METHOD FOR DETERMINING THE ELASTIC PROPERTIES OF A THIN LAYER BY DIFFRACTION OF X-RAY

Description

TECHNICAL FIELD AND PRIOR TECHNOLOGY

[0001] The present invention relates to a method for determining the elastic properties of a thin film by X-ray diffraction.

[0002] Micro- and nanoelectronic devices utilize thin films. During the fabrication of electronic components, the substrates undergo significant thermal stress, which can frequently lead to mechanical problems during manufacturing. These problems arise from phenomena such as thermal expansion, crystallization, phase changes, volume variations, and diffusion. These mechanical issues can include adhesion problems, stress formation, void formation, defect creation, and extrusion formation.

[0003] To limit the occurrence of these mechanical problems, numerical simulation of structures can be a useful approach for better understanding them. However, such simulations require knowledge of certain physical properties, such as the elastic constants of a material, particularly when it is in the form of a thin film.

[0004] We therefore seek to be able to determine the elastic constants of the material in thin film, in particular its elastic modulus or Young's modulus and its Poisson's ratio.

[0005] Known methods employing X-ray diffraction generally require several relatively long measurements and a large sample size.

[0006] For example, the paper by E. Eiper, KJ Martinschitz, and J. Keckes, "Combined elastic strain and macroscopic stress characterization in polycrystalline Cu thin films," Powder Diffraction 21 (1), 2006, describes a technique for measuring the elastic properties of a thin film using curvature and X-map. The elastic constants of thin films are derived from X-ray measurements by combining the sin 2 < ψ method with the substrate curvature technique. By X-ray diffraction, the elastic strains in the films are determined using the sin 2 < ψ method, while the macroscopic stresses are evaluated by measuring the substrate curvature. The stresses are calculated using Stoney's formula from the substrate radius. The curvature is determined by measuring the position of the rocking curve of the substrate reflection at different positions on the sample (X-map method).This method requires several relatively long measurements and involves scanning the sample, therefore requiring a large sample size. It also requires an XY translation stage and a submillimeter beam.

[0007] The document "Determination of Young's modulus and Poisson's ratio of thin films by X-ray method", Fu Wei-En et al, Thin Solid Films, Volume 544, 2013, Pages 201-205 discloses a measurement of the "rocking-curve" at different locations of the sample to determine the elastic stresses of the material by X-ray. DESCRIPTION OF THE INVENTION

[0008] It is therefore an object of the present invention to provide a method for determining the elastic constants of a thin film material by relatively fast X-ray diffraction and offering very good accuracy.

[0009] The goal stated above is achieved by a method comprising: the measurement of in-plane and out-of-plane deformations of the thin film by X-ray diffraction, the determination of the stress from the full width at half maximum value of the rocking curve by X-ray diffraction of the substrate, the calculation of the Poisson's ratio from the in-plane and out-of-plane deformations, the calculation of the modulus of elasticity from the Poisson's ratio and the stress.

[0010] The method according to the invention is very fast and advantageously allows the use of the same equipment which is suitable for determining deformation and determining stress.

[0011] A very advantageous approach is to perform measurements by varying the stress or strain in the elastic range, which allows for obtaining more reliable elastic constant values.

[0012] During the stress or strain variation, three measurements are taken: in-plane strain, out-of-plane strain, and stress variation. All three measurements are performed on the same sample.

[0013] In a preferred example, the variation in stress or strain is obtained at constant temperature.

[0014] One of the objectives of this application is therefore a method for determining the elastic modulus E and the Poisson's ratio v of a thin film formed on a substrate, comprising: a) a determination of an out-of-plane strain by X-ray diffraction, b) a determination of an in-plane strain of the thin film by X-ray diffraction, c) a determination of a stress in the film by measuring the full width at half maximum β RC of the rocking curve by X-ray diffraction of the substrate, d) a calculation of the Poisson's ratio v from the in-plane strain and the out-of-plane strain, e) a calculation of the elastic modulus E from the stress determined in step c) and the Poisson's ratio v determined in step d).

[0015] At least in step c), a variation of stress or strain is applied to the thin film, so that the thin film changes from a first state to a second state, and the variation of stress in the thin film is determined by determining a variation of β RC from a series of X-ray diffraction measurements at different times.

[0016] Steps a) and b) may respectively involve measuring the out-of-plane mesh parameter and measuring the in-plane mesh parameter.

[0017] Preferably, the measurements are carried out using a goniometer, and steps a) to c) are carried out successively on the same goniometer.

[0018] According to an additional feature, the goniometer is set between two determination stages.

[0019] Step c) is preferably a high-resolution X-ray diffraction measurement.

[0020] The determination process according to the request, comprising: in step a), an application of a stress or strain variation to the thin film, such that the thin film transitions from a first state to a second state and a determination of the out-of-plane strain from a series of X-ray diffraction measurements at different times; in step b), an application of a stress or strain variation to the thin film, such that the thin film transitions from the first state to the second state and a determination of the in-plane strain from a series of X-ray diffraction measurements at different times, a plotting of the evolution of the stress as a function of the out-of-plane strain so as to obtain a linear regression over at least an interval of said variation and a calculation of the slope of the linear regression which is equal to -E / 2v,a plotting of the stress evolution as a function of the strain in the plane so as to obtain a linear regression over at least one interval of said variation and a calculation of the slope of said linear regression which is equal to E / 1-v, and a determination of the modulus of elasticity E and the Poisson's ratio v from the slope values ​​obtained.

[0021] Preferably, the application of a stress or strain variation to the thin film during the first and second steps and / or the third phase is carried out at a constant temperature whose value ensures the transition from the first state to the second state. For example, the stress or strain variation of the film is due to a transition from a state that is at least partially amorphous to a state that is at least partially crystalline, to a change in volume, a phase change, densification, or relaxation.

[0022] The sample can then be placed in an annealing chamber allowing X-rays to reach the thin film and the collection of diffracted X-rays.

[0023] It may be planned to apply a treatment to the thin film between two sets of measurements so that it is in the first state, for example amorphous.

[0024] The duration between two moments can be at least equal to the duration of a measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be better understood on the basis of the following description and the accompanying drawings, in which: There figure 1 is a schematic representation of an X-ray diffraction measuring apparatus that can be used to implement the method according to the invention. figure 2 is a representation of the evolution of the lattice parameter in the plane in Angstroms as a function of time t in minutes for a thin GST film at temperature Tx = 125°C. figure 3 is a representation of the evolution of the out-of-plane lattice parameter in Angstroms as a function of time t in minutes for a thin GST film at temperature Tx. figure 4 is a representation of rocking curves at different measurement times for the GST thin film at temperature Tx. figure 5 is a representation of the evolution of β RC in ° as a function of time t in min calculated from the rocking curves of the figure 4 . There figure 6A is a representation of the evolution of the stress variation Δσ in MPa of the GST layer as a function of the in-plane strain at temperature Tx. The figure 6B is a representation of the evolution of the stress variation Δσ in MPa of the GST layer as a function of the out-of-plane strain at temperature Tx. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0026] The method of determination according to the invention aims to determine the elastic constants of a thin film deposited on a substrate.

[0027] The elastic constants are the elastic modulus or Young's modulus, generally designated E, which is the mechanical stress that would cause an elongation of 100% of the initial length of a material, and Poisson's ratio, generally designated v, which allows the contraction of the material to be characterized perpendicular to the direction of the applied force.

[0028] During at least one phase of the determination method, the thin film is made of a material that is at least partially crystalline. The thin film has a thickness hf between 100 nm and 100 µm; more specifically, the thickness of the thin film in the example is 500 nm.

[0029] The substrate has a thickness hs between 10µm and 1000µm. In the example, the substrate thickness is 250 µm.

[0030] The ratio hs 2< / hf is preferentially between 0.1 and 0.3.

[0031] The method, according to an example implementation, includes: a) Determination of the out-of-plane strain of the thin film by X-ray diffraction. b) Determination of the in-plane strain of the thin film by X-ray diffraction. c) Determination of the stress by X-ray diffraction. d) Calculation of Poisson's ratio. e) Calculation of Young's modulus.

[0032] The order of steps a) to c) is not necessarily chronological; step c) may take place before steps a) and b) and step b) may take place before step a). Preferably steps a) and b) follow each other, since the change of optics for measuring out-of-plane deformation and deformation can be done automatically, which simplifies the measurement procedure.

[0033] The different steps will be described in detail below.

[0034] X-ray diffraction or X-ray measurements are performed with a goniometer X-ray diffractometer allowing the sample and detector to be oriented at different angles.

[0035] On the figure 1 A schematic representation of an REF diffractometer can be seen, comprising an X-ray source 2, a sample holder 4, and a detector 6 of the diffracted X-rays. The detector 6 is, for example, a point scintillator device. The X-ray source 2 is, for example, an X-ray tube, a rotating anode generator, a synchrotron source, or a microfocus X-ray source.

[0036] The sample holder 4, designed to support the sample E, is mounted articulated around at least three axes of the plane to modify the orientation of the sample relative to the incident beam. The detector 6 is also advantageously movable around at least two axes.

[0037] The different orientations that can be taken by the sample holder and by the detector are those allowing the different measurements required by the method according to the invention.

[0038] The REF diffractometer also includes optics along the path of the incident beam and along the path of the diffracted X-rays. These optics are advantageously adaptable depending on the measurements being performed.

[0039] Sample E consists of a thin layer C of a given material, whose elastic modulus and Poisson's ratio are to be determined, formed on a substrate S of another given material. The thin layer C is formed, for example, by deposition or by epitaxy.

[0040] The expressions "thin layer" or "thin film" are considered synonymous.

[0041] The thin film, for example, has a thickness on the order of a few hundred nanometers. The thin film is formed, for example, by physical vapor deposition or chemical vapor deposition.

[0042] The determination method according to the invention does not require that the thin film be made with particular care.

[0043] During step a), the diffractometer is set to allow the measurement of the mesh parameters of the thin film.

[0044] In step a), the sample is oriented and the detector rotates to diffract the interplanar planes out of plane. The resulting signals form a diffraction peak which allows the lattice parameter d to be measured in the out-of-plane direction and the out-of-plane strain ε⊥< to be determined using the following formula: ε ⊥ = d ⊥ − d 0 d 0 with d 0 the mesh parameter in a relaxed state.

[0045] This technique for calculating the mesh parameter is known to those skilled in the art.

[0046] In step b) of determining the in-plane deformation, the optics are changed and the goniometer is adjusted to a known value. The sample is then oriented and the detector rotates to diffract the interplanar planes in the plane, allowing the lattice parameter of the thin film to be measured in the direction of the plane.

[0047] The signals obtained form a diffraction peak which allows the lattice parameter d to be measured in the direction of the plane and the deformation in the plane ε to be determined ∥ using the following formula: ε ∥ = d 1 − d 0 d 0

[0048] With d 0 the mesh parameter in a relaxed state.

[0049] To implement step c) for determining the stress in the thin film, the diffractometer settings and optics are modified. In one example, high-resolution optics are used. Step c) consists of measuring the "rocking curve" RC (referred to as the oscillation curve in French) of the substrate, i.e., the variation of the signal as a function of the angle ω between the incident beam and the surface of the sample ( figure 1 ). The curvature of the substrate is measured through the β RC.

[0050] The measurement that interests us is the full width at half maximum (FWHM) of the rocking curve. This measurement is designated βRC.

[0051] We therefore measure the diffracted X-rays by varying the angle ω under diffraction conditions on the substrate. We plot the corresponding curve and measure the β RC by fitting the curve.

[0052] Preferably, we work with relative stress, which allows for faster measurements. Indeed, working with relative stress requires only a single measurement, and it also eliminates the effect of initial curvature and the so-called instrumental broadening effect of βRC, as well as other initial components that are independent of the stress variation. We use the βRC of the rocking curve over a larger sample area than that used in the "x-map" method, which uses the position of the rocking curve as a function of x. Working with relative stress thus allows us to directly correlate the change in ΔβRC with the stress variation.

[0053] It should be noted that it is assumed that the elastic constants of the substrate Es, vs are known from the literature, and that the thickness of the substrate hf and that of the thin film hs can be measured, as well as the geometry of the goniometer, in particular the width W and the Bragg angle θ B.

[0054] The stress variation is then expressed as follows and is therefore directly proportional to the measured variation of β RC. Δσ = E s . h s 2 6 1 − ν s . h f . sin θ B W . Δ β RC

[0055] Measuring the evolution of the full width at half maximum Δβ RC allows us to calculate the variation of the stress Δσ in the C layer.

[0056] In step d), from in-plane and out-of-plane deformation measurements, it is possible to determine Poisson's ratio using the following formula: ε ⊥ ε / / = − 2 ν 1 − v

[0057] Next, in step e), we determine the modulus of elasticity E (Young's modulus) of layer C.

[0058] In a thin polycrystalline film, the deformation as a function of stress is written as: ε φ = 1 + v E si n 2 ψ . σ − 2 v E . σ with ε the strain, σ the biaxial stress, E the Young's modulus and v the Poisson's ratio. The angle ψ is the tilt angle of the planes considered.

[0059] In the out-of-plane direction, ψ = 0°, ε ⊥< = (-2ν / E)×σ (V)

[0060] In the direction in the plane ψ = 90°, ε ∥ = (1-ν / E) ×σ (VI)

[0061] The modulus of elasticity E can therefore be calculated from formula III.

[0062] By making certain assumptions, it would be possible to go back to σ, which would allow E to be calculated directly from relations V or VI.

[0063] One method involves determining the absolute stress using Stoney's relation and assuming that the initial curvature is known, i.e., the curvature of the substrate with the relaxed layer is known. Then, to determine the stress as a function of βRC, βRC as a function of W is measured, thus yielding the stress value.

[0064] Another more advantageous method is to assume that the intrinsic components, other than the resultants of the curvature and invariants of βRC, would be perfectly known, for example the width related to crystal defects, the "Darwin" width related to the XRD dynamic theory, as well as the width related to the parallelism of the beam.

[0065] Knowing these invariants, it is possible to calculate the part of βRC related to the stress (curvature) and calculate the stress using Stoney's equation.

[0066] Thanks to the invention, in a single series of three X-ray diffraction measurements, one measurement for each step a), b), and c), it is possible to calculate the Poisson's ratio and the modulus of elasticity of a thin film. Each measurement consists of illuminating the sample with the incident X-ray beam and collecting the diffracted X-rays. A measurement takes a few minutes, for example, 10 minutes.

[0067] During steps a) and b), the sample is fixed.

[0068] In step c), the sample is rotated to change the angle ω between the incident beam and the sample surface. The measurement consists of acquiring the diffracted X-rays at the different angles to obtain a complete RC curve in order to measure the β RC.

[0069] In a preferred embodiment, the stress or strain is varied in the elastic range during steps a), b), and c), allowing for linear regression over an interval of the resulting curves, thereby improving the accuracy of the calculation of the elastic constants. This is achieved by applying mechanical stress to the thin film and measuring the change in stress or strain in situ.

[0070] Several techniques can be used to stress the thin film.

[0071] For example, one technique uses a sample holder equipped with a specific tensile stage that modifies the biaxial deformation of the thin film. This stage is mounted on the goniometer. However, such a method requires depositing the film onto a flexible substrate, which significantly complicates sample preparation. For example, a silicon substrate cannot be used.

[0072] Another technique involves varying the stress or deformation in the thin film by varying the temperature.

[0073] To achieve this, a substrate is chosen that has a coefficient of thermal expansion different from that of the thin film. By applying temperature cycling, for example by imposing a temperature variation in steps, the stress state in the film is modified. The stress in the thin film is modified by a thermal stress component, which is expressed as follows: σ th = E f 1 − v f α f − α s T 1 − T 0 αf is the coefficient of expansion, also called the coefficient of thermal expansion for the film, and αs is the coefficient of expansion or thermal expansion for the substrate.

[0074] This method involves taking into account a dilation correction on the stress-free mesh parameter for the calculation of associated deformations.

[0075] A particularly advantageous technique consists of modifying the stress or deformation of the thin film by a structural modification of the film itself which takes place at a constant temperature.

[0076] In this application, structural modification means: a change in volume resulting from a phase transition, crystallization from an amorphous or partially amorphous thin film, densification, phase change, relaxation, etc.

[0077] The structural modification alters the stress or strain in the film. Working at a constant temperature does not introduce any error in determining the strain variation, since the expansion is constant in this case.

[0078] The variation in stress or strain can result from one or more structural modifications.

[0079] The mechanisms of stress variation or deformation depend on the material of the thin film.

[0080] Furthermore, this technique does not require the use of any specific platform.

[0081] The value of the constant temperature is chosen so as to cause the structural change and so as to make the measurement kinetics and the kinetics of the structural change of the film compatible, for example the crystallization kinetics, i.e. the chosen constant temperature is such that it causes this structural change in a time suitable for an X-ray diffraction measurement, and to synchronize the measurement kinetics and the crystallization kinetics.

[0082] For example, in the case of a thin copper film, the chosen temperature is typically between 150°C and 250°C, at which point grain growth and relaxation are observed. In the case of a Ni-Si film, a phase transition occurs, causing a volume change at a temperature close to 200°C.

[0083] The temperature is chosen so as to be lower than the melting temperature of the thin film and the substrate.

[0084] Preferably, a good quality single-crystal substrate is chosen, i.e. a substrate without crystalline structural defects to increase measurement accuracy.

[0085] Preferably, a large film thickness and / or a small substrate thickness are chosen to increase measurement accuracy, preferably hs 2< / hf < 0.3.

[0086] An example will be described to illustrate the method of calculating elastic constants by applying stress to the thin film at constant temperature.

[0087] The thin film is an amorphous glass, for example a GST (Germanium Antimony Tellurium). The sample has an oriented silicon substrate. <001> Alternatively, the substrate can be oriented <111> or in another orientation. The thin film has a thickness of 500 nm. The substrate in this example has a thickness of 230 µm.

[0088] The measurement setup includes a primary vacuum annealing chamber that can be mounted on the goniometer. The sample is placed in this chamber to maintain a constant annealing temperature (Tx), thus gradually transforming the thin film from an amorphous state to at least a partially crystallized state. The annealing temperature is, for example, 125°C. The annealing chamber is designed to allow illumination of the sample by the incident beam and collection of the diffracted rays by the detector.

[0089] The progressive crystallization of the thin film causes a variation in both out-of-plane and in-plane deformations of the film, or a variation in stress. The constant temperature value is chosen to ensure compatibility between the measurement kinetics and the crystallization kinetics.

[0090] In step a), the sample is placed at the chosen constant temperature and X-ray diffraction measurements are performed for a sufficient duration to allow crystallization to occur. The measurements are carried out intermittently, for example at regular intervals, with the time interval being at least equal to the acquisition time of the X-ray diffraction signal, for example on the order of 10 minutes.

[0091] On the figure 2 We can see the evolution of the out-of-plane lattice parameter d (d⊥) of the thin film in Angstroms as a function of time in minutes and the area of ​​the diffraction peak , i.e., the intensity of the diffracted beams, during the diffraction measurement. The lattice parameter d ⊥< out-of-plane is calculated from the position of the diffraction peak.

[0092] On the figure 3 We can see the evolution of the lattice parameter d (d / / ) in the plane of the thin film in Angstroms as a function of time in minutes and the area A ∥ of the diffraction peak, i.e., the intensity of the diffracted beams, from the diffraction measurement. The lattice parameter d ∥ in the plane is calculated from the position of the diffraction peak.

[0093] These X-ray diffraction measurements are not simultaneous; for example, measurements are taken first for the out-of-plane lattice parameter and second for the in-plane lattice parameter.

[0094] It is observed that the in-plane and out-of-plane lattice parameters change during the first 500 minutes, then become essentially constant. The in-plane lattice parameter increases while the out-of-plane lattice parameter decreases. This is characteristic of the material being subjected to tension (positive stress) during isothermal annealing. It is also noted that during the initial stages of nucleation, for periods of approximately 100 minutes, the in-plane and out-of-plane lattice parameters are almost identical, around 3.0255 Å, and that this value corresponds to the stress-free lattice parameter.

[0095] In this application, "substantially constant value" means a value that varies within a range of + or - 10% relative to a given value.

[0096] In step b), from the in-plane and out-of-plane mesh parameter values, the in-plane strain ε can be calculated. ∥ and the out-of-plane strain ε⊥< using formula (I). d0 can be determined by assuming that in the very early initial stages of GST nucleation, the material is relaxed, so the value of d0 can be extracted from the figure 2 or of the fig3 , it is equal to 3.0255A.

[0097] In step c), the stress variation is determined.

[0098] To achieve this, the diffractometer optics are advantageously modified to enable high-resolution diffraction measurements of the substrate. As explained above, the sample is rotated to change the angle ω between the incident beam and the sample surface, in order to acquire diffracted X-rays at different angles, with the aim of obtaining a complete RC curve and determining the βRC. On the figure 4, we can see an example of a rocking curve representing the variation of diffracted intensity as a function of the variation of angle Δω in degrees ° at the different times of measurement.

[0099] In this example, the sample was separated into three parts, with one part used for step a), one part used for step b) (different from that used for a)) and another part is used for step c) (different from those used in steps a) and b)).

[0100] In another example, the measurements are automated, and steps a), b), and c) are linked together with an automated change of optics between each step, allowing the series of measurements to be performed on the same part of the sample and during the same annealing. The measurement program is then executed only once.

[0101] In another example, between each step the film is rendered amorphous and undergoes the next step and the following annealing. The film is rendered amorphous by heating it so that the film material reaches its melting temperature and is vitrified.

[0102] On the figure 5 The variation of βRC in degrees (°), determined from the RC curve, can be seen as a function of time in minutes. The βRC measurement also shows a variation during the first 500 minutes. The increase in βRC indicates a change in curvature, generally an increase in curvature. These variations are consistent with a gradual tensioning of the material, demonstrating the effectiveness of constant-temperature loading in varying the stress (or strain) in the thin film. Between 500 and 1000 minutes, βRC decreases very slightly, corresponding to relaxation.

[0103] This variation is directly proportional to the variation in stress Δσ (formula III).

[0104] Knowing the constants of the formula and having measured βRC, we can calculate the stress variation Δσ and plot the stress variation curve Δσ as a function of the strain in the plane ε ∥ and the out-of-plane deformation ε ⊥< using the in-plane deformation calculations ε ∥ and the out-of-plane deformation ε ⊥< ( Figures 6A and 6B ).

[0105] On the figure 6A We observe that the first part of the curve is not linear due to crystallization.

[0106] After 500 minutes, which corresponds roughly to the part of the curve between 60 MPa and 80 MPa on the figure 6A , we find the elastic behavior that corresponds to the completely crystallized material.

[0107] Using measurements on the fully crystallized (quasi-crystalline) phase, for which the part of the stress variation curve (Δσ) as a function of strain is almost linear with respect to both in-plane and out-of-plane strain, we can determine the value of E / 1-v which is the slope of the in-plane strain-stress curve, and the value -E / 2v which is the slope of the out-of-plane strain-stress curve.

[0108] We can then determine E and v by solving the system of two equations with two unknowns. We obtain: E = 34 GPa and v = 0.34

[0109] The invention also makes it possible to determine the Young's modulus E of a material comprising a crystalline phase and an amorphous phase.

[0110] The portion of the strain-stress curve in the plane before 500 minutes is not linear because the thin film material is not fully crystallized. By choosing a Poisson's ratio of, for example, 0.28, a common value for glass, it is possible to determine the Young's modulus of the very weakly crystallized layer by drawing the tangent Ta to the curve and measuring its slope. The Young's modulus of the crystallized material can also be calculated by drawing the tangent Tc to the portion of the curve after 500 minutes. This yields: Ecrystalline = 37 GPa and Eamorphous = 9 GPa. The line Tc corresponds to the crystalline zone, and the line Ta is an extrapolation for the amorphous zone. Between these two boundary states, an intermediate tangent can be drawn, representing an intermediate state with both amorphous and crystalline parts. A Young's modulus for this intermediate state can then be calculated.

[0111] The method according to the invention has many advantages: Determining the stress variation, Δσ, from the measurement of βRC in step c) requires only a single measurement and is faster than pre-existing methods. Furthermore, working in relative terms, i.e., ΔβRC, also eliminates the influence of the initial curvature. The method does not require specific sample preparation; for example, a thin film deposited on a single-crystal substrate, such as a silicon 001 substrate, is suitable.

[0112] The method allows working on a small sample area to measure the curvature of the sample, for example a few mm², whereas the x-map method requires a larger area, for example at least 1 cm².

[0113] The method does not require the use of a diffractometer with a translation stage to perform x-map: this type of stage is often incompatible with diffraction modes in the plane.

[0114] The method according to the invention can be implemented using a diffractometer that automatically changes optics and configurations to perform the three series of measurements successively. Thus, the acquisition of the different measurements required by the method can be carried out in a single execution of the measurement program.

[0115] In the case where the stress is carried out at a constant temperature, the method is not sensitive to the possible lack of knowledge of the expansion of the thin film.

[0116] Operating at a constant temperature minimizes the effects of thermal expansion variations in the goniometer and annealing stage, thus reducing the need for alignment. Measurement reliability is improved by minimizing potential alignment errors, particularly in strain measurements.

[0117] Working at a constant temperature also allows all measurements to be performed on the same sample.

Claims

1. Method for determining the elastic modulus E and the Poisson's ratio v of a thin film formed on a substrate, comprising: a) determining an out-of-plane deformation by X-ray diffraction, b) determining an in-plane deformation of the thin film by X-ray diffraction, c) determining a stress in the film by measuring the half width βRC of the rocking curve by X-ray diffraction of the substrate, d) calculating the Poisson's ratio v from the in-plane deformation and the out-of-plane deformation, e) calculating the elastic modulus E from the stress determined in step c) and the Poisson's ratio v determined in step d); the determination method being such that at least in step c), a change in stress or deformation is applied to the thin film, such that the thin film changes from a first state to a second state and the stress change in the thin film is determined by determining a change in βRC from a series of X-ray diffraction measurements at different times; the method further comprising: - in step a), applying a change in stress or deformation to the thin film, such that the thin film changes from a first state to a second state and determining the out-of-plane deformation from a series of measurements by X-ray diffraction taken at different times, - in step b), applying a change in stress or deformation to the thin film, so that the thin film changes from the first state to the second state and determining the in-plane deformation from a series of measurements by X-ray diffraction taken at different times, - plotting the stress evolution as a function of the out-of-plane deformation so as to obtain a linear regression over at least one interval of said change and a calculation of the slope of the linear regression which is equal to -E / 2v, - plotting the stress evolution as a function of the in-plane deformation so as to obtain a linear regression over at least one interval of said change and a calculation of the slope of said linear regression which is equal to E / 1-v, and - determining the elastic modulus E and the Poisson's ratio v from the slope values obtained.

2. Determination method according to claim 1, wherein steps a) and b) respectively comprise measuring the out-of-plane mesh parameter and measuring the in-plane mesh parameter.

3. Determination method according to claim 1 or 2, wherein the measurements are carried out by means of a goniometer, and wherein steps a) to c) are carried out successively on the same goniometer.

4. Determination method according to claim 3, wherein the goniometer is adjusted between two determination steps.

5. Determination method according to any one of claims 1 to 4, wherein step c) is a high resolution X-ray diffraction measurement.

6. Determination method according to claim 1, wherein the application of a stress or deformation change to the thin film during the first and second steps and / or the third phase is carried out at a constant temperature, the value of which ensures the transition from the first state to the second state.

7. Determination method according to claim 6, wherein the change in stress or deformation of the film is due to a transition from an at least partially amorphous state to an at least partially crystalline state, a change in volume, a phase change, densification or relaxation.

8. Determination method according to claim 7, wherein the sample is placed in an annealing chamber that allows X-rays to reach the thin film and the collection of diffracted X-rays.

9. Determination method according to any one of claims 1 to 8, wherein a treatment is applied to the thin film between two series of measurements so that it is in the first state, for example amorphous.