Creation of a radiation output window for a light-emitting component

Abstract

The invention relates to a method for creating an output window (W) for radiation (R) produced within a silicon carbide substrate (1) by a light-emitting component. For this purpose, the substrate is heat-treated in order to increase a surface roughness (RaW) of said substrate selectively in the output window. Such a method is compatible with mass production of the light-emitting component, and provides for good reproducibility of the output characteristics of the radiation (R) produced by each component.

Description

Description Title: CREATION OF A RADIATION EXIT WINDOW FOR A PHOTOEMITTER COMPONENT technical field

[0001] This description concerns the creation of a radiation exit window for a silicon carbide-based photoemitting component. It also concerns a photoemitting component that has a radiation exit window that can be created in this way. Previous technique

[0002] The use of crystalline silicon carbide (SiC) to produce radiation-emitting components offers numerous advantages, stemming in particular from the material's properties: its chemical inertness, thermal stability, thermal conductivity, and wide band gap, especially compared to silicon (Si), the most widely used semiconductor material in microelectronics today. Silicon carbide allows, in particular, the controlled production of radiation in the visible light spectrum, and also around 1.5 pm (micrometers), for example, in telecommunications applications.

[0003] The efficiency of extracting the radiation produced inside the silicon carbide component, possibly intentionally doped, to the outside of that component so that the radiation can be used for the intended application is therefore a major challenge. Indeed, more efficient radiation extraction reduces the component's energy consumption for the same amount of usable radiation. Furthermore, it is essential to be able to mass-produce components with controlled and reproducible emission efficiency. Technical problem

[0004] One aim of the present invention is therefore to improve the output efficiency of the radiation produced within a silicon carbide-based component, towards the exterior of this component. In particular, this improvement is sought so that it can be implemented in a reproducible and controlled manner for large series of manufactured components. Summary of the invention

[0005] To achieve this or another objective, a first aspect of the invention proposes a method for creating an exit window for radiation produced inside a silicon carbide substrate by a photoemitting component, this method comprising: / 1 / to form a carbon layer on a surface of the substrate, selectively outside a limited portion of that surface which is intended to constitute, during use of the component, the exit window to the outside of the substrate for the radiation produced inside the substrate by the photoemitting component; and / 2 / apply a heat treatment to the substrate, this heat treatment producing an increase in surface roughness of the substrate selectively in areas where the surface is not covered by the carbon layer; then / 3 / remove the carbon layer outside the portion of the substrate surface that is intended to form the radiation exit window.

[0006] Indeed, the increased surface roughness of the substrate within the radiation exit window creates a surface layer inside this window with a lower average refractive index than the effective refractive index within the substrate. This layer with a reduced refractive index produces at least a partial antireflective effect on the radiation originating from within the substrate, particularly the radiation emitted by the component and passing through the substrate surface within the exit window. This antireflective effect promotes the outward emission of radiation from the component, thus improving its radiation output efficiency. Consequently, the component's energy consumption is reduced for the same amount of usable radiation.This anti-reflective effect is particularly effective when the surface of the silicon carbide substrate is exposed to air during the use of the photoemitting component. This is another explanation for the effectiveness of surface roughness. The substrate to promote radiation exit is that variations in the incidence of radiation relative to the actual surface of the substrate, due to roughness, reduce the total reflections of radiation that are internal to the substrate.

[0007] Furthermore, thanks to the fact that the radiation output window is formed by the heat treatment of step 121 by locally increasing the surface roughness of the substrate as an effect of this heat treatment, the process of the invention is compatible with a series manufacturing of the photoemitting component, and it provides good reproducibility of the radiation output characteristics that is produced by each component.

[0008] Advantageously, the heat treatment of step 121 can be carried out at atmospheric pressure, under argon (Ar), with a temperature which is between 1200°C (degree Celsius) and 1900°C, preferably between 1500°C and 1800°C, for a duration of between 1 minute and 1 hour.

[0009] In particular embodiments of the invention, step 71 / may include the following substeps: / 1 -1 / deposit a continuous layer of resin on the surface of the substrate; 71-2 / apply a pyrolysis treatment to the resin layer, this pyrolysis treatment being suitable for transforming the resin layer into the carbon layer; / 1 -3 / form a mask on the carbon layer, selectively outside the portion of the substrate surface that is intended to constitute the radiation exit window; / 1-4 / etch the carbon layer so that it is selectively removed in areas not covered by the mask; and / 1 -5 / Optionally, remove the mask.

[0010] The pyrolysis treatment of substep 71-2 / may include heating the resin layer to a temperature between 700°C and 800°C for a period of between 10 minutes and 1 hour, under a flow of nitrogen (N2) or argon (Ar).

[0011] The carbon layer can be etched in substep / 1-4 / using a reactive etching process with oxygen (O) ions.

[0012] Possibly, substep / 1-3 / of mask formation may involve depositing a layer of a metal or metal alloy onto the carbon layer, and then selectively removing this layer of metal or metal alloy from the portion of the substrate surface intended to form the radiation exit window. In this case, substep / 1-5 / of mask removal may be performed using a suitable removal process, such as wet etching or plasma etching.

[0013] In other specific embodiments of the invention, alternative to the previous ones, step / 1 / may include the following substeps: / 1 -1 / by lithography, deposit a layer of lithographic resin onto the surface of the substrate selectively outside the portion of this substrate surface intended to constitute the radiation exit window; and 71-2 / apply a pyrolysis treatment to the resin layer, this pyrolysis treatment being suitable for transforming the resin layer into the carbon layer. For these other embodiments of the invention, the carbon layer is directly and selectively formed outside the radiation exit window. The lithographic resin used may be photosensitive, i.e., of the UV lithography type, or of the electron beam lithography type. The pyrolysis treatment of substep 71-2 may further include heating the resin layer to a temperature between 700°C and 800°C for a period of between 10 minutes and 1 hour, under a flow of nitrogen or argon.

[0014] For the method of the invention, the photoemitting component may include a light-emitting diode which is located in the substrate, beneath its surface, so that when using the component, the radiation is emitted by the light-emitting diode and passes through the output window.

[0015] A second aspect of the invention provides a photoemitting component, comprising a silicon carbide substrate, this substrate having a surface possessing a first roughness value, in particular an arithmetic roughness, within a portion of the surface which, during use of the component, constitutes an exit window to the outside of the substrate for radiation produced inside the substrate by the photoemitting component. The substrate surface simultaneously has a second roughness value, also an arithmetic roughness value if applicable, outside the portion of the surface that constitutes the radiation exit window, the first roughness value being greater than the second roughness value.

[0016] Such a photoemitting component can be manufactured using a process that conforms to the first aspect of the invention.

[0017] The first roughness value can be between 10 nm (nanometer) and 140 nm, in terms of arithmetic roughness, and the second roughness value can be between 0.1 nm and 5 nm, also in terms of arithmetic roughness.

[0018] Generally for the invention, the silicon carbide substrate can be single-crystal, in particular according to one of the polytypes 3C, 4H or 6H.

[0019] Finally, the photoemitting component of the second aspect of the invention may likewise include a light-emitting diode which is located in the substrate, under its surface, so that when using the component, the radiation is emitted by the light-emitting diode and passes through the output window. Brief description of the figures

[0020] The features and advantages of the present invention will become clearer in the following detailed description of non-limiting embodiments, with reference to the accompanying figures, among which:

[0021] [Fig. 1a] is a cross-sectional view of a substrate used to manufacture a photoemitting component by applying to the invention;

[0022] [Fig. 1 b] corresponds to [Fig. 1a] for a later step in the process;

[0023] [Fig. 1c] corresponds to [Fig. 1a] for an even later step in the process;

[0024] [Fig. 1d] corresponds to [Fig. 1a] for an even later step in the process;

[0025] [Fig. 1e] corresponds to [Fig. 1a] for an even later step in the process; and

[0026] [Fig. 2] is a cross-sectional view of a light-emitting diode component as obtained by applying the invention. Detailed description of the invention

[0027] For clarity, the dimensions of the elements shown in these figures do not correspond to actual dimensions or ratios of actual dimensions. Furthermore, identical reference numerals shown in different figures designate identical elements or elements with identical functions.

[0028] According to [Fig. 1a], a single-crystal silicon carbide (SiC) substrate 1, for example of polytype 4H or 6H, has a surface S. This surface S can have an initial arithmetic roughness value, denoted Ra o, which is approximately equal to 1 nm, for example. The surface S is coated with a layer of resin, for example, a commercially available photolithographic resin. The resin can be applied to the surface S by a spin-coating process, as known to those skilled in the art. The resulting resin layer is hardened and then pyrolyzed. The pyrolysis treatment used can be heating to approximately 750°C for a period of several tens of minutes under a non-oxidizing atmosphere, for example, under a stream of nitrogen or argon. The resin layer is thus transformed into a carbon layer, which is designated by reference numeral 2 in the figure.

[0029] A mask 3 is then deposited onto the carbon layer 2, for example, using an evaporation process. This mask 3 can be composed of a metal such as aluminum (Al), nickel (Ni), chromium (Cr), or another metal alloy. To achieve this, a continuous layer of the metal or metal alloy can first be deposited onto the carbon layer 2, and then an aperture O3 is formed in the metal or metal alloy layer. The aperture O3 defines a radiation output window W, provided by the invention for a photoemitting component that will be fabricated from the substrate 1. The aperture O3 can be created using a known selective removal process, suitable for the material of the mask 3, such as direct wet etching lithography. Alternatively, the mask 3 can be formed using a lift-off process. The configuration shown in [Fig. 1a] is then obtained.

[0030] The surface of substrate 1, which thus carries the carbon layer 2 and the mask 3, is treated to selectively remove the carbon layer 2 through the opening O3. For Therefore, a material removal process is selected that is capable of removing the carbonaceous material without significantly altering the metal or metal alloy of mask 3. For example, substrate 1 can be treated by a reactive ion etching process, commonly referred to by RIE, in which the etching ions are derived from an oxygen plasma. The carbonaceous layer 2 is thus removed by oxidation in the O3 aperture of mask 3, while it remains where it is covered by mask 3, as shown in [Fig. 1b]. Mask 3 is then completely removed at this stage of the process. Such removal of mask 3 can be achieved using wet etching, for example, with an acidic solution. The configuration of [Fig. 1c] is thus obtained.

[0031] Alternatively, it is possible to directly produce the carbon layer 2 outside the W window, using a resin deposition lithographic process. This can be a UV or electron beam lithography process. Thus, the resin layer is formed by lithography on the surface S of the substrate 1, selectively outside the W window. Then it is transformed into the carbon layer 2 using the same pyrolysis treatment as before, again leading to the configuration of [Fig. 1c].

[0032] A micro- or nanostructuring heat treatment is then applied to substrate 1, in which the single-crystal silicon carbide material is selectively coated with carbonaceous material outside the W window. This heat treatment is selected to induce a desired increase in the surface roughness S within the W window, while the surface roughness S is not significantly increased, or is increased to a significantly lesser extent, in areas where this surface S is coated with carbonaceous material. For example, this micro- or nanostructuring heat treatment of surface S by varying the roughness could consist of heating substrate 1 to a temperature approximately 1700°C for half an hour under argon. The resulting configuration is shown in [Fig. 1d].The surface S, made of silicon carbide material, then has a roughness that is increased in the window W compared to the outside of this window W. For the parameters of the roughness structuring heat treatment that were mentioned previously, the surface S has a. arithmetic roughness value R a w within the W window, which is approximately equal to 60 nm. Outside the W window, the surface S coated with carbon material has an arithmetic roughness value R ai which remained close to its initial value R a o. This value R ai was determined to be approximately equal to 1 nm. The R values a w and R aiwere respectively referred to as the first and second arithmetic roughness values ​​in the general part of this description. All roughness values ​​cited in this description were measured using an atomic force microscope, or AFM, or using a mechanical profilometer, for example from one of the DEKTAK® or TENCOR® brands.

[0033] The carbon layer 2 is then removed where it remains, i.e., outside the W window. For example, the substrate 1, lacking the mask 3, can be brought into contact with an oxygen (O2) plasma, which is capable of removing the carbon material by oxidation without altering the silicon carbide material. The configuration shown in [Fig. 1e] is then obtained.

[0034] [Fig. 2] shows a light-emitting diode (LED) fabricated in silicon carbide substrate 1, with its surface S structured by varying roughness as described above. The process of forming the LED within substrate 1, particularly by ion implantation to create doped areas, is not the subject of this invention, and therefore it is not necessary to describe it here; reference may be made to previously published documents on this topic. The window W is preferably aligned with the LED, in a direction orthogonal to a midpoint of surface S.In a known manner, the light-emitting diode can comprise the following elements: a first zone Z1 which is internal to the substrate 1 and doped in an N-type manner, for example with nitrogen ions, a second zone Z2, which is also internal to the substrate 1, doped in a P-type manner for example with aluminium (Al) ions, and contiguous to the zone Z1 by being intermediate between the latter and the surface S, a third electrical connection zone, denoted Z3, which is doped in a P-type manner and which establishes an electrical connection between the zone Z2 and the surface S of the substrate 1, a back electrode, referenced 4 and possibly made of nickel (Ni), which is in. electrical contact with zone Z1, possibly through an unshown intermediate zone and N-type doped, and a top electrode 5, which is possibly made of an aluminum (Al) and titanium (Ti) alloy, and which is carried by the surface S so as to be in electrical contact with zone Z3.

[0035] In [Fig. 2], the upper electrode 5 occupies a central portion of the window W, being smaller than the window itself, so that the surface S of the substrate 1 remains exposed over a sufficient portion of the window W. Alternatively, the upper electrode 5 can occupy a peripheral portion of the window W, leaving the surface S of the substrate 1 exposed over a sufficient central portion of the window W. Alternatively still, transparent or semi-transparent metallic layers, a few nanometers thick, can be used to constitute the upper electrode 5, in which case such layers can cover the window W.

[0036] Such a light-emitting diode produces radiation from the J junction between regions Z1 and Z2 when supplied with forward current through electrodes 4 and 5. When the silicon carbide substrate 1 is of polytype 4H, this radiation is in the visible light spectrum, being predominantly blue. When the substrate 1 is of polytype 6H, the radiation produced is more blue / green. White light illumination can also be obtained.

[0037] The increased roughness created according to the invention in window W constitutes an antireflective layer. This antireflective effect may be only partial, but it facilitates the exit through surface S of the radiation produced by the light-emitting diode within substrate 1. As an illustration of the effectiveness of the invention, [Fig. 2] shows a first light ray R originating from junction J and propagating towards window W. This ray R then passes through surface S to exit substrate 1. It can therefore be used outside substrate 1 according to the desired application for the light-emitting diode. The ray R', which also originates from junction J but is directed outside window W, is reflected internally within substrate 1.

[0038] It is understood that the invention can be reproduced by modifying minor aspects of the embodiments described in detail above, while retaining at least some of the advantages mentioned. In particular, all the numerical values ​​cited are for illustrative purposes only and may be changed depending on the application.

Claims

Demands

1. A method for creating an exit window (W) for radiation (R) which is produced inside a silicon carbide substrate (1) by a photoemitting component, the method comprising: / 1 / form a carbon layer (2) on a surface (S) of the substrate (1 ), selectively outside a limited portion of said surface which is intended to constitute, when using the component, the exit window (W) to the outside of the substrate for the radiation (R) produced inside said substrate by the photoemitting component; / 2 / apply a heat treatment to the substrate (1), said heat treatment producing an increase in the surface roughness (S) of the substrate selectively in areas where said surface is not covered by the carbon layer (2); then / 3 / remove the carbon layer (2) outside the portion of the surface (S) of the substrate (1) which is intended to constitute the exit window (W) of the radiation (R).

2. A method according to claim 1, wherein the heat treatment of step 121 is carried out at atmospheric pressure, under argon, with a temperature between 1200°C and 1900°C, preferably between 1500°C and 1800°C, for a duration of between 1 minute and 1 hour.

3. A method according to claim 1 or 2, wherein step / 1 / comprises the following substeps: / 1 -1 / deposit a continuous layer of resin on the surface (S) of the substrate (1); / 1 -2 / apply a pyrolysis treatment to the resin layer, said pyrolysis treatment being adapted to transform the resin layer into the carbon layer (2); / 1 -3 / form a mask (3) on the carbon layer (2), selectively outside the portion of the surface (S) of the substrate (1) which is intended to constitute the exit window (W) of the radiation (R); / 1-4 / etch the carbon layer (2) so that said carbon layer is selectively removed in areas not covered by the mask (3); and / 1 -5 / Optionally, remove the mask (3).

4. A method according to claim 3, wherein the carbon layer (2) is etched in substep / 1-4 / using a reactive etching process with oxygen ions.

5. Method according to claim 3 or 4, wherein: substep 71-3 / comprises depositing a layer of a metal or metal alloy on the carbon layer (2), and then selectively removing said layer of the metal or metal alloy from the portion of the surface (S) of the substrate (1) which is intended to constitute the exit window (W) of the radiation (R).

6. A method according to claim 1 or 2, wherein step 71 / comprises the following substeps: 71-1 / by lithography, deposit a layer of a lithographic resin onto the surface (S) of the substrate (1) selectively outside the portion of said substrate surface intended to constitute the exit window (W) of the radiation (R); and 71-2 / apply a pyrolysis treatment to the resin layer, said pyrolysis treatment being adapted to transform the resin layer into the carbon layer (2).

7. A method according to any one of claims 3 to 6, wherein the pyrolysis treatment of substep 71-2 / comprises heating the resin layer to a temperature between 700°C and 800°C for a period of between 10 minutes and 1 hour, under a flow of nitrogen or argon.

8. A method according to any one of the preceding claims, wherein the photoemitting component comprises a light-emitting diode which is located in the substrate (1), below the surface (S) of said substrate, such that when using said component, the radiation (R) is emitted by the light-emitting diode and passes through the output window (W).

9. Photoemitter component, comprising a silicon carbide substrate (1), said substrate having a surface (S) which has a first roughness value within a portion of said surface which constitutes, during use of the component, an exit window (W) to the outside of the substrate for radiation (R) produced within said substrate by the photoemitting component, and which has a second roughness value outside said surface portion that constitutes the radiation exit window, the first roughness value being greater than the second roughness value.

10. Component according to claim 9, wherein the first roughness value is between 10 nm and 140 nm, in terms of arithmetic roughness, and the second roughness value is between 0.1 nm and 5 nm, also in terms of arithmetic roughness.

11. Component according to claim 9 or 10, wherein the silicon carbide substrate (1) is single-crystal.

12. Component according to any one of claims 9 to 11, comprising a light-emitting diode located in the substrate (1), below the surface (S) of said substrate, such that when using said component, the radiation (R) is emitted by the light-emitting diode and passes through the output window (W).

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