METHOD FOR FORMING A MONOCRYSTALLINE DIAMOND LAYER, MONOCRYSTALLINE DIAMOND SUBSTRATE AND USE OF SAID SUBSTRATE
The process of micro structuring and homoepitaxial growth of monocrystalline diamond substrates significantly reduces dislocation density, addressing the challenge of optical defects and enabling their application in advanced opto-electronic devices.
Patent Information
- Application Number
- FR2023006048
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-06-14
- Publication Date
- 2025-05-16
- Estimated Expiration
- 2043-06-14
AI Technical Summary
Existing methods for producing monocrystalline diamond substrates struggle with high densities of crystalline defects, particularly dislocations, which hinder their application in opto-electronic devices due to optical birefringence and unwanted luminescence.
A process involving micro structuring of the monocrystalline diamond substrate using non-crossing laser removal to create engraving figures with specific depth and width ratios, followed by homoepitaxial growth, to achieve a density of crystalline defects less than or equal to 10^3 dislocations per cm².
This method effectively reduces the density of dislocations and constraints in the monocrystalline diamond substrates, enabling their use in high-quality opto-electronic applications by minimizing optical defects and improving substrate homogeneity.
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Abstract
Description
Title of the invention: METHOD FOR FORMING A MONOCRYSTALLINE DIAMOND LAYER, MONOCRYSTALLINE DIAMOND SUBSTRATE AND USE OF SAID SUBSTRATE Technical field
[0001] The invention relates to the field of diamond manufacturing, more specifically the preparation of single-crystal diamond having a reduced crystal defect density. Prior art
[0002] Below we describe the known prior art from which the invention was developed.
[0003] Diamond is a material that exhibits physical properties that are particularly valued in many fields. In particular, diamond exhibits unmatched properties as a material suitable for optoelectronics, such as high thermal conductivity, high electron / hole mobility, high dielectric breakdown electric field strength, low dielectric loss and broad band structure, radiation resistance, high chemical stability, and excellent optical properties.
[0004] Single crystal diamond remains one of the most promising materials for the preparation of high power, high frequency, high temperature, severe environment resistant and high voltage withstand optoelectronic devices, quantum technologies and optical windows.
[0005] In particular, in order to put diamond into practice as a material for optoelectronic applications, a single crystal diamond substrate or wafer having few crystal defects, tensile or compressive stresses and high homogeneity is required for most applications.
[0006] To enable the production of monocrystalline diamond substrates with fewer and fewer crystal defects, several growth methods have emerged, among them, the processes for manufacturing monocrystalline diamond plates by lateral homoepitaxial growth have made it possible to obtain good quality monocrystalline diamond substrates.
[0007] The main technical difficulty is linked to the formation of crystalline defects during the growth phases and more particularly of extended defects such as dislocations which can also generate stresses. The appearance of dislocations may be due to the presence of impurities or crystalline defects but also to constraints.
[0008] Several techniques have been developed to attempt to limit the occurrence of dislocations such as in-situ chemical etching treatments using H2 / O2 plasma, ex-situ physical etching with an inductively coupled plasma source or chemical-mechanical polishing of the monocrystalline diamond substrate before growth. These methods limit or even annihilate the formation of new dislocations at the interface upon epitaxial recovery by eliminating mechanical polishing damage on the surface. However, dislocations originating from defects existing directly in the monocrystalline diamond substrate cannot be easily removed and inevitably propagate in the direction of growth, leading to a monocrystalline diamond with a relatively high dislocation density and generally between 105 and 107 dislocations / cm2, or even more.
[0009] The presence of these dislocations affects the propagation of light and generates optical birefringence and undesirable background luminescence, which makes it impossible to use single-crystal diamond for optical windows or certain electronic or quantum technologies.
[0010] Solutions aimed at partially solving the problems mentioned above have emerged, in particular a first solution is described in patent No. EP3325696 B1 which proposes the formation of through windows in diamond substrates before proceeding with lateral growth. The article by Fernando Lloret et al.; MPCVD Diamond Lateral Growth Through Microterraces to Reduce Threading Dislocations Density; Phys. Status Solidi A 2017, 214, 1700242 proposes to use the effect of micrometric terraces on the distribution of extended defects. The evolution of these defects during growth is determined using very thin boron-doped layers. This method, known as the stratigraphic approach, makes it possible to determine the growth orientation every 100 nm. This article thus shows that dislocations can be redirected away from terraced structures, thanks to lateral growth.It is possible to generate crystal defect-free zones as a function of terrace size for a growth direction along the {111} plane family.
[0011] Another solution is also described in the scientific article A. Boussadi et al.; Reduction of dislocation densities in single crystal CVD diamond by confinement in the lateral sector; Diamond & Related Materials 83 (2018) 162-169. In this study, pyramidal-shaped substrates with an angle of 20° having both their lateral and upper faces oriented according to the {100} family of planes are used and the effect of different growth conditions on dislocation propagation is determined. Thus, maintaining a limiting angle of the growth sector of about 45° and the use of moderate power densities allows for respective top and side face growth while ensuring dislocation confinement in the lateral regions of the single crystal diamond substrate.
[0012] Although these solutions make it possible to limit the appearance of dislocations during the growth of a monocrystalline diamond substrate, they are impractical to implement and do not make it possible to generate monocrystalline diamond substrates of sufficient quality for optoelectronic applications. Indeed, the solutions proposed in the state of the art make it possible to obtain monocrystalline diamond substrates that are quite constrained after growth and which include dislocations greater than 3*103 dislocations / cm2. In addition, the solutions presented previously do not make it possible to produce substrates of the order of cm2 or more.
[0013] Thus, there is a need for the provision of single crystal diamond substrates of 1 cm2 and larger which have a much lower dislocation density and whose compressive or extensive stresses are greatly reduced.
[0014] The invention aims to overcome the drawbacks of the prior art. In particular, the invention aims to propose a method for forming a layer of monocrystalline diamond having a dislocation density less than or equal to 103 dislocations per cm2, said method making it possible to ensure the formation of high-quality monocrystalline diamond substrates, i.e. with a density of crystalline defects and consequently limited constraints compared to existing solutions. Summary of the invention
[0015] The invention aims to overcome these drawbacks. The following presents a simplified summary of selected aspects, embodiments and examples of the present invention for the purpose of providing a basic understanding of the invention. However, this summary does not constitute an exhaustive overview of all aspects, embodiments and examples of the invention. Its sole purpose is to present selected aspects, embodiments and examples of the invention in a concise form as an introduction to the more detailed description of the aspects, embodiments and examples of the invention which follow the summary.
[0016] The invention relates in particular to a method for forming a layer of monocrystalline diamond having a density of crystal defects less than or equal to 103 crystal defects per cm2 comprising the following steps: - providing a single crystal diamond substrate having an initial crystal defect density greater than 103 crystal defects per cm2, the single crystal diamond substrate having a misorientation angle, relative to the exact face of the single crystal diamond substrate, greater than 0° and less than or equal to 10°, first microstructuring of a growth surface of the monocrystalline diamond substrate by non-through laser ablation, the microstructuring step comprising the production of first etching figures such that each first etching figure comprises an opening of a predetermined width and is delimited by at least one wall, each of the first etching figures further having a depth of at least 30 pm, said depth being greater than the width of the opening; first homoepitaxial growth, in a reactor by plasma-assisted chemical vapor deposition or by hot filament, the first growth being carried out: • normally relative to the growth surface so as to form a first layer of monocrystalline diamond comprising the crystal defects of the growth surface, and • laterally with respect to the wall delimiting the first etching, so as to form a second layer of monocrystalline diamond comprising the crystalline defects of the wall confined in the first etching figure and a cavity, so that the first etching figure is covered by a third layer of monocrystalline diamond having a density of crystalline defects less than or equal to 103 dislocations per cm2, second microstructuring of the monocrystalline diamond substrate by non-through laser ablation, said second microstructuring step comprising the production of second etching figures at the level of the first monocrystalline diamond layer comprising the crystalline defects of the growth surface, each second etching figure comprises an opening of a predetermined width and is delimited by at least one wall, each of the second etching figures further has a depth of at least 30 pm, said depth being greater than the width of the opening, second homoepitaxial growth of another second layer of monocrystalline diamond, in a reactor by plasma-assisted or hot filament chemical vapor deposition, the second growth being carried out laterally with respect to the wall delimiting the second etching figure, the other second layer of monocrystalline diamond comprising the crystal defects of the wall confined in the second etching figure and a cavity, so that the second etching figure is covered by a third layer of monocrystalline diamond having a defect density crystalline less than or equal to 103 crystal defects per cm2.
[0017] According to other optional features of the method of forming a single crystal diamond layer, the latter may optionally include one or more of the following features, alone or in combination: - the growth surface is a (100) crystallographic face disoriented relative to a family of {100} crystallographic faces parallel to one of the lateral faces of the monocrystalline diamond substrate. - the growth surface is a (100) crystallographic face disoriented with respect to a family of {110} crystallographic faces or to a family of {113} crystallographic faces. - a normal homoepitaxial growth step, in the reactor by plasma-assisted chemical vapor deposition or hot filament, so that the third layer of monocrystalline diamond reaches a thickness of at least 500 pm. - a step of cutting the third layer of monocrystalline diamond, preferably by laser. - an annealing step of the third layer of monocrystalline diamond at a temperature ranging from 1500°C to 2300°C. - at least one intermediate annealing step of the monocrystalline diamond substrate at a temperature ranging from 1500°C to 2300°C, the intermediate annealing step being implemented between the supply step and the first microstructuring step, between the first homoepitaxial growth and the second microstructuring step and / or between the second microstructuring step and the second homoepitaxial growth step. - the width of the opening of the first and second engraving figures is between 20 pm and 200 pm. - a preparation step, prior to the second micro-structuring step, of the growth surface of the monocrystalline diamond substrate by laser cutting or by polishing, when the misorientation angle is less than a predetermined threshold, so as to induce a misorientation at least equal to the predetermined threshold. - the first and / or second micro-structuring and first and / or second homoepitaxial growth steps are repeated until a density of crystalline defects is obtained, in the third layer of monocrystalline diamond, less than or equal to a predetermined threshold, preferably less than or equal to 103 crystalline defects per cm2 and preferably less than or equal to 5* 102 crystalline defects per cm2.
[0018] According to a second object, the invention relates to a monocrystalline diamond substrate comprising a layer of monocrystalline diamond, said layer of monocrystalline diamond having been obtained by: - forming first etching figures by microstructuring a growth surface of the monocrystalline diamond substrate by non-through laser ablation, such that each first etching figure comprises an opening of a predetermined width and is delimited by at least one wall, each of the first etching figures further having a depth of at least 30 pm, said depth being greater than the width of the opening, - a first homoepitaxial growth, the first growth comprising: • a growth normal to the growth surface so as to form a first layer of monocrystalline diamond comprising the crystalline defects of the growth surface, and • lateral growth relative to the wall delimiting the first etching, so as to form a second layer of monocrystalline diamond comprising the crystalline defects of the wall confined in the first etching figure and a cavity, so that the first etching figure is covered by a third layer of monocrystalline diamond having a density of crystalline defects less than or equal to 103 dislocations per cm2, - formation of second etching figures by microstructuring of the first layer of monocrystalline diamond by non-through laser ablation, such that each second etching figure comprises an opening of a predetermined width and is delimited by at least one wall, each of the second etching figures furthermore has a depth of at least 30 μm, said depth being greater than the width of the opening, - a second homoepitaxial growth of another second layer of monocrystalline diamond, the second growth being carried out laterally with respect to the wall delimiting the second etching figure, the other second layer of monocrystalline diamond comprising the crystalline defects of the wall confined in the second etching figure and a cavity, such that,the second etching figure is covered by a third layer of monocrystalline diamond having a crystal defect density less than or equal to 103 crystal defects per cm2.,
[0019] According to other optional features of the single crystal diamond substrate, the latter may optionally include one or more of the following features, alone or in combination: - the first and second non-crossing engraving figures are made over the entire growth surface. - the width of the opening of the first and second engraving figures is between 20 pm and 200 pm.
[0020] According to a third object, the invention relates to a use of a monocrystalline diamond substrate according to the invention for obtaining a monocrystalline diamond layer suitable as a substrate for quantum technologies, for the manufacture of an optical window, a semiconductor substrate or for thermal management. Brief description of the drawings
[0021] Other characteristics and advantages of the invention will be better understood on reading the description which follows and with reference to the appended drawings, given for illustrative purposes and in no way limiting.
[0022] [Fig-1] [Fig.l] represents a diagram of a method of forming a layer of monocrystalline diamond according to the invention. The steps outlined in dotted lines are optional.
[0023] [Fig.2] [Fig.2] represents an illustration of a method of forming a layer of monocrystalline diamond according to the invention.
[0024] [Fig.3] [Fig.3] is a photograph showing a section of a monocrystalline diamond substrate comprising a layer of monocrystalline diamond obtained according to the invention and having been treated by directional laser ablation.
[0025] [Fig.4] [Fig.4] is a photograph of a monocrystalline diamond substrate according to the invention seen from above, comprising a layer of monocrystalline diamond formed by a formation method according to the invention, observed by optical microscopy in transmission after H2 / O2 plasma etching.
[0026] The figures do not necessarily respect the scales, in particular in thickness, and this is for illustration purposes.
[0027] Aspects of the present invention are described with reference to flowcharts and / or functional diagrams of methods according to embodiments of the invention.
[0028] In the figures, flowcharts and block diagrams illustrate the architecture, functionality and operation of possible implementations of systems, methods according to various embodiments of the present invention. In this regard, each block in the flowcharts or block diagrams may represent a system, device, module or code, which includes one or more executable instructions for implementing the specified logical function(s). In some implementations, the functions associated with the blocks may appear in a different order than shown in the figures. For example, two blocks shown in succession may, in fact, be implemented substantially simultaneously, or the blocks may sometimes be implemented in reverse order, depending on the functionality involved. Each block of the block diagrams and / or flowchart, and combinations of blocks in the block diagrams and / or flowchart, may be implemented by special hardware systems that perform the specified functions or acts or carry out combinations of special hardware and computer instructions. Description of the embodiments
[0029] Below, we describe a summary of the invention and the associated vocabulary, before presenting the disadvantages of the prior art, and finally showing in more detail how the invention overcomes them.
[0030] In the remainder of the description, the expression "monocrystalline diamond substrate" may correspond to a block of monocrystalline diamond more than 3 μm thick and with a surface area ranging from 1 mm2 to more than 800 cm2. The term "substrate" within the meaning of the invention may correspond to the elements on which the diamond layers or films grow. These are monocrystalline layers of natural diamond monocrystals or produced by a high pressure-high temperature (HPHT) process or produced by a CVD process (for Chemical vapor deposition or chemical vapor deposition assisted by plasma or by a hot filament).
[0031] When the term "family crystallographic orientation face" is used, it generally refers to a family of crystal planes. Crystal planes that have a particular crystal shape whose surface is substantially planar and bounding a crystal, which is conventionally denoted in braces. This includes all the positional variants that the crystallographic orientation face can take in a crystal. For example, the family of the crystallographic orientation face of the {100} family also includes the variants, positive and negative, such as the (010) and (001) crystallographic faces. These crystallographic faces are conventionally defined by three Miller indices denoted in parentheses "(hkl)", where h, k and 1 can be positive or negative integers.In order to avoid confusion with elements referenced in the figures, the mention of crystallographic faces in the claims, for example of type (100), is made without the parentheses.
[0032] A “terraced structure” according to the invention may correspond to a stepped structure comprising steps characterized by a first crystallographic orientation and terraces characterized by a second crystallographic orientation, the second crystallographic orientation being preferably different from the first crystallographic orientation. The steps of a terraced structure are substantially linear and parallel to each other, while the terraces are substantially linear and parallel to each other. As an illustrative example, the terraces are formed by crystallographic orientation faces of the {100} family of planes.
[0033] The term "growth" within the meaning of the invention may correspond to the step or steps of deposition of carbon in sp3 form of crystalline (monocrystalline) diamond contributing to the production of a layer of monocrystalline diamond. The growth conditions and deposition parameters represent a set of values of the variables: pressure, injected microwave power, total gas flow rate, flow rate of the carbon precursor, flow rate of impurities and dopant, composition of the thermal resistance gas and their flow rate, temperature of the layer or layers being grown for a given reactor.
[0034] The term "diamond" within the meaning of the invention may correspond to one or more layers of monocrystalline diamond of varying thickness, resulting from the deposition of carbon in sp3 form of crystalline (monocrystalline) diamond.
[0035] The expression "diamond layer" within the meaning of the invention corresponds to a layer (or film) of monocrystalline diamond formed after nucleation / condensation on a surface of monocrystalline diamond or another material. Within the meaning of the invention, monocrystalline diamond is generally obtained by thickening in height and / or width of a single crystal of diamond stem (or monocrystalline diamond substrate) originating from a single crystal of natural diamond or produced by high pressure-high temperature (HPHT) process or produced by CVD (for "Chemical vapor deposition" assisted by plasma or hot filament).
[0036] The term "plasma" within the meaning of the invention may correspond to the production, from an electrical discharge in a gas composed of a mixture, of a generally electrically neutral medium but containing ions and electrons as well as fragments of dissociated gaseous species as well as stable molecules.
[0037] The expression “crystallographic disorientation” (denoted ô), within the meaning of the invention, may correspond to the presence of a disorientation angle characterizing the surface of the seed-substrate or of the substrate with respect to an exact plane, for example a crystalline plane of the {100} family of planes.
[0038] The term "substantially" within the meaning of the invention means a value varying by less than 30% relative to the compared value, preferably by less than 20%, even more preferably by less than 10%. When substantially identical is used to compare shapes then the vectorized shape varies by less than 30% relative to the compared vectorized shape, preferably by less than 20%, even more preferably by less than 10%. In particular, when substantially identical is used to compare angles then the angle values are not different. of more than 10°, preferably of more than 5°, even more preferably of more than 2° and even more preferably of more than 1°.
[0039] For many industrial applications, high-quality single-crystal diamond layers are expected. Several methods have already been proposed for producing single-crystal diamond layers that have a reduced dislocation density. However, single-crystal diamonds obtained using these methods generally have a number of crystalline defects, and more particularly dislocations, that are always too high. Furthermore, the stresses generally remain high. The applicant has developed a new method that limits the appearance of these crystalline defects and substantially reduces the stresses in the substrates produced.
[0040] The applicant proposes to use micro-structured monocrystalline diamond substrates, by producing etching figures, using a laser ablation process, preferably directional, which have a predetermined ratio between their depth and their width while positioning them according to a predefined misorientation angle in order to generate a high-quality monocrystalline diamond layer. This makes it possible to block the propagation of dislocations propagating in the direction normal to the initial monocrystalline diamond substrate, and thus the formation of high-quality monocrystalline diamond substrates, i.e. with a dislocation density less than or equal to 103 or preferably less than or equal to 5*102 dislocations per cm2.In particular, the invention proposes to carry out a succession of micro-structuring of a growth surface of a monocrystalline diamond substrate and lateral growth according to a succession of matrices positioned offset in order to generate etching figures of predetermined width and depth and ensure the formation of a monocrystalline layer of optimal quality with few dislocations per unit area. The invention also includes, optionally, the implementation of one or more annealing steps at different stages of the method according to the invention in order to further reduce the appearance of stresses in the monocrystalline diamond layers produced according to the invention.
[0041] Thus, as illustrated in Figures 1 and 2, the invention relates to a method 100 for forming a layer of monocrystalline diamond having a dislocation density less than or equal to 103 dislocations per cm2, preferably less than or equal to 5*102 dislocations per cm2, the method comprises a step 110 of providing a monocrystalline diamond substrate having an initial dislocation density greater than 103 dislocations per cm2, a first micro-structuring step 120, a first homoepitaxial C1 growth step 130, a second microstructuring step 150 and a second homoepitaxial C2 growth step 160.
[0042] One of the objectives of the invention is to make it possible to improve the quality of a layer of monocrystalline diamond from substrates of lower quality, generally inconsistent, marketed by specialized companies. According to the invention, the step of providing 110 the monocrystalline diamond substrate 10 implies that the latter has an initial density of crystal defects greater than 103 crystal defects per cm2. In the invention, the monocrystalline diamond substrate 10 has a misorientation angle δ, relative to the exact face of the monocrystalline diamond substrate greater than 0° and less than or equal to 10°.
[0043] As illustrative examples, the misorientation angle may be at least 0.1°, preferably at least 0.5°, more preferably at least 1°, even more preferably at least 2°. The misorientation angle may be at most 9.9°, preferably at most 9.5°, more preferably at most 9°, even more preferably at most 8°. Thus, the misorientation angle may for example range from 0.1° to 9.9°, preferably from 0.5° to 9.5°, more preferably from 1° to 9°, even more preferably from 2° to 8°.
[0044] In an optional embodiment of the invention, the monocrystalline diamond substrate 10 may comprise a stepped structure or terraced structure which has crystallographic orientation faces of the {100} family of planes or of the {100} and {113} family of planes. The terraced structure may have disorientation angles, in relation to each terrace of the terraced structure, which are substantially identical or at least relatively close. The homoepitaxial growth steps described may thus be implemented by a step flow mechanism in order to limit the appearance of defects, and more particularly the formation of twins, thus limiting dislocations.
[0045] A forming method 100 according to the invention further comprises a step of first microstructuring 120 of a growth surface 12 of the monocrystalline diamond substrate 10 by non-through laser ablation.
[0046] According to the invention, the microstructuring step 120 comprises the production of first etching figures G1. Each first etching figure G1 comprises an opening of a predetermined width L1 and is delimited by at least one wall 11, each of the first etching figures G1 furthermore has a depth PI of at least 30 μm, said depth PI being greater than the width L1 of the opening.
[0047] As shown in [Fig. 2], the non-through laser ablation aims to remove a portion of the material from the monocrystalline diamond substrate 10 in a controlled manner, according to a first predetermined removal matrix M1, in order to form etching figures positioned relative to each other in a predefined manner. The first etching figures G1 are formed by a wall 11 and separated by a portion of the growth surface 12 which has not been subjected to laser ablation and generally takes the form of CRI crenellations. As shown in [Fig. 2], the wall 11 of the first engraving figure G1 corresponds to the contour describing the interior of the first engraving figure G1 after ablation.
[0048] Advantageously, the non-through laser ablation may consist of a directional laser ablation, of the known type, in order to obtain first engraving figures G1 of substantially identical dimensions over the entire growth surface 12.
[0049] As an illustrative example, the growth surface 12 may be a crystallographic face (100) disoriented relative to a family of crystallographic faces {100} parallel to one of the lateral faces 13 of the monocrystalline diamond substrate 10.
[0050] In another illustrative example, the growth surface 12 may be a (100) crystallographic face misoriented relative to a {110} family of crystallographic faces or a {113} family of crystallographic faces.
[0051] Still in the invention, the method 100 for forming a layer of monocrystalline diamond 10' comprises a step of first homoepitaxial Cl growth 130, in a reactor by chemical vapor deposition assisted by plasma or by hot filament.
[0052] The first homoepitaxial Cl growth step 130 is carried out normally and laterally with respect to the growth surface 12. The normal growth is carried out substantially perpendicular to a plane formed by the growth surface 12, so as to form a first layer of monocrystalline diamond 10-1 comprising the crystalline defects of the growth surface 12. Indeed, during the first Cl growth, the crystalline defects of the growth surface 12 will propagate in the first layer of monocrystalline diamond 10-1.
[0053] The first homoepitaxial growth step Cl 130 is further carried out laterally with respect to the wall 11 delimiting the first etching Gl, so as to form a second layer of monocrystalline diamond 10-2 comprising the crystalline defects of the wall 11 confined in the first etching figure Gl and a cavity 15.
[0054] As detailed previously, the first etching figures G1 have a depth P1 of at least 30 μm. This makes it possible, during the first lateral growth C1, to allow the formation of the cavity 15 which describes a hollow space which extends along a longitudinal axis from the deepest part of the first etching G1 and over at least 5% of the depth of the first etching figure G1, preferably at least 15%. Preferably, the cavity 15 represents at least 5% of the space of the first etching G1, preferably at least 10%.
[0055] The first lateral homoepitaxial growth Cl 130 thus makes it possible to cover the first etching figure Gl with a third layer of monocrystalline diamond 10' having a density of crystalline defects less than or equal to 103 dislocations per cm2. Indeed, the formation of the cavity 15 makes it possible to block the propagation of a part of the crystal defects present in the monocrystalline diamond substrate 10 and to limit their presence in the third monocrystalline diamond layer 10'.
[0056] In order to promote lateral growth relative to the wall 11, the growth conditions may comprise the generation of a pressure of between 50 hPa and 400 hPa within the reactor, the injection of microwaves at a power of, for example, between 1 kW and 50 kW (or more), depending on the type of generator used (frequency used), the injection of gas, for example at a total flow rate of at least 100 standard cm3 per minute (sccm), preferably at least 1000 standard cm3 per minute (sccm), the gases comprising, for example, methane, argon and dihydrogen or a mixture of all or part of these gases, and additives such as oxygen, nitrogen, boron, phosphorus and argon, or halogens, and the operation of systems for cooling the enclosure and the substrate to control the temperature of the growth surface in a range preferably ranging from 750°C to 1250°C.
[0057] In one embodiment of the method 100 for forming a single-crystal diamond layer 10', this may include a step 140 of preparing the growth surface 12 of the single-crystal diamond substrate 10 by laser cutting or by polishing. The preparation step 140 may be implemented when the misorientation angle is less than a predetermined threshold so as to induce a misorientation at least equal to the predetermined threshold.
[0058] According to the invention, the method 100 for forming a layer of monocrystalline diamond 10' comprises a second microstructuring 150 of the monocrystalline diamond substrate 10 by non-through laser ablation.
[0059] The second microstructuring step 150 comprises the production of the second predetermined etching figures G2, preferably according to a second removal matrix M2, at the level of the first monocrystalline diamond layer 10-1 comprising the crystalline defects of the growth surface 12, each second etching figure G2 comprises an opening of a predetermined width L2 and is delimited by at least one wall 11', each of the second etching figures G2 further has a depth P2 of at least 30 μm, said depth P2 being greater than the width L2 of the opening.
[0060] The second etching figures G2 are formed by a wall 11' and separated by the second layer of monocrystalline diamond 10-2 topped by the third layer of monocrystalline diamond 10', said second and third layers being able to take the form of a crenel CR2 as indicated by way of example in [Fig.2]. As shown in [Fig.2], the wall 11' of the second etching figure G2 corresponds to the contour describing the interior of the second etching figure G2 after ablation and is in particular formed by the second layer of monocrystalline diamond 10-2 and by the monocrystalline diamond substrate 10.
[0061] As an illustrative example, the engraving figures G1, G2 can be produced with a laser having a wavelength less than or equal to 1 pm.
[0062] Furthermore, in a particular embodiment, the duration of the laser pulse, during the formation of the first and second etchings G1, G2 of the first and second microstructuring steps 120, may be 200 ns.
[0063] According to an optional embodiment, the first and second etching figures G1, G2 can take various forms depending on the power of the laser used, preferably, the etching figures G1, G2 can take the form of a Gaussian curve.
[0064] The method of forming 100 a layer of monocrystalline diamond 10' according to the invention further comprises a second homoepitaxial C2 growth 160 of another second layer of monocrystalline diamond 10-2', in a reactor by plasma-assisted or hot filament-assisted chemical vapor deposition.
[0065] The second lateral homoepitaxial C2 growth 160 is carried out laterally with respect to the wall 11' delimiting the second etching figure G2. The other second layer of monocrystalline diamond 10-2' comprises the crystal defects of the wall 11' confined in the second etching figure G2 and a cavity 15', so that the second etching figure G2 is covered by a third layer of monocrystalline diamond 10' having a crystal defect density less than or equal to 103 crystal defects per cm2.
[0066] In order to promote the second homoepitaxial C2 growth 160 lateral to the wall 11' of the second etching figure G2, the growth conditions may comprise the generation of a pressure of between 50 hPa and 400 hPa within the reactor, the injection of microwaves at a power of for example between 1 kW and 50 kW (or more), depending on the type of generator used (frequency used), the injection of gas, for example at a total flow rate of at least 100 standard cm3 per minute (sccm), preferably at least 1000 standard cm3 per minute (sccm), the gases comprising for example methane, argon and dihydrogen or a mixture of all or part of these gases, and additives such as oxygen, nitrogen, boron, phosphorus and argon, or halogens and the operation of systems for cooling the enclosure, the substrate to control the temperature of the growth surface in a preferably ranging from 750°C to 1250°C.
[0067] In an optional embodiment of a method 100 for forming a layer of monocrystalline diamond 10' according to the invention, the steps of first and / or second micro-structuring 120, 150 and first and / or second homoepitaxial growth 130, 160 may be repeated until a density of crystalline defects is obtained, in the third layer of monocrystalline diamond 10', less than or equal to a predetermined threshold, preferably less than or equal to 103 defects. crystalline defects per cm2 and preferably less than or equal to 5* 102 crystalline defects per cm2. In particular, a step of characterizing the crystalline defects of the monocrystalline diamond layer 10' can be implemented, by known techniques, and if the density of crystalline defects, in the third monocrystalline diamond layer 10', is greater than a predetermined threshold 160-N, the steps of first and / or second micro-structuring 120, 150 and first and / or second homoepitaxial growth 130, 160 are repeated. Advantageously, the steps of first and second micro-structuring and first and second lateral homoepitaxial growth can be repeated between one and twenty times, preferably between one and four times.
[0068] In addition, the method 100 for forming a layer of monocrystalline diamond 10' according to the invention may comprise a normal homoepitaxial C3 growth step 170, in the reactor by plasma-assisted or hot filament-assisted chemical vapor deposition, so that the third layer of monocrystalline diamond 10' reaches a thickness of at least 500 μm. Indeed, depending on the applications for which the layer of monocrystalline diamond 10' is intended or at least to promote the separation of the layer of monocrystalline diamond 10', an additional normal homoepitaxial growth 170 may be necessary.
[0069] In order to recover the monocrystalline diamond layer 10', the forming method 100 according to the invention may comprise a step 180 of cutting the third monocrystalline diamond layer 10', preferably by laser.
[0070] To reduce the crystalline defects and more particularly the stresses in the third layer of monocrystalline diamond 10', the forming method 100 according to the invention may comprise a step of annealing 190 the third layer of monocrystalline diamond 10', after cutting 180, at a temperature ranging from 1500°C to 2300°C, preferably from 1500°C to 1800°C, even more preferably from 1800°C to 2000°C and even more preferably from 2000°C to 2300°C for a duration ranging from 1 h to 72 h, preferably from 5 min to 1 h and even more preferably a duration of less than 5 min.
[0071] Advantageously, the annealing step 190 of the third layer of monocrystalline diamond 10' can be carried out at a temperature ranging from 1500°C to 1800°C for a duration ranging from 10 hours to 24 hours. This makes it possible to reduce the stresses by almost 50%.
[0072] To reduce crystal defects and more particularly stresses, the method 100 for forming a layer of monocrystalline diamond 10' may comprise one or more intermediate annealing steps (not shown in the figures). At least one intermediate annealing step may be implemented after the step 110 of providing a monocrystalline diamond substrate 10, after the first microstructuring step turation 120, after the first homoepitaxial C1 growth step 130, after the second microstructuring step 150, after the second homoepitaxial C2 growth step 160 and / or after the normal homoepitaxial C3 growth step 170. Like the annealing step 190, the intermediate annealing step(s) may be carried out at a temperature ranging from 1500°C to 2300°C, preferably from 1500°C to 1800°C, even more preferably from 1800°C to 2000°C and even more preferably from 2000°C to 2300°C for a duration ranging from 1h to 72h, preferably from 5 min to 1h and even more preferably a duration of less than 5 min.
[0073] The combination of the steps of first and second microstructuring 120, 150, first and second homoepitaxial Cl, C2 growth 140, 160 and annealing 190 and / or intermediate annealing(s) leads to a substantial reduction in dislocations and stresses in the monocrystalline diamond layer 10'.
[0074] According to a second object, the invention relates to a monocrystalline diamond substrate 10 comprising a monocrystalline diamond layer 10', said monocrystalline diamond layer 10' having been obtained by a method 100 of forming a monocrystalline diamond layer 10' according to the invention.
[0075] According to a third object, the invention relates to a monocrystalline diamond substrate 10 comprising a monocrystalline diamond layer 10', said monocrystalline diamond layer 10' having been obtained by: - formation of first etching figures G1 by microstructuring of a growth surface 12 of the monocrystalline diamond substrate 10 by non-through laser ablation, so that each first etching figure G1 comprises an opening of a predetermined width L1 and is delimited by at least one wall 11, each of the first etching figures G1 further having a depth PI of at least 30 pm, said depth PI being greater than the width L1 of the opening, - a first homoepitaxial Cl growth, the first Cl growth comprising: • normal growth relative to the growth surface 12 so as to form a first layer of monocrystalline diamond 10-1 comprising the crystalline defects of the growth surface 12, and • lateral growth relative to the wall 11 delimiting the first etching Gl, so as to form a second layer of monocrystalline diamond 10-2 comprising the crystalline defects of the wall 11 confined in the first etching figure Gl and a cavity 15, so that the first etching figure Gl is covered by a third layer of monocrystalline diamond 10' having a crystal defect density less than or equal to 103 dislocations per cm2, - formation of second etching figures G2 by microstructuring of the first layer of monocrystalline diamond 10-1 by non-through laser ablation, so that each second etching figure G2 comprises an opening of a predetermined width L2 and is delimited by at least one wall 11', each of the second etching figures G2 further has a depth P2 of at least 30 pm, said depth P2 being greater than the width L2 of the opening, - a second homoepitaxial growth C2 of another second layer of monocrystalline diamond 10-2', the second growth C2 being carried out laterally with respect to the wall 11' delimiting the second etching figure G2, the other second layer of monocrystalline diamond 10-2' comprising the crystalline defects of the wall 11' confined in the second etching figure G2 and a cavity 15', so that the second etching figure G2 is covered by a third layer of monocrystalline diamond 10' having a density of crystalline defects less than or equal to 103 crystalline defects per cm2.
[0076] Figures 3 and 4 thus show a monocrystalline diamond substrate 10 comprising a monocrystalline diamond layer 10' obtained according to the invention, it can be observed with the naked eye, in [Fig.4], that the first monocrystalline diamond layer 10-1 has many more crystalline defects than the monocrystalline diamond layer 10'.
Claims
1. Claims A method of forming (100) a layer of monocrystalline diamond (10') having a crystal defect density less than or equal to 103 crystal defects per cm2 comprising the following steps: - providing (110) a single crystal diamond substrate (10) having an initial crystal defect density greater than 103 crystal defects per cm2, the single crystal diamond substrate (10) having a misorientation angle, relative to the exact face of the single crystal diamond substrate (10) greater than 0° and less than or equal to 10°, - first microstructuring (120) of a growth surface (12) of the monocrystalline diamond substrate (10) by non-through laser ablation, the microstructuring step (120) comprising the production of first etching figures (Gl) such that each first etching figure (Gl) comprises an opening of a predetermined width (Ll) and is delimited by at least one wall (11), each of the first etching figures (Gl) further having a depth (PI) of at least 30 pm, said depth (PI) being greater than the width (Ll) of the opening; - first homoepitaxial growth (Cl) (130), in a reactor by chemical vapor deposition assisted by plasma or by hot filament, the first growth (Cl) being carried out: • normally relative to the growth surface (12) so as to form a first layer of monocrystalline diamond (10-1) comprising the crystal defects of the growth surface (12), and • laterally with respect to the wall (11) delimiting the first etching (Gl), so as to form a second layer of monocrystalline diamond (10-2) comprising the crystalline defects of the wall (11) confined in the first etching figure (Gl) and a cavity (15), so that the first etching figure (Gl) is covered by a third layer of monocrystalline diamond (10') having a density of crystalline defects less than or equal to 103 dislocations per cm2, - second microstructuring (150) of the monocrystalline diamond substrate (10) by non-through laser ablation, said second microstructuring step (150) comprising the production of second etching figures (G2) at the level of the first monocrystalline diamond layer (10-1) comprising the crystal defects of the growth surface (12), each second etching figure (G2) comprises an opening of a predetermined width (L2) and is delimited by at least one wall (11'), each of the second etching figures (G2) further has a depth (P2) of at least 30 pm, said depth (P2) being greater than the width (L2) of the opening, - second homoepitaxial growth (C2) (160) of another second monocrystalline diamond layer (10-2'), in a reactor by plasma-assisted or hot filament-assisted chemical vapor deposition,the second growth (C2) being carried out laterally with respect to the wall (11') delimiting the second etching figure (G2), the other second layer of monocrystalline diamond (10-2') comprising the crystalline defects of the wall (11') confined in the second etching figure (G2) and a cavity (15), so that the second etching figure (G2) is covered by a third layer of monocrystalline diamond (10') having a density of crystalline defects less than or equal to 103 crystalline defects per cm2.,
2. Method according to claim 1 characterized in that the growth surface (12) is a crystallographic face 100 disoriented relative to a family of crystallographic faces {100} parallel to one of the lateral faces (13) of the monocrystalline diamond substrate (10).
3. Method according to claim 1 characterized in that the growth surface (12) is a crystallographic face 100 disoriented with respect to a family of crystallographic faces {110} or to a family of crystallographic faces {113}.
4. Method according to any one of claims 1 to 3, characterized in that it comprises a normal homoepitaxial growth step (C3) (170), in the reactor by plasma-assisted or hot filament-assisted chemical vapor deposition, so that the third layer of monocrystalline diamond (10') reaches a thickness of at least 500 pm.
5. Method according to claim 4, characterized in that it comprises a step of cutting (180) the third layer of monocrystalline diamond (10'), preferably by laser.
6. Method according to claim 5 characterized in that it comprises a step of annealing (190) the third layer of monocrystalline diamond (10') at a temperature ranging from 1500°C to 2300°C.
7. Method according to any one of claims 1 to 6, characterized in that it comprises at least one intermediate annealing step of the monocrystalline diamond substrate (10) at a temperature ranging from 1500°C to 2300°C, the intermediate annealing step being carried out between the supplying step (110) and the first microstructuring step (120), between the first homoepitaxial growth (C1) (130) and the second microstructuring step (150) and / or between the second microstructuring step (150) and the second homoepitaxial growth (C2) step (160).
8. Method according to any one of claims 1 to 7, characterized in that the width (L1, L2) of the opening of the first and second engraving figures (G1, G2) is between 20 pm and 200 pm.
9. Method according to any one of claims 1 to 8, said method comprising a step of preparation (140), prior to the second step of micro-structuring (150), of the growth surface (12) of the monocrystalline diamond substrate (10) by laser cutting or by polishing, when the misorientation angle is less than a predetermined threshold, so as to induce a misorientation at least equal to the predetermined threshold.
10. Method according to any one of claims 1 to 9, characterized in that the steps of first and / or second micro-structuring (120, 150) and first and / or second homoepitaxial growth (130, 160) are repeated until a density of crystalline defects is obtained, in the third layer of monocrystalline diamond (10'), less than or equal to a predetermined threshold, preferably less than or equal to 103 crystalline defects per cm2 and preferably less than or equal to 5* 102 crystalline defects per cm2.
11. A single crystal diamond substrate (10) having an initial crystal defect density greater than 103 crystal defects per cm2, the single crystal diamond substrate (10) comprising a growth surface (12) and: - a disorientation angle, relative to the exact face of said substrate, greater than 0° and less than or equal to 10°, - first etching figures (Gl) comprising a first opening of a predetermined width (Ll) delimited by at least one first wall (11), each of the first etching figures (Gl) further having a depth (PI) of at least 30 pm, said depth (PI) being greater than the width (Ll) of the first opening, each of the first etching figures (Gl) further comprising a second layer of monocrystalline diamond (10-2), lateral with respect to the first wall (11), comprising the crystalline defects of the first wall (11) confined in the first etching figure (Gl) by a first cavity (15), - second etching figures (G2) comprising a second opening of a predetermined width (L2) delimited by at least one second wall (11'), each of the second etching figures (G2) further has a depth (P2) of at least 30 pm, said depth (P2) being greater than the width (L2) of the opening, each of the second etching figures (G2) further comprising another second layer of monocrystalline diamond (10-2'), lateral with respect to the second wall (11'), comprising the crystalline defects of the second wall (11') confined in the second etching figure (G2) by a second cavity (15'), - a third layer of monocrystalline diamond (10'), which covers the first and second engraving figures (Gl, G2), having a density of crystalline defects less than or equal to 103 crystalline defects per cm2.
12. A single crystal diamond substrate (10) according to claim 11, wherein the first and second non-through etching figures (G1, G2) are formed over the entire growth surface (12).
13. A single crystal diamond substrate (10) according to one of claims 11 or 12, wherein the width (L1, L2) of the opening of the first and second etching figures (G1, G2) is between 20 pm and 200 pm.
14. Use of a monocrystalline diamond substrate (10) according to any one of claims 10 to 13 for obtaining a monocrystalline diamond layer (10') suitable as a substrate for quantum technologies, for the manufacture of an optical window, a semiconductor substrate or for thermal management.