MANUFACTURE OF A RADIATION EMITTING COMPONENT FROM A SILICON CARBIDE SUBSTRATE

Abstract

A method for fabricating a radiation-emitting component (R) from a crystalline silicon carbide substrate (1) comprises implanting ions at room temperature into said substrate. The implantation produces an amorphization of the substrate in a volume (VS) located below the surface of said substrate. This results in a local decrease in the substrate's density, which enhances the radiation output from within the substrate. The component can be a color center (CC) single-photon emitter or a photodiode. (Shortcut figure: Figure 2a)

Description

Title of the invention: MANUFACTURE OF A RADIATION EMITTING COMPONENT FROM A SILICON CARBIDE SUBSTRATE Technical field

[0001] The present description relates to a method of manufacturing a radiation-emitting component, as well as to a component which can be obtained in this way. Generally, such a radiation-emitting component may be of the color-center type, for example for emitting single photons, or of the bipolar junction type, such as a light-emitting diode. Prior art

[0002] The use of crystalline silicon carbide (SiC) to produce radiation-emitting components has many advantages, which arise in particular from the following properties of the material: its chemical inertness, its thermal stability, its thermal conductivity and its wide band gap, particularly in comparison with silicon (Si), which is the most widely used semiconductor material in microelectronics today. Silicon carbide makes it possible, in particular, to produce radiation in a controlled manner in the spectral range of visible light, and also around 1.5 pm (micrometer), for example for telecommunications applications.

[0003] The efficiency of extracting the radiation produced inside the silicon carbide component, possibly intentionally doped, to the outside of this component so that the radiation can be used for the desired application, is then a major issue. Indeed, more efficient extraction of the radiation makes it possible to reduce the energy consumption of the component for an equal quantity of radiation that is usable. Furthermore, it is essential to be able to mass-produce components whose emission efficiency is controlled and reproducible. Technical problem

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

[0005] To achieve this or another aim, a first aspect of the invention provides a method of manufacturing a radiation emitting component from a substrate of crystalline silicon carbide, this method comprising the following steps: / 1 / in a surface of the substrate, determining at least a portion of this surface which is intended to constitute, during use of the component, an exit window towards the outside of the substrate for the radiation which comes from the inside of the substrate; and / 2 / while the substrate has a temperature below 200°C (degrees Celsius), implanting ions in the substrate, through the portion of the surface of the substrate which is intended to constitute the exit window for the radiation, with ion implantation dose and ion implantation energy values ​​which are adapted to produce an amorphization of the substrate in a volume situated below its surface.

[0006] Indeed, the inventors have discovered that unlike an ion implantation which is carried out while the substrate has a temperature above 300°C, for example between 300°C and 600°C, an ion implantation which is carried out while the temperature of the substrate is below 200°C is more effective for amorphizing the silicon carbide material. This silicon carbide material which is thus amorphized then has a density which is reduced compared to the crystalline material as it existed before the implantation or outside the volume crossed by the implanted ions.For this reason, the refractive index of the silicon carbide material is reduced in the portion of material which is intermediate between the surface of the substrate and the implantation depth of the ions, and this reduction in refractive index produces an at least partial antireflection effect for the radiation which comes from the interior of the substrate, in particular from the volume of the substrate in which the ions have been implanted, and whose direction of emission crosses the surface of the substrate in the exit window. Thanks to this antireflection effect, the exit of the radiation towards the outside of the component is favored, so that the component has an improved radiation production efficiency. In this way, an energy consumption by the component is reduced, for an equal quantity of radiation which is emitted.

[0007] The reduction in the density of the substrate in the amorphization volume can produce a swelling of the latter which appears at its surface. This swelling then constitutes proof of the reduction in the density of the silicon carbide material produced by the ion implantation. In this case, the depth values ​​in the substrate which are cited below are measured from the surface of the substrate as resulting from the swelling.

[0008] In the jargon of those skilled in the art, ion implantation that is carried out while the substrate temperature is below 200°C is said to be at room temperature when no heating is intentionally applied to the substrate, or when limited heating is used. Most often, no means of controlling the substrate temperature may be used during this so-called room temperature implantation. But it is also possible to carry out the ion implantation of step / 2 / while the substrate is cooled using suitable means. Generally, the substrate temperature during step / 2 / can be above 4 K (degrees Kelvin).

[0009] Preferably, in step / 2 / , the ion implantation dose and ion implantation energy values ​​may be selected to produce an amorphization of the substrate between its surface and a depth value which is between 0.2 pm and 1 pm, measured from the surface of the substrate. In particular, these implantation dose and energy values ​​may be adapted with respect to the wavelength of the radiation which will be produced in the substrate during use of the component and intended to exit the substrate. In other words, the amorphization volume, under the surface of the substrate, constitutes an antireflection effect layer whose thickness may be advantageously optimized with respect to the wavelength of the radiation. For example, this radiation which is produced by the component may be visible light or infrared radiation, for example with a wavelength close to 1.5 pm.

[0010] The ions which are implanted in step / 2 / can be selected from aluminum ions (Al), boron ions (B) and nitrogen ions (N). But other ions also suitable for producing desired dopings can be used alternatively.

[0011] Preferably, in step / 2 / , the ion implantation dose value may be between 1014 and 1016 ions per cm2 (square centimeter), and the ion implantation energy value may be between 20 keV (kiloelectron-volt) and 800 keV. Indeed, these values ​​are particularly suitable for producing a reduction in refractive index which is sufficient to significantly increase the output efficiency of the radiation towards the outside of the component.

[0012] Advantageously, and in particular to produce a light-emitting diode in the silicon carbide substrate, the ions can be implanted in the substrate in step / 2 / , 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 suitable for doping at least a portion 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 suitable for producing the amorphization of the substrate in the volume located under 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] Generally speaking, the method of the invention may further comprise the following step, which is carried out where appropriate after step / 2 / : / 3 / apply a heat treatment to the substrate, this heat treatment producing an activation of a doping of the substrate by the implanted ions. A recrystallization that could be caused by this heat treatment is generally partial, and insufficient to significantly modify the density of the substrate material in the amorphization volume. The heat treatment of this step / 3 / can be carried out at atmospheric pressure, under argon (Ar), with a temperature that is between 800°C and 1900°C, preferably between 1600°C and 1800°C, for a duration that is less than 1 hour. Beyond this duration, this heat treatment could reduce the antireflection effect that is provided by the amorphization of the substrate below the radiation exit window. The heat treatment of step / 3 / can be carried out during or after an implantation of ions in the substrate which is intended to dope at least a part of a light-emitting diode that is located in this substrate.

[0014] Up to step / 2 / which produces the amorphization of a part of the silicon carbide substrate, the latter can be monocrystalline, in particular according to the 3C, 6H or 4H polytype.

[0015] A second aspect of the invention provides a radiation emitting component, which comprises a crystalline silicon carbide substrate, this substrate having a surface and having 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 towards the outside of the substrate for radiation coming from the interior 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 quotient 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 may be monocrystalline, at least outside the volume which corresponds to the first density value of the material.

[0018] Such a component may constitute a colored center emitter, for example for emitting single photons, or a light-emitting diode, located in the substrate. Then, when using this component, the radiation is emitted by the colored center or by the light-emitting diode and passes through the exit window. The colored 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 characteristics and advantages of the present invention will appear more clearly in the detailed description below of non-limiting exemplary embodiments, with reference to the appended figures among which:

[0020] [Fig.1a] is a cross-sectional view of a substrate used to manufacture a light-emitting component, in accordance with the invention;

[0021] [Fig.lb] corresponds to [Fig.la] for a later step of the method;

[0022] [Fig. le] corresponds to [Fig. la] for a further stage of the process;

[0023] [Fig.ld] corresponds to [Fig.la] for a further stage of the process;

[0024] [Fig.2a] is a cross-sectional view of a light-emitting component with centers colored, as obtained by a manufacturing process in accordance with the invention; and

[0025] [Fig.2b] corresponds to [Fig.2a] for a photodiode obtained by a manufacturing method in accordance with the invention. Detailed description of the invention

[0026] For the sake of clarity, the dimensions of the elements shown in these figures do not correspond to actual dimensions or to actual dimensional ratios. Furthermore, identical references indicated in different figures designate identical elements or elements which have identical functions.

[0027] According to [Fig.1a], a substrate 1 of monocrystalline silicon carbide (SiC), 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 metal mask 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 which resists implantation processes and which can then be completely removed. In general, the hard mask 3 can be made of any material suitable for being etched locally.

[0028] An optional encapsulating layer 2 may be intermediate 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 which would be likely to occur from the surface S of the substrate 1 during heating, but other methods for avoiding such sublimation of silicon atoms are known, and may be used alternatively. Such an encapsulating layer 2 may be made of graphite carbon (C), for example as obtained in py- in-situ rolyzing a layer of photolithographic resin 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 atmosphere (N2), for example. Such an encapsulation layer 2 is effective in protecting the silicon carbide against thermally activated degradation, in particular against the sublimation of silicon (Si) atoms up to approximately 1800°C.

[0029] The hard mask 3 is then selectively removed inside a portion W of the surface S, which is intended to constitute an exit window for the radiation of a photoemitting component produced in the substrate 1. Such selective removal of the hard mask 3, inside the window W, can be carried out in one of the ways known to those skilled in the art, for example by optical or electronic lithography then using an etching process, wet or plasma, which is adapted to eliminate the hard mask 3 in each zone where the latter is exposed, that is to say in the window W. To create such a window W, a lift-off process can be used alternatively, to obtain the hard mask 3 selectively outside the window W on the substrate 1. The configuration which is shown by [Fig.lb] is then obtained.

[0030] When the encapsulating layer 2 is used, the substrate 1 can then be brought into contact with an oxygen (O2) plasma to remove the encapsulating layer 2 in the places where it is no longer covered by the hard mask 3, as shown in [Fig. 1e]. 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 in the substrate 1, through the opening which was previously made in the hard mask 3, and in the encapsulating layer 2 if applicable. An ion implantation energy is adopted, so that these ions are finally fixed in a portion V of the substrate 1 which extends from a depth P substantially equal to 0.25 μm. Then, the substrate 1 is amorphized between its surface S and this depth P, because of the collisions against the carbon and silicon atoms of the substrate 1, of the implanted ions up to their fixing sites. According to the invention, this ion implantation is carried out at room temperature, or at a cooling temperature, to promote the amorphization of the substrate 1 from its surface S up to the depth P, in line with the window W.For example, the following parameters can be adopted for ion implantation: implantation energy substantially equal to 200 keV, and implanted dose substantially equal to 1.75-1015 ions per cm2. Under these conditions, the depth P is substantially equal to 250 nm (nanometer) if aluminum ions are used for implantation, and the amorphization of the substrate 1 under the window W produces a swelling therein. SW of the surface S, as shown in [Fig.1d]. This swelling SW, which is of the order of 50 nm at the center of the window W, results from a reduction in the density of the material of the substrate 1 produced by its amorphization. It is substantially equal to 50 nm for the aforementioned implantation conditions. Thus, the density of the silicon carbide in the surface volume VS which is limited by the window W, the surface S and a depth under this surface S which is less than or equal to P, is substantially equal to 0.8 times the density of the silicon carbide of the substrate 1 outside this volume VS. This reduction in density causes a reduction in the light refractive index of the material of the substrate 1 in the volume VS. This volume with a reduced light refractive index value will then produce an at least partial antireflection effect, for radiation coming from the fixation zone of the implanted ions.

[0032] The residual part of the hard mask 3, outside the window W, is then removed, again by wet etching, then a heat treatment is applied to the substrate to activate the doping constituted by the implanted ions. During this activation heat treatment, the substrate 1 can be brought to a temperature substantially equal to 1700°C for 30 minutes, at atmospheric pressure under argon (Ar). Such heat treatment parameters make it possible to activate the doping function without significantly increasing the density of the silicon carbide in the volume VS. Thus, the output efficiency through the window W, of the radiation which comes from the interior of the substrate 1 below the volume VS during use of the manufactured component, is maintained.

[0033] According to an improvement of the invention, the implantation of the ions can be carried out in two distinct steps, to differentiate the functions of amorphization of the silicon carbide material in the volume VS, and of doping in a volume V which is located on a side opposite the surface S with respect to the volume VS. In other words, the volume V is located under the volume VS in the substrate 1, the volume VS then being called the superficial volume. Under these conditions, the superficial volume VS is essentially dedicated to producing the antireflection effect to promote the exit of the radiation, and the volume V is dedicated to producing the radiation.Then, the implantation of ions in the volume V can be carried out with a first pair of values ​​for the ion implantation dose and the ion implantation energy in order to dope the substrate 1 in the volume V, then a second pair of values ​​for these implantation parameters in order to amorphize the silicon carbide material in the superficial volume VS. The depth P then corresponds to an upper limit of the volume V, in the direction of the surface S of the substrate 1. For example, the values ​​to amorphize the substrate 1 in the superficial volume VS can be 1015 ions per cm2 for the implantation dose, and 100 keV for the implantation energy, and those to create the doping in the volume V can be 1014 ions per cm2 and 200 keV.

[0034] [Fig.2a] is a sectional view of a component with colored centers, for producing single photons. These colored centers, produced by doping, are located in the volume V and denoted CC, and a portion of the photons they emit is oriented toward the window W. The surface volume VS, in which the refractive index of the material of the substrate 1 is reduced according to the invention, reduces a reflection of these photons on the surface S, internal to the substrate 1. R designates the radiation which is constituted by the photons which exit through the window W. By way of illustration, [Fig.2a] also shows two photons R' which are produced by the colored centers CC by being directed outside the window W, and which are reflected toward the interior of the substrate 1 by the surface S.

[0035] Finally, [Fig.2b] is a sectional view of a photodiode manufactured by the method of the invention. The monocrystalline silicon carbide substrate 1 which is used may be originally N-type doped, and the doping which is carried out to create the surface volume VS may be P-type, like the volume V. The lower limit of the volume V, denoted J in the figure, is the photodiode junction. The component can be completed by a rear electrode 4 and an upper electrode 5. The upper electrode 5 can be formed in a manner known to those skilled in the art, on the swelling SW of the surface S. When a current is injected between the two electrodes 4 and 5, with a direct electrical polarization of the photodiode, radiation R is emitted by the junction J, part of which leaves the substrate 1 through the window W. As previously, this part of the radiation which is produced by the photodiode and which emerges from the substrate 1 is increased thanks to the invention.

[0036] It is understood that the invention may be reproduced by modifying secondary aspects of the embodiments which have been described in detail above, while retaining at least some of the advantages cited. In particular, a component manufactured in accordance with the invention may be of a type other than a single photon emitter or a photodiode. Furthermore, all the numerical values ​​which have been cited have been cited only for illustration purposes, and may be changed depending on the application considered.

Claims

Claims

1. Method for manufacturing a radiation-emitting component from a substrate (1) of crystalline silicon carbide, the method comprising the following steps: / 1 / in a surface (S) of the substrate (1), determining at least a portion of said surface which is intended to constitute, during use of the component, an exit window (W) towards the outside of the substrate of radiation (R) coming from the inside of said substrate; and / 2 / while the substrate (1) has a temperature below 200°C, implanting 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 and ion implantation energy values ​​which are adapted to produce an amorphization of the substrate in a volume (VS) located under said surface of the substrate.

2. Method according to claim 1, according to which, in step / 2 / , 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) of between 0.2 pm and 1 pm, measured from said surface of the substrate.

3. A method according to claim 1 or 2 wherein, in step / 2 / , the ion implantation dose value is between 1014 and 1016 ions per cm2, and the ion implantation energy value is between 20 keV and 800 keV.

4. Method according to any one of the preceding claims, wherein, in step / 2 / , the ions are implanted in the substrate (1), through the portion of the surface (S) of said substrate which is 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 part 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 amorphization volume (VS), 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 under the surface of said substrate.

5. Method according to any one of the preceding claims, further comprising the following step, carried out after step / 2 / : / 3 / applying a heat treatment to the substrate (1), said heat treatment producing an activation of a doping of the substrate by the implanted ions.

6. Method according to claim 5, according to which the heat treatment of step / 3 / 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 duration of less than 1 hour.

7. A method according to any preceding claim, wherein the silicon carbide substrate (1) is monocrystalline before step / 2 / .

8. A radiation emitting component, comprising a substrate (1) of crystalline silicon carbide, 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, during use of the component, an exit window (W) towards the outside of the substrate for radiation (R) coming from the interior 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 the thickness being measured perpendicular to the surface of the substrate, the depth being measured from said surface of the substrate, the component forming a colored 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 colored center or by the light-emitting diode and passes through the output window (W), said colored center or said light-emitting diode being located under 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 material density value.,

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

90.

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

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