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    • 专利摘要:
    A bolometric detection device comprises: - a substrate (14) comprising a read circuit; a matrix of elementary detectors each comprising a membrane (12) suspended above the substrate (14) and connected to the reading circuit by at least two electrical conductors (16, 18), said membrane comprising two electrically conductive electrodes (20, 22) respectively connected to the two electrical conductors, and a volume of transducer material (24) electrically connecting the two electrodes, wherein the reading circuit is configured to apply an electrical stimulus between the two electrodes (20, 22) of the membrane ( 12) and for forming an electric signal in response to said application. Said volume comprises: a volume (34, 38, 40) of a first transducer material electrically connecting the two electrodes (20, 22) of the membrane (12) and forming walls of a closed chamber (42) in which each of the electrodes (20, 22) is housed at least partially; and a volume (44) of a second transducer material electrically connecting the two electrodes (20, 22) and housed in the enclosure (42), the electrical resistivity of the second material being less than the electrical resistivity of the first material; and the two transducer materials having a negative thermal resistivity coefficient TCR.
    公开号:FR3045148A1
    申请号:FR1562347
    申请日:2015-12-15
    公开日:2017-06-16
    发明作者:Sebastien Cortial；Michel Vilain
    申请人:Ulis SAS；
    IPC主号:
    专利说明:

    Detection device with bolometric diaphragms suspended
    ABSORPTION EFFICIENCY AND SIGNAL TO NOISE RATIO
    FIELD OF THE INVENTION The invention relates to the field of electromagnetic radiation detectors, in particular micro-bolometer detectors intended for the detection of radiation, typically in the "thermal", ie infrared, domain.
    State of the art
    Infrared radiation detectors ("IR") are typically manufactured in the form of two-dimensional (eg matrix) juxtaposition of a set of elementary microdetectors disposed on the surface of a support substrate, each micro-detector being intended to form a point of image. Each micro-detector comprises a membrane suspended above the substrate and electrically connected thereto by means of long narrow beams (or "arms") embedded on electrically conductive pillars. The assembly is placed in a hermetic enclosure, for example a very low pressure housing, so as to eliminate the thermal conductance of the surrounding gas.
    Each membrane heats up by absorbing the incident radiation from the thermal scene observed, transmitted and focused by a suitable optics at the focal plane on which the membranes are arranged. This membrane comprises in particular a layer of a "transducer" material whose electrical property, the resistivity in the case of micro-bolometers, changes strongly when the temperature changes, generating for example a variation of current under constant voltage polarization, it is that is, an electrical signal proportional to the incident radiation flux.
    Conventional manufacturing methods for such detectors comprise steps performed directly on the surface of a substrate comprising a plurality of electronic circuits or "reading circuits" or "ROIC" in English terminology (acronym for "Read Out Integrated"). Circuit "), so called" monolithic ". This term refers to a continuous sequence of operations on the same substrate, following the manufacturing process of the integrated circuit, usually silicon. The steps for manufacturing the bolometric micro-detectors are generally analogous to the usual techniques of collective fabrication of the microelectronics industry, usually concerning a few tens to a few hundred matrix detectors arranged on the same substrate.
    During these manufacturing steps, the members implementing the bolometric functions of optical absorption, optical-thermal transduction and thermal resistance, are formed on the surface of a so-called "sacrificial" layer, in that this layer, simply intended to form a construction base, is removed at the end of the process by a suitable method that does not attack the other components of the detector, and in particular the members formed thereon. Typically, a layer of polyimide is used which is ultimately removed by combustion in an oxygen plasma. Alternatively, the sacrificial layer is a silicon oxide layer (generically referred to as "SiO") finally removed by hydrofluoric vapor phase etching (HFv). Following the elimination of the sacrificial layer, the bolometric membranes remain suspended above the substrate, with no other contact or attachment than their support arms embedded in the pillars.
    The most common method of manufacturing suspended membranes is "above IC" or "MEMS-on-top". According to this method, the micro-detectors are constructed directly on the surface of the substrate comprising the reading circuits, by means of specific methods. In particular, the sacrificial layer is of organic nature - in general polyimide - and the transducer material is most often a semiconductor oxide (VOx, NiOx) or amorphous silicon (a-Si). Traditionally, for the usual "far-infrared" (LWIR) detection, a quarter-wave plate is also formed between the absorbent membrane and a reflector disposed on the surface of the substrate, so as to form a maximum absorption of the detector. in the vicinity of 10 micrometers. Thus, in order to connect and maintain the remote membrane adapted to the reflector, to form said quarter-wave plate in the vacuum, electric pillars with a high aspect ratio, usually rather complex and of non-negligible size must be realized through a thick temporary (sacrificial) layer of polyimide of the order of 2 to 2.5 micrometers.
    The dielectric or resistive layers which constitute the "skeleton" of the membrane, are for their part conventionally made of silicon oxide (SiO) or silicon nitride (generically denoted SiN), or else directly of semiconductor amorphous silicon according to, for example US Pat. No. 5,912,464. These materials can be deposited at relatively low temperature and are inert with respect to the method of removing the organic sacrificial layer under oxygenated plasma. This manufacturing process "above IC" typically consists of a dozen "levels" photo-lithographic, that is to say, in a relatively complex and expensive process.
    More recently, it has been proposed a new type of membrane manufacturing which consists of integrating micro-bolometers in the so-called back-end layers (or "BEOL" acronym for "Back End OfLine"). way of organs performing MEMS functions in general. This acronym refers to the manufacturing steps of Γ set of relatively low temperature metal interconnects, characteristics of the end of standard microelectronic manufacturing processes. The purpose of this so-called "MEMS-in-CMOS" approach is to exploit some of the industrially mature features of BEOL to integrate some of the micro-bolometer components. In particular, the metallized vias vertically interconnecting between successive BEOL metal levels, obtained for example by the "damascene" method advantageously constitute the pillars of the micro-detectors. Furthermore, the "IMD" (acronym for "Inter-Metal-Dielectrics"), in particular SiO, a standard microelectronic material, can advantageously be used as sacrificial layers for the construction of membrane structures. In this type of integration, the last photolithographic levels for the fabrication of the reading circuit are also used to directly make the pillars supporting the membranes. It is therefore saved some lithographic levels among the series of levels necessary for the manufacture of micro bolometers, resulting in a significant saving on manufacturing costs. However, the elimination of the SiO sacrificial layer of the "MEMS-in-CMOS" production is in this case only feasible by means of hydrofluoric acid in the vapor phase (HFv). Consequently, all the materials constituting the micro bolometers must imperatively be inert vis-à-vis this chemically very aggressive process.
    Such a "MEMS-in-CMOS" approach, applied to the case of micro bolometers, has been described in document US 2014/319350 which details the integration in the CMOS stack of an SiO sacrificial layer and of a barrier layer. to contain the HFv etching, as well as the realization of the "pillars" of the micro bolometers by exploiting the latest standard inter-level metal (vias metallized) connection structure of the CMOS assembly. This document describes more particularly a construction of micro bolometers based on amorphous silicon which exploits the teaching of US 5 912 464 with regard to the architecture of the membrane. It is thus obtained a structure compatible with the HFv etching and performed using only five photolithographic levels, which brings a very significant gain compared to the much more complex process of the state of the art.
    Although the "MEMS-in-CMOS" technique simplifies manufacturing, it nevertheless suffers from several limitations that penalize the performance of the micro-bolometers thus constructed.
    In particular, the architecture proposed according to this technique requires a sharing of the available space between metallized zones intended in particular to absorb the incident radiation, and areas occupied solely by the transducer material (amorphous silicon). The fraction of the surface occupied by the metal conditions the optical-thermal transduction function (the optical absorption efficiency ε of the membrane), while the remaining surface fraction is devoted to the thermal-electrical transduction function in the material. transducer. This limitation of the volume of material involved in the electrical conduction (relative to the total volume of amorphous silicon present in the structure) results in a reduction in the number of N charge carriers involved in the conduction. This necessarily results in a substantial increase in low-frequency noise ("Bl / f") in accordance with Hooge's relationship, which penalizes the signal / noise ratio ("SNR") of the detector.
    To better understand this problem, reference is made to FIGS. 1 to 3, illustrating an elementary resistive bolometric microdetector 10 (or "micro bolometer") of the state of the art for infrared detection. The bolometer 10 comprises a thin membrane 12 absorbing the incident radiation, suspended above a support substrate 14 by means of two conductive anchoring pillars 16 to which it is fixed by two holding arms and thermal insulation 18. In the example illustrated, the membrane 12 comprises two metal elements 20, 22 having an IR radiation absorber function and polarization electrodes, and an amorphous silicon layer 24 covering each of the two electrodes 12, 14 and filling the space 18 separating them. The layer 24 has a function of warming transduction caused by the absorption of the radiation by the electrodes 20, 22 in a variation of electrical resistance. In this structure, the transducer material therefore consists solely of amorphous silicon, which has the advantage of being inert to the process of releasing the sacrificial layer based on hydrofluoric acid in the vapor phase.
    The response R (V / K) of a constant-voltage biased constant voltage electric resistance micrometer Vpol expresses the output signal variation δ S in relation to a variation of the scene temperature d0sc according to the general relationship: • A is the total area of the sensitive elementary point (detector pixel), • ε is the overall optical absorption efficiency of the bolometer, • TCR is the coefficient of variation of the resistance of the bolometer as a function of the temperature of the membrane, • Rth is the thermal resistance between the membrane and the substrate (i.e. holding arms), and • 0 (6SC) is the radiative flux emitted by the scene at the temperature 6SC.
    As mentioned above, the optical absorption efficiency ε is related to the fraction of the surface of each membrane, occupied by the metal deposited for this purpose.
    The electrical resistance of a micro-detector Rb is expressed as a function of the resistivity p of the transducer material, for example according to the relation:
    (2) where L, W e te are respectively the length, the width and the thickness of the volume of transducer material (assumed, or reduced to a parallelepipedal shape) traversed by the electric current.
    In the membrane example of FIG. 1, these dimensions are substantially those of the zone separating the electrodes 20, 22, corresponding for example to a physical interruption (or groove) made in an initially continuous layer of metal to produce the electrodes ( who are in this typical example qualified as "coplanar" because arranged at the same level).
    The combination of relations (1) and (2) thus makes it possible to specify the response of a microdetector as a function of the dimensional parameters of the resistance Rb involved.
    The current noise power of a resistor biased under a voltage Vpol is expressed by the quadratic sum of the low-frequency noise called "in 1 / f" (hi / d) and a component independent of the frequency called "noise White " (/**). The ultimate noise related to thermal fluctuations can be overlooked in front of these first-rate contributors.
    The power of noise hi / f varies for its part according to the reciprocal of the number N of charge carriers contained in the volume concerned by the current lines, according to the Hooge relation: where aH is the "Hooge parameter" and " BPCL "is the frequency bandwidth of the read circuit. Each material is characterized by a reference ratio - -, in which n is the volume density of charge carriers; this ratio also depends on the temperature. Thus, for a resistance Rb of known dimensions, the real ratio of the element considered is calculated simply from the dimensional parameters W, L, e according to the relation:
    (4)
    The white noise power hb2 depends only on the temperature and the resistance of the element considered according to the relation:
    (5) where k denotes the Boltzmann constant and Tria temperature.
    A micro-detector having a portion of transducer material characterized by its ratio and its resistance Rb, defined from the known dimensions W, L and e, thus has a total noise h which is expressed according to the relation:
    (6)
    The signal-to-noise ratio of the micro-detector (SNR) is calculated by the ratio of the response (1) to the noise (6) taking into account the elements defined by the reading circuit (Vpol, BPCL) and the dimensional parameters. the resistance of each micro-detector (W, L, e) which makes it possible to express the bolometric resistance Rb and the number of charge carriers N. The SNR ratio is thus expressed according to the relation:
    (7)
    In order to exemplify in a simplified, but representative way, a pixel of very small dimensions such as it is useful today, or even necessary to propose industrially, consider the case of an elementary bolometric detector whose surface is 12 x 12pm2 .
    To define the sharing of this available surface between a metallized fraction 20, 22 necessary for the absorption of thermal radiation, and an electrically active fraction 26 intended for thermal-electrical transduction, it is convenient to define a length groove (electrical) Z engraved in a metal layer over the entire width (electric) W = 12pm of this element. The area ratio occupied by the metal is then equal to (12-Z) / 12, while the lengths and width of the resistance are respectively Z and W = 12 μm. Equations (2), (4) and (7) lead to the bolometric resistance (Rb), the ratio and finally to the SNR according to the size of design L.
    Thus, by neglecting to simplify the spaces consumed to form the adjacent inter-diaphragm separations and the substructures such as pillars, holding arms, and other various necessary spaces, it is considered in the following as shown schematically in FIG. 12 * 12 pm 2 area comprising two metallized rectangular portions separated by a groove of length L, which is also the length of an amorphous silicon transducer volume of width W = 12 μm, with a typical resistivity of 100 ccm, of typical thickness e = 200 nm, and ratio ^ = 6.7E-28 m3, the resistance Rb and the SNR show an evolution as a function of the distance L illustrated in FIG.
    In order to produce an optimum optical absorption efficiency ε, it is necessary to set the length of the non-metallized zones to values of at most about 2-3pm. This spacing (length L) is moreover necessary to maintain the resistance Rb of the elementary bolometer in a range of values compatible with an adequate implementation of the reading circuit in the context of the invention, in terms of polarization Vpol, of time. reading integration, and useful dynamics (without saturation) of the output amplifier. This condition is satisfied typically when the bolometric resistance Rb is of the order of, or less than, about 1 MOhm. For further clarification in connection with these elements, we will see for example "Uncooled amorphous Silicone technology enhancement for 25μτη pixel pitch achievement"; E. Mottin et al, Infrared Technology and Application XXVIII, SPIE, vol. 4820E.
    Thus, with a length Z fixed at 2pm to guarantee a state-of-the-art absorption efficiency and acceptable resistance, the SNR of this amorphous silicon-based micro-detector will be limited to about 60% of its value. maximum corresponding to long Z lengths (excluding absorption losses). This limitation is related to the increase in low frequency noise at low values of Z. Obtaining an acceptable compromise between the absorption efficiency and the SNR is therefore difficult, if not impossible, for small-sized sensitive pixels made according to this simplified assembly, particularly for steps less than 20pm. The use of low-noise low-noise transducer materials, such as semiconducting metal oxides (VOx, TiOx, NiOx, for example - the generic name "MOx" will be used later), would in principle make it possible to postpone this limitation. . However, the implementation of these materials in the stack of the state of the art is not possible because these materials would be quickly eliminated or at least greatly degraded under the effect of very aggressive release chemistry HFv.
    There is therefore a need, at least in the context of micro-bolometric assemblies partially integrated into a CMOS die, that is to say whose sacrificial material is made of SiO or any other related material conventional in microelectronics, to have High performance devices and their manufacturing methods compatible with the retina design of very small pitch, typically below 20pm.
    The purpose of the invention is thus to propose a detector with suspended bolometric membranes, whose architecture allows a high performance in terms of absorption efficiency and SNR, and whose architecture can be, at need, manufactured using a technology requiring the use of a very aggressive sacrificial layer release chemistry. For this purpose, the subject of the invention is a bolometric detection device comprising: a substrate comprising a read circuit; a matrix of elementary detectors each comprising a membrane suspended above the substrate and connected to the reading circuit by at least two electrical conductors, said membrane comprising two electrically conductive electrodes respectively connected to the two electrical conductors, and a volume of transducer material connecting electrically the two electrodes, wherein the readout circuit is configured to apply an electrical stimulus between the two membrane electrodes and to form an electrical signal in response to said application,
    According to the invention, said volume comprises: a volume of a first transducer material electrically connecting the two electrodes of the membrane and forming walls of a closed chamber in which each of the electrodes is housed at least partially; and a volume of a second transducer material, electrically connecting the two electrodes and housed in the enclosure, the electrical resistivity of the second material being less than the electrical resistivity of the first material.
    By "transducer" is meant a material whose resistivity is between 0.1 and 104 Ohm.cm and having a negative thermal coefficient of resistance TCR. The invention also relates to a method of manufacturing a bolometric detection device, comprising: manufacturing a substrate comprising a read circuit; depositing on the substrate a sacrificial layer; the manufacture, on the sacrificial layer, of a matrix of membranes, each connected to the reading circuit by at least two electrical conductors, said membrane comprising two electrically conductive electrodes respectively connected to the two electrical conductors, and a volume of transducer material electrically connecting the two electrodes; once the membranes have been made, the removal of the sacrificial layer.
    According to the invention, the manufacture of the transducer volume comprises: depositing a lower layer of a first transducer material on the sacrificial layer; forming, on said layer of the first material, the two electrodes of the membrane; depositing on and between the electrodes a layer of second transducer material; and encapsulating the second transducer material layer with an upper layer of the first material so as to also partially cover the two electrodes.
    In addition: the electrical resistivity of the second material is lower than the electrical resistivity of the first material; the first material is inert to the removal of the sacrificial layer.
    In other words, the transducer material is made of a "shell" and a "core" electrically in parallel with respect to the electrodes forming a radiation absorption member, with the core consisting of a material lower resistivity than the shell, especially at least 5 times lower, and typically 10 to 20 times lower.
    In particular, the shell is made of a resistivity material greater than 10 Ohm.cm.
    This type of architecture allows a reduced low frequency noise component (hi / j), essentially implemented by the core due to the resistivity of the core, while allowing through the shell a choice of suitable material according to the manufacturing technology, for example an inert shell with chemical etching release of the sacrificial layer as part of a MEMS-in-CMOS technology.
    According to one embodiment, the two electrodes are coplanar and separated only by a groove. Alternatively, the two electrodes belong to a series of at least three electrically conductive areas, coplanar, and separated from each other by parallel grooves disposed between the two electrodes.
    According to one embodiment, the membrane comprises a continuous layer of electrical insulation extending between the electrodes and partially covering each of them.
    According to one embodiment, the electrical resistivity of the second material is at least five times lower than the electrical resistivity of the first material, and preferably ten times to twenty times lower.
    According to one embodiment, the first material has an electrical resistivity greater than 10 Ohm.cm, and preferably a resistivity lower than 104 Ohm.cm.
    According to one embodiment, the first material is amorphous silicon, an amorphous silicon and germanium alloy of formula SixGe (I. x K or an amorphous silicon and carbon alloy of formula a-SixC (iX), and the second material is a metal oxide.
    According to one embodiment, the sacrificial layer is removed by hydrofluoric acid etching HFv, and in that the first material is amorphous silicon, an amorphous silicon and germanium alloy of formula a-SixGe (I.xh or an amorphous silicon and carbon alloy of formula a-SixC, i.xl.
    According to one embodiment, the two electrodes are formed by depositing a layer of electrically conductive material and making only a groove in said layer to the lower layer of first material.
    According to one embodiment, the two electrodes are formed by depositing a layer of electrically conductive material and producing at least two parallel grooves in said layer to the lower layer of first material.
    According to one embodiment, the method comprises, before deposition of the second transducer material, the deposition of an electrically insulating layer extending between the electrodes and partially covering each of them.
    BRIEF DESCRIPTION OF THE FIGURES The invention will be better understood on reading the description which follows, given solely by way of example, and carried out with the appended drawings, in which identical references designate identical or equivalent elements, and in which FIG. 1 is a schematic perspective view of a bolometric membrane of the state of the art suspended above a reading circuit; Figures 2 and 3 are schematic views from above and in section of the membrane of Figure 1; Figure 4 is a plot of signal-to-noise ratios as a function of the length of the inter-electrode gap of a membrane of Figure 1; Figures 5 and 6 are schematic views from above and in section of a bolometric membrane according to a first embodiment of the invention; FIG. 7 is a plot of the signal-to-noise ratios as a function of the length of the inter-electrode space of a membrane of FIG. 1 and of a membrane according to the first embodiment of the invention; FIG. 8 is a plot of signal-to-noise ratios as a function of the thickness of amorphous silicon in a membrane according to the invention; Figures 9 and 10 are schematic views from above and in section of a bolometric membrane according to a second embodiment of the invention; FIG. 11 is a plot of the signal-to-noise ratios as a function of the length of the inter-electrode space of a membrane of FIG. 1 and of a membrane according to the first and second embodiments of the invention. ; Figures 12 and 13 are schematic views from above and in section of a bolometric membrane according to a third embodiment of the invention; Figures 14 and 15 are schematic views from above and in section of a bolometric membrane according to a third embodiment of the invention; and Figures 16 and 17 are schematic sectional views illustrating a method of manufacturing a membrane according to the invention.
    Detailed description of the invention
    First embodiment
    Referring to FIGS. 5 and 6, a bolometric micro-detector membrane 30 according to the invention comprises: an encapsulation shell 32, advantageously made of amorphous silicon, comprising a lower or "basal" layer 34, and an upper cover 36 formed of an upper layer 38 and side walls 40, together defining an internal volume 42 of width W, of length Met of height e; two conductive electrodes 20, 22, for example metallic, resting on the lower layer 34 and covering all of the latter, except for an interruption (or groove) of length (electrical) L separating them physically. The upper cover 36 also rests on each of the electrodes 20, 22, thus defining a first conduction channel therebetween as well as a hermetic cavity with aggressive chemical processes for the internal volume 42; a core 44 completely filling the internal volume 42, and consequently resting on each of the electrodes 20, 22, and thus defining a second conduction channel between them, of width W and of thickness e, in parallel with the first channel of conduction. The core 44 is made of a material of lower resistivity than the material of the shell, at least 5 times smaller, and typically 10 to 20 times smaller. In particular, the core 44 is made of a metal oxide with negative TCR coefficient, for example VOx and / or TiOx and / or NiOx, defining a second conduction channel with a low low frequency noise coefficient.
    In this configuration, the current flows between the two metal poles 20, 22, in the W-width metal oxide and in the amorphous silicon over substantially the entire width of the pixel (e.g. 12pm). According to the example considered here, the two lower layers 34 and upper 38 amorphous silicon, are of equal thickness, or 20 nanometers. The width W and the thickness e of the MOx are adjustment variables of the resistance Rb of the pixel. They were fixed here at 6 μm and 40 nm, respectively, in order to obtain a resistance Rb close to 800 ΚΩ for Z = 2 μm.
    The two current contributions, circulating in the two transducer materials, are added for the calculation of the response R, and are quadratic for the estimation of the noise. It is thus obtained for the latter:
    (8)
    The SNR ratio can thus be calculated for the case of the pixel schematized in FIGS. 5 and 6, as a function of the length L of the conduction channel, for example in a simplified manner, assuming that the coefficient TCR is comparable for the two transducer materials.
    The graph of FIG. 7 shows that the insertion of a metal oxide transducer layer ten times less resistive than amorphous silicon and generating low frequency noise for the same resistor Rb makes it possible to largely compensate for the degradation of the SNR. caused by L reduction around 2 pm. It was admitted for the construction of all the graphs a ratio aH / N = 2.6 E-29 m3 for the second transducer material, a value considered representative of the known technique.
    Thus, the SNR obtained for /.=2pm in the configuration of the invention (2 arbitrary units, or "ua", approximately) is equivalent to the accessible value for /.=6pm consisting solely of an a-Si transducer of 200nm thick according to the assemblies described in US 5,912,464.
    The current flowing in the amorphous silicon, which represents 17% of the total current in this example, contributes to the response R thanks to its TCR equivalent to that of the MOx (relation 1), and only weighs marginally on the overall noise (relation 6 ). The extended exploitation of the indicated relations shows that the proportion of the current passing through the amorphous silicon path can vary - in relation with the thickness of the amorphous silicon - in a very wide range without this having a significant impact on the SNR , as shown in Figure 8.
    Second embodiment
    If in the embodiment just described, the introduction of the MOx transducer oxide has allowed a significant gain on the SNR, the low frequency noise //, / / still remains dominant at Z = 2pm, and continues therefore to limit the SNR of the micro-detector.
    In order to further reduce this dominant noise related to the low volume of material traversed by the current through the parameter N, according to a second embodiment, at least two parallel and identical interruptions or grooves, for example each of length Z, are defined. The effective length of the conduction channel thus becomes P * L, where P is the number of grooves. Thus, the volume of active material in the conduction is doubled for P = 2, while the metallized surface fraction corresponding to the electrodes, optically absorbing but which defines inoperative equipotential surfaces in terms of transduction, increases from 83% to 67%. The loss generated on the absorption ε can be evaluated on the order of 10 to 15%, which is lower than the surface loss, thanks to the narrowness of the grooves facing the wavelength of the radiation, or 1 Opm typically for detection in LWIR.
    By taking up the relations exposed for the membrane to a groove (FIGS. 5 and 6), the calculation of the SNR can be made for a sensitive membrane comprising two grooves, thus defining two electrodes 20, 22 interposing a metal zone 50 (FIG. and 10), considering that the effective length of the resistance is here equal to 2 * L. The physical magnitude L (eg of each groove) in this case can be scanned only up to 6 pm, beyond which the entire pixel would be de-metallized (with disappearance of the contacts and therefore of the bolometric resistance) . The stack of layers remains that of the previous example, that is to say two layers a-Si at 100Ω.cm (basal layer and encapsulation layer) of 20 nm each, a layer of MOx oxide at 10Ω.cm, and thickness 40 nm. Only the width W of the MOx channel has been enlarged in this case to 12 μm in order to maintain (with two grooves) a resistor Rb close to that of the pixel having only one groove with W = 6 μm.
    The graph in Figure 11 shows that with two grooves of width L = 2 pm, the SNR is almost doubled compared to the case with a single groove (3.8 vs 2.0 u.a.). This gain can be associated with the reduction of the low frequency noise resulting from the doubling of the volume of active material, and therefore of the number of N carriers involved.
    The degradation of the ε absorption related to the addition of a second groove, estimated at about 10%, is therefore largely overcompensated by the increase of the SNR.
    The third embodiment of the invention, illustrated in Figures 12 to 15, differs from the embodiments described above by the insertion of a layer of electrical insulation, for example dielectric. In particular, this layer 52 is inserted between the metal elements 20, 22 (FIGS. 12 and 13 corresponding to the first completed embodiment) or 20, 22, 50 (FIGS. 14 and 15 corresponding to the second embodiment) and the MOx transducer 44. , in all their common property, except in two strips 54, 56 parallel to the groove or grooves of length Z and located along and near two opposite edges of the membrane. Thus, the effective length Z ', that is to say the total electrical length of the path of the current lines between the two electrical terminals of the conduction channel in the second MOx transducer 44 can be increased in such a way that Z' " L, independently of the optical absorption ε. The consequent increase in the volume of MOx - and therefore the number of charge carriers A - has the effect of reducing the noise 1 / f generated in this layer.
    For example, considering a membrane as illustrated in FIGS. 12 and 13 with a single groove, fixing Z '= 8 μm and having a groove of length Z = 2 μm in the metal layer, in order to meet the criterion imposed in the Previous embodiments on the resistance Rb, the thickness of the MOx layer can be doubled in this case to compensate for the increase in the length Z 'of the conduction channel in this material. The transducer oxide layer at (for example) 10 Ω.cm will therefore be here of a thickness of 80 nm and defined over a width W = 12 μm, which leads to a resistance Rb close to 800 Κ.Ω comparable to previous modes.
    In the third embodiment, a first portion of the current traverses the silicon of the basal layer 34 over a length Z if the pixel has only one groove (case a / of FIGS. 12 and 13), or 2 * Z if two grooves (case b /) of FIGS. 14 and 15 have been positioned. Another portion of the current travels the upper encapsulation layer 36 over a longer length Z ', this other part of the current is thus proportionally smaller.
    Applying equations (1) to (8) on the different current contributions taking place in this embodiment, and using the parameters listed above (MOx 44 with W = 12 μm, e = 80 nm to Q. cm and aH / n = 2.6E-29m3, inserted between two a-Si layers of 20 nm thick each at 100Ω.cm), this results in an SNR estimate of the table below for the configurations a and b / with one and two grooves, respectively.
    The insertion of the layer 52 of electrical insulator, partially isolating the electrodes 20, 22 of the MOx transducer 44, makes it possible to achieve, with a single groove L = 2pm, the same value of SNR, ie 3.8. in the second embodiment (FIGS. 9 and 10), without the insulating layer 52, but with two grooves of length L = 2 μm, as can be seen in the curves of FIG. 11.
    If a second groove of length 2 μm is introduced into this type of membrane (FIGS. 14 and 15), the SNR reaches 5.8 ua. This gain is related to the reduction of the low frequency noise generated by the basal layer a-Si. 34, dominant in the case of a simple groove. This ultimate level of SNR is obtained in return, acceptable in most cases, the addition of an additional dielectric layer in the assembly, and a photo-lithographic additional level.
    It should be noted that this particular construction requires to have the boundaries of the dielectric layer at the periphery of the pixel, at any point within the boundaries of the basal layers and encapsulation, so as not to offer, where appropriate , from entry point to the HFv process for eliminating the sacrificial layer.
    It will also be noted that the limitation introduced previously at one or at most two grooves corresponds to the very particular and exemplary context of the fabrication of very small pixels (elementary detectors) of 12 x 12 pm 2 of footprint. If the technology allows it or for larger pixels, the equally advantageous implementation of the invention can call the definition of three or more grooves, according to the pitch of the pixel. Indeed, it is necessary to keep the W / L ratio approximately constant so as not to excessively modify the resistance Rb, and to maintain spaces (grooves) of limited width in order not to excessively deteriorate the optical absorption.
    Similarly, it is specified the implementation of amorphous silicon for the formation of the hermetic shell vis-à-vis the second transducer material. It should be pointed out that the same result will be obtained by means of alloys of silicon and germanium type a-SixGe, i-x, or amorphous alloys of silicon and carbon of type a-SixC (i.x).
    The range of resistivity to be considered as typical of the invention while providing substantially the advantages attached thus extends between 10 Ohm.cm and 104 Ohm.cm.
    MANUFACTURING PROCESS
    It will now be described a manufacturing method according to an embodiment of the invention, starting on the manufacturing steps of the CMOS substrate stack of the read circuit according to the teachings of US 2014/319350. The method according to the invention allows the manufacture of a bolometric detector using a limited number of photo-lithographic levels but compatible with the implementation of any type of transducer material, preferably essentially MOx.
    More particularly, the manufacturing method according to the invention is a membrane assembly technique compatible with a release of a sacrificial layer of the HFv type, combining the implementation of a second oxide-type low resistivity transducer material. metal, in conjunction with a first transducer material such as amorphous silicon or alloyed alloy, for fully protecting the metal oxide during the final etching of sacrificial dielectric material. It is thus obtained a construction capable of outperforming in terms of performance (Response / Noise ratio) the state of the art, in a cost-effective and compatible way of integration into the CMOS manufacturing flow of the support ROIC.
    Referring to FIGS. 16 and 17, the method according to the invention begins, for example, in a conventional manner by the construction of an electronic reading circuit in CMOS technology 60 comprising one or more levels 62 of interconnection 64 (part "Back End Of the CMOS circuit 60) connecting in particular functional blocks of the read circuit 60 to each other, and intended to form input / output connections of the reading circuit 60. The metallic continuity between the back-end layer of the circuit 60 and each bolometric membrane is also achieved by means of a metallized via 66 through a barrier layer 68, the mineral sacrificial layer (SiO) 70 and the basal layer 34 from the last metal of the CMOS to the metal layer 74 from which will be formed the electrodes 20, 22 of the membrane (Figure 16). The sequence of operations is essentially described for example in document US 2014/319350.
    The process continues with the construction of the membrane compatible with the HFv release process with integration of a second lower resistivity transducer material, without additional steps. Referring to Figure 16, the manufacture of the membrane comprises: etching the metal layer 74 to define one or more grooves 76 of length L over the entire width of the membrane and therefore also two metal electrodes 20, 22; the deposition of the second low-resistivity transducer material 44, for example and typically a vanadium oxide (of general formula VOx) or of nickel (of generic formula NiOx) or of titanium (of generic formula TiOx) directly on the metal of electrodes 20 , 22, so as to form the electrical resistance Rb in the plane of the semiconductor layers, delimited by the non-metallized spaces, the definition by means of a dry or wet etching of the extension in the plane of the layer 44 of the second transducer material, typically a simple rectangle, of smaller dimensions than the final contour of the membrane, that is to say at any point of its perimeter inscribed within this (future) contour, said transducer material 44, selectively on the underlying amorphous metal and silicon. depositing a second amorphous silicon encapsulation layer 36 preferably, but not necessarily, identical in resistivity and thickness to the basal layer 34; defining the contour of the membrane and the heat insulating arms and etching all the layers in place, that is to say the two layers a-Si 34, 36, and the metal of the electrodes 20, 22 The perimeter of this mask preferably does not intersect the pattern of the second transducer material 44 at any point, so as not to produce local exposure of the latter on the wafer (that is to say at least at certain points). the perimeter of the membrane) of the structure. Incidentally, this arrangement facilitates the definition of the etching process.
    According to this construction, which is comparable at the level of the support structures for the reference technique, the arms are formed solely of the two layers a-Si which sandwich the metal layer 74. The layers a-Si 34 and 36 are thus of thicknesses comparable and preferably identical, so as to avoid possible deformations related to differential internal stresses. The stack incorporating a layer of electrical insulation, for example dielectric, of the third embodiment is shown in Figure 17. It can be obtained from the manufacturing illustrated in the sectional figure 16 once the groove or grooves in the metal layer 74 produced, by the application of the following steps: the deposition of the dielectric layer 52 (eg of SiO, SiOxNy or equivalent), preferably using the BEOL standard materials and techniques of the CMOS die; the definition of the openings 54, 56 in the dielectric layer 52 for making electrical contacts opening onto the metal 74. These contacts are typically made along two opposite edges of the membrane, and define the two ends of the parallelepiped of main transducer material 44 , subsequently filed; the deposition of the second transducer material 44 with lower resistivity, for example and typically a vanadium oxide (of generic formula VOx) or of nickel (of generic formula NiOx) or of titanium (of generic formula TiOx). The main transducer 44 is then isolated outside the openings 54, 56 of the electrode metal, so as to form the least resistive parallel portion of the resistor Rb in the plane of the transducer layers, delimited by the contacts made before; the definition of the contour of the second transducer material, according to, for example, a simple rectangle, or more generally according to a simple polygon of smaller dimensions than the final end of the membrane, and dry or wet etching of said transducer, for example selective on the layer; dielectric 52. This etching may not be particularly selective on the dielectric layer 52, in which case it must be relative to the metal layer 74, which offers a wide latitude of definition to the skilled person; the etching of the dielectric 52 (if it remains at this stage according to the method implemented in the preceding step), for example and preferably (so as to advantageously use the same mask as the previous one) following the same contour as the second transducer material, by means of wet chemistry, or preferably dry, selective with respect to the underlying metal 74. This preferred arrangement is intended to remove the dielectric 52 from the surface of the arms of the membrane, so that only the two a-Si layers and the metallic material remain there. It is thus obtained a thermal resistance (e.g., a response) maximum of the suspended membrane; depositing a second layer 36 of amorphous silicon encapsulation preferentially (but not necessarily) equivalent in resistivity and thickness to the basal layer 34; defining the contour of the membrane and the heat insulating arms and etching all the layers in place, that is to say the two layers a-Si 34, 36, and the metal of the electrodes 20, 22 The perimeter of this mask preferably does not intersect at any point the pattern (the extension) of the second transducer material 44 or the intermediate dielectric 52, so as not to leave one or the other layer exposed locally on the wafer. the structure. Incidentally, this arrangement facilitates the definition of the etching process.
    Particular embodiments have been described in which the polarization function of the resistor Rb is implemented by two electrodes also implementing the absorption function.
    In a variant, the metal used for the electrodes and the metal used for the absorption can be formed from two distinct layers, in particular non-coplanar layers.
    In a variant, the metal used for the electrodes and the absorption layer can be implemented after the definition of the second transducer material, the polarization thereof (the electrical continuity) being obtained by the upper interface.
    The present invention is developed in the particular case specifically relevant for implementation as a first material, for the formation of the basal layer and the encapsulation layer, in other words of the hermetic shell, of amorphous silicon of resistivity of the order of 102 Ohm.cm. However, the use of amorphous materials alloyed with germanium of the type aS / xGe, i.xl, or with carbon of the type a-Six-C (iX), easily provides, according to doping and particular composition x, materials covering the range typically between 10 Ohm. cm and 101 Ohm.om (beyond which we can consider in this particular context said material as almost "dielectric"), without departing from the scope of the invention. Indeed, all these materials are inert vis-à-vis the methods of etching sacrificial layers SiO HFv form. 1
    权利要求:
    Claims (13)
    [1]
    A bolometric detection device comprising: - a substrate (14) comprising a read circuit; a matrix of elementary detectors each comprising a membrane (12) suspended above the substrate (14) and connected to the reading circuit by at least two electrical conductors (16, 18), said membrane comprising two electrically conductive electrodes (20, 22) respectively connected to the two electrical conductors, and a volume of transducer material (24) electrically connecting the two electrodes, wherein the reading circuit is configured to apply an electrical stimulus between the two electrodes (20, 22) of the membrane ( 12) and for forming an electrical signal in response to said application, characterized in that said volume comprises: a volume (34, 38, 40) of a first transducer material electrically connecting the two electrodes (20, 22) of the membrane (12) and forming walls of a closed chamber (42) in which each of the electrodes (20, 22) is housed at least partially; and a volume (44) of a second transducer material electrically connecting the two electrodes (20, 22) and housed in the enclosure (42), the electrical resistivity of the second material being less than the electrical resistivity of the first material; and in that the two transducer materials have a negative thermal resistivity coefficient TCR.
    [2]
    2. bolometric detection device according to claim 1, characterized in that the two electrodes (20, 22) are coplanar and separated only by a groove.
    [3]
    3. bolometric detection device according to claim 1, characterized in that the two electrodes (20, 22) belong to a series of at least three electrically conductive areas, coplanar, and separated from each other by parallel grooves arranged between the two electrodes. 1
    [5]
    5. bolometric detection device according to any one of the preceding claims, characterized in that the electrical resistivity of the second material is at least five times lower than the electrical resistivity of the first material, and preferably ten times to twenty times lower .
    [6]
    6. bolometric detection device according to any one of the preceding claims, characterized in that the first material has an electrical resistivity greater than 10 Ohm.cm, and preferably a resistivity lower than 101 Ohm.cm.
    [7]
    7. bolometric detection device according to any one of the preceding claims, characterized in that the first material is amorphous silicon, an amorphous silicon and germanium alloy of formula SixGe (I.xK or an amorphous silicon and carbon alloy of formula a-SixC (iX), and the second material is a metal oxide.
    [8]
    A method of manufacturing a bolometric detection device, comprising: manufacturing a substrate (60) comprising a read circuit; depositing on the substrate a sacrificial layer (70); manufacturing, on the sacrificial layer (70), a matrix of membranes (12), each connected to the reading circuit by at least two electrical conductors (66), said membrane comprising two electrically conductive electrodes (20, 22) respectively connected to the two electrical conductors, and a volume of transducer material electrically connecting the two electrodes; once the membranes are made, the removal of the sacrificial layer (70), characterized in that the manufacture of the transducer volume comprises: the deposition of a lower layer of a first transducer material (34) on the sacrificial layer (70); ); forming, on said layer of the first material, the two electrodes of the membrane (20, 22); depositing on and between the electrodes a second transducer layer (44); and encapsulating the second transducer material layer (44) with an upper layer of the first material (36) so as to also partially cover the two electrodes, and in that: the two transducer materials have a thermal resistivity coefficient TCR negative, and the electrical resistivity of the second material is less than the electrical resistivity of the first material; the first material is inert to the removal of the sacrificial layer.
    [9]
    9. A method of manufacturing a bolometric detection device according to claim 8, characterized in that the sacrificial layer is removed by an attack of hydrofluoric acid HFv, and in that the first material is amorphous silicon, an amorphous alloy. of silicon and germanium of formula a-SixGe (I.xh) or an amorphous silicon and carbon alloy of formula a-SixC, i.xl.
    [10]
    10. A method of manufacturing a bolometric detection device according to claim 8 or 9, characterized in that the two electrodes are formed by depositing a layer of electrically conductive material and making only a groove in said layer to the layer. lower first material.
    [11]
    11. A method of manufacturing a bolometric detection device according to claim 8 to 10, characterized in that the two electrodes are formed by depositing a layer of electrically conductive material and making at least two parallel grooves in said layer to the lower layer of first material.
    [12]
    12. A method of manufacturing a bolometric detection device according to one of claims 8 to 11, characterized in that the electrical resistivity of the second material is at least five times lower than the electrical resistivity of the first material, and preferably ten times to twenty times lower.
    [13]
    13. A method of manufacturing a bolometric detection device according to one of claims 8 to 12, characterized in that the first material has an electrical resistivity greater than 10 Omh.com, and preferably a resistivity less than 104 Ohm. cm.
    [14]
    14. A method of manufacturing a bolometric detection device according to one of claims 8 to 13, characterized in that it comprises, before deposition of the second transducer material, the deposition of an electrically insulating layer extending between them. electrodes and partially covering each of them. 1 bolometric detection device according to claim 1, 2 or 3, characterized in that the membrane comprises a continuous layer of electrical insulator (52) extending between the electrodes and partially covering each of them.
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    同族专利:
    公开号 | 公开日
    TW201728882A|2017-08-16|
    CN107063470A|2017-08-18|
    FR3045148B1|2017-12-08|
    EP3182081B1|2018-03-14|
    CN107063470B|2019-04-26|
    IL249208D0|2017-03-30|
    KR20170071415A|2017-06-23|
    EP3182081A1|2017-06-21|
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    IL249208A|2019-01-31|
    CA2949887A1|2017-06-15|
    US20170167922A1|2017-06-15|
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    法律状态:
    2016-12-23| PLFP| Fee payment|Year of fee payment: 2 |
    2017-06-16| PLSC| Publication of the preliminary search report|Effective date: 20170616 |
    2017-12-23| PLFP| Fee payment|Year of fee payment: 3 |
    2018-12-21| PLFP| Fee payment|Year of fee payment: 4 |
    2020-10-16| ST| Notification of lapse|Effective date: 20200910 |
    优先权:
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    FR1562347A|FR3045148B1|2015-12-15|2015-12-15|DETECTION DEVICE WITH SUSPENDED BOLOMETRIC MEMBRANES WITH HIGH ABSORPTION EFFICIENCY AND SIGNAL-TO-NOISE RATIO|FR1562347A| FR3045148B1|2015-12-15|2015-12-15|DETECTION DEVICE WITH SUSPENDED BOLOMETRIC MEMBRANES WITH HIGH ABSORPTION EFFICIENCY AND SIGNAL-TO-NOISE RATIO|
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