Method for preparing a microbolometer comprising a sensitive material based on vanadium oxide

Abstract

The present invention relates to a method for preparing a microbolometer 10, the microbolometer comprising a vanadium oxide-based sensitive material 15, the sensitive material containing an additional chemical element selected from arsenic, germanium, silicon and phosphorus, the method comprising the following steps: ○ Determining an effective amount of the additional chemical element, wherein the modified compound has a resistivity ρ r at room temperature after undergoing the step of exposure to a temperature T r for a duration Δt a|r greater than 10% of its intrinsic value; ○ Preparing the sensitive material (15) in a thin layer, the material being formed from a modified compound having an amount of the additional chemical element greater than or equal to the effective amount; ○ Exposing the sensitive material (15) to a temperature T r for a duration Δt r .

Description

Technical Field

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, such as infrared or terahertz electromagnetic radiation, comprising at least one resistive thermal detector comprising a sensitive material based on vanadium oxide. The invention is particularly applicable in the field of infrared imaging and thermal imaging. Background Art

[0002] The electromagnetic radiation detection device may comprise an array of resistive thermal detectors, also called microbolometers, each microbolometer comprising an absorbing portion capable of absorbing the electromagnetic radiation to be detected.

[0003] In order to thermally insulate the sensitive material of the microbolometer, the absorbing part is usually in the form of a membrane suspended above the substrate by anchoring posts and thermally insulated from it by retaining arms and thermally insulating arms. These anchoring posts and thermally insulating arms also have an electrical function by electrically connecting the suspended membrane to a reading circuit usually arranged in the substrate.

[0004] The absorber film contains a sensitive material whose resistivity p changes with the temperature of the material. The sensitive material is characterized by the value of the resistivity p at ambient temperature a and its coefficient α (or TCR), which is defined by the relationship α = 1 / ρ × dρ / dT. The sensitive material can be typically selected from amorphous silicon and vanadium oxide VO x semiconductor materials.

[0005] The choice of sensitive material depends mainly on its compatibility with the conventional deposition and etching steps typically used in microelectronics, especially in silicon technology. However, it seems that sensitive materials based on vanadium oxide may degrade their electrical performance after the microbolometer fabrication process. Summary of the invention

[0006] The object of the present invention is to at least partially remedy the disadvantages of the prior art and more specifically to propose a method for manufacturing at least one microbolometer comprising a sensitive material based on vanadium oxide, the electrical properties of said sensitive material being preserved during the manufacturing process and, more precisely, the risks of 1 / f noise degradation of the sensitive material being limited or even eliminated after the manufacturing process.

[0007] To this end, the subject of the invention is a method for manufacturing at least one microbolometer comprising a sensitive material, which method allows limiting the noise degradation associated with said sensitive material. The sensitive material is formed of a substance based on vanadium oxide (VO x );And at least one additional chemical element added to the first compound and selected from arsenic (As), germanium (Ge), silicon (Si) and phosphorus (P) and excluding nitrogen (N). The method comprises the following steps:

[0008] - a step of preparing said sensitive material in a thin layer;

[0009] - Expose sensitive materials to temperatures T above ambient r Duration Δt r The step is performed after the step of preparing the sensitive material, and the temperature T r and duration Δt r The first compound is amorphous and has an intrinsic resistivity value of 1 Ω.cm to 30 Ω.cm at ambient temperature, and is exposed to a temperature T r Duration Δt r After the step, the resistivity of the first compound at ambient temperature is less than or equal to 10% of its intrinsic value.

[0010] The method further comprises the following steps:

[0011] - Determine the amount of the compound added to the first x ) of a non-zero so-called effective amount of an additional chemical element (As, Ge, Si, P), thereby forming a modified compound, starting from which, after exposure to a temperature T r Duration Δt r After the step, the resistivity of the modified compound at ambient temperature is a|r Greater than its intrinsic value ρ a 10%;

[0012] - in said step of preparing the sensitive material in a thin layer, said thin layer is formed by said modified compound having an amount of the additional chemical element (As, Ge, Si, P) greater than or equal to a predetermined effective amount, the sensitive material is amorphous and has an intrinsic resistivity value ρ between 0.1 Ω.cm and 30 Ω.cm at ambient temperature a , and uniform chemical composition;

[0013] - Thus, when the sensitive material is exposed to temperature T r Duration Δt r After said steps, the sensitive material then has noise whose degradation is limited.

[0014] Certain preferred but non-limiting aspects of the manufacturing method are as follows.

[0015] The additional chemical element is preferably selected from arsenic, germanium and silicon, and is preferably arsenic.

[0016] The step of exposing the sensitive material may include the step of depositing a protective layer covering the sensitive material.

[0017] The step of exposing the sensitive material may comprise a step of depositing an encapsulation layer transparent to the electromagnetic radiation to be detected and intended to define a cavity in which the microbolometer is located.

[0018] Temperature T r Preferably it is greater than or equal to 330°C, or even equal to 350°C, and within the range of ±5°C.

[0019] Duration Δt r Preferably greater than or equal to 90 minutes.

[0020] Sensitive materials are preferably kept below temperature T r prepared at a temperature of .

[0021] The present invention also relates to a micro-thermal bolometer, the micro-thermal bolometer comprising a sensitive material formed by: a vanadium oxide (VO x );and at least one additional chemical element selected from arsenic, germanium, silicon and phosphorus, and excluding nitrogen. The sensitive material is amorphous; has a resistivity of 0.1 Ω.cm to 30 Ω.cm at ambient temperature; has a uniform chemical composition; and contains a certain amount of the additional chemical element, the ratio of the number of atoms of the additional chemical element to the number of atoms of vanadium is at least equal to 0.012 when the additional chemical element is arsenic, at least equal to 0.04 when the additional chemical element is germanium and silicon, and at least equal to 0.12 when the additional chemical element is phosphorus.

[0022] The amount of oxygen, defined as the ratio of the number of oxygen atoms to the number of vanadium atoms, may be from 1.42 to 1.94, within a range of plus or minus 0.05.

[0023] Sensitive materials can be covered by a protective layer of silicon nitride.

[0024] The present invention also relates to a device for detecting electromagnetic radiation, comprising an array of micro-thermal radiation meters according to any of the preceding features, wherein the micro-thermal radiation meters are arranged in at least one airtight cavity defined by a packaging structure that is transparent to the electromagnetic radiation to be detected, wherein the packaging structure comprises at least one layer made of amorphous silicon.

[0025] The detection device may include a getter material located in an airtight cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other aspects, objects, advantages and features of the present invention will become more apparent when reading the detailed description of the preferred embodiments of the present invention provided by way of non-limiting examples with reference to the accompanying drawings, in which:

[0027] Figure 1A and Figure 1Bare respectively a partial schematic perspective view and a partial schematic view of a cross section along the plane AA' of a microbolometer according to one embodiment, the microbolometer comprising a sensitive material based on vanadium oxide;

[0028] FIG. 2A to FIG. 2C They respectively explain:

[0029] o The resistivity of the base compound prepared from vanadium oxide (referred to as the first compound) at ambient temperature as a function of the thermal exposure temperature T r In an example of a variation, the base compound does not contain an additional chemical element selected from the group consisting of arsenic, germanium, silicon and phosphorus;

[0030] οVO x Example of the change in the value of the TCR coefficient of the base compound according to its resistivity without heat exposure and after heat exposure to 310°C for 90 minutes;

[0031] ο means VO x Examples of parameter values ​​of 1 / f noise of the base compound according to its resistivity without thermal exposure and after thermal exposure to 310°C for 90 minutes;

[0032] Figure 3A and Figure 3B It is VO x Examples of Raman spectra of the base compound without heat exposure and after 90 minutes of heat exposure at different temperatures;

[0033] 4A to 4D It is shown that when the sensitive material based on vanadium oxide is exposed to temperature T r Duration Δt r Then, for different amounts of additional chemical elements, the resistivity ρ of the sensitive material at ambient temperature a|r Evolution diagram, the additional chemical element is arsenic ( Figure 4A ),germanium( Figure 4B ),silicon( Figure 4C ) and phosphorus ( Figure 4D ). DETAILED DESCRIPTION

[0034] In the drawings and the rest of the specification, the same reference numerals represent the same or similar elements. In addition, in order to improve the clarity of the drawings, the various elements are not shown to scale. In addition, the various embodiments and modifications are not mutually exclusive and can be combined with each other. Unless otherwise specified, the terms "substantially", "approximately", "about" refer to within 10%, preferably within 5%, and in terms of temperature, within 10°C, preferably within 5°C. In addition, unless otherwise specified, the expression "including" should be understood as "including at least one".

[0035] Indications relating to the chemical composition of a compound are given by its empirical formula, usually represented by one (1) vanadium atom. Thus, for the compound VO x As y , the value of oxygen amount x is the number of oxygen atoms per vanadium atom, and the value of arsenic amount y is the number of arsenic atoms per vanadium atom. The values ​​of the amounts of chemical elements are within 10%. In addition, the compound VO x As y The atomic percentage of each chemical element in the graph is: vanadium is 1 / (1+x+y), oxygen is x / (1+x+y), and arsenic is y / (1+x+y).

[0036] The present invention relates in particular to a method for manufacturing at least one resistive thermal detector, also called microbolometer, comprising a vanadium oxide-based x The micro-bolometer can be designed to detect infrared or terahertz radiation. The sensitive material contains a non-zero sufficient amount of at least one additional chemical element selected from arsenic As, germanium Ge, silicon Si and phosphorus P, and excludes nitrogen N, so that the thermal stability of the sensitive material is improved. In the rest of the specification, "basic compound" refers to a VO-based compound without additional chemical elements. x A "modified compound" refers to a base compound to which additional chemical elements have been added.

[0037] The manufacturing method implements at least one step in which the sensitive material is exposed to a temperature higher than the ambient temperature and less than or equal to the temperature T r Temperature, duration less than or equal to Δt r , for example, less than or equal to 330°C or less than or equal to 350°C, or even less than or equal to 390°C, for 10 minutes, 30 minutes, or even 90 minutes or longer. r Above ambient temperature.

[0038] This thermal exposure step may correspond to the deposition, at about 330° C., of a protective layer, for example made of silicon nitride SiN or silicon oxide SiO, which covers the sensitive material to protect it from any subsequent contamination by chemical elements that may be present. The thermal exposure step may also correspond to the preparation of an encapsulation layer of amorphous silicon, said layer intended to define an airtight cavity in which the microbolometer is located. The thermal exposure step may also involve the activation, at about 330° C., of a getter material located in the airtight cavity, intended to react with any residual gas that may be present in the cavity in order to maintain it at a sufficient vacuum level.

[0039] These examples are for illustration purposes. Thermal exposure to temperature T r Duration Δt rThe steps can generally be implemented within the framework of technical steps for producing a microbolometer after the sensitive material has been prepared, or even within the framework of technical steps for producing a detection device after the microbolometer has been prepared, in particular in order to integrate additional functions in the detection chip.

[0040] Figure 1A and Figure 1B A perspective schematic diagram of a micro-bolometer 10 of a device 1 for detecting electromagnetic radiation and a partial cross-sectional view along a plane AA' are shown, respectively, wherein the micro-bolometer 10 comprises a vanadium oxide VO based x Sensitive materials15.

[0041] The micro-bolometer 10 comprises an absorption film 11 containing a vanadium oxide-based VO2 and an electronic control and reading circuit (not shown) located in the substrate 2. x The absorber film 11 is suspended above the substrate 2 by anchoring posts 12 and thermally insulating arms 13. The micro-bolometer 10 is designed here to absorb infrared radiation contained in the long wavelength infrared (referred to as LWIR) band of about 8 μm to 14 μm.

[0042] Here, and for the remainder of the specification, a direct three-dimensional orthogonal reference system (X, Y, Z) is defined, wherein the plane XY is substantially parallel to the plane of the substrate 2 and the Z axis is oriented in a direction substantially perpendicular to the plane of the substrate 2. Furthermore, the terms "lower" and "upper" are understood to relate to increasing positions when moving away from the substrate 2 in the direction +Z.

[0043] The microbolometer 10 comprises a substrate 2, in this example based on silicon, comprising an electronic circuit (not shown) allowing the microbolometer to be controlled and read. The electronic circuit comprises portions of electrically conductive lines, for example made of metal, separated from one another by dielectric materials, for example mineral materials based on silicon, such as silicon oxide SiO, silicon nitride SiN or alloys thereof. To this end, the electronic circuit may comprise active electronic components, such as diodes, transistors, capacitors, resistors, etc., connected on the one hand to the microbolometer 10 by electrical interconnections and on the other hand to interconnection pads (not shown) intended to electrically connect the detection device 1 to external electronic devices.

[0044] The upper surface of the substrate 2 may be covered with a protective layer (not shown), in particular when the absorbing film is produced on a mineral sacrificial layer, which is then eliminated by chemical attack of an acidic medium. The upper surface of the substrate may cover or be covered by a reflective layer 14 arranged below the absorbing film 11. When the upper surface of the substrate is covered with a reflective layer 14, it is made of a material that is at least partially transparent to the electromagnetic radiation to be detected. The protective layer has an etching stop function and is designed to protect the substrate and the intermetallic dielectric layer from chemical attack when they are made of mineral materials, such as chemical attack of the HF (hydrofluoric acid) acidic medium used subsequently to etch the mineral sacrificial layer used to prepare the absorbing film. The protective layer thus forms an airtight and chemically inert layer. The protective layer is electrically insulating to avoid any short circuits between the metal line parts. The protective layer can thus be made of aluminum oxide Al2O3, or even of aluminum nitride or aluminum fluoride. The thickness of the protective layer can be from tens of nanometers to hundreds of nanometers, for example from 10 nanometers to 500 nanometers, preferably from 10 nanometers to 30 nanometers.

[0045] The micro-bolometer 10 includes an absorption film 11, wherein the absorption film 11 includes a vanadium oxide VO based x The absorber film 11 is suspended above the substrate 2 by anchoring posts 12 and thermally insulating arms 13. The anchoring posts 12 are electrically conductive and partially penetrate the protective layer to make electrical contact with the electronic circuit. The absorber film 11 is spaced a non-zero distance from the substrate 2, in particular from the reflective layer 14. The distance is preferably adjusted to form a quarter-wave cavity that optimizes the absorption of the electromagnetic radiation to be detected by the suspended film 11.

[0046] like Figure 1B As shown, the absorber film 11 may comprise a lower support layer 20 made of an electrically insulating material on which are placed two electrodes 21.1, 21.2, different from one another and made, for example, of TiN, which exhibit good absorption of infrared radiation. A thin layer of sensitive material 15 is placed on the support layer 20 and in contact with each of the two electrodes 21.1, 21.2. In this case, the sensitive material 15 is covered with a protective layer 22, for example made of silicon nitride SiN or silicon oxide SiO, which makes it possible to avoid any subsequent contamination of the sensitive material 15. This example is for illustration only and other arrangements of electrodes and sensitive materials are also possible.

[0047] Furthermore, the microbolometer 10 may be located in a sealed cavity defined by a packaging structure (not shown), as described in particular in the publication "Current progress on pixel level packaging for uncooled IRFPA, SPIE Proceedings Vol. 8353 (2012)" by Dumont et al. The packaging structure may be formed by a stack of various thin layers of packaging layers, for example made of amorphous silicon deposited by CVD or iPVD, covered with a sealing layer and an antireflection layer, for example made of various sublayers of germanium and zinc sulfide, for example deposited by EBPVD, IBS, etc. Such a packaging structure is described in particular in patent application EP3067675.

[0048] Sensitive material 15 is based on vanadium oxide VO x , that is, it is made of so-called vanadium oxide VO x The basic compound is formed, to which an additional chemical element selected from arsenic, germanium, silicon and phosphorus and except nitrogen is added. The sensitive material 15 therefore does not contain nitrogen: the amount of nitrogen in the sensitive material 15 is therefore zero or almost zero, i.e. less than or equal to 0.1% by atomic percentage. The additional chemical element is a chemical element intentionally added to the basic compound, i.e. vanadium oxide. The sensitive material 15 is amorphous, that is to say it does not substantially contain a crystalline phase. In addition, its resistivity is 0.1 Ω.cm to 30 Ω.cm, which corresponds, for example, to an oxygen amount x (defined as the ratio of the number of oxygen atoms to the number of vanadium atoms) of 1.42 to 1.94 (within the range of plus or minus 0.05). More precisely, the resistivity of the basic compound is 1 Ω.cm to 30 Ω.cm. The modified compound corresponding to the basic compound to which the additional chemical element is added has a resistivity of 0.1 Ω.cm to 30 Ω.cm. The oxygen amount x in the basic compound and the modified compound is the same. Furthermore, it has a homogeneous chemical composition, that is, its chemical composition (defined as a basic volume with a diameter of the order of 3 nm) is constant over a large area (at least 90%, 95% or even 99% of its volume).

[0049] The base compound is amorphous and based on VO x , where x is from 1.42 to 1.94, within the range of plus or minus 0.05, preferably from 1.56 to 1.94, within the range of ±0.05. It does not have a stoichiometric form. Therefore, it is different from stoichiometric compounds such as VO2, V2O5, V3O5. As mentioned above, in this case, the compound with the empirical chemical formula V2O5 has 5 oxygen atoms for every 2 vanadium atoms (x=5 / 2), while the compound V3O5 has 5 oxygen atoms for every 3 vanadium atoms (x=5 / 3). It should be noted that the stoichiometric compound V3O5 is in this microbolometer VO xCompounds that cannot be obtained under the usual preparation conditions of the base compound (temperatures are usually below the maximum thermal budget of the reading circuit located in the substrate 2, i.e. below 400° C.). x The sensitive material can have an amount x equal to 1.67, but not corresponding to the stoichiometric form V3O5. Moreover, with respect to the stoichiometric compound V2O3, the probability that such a base compound (i.e. amorphous and with a resistivity of about 1 Ω.cm to 30 Ω.cm) will be r After annealing, a single V2O3 stoichiometric crystalline phase is formed. Therefore, even for an amorphous base compound with an oxygen content of about 1.5, within the range of ±0.05, the T r After annealing, several stoichiometric crystalline phases may also be formed, including a V2O3 crystalline phase, which differs in the amount of oxygen. In any case, if the amount of oxygen in the amorphous base compound is between 1.56 and 1.94 (within the range of ±0.05), then at T r A single V2O3 stoichiometric crystalline phase cannot be formed after annealing. In addition, it should be noted that if the base compound or sensitive material has an oxygen content x of 1.56 to 1.94 (within the range of ±0.05), the intrinsic resistivity is about 2 Ω.cm to 30 Ω.cm.

[0050] The sensitive material 15 then corresponds to a modified compound, that is to say it corresponds to a base compound that has been modified by the addition of at least one additional chemical element chosen from arsenic As, germanium Ge, silicon Si and phosphorus P. As further described below, it is preferably chosen from arsenic, germanium and silicon, and is preferably arsenic.

[0051] The amount of the additional chemical element, in particular the amount of arsenic As, germanium Ge, silicon Si or phosphorus P atoms compared to the amount of vanadium, is selected to provide a sensitive material which has been exposed to a temperature T r Duration Δt r , with improved thermal stability, more precisely, the resistivity ρ at ambient temperature a|r Greater than its intrinsic value ρ a 10%, preferably greater than or equal to 50% of its intrinsic value. "At least equal" is understood to mean greater or equal. The intrinsic value of the resistivity ρ a Is the sensitive material exposed to temperature T r Duration Δt r The resistivity before.

[0052] Temperature T r The value and duration Δt r The value of VO xThe first compound (thus without additional chemical elements) has a resistivity at ambient temperature less than or equal to 10% of its intrinsic value. These are values ​​of temperature and duration of thermal exposure to which the sensitive material 15 may be subjected in subsequent steps of manufacturing the microbolometer.

[0053] The amount of the additional chemical element (As, Ge, Si and / or P) is then greater than or equal to the so-called effective value, called the effective amount. The effective amount is the minimum non-zero amount of the additional chemical element (As, Ge, Si and / or P) that, starting from the sensitive material, has been exposed to the temperature T r A step of duration Δtr, at ambient temperature, has a resistivity ρ a|r Greater than the intrinsic value ρ of the sensitive material at ambient temperature a 10% and preferably greater than or equal to the intrinsic value ρ a The ambient temperature may be equal to 30°C. Temperature T r Greater than ambient temperature, preferably greater than or equal to 330° C., and preferably greater than or equal to 350° C. It may be less than or equal to 400° C. Duration Δt r Preferably, it is greater than or equal to several minutes or tens of minutes, or even several hours.

[0054] In other words, when the amount of the additional chemical element (As, Ge, Si and / or P) in the sensitive material is greater than or equal to the effective amount and is not exposed to the temperature T r Duration Δt r , then the resistivity of the sensitive material at ambient temperature has an inherent value ρ a . During thermal exposure to T r Δt r After that, the resistivity ρ of the sensitive material at ambient temperature a|r Greater than the intrinsic value ρ a 10% and preferably greater than or equal to the intrinsic value ρ a 50% of.

[0055] The effective amount depends mainly on the base compound under consideration, as well as the temperature T r and the duration of thermal exposure Δt r A person skilled in the art is able to determine the effective amount, i.e. the minimum amount of additional chemical elements (As, Ge, Si and / or P) added to the base compound so that the resistivity p of the sensitive material at ambient temperature is a|r Greater than the intrinsic value ρ a If desired, the effective amount can be selected so that the value ρ a|r greater than 10%, for example at least equal to 50%, or even at least equal to the intrinsic value ρ a 90% of.

[0056] The resistivity of the sensitive material at ambient temperature can be determined using the conventional four-point measurement technique, and the atomic composition of the sensitive material and therefore the amount of additional chemical elements can be determined in particular by NRA (Nuclear Reaction Analysis), by RBS (Rutherford Backscattering Spectroscopy), by SIMS (Secondary Ion Mass Spectroscopy), by XPS (X-ray Photoelectron Spectroscopy), using suitable standards.

[0057] As we all know, vanadium oxide VO x The resistivity of a compositionally sensitive material at ambient temperature may decrease when it is exposed to temperatures of 300°C or 400°C, especially in an inert atmosphere (under nitrogen), as shown in Venkatasubramanian et al., “Correlation of temperature response and structure of annealed VO x Thin films for IR detector applications, J. Vac. Sci. Technol. A 27 (4), 2009, 956-961". Therefore, the sensitive material composed of vanadium oxide, and in the absence of additional chemical elements such as arsenic, germanium, silicon and phosphorus, has a resistivity of ρ at ambient temperature. a|r Its intrinsic value ρ after exposure to a temperature of about 200°C in an inert atmosphere a However, when the sensitive material is exposed to a temperature of 300°C or 400°C for 10 minutes or 30 minutes in an inert atmosphere, the resistivity ρ a|r Drop by an order of magnitude, or even several orders of magnitude.

[0058] However, the inventors have discovered that adding a sufficient amount of additional chemical elements selected from arsenic, germanium, silicon and phosphorus to a vanadium oxide-based sensitive material can unexpectedly improve the thermal stability of the sensitive material during thermal exposure to, for example, about 330°C or higher for tens of minutes, as well as more accurately limit or even eliminate possible 1 / f noise degradation of the sensitive material after the thermal exposure step.

[0059] Sensitive materials based on vanadium oxide, to which additional chemical elements (As, Ge, Si and / or P) are added in sufficient amounts, have a resistivity of ρ at ambient temperature. a|r Greater than the intrinsic value ρ a 10% added to the VO xThe effective amount in the first compound is an amount greater than or equal to the determined effective amount. The sensitive material does not show a significant decrease in its electrical properties, in particular its resistivity or its 1 / f noise at ambient temperature, after the microbolometer manufacturing method, which includes exposing the sensitive material to a temperature of at least T r Lasts up to Δt r at least one step of the process, for example a step of depositing a thin layer, a step of encapsulating the microbolometer in a gas-tight cavity, or even a step of activating a getter material.

[0060] More precisely, it can be seen that when based on VO x The compound is amorphous and has an intrinsic resistivity ρ at ambient temperature. a When the compound is exposed to a temperature T r Duration Δt r , so that its resistivity ρ a|r At least less than its intrinsic value ρ a 50% of the TCR factor also results in a degradation of the 1 / f noise without affecting the TCR factor. The 1 / f noise, also called flicker noise or low-frequency noise, originates in particular from fluctuations in the mobility and / or density of free carriers.

[0061] In addition, vanadium oxide-based x The amorphous compound (whose resistivity is 1Ω.cm to 30Ω.cm) at T r After annealing, the VO used to prepare this micro-thermal bolometer x Under normal conditions of the base compound (temperature below 400°C), it is unlikely to form a single stoichiometric crystalline phase. In such a resistivity range, the base compound has an oxygen content x of the order of about 1.42 to 1.94. Approximately is here understood to mean an absolute uncertainty of ±0.05. As mentioned above, the resistivity of the base compound can be 2Ω.cm to 30Ω.cm, and its oxygen content x is then 1.56 to 1.94, within the range of ±0.05.

[0062] The inventors have found that the 1 / f noise of this base compound is r According to the thermal exposure temperature T r The evolution of is related to the resistivity but not to the TCR coefficient.

[0063] therefore, Figure 2A Shown by VO 1.8 The resistivity of the base compound (without arsenic, germanium, silicon or phosphorus) is a|r According to the duration Δt r Equal to 90 minutes temperature T r Example of change. Resistivity ρa|r It therefore remains constant and equal to approximately 10Ω.cm until a temperature T of approximately 280°C r Then it shows a strong decrease, especially between 300 °C and 325 °C.

[0064] In addition, it can be seen that when the heat is exposed to T r Continuous Δt r While the resistivity decreased, the temperature coefficient of resistance (TCR) did not experience any significant decrease.

[0065] therefore, Figure 2B Shown by VO x TCR coefficient (in arbitrary units) of the prepared base compound after annealing at 310 °C for 90 minutes for a duration Δt r After (solid diamond) according to the resistivity ρ a|r The various measured values ​​of the change, the resistivity is 5Ω.cm to 15Ω.cm. Also shown is the temperature T r The same type of VO without annealing x The TCR coefficient value of the basic compound (open circle). x The TCR coefficient of the base compound remains essentially constant, regardless of whether the base compound has been heated to a high temperature T of 310°C. r This is true for all devices subjected to heat exposure. Figure 2B As shown in the figure, the VO x The resistivity values ​​of the base compound (solid diamonds) correspond to the reduced resistivity after annealing.

[0066] The intrinsic value of resistivity is higher and is not shown in the figure. In addition, for unannealed VO x The resistivity values ​​of the base compounds (open circles) correspond to the intrinsic resistivity of the corresponding compounds. The values ​​after annealing are lower but not shown in the figure.

[0067] On the other hand, it can be seen that with this type of VO x The 1 / f noise associated with the base compound increases with the resistivity ρ a|r This occurs when the heat is exposed to temperature T r Duration Δt r hour.

[0068] therefore, Figure 2C The parameter N is shown 1 / f Various measurement values, this parameter represents Figure 2B VO x 1 / f noise of base compound annealed at 310℃ for 90 minutes duration Δt r Then according to the resistivity ρ a|r(solid diamond). Also shown is the change in temperature T r Under these unannealed VO x The value of the 1 / f noise parameter of the basic compound (open circles). r Under these unannealed VO x The resistivity value of the base compound (open circles) is similar to that of the 1 / f noise, which remains constant. However, it can be seen that when VO is heated to 310°C, the x Annealing the base compound for 90 minutes resulted in a significant increase in the 1 / f noise (solid diamonds).

[0069] Parameter N representing 1 / f noise 1 / f Here it is estimated based on the spectral analysis of the reference current flowing through the sensitive material. For this purpose, the sensitive material is set to be biased by a direct current (DC) voltage source so that the reference current is applied to the sensitive material. A very low-noise voltage source is also used in order not to bias the noise measurement of the sensitive material. Therefore, the reference current is corrupted by the only noise current of the sensitive material. This current is then amplified by a transimpedance amplifier that provides a voltage output signal that is a mirror image of the input current. The voltage signal is sampled, digitized and digitally processed (Fourier transform) to obtain its spectrum. The amplitude of the 1 / f noise can be obtained by reading a specific point of the spectrum (for example at 1Hz), or by using a least squares calculation method on the low-frequency part of the spectrum (where the 1 / f noise is most obvious).

[0070] Therefore, it can be seen that the intrinsic resistivity ρ will be between 1Ω.cm and 30Ω.cm at ambient temperature. a Amorphous VO x The base compound (i.e. non-stoichiometric form) is exposed to temperature T r Duration Δt r , so that its resistivity ρ a|r Relative to its original value ρ a A decrease in the 1 / f noise will also lead to a degradation without affecting the TCR coefficient.

[0071] This VO x The increase in the 1 / f noise of the base compound may lead to the onset of crystallization of the compound, where different crystalline phases appear, which differ from each other in the amount of oxygen, and these crystalline phases are in stoichiometric form. So, for example, the initially amorphous VO xAt least partial crystallization of the base compound, where x is about 1.8, leads to the appearance of various stoichiometric crystalline phases, including VO2 and V2O5 (i.e. x=2.5). The increase in 1 / f noise can therefore be associated with the appearance of several stoichiometric crystalline phases, which differ from each other in the amount of oxygen and therefore in the loss of homogeneity of the chemical composition of the sensitive material and in its local electrical properties.

[0072] in this regard, Figure 3A and Figure 3B The initial amorphous VO x Example of Raman spectra of the base compound (so no As, Ge, Si or P added), where x is approximately equal to 1.85, for various exposure temperatures T r The duration Δt of 90 minutes r . Figure 3A The Raman spectrum is approximately 100 to 300 cm -1 The Raman shift range is centered on Figure 3B The Raman spectrum is approximately 700 to 950 cm -1 The Raman shift range is centered. Curve A0 corresponds to the unannealed VO 1.85 Raman spectrum of the compound, curve A s Corresponds to the Raman spectra of the carrier in which the compound in question is located. Curves A1, A2, A3 and A4 correspond to VO 1.85 The compound is heated to 300°C, 310°C, 320°C and 330°C. r Raman spectra of the samples exposed for 90 minutes. It can be seen that when the temperature T r When raised, 149cm -1 A peak at 197 cm appears and increases in intensity, which is associated with the stoichiometric crystalline phase V2O5 (x = 2.5). -1 and 224cm -1 A peak associated with the stoichiometric crystalline phase VO2 appears at , and increases with temperature T r Correspondingly, the 860 cm- -1 The peak at r decreases with the increase of .

[0073] Therefore, by VO xHigh temperature exposure of an initially amorphous base compound, made without any arsenic, germanium, silicon or phosphorus and having an intrinsic resistivity of 1 Ω.cm to 30 Ω.cm, appears to lead to at least partial crystallization of the sensitive material, resulting in a decrease in its resistivity and an increase in 1 / f noise. In other words, the resistivity at ambient temperature is a parameter that characterizes the amorphous or crystalline nature of the compound and the 1 / f noise. Therefore, by adding a sufficient amount of arsenic, germanium, silicon or phosphorus as an additional chemical element to the base compound (or "first compound") to obtain a modified compound, it is possible to limit crystallization and even drive down the crystallization threshold of the modified compound, thereby limiting or even eliminating 1 / f noise degradation.

[0074] As described above, the manufacturing method then comprises a step of adding an additional chemical element selected from arsenic, germanium, silicon and phosphorus to the base compound to obtain a modified compound. The intrinsic resistivity is between 0.1 Ω.cm and 30 Ω.cm, which corresponds to a non-stoichiometric amount of oxygen x. The amount of oxygen x in the base compound is not changed by the addition of the additional chemical element.

[0075] Thus, if the additional chemical element is arsenic, the amount of arsenic to be added to the base compound is determined so that the compound thus modified, when exposed to a temperature T r for a predetermined duration Δt r The resistivity ρ a|r is greater than or equal to 10% of its intrinsic value. Therefore, partial crystallization of the modified compound is limited, thereby producing stoichiometric crystalline phases that differ from each other in terms of the amount of oxygen x, and 1 / f noise degradation is also limited. Therefore, when the sensitive material is subsequently exposed to a temperature T r Duration Δt r When the thermal stability of the properties of sensitive materials is improved.

[0076] Therefore, such sensitive materials are particularly advantageous in the context of a collective manufacturing method for a micro-bolometer array for manufacturing an electromagnetic radiation detection device. In particular, during the thermal exposure step, the temperature field may exhibit spatial inhomogeneities within a thin film deposition reactor or an annealing furnace, which may lead to a dispersion of the electrical characteristics of the micro-bolometers. Therefore, by using a sensitive material with a sufficient amount of arsenic, germanium, silicon and / or phosphorus, the micro-bolometers are thermally exposed to a temperature T r During this period, better thermal stability is exhibited, thereby reducing the dispersion of the electrical characteristics of the micro-bolometer.

[0077] In addition, the sensitive material may also include transition metals belonging to the 4th period of the periodic table, namely scandium Sc, titanium Ti, chromium Cr, manganese Mn, iron Fe, cobalt Co, nickel Ni, copper Cu and / or zinc Zn. The sensitive material may also include other chemical elements, such as yttrium Y, niobium Nb, molybdenum Mo, tantalum Ta, tungsten W, etc.

[0078] Figure 4A shows the resistivity ρ of the sensitive material at ambient temperature a|r According to the thermal exposure temperature T r Duration Δt r Example of a 90-minute variation in which different amounts of arsenic As were added to VO x These examples demonstrate that the thermal stability of the sensitive material is enhanced when it contains an effective amount of arsenic.

[0079] In these examples, the VO of the sensitive material x As y The samples of the modified compounds were prepared using ion beam sputtering (IBS) deposition technique to deposit VO x The first compound is prepared by sputtering a vanadium target, for example, about 10 -4 Torr level, and then arsenic is implanted into the VO x In the first compound, VO is obtained. x As y Modified compounds. Other materials used to produce VO x As y The resistivity ρ of the sensitive material was measured at ambient temperature (here 30°C) after the sensitive material was exposed to temperatures of 270°C, 310°C, 330°C, 350°C, 370°C and 390°C for 90 minutes. a|r Arsenic is added in different amounts, here 0.004, 0.012, 0.04 and 0.12. In these examples, the oxygen amount x is equal to 1.9 (within the range of 0.14), and the first compound VO 1.9 It exhibits an intrinsic resistivity of approximately 20Ω.cm.

[0080] It can be seen that for an arsenic content y of 0.004, the resistivity ρ a|r From a first threshold temperature T equal to about 330°C th,1 Relative to its intrinsic resistivity ρ a In other words, for y = 0.004, the resistivity ρ a|r Less than or equal to the intrinsic value ρ a 10% of.

[0081] On the other hand, it can be seen that for arsenic amounts y of 0.012, 0.04 and 0.12, at this temperature T th,1 When it is equal to 330℃, the resistivity ρ a|r Greater than the corresponding intrinsic resistivity ρ a Therefore, starting from the effective amount of arsenic y = 0.012, the sensitive material shows better thermal stability. More precisely:

[0082] - With respect to the arsenic amounts y equal to 0.012 and 0.04, it can be seen that from the second threshold temperature T equal to about 360°C th,2 Initially, the resistivity is relative to the corresponding intrinsic resistivity ρ a It is therefore obvious that adding an amount of arsenic equal to at least 0.012 of VO x The base compound provides the sensitive material with an additional thermal stability of at least about 30°C.

[0083] - For an arsenic amount y equal to 0.12, it can be seen that until at least 390°C, the resistivity is relative to its intrinsic resistivity ρ a Therefore, the addition of arsenic in an amount of at least 0.12 can provide additional thermal stability of at least about 60°C to the sensitive material.

[0084] Finally, it should be noted that the addition of up to 0.12 arsenic to VO x Basic compounds can cause VO x As y≤0.12 The intrinsic resistivity of the modified compounds relative to VO 1.9 The intrinsic resistivity of 20Ω.cm for VO1.9 is reduced by a factor of about 60 at most. Therefore, the intrinsic resistivity changes from 20Ω.cm for VO1.9 to 1.9 As 0.12 0.49Ω.cm. In addition, for ambient temperature to 390℃ temperature T r , VO 1.9 As 0.12 Resistivity ρ of modified compound a|r Maintained greater than or equal to 0.18Ω.cm.

[0085] It is therefore clear that an amount y of arsenic greater than or equal to 0.012, preferably greater than or equal to 0.12, provides greater thermal stability to the sensitive material in terms of resistivity and in terms of 1 / f noise. Here, when y is equal to 0.012 and 0.04, the thermal stability is improved by 30°C, while in the case of y=0.12, the thermal stability is improved by at least 60°C. Furthermore, it is advantageous that the additional chemical element is arsenic, since it results in a greater resistivity of the sensitive material relative to VO 1.9 The reduction in the resistivity of the base compound is limited.

[0086] Finally, it can be seen that the modified compound VO x As 0.12 In the resistivity ρ a|r The temperature T rParticularly small relative variations up to at least 390° C. This can then limit the dispersion of the electrical properties of the microbolometer caused by any spatial inhomogeneities in the temperature field within the deposition reactor or annealing furnace.

[0087] Figure 4B shows the resistivity ρ of the sensitive material at ambient temperature a|r According to the thermal exposure temperature T r Duration Δt r Example of a 90 minute variation where different amounts of Ge were added to VO x These examples show that when the sensitive material contains an effective amount of germanium, its thermal stability is improved.

[0088] In these examples, VO x Ge y The samples of the sensitive material were obtained in a similar manner to that described above, that is, by implanting Ge into VO2 previously sputtered by IBS. x The oxygen content x is here equal to 1.9 (within the range of 0.14), which corresponds to the first compound VO 1.9 The inherent resistivity is equal to 20Ω.cm.

[0089] It can be seen that for germanium amounts y of 0.004 and 0.012, from the first threshold temperature T equal to about 330°C th,1 Initially, the resistivity ρ a|r Relative to its intrinsic resistivity ρ a Down to 1 / 10.

[0090] On the other hand, it can be seen that for germanium amounts y of 0.04 and 0.12, at this temperature T th,1 When it is equal to 330℃, the resistivity ρ a|r Greater than its intrinsic resistivity ρ a Therefore, starting from the effective amount of germanium y = 0.04, the sensitive material shows better thermal stability. More precisely:

[0091] - with respect to a germanium amount of y=0.04, from a second threshold temperature T equal to about 350°C th,2 Initially, the resistivity is relative to the corresponding intrinsic resistivity ρ a It is therefore obvious that adding at least 0.04 of germanium to VO x The base compound provides the sensitive material with an additional thermal stability of at least about 20°C.

[0092] - Relative to the amount of germanium y = 0.12, until at least 390 ° C, the resistivity relative to its intrinsic resistivity ρ aTherefore, the addition of germanium in an amount equal to at least 0.12 provides the sensitive material with an additional thermal stability of at least about 60°C.

[0093] It is therefore clear that a germanium amount y greater than or equal to 0.04, preferably greater than or equal to 0.12, provides greater thermal stability to the sensitive material in terms of resistivity and in terms of 1 / f noise. Here, for y=0.04, the thermal stability is increased by 20°C, while for y=0.12, the thermal stability is increased by at least 60°C.

[0094] Finally, it can be seen that the modified compound VO x Ge 0.12 In the resistivity ρ a|r The temperature T r Particularly small relative variations up to at least 390° C. This can then limit the dispersion of the electrical properties of the microbolometer caused by any spatial inhomogeneities in the temperature field within the deposition reactor or annealing furnace.

[0095] Figure 4C shows the resistivity ρ of the sensitive material at ambient temperature a|r According to the thermal exposure temperature T r Duration Δt r Example of a 90 minute variation where different amounts of Si are added to VO x These examples demonstrate that the thermal stability of the sensitive material is enhanced when it contains an effective amount of silicon.

[0096] In these examples, VO x Si y Samples of the sensitive material were obtained in a manner similar to that described above, that is, by implanting silicon into VO2 pre-sputtered by IBS. x The oxygen content x is here equal to 1.9 (within the range of 0.14), which corresponds to the first compound VO 1.9 The inherent resistivity is equal to 20Ω.cm.

[0097] It can be seen that for silicon amounts y of 0.004 and 0.012, from the first threshold temperature T equal to about 315°C th,1 Initially, the resistivity ρ a|r Relative to its intrinsic resistivity ρ a Down to 1 / 10.

[0098] On the other hand, it can be seen that for silicon amounts y of 0.04 and 0.12, at this temperature T th,1 When it is equal to 315℃, the resistivity ρ a|r Greater than its intrinsic resistivity ρ aTherefore, starting from an effective amount of silicon y = 0.04, the sensitive material exhibits better thermal stability. More precisely:

[0099] - with respect to a silicon amount of y=0.04, from a second threshold temperature T equal to about 350°C th,2 Initially, the resistivity is relative to the corresponding intrinsic resistivity ρ a It is therefore obvious that adding at least 0.04% of silicon to VO x The base compound provides the sensitive material with additional thermal stability of at least about 35°C.

[0100] - Relative to the amount of silicon with y = 0.12, until at least 390°C, the resistivity relative to its intrinsic resistivity ρ a It does not drop to 1 / 10. Therefore, adding an amount of silicon equal to at least 0.12 provides the sensitive material with an additional thermal stability of at least about 60°C.

[0101] It is therefore clear that a silicon amount y greater than or equal to 0.04, preferably greater than or equal to 0.12, provides greater thermal stability to the sensitive material in terms of resistivity and in terms of 1 / f noise. Here, for y=0.04, the thermal stability is increased by 35°C, while for y=0.12, the thermal stability is increased by at least 75°C.

[0102] Finally, it can be seen that the modified compound VO x Si 0.12 In the resistivity ρ a|r The temperature T r Particularly small relative variations up to at least 390° C. This can then limit the dispersion of the electrical properties of the microbolometer caused by any spatial inhomogeneities in the temperature field within the deposition reactor or annealing furnace.

[0103] Figure 4D shows the resistivity ρ of the sensitive material at ambient temperature a|r According to the thermal exposure temperature T r Duration Δt r Example of a 90-minute variation in which different amounts of phosphorus P were added to VO x These examples demonstrate that the thermal stability of the sensitive material is enhanced when it contains an effective amount of phosphorus.

[0104] In these examples, VO x P y Samples of the sensitive material were obtained in a manner similar to that described above, that is, by implanting phosphorus into VO2 previously sputtered by IBS. x The oxygen content x is here equal to 1.9 (within the range of 0.14), which corresponds to the first compound VO1.9 The inherent resistivity is equal to 20Ω.cm.

[0105] It can be seen that for phosphorus amounts y of 0.004 and 0.012, from the first threshold temperature T equal to about 320°C th,1 Initially, the resistivity ρ a|r Relative to its intrinsic resistivity ρ a Down to 1 / 10.

[0106] On the other hand, it can be seen that for a phosphorus amount y of 0.12, at this temperature T th,1 When it is equal to 320℃, the resistivity ρ a|r Greater than its intrinsic resistivity ρ a Therefore, starting from the effective amount of phosphorus y = 0.12, the sensitive material exhibits better thermal stability.

[0107] More specifically, with respect to the phosphorus amount y=0.12, from the second threshold temperature T equal to about 360°C th,2 Initially, the resistivity is relative to the corresponding intrinsic resistivity ρ a It is therefore obvious that adding at least 0.12 phosphorus to VO x The base compound provides the sensitive material with an additional thermal stability of at least about 40°C in terms of resistivity and in terms of 1 / f.

[0108] Therefore, the additional chemical element is selected from arsenic, germanium, silicon and phosphorus. However, it is preferably selected from arsenic, germanium and silicon, since these three chemical elements allow the thermal stability of the sensitive material to be increased to at least 390° C., which is not the case with phosphorus. This is all the more surprising considering that these four chemical elements, together with boron, form part of the chemical elements that form the glassy network, that is to say that they form part of the chemical elements of which the oxides can form by themselves (without any other addition) a stable amorphous material. The oxides of the network formers are SiO2 for silicon, P2O5 for phosphorus, GeO2 for germanium and As2O3 for arsenic. Nevertheless, surprisingly, in this family of network formers, arsenic, germanium and silicon enable better thermal stability to be obtained than phosphorus. Incidentally, considering that silicon and phosphorus, like boron, are smaller ions than arsenic and germanium, it might be considered that they are equally effective chemical elements relative to each other. Nevertheless, surprisingly, phosphorus does not seem to be as effective as silicon. Therefore, the additional chemical element is preferably selected from arsenic, germanium and silicon.

[0109] While specific embodiments have been described above, various modifications and variations will be apparent to those skilled in the art.

Claims

1. A method for manufacturing at least one microbolometer (10) comprising a sensitive material (15), said method allowing to limit the noise degradation associated with said sensitive material (15), o The sensitive material (15) is formed of the following substances: based on vanadium oxide (VO x ) of the first compound; and at least one additional chemical element added to the first compound and selected from arsenic (As), germanium (Ge), silicon (Si) and phosphorus (P) and excluding nitrogen (N), o The method comprises the following steps: ● a step of preparing the sensitive material (15) in a thin layer; ● Exposing the sensitive material (15) to a temperature T higher than the ambient temperature r Duration Δt r The step is performed after the step of preparing the sensitive material (15), -Temperature T r and duration Δt r The first compound is amorphous and has an intrinsic resistivity value of 1 Ω.cm to 30 Ω.cm at ambient temperature, and is r Duration Δt r After the step of: the resistivity of the first compound at ambient temperature is less than or equal to 10% of its intrinsic value; o The method further comprises the following steps: = Determine a non-zero so-called effective amount of an additional chemical element added to said first compound, thereby forming a modified compound, starting from which, after exposure to a temperature T r Duration Δt r After the step, the resistivity of the modified compound at ambient temperature is a|r Greater than its intrinsic value ρ a 10%; In said step of preparing the sensitive material (15) in a thin layer, the thin layer is formed of said modified compound having an amount of the additional chemical element greater than or equal to a predetermined effective amount, the sensitive material (15) is amorphous and has an intrinsic resistivity value ρ of 0.1 Ω.cm to 30 Ω.cm at ambient temperature a , and uniform chemical composition; Thus, when the sensitive material (15) is exposed to a temperature T r Duration Δt r After said steps, said sensitive material (15) then has noise whose degradation is limited.

2. The manufacturing method according to claim 1, wherein the additional chemical element is selected from arsenic, germanium and silicon. The manufacturing method according to claim 1 , wherein the additional chemical element is arsenic.

4. The manufacturing method according to claim 1, wherein the step of exposing the sensitive material (15) comprises the step of depositing a protective layer (22) covering the sensitive material.

5. Manufacturing method according to claim 1, wherein the step of exposing the sensitive material (15) comprises a step of depositing an encapsulation layer transparent to the electromagnetic radiation to be detected and intended to define a cavity in which the microbolometer is located.

6. The manufacturing method according to claim 1, wherein the temperature T r Greater than or equal to 330°C or even equal to 350°C, with a deviation within the range of ±5°C.

7. The manufacturing method according to claim 1, wherein the duration Δt r Greater than or equal to 90 minutes.

8. The manufacturing method according to claim 1, wherein the sensitive material (15) is heated to a temperature less than T r prepared at a temperature of .

9. A micro-bolometer (10) comprising a sensitive material (15) formed of: a vanadium oxide (VO x ) of the first compound; and at least one additional chemical element selected from arsenic, germanium, silicon and phosphorus and excluding nitrogen, wherein the sensitive material (15): o is amorphous, oResistivity at ambient temperature is 0.1Ω.cm to 30Ω.cm, o have a uniform chemical composition, and o contains an amount of an additional chemical element, the ratio of the number of atoms of the additional chemical element to the number of atoms of vanadium being at least 0.012 when the additional chemical element is arsenic, at least 0.04 when the additional chemical element is germanium and silicon, and at least 0.12 when the additional chemical element is phosphorus.

10. The microbolometer (10) according to claim 9, wherein the oxygen content defined as the ratio of the number of oxygen atoms to the number of vanadium atoms is 1.42 to 1.94 with a deviation within the range of plus or minus 0.

05.

11. The microbolometer (10) according to claim 9, wherein the sensitive material (15) is covered by a protective layer (22) of silicon nitride.

12. A device (1) for detecting electromagnetic radiation, comprising an array of micro-bolometers according to claim 9, wherein the micro-bolometers (10) are arranged in at least one airtight cavity defined by a packaging structure that is transparent to the electromagnetic radiation to be detected, the packaging structure comprising at least one layer made of amorphous silicon.

13. The detection device (1) according to claim 12, comprising a getter material located in the airtight cavity.

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