DE102009018112B3 - Method for producing a semiconductor component, in particular a solar cell, with a locally opened dielectric layer and corresponding semiconductor component - Google Patents

Abstract

A method for producing a semiconductor component 100 and a corresponding semiconductor component are presented. The manufacturing method comprises the following method steps: providing a silicon substrate (1); Forming a first layer (3) of amorphous silicon on a surface of the silicon substrate (1); Forming a second layer (5) of a dielectric on the first layer (3); and locally removing the second layer (5) in ablation regions (9) by irradiating the silicon substrate (1) and the layers (3, 5) thereon with laser light (7). In this case, the laser light (7) is absorbed primarily in the amorphous silicon layer (3), whereby evaporation of amorphous silicon leads to ablating of the overlying dielectric layer (5). However, the amorphous silicon layer (3) is not completely removed. A residual layer remains and serves to reliably form an electrical contact with the silicon substrate (1).

Description

FIELD OF THE INVENTION

The The invention relates to a method for producing a semiconductor component, in particular a solar cell, wherein one on a surface of a Silicon substrate formed dielectric layer is opened locally. The invention further relates to a corresponding semiconductor component.

BACKGROUND OF THE INVENTION

at Many semiconductor devices may require a surface of a Contact silicon substrate locally with a metal contact. For example can In a solar cell locally applied metal contacts for dissipation serve the electricity generated in the solar cell. To the silicon substrate For example, one can contact locally as an insulation layer serving dielectric layer are deposited on the substrate surface and subsequently be removed locally in the areas to be contacted. About the Dielectric layer can then be deposited a metal layer, those in areas where the dielectric layer was previously local was removed, the underlying silicon substrate can contact directly.

Around To open a dielectric layer locally are conventional Photolithography known in which a surface of the Dielectric layer first locally protected with a varnish is, then the paint after local exposure in subregions is removed and then in These subregions, the underlying dielectric layer locally is etched away by means of an etching solution.

alternative can etch pastes can be used, which are printed locally on the dielectric layer and etch them out there.

One Another known from the prior art method for local Removal of a dielectric layer is the so-called "laser ablation". in this connection becomes laser light of high intensity focused on the areas to be removed of the dielectric layer. In order to achieve the energy densities required for ablation, the laser light is usually pulsed. The laser light will this mostly in the silicon substrate under the dielectric layer absorbed. It comes to an abrupt heating and evaporation of silicon material, whereby the overlying areas of the dielectric layer are "blown off", the is called, flake off locally. In this way, for example, silicon dioxide layers or silicon nitride layers are ablated locally.

by virtue of the strong heating occurring in the absorption of the laser light or melting of the surface areas of the silicon substrate can be damaged there, the crystal structure of the silicon. In extreme cases, a near-surface is Area of the silicon substrate together with the overlying Dielectric layer ablated. The damage to the crystal structure as well as the unwanted Ablating the silicon substrate surface itself can damage the Lead semiconductor device. For example, in a solar cell directly on the surface of the silicon substrate the thin, sensitive emitters are located. Damage or even ablation of the Emitter layer can lead to a reduction of the carrier lifetime or even local shorts in the solar cell and ultimately lead to a loss of efficiency.

US 2007/0295399 A1 describes a back contact solar cell with electrical point contacts that contact a substrate through overlying passivation or antireflection layers.

EP 0 536 431 A1 describes a laser processing method for a thin-film structure, in which a thin-layer area irradiated with laser light, together with optionally overlying layers, is blasted off a transparent layer without residue.

US Pat. No. 7,517,709 B1 describes a method for forming a silicon dot solar cell backside contact structure using laser radiation to form openings in layers above a substrate.

DE 199 15 666 A1 describes a method and a device for selective contacting of solar cells, in which also dielectric layers are removed by means of light.

SUMMARY OF THE INVENTION

It can therefore be a need for a method for producing a semiconductor device is made, wherein a dielectric layer deposited on a silicon substrate can be removed locally without affecting the surface of the silicon substrate significantly damage its electronic properties. Further there may be a need for a semiconductor device, in particular one Silicon solar cell consist, in particular as a result of such careful manufacturing process has a structure in which a damage a silicon substrate in areas where an overlying Dielectric layer is removed locally, is avoided.

a Such need can be met with the method of manufacturing a semiconductor device or with the semiconductor device according to the independent claims become. Advantageous embodiments are given in the dependent claims.

According to one The first aspect of the present invention is a method for Producing a semiconductor component, in particular a solar cell, proposed. The method preferably comprises the subsequent steps in the order given: (a) providing a silicon substrate; (b) forming a first layer of amorphous silicon on one surface the silicon substrate; (c) forming a second layer from a Dielectric on the first layer; and (d) locally removing the second layer in Ablationsbereichen by irradiation of the silicon substrate and the layers thereon with laser light, with properties of the laser light and properties of the first layer adapted are that when locally removing the second layer in the ablation areas at the most a partial thickness of the first layer is removed and at least a residual thickness of the first layer of at least 1 mm remains.

According to one The second aspect of the present invention is a semiconductor device proposed. It has a silicon substrate, a first layer of amorphous silicon on a surface of the silicon substrate and a second layer of a dielectric layer on the first Shift up. The second layer is local in ablation areas away. The first layer has a in the ablation areas Thickness of at least 1 nm, preferably at least 5 nm. moreover the first layer in the ablation regions has a smaller one Thickness of the outside the ablation areas.

aspects of the present invention can be described as based on the following idea: on a silicon substrate, which for the production of a semiconductor device is to serve, is between an example serving as an electrical insulation layer Dielectric layer and the substrate surface an additional Layer deposited. This additional Layer consists of amorphous silicon (a-Si). This a-Si layer can be designed to prevent that when ablating, this means local removal, the dielectric layer an underlying surface of the silicon substrate damaged becomes. Furthermore, it can be advantageously used that the a-Si layer, for example, due to a contained therein high hydrogen content good for passivation of the surface of the Silicon substrates can serve. Furthermore, in an advantageous Be used manner that experience shows an electrical contact between an aluminum layer and the a-Si layer to very low and especially reliable reproducible low electrical contact resistance leads.

With Help of the method or in the semiconductor device according to the invention can thus be a surface a silicon substrate locally in areas where one above the Silicon substrate deposited dielectric layer locally removed was exposed, and contacted, for example, electrically. On the one hand, near-surface damage to the Silicon substrate can be avoided and on the other hand, a good surface passivation, especially in the non-exposed areas, as well as in reliably reproducible Do a low contact resistance with a metal contact forming aluminum layer containing the silicon substrate in the previously locally opened, contacted exposed areas in the dielectric layer achieved become.

Further possible Features and advantages of embodiments the production process according to the invention or the semiconductor device are described in detail below.

The inventive method can for producing any semiconductor device, in a local removal of a example as an isolation layer Serving dielectric layer is necessary serve. Examples of such Semiconductor devices can Solar cells, light-emitting diodes and complex, in a silicon substrate be integrated circuits. The dielectric layer can in this case be opened locally by ablation with laser light to expose areas in which the underlying silicon substrate, for example, electrically contacted can be.

The Silicon substrate, for example, in the form of a silicon wafer or in the form of a silicon thin film to be provided.

The first layer of amorphous silicon is preferably formed directly on a surface of the silicon substrate, that is, without further intermediate layers located between the silicon substrate surface and the amorphous silicon layer. In other words, the amorphous silicon layer may be in direct contact with the surface of the silicon substrate. In this way, the amorphous silicon layer can easily passivate the substrate surface, for example by saturating free bonds (so-called "dangling bonds") or by allowing hydrogen contained in the amorphous silicon layer to diffuse into the silicon substrate surface. As described in more detail below, the amorphous silicon layer may have certain structural and chemical properties in order to give it both good surface-passivating properties and to provide for a low contact resistance, for example, between an aluminum layer contacting the amorphous silicon layer and the silicon substrate.

The second layer is formed of a dielectric such as silicon oxide (SiO ₂ or SiO ₂ ) or silicon nitride (SiN _x , for example, Si ₃ N ₄ ). The dielectric layer may contact the amorphous silicon layer directly. Alternatively, between the dielectric layer and the amorphous silicon layer also further, preferably for the laser light used optically transparent layers may be stored. The dielectric layer may be formed as a single homogeneous layer or as a stack of several different layers. The dielectric layer may serve, for example, for electrical insulation between an overlying aluminum layer and the silicon substrate in regions outside the previously opened ablation regions. Alternatively or additionally, the dielectric layer can also fulfill further tasks. It can serve, for example, as an antireflection layer or backside mirror for a solar cell or has a stabilizing effect on the passivation of the amorphous silicon layer, for example. B. during a high temperature step, such. As in the firing metal-containing pastes for metal contact.

At the subsequent Locally removing the dielectric layer becomes the silicon substrate with the amorphous silicon layer thereon and also local thereon dielectric layer is illuminated locally with laser light. The properties of the laser light can be chosen so that there is a local ablation of the dielectric layer. influencing parameters can Here, the focus of the laser light, the power density of the Laser light, the wavelength of the laser light and the irradiation time.

According to one embodiment According to the present invention, the method of manufacturing a Component further comprises the deposition of an aluminum layer at least in the ablation areas where the previously deposited dielectric layer was removed locally. The aluminum layer can be a good one Ohmic contact with the underlying one exposed in the ablation areas form the first layer of amorphous silicon.

Around the formation of such a good electrical contact continues to support, The manufacturing process can complement the step of tempering the aluminum layer at least 180 ° C, preferably at least 200 ° C, for example over more than 10 minutes, preferably more than 1 hour. The training of metal contacts using an aluminum layer, the one underneath Layer of amorphous silicon contacted and preferably according to annealed, has proved to be beneficial. Such Contacts are sometimes called "COSIMA" contacts (Contacts to a-Si: H passivated Si by means of annealing). Such contacts can by a constantly low contact resistance between the Aluminum and the amorphous silicon resulting in a small series resistance, for example, for a solar cell distinguished. For example, the formation and properties of COSIMA contacts are described in H. Plagwitz et al .: "Low-temperature formation of local Al contacts to a-Si: H-passivated Si wafers ", Progress in Photovoltaics: Research and Applications, 2004; 12: 47-54.

According to one embodiment of the present invention, the properties of the laser light used for ablation and the properties of the amorphous silicon layer are selected such that at least a portion of the underlying amorphous silicon layer is removed during local removal of the dielectric layer in the ablation regions, so that at least one residual thickness of the amorphous silicon layer is removed Silicon layer of at least 1 nm, preferably 3 nm, preferably at least 6 nm remains. For this purpose, for example, the thickness of the originally deposited amorphous silicon layer can be selected to be correspondingly large. For example, the amorphous silicon layer may be deposited to a thickness of between 1 nm and 100 nm, preferably between 5 nm and 50 nm, and more preferably between 10 nm and 30 nm. The thickness of the amorphous silicon layer can be chosen to be thick enough so that even with a partial ablation of the amorphous silicon layer in the context of local removal of the dielectric layer remains a sufficiently thick residual amorphous silicon layer. This remaining amorphous silicon layer can serve to form a good, in particular ohmic, contact with an aluminum layer subsequently deposited over the amorphous silicon layer. It is currently assumed that silicon is incorporated from the amorphous silicon layer during an annealing step in the aluminum, whereby it comes in a very reliable way to form an ohmic contact. In addition, the remaining amorphous silicon layer can also ensure a certain passivation of the surface of the underlying silicon substrate in the ablation regions freed from the dielectric layer. On the other hand, the thickness of the amorphous silicon layer should not exceed a certain upper limit. Too thick an amorphous silicon layer could adversely affect the properties of the half affect the conductor component. For example, in a solar cell, a thick amorphous silicon layer could lead to excessive absorption of incident light and thus to a loss of efficiency.

The Properties of the laser light used for ablation and the properties The amorphous silicon layer should also be against each other be adapted to the highest possible absorption of the Laser light in the amorphous silicon layer, preferably on the outer surface of the amorphous silicon layer comes. This can be achieved that the amorphous silicon layer by irradiation with the laser light heated locally and preferably parts of it is suddenly evaporated so be one about it located dielectric layer is locally "blasted" is. The properties of the laser light and the properties of the dielectric layer should preferably be tuned such that it at best to a slight Absorption of laser light in the dielectric layer comes, so that the dielectric layer is hardly heated and certainly not vaporized, but the vast one Share of the laser light power only in the amorphous silicon layer is absorbed.

Preferably For example, the laser light used for ablation is pulsed with a pulse duration of between 1 ps and 100 ns, preferably between 2 ps and 5 ns, stronger preferably between 5 ps and 200 ps, irradiated. On the one hand can it may be advantageous to choose the light pulses short enough that it while a light pulse does not cause a significant spread of the registered Heat comes but the registered laser light power preferably to a immediate evaporation of the absorbent amorphous silicon material leads, without significantly heating surrounding areas. On the other hand it can be advantageous, the light pulses are not too short, that is shorter than 1 ps or shorter in particular than 100 fs, to choose to avoid causing non-linear light absorption effects comes with such short pulse durations, especially with the most associated with high power densities, may occur. Such non-linear absorption phenomena could cause that the laser light is no longer preferably in the amorphous silicon layer is absorbed, but also in the overlying dielectric layer.

Preferably becomes laser light with a wavelength of less than 450 nm, stronger preferably less than 380 nm, that is with a wavelength in the blue or UV range, irradiated. Such short-wave light is transmitted through the dielectric layer mostly transmitted but strongly absorbed in the amorphous silicon layer, so that there is already a strong local heating right at the Outside lying surface the amorphous silicon layer can come. However, it can too when using longer-wave Light to a sufficient absorption in the amorphous silicon layer which may be advantageous, this amorphous silicon layer then due to the greater penetration depth the longer-wave Light with a greater thickness train.

According to one another embodiment According to the present invention, the amorphous silicon layer has a Hydrogen content, which is used to passivate the surface of Silicon substrate is suitable. It is known that amorphous silicon layers a certain proportion of the atomic or molecular embedded therein Contain hydrogen. Such amorphous silicon becomes common as a-Si: H denotes. The stored hydrogen can be released Bonds or impurities diffuse within an adjacent silicon substrate and passivate them. Such diffusion can be achieved by annealing at elevated Temperatures supported become. It may thereby have a carrier lifetime in the silicon substrate be increased considerably.

It is noted that the manufacturing method of the invention in addition to the manufacturing steps already described further manufacturing steps may comprise and that the semiconductor device according to the invention in addition to the features described or structures even more features or structures may have. For example, the manufacturing process still further purification steps, diffusion steps, high-temperature steps, Anneal steps, metallization steps, passivation steps, etc. have. The semiconductor device can additionally additional Layers or structures, for example in the form of dielectric layers or metal layers or the like exhibit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further Features and advantages of the present invention will become apparent to those skilled in the art from the following description of exemplary embodiments, which, however, should not be construed as limiting the invention, and with reference to the accompanying drawings.

1a) - 1c) illustrate various stages during a method of manufacturing a semiconductor device according to an embodiment of the present invention.

The Figures are merely schematic and not to scale.

DESCRIPTION OF A PREFERRED Embodiment

With reference to the 1a) - 1c) become essential process stages during the manufacture of a semiconductor device 100 according to an embodiment of the present invention.

On a crystalline silicon substrate 1 becomes a 10-20 nm thick first layer 3 deposited from amorphous silicon. The amorphous silicon layer is deposited so as to have a high hydrogen content of 10 to 40 at%. One possible production method is, for example, PECVD (Plasma Enhanced Chemical Vapor Deposition). The two options direct plasma method and remote plasma method can be distinguished. Another possibility is the so-called hot-wire CVD. Over the amorphous silicon layer becomes a second layer 5 deposited from silicon nitride or silicon oxide. Such layers can be deposited, for example, by PECVD (Plasma Enhanced Chemical Vapor Deposition).

As in 1b shown, the silicon substrate 1 with the amorphous silicon layer thereon 3 and the dielectric layer formed over it 5 locally with a laser light beam 7 be illuminated. The laser light beam 7 has a wavelength at which the dielectric layer 5 barely absorbed, the amorphous silicon layer 3 but strongly absorbed. The laser light beam is irradiated with a high power density of, for example, 10 ¹⁰ -10 ¹² W / cm ^2. This high power density is largely in the uppermost edge region of the amorphous silicon layer 3 absorbs and leads there to a sudden evaporation of the amorphous silicon and, associated with this, to a bursting off of the dielectric layer located above it. Thus, the dielectric layer becomes 5 in the so-called ablation area 9 locally removed. At the same time, the upper edge region of the amorphous silicon layer is removed at this point, but the thickness of the amorphous silicon layer is chosen thick enough that not the entire amorphous silicon layer during the ablation 3 is removed, but at least a residual thickness of at least 1 nm remains. This remaining amorphous silicon layer allows the reliable formation of an ohmic contact in a subsequent deposition of an aluminum layer. In a subsequent process step then becomes an aluminum layer 11 over the entire surface of the silicon substrate 1 deposited and covers both the dielectric layer 5 in the non-ablated areas 13 as well as locally the amorphous silicon layer 3 in the ablation areas 9 , Thus, there is an electrical contact between the aluminum layer locally 11 and the amorphous silicon layer 3 in the ablation areas 9 whereas the aluminum layer 11 in the non-ablated areas 13 through the intervening dielectric layer 5 from the amorphous silicon layer 3 is electrically isolated. By subsequent tempering, the amorphous silicon can be incorporated into the aluminum layer. Thus, ultimately, a reliable COSIMA contact between the silicon substrate 1 and the aluminum layer 11 arise.

Finally, it will It should be noted that the terms "comprising", "comprising" etc. include the presence of others Do not exclude elements. The term "one" also includes the presence of a plurality of objects is not enough. The reference numerals in the claims are only for better readability and should the scope of protection the claims restrict in any way.

Claims (10)

Method for producing a semiconductor component, in particular a solar cell, the method comprising: providing a silicon substrate ( 1 ); Forming a first layer ( 3 ) of amorphous silicon on a surface of the silicon substrate ( 1 ); Forming a second layer ( 5 ) from a dielectric on the first layer ( 3 ); and locally removing the second layer ( 5 ) in ablation areas ( 9 ) by irradiating the silicon substrate ( 1 ) and the layers ( 3 . 5 ) with laser light ( 7 ), whereby properties of the laser light and properties of the first layer ( 3 ) are adapted in such a way that, when the second layer is locally removed in the ablation regions, at most a partial thickness of the first layer ( 3 ) and at least one residual thickness of the first layer ( 3 ) of at least 1 nm remains. The method of claim 1, wherein the method further comprises: depositing an aluminum layer ( 11 ) in ablation areas ( 9 ). The method of claim 2, wherein the method further comprises annealing the aluminum layer ( 11 ) at least 180 ° C. Method according to one of claims 1 to 3, wherein the first layer ( 3 ) is formed to a thickness of between 1 nm and 100 nm. Method according to one of claims 1 to 4, wherein properties of the laser light ( 7 ) and absorption properties of the second layer ( 5 ) are adapted so that there is no significant absorption of the laser light in the second layer. Method according to one of claims 1 to 5, wherein the laser light ( 7 ) is pulsed with a pulse duration of between 1 ps and 100 ns. Method according to one of claims 1 to 6, wherein the laser light ( 7 ) is irradiated with a wavelength of less than 450 nm. Method according to one of claims 1 to 7, wherein the first layer ( 3 ) has a hydrogen content which is used to passivate the surface of the silicon substrate ( 1 ) suitable is. A semiconductor device comprising: a silicon substrate ( 1 ); a first layer ( 3 ) of amorphous silicon on a surface of the silicon substrate ( 1 ); a second layer ( 5 ) from a dielectric on the first layer ( 3 ); the second layer ( 5 ) in ablation areas ( 9 ) is locally removed; the first layer ( 3 ) in the ablation areas ( 9 ) has a thickness of at least 1 nm and wherein the first layer ( 3 ) has a smaller thickness in the ablation areas than outside ablation areas. A semiconductor device according to claim 9, further comprising: an aluminum layer ( 11 ), wherein the aluminum layer ( 11 ) the first layer at least in the ablation areas ( 9 ) contacted.