EP2174355A1

EP2174355A1 - Avalanche photodiode

Info

Publication number: EP2174355A1
Application number: EP08773493A
Authority: EP
Inventors: Rainer Richter; Ladislav Andricek; Gerhard Lutz
Original assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; PNSensor GmbH
Current assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; PNSensor GmbH
Priority date: 2007-08-06
Filing date: 2008-06-18
Publication date: 2010-04-14
Also published as: WO2009018872A1; US20110095388A1; US8258594B2; JP2010536165A; DE102007037020B3; JP5523317B2

Abstract

The invention relates to an avalanche photodiode (1) for detecting radiation, comprising a semiconductor substrate (11), an upper diode layer (15), an oppositely doped, laterally delimited lower diode layer (16), an avalanche region situated between the upper diode layer (15) and the lower diode layer (16), wherein the radiation to be detected triggers an avalanche breakdown in the avalanche region, and also comprising a contact-making layer (12) at the underside (10) of the semiconductor substrate (11), a laterally delimited quenching resistance layer (18) arranged in the semiconductor substrate (11) between the lower diode layer (16) and the contact-making layer (12), wherein the quenching resistance layer (18) quenches the radiation-generated avalanche breakdown in the avalanche region, and also comprising a depletion electrode (15) arranged laterally alongside the laterally delimited lower diode layer (16), such that the depletion electrode (15) depletes the semiconductor substrate (11) laterally alongside the laterally delimited lower diode layer (16), while the quenching resistance layer (18) is screened from the depletion electrode (15) by the lower diode layer (16) and is therefore not depleted.

Description

Avalanche photodiode

The invention relates to an avalanche photodiode for radiation detection according to the preamble of the main claim.

Sadygov Z. "Three advanced designs of micro-pixel avalanche photodiodes: their present status, maximum possibili- ties and limitations", Nuclear Instruments and Methods in Physics Research A 567 (2006) 70-73 is such an avalanche Photodiode known that can be used for radiation detection. In this case, an avalanche region is formed in a semiconductor substrate, which is formed by a pn junction between a cathode layer and an anode layer and in which the radiation to be detected triggers a windrow breakdown. In addition, in this case a Löschwiderstand (quench resistor) is provided, which is connected in series with the avalanche area and has the task to end a radiation-generated avalanche breakdown by the voltage drop across the Löschwiderstand the current lowers so far that the charge carrier multiplication in the Avalanche area dies.

In a variant of this known avalanche photodiode, the erasure resistance lies partially on the radiation entrance window and must at least partially still be contacted with thin metallic layers. The erosion resistance thus forms an obstacle to the radiation to be detected, whereby the detection efficiency deteriorates drastically, especially for ultraviolet (UV) and blue light.

In another variant, the above-mentioned publication by Sadygov et al. that the Löschwider was integrated together with a coupling capacitor in the semiconductor substrate (bulk), wherein the avalanche region deep buried in the semiconductor substrate is located on an E-pitaxieschichtgrenzflache.

First, as stated in the cited publication, this is associated with technological difficulties, since deep ion implantation and epitaxial growth on high purity silicon wafers is required.

On the other hand, a common erosion resistance is provided in each case for many avalanche photodiodes, so that large neighborhood areas become insensitive after the response of a diode.

Another problem of the known avalanche photodiodes is based on the fact that radiation detectors are usually operated in a radiation-loaded environment. Extensive preliminary tests are therefore required, especially for space applications, to ensure sufficient long-term stability of the avalanche photodiodes. Although silicon as a semiconductor material for avalanche photodiodes has the great advantage of a passivating oxide, which has excellent dielectric properties and can be produced with relatively small defects and strains at the silicon-silicon dioxide interface. Nevertheless, this interface is the most sensitive part to ionizing radiation. Both the additional interfacial charges and the interface generation current (leakage current) may exceed the initial values before irradiation by orders of magnitude. In particular, the isolation structures of conventional radiation detectors often fail for this reason. More radiation-hardened detectors are therefore desirable. Further reference is made to the prior art EP 1 840 967 A1 and JP 09-64398 AA, EP 1 755 171 A1, US 2006/0249747 A1 and US Pat. No. 6,222,209 B1.

The invention is therefore based on the object to improve the conventional avalanche photodiode described above accordingly.

Preferably, the avalanche photodiode according to the invention should be able to be arranged in matrix form in a radiation detector in order to detect individual optical photons.

Furthermore, the avalanche photodiode according to the invention should be as easy as possible to produce.

In addition, it is desirable that the avalanche photodiode according to the invention is as resistant to ionizing radiation as possible.

Furthermore, the avalanche photodiode according to the invention should have a high quantum efficiency and a high sensitivity in the ultraviolet and blue spectral range.

The above objects are achieved by an avalanche photodiode according to the invention according to the main claim or the dependent claims.

The avalanche photodiode according to the invention is partly of conventional design and has a semiconductor substrate with an upper side and a lower side, wherein the semiconductor substrate is doped in accordance with a first doping type (eg n-type doping). Preferably, the semiconductor substrate is made of silicon, but the invention is not limited to silicon with respect to the semiconductor material basically feasible with other semiconductor materials.

In addition, the avalanche photodiode according to the invention conventionally comprises two oppositely doped diode layers (cathode and anode), which are arranged in the semiconductor substrate near the surface at the top and enclose an avalanche region in which the radiation to be detected at a corresponding Bias causes an avalanche breakdown.

Preferably, the cathode layer is at the top and the anode layer at the bottom, but the invention is not limited to this arrangement. Rather, it is also possible in principle that the anode layer is arranged at the top, while the cathode layer is located underneath.

In addition, the avalanche photodiode according to the invention has a contacting layer which is arranged on the underside of the semiconductor substrate and doped in accordance with the first doping type (for example n-doping). The contacting layer makes it possible, for example, to apply an electrical bias to the avalanche photodiode so that the avalanche photodiode is operated in the so-called Geiger mode, so that both electrons and holes contribute to carrier multiplication and thereby cause avalanche breakdown the current is limited in principle only by serial resistors.

Furthermore, the avalanche photodiode according to the invention provides an erase resistance (quench resistor) which is electrically connected in series with the avalanche region and, in the event of an avalanche breakdown in the avalanche region, should ensure that the avalanche breakdown is achieved by means of a current vector. is deleted by the erosion resistor. In contrast to the prior art, however, the erasure resistance in the invention is embodied as an erasure resistance layer and integrated into the semiconductor substrate, wherein the erosion resistance layer is located between the avalanche region and the contact layer, ie below the lower diode layer, wherein it is preferably is the anode layer. This is advantageous because the lower diode layer shields the soldering resistor layer in this way from the damaging effect of the upper diode layer, as will be described in detail below.

Furthermore, the avalanche photodiode according to the invention provides a depletion electrode which is arranged at least partially laterally next to the laterally delimited lower diode layer and doped in accordance with the second doping type. The purpose of the depletion electrode is to deplete the semiconductor substrate laterally adjacent to the laterally delimited lower diode layer in order to electrically isolate the avalanche photodiode in the lateral direction. This is particularly advantageous if numerous avalanche photodiodes according to the invention are arranged next to one another in an avalanche radiation detector, since the depletion electrode then ensures that the immediately adjacent avalanche photodiodes are electrically isolated from one another.

In this case, the lower diode layer (preferably the anode layer) located above the soldering resistance layer electrically shields the soldering resistor layer from the depletion electrode so that the soldering resistor layer is not or only partially depleted.

The depletion of the semiconductor substrate occurs in the region laterally adjacent to the laterally delimited lower diode layer Preferably, completely over the entire thickness of the semiconductor substrate, ie the semiconductor substrate is completely depleted laterally next to the lower diode layer from the top to the bottom.

However, there is also the possibility within the scope of the invention that the depletion effect of the depletion electrode in the semiconductor substrate only reaches a certain depth, so that in the semiconductor substrate laterally next to the laterally delimited lower diode layer only depletion islands are formed which do not rise in the vertical direction reach to the bottom of the semiconductor substrate.

In a variant of the invention, the depletion electrode is formed by the upper diode layer, which for this purpose projects laterally beyond the laterally delimited lower diode layer with a side section and forms the depletion electrode with the protruding side section. In this case, no separate electrical control of the depletion electrode is required, since the upper diode layer is in any case electrically contacted.

In contrast, in another variant of the invention, the depletion electrode is electrically and spatially separated from the upper diode layer and formed as a separate electrode.

This advantageously makes it possible to drive the depletion electrode with an independent electrical potential in order to achieve the desired depletion effect in the semiconductor substrate. This may be necessary, for example, if the spacings between the adjacent avalanche photodiodes are very small and the cathode voltage is no longer sufficient for a complete depletion of the semiconductor substrate in the gap between the adjacent avalanche photodiodes. In addition, the inventive Löschwiderstandsstandsschicht forms a coupling capacitance, as it is already known from conventional avalanche photodiodes.

An advantage of the integration of the soldering resistor as Löschwiderstandsstandsschicht in the semiconductor substrate is the fact that the upper diode layer can be completely unstructured at the top of the semiconductor substrate, whereby the detection efficiency is improved dramatically, especially in the ultraviolet and blue spectral range.

In addition, this offers the possibility that an optical filter layer is applied to the upper side of the avalanche photodiode, which can also be laterally unstructured above the avalanche region.

It was already mentioned above that the Löschwiderstandsstandsschicht has the task to end a radiation-generated avalanche. The erosion resistance must therefore have such a high resistance that the current during an avalanche breakdown is less than approximately 20 μA. For a current of this magnitude, it is very likely that the carrier density representing it in the avalanche region at least briefly fluctuates to zero, resulting in the desired collapse of the carrier avalanche. In the avalanche photodiode according to the invention, therefore, the soldering resistor layer preferably has such a high resistance value that the current in the avalanche region dies at least temporarily in the event of avalanche breakdown and thus ends the avalanche breakdown. The resistance of the soldering resistor should be at least 0.1 MΩ, 0.5 MΩ, 1 MΩ or at least 2 MΩ. However, the invention is in terms of the resistance value of the Löschwiderstandsschicht not limited to the above limits, but depending on other boundary conditions with other resistance values realized.

In addition, it should be noted that the soldering resistance layer preferably has a thickness in the range of 10 .mu.m to 100 .mu.m. Preferably, the thickness of the Löschwiderstandsschicht is thus greater than 10 microns, 20 microns or 50 microns. Furthermore, the thickness of the Löschwiderstandsschicht is preferably less than 1000 microns, 500 microns, 200 microns, 100 microns or 50 microns. However, the invention is not limited to the above numerical values in terms of the thickness of the soldering resistor layer.

It should also be mentioned that the lower diode layer (preferably the anode layer) generally has a thickness that is greater than the thickness of the avalanche region. The thickness of the lower diode layer is preferably greater than 1 μm, 2 μm, 5 μm or 10 μm. However, the invention is not limited to the above numerical values in the thickness of the lower diode layer.

It should also be mentioned that the upper diode layer preferably has a thickness of a few 10 nm to a few

100 nm. Thus, the thickness of the upper diode layer is preferably greater than 5 nm, 10 nm, 20 nm or 50 nm. In addition, the thickness of the upper diode layer is preferably less than 1000 nm, 500 nm, 400 nm, 300 nm, 200 nm or more 100 nm. However, the invention is not limited to the above numerical values in terms of the thickness of the upper diode layer. It should further be mentioned with regard to the soldering resistor layer that its doping concentration is preferably in the range from 0.5 "10 ¹² cm ^-3" to 10 ¹⁴ cm ^"3. The doping concentration in the soldering resistor layer is in particular greater than 0.5-10 ¹² cm ^-3 , 0,7'10 ¹² ^{cm -3} or 10 ¹² cm ^{'. 3} However, the invention is not limited to the aforementioned number ranges in terms of the doping concentration in the photo-resistance layer.

It should also be mentioned that the first doping type is preferably an n-doping, while the second doping type is preferably a p-doping. However, the invention can also be implemented with an inverse doping, wherein the first doping type is a p-type doping, while the second doping type is an n-type doping.

It should also be mentioned that the upper diode layer and the contacting layer are preferably relatively heavily doped, while the semiconductor substrate and thus the solder resistor layer are preferably relatively weakly doped.

It should also be mentioned that the semiconductor substrate is preferably monocrystalline.

Further structural details of avalanche photodiodes are known, for example, from Lutz, G.: "Semiconductor Radiation Detectors", 2nd edition, Springer Verlag 2001, pages 239-242, so that the content of this textbook of the present description in terms of structure and operation the avalanche photodiode according to the invention is fully attributable.

It should also be mentioned that in the avalanche photodiode according to the invention the radiation entrance window is the radiation to be detected is preferably arranged on the upper side, ie on the same side as the avalanche region.

The vertical extent of the semiconductor substrate and thus also the thickness of the avalanche photodiode according to the invention is essentially determined by the thickness of the soldering resistor layer. Normally, however, common semiconductor wafers are several hundred μm thick in order to ensure mechanical stability required for processing. The usually n-doped contacting layer on the underside of the avalanche photodiode can of course be extended almost arbitrarily in the vertical direction.

Another advantage is achieved when the Löschwiderstandsschicht has a lateral and / or vertical doping profile. It can, for. For example, a doping gradient may be provided, in which the doping concentration in the quenching resistor layer increases upward. Particularly in the case of relatively small avalanche photodiodes or in the case of relatively thick resistive layers, the effect of the depletion electrode (space charge zone) can lead to a strong lateral depletion, especially in the upper region of the resistive layer. This can even lead to pinch off of the extinguishing resistor layer. By increasing the doping concentration in the upper region of the semiconductor substrate, the lateral expansion of the space charge zone is advantageously suppressed and the pinch-off avoided. The change in the doping concentration may, for. Locally, by an n-type ion implantation layer introduced below the high energy anodes. However, if the erosion resistance layer is epitaxially grown, it is also possible during the epitaxy process to deliberately produce a vertical, laterally unstructured, doping profile, in particular set within the lightly doped n-layer.

In terms of production, it makes sense to epitaxially grow the weakly n-doped soldering resistor layer on a highly n-doped wafer. In a variant of the invention, the contacting layer is therefore formed by a highly doped wafer onto which the soldering resistor layer is applied.

An alternative possibility is the use of the method known as wafer-bonding, which is described, for example, in Tong, QY; Gösele, U .: "Semiconductor Wafer Bonding", John Wiley and Sons, New York, 1999, so that the content of this publication is fully within the scope of the present invention in terms of wafer bonding technology. Here, two silicon wafers are monolithically bonded together after a suitable surface pretreatment. The lower wafer serves as a stable mechanical carrier and is highly n-doped, so that it fulfills the function of the contacting layer in the context of the invention. The upper wafer, on the other hand, is lightly doped and after wafer bonding is ground to about the target thickness of the arc resistor layer and then lapped and polished to produce the required surface quality. In further processing, the sandwich structure obtained in this way can be treated like a standard wafer. Frequently, the wafers are hereby oxidized before bonding, resulting in an SOI structure (SOI: silicon on I_nsulator), as described in the above textbook by Tong / Gösele. The advantage of wafer bonding over the epitaxial approach is that it provides more flexibility in doping choice for the quenching resistor layer. Although modern epitaxy systems nowadays grow up very high-resistance layers For example, the FZ crystal growth process (FZ: Float Zone) available for wafer fabrication is superior to producing ultra-pure silicon.

In this variant of the invention, the avalanche

Photodiode thus a carrier layer, which is arranged on the underside of the contacting layer and mechanically carries the avalanche photodiode. The carrier layer can be made, for example, of silicon, silicon dioxide, glass, in particular quartz glass, sapphire, a ceramic or a highly doped one

Semiconductor material exist, but in principle, other materials for the carrier layer are possible.

Furthermore, an insulating layer, which can consist of silicon dioxide, for example, is preferably arranged between the contacting layer and the carrier layer. This is particularly the case with the above-mentioned SOI structure in which two wafers are bonded together, wherein at least one wafer has been oxidized before bonding.

For the realization of detector arrays with matrix elements larger than 100 × 100 μm, with which high detection efficiencies can be achieved, very high-resistance resistance layers are required due to the large cross section of the vertical erosion resistors. For such large matrix elements, it makes sense to start from a high-impedance FZ wafer. Due to its thickness, the isolation region can only be partially depleted, so that the erosion resistors in the lower region are not separated. When a matrix element (ie one of the avalanche photodiodes according to the invention) responds, the anodes of the neighboring elements are also slightly discharged. If these neighbors trigger within the recharge time, their signal is reduced, resulting in broadening of the single photon spectra. For applications with Small signal rates, this disadvantage is not significant, so that there can be dispensed in favor of a cost-effective process to the complete separation of the adjacent Avalache photodiodes.

According to another embodiment of the invention, the effect of the depletion electrode can be enhanced by providing a doped region in the semiconductor substrate. The doped region is provided laterally adjacent to the solder resist layer and doped according to the second doping type. Advantageously, a further possibility is thereby achieved (in addition to the separated depletion electrode) to deplete the insulating, depleted part of the semiconductor substrate with smaller voltages. That between the p-doped layer and the adjacent n-doped layer (s)

Layer (s) resulting build-in potential leads to an intrinsic space charge zone, which has a significant extent just in the lightly doped semiconductor substrate. Because of the wurzelförmigen dependence of the expansion of the space charge zone of the voltage, such a p-layer is particularly effective when it is located on the underside of the semiconductor substrate.

However, the invention is not limited to the above-described avalanche photodiode according to the invention as a single component, but also includes an avalanche radiation detector with a plurality of juxtaposed avalanche photodiodes according to the invention. The avalanche photodiodes are preferably arranged in matrix form in straight rows and columns or with a regular hexagonal geometry or with a modified geometry. The regular hexagonal geometry has the advantage that the avalanche photodiodes of particularly high density and less dead space can be arranged. Preferably, the individual avalanche photodiodes are in this case connected in parallel to a common amplifier. Although this dispenses with the spatial resolution of the avalanche radiation detector, such an arrangement offers the advantage that when one of the avalanche photodiodes responds, the other avalanche photodiodes remain sensitive and thus have the possibility of counting photons, if they are in different elements arrive. From the strength of the signal measured by the amplifier can then be concluded that the number of diodes addressed and thus on the radiation intensity.

In a variant of the avalanche radiation detector according to the invention, the upper diode layer (preferably the cathode layer) of the individual avalanche photodiodes extends in a lateral direction over a plurality of adjacent avalanche photodiodes, wherein the upper diode layer preferably covers all avalanche photodiodes. In contrast, the lower diode layer (preferably the anode layer) of the individual avalanche photodiodes is interrupted in each case between the adjacent avalanche photodiodes and has a gap. Thus, the upper diode layer is not shielded from the lower diode layer in the spaces between the adjacent avalanche photodiodes, so that the upper diode layer acts as a depletion electrode in the gaps and depletes the semiconductor substrate in the gaps, electrically isolating the adjacent avalanche photodiodes from each other ,

Alternatively, however, there is the possibility that the upper diode layer is interrupted in each case between the adjacent avalanche photodiodes, in which case a separate depletion electrode is arranged in the interspaces, in order to prevent the To deplete semiconductor substrate in the interstices. In the case of a matrix-like arrangement of the individual avalanche photodiodes, the depletion electrodes can then also be arranged in grid form and controlled independently of the avalanche photodiodes.

In a variant of the avalanche radiation detector according to the invention, the individual avalanche photodiodes are connected to the amplifier via a common connecting line, wherein the connecting line makes contact with the common upper diode layer, which all avalanche photodiodes have in common.

However, it is alternatively possible for the individual avalanche photodiodes to be connected to the amplifier via a plurality of parallel connection lines, wherein the individual connection lines respectively contact the upper diode layer in the vicinity of the respective avalanche photodiodes. This offers the advantage that only lower voltage drops occur along the upper diode layer, since the

Signal is discharged directly through the nearest connection lines.

It is further provided in a development of the invention that the adjacent avalanche photodiodes are optically isolated from one another in order to prevent optical crosstalk between the adjacent avalanche photodiodes. This optical isolation preferably consists of isolation trenches which are etched between the adjacent avalanche photodiodes and absorb or reflect photons generated in the avalanche photodiodes. In this case, the isolation trenches may have trench walls that are doped in accordance with the second doping type and / or that are at the potential of the upper diodes. Other advantageous developments of the invention are characterized in the subclaims or are explained in more detail below together with the description of the preferred exemplary embodiments of the invention with reference to the figures. Show it:

FIG. 1 shows an equivalent circuit diagram of an avalanche photodiode according to the invention, including the erosion resistance and the coupling capacitance,

FIG. 2 shows the current-voltage characteristic of the avalanche photodiode according to FIG. 1,

FIG. 3 shows a cross-sectional view of a part of an avalanche radiation detector according to the invention, the cross-sectional view showing two avalanche photodiodes according to the invention,

FIG. 4 shows a modification of the exemplary embodiment according to FIG. 3 with a carrier wafer on the underside,

FIG. 5 shows a modification of the embodiment according to FIG. 4, which is produced by wafer bonding,

FIG. 6 shows a modification of the exemplary embodiment according to FIG. 3, wherein the semiconductor substrate is not completely depleted to the bottom in the spaces between the adjacent avalanche photodiodes,

FIG. 7 shows a modification of the exemplary embodiment according to FIG. 3, wherein the cathode layer is arranged in the space between the adjacent avalanche photodiodes. broken and depleted by a separate depletion electrode,

FIG. 8 shows a modification of the exemplary embodiment according to FIG. 3, wherein optical isolation is provided in the space between the adjacent avalanche photodiodes,

9 shows a modification of the exemplary embodiment according to FIG. 3, wherein a plurality of connection lines are provided, FIG.

FIG. 10 shows a modification of the exemplary embodiment according to FIG. 3, wherein a doped region is provided,

Figure 11 shows a modification of the embodiment of Figure 5, wherein in addition an amplifier is additionally provided for each diode.

FIG. 1 shows an equivalent circuit diagram of an avalanche photodiode 1 according to the invention, which is arranged in matrix form in an avalanche radiation detector with numerous further avalanche photodiodes 1 and serves for radiation detection.

The avalanche photodiode 1 is a real component of a parallel circuit of an ideal avalanche diode AD with an ideal diode capacitance C _D , which are connected together between a read-out node 2 (virtual ground) and a transfer node 3.

Furthermore, the avalanche photodiode 1 has, as a real component, a parallel connection consisting of an ideal erosion resistance RQ and an ideal coupling capacitance C _c . Rallelschaltung between the transfer node 3 and a bias node 4 is connected.

The readout node 2 is connected to an amplifier 5, which measures the output signals of all the avalanche photodiodes 1 of the matrix-shaped detector structure.

The bias node 4, however, is biased U _BIAS during operation, the bias voltage U _B IAS is greater than the breakdown voltage UAVALAN _CHE the avalanche photodiode 1, so that a radiation-generated generation of a signal charge carrier in the avalanche diode immediately generates an avalanche. The avalanche photodiode then passes in the characteristic diagram according to FIG. 2 from an operating point 6 along the dashed line to an operating point 7. At the operating point 7, the electrical voltage dropping across the soldering resistor R _Q then increasingly delimits the electric current, so that the avalanche photodiode 1 changes from the operating point 7 to an operating point 8 along the characteristic curve. At the operating point 8, the electrical current through the avalanche photodiode 1 is then only about 20 μA. This has the consequence that the electric current fluctuates at least briefly to zero, which leads to the extinction of the avalanche, so that the avalanche photodiode 1 passes from the operating point 8 in the operating point 9 and then in the original operating point 6.

The construction of the avalanche photodiode 1 according to the invention will now be described below with reference to FIG. 3, two avalanche photodiodes being shown side by side here. A plurality of avalanche photodiodes form the avalanche radiation detector according to the invention. On an underside 10 of a semiconductor substrate 11, the avalanche photodiode 1 has a laterally continuous and highly n-doped contacting layer 12.

On an opposite upper side 13 is an optical filter layer 14, as they are, for. B. for reflection reduction, known from the prior art and need not be further described.

Below the optical filter layer 14 is a highly p-doped cathode layer 15 having a layer thickness d _k of 10 nm to a few 100 nm. The cathode layer 15 is laterally unstructured and extends over the entire width of the detector structure, as will be explained in detail. In the avalanche radiation detector, the cathode layer 15 is connected to the amplifier 5 via a contact 24.

Below the cathode layer 15 there is an n-doped anode layer 16, wherein the anode layer 16 is bounded laterally and leaves a gap 17 between the adjacent avalanche photodiodes 1. The gap 17 allows the cathode layer 15 to completely deplete the semiconductor substrate 11 in the gap 17 between the two adjacent avalanche photodiodes 1, so that the adjacent avalanche photodiodes 1 are electrically isolated from each other by the depletion in the gap 17.

Between the cathode layer 15 and the underlying anode layer 16 there is an avalanche region in which the incident radiation generates an avalanche breakdown.

Below the anode layer 16 there is furthermore an erosion resistance layer 18, which is weakly n-doped. The Anode layer 16 here shields the laterally limited erase resistance layer 18 from the depletion effect of the cathode layer 15 located above it, so that the erosion resistance layer 18 is not depleted.

It is therefore important in this exemplary embodiment that the cathode layer 15 protrudes in the lateral direction via the anode layer 16 into the intermediate space 17, so that the cathode layer 15 forms a depletion electrode in the interspace 17, which depletes the semiconductor substrate 11 in the interspace 17.

The anode layer 16 in this case has a thickness d _A in the range of micrometers, while the Löschwiderstandsschicht 18 has a thickness d _R in the range of 10 microns to about 100 microns.

The exemplary embodiment according to FIG. 4 largely corresponds to the exemplary embodiment described above and illustrated in FIG. 3, so that reference is made to the above description to avoid repetition, the same reference numerals being used for corresponding details.

A special feature of this embodiment is that the lower contacting layer 12 is formed by a highly n-doped carrier wafer.

In the fabrication of this embodiment, the quenching resistor layer 18 is epitaxially grown on the contacting layer 12.

The exemplary embodiment according to FIG. 5 largely agrees again with the exemplary embodiments described above, so that in order to avoid repetition on the above description, with the same reference numerals being used for corresponding details.

A special feature of this embodiment is that under the contacting layer 12 is still an insulating layer 19 is arranged.

In this case, a carrier layer 20, which may be made of silicon or glass, for example, is disposed below the insulating layer 19.

This is therefore the already mentioned SOI structure, which is produced by wafer bonding.

The exemplary embodiment according to FIG. 6 again largely corresponds to the exemplary embodiment described above and illustrated in FIG. 3, so that reference is made to the above description to avoid repetition, the same reference numbers being used for corresponding details.

A special feature of this exemplary embodiment is that the depletion effect of the cathode layer 15 in the intermediate space 17 does not extend to the contacting layer 12 on the underside 10. Instead, the cathodic layer 15, which acts as a depletion electrode, forms only a depletion island in the intermediate space 17, which extends only partially into the depth.

The exemplary embodiment according to FIG. 7 in turn largely corresponds to the exemplary embodiment described above and illustrated in FIG. 3, so that reference is made to the above description in order to avoid repetition. is taken, with the same reference numerals are used for corresponding details.

A special feature here is that the cathode layer 15 does not pass laterally, but is interrupted in the intermediate space 17.

Instead, a separate depletion electrode 21 is arranged in the gap 17, which can be controlled independently of the avalanche photodiodes 1, which is not shown here for the sake of simplicity.

In addition, the cathode layers 15 of the adjacent avalanche photodiodes are in this case electrically connected to one another by a line element 22.

Furthermore, FIG. 8 again shows an exemplary embodiment which in turn largely corresponds to the exemplary embodiment according to FIG. 3, so that reference is made to the above description to avoid repetition, the same reference numerals being used for corresponding details.

A special feature is that in the gap 17 between the adjacent avalanche photodiodes, an optical isolation is provided, which optically isolated the adjacent avalanche photodiodes from each other to prevent optical crosstalk.

The optical isolation consists of isolation trenches 23 etched into the gap 17 in the semiconductor substrate 11, the isolation trenches absorbing and / or reflecting photons. Finally, the embodiment according to FIG. 9 is also largely identical to the exemplary embodiment described above and illustrated in FIG. 3, so that reference is made to the above description to avoid repetition, the same reference numbers being used for corresponding details.

A special feature of this embodiment is that the connection to the amplifier 5 is not made by a single connecting line, but by a plurality of connecting lines 24, 25, which are electrically connected in parallel. This prevents that along the cathode layer 15 excessively high voltage drops occur.

FIGS. 10 and 11 show further modifications of the embodiment described above and shown in FIG. To avoid repetition, reference is made to the above description, wherein the same reference numerals are used for corresponding details.

The peculiarity of the exemplary embodiment shown in FIG. 10 consists in the provision of a p-doped region 25 in the lower part of the interspace 17. The doped region 25 generates an intrinsic space charge zone, by means of which the semiconductor substrate 11 is additionally depleted laterally next to the erosion resistor 18. The space charge zone is superimposed with the upper space charge zone, which is generated by the depletion electrode 15 laterally to the anode layer 16.

The p-doped region 25 does not have to be on the lower one

Be limited part of the space 17. By a lateral extent of this area below the anode layer 16, the Löschwiderstandsschicht 18 can be further limited and thus their resistance can be increased. In the exemplary embodiment shown in FIG. 11, readout amplifiers 5 are arranged on the rear side of the photodiode, which enable spatially resolved readout of measurement signals.

The geometric arrangements described so far enable the time-resolved counting of individual photons, but not their spatially resolved detection (imaging). To achieve this goal, one of the readout nodes must be segmented, which ideally gives each avalanche photodiode its own readout node. For larger finely segmented detectors, however, the required connecting cables can no longer be supplied laterally for reasons of space. Using three-dimensional integration techniques such as bump bonding or SLID (Solid Liquid Interdiffusion, see A. Kumpp et al., "Vertical System Integration by using interchip and solid liquid interdiffusion bonding", "J.Jap. Appl. Phys.", Vol 7A, 2004), system components manufactured in various technologies can be vertically connected via metal contacts. Such a system can, for. B. from an avalanche diode sensor chip and a plurality of amplifiers containing highly integrated readout chip. In this case, the read-out chip must be attached to the back in order not to obscure the optical entrance window on the top.

The embodiment illustrated in FIG. 5, in which the wafer-bonding method is used, can be changed to a position-sensitive detector according to FIG. For this purpose, the back-side contacting layer 12 is preferably introduced in a structured manner before the wafer bonding. In the embodiment with an n + doped contacting layer 12, an insulating p-layer 25 is required in the interspaces. lent (Figure 11). After processing the wafer with the sensor chips, the carrier wafer 20 is preferably removed by etching, wherein the insulating layer 19 can serve as an etch stop. Contact holes are then etched and metallized in the insulating layer. With the help of the mentioned techniques the read-out chip is contacted. In Figure 11, the amplifier 5 are shown schematically on the readout chip.

The invention is not limited to the preferred embodiments described above. Rather, a variety of variants and modifications is possible, which also make use of the inventive idea and therefore fall within the scope.

Reference sign list

1 avalanche photodiode

2 selection nodes

3 transshipment nodes

4 bias nodes

5 amplifiers

6 operating point

7 operating point

8 operating point

9 operating point

10 bottom

11 semiconductor substrate

12 contacting layer

13 top

14 optical filter layer

15 cathode layer

16 anode layer

17 gap

18 Löschwiderstand layer

19 insulating layer

20 carrier layer

21 depletion electrode

22 cable manager

23 isolation trenches

24 contact

25 doped area

AD avalanche diode

Cc coupling capacity

C ₀ diode capacitance

RQ erosion resistance

UBIAS bias

Claims

An avalanche photodiode (1) for detecting radiation, comprising a) a semiconductor substrate (11) having an upper side (13) and a lower side (10), wherein the semiconductor substrate

(11) is doped according to a first doping type (n ^~)) (corresponding to a second type of doping p ⁺⁾ doped b of an upper diode layer (15) which is arranged (in the semiconductor substrate (11) at the top 13), c) a laterally delimited lower diode layer (16) arranged in the semiconductor substrate (11) between the upper diode layer (15) and the lower side (10) of the semiconductor substrate (11) and corresponding to the first doping type (11) d) an avalanche region which extends below the upper diode layer (15), the radiation to be detected triggering avalanche breakdown in the avalanche region, and e) a contacting layer (12) arranged on the underside (10) of the semiconductor substrate (11) and doped in accordance with the first doping type (n ⁺ ), characterized by f) a laterally limited arc resistor layer (18; RQ) disposed in the semiconductor substrate (11) is arranged the lower diode layer (16) and the contacting layer (12) and doped according to the first doping type (n), wherein the Löschwiderstandsschicht (18; RQ) deletes the radiation-generated avalanche breakdown in the avalanche area, as well as g) a depletion electrode (15; 21) arranged at least partially laterally of the laterally delimited lower diode layer (16) and doped according to the second doping type (p) such that the depletion electrode (15; 21) laterally directs the semiconductor substrate (11) in addition to the laterally delimited lower diode layer (16) depleted, while the Löschwiderstandsstandsschicht (18; RQ) of the lower diode layer (16) opposite the depletion electrode (15; 21) is shielded and therefore not or only partially depleted.

2. avalanche photodiode (1) according to claim 1, characterized in that the upper diode layer (15) protrudes laterally with a side portion over the laterally limited lower diode layer (16) and forms with the protruding side portion of the depletion electrode.

3. avalanche photodiode (1) according to claim 1, character- ized in that the depletion electrode (21) from the upper diode layer (15) is separated.

4. avalanche photodiode (1) according to any one of the preceding claims, characterized by an optical filter layer (14) which is applied to the top (13).

5. avalanche photodiode (1) according to any one of the preceding claims, characterized in that the upper diode layer (15) and / or the contacting layer (12) a) in the lateral direction without interruption over the entire width of the avalanche photodiode (1) extends and / or b) laterally unstructured.

6. avalanche photodiode (1) according to any one of the preceding claims, characterized in that the optical filter layer (14) extends without interruption over the avalanche region (3).

7. avalanche photodiode (1) according to any one of the preceding claims, characterized in that the Löschwiderstandsschicht layer (18; R _Q ) has such a large resistance value that the current in the avalanche region temporarily dies in an avalanche breakthrough, and so that the avalanche breakthrough ends.

8. Avalanche photodiode (1) according to one of the preceding claims, characterized in that a) that the upper diode layer (15) is a cathode layer, while the lower diode layer (16) is an anode layer, or b) that the upper diode layer (15 ) is an anode layer while the lower diode layer (16) is a cathode layer.

9. avalanche photodiode (1) according to one of the preceding claims, characterized by a at the top (13) arranged radiation entrance window for receiving the radiation to be detected.

10. avalanche photodiode (1) according to any one of the preceding claims, characterized in that the contacting layer (12) is a highly doped wafer on which the erase resistance layer is applied.

11. avalanche photodiode (1) according to any one of the preceding claims, characterized by: a carrier layer which is arranged on the underside (10) of the contacting layer (12) and the avalanche photodiode (1) carries mechanically.

12. avalanche photodiode (1) according to claim 11, characterized in that the carrier layer comprises silicon, silicon dioxide, glass, sapphire, a ceramic and / or a highly doped semiconductor material.

13. Avalanche photodiode (1) according to claim 11 or 12, characterized by an insulating layer (19) which is arranged between the contacting layer (12) and the carrier layer.

14. avalanche photodiode (1) according to claim 13, characterized in that the insulating layer consists of silicon dioxide.

15. avalanche photodiode (1) according to any one of the preceding claims, characterized in that the semiconductor substrate (11) has at least one doping profile of the first doping type.

16. avalanche photodiode (1) according to any one of the preceding claims, characterized in that in the semiconductor substrate (11) laterally next to the Löschwiderstandsschicht (18; R _Q ) a doped region (25) is provided in which the semiconductor substrate (11) accordingly doped to the second doping type.

An avalanche radiation detector comprising a plurality of avalanche photodiodes (1) according to any one of the preceding claims.

18. avalanche radiation detector according to claim 17, characterized in that the individual avalanche photodiodes (1) are connected in parallel with a common amplifier.

19. An avalanche radiation detector according to claim 18, characterized in that a) that extends the upper diode layer (15) of the individual avalanche photodiodes (1) in a lateral direction over a plurality of adjacent avalanche photodiodes (1), b) that the lower diode layer (16) of the individual avalanche photodiodes (1) is interrupted in each case between the adjacent avalanche photodiodes (1) and has a gap (17), c) that the upper diode layer (15) forms the semiconductor substrate (11) in the intermediate space (17) between the adjacent avalanche photodiodes (1) depleted and the adjacent avalanche photodiodes (1) thereby electrically isolated from each other.

20. Avalanche radiation detector according to claim 19, characterized in that the individual avalanche photodiodes (1) are connected to the amplifier via a common connecting line, the connecting line contacting the common upper diode layer (15).

21. Avalanche radiation detector according to claim 19, characterized in that the individual avalanche photodiodes (1) are connected to the amplifier via a plurality of parallel connection lines, wherein the individual connection lines each comprise the upper diode layer (15) in the vicinity of the respective avalanche photodiode (1) contact.

22. Avalanche radiation detector according to claim 21, characterized in that the individual connection lines contact the upper diode layer (15) in each case in the intermediate space (17) between the adjacent avalanche photodiodes (1).

23. An avalanche radiation detector according to one of claims 17 to 22, characterized in that a) that the depletion electrodes of the individual avalanche photodiodes (1) each of the upper diode layer

(15) are separated, b) that the depletion electrodes are respectively arranged in the spaces between the adjacent avalanche photodiodes (1), c) that the depletion electrodes are connected together to a voltage source, and / or d) that the upper diode layers of the adjacent ones Avalanche photodiodes (1) are each connected to each other by a line which bridge the gap (17) between the adjacent avalanche photodiodes (1) bridged.

24. avalanche radiation detector according to one of claims 17 to 23, characterized by an optical isolation between see the adjacent avalanche photodiodes (1) to prevent optical crosstalk between the adjacent avalanche photodiodes (1).

25. Avalanche radiation detector according to claim 24, characterized in that the optical isolation consists of isolation trenches (23) which are etched between the adjacent avalanche photodiodes (1) and absorb or reflect photons generated in the avalanche photodiodes (1).

26. Avalanche radiation detector according to claim 25, characterized in that the isolation trenches (23) have trench walls, which are doped according to the second doping type (p) and / or are at the potential of the upper diode layer (15).

27. Avalanche radiation detector according to one of claims 23 to 26, characterized in that the avalanche photodiodes (1) are individually connected to one amplifier each.

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