Micro-channel array CsI: T1 scintillation screen and preparation method thereof

Abstract

The invention relates to a micro-channel array type CsI: T1 scintillation screen and a preparation method thereof. The micro-channel array type CsI: T1 scintillation screen comprises a micro-channel array substrate; the micro-channel array substrate is of a channel structure, the channel structure is square holes, and the holes are vertically arranged in a square mode. The inner wall of a channel of the micro-channel array substrate is plated with a mirror surface metal reflecting film, and the channel is filled with a scintillator thallium-doped cesium iodide; and an aluminum film or a heavy metal film is evaporated on the incident surface of the micro-channel array CsI: T1 scintillation screen. The area of the channels of the scintillation screen relative to the surface of the base body is large, the larger the area ratio is, the larger the proportion of the scintillator is, the detection efficiency of the scintillation screen is better improved, and the radiation dosage of the back face is reduced. According to the scintillation screen, mirror surface metal such as an Al film is selected as the reflecting film, and the light output of the scintillation screen can be greatly improved. The test result shows that the X-ray detector integrated by the scintillation screen can realize the high spatial resolution of 101p / mm, and the effect is very excellent in the actual test.

Description

Technical Field

[0001] The present invention relates to the technical field of X-ray detection, and in particular to a microchannel array type CsI:Tl scintillation screen and a preparation method thereof. Background Art

[0002] The indirect X-ray imaging detector system (IXD) relies on scintillation imaging technology. After the scintillator material converts high-energy X-rays into low-energy fluorescence, it is imaged and detected using an image sensor. As the core components of IXD, the performance parameters of the scintillation screen and image sensor play a key role in the performance of the detector. Generally speaking, the detection efficiency can be improved by increasing the thickness of the scintillation screen. However, due to the lateral propagation of scintillation fluorescence, the increase in screen thickness will lead to a decrease in spatial resolution. Therefore, the development of X-ray imaging detectors with high spatial resolution has always attracted widespread attention from researchers at home and abroad. Summary of the invention

[0003] In view of this, the present invention provides a microchannel array CsI:Tl scintillating screen and a preparation method thereof. The X-ray detector integrated with the microchannel array CsI:Tl scintillating screen of the present invention can achieve a high spatial resolution of 101 p / mm.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] A microchannel array CsI:Tl scintillating screen, comprising: a microchannel array substrate;

[0006] The microchannel array substrate is a channel structure, and the channel structure has square holes, the holes are vertically arranged in a square;

[0007] The inner wall of the channel of the microchannel array substrate is plated with a mirror metal reflective film, and the channel is filled with scintillator thallium-doped cesium iodide (CsI(Tl));

[0008] The incident surface of the microchannel array CsI:Tl scintillator screen is evaporated with an aluminum film or a heavy metal film.

[0009] In the above technical solution, the microchannel array substrate is an n-type silicon wafer with a (100) crystal plane.

[0010] In the above technical solution, the channel structure has a side length of 8 μm×8 μm, a channel center distance of 10 μm, a channel depth of 300 μm, and a channel wall thickness of 1 μm.

[0011] In the above technical solution, the scintillator is doped with cesium iodide (CsI(Tl)), which is doped with Tl + The concentration is 0.09 mol%.

[0012] In the above technical solution, the mirror metal reflective film is an aluminum reflective film with a film thickness of 10-20 nm.

[0013] In the above technical solution, the film thickness of the aluminum film or heavy metal film is 200 nm.

[0014] In the above technical solution, the heavy metal film is a copper, lead, zinc, iron, cobalt, nickel, manganese, gold or silver film.

[0015] A method for preparing a microchannel array CsI:Tl scintillation screen comprises the following steps:

[0016] Step 1, manufacturing an inductive pit structure with an inverted pyramid structure on an n-type silicon wafer with a (100) crystal plane, and then performing photoelectrochemical etching, shaping and back thinning, polishing and cleaning, and etching and expanding the holes to obtain a microchannel array substrate of a silicon substrate;

[0017] Step 2, coating the inner wall of the channel of the microchannel array substrate obtained in step 1 with a mirror-like metal reflective film;

[0018] Step 3, filling the channels of the microchannel array substrate obtained in step 2 with scintillator thallium-doped cesium iodide (CsI(Tl));

[0019] Step 4: After polishing one side of the microchannel array substrate obtained in step (3) by a positive polishing method, an aluminum film or a heavy metal film is evaporated on the surface, and finally the other side of the microchannel array substrate is polished to obtain the final microchannel array CsI:Tl scintillation screen.

[0020] The beneficial effects of the present invention are:

[0021] The microchannel array type CsI:Tl scintillator screen of the present invention comprises a microchannel array substrate, which is a channel structure, the channel structure is a square hole, the holes are vertically arranged in a square, the area of ​​the substrate channel of this channel structure is relatively large relative to the surface of the substrate, the larger the area ratio, the larger the proportion of the relative scintillator, which is more conducive to the detection efficiency of the scintillator screen and reduces the radiation dose on the back. The microchannel array type CsI:Tl scintillator screen of the present invention selects a mirror metal such as an Al film as a reflective film, which can greatly improve the light output of the scintillator screen.

[0022] The test results show that the X-ray detector integrated by the microchannel array CsI:Tl scintillation screen of the present invention can achieve a high spatial resolution of 10l p / mm, and the integrated X-ray detector of the present invention is used to detect eight-pin chip integrated circuits. Fig.12 , showing that the detector performs very well in actual tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] Figure 1 It is a schematic diagram of the three-dimensional structure of the microchannel array CsI:Tl scintillating screen of the present invention.

[0025] Figure 2 This is the SEM image of the induced pit structure of the microchannel array substrate.

[0026] Figure 3 This is a metallographic microscope image of the back of the microchannel array substrate obtained after shaping, back thinning, polishing and cleaning.

[0027] Figure 4 This is a schematic diagram of the microchannel array substrate after hole expansion. The left picture is a top view after hole expansion, and the right picture is a cross-sectional view after hole expansion.

[0028] Figure 5 This is a SEM photograph of the side wall of the microchannel array substrate channel coated with a mirror-finished metal aluminum reflective film.

[0029] Figure 6 This is a schematic diagram of the filling equipment structure.

[0030] Figure 7 This is a sample picture of the microchannel array matrix channel filled with scintillator thallium-doped cesium iodide (CsI(Tl)).

[0031] Figure 8 This is a test chart of the light-to-light conversion efficiency of the microchannel array CsI:Tl scintillating screen prepared by the present invention.

[0032] Fig. 9 This is a test curve diagram of the afterglow response time of the microchannel array CsI:Tl scintillation screen prepared by the present invention.

[0033] Fig.10 The exposure diagrams are of the array structure X-ray detector integrated with the microchannel array CsI:Tl scintillating screen prepared by the present invention under different ray source tube voltages.

[0034] Fig.11 This is a diagram of the detection results of the array structure X-ray detector integrated with the microchannel array CsI:Tl scintillating screen prepared by the present invention.

[0035] Fig.12 This is a diagram showing the effect of detecting an eight-pin chip integrated circuit. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the accompanying drawings.

[0037] The three-dimensional structure diagram of the microchannel array CsI:Tl scintillator screen of the present invention is as follows: Figure 1As shown, it includes: a microchannel array substrate; the microchannel array substrate is a channel structure, the channel structure is a square hole, the holes are vertical and arranged in four directions; the side length of the channel structure is 8μm×8μm, the channel center distance is 10μm, the channel depth is 300μm, and the channel wall thickness is 1μm; the channel inner wall of the microchannel array substrate is plated with a mirror metal aluminum reflection film, the film thickness of the aluminum reflection film is about 10-20nm, and the scintillator filled in the channel of the microchannel array substrate is thallium-doped cesium iodide (CsI(Tl)), and the scintillator CsI(Tl) is doped with Tl + The concentration is 0.09 mol %, and the incident surface of the microchannel array CsI:Tl scintillator screen is evaporated with an aluminum film with a thickness of 200 nm.

[0038] The method for preparing the microchannel array CsI:Tl scintillation screen of the present invention specifically comprises the following steps:

[0039] Step 1: an induction pit structure with an inverted pyramid structure is manufactured on an n-type silicon wafer with a (100) crystal plane, and then subjected to photoelectrochemical etching, shaping and back thinning, polishing and cleaning, and then etching and expanding the holes to obtain a microchannel array substrate of a silicon substrate; more specific steps are as follows:

[0040] 1) Preparation of induced pit structure

[0041] (1) Select an n-type silicon wafer with a (100) crystal plane, perform a phosphorus diffusion process on the back, select P2O5 as the diffusion source, diffuse at 1000°C for 30 minutes, and form an ohmic contact layer;

[0042] (2) The silicon wafer is oxidized in a high-temperature diffusion furnace at 1000°C for 30 minutes to prepare a silicon dioxide mask;

[0043] (3) The mask period is 10 μm, and a square array image is obtained after coating, pre-baking, exposure, development, and hardening;

[0044] (4) ICP etching removes the silicon dioxide film layer, and concentrated sulfuric acid removes the photoresist layer;

[0045] (5) Using 20.83% TMAH etching solution, the product was etched in a 90°C water bath for 30 min to produce an inverted pyramid induced pit structure. The SEM image of the induced pit structure is shown in Figure 2 ;

[0046] 2) Perform photoelectrochemical etching on the substrate obtained in step 1)

[0047] The three-electrode system was controlled by a PARSTAT 2273 constant potential instrument. The silicon wafer was used as the working electrode, the reference electrode (RE) was a 232-type saturated calomel electrode, and the auxiliary electrode was 25 cm 2The Pt screen was scanned with a photocurrent at a voltage range of -1 to 3 V, and then at a current density of 7.86 mA / cm 2 ~4.57mA / cm 2 ) conditions for electrochemical corrosion;

[0048] 3) The substrate obtained in step 2) is shaped and the back is thinned, polished and cleaned. The back metallographic microscope image of the microchannel array substrate obtained is shown in Figure 3 ;

[0049] 4) performing corrosion and hole expansion on the microchannel array substrate obtained in step 3);

[0050] (1) Substrate pretreatment: Use HF and a small amount of isopropanol to remove the natural oxide layer of the substrate;

[0051] (2) Wafer loading: placing the silicon wafer in the fixture;

[0052] (3) Preparing shaping solution: Pour a mixed solution of HF, isopropanol and tetramethylammonium hydroxide (TMAH) into a polytetrafluoroethylene tank;

[0053] (4) Temperature setting: Set the temperature of the constant temperature water bath to 40°C through the temperature control system;

[0054] (5) Shaping: Turn on the stirrer and time for 1.5 h;

[0055] (6) Removing the wafer: Turn off the instruments required for the experiment, disconnect the circuit, remove the silicon wafer from the homemade fixture after etching, put it into anhydrous ethanol for ultrasonic cleaning for 10 minutes and blow it dry to obtain a silicon-based microchannel array substrate; see the schematic diagram after hole expansion for details. Figure 4 .

[0056] Step 2, coating the inner wall of the channel of the microchannel array substrate obtained in step 1 with a mirror-like metal aluminum reflective film;

[0057] The aluminum reflective film is deposited on the inner wall of the channel of the microchannel array substrate by atomic layer deposition. The film thickness is about 10-20nm. The SEM photo of the side wall is shown in Figure 5 .

[0058] Step 3, filling the channels of the microchannel array substrate obtained in step 2 with scintillator thallium-doped cesium iodide (CsI(Tl));

[0059] See the structural diagram of the filling equipment for Figure 6 , the filling steps are as follows:

[0060] (1) cleaning the microchannel array of the oxidized silicon substrate;

[0061] (2) Spreading a powdered CsI (Tl) scintillation crystal flat in a quartz crucible, and placing the microchannel array of the silicon substrate flat on top of the CsI (Tl) scintillation crystal with its front side facing downward;

[0062] (3) Adjust the quartz crucible to a horizontal position in the tube furnace and slowly push it to the center of the tube furnace;

[0063] (4) The temperature of the tube furnace was raised to 580°C within 30 min, during which high-purity N2 was continuously introduced at an inlet flow rate of 0.1 L / min;

[0064] (5) Maintain the temperature of the tube furnace at 580°C, close valve 1 and valve 3, open valve 2, turn on the vacuum pump, and pump the internal pressure of the tube furnace to 10 Pa within 4 minutes, close valve 2 and valve 3, and maintain the vacuum degree in the tube furnace;

[0065] (6) After heating the tube furnace to 660°C within 5 minutes, high-purity N2 was continuously introduced at an inlet flow rate of 0.1 L / min to fill the molten CsI(Tl) scintillating crystals into the channels of the microchannel array of the silicon substrate, and then the scintillating crystals were taken out after cooling to room temperature. Figure 7 .

[0066] Step 4: After polishing one side of the microchannel array substrate scintillator screen of the silicon substrate obtained in step (3) by using a deerskin upright polishing method, remove the CsI (Tl) crystals remaining on the surface of the scintillator screen to reduce the damage to the surface of the scintillator screen and ensure that the scintillator crystals will not fall out. After completing the polishing operation on one side of the scintillator screen, an aluminum film with a film thickness of 200 nm is plated by an evaporation coating method. Finally, the other side of the scintillator screen is polished to obtain the final microchannel array CsI: Tl scintillator screen. The light-to-light conversion efficiency test diagram is shown in FIG. Figure 8 , afterglow response time test curve see Fig. 9 .

[0067] like Fig. 9 As shown in the figure, the afterglow lifetime spectrum of CsI:Tl shows the number of photons recorded in different channels. The descending part in the figure represents the fluorescence decay of CsI:Tl. The quadratic fitting of the least square method is performed on the descending trend part of the figure, that is, the channel interval of 320 to 500, to obtain the lifetime value of the sample. This sample has two afterglow components, the fast component is only 0.306ns, and the slow component is 2.191ns. The fast component accounts for as high as 94.877%, and the slow component is only 5.123%. The criterion for the fitting result is χ 2 It is only 1.002, which is very close to 1, and the residual weight curve fluctuates around 0, and the deviation amplitude is basically locked between 3 and -3. It can be seen that the fluorescence lifetime obtained by quadratic fitting is very close to the actual value. The fluorescence lifetime spectrum of the sample and the average afterglow response time τ are calculated using the following formula:

[0068] τ=τ1×f1+τ2×f2

[0069] Table 1 Afterglow time measurement results

[0070]

[0071] The scintillator screen of the microchannel array CsI:Tl scintillator screen of the present invention is bonded to the photoelectric conversion device to obtain an array structure X-ray detector. When bonding the two, Dow Corning SYLGARD184 silicone rubber can be filled between the scintillator screen and the photoelectric conversion device. The PDMS basic components and the curing agent are completely mixed in a weight ratio of 10:1, and applied to the surface of the photoelectric sensor with a cotton swab. The microchannel substrate and the photoelectric sensor are bonded and fixed with a rubber rope, and placed in a high-temperature drying furnace at a temperature of 100°C for 35 minutes to complete the curing. The exposure diagram of the obtained X-ray detector under different radiation source tube voltages is shown in FIG. Fig.10 , see the test result diagram Fig.11 As can be seen from the figure, the performance of the microchannel array CsI:Tl scintillating screen integrated array structure X-ray detector prepared by the present invention is excellent, and a spatial resolution of 10lp / mm can be achieved. Fig.12 It is a diagram showing the effect of detecting an eight-pin chip integrated circuit. It can be seen that in actual testing, the X-ray detector of the present invention has excellent effect.

[0072] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For example, the aluminum film can be replaced by other heavy metal films, and the technical effects of the present invention can also be achieved. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the invention.

Claims

1. A microchannel array CsI:Tl scintillating screen, characterized in that: include: microchannel array substrate; The microchannel array substrate is a channel structure, and the channel structure has square holes, the holes are vertically arranged in a square; The inner wall of the channel of the microchannel array substrate is plated with a mirror metal reflective film, and the channel is filled with scintillator thallium-doped cesium iodide; The incident surface of the microchannel array CsI:Tl scintillator screen is evaporated with an aluminum film or a heavy metal film.

2. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The microchannel array substrate is an n-type silicon wafer with a (100) crystal plane.

3. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The channel structure has a side length of 8 μm×8 μm, a channel center distance of 10 μm, a channel depth of 300 μm, and a channel wall thickness of 1 μm.

4. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The scintillator is doped with cesium iodide doped with Tl + The concentration is 0.09 mol%.

5. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The mirror metal reflection film is an aluminum reflection film with a film thickness of 10-20nm.

6. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The film thickness of the aluminum film or the heavy metal film is 200 nm.

7. The microchannel array CsI:Tl scintillator screen according to claim 1, characterized in that: The heavy metal film is a copper, lead, zinc, iron, cobalt, nickel, manganese, gold or silver film.

8. A method for preparing a microchannel array CsI:Tl scintillating screen according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1, manufacturing an inductive pit structure with an inverted pyramid structure on an n-type silicon wafer with a (100) crystal plane, and then performing photoelectrochemical etching, shaping and back thinning, polishing and cleaning, and etching and expanding the holes to obtain a microchannel array substrate of a silicon substrate; Step 2, coating the inner wall of the channel of the microchannel array substrate obtained in step 1 with a mirror-like metal reflective film; Step 3, filling the channels of the microchannel array substrate obtained in step 2 with scintillator thallium-doped cesium iodide; Step 4: After polishing one side of the microchannel array substrate obtained in step (3) by a positive polishing method, an aluminum film or a heavy metal film is evaporated on the surface, and finally the other side of the microchannel array substrate is polished to obtain the final microchannel array CsI:Tl scintillation screen.

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