JPH01500536A - semiconductor radiation detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Rear contact type restraint impurity band detector [Background of the invention] The present invention is a radiation detector, particularly a suppressed impurity band detector, which uses long wave infrared radiation (LWl). , R).

The design of high-quality radiation detectors involves maximizing the incident radiation within some desired frequency. The natural goal is to create a detector that can detect the Setting up a high quality radiation detector One of the most common problems meterers encounter is what is collectively known as dark current. It is a phenomenon. This phenomenon is due to various mechanical phenomena in the operation inside the detector. As a result, a current flows through the detector in the absence of incident radiation.

The dark current flowing through the detector is generally considered as electrical noise, and the magnitude of the noise The intensity is directly proportional to the strength of the dark current.

This dark current noise is inversely proportional to the detector's signal-to-noise ratio and is sensitive to changes in the incident radiation. This reduces the sensitivity of the detector.

One of the well-known mechanisms of this dark current is the generation of thermal charge carriers. There is life. This mechanism works by freeing donor impurity electrons from the atom. , which has the effect of absorbing thermal energy from semiconductors. The band in which these electrons are conductors and is swept into positive detector electrical contact by the electric field. Normal operation In this case, an electric field is created in the detector due to the potential difference, which is mainly due to the External integrated circuit reading devices, such as hybridized thin film or charge-coupled devices. is given by Additional electrons are transferred to the detector by the negative potential contact of this reader. injected into the. As a result, the two mechanisms work together to detect in the absence of incident radiation. A current is generated in the device, that is, a dark current is generated.

A well-known method of extinguishing thermally induced components by dark current One method is to cool the radiation detector at its absolute temperature. but In this way, a detector cooled at an extremely low temperature can be housed in an assembly compactly and at low cost. It is difficult to fit into the

Other common methods used to reduce dark current are strongly doped, A relatively high resistance layer is interposed between the low resistance sensing layer and one electrical contact of the detector. There is a method "C" to place it.

This high-resistance layer blocks the conductive path of the impurity band conduction mechanism, resulting in a dark current. decrease. Therefore, generally a relatively high resistance layer is used as a stop layer, and thus A detector using such a layer is known as a suppressed impurity band detector.

One of the special problems with this suppressed impurity band detector is that the electrical contacts and The physical mounting of this and the associated reader is a matter of method. This detector 8 A typical array of is of very small dimensions, so that the space between each detector is 10 At 0 micron or less, general wiring is often difficult. Further to this problem , many independent detector elements contained within one array, small or larger , certain things overlap.

One way to solve this wiring problem is to use the following integrated circuit reader. i.e. the device is made with dimensions comparable to these parts of the radiation detector. Typically, each contact in this reader is connected to each detector element and register. It is arranged so that it is controlled. Therefore, this detector and reader back such that they are physically coupled, which allows the reader to connect to each detector. The device is electrically connected to the device. i.e. a radiation detector compatible with integrated circuit reading technology. can have a number of advantages over unmatched detectors.

However, one of the problems with this type of readout technique is the fill factor of this detector. (fill f'actor) decreases.

Fill factor is a measure of the surface of the array that can receive the incident radiation. be. The installation of electrical contacts and their associated reading devices usually results in The fill factor of a given array is reduced due to partial occlusion of the surface. .

Many conventional detectors, known as stop impurity transducers (BITs), All of its electrical contacts are exposed to the surface of the radiation receiver. This arrangement is for the reading circuit. There are strict limitations on the physical properties of such detectors, which make them difficult to read integrated circuits. Technology is often not compatible.

In response to the obvious drawbacks caused by this type of detector, an alternative form was devised. That is, in this case, all electrical connection points are on the opposite side of the side receiving the radiation. has been moved to. Reverse illumination inhibiting impurity transgenics (RI) is commonly used. This device, known as BIT, is compatible with integrated circuit reading technology. There is. No. 4,507,674, which is assigned as an infringement of this patent. An inverted detector is described. This R is due to the low fill factor of the BIT detector. This problem has been overcome through IBIT research. RIBIT array fill factor can be approached as a single body, with a very large number of hybrids per focal plane. It is possible to install a detector compatible with the standard. However, the structure of this RIBIT is It has certain problematic parts related to processing and processing, and this part The construction is experimental. In the tBIT structure, to create a back contact area is a bulk silicone with a surface area heavily seeded with the first epitaxial layer. Must be built on a recon board. epitaxial fabricated above this area The crystalline and electrical properties of the film are difficult to control and can result in poor detector performance. Become. The RIBIT method also provides a means of bringing the heavily planted area into contact with the substrate. A V-groove etch is required in both epitaxial layers to provide a.

This (1) groove contact work is also difficult to control.

[Summary of the invention] The above-mentioned problems are overcome by radiation-suppressed impurity band detectors, and other create benefits. According to one of the preferred embodiments of the invention, this detector It is formed as an array of device elements, and has electrical contacts on the front and back sides of the device. It contains a layered semiconductor structure. The shape of this contact receives radiation on its front surface. It is also possible to attach an integrated circuit reader to the back of the device. A contact device is connected to the front and back contacts.

The detector includes two insulating semiconductor layers, each serving as one substrate and the other as a substrate. acts as a restraining layer. A radiation detection layer is provided between them.

In this embodiment of the invention, the two layers are made of silicon; Other semiconductor materials may be used in accordance with the theory of the invention. This detection The layer is doped and the band gap between this conduction band and the following valence band is The valence band structure has been changed to reduce the gap, and the photons of the incident radiation are transferred to the valence band. electrons from the conduction band to the conduction band. This restraining layer is very thin and electrons can pass through the above-mentioned blocking layer without going back to the valence band. .

This electrical connection between the detection layer and the stop layer is made with the help of two contact layers, immediately One of them is placed between the detection layer and the substrate, and the other is placed on the opposite side of the detection layer. placed on the surface of the layer. The two contacts are made of silicon and doped to make them conductive. Electricity is given. In the first contact layer, each area of doped material is of an array of detector elements distributed between areas of uncirculated electrically insulated area. forming each detector element. In the second layer, doping is done uniformly. , all detector elements are electrically connected in common. This second layer is very thin and the incident It is designed so that there is no significant interference with radiation. Each layer mentioned above is epitaxial They are deposited one on top of the other by a growth method.

Prior to stacking each layer, backside contacts are formed in the substrate. This is the base This is done by passing multiple metal conductors through the positions where the plate connects with each detector element. One end of the conductor is led to the back of the board, which is also the back of the detector. , connected to the reading device. The other end of each conductor leads to the opposite surface of the board. and is connected to the next first contact layer.

the electrical contacts on the front side of the detector are formed as a single metallization in the form of a grid; Serves as a common contact to the detector elements. The thickness of this grid line is very It is thin and does not significantly inhibit incident radiation.

When using this detector, the insulating properties of the above-mentioned blocking layer prevent dark current from flowing. I can escape. A high fill factor is achieved due to the shape and arrangement of this electrical contact. , it does not suffer from the drawbacks inherent in the complex physical structure of the inverted arrest detectors described above.

[Brief explanation of the drawing] The present invention will be explained below using drawings, but common parts in each drawing will be explained below. The same reference numerals are used.

FIG. 1 shows a restraining impurity bar with electrodes disposed on opposite sides according to one embodiment of the present invention. Figure 2 is a perspective view of the infrared detector, and Figure 2 is a cross-section of the detector taken along line 2-2 in Figure 1. FIG.

[Example code] One embodiment of a suppressed impurity band detector 10 is shown in FIGS. 1 and 2. FIG. child The detectors are made to be particularly sensitive to longwave infrared (LWIR) radiation. There is. Generally, LWIR radiation corresponds to a wavelength range of approximately 14 to 30 microns. It is considered to be a matter of frequency. Therefore, the impurities used in the detector are Forbidden band between valence band and conduction band corresponding to wavelength energy of R radiation This is an element that reduces the width of the dot.

The operation of the detector 10 is such that the detector 10 uses a relatively lightly doped device that inhibits the flow of dark current. It is based on the use of a doped detection layer with a free insulating layer. Detector 10 In the presence of incident radiation of a wavelength suitable for use in and by an external reading device connected to the detector 1o, as described below. It runs through the restraining layer due to the applied electric field.

It should be noted that in the detection layer, the doping has already sufficiently reduced the band gap. This allows the electrons to rise and proceed to the conduction band, causing one-sided control. In the stop layer, the undoped layer preserves the original relatively large bandgap. That is what is happening. This blocking layer is thin enough that electrons can easily pass through it. , and there is no possibility of dropback to the valence band of the stopping layer. restraining layer The thickness is very thick and is sufficient to block the advance of dark current. hung by the reader In the presence of an electric field, the detector 10 has the characteristics of a variable resistor; If the current produced by the applied voltage varies with the intensity of the incident radiation, Ru. The structure of the detector 10 with the novel features of the present invention will be described in more detail below. do.

Detector 10 includes a radiation detection layer 20, a stop layer 22, and a front or top and rear or bottom layer. include front and bottom detector contact layers 24 and 16, respectively, which are placed on top of the substrate 12. It is formed. A plurality of electrical contacts from the detector 1o to the integrated circuit reader 36 metal conductor 14 and back metallization 32 and 34, while the front grid metal It is done by a monster. LWIR radiation, shown conceptually by arrow 28, is detected by the detector. 10, a substantially transparent contact layer 24 and an underlying restraining layer 24. layer 22 to reach radiation detection layer 20. Here the detector The absorption of radiation by impurities causes a change in the electrical resistance of the detector lO to the reader 3. 6 is sensed by an electrical circuit (not shown).

Considering the overall configuration, the radiation detector 1.0 is assembled on a substrate 12.

Substrate 12 is typically made of intrinsic silicon and is approximately 29 mils thick.

A metal conductor 14, known as a via, passes through the substrate 12 and is connected to the substrate 1. On the upper surface of 2 a metal, typically aluminum, is deposited in defined areas. Next the board A sufficiently strong thermal gradient is applied to 12 to melt the metals mentioned above. This molten metal Move into the substrate material and go all the way down. This molten metal flows inside the substrate 12. As it descends, some of the metal is deposited onto the substrate, thereby selectively doping the substrate. A continuous aluminum conductor 14 is formed from the front surface to the rear surface of the substrate 12. be done. The ends of the conductors 14 exposed on the front surface of the substrate 12 are polished by a conventional method. , to eliminate surface defects that would prevent uniform epitaxial layer growth on the top surface of the substrate 12. lose. Where the plurality of conductors 14 exit from the rear surface of the board 12, typically aluminum A backside metallized pad 32 made of aluminum is formed in contact with the conductor 14. child There are metallization points 34 on the surface of each of the pads 32, which typically conductive pad 32 and conductor 14 to an integrated circuit reader 36. Connecting.

A contact layer is provided to bring the conductor 14 into favorable electrical contact with the internal radiation detection layer 20. 16 is made of substantially pure crystalline silicon and is placed on top of the top surface of substrate 12. It is grown epitaxially, typically to a thickness of 3 microns. Layer 16 is rag It is doped with acceptor impurities such as ions as follows. First, the boron layer] 6, typically 0. Plant in a checkerboard pattern at a depth of 1 to 0.2 mils. It will be done. This planted portion corresponds to the metal conductor 14 placed on the front surface of the substrate 12. It has a registration relationship with the edge. After planting, this device is In its original form, it is annealed to repair possible scratches in the crystal structure of layer 16. Ru. During this annealing, the implanted boron atoms migrate down through the layer 16, It makes contact with the exposed end of the conductor 14 below. As shown in the drawing, layer 18 includes each conductor. 14, which causes layer 16 to be heavily doped. a first area lea of silicon and a second area 16b of substantially pure silicon. divided. Zone 16a contains acceptor impurities, the concentration of which is typically cubic cell. 1×10 19 acceptor atoms per nanometer. Thus, each area lea becomes conductive and makes electrical contact with the end of the corresponding conductor 14.

The extent of the surface area of the layer thus planted]6 is determined by the design specifications. Ru. This percentage of planting area can vary widely from 1% to typically 75%. be.

A detection layer 20 is engineered and taxially grown on the contact layer 16, the thickness of which varies. Typically from 4 to 25 microns. The layer 20 imparts p-type semiconductor properties to the layer 20. Doped with an acceptor-type impurity, such as gallium, suitable for It will be done.

The concentration of acceptor type impurity atoms in layer 20 is typically on the order of 1,000 cubic centimeters. 1X1018 acceptor atoms per molecule.

Gallium is a material whose ionization energy corresponds to the energy of LWIR radiation. It is one of the basics. Therefore, LWIR radiation 28 entering layer 20 is bound to gallium atoms. ionizes the electrons that are present, and these electrons then freely enter the conduction band.

A stop layer 22 is epitaxially grown on top of the detection layer 20 . Control layer 22 consists of substantially pure intrinsic silicon. The resultant restraining layer 20 The doped detection layer if the crystal structure does not contain substantially any impurity atoms. It has a much higher electrical resistance than 20.

As previously explained, this relatively high resistance blocking layer 22 serves as a dark current impurity barrier. acts as a barrier to conductive components. To fully perform this function In this case, the blocking layer 22 connects the radiation detection layer 20 and the electric current of each detection element of the radiation detector IO. It is necessary to be sandwiched between one of the contacts. As mentioned above, multiple severities doped area], 8a together with the conductor 14 form a set of contacts; It is necessary to ensure that several detection areas are scanned by the reading device 36. read To create circuit continuity between the detector 36 and the detector 1°, the detector JO A ground electrical connection must be provided to the Ru.

In this embodiment of the invention, the ground connection is formed by ion implantation; is typically 0.2 microns deep at the surface of the stop layer 22 opposite the detection layer 20. This is done by a p-type acceptor impurity, typically boron, implanted into the . After implantation, the surface of layer 22 is exposed to physical defects in the crystal structure that may have been created during implantation. is annealed to repair it. During this annealing, the implanted boron atoms are directed downwards. and enters layer 22. The annealing time is determined as follows: Due to the downward movement of the atoms, the stop layer 22 is not yet completely wrapped, so Layer 22 includes an area of substantially pure crystalline silicon adjacent to sensing layer 20 and a region of p-type amorphous silicon. The receptor impurities are separated into an upper region containing boron atoms. This upper ward The area forms the contact layer 24. The concentration of acceptor impurity atoms in layer 24 is typically Specifically, 1.0 cm per cubic centimeter. X1019 acceptor atom, thereby A conductive layer 24 is created.

A thin layer of metallization is deposited over the contact layer 24, which is typically made of aluminum. It has the shape of a grid 30 and has two sets of parallel members spaced apart. , the members of one set are arranged at right angles to the members of the other set.

As shown in the figures, LWIR radiation enters the detector 10 via a transparent front contact layer 24. to go into. Also, since the grating 30 is formed as a thin layer, it is less sensitive to LWIR radiation. Substantially transparent.

Thus, the present invention achieves a high fill factor comparable to that of RIBIT devices; Moreover, it does not have the above-mentioned problems associated with the complicated manufacturing process of RIBIT equipment. .

After passing through the substantially transparent front contact layer 24, the LWIR radiation 28 then passes through the transparent front contact layer 24. It passes through the transient stop layer 22 and enters the detection layer 20 .

As mentioned above, the doping level of layer 20 is so high that LWIR radiation is Everything is absorbed into layer 20. The results of this are favorable. released into layer 20. As a result of the absorption of radiation, the electrons of the impurity atoms are raised from the valence band to the conduction band. Therefore, charge carriers are generated.

The detection layer 20 has a certain resistance, such as a multiplexer in an integrated circuit. It is possible to conduct a current flowing in response to the bias voltage supplied by the reader. come. When the incident radiation 28 is absorbed, the resistance of the detection layer 20 changes. As a result, The current flowing through the detector 10 changes and this change is then sensed by the reader 36. be done.

As mentioned above, substantially all of the incident radiation 28 is absorbed by layer 20. front and back The small amount of radiation absorbed by the surface contact layers 24 and 16 has a negligible effect. However, the conductivity of this area is much higher than that of layer 20 and is harmless. Therefore, the contact Additional radioactive charge carriers generated in the contact layers 24 and 16 are not detected. stomach.

In terms of the structure of the essentially pure crystalline silicon stop layer 22, layer 22 is comparable to layer 20 has a high electrical resistance and therefore the mobility of charge carriers in this area is The small amount of radiation absorbed by layer 22 is much smaller than that in detector 10. Has a negligible effect on operation.

The embodiments of the present invention described above are merely for illustrative purposes, and variations thereof are within the skill of the art. It is considered easy to do so. For example, as a variant, the main unit that needs to be doped Examples include replacing p-type impurities in these layers with n-type impurities. follow Therefore, the present invention is not limited by the embodiments disclosed herein, and is not limited to the embodiments disclosed herein. It is intended to be limited only by the scope of the claims.

international search report ANNEX τOTKE INTERNATIONAL 5EARC) I RE PORT ONυ5-A-445184229105/84 None

Claims (8)

[Claims] 1. In the semiconductor array of a radiation detector, one electrically insulating substrate is used to one set extending apart from each other and between opposing first and second surfaces of the substrate; having an electrical conductor of one detection layer of radiation detection material disposed along the first side of the substrate; One in which the above detection substance is doped in order to impart chargeability, The above detection layer on the opposite side of the above board is used to suppress the flow of dark current with a low conductivity blocking layer. placed on the surface of the output layer, and one lattice-like structure made of conductive material. a common terminal for the entire radiation detector located on the surface of the stop layer opposite to the detection layer; for each one of the radiation detectors, with said conductor serving as a Things that act as individual terminals, A semiconductor array of radiation detectors, including: 2. The lattice-like structure is a layer of doped semiconductor on which a lattice-like structure is formed. 2. The semiconductor component of the radiation detector according to claim 1, wherein a metallization is arranged. Leh. 3. The opening of the lattice metallization is in registration with the conductor. , each having substantially the same dimensions as one of the radiation detectors, and one set of radiation detectors. such that it receives incident radiation from the surface of the array opposite the conductor of the 3. A semiconductor array for a radiation detector according to claim 2. 4. a radiation detector having a plurality of radiation detection zones disposed therein; includes a first surface receiving the radiation and a second surface opposite the first surface; 1 is transparent to radiation in a predetermined frequency range impinging on it, and a first surface is electrically conductive and a common electrical connection between said area and one reading device; through which it is electrically conductively connected to the detection zone to form a conductive contact. , wherein the second surface has a plurality of conductors extending outward therethrough, each of the conductors extending outwardly through the second surface; a radiation detector arranged to connect one of the recording areas to the reading device; 5. 5. The radiation detector of claim 4, further comprising a first radiation detector constituting said detection area. a semiconductor layer, the semiconductor layer has a certain thickness and impurity concentration, and has a predetermined frequency range; a substance that absorbs the radiation of a charge carrier and, as a result, emits a signal indicating the presence of charge carriers. and, a second semiconductor layer adjacent to the first layer, the second layer comprising an intrinsic semiconductor material; and wherein the second layer is an electrical insulator; a first layer adjacent to and conductively connected to the first and second layers, respectively; and a second contact, wherein the second layer is sufficiently thin and has a sufficiently low concentration of impurities. This causes charge carriers to be transferred from the second contact to impurities in the first layer. substantially prevents injection into the first layer at energy levels in the conduction band. a substrate adjacent to the first contact; a plurality of conductors provided through the substrates, each one of the substrates having a first and a second conductor; 2 ends, the first end being conductively connected to the first contact, and the first end being conductively connected to the first contact; the second end of each of the is used to connect to the reading device; as well as, a metallization layer disposed over and in conductive connection with the second contact; The layer is thin enough that virtually all radiation in a given frequency range incident on it is the metallization layer has a connection to the reading device; do, things, including a radiation detector. 6. The metallized layers are in the form of a lattice, spaced apart and orthogonal. radiation can enter the detector through the spaces between the grid-like members. , wherein the space forms a surface area over the second contact therebeneath. Radiation detector on board. 7. a high electrical conductivity, wherein said first contact is in connection with said area of said second contact; , each of said areas of high conductivity being conductively connected to one of said conductors. each of said areas of high conductivity radiates said radiation adjacent to said area of high conductivity. conductively connected to the absorbing first layer volume, whereby each of the detection areas 7. A radiation source according to claim 6, configured to detect radiation in a predetermined frequency range. radiation detector. 8. The above frequency range has a wavelength of about 14 to 30 microns for longwave infrared radiation. 8. A radiation detector according to claim 7, which corresponds to a radiation detector according to claim 7.