EP2671095A1 - Measurement of radiations of high fluence by a capacitive element of mos type - Google Patents

Measurement of radiations of high fluence by a capacitive element of mos type

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Publication number
EP2671095A1
EP2671095A1 EP12708560.3A EP12708560A EP2671095A1 EP 2671095 A1 EP2671095 A1 EP 2671095A1 EP 12708560 A EP12708560 A EP 12708560A EP 2671095 A1 EP2671095 A1 EP 2671095A1
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EP
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Prior art keywords
capacitive element
radiation
dose
capacitance
measurement
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EP12708560.3A
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German (de)
French (fr)
Inventor
Richard Arinero
Julien MEKKI
Antoine TOUBOUL
Frédéric SAIGNE
Jean-Roch VAILLE
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Universite Montpellier 2 Sciences et Techniques
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Universite Montpellier 2 Sciences et Techniques
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/02—Dosimeters
    • G01T1/026—Semiconductor dose-rate meters

Definitions

  • the invention relates to the dosimetry of particle radiation, and more particularly to the dosimetry of high-fluence non-ionizing radiation.
  • LHC Large Hadron Collider
  • CERN European Center for Nuclear Research
  • Ionizing radiation results in the creation and trapping of electrical charges (ions) in the materials of electronic components.
  • Single Event Effects SEE are characterized by local ionization caused by a single particle.
  • non-ionizing dose effects are related to atomic displacements in semiconductor materials, following collisions of particles with nuclei of the crystal lattice.
  • the radiation dose can be expressed as a fluence, i.e. a particle flux over a given period of time.
  • the fluence of a certain type of particles is converted into an equivalent fluence of neutrons with an energy of 1 MeV. This makes it possible to compare the damage caused by particles of different natures.
  • the equivalent fluence over a 10-year period varies between 10 9 and 10 15 n eq / cm 2 (neutrons at 1 MeV per cm 2 ).
  • Current dosimeters consist of silicon PIN diodes.
  • the PIN diode is polarized in direct mode after being exposed to radiation.
  • the PIN diode is sensitive to fluences ranging from 2.10 12 n eq / cm 2 to 4.10 14 n eq / cm 2 . However, it is possible to extend this fluence range up to 6.3 ⁇ 15 n eq / cm 2 , by injecting a current less than 1 mA, to the detriment of the detection sensitivity.
  • FIG. 1 represents a device for measuring a dose of non-ionizing radiation provided with a capacitive element
  • FIG. 2 is a graph of evolution of the capacitance C of the irradiated capacitive element as a function of the voltage V applied to its terminals, for several radiation levels ⁇ ⁇
  • FIG. 3 is an abacus linking the capacitance C to the equivalent fluence ⁇ ⁇
  • FIG. 4 is an abacus linking the parasitic resistance Rs of the substrate at the equivalent fluence ⁇ ⁇ .
  • the inventors have found that the capacity of a capacitive element in the accumulation regime varies according to the dose related to the non-ionizing effects of particle radiation.
  • the capacity evolves continuously and monotonously up to high fluences, of the order of 10 17 n eq / cm 2 . It is proposed here to implement this finding in order to achieve a performance non-ionizing radiation dosimeter.
  • FIG. 1 represents a non-ionizing radiation dosimeter provided with a capacitive element 2.
  • the capacitive element 2 comprises a metal or polysilicon electrode 4 (gate), a dielectric layer 6 (SiO 2 , Si 3 N 4 , HFO 2 , TaaOs ...) and an electrode 8 made of a semiconductor material, for example a silicon substrate.
  • the capacitive element is preferably a capacitor of the MOS type: metal / oxide / semiconductor.
  • the dosimeter further comprises an alternating voltage generator 10 connected across the terminals of the element 2, that is to say to the electrodes 4 and 8, and a measuring circuit 12 of the current I flowing through the element 2.
  • the circuit 12 is connected to a computer 14 which determines the capacity in the accumulation mode of the element 2 from the value of the current.
  • the computer 14 determines the dose of radiation eq corresponding to the capacitance value, for example using a table 16 or abacus.
  • the generator 10, the measurement circuit 12 and the computer 14 (the table 16 can be integrated in the computer 14) can form a single device, for example a semiconductor parameter analyzer.
  • the accumulation regime corresponds to a state of polarization of the capacitive element in which the majority charge carriers of the substrate (electrons in an n-type substrate and holes in a p-type substrate) are attracted to the dielectric / semiconductor interface.
  • a measurement of the capacity of the capacitive element in the accumulation mode is first made. This measurement can be performed during the irradiation or after the irradiation, for example by the acquisition of the C-V curves of the capacitive element.
  • the measurement of the capacitance can be carried out both at high frequency and at low frequency.
  • FIG. 2 represents an example of a reading of the capacitance C of a standard capacitive element as a function of the voltage V applied to its terminals, for different levels of radiation.
  • the dotted line curve represents the capacitance of the non-irradiated capacitive element.
  • the capacitive element is irradiated by a stream of protons charged at 1.8 MeV.
  • the proton fluence varies between 10 12 cm -2 and 5.10 13 cm -2 , which corresponds to an equivalent fluence of between 1.8 ⁇ 10 13 n eq / cm 2 and
  • the gate of the capacitive element is polysilicon, the dielectric layer of silicon dioxide is 7 nm thick and the silicon substrate is doped n-type. Its doping level is equal to 10 15 cm "2 -. The thickness of the substrate is 540 microns and the surface of the capacitive element is equal to 500x500 pm 2.
  • the substrate is grounded during exposure to radiation.
  • the capacitance C For each equivalent fluence ⁇ ⁇ , the capacitance C reaches a maximum value CM for positive V voltages.
  • these voltages correspond to an accumulation regime.
  • the value of the capacitance in the C M accumulation regime decreases as the fluence ⁇ ⁇ increases.
  • the inventors have calculated, for each fluence of protons, the equivalent dose of X-radiation.
  • X-radiation is exclusively ionizing. They then exposed a capacitive element (identical to that described above) to these doses of X-rays and found no change in the capacitance of the capacitive element.
  • CM capacity is related to a non-ionizing dose effect only.
  • non-ionizing radiation is characterized by a displacement of atoms in the substrate, which causes a decrease in the mobility of the charge carriers and their lifetime. This results in an increase in the resistivity of the substrate.
  • the capacity related to the substrate can be neglected.
  • the capacitive element can then be modeled as a Cox oxide capacitance and a substrate resistance Rs in series.
  • the Cox capacity varies depending on the nature and thickness of the oxide. In the example above, the theoretical value of the Cox capacitance is 1200 pF.
  • the current I passing through the capacitive element during the capacitance measurement C is given by the relation: jR s C 0X w AC ⁇ 1 >'with V A c the amplitude of the AC signal applied to the gate by the meter and ⁇ its angular frequency.
  • Figure 3 shows such an abacus.
  • the reading of the abacus makes it possible to determine the corresponding dose ⁇ ⁇ accumulated in the capacitive element.
  • the evolution of the capacitance CM of a capacitive element as a function of the non-ionizing radiation dose can be established for fluences of between 5.10 12 n eq / cm 2 and 10 16 n eq / cm 2 approximately.
  • the low and high limits of detection may vary depending on the nature and dimensions of the capacitive element, in particular as a function of its surface.
  • the capacitive element makes it possible to measure high levels of radiation, such as those encountered in nuclear power plants.
  • Figure 4 shows a second chart that can be used for reading the dose.
  • This abacus binds the series resistance Rs to the equivalent fluence (j) eq . It was obtained by calculating the value of the resistance Rs from the relation (3) and the capacitance values CM of FIG. 2. It is noted that the series resistance Rs varies linearly with the fluence from a detection threshold. This threshold is about 7.10 13 n eq / cm 2 in the example of FIG. 4.
  • the response of the capacitive element is generally linear, which facilitates the reading of the dosimeter and improves its reliability.
  • the capacitive element OS is a common component of microelectronics. The dosimeter is therefore easy to implement. Unlike the PIN diode, the MOS capacitive element allows to measure high fluences while maintaining a good sensitivity, about 20 ⁇ 10 9 cm 2 (fluence per unit of series resistance).
  • the dosimeter is not limited to a particular capacitive element structure.
  • the capacitive element may in particular be formed on semiconductor substrates of various types, for example germanium or silicon-germanium alloy, doped n-type or p-type.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)
  • Light Receiving Elements (AREA)

Abstract

A method for measuring a dose related to the non-ionizing effects of a radiation of particles comprises the irradiation of a capacitive element provided with an electrode made from a semiconductor material, the measurement of the capacitance of the capacitive element in an accumulation regime and the determination of the dose related to the non-ionizing effects from the measurement of capacitance of the capacitive element in the accumulation regime.

Description

MESURE DE RADIATIONS DE HAUTE FLUENCE  MEASUREMENT OF HIGH FLUENCE RADIATION
PAR UN ELEMENT CAPACITIF DE TYPE MOS  BY A CAPACITIVE ELEMENT OF MOS TYPE
Domaine technique de l'invention Technical field of the invention
L'invention est relative à la dosimétrie d'un rayonnement de particules, et plus particulièrement la dosimétrie d'un rayonnement non ionisant de haute fluence. The invention relates to the dosimetry of particle radiation, and more particularly to the dosimetry of high-fluence non-ionizing radiation.
État de la technique State of the art
En environnement spatial, les systèmes électroniques sont soumis à un rayonnement de particules constituées majoritairement de protons et d'électrons. Ce rayonnement entraîne une dégradation des performances des systèmes électroniques. Cette sensibilité aux radiations tend à s'accentuer avec la miniaturisation des composants électroniques. In the space environment, electronic systems are subjected to particle radiation consisting mainly of protons and electrons. This radiation causes degradation of the performance of electronic systems. This sensitivity to radiation tends to increase with the miniaturization of electronic components.
Certaines applications terrestres génèrent également un environnement radiatif contraignant pour les systèmes électroniques, comme au grand collisionneur de particules (« Large Hadron Collider », LHC) du centre européen de la recherche nucléaire (CERN). Some terrestrial applications also generate a constraining radiative environment for electronic systems, such as the Large Hadron Collider (LHC) of the European Center for Nuclear Research (CERN).
On distingue trois types de défaillance des composants électroniques en environnement radiatif : les effets de dose ionisante, les effets singuliers et les effets de dose non ionisante. There are three types of failure of electronic components in the radiative environment: ionizing dose effects, singular effects and non-ionizing dose effects.
Le rayonnement ionisant se traduit par la création et le piégeage de charges électriques (ions) dans les matériaux des composants électroniques. Les effets singuliers (« Single Event Effects », SEE) se caractérisent par une ionisation locale causée par une seule particule. Enfin, les effets de dose non ionisante sont liés à des déplacements d'atomes dans les matériaux semi-conducteurs, suite aux collisions des particules avec les noyaux du réseau cristallin. La dose de rayonnement peut être exprimée par une fluence, c'est-à-dire un flux de particules sur une période de temps donné. Par convention, on convertit la fluence d'un certain type de particules dans une fluence équivalente de neutrons ayant une énergie de 1 MeV. Cela permet de comparer les dégradations causées par des particules de natures différentes. Au LHC, la fluence équivalente sur une période de 10 ans varie entre 109 et 1015 neq/cm2 (neutrons à 1 MeV par cm2). Afin d'évaluer la dégradation des systèmes électroniques, on souhaite mesurer la dose de rayonnement accumulée dans les composants. Les dosimètres actuels sont constitués de diodes PIN en silicium. Ionizing radiation results in the creation and trapping of electrical charges (ions) in the materials of electronic components. Single Event Effects (SEE) are characterized by local ionization caused by a single particle. Finally, non-ionizing dose effects are related to atomic displacements in semiconductor materials, following collisions of particles with nuclei of the crystal lattice. The radiation dose can be expressed as a fluence, i.e. a particle flux over a given period of time. By convention, the fluence of a certain type of particles is converted into an equivalent fluence of neutrons with an energy of 1 MeV. This makes it possible to compare the damage caused by particles of different natures. At the LHC, the equivalent fluence over a 10-year period varies between 10 9 and 10 15 n eq / cm 2 (neutrons at 1 MeV per cm 2 ). In order to evaluate the degradation of electronic systems, it is desired to measure the amount of radiation accumulated in the components. Current dosimeters consist of silicon PIN diodes.
La diode PIN est polarisée en mode direct après avoir été exposée au rayonnement. On applique généralement une impulsion de courant, d'amplitude égale à 1 mA et de durée comprise entre 00 ms et 700 ms, puis on mesure la tension aux bornes de la diode. A l'aide d'abaques, on détermine la fluence équivalente à partir de la tension directe. The PIN diode is polarized in direct mode after being exposed to radiation. A pulse of current, of amplitude equal to 1 mA and of duration between 00 ms and 700 ms, is generally applied, then the voltage across the diode is measured. Using abacuses, the equivalent fluence is determined from the direct voltage.
La diode PIN est sensible aux fluences allant de 2.1012 neq/cm2 à 4.1014 neq/cm2. Il est toutefois possible d'étendre cette gamme de fluences jusqu'à 6,3.1015 neq/cm2, en injectant un courant inférieur à 1 mA, au détriment de la sensibilité de détection. The PIN diode is sensitive to fluences ranging from 2.10 12 n eq / cm 2 to 4.10 14 n eq / cm 2 . However, it is possible to extend this fluence range up to 6.3 × 15 n eq / cm 2 , by injecting a current less than 1 mA, to the detriment of the detection sensitivity.
Pour les expériences futures du LHC, on prévoit d'atteindre des fluences encore plus élevées, jusqu'à 1017 neq/cm2'. Ce niveau de radiation correspondrait à celui rencontré actuellement dans les centrales nucléaires. Pour de telles fluences, les dosimètres classiques ne sont plus adaptés. En effet, la réponse en tension des diodes PIN sature, ce qui rend impossible la lecture de la dose. For future LHC experiments, even higher fluences are expected, up to 10 17 n eq / cm 2 ' . This level of radiation would correspond to that currently encountered in nuclear power plants. For such fluences, conventional dosimeters are no longer suitable. Indeed, the voltage response of the PIN diodes saturates, which makes it impossible to read the dose.
Résumé de l'invention On constate qu'il existe un besoin de prévoir un procédé pour mesurer des niveaux de radiation élevés avec une bonne sensibilité. SUMMARY OF THE INVENTION It is found that there is a need to provide a method for measuring high radiation levels with good sensitivity.
On tend à satisfaire ce besoin en prévoyant l'irradiation d'un élément capacitif muni d'une électrode en matériau semi-conducteur, la mesure de la capacité de l'élément capacitif en régime d'accumulation et la détermination de la dose liée aux effets non-ionisants d'un rayonnement de particules à partir de la mesure de capacité de l'élément capacitif en régime d'accumulation. This need is satisfied by providing for the irradiation of a capacitive element provided with an electrode made of semiconductor material, the measurement of the capacity of the capacitive element in the accumulation regime and the determination of the dose related to non-ionizing effects of a particle radiation from the capacity measurement of the capacitive element in the accumulation regime.
Description sommaire des dessins Brief description of the drawings
D'autres avantages et caractéristiques ressortiront plus clairement de la description qui va suivre de modes particuliers de réalisation donnés à titre d'exemples non limitatifs et illustrés à l'aide des dessins annexés, dans lesquels : la figure 1 représente un dispositif de mesure d'une dose de rayonnement non ionisant muni d'un élément capacitif ; la figure 2 est un graphique d'évolution de la capacité C de l'élément capacitif irradié en fonction de la tension V appliquée à ses bornes, pour plusieurs niveaux de radiation Φβς ; la figure 3 est un abaque liant la capacité C à la fluence équivalente Φβς ; et la figure 4 est un abaque liant la résistance parasite Rs du substrat à la fluence équivalente Φβς . Description d'un mode de réalisation préféré de l'invention Other advantages and features will emerge more clearly from the following description of particular embodiments given as non-limiting examples and illustrated with the aid of the accompanying drawings, in which: FIG. 1 represents a device for measuring a dose of non-ionizing radiation provided with a capacitive element; FIG. 2 is a graph of evolution of the capacitance C of the irradiated capacitive element as a function of the voltage V applied to its terminals, for several radiation levels Φ βς ; FIG. 3 is an abacus linking the capacitance C to the equivalent fluence Φ βς ; and FIG. 4 is an abacus linking the parasitic resistance Rs of the substrate at the equivalent fluence Φ βς . Description of a preferred embodiment of the invention
Les inventeurs ont constaté que la capacité d'un élément capacitif en régime d'accumulation varie en fonction de la dose liée aux effets non-ionisants d'un rayonnement de particules. La capacité évolue de façon continue et monotone jusqu'à des fluences élevées, de l'ordre de 1017 neq/cm2. On propose ici de mettre en application ce constat afin de réaliser un dosimètre de rayonnement non ionisant performant. The inventors have found that the capacity of a capacitive element in the accumulation regime varies according to the dose related to the non-ionizing effects of particle radiation. The capacity evolves continuously and monotonously up to high fluences, of the order of 10 17 n eq / cm 2 . It is proposed here to implement this finding in order to achieve a performance non-ionizing radiation dosimeter.
La figure 1 représente un dosimètre de rayonnement non ionisant muni d'un élément capacitif 2. L'élément capacitif 2 comprend une électrode 4 (grille) en métal ou polysilicium, une couche diélectrique 6 (SiO2, Si3N4, HFO2, TaaOs...) et une électrode 8 en matériau semi-conducteur, par exemple un substrat en silicium. L'élément capacitif est, de préférence, un condensateur de type MOS : métal/oxyde/semi-conducteur. FIG. 1 represents a non-ionizing radiation dosimeter provided with a capacitive element 2. The capacitive element 2 comprises a metal or polysilicon electrode 4 (gate), a dielectric layer 6 (SiO 2 , Si 3 N 4 , HFO 2 , TaaOs ...) and an electrode 8 made of a semiconductor material, for example a silicon substrate. The capacitive element is preferably a capacitor of the MOS type: metal / oxide / semiconductor.
Le dosimètre comprend en outre un générateur de tension alternative 10 relié aux bornes de l'élément 2, c'est-à-dire aux électrodes 4 et 8, et un circuit de mesure 12 du courant I parcourant l'élément 2. Le circuit 12 est relié à un calculateur 14 qui détermine la capacité en régime d'accumulation de l'élément 2 à partir de la valeur du courant. Le calculateur 14 détermine ensuite la dose de rayonnement eq correspondant à la valeur de capacité, par exemple à l'aide d'une table 16 ou abaque. Le générateur 10, le circuit de mesure 12 et le calculateur 14 (la table 16 pouvant être intégrée au calculateur 14) peuvent former un seul appareil, par exemple un analyseur de paramètres semi-conducteurs. The dosimeter further comprises an alternating voltage generator 10 connected across the terminals of the element 2, that is to say to the electrodes 4 and 8, and a measuring circuit 12 of the current I flowing through the element 2. The circuit 12 is connected to a computer 14 which determines the capacity in the accumulation mode of the element 2 from the value of the current. The computer 14 then determines the dose of radiation eq corresponding to the capacitance value, for example using a table 16 or abacus. The generator 10, the measurement circuit 12 and the computer 14 (the table 16 can be integrated in the computer 14) can form a single device, for example a semiconductor parameter analyzer.
Par définition, le régime d'accumulation correspond à un état de polarisation de l'élément capacitif dans lequel les porteurs de charge majoritaires du substrat (électrons dans un substrat de type n et trous dans un substrat de type p) sont attirés à l'interface diélectrique/semi-conducteur. By definition, the accumulation regime corresponds to a state of polarization of the capacitive element in which the majority charge carriers of the substrate (electrons in an n-type substrate and holes in a p-type substrate) are attracted to the dielectric / semiconductor interface.
Pour déterminer la dose, on réalise dans un premier temps une mesure de la capacité de l'élément capacitif en régime d'accumulation. Cette mesure peut être réalisée pendant l'irradiation ou après l'irradiation, par exemple par l'acquisition des courbes C-V de l'élément capacitif. La mesure de la capacité peut être réalisée aussi bien à haute fréquence qu'à basse fréquence. In order to determine the dose, a measurement of the capacity of the capacitive element in the accumulation mode is first made. This measurement can be performed during the irradiation or after the irradiation, for example by the acquisition of the C-V curves of the capacitive element. The measurement of the capacitance can be carried out both at high frequency and at low frequency.
La figure 2 représente un exemple de relevé de la capacité C d'un élément capacitif étalon en fonction de la tension V appliquée à ses bornes, pour différents niveaux de radiation. La courbe en traits pointillés représente la capacité de l'élément capacitif non irradié. Les conditions opératoires sont les suivantes : FIG. 2 represents an example of a reading of the capacitance C of a standard capacitive element as a function of the voltage V applied to its terminals, for different levels of radiation. The dotted line curve represents the capacitance of the non-irradiated capacitive element. The operating conditions are as follows:
L'élément capacitif est irradié par un flux de protons chargés à 1 ,8 MeV. The capacitive element is irradiated by a stream of protons charged at 1.8 MeV.
La fluence protonique varie entre 1012 cm"2 et 5.1013 cm"2, ce qui correspond à une fluence équivalente comprise entre 1 ,8.1013 neq/cm2 etThe proton fluence varies between 10 12 cm -2 and 5.10 13 cm -2 , which corresponds to an equivalent fluence of between 1.8 × 10 13 n eq / cm 2 and
9.1014 neq/cm2 (facteur de conversion k de l'ordre 17,9). 9.10 14 n eq / cm 2 (conversion factor k of the order 17.9).
La grille de l'élément capacitif est en polysilicium, la couche diélectrique en dioxyde de silicium mesure 7 nm d'épaisseur et le substrat en silicium est dopé de type n. Son niveau de dopage est égal à 1015 cm"2. - L'épaisseur du substrat vaut 540 pm et la surface de l'élément capacitif est égale à 500x500 pm2. The gate of the capacitive element is polysilicon, the dielectric layer of silicon dioxide is 7 nm thick and the silicon substrate is doped n-type. Its doping level is equal to 10 15 cm "2 -. The thickness of the substrate is 540 microns and the surface of the capacitive element is equal to 500x500 pm 2.
Le substrat est relié à la masse pendant l'exposition aux radiations. The substrate is grounded during exposure to radiation.
Pour chaque fluence équivalente φβς, la capacité C atteint une valeur maximale CM pour des tensions V positives. Dans le cas d'un élément capacitif de type n, c'est-à-dire formé sur un substrat dopé de type n, ces tensions correspondent à un régime d'accumulation. Ainsi, on remarque que la valeur de la capacité en régime d'accumulation CM diminue lorsque la fluence φβς augmente. For each equivalent fluence φ βς , the capacitance C reaches a maximum value CM for positive V voltages. In the case of an n-type capacitive element, that is to say formed on an n-type doped substrate, these voltages correspond to an accumulation regime. Thus, it is noted that the value of the capacitance in the C M accumulation regime decreases as the fluence φ βς increases.
Afin d'expliquer ce phénomène, les inventeurs ont calculé, pour chaque fluence de protons, la dose équivalente de rayonnement X. Le rayonnement X est exclusivement ionisant. Ils ont ensuite exposé un élément capacitif (identique à celui décrit précédemment) à ces doses de rayons X et n'ont constaté aucune modification de la capacité de l'élément capacitif. In order to explain this phenomenon, the inventors have calculated, for each fluence of protons, the equivalent dose of X-radiation. X-radiation is exclusively ionizing. They then exposed a capacitive element (identical to that described above) to these doses of X-rays and found no change in the capacitance of the capacitive element.
Il semblerait donc que la diminution de la capacité CM soit liée à un effet de dose non ionisante uniquement. Or, un rayonnement non ionisant se caractérise par un déplacement d'atomes dans le substrat, ce qui provoque une diminution de la mobilité des porteurs de charge et de leur durée de vie. Il en résulte une augmentation de la résistivité du substrat. It would seem, therefore, that the decrease in CM capacity is related to a non-ionizing dose effect only. However, non-ionizing radiation is characterized by a displacement of atoms in the substrate, which causes a decrease in the mobility of the charge carriers and their lifetime. This results in an increase in the resistivity of the substrate.
Ainsi, la diminution de la capacité CM peut être attribuée à une résistance parasite du substrat qui augmente avec la dose de rayonnement. Le modèle ci- après, tiré de l'article [« Note on the analysis of C-V curves for high resistivity substrates », Estrada Del Cueto, Solid-State Electronics, 39(10), p.1519, 1996] permet d'obtenir la relation entre la capacité C mesurée par le dosimètre et cette résistance. Thus, the decrease in CM capacity can be attributed to a parasitic resistance of the substrate which increases with the radiation dose. The following model, taken from the article ["Note on the analysis of CV curves for high resistivity substrates", Estrada Del Cueto, Solid-State Electronics, 39 (10), p.1519, 1996] provides the relation between the capacitance C measured by the dosimeter and this resistance.
En régime d'accumulation, la capacité liée au substrat peut être négligée. L'élément capacitif peut alors être modélisé sous la forme d'une capacité d'oxyde Cox et d'une résistance du substrat Rs en série. La capacité Cox varie en fonction de la nature et de l'épaisseur de l'oxyde. Dans l'exemple ci-dessus, la valeur théorique de la capacité Cox est égale à 1200 pF. In the accumulation regime, the capacity related to the substrate can be neglected. The capacitive element can then be modeled as a Cox oxide capacitance and a substrate resistance Rs in series. The Cox capacity varies depending on the nature and thickness of the oxide. In the example above, the theoretical value of the Cox capacitance is 1200 pF.
Ce modèle a également été utilisé dans l'article [« High-energy proton irradiation effects on tunelling MOS capacitors », Fleta et al., Microelectronics Engineering, 72, pp.85-89, 2004]. L'auteur met en évidence l'apparition d'une résistance série lors de l'exposition d'une capacité MOS à un flux de protons. Toutefois, il attribue celle-ci à une dégradation du contact en face arrière du substrat, et non à une augmentation de la résistivité du substrat car la résistance série est indépendante de la surface de la capacité. This model has also been used in the article ["High-energy proton irradiation effects on tuning MOS capacitors", Fleta et al., Microelectronics Engineering, 72, pp.85-89, 2004]. The author highlights the emergence of serial resistance when exposing a MOS capacitance to a proton flux. However, it attributes this to a degradation of the contact on the rear face of the substrate, and not to an increase in the resistivity of the substrate because the series resistance is independent of the surface of the capacitance.
Avec ce modèle, le courant I traversant l'élément capacitif lors de la mesure de la capacité C est donné par la relation : jRsC0Xw AC <1>' avec VAc l'amplitude du signal alternatif appliqué sur la grille par l'appareil de mesure et ω sa fréquence angulaire. With this model, the current I passing through the capacitive element during the capacitance measurement C is given by the relation: jR s C 0X w AC < 1 >'with V A c the amplitude of the AC signal applied to the gate by the meter and ω its angular frequency.
La partie imaginaire du courant s'écrit alors : The imaginary part of the current is written then:
On en déduit la relation entre la capacité mesurée en régime d'accumulation C et la résistance série Rs : We deduce the relation between the capacitance measured in the accumulation regime C and the series resistance Rs:
A partir des courbes de la figure 2, il est possible d'établir un abaque liant la capacité C en régime d'accumulation à la dose de rayonnement non-ionisantFrom the curves of FIG. 2, it is possible to establish an abacus which binds the capacitance C in the accumulation mode to the dose of non-ionizing radiation.
<ï>eq. <Ï> eq.
La figure 3 représente un tel abaque. Après la mesure de la capacité CM, la lecture de l'abaque permet de déterminer la dose correspondante Φβς accumulée dans l'élément capacitif. L'évolution de la capacité CM d'un élément capacitif en fonction de la dose de radiation non ionisante peut être établie pour des fluences comprises entre 5.1012 neq/cm2 et 1016 neq/cm2 environ. Les limites basse et haute de détection peuvent varier en fonction de la nature et des dimensions de l'élément capacitif, notamment en fonction de sa surface. Ainsi, l'élément capacitif permet de mesurer des niveaux de radiation élevés, comme ceux rencontrés dans les centrales nucléaires. Figure 3 shows such an abacus. After the measurement of the capacitance CM, the reading of the abacus makes it possible to determine the corresponding dose Φ βς accumulated in the capacitive element. The evolution of the capacitance CM of a capacitive element as a function of the non-ionizing radiation dose can be established for fluences of between 5.10 12 n eq / cm 2 and 10 16 n eq / cm 2 approximately. The low and high limits of detection may vary depending on the nature and dimensions of the capacitive element, in particular as a function of its surface. Thus, the capacitive element makes it possible to measure high levels of radiation, such as those encountered in nuclear power plants.
La figure 4 représente un second abaque pouvant être utilisé pour la lecture de la dose. Cet abaque lie la résistance série Rs à la fluence équivalente (j)eq. Il a été obtenu en calculant la valeur de la résistance Rs à partir de la relation (3) et des valeurs de capacité CM de la figure 2. On remarque que la résistance série Rs varie linéairement avec la fluence à partir d'un seuil de détection. Ce seuil vaut environ 7.1013 neq/cm2 dans l'exemple de la figure 4. Figure 4 shows a second chart that can be used for reading the dose. This abacus binds the series resistance Rs to the equivalent fluence (j) eq . It was obtained by calculating the value of the resistance Rs from the relation (3) and the capacitance values CM of FIG. 2. It is noted that the series resistance Rs varies linearly with the fluence from a detection threshold. This threshold is about 7.10 13 n eq / cm 2 in the example of FIG. 4.
La réponse de l'élément capacitif est globalement linéaire, ce qui facilite la lecture du dosimètre et améliore sa fiabilité. L'élément capacitif OS est un composant usuel de la microélectronique. Le dosimètre est donc facile à mettre en œuvre. Contrairement à la diode PIN, l'élément capacitif MOS permet de mesurer des fluences élevées tout en conservant une bonne sensibilité, environ 20.109 cm'2.û (fluence par unité de résistance série). The response of the capacitive element is generally linear, which facilitates the reading of the dosimeter and improves its reliability. The capacitive element OS is a common component of microelectronics. The dosimeter is therefore easy to implement. Unlike the PIN diode, the MOS capacitive element allows to measure high fluences while maintaining a good sensitivity, about 20 × 10 9 cm 2 (fluence per unit of series resistance).
De nombreuses variantes et modifications du dosimètre apparaîtront à l'homme du métier. En effet, le dosimètre n'est pas limité à une structure particulière d'élément capacitif. L'élément capacitif pourra notamment être formé sur des substrats semi-conducteurs de natures variées, par exemple en germanium ou en alliage silicium-germanium, dopés de type n ou de type p. Many variations and modifications of the dosimeter will be apparent to those skilled in the art. Indeed, the dosimeter is not limited to a particular capacitive element structure. The capacitive element may in particular be formed on semiconductor substrates of various types, for example germanium or silicon-germanium alloy, doped n-type or p-type.

Claims

Revendications claims
1. Procédé de mesure d'une dose ( E>eq) liée aux effets non-ionisants d'un rayonnement de particules, caractérisé en ce qu'il comporte les étapes suivantes : irradier un élément capacitif (2) muni d'une électrode en matériau semi-conducteur ; mesurer la capacité (CM) de l'élément capacitif en régime d'accumulation ; et déterminer la dose (3 eq) liée aux effets non-ionisants à partir de la mesure de capacité de l'élément capacitif en régime d'accumulation. 1. A method for measuring a dose (E> eq ) related to the non-ionizing effects of a particle radiation, characterized in that it comprises the following steps: irradiating a capacitive element (2) provided with an electrode in semiconductor material; measuring the capacity (C M ) of the capacitive element in accumulation mode; and determining the dose (3 eq ) related to the non-ionizing effects from the capacity measurement of the capacitive element in the accumulation mode.
2. Procédé selon la revendication 1 , comprenant les étapes suivantes : construire initialement un abaque liant la capacité (CM) à la dose ( eq) liée aux effets non-ionisants, à l'aide d'un élément capacitif étalon soumis à différents niveaux de radiation ; lire l'abaque pour déterminer la dose (Φβς) liée aux effets non- ionisants. 2. Method according to claim 1, comprising the following steps: initially constructing a capacity-binding abacus (CM) at the dose ( eq ) related to the non-ionizing effects, using a standard capacitive element subjected to different levels radiation; read the chart to determine the dose (Φ βς ) related to non-ionizing effects.
EP12708560.3A 2011-02-01 2012-01-31 Measurement of radiations of high fluence by a capacitive element of mos type Withdrawn EP2671095A1 (en)

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PCT/FR2012/000040 WO2012104505A1 (en) 2011-02-01 2012-01-31 Measurement of radiations of high fluence by a capacitive element of mos type

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LI Z ET AL: "Studies of the dependence on oxidation thermal processes of effects on the electrical properties of silicon detectors by fast neutron radiation", PROCEEDINGS OF THE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE. SANTA FE, NOV. 2 - 9, 1991; [PROCEEDINGS OF THE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE], NEW YORK, IEEE, US, 2 November 1991 (1991-11-02), pages 239 - 245vol.1, XP032138381, ISBN: 978-0-7803-0513-7, DOI: 10.1109/NSSMIC.1991.258884 *
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