the semiconductor surface is not completely covered by the first passivation layer before the second passivation layer is deposited or deposited. The first passivation layer can be used in the manufacturing process, for example, as a diffusion barrier and mask to form diffusion regions in the semiconductor surface. In this case, the second passivation layer is also applied to areas of the semiconductor surface not covered by the first passivation layer, ie, there directly to the semiconductor surface.

In certain combinations of doping type of the semiconductor surface or surface areas and sign of the solid surface charge of the second passivation layer, an inversion channel can form in the semiconductor, which can lead to a short-circuit effect called shunting. To avoid this, the second passivation layer should be removed as far as possible.

According to a preferred development, it is provided that the second passivation layer is essentially formed from a metal oxide. Advantageously, it is provided that the second passivation layer is formed from aluminum oxide. This may be the specific stoichiometric composition Al ₂ O ₃ or, more generally, an AlO _x layer of suitable stoichiometry. Alternatively, another suitable compound of aluminum oxide and one or more further elements may be used as the second dielectric material, in particular aluminum oxynitride (Al _x O _y N _z ). The second passivation layer is in each case preferably produced by means of an atomic layer deposition process (ALD).

According to a preferred embodiment, it is provided that the first passivation layer is essentially formed from silicon nitride and / or silicon oxide. It is also advantageous to use silicon oxynitride or another suitable compound of silicon oxide and one or more further elements as the first dielectric material.

Preferably, it is provided that the first passivation layer is deposited on the semiconductor surface. Alternatively, in particular in the case of silicon semiconductor substrates, the first passivation layer can be produced as a native oxide by oxidation of the semiconductor surface, wherein the oxidation can be carried out in a gas atmosphere or wet-chemically.

In an expedient refinement, it is provided that the first passivation layer and the second passivation layer are formed on both sides of the substrate, that is to say both on the front side and on the back side of the substrate. In this case, the two passivation layers may each have different layer thicknesses on the two substrate sides. Preferably, however, the passivation on the substrate front side is substantially identical to that on the substrate back side. Expediently, the first passivation layer and / or the second passivation layer are each formed on both sides in a single deposition or oxidation step.

In special embodiments, it is also expedient to form only the second passivation layer made of the second dielectric material on both sides of the substrate. Is located For example, alumina on a semiconductor surface of n- or n ⁺ -type, only an insufficient surface passivation can be achieved here. In the case of wafer solar cells with base and emitter on opposite wafer surfaces, it is therefore advantageous to remove the aluminum oxide layer on the n- or n ⁺ -type surface according to the nature of the passivation. This is usually realized in a one-sided etching process. The application of a second passivation layer of aluminum oxide also on the p- or p ⁺ -type semiconductor surface to be passivated allows a more cost-effective removal of the aluminum oxide layer on the n- or n ⁺ -type surface, since the etching process no longer has to be unilateral.

It is expediently provided that the passivation layers on the substrate are subjected to a heat treatment (tempering) after or during the application of the second passivation layer to the first passivation layer and before the layer sacrificial treatment. This heat treatment has the consequence that the passivation effect of the first passivation layer improves substantially and sustainably. For example, the heat treatment may promote diffusion of hydrogen from the second passivation layer into the first passivation layer.

Whether and to what extent the heat treatment is expedient and with which parameters it must be carried out depends on the type of application of the passivation layers, in particular of the second passivation layer. If the second passivation layer is deposited on the first passivation layer already at a high temperature, subsequent heat treatment may also be omitted. Preferably, a heat treatment is carried out at a temperature between about 200 and 600 ° C, since at a higher temperature out-diffusion of hydrogen from the passivation is to be feared. Preferably, a heat treatment temperature of about 300 to 450 ° C is used, in particular of about 400 ° C. The heat treatment preferably lasts for at least about 5 minutes, more preferably about 5 to 20 minutes, more preferably at least 10 minutes, especially about 10 to 15 minutes.

In all of the embodiments described above, an additional covering layer after the layer sacrificial treatment can be applied to the first passivation layer or to residues of the second passivation layer, for example to optimize the optical adaptation of a light incidence side of the solar cell. This cover layer can be formed, for example, from silicon nitride.

The invention will be explained below with reference to embodiments with reference to the figures. Shown here by schematic cross-sectional drawings of intermediate states of a solar cell:

1a to 1e a sequence of method steps according to an embodiment of the invention; and

2a to 2e a sequence of method steps according to another embodiment of the invention.

The 1a to 1e illustrate a sequence of process steps according to an embodiment of a manufacturing method of a solar cell with a full-area passivation.

First, according to the 1a a substrate 3 , For example, a silicon wafer, with a semiconductor surface 31 provided. From the semiconductor surface 31 becomes a first passivation layer 1 formed as a result the product in 1b to obtain. The first dielectric material from which the first passivation layer 1 is formed, for example, be silicon oxide, which is grown by thermal or wet chemical oxidation.

In a subsequent process step, a second passivation layer 2 on the first passivation layer 1 applied, for example by means of a deposition process. The second passivation layer 2 is formed of alumina as a second dielectric material. The substrate 3 with the two passivation layers formed thereon 1 . 2 is in 1c shown.

Subsequently, during the production of the solar cell, a layer sacrificing treatment follows, which leads to a reduction of the layer thickness of the second passivation layer 2 leads. While according to an in 1d illustrated first embodiment, the second passivation layer 2 is partially removed, for example, as a result of a wet chemical etching treatment, according to a in 1e illustrated second embodiment, a functional layer 4 applied, which for layer thickness reduction of the second passivation 2 leads.

At the functional layer 4 it is a screen-printed metal paste for producing a contact layer or metallization layer. Here, the sacrificial treatment layer is a firing step for drying the applied metal paste. The second dielectric material in this case reacts with the material of the metal paste and converts partially or completely, so that the remaining aluminum oxide layer has a smaller layer thickness.

An alternative embodiment of the manufacturing method will be described with reference to FIG 2a to 2e illustrated. Again, first a substrate 1 with a semiconductor surface 31 according to the 2a provided. On the substrate 1 becomes a structured first passivation layer 1 formed, as in the 2 B shown. Here, the first passivation layer 1 initially on the entire semiconductor surface 31 are formed and then patterned by means of conventional masks / etching, so that areas of the semiconductor surface 31 be exposed.

The structured first passivation layer 1 is then used as a diffusion barrier to form a diffusion layer 5 in the substrate 1 to create. According to the structuring of the first passivation layer 1 has the diffusion layer 5 at the exposed areas of the semiconductor surface 31 Diffusion areas on.

The entire structure thus formed is then followed by a second passivation layer 1 deposited, for example from alumina by atomic layer deposition (ALD) to the in 2d to obtain the product shown. The second passivation layer 1 sits down on both the first passivation layer 2 as well as in the exposed areas directly on the semiconductor surface 31 from.

Finally, the second passivation layer 2 completely removed during a sacrificial treatment. The treatment sacrificing the layer can be a treatment to be carried out anyway in solar cell manufacture, for example a texture etching step. Alternatively, an additional etching step for removing the second passivation layer 2 be inserted in the manufacturing process.

LIST OF REFERENCE NUMBERS

1

first passivation layer

2

second passivation layer

3

substratum

31

Semiconductor surface

4

functional layer

5

diffusion layer

Claims (14)

A manufacturing method of a semiconductor device, comprising the following steps: - providing a substrate ( 3 ) with a semiconductor surface ( 31 ); Forming a first passivation layer ( 1 ) of a first dielectric material on the semiconductor surface ( 31 ); Application of a second passivation layer ( 2 ) of a second dielectric material on the first passivation layer ( 1 ) and / or on one of the semiconductor surface ( 31 ) disposed opposite another semiconductor surface on the substrate ( 3 ); and - submitting the substrate ( 3 ) sacrificing a layer in which a layer thickness of the second passivation layer ( 2 ) substantially along the entire semiconductor surface ( 31 ) or the entire further semiconductor surface is reduced by a predominant part of the layer thickness. Manufacturing method according to claim 1, characterized in that the second passivation layer ( 2 ) sacrifices its layer thickness substantially completely during the sacrificial treatment. Manufacturing method according to claim 1 or 2, characterized in that the second passivation layer ( 2 ) during the sacrificial treatment at least partially in one over the second passivation layer ( 2 ) arranged functional layer ( 4 ) is resolved. Manufacturing method according to one of claims 1 to 3, characterized in that the second passivation layer ( 2 ) is at least partially removed during the sacrificial treatment. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) directly on the semiconductor surface ( 31 ) and / or the second passivation layer ( 2 ) directly on the first passivation layer ( 1 ) are formed. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) on an n-type and / or p-type doped semiconductor surface ( 31 ) is formed. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) before applying the second passivation layer ( 2 ) is structured. Manufacturing method according to one of the preceding claims, characterized in that the second passivation layer ( 2 ) is formed substantially from a metal oxide. Manufacturing method according to claim 8, characterized in that the second passivation layer ( 2 ) is formed of alumina. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) is formed essentially of silicon nitride and / or silicon oxide. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) on the semiconductor surface ( 31 ) is deposited. Manufacturing method according to one of the preceding claims, characterized in that the first passivation layer ( 1 ) and the second passivation layer ( 2 ) on both sides of the substrate ( 3 ) are formed. Manufacturing method according to one of the preceding claims, characterized in that after or during the application of the second passivation layer ( 2 ) to the first passivation layer ( 1 ) and before sacrificing treatment the passivation layers ( 1 . 2 ) on the substrate ( 3 ) are subjected to a heat treatment. Production method according to one of the preceding claims, characterized by the production of a solar cell.

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