Method for manufacturing a diode radiation sensor

Abstract

A method for implementing a diode radiation sensor (1) having a charge multiplication diode (2), comprising the steps of providing a substrate (3) made of a semiconductor material having a front surface (4) and a back surface (4b), forming a first layer (5) of semiconductor material doped with a first predetermined amount of a first type of doping near the front surface (4), and forming at least a second layer (8) of semiconductor material doped with a second predetermined amount of a second type of doping, electrically opposite to the first type, deep in the substrate (3), the second layer (8) being obtained by inserting into the substrate (3) a first predetermined amount of a first dopant of the first type and a second predetermined amount of a second dopant of the second type.

Description

Technical Field

[0001] The present invention can be applied in the field of diode sensors, specifically in the field of radiation sensors.

[0002] More specifically, the present invention finds use in the field of diode radiation sensors having one or more diodes, comprising a charge multiplication structure powered to operate in a linear multiplication regime, although not limited thereto.

Background Art

[0003] Radiation sensors are used in a wide range of applications from industrial to scientific. Often, the detector is built on a single body of a semiconductor material such as silicon and is divided into several microcells or channels (also called pixels and / or microstrips), each typically consisting of individually accessible diodes.

[0004] A typical example of an ionization radiation detector consists of silicon microstrips with a typical thickness of several hundred μm. Such devices are used to detect ionizing radiation (such as charged particles or X-rays) in scientific experiments and industrial applications.

[0005] The active area of the detector is usually 25 μm to several hundred micrometers wide and is divided into several parallel strips.

[0006] As a first trend, since the above sensors have no internal gain, there is a limit when the amount of charge generated by ionizing radiation is too low to be accurately measured.

[0007] To improve performance, we decided to introduce a charge multiplication structure within the diode, which, when properly polarized, allows it to operate in a linear charge multiplication regime; that is, the charge collected at the output of each channel is proportional to the charge generated by the radiation interacting with the sensor.

[0008] In some cases, such as when measuring the interaction time of charged particles at minimum ionization in high-energy physics experiments, the charge amplification provided by a diode must be sufficient to enable the detection of radiation and to obtain an optimal operating point, taking into account the signal-to-noise ratio. However, it must not be over-amplified to avoid degrading the accuracy of the measurement due to deterioration of the signal / noise ratio caused by excessive noise determined by the charge multiplication process. For this reason, diodes typically used are fed so that their gain is particularly limited, with a value in the range of 10 to 30. In such cases, they are called LGADs, or low-gain avalanche diodes.

[0009] Considering the types of functions that LGADs possess and the types of radiation that need to be measured, the active thicknesses of the sensors that implement them are typically in the range of tens to hundreds of micrometers.

[0010] One of the most significant problems the above sensors face is the fact that they gradually degrade when exposed to stronger radiation.

[0011] As is well known, the diode multiplication structure at the base of such sensors is actually manufactured by appropriately doping a substrate made of semiconductor material (usually silicon, but not limited to silicon). The radiation described above can interact with the thus doped substrate, causing the deactivation of the dopant, that is, the removal of the dopant from the crystal lattice and the return of the semiconductor atom that the dopant replaced to its original position. In other words, exposure to radiation reduces the concentration of the active dopant in the diode forming the sensor, and the gain of the junction region of such a diode decreases. This impairs the detection accuracy of the sensor.

[0012] In particular, the first drawback is that the sensor's gain decreases over time.

[0013] A further drawback, particularly for LGAD applications, is that diodes are powered to achieve a limited gain (typically 10-30), so a decrease in doping leads to a decrease in gain at the same power supply voltage for the diode. [Overview of the project] [Problems that the invention aims to solve]

[0014] The object of the present invention is to at least partially overcome the above-mentioned drawbacks by providing an execution method (manufacturing method) for such a diode radiation sensor so that the sensor is less susceptible to degradation due to exposure to radiation.

[0015] Specifically, the object of the present invention is to provide a method for carrying out (manufacturing) a diode sensor that can limit, if not completely cancel out, the deactivation effect of dopant particles in the diode forming the sensor.

[0016] Another object of the present invention is to provide a diode sensor that is low-cost and as close as possible to the cost of known equivalent methods. Manufacturing method The objective is to provide.

[0017] Next, a further object of the present invention is to introduce a diode sensor that minimizes changes to known methods of implementation currently used in the execution of such a sensor. Manufacturing method The objective is to provide.

[0018] As is clear from what has been described so far, another object of the present invention is to provide a diode radiation sensor that is more resistant to the radiation it is supposed to receive, so as to limit, if not offset, the attenuation of the gain of the diodes forming the diode radiation sensor. [Means for solving the problem]

[0019] For such purposes, and other purposes which will become more apparent below, the diode radiation sensor relating to the following claims which should be considered an integral part of this disclosure Manufacturing method This is achieved by [method].

[0020] In particular, the method of the present invention makes it possible to manufacture a type of diode radiation sensor that includes at least one charge multiplier diode.

[0021] First, this method includes the step of preparing a substrate made of a semiconductor material. Such a substrate has a front surface and a back surface opposite to the front surface.

[0022] Next, at least a first layer of semiconductor material doped with a first predetermined amount of the first type of doping (impurity addition) is fabricated near the front surface of the substrate.

[0023] Next, the first type of dopant is electrically Opposition (opposite) It is a type of Then, at least a second layer of semiconductor material doped with a second predetermined amount of the second type of doping is fabricated deep within the substrate.

[0024] However, in the present invention, the order of the doping operations is arbitrary without limitation, and the formation of the two layers may be reversed. Further, in the present invention, in order to create various types of electronic components, numerous other steps before, during, and in between the two aforementioned steps can be envisioned without limitation.

[0025] In any case, according to one aspect of the present invention, a second layer is obtained by inserting a first predetermined amount of a first dopant of a first type and a second predetermined amount of a second dopant of a second type (using implantation or surface diffusion techniques) into the same zone of the substrate on which the second layer is disposed. In particular, the second predetermined amount of the doping characteristics of the second layer is obtained by the difference between the effect of the insertion of the first predetermined amount of the first dopant and the effect of the insertion of the second predetermined amount of the second dopant.

[0026] Also in this case, the execution order of the two insertion steps is arbitrary, and the important thing is that the final result, that is, the amount of doping of the second type in the second layer reaches the second amount. Further, according to some embodiments of the present invention, the two insertion steps are carried out according to the situation.

[0027] It should be noted that the techniques used are compensatory, that is, in order to obtain the second amount of the aforementioned doping, two dopants of opposite signs are inserted into the same region of the substrate, and one of them compensates for the second amount.

[0028] In the case of the present invention, usually, a layer of doped semiconductor material is obtained by inserting a single type of dopant that is not two competing types, depending on one compensating the other. In this case, several basic advantages can be obtained by such techniques.

[0029] Firstly, the above compensation makes it possible to increase the presence density of the second dopant without compromising the second predetermined amount of the second layer doping. Since the use of a high density of the second dopant inhibits the aforementioned radiation-induced recombination, this increase in density makes it possible to mitigate the harmful effects of radiation irradiated to the sensor of the present invention during use.

[0030] A further advantage is that the second predetermined amount of the second dopant can be freely increased, making it possible to manufacture radiation sensors with optimized resistance to the harmful effects of radiation.

[0031] Even more advantageously, if radiation can deactivate a very small portion of the second dopant in the second predetermined amount, the same effect is induced in the first predetermined amount of the first dopant, and as a result, the diode's gain remains substantially unchanged according to its operating polarization.

[0032] Therefore, an advantage is that the implementation of a second layer using compensation technology can mitigate, if not completely offset, the degradation of the sensor when exposed to radiation.

[0033] Since such results can be obtained with a simple addition of an insertion operation with respect to known equivalent methods (injection or compensation diffusion), the radiation sensor of the present invention manufacturing The cost is equivalent to that of conventional sensors. manufacturing It is clear that this is practically equivalent to the cost.

[0034] Furthermore, standard of known sensors manufacturing The changes introduced in the method are for the radiation sensor. manufacturing Without increasing the complexity of time, manufacturing can.

[0035] Based on the above, it is clear that the aforementioned objective can also be achieved by a diode radiation sensor manufactured using the method described above. Further features and advantages of the present invention should become more apparent in light of a detailed description of preferred but non-exclusive embodiments of the radiation sensor according to the present invention, illustrated with non-limiting examples with reference to the accompanying drawings. [Brief explanation of the drawing]

[0036] [Figure 1] In this drawing, Figure 1 shows a radiation sensor manufactured according to the method of the present invention. [Modes for carrying out the invention]

[0037] Referring to the figure above, a diode radiation sensor 1 having one or more charge multiplier diodes 2 manufacturing The method will now be described. According to the embodiment described, such charge multiplier diode 2 is intended to be polarized to operate in a linear multiplication zone corresponding to LGAD, but this embodiment is not considered to limit the present invention.

[0038] For the sake of simplicity, the sensor 1 depicted in the figure includes a single diode 2, but it is clear that such an embodiment should not be considered limiting to the present invention.

[0039] The method of the present invention first includes the step of preparing a substrate 3 made of a semiconductor material and having two surfaces, a front surface 4 and a back surface 4b opposite to the front surface 4. Considering the use of the embodiments described above in the context of LGAD, such a substrate 3 generally has a large depth, several hundred micrometers, or typically, but not necessarily, a depth of at least 20 micrometers. It is also usually lightly doped, but such embodiments do not limit the present invention.

[0040] In the embodiments described, the substrate 3 is always made of silicon, but such embodiments should not be considered to limit the present invention.

[0041] According to one aspect of the present invention, the next step is to fabricate a first layer 5 of a semiconductor material doped with a first predetermined amount of a first type of doping near the front surface 4 of the substrate 3.

[0042] In the embodiments described, the first type of doping is N-type doping obtained by injecting phosphorus into the substrate 3, but this should not be considered limiting to various embodiments of the present invention where the doping is different and / or the first type of dopant is a P-type dopant (in this case, boron is commonly used, but not necessarily required). Furthermore, the injection technique used should not be considered limiting to various embodiments of the present invention where it is carried out by diffusion from the front.

[0043] Furthermore, the position of the first layer 5 near the front surface 4 of the substrate 3 is a feature that should not be considered limiting in this invention, and the depth, size, and number of the first layer within the substrate can be arbitrary depending on the design requirements of the radiation sensor.

[0044] According to another aspect of the present invention, further, in the depths of the substrate 3, the first type and Electrically They are opposite types. The procedure involves fabricating a second layer 8 of a semiconductor material doped with a second predetermined amount of a second type of doping.

[0045] In accordance with what has been described above regarding the first layer 5, the second type in the embodiments described is generally P-type doping, which is performed by injecting boron into the substrate 3, but again, the invention should not be considered to be limited to specific dopants, electrical codes, and techniques used.

[0046] Furthermore, the position, size, and number of the second layer are not limiting features in this invention.

[0047] As described above, the order of the doping operations is arbitrary as intended by the present invention, and the formation of the two layers may be reversed. Furthermore, in the present invention, a number of other steps can be envisioned without limitation before, during, and between the two steps described above in order to create various types of electronic components.

[0048] In any case, according to another aspect of the present invention, the second layer 8 is obtained by inserting a first predetermined amount of a first dopant of a first type and a second predetermined amount of a second dopant of a second type (whether by injection or by diffusion from the front surface 4) into the same zone of the substrate 3 on which the second layer 8 is to be placed. In particular, the second predetermined amount of the doping characteristics of the second layer 8 is obtained by the difference between the effect of inserting the first predetermined amount of the first dopant and the effect of inserting the second predetermined amount of the second dopant.

[0049] Even in this case, the order in which the two insertion steps are performed is arbitrary. In fact, a relevant aspect of the present invention is that the amount of the second type of doping in the second layer 8 reaches a second predetermined amount.

[0050] In particular, the technology used is a compensation method; that is, in order to obtain the aforementioned second predetermined amount of doping, two dopants with opposite signs and mutual compensation are inserted into the substrate 3 in the zone where the second layer 8 is positioned according to the design, so that the result corresponds to the second predetermined amount of doping.

[0051] In known equivalent radiation sensors, a doped layer of semiconductor material is obtained by injecting two non-competitive, single-type dopants, relying on one to compensate for the other. In this case, such compensation techniques offer several fundamental advantages.

[0052] Firstly, the above compensation makes it possible to increase the density of the second dopant while maintaining the second predetermined amount of doping in layer 8. Since the use of a high-density dopant inhibits the aforementioned radiation-induced recombination, this increase in density makes it possible to mitigate the harmful effects of radiation irradiated onto the sensor 1 of the present invention.

[0053] A further advantage is that the first predetermined amount of the first dopant and the second predetermined amount of the second dopant can be freely coordinated and increased, making it possible to manufacture a radiation sensor 1 with optimized resistance to the harmful effects of radiation.

[0054] Furthermore, advantageously, even if the radiation can deactivate a very small portion of the second predetermined amount of the second dopant, the same effect is induced in the first predetermined amount of the first dopant, thereby causing the gain of diode 2 to remain substantially unchanged according to its operating polarization.

[0055] Therefore, from the above explanation, the compensation technology for Layer 2 8 manufacturing This makes it possible to significantly reduce, if not completely eliminate, the degradation of the sensor when exposed to radiation.

[0056] Since such results can be obtained with respect to known equivalent methods, the radiation sensor 1 of the present invention is obtained with a simple addition of an insertion operation. manufacturing The cost is equivalent to that of conventional sensors. manufacturing It is clear that this is practically equivalent to the cost.

[0057] Furthermore, standard of known sensors manufacturing The modifications introduced in the method are of the radiation sensor 1 of the present invention. manufacturing Without increasing the complexity, manufacturing can.

[0058] The second predetermined amount of doping in the second layer 8 is determined by the design parameters of the sensor 1.

[0059] Specifically, this is calculated based on the following characteristics of radiation sensor 1: - The thickness of the detector's active volume, defined by the high-resistance substrate portion. - The bonding doping profile, that is, the doping profile of the zone sandwiched between the front surface 4 of sensor 1 and the second layer 8 (the zone where the first layer 5 is located), - Doping profile of layer 8 (In the case of doping obtained by injection, the profile (characteristics) is influenced by the injection energy, its activation time, and the subsequent thermal load; in the case of diffusion from the surface, the profile is influenced by the diffusion time, technique, activation temperature, and the subsequent thermal load.) - Thermal load during the process, - Resistivity of substrate 3, -Possible co-injection of other non-electrically active elements, - Constraints regarding the voltage to be applied to radiation sensor 1 during the operation step, - Compensatory doping profile.

[0060] From the above explanation, it is clear that the object of this patent is the radiation sensor 1 obtained by the method described above.

[0061] In that sense, this includes the following, identified charge multiplier diode 2: - A substrate 3 formed from semiconductor material, -First layer 5 of semiconductor material doped with the first type of dopant, - A second layer 8 of the semiconductor material doped with the second type of doping obtained as a result.

[0062] Based on the above, the radiation sensor of the present invention manufacturing The method will be understood to achieve all pre-defined objectives.

[0063] In particular, this makes the diode radiation sensor especially resistant to the effects of degradation from the radiation it receives.

[0064] In fact, the method of the present invention has produced a radiation sensor in which the effect of deactivation of the dopant particles of the diode forming the sensor is limited, if not completely offset.

[0065] Upon closer examination, the present invention manufacturing The method involves a second layer of compensation technology. manufacturing The sensor consists of manufacturing Because it shows a small but significant change in the process, the cost is low and comparable to that of known equivalent methods.

[0066] The present invention is capable of numerous modifications and variations, all of which are included in the appended claims. Furthermore, without departing from the scope of protection of the present invention as defined by the appended claims, all details may be replaced by other technically equivalent elements, and the materials may differ as needed.

Claims

1. A method for manufacturing a diode radiation sensor (1) having at least one charge multiplier diode (2), the method comprising the following steps: - A step of arranging a substrate (3) made of a semiconductor material having a front surface (4) and a back surface (4b) facing the front surface (4), - A step of forming at least a first layer (5) of semiconductor material doped with a first predetermined amount of a first type of doping near the front surface (4) of the substrate (3), - A step of forming at least a second layer (8) of semiconductor material doped in the depth of the substrate (3) with a second predetermined amount of a second type of doping which is electrically opposite to the first type, Includes, The method described above involves inserting the first dopant of the first type and the second dopant of the second type into the same zone of the substrate (3) on which the second layer (8) is to be placed, thereby obtaining the second layer (8). The final result of the doping of the second layer (8) is achieved by the difference between the first dopant and the second dopant, and the final result of the doping is pre-set so that the charge multiplier diode operates at the operating point. A method characterized in that the density of the second dopant is increased, thereby mitigating the variation in the final result of the doping caused by the deactivation of the first and second dopants due to radiation, and the gain of the charge multiplier diode is maintained in accordance with the operating polarization of the charge multiplier diode.

2. The method according to claim 1, characterized in that the first type of dopant is an n-type dopant and the second type of dopant is a p-type dopant.

3. The method according to claim 2, characterized in that the first dopant is phosphorus and the second dopant is boron.

4. The method according to claim 1, characterized in that the first type of dopant is a p-type dopant and the second type of dopant is an n-type dopant.

5. The method according to claim 4, characterized in that the first dopant is boron and the second dopant is phosphorus.

6. The method according to claim 1, characterized in that the semiconductor material is silicon.

7. The method according to claim 1, characterized in that the insertion of the first predetermined amount of the first dopant and the second predetermined amount of the second dopant is carried out by injection technology.

8. The method according to claim 1, characterized in that the insertion of the first predetermined amount of the first dopant and the second predetermined amount of the second dopant is carried out by a diffusion technique from the front surface.

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