WO2015114193A1 - Microdosimètre basé sur des structures 3d à semiconducteurs, procédé de fabrication dudit microdosimètre et utilisation de ce dernier - Google Patents

Microdosimètre basé sur des structures 3d à semiconducteurs, procédé de fabrication dudit microdosimètre et utilisation de ce dernier Download PDF

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WO2015114193A1
WO2015114193A1 PCT/ES2015/070056 ES2015070056W WO2015114193A1 WO 2015114193 A1 WO2015114193 A1 WO 2015114193A1 ES 2015070056 W ES2015070056 W ES 2015070056W WO 2015114193 A1 WO2015114193 A1 WO 2015114193A1
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microdosimeter
cell
radiation
cylindrical
semiconductor
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Consuelo GUARDIOLA SALMERÓN
Giulio Pellegrini
Manuel Lozano Fantoba
María Celeste FLETA CORRAL
David QUIRION
Faustino GÓMEZ RODRIGUEZ
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Universidade de Santiago de Compostela
Consejo Superior de Investigaciones Cientificas CSIC
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Universidade de Santiago de Compostela
Consejo Superior de Investigaciones Cientificas CSIC
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/02—Dosimeters
    • G01T1/026—Semiconductor dose-rate meters
    • 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
    • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
    • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
    • H10F30/29—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to radiation having very short wavelengths, e.g. X-rays, gamma-rays or corpuscular radiation

Definitions

  • This invention relates to a microdosimeter formed by cells that form a matrix, where inside each cell there is a radiation sensitive volume, which is manufactured on semiconductors by means of three-dimensional processes that define the components of a PN junction.
  • the microdosimeter may include a signal processing system obtained with the microdosimeter to obtain radiobiological quantities as the equivalent of H dose by an algorithm comprising geometric corrections and equivalent tissue.
  • the invention indicates manufacturing processes of different configurations that these microdosimeters may have, and their use for radiation detection in different fields including medical and aerospace applications.
  • the main application is the medical and radiological personal protection area, for example to obtain physical parameters with which to derive the dose equivalent in radiation fields such as those generated in nuclear medicine and hadron pets, aviation, aerospace exploration, nuclear facilities and accelerators of particles, among others.
  • Fluctuations in the micrometric scale energy deposit is one of the most relevant topics in radiobiology. While the energy imparted or absorbed on a macroscopic scale can be considered a continuous magnitude, the dose is deposited in practice through multiple individual interactions of the quanta of the incident radiation in the medium that they pass through. On a microscopic scale the energy imparted behaves like a random variable whose distribution of values follows a certain statistical distribution. The biological effect of radiation depends not only on the energy absorbed in a certain tissue but also on the type of incident radiation that we can call radiation quality.
  • microdosimetry The technique for measuring microscopic energy distributions is known as microdosimetry, this is the study of the ionization distribution or the deposit of energy in microscopic volumes (specific energy), especially in biological matter, as well as its relationship in physical / chemical consequences. and / or biological.
  • Such a branch of dosimetry is essential for both radiation therapy and radiation protection and requires adequate instrumentation for quantification.
  • a microdosimeter is a device or instrument capable of evaluating the dose (energy deposited per unit mass) deposited in small volumes of micrometric scale masses when placed in a radiation field. Examples of these events are, for example, those that take place on a cellular or subcellular scale (eg cell nucleus) when organisms are irradiated, either for reasons of medical treatment (eg hadron therapy) or for being involuntarily subjected to natural radiation (eg cosmic radiation ) or artificial (eg in nuclear reactors, industry, etc.).
  • the data obtained through a microdosimeter allow obtaining information on the characteristics associated with the deposit of energy dependent on the quality of the radiation. These features are usually inaccessible for conventional macroscopic detectors.
  • the microdosimeters can be used to detect radiation / particles, so phototherapy is used in radiotherapy, and in prototypes, carbon protons and ions are detected mainly, although any other charged particle can be detected.
  • the microdosimeters can be used in the medical field of application for the detection of ionizing radiation, but also in the aerospace area as high energy cosmic particle detectors.
  • the average diameter of mammalian cells is in the range of a few micrometers. For example, in the case of human cells they have a size ranging from 7 ⁇ , for red blood cells, to 150 ⁇ for ovules.
  • the radiation dose effectiveness factor and dose rate describe the biological efficacy of different types of radiation to estimate cancer risk.
  • Other factors used to assess biological efficiency are the relative biological efficiency (RBE) and the weighting factor (W r ). It is the distribution of the dose imparted - which depends on the type of particle and its energy - on structures such as the cell nucleus, which contains the DNA, which determines the level of cellular damage and consequently its survival / repair.
  • the cellular DNA will be able to repair itself or be inactivated;
  • the first thing would be as desired, while in radiotherapy / hadronbib the second is what is required (on tumor cells, but not on the surrounding healthy tissue).
  • the microdosimeters allow estimating radiation parameters in real time such as, mainly, those related to the energy deposited by the radiation, but to quantify the radiobiological damage it is necessary to derive some physical parameters from said deposited energy and perform a postprocessing with an electronics additional and specific software.
  • One of the most relevant dosimetric parameters to quantify the effectiveness of radiation is the Linear Energy Transfer (LET) since it defines the local deposit of radiation energy along the path of the charged particles associated with the exposure. to this radiation and is directly correlated with radiobiological effects on the irradiated tissue (through another radiobiological parameter: relative biological efficacy (RBE)).
  • LET Linear Energy Transfer
  • RBE relative biological efficacy
  • the LET varies when penetrating the tissue / white (understood in this context as 'white' to a compendium of mixed tissue with variable and highly heterogeneous densities, compositions and geometries, eg human tissue) and for some types of irradiation , such as those used in hadronbib, its value varies considerably throughout its incidence with the target. But it is also that when the irradiated target has a micrometric size, the energy deposit is not deterministic, but stochastic. Then, in microdosimetry it is necessary to use other stochastic variables to quantify experimentally [ICRU Report 36, Microdosimetry, The International Commission on Radiation Units and measurements, 1983], such as:
  • microdosimeter 4— [ M m]
  • V is the microscopic volume of the region of interest irradiated and S the area of such volume.
  • "and” is the magnitude analogous to the LET at micrometric scales.
  • the microdosimeter must be designed in such a way that its radiation-sensitive volume has an equivalent to the average size of the cellular structures to be studied.
  • the absorbed dose in the microdosimeter can be derived from the distribution of linear energy values ("and") within the material that forms the microdosimetric cavities where the energy of the incident radiation is deposited and the characteristics associated with the quality of the radiation.
  • Said material is the so-called "sensitive volume” and is instrumentally a particle / radiation detector, ie a device or part of it that is technologically capable of characterizing a radiation field.
  • sensitive volume detectors with sizes comparable to biological cells, ie micrometric volumes [Rossi HH, Zaider M., Microdosimetry and its Applications, Springer 1996].
  • proportional gas meters have been traditionally used, such as Tissue Equivalent Proportional Chambers (PTSD) or Rossi Chambers [Rossi HH and Rosenzweig W., Measurements of neutron dose as a function of linear energy transfer, Radiology, vol.
  • microdosimetry One of the great attractions of using silicon and other semiconductors in microdosimetry is the possibility of producing structures of micrometric dimensions. In addition, these do not require any gas supply system, operate at low voltage, are light and easily portable. Since the 1980s, several studies have proposed and developed semiconductor detectors based on microdosimetry. The semiconductor radiation sensors act as detectors that quantify the ionization produced by the radiation when it affects a radiation sensitive volume of said sensor. The semiconductor microdosimeters proposed since then can be grouped into three types and are based on PN junctions, where a PN junction is a two-component structure formed by the metallurgical junction of two crystals, such as silicon, germanium, etc., one of type P and another type N.
  • these are usually doped with impurities, eg Boron or Phosphorus respectively.
  • impurities eg Boron or Phosphorus respectively.
  • an electrical conductive part eg aluminum layer in contact with each doped zone
  • two electrodes are created, one positive and one negative, to which a potential difference can be applied ( "polarization") to create an electric field within said PN junction.
  • the Rozenfeld group shows the first silicon microdosimeters with diode series of rectangular parallelepiped structures made of Silicon-on-Insulation (what is known as "SOI" wafers) [Bradley PD. et al., Solid state microdosimetry, Nuc ⁇ . Inst. And Meth. B 2001; 184: 135-157].
  • SOI Silicon-on-Insulation
  • the proposed technology has a matrix of columnar electrodes (containing the P + or N + part) arranged at the vertices of a square in whose center there is another columnar electrode (type N + or P + respectively).
  • This arrangement causes the sensitive volume around said electrodes to have a well defined geometric delimitation (since the electric field created between said electrodes, although radial, does not confine a sensitive volume with symmetric geometry), ie does not form an equivalent to a simple and clear geometric figure and therefore cannot be used for microdosimetry (since a geometric volume similar to cellular structures or substructures, cylindrical or spherical type) is required.
  • US20100090118 presents devices for aerospace application (pilots and astronauts). These last works show different technologies, although they reproduce, by means of planar technology, externally cylindrical shapes as sensitive volumes (within the substrate N + and P + standard structures are created by diffusion or implantation and then the surrounding silicon area is recorded (removed) with a circular shaped mask, to leave a cylindrical geometric shape around the PN junction.
  • a first aspect of the invention is a microdosimeter comprising a set of cells that form a matrix characterized in that - the substrate where the cell is manufactured is a semiconductor wafer,
  • the cell has a diameter between 5 and 150 ⁇ and a depth between 1 and 300 ⁇
  • the cell comprises a radiation-sensitive volume
  • the volume-sensitive is defined by the 3D cylindrical engraving of one of the components of at least one PN junction
  • the components of the PN junction can form two asymmetric electrodes with different thickness and / or shape.
  • the substrate is a semiconductor wafer of the Semiconductor-over-Insulator (SOI) type, comprising at least one of the following materials: Si, Ge, SiC, CdTe, CdZnTe, GaAs, B 4 C; or is a standard wafer.
  • SOI Semiconductor-over-Insulator
  • the reading of the electrical signal can be of continuous and / or independent type for each of the cells.
  • the microdosimeter may comprise layers of various equivalent biological tissue materials.
  • the microdosimeter can comprise a signal processing system that obtains radiobiological quantities by means of an algorithm.
  • the microdosimeter can correlate the variable measured by the microdosimeter, the energy deposited by ionizing radiation, ⁇ , with radiobiological quantities such as the equivalent dose H by an algorithm comprising geometric corrections and equivalent tissue.
  • the algorithm can comprise the following stages: as measured by the pulse height or load collected in each cell of the microdosimeter matrix as a spectrum or pulse height distribution in each pixel of the semiconductor that acts as a substrate of the matrix that forms said microdosimeter ,
  • a second aspect of the invention is the manufacturing method of the microdosimeter of the invention comprising the following steps:
  • the procedure can have two alternative configurations.
  • step a) the central component type P + or N + is created by diffusion or implantation and in step b) a cylindrical-3D ring-shaped engraving, centered on the semiconductor pixel, is made and filled with doped polysilicon or with undoped polysilicon that is subsequently doped with a N + or P + type dopant respectively.
  • step a) a component type P + or N + is diffused or implanted or a cylindrical-3D-ring engraving is made that is filled with already doped polysilicon or with undoped polysilicon and later this will be doped type P + or N + and in step b) a cylindrical-3D column is formed in the center of the cell, whose internal walls are filled with polysilicon, which is engraved and subsequently doped type N + or P +.
  • the cylindrical etching process may comprise a reactive beam process by ion beam or a deep etching process by reactive ions (DRIE).
  • DRIE reactive ions
  • a thinning process of the substrate can be done by chemical etching or reactive ion processes.
  • a third aspect of the invention is the use of the microdosimeter of the invention for radiation detection in the field of medical application, preferably in hadron therapy.
  • the microdosimeter can be used to perform measurements at the surface level such as on the surface of the skin or at a biological interface, and / or at a certain depth such as under the skin or irradiated tissue.
  • the microdosimeter can be coupled to a tissue equivalent material that simulates specific biological tissue including water, muscle and / or bone.
  • the microdosimeter can also be used in other fields derived from other radiation environments, such as secondary neutrons generated in therapy, in mixed radiation fields, including radiation protection in personal use and area monitoring, for portable systems, and in the field of application aerospace
  • microdosimeters The design configuration of such microdosimeters is of the pixel type, such that an array of cells (205) is created, and the center of the cell (205) defines the position of the pixel itself.
  • the term "cell” (205) is understood as the simplest portion of the microdosimeter which, when repeated by translation, reproduces the entire assembly, presenting translation symmetry centered on the pixel.
  • the step (108) between two cells (205) is what we define as "piten”.
  • the interior of the cell (205) ( Figure 2) contains a "radiation sensitive volume” (208) made of a semiconductor material that is capable of detecting the energy deposit left by the eh pairs (203) created by the ionization produced by radiation (201) when passed through it.
  • the microdosimeters can be manufactured to cover from micrometric areas up to cm 2 .
  • said cell matrix (205) can be replicated on a large scale to simulate cell tissues through the ability to "large-scale integration” (VLSI), possible in the process of manufacturing MEMS devices.
  • each cell (205) of the microdosimeter acts as a microsensor on a cellular scale ( Figure 2).
  • the radiation or particles (201) pass through the cell (205) of the microdosimeter, it ionizes matter, particularly the sensitive volume (208) of the cells (205), thereby creating charges, in particular, electron-hollow pairs ( eh) (203) in that volume (208).
  • the total number of pairs eh (203) created is proportional to the energy of the radiation or particles (201) that they affect said cell (205).
  • a first object of the invention is a microdosimeter, hereinafter referred to as a microdosimeter of the invention, formed by a set of cells (205) that are part of a matrix characterized in that
  • the substrate where the cell (205) is made is a semiconductor wafer (101), - the cell (205) has a diameter between 5 and 150 ⁇ and a depth between 1 and 300 ⁇ ,
  • the cell (205) comprises a radiation sensitive volume (208),
  • the sensitive volume (208) is delimited by cylindrical-3D engraving of the components of at least one PN junction
  • the components of the PN junction can have different thicknesses and shape giving rise to two asymmetric electrodes.
  • the configuration of asymmetric electrodes by perforating the semiconductor of the substrate (101) that limit the sensitive volume (208) is a configuration that allows that there is no contact layer in the window through which the particles enter, but which at the same time allows there is more sensitive volume (208) with a charge collection close to 100% without the inner intrinsic zone of the column electrode (Example 3).
  • the substrate can be of two types: Semiconductor-over-Insulation (SOI) wafers, where the semiconductor (101) can be Si, Ge, SiC, CdTe, CdZnTe, GaAs, B 4 C, among others., Eg Figures 1A and 1 B: or standard wafers, eg Figures. 1 C and 1 D.
  • SOI Semiconductor-over-Insulation
  • the microdosimeter can be designed with cells (205) of such small areas such that the diameter of the cell (205) is comparable to the average diameter of the biological cells (204), of the order of ⁇ , and with thicknesses from 1 ⁇ , such that the sensitive volume (208) is equivalent to that which has, on average, a cell.
  • the cell (205) in turn contains a smaller volume of equivalent size to the cell nucleus, the so-called volume-sensitive (208), the only volume really sensitive to radiation within the cell (205), of which obtains the energy deposited by the pairs eh (203) of the radiation (201) that crosses the cell.
  • the sensitive volume (208) is delimited by the cylindrical-3D engraving technique.
  • This three-dimensional etching (or definition or attack or subtraction) process of semiconductor material (101) includes physical or chemical processes of ionic attack or other etching technique. With this technique, part of the substrate is removed creating a three-dimensional perforated shape inside the semiconductor (101) ( Figure 2). This perforation leaves a hollow volume in the semiconductor (101), preferably a 3D cylindrical engraving with a column (601) or perforated cylindrical ring (105).
  • the material that is between the two components mainly a semiconductor (101)
  • the sensitive volume (208) is a volume delimited by the components of the PN junction.
  • the volume-sensitive (208) is "delimited" by the internal part of the cylindrical-3D engraving (105) and the entire internal part of said cylindrical volume is volume-sensitive (208) of the semiconductor (101) to the radiation, so when a charged particle, for example proton or carbon ion (201) passes through it, it will ionize said medium leaving pairs eh (203) as a function of the initial energy with the I will interact there and these charges will be collected by the electrodes (209 and 210).
  • Figure 6 where a cylindrical-3D-columnar engraving is presented in the middle (601), the volume-sensitive (208) is also intended to be the same as in Figure 5.
  • the two components of the PN junctions are three-dimensional, and they can have one of the following two configurations.
  • the external component of the PN junction is produced by doping the inside of said ring, formed by a perforation in the semiconductor (101) in the form of a cylindrical ring (105), and on whose walls (hollow) deposit polysilicon and then its walls are doped by diffusion P + or N +, or else the polysilicon is already doped; and a central disk (104) where the other component of the PN junction is formed that is formed by diffusing / implanting, in the center of said central shape (104), a dopant to create a N + or P + type motif respectively (104) .
  • Figure 5 Figure 5).
  • the column electrode array has a cell delimitation (205) not entirely cylindrical, while in the case of this invention each cylindrical-3D engraving (105, 601) is either surrounding a P + or N + implantation (104) or surrounded by it (602), respectively. In any case, the cylindrical shape of the volume-sensitive (208) is more clearly defined.
  • the geometry of the cell (205) can be manufactured with a well-defined volume and controlled by the use of Latest generation techniques in MEMS devices and the volume can be equivalent to the average size of the cells that contain the tissue to be irradiated, object of study.
  • the sensitive volume (208) is well confined in a cylindrical region of known dimensions and controlled in the manufacturing process, this sensitive volume (208) can have a diameter (107) between 5 and 150 ⁇ and depths (109) between 1 and 300 ⁇ .
  • the pixel configuration of the detector that is to say that it forms a matrix that covers a controllable surface area (equivalent to a portion of irradiated tissue) allows the radiation traces to be independently delimited since each cell (205) is equivalent to a volume-sensitive (208) cell.
  • the 3D architecture avoids the 'field-funnelling effect' since it favors the confinement of the load of the pairs eh thanks to the design of well-defined empty volumes.
  • 3D technology is resistant to radiation because its structure is based on 3D technology for radiation detectors. This advantage makes it especially useful for use in high-rate environments, such as radio / hadron therapy.
  • the proposed technology allows to manufacture the smallest silicon radiation detectors to date (from 2 ⁇ thick with 3D electrodes), but which can be additionally emptied from the back of the wafer (etch the wafer support silicon SOI ) so that there is a "membrane" (cellular) of 2 ⁇ thick (avoiding the backscatter of the particles that could interact there).
  • one of the smallest silicon radiation detectors has been made by S. Agosteo using planar technology, although without emptying the wafer, with mechanical support and for them it also acts as a sensitive volume, about 500 ⁇ thick .
  • the reading of the unit cells (106) that collect the information from the cells (205) can be continuous or independent type ( Figures 7).
  • the central metallizations (210) are connected to metal pads (701) with a metal track (704) and the external metallizations (209) are joined with a metal track (703) that connects the cylindrical electrodes with strip 702 to polarize the PN junction.
  • each cell (205) is read independently, where individual tracks (802) connect with independent pads (801). The pads are to which the reading electronics (106) will be connected to read the obtained signal.
  • Another object of the invention is the method of processing the signal obtained with the microdosimeter in a radiation field in order to correlate the variables measured with radiobiological quantities such as the equivalent of dose H, this is done with an algorithm that contains geometric corrections and of equivalent tissue.
  • the device is capable of quantifying the energy imparted ( ⁇ ) by the incident radiation, it will be in the postprocessing / data analysis where these magnitudes must be convolved to evaluate the parameters that predict radiobiological effects. This procedure can be integrated into a single end device.
  • the microdosimeter can be coupled to analysis means, such as a Multichannel Analyzer (MCA) to acquire the spectrum in energy for its subsequent post-processing until the dose equivalent (H) is estimated.
  • MCA Multichannel Analyzer
  • the analysis means allows to implement an algorithm that includes equivalent tissue correction and geometric correction steps.
  • An example shows a possible algorithm tissue-equivalent correction:
  • the scaling factor it depends on the type of incident particle and its energy [Rossi HH, Zaider M., Microdosimetry and its Applications, Springer 1996], which assumes two conditions: (i) the deposited dose is only due to charged particles and (ii) creep does not change on the irradiated target
  • the procedure consists preferably, but not exclusively, of the following steps [Rossi HH, Zaider M., Microdosimetry and its Applications, Springer 1996]: a) measurement of the pulse height (potential difference produced by the charges of the pairs eh (203) when read in 106) in each cell (205) of the microdosimeter matrix, ie spectrum or pulse height distribution in each pixel of the semiconductor that acts as a substrate of the matrix that makes up said microdosimeter.
  • V the microscopic volume-sensitive (208) irradiated
  • S the area of such volume.
  • V and S are fixed according to the dimensions of each design, ie diameter (107) and height (109) and therefore is determined geometrically. These values are calculated during the manufacturing process of the microdosimeter
  • the device can be calibrated with radioactive sources or beams of well-known energy particles so that the dose deposited on the silicon by the incident radiation is directly derived.
  • a standard electronic reading system is coupled so that the voltage pulses induced by the passage of the radiation in the cells are deconvolved to a final equivalent dose reading (H).
  • the reading electronics (106) which contains a preamplifier that integrates the voltage pulse over time and generates a signal that is proportional to the number of e-h pairs (203) deposited by the radiation in the cell;
  • the reading electronics (106) also contain a shaping amplifier, which amplifies the signal that is then converted into a digital signal via an analog-to-digital converter (ADC); subsequently it is registered to be analyzed by a pulse height analyzer.
  • ADC analog-to-digital converter
  • Another aspect of the invention is the process for manufacturing the microdosimeter of the invention, which comprises the following steps: (a) Preparation of the semiconductor substrate (101) by microelectronic or MEMS processes. This stage is followed depending on the type of cell (205) ( Figure 5 and 6):
  • type Figure 6 either a P + or N + type component is disseminated or implanted or a cylindrical-3D-ring engraving (602) of height (605) is made, which will be filled with already doped polysilicon or with undoped polysilicon and later this will be doped type P + or N +.
  • step (c) Creation of the metallizations (209) on (105) (in cell type Figures 6) or (602) (in cell type Figures 6), and the other metallization of (210), on the central component (104) or (601) respectively and independently.
  • the union of metallizations with their corresponding P + or N + motifs constitutes the electrodes themselves of the cell.
  • the metallizations allow the connection with the reading electronics (106) of the load, pairs e-h (203), which has deposited the radiation or incident particles (201) on the cell (205).
  • the cylindrical-3D etching process is preferably performed using deep reactive attack techniques with ion beam (Deep Reactive Ion Etching or DRIE). Additionally, part of the wafer insensitive volume can be eliminated by thinning the substrate by chemical etching or reactive ion processes, avoiding possible backscattering or backscattering contributions to the signal during irradiation of the secondary particles generated in the irradiation, thus The energy resolution is improved, as it avoids contributions around the sensitive volume (208), which is the area that will eventually simulate the cell ( Figures 3 and 4).
  • DRIE deep reactive attack techniques with ion beam
  • microdosimeter configuration is especially indicated in the case of hadronbib since the thicknesses between 2 ⁇ and 10 ⁇ (lower than the thicknesses of conventional wafers) are suitable for heavy particles used in hadronbib, eg carbon ions, helium, neon, lithium, silicon, etc.
  • a low thickness of the detectors (109) would not be very suitable since the detection of the radiotherapy particles (photons) would be very low because the photon absorption is proportional to the volume of the semiconductor (101).
  • Another object of the invention is the use of the microdosimeter of the invention for detection of radiation in the field of medical application, preferably in hadronbib where it is necessary to detect protons and carbon ions mainly.
  • the microdosimeter can perform both surface level measurements, eg surface from the skin or biological interface, or at a certain depth, eg under the skin or irradiated tissue.
  • the microdosimeter of the invention can be coupled to a tissue equivalent material that simulates specific biological tissue, for example water, muscle, bone, etc., in order to that the latter generates the particles - due to the ionization of the primary beam in the tissue-equivalent - that the microdosimeter can in turn detect by means of the method of the invention, to carry out other dosimetric research studies.
  • a tissue equivalent material that simulates specific biological tissue, for example water, muscle, bone, etc.
  • the microdosimeter can in turn detect by means of the method of the invention, to carry out other dosimetric research studies.
  • the fields used in radio / hadron therapy could be parameterized, as well as other fields derived from other radiation environments, e.g. secondary neutrons generated in these therapies.
  • the microdosimeter can be used in other fields derived from other radiation environments, such as secondary neutrons generated in radio / hadron therapy.
  • mixed radiation fields can be included using a matrix of multiple microdosimeters so that each of them is more sensitive to each type of radiation (in a mixed radiation field).
  • This field includes radiation protection in personal use and area monitoring, for portable systems, hadronrick and in the field of aerospace application, such as detection of high energy charged cosmic particles.
  • FIG. 1 Equivalence of the functioning of the biological cell and microdosimeter cell of the invention.
  • A) Biological cell scheme B) Example of cell of the invention
  • FIG. 1 Cylindrical-3D-ring engraved type cell.
  • Upper scheme three-dimensional scheme.
  • Central figure cross section of said cells with diffusion or central implantation type P + surrounded by cylindrical-3D engraving type N +.
  • Lower scheme idem than superior but with doping (P + or N +) inverted.
  • Cylindrical-3D-column engraved type cell Upper scheme: three-dimensional scheme. Central and lower figure: representation of a cell with cylindrical-3D-column engraving, whose internal walls are doped type P + / N + and is surrounded by an implantation ring N + / P + respectively.
  • Figure 7 Diagram of the connection of the reading electronics of the microdosimeter with continuous reading
  • Figure 8. Diagram of the connection of the reading electronics of the microdosimeter with independent reading.
  • Figure 9. Field distribution model inside the cell limited by cylindrical ring.
  • Fig. 10a. Sketch of the arrangement of a microsensor (not to scale) of example 4. The holes of type n and of type p are connected with metal lines.
  • Fig. 10b Scheme of two microsensors of example 4 at a distance P.
  • Fig. 11 a SEM image of the top view of a microdosimeter with 9 ⁇ diameter, 100 ⁇ field and 6 ⁇ thickness, described in example 4.
  • Fig. 12 Tension characteristic curve of some track type microdosimeters in one of the wafers manufactured, described in example 4.
  • Example 1 This example shows the structure / manufacture of a SOI wafer microdosimeter
  • the base material is SOI wafers with active silicon type N, high resistivity and thickness (109) between 1 ⁇ and 100 ⁇ . After a standard cleaning (RCA or other) a thermal silicon oxide is grown to passivate the silicon surface.
  • a small circular window for example 4 ⁇ in diameter, is opened in silicon oxide by ion-reactive etching or wet etching.
  • the silicon is then implanted or diffused with boron or other P-type dopant to create a P + contact, of the PN junction.
  • the cylindrical-3D ring-shaped engraving (105) (of typical width 3 ⁇ ), and centered on the previous P + contacts, is etched on the active silicon by deep-reactive ion-reactive etching DRIE (with the Bosch process for example) up to the buried rust.
  • DRIE deep-reactive ion-reactive etching
  • Polysilicon is deposited by chemical vapor deposition techniques or other conformal deposition technique.
  • This material is doped with phosphorus or other type N dopant, during deposit or after that, to create an ohmic contact on the walls of the cylindrical-3D ring-shaped engraving.
  • the polysilicon is defined by photolithography and is recorded to form separate contacts around the ring.
  • An intermetal dielectric with a typical thickness of 1 ⁇ and composed of silicon oxide, silicon nitride or other dielectric suitable for the protection of the holes of the following processes is deposited by vapor phase chemical deposit. In this dielectric, pathways to the P + and N + contacts are recorded by ion-reactive etching or wet etching.
  • a passivation for example a silicon oxide and silicon nitride bilayer which is defined by ion-reactive etching, is deposited by chemical vapor deposition assisted by plasma.
  • the layers of non-sensitive silicon (103) or (405) on the back of the wafer are engraved to form a window whose area corresponds to the active area of the sensor.
  • the silicon on the back of the wafer is treated with ion-reactive etching or wet etching until the buried oxide is reached. In this way a thinned substrate is produced.
  • Irradiation can be performed interchangeably both on the upper face of the microdosimeter and on the lower side. Since (107) and (109) are 10 ⁇ respectively, the cell is a cylinder with a diameter equal to its height.
  • Example 3 Structure model of the PN junction manufactured with 3D cylindrical engraving and technological processes that shows its viability as a microdosimeter.
  • Figures 9A and 9B show the distribution of electric field and potential in a cell.
  • the example of this geometry in both figures refers to a cell as defined in Figure 5, with a diameter (112) of the motif (104) of 20 ⁇ and a diameter (113) of the motif (105) of 5 ⁇ and a diameter (107) of the volume-sensitive of 70 ⁇ .
  • the PN junction designed there created between (104) and (105)) through the metallizations (209) and (210) give rise to an electric field.
  • Figures 9 A and 9B it is observed how the emptying of the total sensitive volume (208) is achieved and said sensitive volume (208) has a well defined geometrically cylindrical shape that simulates the cellular structure and / or substructure.
  • Example 4 Silicon microdosimeters based on cylindrical diodes. A new microdosimeter has been developed as the base detector for microdosimetric applications. These devices are manufactured in three types of SO ⁇ wafers with a substrate of type n high resistivity and with active volumes of 6, 10 and 20 ⁇ thickness, for each type of wafer. The collector electrodes are columns recorded through silicon instead of being surface implants as in standard flat diodes, which allows for a much smaller capacity and therefore a lower electronic noise compared to a flat sensor of the same thickness. The sensors are manufactured in cleanroom facilities.
  • Figure 10 shows the schematic arrangement of these microdosimeters showing the pn electrodes and the metal strips that connect them to the contacts:
  • the p-electrode has a diameter of 4 ⁇ and is surrounded by n-ring holes of 3 ⁇ thickness with 6, 10 and 20 ⁇ depth (for each type of wafer) distributed in a square geometry.
  • a wafer contains microdosimeters with locations of 25, 50, 100 and 200 ⁇ (where P is the distance between p-columns) and with an internal diameter (D) of 9, 10, 15, 20 and 25 ⁇ , in order to include a greater number of distribution of cells and sizes.
  • the p-type electrode is circular and an ion implantation with boron (p +) has been carried out.
  • a cylindrical ring is etched using the technique of deep etching by reactive ions (DRIE), and then partially filled with phosphorus doped polysilicon (n +) to form the pn junction.
  • DRIE reactive ions
  • the top of the holes is metallized with aluminum and each electrode is connected with an aluminum line to provide electrical contact.
  • Each microdosimeter consists of 121 independent microsensors arranged in a square matrix.
  • Three main types of detector structures were developed: track detector (pixel-array detector), strip detector and pixel detector.
  • the simplest configuration is the track detector in which all the n + electrodes are connected to the n + contact on one side of the sensor, while all the p + electrodes are connected to the p + contact on the opposite side, thus collecting all the load in all unit cells or sensitive volumes.
  • the consecutive p-type electrodes are aligned, resulting in a strip of microsensors connected in a row.
  • each microsensor is routed through a metal line to a connecting pad for reading electronic microtira to make reading easier. Tapping the wafer silicon support SO! from e! back side on this side, it is expected that finer microsensors will be obtained for the three configurations mentioned above.
  • the Figure 11 shows two SEM images of a processed obiea that contains some pixel microsensors.
  • microdosimeters are connected to an appropriate electronic reading system to carry out the experimental tests.
  • the results of the electrical characterization of the first track-type prototypes are detailed below.

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  • Measurement Of Radiation (AREA)

Abstract

La présente invention comprend un microdosimètre formé de cellules qui constituent une matrice et qui comprennent à l'intérieur de chaque cellule, un volume sensible aux radiations, ces cellules étant fabriquées sur des semiconducteurs au moyen de procédés tridimensionnels qui définissent les constituants d'une liaison PN pour assurer qu'on délimite avec une précision de quelques μm, un volume sensible similaire au volume moyen du noyau de la cellule, avec un diamètre approximatif égal ou inférieur à 10 μm, le substrat sur lequel est fabriqué la cellule étant une tranche de semiconducteur et la cellule ayant un diamètre compris entre 5 et 150 μm et une profondeur comprise entre 1 et 300 μm. L'invention porte également sur des procédés de fabrication de différentes configurations que peuvent présenter ces microdosimètres et sur leur utilisation pour détecter des radiations dans différents domaines incluant des applications médicales et des applications liées à l'aérospatiale.
PCT/ES2015/070056 2014-01-28 2015-01-28 Microdosimètre basé sur des structures 3d à semiconducteurs, procédé de fabrication dudit microdosimètre et utilisation de ce dernier Ceased WO2015114193A1 (fr)

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Citations (1)

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Publication number Priority date Publication date Assignee Title
US20100090118A1 (en) * 2006-12-19 2010-04-15 University Of Wollongong Method and apparatus for tissue equivalent solid state microdosimetry

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100090118A1 (en) * 2006-12-19 2010-04-15 University Of Wollongong Method and apparatus for tissue equivalent solid state microdosimetry

Non-Patent Citations (3)

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Title
GARCIA F ET AL.: "A novel ultra-thin 3D detector- For plasma diagnostics at JET and ITER tokamaks.", NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION A., vol. 607, no. 1, 1 August 2009 (2009-08-01), pages 57 - 60, XP026320944 *
LIM, W. H. ET AL.: "Cylindrical Silicon-on-Insulator Microdosimeter: Design, Fabrication and TCAD Modeling.", IEEE TRANSACTIONS ON NUCLEAR SCIENCE, vol. 56, no. 2, pages 424 - 428, XP011255135 *
ZIEBELL, A. L. ET AL.: "A Cylindrical Silicon-on-Insulator Microdosimeter: Charge Collection Characteristics.", IEEE TRANSACTIONS ON NUCLEAR SCIENCE, vol. 55, no. 6, 1 December 2008 (2008-12-01), pages 3414 - 3420, XP011240759 *

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