Method for manufacturing a composite structure including a stack of layers of single-crystal III-V materials

Abstract

The invention relates to a method for manufacturing a composite structure comprising the following steps: a) the provision of a composite substrate including a support substrate and a seed layer of single-crystal III-V material disposed on the support substrate via a bonding interface, the support substrate having a coefficient of thermal expansion different from that of the seed layer, and the seed layer having an intrinsic lattice parameter; b) the growth by epitaxy of a stack of single-crystal III-V type layers, called epitaxial layers, on the seed layer, each epitaxial layer having an intrinsic lattice parameter.When the coefficient of thermal expansion of the supporting substrate is lower than that of the seed layer, at least one epitaxial layer of the stack has a composition chosen such that its intrinsic lattice parameter is reduced by 200 ppm to 3000 ppm relative to the intrinsic lattice parameter of the seed layer. When the coefficient of thermal expansion of the supporting substrate is greater than that of the seed layer, at least one epitaxial layer of the stack has a composition chosen such that its intrinsic lattice parameter is increased by 200 ppm to 3000 ppm relative to the intrinsic lattice parameter of the seed layer. The invention also relates to a composite structure. Figure to be published with the abstract: No figure.

Description

Title of the invention: Method for manufacturing a composite structure comprising a stack of layers of single-crystal III-V materials FIELD OF INVENTION

[0001] The present invention relates to the field of semiconductor materials for microelectronic components. It relates in particular to a method for manufacturing a composite structure comprising a support substrate and a seed layer of III-V material assembled via a bonding interface and transferred onto said support substrate, the growth of at least one epitaxial layer then being carried out on the seed layer. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] For the fabrication of certain microelectronic or optoelectronic components, particularly HBT and HEMT transistors, lasers, and photodiodes, it is desirable to use composite substrates that provide a thin seed layer of single-crystal III-V material, deposited on a support substrate of a different nature than the seed layer, for economic reasons or to improve certain performance characteristics. As an example, one can cite an InP (indium phosphide)-on-silicon composite substrate, in which the single-crystal InP layer serves as a seed for the epitaxial growth of a functional stack of III-V layers, traditionally grown on a bulk InP substrate. The silicon substrate provides mechanical robustness to the composite substrate and allows for optimization of material costs.

[0003] Composite substrates can be developed in various ways, including by assembling (bonding) a donor substrate onto the support substrate, and transferring the seed layer (from the donor substrate) onto said support substrate, via thinning, delamination, or separation steps along a buried brittle plane formed in the donor substrate, as is notably the case in the well-known Smart Cut process.

[0004] Components produced using III-V epitaxy are generally very sensitive to the crystalline quality of the functional stacking of layers, particularly to crystalline defects (stacking faults, dislocations, etc.). Some crystalline defects may pre-exist in the seed layer; epitaxy then merely propagates them into the functional stack. Defects can also be generated during epitaxial growth, notably due to poor initial nucleation or unfavorable growth conditions (temperature, pressure, gas flow, contamination, etc.). adapted, or even excessively high mechanical stresses leading to irreversible relaxation phenomena, generally synonymous with dislocations.

[0005] The authors observed that, in many cases, epitaxial growth on an InP-on-Si composite substrate, instead of a bulk InP substrate, induces texturing or undulations on the surface of the epitaxially grown layers of the resulting composite structure. The shape of these undulations can vary, but a frequently observed pattern is a grid-like structure known as a "cross hatch".

[0006] This phenomenon also occurs in epitaxial stacks on InP bulk substrates, as well as in other systems, for example on GaAs bulk substrates, or even in Si / SiGe systems. It is generally associated with mechanical stress issues and appears in situations where the lattice parameter of the epitaxial layer differs from that of the seed layer. In this case, the epitaxial layer is generally under stress, and since the energy stored in the epitaxial layer is an increasing function of the thickness of this layer, it eventually relaxes irreversibly beyond a certain limit.

[0007] It appears important to resolve this problem of texturization, and consequently of defectivity, of epitaxial layers on composite substrate. SUBJECT OF THE INVENTION

[0008] The present invention proposes a method for manufacturing a composite structure comprising the epitaxial growth of a functional stack of layers on the seed layer of a composite substrate. The method provides for a specific adjustment of the intrinsic lattice parameter of at least one epitaxially grown layer relative to the intrinsic lattice parameter of the seed layer, depending on the differential expansion properties of the support and the seed layer of the composite substrate. BRIEF DESCRIPTION OF THE INVENTION

[0009] The invention relates to a method for manufacturing a composite structure comprising the following steps:

[0010] a) the supply of a composite substrate including a support substrate and a seed layer of single-crystal IILV material disposed on the support substrate via a bonding interface, the support substrate having a coefficient of thermal expansion different from that of the seed layer, and the seed layer having an intrinsic lattice parameter;

[0011] b) the growth by epitaxy of a stack of single-crystal layers of type IILV, called epitaxial layers, on the germ layer, each epitaxial layer having an intrinsic lattice parameter. The manufacturing process is remarkable in that:

[0012] - when the coefficient of thermal expansion of the supporting substrate is less than - when the coefficient of thermal expansion of the supporting substrate is greater than that of the seed layer, at least one epitaxial layer of the stack has a composition chosen so that its intrinsic lattice parameter is reduced by 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer; - when the coefficient of thermal expansion of the supporting substrate is greater than that of the seed layer, at least one epitaxial layer of the stack has a composition chosen so that its intrinsic lattice parameter is increased by 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer.

[0013] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - the single-crystal III-V material of the seed layer is a binary compound, in particular indium phosphide (InP) or gallium arsenide (GaAs); - the binary compound of the seed layer is indium phosphide (InP), the coefficient of thermal expansion of the supporting substrate is less than that of the seed layer, and at least one epitaxial layer is formed of a ternary compound of the type Ini xGaxP or InbxA1XP, in which x is between 0.0025 and 0.03; - x is between 0.0075 and 0.025, preferably between 0.01 and 0.02; - the binary compound of the germ layer is indium phosphide (InP), the the coefficient of thermal expansion of the supporting substrate is less than that of the seed layer, and at least one epitaxial layer is formed of a quaternary compound of the type Ini_x yGaxAlyP, in which the sum of x and y is between 0.0025 and 0.03; - the sum of x and y is between 0.0075 and 0.025, preferably between 0.01 and 0.02; - the binary compound of the seed layer is gallium arsenide (GaAs), the coefficient of thermal expansion of the supporting substrate is lower than that of the seed layer, and at least one epitaxial layer is formed of a ternary compound of the GaAsi ZPZ type in which z is between 0.0025 and 0.08; - the binary compound of the seed layer is indium phosphide (InP), the coefficient of thermal expansion of the supporting substrate is greater than that of the seed layer, and at least one epitaxial layer is formed of a ternary compound of the type InAswPi w in which w is between 0.0025 and 0.03, preferably between 0.01 and 0.02; - at least two epitaxial layers of the stack have compositions chosen such that their intrinsic lattice parameter is reduced or increased relative to the intrinsic mesh parameter of the seed layer; - each of the epitaxial layers of the stack has compositions chosen so that their intrinsic lattice parameter is reduced or increased relative to the intrinsic lattice parameter of the seed layer; - the support substrate is formed from a single-crystal or polycrystalline material chosen from silicon, sapphire, gallium arsenide, germanium, aluminium nitride and silicon carbide; - step a) includes the following sub-steps: the provision of a donor substrate in single-crystal III-V material, having a front face and a back face, the bonding by molecular adhesion of the front face of the donor substrate to the support substrate, and the thinning of the back face of the donor substrate to obtain the composite substrate; - Step a) includes the following sub-steps: a1) the provision of a donor substrate in single-crystal III-V material, a2) the formation of a brittle plane buried in the donor substrate, delimiting, with a front face of said donor substrate, the seed layer to be transferred, a3) the bonding by molecular adhesion of the front face of the donor substrate to the support substrate, a4) the separation along the buried fragile plane to transfer the germ layer onto the support substrate and obtain the composite substrate, on the one hand, and the rest of the donor substrate, on the other hand.

[0014] The invention also relates to a composite structure comprising: - a composite substrate including a support substrate and a seed layer of single-crystal III-V material disposed on the support substrate via a bonding interface, the support substrate having a coefficient of thermal expansion different from that of the seed layer, the seed layer having an intrinsic lattice parameter; - a stacking of type III-V single-crystal layers, called epitaxial layers, on the seed layer, each epitaxial layer having an intrinsic lattice parameter.

[0015] When the coefficient of thermal expansion of the supporting substrate is lower than that of the seed layer, the intrinsic lattice parameter of at least one epitaxial layer of the stack is reduced by 200 ppm to 3000 ppm relative to the intrinsic lattice parameter of the seed layer. When the coefficient of thermal expansion of the supporting substrate is greater than that of the seed layer, the parameter of The intrinsic mesh size of at least one epitaxial layer of the stack is increased by 200 to 3000 ppm relative to the intrinsic mesh size parameter of the seed layer.

[0016] Preferably, the intrinsic lattice parameter of the -at least one- epitaxial layer, reduced or increased relative to the lattice parameter of the seed layer, is defined by the composition of said layer, in particular by a substitution of 0.25% to 8% of III or V elements by III or V elements respectively smaller or larger. BRIEF DESCRIPTION OF THE FIGURES

[0017] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0018] [Fig. la]

[0019] [Fig. 1b] Fig. 1a and Fig. 1b respectively present a composite substrate and a composite structure according to the present invention;

[0020] [Fig.2a]

[0021] [Fig.2b]

[0022] [Fig.2c]

[0023] [Fig.2d] Fig.2a, Fig.2b, Fig.2c and Fig.2d present sub-steps of step a) of a manufacturing process according to the invention;

[0024] [Fig.3] Fig.3 shows the evolution of the lattice parameter of an InP layer (in particular the lattice parameter in the plane of the layer) as a function of temperature, in two cases: [azz - bulk InP] where the InP layer has been epitaxially grown on a bulk substrate also made of InP; [azz - InPOSi] where the InP layer is assembled on a silicon support substrate.

[0025] The same reference numerals in the figures may be used for elements of the same type. Some figures are schematic representations which, for the sake of readability, are not to scale. In particular, the thicknesses of the layers along the z-axis are not to scale with respect to the lateral dimensions along the x and y axes; and the relative thicknesses of the layers are not necessarily to scale in the figures. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention relates to a method for manufacturing a composite structure comprising a stack of single-crystal layers, epitaxially grown on a seed layer 2 forming part of a composite substrate 10.

[0027] Thus, the process comprises a step a) corresponding to the provision of a composite substrate 10 including a support substrate 1 and a seed layer 2 disposed on the support substrate 1 via a bonding interface 3 ([Fig. 1a]). The seed layer 2 is made of single-crystal IILV material (III: In, Ga, Al,...; V: As, P, Sb,...). It has a thickness typically between a few nanometers and 2 micrometers, preferably less than or equal to 1000 nm, 500 nm, 250 nm, or even 100 nm. This small thickness avoids the generation of defects during subsequent temperature rises and falls, required for the fabrication of the composite structure 100, because the support substrate 10 has a coefficient of thermal expansion different from that of the seed layer 2, higher or lower.

[0028] It should be noted that the coefficient of thermal expansion of a material depends on the temperature. For the sake of simplicity, we can consider an average value of the coefficient of thermal expansion over the temperature range. This range extends from the assembly temperature between the seed layer 2 and the support substrate 1 (for example, ambient temperature, approximately 20°C) up to the epitaxial temperature, which varies depending on the nature of the epitaxially formed materials. It should be noted that the assembly could also be carried out at lower or higher temperatures, which would shift the calculated average value of the coefficient of thermal expansion.

[0029] Typically, if we consider average coefficients of thermal expansion, the ratio between the upper coefficient of thermal expansion (that of the support substrate 1 or the seed layer 2) and the lower coefficient of thermal expansion (that of the support substrate 1 or the seed layer 2) is here between 1.05 and 2.5.

[0030] The support substrate 1 can have a thickness ranging from a few hundred micrometers to 800qm.

[0031] The single-crystal III-V material of the seed layer 2 is advantageously a binary compound, in particular indium phosphide (InP) or gallium arsenide (GaAs). The supporting substrate 1 can be formed from a single-crystal or polycrystalline material selected from silicon, sapphire, gallium arsenide, germanium, silicon carbide, etc.

[0032] The composite substrate 10 can for example be of the type InP on Silicon, InP on Sapphire, InP on GaAs, InP on Germanium, InP on SiC, GaAs on Silicon, GaAs on Sapphire, GaAs on Germanium, GaAs on SiC, etc.

[0033] The germ layer 2 has an intrinsic lattice parameter. In the remainder of this description, the intrinsic lattice parameter qualifies the natural lattice parameter, in the relaxed state, of the material forming the layer in question.

[0034] Even though the nature of the seed layer 2 and the nature of the supporting substrate 1 are different, the seed layer 2 is in a substantially relaxed state because said layer 2 is taken from a massive donor substrate 20 and transferred to the supporting substrate 1, and not formed by epitaxy on the latter. The lattice parameter of the seed layer 2 is therefore not crystallographically related to that of the supporting substrate 1: the respective lattice parameters of the seed layer 2 and the supporting substrate 1 are completely independent. The lattice parameter of the seed layer 2, in the substrate composite 10, is therefore equal to or very close to the intrinsic lattice parameter of the material constituting the seed layer 2.

[0035] Note that the seed layer 2 could possibly have a non-zero stress level due to the assembly temperature on the support substrate 1, due to fining phenomena at the bonding level or other deformations related to the transfer process used to manufacture the composite substrate 10. In such a case, the actual lattice parameter of the seed layer 2, in the plane of said layer (az / ) could be somewhat different from the intrinsic lattice parameter.

[0036] By way of example, if the seed layer 2 is formed in InP, its intrinsic lattice parameter at room temperature is approximately 5.869 Angstroms; if the seed layer 2 is formed in GaAs, its intrinsic lattice parameter at room temperature is approximately 5.654 Angstroms.

[0037] The composite substrate 10 is produced by a thin film transfer technique, involving an assembly between said thin film and the support substrate 1 via a bonding interface 3.

[0038] Advantageously, and with reference to the Smart Cut process, step a) comprises the following substeps:

[0039] a) the supply of a donor substrate 20 made of single-crystal III-V material, from which the seed layer 2 will be taken, and the supply of the support substrate 1, whose coefficient of thermal expansion differs from that of the donor substrate 20 ([Fig.2a]). The donor substrates 20 and support 1 are usually in the form of circular platelets, with diameters ranging from 50mm to 300mm, depending on the availability of the materials;

[0040] a2) the formation of a fragile plane buried 4 in the donor substrate 20, delimiting with a front face of said donor substrate 20, the germ layer 2 to be transferred ([Fig.2b]);

[0041] a3) the molecular adhesion of the front face of the donor substrate 20 to the support substrate 1, to form a glued assembly 120 including a bonding interface 3 between the two substrates 20,1 ([Fig.2c]);

[0042] a4) the separation along the buried fragile plane 4 to transfer the germ layer 2 on the support substrate 1 and obtain the composite substrate 10, on the one hand, and the rest of the donor substrate 20', on the other hand ([Fig.2d]).

[0043] Substep a2) can in particular be carried out by ion implantation of light species such as hydrogen and / or helium.

[0044] The front face of the donor substrate 20 and / or the front face (assembled) of the support substrate 1 may include an intermediate insulating, conductive or semiconducting layer, capable of facilitating bonding, improving the quality and strength of the interface, or providing insulating or conductive properties. interesting for future component development. Cleaning and surface treatments (polishing, plasma, etc.) are usually applied to the substrates before assembly.

[0045] As a reminder, direct molecular adhesion bonding (substep a3) does not require an adhesive material, as bonds are established at the atomic scale between the surfaces being joined. Several types of molecular adhesion bonding exist, which differ in particular in their temperature, pressure, atmospheric conditions, or pretreatments prior to contacting the surfaces. Examples include room-temperature bonding with or without prior plasma activation of the surfaces to be joined, atomic diffusion bonding (ADB), surface-activated bonding (SAB), etc.

[0046] Substep a4) of separation along the buried fragile plane is usually achieved by applying a heat treatment at a temperature between 100°C and 500°C, depending on the materials involved. Such a heat treatment induces the development of cavities and microcracks in the buried fragile plane, and their pressurization by the light species present in gaseous form, until a fracture propagates along said fragile plane. Alternatively or concurrently, mechanical stress may be applied to the bonded assembly, and in particular to the buried fragile plane 4, so as to propagate or help propagate mechanically the fracture leading to separation.

[0047] The free surface of the germ layer 2 is usually rough after separation.

[0048] A finishing substep a5) is preferably applied to the composite substrate 10, with a view to restoring the crystalline quality and surface condition of the seed layer 2, and to consolidate the bonding interface 3. The finishing process may include thermal, mechanical, and / or chemical treatments. It also aims to make the surface of the seed layer 2 compatible with the epitaxial growth of a stack of type III-V single-crystal layers. For this purpose, polishing and cleaning treatments, in particular, may be used.

[0049] As an example of an embodiment, reference may be made to the publication by B. Ghyselen et al "Large-Diameter III-V on Si Substrates by the Smart Cut Process: The 200 mm InP Film on Si Substrate Example", physica status solidi (a) Volume 219, Issue 4.

[0050] Alternatively, the thin-film transfer technique may be based on mechanical and / or chemical bonding and thinning. Step a) may then include:

[0051] - the supply of a donor substrate 20 in single-crystal III-V material, exhibiting a front panel and a back panel,

[0052] - the molecular adhesion bonding of the front face of the donor substrate 20 onto the substrate support 1, to form a bonded assembly including a bonding interface 3 between the two substrates 20,1,

[0053] - thinning the rear face of the donor substrate 1 to obtain the substrate composite 10.

[0054] Thinning can be achieved by all known techniques, including grinding (rectification), mechanical or mechano-chemical polishing, and / or chemical etching.

[0055] The process then comprises a step b) corresponding to the epitaxial growth of a stack 50 of type III-V single-crystal layers, referred to as epitaxial layers 51, 52, 53, 54, on the seed layer 2 ([Fig. 1b]). Each epitaxial layer 51, 52, 53, 54, according to its composition, is characterized by an intrinsic lattice parameter.

[0056] Epitaxy of IILV materials, particularly epitaxy on InP- or GaAs-based substrates, is usually carried out at temperatures between 500°C and 700°C, depending on the epitaxy technique used, for example, metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). The epitaxial layers may be formed from binary, ternary, quaternary, or even more than four-element IILV compounds, arranged in a functional stacking configuration for the fabrication of microelectronic components such as HBT and HEMT transistors, lasers, or photodiodes.

[0057] For example, to fabricate a photodiode in the short wavelength IR (SWIR for "short wavelength infrared" according to Anglo-Saxon terminology) of PIN structure, it is known to carry out a stacking of layers such as below, by epitaxy on a bulk InP substrate, following the order indicated (1 = first layer deposited on the bulk substrate, 2 = second layer deposited on the first layer, etc): 1. InP, N-doped, with a typical thickness of 300 to 500 nm; 2. Ino.53Gao.47As, intrinsic, with a typical thickness of 2.5 to 3 pm; 3. InP, doped P, with a thickness of 0.5 to Ipm; 4. Ino.53Gao.47As, P-doped, with a typical thickness of 30 to 100 nm.

[0058] The ternary compound Ino.53Gao.47As provides a perfect lattice match with InP, avoiding the development of stresses in the layers during the epitaxial growth of the stack on the bulk InP substrate.

[0059] Within the framework of the present invention, due to the difference in thermal expansion between the seed layer 2 and the support substrate 1, certain conditions are required for the intrinsic lattice parameter of all or part of the epitaxial layers 51,52,53,54 of the stack 50 formed during step b).

[0060] According to a first aspect, when the coefficient of thermal expansion of the support substrate 1 is less than that of the seed layer 2, at least one epitaxial layer of the stack 50 has a composition chosen so that its intrinsic lattice parameter is reduced from 200 ppm (i.e. 0.020%) to 3000 ppm (i.e. 0.3%) relative to the intrinsic lattice parameter of the seed layer 2. In some particular cases, the reduction of the intrinsic lattice parameter of the epitaxial layer can be between 500 ppm and 2500 ppm, between 750 ppm and 1800 ppm, or even between 900 ppm and 1300 ppm.

[0061] Thus, at the epitaxial temperature, the germinal layer 2, whose lattice parameter in the (az / ) plane is substantially reduced due to the lower dilation of the supporting substrate 1, is found to be favorable to the growth of the epitaxial layer 51,52,53,54 chosen with an intrinsic lattice parameter shifted.

[0062] By way of illustration, consider a 100 InP-on-Si composite substrate (InPOSi). Between room temperature (or more broadly the low temperatures at which the assembly of the seed layer 2 and the support substrate 1 can take place) and the typical epitaxial temperature on InP (i.e., from 500 to 650°C), silicon expands by about half compared to InP. In a simplified model, considering on the one hand the difference between the average thermal expansion coefficients of Si and InP (average difference of the order of 2 to 3E-6) and on the other hand the temperature amplitude between the epitaxial temperature and the ambient temperature (amplitude of the order of 600°C), the calculation shows that the lattice parameter of the InP layer can be affected (relative to massive relaxed InP) by the order of 900 to 1300 ppm ([Fig.3]).

[0063] Although this order of magnitude is derived from an extremely simplified calculation, and does not take into account the exact conditions of growth (temperature, growth techniques, presence of other sources of stress, ...) nor the exact composition of the epitaxial stack (nature, thickness, coefficient of thermal expansion of each of the layers which compose it), the applicant observed that the choice of one or more epitaxial layers 51,52,53,54 having an intrinsic lattice parameter shift of this order of magnitude, with respect to the seed layer 2, had a particularly beneficial effect on the quality of the epitaxial layers obtained.

[0064] The simplified calculation does not take into account any other compromises that one might seek to make. For example, upon cooling after epitaxial treatment, opposite effects may come into play, again based on the differences in the coefficient of thermal expansion between the IILV material layers and the support substrate 1. Let us consider the case of an InP / Si type composite substrate 10. Upon cooling At temperature, the effect is that the epitaxial layers 51, 52, 53, and 54 are now under tension. If the composition adjustment of the epitaxial layer (shift in the intrinsic lattice parameter), an adjustment beneficial for addressing waviness and cross-hatch during epitaxy, is too large, the resulting tension upon cooling can conversely be too strong and lead to mechanical damage of the epitaxial stack (cracking and fissures in the case of tensioning). Therefore, the authors recommend, in some cases, only partially adjusting the intrinsic lattice parameter of the epitaxial layer relative to the seed layer 2. Thus, a only partial composition adjustment may be desirable.

[0065] Conversely, other effects, such as the presence of another source of stress (for example, the stress state of the seed layer 2, which would significantly shift the lattice parameter in the real (az / ) plane of this layer away from the intrinsic lattice parameter), could lead to a greater magnitude of compensation compared to this same simplified calculation. Thus, even if a stress reduction of the order of 900-1300 ppm appears to be a good target value as a first approximation, a wider reduction range should be considered, depending on the specific real-world case, from 200 to 3000 ppm.

[0066] Thus, starting from a composite substrate 10 of the InP-on-silicon type, with a seed layer 2 in InP of 0.2qm thickness and a support substrate 1 in silicon of 525qm thickness (for example for a composite substrate of 100mm diameter), it is possible to create in particular a stacking of layers 50 such as below, to form a composite structure 100 according to the present invention: 1. Ino.985Gao.o15P, N-doped, with a thickness of 300 to 500 nm; 2. Ino.5i5Gao.485As, intrinsic, with a thickness of 2.5 to 3qm; 3. Ino.985Gao.o15P, doped P, with a thickness of 0.5 to Ipm; 4. Ino.5i5Gao.485As or Ino.53Gao.47As, doped P, with a thickness of 50 to 100 nm.

[0067] In this example, compared with the conventional stacking on bulk InP described previously for the fabrication of a SWIR photodiode, the first epitaxial layer 51 is a ternary compound Ino.985Gao.o15P, resulting from the fact that 1.5% of the indium atoms have been replaced by gallium atoms, inducing a reduction in the intrinsic lattice parameter of the first epitaxial layer of about 900-1300 ppm compared to the intrinsic lattice parameter of the seed layer 2 (InP). In the second epitaxial layer 52, the indium composition of element III was also reduced by 1.5% (expressed as a percentage of total element III), in favor of gallium, compared to the compound Ino.53Gao.47As paired with InP as an intrinsic lattice parameter, resulting in a final compound Ino.515Gao.485As; the The lattice parameter reduction of the second epitaxial layer relative to the intrinsic lattice parameter of the germinal layer 2 is on the order of 900–1300 ppm. The third epitaxial layer 53 was chosen to be identical to the first 51, with the same lattice parameter reduction. Finally, the fourth epitaxial layer 54 may or may not have a lattice parameter shift; its small thickness makes it less likely to develop stresses leading to irreversible relaxation.

[0068] The SWIR photodiode fabricated from this composite structure 100 is perfectly functional and efficient due to the crystallographic quality of the epitaxial layers 51, 52, 53, 54 of the stack 50, which are free of defects and dislocations related to cross-hatching. In this particular example, three (at least) of the four epitaxial layers 51, 52, 53, 54 have a composition chosen such that their intrinsic lattice parameter is reduced by approximately 0.09% - 0.13% compared to the intrinsic lattice parameter of the seed layer 2. Alternatively, it could be considered to reduce the intrinsic lattice parameter of only the second epitaxial layer 52 (by choosing the compound Ino,5i5Gao>485As) and to retain the first, third, and fourth epitaxial layers 51, 53, 54 of the conventional stack usually made on InP.Alternatively, it could be chosen to reduce the intrinsic lattice parameter of the first 51 and third 53 epitaxial layers, and to retain the second 52 and fourth 54 epitaxial layers of the classical stacking.

[0069] More generally, to reduce the intrinsic lattice parameter of a III-V compound, it is possible to substitute a certain proportion of III elements with a smaller III element.

[0070] In the case of InP, the substitution of 0.3% to 4% of the indium atoms by gallium or aluminium allows a reduction of the intrinsic lattice parameter of the layer of about 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of InP.

[0071] For a germ layer 2 formed in InP (binary compound), an epitaxial layer 51,52,53,54 can advantageously consist of a ternary compound, such as In[x GaxP or Ini xAlxP, in which x is between 0.003 and 0.04 (0.3% to 4%), between 0.006 and 0.03 (0.6% to 3%), or even between 0.01 and 0.02 (1% to 2%).

[0072] Still for a seed layer in InP (binary compound), an epitaxial layer 51,52,53,54 can advantageously consist of a quaternary compound, such as In[ x_ yGaxAlyP in which the sum of x and y is between 0.003 and 0.04 (0.3% to 4%), between 0.006 and 0.03 (0.6% to 3%), or even between 0.01 and 0.02 (1% to 2%).

[0073] Other compositions are also possible, involving a substitution of element V by a smaller element V (for example, substitution of a certain proportion of arsenic to phosphorus). For example, considering an InGaAs layer (e.g., Ino^Gao^As) whose intrinsic lattice parameter we wish to reduce relative to the intrinsic lattice parameter of InP, it is possible to replace As atoms with P atoms to form a quaternary compound of the type InGaAs i XPX, in which x is between 0.003 and 0.04 (0.3% to 4%), between 0.006 and 0.03 (0.6% to 3%), or even between 0.01 and 0.02 (1% to 2%). As an example, we can cite the compound Ino,53Gao>47Aso,985Po,oi5, whose intrinsic lattice parameter is reduced by 900-1300 ppm relative to the intrinsic lattice parameter of the InP seed layer 2.

[0074] It is also possible to manipulate both elements III and elements V to form a quaternary compound of the type Iri| XGaxAsi ZPZ, in which x and z are respectively between 0.003 and 0.04 (0.3% to 4%), between 0.006 and 0.03 (0.6% to 3%), or even between 0.01 and 0.02 (1% to 2%). For example, consider the compound InOj52Ga o,48Aso,99Po,oi, whose intrinsic lattice parameter is reduced by 900-1300 ppm compared to the intrinsic lattice parameter of the germ layer 2 in InP.

[0075] These rules and proportions of substitution also apply to ternary compounds (as illustrated in the previous example, with the third epitaxial layer 53), quaternary compounds, or compounds comprising more than four elements, whose intrinsic lattice parameter is matched to that of InP and which one would aim to reduce in the stacking of layers 50 of the composite structure 100, such as InAlAs, InGaAsP, etc. The common feature remains a shift in composition within the stacking 50 of epitaxial layers 51, 52, 53, 54, to migrate towards compositions with an intrinsic lattice parameter 200 ppm to 3000 ppm below that of InP, or even more specifically reduced by 500 ppm to 2500 ppm, or even by 750 ppm to 1800 ppm relative to that of InP.By playing on substitutions between the different elements III and V as much as possible, the variations in composition in each of these elements III and / or elements V remain limited to the order of % to a few percent, as mentioned previously.

[0076] In the case of a GaAs seed layer 2, for example when using a 10 GaAs-on-Si composite substrate, the reasoning is generally the same as when the seed layer 2 is made of InP. However, since the difference in coefficient of thermal expansion is greater between gallium arsenide and silicon (compared to the InP-on-silicon system), a significantly greater reduction in the intrinsic lattice parameter of all or part of the epitaxial layers 51, 52, 53, 54 will preferably be chosen, ideally between 1200 ppm and 1800 ppm, and more broadly within a range of 750 ppm to 3000 ppm. This reduction in the lattice parameter would typically correspond to a 2% substitution. up to 8% of arsenic atoms are replaced by phosphorus, or even between approximately 3% and 5%. For example, the ternary compound GaAso.96Po.04 has an intrinsic lattice parameter reduced by approximately 1300–1600 ppm compared to the intrinsic lattice parameter of the GaAs seed layer 2. As with the InP seed layer 2, these adjustments can be achieved through numerous combinations of elements III and V.

[0077] More generally, when the binary compound of the seed layer 2 is gallium arsenide (GaAs) and the coefficient of thermal expansion of the support substrate 1 is less than that of the seed layer 2, at least one epitaxial layer 51,52,53,54 can be formed of a ternary compound of the type GaAsi ZPZ in which z is between 0.0025 and 0.08, so that its intrinsic lattice parameter is reduced from 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer 2.

[0078] According to a second aspect, when the coefficient of thermal expansion of the support substrate 1 is greater than that of the seed layer 2, at least one epitaxial layer 51, 52, 53, 54 of the stack 50 has a composition chosen so that its intrinsic lattice parameter is increased from 200 to 3000 ppm relative to the intrinsic lattice parameter of the seed layer 2. In some particular cases, the increase in the intrinsic lattice parameter of the epitaxial layer 51, 52, 53, 54 can be between 250 ppm and 2000 ppm, or even between 300 ppm and 800 ppm.

[0079] Here again, at the epitaxial temperature, the germinal layer 2, whose lattice parameter in the (az / ) plane is substantially increased due to the greater dilation of the supporting substrate 1, is found to be favorable to the growth of the epitaxial layer 51,52,53,54 whose intrinsic lattice parameter has been intentionally shifted.

[0080] Thus, starting from a composite substrate 10 of the InP on GaAs type, with a seed layer 2 in InP of 0.2 pm thickness, it is possible to carry out in particular a stacking 50 of layers such as below, to form a composite structure 100 according to the present invention: 1. InAs0.007P0.993, N-doped, with a thickness of 300 to 500 nm; 2. In0.537Ga0.463As, intrinsic, with a thickness of 2.5 to 3pm; 3. InAs0.007P0.9993, doped P, with a thickness of 0.5 to Ipm; 4. Ino,537Gao,463As or Ino.53Gao.55As, P-doped, with a thickness of 50 to 100 nm.

[0081] In this example, the first epitaxial layer is a ternary compound, in which 0.7% of the phosphorus atoms have been replaced by arsenic atoms, inducing an increase in the intrinsic lattice parameter of the first epitaxial layer 51 (InAs0.007P0.993) of approximately 400-600 ppm compared to the intrinsic lattice parameter of the seed layer 2 (InP). In the second epitaxial layer 52, the composition The indium content of the ternary compound was also increased by 0.7% (expressed as a percentage of the total element V), compared to the Ino.53Gao.47As compound matched to InP in intrinsic lattice parameter, resulting in a final compound Ino.537Ga 0.463AS. The increase in intrinsic lattice parameter of the second epitaxial layer 52 compared to the intrinsic lattice parameter of the seed layer 2 is on the order of 400–600 ppm. The third epitaxial layer 53 was chosen to be identical to the first, with the same increase in lattice parameter. Finally, the fourth epitaxial layer 54 can be staggered or not; its small thickness makes it less likely to develop stresses leading to irreversible relaxation.

[0082] The SWIR photodiode fabricated from this composite structure 100 is perfectly functional and efficient due to the crystallographic quality of the epitaxial layers 51, 52, 53, 54 of the stack 50, which are free of defects and dislocations related to cross-hatching. In this particular example, three (at least) of the four epitaxial layers 51, 52, 53, 54 have a composition chosen such that their intrinsic lattice parameter is increased by approximately 0.04% - 0.06% compared to the intrinsic lattice parameter of the seed layer 2.Alternatively, consideration could be given to increasing the intrinsic lattice parameter of one or two of the epitaxial layers 51,52,53,54; for example, one could shift the intrinsic lattice parameter of the second epitaxial layer 52 only (by choosing the compound Ino,537Gao,463As) and keep the first, third and fourth epitaxial layers 51,53,54 of the classical stacking usually done on InP. .

[0083] More generally, to increase the relaxed lattice parameter of a III-V compound, it is possible to substitute a certain proportion of elements III and / or V with, respectively, a larger element III and / or V. The substitution proportions remain within the same ranges as according to the first aspect of the invention, namely on the order of % to a few percent, typically between 0.3% and 8% (expressed as a percentage relative to the total element III and / or V), to achieve an increase in the intrinsic lattice parameter of the epitaxial layer from 200 ppm to 3000 ppm relative to the intrinsic lattice parameter of the germ layer 2.

[0084] According to the first and second aspects, the invention proposes a shift in traditional compositions at the level of epitaxy III-V in order to promote the quality of epitaxial growth of the stack 50 on the germ layer 2 of the composite substrate 10.

[0085] The -at least one- epitaxial layer 51,52,53,54 whose intrinsic lattice parameter is offset with respect to the intrinsic lattice parameter of the seed layer 2 can be the layer of the raw stacking 50 directly on the seed layer 2 (called first epitaxial layer 51) or an nth epitaxial layer 52,53,54 of the stacking 50.

[0086] All or part of the epitaxial layers 51,52,53,54 of the stack 50 may have compositions chosen so that their intrinsic lattice parameter is reduced or increased relative to the intrinsic lattice parameter of the seed layer 2.

[0087] Advantageously, the epitaxial layers which have a thickness greater than 500 nm, greater than 250 nm, or even greater than 100 nm, have their compositions adjusted so that their intrinsic lattice parameters are shifted (down or up as the case may be) with respect to the lattice parameter of the seed layer 2, depending on the nature of the composite substrate 10.

[0088] The invention also relates to a composite structure 100 comprising:

[0089] - the composite substrate 10 which includes the support substrate 1 and the seed layer 2 in single-crystal III-V material disposed on the support substrate 1 via a bonding interface 3, the support substrate 1 having a coefficient of thermal expansion different from that of the seed layer 2, and the seed layer 2 having an intrinsic lattice parameter;

[0090] - the stacking of 50 single-crystal layers of type III-V, called epitaxial layers 51, 52, 53, 54, on germ layer 2, each epitaxial layer presenting an intrinsic lattice parameter.

[0091] In the composite structure 100, at least one epitaxial layer 51, 52, 53, 54 of the stack 50 is chosen so that it has an intrinsic lattice parameter reduced by 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer 2, when the coefficient of thermal expansion of the support substrate 1 is less than that of the seed layer 2. When the coefficient of thermal expansion of the support substrate 1 is greater than that of the seed layer 2, at least one epitaxial layer of the stack 50 is chosen so that its intrinsic lattice parameter is increased by 200 to 3000 ppm compared to the intrinsic lattice parameter of the seed layer 2.

[0092] According to a preferred embodiment, the intrinsic lattice parameter of -at least one- epitaxial layer 51,52,53,54, reduced or increased relative to the intrinsic lattice parameter of the seed layer 2, is defined by the composition of said layer, in particular on a substitution of 0.3% to 8% of III or V elements by III or V elements respectively smaller or larger.

[0093] An example of a composite structure 100 can be given for the fabrication of a heterojunction bipolar transistor, based on InP.

[0094] A stacking of twelve epitaxial layers on a massive intrinsic InP substrate, such as below, was described by Sara Hamzeloui et al. (“High power InP / Ga(In)AsSb DHBTs for millimeter-wave Pas: 14.5 dBm output power and 10.4 mw / iim2 power density at 94 GHz”, IEEE Journal of Microwaves, Oct 2022) for the manufacture of an InP / GaAsSb DHBT (“double hetero-junction bipolar transistor”) transistor:

[0095] 1. inP, Si-doped: 2.8E19 / cm3, 300nm

[0096] 2. Gao>47Ino,53As, Si-doped: 3E19 / cm3, 20nm

[0097] 3. inP, Si-doped: 2.8E19 / cm3, 50nm

[0098] 4. Si-doped InP: 9.lE16 / cm3, 125nm

[0099] 5. Gaso.4iSbo.59 Gaso,58Sbo,42, C-doped: 8.6E19 / cm3, 20nm

[0100] 6. Gao.22Ino.7sP, doped Si:2.5E16 / cm3, 5nm

[0101] 7. Gao.22Ino.7sP InP, doped Si:2.5E16 / cm3, lOnm

[0102] 8. Si-doped InP: 2.5E16 / cm3, 5nm

[0103] 9. Si-doped InP: l.5E19 / cm3, 130nm

[0104] 10. Gao.47Ino.53As, doped Si:3.8E19 / cm3, 20nm

[0105] 11. Gao.47Ino.53As Gao.25Ino.75As, doped Si: 3.8E19 / cm3, lOnm

[0106] 12. Gao.25Ino.75As, Si-doped: 3.8E19 / cm3, 5nm.

[0107] On a composite substrate 10 of the InP on silicon type, with a seed layer 2 in InP of 0.2pm thickness and a support substrate 1 in silicon of 525 pm thickness (for example for a composite substrate of diameter 100mm), an approximate stacking 50 of epitaxial layers can be achieved, the difference being that at least one of the twelve epitaxial layers has its composition modified so that its intrinsic lattice parameter is reduced relative to the intrinsic lattice parameter of the seed layer 2 in InP from 200 ppm to 3000 ppm, preferably from about 900-1300 ppm.

[0108] According to one embodiment, the first layer, 300 nm thick, may be the only one whose intrinsic lattice parameter is reduced: for example, an InGaP layer will be chosen instead of an InP layer, with a Ga content between 1.0% and 1.5% replacing the In, in particular Ino.985Gao.o15P or Ino.98sGao.o12P-

[0109] According to another embodiment, all or part of the InP-based layers (layers referenced 1, 3, 4, 7, 8, 9 above) are modified in composition so that their intrinsic lattice parameter is reduced within the range according to the invention. Among these cases, we can cite the particular case where only the InP layer referenced 1 is modified. Conversely, another embodiment consists of modifying only layers (all or some of them) that are not InP. Finally, according to yet another embodiment, all or a majority of the twelve layers of the stack 50 are adjusted in composition so as to present a reduced intrinsic lattice parameter within the recommended range.

[0110] The manufacturing process of a composite structure 100 according to the invention solves the problem of texturing, and consequently of defects, of the epitaxial layers on composite substrate 10, due to the particular adjustment of the intrinsic lattice parameter of at least one epitaxial layer 51, 52, 53, 54 of the composite structure 100 with respect to the intrinsic lattice parameter of the seed layer 2, depending on the differential expansion properties of the support 1 and the seed layer 2 of the composite substrate 10. The composite structure 100 obtained is thus formed of epitaxial layers exhibiting excellent crystallographic quality, free from defects and dislocations linked to cross-hatching.

[0111] The invention makes it possible to minimize stresses in the epitaxial stack 50. As already described earlier, the solution proposed here is characterized in particular in that it does not alter the nature (constituents, composition, doping) of the seed layer 2, which, for example in an InPOSi substrate, remains InP (binary). It differs in particular from solutions that would consist of changing the composition of this seed layer itself, by substituting at least part of one or more of the two In and P elements with other III or V (or other) elements to address the stress problem in the composite substrate. This would have the effect of causing migration at the level of the substrate itself towards ternary or quaternary or higher-order materials for the seed layer, significantly complicating the manufacturing processes of the composite substrate.

[0112] Of course, the invention is not limited to the embodiments and examples described, and alternative embodiments can be made without departing from the scope of the invention.

Claims

Demands

1. A method for manufacturing a composite structure (100) comprising the following steps: a) supplying a composite substrate (10) including a support substrate (1) and a seed layer (2) of single-crystal III-V material disposed on the support substrate (1) via a bonding interface (3), the support substrate (1) having a coefficient of thermal expansion different from that of the seed layer (2), and the seed layer (2) having an intrinsic lattice parameter; b) growing by epitaxy a stack (50) of single-crystal III-V type layers, called epitaxial layers (51, 52, 53, 54), on the seed layer (2), each epitaxial layer (51, 52, 53, 54) having an intrinsic lattice parameter;the manufacturing process being characterized in that: - when the coefficient of thermal expansion of the support substrate (1) is less than that of the seed layer (2), at least one epitaxial layer (51, 52, 53, 54) of the stack (50) has a composition chosen such that its intrinsic lattice parameter is reduced by 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer (2); - when the coefficient of thermal expansion of the support substrate (1) is greater than that of the seed layer (2), at least one epitaxial layer (51, 52, 53, 54) of the stack (50) has a composition chosen such that its intrinsic lattice parameter is increased by 200 ppm to 3000 ppm compared to the intrinsic lattice parameter of the seed layer (2).

2. A manufacturing process according to claim 1, wherein the single-crystal III-V material of the seed layer (2) is a binary compound, in particular indium phosphide (InP) or gallium arsenide (GaAs).

3. A manufacturing method according to claim 2, wherein the binary compound of the seed layer (2) is indium phosphide (InP), the coefficient of thermal expansion of the support substrate (1) is less than that of the seed layer (2), and at least one epitaxial layer (51,52,53,54) is formed of a ternary compound of the type Inb xGaxP or Ini xAlxP, in which x is between 0.0025 and 0.

03.

4. A manufacturing method according to claim 3, wherein x is between 0.0075 and 0.025, preferably between 0.01 and 0.

02.

5. A manufacturing method according to claim 2, wherein the binary compound of the seed layer (2) is indium phosphide (InP), the coefficient of thermal expansion of the support substrate (1) is less than that of the seed layer (2), and at least one epitaxial layer (51,52,53,54) is formed of a quaternary compound of the type Ini x yGaxAlyP, in which the sum of x and y is between 0.0025 and 0.

03.

6. A manufacturing method according to claim 5, wherein the sum of x and y is between 0.0075 and 0.025, preferably between 0.01 and 0.

02.

7. A manufacturing method according to claim 2, wherein the binary compound of the seed layer (2) is gallium arsenide (GaAs), the coefficient of thermal expansion of the support substrate (1) is less than that of the seed layer (2), and at least one epitaxial layer (51,52,53,54) is formed of a ternary compound of the type GaAsi ZPZ in which z is between 0.0025 and 0.

08.

8. A manufacturing method according to claim 2, wherein the binary compound of the seed layer (2) is indium phosphide (InP), the coefficient of thermal expansion of the support substrate (1) is greater than that of the seed layer (2), and at least one epitaxial layer (51,52,53,54) is formed of a ternary compound of the type InAswPi w in which w is between 0.0025 and 0.03, preferably between 0.01 and 0.

02.

9. A manufacturing method according to any one of the preceding claims, wherein at least two epitaxial layers (51,52,53,54) of the stack (50) have compositions selected such that their intrinsic lattice parameter is reduced or increased relative to the intrinsic lattice parameter of the seed layer (2).

10. A manufacturing method according to any one of the preceding claims, wherein each of the epitaxial layers (51,52,53,54) of the stack (50) has compositions chosen so that their intrinsic lattice parameter is reduced or increased relative to the intrinsic lattice parameter of the seed layer (2).

11. A manufacturing method according to any one of the preceding claims, wherein the support substrate (1) is formed from a single-crystal or polycrystalline material selected from silicon, sapphire, gallium arsenide, germanium, aluminium nitride and silicon carbide.

12. A manufacturing process according to any one of the preceding claims, wherein step a) comprises the following substeps: - supplying a donor substrate (20) of single-crystal III-V material, having a front face and a back face, - bonding by molecular adhesion of the front face of the donor substrate (20) to the support substrate (1), - thinning the back face of the donor substrate to obtain the composite substrate (10).

13. A manufacturing process according to any one of the preceding claims, wherein step a) comprises the following substeps: a1) the provision of a donor substrate (20) of single-crystal III-V material, a2) the formation of a buried brittle plane (4) in the donor substrate (20), delimiting with a front face of said donor substrate, the seed layer (2) to be transferred, a3) the bonding by molecular adhesion of the front face of the donor substrate (20) to the support substrate (1), a4) the separation along the buried brittle plane (4) to transfer the seed layer (2) to the support substrate (1) and obtain the composite substrate (10), on the one hand, and the remainder (20') of the donor substrate, on the other hand.

14. Composite structure (100) comprising: - a composite substrate (10) including a support substrate (1) and a seed layer (2) of single-crystal III-V material disposed on the support substrate (1) via a bonding interface (3), the support substrate (1) having a coefficient of thermal expansion different from that of the seed layer (2), and the seed layer (2) having an intrinsic lattice parameter; - a stack (50) of single-crystal III-V layers, called epitaxial layers (51, 52, 53, 54), on the seed layer (2), each epitaxial layer (51, 52, 53, 54) having an intrinsic lattice parameter; wherein, - when the coefficient of thermal expansion of the support substrate (1) is less than that of the seed layer (2), the intrinsic lattice parameter of at least one epitaxial layer (51, 52, 53, 54) of

15. the stacking (50) is reduced from 200 ppm to 3000 ppm compared to the intrinsic mesh parameter of the seed layer (2); - when the coefficient of thermal expansion of the support substrate (1) is greater than that of the seed layer (2), the intrinsic lattice parameter of at least one epitaxial layer (51,52,53,54) of the stack (50) is increased by 200 to 3000 ppm compared to the intrinsic lattice parameter of the seed layer (2). Composite structure (100) according to the preceding claim, wherein the intrinsic lattice parameter of the -at least one-epitaxial layer (51,52,53,54), reduced or increased with respect to the lattice parameter of the seed layer (2), is defined by the composition of said layer, in particular by a substitution of 0.25% to 8% of III or V elements by III or V elements respectively smaller or larger.

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