Abstract:
A radiation detector of the ΔE-E type is proposed. The detector is integrated in a chip of semiconductor material with a front surface and a back surface opposite the front surface, the detector having at least one detection cell arranged on the front surface for receiving a radiation to be evaluated, wherein the detector includes: a first region of a first type of conductivity extending into the chip from the front surface to a first depth; a second region of a second type of conductivity extending into the chip from the back surface to a second depth so as to reach the first region; and for each detection cell a third region of the second type of conductivity extending into the first region from the front surface to a third depth lower than the first depth and the second depth, a thin sensitive volume for absorbing energy from the radiation being defined by a junction between the first region and each third region, and a thick sensitive volume for absorbing further energy from the radiation being defined by a further junction between the first region and the second region. For each detection cell the detector further includes insulation means arranged around the third region and extending from the front surface into the first region to an insulation depth comprised between the first depth and the third depth.

Description:
PRIORITY CLAIM 
     This application claims priority from European patent application No. EP06114962.1, filed Jun. 5, 2006, which is incorporated herein by reference. 
     TECHNICAL FIELD 
     An embodiment of the present invention relates to the microdosimetry field. More specifically, the present invention relates to radiation detectors of the ΔE-E type. 
     BACKGROUND 
     Microdosimetry is a branch of radiological physics that provides a quantitative characterization on micrometric scale of the spatial and temporal distribution of the energy deposition in matter exposed to ionizing radiation. For example, the microdosimetry may provide an indication of the action of the radiation on biological matter (molecules, cells, tissues, and whole organisms, including humans) related to the energy absorbed in subcellular volumes. 
     Typical applications of the microdosimetry include radiobiology (which seeks to discover the molecular changes responsive to radiation, such as cancer induction, genetic mutations, and cell death), radiation protection (i.e. protection against harmful effects of radiation), and radiotherapy (which is the use of high-energy radiation—from x-rays, gamma rays, neutrons, and other sources—to kill cancer cells and shrink tumors). Moreover, the microdosimetry may also be applied in the study of the effects of radiation on electronic devices. 
     A microdosimeter typically includes a radiation detector and a measuring system, which is adapted to evaluate a response of the radiation detector to obtain information about the incident radiation. Typically, in the above-mentioned applications to biological matter, the detector is covered by a layer made of a tissue-equivalent material; the tissue-equivalent layer is designed to mimic the response of biological tissue, i.e. to absorb and scatter radiation to the same degree, so as to simulate a radiation field generated under an equivalent biologic tissue when struck by radiation. 
     As a result, the energy deposited in the detector is related to the so-called linear energy transfer (LET) in tissue. The LET of a charged particle (ion) traversing a microscopic volume is approximated by the quantity lineal energy, i.e. the quotient of the energy deposited in the volume and the mean chord length of the volume. This relation to LET enables microdosimetry to distinguish between recoil electrons, protons, alpha particles and heavy ions. This, in turn, enables the determination of neutron and gamma ray absorbed doses, quality factors, and dose equivalents. 
     A first experimental detector has been the Tissue-equivalent Proportional Counter (TEPC), which uses a low-pressure gas (with an atomic composition similar to that of biological tissue) to fill a cavity roughly of some centimeters in diameter. The cavity lies at the center of a sphere of conducting plastic (also with an atomic composition similar to that of biological tissue). The TEPC “samples” a particle&#39;s track, so that the energy deposited in the gas is related to the LET of the particle. The TEPC presents some disadvantages, such as the impossibility of producing detectors of small sizes that can be easily located in an anthropomorphous puppet or in-vivo on a patient, and the impossibility of observing physical phenomena directly at micrometric sizes without simulating them acting on the gas pressure. 
     Detectors of the semiconductor type have also been proposed; the semiconductor detectors are stable, linear in their energy response to all types of particles, and can be made small and very thin (less than 0.01 mm). Typically, a semiconductor detector provides a sensitive volume (wherein energy is collected) restricted to the depletion zone around a PN junction. When a particle reaches the depletion zone, it causes the formation of electron-hole pairs and, then, it deposes energy. The depletion zone ensures a minimal recombination of electron-hole pairs and, accordingly, the amount of recombination of charge can be related to the LET of the particle with a high degree of accuracy. 
     Tests of microdosimetry feasibility have been performed on different semiconductor detectors. The test results agree with the theoretical expectations, but they have also pointed out the influence of the electronic noise, which limits a minimum LET to be detected, and of a so-called field-funneling effect. 
     The field-funneling effect consists of a transient local distortion of the electric field in the depletion zone, which occurs when a particle&#39;s track intercepts a PN junction. The equipotential lines are stretched in the shape of a funnel along the track, and the excess charges produced by the track inside this funneling region are collected very rapidly (typically within a fraction of a nanosecond), which results in a return of the electric field to the steady-state condition. The field-funneling effect is induced by high-LET particles, leading to the collection of electron-hole pairs produced in a non-depleted zone. Accordingly, this effect causes an undesired dependence of the sensitive volume thickness on the particle LET. 
     For example, let us consider a commercial photodiode Hamamatsu S3590-06, not biased, having a depletion zone of 20 μm and an effective area of about 1 cm 2 . Test results show that the field-funneling effect has brought the sensitive volume to even double the thickness (40 μm). 
     It has been also realized a microdosimeter with an ASIC (Application Specific Integrated Circuit) in BiCMOC 0.8 μm technology, including a matrix of PN diodes, each one having a sensitive area of 1 mm 2  and a depletion zone of about 2 μm. The electronic noise, measured on the microdosimeter with its measure system, has limited the detectable LET to 10 keV·μm −1 . In addition, the field-funneling effect has brought the sensitive volume thickness to about 12 μm. 
     U.S. Pat. No. 5,854,506 (the entire disclosure of which is incorporated herein by reference) discloses a semiconductor detector of the so-called ΔE-E type. This ΔE-E detector includes a detection cell having a vertical structure consisting of a thick diode (with a thickness of about some hundreds of μm) and a thin diode (with a thickness of about some μm). The two diodes are integrated in a same chip of semiconductor material and have a common anode buried in the chip, a front cathode and a back cathode. 
     In operation, the two diodes are reverse biased in total depletion conditions. When the detector is irradiated, a particle interacts firstly with the thin diode, losing only a small first part of its energy (ΔE), and then with the thick diode, to which it yields a greater second part of its energy, up to all the residual one (E-ΔE). Accordingly, the detection cell includes two distinct sensitive volumes, a ΔE region and an E region, separated by the common buried anode having a heavily doping concentration; the clear separation between the two regions provides an effective limitation of the field-funneling effect, with the excess charges that are collected into the E region. 
     A ΔE-E detector for microdosimetric applications typically has a modular structure with a matrix of detection cells; each detection cell has a sensitive volume comparable with the biological cell size, in order to improve the detection efficiency. 
     However, such a detector shows a high capacitance and, accordingly, a significant electronic noise. Then, the microdosimetric requirement of a detectable LET lower than 10 keV·μm −1  imposes very high performance in terms of noise to circuits coupled to the detector. 
     Furthermore, the sensitive volume of each detection cell is increased to include a region surrounding each detecting cell; this drawback is particular acute in microdosimetric applications, wherein it is very important to keep the sensitive volume comparable with the biological cell size. 
     SUMMARY 
     An embodiment of the present invention proposes a solution, which is based on the idea of insulating the sensitive volume of each detection cell of the ΔE-E detector. 
     More specifically, an embodiment of the present invention provides a radiation detector of the ΔE-E type; the detector is integrated in a chip of semiconductor material (with a front surface and a back surface, opposite the front surface). The detector has one or more detection cells arranged on the front surface (for receiving a radiation to be evaluated). The detector includes a first region (anode) of a first type of conductivity extending into the chip from the front surface to a first depth. A second region (cathode) of a second type of conductivity extends into the chip from the back surface to a second depth, so as to reach the first region. For each detection cell a third region (cathode) of the second type of conductivity extends into the first region from the front surface to a third depth (lower than the first depth and the second depth). A thin sensitive volume (for absorbing energy from the radiation) is then defined by a junction between the first region and each third region; a thick sensitive volume (for absorbing further energy from the radiation) is defined by a further junction between the first region and the second region. For each detection cell the detector further includes insulation means (such as a trench) arranged around the third region; this insulation means extends from the front surface into the first region to an insulation depth comprised between the first depth and the third depth. 
     The detector may have two active regions having a lower doping concentration (with respect to distinct contact regions). 
     For example, this result is achieved by providing lightly doped fourth regions extending into the first region from the front surface, wherein each third region is formed (with the insulation means that extends substantially to the same depth as the corresponding fourth region for insulating the active region from its remaining part). 
     In this way, in each forth region a buried contact region (accessed through a sinker region) is obtained. 
     In an embodiment of the present invention, the desired result is achieved by means of a trench that is filled with an insulating material. 
     Each detection cell may have a circular section. 
     In an embodiment of the present invention the detector includes a plurality of detection cells, which are electrically connected together. 
     The detector may further include a channel-stopper region arranged around the detection cells. 
     A further embodiment of the present invention provides a solid-state microdosimeter including this radiation detector. 
     A still further embodiment of the invention provides a corresponding process for integrating the radiation detector in a chip of semiconductor material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the invention, however, as well as features and the advantages thereof will be best understood by reference to the following detailed description, given purely by way of a non-restrictive indication, to be read in conjunction with the accompanying drawings. 
       In this respect, it is expressly intended that the figures are not necessary drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. 
       Particularly: 
         FIG. 1  schematically illustrates a semiconductor microdosimeter in terms of the functional blocks relevant to the understanding of an embodiment of the present invention; 
         FIG. 2A  shows a cross-section view of a ΔE-E detector included in the microdosimeter of  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 2B  shows a top view of the ΔE-E detector of  FIG. 2A ; and 
         FIGS. 3A-3G  are cross-section views of the ΔE-E detector of  FIGS. 2A-2B  at various stages of a manufacturing process according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the drawings,  FIG. 1  schematically illustrates a semiconductor microdosimeter  100  according to an embodiment of the invention. The microdosimeter  100  includes a monolithic ΔE-E detector  105 , which is integrated in a chip of semiconductor material. The type of doping ions (acceptor and donor dopants) in the various regions of the chip are indicated in the following, as usual in the art, by the letters P and N, respectively; the letters N and P may have an added minus ‘−’ or plus ‘+’ sign to denote light or heavy doping ions concentrations, respectively. 
     The ΔE-E detector  105  comprises a P-doped region  110 , buried into the chip and interposed between two N-doped regions  115  and  120 . Metal electrodes  125 ,  130  and  135  contact the regions  110 ,  115  and  120 , respectively. In such a structure the P-doped region  110  acts as a common anode of two diodes, thus produced on the same chip, which have respective cathodes in the N-doped regions  115  and  120  (with the metal electrode  125  that defines their common anode electrode, and the metal electrodes  130  and  135  that define the corresponding cathode electrodes). The diode formed by the anode region  110  and the cathode region  115  is thinner than the diode formed by the anode region  110  and the cathode region  120 ; in this way, the (thin) diode  110 , 115  constitutes a ΔE section of the detector  105  and the (thick) diode  110 , 120  constitutes an E section of the detector  105 . 
     The ΔE-E detector  105  (and more specifically an exposed surface of the cathode region  115 ) is covered by a layer  140  of tissue-equivalent material; for example, the tissue-equivalent layer  140  is made of a hydrogenated plastic material with an atomic composition similar to that of biological tissue, such as polyethylene. 
     The microdosimeter  100  also includes measuring circuits  145  and  150 , which are coupled to the cathode electrode  130  and to the cathode electrode  135 , respectively. The measuring circuits  145  and  150  provide respective measuring signals I(ΔE) and I(E-ΔE) corresponding to an energy absorbed by the thin diode  110 , 115  and by the thick diode  110 , 120 , respectively. Moreover, the microdosimeter  100  comprises an analogic circuit  155 , which receives the measuring signals I(ΔE),I(E-ΔE) and provides an output signal OUT accordingly. 
     In operation, two voltages V 1  and V 2  (with respect to a reference voltage, or ground) are applied to the cathode electrodes  130  and  135 , respectively; the anode electrode  125  is instead coupled to a terminal providing the ground voltage. The voltages V 1  and V 2  are such that both the thin diode  110 , 115  and the thick diode  110 , 120  are reverse biased and completely depleted. Accordingly, two depletion zones of the diodes  110 , 115  and  110 , 120  are formed, so as to define the sensitive volume of the ΔE-E detector  105 . 
     During irradiation, ionizing particles strike the tissue-equivalent layer  140  covering the ΔE-E detector  105 . Any particle having an energy E so as to allow it to cross the tissue-equivalent layer  140  (represented by an arrow in the figure), reaches the depletion zones of the diodes  110 , 115  and  110 , 120  causing the formation of electron-hole pairs, i.e. it deposes a quantity of its energy E into the ΔE-E detector  105 . Particularly, only a first part of the energy E (ΔE) is deposited in the thin diode  110 , 115 , while a second part of the energy E—greater than the energy part ΔE—is deposited into the thick diode  110 , 120  (with this energy part that is equal to the “residual” energy, i.e. E-ΔE, when the particle stops in the ΔE-E detector  105 ). 
     The electron-hole pairs so formed move towards the electrodes  125 - 135  and they are collected separately by the thin diode  110 , 115  and by the thick diode  110 , 120 , so as to generate two pulsed currents corresponding to the energy part ΔE and to the energy part E, respectively. These currents are amplified and detected by the measuring circuits  145  and  150 , which provide the respective measuring signals I(ΔE) and I(E-ΔE). 
     The analogic circuit  155  can then generate the output signal OUT, according to the received measuring signals I(ΔE) and I(E-ΔE). For example, it is possible to identify the particle by measuring the signal I(ΔE)—proportional to its electrical charge—and the sum of the two signals I(ΔE) and I(E-ΔE)—proportional to its mass. 
     Referring now to  FIG. 2A , a cross-section view of the ΔE-E detector  105  according to an embodiment of the present invention is shown in greater detail. 
     Particularly, the chip wherein the ΔE-E detector  105  is integrated is denoted with the reference  205 ; for example, the chip  205  (made of silicon) has a thickness of 400-600 μm, between a back (lower) surface  215  and a front (upper) surface  216 . 
     An N+ contact layer  220  extends within the chip  205  from the back surface  215  for a thickness of about 1 μm. An N+ channel-stopper region  222  surrounds the whole chip on the front surface  216  for a thickness of about 1 μm; in this way, the channel-stopper region  222  defines a lateral edge surrounding an area wherein the ΔE-E detector  105  will be integrated. 
     A P+ region  224  extends from the front surface  216  into the chip  205  to a depth of about 2 μm. The P+ region  224  is arranged within the channel-stopper region  222  and spans most of the area surrounded by it. In this way, an N− guard region  230  of the silicon chip  205  (with a width of about 200 μm) remains between the P+ region  224  and the channel-stopper region  222 ; at the same time, a buried N− active region  235  (which will define a cathode of the thick diode) is interposed between the P+ region  224  and the contact layer  220  (with a thickness of about 397-597 μm in the example at issue). 
     The ΔE-E detector  105  includes multiple detection cells  236  (for example, from 24 to 48, such as 36). For each detection cell  236 , a P− region  237  extends from the front surface  216  into the P+ region  224  to a lower depth (for example, of about 1.7 μm). In this way, the P+ region  224  is partitioned into a buried contact region  240  (with a thickness of about 0.3 μm in the example at issue) arranged between the P− regions  237  and the cathode region  235 , and a sinker region  241  surrounding the P− regions  237  (connecting the buried contact region  240  to the front surface  216 ). An N+ active region  255  (which will define the cathode of the thin diode) in turn extends from the front surface  216  into each P− region  237  to a far lower depth (for example, of about 0.2-0.4 μm). Likewise, the P− region  237  is partitioned into a buried active region  263  (which will define the common anode of the thick and thin diodes) and an edge region  264  surrounding the cathode region  255 ; particularly, the anode region  263  (with a thickness of about 1.3-1.5 μm in the example at issue) is arranged between the corresponding cathode region  255  and the common buried contact region  240 . 
     In the solution according to an embodiment of the present invention, a trench  270  (filled with insulating material, such as silicon dioxide and polysilicon) is formed in the chip  205  around each cathode region  255 . The trench  270  extends from the front surface  216  to reach the buried contact region  240  (i.e., at a depth of at least 1.7 μm in the example at issue). In this way, the trench  270  completely insulates the anode region  263  from the corresponding edge region  264 . 
     A plurality of spacers  275  of insulating material (e.g., SiO 2 ), one for each detection cell  236 , is formed over the front surface  216 . Particularly, each insulating spacer  275  lies over a part of the surrounding sinker region  241 , the trench  270 , the edge region  264 , and an outer portion of the cathode region  255  of the respective detection cell  236 ; in this way, a sensitive area of the detection cell  236  is defined over the cathode region  255  within the insulating spacer  275 , while multiple contact windows remain opened over the sinker region  241 . 
     A metal strip  280  (for example, of titanium) lies in contact with this sensitive area of the detection cell  236  (partially covering the surrounding insulating spacer  275 ), so as to define an electrical contact of the cathode region  255 . A further metal strip  285  (for example, of titanium) lies in contact with the sinker region  241  through the respective contact windows (partially covering the adjacent insulating spacers  275 ); a metal strip  287  (for example, of aluminum) is formed over the metal strip  285 , so as to define an electrical contact of the anode regions  263  (through the buried contact region  240  and the sinker region  241 ). A metal layer  290  (for example, of aluminum) is instead formed over the whole back surface  215 , so as to define an electrical contact of the cathode region  235  (through the contact region  220 ). 
     In the above-described structure of the ΔE-E detector  105 , each detection cell  236  consists of two diodes having a vertical arrangement and a common anode buried into the chip. Particularly, for each detection cell  236  the thin diode is formed by the P− region  263  (anode) and the N+ region  255  (cathode), whereas the thick diode is formed by the P+ region  240  (anode) and the N− region  235  (cathode); the common anode electrode is formed by the metal strips  285 , 287 , whereas the cathode electrodes for the thin diode and for the thick diode are formed by the metal strip  280  and the metal layer  290 , respectively. 
     In this way, the depletion zone of the thin diode mainly extends into the (more lightly doped) anode region  263  and the depletion zone of the thick diode mainly extends into the (more lightly doped) cathode region  235 ; the two depleted regions are then clearly separated by the heavily doped (anode) buried contact region  240 . Therefore, the electron-hole pairs generated in the two diodes by the energy that is lost by any ionizing particle are collected in a completely distinct way. This strongly reduces the field-funneling effect. Moreover, the sinker region  241  surrounding each detection cell  236  prevents a capacitive coupling with adjacent detection cells  236 , allowing the ΔE-E detector  105  to show a limited capacitance. 
     In the solution according to an embodiment of the present invention, the addition of the trenches  270  strongly improves the performance of the ΔE-E detector  105 . Indeed, in each detection cell  236  the corresponding trench  270  limits a corresponding sensitive volume of the thin diode to the anode region  263  (surrounded and insulated by the trench  270 ); in this way, the edge region  264  does not contribute to collect hole-electron pairs. Then, the sensitive volume may be maintained to the desired value (i.e., comparable to the biological cell size). 
     Moving now to  FIG. 2B , a top view of the ΔE-E detector  105  described-above is illustrated (the elements corresponding to those depicted in  FIG. 2A  are denoted with the same references and their description is omitted for the sake of simplicity). 
     In an embodiment of the invention, each detection cell  236  has a circular section (since this shape better emulates the behavior of a corresponding biological cell). Typically, the detection cells  236  are arranged in a matrix (for example, six rows and six columns). The cross section of the ΔE-E detector  105  illustrated in  FIG. 2A  is taken at a plane AA along a column of the detection cells  236 . The number of detection cells  236  is chosen in such a way to have a sensitive area of the ΔE-E detector  105  (at the front surface thereof) sufficiently large to ensure good detection efficiency. A limit to the widening of the ΔE-E detector  105  is due to the capacitance shown by all the detection cells  236  connected in parallel, because a small capacitance permits to keep low the electronic noise. 
     The anode electrode (with only the upper metal strip  287  visible in the figure) covers most of the P+ region  224  (only leaving an external edge thereof exposed); for example, the metal strip  287  has a square shape surrounding the matrix of the detection cells  236 . On the other hand, the cathode electrode (formed by the metal strip  280 ) has a circular portion for each detection cell  236 . A strip  292  connects the circular portions of each pair of adjacent columns of the matrix (through corresponding interconnection segments); the strips  292  are in turn connected together in an area overlying the external edge of the P+ region  224 , where a bonding pad  294  is provided for applying the desired biasing voltage. Similarly, a further bonding pad  296  is provided for applying a biasing voltage to the metal strip  287 . The metal strip  280  and the metal strip  287  are separated by the insulating spacer  275  (with a partially cut-away circular crown shape around each detection cell  236 ). 
     The guard portion  230  separates the P+ region  224  from the channel-stopper region  222 , which in turn surrounds the whole ΔE-E detector  105  as a square frame; this additional feature further improves the electrical characteristics of the ΔE-E detector  105  (and especially its noise immunity). 
     The main stages of an exemplary process for the fabrication of the ΔE-E detector according to an embodiment of the present invention are described hereinafter with reference to  FIGS. 3A-3G  (the elements corresponding to those depicted in  FIGS. 2A and 2B  are denoted with the same reference numerals and their description is omitted for the sake of simplicity). 
     Referring to  FIG. 3A , the process starts from a silicon wafer  305  lightly doped by N type dopants and, for example, with a crystallographic orientation {1.0.0}. The wafer  305  is obtained with a floating zone (FZ) process (by establishing a melt zone between a seed material and a feed material through the application of localized heating), so as to obtain a substantially pure material. In this way, it is possible to have a very high resistivity (e.g., of about 4.000-6.000 Ω·cm). 
     The whole surface of the wafer  305  is then covered by a layer of silicon dioxide  310  (as shown for the back surface  215  and for the front surface  216  in the figure); for example, this result is achieved by oxidation in an oxidizing atmosphere at high temperature. The oxide layer  310  on the front surface  216  is then selectively etched with conventional photolithographic techniques (by means of a resist mask suitably shaped, not shown in the figure), so as to open windows corresponding to the sinker region  241 . An implant of P type dopants (for example, boron ions) is now performed through the portion of the front surface  216  uncovered by the above-mentioned etching. The implant may be executed in two steps, which differ for the implant doses and energies (with a total dose of about 1·10 15  cm −2  and energies of about 80 keV to 450 keV). Successively, a thermal diffusion in oxidizing atmosphere is performed, so as to obtain the sinker region  241  with a peak of dopant concentration (at a depth of 0.5-1.5 μm) of about 1.1019 cm −3 . 
     As illustrated in  FIG. 3B , the oxide layer  310  is again selectively etched with conventional photolithographic techniques so as to open a (larger) window corresponding to the P+ region  224 . An implant of P type dopants (for example, boron ions) is now performed through the portion of the front surface  216  uncovered by the above-mentioned etching. The implant has a very high energy (e.g., 1 MeV) and with a dose of about 1·10 14  cm −2 ; this allows obtaining the buried contact region  240 . The P− regions  237 , within the sinker region  241 , are then formed by diffusion of the P doping ions from the buried contact region  240  towards the front surface  216 . Accordingly, a retrograde implant of P doping ions is obtained having a peak dopant concentration of about 1·10 18  cm −3  in the buried contact region  240 . The (remaining) oxide layer  310  is then etched from both the back surface  215  and the front surface  216 . 
     Likewise, as illustrated in  FIG. 3C , the whole surface of the wafer  305  is again covered by another layer of silicon dioxide  320 , which is then selectively etched with conventional photolithographic techniques so as to open windows corresponding to the channel-stopper region  222  and to the cathode region  255 . An implant of N type dopants (for example, arsenic ions) is now performed through the portion of the front surface  216  uncovered by the above-mentioned etching; for example, the implant is carried out with a dose of about 5·10 14  cm −2  and an energy of about 60 keV.| 
     Then, as illustrated in  FIG. 3D , a hard-mask  327  is formed on top of the silicon wafer  305 , thereby also covering the oxide layer  320 ; the hard mask  327  is realized by deposing a layer of a different dielectric, such as nitride or P-vapox. Both the hard-mask  327  and the dioxide layer  320  are selectively etched with conventional photolithographic techniques so as to open windows corresponding to the trenches  270 . A dry etching of the wafer  305  is then carried out through the portion of the front surface  216  uncovered by the above-mentioned etching. The trenches  270 , having a circular crown section (for example, with a width of about 1 μm) are obtained, extending roughly orthogonally down to the buried contact region  240 . The process continues by growing a dioxide layer  332  on the walls of the trenches  270 . The whole wafer  305  is now covered by a polysilicon layer  335  (through deposition), in such a way to completely fill the trenches  270 . 
     Successively, as shown in  FIG. 3E , the polysilicon layer  335  and the hard-mask  327  are completely removed (without impairing the dioxide layer  320 ). The dioxide layer  320  is now removed from the back surface  215 ; an implantation of Phosphorus ions with dose of, for example, 1·10 16  cm −2  and energy of, for example, 80 keV is performed so as to realize the contact layer  220  at the back surface  215 . 
     Referring to  FIG. 3F , a diffusion in oxidizing atmosphere is performed, so as to form a further dioxide layer  340  over the front and back surfaces  216  and  215 ; this step is followed by a segregation annealing process. 
     As depicted in  FIG. 3G , the oxide layers  320  and  340  are selectively etched with conventional photolithographic techniques so as to open contact windows for the sinker region  241  and the cathode regions  255 . A first thin metal layer  350  (for example, of titanium) and a second thick metal layer  355  (for example, of aluminum) are deposited over the whole front surface  216 , so as to fill the contact windows defined by the above-mentioned etching. The metal layers  350  and  355  are then selectively etched with conventional photolithographic techniques so as to shape them according to the desired electrical contacts of the sinker region  241  and of the cathode regions  255 . 
     A further selective etching is exploited for removing only the excess of the aluminum layer  355  over the portion of the front surface  216  intended to be the sensitive area of the ΔE-E detector (i.e., over the cathode regions  255 ). Therefore, as shown in  FIG. 2A , the metal strips  285 , 287  in contact with the sinker region  241  and the metal strip  280  in contact with each cathode region  255  are obtained. The process then ends with the deposition of the metal layer  290  (for example, aluminum) over the back surface  215 . 
     Naturally, in order to satisfy local and specific requirements, a person skilled in the art may apply to the solution described above many modifications and alterations. Particularly, although the present invention has been described with a certain degree of particularity with reference to embodiment(s) thereof, it should be understood that various omissions, substitutions and changes in the form and details as well as other embodiments are possible; moreover, it is expressly intended that specific elements and/or method steps described in connection with any disclosed embodiment of the invention may be incorporated in any other embodiment as a general matter of design choice. 
     For example, similar considerations apply if the ΔE-E detector has an equivalent structure. For example, the wafer can be made of a different semiconductor material and, particularly, can be different from a floating-zone silicon wafer. Likewise, the regions may have different size, thickness and/or dopant concentrations, or the regions of the N-type may be replaced by regions of the P-type, and vice-versa; furthermore, alternative materials can be utilized for fabricating the ΔE-E detector, such as different dopants, metals, or dielectrics. 
     Likewise, the ΔE-E detector may be realized with an equivalent structure of its (thin and/or thick) diodes. 
     In addition, nothing prevents extending the insulation trench of each detection cell to a different depth (for example, more deeply into the buried contact region); however, an implementation wherein the depth of the insulation trench is slightly lower than the one of the anode region is contemplated (even if it might be less advantageous). 
     Similar considerations apply if each trench has a different structure, shape and/or size; more generally, whatever equivalent insulation means may be used to implement the proposed solution. 
     Although in the present description reference has been made to detection cells with circular shape, this is not to be interpreted in a limitative manner (the solution may be implemented with any other section of the detection cells, such as a square). 
     Likewise, alternative layouts of the detection cells are feasible (for example, with a different number of detection cells, a different arrangement, and the like); in any case, an implementation of the ΔE-E detector with a single detection cell is within the scope of the invention. 
     It is also possible to use a channel-stopper with a different shape or structure; in any case, this feature is not strictly necessary and it may be omitted in some implementations of the ΔE-E detector. 
     Similar considerations apply if the proposed ΔE-E detector is used in different microdosimeters (for example, without any tissue-equivalent layer for microelectronics applications), or more generally in any other system. 
     At the end, the fabrication process of the ΔE-E detector can comprise additional stages or the stages can be executed in a different order and/or exploiting alternative techniques; particularly, the masks used during the process can be different in number and in type. 
     It should be readily apparent that the design of the ΔE-E detector may be created in a programming language; moreover, if the designer does not fabricate chips or masks, the design may be transmitted by physical means to others. In any case, the resulting integrated circuit may be distributed by its manufacturer in raw wafer form, as a bare die, or in packages form. Moreover, the ΔE-E detector may be integrated with other circuits on the same chip, and it may be mounted in intermediate products (such as electronic boards), or in complex systems. 
     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention.