WO1992004736A1 - Front-illuminated infrared detector having a heavily doped substrate - Google Patents

Front-illuminated infrared detector having a heavily doped substrate Download PDF

Info

Publication number
WO1992004736A1
WO1992004736A1 PCT/FR1991/000712 FR9100712W WO9204736A1 WO 1992004736 A1 WO1992004736 A1 WO 1992004736A1 FR 9100712 W FR9100712 W FR 9100712W WO 9204736 A1 WO9204736 A1 WO 9204736A1
Authority
WO
WIPO (PCT)
Prior art keywords
substrate
detector
infrared
radiation
detector according
Prior art date
Application number
PCT/FR1991/000712
Other languages
French (fr)
Inventor
Pierre Dautriche
Original Assignee
Thomson Composants Militaires Et Spatiaux
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Composants Militaires Et Spatiaux filed Critical Thomson Composants Militaires Et Spatiaux
Publication of WO1992004736A1 publication Critical patent/WO1992004736A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14643—Photodiode arrays; MOS imagers
    • H01L27/14649—Infrared imagers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
    • H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier
    • H01L31/108—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier the potential barrier being of the Schottky type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
    • H01L2224/732—Location after the connecting process
    • H01L2224/73251—Location after the connecting process on different surfaces
    • H01L2224/73265—Layer and wire connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/11—Device type
    • H01L2924/12—Passive devices, e.g. 2 terminal devices
    • H01L2924/1203—Rectifying Diode
    • H01L2924/12032—Schottky diode

Definitions

  • the invention relates to infrared detectors, in particular matrix detectors for providing an image of an object emitting thermal radiation in the infrared.
  • arrays of schottky diodes with platinum silicide deposited on silicon are used. These diodes can absorb infrared rays of wavelength located in the band from 3 to 5 micrometers and provide an electrical signal depending on the intensity of the radiation received.
  • These matrices have the advantage of being able to be produced by technologies similar to those of silicon integrated circuits and therefore they allow a very high image resolution with a high density of integration.
  • the low quantum efficiency (number of electrons generated by photons passing through the diode) of these diodes is low and requires precautions to be taken if we want to obtain sufficient detection sensitivity.
  • the matrix detectors can be produced either in purely monolithic technology, in which one integrates on the same silicon substrate both a matrix of detection diodes and a multiplexer making it possible to transmit the charges generated by the illumination of each diode; manufacturing is then particularly advantageous for matrices with a large number of image points, but the sensitivity is lower since the surface of the pixels is limited by the need to reserve a place for an element of the multiplexer at each image point;
  • the detector is illuminated by the rear face of the substrate, that is to say the one which does not carry the detection diodes.
  • the front face is masked by the substrate carrying the multiplexer.
  • the high refractive index of platinum silicide (index n close to 5 around a wavelength of 4 micrometers) makes direct lighting undesirable without adaptation of index ; 50% of the incident radiation would be lost, by simple reflection on the platinum silicide: by illuminating from the rear face, it is easier to introduce the infrared radiation without losses: on the one hand the silicon substrate has an index of about 3 , and on the other hand, the rear face can be covered with a layer of silicon oxide (index 1.5) to further facilitate the introduction of the radiation.
  • an infrared detector is proposed, the photosensitive detection elements of which, consisting of Schottky diodes, are integrated into a semiconductor substrate, the rear face of which is very strongly doped to absorb most of the infrared radiation, the illumination of elements being provided by the front face.
  • the substrate is preferably a doped silicon substrate
  • the rear face of the substrate (that which does not carry the photosensitive elements) is preferably provided with a metallization to bring the substrate to a reference potential.
  • the metallization can be aluminum deposited by conventional evaporation under vacuum, or nn a "black" metal, that is to say deposited under conditions such that it is pulverulent and very absorbent for radiation which would not have has been fully absorbed by the heavily doped substrate.
  • the photosensitive elements are preferably covered not only with a passivation layer, but also with one or more adaptation layers of optical index (anti-reflective layers) making it possible to best avoid a reflection of the incident radiation on the elements.
  • photosensitive in the case of platinum silicide in particular. Strong IP index refraction of this material would lead, if direct lighting was carried out, to a reflection of 40% of the incident energy.
  • FIG. 1 schematically shows a matrix infrared detector illuminated by its rear face
  • FIG. 2 represents a modified detector according to the invention.
  • FIG. 3 shows the detector mounted on a ceramic substrate.
  • FIG. 1 which very schematically represents a conventional infrared detector (either monolithic or hybrid), 10 is designated a silicon substrate, on the front face of which are integrated detection diodes 12 made of platinum silicide. Most often a layer of silicon oxide 14 covers the rear face of the substrate to facilitate the introduction without reflection of the infrared radiation arriving from the rear face.
  • the platinum silicide diodes 12 are themselves covered by a sort of optical cavity constituted by a layer of silicon oxide 16 then a layer of aluminum 18 forming a mirror to reflect the radiation towards the rear. bright after it has passed through the diode; since the absorption in the diode is hardly more than 0.5%, it is in fact advantageous to pass the radiation twice through the diode by means of this mirror.
  • the radiation is reflected perpendicularly towards the rear and emerges from the substrate.
  • the substrate has for example a thickness of 500 micrometers and if a significant fraction of radiation is reflected for example with an incidence of approximately 30 ° compared to normal, a spurious image will be produced at approximately 500 micrometers away from the main image, that is to say at a distance of about twenty pixels for pixel dimensions of the order of 25 micrometers.
  • the semiconductor substrate is slightly P-type doped and constitutes the anode of the schottky diodes whose cathodes are made of platinum silicide.
  • it is proposed to very strongly dop the semiconductor substrate in its rear part, so that it becomes very absorbent for infrared wavelengths.
  • the front face, carrying the photosensitive elements remains slightly doped if the nature of the photosensitive elements requires it, which is the case for the diodes with platinum silicide. Illumination is then performed by the front face of the substrate.
  • FIG. 2 schematically represents the invention. As in Figure 1, the dimensional scales are not respected so that the general structure remains intelligible.
  • the semiconductor substrate can consist of a
  • the transition between the epitaxial layer and the substrate after the epitaxial growth phase is gradual, and this progressiveness makes it possible to avoid any reflection towards the front of radiation which would direct from the front facp towards the rear face of the substrate, than these radiation are perpendicular or oblique to the plane of the substrate.
  • the thickness of the epitaxial layer is of the order of 10 micrometers and the thickness of the substrate is of the order of a few hundred micrometers.
  • the substrate can also be produced from a lightly doped semiconductor wafer which is doped very strongly from the rear face. However, the heavily doped zone will then extend over a depth which can hardly exceed a few tens of micrometers, which is not necessarily sufficient to completely absorb infrared radiation, especially for long wavelengths.
  • the photosensitive elements are directly covered by a transparent passivation wheel 20 (silicon oxide and / or nitride) itself optionally covered with one or more adaptation layers of index 22, transparent in infrared and having an anti-reflection effect for incident radiation.
  • a transparent passivation wheel 20 silicon oxide and / or nitride
  • a conductive layer 24 (aluminum metallization in general) serving to uniformly bring the substrate (and therefore the epitaxial layer 11) to a reference potential.
  • this rear contact metallization is made of an electrically conductive material but not reflective for the infrared wavelengths considered. Black (powdered) aluminum may be suitable.
  • the silicon substrate thus produced carrying the photosensitive elements as well as the multiplexing circuitry necessary for transmitting and processing the electric charges generated by each photosensitive element, will generally be mounted on another substrate, preferably ceramic, intended to provide cooling. .
  • the ceramic substrate 30 conventionally carries electrical connections and connection pads allowing soldering by wires with connection pads carried by the silicon substrate 10. Therefore, the flip soldering technique is not used ("flip chip ”) used when the detector must be lit by the rear face, but we return to the older technique of connection by soldered wires (" ire-bonding ”) so that the detector can be lit by the front side of the substrate 10
  • the rear face of the silicon substrate is welded or bonded using a conductive adhesive on a conductive pad of the ceramic substrate.
  • infrared detectors the photosensitive elements of which are schottky diodes with platinum silicide on silicon. It will however be understood that it would be transposable to infrared detectors whose photosensitive elements are different, given that the problem does not come mainly from these diodes but rather from parasitic reflections under non-normal incidence.

Abstract

Infrared detectors, particularly matrix detectors comprising platinum silicide diodes as light-sensitive elements, are described. To prevent secondary images whenever a given point is intensely illuminated, said images appearing as spots away from said point, it is suggested that the light-sensitive elements be integrated with the front surface of a heavily doped semiconductor substrate (10) supporting said elements (12), and that said detector then be illuminated via said front surface of the substrate. This doping allows the absorption of the obliquely reflected stray radiation which causes the secondary images. The substrate preferably comprises a lightly doped epitaxial surface layer (11) on which said light-sensitive elements are formed.

Description

DETECTEUR INFRAROUGE A SUBSTRAT FORTEMENT DOPE ET ECLAIREMENT PAR T.A FACE AVANT INFRARED DETECTOR WITH HIGHLY DOPED SUBSTRATE AND FRONT LIGHT
L'invention concerne les détecteurs infrarouge, notamment les détecteurs matriciels permettant de fournir une image d'un objet émettant un rayonnement thermique dans l'infrarouge.The invention relates to infrared detectors, in particular matrix detectors for providing an image of an object emitting thermal radiation in the infrared.
Pour réaliser de tels détecteurs infrarouge, on utilise notamment des matrices de diodes schottky au siliciure de platine déposé sur silicium. Ces diodes peuvent absorber les rayons infrarouge de longueur d'onde située dans la bande de 3 à 5 micromètres et fournir un signal électrique fonction de l'intensité du rayonnement reçu.To produce such infrared detectors, arrays of schottky diodes with platinum silicide deposited on silicon are used. These diodes can absorb infrared rays of wavelength located in the band from 3 to 5 micrometers and provide an electrical signal depending on the intensity of the radiation received.
Ces matrices ont l'intérêt de pouvoir être réalisées par des technologies similaires à celles es circuits intégrés silicium et par conséquent elles permettent une très haute résolution d'image avec une grande densité d'intégration .These matrices have the advantage of being able to be produced by technologies similar to those of silicon integrated circuits and therefore they allow a very high image resolution with a high density of integration.
Mais le faible rendement quan tique (nombre d'électrons engendrés par photons traversant la diode) de ces diodes est faible et nécessite des précautions de réalisation si on veut obtenir une sensibilité de détection suffisante .However, the low quantum efficiency (number of electrons generated by photons passing through the diode) of these diodes is low and requires precautions to be taken if we want to obtain sufficient detection sensitivity.
Les détecteurs matriciels peuvent êtro réalisés soit en technologie purement monolithique, dans laquelle on intègre sur un même substrat de silicium à la fois une matrice de diodes de détection et un multiplexeur permettant de transmettre les charges engendrées par l'illumination de chaque diode; la fabrication est alors particulièrement avantageuse pour des matrices à grand nombre de points d'image, mais la sensibilité est plus faible puisque la surface des pixels est limitée par la nécessité de réserver une place pour un élément du multiplexeur à chaque point d'image ;The matrix detectors can be produced either in purely monolithic technology, in which one integrates on the same silicon substrate both a matrix of detection diodes and a multiplexer making it possible to transmit the charges generated by the illumination of each diode; manufacturing is then particularly advantageous for matrices with a large number of image points, but the sensitivity is lower since the surface of the pixels is limited by the need to reserve a place for an element of the multiplexer at each image point;
. soit en technologie hybride dans laquelle un premier substrat, portant une matrice de diodes , est collé sur un deuxième substrat portant un multiplexeur, chaque diode étant connectée directement à un élément p multiplexeur placé exactement en regard de la diode; le collage est difficile pour des matrices à grand nombre de points mais la sensibilité est meilleure puisque la surface utile de chaque diode de détection peut être plus grande.. either in hybrid technology in which a first substrate, carrying a matrix of diodes, is bonded to a second substrate carrying a multiplexer, each diode being connected directly to a multiplexer element p placed exactly opposite the diode; bonding is difficult for arrays with a large number of points but the sensitivity is better since the useful surface of each detection diode can be larger.
En principe le détecteur est illuminé par la face arrière du substrat, c'est-à-dire celle qui ne porte pas les diodes de détection. Dans le cas de la technologie hybride , la raison en est évidente :1a face avant est masquée par le substrat portant le multiplexeur. Dans le cas de la technologie monolithique c'est parce que l'indice de réfraction élevé du siliciure de platine (indice n voisin de 5 autour d'une longueur d'onde de 4 micromètres) rend peu souhaitable un éclairage direct sans adaptation d'indice ; on perdrait 50% du rayonnement incident, par simple réflexion sur le siliciure de platine : en éclairant par la face arrière, on peut plus facilement introduire le rayonnement infrarouge sans pertes : d'une part le substrat de silicium a un indice d'environ 3, et d'autre part on peut recouvrir la face arrière d'une couche d'oxyde de silicium (indice 1 , 5) pour faciliter encore l'introduction du rayonnement.In principle, the detector is illuminated by the rear face of the substrate, that is to say the one which does not carry the detection diodes. In the case of hybrid technology, the reason is obvious: the front face is masked by the substrate carrying the multiplexer. In the case of monolithic technology, this is because the high refractive index of platinum silicide (index n close to 5 around a wavelength of 4 micrometers) makes direct lighting undesirable without adaptation of index ; 50% of the incident radiation would be lost, by simple reflection on the platinum silicide: by illuminating from the rear face, it is easier to introduce the infrared radiation without losses: on the one hand the silicon substrate has an index of about 3 , and on the other hand, the rear face can be covered with a layer of silicon oxide (index 1.5) to further facilitate the introduction of the radiation.
Dans les matrices réalisées jusqu'à présent, on a remarqué que des images parasites se formaient parfois sur la matrice. Cela a été constaté en particulier lorsque l'image observée comporte des points fortement éclairés Tl apparaît alors des taches claires parasites autour de l'image du point fortement éclairé et à une certaine distance de celui-ci , à des endroits où l'image devrait normalement être sombro. Ces taches sont gênantes puisqu'elles font croire à la présence d'objets émettant fortement un rayonnement infrarouge à des endroits où il n'y a en fait pas de tels objets.In the matrices produced so far, it has been observed that parasitic images sometimes form on the matrix. This has been observed in particular when the observed image comprises highly illuminated points Tl then appears parasitic clear spots around the image of the highly illuminated point and at a certain distance from it, at places where the image should normally be sombro. These spots are annoying since they make believe in the presence of objects emitting strongly infrared radiation at places where there are in fact no such objects.
On a pensé d'abord que ce phénomène était dû à des diffractions de rayonnement : il ne faut pas oublier qu'on travaille à des longueurs d'onde qui sont p l'ordre de grandeur des dimensions des motifs intégrés dans la surface du substrat portant les diodes de détection. L'invention part de la remarque que ces images parasites seraient plutôt dues en fait à des réflexions . parasites des rayonnements infrarouge .We first thought that this phenomenon was due to radiation diffractions: we must not forget that we are working at wavelengths which are p the order of magnitude of the dimensions of the patterns integrated into the surface of the substrate. carrying the detection diodes. The invention starts from the remark that these parasitic images are rather due in fact to reflections. parasites from infrared radiation.
Selon l'invention , on propose un détecteur infrarouge dont les éléments de détection photosensibles , constitués par des diodes Schottky, sont intégrés dans un substrat semiconducteur dont la face arrière est très fortement dopée pour absorber la majeure partie du rayonnement infrarouge, l'éclairement des éléments étant assuré par la face avant .According to the invention, an infrared detector is proposed, the photosensitive detection elements of which, consisting of Schottky diodes, are integrated into a semiconductor substrate, the rear face of which is very strongly doped to absorb most of the infrared radiation, the illumination of elements being provided by the front face.
On pense en effet que le relief accidenté de la surface avant du substrat provoque des réflexions dans des directions non normales au plan du substrat, et qup IP rayonnement réfléchi sur la face arrière peut venir frapper des diodes éloignées de celle sur laquelle le rayonnement direct produit une image . Et on pense selon l'invention que ce dopage t rès fort du substrat permet d'éliminer les conséquences de ces réflexions en empêchant le retour vers les diodes d'un rayonnement réfléchi .It is indeed believed that the rugged relief of the front surface of the substrate causes reflections in directions not normal to the plane of the substrate, and that IP radiation reflected on the rear face can strike diodes distant from that on which the direct radiation produces a picture . And it is believed according to the invention that this very strong doping of the substrate makes it possible to eliminate the consequences of these reflections by preventing the return to the diodes of reflected radiation.
Le substrat est de préférence un substrat de silicium dopéThe substrate is preferably a doped silicon substrate
20 3 de type P++ (environ 10 atomes/cm ) sur lequel on a fait croître une couche épitaxiale faiblement dopée de type P (environ20 3 of P ++ type (approximately 10 atoms / cm) on which a lightly doped P-type epitaxial layer is grown (approximately
10 atomes/cm par exemple) .10 atoms / cm for example).
La face arrière du substrat (celle qui ne porte pas les éléments photosensibles) est de préférence pourvue d'une métallisation pour porter le substrat à un potentiel de référence . La métallisation peut être en aluminium déposé par évaporation classique sous vide , ou nn un métal "noir" , c'est-à-dire déposé dans des condit ions telles qu'il soit pulvérulent et très absorbant pour le rayonnement qui n'aurait pas été intégralement absorbé par le substrat fortement dopé .The rear face of the substrate (that which does not carry the photosensitive elements) is preferably provided with a metallization to bring the substrate to a reference potential. The metallization can be aluminum deposited by conventional evaporation under vacuum, or nn a "black" metal, that is to say deposited under conditions such that it is pulverulent and very absorbent for radiation which would not have has been fully absorbed by the heavily doped substrate.
Les éléments photosensibles sont de préférence recouverts non seulement d'une couche de passivation , mais aussi d'une ou plusieurs couches d'adaptation d'indice optique (couches antireflet) permettant d'éviter le mieux possible une réflexion du rayonnement incident sur les éléments photosensibles : dans le cas du siliciure de platine notamment . IP fort indice de réfraction de ce matériau conduirait, si on effectuait un éclairement direct, à une réflexion de 40% de l'énergie incidente .The photosensitive elements are preferably covered not only with a passivation layer, but also with one or more adaptation layers of optical index (anti-reflective layers) making it possible to best avoid a reflection of the incident radiation on the elements. photosensitive: in the case of platinum silicide in particular. Strong IP index refraction of this material would lead, if direct lighting was carried out, to a reflection of 40% of the incident energy.
D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture de la description détaillée qui suit et qui est faite en référence aux dessins annexés dans lesquels :Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:
- la figure 1 représente schématiquement un détecteur infrarouge matriciel éclairé par sa face arrière ; la figure 2 représente un détecteur modifié selon l'invention .- Figure 1 schematically shows a matrix infrared detector illuminated by its rear face; FIG. 2 represents a modified detector according to the invention.
- la figure 3 représente le détecteur monté sur un substrat de céramique.- Figure 3 shows the detector mounted on a ceramic substrate.
Sur la figure 1, qui représente très schématiquement un détecteur infrarouge (soit monolithique soit hybride) classique, on a désigné par 10 un substrat de silicium, sur la face avant duquel sont intégrées des diodes de détection 12 en siliciure de platine . Le plus souvent une couche d'oxyde de silicium 14 recouvre la face arrière du substrat pour faciliter l'introduction sans réflexion du rayonnement infrarouge arrivant par la face arrière.In FIG. 1, which very schematically represents a conventional infrared detector (either monolithic or hybrid), 10 is designated a silicon substrate, on the front face of which are integrated detection diodes 12 made of platinum silicide. Most often a layer of silicon oxide 14 covers the rear face of the substrate to facilitate the introduction without reflection of the infrared radiation arriving from the rear face.
Le plus souvent aussi, les diodes de siliciure de platine 12 sont elles-mêmes recouvertes par une sorte de cavité optique constituée par une couche d'oxyde de silicium 16 puis une couche d'aluminium 18 formant miroir pour renvoyer vers l'arrière le rayonnement lumineux après qu'il a traversé la diode ; étant donné que l'absorption dans la diode n'est guère que de 0,5%, on a en effet intérêt à faire passer le rayonnement deux fois à travers la diode grâce à ce miroir.Most often also, the platinum silicide diodes 12 are themselves covered by a sort of optical cavity constituted by a layer of silicon oxide 16 then a layer of aluminum 18 forming a mirror to reflect the radiation towards the rear. bright after it has passed through the diode; since the absorption in the diode is hardly more than 0.5%, it is in fact advantageous to pass the radiation twice through the diode by means of this mirror.
Là où le miroir est bien perpendiculaire au plan du substrat, le rayonnement est réfléchi perpendiculairement vers l'arrière et ressort du substrat.Where the mirror is well perpendicular to the plane of the substrate, the radiation is reflected perpendicularly towards the rear and emerges from the substrate.
Mais là où des surfaces réfléchissantes obliques sont présentes, que ce soit des portions obliques du miroir ou d'autres surfaces inclinées ou toute autre cause de réflexion oblique, une fraction importante de rayonnement peut être réémise vers l'arrière avec une incidence telle qu'elle ne puisse pas ressortir du substrat; cette fraction est renvoyée à nouveau vers les diodes de siliciure de platine , mais loin de l'endroit d'incidence initiale .But where oblique reflecting surfaces are present, whether oblique portions of the mirror or other inclined surfaces or any other cause of reflection oblique, a significant fraction of radiation can be re-emitted backwards with an incidence such that it cannot emerge from the substrate; this fraction is returned again to the platinum silicide diodes, but far from the place of initial incidence.
Il faut comprendre que ce phénomène est d'autant plus important que le rayonnement réfléchi est peu atténué puisque l'atténuation dans les diodes de siliciure de platine n'est guère que de 1% après passage dans les deux sens .It should be understood that this phenomenon is all the more important that the reflected radiation is little attenuated since the attenuation in the diodes of platinum silicide is hardly more than 1% after passing in both directions.
Si le substrat a par exemple une épaisseur de 500 micromètres et si une fraction importante de rayonnement est réfléchie par exemple avec une incidence d'environ 30° par rapport à la normale, il se produira une image parasite à environ 500 micromètres de distance de l'image principale, c'est-à-dire à une vingtaine de pixels de distance pour des dimensions de pixels de l'ordre de 25 micromètres .If the substrate has for example a thickness of 500 micrometers and if a significant fraction of radiation is reflected for example with an incidence of approximately 30 ° compared to normal, a spurious image will be produced at approximately 500 micrometers away from the main image, that is to say at a distance of about twenty pixels for pixel dimensions of the order of 25 micrometers.
Dans cette réalisation classique de la figure 1, le substrat semiconducteur est faiblement dopé de type P et constitue l'anode des diodes schottky dont les cathodes sont en siliciure de platine . Selon l'invention, on propose de doper très fortement le substrat semiconducteur dans sa partie arrière, de sorte qu'il devienne très absorbant pour les longueurs d'onde infrarouges . La face avant, portant les éléments photosensibles, reste faiblement dopée si la nature des éléments photosensibles l'exige, ce qui est le cas pour les diodes au siliciure de platine . L'éclairement est alors effectué par la face avant du substrat .In this conventional embodiment of FIG. 1, the semiconductor substrate is slightly P-type doped and constitutes the anode of the schottky diodes whose cathodes are made of platinum silicide. According to the invention, it is proposed to very strongly dop the semiconductor substrate in its rear part, so that it becomes very absorbent for infrared wavelengths. The front face, carrying the photosensitive elements, remains slightly doped if the nature of the photosensitive elements requires it, which is the case for the diodes with platinum silicide. Illumination is then performed by the front face of the substrate.
Dans ce cas, on ne place pas de miroir d'aluminium devant les éléments photosensibles . Cependant on prévoit de préférence des couches d'adaptation optique au dessus des éléments photosensibles (des couches de passivation sont, de toutes façons nécessaires et jouent en partie le rôle p couche d'adaptation optique) . La figure 2 représente schématiquement l'invention . De même qu'à la figure 1, les échelles de dimensions ne sont pas respectées pour que la structure générale reste intelligible .In this case, an aluminum mirror is not placed in front of the photosensitive elements. However, optical adaptation layers are preferably provided above the photosensitive elements (passivation layers are, in any case necessary and partly play the role of optical adaptation layer). FIG. 2 schematically represents the invention. As in Figure 1, the dimensional scales are not respected so that the general structure remains intelligible.
Le substrat semiconducteur peut être constitué par unThe semiconductor substrate can consist of a
20 3 substrat 10 de type P+ de dopage environ 10 atomes/cm , sur lequel on a fait croître par épitaxie une couche de silicium20 3 substrate 10 of type P + doping about 10 atoms / cm, on which a layer of silicon has been grown by epitaxy
14 314 3
11 de type P faiblement dopé (environ 10 atomes/cm ) . La transition entre la couche épitaxiale et le substrat après la phase de croissance épitaxiale est progressive , et cette progressivité permet d'éviter toute réflexion vers l'avant de rayonnements qui se dirigeraient de la facp avant vers la face arrière du substrat, que ces rayonnements soient perpendiculaires ou obliques par rapport au plan du substrat. L'épaisseur de la couche épitaxiale est de l'ordre de 10 micromètres et l'épaisseur du substrat de l'ordre de quelques centaines de micromètres .11 P-type lightly doped (about 10 atoms / cm). The transition between the epitaxial layer and the substrate after the epitaxial growth phase is gradual, and this progressiveness makes it possible to avoid any reflection towards the front of radiation which would direct from the front facp towards the rear face of the substrate, than these radiation are perpendicular or oblique to the plane of the substrate. The thickness of the epitaxial layer is of the order of 10 micrometers and the thickness of the substrate is of the order of a few hundred micrometers.
Le substrat peut aussi être réalisé à partir d'une tranche semiconductrice faiblement dopée que l'on dope très fortement par la face arrière . Toutefois , la zone très dopée s'étendra alors sur une profondeur qui ne peut guère dépasser quelques dizaines de micromètres, ce qui n'est pas forcément suffisant pour absorber complètement les rayonnements infrarouge , surtout pour les grandes longueurs d'onde .The substrate can also be produced from a lightly doped semiconductor wafer which is doped very strongly from the rear face. However, the heavily doped zone will then extend over a depth which can hardly exceed a few tens of micrometers, which is not necessarily sufficient to completely absorb infrared radiation, especially for long wavelengths.
Sur la face avant du substrat, les éléments photosensibles sont directement recouverts par une rouche de passivation transparente 20 (oxyde et/ou nitrure de silicium) elle-même éventuellement recouverte d'une ou plusieurs couches d'adaptation d'indice 22, transparentes en infrarouge et ayant un effet anti-reflet pour les rayonnements incident s .On the front face of the substrate, the photosensitive elements are directly covered by a transparent passivation wheel 20 (silicon oxide and / or nitride) itself optionally covered with one or more adaptation layers of index 22, transparent in infrared and having an anti-reflection effect for incident radiation.
Sur la face arrière, on peut, prévoir une couche conductrice 24 (métallisation en aluminium en général) servant à porter uniformément le substrat (et donc la couche épitaxiée 11) à un potentiel de référence. Dans les réalisations de l'art antérieur, avec éclairage par l'arrière , il était nécessaire de prévoir une prise de contact sur la face avant pour accéder au substrat et le porter à un potentiel de référence . Pour améliorer l'élimination des rayonnements ayant déjà traversé les éléments photosensibles , on peut aussi prévoir que cette métallisation de contact face arrière est réalisée en un matériau conducteur de l'électricité mais non réfléchissant pour les longueurs d'onde infrarouge considérées . De l'aluminium noir (pulvérulent) peut convenir .On the rear face, it is possible to provide a conductive layer 24 (aluminum metallization in general) serving to uniformly bring the substrate (and therefore the epitaxial layer 11) to a reference potential. In the embodiments of the prior art, with rear lighting, it was necessary to provide a contact on the front face to access the substrate and bring it to a reference potential. To improve the elimination of radiation which has already passed through the photosensitive elements, it can also be provided that this rear contact metallization is made of an electrically conductive material but not reflective for the infrared wavelengths considered. Black (powdered) aluminum may be suitable.
Le substrat de silicium ainsi réalisé , portant les éléments photosensibles ainsi que la circuiterie de multiplexage nécessaire pour transmettre et traiter les charges électriques engendrées par chaque élément photosensible , sera en général monté sur un autre substrat, de préférence en céramique , destiné à assurer le refroidissement .The silicon substrate thus produced, carrying the photosensitive elements as well as the multiplexing circuitry necessary for transmitting and processing the electric charges generated by each photosensitive element, will generally be mounted on another substrate, preferably ceramic, intended to provide cooling. .
Le substrat de céramique 30 porte classiquement des connexions électriques et des plages de connexion permettant une soudure par fils avec des plots de connexion portés par le substrat de silicium 10. On n'utilise donc pas la technique de soudure avec retournement de puce ( "flip chip" ) utilisée lorsque le détecteur doit être éclairé par la face arrière , mais on revient à la technique plus ancienne de connexion par fils soudés (" ire-bonding") de sorte que le détecteur peut être éclairé par la face avant du substrat 10. La face a rrière du substrat de silicium est soudée ou collée à l'aide ri 'une colle conductrice sur une plage conductrice du substrat de céramique .The ceramic substrate 30 conventionally carries electrical connections and connection pads allowing soldering by wires with connection pads carried by the silicon substrate 10. Therefore, the flip soldering technique is not used ("flip chip ") used when the detector must be lit by the rear face, but we return to the older technique of connection by soldered wires (" ire-bonding ") so that the detector can be lit by the front side of the substrate 10 The rear face of the silicon substrate is welded or bonded using a conductive adhesive on a conductive pad of the ceramic substrate.
L'invention a été décrite en détail à propos de détecteurs infrarouges dont les éléments photosensibles sont des diodes schottky au siliciure de platine sur silicium . On comprendra cependant qu'elle serait transposable à des détecteurs infrarouges dont les éléments photosensibles sont différents, étant donné que le problème ne vient pas principalement du fait de ces diodes mais bien plutôt de réflexions parasites sous incidence non normale . The invention has been described in detail with respect to infrared detectors, the photosensitive elements of which are schottky diodes with platinum silicide on silicon. It will however be understood that it would be transposable to infrared detectors whose photosensitive elements are different, given that the problem does not come mainly from these diodes but rather from parasitic reflections under non-normal incidence.

Claims

REVENDICATIONS
1. Détecteur infrarouge comportant un ensemble d'éléments photosensibles en infrarouge (12) constitués par des diodes Schottky etintégrés sur la face avant d'un substrat semiconducteur (10) , caractérisé en ce que la face arrière du substrat semiconducteur est très fortement dopée pour absorber la majeure partie du rayonnement infrarouge reçu par le détecteur, l'éclairement du détecteur étant assuré par la face avant .1. Infrared detector comprising a set of infrared photosensitive elements (12) constituted by Schottky diodes and integrated on the front face of a semiconductor substrate (10), characterized in that the rear face of the semiconductor substrate is very strongly doped for absorb most of the infrared radiation received by the detector, the illumination of the detector being provided by the front face.
2. Détecteur selon la revendication 1 , caractérisé en ce que les éléments photosensibles sont des diodes schottky au siliciure de platine sur silicium.2. Detector according to claim 1, characterized in that the photosensitive elements are schottky diodes with platinum silicide on silicon.
3. Détecteur selon l'une des revendications précédentes, caractérisé en ce que le substrat est un substrat de silicium dopé de type P++ sur lequel on a fait croître une couche épitaxiale (11) faiblement dopée de type P.3. Detector according to one of the preceding claims, characterized in that the substrate is a P ++ type doped silicon substrate on which a lightly doped P type epitaxial layer (11) has been grown.
4. Détecteur selon l'une des revendications précédentes, caractérisé en ce que la face arrière du substrat est pourvue d'une couche conductrice (24) pour porter le substrat à un potentiel de référence.4. Detector according to one of the preceding claims, characterized in that the rear face of the substrate is provided with a conductive layer (24) to bring the substrate to a reference potential.
5. Détecteur selon la revendication 4 , caractérisé en ce que la couche conductrice est non- réfléchissante pour les rayonnements infrarouge .5. Detector according to claim 4, characterized in that the conductive layer is non-reflective for infrared radiation.
6. Détecteur selon l'une des revendications précédentes, caractérisé en ce que les éléments photosensibles sont recouverts d'une couche de passivation et d'une ou plusieurs couches d'adaptation d'indice optique . 6. Detector according to one of the preceding claims, characterized in that the photosensitive elements are covered with a passivation layer and with one or more adaptation layers of optical index.
7. Détecteur selon l'une des revendications précédentes , caractérisé en ce que le substrat de silicium est soudé ou collé par sa face arrière sur un substrat de céramique (30) . 7. Detector according to one of the preceding claims, characterized in that the silicon substrate is welded or bonded by its rear face to a ceramic substrate (30).
PCT/FR1991/000712 1990-09-07 1991-09-06 Front-illuminated infrared detector having a heavily doped substrate WO1992004736A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR90/11122 1990-09-07
FR9011122A FR2666689A1 (en) 1990-09-07 1990-09-07 INFRARED DETECTOR WITH HIGHLY DOPED SUBSTRATE AND ILLUMINATION FROM THE FRONT PANEL.

Publications (1)

Publication Number Publication Date
WO1992004736A1 true WO1992004736A1 (en) 1992-03-19

Family

ID=9400162

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FR1991/000712 WO1992004736A1 (en) 1990-09-07 1991-09-06 Front-illuminated infrared detector having a heavily doped substrate

Country Status (4)

Country Link
EP (1) EP0499632A1 (en)
JP (1) JPH05502554A (en)
FR (1) FR2666689A1 (en)
WO (1) WO1992004736A1 (en)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4028719A (en) * 1976-03-11 1977-06-07 Northrop Corporation Array type charge extraction device for infra-red detection

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57139969A (en) * 1981-02-23 1982-08-30 Nippon Telegr & Teleph Corp <Ntt> Semiconductor device for high frequency amplification

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4028719A (en) * 1976-03-11 1977-06-07 Northrop Corporation Array type charge extraction device for infra-red detection

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
ELECTRONICS. vol. 61, no. 12, Juin 1988, NEW YORK US page 32; L. WALLER: 'Can silicon IR sensors beat exotics?' voir le document en entier *
INTERNATIONAL ELECTRON DEVICES MEETING 13 Décembre 1982, SAN FRANCISCO, CA pages 521 - 524; S.Y. WANG ET AL.: 'GaAs schottky photodiode with 3dB bandwidth of 20 GHz' voir abrégé; figure 1 *
PATENT ABSTRACTS OF JAPAN vol. 6, no. 238 (E-144)(1116) 26 Novembre 1982 & JP,A,57 139 969 ( NIPPON DENSHIN DENWA KOSHA ) 30 Août 1982 voir abrégé *

Also Published As

Publication number Publication date
EP0499632A1 (en) 1992-08-26
JPH05502554A (en) 1993-04-28
FR2666689A1 (en) 1992-03-13

Similar Documents

Publication Publication Date Title
EP1883112B1 (en) Back illuminated image sensor with an uniform substrate temperature
EP3503192B1 (en) Device for acquiring a 2d image and a depth image of a scene
FR2935839A1 (en) CMOS IMAGE SENSOR WITH LIGHT REFLECTION
EP3660930B1 (en) Method for manufacturing a photodiode array made of germanium and with low dark current
EP2786412B1 (en) Optical detector unit
FR3089062A1 (en) process for manufacturing at least one passive planar photodiode with reduced dark current
FR2893765A1 (en) Photosensible integrated circuit, e.g. electronic chip, production, for e.g. webcam, involves forming reflective layer between transistors and integrated circuit, where layer reflects photons not absorbed by silicon layers
FR2719159A1 (en) Optoelectronic device incorporating a photodetector with two diodes.
EP2865017A1 (en) Semiconductor structure comprising an absorbing area placed in a focusing cavity
EP0007878B1 (en) Photoelectric generator
FR2928034A1 (en) Matrix sensor for intensified camera in monitoring application, has screen defining windows formed above detection elements to allow incident electrons to bombard elements, and conductive layer providing electrical potential to form lenses
JPH0677518A (en) Semiconductor photodetector
EP0005160B1 (en) Pin photodiode
FR2691579A1 (en) System for converting an infrared image into a visible or near infrared image.
EP0089278B1 (en) Infrared matrix detector
EP3471151B1 (en) Helmholtz resonator photodetector
EP0702409A1 (en) Stack of series-connected photosensitive thyristors
WO1992004736A1 (en) Front-illuminated infrared detector having a heavily doped substrate
EP1432044A1 (en) Photodiode with an integrated polysilicon filter
FR3087939A1 (en) LIGHT SENSOR
FR2666690A1 (en) INFRARED DETECTOR WITH THINNED SUBSTRATE AND MANUFACTURING METHOD.
KR102558515B1 (en) Short wave infrared focal plane array, utilization and manufacturing method thereof
FR2682815A1 (en) Photosensitive detector with enhanced resolution
FR2768566A1 (en) Curved mirror resonator
EP0923141A1 (en) Photodetecting device, process of manufacturing and use for multispectral detection

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IT LU NL SE

WWE Wipo information: entry into national phase

Ref document number: 1991916066

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 1991916066

Country of ref document: EP

WWW Wipo information: withdrawn in national office

Ref document number: 1991916066

Country of ref document: EP