Method for manufacturing a light-emitting diode

Abstract

The invention relates to a method for manufacturing a light-emitting diode comprising: having a sapphire substrate; depositing an epitaxial intermediate layer on the substrate made of transition metal nitride selected from: TiN, ZrN, HfN, NbN, TaN, VN, MoN, WN, CrN; depositing a buffer layer on the intermediate layer so as to obtain an epitaxial layer, the buffer layer being made of AlxGa1-xN with 0

Description

Title of the invention: Method for manufacturing a light-emitting diode technical field

[0001] The invention relates to a method for manufacturing a light-emitting diode, and in particular a method for manufacturing a light-emitting diode using laser detachment of a sapphire substrate. STATE OF THE ART

[0002] The fabrication of light-emitting diodes on a sapphire substrate has many advantages, such as compatibility in terms of lattice parameter with an active material in AlGaN used for light-emitting diodes emitting in the UV and the limitation of manufacturing defects of the different layers of the light-emitting diodes.

[0003] However, sapphire is a material with a refractive index much higher than that of air. This difference in refractive index results in a critical angle, i.e., the maximum angle of incidence at which a photon can escape from the light-emitting diode (LED), which is small at the interface between air and sapphire. This induces significant internal reflection of the photons emitted by the active layer in the LED. The photons therefore cannot escape from the LED and are thus lost to emission into the air. Consequently, state-of-the-art LEDs with a sapphire substrate exhibit low light extraction efficiency (LEE).

[0004] One solution for increasing the light extraction efficiency of light-emitting diodes on a sapphire substrate is to roughen ("rugose") the face of the sapphire substrate that is in contact with the air. This allows for a change in the angle of incidence of the photons and therefore the critical angle. However, sapphire is a hard material and is therefore difficult and expensive to roughen.

[0005] Another solution is to use AIN substrates, which have a refractive index closer to that of air than that of sapphire. However, existing AIN substrates are too thin and / or too expensive for commercial applications.

[0006] Another solution is to remove the sapphire substrate once the light-emitting diode has been manufactured, by laser lift-off. This process is already used for blue and UV-A light-emitting diodes (between 315 and 400 nm), using a GaN buffer layer deposited between the The sapphire substrate and the other functional layers of the diode are detached from the sapphire substrate. The GaN buffer layer allows for strong absorption of the emitted laser beam to achieve detachment, thus removing the sapphire substrate (see, for example, Kawan, A. et al. Trans. Elec. Mat. 2021 (22), 128-132). However, the use of the GaN buffer layer is not possible at wavelengths in the UV-C range (between 100 nm and 280 nm) because GaN absorbs wavelengths in the UV-C range, including those emitted by the LED itself. Furthermore, in the UV-A range, a thick GaN buffer layer is required for laser detachment, resulting in a significant deposition time. Furthermore, the difference in lattice parameter between GaN and an AlGaN active material used for UV-emitting LEDs leads to significant defects in the layers deposited above the buffer layer.

[0007] A AIN buffer layer would reduce defects in the layers deposited above the buffer layer, given the lattice parameters of AlN, which are closer to those of AlGaN. Results have been demonstrated with AIN buffer layers, which would generate fewer manufacturing defects. However, in the state of the art, laser detachment of sapphire substrates with an AIN buffer layer requires an energy density approximately four times higher than that used with a GaN buffer layer (see, for example, Aoshima, H. et al. Phys. Status. Solidi 2012, 753-756). Moreover, the high energy density of the laser damages the other layers of the light-emitting diode. ABSTRACT

[0008] In order to overcome the aforementioned drawbacks of laser sources, the invention proposes a method for manufacturing a light-emitting diode, the method comprising the following steps: a- have a sapphire substrate; b- deposit an intermediate layer on the substrate so as to obtain an epitaxial intermediate layer, the intermediate layer being in nitride of transition metals chosen from: TiN, ZrN, HfN, NbN, TaN, VN, MoN, WN, CrN; c- deposit a so-called buffer layer on the intermediate layer in order to obtain an epitaxial layer, the buffer layer being made of AlxGal-xN material with 0 <x<l ; d- déposer, sur la couche tampon, un empilement réalisant une fonction de diode électroluminescente, l’empilement comprenant au moins une couche active, et une couche d’injection de part et d’autre de la couche active ; e- to adhere a substrate, known as a transfer substrate, to the stack using at least one layer of adhesive; and f- perform a laser detachment of the sapphire substrate by applying a laser beam at least through the sapphire substrate and the intermediate layer, the laser beam having an emission wavelength configured to be absorbed by the intermediate layer.

[0009] In one embodiment, the process further comprises the following step, carried out after step d): d'- to anneal the substrate, buffer layer and intermediate layer at a temperature above 1500 C;

[0010] In one embodiment, the buffer layer comprises a first face in contact with the stack and a second face opposite the first face, the process further comprising the following step, carried out after step f): g- roughening the second face of the buffer layer;

[0011] In one embodiment, the intermediate layer has a thickness between 5 and 50 nm.

[0012] In one embodiment, step e) of gluing is carried out by placing a layer of glue on the transfer substrate or on the stack.

[0013] In one embodiment, step e) of bonding is carried out with a first layer of bonding and a second layer of bonding, step e) of bonding comprising the substeps: el- apply the first layer of adhesive onto the transfer substrate; e2- apply the second layer of adhesive onto the stack; e3- bring the first layer of adhesive into contact with the second layer of adhesive; and e4- Heat the first layer of glue and the second layer of glue so that they stick together.

[0014] In one embodiment, in step c) the deposition of the buffer layer on the intermediate layer is carried out by physical vapor deposition (PVD) or by metal-organic vapor deposition (MOCVD).

[0015] In one embodiment, step d) of stack deposition is done by metal-organic vapor deposition (MOCVD).

[0016] In one embodiment, an intermediate layer material deposited in step b) is configured to absorb ultraviolet light, and wherein the laser beam implemented in step f) is configured to emit ultraviolet light.

[0017] In one embodiment, the laser beam has an emission wavelength of 265 nm.

[0018] In one embodiment, the intermediate layer is made of TiN and the buffer layer is made of AIN.

[0019] In one embodiment, at least one of the bonding layers comprises titanium and / or copper.

[0020] In one embodiment, step d) of depositing said stack realizing a light-emitting diode function is configured to realize a light-emitting diode emitting in a range of 200-280 nm.

[0021] In one embodiment, the intermediate layer is made of transition metal nitride selected from: TiN, ZrN, HfN, NbN, TaN, VN.

[0022] The following description presents several embodiments of the device of the invention: these examples are not limiting to the scope of the invention. These embodiments present both the essential features of the invention and additional features related to the embodiments considered. Brief description of the drawings

[0023] The invention will be better understood and other advantages will become apparent upon reading the following description, given by way of non-limiting example, and from the figures, among which:

[0024] [Fig.1] [Fig.1] illustrates a method for manufacturing a light-emitting diode according to the invention. DETAILED DESCRIPTION

[0025] The invention relates to a method for manufacturing a light-emitting diode. Figure 1 illustrates a method for manufacturing a light-emitting diode (LED) according to the invention. The method comprises at least steps a) to f) described below.

[0026] In step a), the process 1000 consists of having a sapphire SubS substrate.

[0027] In step b), process 1000 consists of depositing an intermediate layer called CInter on the SubS substrate so as to obtain an epitaxial CInter intermediate layer, the intermediate layer being in transition metal nitride chosen from: TiN, ZrN, HfN, NbN, TaN, VN.

[0028] In step c), the process 1000 consists of depositing a so-called buffer layer CT on the intermediate layer CInter so as to obtain an epitaxial layer, the buffer layer CT being made of AlxGal-xN material with 0 <x<l.

[0029] In step d), the process consists of depositing, on the buffer layer, a CFLED stack performing a light-emitting diode function, the stack comprising at least one active layer (CA), and an injection layer (Cil, CI2) on either side of the active layer.

[0030] The CFLED stack comprises a first p-type doped Cil injection layer and a second n-type doped CL2 injection layer.

[0031] The CT buffer layer is placed between the CFLED stack and the sapphire SubS substrate. The CT buffer layer facilitates the transition between the sapphire SubS substrate and the CFLED stack in terms of lattice parameter. Indeed, the lattice parameter between the sapphire and the active material of the light-emitting diode included in the CFLED stack is far away, and the CT buffer layer thus helps to limit the defects that would be caused by this difference in mesh parameter.

[0032] In step e) the process 1000 consists of gluing a substrate called a transfer substrate SubR onto the stack by means of at least one bonding layer (CC).

[0033] In step f), the method 1000 consists of performing a laser lift-off of the sapphire SubS substrate by applying a laser beam RL at least through the sapphire SubS substrate and the intermediate layer CInter, the laser beam RL having an emission wavelength configured to be absorbed by the intermediate layer CInter. The intermediate layer CInter thus enables the laser lift-off through its absorption of the laser beam RL.

[0034] The method according to the invention makes it possible to benefit from the advantages of a sapphire substrate for the growth and fabrication of the CFLED stack, but the subsequent detachment of this substrate allows the fabrication of laser diodes that emit at a wavelength that would have been absorbed by the sapphire substrate. The detachment also makes it possible to roughen the CT buffer layer in order to limit the internal reflection of photons.

[0035] Advantageously, the invention uses an intermediate layer CInter whose material absorbs in the UV, thus enabling, in combination with an RL laser beam also emitting in the UV, the lift-off of the sapphire SubS substrate with a reduced energy density and by limiting the degradation of the other layers of the light-emitting diode. Furthermore, an intermediate layer CInter made of materials selected from: TiN, ZrN, HfN, NbN, TaN, VN, MoN, WN, CrN allows the various layers deposited on the intermediate layer to grow epitaxially. These materials absorb in the UV-C. The material of the intermediate layer is preferably selected from TiN, ZrN, HfN, NbN, TaN, VN, which are easier to process.

[0036] In one embodiment, also illustrated [Fig. 1], the process includes a step d') after step d). In step d'), the process 1000 consists of annealing the SubS substrate, the CT buffer layer, and the CInter intermediate layer at a temperature above 1500°C. The annealing allows the CT buffer layer and the CInter intermediate layer to crystallize, enabling good quality CFLED stack growth, i.e., with a limited number of defects.

[0037] In one embodiment, an intermediate layer material deposited in step b) is configured to absorb ultraviolet light, and wherein the RL laser beam implemented in step f) is configured to emit ultraviolet light.

[0038] In one embodiment, step d) of depositing the stack realizing a CFLED light-emitting diode function is configured to realize a light-emitting diode LED emitting in a range of 200-280 nm.

[0039] In one embodiment, the CFLED stack comprises at least one contact layer, at least one of which is made of metal. For example, at least one contact layer is deposited between the upper injection layer and the bonding layer. The upper injection layer is understood to be the layer located on the side opposite the sapphire substrate relative to the active layer. In one embodiment, a contact layer is deposited on both sides of the stack.

[0040] In one embodiment, the method 1000 further comprises the deposition of one or more transition layers to limit defects. For example, a transition layer is deposited, after step c), on the CT buffer layer. The CT buffer layer and the transition layer thus enable a mesh transition between the sapphire and the CFLED stack layers.

[0041] For example, the CT buffer layer is made of AIN and the active layer is made of GaN. In this case, the transition layer is made of AlGaN, thus allowing a transition between the CT buffer layer and the layers of the LED stack in terms of lattice, which limits defects.

[0042] In one embodiment, the active layer of the CFLED stack is in quantum wells, for example in AlGaN quantum wells.

[0043] The CT buffer layer comprises a first face in contact with the CFLED stack and a second face opposite the first face. According to one embodiment, the method further comprises a step g) which consists of roughening ("rugosifying") the second face of the buffer layer, step h) being carried out after step f). Roughening the CT buffer layer limits internal reflections and increases the light extraction efficiency of the light-emitting diode, i.e., increases the number of photons exiting the diode.

[0044] In one embodiment, the intermediate Cinter layer has a thickness between 5 and 50 nm. Advantageously, this thickness allows strong absorption of the RL laser beam having a wavelength in the UV, thus enabling a lift-off with a reduced laser energy density, and limiting the defects in the lower layers caused by the lift-off.

[0045] In one embodiment, in which step e) of bonding is carried out by placing the CC bonding layer on the SubR transfer substrate or on the CFLED stack.

[0046] In a first example, the CC bonding layer is disposed only on the SubR transfer substrate. In this case, the bonding step e) comprises the following substeps: a step e1') which consists of depositing the bonding layer onto the SubR transfer substrate, a step e2') which consists of bringing the layer into contact with bonding and stacking CFLED, and a step e3') which consists of heating the bonding layer so as to bond the CFLED stack and the SubR transfer substrate.

[0047] In a second example, the CC adhesive layer is disposed only on the CFLED stack. In this case, the bonding step e) comprises the following substeps: a step e1”) which consists of depositing the adhesive layer on the CFLED stack, a step e2”) which consists of bringing the adhesive layer into contact with the SubR transfer substrate, and a step e3”) which consists of heating the adhesive layer so as to bond the CFLED stack and the SubR transfer substrate.

[0048] In another embodiment, step e) of bonding is carried out by applying a first bonding layer and a second bonding layer, step e) of bonding comprising the following substeps: a step e1) which consists of depositing the first bonding layer onto the SubR transfer substrate, a step e2) which consists of depositing the second bonding layer onto the CFLED stack, a step e3) which consists of bringing the first and second bonding layers into contact, and a step e4) which consists of heating the first and second bonding layers so as to bond them. Thus, in this example, two CC bonding layers are deposited respectively on the SubR transfer substrate and on the CFLED stack, which are then brought into contact in order to bond the SubR transfer substrate to the CFLED stack.

[0049] For example, the heating step is carried out at 110 C.

[0050] In one embodiment, at least one of the bonding layers comprises titanium and / or copper.

[0051] In one embodiment, step c) of depositing the CT buffer layer onto the CInter intermediate layer is carried out by physical vapor deposition (PVD) such as reactive sputtering or pulsed laser ablation (PLD) or by metal-organic vapor deposition (MOCVD). Advantageously, deposition by metal-organic vapor deposition (MOCVD) makes it possible to limit defects in the CT buffer layer.

[0052] In one embodiment, step d) of depositing the CFLED stack is performed by metal-organic vapor deposition (MOCVD). Advantageously, this makes it possible to limit defects in the CFLED stack.

[0053] In one embodiment, the RL laser beam has an emission wavelength of 265 nm. Advantageously, this allows the use of a low energy density to perform the laser detachment, without causing degradation during the detachment step.

[0054] In one embodiment, the intermediate layer is made of TiN and the buffer layer is made of AIN.

[0055] To highlight the effects of the intermediate layer in the present invention, the inventors conducted tests on two light-emitting diodes (LEDs) produced by the process described above, using a TiN intermediate layer of 5 nm and 20 nm respectively, and on a light-emitting diode produced by a manufacturing process without the CInter intermediate layer deposition step. All three LED examples have a 400 nm AIN CT buffer layer.

[0056] A first X-ray diffraction test was performed on the three light-emitting diodes. A rocking curve scan was performed on the three LEDs. The diffraction peaks obtained by X-ray diffraction for two crystal planes were measured, and their full width at half maximum (FWHM) was determined. Table 1 below shows the results of the determined FWHM of the peaks.

[0057] The results clearly indicate that the full width at half maximum of the peaks remains about constant and therefore that the intermediate layer CInter does not degrade the crystallinity of the layers of the light-emitting diode.

[0058] A second roughness test was performed on the three light-emitting diodes. The root mean square (RMS) surface area in contact with air of the CT buffer layer before step d), i.e., before the CFLED stack growth, was measured. Table 1 above shows the results of the measured RMS.

[0059] The results clearly indicate that the root mean square decreases when the CInter intermediate layer is used for manufacturing the light-emitting diode. This means that the surface roughness of the CT buffer layer in contact with air decreases when the CInter intermediate layer is used for manufacturing. Minimal roughness is necessary to grow a CFLED stack with a minimum of defects.

[0060] Thus, the intermediate layer CInter makes it possible to maintain the crystallinity of the layers while reducing the roughness. AIN 400 nm TiN 5 nm + AIN 400 nm TiN 20 nm + AIN 400 nm XRD peak width crystal plane (002) 0.21 0.23 0.25 XRD peak width crystal plane (102) 0.38 0.30 0.36 RMS 1.04 nm 0.77 nm 0.80 nm

[0061] Table 1: Full width at half maximum (FWHM) of the diffraction peaks obtained by X-ray diffraction for different crystal planes and the root mean square of the surface buffer layer of different examples of light-emitting diodes obtained with or without an intermediate layer in TiN

[0062] It is noted that in the preceding description, epitaxy is understood to mean a process of ordered growth.

[0063] Although the invention has been illustrated and described in detail using a preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deduced by a person skilled in the art without departing from the scope of protection of the claimed invention.

Claims

Demands

1. A method (1000) for manufacturing a light-emitting diode (LED), the method comprising the following steps: a. having a sapphire substrate (SubS); b. depositing an intermediate layer (CInter) on the substrate so as to obtain an epitaxially grown intermediate layer, the intermediate layer being made of transition metal nitride selected from: TiN, ZrN, HfN, NbN, TaN, VN, MoN, WN, CrN; c. depositing a buffer layer (CT) on the intermediate layer so as to obtain an epitaxially grown layer, the buffer layer being made of AlxGabxN material with 0 <x<l ; d. déposer, sur la couche tampon, un empilement (CFLED) réalisant une fonction de diode électroluminescente, l’empilement comprenant au moins une couche active (CA), et une couche d’injection (Cil, CI2) de part et d’autre de la couche active ; e.to glue a so-called transfer substrate (SubR) onto the stack by means of at least one bonding layer (CC); and f- to perform a laser detachment of the sapphire substrate by applying a laser beam at least through the sapphire substrate and the intermediate layer, the laser beam (RL) having an emission wavelength configured to be absorbed by the intermediate layer.

2. The method according to claim 1, the method further comprising the following step, carried out after step d): d'- annealing the substrate, buffer layer and intermediate layer at a temperature above 1500 C;

3. Method according to claim 1 or 2, the buffer layer comprising a first face in contact with the stack and a second face opposite the first face, the method further comprising the following step, carried out after step f): g- roughening the second face of the buffer layer;

4. A method according to any one of the preceding claims, wherein the intermediate layer (Cinter) has a thickness between 5 and 50 nm.

5. A method according to any one of the preceding claims, wherein step e) of bonding is carried out by placing a layer of adhesive on the transfer substrate or on the stack.

6. A method according to any one of claims 1 to 3, wherein step e) of bonding is carried out with a first bonding layer and a second bonding layer, step e) of bonding comprising the substeps: e1- depositing the first bonding layer on the transfer substrate; e2- depositing the second bonding layer on the stack; e3- bringing the first bonding layer and the second bonding layer into contact; and e4- heating the first bonding layer and the second bonding layer so as to bond them.

7. A method according to any one of the preceding claims, wherein step c) of depositing the buffer layer on the intermediate layer is carried out by physical vapor deposition (PVD) or by metal-organic vapor deposition (MOCVD).

8. A method according to any one of the preceding claims, wherein step d) of stack deposition is carried out by metal-organic vapor deposition (MOCVD).

9. A method according to any one of the preceding claims, wherein an intermediate layer material deposited in step b) is configured to absorb ultraviolet light, and wherein the laser beam (RL) implemented in step f) is configured to emit ultraviolet light.

10. Method according to the preceding claim, wherein the laser beam has an emission wavelength of 265 nm.

11. A method according to any one of the preceding claims, wherein the intermediate layer is made of TiN and the buffer layer is made of AIN.

12. A method according to any one of the preceding claims, wherein one of at least one bonding layer comprises titanium and / or copper.

13. A method according to any one of the preceding claims, wherein step d) of depositing said stack realizing a light-emitting diode function is configured to realize a light-emitting diode emitting in a range of 200-280 nm.

14. A method according to any one of the preceding claims, wherein the intermediate layer is made of transition metal nitride selected from: TiN, ZrN, HfN, NbN, TaN, VN.

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