Production of a radiation-emitting component from a silicon carbide substrate

Abstract

The invention relates to a method for producing a radiation-emitting component (R) from a crystalline silicon carbide substrate (1), comprising the implantation of ions at ambient temperature into said substrate. The implantation produces an amorphization of the substrate in a volume (VS) that is located below the surface (S) of said substrate. This results in a local decrease in the density of the substrate, which improves an output of the radiation (R) from the interior of the substrate. The component may be a single-photon emitter based on color centers (CC), or a light-emitting diode.

Description

Description Title: Fabrication of a Radiation Emitting Component from a Silicon Carbide Substrate technical field

[0001] This description relates to a method for manufacturing a radiation-emitting component, as well as a component that can be obtained in this way. Generally, such a radiation-emitting component can be of the color-center type, for example to emit single photons, or of the bipolar junction type, such as a light-emitting diode. 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 objective of the present invention is therefore to improve the efficiency of radiation output from a silicon carbide-based component to the outside of that component. In particular, this improvement is sought in such a way that it can be implemented reproducibly and in a controlled manner for large series of manufactured components. Summary of the invention

[0005] To achieve this or another goal, a first aspect of the invention proposes a method for manufacturing a radiation-emitting component from a crystalline silicon carbide substrate, this method comprising the following steps: / 1 / in a surface of the substrate, determine at least a portion of this surface which is intended to constitute, when using the component, an exit window to the outside of the substrate of the radiation which comes from inside the substrate; and 121 while the substrate has a temperature below 200°C (degrees Celsius), implant ions into the substrate, through the portion of the surface of the substrate which is intended to constitute the exit window of the radiation, with ion implantation dose values ​​and ion implantation energy values ​​which are suitable to produce amorphization of the substrate in a volume located below its surface.

[0006] Indeed, the inventors discovered that, unlike ion implantation performed when the substrate temperature exceeds 300°C (for example, between 300°C and 600°C), ion implantation performed when the substrate temperature is below 200°C is more effective at amorphizing silicon carbide. This amorphized silicon carbide material then has a reduced density compared to the crystalline material as it existed before implantation or outside the volume through which the implanted ions pass.For this reason, the refractive index of the silicon carbide material is reduced in the portion of the material intermediate between the substrate surface and the ion implantation depth. This reduction in refractive index produces at least a partial antireflective effect on radiation originating from within the substrate, particularly from the volume of the substrate in which the ions have been implanted, and whose emission direction passes through the substrate surface in the exit window. Thanks to this... The anti-reflective effect promotes the outward emission of radiation from the component, thus improving its radiation production efficiency. In this way, the component's energy consumption is reduced for the same amount of radiation emitted.

[0007] The reduction in substrate density within the amorphization volume can cause swelling at the substrate surface. This swelling then constitutes evidence of the reduction in silicon carbide material density resulting from ion implantation. In this case, the substrate depth values ​​cited below are measured from the substrate surface as it appears after the swelling.

[0008] In the jargon of those skilled in the art, ion implantation performed when the substrate temperature is below 200°C is referred to as room temperature implantation when no heating is intentionally applied to the substrate, or when limited heating is used. Most often, no means of controlling the substrate temperature can be used during this so-called room temperature implantation. However, it is also possible to perform the ion implantation of step 121 while the substrate is being cooled using appropriate methods. Generally, the substrate temperature during step 121 can be above 4 K (kelvin).

[0009] Preferably, in step 121, the ion implantation dose and ion implantation energy values ​​can be selected to produce amorphization of the substrate between its surface and a depth value between 0.2 pm and 1 pm, measured from the substrate surface. Specifically, these dose and implantation energy values ​​can be adapted to the wavelength of the radiation produced within the substrate during component operation and intended to exit the substrate. In other words, the amorphized volume below the substrate surface constitutes an antireflective layer whose thickness can be advantageously optimized with respect to the radiation wavelength. For example, this radiation produced by the component could be visible light or infrared radiation, for instance, with a wavelength close to 1.5 pm.

[0010] The ions implanted in step 121 can be selected from aluminium (Al), boron (B), and nitrogen (N) ions. However, other ions equally suitable for producing the desired doping can be used alternatively.

[0011] Preferably, in step 121, the ion implantation dose value can be between 10 14 and 10 16 ions per cm 2 (square centimeter), and the ion implantation energy value can range from 20 keV (kiloelectronvolt) to 800 keV. Indeed, these values ​​are particularly suitable for producing a refractive index reduction sufficient to significantly increase the efficiency of radiation emitted outside the component.

[0012] Advantageously, and especially for making a light-emitting diode in the silicon carbide substrate, ions can be implanted in the substrate at step 121, through the portion of its surface which is intended to constitute the radiation exit window, with a first pair of values ​​for the ion implantation dose and the ion implantation energy, and with a second pair of values ​​for these ion implantation parameters, the first pair of values ​​being adapted to dope at least a part of a light-emitting diode located in the substrate, at a depth measured from the surface of the substrate which is greater than a thickness of the amorphization volume, this thickness being measured perpendicular to the surface of the substrate, and the second pair of values ​​being adapted to produce the amorphization of the substrate in the volume located below its surface.Such a combination of ion implantation is particularly advantageous for reducing the manufacturing cost of the light-emitting diode. Preferably, the implantation with the first pair of values ​​is carried out before that with the second pair of values.

[0013] In general, the process of the invention may further include the following step, which is carried out where appropriate after step 121: / 3 / apply a heat treatment to the substrate, this heat treatment producing an activation of a doping of the substrate by the implanted ions. Recrystallization that might be induced by this heat treatment is generally partial and insufficient to significantly alter the density of the substrate material within the amorphization volume. The heat treatment of this step / 3 / can be The heat treatment is carried out at atmospheric pressure, under argon (Ar), at a temperature between 800°C and 1900°C, preferably between 1600°C and 1800°C, for a duration of less than one hour. Beyond this duration, this heat treatment could reduce the antireflective effect provided by the amorphization of the substrate below the radiation exit window. The heat treatment in step / 3 / can be performed during or after ion implantation in the substrate, which is intended to dope at least a portion of a light-emitting diode located within that substrate.

[0014] Until step 121, which produces the amorphization of part of the silicon carbide substrate, the latter can be single-crystal, notably according to the 3C, 6H or 4H polytype.

[0015] A second aspect of the invention proposes a radiation-emitting component, which comprises a crystalline silicon carbide substrate, this substrate having a surface and possessing a first material density value in a volume located under a portion of this surface which is intended to constitute, during use of the component, an exit window to the outside of the substrate for radiation from the inside of the substrate, this first material density value being less than a second material density value which is effective in the substrate at a depth greater than a thickness of the volume corresponding to the first density value, the depth and the thickness being measured perpendicular to the surface of the substrate, the depth being measured from the surface of the substrate.

[0016] To achieve a greater increase in radiation output efficiency, a ratio of the first material density value to the second material density value may be less than 0.95, preferably less than 0.90.

[0017] In such a component, the silicon carbide substrate can be single-crystal, at least outside the volume that corresponds to the first density value of the material.

[0018] Such a component can be a color center emitter, for example, to emit single photons, or a light-emitting diode (LED), located within the substrate. Then, when using this component, radiation is emitted from the color center or the LED and passes through the output window. The color center or the light-emitting diode, as the case may be, is located below the surface of the substrate at a depth that is greater than or equal to the thickness of the volume corresponding to the first density value of the material. Brief description of the figures

[0019] 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:

[0020] [Fig. 1a] is a cross-sectional view of a substrate used to manufacture a photoemitting component, according to the invention;

[0021] [Fig. 1 b] corresponds to [Fig. 1a] for a later step in the process;

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

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

[0024] [Fig. 2a] is a cross-sectional view of a color-centered photoemitting component, as obtained by a manufacturing process according to the invention; and

[0025] [Fig. 2b] corresponds to [Fig. 2a] for a photodiode obtained by a manufacturing process according to the invention. Detailed description of the invention

[0026] 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.

[0027] According to [Fig. 1a], a single-crystal silicon carbide (SiC) substrate 1, for example of polytype 3C, has a surface S. This surface S can be covered with a mask 3, called a hard mask. The hard mask 3 can be of the metallic type, for example based on nickel (Ni), aluminum (Al), or chromium (Cr). Alternatively, the hard mask 3 can be made of a dielectric material, such as silica (SiO2), or of a resin that is resistant to implantation processes and can be removed. completely then. Generally speaking, the hard mask 3 can be made of any material suitable for local engraving.

[0028] An optional encapsulating layer 2 can be intermediated between the surface S of the substrate 1 and the hard mask 3. When used, the encapsulating layer 2 is intended to limit or suppress sublimation of silicon atoms that might occur from the surface S of the substrate 1 upon heating, but other methods for preventing such sublimation of silicon atoms are known and can be used alternatively. Such an encapsulating layer 2 can be made of graphite carbon (C), for example, as obtained by in-situ pyrolysis of a photolithographic resin layer deposited on the surface S of the substrate 1. The pyrolysis treatment of the resin can be carried out at 750°C for 30 minutes under a nitrogen (N2) atmosphere, for example.Such an encapsulation layer 2 is effective in protecting silicon carbide against thermally activated degradation, in particular against the sublimation of silicon (Si) atoms up to about 1800°C.

[0029] The hard mask 3 is then selectively removed from within a portion W of the surface S, which is intended to form an exit window for the radiation of a photoemitting component fabricated in the substrate 1. Such selective removal of the hard mask 3, within the window W, can be achieved in one of the ways known to those skilled in the art, for example, by optical or electron beam lithography followed by a wet or plasma etching process, which is suitable for removing the hard mask 3 in each area where it is exposed, i.e., within the window W. To create such a window W, a lift-off process can alternatively be used to selectively remove the hard mask 3 outside the window W on the substrate 1. The configuration shown in [Fig. 1b] is then obtained.

[0030] When the encapsulating layer 2 is used, the substrate 1 can then be contacted with an oxygen (O2) plasma to remove the encapsulating layer 2 in areas where it is no longer covered by the hard mask 3, as shown in [Fig. 1c]. Alternatively, an oxygen ion beam etching process or a thermal oxidation treatment can also be used to remove the exposed portions of the encapsulating layer 2.

[0031] Ions, for example aluminum (Al), boron (B), or nitrogen (N) ions, depending on the desired doping type, are then implanted into the substrate 1 through the opening previously made in the hard mask 3, and into the encapsulating layer 2 if applicable. An ion implantation energy is applied so that these ions are ultimately fixed in a portion V of the substrate 1 extending from a depth P approximately equal to 0.25 pm. Substrate 1 is then amorphized between its surface S and this depth P by collisions of the implanted ions with the carbon and silicon atoms of substrate 1, up to their binding sites. According to the invention, this ion implantation is carried out at room temperature or at a cooling temperature to promote the amorphization of substrate 1 from its surface S to the depth P, in line with the window W.For example, the following parameters can be adopted for ion implantation: implantation energy approximately equal to 200 keV, and implanted dose approximately equal to 1.75-10. 15 ions per cm 2Under these conditions, the depth P is approximately 250 nm (nanometers) if aluminum ions are used for implantation, and the amorphization of substrate 1 below the window W produces a swelling SW of the surface S within it, as shown in [Fig. 1d]. This swelling SW, which is on the order of 50 nm at the center of the window W, results from a decrease in the density of the substrate 1 material caused by its amorphization. It is approximately 50 nm for the aforementioned implantation conditions. Thus, the density of silicon carbide in the surface volume VS, which is bounded by the window W, the surface S, and a depth below this surface S less than or equal to P, is approximately 0.8 times the density of the silicon carbide of substrate 1 outside this volume VS. This reduction in density causes a decrease in the refractive index of the substrate 1 material within the volume VS.This volume with a reduced value of light refractive index will then produce at least a partial anti-reflective effect for radiation coming from the area of ​​fixation of the implanted ions.

[0032] The remaining portion of the hard mask 3, outside the W window, is then removed, again by wet etching, and the substrate is then heat-treated to activate the doping provided by the implanted ions. During this activation heat treatment, the substrate 1 can be brought to a temperature approximately equal to 1700°C for 30 minutes at atmospheric pressure under argon (Ar). Such The heat treatment parameters allow the doping function to be activated without significantly increasing the silicon carbide density in the VS volume. Thus, the output efficiency through the W window of the radiation originating from the interior of the substrate 1 below the VS volume during use of the fabricated component is maintained.

[0033] According to an improvement of the invention, the ion implantation can be carried out in two distinct steps, to differentiate the amorphization functions of the silicon carbide material in volume VS, and the doping functions in a volume V located on the opposite side of surface S from volume VS. In other words, volume V is located below volume VS in substrate 1, volume VS then being called the surface volume. Under these conditions, the surface volume VS is essentially dedicated to producing the antireflective effect to promote radiation emission, and volume V is dedicated to producing the radiation.Therefore, ion implantation in volume V can be performed using a first pair of values ​​for the ion implantation dose and ion implantation energy to dope substrate 1 in volume V, and then a second pair of values ​​for these implantation parameters to amorphize the silicon carbide material in the surface volume VS. The depth P then corresponds to an upper limit of volume V, in the direction of the surface S of substrate 1. For example, the values ​​for amorphizing substrate 1 in the surface volume VS could be 10. 15 ions per cm 2 for the implantation dose, and 100 keV for the implantation energy, and those for creating the doping in volume V can be 10 14 ions per cm 2 and 200 keV.

[0034] [Fig. 2a] is a cross-sectional view of a color center component designed to produce single photons. These color centers, produced by doping, are located in volume V and are labeled CC, and some of the photons they emit are directed towards window W. The surface volume VS, in which the refractive index of the substrate 1 material is reduced according to the invention, reduces the reflection of these photons on the surface S, internal to substrate 1. R denotes the radiation consisting of the photons exiting through window W. By way of illustration, [Fig. 2a] also shows two photons R' produced by the color centers CC, directed outwards from window W, and reflected back into substrate 1 by surface S.

[0035] Finally, [Fig. 2b] is a cross-sectional view of a photodiode fabricated by the process of the invention. The single-crystal silicon carbide substrate 1 used may be originally N-doped, and the doping performed to create the surface volume VS may be P-doped, like the volume V. The lower boundary of volume V, denoted J in the figure, is the photodiode junction. The component may be completed by a back electrode 4 and an upper electrode 5. The upper electrode 5 may be formed in a manner known to those skilled in the art, on the SW bulge of the surface S. When a current is injected between the two electrodes 4 and 5, with forward electrical biasing of the photodiode, radiation R is emitted by the junction J, a portion of which exits the substrate 1 through the window W. As before, this portion of the radiation produced by the photodiode and emerging from the substrate 1 is increased by the invention.

[0036] 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, a component manufactured according to the invention may be of a different type than a single-photon emitter or a photodiode. Furthermore, all the numerical values ​​cited are for illustrative purposes only and may be changed depending on the application.

Claims

Demands

1. A method for manufacturing a radiation-emitting component from a crystalline silicon carbide substrate (1), the method comprising: / 1 / in a surface (S) of the substrate (1), determine at least a portion of said surface which is intended to constitute, during use of the component, an exit window (W) to the outside of the substrate of the radiation (R) coming from the inside of said substrate; and 121 while the substrate (1) has a temperature below 200°C, implant ions into the substrate, through the portion of the surface (S) of said substrate which is intended to constitute the exit window (W) of the radiation (R), with ion implantation dose values ​​and ion implantation energy values ​​which are adapted to produce an amorphization of the substrate in a volume (VS) located below said surface of the substrate.

2. A method according to claim 1, wherein, in step 121, the ion implantation dose and ion implantation energy values ​​are selected to produce an amorphization of the substrate (1) between the surface (S) of said substrate and a depth value (P) between 0.2 pm and 1 pm, measured from said surface of the substrate.

3. A method according to claim 1 or 2 wherein, at step 121, the ion implantation dose value is between 10 14 and 10 16 ions per cm 2 , and the ion implantation energy value is between 20 keV and 800 keV.

4. A method according to any one of the preceding claims wherein, in step 121, ions are implanted into the substrate (1), through the portion of the surface (S) of said substrate intended to constitute the radiation exit window (W), with a first pair of values ​​for the ion implantation dose and the ion implantation energy, and with a second pair of values ​​for said ion implantation dose and said ion implantation energy, the first pair of values ​​being adapted to dope at least a portion of a light-emitting diode located in the substrate, at a depth (P) measured from the surface of the substrate which is greater than a thickness of the volume (VS) of amorphization, said thickness being measured perpendicular to the surface of the substrate, and the second pair of values ​​being adapted to produce the amorphization of the substrate in the volume (VS) located below the surface of said substrate.

5. A method according to any one of the preceding claims, further comprising the following step, carried out after step 121: / 3 / apply a heat treatment to the substrate (1), said heat treatment producing an activation of a doping of the substrate by the implanted ions.

6. A method according to claim 5, wherein the heat treatment of step 73 / is carried out at atmospheric pressure, under argon, with a temperature between 800°C and 1900°C, preferably between 1600°C and 1800°C, for a period of less than 1 hour.

7. A method according to any one of the preceding claims, wherein the silicon carbide substrate (1) is single-crystal prior to step 121.

8. Radiation-emitting component, comprising a crystalline silicon carbide substrate (1), said substrate having a surface (S) and having a first material density value in a volume (VS) located under a portion of said surface which is intended to constitute, in use of the component, an exit window (W) to the outside of the substrate for radiation (R) from the inside of said substrate, said first material density value being less than a second material density value which is effective in the substrate at a depth greater than a thickness of the volume corresponding to the first material value, the depth and thickness being measured perpendicular to the surface of the substrate, the depth being measured from said surface of the substrate.

9. Component according to claim 8, wherein a quotient of the first material density value over the second material density value is less than 0.95, preferably less than 0.

90.

10. Component according to claim 8 or 9, wherein the silicon carbide substrate (1) is single-crystal, at least outside the volume (VS) corresponding to the first material density value.

11. Component according to any one of claims 8 to 10, forming a color center emitter or a light-emitting diode, located in the substrate (1), and such that when using said component, the radiation (R) is emitted by the color center or by the light-emitting diode and passes through the output window (W), said color center or light-emitting diode being located below the surface (S) of the substrate at a depth (P) which is greater than or equal to the thickness of the volume (VS) corresponding to the first value of material density.

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