JP4634209B2 - Electronic detector - Google Patents

Description

  The present invention relates to an electron detection device.

As one kind of conventional electron detectors, one that detects electrons emitted from a photocathode is known as described in Non-Patent Document 1, for example. In this electron detector, a p-type impurity region serving as an electron incidence region is formed on one surface of an n-type semiconductor substrate, and between the semiconductor substrate and the p-type impurity region. A pn junction region is formed. The pn junction region is exposed on the surface of the semiconductor substrate and is covered with an insulating film formed on the surface of the semiconductor substrate.
GA Johansen, CB Johnson, Nuclear Instruments and Methods inPhysics Research A326, pp.295-298 (1993)

  In the above-described electron beam detector, when electrons emitted from the photocathode are incident on a pn junction region exposed on the surface of the semiconductor substrate, crystal defects are generated in the region, resulting in an increase in dark current. May occur. An increase in dark current leads to deterioration of the characteristics of the electron detector. In order to avoid this problem, a shielding plate that restricts the path of electrons may be provided between the photocathode and the electron detector. In this case, the shielding plate has an opening above the p-type impurity region, and electrons emitted from the photocathode are incident on the p-type impurity region.

  However, even when such a shielding plate is provided, the dark current increases as described above.

  As a result of intensive studies to solve the above-mentioned problems, the inventors have thought that the dark current increases due to the following reasons. That is, some of the electrons emitted from the photocathode in a direction non-perpendicular to the electron detector pass through the opening obliquely. It has been found that electrons passing obliquely through the opening travel between the shielding plate and the electron detector and may enter a pn junction region exposed on the surface of the semiconductor substrate located under the shielding plate. It was.

  The present inventors have further studied based on these findings, found that the above-described problems can be solved by the following invention, and have completed the present invention.

In other words, an electron detection device according to the present invention includes a first conductive type semiconductor substrate and a second conductive type impurity layer provided on one surface of the semiconductor substrate, and the gap between the semiconductor substrate and the impurity layer. An electron detector having a pn junction region formed thereon, and an electron shielding member that shields electrons emitted from the electron source toward one surface of the semiconductor substrate. The electron shielding member exposes the pn junction region. together provided to cover the surface, the electrons have a opening for entering the impurity layer, an electron detector having a first electrode on the exposed surface of the impurity layer, the first electrode, the electron It is connected to an external circuit through a conductive wire inserted through the opening of the shielding member

  In the electron detector according to the present invention, since the electron shielding member has an opening, electrons emitted from the electron source pass through the opening and enter the electron detector. Thereby, for example, it becomes possible to perform various measurements by detecting electrons on the electron detector side. Since the electron shielding member covers the exposed surface of the pn junction region, the pn junction region is protected by the electron shielding member. Therefore, for example, even when electrons emitted from the electron source obliquely pass through the opening, the electrons do not enter the exposed surface of the pn junction region. As a result, an increase in dark current can be suppressed.

  By the way, when electrons collide with the shielding member, X-rays are radiated in each direction by bremsstrahlung. If a part of the radiated X-ray passes through the opening and enters the exposed surface of the pn junction region, the dark current also increases. In the electron detection device according to the present invention, since the electron shielding member covers the exposed surface of the pn junction region, not only electrons but also such X-rays are prevented from entering the exposed surface of the pn junction region. Therefore, an increase in dark current can be more reliably suppressed.

Further, the electron shielding member is preferably provided so as to be separated from the first electrode by the height of the conductive bump so as to prevent the electrons and the electrons from entering the exposed surface of the pn junction region. If the electron shielding member is provided close to the exposed surface of the pn junction region in this way, it is possible to more reliably prevent electrons from entering between the electron shielding member and the electron detector. Further, as described above, it is possible to more reliably prevent the X-ray from entering between the electron shielding member and the electron detector.

  Moreover, it is preferable that an electronic shielding member has insulation. In this way, even when an APD (avalanche photodiode) to which a high voltage is applied is used as an electron detector, for example, a discharge is generated between the electron shielding member and the electron detector when the voltage is applied. The possibility of occurrence can be suppressed. Therefore, discharge breakdown of the electron detector can be prevented.

  The electron detector preferably has a first electrode on the exposed surface of the impurity layer, and the electron shielding member preferably has an electrode connected to the first electrode through a conductive bump. In this way, the exposed surface of the impurity layer and the electrode are electrically connected via the bump, so that charging (charge-up) that can occur when electrons enter the exposed surface of the impurity layer, that is, the surface of the electron detector. ) Can be reliably prevented. In particular, when this electrode is grounded, charge-up can be avoided more reliably.

  The electron detector preferably has a first electrode on the exposed surface of the impurity layer, and the first electrode is preferably connected to an external circuit through a wire. In this way, the impurity layer can be reliably connected to the potential of the external circuit. As a result, it is possible to reliably prevent charging (charge-up) that may occur when electrons enter the surface of the electron detector. In particular, when the first electrode is grounded in an external circuit, charge-up can be avoided more reliably.

  The electron source preferably further includes a photocathode that converts incident light into electrons and emits the electrons toward an electron detector. In this way, the electron detection device of the present invention can be used as a phototube.

  By the way, when an electron detector is used as a phototube, an alkali metal or the like may be deposited on the photocathode for the purpose of facilitating electron emission. For example, in the case where the electron detection device has a photocathode and an electron detector enclosed in a bulb, such vapor deposition is performed by introducing an alkali metal into the bulb. When vapor deposition is performed, if an alkali metal adheres not only to the photocathode but also to an electrode provided near the exposed surface of the pn junction region of the electron detector, dark current may increase. In the electron detection device according to the present invention, since the exposed surface of the pn junction region of the electron detector is covered with the electron shielding member, the possibility that alkali metal adheres to the electrode provided in the vicinity of the exposed surface can be suppressed. . Therefore, a photocathode that can easily emit electrons can be obtained without increasing the dark current.

  ADVANTAGE OF THE INVENTION According to this invention, the electronic detection apparatus which can suppress the increase in dark current can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

1113459882105_0
These are the block diagrams which show 1st Embodiment of the electron detection apparatus which concerns on this invention. The electron detection device 1 is a phototube. The electron detection device 1 has a cylindrical valve 12, and an opening on one end side of the valve 12 is sealed by a photocathode plate (electron source) 10. A photocathode 11 that emits electrons (photoelectrons) in response to the incidence of light is provided on the surface of the photocathode plate 10 on the bulb 12 side. On the other hand, the opening on the other end side of the valve 12 is sealed by a stem 14. The stem 14 has a plurality of through holes 16, and lead pins 18 and 18 a are fixed in each through hole 16 by a member 20 such as glass.

  A first grid 22 and a second grid 24, an electron shielding member 60, and an electron detector 40 are provided at an intermediate portion in the bulb 12. The first grid 22 and the second grid 24 serve to narrow down the electrons emitted from the photocathode 11.

  An electron detector 40 and an electron shielding member 60 are provided between the second grid 24 and the stem 14. FIG. 2 is a top view of the electron detector 40 and the electron shielding member 60. FIG. 3 is a cross-sectional view taken along line II of the electron detector 40 and the electron shielding member 60 shown in FIG. FIG. 4 is a side view of the electron detector 40 and the electron shielding member 60. As shown in FIGS. 1 to 4, the electron shielding member 60 is disposed on the upper surface of the electron detector 40.

The electron detector 40 is an electron multiplication type semiconductor electronic sensor that outputs a signal in response to the incidence of electrons. More specifically, the electron detector 40 has a structure equivalent to an APD (avalanche photodiode). As shown in FIG. 3, the electron detector 40 is n ^−, which is an n-type semiconductor layer having a lower concentration than the Si substrate 41 on one surface of an n-type (first conductivity type) Si substrate 41. The layer 42 and the p ⁻ layer 43 which is a p-type (second conductivity type) impurity layer are sequentially formed and laminated. On the periphery of the p ⁻ layer 43, an n ⁺ layer 44 having a higher concentration than the n ⁻ layer 42 is formed by diffusion. A pn junction region 51 is formed between the n ⁺ layer 44 and the n ⁻ layer 42 and the p ⁻ layer 43.

On the p ⁻ layer 43, a p ⁺ layer 45 having a higher concentration than the p ⁻ layer 43 is partially formed by diffusion. The exposed surface of the p ⁺ layer 45 becomes an electron incident surface in the electron detector 40. An SiO ₂ film 46 is formed on the n ⁺ layer 44 and the p ⁺ layer 45. An opening (contact hole) 50 is formed in the SiO ₂ film 46, and the p ⁺ layer 45 is exposed from the opening 50. An incident surface electrode (first electrode) 47 is formed on the SiO ₂ film 46 by aluminum vapor deposition. The incident surface electrode 47 is provided so as to fill the opening 50 described above. As a result, the incident surface electrode 47 comes into contact with the exposed surface of the p ⁺ layer 45 through the opening 50.

  A passivation oxide film 48 is formed on the incident surface electrode 47. An opening 52 is formed in the passivation oxide film 48, and the incident surface electrode 47 is exposed from the opening 52. Further, a passivation nitride film 49 is formed so as to cover a part of the passivation oxide film 48.

  As shown in FIGS. 1 to 4, the upper surface of the electron detector 40 is covered with an electron shielding member 60. The electron shielding member 60 restricts the path of electrons that have passed through the first grid 22 and the second grid 24. The electron shielding member 60 is a plate made of an insulating material such as ceramic, and has a sufficient thickness (for example, about 300 μm) to shield electrons.

As shown in FIG. 2, an opening 62 is formed in the electron shielding member 60. As shown in FIG. 3, the edge of the opening 62 is located sufficiently inside the outer edge 45 a of the p ⁺ layer 45. As a result, a part of the surface of the p ⁺ layer 45 is exposed from the opening 62. A conductive portion (electrode) 64 is provided around the opening 62 and its periphery, and the conductive portion 64 is formed by covering the opening 62 and its periphery with conductive plating. As shown in FIG. 4, the conductive portion 64 is connected to a lead pin 18 a connected to an external circuit via a wire 66.

  Conductive bumps 68 are provided on the lower surface of the conductive portion 64. Since the bump 68 is in contact with the incident surface electrode 47 of the electron detector 40, the conductive portion 64 connected to the external circuit and the electron detector 40 are electrically connected. Therefore, the charge-up that can occur in the electron detector 40 due to the incidence of electrons can be prevented. In addition, since the height H of the bump 68 is about 30 μm, the electron shielding member 60 is disposed very close to the electron detector 40.

  The operation of the above-described electron detection device 1 will be described with reference to FIG.

A reverse bias voltage is applied to the electron detector 40 of the electron detector 1 via the lead pin 18. Although not shown, the reverse bias voltage is applied via the lead pin 18 from the Si substrate 41 side of the electron detector 40. The reverse bias voltage to be applied is, for example, 3 to 400V. On the other hand, the photocathode plate 10 is irradiated with light. The photocathode 11 of the photocathode plate 10 emits electrons into the bulb 12 when irradiated with light. The emitted electrons pass through the first grid 22 and the second grid 24, further pass through the opening 62 of the electron shielding member 60, and collide with the surface of the p ⁺ layer 45 of the electron detector 40 shown in FIG. To do. When the electrons collide, a pair of electrons and holes are generated in the electron detector 40 per 3.6 eV of energy lost by the collision. The generated electron / hole pair drifts in the electron detector 40 to which the reverse bias voltage is applied, and is described above in the pn junction region 51 between the n ⁻ layer 42 and the p ⁻ layer 43. Avalanche multiplication is performed at an avalanche multiplication factor corresponding to the reverse bias voltage.

Here, for example, when an electron having an energy of 10 keV collides with the p ⁺ layer 45 and releases all the energy, about 2800 electron-hole pairs are generated in the electron detector 40. At this time, if the avalanche multiplication factor is 50 times, the gain of about 10 ⁵ times the electron detector 40 is to be obtained.

On the other hand, as shown in FIG. 5, some of the electrons emitted from the photocathode 11 pass through the original trajectory R1 (that is, the opening 62 of the electron shielding member 60 and the p ⁺ layer 45 of the electron detector 40). In some cases, the object moves toward the exposed surface of the pn junction region 51 of the electron detector 40 in some cases. Such electrons P1 collide with a portion of the electron shielding member 60 that covers the pn junction region 51 between the n ⁺ layer 44 and the p ⁻ layer 43. Since the electron shielding member 60 is an insulating plate and has a sufficient thickness, the electrons P1 cannot penetrate the electron shielding member 60, and the path is blocked.

  In addition, some electrons that deviate from the original trajectory R1 may be incident on the opening 62 of the electron shielding member 60 from an oblique direction. Such electrons P <b> 2 may enter between the upper surface of the electron detector 40 and the lower surface of the electron shielding member 60. However, since the electron shielding member 60 has a sufficient thickness and the distance between the upper surface of the electron detector 40 and the lower surface of the electron shielding member 60 is as extremely small as about 30 μm, the electron P2 is an electron shielding member. It will collide with the upper surface of 60 or the inner wall in which the electroconductive part 64 was formed, and the progress is blocked | prevented.

  Further, when the electrons P2 collide with the inner wall of the electron shielding member 60, the electrons P2 emit X-rays. Among such X-rays, the X-ray 70 emitted in the direction of the pn junction region 51 of the electron detector 40 may enter between the upper surface of the electron detector 40 and the lower surface of the electron shielding member 60. The progress of the electron shielding member 60 is also hindered by the electron shielding member 60 which has a sufficient thickness and is disposed very close to the electron shielding member 60.

As described above, in this embodiment, the electron shielding member 60 has the opening 62, and the opening 62 is located on the p ⁺ layer 45 of the electron detector 40. Accordingly, electrons emitted from the photocathode 11 of the photocathode plate 10 can be incident on the p ⁺ layer 45. The electron shielding member 60 is disposed very close to the electron detector 40 and covers the upper surface of the pn junction region 51 between the n ⁺ layer 44 and the p ⁻ layer 43 of the electron detector 40. . That is, since the electron shielding member 60 protects the upper surface of the pn junction region 51, that is, the exposed surface of the pn junction region, the incidence of electrons and X-rays on the exposed surface of the pn junction region 51 can be prevented. . As a result, an increase in dark current can be suppressed.

  In the electron detection device as shown in FIG. 1, alkali metal or the like may be deposited on the photocathode 11. When an alkali metal is vapor-deposited on the photocathode 11, the work function is lowered, so that electrons can be easily emitted. The alkali metal is deposited by introducing an alkali metal into the bulb 12. In the conventional electron detector, when an alkali metal is introduced into the bulb, the alkali metal may adhere not only to the photocathode but also to the electrode provided on the upper surface of the pn junction region of the electron detector. In some cases, the dark current increased. In order to suppress such an increase in dark current, it is necessary to limit the amount of alkali metal introduced into the bulb. As a result, it has been difficult to obtain a photocathode having optimum sensitivity. In the electron detection device 1 of the present embodiment, the electron shielding member 60 is disposed very close to the electron detector 40, so even when an alkali metal is introduced into the bulb 12, it is provided on the upper surface of the pn junction region 51. It is possible to prevent the alkali metal from adhering to the formed electrode. Therefore, there is no need to limit the amount of alkali metal in order to suppress the dark current, so that the photocathode 11 having the optimum sensitivity can be obtained.

  Next, a second embodiment of the electron detection device according to the present invention will be described. FIG. 6 is a side view of the electron detector and the electron shielding member in the second embodiment of the electron detector according to the present invention. FIG. 7 is an enlarged cross-sectional view of the electron detector and the electron shielding member in the second embodiment. In the electron detection device in the previous embodiment, the electron detector 40 is in contact with the conductive bump, whereas in the electron detection device 100, the electron detector 40 is in contact with the conductive wire 108.

As shown in FIGS. 6 and 7, the electron shielding member 102 of the electron detection device 100 is bonded and fixed to the passivation nitride film 49 of the electron detector 40 via a nonconductive resin 104. Further, the opening 106 of the electron shielding member 102 has a larger diameter than the opening 62 in the electron shielding member 60 of the above-described embodiment. More specifically, the diameter of the opening 106 is large enough to expose the incident surface electrode 47 of the electron detector 40. However, also in the present embodiment, the opening 106 is located sufficiently inside the outer edge 45 a of the p ⁺ layer 45.

  As shown in FIG. 7, the incident surface electrode 47 of the electron detector 40 is connected to one end of a conductive wire 108 inserted through the opening 106. As shown in FIG. 6, the other end of the wire 108 is connected to a lead pin 18a fixed to the ground potential. By connecting the wire 108 directly to the incident surface electrode 47, the incident surface electrode 47 can be reliably connected to the potential of the external circuit. As a result, it is possible to reliably prevent the charge-up of the surface of the electron detector 40 caused by the incidence of electrons. Further, by adopting such a configuration for the electron detection device 100, it is not necessary to provide the electron shielding member with the conductive portion used in the previous embodiment, and bumps are also unnecessary.

  Next, a third embodiment of the electron detection device according to the present invention will be described. FIG. 8 is a top view of the electron detector and the package in the third embodiment of the electron detector according to the present invention. FIG. 9 is a cross-sectional view taken along the line II-II of the electron detector and the package according to the third embodiment. In the electron detection device 1 in the previous embodiment, the upper surface of the electron detector 40 is covered with an electron shielding member, whereas in the electron detection device 200, the electron detector 40 is a package 202 that is an electron shielding member. It is configured to be put in.

The package 202 is fixed to the mounting substrate 206 and is made of an insulating material such as ceramic. Of the entire surface of the package 202, a portion excluding an attachment portion of metal wirings 214 and 220 described later and the periphery of the attachment portion is covered with a conductive plating 203. The plating 203 is connected to a potential set by an external circuit through a metal wiring (not shown). An opening 204 is formed on the upper surface of the package 202. This opening 204 is formed so as to be located sufficiently inside the outer edge of the p ⁺ layer 45 of the electron detector 40, similarly to the opening 62 of the electron shielding member 60 described above. The package 202 is disposed very close to the upper surface of the electron detector 40.

Metal bumps 208 and 212 are provided between the package 202 and the electron detector 40. The bump 208 electrically connects the p ⁺ layer 45 and the metal wiring 214. Metal wire 214 is inserted into a hole provided in the package 202, and a conductive pattern formed on the mounting substrate 206 ^- are connected via the emission 216 and the solder 218. The bump 212 electrically connects the n ⁺ layer 44 and the metal wiring 220. The metal wiring 220 is inserted into a hole provided in the package 202 and is connected to the conductive pattern 222 formed on the mounting substrate 206 via the solder 224.

  As described above, in the electron detection device 200, the upper surface of the pn junction region 51 of the electron detector 40, that is, the exposed surface of the pn junction region is protected by the package 202. Therefore, the incidence of electrons and X-rays on the exposed surface of the pn junction region 51 can be prevented. As a result, an increase in dark current can be suppressed. Further, since the electron detector 40 can be put in the package 202, the electron detection device 200 can be mounted on the mounting substrate 206.

  The present invention is not limited to the above-described embodiment, and various modifications can be made.

  For example, in the above embodiment, the electron detection device is a phototube, but the electron detection device can also be applied to an SEM (scanning electron microscope). In that case, the electron detector can be used as a detector for SEM.

  Although the electron detector is an APD, the electron detector may be a PD to which a voltage lower than that of the APD is applied. In this case, the electron shielding member may be made of a metal material instead of an insulating material.

It is a lineblock diagram showing a 1st embodiment of an electron detection device concerning the present invention. It is a top view of an electron detector and an electron shielding member. It is sectional drawing of an electron detector and an electron shielding member. It is a side view of an electron detector and an electron shielding member. It is a figure for demonstrating operation | movement of an electron. It is a side view of an electron detector and an electron shielding member in a 2nd embodiment of an electron detection device concerning the present invention. It is sectional drawing of an electron detector and an electron shielding member. It is a top view of the electron detector and package in 3rd Embodiment of the electron detection apparatus which concerns on this invention. It is sectional drawing of an electron detector and an electron shielding member.

Explanation of symbols

1, 100, 200 ... electronic detection device, 10 ... photocathode plate, 11 ... photocathode, 40 ... electron detector, 41 ... semiconductor substrate, 42 ... n ^- layer 43 ... p ^- layer, 44 ... ^{n +} layer, 45 ... p ⁺ layer, 51 ... pn junction region, 60,102 ... electron shielding member, 62,106,204 ... opening, 64 ... conductive portion, 68,208,212 ... bump, 108 ... wire, 202 ... package, 206 ... Mounting board.

Claims (5)

A first conductivity type semiconductor substrate; and a second conductivity type impurity layer provided on one surface of the semiconductor substrate, wherein a pn junction region is formed between the semiconductor substrate and the impurity layer. An electron detector;
An electron shielding member that shields electrons emitted from an electron source toward one surface of the semiconductor substrate;
The electron shield member, as well is provided so as to cover the exposed surface of the pn junction region, have a opening for incident the electrons to the impurity layer,
The electron detector has a first electrode on an exposed surface of the impurity layer, and the first electrode is connected to an external circuit through a conductive wire inserted through the opening of the electron shielding member. An electronic detection device characterized by being connected . A first conductivity type semiconductor substrate; and a second conductivity type impurity layer provided on one surface of the semiconductor substrate, wherein a pn junction region is formed between the semiconductor substrate and the impurity layer. An electron detector;
An electron shielding member that shields electrons emitted from an electron source toward one surface of the semiconductor substrate;
The electron shield member, as well is provided so as to cover the exposed surface of the pn junction region, it has a openings for incident the electrons to the impurity layer,
The electron detector has a first electrode on an exposed surface of the impurity layer, and the electron shielding member has an electrode connected to the first electrode through a conductive bump. Electronic detection device. The electron shielding member is provided apart from the first electrode by a height of the conductive bump so as to prevent the electrons from entering the exposed surface of the pn junction region. 3. The electron detection device according to 2. The electron shield member, electron sensing device of any one of claims 1 to 3, characterized in that it has an insulating property. The electron detection according to any one of claims 1 to 4 , wherein the electron source further comprises a photocathode that converts incident light into electrons and emits the electrons toward the electron detector. apparatus.

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