RU2820464C1 - Method of making ionizing radiation and light sensor - Google Patents

Abstract

FIELD: semiconductor devices.

SUBSTANCE: invention relates to the technology of making semiconductor devices intended for converting the effect of ionizing radiation and light into an electrical signal. Sensor for converting the effect of ionizing radiation and light into an electrical signal. Method of producing an ionizing radiation and light sensor, comprising etching silicon on a semiconductor plate cut from an ingot of ultrapure silicon of n-type conductivity, chemical washing of semiconductor plate, formation of silicon oxide layer by thermal oxidation in atmosphere of dry oxygen with addition of chlorine-containing component, 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, a second chemical washing, application of an aluminium layer, two-stage post-implantation annealing, wherein both chemical washes of the plate are carried out in a solution of diluted hydrofluoric acid, the second oxidation is carried out in two steps: first step is carried out in a dry oxygen atmosphere, including a chlorine-containing component; second step is carried out in a nitrogen atmosphere with the addition of oxygen, which includes a chlorine-containing component, followed by diffusion of the n-type impurities and the last implantation of p-type impurities, further, chemical treatment is carried out with finishing freshening in a diluted solution of hydrofluoric acid for at least 5 seconds, then two-stage post-implantation annealing is performed: first annealing at temperature of 800–900 °C and second annealing at temperature of 675–775 °C in an inert atmosphere or in an inert atmosphere with oxygen content.

EFFECT: invention enables to manufacture a highly sensitive element of the detector, as well as simpler manufacturing thereof based on a planar technology.

1 cl, 1 dwg

Description

The invention relates to the technology of manufacturing semiconductor devices designed to convert the effects of ionizing radiation and light into an electrical signal. In particular, the invention relates to the technology of manufacturing semiconductor sensitive elements, which are p-i-n diodes intended for use in various systems for measuring radiation levels and recording photons of light. Currently, sensors based on p-i-n diodes continue to be improved taking into account modern advances in microelectronics technology.

A patent is known from the prior art, a method for manufacturing a photodiode (PD), which describes the technology for manufacturing a PD with photosensitive areas in the form of planar p+-n junctions /1/. A planar p+-n junction is fabricated by diffusion of boron into n-type silicon, which results in a higher level of BDP contamination than creating a p+-n junction using boron ion implantation, since modern implantation equipment has very low levels of metal contamination and with the help of this equipment it is very easy to obtain a controlled implantation profile.

When boron diffuses, a profile is formed, the maximum concentration of which is located on the silicon surface. During subsequent acceleration in an inert environment, an oxygen-containing environment, or during the diffusion of phosphorus, part of the boron goes to the interface and it becomes inactive /2/. The maximum boron concentration shifts deeper into the silicon wafer, and a boron-depleted layer is formed on the surface. As a result of such a profile, a field is formed that prevents the passage of holes through the interface, and some of these holes will recombine in this place, which leads to a decrease in the amplitude of the electrical signal. Therefore, they try to create a boron distribution profile in which the maximum concentration is located at the SiO ₂ - Si interface, and subsequent heat treatments do not affect (the profile maximum). The easiest way to obtain such a profile is by implanting boron, adjusting the ion energy so that the maximum falls on the interface.

This patent does not indicate which silicon growth method is used to produce the wafers used in the process. Therefore, in the case of manufacturing a p-i-n diode on high-resistance silicon grown by the Czochralski method, which contains oxygen in high concentrations, secondary thermal donors are formed at a temperature of 650°C, which can simultaneously affect the conductivity of the substrate and reduce the lifetime of minority charge carriers, which leads to increase in leakage current /3/.

There is a known patent for the manufacturing technology of silicon p-i-n photodiodes that are sensitive to radiation with wavelengths of 0.9-1.06 microns /4/. At a given wavelength, light absorption in silicon occurs from several tens of microns to hundreds of microns /5/. The formation of internal sinks (centers) in the volume of the plate, on which the BDP will segregate, will lead to additional generation and recombination centers, which will increase the leakage current. The formation of the p+ region after removal of the n+ layer will lead to additional contaminants that will be weakly gettered, since the p+ layer itself, formed by boron, does not have the same gettering properties as the phosphorus layer.

There is a known patent for a method of manufacturing an ionizing radiation sensor, which we adopted as a prototype. The disadvantage of this manufacturing method is that there is a p+ layer on the cut line, from which charge carriers can be injected into the space charge region (SCR) of the recording p-n junction /6/. To prevent this from happening, it is necessary to increase the distance from the last guard ring to the cutting line, which leads to an increase in the “dead” space, which is necessary for recording ionizing radiation and light photons.

Limitation on the energy of implantation of phosphorus and boron leads to additional operations to protect the back side of the wafer from mechanical damage that can enter the SCR, which can lead to an increase in leakage currents.

The absence of an operation to eliminate scratches and scratches that may remain after the chemical-mechanical polishing process, on which, if they are not annealed in oxidation processes or in various annealing processes, BDP can segregate, which will lead to an increase in leakage currents or to microplasma breakdown.

Operations such as washing in Caro and in an ammonia peroxide solution involve acidifying the surface of the silicon wafer. This oxide contains BDP, which is present in the original chemical reagents. If the oxide is not removed, then the volume of the silicon wafer is contaminated, which leads to an additional increase in the leakage current.

The objective of the invention is to increase the efficiency of serial production of a sensor for recording ionizing radiation and light photons.

The essence of the invention is that a method for manufacturing an ionizing radiation and light sensor, including etching silicon on a semiconductor wafer cut from an ingot of ultra-pure n-type silicon, chemically washing the semiconductor wafer, forming a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of chlorine component, 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, second chemical washing, application of an aluminum layer, two-stage post-implantation annealing, characterized in that both chemical washings of the plate are carried out in a solution of dilute hydrofluoric acid, the second oxidation is carried out in two stages: the first stage is carried out in an atmosphere of dry oxygen, including a chlorine-containing component; the second stage is carried out in a nitrogen atmosphere with the addition of oxygen, including a chlorine-containing component, after which the diffusion of n-type impurities and the last implantation of p-type impurities are carried out, followed by chemical treatment with final refreshment in a dilute solution of hydrofluoric acid for at least 5 seconds, then two-stage post-implantation annealing is performed: the first annealing at a temperature of 800-900°C and the second annealing at a temperature of 675-775°C in an inert atmosphere or in an inert atmosphere containing oxygen.

During the first annealing, this temperature range is necessary both to maximize activation of the p-type impurity and to prevent annealing of point defects, which are necessary for gettering of the BDP in the second stage. In the second annealing, this temperature range is necessary for optimal gettering by the external BDP getter.

The use of etching of the original silicon wafer eliminates the risks and scratches remaining after chemical-mechanical polishing of the wafer, which reduce the yield of usable p-in diodes. The use of a dilute solution of hydrofluoric acid allows you to remove sulfur and BDP ions from the surface of the plate, which may remain after treatment in the Caro solution. The use of two-stage post-implantation annealing after the last implantation of the p-type impurity leads to more complete activation of the p-type impurity. When creating an n+ layer on the cut line, it is preferable to use the diffusion process, since it allows you to create an n+ region on the cut line and on the reverse side in one process, and by removing the FSS, you can obtain the required thickness of thin SiO ₂ and at the same time an n+ layer on the reverse side side, which will act as a getter for the BDP and protect the non-working side from mechanical damage. The use of chemical washing before post-implantation, activation annealing, either in KARO or in APR, or together, or washing in megasonic, but with final washing in a dilute solution of hydrofluoric acid, reduces the leakage current by at least 2 times due to the removal of thin oxide containing BDP. In this method, obtaining a boron profile with a maximum concentration at the Si-SiO ₂ interface is done using ion implantation by selecting the energy of boron or BF2+ ions, followed by activation of the impurity at a temperature of 800-900 ° C in an inert atmosphere, which ensures activation of the impurity by approximately 90 %. In this case, the position of the maximum of the impurity distribution does not change /7/.

Fig. 1 - Structure of a pin diode manufactured according to IDT, where 1 - guard ring, 2 - diode body, 3 - n+-type cutting path, 4 - Al contacts, 5 - gettering layer, 6 - SiO ₂ dielectric layer.

Example of concrete implementation

1) Etching silicon on a semiconductor wafer;

2) Chemical washing, including refreshment in a dilute solution of hydrofluoric acid;

3) Oxidation in an atmosphere of dry oxygen and chlorine-containing component;

4) Photolithography for deep implantation of p-type impurity ions;

5) SiO ₂ etching;

6) Implantation of p-type impurity ions into the working side;

7) Photolithography for opening the diode body;

8) Oxidation - high-temperature distillation of boron: the first stage in an atmosphere of dry oxygen and a chlorine-containing component; the second stage in an inert gas atmosphere with the addition of oxygen and a chlorine-containing component;

9) Photolithography under n+;

10) SiO ₂ etching;

11) Chemical washing, including refreshment in a dilute solution of hydrofluoric acid;

12) Diffusion of n-type impurity;

13) Removing FSS;

14) Implantation of p-type impurity ions into the working side through a thin dielectric;

15) Photolithography for contacts;

16) Etching SiO ₂ ;

17) Chemical washing and refreshing in a dilute solution of hydrofluoric acid

18) Activation of p and n type impurities at a temperature of 800-900°C;

19) Annealing for gettering of BDP on the reverse side at a temperature of 675-775°C;

20) Refresh contacts;

21) Al spraying on both sides;

22) Photolithography for Al;

23) Al etching;

24) Burning Al;

As a result of manufacturing p-i-n diodes using this technology (IDT), the following structure was obtained, schematically presented in Fig. 1.

By minimizing the amount of BDP and other impurities that affect the conductivity of the substrate, remnants of organic contaminants and remnants of the near-surface damaged layer, the number of intrinsic free electrons is reduced. At the same time, higher sensitivity compared to analogues is determined by the fact that the leakage current is no more than 5 nA/cm ² , the charge collection efficiency (element signal level) is no less than 99%.

The invention is a technological process for manufacturing a sensor using planar technology, which makes it possible to obtain sensors with a uniquely high lifetime of minority charge carriers, which is ensured by the use of a sequence of operations and processing conditions for silicon wafers.

Information sources:

1. RF Patent No. 2654992.

2. Bubennikov A.M. Modeling of integrated microtechnologies, devices and circuits: Textbook. manual for special “Physics and technology of materials and components of electronic equipment.” - M.: Higher. school, 1989. - 320 p.: ill.

3. Astashenkov A.S., Brinkevich D.I., Petrov V.V. Properties of silicon doped with nickel impurities by diffusion // Reports of BSUIR. - 2008. - No. 8. - P. 37-43.

4. RF patent No. 2532594.

5. An Introduction to the Silicon Photomultiplier // SensL. - 2011. - pp. 1-16.

6. RF Patent No. 2575939. - prototype.

7. Maria Jose Caturla, Mark D. Johnson and T. Diaz de la Rubia The fraction of substitutional boron in silicon during ion implantation and thermal annealing // American Institute of Physics. - 1998. - Vol.72, rn21. - pp. 2736-2738.

Claims (1)

A method for manufacturing a sensor of ionizing radiation and light, including etching silicon on a semiconductor wafer cut from an ingot of ultra-pure n-type silicon, chemical washing of the semiconductor wafer, formation of a layer of silicon oxide by thermal oxidation in an atmosphere of dry oxygen with the addition of a chlorine-containing component, implantation of p-impurity ions type to the working side of the plate and n-type impurity ions to the non-working side of the plate, second chemical washing, application of an aluminum layer, two-stage post-implantation annealing, characterized in that both chemical washings of the plate are carried out in a solution of dilute hydrofluoric acid, the second oxidation is carried out in two stages: the first stage is carried out in an atmosphere of dry oxygen, including a chlorine-containing component; the second stage is carried out in a nitrogen atmosphere with the addition of oxygen, including a chlorine-containing component, after which the diffusion of n-type impurities and the last implantation of p-type impurities are carried out, followed by chemical treatment with final refreshment in a dilute solution of hydrofluoric acid for at least 5 seconds, then two-stage post-implantation annealing is performed: the first annealing at a temperature of 800-900°C and the second annealing at a temperature of 675-775°C in an inert atmosphere or in an inert atmosphere containing oxygen.