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WO2006018470A1 - Detecteur de rayonnement a semiconducteur comprenant une structure de porte interne modifiee - Google Patents

Detecteur de rayonnement a semiconducteur comprenant une structure de porte interne modifiee Download PDF

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Publication number
WO2006018470A1
WO2006018470A1 PCT/FI2004/000492 FI2004000492W WO2006018470A1 WO 2006018470 A1 WO2006018470 A1 WO 2006018470A1 FI 2004000492 W FI2004000492 W FI 2004000492W WO 2006018470 A1 WO2006018470 A1 WO 2006018470A1
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pixel
layer
radiation detector
semiconductor
detector device
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PCT/FI2004/000492
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Artto Aurola
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Priority to PCT/FI2004/000492 priority Critical patent/WO2006018470A1/fr
Priority to RU2007104786/28A priority patent/RU2376678C2/ru
Priority to US11/660,562 priority patent/US7816653B2/en
Priority to KR1020077003995A priority patent/KR101143346B1/ko
Priority to EP14197959.1A priority patent/EP2950346A3/fr
Priority to CN200580028112.7A priority patent/CN100533751C/zh
Priority to JP2007526477A priority patent/JP5081621B2/ja
Priority to PCT/FI2005/000359 priority patent/WO2006018477A1/fr
Priority to AU2005273818A priority patent/AU2005273818B2/en
Priority to MX2007002133A priority patent/MX2007002133A/es
Priority to CA2577198A priority patent/CA2577198C/fr
Priority to BRPI0514449-3A priority patent/BRPI0514449B1/pt
Priority to EP05774699A priority patent/EP1790011A4/fr
Publication of WO2006018470A1 publication Critical patent/WO2006018470A1/fr
Priority to IL181187A priority patent/IL181187A/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/80—Constructional details of image sensors
    • H10F39/802—Geometry or disposition of elements in pixels, e.g. address-lines or gate electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/10—Integrated devices
    • H10F39/12—Image sensors
    • H10F39/15—Charge-coupled device [CCD] image sensors
    • H10F39/151—Geometry or disposition of pixel elements, address lines or gate electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/10—Integrated devices
    • H10F39/12—Image sensors
    • H10F39/196—Junction field effect transistor [JFET] image sensors; Static induction transistor [SIT] image sensors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/10—Integrated devices
    • H10F39/12—Image sensors
    • H10F39/199—Back-illuminated image sensors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/10—Integrated devices
    • H10F39/12—Image sensors
    • H10F39/18—Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors
    • H10F39/186—Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors having arrangements for blooming suppression
    • H10F39/1865—Overflow drain structures

Definitions

  • This invention concerns generally the technology of semiconductor radiation detectors. Especially the invention concerns the way in which the differently doped semiconductor regions are arranged with respect to each other in the detector, and how their electric potentials are handled, in order to maximise the performance of a semiconductor radiation detector.
  • the operation principle of semiconductor radiation detectors is based on a reverse biased pn-junction, creating a so-called depleted semiconductor volume, where an electric field is present.
  • An incident photon or a particle, such as alfa or beta particle or proton
  • causes a photoelectric effect locally creating electron/hole pairs.
  • the electric field of the depleted region segre ⁇ gates the charge carriers, one type of which is used as the signal charge.
  • the measured amount of signal charge is used to determine the intensity of the radiation.
  • CCD charge-coupled de ⁇ vice
  • CCD charge transfer device
  • the early CCDs were of surface channel type devices, meaning that charge is transported at the silicon silicon-dioxide interface.
  • the inter ⁇ face has, however, plenty of surface defects trapping the charge to be transported, thus decreasing the charge transport efficiency.
  • a major im ⁇ provement to the performance of CCDs was the transition to buried channel CCDs, where the signal charge is transported in a channel below the sur ⁇ face.
  • the gate and isolation materials absorb a part of the radiation.
  • the absorption is particularly in ⁇ tense for blue light, ultra violet (UV) and soft X-ray radiation and for low en ⁇ ergy particles, impairing the so-called blue response of a radiation detector.
  • An obvious way to improve the blue response is to use back illuminated de ⁇ vices, where all charge manipulating circuitry, i.e. thick material layers in ⁇ sensitive to radiation, are on the front side of the device.
  • the neutral substrate at the backside of traditional back illuminated CCDs must be etched away in order to obtain a good blue response, making these devices very thin: less than 50 ⁇ m and typically around 10 ⁇ m.
  • the thinning process is difficult and likely to result in low manufacturing yield.
  • the thin substrate causes also other problems.
  • the penetration depth of red and near infrared photons in silicon is easily greater than the substrate thick ⁇ ness, resulting in bad red response and fringing, i.e. wavelike patterns in an image.
  • the introduction of a thin biased backside layer described e.g. in patents US 6,025,585 and US 6,259,085, combined with a high resistivity substrate, enabled the use of thick fully depleted substrates in back illumi ⁇ nated CCDs resulting both good red and blue response.
  • Blooming is an interfering effect that takes place when a bright spot in an image results enough of signal charge to fill the charge collection well of the corresponding pixel and starts to fill neighbouring pixels.
  • Antiblooming struc ⁇ tures could be implemented to US 6,259,085, but they are likely to decrease the fill factor. Smearing is another problem observed during the charge transportation phase when a bright spot adds charge to all charge packets transported through it.
  • the best way to accomplish the amplifier is to use the collected charge as an internal gate of a unipolar transistor like junction field effect transistor (JFET) or metal OX- ide semiconductor FET (MOSFET). From these transistors JFET is favoured because it is more tolerant to radiation damage than MOSFET.
  • the internal gate structure consists of a potential energy minimum for the signal charges underneath the channel of a FET. The signal charges gathered in the poten ⁇ tial energy minimum widen the channel, thus decreasing the channel resis ⁇ tance.
  • the good amplifier properties of an internal gate FET are related to its small parasitic capacitance to total capacitance ratio and to the possibility of non-destructive reading allowing the signal charge to be read many times.
  • the ultimate performance limit for semiconductor radiation detectors is set by the leakage or dark current, which mixes with the signal charge distorting the signal measurement.
  • the leakage current can be divided to three com ⁇ ponents.
  • One component arises from depleted regions in the device. Since operation of semiconductor detectors is based on the depletion region, this current component cannot be eliminated. Reducing the depletion region size decreases this current component, but on the other hand this degrades the sensitivity for deeply penetrating radiation.
  • the only reasonable way to minimise this current component is to minimise the amount of defects in the semiconducting material, i.e. one should use high quality substrates and carefully selected manufacturing processes.
  • a second leakage current component is the diffusion current arising from depletion region boundaries. This component is, however, only significant at depletion regions borders in high resistance material. In fully depleted detec ⁇ tors made of highly resistive material this is the case only outside the active area, i.e. outside the area where the pixels are situated. This current com ⁇ ponent can be easily eliminated for instance by surrounding the active area with a biased guard ring.
  • inter ⁇ face current also known as the surface generation current.
  • This current component arises from depleted areas in the semiconductor next to the semiconductor surface or interfaces with different materials, and is referred later on in the text as surface current.
  • An objective of the present invention is to provide a semiconductor radiation detector structure, in which the above-explained prior art problems are avoided.
  • An additional objective of the invention is to provide a semiconduc ⁇ tor radiation detector with improved accuracy and reduced susceptibility to leakage current in the measurement.
  • Another objective of the invention is to present an enhanced semiconductor radiation detector structure for measur ⁇ ing the signal charge non-destructively.
  • Yet another object of the present in ⁇ novation is to provide a vertical antiblooming structure allowing a 100 % fill factor.
  • the objectives of the invention are achieved by isolating the surface current carriers from the signal charge.
  • a semiconductor radiation detector according to the invention is character ⁇ ised by the features recited in the characterising part of the independent claim directed to a semiconductor radiation detector.
  • a method for detecting radiation according to the invention is characterised by the features recited in the characterising part of the independent claim di ⁇ rected to such a method.
  • An important principle behind the present invention is isolating the signal charge from depleted interfaces, which helps to reach a significant reduction in leakage current.
  • the signal charge is not isolated from depleted interface regions, which means that charges gener ⁇ ated at some areas of a depleted interface will add to the signal charge. If the signal charge could be totally isolated from depleted interfaces and read non-destructively, one could use more easily different materials than silicon for radiation detectors and the measurement accuracy would improve due to the smaller leakage current.
  • such isolation is achieved with a layered structure, in which semiconductor layers or regions of different conductivity types alternate in a suitable way.
  • the advantages resulting from the surface current isolation may be reaped starting from any of a number of different viewpoints.
  • One possibility is to trade off the improved accuracy with a higher operation temperature of the device, decreasing the need for cooling. This would be of great importance if one could shift from liquid or gas cooling to peltier element cooling, simplify ⁇ ing the detector structure.
  • germanium, silicon and other indirect band gap materials the photon absorption is based on phonon interaction below cer ⁇ tain energy limit.
  • the phonon assisted photon absorption probability is de ⁇ pendent on the phonon density, which is temperature dependent.
  • an increased operation temperature enhances the detectors quantum efficiency for near band gap energy photons, like near infrared photons in silicon.
  • An ⁇ other important issue is that the interfaces are prone to radiation damage, increasing the surface current of a depleted interface and thus decreasing the lifetime of conventional detectors; isolating the signal charge from the surface current according to the invention helps to avoid this disadvantage.
  • Fig. 1 illustrates a structural principle according to an embodiment of the invention
  • fig. 2 illustrates electron potentials in an n- type detector
  • fig. 3 illustrates electron potential in three-dimensional form
  • fig. 4 illustrates electron potentials in a p- type detector
  • fig. 5 illustrates an alternative structural principle
  • fig. 6 illustrates an advanced trench isolation arrangement
  • fig. 7 illustrates another advanced trench isolation arrangement
  • fig. 8 illustrates a JFET on top of a pixel doping
  • fig. 9 illustrates a variation of the basic structure of fig. 8
  • fig. 10 illustrates yet another possible transistor structure
  • fig. 11 illustrates electron potentials at pixel and channel stop locations
  • fig. 12 illustrates a JFET inside the pixel doping
  • FIG. 13 illustrates another JFET structure
  • fig. 14 illustrates a modified JFET structure
  • fig. 15 illustrates a MOSFET structure
  • fig. 16 illustrates a bipolar transistor inside the pixel doping
  • fig. 17A illustrates a traditional internal gate structure of a JFET
  • fig. 17B illustrates a MIG structure according to the JFET in fig. 8
  • fig. 17C illustrates a different MIG structure
  • fig. 2OB illustrates another pixel detector structure
  • fig. 2OC illustrates another pixel detector structure
  • fig. 2OD illustrates a structure that corresponds to fig. 5.
  • Fig. 1 is a schematic cross section of a back-illuminated semiconductor de ⁇ tector.
  • the back surface through which radiation enters the detector, is downwards in the drawing.
  • the conducting material being for instance metal or transparent conducting oxide (TCO).
  • TCO transparent conducting oxide
  • a thin conducting layer 102 which is used to transport the secondary current outside the active area. This layer is formed for instance by doping the back surface of the bulk layer 103 with a first conductivity type dopant.
  • Alternatives to the two layers 101 and 102 have been presented in a co-pending patent application number Fl 20040966, the contents of which are incorporated herein by reference.
  • the bulk layer 103 of the detector is preferably made of a highly resistive (doping concentration around 10 12 /cm 3 or less) semiconductor material of a first conductivity type.
  • the bulk layer 103 could also be of a second conduc ⁇ tivity type, but this arrangement is not considered to be as beneficial.
  • the conductivity types refer here to positively and negatively doped semiconduc ⁇ tors, with an excess of positive and negative charges respectively.
  • a layer 104 of the second conductivity type made for instance by implantation.
  • the layer 104 is in the following referred to as the modified internal gate (MIG) layer.
  • a layer 105 of the first conductivity type designated here as the epitaxial layer or simply the epilayer for short, referring to its most typical manufacturing method by epitaxial growth.
  • the frontmost layer in fig. 1 is a protective insulation layer 106.
  • Patterned, preferably pixel-like implantations, having the second conductiv ⁇ ity type, are made in the epilayer 105.
  • pixel electrodes 112 and 110 are separately designated. Electrodes like 110 and 112 are later re ⁇ ferred to as pixel dopings.
  • the area between the pixel dopings, like between 110 and 112, functions as the channel stop isolating the pixels and collect ⁇ ing the secondary charge generated for example at depleted interfaces. Electrical connections to the patterned implantations of either type are made with conductive contacts 113 through the insulation layer 106.
  • Optional floating or biased channel stop implants 114 of first conductivity type can be placed between the pixels. There can also be one or more float ⁇ ing or biased implants, having the second type conductivity, between the pixels. Even floating or biased MOS guard rings between the pixels can be used.
  • a guard ring implant 111 of the second conductivity type surrounds the pixel area, and can be surrounded by another guard ring implant 118 of the first type of conductivity. Instead of one or two guard rings 111 and/or 118, there can be several floating or biased guard rings, and they can con ⁇ tain pixel selection and read electronics.
  • a front side contact 115 is provided outside the pixel area for bringing the necessary bias voltage to the structure, preferably through a trench reaching to the bulk layer 103.
  • the bottom of the trench can be implanted with a dopant of first conductivity type and the trench is filled with conducting mate ⁇ rial like metal or highly doped polycrystalline material of the same type of doping as the bulk layer 103.
  • the polysilicon trench is not mandatory; in ⁇ stead of it one could use an implant or one could make a direct contact to the backside layer 102.
  • the active area containing the pixel dopings is iso ⁇ lated from the front side contact 115 with a trench isolation 116. In this man ⁇ ner the chip borders are neutral and the current arising from the borders is reduced substantially.
  • the bottom of the trench isolation 116 is preferably doped heavily with a dopant of the same type as the bulk layer 103 to stop the depletion region; the depletion region boundary will be located beneath the trench isolation approximately like the dashed line 117 in fig. 1. Alterna ⁇ tively one could use the trench structure under 115 to stop the depletion re ⁇ gion.
  • the electrical potential difference between a pixel doping 112 and a biased backside layer is here referred to as the pixel voltage V P .
  • the location exactly in the middle between the pixel dop ⁇ ings 110 and 112 is referred to as the channel stop location.
  • the electrical potential difference between a channel stop location and the biased back ⁇ side layer is referred to as the channel stop voltage V C s-
  • the electrical po ⁇ tential difference between a front side pixel doping and the biased backside layer 102 during a signal charge clearing phase is the drain voltage V 0 .
  • Fig. 2 illustrates po ⁇ tential functions for electrons measured along straight front-to-back lines through the layered structure of fig.1 at the pixel doping and the channel stop location when different voltages are applied between them and the bi ⁇ ased backside layer 102.
  • Flat sections in the potential function correspond to neutral areas and sloping sections correspond to depleted areas.
  • Curve 201 represents the case when the potential difference is V D between the pixel doping and the biased backside layer.
  • the relatively large negative value of the voltage V D means that the electron potential is a monotonously falling line from a maximum in the pixel doping to a minimum in the biased backside layer 102.
  • the conductive layer and the optional layer 101 can be replaced with a structure utilising an accumulation layer in the bulk layer 103 very next to said structure, see location 211 in fig. 2. Concerning details of the formation of an accumulation layer and its utilisation for detec ⁇ tor operation reference is made to the co-pending patent application number Fl 20040966.
  • Curve 202 represents the electron potential along a line extending perpen ⁇ dicularly from a pixel doping having a pixel voltage V P between it and the bi ⁇ ased backside layer.
  • V P pixel voltage
  • VD pixel voltage
  • a local maximum 215 is found at the pixel doping, from which the potential function falls to a local minimum 216 in the epilayer 105. From this local minimum the poten ⁇ tial function rises upwards to a local maximum 212 in the MIG layer 104, from which it then falls monotonously to a local minimum at the surface of the conductive layer 102.
  • the respective electron potential function along a perpendicular line extending from a channel stop location to the biased backside layer is represented by curve 203, corresponding to a voltage dif ⁇ ference of Vcs between the channel stop location and the biased backside layer.
  • the potential function has a local potential minimum 215 in the channel stop location and a potential maximum 214 in the MIG layer 104, from where the function falls monotonously to a local minimum at the surface of the conducting layer 102.
  • the channel stop voltage V C s is the electrical potential difference between the biased backside layer and a floating or biased channel stop location.
  • the channel stop can be biased when electrical contact is made through the isolation layer 106 to a first type dopant 114 between the pixel dopings. It should be noted that if a voltage on the front surface of the detector is de ⁇ creased even more from V C s, at some point the reverse biasing of the pn in ⁇ terface between the MIG- and bulk layers gets too low, which means that the bulk layer would not be completely depleted any more. Graphically this would be represented by a curve below curve 203 in fig. 2, with a flat section appearing at its rightmost end. Full depletion of the bulk layer is essential to the correct operation of the detector.
  • the elec ⁇ tric field drives electrons towards the back surface of the detector, where they are collected by the conductive backside layer and possible accumula ⁇ tion layer. Holes are driven towards the MIG layer, where they get trapped to locations 212 coinciding with the pixels, due to the behaviour of the elec ⁇ tron potential described above.
  • Fig. 4 illustrates electron potentials in a detector where the layer 102 is of the p+ type and the bulk layer is of the p- type.
  • curve 401 is the monotonously rising electron potential curve between the pixel dopings and the back surface dur ⁇ ing signal charge clearing with V D
  • curve 402 illustrates electron potential at a pixel location (V P )
  • curve 403 illustrates electron potential at a channel stop location (V C s)- Radiation-induced electrons are collected at location 412, while surface current holes get trapped at 413 and the surface gener ⁇ ated electrons are collected at 415, i.e. at the pixel dopings.
  • 411 , 414 and 416 correspond to locations 211 , 214 and 216 in fig. 2.
  • Fig. 5 illustrates an alternative structure, in which a blank implantation 506 of the second type conductivity type is made to the epilayer 105.
  • the pixel dopings 512 and 510 are separated by preferably reverse biased channel stop implants 514 of the first conductivity type, these being inside the blank implantation layer 506.
  • a channel stop implant 514 referred to later also as a channel stop location, can be the same as the JFET gate or the bipolar emitter implant, which will be introduced later on.
  • the channel stop location 514 is in this case preferably reverse biased in contrast to the pixel doping. If the implant 514 reaches through the layer 506 the situation is essentially the same as in fig. 1.
  • bi ⁇ ased or floating areas of the first and second type of doping between the pixels there can also be several bi ⁇ ased or floating areas of the first and second type of doping between the pixels. Biased or floating MOS guard structures can also be added between the pixels.
  • the location 511 surrounding the pixel area represents a biased guard ring of the second conductivity type, which can be surrounded by a guard ring of first conductivity type.
  • the electron potential functions of the structure in fig. 5 are presented in fig. 6.
  • the potential functions 201 and 202 ranging perpendicularly from the pixel dopings 510 and 512 to the biased backside layer 102 represent the cases when the pixel dopings are at drain and pixel potentials respectively. These are identical to fig. 2.
  • the corresponding potential function 603 is different from 203 presented in fig. 2.
  • the electron potential local minimum 213 collects the surface generated electrons and the channel 617 guides the surface generated holes to the electron potential maximum 215 at the pixel doping.
  • the poten ⁇ tial function 604 represents a possible channel stop voltage configuration in which the electrons in the potential minimum 618 are drained. This can be done for instance by lowering the absolute magnitude of the voltage differ ⁇ ence between the front and backside of the chip.
  • the structures in figs 1 and 5 can be produced with different techniques.
  • the layer 104 can be made by epi ⁇ taxial growth and the layer 105 can be an implant.
  • both layers 104 and 105 can be made by implantation or by epitaxy.
  • the layer 506 could also be made by epitaxy. All the aforementioned implantations can either be blank implants or implanted through a patterned fotoresist. High dose contact implants are also typically associated with the contacts made to different areas. Instead of implantation diffusion could equally well be used.
  • Figs 7A and 7B illustrate some more advanced trench isolation structures.
  • the trench isolation comprises a first trench 116, which with its bot ⁇ tom implantation 116' is similar to what was shown in fig. 1.
  • additional trenches 701 , 702 and 703 which are sim ⁇ ply cuts through the topmost layers.
  • fig. 7B there is a single, relatively wide isolation trench 704, with only a part of its bottom containing a bottom implantation 705.
  • the upper part of fig. 8 presents a planar view of a basic JFET, which in the lower part of fig. 8 is presented as a cross section along a line marked in the upper part.
  • the drawing illustrates a source contact 801 , a gate contact 802 and a drain contact 803.
  • the pixel doping is illustrated as 806 and the JFET gate implant as 807.
  • Also shown in fig. 8 is an optional buckling 810 in the pixel doping.
  • Fig. 9 illustrates a variation of this basic structure where the JFET gate is replaced with a MOS gate 902.
  • the source contact 901 and the drain contact 903 resemble those shown in fig. 8.
  • the pixel doping 906 and the optional buckling 910 in the pixel doping also appear in fig.
  • Fig. 10 illus ⁇ trates yet another possible transistor structure, namely a bipolar transistor, having a base contact 1001 and an emitter contact 1002. Pixel doping 1006 and an emitter implant 1007 are also shown. An optional buckling 1010 ap ⁇ pears below the pixel doping 1006.
  • fig. 11 illustrates how the electron po ⁇ tentials change as a result of signal charges being collected to pixel dopings and surface current carriers of the opposite type being collected to channel stop locations.
  • Vj the absolute value of which is smaller than the absolute value of V P .
  • the physical implantations of the JFET and its coupling to a pixel may follow e.g. the schematic models described above with reference to figs 8 and 9.
  • curves 1101 and 1102 represent electron potentials at pixel and channel stop locations respectively before signal charge begins to accumu ⁇ late in the MIG layer.
  • Curves 1111 and 1112 illustrate how these signal po- tentials change after a photon has hit the detector, in case of a floating channel stop structure. If the channel stop structure is biased, 1112 would obviously be the same as 1102.
  • the signal charge (holes) accumulating in the MIG layer 104 at pixel doping lowers the electron potential at that point, causing a neutral (i.e. flat) section 1114 to appear in the potential curve 1111. This is of importance, because simultaneously the flat section of the potential curve in the pixel doping decreases in length from X1 to X2.
  • the length of said flat section represents the dimensions and correspondingly the current-carrying capability of the channel of the JFET.
  • the decreasing channel dimensions can be accurately measured simply by observing changes in the amplification factor of the JFET.
  • the bipolar transistor in fig. 10 is used instead of a JFET, one uses a specific forward bias to the emitter and measures the change in the emitter current due to the narrowing of the base.
  • a vertical antiblooming mechanism can be explained with the help of fig. 11.
  • the potential function 1113 describes a situation where the MIG structure under the pixel doping is completely full of signal charges. In this case the absolute magnitude of the potential in the flat section 1115 of the MIG struc ⁇ ture is bigger than the absolute magnitude of the local maximum in the MIG layer 1116 under the channel stop location. Thus the excess signal charge flows vertically to the pixel doping instead of blooming horizontally to the neighbouring pixels. In other words, a full pixel has still a potential barrier in the horizontal but none in the vertical direction and not vice versa.
  • the signal charge in the MIG layer can be cleared by applying the drain po ⁇ tential V D between the pixel doping and the biased backside layer 102. If the backside potential is adjusted to perform the signal charge clearing, part of the charge in the floating channel stops will flow to the biased backside layer and the electron potential diagram 1112 returns back to the original position 1102.
  • the pixel doping has a different depth under the JFET channel or the emitter of the bipolar transistor. With the help of the bucklings 810, 910 and 1010 one can confine the signal charge under the JFET channel and the emitter improving the sensitivity of the devices.
  • the signal charge would fill first the location under the drain of the JFET pixel, where the signal charge has only a minor effect on the channel width.
  • the signal charge would spread under the whole pixel doping without the buckling, having a lesser effect on the base width.
  • the pixel doping is deeper under the desired ar ⁇ eas and in 9 it is shallower. Which one of these cases should be chosen de ⁇ pends on the doping levels and thickness of the layers in the layered struc ⁇ ture. The deeper buckles, however, give rise to a smaller parasitic to total capacitance ratio of the MIG structure.
  • the emitter push ef ⁇ fect can be utilized to achieve self-alignment of the buckles under the bipo ⁇ lar emitter and JFET gate implants.
  • a part of the excess signal charge arising from a full MIG structure will add to the measured drain current in the JFET structures corresponding to figs 8 and 9, if the antiblooming mechanism is functional. This is, however, only a problem in case there is a very bright spot in the image.
  • the bipolar transis ⁇ tor shown in fig. 10 should be far more tolerant to the overflow current.
  • the vertical overflow current can be totally isolated from the drain current in JFETs by building a JFET inside the pixel doping, however, at the cost of a more complex structure and a higher parasitic capacitance to total capaci ⁇ tance ratio.
  • Such a JFET structure is presented in fig. 12. 1201 is a contact to the pixel doping 1206.
  • 1202 is the source contact and 1204 is the drain contact to the JFET implant 1207.
  • 1203 is the gate contact to the gate im ⁇ plant 1208.
  • 1210 is a optional buckling in the pixel doping. One could, how ⁇ ever, choose to make such a buckling to the JFET implant instead of the pixel doping, or to both of them.
  • fig. 13 is another JFET structure, where the gate implant 1308 is con ⁇ nected to the pixel doping 1308, i.e. they are at the same potential.
  • the source and drain contacts 1302 and 1304 are made to the JFET implant 1307.
  • the optional buckling 1310 in the pixel doping could also be associ ⁇ ated to the JFET implant or to both of them.
  • Fig. 14 corresponds to a modi ⁇ fied JFET structure, where the JFET gate is replaced with a MOS gate 1403.
  • the source and drain contacts 1402 and 1404 are made to the JFET implant 1407. 1401 is a contact to the pixel doping 1406.
  • the buckling 1410 is in the pixel doping but could also be associated to the JFET implant or to both of them.
  • fig. 15 is presented a MOSFET structure having a MOS gate 1503, and source 1502 and drain 1504 contacts to source 1507 and drain 1509 implants.
  • 1501 is a contact to the pixel doping 1506.
  • An optional buckling 1510 is made to the pixel doping.
  • the structure in fig. 16 inside the pixel doping 1606 is a bipolar transistor having the emitter contact 1603 to the emitter implant 1608.
  • the base contact 1602 is made to the base im ⁇ plant 1607 and pixel contact 1601 is made to the pixel doping.
  • the pixel doping has an optional buckling, but buckling could equally well be incorpo ⁇ rated to the base implant or to both of them.
  • fig. 17A is presented the traditional internal gate (IG) structure of a JFET, where the IG is formed in the layer 1704.
  • the layer 1706 is the JFET gate implant
  • the layer 1705 is the JFET channel area
  • 1703 is the substrate.
  • the electron potential function 1711 repre ⁇ sents the situation, when no charge is in the IG structure and 1712 when charge is present in the IG.
  • the charge in the IG structure widens the JFET channel, i.e.
  • the IG structure does not allow bipolar op ⁇ eration, since the emitter current from the area 1706 would flow to the IG in 1704.
  • the IG allows the use of a floating source, because the charge in IG widens the JFET channel.
  • the MIG structure according to the JFET in fig. 8 is presented in fig. 17B.
  • the electron potential function 1713 presents the case when no charge is in the MIG layer 104, and the function 1714 the case when charge is in the MIG layer. This charge narrows the JFET channel in the layer 806, and this is the reason why floating source cannot be used in this case.
  • the MIG structure in fig. 17B allows bipolar operation.
  • fig. 17C is presented a different MIG structure according to the amplifier structure presented in 12. When charge is added to the MIG layer 104 it changes the electron potential function from 1715 to 1716. In this case the charge in the MIG layer widens the JFET channel in the layer 1207, allowing floating source operation.
  • the bipolar operation is also possible, but in this case the emitter current runs to the pixel doping 1206 and not to the channel stop structure, which is the case in fig. 17B. This is a benefit if floating channel stops are used.
  • Another benefit of the arrangement in fig. 17C is that the overflow current associated with vertical antiblooming is collected by the pixel doping 1206, and not by the JFET channel in 1207 or by the JFET drain.
  • the operation of the MOSFET amplifier in fig. 15 is similar to the case in figs 12 and 17C. All the areas between the MOSFET channel and the MIG layer are depleted due to a proper voltage configuration. Charge in the MIG layer lowers the resistance in MOSFET channel allowing also the use of an float ⁇ ing source. However the ratio of parasitic to total capacitance is most likely highest of all the amplifier structures.
  • the signal charge in the MIG layer can be read for instance by a technique, where the drains of the amplifiers are connected in columns and the gates are connected in rows.
  • a desired pixel can be selected by opening up the JFET or MOSFET channels in one row with a suitable gate voltage and by connecting a voltage difference of correct polarity between the drain and source in one column of drains. The gates in all other rows remain closed and the voltages in all other columns of drains are same as the source volt ⁇ age.
  • the signal charge in the MIG layer can then be determined from the drain current or from a corresponding voltage output. This result can also be also be compared to the measurement result of an empty MIG structure.
  • the bipolar transistors can be read by a similar fashion, i.e.
  • the amplifier structures in 12 - 15 can be de ⁇ signed in a manner that the source is floating. There is an additional benefit in the floating source structure: the start and the end times of the integration period can be exactly the same for all of the pixels.
  • the JFET channel is completely depleted.
  • the potential barrier formed by the channel for the charge in the source is lowered. Then current will flow out of the source until the source potential is adjusted to the changed channel potential.
  • the source can be refilled by inverting the roles of the source and the drain by appropriate voltages applied to the gate and the drain, which func ⁇ tions for a short while as the source.
  • the source could also be refilled by applying blue or green light through for instance a transparent conducting oxide (TCO) layer replacing the metal.
  • TCO transparent conducting oxide
  • FIG. 18 An structure functioning in the manner described above and based on the amplifier structure in fig. 12 is presented in fig. 18, but it could equally well be based on any of the structures in figs 12 - 15.
  • the structure in fig. 18 is the same than in 12 except that there is no source contact and the source 1807 is thus floating.
  • On top of the source is a biased metal layer 1802, which is isolated from the source by an isolator layer. It is beneficial to make the isolation layer as thin as possible to maximise the ratio of source and MIG capacitances.
  • 1801 is the pixel contact
  • 1803 is gate contact
  • 1804 is drain contact.
  • the radiation detector functions as a X-ray, gamma or medium or high en ⁇ ergy particle detector, and if one needs to find out the exact time, location and energy of a radiation incident amongst several simultaneous events, one can split the metal layer in fig. 18 into three (or more) different sectors preferably of the same size. These sectors are further connected to other sectors of different amplifiers forming a line. In this manner every amplifier is connected to three different lines being electrically isolated from each other and proceeding into three different directions. The events can then be traced by observing the signals arriving from three multitudes of lines ex ⁇ tending into three different directions.
  • fig. 19 is also based on the JFET in fig. 12, but it could be based to any of the structures in figs 12 - 15.
  • the metal layer 1902 is floating and it covers completely the floating source region 1907.
  • An isolation layer is used to isolate these rings from the floating metal layer which covers the rings completely except at locations where contacts 1921 , 1922 and 1923 are made to bias the rings, a situation presented on the right side of the struc ⁇ ture in fig. 19.
  • the three different rings can be further connected to three dif ⁇ ferent lines, like already explained before, for monitoring charge pulses on these lines caused by charge collection in the MIG structures.
  • the three dopants are preferably held at three different potentials providing a gradient for charges in the MIG layer and for secondary charges in the epilayer.
  • the pixels presented in figs 8 - 10, 12 - 16 and 18 can be surrounded by floating and/or biased guard rings in a similar fashion than in fig. 19.
  • the biased rings are of same type of conductivity than the pixel im ⁇ plant forming the pixel doping.
  • the biased rings are same of the same type of conduc ⁇ tivity than the channel stop implant being in channel stop location.
  • the layers on top of the substrate should be made as thin as possible, i.e. as thin as the process tolerances allow.
  • the pixel structures in 8 - 10, 12 - 16 and 18 - 19 can be of any shape; instead of the ring like metal contacts one should use point contacts for instance. However, this structure would not be as functional.
  • a benefit in the structure described above compared e.g. to the prior art structure known from publication US 5,786,609 is also that no reset contact is needed.
  • the invention does not necessarily require a transis ⁇ tor to be implemented at each pixel. It is completely possible to only bring an electrical contact to each pixel and to operate the detector in CTD mode, in which alternately coupling the pixels to certain charge transfer voltages will cause the signal charge to migrate towards the end of each pixel row or col ⁇ umn, where a specific readout pixel is used to synchronously detect the transferred charge of each pixel in the row in turn.
  • CTD mode the detector is much more prone to the adverse effects of smearing than in APS mode, in which each individual pixel can be read separately.
  • An addi ⁇ tional advantage of utilising the invention in APS mode is the possibility of concentrating rapid consecutive read operations to only some arbitrarily se ⁇ lected part of the active area, where an interesting phenomenon has been noted to appear, possibly combined with only "updating" overall read opera ⁇ tions at some regular, longer intervals.
  • figs 2OA, 2OB and 2OC are presented different pixel detector structures corresponding to the structure in fig. 1, where 2006 and 2005 correspond to pixel doping and to the epilayer respectively.
  • Fig. 2OA presents a very sim ⁇ ple detector structure.
  • a floating channel stop doping 2009 is added to the structure in fig. 2OA.
  • a contact 2010 is made to the channel stop doping.
  • the structure in fig. 20 D corre ⁇ sponds to fig. 5; 2011 is the channel stop doping, and 2012 is the contact to 2011.
  • the shape of the contact is naturally not limited to that shown in figs 2OC and 2OD; one should actually use point contacts instead. In the same way the channel stop doping in figs.
  • 2OB, 2OC and 2OD can be discontinu ⁇ ous.
  • floating or biased guard rings can be added between the pixel doping and the channel stop locations in figs 2OA, 2OB, 2OC and 2OD.
  • the active area constituting of pixels, like shown in figs 2OA, 2OB, 2OC and 2OD can be surrounded by floating or biased guard rings or areas of first or second type of conductivity and these areas may contain read and selection electronics.
  • a semiconductor radiation detector can most advantageously be used for detecting visible light, near infrared radiation and/or soft X-rays.
  • the area of application can be extended remarkably to- wards energetic X-rays having quantum energy of over 10 keV by covering the back surface of the detector with a scintillator material. In such a case the detector would not detect the incident X-rays as such but the scintillation quanta that arise when the X-rays hit the scintillator material.
  • the decreased levels of leakage current that can be achieved through the invention allow the detector to be made of other semiconductor materials than silicon, which other materials may have been previously considered to involve prohibitively high levels of leakage current.
  • Such other semiconduc ⁇ tor materials include (but are not limited to) germanium, gallium arsenide and cadmium telluride.
  • a device that includes a detector according to an embodiment of the inven ⁇ tion may also include other semiconductor chips, some of which may have bonded connections to the pixels of the detector. This enables building very compact structures that include detection, amplification, reading and in some cases even storage in a very small space, like an MCM (multi-chip module).
  • MCM multi-chip module
  • the non-destructive way of reading the amount of accumulated signal charge by observing the way in which it affects the electrical behaviour of a field-effect transistor allows reading the same charge many times before it is cleared. In other words, the accumulation of charge at different pixels can be monitored essentially continuously.

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Abstract

Un dispositif détecteur de rayonnement à semiconducteur comprend une couche inférieure conductrice (102) possédant un premier type de conductivité et une couche substrat (103). A l'opposé de la couche inférieure conductrice (102) se trouvent une couche de porte interne modifiée (104) possédant un second type de conductivité, une couche (105) possédant le premier type de conductivité et des zones de dopage de type pixel (110, 112, 510, 512) présentant le second type de conductivité. Ces zones de dopage de type pixel sont conçues pour être couplées à un tension de pixel, qui est définie en tant que différence de potentiel avec un potentiel de la couche inférieure conductrice (102), et qui crée des minima de potentiel à l'intérieur du matériau détecteur pour piéger les charges de signal.
PCT/FI2004/000492 2004-08-20 2004-08-20 Detecteur de rayonnement a semiconducteur comprenant une structure de porte interne modifiee Ceased WO2006018470A1 (fr)

Priority Applications (14)

Application Number Priority Date Filing Date Title
PCT/FI2004/000492 WO2006018470A1 (fr) 2004-08-20 2004-08-20 Detecteur de rayonnement a semiconducteur comprenant une structure de porte interne modifiee
PCT/FI2005/000359 WO2006018477A1 (fr) 2004-08-20 2005-08-22 Detecteur de rayonnement de semi-conducteur a structure de grille interne modifiee
AU2005273818A AU2005273818B2 (en) 2004-08-20 2005-08-22 Semiconductor radiation detector with a modified internal gate structure
KR1020077003995A KR101143346B1 (ko) 2004-08-20 2005-08-22 변형 내부 게이트 구조를 갖는 반도체 방사선 검출기
EP14197959.1A EP2950346A3 (fr) 2004-08-20 2005-08-22 Détecteur de rayonnement à semi-conducteurs avec une structure de grille interne modifiée
CN200580028112.7A CN100533751C (zh) 2004-08-20 2005-08-22 具有改进的内部栅极结构的半导体辐射检测器及其检测方法
JP2007526477A JP5081621B2 (ja) 2004-08-20 2005-08-22 改変内部ゲート構造を用いた半導体放射線検出器
RU2007104786/28A RU2376678C2 (ru) 2004-08-20 2005-08-22 Полупроводниковый детектор излучения с модифицированной структурой внутреннего затвора
US11/660,562 US7816653B2 (en) 2004-08-20 2005-08-22 Semiconductor radiation detector with a modified internal gate structure
MX2007002133A MX2007002133A (es) 2004-08-20 2005-08-22 Detector de radiacion de semiconductor con una estructura de compuerta interna modificada.
CA2577198A CA2577198C (fr) 2004-08-20 2005-08-22 Detecteur de rayonnement de semi-conducteur a structure de grille interne modifiee
BRPI0514449-3A BRPI0514449B1 (pt) 2004-08-20 2005-08-22 Radiation semiconductor detector with modified internal door structure
EP05774699A EP1790011A4 (fr) 2004-08-20 2005-08-22 Detecteur de rayonnement de semi-conducteur a structure de grille interne modifiee
IL181187A IL181187A (en) 2004-08-20 2007-02-06 Semiconductor radiation detector with an internal gate structure adapted to the radiation detection method

Applications Claiming Priority (1)

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PCT/FI2004/000492 WO2006018470A1 (fr) 2004-08-20 2004-08-20 Detecteur de rayonnement a semiconducteur comprenant une structure de porte interne modifiee

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GB2466502A (en) * 2008-12-23 2010-06-30 E2V Tech CCD sensor
US20200273664A1 (en) * 2019-02-26 2020-08-27 Asml Netherlands B.V. Charged particle detector with gain element
US11355532B2 (en) * 2018-07-12 2022-06-07 Shenzhen Xpectvision Technology Co., Ltd. Radiation detector
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WO2007077292A1 (fr) 2006-01-05 2007-07-12 Artto Aurola Detecteur de rayonnements de semi-conducteurs detectant la lumiere visible
EP1969632A4 (fr) * 2006-01-05 2012-07-04 Artto Aurola Detecteur de rayonnements de semi-conducteurs detectant la lumiere visible
GB2466502A (en) * 2008-12-23 2010-06-30 E2V Tech CCD sensor
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