RU2575939C1 - Method of making ionising radiation sensor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: sensor is formed on a polished plate which is cut from an ingot of n-type ultrapure silicon, for which the method comprises consecutively performing the first chemical washing of the plate in a surfactant solution containing complexons, forming a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components, implanting p-type impurity ions into the working side of the plate and n-type impurity ions into the non-working side of the plate at a temperature not lower than 50°C with the implantation energy of not more than 200 keV and with an implantation dose of not more than 1000 mcC/cm², repeating chemical washing of the plate in a surfactant solution containing complexons, forming a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components, repeating the implantation of p-type impurity ions into the working side of the plate and n-type impurity ions into the non-working side of the plate at a temperature not higher than 25°C with the implantation energy of not more than 200 keV, depositing an aluminium layer on both sides of the plate, forming an ohmic contact by burning aluminium and depositing a passivating coating on the working side of the plate, and then performing two-step post-implantation annealing.

EFFECT: producing a detector element with higher sensitivity, based on the planar technology.

15 cl, 8 dwg

Description

FIELD OF THE INVENTION

The invention relates to the technology of semiconductor devices designed to convert the effects of ionizing radiation into an electrical signal, the measurement of which allows you to determine the level of radiation or the dose of radiation and the parameters of the ionizing radiation itself. In particular, the invention relates to a technology for manufacturing semiconductor sensitive elements (a sensor or particle counter or detector), which are a p-i-n-diode intended for use in various systems for measuring radiation levels, dosimeters, background excess indicators, including for individual control of radiation exposure and for warning of radioactive hazard. Currently, sensors based on p-i-n-diodes continue to be improved taking into account modern advances in microelectronics technology.

The invention is a technological process (method) of manufacturing a sensor according to planar technology, which allows to obtain sensors with a uniquely high value of the lifetime of minority charge carriers, which is ensured by the application of a sequence of special operations and processing conditions of silicon wafers.

State of the art

Semiconductor detectors (PDDs) based on p-i-n-diodes are widely used as particle counters and as high-resolution particle energy meters (spectrometers). The principle of their work is based on the fact that when passing through the counter (sensitive element) of an ionizing particle, the charges formed in the substance of the counter are collected on the electrodes.

An important feature of semiconductor counters is their small size. This greatly expanded the possibilities of using such detectors not only in the field of physical experiment, but also in technology - in technological control devices and in medicine.

A semiconductor pin-diode converter of the effects of radiation, mainly neutron, into an electrical signal containing a high-resistance n-type silicon substrate and several p-type injection electrodes, p-type emitters of a pin-diode neutron radiation converter, are known from the prior art. located in the form of a matrix on the front side of the substrate, and the value of the base length varies with the etching depth of silicon on the back of the substrate, in the region between the emit erom and the contact area to the n-type conductivity. This allows a real product to provide a wide range of operating radiation doses due to the integral design of silicon pin diodes in the form of a matrix on a single substrate with a variable length of the base region and electrode sizes, and also allows to expand the range of radiation dose measurements, and detects neutron radiation, however , a manufacturing method (process) of such a converter is not given (RU 2408955).

Known semiconductor radiation detector used in a mobile radio device with the function of monitoring the radiation situation. The semiconductor radiation detector is made in the form of a honeycomb structure of sensitive elements made of inorganic crystalline semiconductor material connected in parallel with its paired electrodes. The sensitive elements are made in the form of rectangular parallelepipeds made of silicon, and both electrodes are sprayed on one side (surface) of each sensitive element and are connected by microelectronic soldering (golden hairs) through the amplifier to the processor. In this case, the best result is achieved when sensitive elements are made from a plate of highly pure silicon in the form of cubes, which are oxidized on five sides with the formation of an insulating film of silicon oxide, and electrodes are deposited on the sixth side. Sensitive elements are glued onto a common substrate with high insulation resistance and electric strength, low dielectric constant, for example, of ceramic. However, such a device does not contain a pn junction, and therefore, therefore, has high leakage currents, which allows it to operate stably only to detect large radiation fluxes and makes it impossible to register single particles or quanta (RU 116725).

A known method of manufacturing a detector of short-range charged particles, including the oxidation of an n-type silicon substrate, etching of the oxide layer on the front side of the substrate in the working area and on its reverse side, the formation of a p ⁺ -n junction from the working side of the substrate by introducing boron and a heavily doped layer n ⁺ -type of conductivity on its reverse side and the creation of contacts by sputtering in vacuum, characterized in that, in order to improve the resolution of the detector, the oxidation is etched after oxidation layer on the reverse side of the substrate in the working region and etching the substrate in the same region to thin it, and after the formation of a heavily doped layer of n ⁺ type conductivity, the oxide layer is etched from the front side of the substrate in the working region and then p ⁺ -n- junction (SU 1371475).

Publications are known in which methods for producing detectors using planar technology for detecting radiation and having semiconductor pn junctions are presented. However, they do not consider ways to increase the lifetime of carriers, methods of additional cleaning the material (volume) of the plate in order to reduce the leakage current (dark current). (Kemmer J. Fabrication of low noise silicon radiation detectors by the planar process // Nuclear Instruments and Methods. - 1980. - V. 169. - P. 499-502).

A known method of manufacturing a silicon detector of weak ionizing radiation (charged particles, gamma and x-rays), which creates a low signal level in the readout electronics. The method involves the following operations: manufacturing of initial silicon wafers 300 microns thick; oxidation of 0.2 μm, thinning of the oxide around the periphery of the detector’s working area, ion implantation of boron with an energy of 15 keV, a dose of 5 ∙ 10 ¹⁴ cm ^-2 in the front side of the plate, ion implantation of arsenic in the back of the plate with an energy of 30 keV and a dose of 5 ∙ 10 ¹⁵ cm ^-2 , heat treatment to activate the introduced impurities at a temperature of 600 ° C. The current-voltage characteristic of a detector with an area of 1 cm ² and a reverse current of more than 4 nA is given (US 4442592).

However, silicon detectors obtained by known methods have insufficient sensitivity, since they contain undesirably many intrinsic free electrons, since it is not possible to minimize the content of rapidly diffusing impurities, residues of organic impurities and residues of the near-surface disturbed layer, which reduce the lifetime of nonequilibrium charge carriers and increase the reverse current of the detector, by known methods. which leads to a decrease in the signal-to-noise ratio. The presence of these impurities prevents the return current from being obtained when the voltage is full depletion of less than 1 nA / cm ² .

At the same time, the lifetime of minority charge carriers of the product obtained by the method used in the closest analogue is less than 10 ms, leakage current is more than 10 nA / cm ² , charge collection efficiency (element signal level) is not more than 90%.

To increase the sensitivity, it is necessary to increase the volume of the semiconductor in order to increase the likelihood of hitting and scattering in it, for example, a gamma quantum and, accordingly, increase the count rate of particles of the radiation flux. But with an increase in volume, its dimensions increase, and the number of intrinsic carriers also increases proportionally, against which additional carriers caused by the action of a radiation quantum become invisible, and isolating them for recording penetrating radiation events is not an easy task requiring precisely an increase in the lifetime of minority carriers and creating an area depleted in major carriers.

Disclosure of invention;

The objective of the invention is to develop an effective commercially suitable method of manufacturing a semiconductor sensor for detecting ionizing radiation and expanding the arsenal of such methods.

The technical result to which the claimed invention is directed is to ensure the production of a more highly sensitive detector element based on planar technology, operating in the mode of complete depletion at reverse bias by minimizing the amount of rapidly diffusing impurities, residues of organic impurities and residues of the surface disturbed layer, and, thereby thereby, reducing the number of intrinsic free electrons. Moreover, a higher sensitivity compared to analogs is determined by the fact that the lifetime of minority charge carriers is at least 15 ms, the leakage current is not more than 10 nA / cm ² , and the charge collection efficiency (element signal level) is at least 99%.

The essence of the invention lies in the fact that the method of manufacturing a sensor of ionizing radiation, provides that a sensor is formed on a polished plate cut from an ultrapure n-type silicon ingot, for which the first chemical washing of the plate in a solution of surface-active substances containing complexones is performed, forming layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components, implantation of p-type impurity ion ions in the working side of the plate and the impurity ions of the n-type conductivity to the non-working side of the plate at a temperature of at least 50 ° C with an implantation energy of not more than 200 keV and with an implantation dose of not more than 1000 μC / cm ² , repeated chemical washing of the plate in a solution of surface-active substances, containing complexones, the formation of a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components, re-implantation of p-type impurity ions into the working side of the plates and p-type impurity ions the irreducibility of the non-working side of the plates at a temperature of no more than 25 ° C with an implantation energy of no more than 200 keV, the deposition of an aluminum layer on both sides of the plates, the formation of an ohmic contact by burning aluminum and the deposition of a passivating coating on the working side of the plates, and then two-stage post-implantation annealing.

Preferably, a plate with a thickness of 250 μm to 1000 μm is used, cut from an ultrapure silicon ingot grown by a crucible-free zone melting (BZP) method, with a specific silicon resistance of 1000-800000 Ohm ∙ cm.

Preferably, the formation of a layer of silicon oxide is produced by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components.

Preferably, the chemical washing of the plate in a solution of surfactants is carried out in a solution of surfactants containing complexones from the group: phosphonic acids, nitrile triacetic acid, choline.

Preferably, before implantation of impurity ions, windows are opened in the photoresist for subsequent etching of local areas of silicon oxide by photolithography and etching of silicon oxide in local areas to a residual thickness of 0.01 μm to 0.10 μm, as well as chemical washing of the plates in a solution containing hydrogen peroxide and sulfur acid in a ratio of 1: 3 at a temperature of 90-120 °.

Preferably, the initial implantation of p-type impurity ion ions to the working side of the plates is carried out with an implantation energy of 10-200 keV, an implantation dose of 50-1000 μC / cm ² , and the p-type impurity ion is re-implanted into the working side of the plates with implantation energy 1-200 keV, implantation dose of 1-500 μC / cm ² .

Preferably, the initial implantation of p-type impurity ion ions into the non-working side of the plates is carried out with an implantation energy of 10-200 keV, an implantation dose of 10-1000 μC / cm ² , and the second implantation of p-type impurity ion ions into the non-working side of the plates is carried out with implantation energy 10-200 keV, implantation dose of 10-1000 μC / cm ² .

Preferably, the initial implantation of impurity ions into the working and non-working sides of the plate is carried out at a plate temperature above 50 ° C, and the second implantation of impurity ions into the working and non-working sides of the plate is carried out at a plate temperature (-196 ° C) - (+ 25 ° C )

Preferably, the formation of a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components is carried out by heat treatment of the plate at a temperature of 650-1300 ° C in an atmosphere of dry oxygen, nitrogen or argon, chlorine-containing components, with a chlorine-containing component of 1-10 volume percent.

Preferably, the implantation of p-type impurity ion ions into the working side of the plate is carried out with an implantation energy of 1-200 keV, an implantation dose of 1-500 μC / cm ² at a plate temperature of implantation (-196 ° С) - (+ 25 ° С).

Preferably, after the implantation of ions before applying the aluminum layer, the plates are heat treated at a temperature of 500-900 ° C in an atmosphere containing oxygen, nitrogen (argon), chlorine-containing components with a content of chlorine-containing components 1-10 volume percent, and then etching of silicon oxide with a thickness of 0.01 -0.1 μm in an aqueous solution of hydrofluoric acid, washing the plate in deionized water and chemical washing of the plate in a solution containing hydrogen peroxide and aqueous ammonia.

Preferably, an aluminum layer of 0.1-1 μm is applied with a silicon content of not more than 1% on both sides of the wafer.

Preferably, the burning of aluminum is carried out at a temperature of 400-500 ° C in an atmosphere of nitrogen or argon.

Preferably, the passivation coating is deposited on the working side of the wafer using silicon oxide and / or phosphorosilicate glass with a phosphorus content of 1-4%, and then etching the passivation coating to an aluminum layer and reducing the positive charge in silicon oxide by re-burning aluminum at a temperature of 400 -500 ° C in an atmosphere of nitrogen (argon).

As a rule, plate scribing is performed.

List of drawings

In drawings 1-8, a diagram illustrates the overall sequence of operations for processing a plate. Moreover, in the drawing of FIG. 1 shows an initial plate cut from an ultrapure high-resistance silicon ingot of a crucible-free zone melting (BZP), in FIG. 2 - formation of masking silicon oxide, in FIG. 3 - creation of a topological drawing on the planar (working) side of the plate, in FIG. 4 - ion implantation in the planar and posterior side, distillation of the impurity, washing of the plates, in FIG. 5 - removal of photoresist, washing, preparation for applying aluminum, FIG. 6 - deposition of aluminum, in FIG. 7 - photolithography on aluminum, in FIG. 8 - making contacts on the non-planar (non-working) side, conducting annealing, burning aluminum, and a series of washes.

DETAILED DESCRIPTION OF THE INVENTION

A method of manufacturing a semiconductor sensor (detector) of ionizing radiation is implemented as follows.

A semiconductor ionizing radiation sensor is formed on a polished wafer cut from an ingot of high-resistance ultra-pure n-type silicon, grown by the crucible-free zone melting (BZP). Plate thickness from 250 microns to 1000 microns. The specific resistance of silicon is 1000-800000 Ohm ∙ cm. The lifetime of nonequilibrium charge carriers is more than 12 ms.

In the manufacturing process, the following operations are performed:

1. Chemical washing of the plates with the help of surfactants containing complexones (organic compounds that combine basic and acid centers in the molecule and are able to bind metal ions and thereby contribute to cleaning the surface of rapidly diffusing metal impurities), for example: phosphonic acids, nitrile triacetic acid, choline, etc. Surface active substances (surfactants) - organic compounds having an amphiphilic structure, that is, their molecules include a polar part, a hydrophilic component (functional groups —OH, —COOH, —SOOOH, —O—, etc., or, more often, their salts are -ONa, -COONa, -SOOONa, etc.) and non-polar (hydrocarbon) part, hydrophobic component. An example of a surfactant is ordinary soap and CMC (synthetic detergents), as well as alcohols, carboxylic acids, amines, etc. The purpose of the operation: reducing the concentration of rapidly diffusing metal impurities from the surface of the plates, removing residues of organic contaminants and residues of the near-surface disturbed layer. In FIG. 1 shows the initial (blank) plate of high-resistance BZP silicon n-Si after this operation of the method (process).

2. The formation of a layer of silicon oxide SiO _{2 by} thermal oxidation at a temperature of 650-1300 ° C in an atmosphere of dry oxygen with the addition of chlorine-containing components in a concentration of from 1 to 10 volume percent. The purpose of the operation: the creation of a masking oxide before ion implantation. In FIG. 2 shows a plate after the formation of a masking oxide layer.

3. Conducting the first photolithography process ^1. ( ¹ Photolithography is a multi-stage process consisting of operations:

- application of a photoresist (protective photosensitive, resistant to acids and other etchants after manifestation and subduing);

- Photoresist flare, through a photomask;

- the manifestation of photoresist, as a result of which “windows” appear in it (holes in the right places);

- killing of the photoresist - treatment with a reagent causing the polymerization of the substance.) Purpose of the operation: applying a photoresist with subsequent opening of windows in it for subsequent etching of the local areas of silicon oxide.

4. Partial etching of silicon oxide in local areas to a residual thickness of 0.01 μm to 0.10 μm. Purpose: window etching in silicon oxide for subsequent implantation of p-type ions.

5. Removing the photoresist from the surface of the plates.

6. Chemical washing of the plates in a solution containing hydrogen peroxide and sulfuric acid in a ratio of 1: 3 at a temperature of 90-120 °.

7. Washing plates in deionized water.

8. Chemical washing of the plates in a solution containing hydrogen peroxide and aqueous ammonia.

9. Washing plates in deionized water. In FIG. 3 shows the plate after creating a topological pattern on the planar side of the plate as a result of the described operations No. 3-9.

10. Initial implantation of p-type impurity ions (for example, boron ions B) of conductivity in the working (planar) side of the plates. The implantation energy of 10-200 keV, the implantation dose of 50-1000 µC / cm ² , the temperature of the plates during implantation above 50 ° C.

11. Initial implantation of p-type impurity ions (for example, arsenic -As ions) of conduction into the non-working side of the plates. The implantation energy of 10-200 keV, the implantation dose of 10-1000 µC / cm ² , the temperature of the plates during implantation above 50 ° C.

12. Chemical washing of plates with the help of surfactants containing complexones (organic compounds that combine basic and acid centers in the molecule and are able to bind metal ions and thereby contribute to cleaning the surface of rapidly diffusing metal impurities), for example: phosphonic acids, nitrile triacetic acid, choline, etc. Surface active substances (surfactants) - organic compounds having an amphiphilic structure, that is, their molecules include a polar part, a hydrophilic component (functional groups —OH, —COOH, —SOOOH, —O—, etc., or, more often, their salts are -ONa, -COONa, -SOOONa, etc.) and non-polar (hydrocarbon) part, hydrophobic component. An example of a surfactant is ordinary soap and CMC (synthetic detergents), as well as alcohols, carboxylic acids, amines, etc. The purpose of the operation: the removal of rapidly diffusing metal impurities and traces of organic contaminants from the surface of the plates.

13. Heat treatment of plates at a temperature of 650 ° C-1300 ° C in an atmosphere of dry oxygen, nitrogen or argon, chlorine-containing components. The content of chlorine-containing components is 1-10 volume percent. Purpose of operations 10-13: creating a p + p transition in the working areas of the plate and an isotype p + p transition on the back of the plate. In FIG. 4 shows the plate after the initial ion implantation in the planar and posterior sides, i.e. after the described operations No. 10-13.

14. The process of the second photolithography.

15. Partial etching of silicon oxide in local areas to a residual thickness of 0.01 μm to 0.10 μm. Purpose: window etching in silicon oxide for subsequent implantation of p-type ions.

16. Removing the photoresist from the surface of the plates.

17. Chemical washing of the plates in a solution containing hydrogen peroxide and sulfuric acid in a ratio of 1: 3 at a temperature of 90 ° -120 °.

18. Washing plates in deionized water.

19. Chemical washing of the plates in a solution containing hydrogen peroxide and aqueous ammonia.

20. Washing plates in deionized water.

21. Re-implantation of p-type impurity ions (for example, boron ions B) of conductivity in the working side of the plates. The implantation energy is 1-200 keV, the implantation dose is 1-500 μC / cm ² , the temperature of the plates during implantation (-196 ° С) is (+ 25 ° С).

22. Re-implantation of p-type impurity ions (for example, arsenic ions -As) conductivity in the non-working side of the plates. The implantation energy of 10-200 keV, the implantation dose of 10-1000 μC / cm ² , the temperature of the plates during implantation (-196 ° C) - (+ 25 ° C).

23. Chemical washing of plates with the help of surfactants containing complexones (phosphonic acids, nitrile triacetic acid, choline, etc.)

24. Heat treatment of plates at a temperature of 500 ° -900 ° C in an atmosphere containing oxygen, nitrogen (argon), chlorine-containing components. The content of chlorine-containing components is 1-10 volume percent (at least 1% of chlorine-containing components). The purpose of operations for PP. 21-24 - activation of implanted impurities, gettering ² ( ² Gettering - the process of binding to electrically neutral associations of mobile, undesirable impurities and defects at the interfaces formed by the outer surface of the crystals or the surface of the boundaries of bulk defects. The process of gettering occurs due to the following physical effects:

1 - the release of impurities or the decay of extended defects into smaller components; 2 - diffusion of impurities or components of dislocations; 3 - absorption of impurities or intrinsic interstitial atoms by some sink;) of rapidly diffusing metal impurities.

25. Etching of silicon oxide with a thickness of 0.01-0.1 microns in an aqueous solution of hydrofluoric acid.

26. Washing plates in deionized water.

27. Chemical washing of the plates in a solution containing hydrogen peroxide and aqueous ammonia. In FIG. 5 shows the plate after removing the photoresist, washing, preparation for applying aluminum, i.e. after the described operations No. 14-27 of the method.

28. Application of a layer of aluminum with a silicon content of not more than 1% on both sides of the plates. The thickness of the aluminum layer is 0.1-1 μm. In FIG. 6 shows a plate after applying aluminum according to operation No. 28 of the method.

29. Carrying out the process of the third photolithography on an aluminum layer with protection of the side of the plate by a layer of photoresist. In FIG. 7 shows a plate after photolithography on aluminum, i.e. after operation No. 29 of the method.

30. Etching of aluminum in local areas on the working side of the plate.

31. Removing photoresist in acetone, isopropyl alcohol at a temperature of 20-25 ° C.

32. Washing plates in deionized water.

33. The burning of aluminum at a temperature of 400-500 ° C in an atmosphere of nitrogen (argon). The purpose of the operation is the formation of an ohmic contact. In FIG. Figure 8 shows the plate after creating contacts on the non-planar (back) side, i.e. after annealing, burning aluminum, and a series of washes, i.e. after operations No. 30-33 of the method.

34. The deposition of a passivating (silicon oxide, phosphorosilicate glass with a phosphorus content of 1-4%) coating on the working side of the plates.

35. Carrying out the process of the fourth photolithography on a passivating coating with photoresist protection on the back of the plate.

36. Etching (liquid or dry) of a passivating coating to an aluminum layer.

37. Removal of the photoresist in acetone, isopropyl alcohol at a temperature of 20-25 ° C.

38. Washing plates in deionized water.

39. The burning of aluminum at a temperature of 400 ° -500 ° C in an atmosphere of nitrogen (argon). The purpose of the operation is to reduce the positive charge in silicon oxide.

40. Scribing plates ³ . ( ³ Scribing is a technological process in the electronics industry, namely, the process of dividing semiconductor wafers into individual crystals. Scribing includes in this case, through cutting, in which the plate is cut through in one step by a cutting tool (diamond blade, wire) - which allows you to cut a plate with a thickness of up to 1 mm and a diameter of 100-150 mm at a speed of up to 150 mm / s, to a depth of 300 microns or more in one pass.)

Operations No. 34-39 provide protection for the manufactured sensor from mechanical and environmental influences. The specified operation No. 40 is intended to obtain the final product of a given size

In special cases of implementation, after step 21, it is possible to perform the chemical treatment of the plates in a solution of surfactants, then carry out a two-stage heat treatment of the plates at a temperature of 400-650 ° C in an atmosphere of nitrogen (argon), then anneal at a temperature of 500-900 ° C in the atmosphere nitrogen (argon).

In particular cases of the implementation of Clause 22, it is possible to carry out the chemical treatment of the plates in a solution of surfactants, then conduct a two-stage heat treatment of the plates at a temperature of 400-650 ° C in an atmosphere of nitrogen (argon), then anneal at a temperature of 500-800 ° C in a nitrogen atmosphere (argon).

Preferably, the chemical treatment of the plate in a solution of surfactants is as follows.

1. Washing the plates in deionized water at a temperature of 50-100 ° C.

2. Washing the plates in flowing deionized water at room temperature.

3. Processing plates in an oxidizing solution containing ammonium sulphate and sulfuric acid at a temperature of 50-100 ° C.

4. Washing the plates in flowing deionized water at room temperature.

5. Etching of the plates in an aqueous solution of nitric and / or hydrofluoric acid.

6. Washing the plates in flowing deionized water at room temperature.

7. Processing plates in an oxidizing solution containing ammonium sulphate and sulfuric acid at a temperature of 50-100 ° C.

8. Washing the plates in running deionized water at room temperature.

9. Processing plates in an aqueous solution of hydrofluoric acid with the addition of an aqueous solution of ammonium iodide and iodine.

10. Washing the plates in running deionized water at room temperature.

11. Chemical washing of the plates in a solution containing hydrogen peroxide and aqueous ammonia.

12. Washing the plates in flowing deionized water at room temperature.

13. Processing of plates in a solution containing monoethanolamine, nitrile triacetic acid, ethylenediaminetetraacetic acid, phosphonic acids, a solution of iodine in monoethanolamine.

14. Washing the plates in running deionized water at room temperature.

In the present technological process, in the case of using plates initially doped with phosphorus, some impurities, such as, for example, copper, are distributed so that the distribution profile takes the form close to the profile of impurity phosphorus. As a result, neutral pairs of the form Cu ⁺ P _-

Gettering is also used using broken layers, namely: single-sided polishing plates are used, and the reverse side is polished, it is the drain for defects and impurities. Strong doping (until practically amorphous or strongly radiation-damaged layers are obtained) with arsenic or phosphorus on the back side can significantly increase the gettering ability of the back side of the plate.

When implementing the method, a two-fold (operations Nos. 1, 12) decrease in the concentration of rapidly diffusing metal impurities from the surface of the plates, the removal of residues of organic impurities and residues of the surface disturbed layer by washing with the help of surface-active substances are provided.

The formation of a layer of silicon oxide in an oxidizing chlorine-containing medium by thermal oxidation at a temperature of 650-1300 ° C in an atmosphere of dry oxygen with the addition of chlorine-containing components in a concentration of 1 to 10 volume percent can effectively prevent the ingress and removal of contaminating metallic rapidly diffusing impurities.

Initial implantation of p-type impurity ion ions into the working side of the plates with process parameters: implantation energy of 10-200 keV, implantation dose of 50-1000 μC / cm ² , the temperature of the plates during implantation is above 50 ° C. The implantation temperature above 50 ° C reduces the number of radiation defects. The initial implantation of n-type impurity ion ions (phosphorus or arsenic) into the non-working side of the plates with process parameters: implantation energy of 10-200 keV, implantation dose of 10-1000 μC / cm ² , the temperature of the plates during implantation above 50 ° C also allows you to reduce the number radiation defects.

All this allows, during subsequent chemical treatment, to reduce the absorption of contaminants from chemical solutions by implanted surfaces (working and non-working sides), as well as more effectively annealing radiation defects ⁴ . ( ⁴ Radiation defects are formed during ion implantation. As a rule, these are interstitial silicon atoms and vacancies (the absence of a regular atom in the lattice)). Efficiency is ensured by the fact that radiation defects do not combine into complexes with a rapidly diffusing impurity and, as a result, do not form large clusters. This makes it possible to apply a lower annealing temperature and low-temperature gettering conditions during subsequent heat treatments.

The heat treatment of the plates at a temperature of 650-1300 ° C in an atmosphere of dry oxygen, nitrogen or argon, including a chlorine-containing component with a chlorine-containing component of 1-10 volume percent, can effectively prevent the ingress and remove contaminating metal rapidly diffusing impurities.

Re-implantation of p-type impurity ion ions into the working side of the plates with process parameters: implantation energy 1-200 keV, implantation dose 1-500 μC / cm ² , at implant temperature (-196 ° С) - (+ 25 ° С ) At such a low temperature, implantation is performed to obtain an amorphized implanted layer that facilitates the formation of a structurally perfect p + layer during subsequent heat treatment.

Re-implantation of n-type impurity ion ions into the non-working side of the plates by process parameters: implantation energy of 10-200 keV, implantation dose of 10-1000 μC / cm ² , at implant temperature (-196 ° С) - (+ 25 ° С) . At such a low temperature, implantation is performed to prevent self-annealing of radiation defects, which are necessary for the efficient gettering of rapidly diffusing metal contaminants from the volume of the plate.

Conducting two stages of post-implantation annealing is necessary for more complete activation of the impurity and effective gettering. The prototype uses only one-stage annealing at a temperature that does not provide complete activation of the implanted impurity and effective gettering.

The proposed technology is universal. It can be used for plates up to 1000 microns thick, which is important for recording x-ray radiation. The technology also allows obtaining highly sensitive detectors for detecting alpha, beta particles and charged high-energy particles.

Compared with the prototype, the proposed technology is applicable for the use of silicon wafers with a large (from 100 to 80,000 Ohm ∙ cm) resistivity range.

The resulting sensing element is a large-area silicon pin diode with a sharp pn junction. The area is determined by the size of the plate and the scope. So for household dosimetry, an active area of the order of 1 square centimeter will be sufficient, while for high-precision and fast measurements, the area can reach 100 cm ² .

The thickness of the passivation layer is about 1 μm, the thickness of the aluminum layer is about 0.8 μm, the depth of the p-region is about 0.5 μm, the thickness of the passivation layer above the p-region is 0.5 μm.

The principle of operation of silicon detectors is based on the registration of primary ionization caused by the passage of an ionizing particle through the detector and, generally speaking, is no different from the principle of operation of the ionization chamber.

When an ionizing particle passes through the detector volume, part of the particle’s energy is spent on the ionization of the atoms of the material. As a result, a region with a high (up to 10 ¹⁷ cm ^-3 ) concentration of free carriers is formed along the particle’s track over a period of about 10 ^-12 s, the so-called electron-hole pairs. The experimental data show that for various types of ionizing particles in a wide range of their energies, the average number of carrier pairs formed in silicon by the passage of an ionizing particle linearly depends on the amount of energy lost, and the average energy loss for the formation of one electron-hole pair is 3.66 eV. This value significantly exceeds the band gap in silicon - 1.12 eV, since most of the lost energy is spent on exciting lattice vibrations. The ionization energy loss of a charged particle in a layer of matter is usually described by the Bethe Bloch formula:

where: = 0.1535 MeV · s ² / g;

x is the thickness of the layer of substance in g / cm ² ;

r _e = 2.817 · 10 ^-13 cm is the classical radius of the electron;

m _e is the mass of the electron;

N _A = 6.022 · 10 ²³ mol ^-1 is the Avogadro number;

I is the effective ionization potential of the atoms of a substance averaged over all electrons (173 eV for silicon);

Z is the atomic number of the substance;

A is the atomic mass of a substance;

ρ is the density of the substance;

Z is the charge of the ionizing particle;

W _max is the maximum energy given by the incident particle in one interaction, in the approximation that M >> m _e , where M is the mass of the incident particle;

эВ/мкм (или 170·10^-19 К/мкм, или 106 электрон-дырочных пар на 1 мкм). $${\left(\raisebox{1ex}{$dE$}\!\left/ \!\raisebox{-1ex}{$dx$}\right.\right)}_{min}=388$$

eV / μm (or 170 · 10 ^-19 K / μm, or 106 electron-hole pairs per 1 μm).

Then the average number of electron-hole pairs created by an ionizing particle in a detector of thickness d will be:

As in any ionization chamber, in order to register a signal from an ionizing particle, it is necessary to collect the created charge carriers in a time significantly shorter than their recombination time (or in other words, the lifetime) - τ _r . The recombination time shows how much of N from the initial charge N _{0 is} retained (and can be collected) after time t.

N = N ₀ exp (-t / τ _r ).

The time of charge collection from the detector volume is determined by the electric field strength inside the semiconductor and the mobility of the collected carriers.

Quick charge collection is achieved with a sufficiently large value of the electric field inside the detector. The simplest way to create a high field strength is to increase the voltage applied to the semiconductor. However, this also increases the current flowing through the semiconductor, the fluctuations of which quickly begin to exceed the signal from ionizing particles. To solve this problem, as a detector, they use a special structure similar to a high-voltage one, the so-called pin diode. To date, the achievable purity level of single-crystal silicon is ~ 10 ¹¹ impurity atoms per cm ³ . The technology for producing such a material includes two stages: growing a single crystal from a melt of pre-purified silicon and repeated recrystallization of the obtained ingot by the method of crucible-free zone melting (BZP). With each recrystallization, impurities are pulled to the periphery of the ingot. Also, at the recrystallization stage, a fixed amount of dopant is introduced into the ingot, in our case it is phosphorus with a concentration of N _d ~ 10 ¹² atom / cm ³ . This method allows to achieve high uniformity of the concentration of impurities in the volume of the ingot, and, therefore, to obtain a high uniformity of its electrical properties.

Phosphorus in silicon is a donor impurity - its level is located near the upper boundary of the forbidden zone and is completely ionized at a temperature of ~ 300 K. In this case, free carriers appear in the conduction band — electrons with a concentration close to that of the donor impurity. Note that the introduction of an impurity giving one level close to the upper (donor impurity) or lower (acceptor impurity) boundary of the forbidden band with a low concentration slightly changes the carrier lifetime in the semiconductor. To a much greater extent, the lifetime depends on the concentration of residual impurities giving deep levels lying near the middle of the forbidden zone. In particular, such impurities are alkali metals, copper, gold, therefore, in the manufacture of the material for silicon detectors, special attention is paid to low levels of residual impurities of these elements.

A practical test confirmed that for products manufactured using the proposed method, the lifetime of minority charge carriers is at least 15 ms, the leakage current is not more than 10 nA / cm ² , the charge collection efficiency (element signal level) is at least 99%. Low leakage currents provide a low value of shot (current) noise, and high efficiency of charge collection - to avoid signal loss in the sensor volume.

The proposed technology is universal. It can be used for plates up to 1000 microns thick, which is important for recording x-ray radiation. The technology also allows obtaining highly sensitive detectors for detecting alpha, beta particles and charged high-energy particles.

As a result of using this method, the production of a sensitive element based on planar technology is ensured, the lifetime of minority charge carriers is at least 15 ms, the leakage current is not more than 10 nA / cm ² , the charge collection efficiency (element signal level) is at least 99%. operating in the mode of complete depletion at reverse bias by minimizing the amount of rapidly diffusing impurities, residues of organic impurities and residues of the surface disturbed layer, and, thereby, reducing the number of free free electrons.

Industrial applicability

The present invention is implemented using universal equipment widely used in industry.

Claims (15)

1. A method of manufacturing an ionizing radiation sensor, in which a sensor is formed on a polished plate cut from an ultrapure n-type silicon ingot, for which the first chemical washing of the plate in a solution of surface-active substances containing complexones is performed, forming a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components, implantation of p-type impurity ions into the working side of the plate and p-type impurity ions and conductivity to the non-working side of the plate at a temperature of at least 50 ° C with an implantation energy of not more than 200 keV and with an implantation dose of not more than 1000 μC / cm ² , repeated chemical washing of the plate in a solution of surface-active substances containing complexones, the formation of a silicon oxide layer by thermal oxidation of dry oxygen in the atmosphere with the addition of chlorine-containing components, re-implantation of p-type impurity ions in the working side of the plates and p-type impurity ions in the non-working side of the plates at at a temperature of no more than 25 ° C with an implantation energy of no more than 200 keV, applying an aluminum layer on both sides of the plates, forming an ohmic contact by burning aluminum and depositing a passivating coating on the working side of the plates, and then conducting a two-stage post-implantation annealing. 2. The method according to claim 1, characterized in that a plate with a thickness of 250 μm to 1000 μm is used, cut from an ingot of ultrapure silicon grown by the method of zoneless melting (BZP), with a specific silicon resistance of 1000-800000 Ohm ∙ cm. 3. The method according to any one of claims 1 and 2, characterized in that the formation of a layer of silicon oxide is produced by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components. 4. The method according to any one of claims 1 and 2, characterized in that the chemical washing of the plate in a solution of surfactants is carried out in a solution of surfactants containing complexones from the group: phosphonic acids, nitrile triacetic acid, choline. 5. The method according to any one of claims 1 and 2, characterized in that before the implantation of impurity ions, windows are opened in the photoresist for subsequent etching of the local areas of silicon oxide by photolithography and etching of silicon oxide in the local areas to a residual thickness of 0.01 μm to 0.10 μm , as well as chemical washing of the plates in a solution containing hydrogen peroxide and sulfuric acid in a ratio of 1: 3 at a temperature of 90-120 ° 6. The method according to any one of claims 1 and 2, characterized in that the initial implantation of p-type impurity ion ions into the working side of the plates is carried out with an implantation energy of 10-200 keV, an implantation dose of 50-1000 μC / cm ² , and repeated implantation p-type impurity ions to the working side of the plates are carried out with an implantation energy of 1-200 keV, an implantation dose of 1-500 µ C / cm ² . 7. The method according to any one of claims 1 and 2, characterized in that the initial implantation of p-type impurity ion ions into the non-working side of the plates is carried out with an implantation energy of 10-200 keV, an implantation dose of 10-1000 μC / cm ² , and repeated implantation impurity ions of the n-type conductivity in the non-working side of the plates is carried out with an implantation energy of 10-200 keV, an implantation dose of 10-1000 μC / cm ² . 8. The method according to any one of claims 1 and 2, characterized in that the initial implantation of impurity ions in the working and non-working sides of the plate is carried out at a plate temperature above 50 ° C, and the second implantation of impurity ions in the working and non-working sides of the plates is plate temperature (-196 ° С) - (+ 25 ° С). 9. The method according to any one of claims 1 and 2, characterized in that the formation of a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine-containing components is carried out by heat treatment of the plate at a temperature of 650-1300 ° C in an atmosphere of dry oxygen, nitrogen or argon, chlorine-containing component, with a chlorine-containing component 1-10 volume percent. 10. The method according to any one of claims 1 and 2, characterized in that the implantation of p-type impurity ions into the working side of the plate is carried out with an implantation energy of 1-200 keV, an implantation dose of 1-500 μC / cm ² at the temperature of the plates during implantation (-196 ° С) - (+ 25 ° С). 11. The method according to any one of claims 1 and 2, characterized in that after the implantation of the ions before applying the aluminum layer, the plates are heat treated at a temperature of 500-900 ° C in an atmosphere containing oxygen, nitrogen (argon), chlorine-containing components containing chlorine-containing component 1-10 volume percent, and then etching of silicon oxide with a thickness of 0.01-0.1 μm in an aqueous solution of hydrofluoric acid, washing the plate in deionized water and chemical washing of the plate in a solution containing hydrogen peroxide and aqueous ammonia. 12. The method according to any one of claims 1 and 2, characterized in that a 0.1-1 μm layer of aluminum is applied with a silicon content of not more than 1% on both sides of the wafer. 13. The method according to any one of claims 1 and 2, characterized in that the burning of aluminum is carried out at a temperature of 400-500 ° C in an atmosphere of nitrogen or argon. 14. The method according to any one of claims 1 and 2, characterized in that the deposition of the passivating coating on the working side of the plate is carried out using silicon oxide and / or phosphorosilicate glass with a phosphorus content of 1-4%, and then etching the passivating coating to an aluminum layer and reducing the positive charge in silicon oxide by re-burning aluminum at a temperature of 400-500 ° C in an atmosphere of nitrogen (argon). 15. The method according to any one of claims 1 and 2, characterized in that the plate is scribed.

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