CN101752391A - Snow slide drifting detector with MOS fully-depleted drifting channel and detecting method thereof - Google Patents

Abstract

The novel MOS-ADD detector of the present invention is made by silicon single wafer. When applied to SiPM multi-unit integration, the MOS-ADD structure can easily solve the contradiction between the SiPM unit area and the output capacitance requirement, and can provide a high fill factor (greater than 70%) and detection efficiency. At the same time, due to the use of a small area of "point-like" avalanche area, the area of the high field area is greatly reduced, which can effectively reduce the leakage current and the number of dark marks (compared to SiPM devices with the same effective detection area). MOS-ADD adopts the front incident method, and all electrodes on the incident surface can use transparent conductive films, which can effectively reduce the blocking of electrodes and the absorption of light. The fully depleted active region can be as deep as a few microns or tens of microns, and is sensitive to blue to near-infrared light. When the MOS-ADD structure is used to make a unit large-area single-photon detector, because the output capacitance is small and does not depend on the area of the detector, its electronic noise is generally much smaller than that of a conventional avalanche photoelectric with the same light-passing window area and light-absorbing region thickness. Diodes are suitable for the detection of soft X-rays and visible light with shallow penetration depth. If combined with a scintillator, it can also be used to detect high-energy X or gamma rays.

Description

Avalanche drift detector with MOS fully depleted drift channel and its detection method

The invention relates to a device structure and working principle of a novel semiconductor photodetector MOS-ADD, belonging to the technical field of HO1L 27/00 semiconductor devices.

Multivariate Geiger avalanche photodiode (M-GAPD), also known as silicon photomultiplier tube SiPM (Silicon Photomultiplier), is used for weak light detection. Its working principle and development history refer to the literature D. Renker. Geiger-mode avalanche photodiodes, history, properties and problems. Nuclear Instruments and Methods in Physics Research A 567 (2006) 48-56. Compared with the traditional photomultiplier tube PMT, SiPM has the advantages of single photon response, large gain, insensitivity to magnetic field, simple manufacturing process, low cost, small size, easy CMOS process integration, low working voltage, and relatively safe. It has been developed rapidly and is considered to be a substitute for some photomultiplier tubes in the near future. The application of SiPM in high-energy physics research, ray detection, biomedicine, quantum communication and other weak light detection fields is a hot research topic today. For example, SiPM can be used for large astronomical telescopes (see MRSquillante, RAMyers, F.Robertson, R.Farrell, JFChristian, G.Entine. Avalanche photodiode arrays for a high-angular resolution X-ray and gamma-ray imaging telescopes. Nuclear Instruments and Methods inPhysics Research Section A:, Volume 580, Issue 2, 1 October 2007, Pages848-852), particle physics detection (see D. Renker. New developments on photo-sensors for particle physics. Nuclear Instruments and Methods in Physics Research Section A: In Press, Corrected Proof, Available online 15 August 2008), Genetic diagnosis in medical research (see I. Rech, A. Restelli, S. Cova, M. Ghioni, M. Chiari, M. Cretich. Microelectronic photosensors for genetic diagnostic Microsystems. Sensors and Actuators B 100, pp.158-162, 2004) and biotechnology (see Schwartz, David Eric; Gong, Ping; Shepard, Kenneth L. Time-resolved Forster-resonance-energy-transfer DNA assay on an active CMOS microarray. Biosens Bioelectron, 2008, 24(3): 383-390) etc. However, due to the current immaturity of SiPM technology, there are still many disadvantages, such as low detection efficiency (generally <30%, slightly better than PMT), narrow dynamic range (10 ² -10 ³ /mm ² ), low dark count rate High, serious optical crosstalk, small area, etc. (see Yuri Musienko, "Advances in multipixel Geiger-mode avalanche photodiodes (silicon photomultipliers)", Nuclear Instruments and Methods in Physics Research A:, Corrected Proof, Available online 19 August 2008), limited The practical application of SiPM. New device unit structure design and process improvement are being actively explored.

SiPM consists of a large number of small-area avalanche diode cells. The low detection efficiency of existing SiPMs is mainly due to their low geometric efficiency (or fill factor). Due to the requirements of time-correlation measurement and detector performance, the output capacitance of the unit should not be too large, and the lower the dark count and leakage current, the better, that is, the area of the avalanche photodiode detection unit should not be too large. SiPMs with high cell counts (above 10 ³ ) tend to have low fill factors (typically less than 50%) due to the "dead space" (non-sensitive area) between cells and the cell lead and electrode preparation occupied, which leads to probing less efficient. At the same time, the depth of the absorption region of SiPM is limited. In order to reduce the absorption of light by the material and the need to detect short-wavelength light, the junction depth of the unit is generally very shallow, and the detection efficiency of light with longer wavelengths is low (see S. Gomi, H. Hano, T. Iijima, S. Itoh, K. Kawagoe, et al. "Development and study of the multi pixel photon counter" Nuclear Instruments and Methods in Physics Research Section A:, Volume 581, Issues 1-2, 21 October 2007, Pages 427-432).

In view of the above problems, the object of the present invention is to propose a novel avalanche detector unit structure---an avalanche drift detector with a MOS fully depleted drift channel, hereinafter referred to as MOS-ADD (MOS depletion drift channel Avalanche Drift Detector). It can be used as the basic detection unit of SiPM for large-scale integration, and can also be made into a large-area unit detector. The basic structure of MOS-ADD is a fully depleted region formed by a large-area MOS structure and a buried reverse-biased PN junction as the depleted active region of the detector and a line of photogenerated carriers (electrons or holes) is formed in it. The energy valley is used as a drift channel, and the inner and outer drift rings generate a lateral drift electric field in the channel, and the "point-like" Geiger avalanche diode (GAPD) located in the center of the unit serves as a collection area for photogenerated carriers. So far there is no literature report or practical application of this structure.

When applied to SiPM multi-unit integration, the MOS-ADD structure can easily solve the contradiction between the SiPM unit area and the output capacitance requirement, and can provide a high fill factor (greater than 70%) and detection efficiency. At the same time, due to the use of a small area of point-shaped avalanche area, the area of the high field area is greatly reduced, which can effectively reduce the leakage current and the dark count rate (compared to the APD device with the same effective detection area). MOS-ADD adopts the front-incidence method, and all electrodes on the incident surface can use transparent conductive films, such as indium tin oxide (ITO) films or very thin metal films as electrode materials, which can effectively reduce the shielding and absorption of light by the electrodes.

When the MOS-ADD structure is used to make a unit large-area single-photon detector, because the output capacitance is small and does not depend on the area of the detector, its electronic noise is generally much smaller than that of a conventional avalanche photoelectric with the same light-passing window area and light-absorbing region thickness. Diodes (see S. Tanaka, J. Kataoka, Y. Kanai, Y. Yatsu, M. Arimoto, M. Koizumi, N. Kawai, Y. Ishikawa, S. Kawai, N. Kawabata, "Development of wideband X-ray and gamma-ray spectrometer using transmission-type, large-areaAPD", Nuclear Instruments and Methods in Physics Research Section A, Volume582, Issue 2, 21 November 2007, Pages 562-568), suitable for soft X with shallow penetration depth Rays, ultraviolet light, visible light and near-infrared light detection. If combined with scintillators, it can also be used to detect high-energy X or γ-rays, and has broad application prospects in low-light detection, nuclear medical imaging, high-energy physics research and other fields.

To achieve the above object, the present invention takes the following technical solutions:

A new type of avalanche drift detector with MOS full depletion drift channel, referred to as MOS ADD (MOS depletion drift channel Avalanche Drift Detector) in English, is characterized in that the semiconductor material for making the detector is a silicon single wafer, and each detector unit It is composed of "point-like" avalanche diode collection area, depleted active area, large-area transparent gate MOS structure, buried pn junction, inner drift electrode, outer drift electrode and grounding.

The doping type of the silicon single wafer is N-type or P-type, the doping concentration is lower than 1×10 ¹⁷ cm ^-3 , the thickness is 100 μm-0.5 mm, and the crystal orientation is <100>, <110> or <111>, Single-sided or double-sided polishing sheet;

The "point-shaped" avalanche diode collection area is located in the center of the detector unit, and its area is less than 1000 μm ² ;

The doping type of the depleted active region is opposite to the doping type of the silicon single wafer, and the depth is 0.1 μm-10 μm;

The large-area transparent gate MOS structure is composed of a transparent conductive film-SiO ₂ -Si, and the transparent conductive film is also used as an electrode and an anti-reflection film, which can be ITO or a very thin metal (such as silver, gold, aluminum, titanium, etc.) , its thickness is 1nm-10μm, the thickness of SiO ₂ layer is 1nm-1μm;

The buried pn junction is composed of a depleted active region and a silicon single wafer substrate;

The doping type of the inner and outer drift electrodes is opposite to that of the depleted active region, the doping type of the ground electrode is the same as that of the depleted active region, and transparent conductors or aluminum films are used as electrode leads;

The novel MOS-ADD detector has a circular pie and a ring shape, and has a square or bar shape;

The novel MOS-ADD detector has a unit or multi-element array structure, and the output ends of the multi-array structure can be independent outputs, or all can be connected in parallel, sharing one load;

The present invention also relates to a method for detecting light signals of the novel MOS-ADD detector. Its characteristics are:

The measured light signal enters the detector from the front of the MOS-ADD detector (through the transparent electrode);

When the detector is working, the buried pn junction is reverse-biased, the MOS structure works in a depleted state, the inner and outer drift electrodes form a reverse-biased pn junction with the depleted active region, and the outer electrodes are biased The absolute value is greater than the absolute value of the internal electrode bias;

The optical signal refers to near-infrared light, visible light, ultraviolet light (wavelength range of 0.2-1.1 microns) and soft X-ray (energy range of 1-20keV).

The present invention is specifically described below in conjunction with examples.

Figure 1 shows a schematic diagram of the structure of a new MOS-ADD unit based on an N-type silicon single wafer with hole drift. The detector consists of "point-like" avalanche diode collection area Collecting electrode, depleted active area P well (p-well, doped acceptor area), ITO transparent gate MOS structure, buried pn junction, inner drift ring electrode R1, The outer drift ring electrode R2, the ground ring electrode GND.

The method of using the novel MOS-ADD detector of the present invention to detect the optical signal is: the optical signal enters the detector from the front of the detector. GND is grounded, and the electrode of Collecting electrode is negatively biased to above the avalanche breakdown voltage. When a photogenerated hole drifts to the avalanche area, it will cause avalanche multiplication and output an amplified pulse current signal; the ITO transparent grid Gate and the back electrode Back electrode respectively Apply an appropriate positive bias (relative to GND) to completely deplete the P well (pwell) and form a hole potential energy valley in the P well, so that the photogenerated holes are concentrated in the energy valley to reduce the surface recombination loss; internal drift Apply a small positive voltage (about 1-4V) to the ring electrode R1, apply a positive voltage a few volts higher than R1 to the outer drift ring electrode R2, and form a lateral drift electric field pointing to the center of the detector unit in the P well depletion region (The potential distribution in the drift region obtained by software simulation as shown in FIG. 2 ). The MOS structure is in a weak inversion or depletion state, and the weak inversion layer acts as a voltage divider resistor to make the lateral drift electric field more uniform. The light signal to be measured enters the device from the front of the MOS-ADD detector (through the ITO electrode), and electron-hole pairs are generated in the depletion region, and the electrons are repelled into the inversion layer or substrate under the MOS channel. bottom, and the holes will gather in the drift channel (that is, the hole potential energy valley) and drift to the avalanche region in the center of the detector under the lateral electric field generated by the drift ring (as shown in Figure 3 obtained by software simulation The distribution and flow direction of the hole current), the impact ionization multiplies in the avalanche area and is amplified and outputs a pulse current signal.

In other embodiments of the invention:

The new MOS-ADD detector is made of P-type silicon single wafer, its crystal orientation is <100>, <111> or <110>, the doping concentration is lower than 1×10 ¹⁷ cm ^-3 , and the thickness is 100 microns-0.5 mm;

"Spot-shaped" avalanche diodes with an area of less than 1000 μm ² ;

N-well (N-well) depletes the active region to a depth of 0.1 microns to 10 microns, which is achieved by ion implantation, diffusion or epitaxy;

The transparent gate MOS structure is composed of a transparent conductive film-SiO ₂ -Si. The transparent conductive film is also used as an electrode and an anti-reflection film. It can be ITO or a very thin metal, such as aluminum, titanium, silver, gold, etc., and its thickness is 1nm. -10μm, SiO ₂ layer thickness 1nm-1μm;

The inner and outer drift electrodes R1, R2 and the ground electrode GND can use the same ITO film or very thin metal as the transparent gate MOS structure, and its thickness is 1nm-10μm;

MOS-ADD detectors can have a square or bar shape in addition to the pie and donut shape;

In addition to the unit structure, the MOS-ADD detector can also have a multi-element array or other variant structures. The output terminals of the multi-element array structure can be output independently, or all connected in parallel, sharing one load.

It should be noted that the above-mentioned embodiments are only for illustrating the present invention but not limiting the patent scope of the present invention, and any equivalent transformation technology based on the present invention shall be within the scope of the patent protection of the present invention.

Claims (11)

1. A novel MOS-ADD detector, characterized in that: The semiconductor material used to make the detector is a single crystal silicon wafer. Each detector unit consists of a "point-like" avalanche diode collection area, a depletion active area, a large-area transparent gate MOS structure, a buried pn junction, an inner drift electrode, External drift electrode and grounding structure; 2. The novel MOS-ADD detector according to claim 1, characterized in that: the doping type of the silicon single wafer is N-type or P-type, the doping concentration is lower than 1×10 ¹⁷ cm ^-3 , and the thickness is 100μm-0.5mm, crystal orientation <100>, <110> or <111>, single-sided or double-sided polished sheet; 3. The novel MOS-ADD detector according to claim 1, characterized in that: the "point-like" avalanche diode collection area is located at the center of the detector unit, and its area is less than 1000 μm ² ; 4. The novel MOS-ADD detector according to claim 1, characterized in that: the doping type of the depleted active region is opposite to the doping type of the silicon single wafer described in claim 2, and the depth is 0.1 μm-10 μm; 5. novel MOS-ADD detector as claimed in claim 1, is characterized in that: described large-area transparent gate MOS structure is made of transparent conductive film-SiO ₂ -Si (that is, depletion active region described in claim 4 ), the transparent conductive film doubles as an electrode and an anti-reflection film, the thickness is 1nm-10μm, and the thickness of the SiO ₂ layer is 1nm-1μm; 6. The novel MOS-ADD detector according to claim 1, wherein the buried pn junction is composed of the depleted active region as claimed in claim 4 and the silicon single wafer substrate as claimed in claim 2; 7. The novel MOS-ADD detector according to claim 1, characterized in that: the doping type of the inner and outer drift electrodes is opposite to that of the depleted active region as claimed in claim 4, and the doping type of the grounding is the same as that of the claim 4. The depletion active region is the same, and a transparent conductor or an aluminum or titanium film with a thickness of 1nm-10μm is used as the electrode lead; 8. novel MOS-ADD detector as claimed in claim 1, is characterized in that: have circular pie and ring shape, obtain square or strip shape; 9. The novel MOS-ADD detector according to claim 1, characterized in that: it has a unit or multi-element array structure, and the output ends of the multi-element array structure can be independently output, or all connected in parallel, sharing one load; 10. A method of using the novel MOS-ADD detector as claimed in claim 1 to detect optical signals, characterized in that: The light signal to be measured enters the detector from the front of the MOS-ADD detector (through the transparent electrode). When the detector is working, the buried pn junction in claim 6 is reverse biased, and the MOS described in claim 5 The structure works in a weak inversion or depletion state, the inner and outer drift electrodes described in claim 7 and the depleted active region described in claim 4 form a reverse-biased pn junction, and the absolute value of the bias voltage of the outer electrodes is greater than the bias voltage of the inner electrodes. absolute value of pressure; 11. The optical signal according to claim 10 refers to near-infrared light, visible light, ultraviolet light (wavelength range is 0.21.1 micron) or X-ray (energy range is 1-20keV).

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