Method for manufacturing a growth substrate comprising mesas of different deformabilities, by electrochemical etching and porosification

Abstract

The invention relates to a method for manufacturing a growth substrate suitable for the production by epitaxy of an InGaN-based diode matrix (D1, D2, D3), comprising the following steps: production of a crystalline stack (10) comprising, from a conductive buffer layer (11): a lower layer (12) based on doped GaN; then an intercalated separation layer (13) based on InGaN; then an upper layer (14) based on AlGaN; production of mesas of three categories M1, M2, M3, by localized etching of the crystalline stack (10); removal, by etching, of the upper portion (24) of at least the M3 mesas, the upper portion (24) of the M1 mesas being preserved; electrochemical non-photo-assisted porification of the lower portions (22) of mesas M1 and M3 only, the lower portion (22) of mesas M2 being non-porified. Figure for the abstract: Fig. 1H

Description

Title of the invention: Method for manufacturing a growth substrate comprising mesas of different deformabilities, by etching and electrochemical porosification Technical field

[0001] The field of the invention is that of methods for manufacturing a growth substrate comprising mesas, and making it possible to produce a matrix of diodes adapted to emit or detect, natively, light radiation at different wavelengths. STATE OF THE PRIOR ART

[0002] There are methods for manufacturing a matrix of light-emitting diodes adapted to emit, natively, light radiation at different wavelengths. The matrix of diodes can then comprise diodes adapted to emit red light, other diodes green light, and still others blue light. Such a matrix of diodes then forms a micro-screen with native RGB emission (for Red, Green, Blue, in English).

[0003] The diodes are said to have native emission, in the sense that the active zone of each diode emitting at a given wavelength differs from the active zones of the diodes emitting at another wavelength. In the case of diodes made from InGaN, the active zones differ from each other by the proportion of indium in the quantum wells.

[0004] Such a matrix of native emission diodes is thus distinguished from color conversion technologies where the diodes all emit at the same wavelength, for example in blue, and are each coated with a pad comprising luminophores, for example semiconductor nanocrystals forming quantum dots, to convert at least part of the incident light into light of another wavelength.

[0005] To fabricate a native emitting diode array, one approach is to use a growth substrate having mesas that have been partially made porous during an electrochemical porosification step. This electrochemical porosification technique is presented in particular in the article by Griffin and Oliver entitled Porous nitride semiconductors reviewed, J. Phys. D: Appl. Phys. 53 (2020) 383002.

[0006] Document EP3840065A1 describes an example of a method for manufacturing a growth substrate and then a diode matrix using the electrochemical porosification technique. The method comprises producing a growth substrate growth (also called pseudo-substrate) having several InGaN mesas, each formed of a doped portion of InGaN made porous during an electrochemical porosification step, and an epitaxial recovery portion of InGaN not intentionally doped or weakly doped so that it is not porosified (it remains intact or dense, therefore non-porous). The diodes are then produced by epitaxy from the epitaxial recovery portions.

[0007] The doped portions of the mesas may have different doping levels from one mesa to another, so that the mesas have different porosification levels and therefore different relaxation rates. The diodes produced from the different mesas then comprise quantum wells having a more or less significant proportion of indium, thus making it possible to obtain pixels emissive at different wavelengths.

[0008] However, to obtain mesas whose InGaN-doped layers have different doping levels from one mesa to another, it is necessary to carry out, before the step of producing the mesas, a step of spatially localized implantation of dopants in a full-plate InGaN layer, which complicates the manufacturing process. Statement of the invention

[0009] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a method for manufacturing a growth substrate, suitable for producing an array of InGaN-based diodes, and comprising mesas of different deformabilities, without it being necessary to carry out spatially localized implantations of dopants. These mesas of different deformabilities thus make it possible to natively produce InGaN-based diodes each capable of emitting or detecting light radiation at different wavelengths, for example in the three RGB colors.

[0010] For this, the object of the invention is a method for manufacturing a growth substrate suitable for the production by epitaxy of a matrix of diodes based on InGaN, comprising the following steps: - production of a crystalline stack based on GaN, comprising, from a conductive buffer layer made from doped GaN: a lower layer based on doped GaN; then an intermediate separation layer, based on InGaN; then an upper layer based on AlGaN; - production of mesas of three categories M1, M2, M3, by localized etching of the crystalline stack, each mesa then being formed of a stack of a lower portion, an intermediate separation portion, and an upper portion, originating respectively from the lower layer, from the layer separating interlayer and top layer; - removal, by etching, of the upper portion of at least the M3 mesas, the upper portion of the M1 mesas being preserved; then - non-photo-assisted electrochemical porosification of the lower portions of the M1 and M3 mesas only, the lower portion of the M2 mesas being non-porosified.

[0011] Some preferred but non-limiting aspects of this manufacturing method are as follows.

[0012] The removal step can be carried out by photoelectrochemical etching of the intermediate separation portion of at least the mesas M3, the mesas M1 being covered by an encapsulation layer.

[0013] The removal step can be carried out by dry etching of the upper portion of at least the mesas M3, with etching stopping on the intermediate separation portion, the mesas M1 being covered by an etching mask.

[0014] Following the step of producing the mesas, the intermediate separation portion may be, in each mesa, on and in contact with the lower portion, the method then comprising a step of producing epitaxy recovery portions produced on the basis of InGaN, carried out after the electrochemical porosification step, resting on the upper portion in the mesas M1, and resting on the lower portion in the mesas M3.

[0015] The method may comprise, following the removal and porosification steps and before the step of producing the epitaxial resumption portion, a step of producing a sealing portion deposited at least on and in contact with the lower portion of the mesas M3 then porosified.

[0016] During the step of producing the crystalline stack, an epitaxial recovery layer may be located on and in contact with the lower layer, so that, following the removal and porosification steps, the M3 mesas have an upper face formed by an epitaxial recovery portion originating from the epitaxial recovery layer.

[0017] The invention also relates to a method for manufacturing a matrix of diodes of categories D1, D2, D3 from a growth substrate, comprising the following steps: manufacturing the growth substrate by the method according to any one of the preceding characteristics; then depositing a growth mask, leaving free an upper surface of the mesas M1, M2, M3; then producing the matrix of diodes D1, D2, D3, respectively from the mesas M1, M2, M3.

[0018] The invention also relates to a growth substrate suitable for the production by epitaxy of a matrix of diodes based on InGaN, comprising: - a conductive buffer layer, made from doped GaN; - mesas of three categories M1, M2, M3, resting on the conductive buffer layer, each comprising a lower portion made from doped GaN, and • the Ml mesas further comprising a non-porous intermediate separation portion made from InGaN, resting on the lower portion; then a non-porous upper portion made from AlGaN; • the M2 mesas being formed from the non-porous lower portion; • the M3 mesas being formed from the porous lower portion, and not having no non-porous upper portion made from AlGaN resting on the lower portion.

[0019] Each mesa M1, M2, M3 may comprise a non-porous epitaxial resumption portion made from doped InGaN, resting, in the mesas M1, on the upper portion, and, in the mesas M3, on the lower portion.

[0020] Each mesa M1, M2, M3 may comprise a non-porous sealing portion made from GaN, located, in the mesas M1, between and in contact with the upper portion and the epitaxy recovery portion, and in the mesas M3, between and in contact with the lower portion and the epitaxy recovery portion.

[0021] Each mesa M1, M2, M3 may comprise an intercalated epitaxy resumption portion made from InGaN and located, in the mesas M1, between the lower portion and the intercalated separation portion, in the mesas M3, on the lower portion.

[0022] The intercalary epitaxial resumption portion of each mesa M1, M2, M3 may be non-porous.

[0023] The intercalary portion for epitaxial resumption may be porous in the mesas M1, and non-porous in the mesas M2 and M3. Brief description of the drawings

[0024] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0025] Figures 1A to 1H illustrate steps of a method for manufacturing a growth substrate, then a diode matrix, according to a first embodiment where the step of removing the upper AlGaN-based portions is carried out by photoelectrochemical etching;

[0026] Figures 2A to 2D illustrate steps of a method for manufacturing a growth substrate, then a diode matrix, according to a variant of the first embodiment. lization, where the crystalline stack comprises a thin intercalary epitaxial recovery layer intended not to be porosified;

[0027] Figures 3A to 3E illustrate steps of a method of manufacturing a substrate of growth, then of a matrix of diodes, according to another variant of the first embodiment, where the crystalline stack comprises an intercalary layer for resuming epitaxy intended to be porosified, and which may have a greater thickness than in the case of [Fig.2A]-2D;

[0028] Figures 4A to 4F illustrate steps of a method for manufacturing a growth substrate, then a diode matrix, according to a second embodiment where the step of removing the upper AlGaN-based portions is carried out by dry etching.

[0029] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0030] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "in the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise stated.

[0031] The invention relates to a growth substrate and its manufacturing method. The growth substrate is suitable for the production by epitaxy of a matrix of InGaN-based diodes, the diodes making it possible to emit or detect, natively, light radiation at different wavelengths, for example of the RGB (red, green, blue) type.

[0032] The growth substrate comprises mesas of at least three different categories, denoted M1, M2 and M3, having different deformabilities d1, d2, d3, depending on whether or not the mesas comprise an upper portion based on AlGaN, and depending on whether or not they comprise a lower portion based on GaN and / or an epitaxy recovery portion based on porosified InGaN. Generally speaking, the deformability is the capacity of the mesa to deform during the production of the diode.

[0033] The different deformabilities dl, d2, d3 of the mesas result in the fact that the mesas Ml, M2, M3 then have different values ​​of the effective lattice parameter, from one category of mesas to another, at the level of their upper face, during the growth of the diodes. The effective lattice parameter is the lattice parameter, defined in a main plane XY (orthogonal to the growth axis of the layers), of the layer or portion of layer considered. Also, the diodes of categories Dl, D2 and D3, produced during the same epitaxy step from the growth substrate, pre will have different active areas in terms of the proportion of indium incorporated in the quantum wells, and will therefore be suitable for emitting or detecting light radiation at different wavelengths.

[0034] The manufacturing method proposes to firstly produce GaN-based mesas M1, M2, M3, each comprising a lower GaN-based portion, an intermediate portion called a separation portion based on InGaN, and an upper AlGaN-based portion. Then, the upper AlGaN-based portion of at least the M3 mesas, and possibly also the M2 mesas, are removed by etching, while they are kept in the M1 mesas. This removal step can be, in a first embodiment, carried out by photoelectrochemical etching of the InGaN-based separation intermediate portion, or, in a second embodiment, carried out by dry etching of the upper AlGaN-based portions with etching stopping on the InGaN-based separation intermediate portions.The method also provides for porosifying by electrochemical porosification the lower portions of only the mesas M1 and M3, while they are not porosified in the mesas M2.

[0035] Let us recall that photoelectrochemical etching is carried out by immersing the growth substrate in a liquid electrolyte, and illuminating the mesas with an excitation light beam capable of being absorbed by the intermediate separation portions only. The material of these intermediate portions is then oxidized and dissolved by the liquid electrolyte. A low electrical voltage VPEce can be applied to collect the photogenerated electrons. Furthermore, let us also recall that electrochemical porosification (porosification by electrochemical anodization) is carried out by also immersing the growth substrate in a liquid electrolyte. An electrical voltage with a higher value VECe is applied, causing the porosification of the desired layer portions. In the context of the invention, electrochemical porosification is non-photo-assisted.

[0036] Let us recall here that an electrochemical porosification reaction is a selective reaction in the sense that, for the same electrical voltage of value VEce, a GaN-based crystalline semiconductor material will be porosified if its Nd doping level is greater than or equal to a predefined minimum doping level NDjmin(VEcE). Otherwise, it will not be porosified and will remain intact (dense). In this respect, document EP3840016A1 illustrates an example of the domain of existence of electrochemical porosification as a function of the ND doping level (here in donors) of the GaN-based crystalline material and the applied electrical voltage VEce.

[0037] We thus obtain a growth substrate, where: • M2 mesas have minimal deformability d2, since they do not have porosified portions. The effective lattice parameter aM2 is that of a GaN-based conductive buffer layer on which the mesas rest (with a slight relaxation linked to the realization of the mesas). Preferably, we will therefore have: aM2 ~ aGaN; • the Ml mesas have a deformability dl greater than d2, insofar as they comprise a lower portion based on porosified GaN and an upper portion based on non-porosified AlGaN. This then constrains the Ml mesas in compression, and leads to an effective lattice parameter aMb during the production of the diodes, lower than that of the M2 mesas: aMi < aM2; • M3 mesas also have a deformability d3 greater than d2, since they have a lower portion based on porosified GaN. M3 mesas also have an epitaxial recovery portion based on non-porosified InGaN, which then stresses the M3 mesas in tension, and leads to an effective lattice parameter aMb during the production of the diodes, higher than that of M2 mesas: aM3 > aM2.

[0038] Figures 1A to 1H illustrate steps of a method for manufacturing a growth substrate 20, then a diode matrix, according to a first embodiment where the step of separating the upper portions 24 based on AlGaN is carried out by photoelectrochemical etching. The diode matrix forms, in this example, a micro-screen with native RGB emission.

[0039] Here and for the remainder of the description, a direct three-dimensional orthogonal reference frame XYZ is defined, where the X and Y axes form a main plane of the support substrate 2 and where the Z axis is oriented along the thickness of the growth substrate 20 in the direction of the mesas.

[0040] With reference to [Fig. 1 A], a crystalline stack 10 based on GaN resting on a support substrate 2 is produced. Generally speaking, by “GaN-based material”, it is meant that the material can be GaN or can be a ternary or quaternary compound of GaN. It can thus be, generally speaking, InxAlyGaixyN where the proportion of indium x can be zero and where the proportion of aluminum y can also be zero. On the other hand, by “InGaN-based material”, it is meant that it is made of InGaN or InAlGaN, that is to say that it can be made of InxAlyGaixyN where the proportion of indium x is non-zero and where the proportion of aluminum y can be zero. Similarly, "by AlGaN-based material" we mean that it is made of AlGaN or InAlGaN, that is to say that it can be made of InxAlyGai x yN where the proportion of indium x can be zero and where the proportion of aluminum y is non-zero.

[0041] The support substrate 2 is made here of a non-porous material, so that it remains non-porous (dense) during the subsequent porosification of the mesas M1 and M3. It may be a material inert to the electrochemical porosification reaction, such as an insulating material (sapphire, etc.) or a semiconductor material (SiC, Si, etc.) not intentionally doped (nest) or lightly doped. It may also be a material GaN-based semiconductor not intentionally doped or lightly doped so as not to be porosifiable at the porosification voltage VECe- For example, the support layer can be made of sapphire, silicon, SiC, freestanding GaN, among others. It has a thickness for example between 200pm and 1.2mm approximately. Intermediate layers can be present between the support substrate 2 and the conductive buffer layer 11, made for example from AlN. Thus, as examples, the following stacks can be used: Si / AlN / AlGaN / GaN; sapphire / GaN nest; SiC / AlN / AlGaN etc... The support substrate 2 can be absent if the conductive buffer layer 11 has a sufficient thickness to ensure the mechanical strength of the growth substrate 20.

[0042] The crystalline stack 10 comprises a conductive buffer layer 11, on which the mesas M1, M2, M3 will rest and which will make it possible to apply an electrical potential to the lower portions 22 of the mesas from a polarization electrode 3. For this, the conductive buffer layer 11 is made of a crystalline material based on doped GaN (here n-type) over at least part of its thickness, with for example a doping level of 1018 cm 3. The conductive buffer layer 11 is made by epitaxy from the support substrate 2. It can have a thickness of between approximately 1 and 100 m. With this doping level, the conductive buffer layer 11 is not porosified during the subsequent step of electronic porosification (at an electrical voltage of the order of approximately 15 V), and allows the circulation of the charge carriers.

[0043] The lower layer 12 rests on the conductive buffer layer 11 and is in electrical contact with it (and here in physical contact). It is intended to form the lower portions 22 of the mesas, of which only the lower portions 22 of the mesas M1 and M3 will be porosified. It is made from GaN, and can, in general, be made from InxGaExN with a proportion of indium x, positive or zero, lower than that of the intermediate separation layer 13 so as not to absorb the excitation light beam during the subsequent photoelectrochemical etching step. It is doped sufficiently so that the lower portions 22 of the mesas M1 and M3 are porosified during the subsequent electrochemical porosification step. In this example, it is made from n-type doped GaN with a doping level of approximately 6x1018 cm3.Its thickness is of the order of several hundred nanometers to allow good relaxation of the mechanical constraints of the mesas Ml and M3, for example at least equal to 500nm, and is here equal to approximately 1000nm.

[0044] The intermediate separation layer 13 rests on the lower layer 12, and is here in contact with it. It is intended to be etched, during the subsequent photoelectrochemical etching step, to ensure the removal of the upper portions 24 of only the mesas M2 and M3 (and not of the mesas M1). It is therefore a sacrificial layer. It is made from InxGaExN, with a non-zero proportion of indium x on lower than those of the lower 12 and upper 14 layers, for example between 10 and 15%, to be the only one to absorb the excitation light beam during the subsequent photoelectrochemical etching step. In other words, its band gap energy is lower than that of the lower 12 and upper 14 layers. In this example, it is made of unintentionally doped InGaN, with a proportion of indium x of approximately 15%. Its thickness is of the order of a few nanometers, for example approximately 3nm. It can thus form a single quantum well or several quantum wells. Note that InGaN porosifies at an electrical voltage VECe lower than that of GaN, at an equivalent doping level. The proportion of indium x and the doping level are chosen here so that the intermediate separation portion 23 is not porosified during the porosification step of [Fig.lE].

[0045] The upper layer 14 rests on the intermediate separation layer 13, and is here in contact with it. It is intended to form the upper portions 24 of the mesas, of which that of the mesas M3 will be removed (and here also that of the mesas M2) during the subsequent photoelectrochemical etching step, and that of the mesas M1 will be preserved. It is made from AlGaN yN, with a non-zero proportion of aluminum y, higher than those of the lower 12 and intermediate 13 layers. The doping level is chosen so that the upper portion 24 of the mesas M1 is not porosified during the subsequent electrochemical porosification step. The material can therefore be unintentionally doped or lightly doped. In this example, it is made from AlGaN unintentionally doped with a proportion of aluminum y of approximately 10%. Its thickness is of the order of a hundred nanometers, for example around 100nm.Note that the upper layer 14 can be covered with a thin protective layer (not shown), for example in GaN or InGaN with a thickness of the order of 1 to 3nm, to prevent oxidation of the AlGaN.

[0046] Note here that the lower 12, intermediate 13 and upper 14 layers each have a thickness less than their critical thickness at which there is a plastic relaxation of the mechanical stresses. The total thickness of the crystalline stack 10 is also less than a predefined critical thickness. Thus, the conductive buffer layer 11 generates, in the lower 12, intermediate 13 and upper 14 layers, mechanical stresses (oriented in the XY plane) whose value is such that, before porosification, the effective lattice parameter is close to or substantially equal to the effective lattice parameter of the conductive buffer layer 11, here substantially equal to that of the relaxed GaN (or slightly in compression if it is made from sapphire).

[0047] With reference to [Fig. 1B], the mesas M1, M2 and M3 are produced by structuring the crystal stack 10 by lithography and localized etching. The etching is carried out here until it reaches the upper face of the conductive buffer layer 11. The etching may be a dry etching, for example of the ICP-RIE plasma type with chlorine gas, so that the sides of the mesas are substantially vertical. Each mesa is formed of a stack, along the +Z direction, of a lower portion 22 based on GaN (from the lower layer 12), of an intermediate separation portion 23 based on InGaN (from the intermediate layer 13), and of an upper portion 24 based on AlGaN (from the upper layer 14). Insofar as the mesas are produced from the same crystalline stack 10, each portion of a mesa is coplanar with the corresponding portions of the other mesas and has the same thickness.

[0048] A polarization electrode 3 is then deposited on and in contact with the conductive buffer layer 11, which will make it possible to apply an electrical potential to the mesas.

[0049] With reference to [Fig.lC], the upper portions 24 of at least the mesas M3 (and here also the mesas M2) are removed, and not the mesas M1. In this embodiment, this removal is obtained by photoassisted electrochemical etching of the entire intermediate portion 23 of the mesas M2 and M3. On the other hand, the mesas M1 are protected by an encapsulation layer 4 preventing the etching of the intermediate portion 23 of the mesas M1.

[0050] To do this, the encapsulation layer 4 is first deposited on the mesas M1, so as to cover them entirely. The mesas M2 and M3 are not covered by this layer 4. It may be a photosensitive resin, or even a conformal layer of an oxide. The intermediate portion 23 of the mesas M1 will therefore not be in contact with the liquid electrolyte.

[0051] Next, the etching of the intermediate portions 23 of the mesas M2 and M3 is carried out. The growth substrate 20 is immersed in a liquid electrolyte allowing the oxidized InGaN formed by the absorption of the excitation light beam to be dissolved. The liquid electrolyte may be acidic or basic, and may be oxalic acid. It may also be KOH, HF, HNO3, NaNO3, H2SO4 or a mixture thereof. It is thus also possible to use a mixture of oxalic acid and NaNO3. The growth substrate 20 is also subjected to an excitation light beam whose spectrum allows only the intermediate portion 23 to be excited. This may be a white light lamp associated with a filter, an LED, or even a laser source. Thus, a 405nm laser can be used to excite only the 23-intercalated portions of 15% indium InGaN.Furthermore, an electrical voltage VPEce can be applied by an electrical generator between the polarization electrode and a counter-electrode inserted in the electrolyte (for example, a wire or a platinum grid). It can be equal to, for example, 2V. This electrical voltage VPEce makes it possible to improve the collection of photogenerated electrons.

[0052] With reference to [Fig.lD], following the removal step by photoelectrochemical etching, the encapsulation layer 4 is removed. The mesas M2 and M3 have therefore lost their upper portion 24, due to the total etching of the intermediate portions 23. The upper face therefore corresponds to that of the lower portions 22. On the other hand, the upper face of the mesas M1 still corresponds to the upper portion 24 (or to the thin protective portion).

[0053] With reference to [Fig. 1E], a non-photo-assisted electrochemical porosification is carried out on the lower portions 22 of only the mesas M1 and M3, and not on that of the mesas M2. For this, an encapsulation layer 5 is deposited on only the mesas M2, for example a photosensitive resin or a layer of silicon oxide or nitride (conformal deposition). Thus, the mesas M2 will not be in contact with the liquid electrolyte. On the other hand, the mesas M1 and M3 are not covered by this encapsulation layer 5.

[0054] Next, the growth substrate 20 is again immersed in a liquid electrolyte. The polarization electrode 3 is then connected to the electrical generator so as to apply an electrical voltage of value VECe, for example here equal to 15V. This results in a porosification of the lower portions 22 of the mesas M1 and M3, which alone are in contact with the liquid electrolyte. The lower portion 22 of the mesa M2 is therefore not porosified. The electrical voltage can be applied for a period ranging from a few seconds to a few hours. A reference electrode can be used to precisely control the applied electrical voltage. During this step, there is no emission of the excitation light beam towards the mesas. The growth substrate 20 is then removed from the electrolytic bath, and the encapsulation layer 5 is removed.

[0055] Thus, a growth substrate 20 is obtained, the mesas of which, which have different deformabilities, have been obtained from the same initial crystalline stack 10. It is therefore suitable for the production by epitaxy of a matrix of diodes making it possible to emit or receive light radiation at different wavelengths natively, in particular after having produced epitaxy recovery portions 27 based on InGaN.

[0056] Thus, the mesas M2 have a minimal deformability d2, due to the fact that it is not porosified. In this example, it no longer includes the upper portion 24 based on AlGaN. Alternatively, as indicated previously, it could have kept it, in which case the upper portion 24 would be non-porosified (like the lower portion 22). In any case, the mesas M2 have an effective lattice parameter which is substantially equal to that of the conductive buffer layer 11, or even is substantially equal to the lattice parameter of the relaxed material of the layer 11, due to the low relaxation of the mesas during their production ([Fig.lB]). They will allow the production of D2 diodes emitting, for example, in green.

[0057] The mesas M1 have a deformability d1 greater than d2 due to the porosification of the lower portion 22. In addition, the porosified lower portion 22 allows the mesas M1 to relax under the effect of the mechanical compressive stresses generated by the upper portion 24 based on non-porosified AlGaN, so that the effective lattice parameter is then lower than that of the mesas M2. However, after this relaxation, the portion 24 will limit the deformation of the mesa M1 during the production of the diodes, and therefore limit the incorporation of indium. The mesas M1 will allow the production of diodes D1 emitting for example in the blue.

[0058] Finally, the M3 mesas have a deformability d3 greater than d2 and different from d1, due to the porosification of the lower portion 22 and the absence of the upper portion 24 based on AlGaN. The M3 mesas may have, during the production of the epitaxy recovery portion 27 based on InGaN, an effective lattice parameter greater than that of the M2 mesas due to the mechanical stresses in tension generated by the portion 27. The M3 mesas will allow the production of D3 diodes emitting for example in the red.

[0059] With reference to [Fig. 1F], the diode matrix is ​​then produced by epitaxy resumption from the mesas of the growth substrate 20. First of all, a growth mask 6 is deposited, made of a dielectric material, here in a conformal manner (for example by PECVD), so as to cover the sides of the mesas as well as the conductive buffer layer 11. The growth mask 6 can be produced, for example, from a silicon nitride or from a bilayer of a nitride and a silicon oxide with a thickness of approximately 80 nm. Only a surface of the upper faces of the mesas M1, M2, M3 is left free by the growth mask 6, so as to form a germination surface. Then, an annealing under ammonia and at high temperature (e.g., between 750 and 900°C) can be carried out to clean the upper surfaces of the mesas M1, M2, M3.

[0060] With reference to [Fig. IG], a thin GaN-based layer 26 is deposited by epitaxy on the upper surfaces of the mesas, and in particular on that of the mesas M3, so as to seal the pores of the porosified lower portion 22 which open onto the upper surface. For example, this sealing layer 26 can be made of InGaN with an indium proportion of approximately 1% and a thickness of between approximately 10 and 100nm.

[0061] Then, epitaxial recovery portions 27 are produced on the mesas M1, M2 and M3 and in particular on that of the mesas M3. These portions 27 can have a thickness of approximately 200nm and can be produced in InGaN with a proportion of indium of the order of approximately 8%. The epitaxial recovery portion 27 then causes the deformation of the porosified lower portion 22 of the mesas M3 (stresses in tension), which in turn allow the epitaxial recovery portions 27 to relax. In addition, the lattice parameter at the upper face of the M3 mesas is different from that of the M1 mesas.

[0062] With reference to [Fig. 1H], the diodes D1, D2, D3 are produced from the growth substrate 20, simultaneously, by epitaxy resumption from the mesas M1, M2, M3. Thus, a first portion based on n-type doped InGaN is deposited on each mesa during the same epitaxial deposition step, which will then be more or less relaxed depending on the categories M1, M2, M3 of mesas. Thus, a thickness of 200nm of a first portion of InGaN with 8.5% indium makes it possible to obtain an effective lattice parameter of 3.208Å on the mesas M3. During the same deposition, on the M1 mesas, the first portion contains less indium because of the upper portion 24 based on AlGaN, and on the M3 mesas, the first portion contains more indium thanks to the porosified lower portion 22 and the absence of the upper portion 24 of non-porosified AlGaN. Then, the active quantum well zone is produced, a second portion based on p-doped InGaN.An interposed electron-blocking portion of GaN or AlGaN may be provided between the active area and the second p-doped portion.

[0063] Thus, the manufacturing method makes it possible to natively produce diodes D1, D2, D3 which will emit at different wavelengths, here in the three RGB colors. This is possible because the mesas M1, M2, M3 have different deformabilities d1, d2, d3. Also, the incorporation of indium in the diodes, and in particular in the first n-doped portions then in the quantum wells of the active zones, depends in fact on the deformability of the mesas and the effective lattice parameter. The greater the effective lattice parameter of the epitaxial recovery portion (after production of the diodes), the greater the main wavelength of the corresponding diode will be. The manufacturing method of the growth substrate 20 thus involves a photoelectrochemical etching step, and at least one electrochemical porosification step.It was therefore not necessary to carry out, as in the prior art mentioned above, steps of localized ionic implantation of dopants to obtain the different types of mesas.

[0064] Figures 2A to 2D illustrate steps of a method for manufacturing a growth substrate 20, then a matrix of diodes D1, D2, D3, according to a variant of the first embodiment, where the crystalline stack 10 comprises a thin intercalary epitaxial recovery layer 15 intended not to be porosified.

[0065] With reference to [Fig.2A], a crystalline stack 10 similar to that of [Fig.1A] is produced, which differs therefrom in that it comprises an intercalary epitaxy recovery layer 15, located between and in contact with the lower layer 12 and the intercalary separation layer 13. This intercalary epitaxy recovery layer 15 is intended to form the epitaxy recovery portions 25 of the mesas M2 and M3 after the removal of the upper portions 24 based on AlGaN and the intermediate portions 23 based on InGaN. It can be made based on GaN, for example in GaN or InGaN (with a low proportion of indium, lower than that of the intermediate layer so as not to be etched during the photoelectrochemical etching step). It is not intentionally doped, or weakly doped so as not to be porosified during the electrochemical porosification step (doping level lower than that of the lower layer 12). Its thickness is small, for example of the order of 10 nm, so as not to impact the deformability of the mesas M1 and M3.

[0066] With reference to [Fig.2B], the photo-assisted electrochemical etching of the intermediate portion 23 of at least the mesas M3 and not the mesas M1, and here also the mesas M2 is carried out. This step is identical to that described previously in connection with [Fig.1C]. Following this step, the upper faces of the mesas M2 and M3 are those of the epitaxy recovery portions 25.

[0067] With reference to [Fig.2C], the electrochemical porosification of the lower portions 22 of only the mesas M1 and M3 is carried out and not of the mesas M2. This step is identical to that described previously in connection with [Fig.1E]. Due to the composition of the material of the epitaxy recovery portions 25 of the mesas M1 and M3 in terms of the proportion of indium and the doping level, these portions are not porosified (like the upper portion 24 of the mesas M1, and unlike the lower portions 22 of the mesas M1 and M3).

[0068] With reference to [Fig.2D], the diodes D1, D2, D3 are produced. This step is similar to those described previously in connection with [Fig.1F] and 1H. Note that it is not necessary here to deposit a thin pore-closing portion on the upper face of the mesas M3, since it is formed here from the epitaxial recovery portion 25 (non-porosified) and not from the porosified lower portion 22.

[0069] Figures 3A to 3E illustrate steps of a method of manufacturing a substrate of growth 20, then of a matrix of diodes D1, D2, D3, according to another variant of the first embodiment, where the crystalline stack 10 comprises an epitaxial recovery layer 15 intended to be porosified, the latter having a greater thickness than that described in connection with [Fig.2A]-2D.

[0070] With reference to [Fig.3A], a crystalline stack 10 similar to that of [Fig.2A] is produced, which differs in that the interlayer for epitaxy recovery 15, located between and in contact with the lower layer 12 and the interlayer separation layer 13, is intended to be porosified, and can therefore have a thickness greater than that of [Fig.2A]. As in [Fig.2A], it can be produced based on GaN, preferably InGaN with a low proportion of indium, lower than that of the interlayer 13 so as not to be etched during the etching step photoelectrochemical but sufficient to be porosified during the step of [Fig.3C]. It is doped in such a way that it is not porosified during the electrochemical porosification step of [Fig.3D] (less than that of the lower layer 12). Its thickness is greater than that of [Fig.2A], for example of the order of several hundred nanometers. In this example, it is made of InGaN with a proportion of indium of the order of 5 to 8%, doped n-type with a doping level between 1017 and 5xl018 cm3, and with a thickness equal to approximately 200nm.

[0071] With reference to [Fig.3B], the photo-assisted electrochemical etching of the intermediate portion 23 of at least the mesas M3, and here also of the mesas M2, and not of the mesas M1, is carried out. This step is identical to that of [Fig.2B]. Following this step, the upper faces of the mesas M2 and M3 are those of the epitaxy recovery portions 25.

[0072] With reference to [Fig.3C], a first electrochemical porosification (not photo-assisted) of the lower portion 22 and of the epitaxial recovery portion 25 of the mesas M1 is carried out only. The lower portion 22 of the mesas M3 will be porosified during another electrochemical porosification step. Obviously, the two porosification steps can be reversed. The encapsulation layer 5 therefore covers the mesas M2 and M3. The growth substrate 20 is immersed in the liquid electrolyte, and the voltage VECei is applied (approximately 16V). Also, the lower portion 22 and the epitaxial recovery portion 25 of the mesas M1 are porosified, and not the upper portion 24 based on AlGaN.

[0073] With reference to [Fig.3D], a second electrochemical porosification (non-photo-assisted) of the lower portion 22 of only the mesas M3 is then carried out. Here, the encapsulation layer 5 covers the mesas M1 and M3. A voltage Vecf? is applied (approximately 15V) whose value is lower than VECei to porosify only the lower portion 22 and not the epitaxial recovery portion 25 of the mesas M3. Following these two electrochemical porosification steps, the upper face of the mesas M1 is formed by the upper portion 24 made of non-porosified AlGaN, and those of the mesas M2 and M3 are formed by the non-porosified epitaxial recovery portions 25.

[0074] With reference to [Fig.3E], the diodes D1, D2, D3 are produced. Since the upper face of one or other of the mesas is not formed by a porosified portion, it is not necessary to deposit a thin layer to seal the pores. The production of the diodes D1, D2, D3 is carried out as described previously in connection with [Fig.2D].

[0075] Figures 4A to 4F illustrate steps of a method for manufacturing a growth substrate 20, then a matrix of diodes D1, D2, D3, according to a second embodiment where the step of etching the upper portions 24 based on AlGaN is carried out by dry etching. In this example, the crystal stack 10 is similar to that of [Fig.lA], but it could also be that of [Fig.2A] (with an epitaxial recovery layer 15 intended not to be porosified), as that of [Fig.3A] (with an epitaxial recovery layer 15 intended to be porosified).

[0076] With reference to [Fig.4A], a crystalline stack 10 is produced resting on the support substrate 2. It is here similar to that of [Fig.1A], and differs essentially in that the intermediate separation layer 13 provides an etching stop function during the step of removing the upper portions 24 of at least the mesas M3 (and here also the mesas M2). It is produced based on InGaN with a sufficient proportion of indium to ensure etching selectivity at the AlGaN / InGaN interface.

[0077] With reference to [Fig.4B], the mesas M1, M2 and M3 are then produced during a first dry etching step, for example by RIE etching with a first etching agent. Here, the etching agent is chosen to be able to locally etch the upper layer 14 based on AlGaN, then the interlayer 13 based on InGaN, and finally the lower layer 12 based on GaN. The etching mask can be arranged here so as to protect the top of the mesas.

[0078] A second dry etching step is then carried out, for example by RIE etching with a second etching agent. An etching mask 7 (hard mask) is deposited to cover the mesas M1 and leave free the upper face of at least the mesas M3, and here also that of the mesas M2. It can also cover the free face of the conductive buffer layer 11. Here, the second etching agent is chosen to be able to locally etch the upper AlGaN-based portions 24 of the mesas M2 and M3, and stop on the intermediate portions 23. Then, the hard mask 7 is removed. Following this step, the upper face of the mesas M1 is formed by the upper portion 24 based on non-porosified AlGaN, and those of the mesas M2 and M3 are formed by the intercalary portion 23 still present (which can be etched over part of its thickness, depending on the operating conditions of the dry etching).

[0079] With reference to [Fig.4C], electrochemical porosification is carried out on the lower portions 22 of only the mesas M1 and M3, and not on the mesas M2. This step is identical to that of [Fig.1E]. First, the electrode 3 is produced on and in contact with the conductive buffer layer 11. Then, the encapsulation layer 5 is produced which covers only the mesas M2. The growth substrate 20 is immersed in the liquid electrolyte and the electrical voltage VECe is applied. The lower portions 22 of the mesas M1 and M3 are porosified, and not the upper portion 24 based on AlGaN of the mesas ML. The encapsulation layer 5 is then removed.

[0080] With reference to [Fig.4D], the growth mask 6 is deposited on the layer conductive pad 11 and on the sides of the mesas M1, M2, M3, leaving free a surface of the upper face of the mesas M1, M2 and M3. It is also possible to carry out a cleaning annealing of the upper face of the mesas, for example under ammonia and at high temperature. This annealing can here remove by sublimation the etching stop portions 23 of the mesas M2 and M3 which may have surface defects linked to dry etching. Following this step, the upper face of the mesas M1 is formed by the non-porosified upper portion 24, that of the mesas M2 is formed by the non-porosified lower portion 22, and that of the mesas M3 is formed by the porosified lower portion 22.

[0081] With reference to [Fig.4E], a thin GaN-based sealing layer 26 is deposited on the upper surfaces of the mesas, and in particular on that of the M3 mesas, so as to seal the pores of the porosified lower portion 22 which open onto the upper face. The epitaxy recovery portions 27 are then produced on the M1, M2, M3 mesas, and in particular on the M3 mesas.

[0082] With reference to [Fig.4F], the diodes D1, D2, D3 are produced from the growth substrate 20, simultaneously, by resumption of epitaxy from the mesas M1, M2, M3, as described in connection with [Fig.1H].

[0083] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

[0084] Thus, as described previously, the upper portion 24 of the mesas M2 can be kept, as for the mesas M1. Furthermore, the non-photo-assisted electrochemical porosification step(s) can be carried out before the step of removing the upper portion 24 of at least the mesa M3. Finally, the epitaxy recovery portions 25, 27 can be carried out before or during the step of producing the diodes. When they are produced before that of the diodes, they can be porosified, in which case they have a small thickness, or they can not be porosified, in which case they can have a greater thickness.

Claims

Claims

1. Method for manufacturing a growth substrate (20) suitable for producing by epitaxy a matrix of diodes (D1, D2, D3) based on InGaN, comprising the following steps: • producing a crystalline stack (10) based on GaN, comprising, from a conductive buffer layer (11) produced based on doped GaN: • a lower layer (12) based on doped GaN; then • an intermediate separation layer (13), based on InGaN; then • an upper layer (14) based on AlGaN; • production of mesas of three categories M1, M2, M3, by localized etching of the crystalline stack (10), each mesa then being formed from a stack of a lower portion (22), an intermediate separation portion (23), and an upper portion (24), originating respectively from the lower layer (12), the intermediate separation layer (13) and the upper layer (14);• removal, by etching, of the upper portion (24) of at least the mesas M3, the upper portion (24) of the mesas M1 being preserved; then • non-photo-assisted electrochemical porosification of the lower portions (22) of only the mesas M1 and M3, the lower portion (22) of the mesas M2 being non-porosified.;

2. Manufacturing method according to claim 1, wherein the removal step is carried out by photoelectrochemical etching of the intermediate separation portion (23) of at least the mesas M3, the mesas M1 being covered by an encapsulation layer (4).

3. Manufacturing method according to claim 1, in which the removal step is carried out by dry etching of the upper portion (24) of at least the mesas M3, with etching stopping on the intermediate separation portion (23), the mesas M1 being covered by an etching mask (7).

4. A manufacturing method according to any one of claims 1 to 3, wherein, following the step of producing the mesas, the in- separation intercalary (23) is, in each mesa, on and in contact with the lower portion (22), the method comprising a step of producing epitaxial recovery portions (27) produced from InGaN, carried out after the electrochemical porosification step, resting on the upper portion (24) in the M1 mesas, and resting on the lower portion (22) in the M3 mesas.

5. Manufacturing method according to claim 4, comprising, following the removal and porosification steps and before the step of producing the epitaxial resumption portion (27), a step of producing a sealing portion (26) deposited at least on and in contact with the lower portion (22) of the mesas M3 then porosified.

6. Manufacturing method according to any one of claims 1 to 3, wherein, during the step of producing the crystalline stack (10), an epitaxial recovery layer (15) is located on and in contact with the lower layer (12), so that, following the removal and porosification steps, the mesas M3 have an upper face formed by an epitaxial recovery portion (25) originating from the epitaxial recovery layer (15).

7. Method for manufacturing a matrix of diodes of categories Dl, D2, D3 from a growth substrate (20), comprising the following steps: • manufacturing the growth substrate (20) by the method according to any one of the preceding claims; then • depositing a growth mask (6), leaving free an upper surface of the mesas Ml, M2, M3; then • producing the matrix of diodes Dl, D2, D3, respectively from the mesas Ml, M2, M3.

8. Growth substrate (20) suitable for producing by epitaxy a matrix of diodes based on InGaN, comprising: • a conductive buffer layer (11), produced from doped GaN; • mesas of three categories M1, M2, M3, resting on the conductive buffer layer (11), each comprising a lower portion (22) produced from doped GaN, and • the mesas M1 further comprising an intermediate separation portion (23) which is non-porous and produced from InGaN base, resting on the lower portion (22); then a non-porous upper portion (24) made from AlGaN; • the mesas M2 being formed from the non-porous lower portion (22); • the mesas M3 being formed from the porous lower portion (22), and not comprising a non-porous upper portion (24) made from AlGaN resting on the lower portion (22).

9. Growth substrate according to claim 8, in which each mesa M1, M2, M3 comprises a non-porous epitaxial recovery portion (27) made from doped InGaN, resting, in the mesas M1, on the upper portion (24), and, in the mesas M3, on the lower portion (22).

10. Growth substrate according to claim 9, in which each mesa M1, M2, M3 comprises a non-porous sealing portion (26) made from GaN, located, in the mesas M1, between and in contact with the upper portion (24) and the epitaxy recovery portion (27), and in the mesas M3, between and in contact with the lower portion (22) and the epitaxy recovery portion (27).

11. Growth substrate according to claim 8, in which each mesa M1, M2, M3 comprises an intermediate epitaxy recovery portion (25) made from InGaN and located, in the mesas M1, between the lower portion (22) and the intermediate separation portion (23), in the mesas M3, on the lower portion (22).

12. The growth substrate of claim 11, wherein the epitaxial resumption intercalary portion (25) of each mesa M1, M2, M3 is non-porous.

13. The growth substrate of claim 11, wherein the epitaxial resumption intercalary portion (25) is porous in the mesas M1, and non-porous in the mesas M2 and M3.

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