KR100987057B1 - Silicon photomultiplier tube with improved photodetection efficiency and gamma ray detector comprising the same - Google Patents

Abstract

Disclosed are a silicon photomultiplier tube with improved photodetection efficiency and a gamma ray detector comprising the same.

Silicon photomultiplier tube with improved photodetection efficiency according to the present invention is a semiconductor substrate of the p + conductivity type, formed on top of the semiconductor substrate, a p-conductivity type epitaxy layer, of the conductive type doped to the epitaxy layer a unit including a p region, an n + region of a conductivity type formed on top of the p region of the conductivity type, and a doped epitaxial layer, and an insulating layer formed on the epitaxy layer and an n + region of the conductivity type Micro cells; A metal line of the unit micro cell formed on the n + region; And a quenching polysilicon resistor connected to the metal line by a contact and formed on an upper portion of the insulating layer, wherein the quenching polysilicon resistor has a multilayer structure and is formed in a depth direction of the silicon photomultiplier tube. It is characterized in that a plurality formed to overlap each other.

According to the present invention, by forming a multi-layered polysilicon resistor and a micro lens, the visible light generated from the scintillator can be minimized to enter the dead region, thereby improving the fill factor, and further, photodetection of the silicon photomultiplier tube. There is an effect that can reduce the size of the micro cell according to the efficiency improvement

Description

Silicon photomultiplier with improved photodetecting efficiency and Gamma radiation detector comprising the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor. In particular, the photodetection efficiency of the silicon photoelectron multiplier, which is an optical sensor for detecting visible light of a scintillator, can be improved to improve photodetection efficiency. It relates to a photomultiplier tube and a gamma ray detector comprising the same.

Optical sensors are generally referred to as light sensors. The optical sensor detects the amount of light, the shape, state, and movement of an object. In the past, the optical sensor merely detected natural light, but now emits light artificially and accepts that the light hits an object and is reflected. As a result, structures for detecting the movement and speed of the object are increasing.

The optical sensor mainly used in the conventional gamma ray detector uses a vacuum photoelectric multiplier tube, and PIN photodiode has been used as semiconductor technology has developed.

In addition, avalanche photodiodes with high sensitivity due to avalanche gains have been developed and replaced, and silicon photoelectron deposition with a structure similar to avalanche photodiodes that will improve avalanche photodiodes. Piping is being developed.

The avalanche photodiode operates below the breakdown voltage, while the silicon photomultiplier operates above the breakdown voltage, and the avalanche is discharged by quenching when an optical signal is incident. The battery is then recharged to generate an electrical signal.

1 illustrates a one-pixel cross-sectional view of a silicon photomultiplier tube having a plurality of conventional microcells.

Referring to FIG. 1, it can be seen that one pixel of the silicon optoelectronic multiplier consists of a plurality of micro cells.

One pixel 100 of a silicon photomultiplier has dozens or thousands of avalanche photodiodes (hereinafter referred to as 'micro cells'), depending on the intended use, and each micro cell 120 is turned on and off. The micro cells 120 are connected to the common electrode 130 in parallel to generate linear and nonlinear signals according to the magnitude of the incident optical signal.

Meanwhile, in each micro cell, a quenching resistor 140 is connected to the common electrode 130 along the metal line 110 to read out an electrical signal.

Generally, a p− epitaxy layer is formed on a P + conductive semiconductor substrate, a p region and an n + region are formed by an implant process, and a resistance for quenching is formed through polysilicon deposition.

2a to 2c show the area occupied by the quenching resistance according to the size of the conventional microcell.

First, referring to FIG. 2A, as described above with reference to FIG. 1, the microcell 220, the metal line 210 surrounding the microcell 220, and the quenching resistor 240 connected to the metal line are configured in one pixel of the photomultiplier tube. 2B is a cross-sectional view taken along the line 'B' in FIG. 2B.

As shown in FIG. 2B, each micro cell 220 has a sequential doping structure of a quenching resistor 240, a metal line 210, and n + / p / p− / p +.

Here, the doping structure may be generated by a general method applied in the field to which the present invention belongs, so a detailed description thereof will be omitted.

FIG. 2C illustrates that when the quenching resistor 240 is formed for each microcell, the size of the quenching resistor of each microcell of the silicon photomultiplier should generally be 100 kΩ to 1 MΩ. Since the minimum line width of is generally 2 u m or more, a polysilicon resistor having a large sheet resistance should be used, or if the sheet resistance is small, the length of the sheet resistance should be increased as shown in FIG.

However, even if all four sides are surrounded, it is difficult to obtain the required performance when it is difficult to obtain the necessary resistance.

On the other hand, photodetection efficiency (PDE) which is one of the performance of the silicon photoelectron multiplier is defined by Equation 1 below.

는 입사 광신호의 파장에 따른 양자 효율,

는 인가 전압에 따른 아발란치 기폭 확률(avlanche initiation probability),

는 필 팩터(fill factor)이다.In Equation 1

Quantum efficiency according to the wavelength of the incident optical signal,

Is the avalanche initiation probability according to the applied voltage,

Is the fill factor.

와

는 소자의 표면 코팅과 도핑 구조에 따라 달라지는 가시관의 파장과 인가 전압에 따른 함수이며, 상기 필 팩터는 광신호를 받아 반응하여 전기 신호를 생성하는 액티브 영역(active region)과 그렇지 않은 데드 영역(dead region)의 비이다.

Wow

Is a function of the wavelength of the visible tube and the applied voltage depending on the surface coating and the doping structure of the device, and the fill factor is an active region or a dead region that receives and reacts with an optical signal to generate an electrical signal. region).

Here, unlike general avalanche photodiodes having a fill factor of 80 to 90%, the maximum fill factor drops to 50% or less in a silicon photoelectron multiplier because the number of microcells per pixel is large.

In particular, when there are a large number of microcells in one pixel of silicon photomultiplier tube, the area of quenching resistance does not decrease, but only the active area of each microcell is reduced, so the smaller the microcell size, the fill factor is Remarkably falls.

Therefore, in order to improve the light detection efficiency, a surface structure for improving the fill factor in the silicon photomultiplier is required.

That is, the conventional silicon photomultiplier tube has a problem in that the photodetection efficiency is significantly low because the fill factor, which is a ratio between an active region that receives an optical signal and reacts to generate an electrical signal and a dead region that is not, is significantly low.

The first problem to be solved by the present invention is to provide a silicon photomultiplier tube with improved photodetection efficiency that can improve the fill factor when the microcell is increased to ensure linearity for the incident gamma energy.

In addition, a second problem to be solved by the present invention is to provide a gamma ray detector to which the silicon photoelectron multiplier with improved photodetection efficiency is applied.

The present invention to solve the first problem,

A silicon photomultiplier tube comprising a plurality of micro cells, comprising: a semiconductor substrate of p + conductivity type, an epitaxial layer of p- conductivity type, and a p of conductivity type doped to the epitaxy layer A unit micro that includes a region, an n + region of conductivity type formed on top of the p region of the conductivity type, and a doped epitaxial layer, and an insulating layer formed on the epitaxy layer and n + region of the conductivity type Cell; A metal line of the unit micro cell formed on the n + region; And a quenching polysilicon resistor connected to the metal line and formed on the insulating layer, wherein the quenching polysilicon resistor has a multilayer structure and overlaps each other in the depth direction of the silicon photomultiplier tube. Provided is a silicon photomultiplier tube with improved photodetection efficiency, characterized in that a plurality is formed.

The unit micro cell may further include a convex micro lens formed to surround the unit micro cell.

The convex micro lens may be made of PDMS, PMMA, or photoresist.

In addition, the polysilicon resistor for quenching of the multilayer structure may be connected to the polysilicon resistor of one end and the polysilicon resistor of the other end are alternately connected by a contact.

In addition, the polysilicon resistor for quenching may be connected by the contact and the ohmic junction.

The photomultiplier may include a dielectric formed on the quenching polysilicon resistor and the metal line; And a reflective layer formed on the dielectric to surround the unit micro cell.

On the other hand, the reflective layer may be made of one or more compounds selected from the group consisting of aluminum, tungsten, titanium.

The present invention to solve the second problem,

A gamma ray detector comprising a silicon photomultiplier, comprising: a semiconductor substrate of p + conductivity type, an epitaxial layer of p- conductivity type, a p region of conductivity type doped to the epitaxy layer, A unit micro cell formed on the p region of the conductivity type and including an n + region of the conductivity type doped to the epitaxy layer, and an insulating layer formed on the epitaxy layer and the n + region of the conductivity type; And a metal line of the unit micro cell formed on the n + region, a metal line connected to the metal line and a contact and formed on the insulating layer, and overlapping each other in a depth direction of the silicon photomultiplier tube. A polysilicon resistor for quenching of a multi-layered structure formed as plural as possible, and a micro formed to surround the unit micro cell A silicon photomultiplier tube comprising a lens; And an optical grease formed on an upper portion of the silicon photomultiplier tube.

The silicon optoelectronic multiplier may include a dielectric formed on the quenching polysilicon resistor and the metal line; And a reflective layer formed on the dielectric to surround the unit micro cell.

The insulating layer may be formed of at least one compound selected from the group consisting of silicon oxide (SiO 2), silicon oxy nitride (SiON), silicon nitride (SiN), and heartnium oxide (HfO).

In addition, the micro lens may be formed as a convex or concave micro lens according to the refractive index of the optical grease.

According to the present invention, by forming a multi-layered polysilicon resistor, the visible light generated from the scintillator is minimized from entering the dead region, and the fill factor can be improved by providing a microlens in each microcell. Since the size of the microcell can be reduced according to the improvement of the photodetection efficiency of the silicon photomultiplier tube, it can have sufficient linearity with respect to the gamma ray energy used in the gamma camera or the Positron Emission Tomography (PET). .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, embodiments of the present invention illustrated below may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

Embodiments of the invention are provided to more fully illustrate the invention to those skilled in the art.

3A to 3C illustrate a silicon photomultiplier tube with improved photodetection efficiency according to an embodiment of the present invention.

FIG. 3A illustrates a structural diagram of a silicon photomultiplier tube with improved photodetection efficiency according to an embodiment of the present invention, and FIG. 3B illustrates a cross-sectional view taken along the line 'A' of FIG. 3A, and FIG. 3C 3A is a cross-sectional view taken along the line 'B' of FIG. 3A.

Silicon photomultiplier tube according to an embodiment of the present invention is provided with a metal line 310 in each micro cell 320 and a polysilicon resistor 340 for quenching connected to the metal line and the contact 315 is provided. have.

On the other hand, as shown in the cross-sectional structure of the silicon photomultiplier tube according to an embodiment of the present invention, as shown in Figure 3b, there is a p + conductive type semiconductor substrate 301 in the lowermost layer, the upper portion of the semiconductor substrate A p-conductive type epitaxy layer 302 formed, a p type 303 of conductive type doped to the epitaxy layer, a conductive type formed on top of the p type of conductive type and doped to the epitaxy layer It can be seen that the n + region 304 and the insulating layer 305 formed on the epitaxial layer and the n + region of the conductivity type.

On the other hand, the structure of the 301 to 305 can be used a structure commonly used in the field to which the present invention belongs, which can be modified in various other forms depending on the embodiment and the use form.

Meanwhile, as shown in FIG. 3B, a metal line 310 is formed to connect the polysilicon resistor 340 and the n + region 304 which is the active region, which is the n + region 304 and the polysilicon which are the active regions. The connection between the resistors 340 through the contact 315 serves to form a path of charge transfer.

To this end, first, a hole is formed by etching a predetermined size in an insulating layer formed on the upper layer of the n + region 304 which is an active region in a semiconductor process, and a contact is formed by filling a metal with the hole, and a metal line Can be connected to

Here, the metal line may generally use aluminium (Al) having excellent electrical conductivity, and the above-described insulation layer may include silicon oxide (SiO 2), silicon oxy nitride (SiON), or silicon nitride (SiN). ), And may be composed of one or more compounds selected from the group consisting of hartnium oxide (HfO).

Meanwhile, the quenching polysilicon resistor 340 is connected to the metal line 310 and is formed on the insulating layer 305, and the quenching polysilicon resistor 340 has a multilayer structure. A plurality of silicon optoelectronic multiplier may be formed to overlap each other in the depth direction.

As described above, the polysilicon resistance for quenching of each microcell of a typical silicon optoelectronic multiplier should be at least 100 kW or 1 kW when forming the polysilicon resistor for quenching. Since the minimum line width of is generally 2 u m or more, a polysilicon resistor with a large sheet resistance should be used, or if the sheet resistance is small, the length of the polysilicon resistor should be increased.

For example, when the size of the sheet resistance is 1 ㏀, 200 u m length is required to obtain a resistance of 100 ㏀.

On the other hand, if the size of the microcells 100 u m be taken if the two sides, 50 u m were surrounding the four sides must It can get resistance 100㏀ one case, the size of the microcells 50 u m or less days Even if it surrounds all four sides, it is impossible to obtain 100㏀ resistance.

Further, when the microcell size is smaller, the polysilicon sheet resistance is not increased, the fill factor is reduced in the microcell of small size. To overcome this problem, the present invention proposes a new structure of the polysilicon resistance.

In the silicon optoelectronic multiplier according to the exemplary embodiment of the present invention illustrated in FIGS. 3B and 3C, the polysilicon resistor 340 has a multi-layer structure, and a plurality of polysilicon resistors 340 may be formed to overlap each other in the depth direction of the silicon photomultiplier. Can be.

As described above, by configuring a plurality of polysilicon resistors formed in a multilayer structure, the area occupied by polysilicon can be reduced, and the fill factor can be improved compared to when polysilicon resistors are formed in one layer.

When forming a polysilicon resistor in a multi-layered structure, one end of one polysilicon resistor and the other end of the polysilicon resistor of the other layer using the contact 315 so that the polysilicon resistance of each layer is connected, as shown in Figure 3c. By alternately connecting the polysilicon resistors, the polysilicon resistors having a high resistance value can be formed without connecting a large area by connecting the polysilicon resistors in parallel by the contacts 315 and connecting them in series.

The contact 315 serves to interconnect the polysilicon resistors of each layer, and the contact and the polysilicon resistors are interconnected by ohmic junctions.

In addition, the unit microcell may further include a convex micro lens 370 formed to surround the unit microcell.

The convex micro lens 370 is formed to make it easier for the optical signal to enter the photodiode region of the micro cell, which is an active region, thereby further improving the fill factor.

Here, the convex micro lens 370 may be made of PDMS, PMMA, or photoresist.

4A and 4B illustrate a silicon photomultiplier tube with improved photodetection efficiency according to another embodiment of the present invention.

FIG. 4A illustrates a reflective layer 480 formed on a dead region of a micro cell having the structure of FIG. 2C.

4B is a cross-sectional view taken along line 'C' of FIG. 4B to more clearly examine its structure.

Referring to FIG. 4B, similar to FIG. 3B, a p + conductive semiconductor substrate 401 is formed on a lowermost layer, and an epitaxial layer 402 of a p− conductive type is formed on an upper portion of the semiconductor substrate. A p region 403 of a conductive type doped in the taxi layer, a n + region 404 of a conductive type doped in the epitaxy layer and formed on top of the p region of the conductive type, and the epitaxy layer and the conductive It can be seen that the insulating layer 405 is formed on the n + region of the type.

Likewise, the structures of 401 to 405 may use structures commonly used in the art to which the present invention pertains, which may be modified in various other forms according to the embodiment and the use form.

Meanwhile, as shown in FIG. 4B, a metal line 410 is formed to connect the polysilicon resistor 440 and the n + region 404 which is the active region, which is the n + region 404 and the polysilicon which are the active regions. A metal line 410 is connected between the resistors 440 to form a path of charge transfer.

To this end, in the semiconductor process, a strip-shaped trench is formed by etching a predetermined size in an insulating layer formed on the upper layer of the n + region 404, which is an active region, and forming a contact by filling a metal with the trench, thereby forming a metal line. can be connected to a (metal line).

In addition, the polysilicon resistor 440 may have a multilayer structure as described above, and a plurality of polysilicon resistors 440 may be formed to overlap each other in a depth direction of the silicon photomultiplier tube.

4B, the dielectric 490 is formed on the quenching polysilicon resistor 440 and the metal line 410, and surrounds the unit micro cell. The reflective layer 480 may be formed on the upper portion 490.

That is, by forming the reflective layer 480, the visible light entering the dead region is reflected, passes through a plurality of reflections in the scintillator, and then enters the micro cell, thereby further increasing the light collection effect.

Here, the reflective layer may be made of one or more compounds selected from the group consisting of aluminum, tungsten, titanium, and gold.

On the other hand, general optical cameras can achieve near 100% light collection efficiency even if the fill factor is low through microlenses, but unlike general optical cameras, scintillator and optical grease should be considered in gamma detectors that detect gamma rays. In addition, unlike optical cameras, since the angle of visible light incident on the microlens is not constant, the microlens cannot be accurately designed using only a focal length calculation formula applied to a general optical camera.

Accordingly, in the gamma ray detector using the silicon photomultiplier tube, as shown in FIG. 5, the optical sensor 580 by the scintillator 590 and the microcell, the microlens 570 and the optical grease formed on the optical sensor. 560.

Since the optical sensor 580 has the same structure as that of the microcell in the aforementioned silicon opto-electronic multiplier, the detailed description thereof will be omitted for clarity.

 The optical sensor 580 may further include a dielectric formed on the quenching polysilicon resistor and the metal line, and a reflective layer formed on the dielectric to surround the unit micro cell.

Such a gamma ray detector should take into account the microlens refractive index when designing a microlens. Since the gamma ray detector uses various scintillators according to the field of use, a microlens for a specific scintillator is designed as follows.

Meanwhile, the microlens 570 may be a convex or concave microlens according to the refractive index of the optical grease 560.

FIG. 6 is a graph illustrating a fill factor according to curvature and refractive index of a microlens with a focal length when an angle of incident visible light is not constant in a specific geometric fill factor 610.

FIG. 6 illustrates a microlens of a silicon photomultiplier tube using LSO (Lu ₂ SiO ₅ ) having a refractive index of 1.82 and optical grease having a refractive index of 1.46 among various scintillators according to FIG. 3C.

Here, the pitch of the microcell is 50 u m, and the conductive type n + region 304, which is an active region as shown in Fig. 3c, is 35 u m, and the geometric fill factor is microscopic at 49%. The light collection efficiency for the curvature and refractive index of the lens was modeled.

As can be seen in FIG. 6, the light collection efficiency of the focused focal length microlenses used in the optical camera shows that the fill factor has a maximum refractive index of 1.6 to 2.0 when the angle of visible light incident on the microlens is not constant. However, by showing a fill factor value of 55%, it can be seen that there is no great effect when the angle of incident visible light is not constant.

7 is a graph showing light collection efficiency according to curvature and refractive index of a microlens applied to the present invention.

Corresponding to the geometric fill factor 710, the refractive index of the microlenses when the lens curvature is 35 u m (720), 30 u m (730), and 25 u m (740) in the microlenses without focusing distance. The light collection efficiency is shown.

As can be seen in Figure 7, as a whole to the greater the refractive index of the microlens increases the light collection efficiency, the refractive index shows the same refractive index is almost saturated in 2.0 above, the whole of the high light collection efficiency at a curvature of 25 u m It can be seen that.

As such, when the LSO scintillator and the optical grease having the refractive index of 1.46 are used, the optimum micro lens condition applied to the present invention can be found.

As described above, the microlenses set the optimum curvature according to the refractive index of the optical grease and the type of the scintillator, and then, by applying the microlens having the optimal curvature to the present invention, the microlens is derived to obtain the best light collection efficiency.

As such, the present invention has been described above with reference to the embodiments shown in the drawings, which are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. .

Therefore, the true technical protection scope of the present invention will be defined by the technical details of the appended claims.

1 illustrates a one-pixel cross-sectional view of a silicon photomultiplier tube having a plurality of conventional microcells.

2a to 2c show the area occupied by the quenching resistance according to the size of the conventional microcell.

FIG. 3A illustrates a structure diagram of a silicon photomultiplier tube with improved photodetection efficiency according to an embodiment of the present invention.

3B is a cross-sectional view taken along the line 'A' of FIG. 3A;

3C is a cross-sectional view taken along the line 'B' of FIG. 3A.

FIG. 4A illustrates a reflective layer 480 formed on a dead region of a micro cell having the structure of FIG. 2C.

4B is a cross-sectional view taken along line 'C' of FIG. 4A.

5 illustrates a gamma ray detector using a silicon photomultiplier tube according to an embodiment of the present invention.

FIG. 6 is a graph illustrating light collection efficiency according to curvature and refractive index of a microlens with a focal length when an angle of incident visible light is not constant in a specific geometric fill factor 610.

7 is a graph showing light collection efficiency according to curvature and refractive index of a microlens applied to the present invention.

Claims (11)

In a silicon photomultiplier tube comprising a plurality of micro cells, a semiconductor substrate of a p + conductivity type, formed on top of the semiconductor substrate, and formed on top of a p-conductive type epitaxy layer, a p region of a conductive type doped into the epitaxy layer, and a p region of the conductive type, An n + region of a conductivity type doped to the epitaxy layer, an insulating layer formed on top of the epitaxy layer and an n + region of the conductivity type, and surrounding the semiconductor substrate, an epitaxy layer, a p region, an n + region and an insulating layer A unit micro cell including a convex micro lens formed to have a convex shape; A metal line of the unit micro cell formed on the n + region; And A quenching polysilicon resistor connected to the metal line by a contact and formed on the insulating layer, The polysilicon resistor for quenching is It has a multi-layer structure, a plurality of silicon photoelectric multiplier tube is improved, characterized in that formed in a plurality of overlapping with each other in the depth direction of the silicon photomultiplier tube. delete The method of claim 1, The convex micro lens Silicon photomultiplier tube with improved photodetection efficiency, characterized in that consisting of PDMS, PMMA, or photoresist. The method of claim 1, The polysilicon resistor for quenching having the multilayer structure And a polysilicon resistor of one end and a polysilicon resistor of the other end are alternately connected by the contact. The method of claim 4, wherein The polysilicon resistor for quenching is Silicon photoelectric multiplier tube with improved photodetection efficiency, characterized in that connected by the contact and the ohmic junction. The method of claim 1, A dielectric formed on the quenching polysilicon resistor and the metal line; And And a reflective layer formed on the dielectric so as to surround the unit micro cell. The method of claim 6, The reflective layer A photoelectric efficiency-enhanced silicon photoelectron multiplier tube, comprising at least one compound selected from the group consisting of aluminum, tungsten and titanium. A gamma ray detector comprising a silicon photomultiplier tube, a semiconductor substrate of a p + conductivity type, formed on top of the semiconductor substrate, and formed on top of a p-conductive type epitaxy layer, a p region of a conductive type doped into the epitaxy layer, and a p region of the conductive type, A unit micro cell comprising an n + region of a conductivity type doped to the epitaxy layer, and an insulating layer formed on the epitaxy layer and the n + region of the conductivity type; A metal line of the unit micro cell formed on the n + region, A polysilicon resistor for quenching having a plurality of multilayer structures connected to the metal lines by contact with each other and overlapping each other in the depth direction of the silicon photomultiplier tube on the insulating layer;  A silicon photodetector multiplier tube including a microlens formed to surround the unit microcell; And A gamma ray detector comprising an optical grease formed on an upper portion of the silicon photodetection multiplier. The method of claim 8, The photodetector multiplier is A dielectric formed on the quenching polysilicon resistor and the metal line; And And a reflective layer formed on the dielectric to surround the unit micro cell. The method of claim 8, The insulating layer is A gamma ray detector comprising at least one compound selected from the group consisting of silicon oxide (SiO 2), silicon oxy nitride (SiON), silicon nitride (SiN), and heartnium oxide (HfO). The method of claim 8, The micro lens A gamma ray detector, characterized in that it is formed of a convex or concave micro lens according to the refractive index of the optical grease.

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