A method for improving the contact between vanadium oxide and titanium electrode in microbolometer

Abstract

The present invention discloses a method for improving the contact between vanadium oxide and titanium electrode in a microbolometer, and the method can be used to improve the contact between vanadium oxide and titanium electrode in a microbolometer. First, the method uses ion implantation technology to use tungsten and titanium as doping elements, and the implantation area is the area in the vanadium oxide film that contacts the titanium electrode. Secondly, the selection of tungsten and titanium as implanted elements can effectively reduce the resistance of the vanadium oxide contact area, obtain excellent gold-semiconductor contact, thereby reducing the 1 / f noise of the vanadium oxide itself, and helping to obtain a low-noise device; in addition, by doping tungsten elements, the TCR of the vanadium oxide film can be increased, thereby improving the signal-to-noise ratio of the device. Third, the heat treatment method after ion implantation is pulse current rapid annealing, which can achieve lattice repair. At the same time, rapid annealing can avoid oxygen loss during the heating process, thereby reducing oxygen vacancies and preventing the resistance of the vanadium oxide from decreasing too much.

Description

Technical Field

[0001] The invention relates to the field of infrared detection and imaging, and in particular to utilizing an ion implantation method to improve the contact between vanadium oxide and a titanium electrode in a microbolometer. Background Art

[0002] Infrared detectors are infrared imaging devices that detect, identify and analyze infrared information of objects. They can be divided into two categories: cooled and uncooled. Uncooled infrared detectors mainly include microbolometers, pyroelectric infrared detectors, thermopile infrared detectors and photomechanical infrared detectors. Among them, microbolometers based on thermistor materials are compatible with MEMS micromachining processes and can be produced in high throughput. Microbolometers are usually integrated by microbolometer arrays (pixels) on a single substrate. The structure of each pixel unit includes a sensor part, a readout circuit and a connection part. The sensor structure mainly includes two parts. The first part is the infrared absorption structure, which determines the absorption rate of the microbolometer to infrared radiation; the second part is the core of the entire detection unit, that is, the thermistor layer. Vanadium oxide has a high temperature coefficient of resistance (TCR) and is sensitive to changes in ambient temperature. It is widely used in thermistor sensors.

[0003] Generally speaking, a conductive path is required to achieve the interconnection between the thermistor layer vanadium oxide (VOx) and the underlying readout integrated circuit. This connection is mainly achieved by depositing a layer of electrode metal. The electrode metal is mainly divided into two parts. One is the metal connection from the pixel bridge to the metal support structure. This part mainly realizes the connection between the electrode metal and the underlying readout circuit; the other part of the connection is mainly the direct contact between the electrode metal and the thermosensitive layer vanadium oxide, which is generally an ohmic contact. This requires that the vanadium oxide in the contact part has good conductivity and low resistivity. As a high TCR material, vanadium oxide has a large resistance, and excessive resistance in the contact area will reduce device performance. Therefore, the vanadium oxide in the connection area needs to be properly treated to reduce its resistivity.

[0004] Reverse sputtering can effectively reduce the resistivity of the film, and sputtering the electrode contact part VOx backward can change its electrical properties. However, reverse sputtering may erode the protective dielectric layer in the bridge area, especially the bridge edge, which may cause a short circuit in the contact area. In addition, reverse sputtering is mainly a surface phenomenon, and the control of VOx depth is poor, resulting in poor predictability of the resistance in the contact area. Argon reverse sputtering is essentially a cleaning process and cannot provide effective control. Therefore, a highly controllable, precise and repeatable method is needed to achieve better electrical contact between vanadium oxide and electrode metal and improve the signal-to-noise ratio of the device.

[0005] To this end, we propose a method for improving the contact between vanadium oxide and titanium electrode in a microbolometer to solve the problems existing in the prior art. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a highly controllable, precise and repeatable method to achieve better gold-semiconductor contact. Ion implantation technology, due to its good controllability and repeatability, simple equipment operation, has unparalleled advantages in the preparation of semiconductor oxide thin films, precise control of their microstructures and modifications, etc., which are unmatched by other processes. Ion implantation technology accelerates ionized elements to give them higher kinetic energy, and finally implants doping elements into the material. In this process, the implantation depth and composition are mainly controlled by ion energy and ion dose to solve the problems in the prior art mentioned in the above background technology.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for improving the contact between vanadium oxide and titanium electrode in a microbolometer is provided. The method is ion implantation, and the implantation area is the contact area between vanadium oxide and titanium electrode in the microbolometer structure.

[0009] Preferably, the implanted element is one or two of Ti, W, Mo, V, and Ta, and the mass ratio of the elements is 50% to 75%.

[0010] Preferably, the injection dose is 6×10 15 ~9×10 16 The implantation depth is 10nm~20nm.

[0011] Preferably, after the implantation, the structure is subjected to pulse current rapid annealing, and the vacuum degree is specified to be better than 1×10 -3 Pa, the pulse frequency is 10~100Hz, and the required current density is (4~7)×10 3 A / mm2, pulse width is 5~50μs, annealing temperature is 250~400℃, and heating time is 0.1~15s.

[0012] Some lower valence oxides in the vanadium oxide family, such as V 2 O 3 or VO, which are metallic at room temperature, and their TCR is lower than VO 2 , but it is higher than the electrode metals commonly used. High-energy ion bombardment of transition metal oxides can cause oxygen loss, which significantly reduces their resistivity. Therefore, they can be applied to the electrode connection area of ​​the thermistor layer to convert these areas into low-resistivity mixed-phase vanadium oxide to achieve better contact, thereby reducing contact noise and improving the overall performance of the device. By adding an ion implantation mask to protect the sensing area of ​​the thermistor layer, and then ion implantation is performed in the electrode contact area of ​​vanadium oxide, the high-valent VOx mixture is converted to a low-valent VO 2 / V2 O 3 The mixed phase of V / VO can realize the interconnection between low resistivity vanadium oxide and metal. The composition change of VOx depends on the implantation energy and implantation dose, and the composition change of VOx will also affect the resistivity. 2 O 3 The amount can reduce the resistivity to about 10 -2 Ω·cm, while increasing the proportion of VO can reduce the resistivity to 10 -3 Ω·cm. Therefore, the mixed phase VO 2 / V 2 O 3 The resistivity of VO / VO depends on the ratio of each VOx phase.

[0013] Technical effects and advantages of the present invention: The method for improving the contact between vanadium oxide and titanium electrode in a microbolometer proposed by the present invention has the following advantages compared with the prior art:

[0014] By adding an ion implantation mask layer (such as photoresist), the area to be implanted can be accurately located. In addition, the ion implantation process can be simulated by SRIM software. By selecting the implanted element, implantation energy, implantation dose, etc., the distribution of the implanted element in the depth direction of the film can be obtained, and the distribution map of the back-splashing atoms can also be obtained. By analyzing the back-splashing atom distribution, the oxygen loss ratio of the VOx film can also be determined. Therefore, the implantation depth and film composition can be more accurately controlled by selecting the appropriate implantation energy and implantation dose.

[0015] Ion implantation will cause damage to the lattice and produce a large number of defects. These defects will have a negative impact on the physical and chemical properties of the material, and these effects can be eliminated through subsequent annealing. For VOx thin films, ordinary vacuum annealing will cause the VOx resistance to decrease, thereby reducing its resistance temperature coefficient, and the resistance will continue to decrease as the annealing time increases. Pulse current rapid annealing can change the material microstructure, increase the film resistance through recrystallization and grain refinement, and ensure that the VOx resistance will not decrease too much after annealing. Rapid heating and rapid cooling of pulse current can achieve grain refinement and obtain fine-grained structure; in addition, pulse current can also reduce the nucleation barrier during phase change and thus increase the nucleation rate.

[0016] According to an embodiment of the present invention, the resistivity of the electrode metal contact area in the VOx bridge is reduced by ion implantation to achieve better electrical connection. This process provides the electrical connection required to connect the suspended thermistor layer VOx to the underlying readout circuit.

[0017] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of growing a sacrificial layer ② and a first dielectric layer ③ on a readout integrated circuit substrate ① in an embodiment of the present invention;

[0019] Figure 2 Schematic diagram of depositing a second dielectric layer ⑤ and an ion implantation mask layer ⑥ on the VOx layer ④ in an embodiment of the present invention, wherein a low resistance region ⑦ is formed by ion implantation;

[0020] Figure 3 It is a schematic diagram of stripping the ion implantation mask layer in an embodiment of the present invention;

[0021] Figure 4 is a schematic diagram of the final deposition of a metal electrode layer⑧ in an embodiment of the present invention;

[0022] Figure 5 Schematic diagram of a rapid annealing device in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] The present invention provides Figure 1-5 The example shown:

[0025] A method for improving the contact between vanadium oxide and titanium electrode in a microbolometer is provided. The method is ion implantation, and the implantation area is the contact area between vanadium oxide and titanium electrode in the microbolometer structure.

[0026] The implanted elements are one or two of Ti, W, Mo, V, and Ta, with a mass ratio of 50% to 75%; the implanted dose is 6×10 15 ~9×10 16 The implantation depth is 10nm to 20nm. After implantation, the structure is subjected to pulse current rapid annealing, and the vacuum degree is specified to be better than 1×10 -3 Pa, the pulse frequency is 10~100Hz, and the required current density is (4~7)×103 A / mm2, pulse width is 5~50μs, annealing temperature is 250~400℃, and heating time is 0.1~15s.

[0027] An embodiment of a process for manufacturing a pixel of the present invention comprises the following steps:

[0028] like Figure 1 As shown, a sacrificial layer ② and a first dielectric layer ③ are grown on a readout integrated circuit substrate ①, and a support column is arranged between the integrated circuit substrate and the dielectric layer, and the support column should also include a through hole for connection;

[0029] Forming a layer of VOx on the dielectric layer as a thermistor sensing layer④;

[0030] like Figure 2 As shown, a second dielectric layer ⑤ is deposited on the VOx layer as a passivation insulating layer;

[0031] like Figure 2 As shown, an ion implantation mask layer ⑥ is deposited on the dielectric layer, the mask layer is patterned and the second dielectric layer ⑤ is etched, leaving a protected VOx thermal sensitive bridge area;

[0032] like Figure 2 As shown, W ions are injected, thereby converting the VOx thermal sensitive layer electrode region into a low-valent mixed phase vanadium oxide (V 2 O 5 / VO 2 / V 2 O 3 / VO), thereby reducing the resistivity of the electrode region of the VOx layer to form a VOx low resistance region⑦;

[0033] like Figure 3 As shown, the ion implantation mask layer is stripped. The vanadium oxide is subjected to a pulse current rapid annealing treatment. The rapid annealing device is as shown in FIG. Figure 5 As shown, after the vanadium oxide electrode is connected, the pulse frequency is 10 to 100 Hz and the current density is 4 to 7×10 3 A / mm2, pulse current with pulse width of 5 to 50μs, and heating time of 0.1-15s.

[0034] Finally, a metal electrode layer ⑧ is deposited, such as Figure 4 As shown, the holes formed by the column holes and etching the second dielectric layer are interconnected with the bottom readout circuit and vanadium oxide. The deposition mask layer and ion implantation are targeted at the selected discrete areas, that is, the areas in contact with the metal electrode in the vanadium oxide bridge, to reduce the resistivity of the area and achieve better contact, thereby reducing the noise in the contact area and improving the signal-to-noise ratio of the device.

[0035] The preparation method of the mixed phase VOx film in the present invention includes DC sputtering, RF sputtering, vacuum evaporation and ion implantation. The passivation layer of the VOx film is a SiN film formed by CVD process. The patterning method of the passivation layer SiN and the ion mask layer includes stripping, dry etching and wet etching. The ion implantation energy is 50-150keV and the ion implantation dose is 6×10 15 , the implanted elements are W / Ti, and the substrate is VOx. VOx-W / Ti with different implantation depths is obtained. The annealing method after ion implantation is pulse current rapid annealing, and the annealing temperature is controlled by defining current density, pulse frequency, pulse interval, and heating time.

[0036] Beneficial effects of the present invention: Aiming at the contact requirements between the thermal sensitive layer VOx and the electrode metal titanium in the microbolometer, the present invention utilizes the ion implantation method to perform ion implantation in the vanadium oxide electrode contact area. The back-splash effect of the high-energy ion implantation will cause significant oxygen loss, thereby reducing the resistance of the area and achieving better gold-semiconductor contact. In addition, the implanted elements are Ti and W. W element doping can reduce the phase transition temperature, reduce the thermal hysteresis width of the film, and increase the temperature coefficient of film resistance, thereby improving the overall performance of the device; the electrode metal is Ti, and the implanted element is also Ti, which can achieve better contact between vanadium oxide and the Ti electrode. After the implantation, rapid pulse current annealing of the film can effectively optimize the crystallization and refine the grains, so that the overall resistance of the film will not be reduced too much.

[0037] The following are specific embodiments of the present invention:

[0038] Embodiment 1:

[0039] like Figure 1 As shown in the figure, a 640×640 focal plane array bridge structure with a pixel size of 17×17um is formed on a substrate by MEMS technology. The bridge surface is a first dielectric layer SiN film with a thickness of 120nm prepared by CVD technology. Then, a VOx film with a thickness of 80nm and a square resistance of 170kΩ / port is prepared by reactive magnetron sputtering technology. Ar and O 2 As the reaction gas, the oxygen-argon ratio is 3:100; the second dielectric layer SiN and the ion implantation mask layer are deposited; the mask layer is patterned by combining the photolithography process and the energy is 450eV and the beam density is 3mA / cm 2 The mask layer and the second dielectric layer are etched by an Ar ion beam to expose the VOx electrode area. Then, ions are implanted into the VOx electrode area with an implantation energy of 150 keV and an implantation dose of 6×10 15The implanted element is Ti, and the resistance of the VOx film implantation area is 600Ω; then the ion implantation mask layer is peeled off; finally, a metal Ti layer is prepared by DC magnetron sputtering process as an electrode directly contacting VOx. The post-implantation annealing method is pulse current rapid annealing, the annealing temperature is 275℃, the heating time is 7s, and the vacuum degree is better than 1×10 -3 The required pulse frequency is 75 Hz and the current density is 4 × 10 3 A / mm2, pulse width is 25μs. After the array is vacuum packaged, the performance is tested with a bias pulse of 5μs and 200μA at an operating temperature of 25°C. The NETD of the focal plane array device is 41mk.

[0040] Embodiment 2:

[0041] A 640×640 focal plane array bridge structure with a pixel size of 17×17um was formed on the substrate by MEMS technology. The bridge surface was a first dielectric layer SiN film with a thickness of 120nm prepared by CVD process. Then, a VOx film with a thickness of 80nm and a square resistance of 170kΩ / port was prepared by reactive magnetron sputtering process. Ar and O 2 As the reaction gas, the oxygen-argon ratio is 3:100; the second dielectric layer SiN and the ion implantation mask layer are deposited; the mask layer is patterned by combining the photolithography process and the energy is 450eV and the beam density is 3mA / cm 2 The mask layer and the second dielectric layer were etched by an Ar ion beam to expose the VOx electrode area; ions were implanted into the VOx electrode area with an implantation energy of 150 keV and an implantation dose of 6×10 15 The implanted element is W, and the resistance of the VOx film implantation area is 410Ω; then the ion implantation mask layer is peeled off; and then a DC magnetron sputtering process is used to prepare a metal Ti layer as an electrode directly in contact with VOx. The post-implantation annealing method is pulse current rapid annealing, the annealing temperature is 275℃, the heating time is 7s, and the vacuum degree is better than 1×10 -3 The required pulse frequency is 75 Hz and the current density is 4 × 10 3 A / mm2, pulse width is 25μs. After the array is vacuum packaged, the performance is tested with a bias pulse of 5μs and 200μA at an operating temperature of 25°C. The NETD of the focal plane array device is 33mk.

[0042] Embodiment 3:

[0043] A 640×640 focal plane array bridge structure with a pixel size of 17×17um was formed on the substrate by MEMS technology. The bridge surface was a first dielectric layer SiN film with a thickness of 120nm prepared by CVD process. Then, a VOx film with a thickness of 80nm and a square resistance of 170kΩ / port was prepared by reactive magnetron sputtering process. Ar and O 2 As the reaction gas, the oxygen-argon ratio is 3:100; the second dielectric layer SiN and the ion implantation mask layer are deposited; the mask layer is patterned by combining the photolithography process and the energy is 450eV and the beam density is 3mA / cm 2 The mask layer and the second dielectric layer were etched by an Ar ion beam to expose the VOx electrode area; ions were implanted into the VOx electrode area with an implantation energy of 150 keV and an implantation dose of 3×10 15 The implanted element is W. After the W element is implanted, the same implant energy of 150 keV and implant dose of 3×10 15 The same area was injected with Ti element to achieve W and Ti co-doping, and the resistance of the injected area was reduced to 450Ω; then the ion implantation mask layer was stripped off; and then a DC magnetron sputtering process was used to prepare a metal Ti layer as an electrode directly in contact with VOx. The post-implantation annealing method was pulse current rapid annealing, the annealing temperature was 275℃, the heating time was 7s, and the vacuum degree was better than 1×10 -3 The required pulse frequency is 75 Hz and the current density is 4 × 10 3 A / mm2, pulse width is 25μs. After the array is vacuum packaged, the performance is tested with a bias pulse of 5μs and 200μA at an operating temperature of 25°C. The NETD of the focal plane array device is 29mk.

[0044] Embodiment 4:

[0045] A 640×640 focal plane array bridge structure with a pixel size of 17×17um was formed on a substrate by a MEMS process. The bridge deck was a first dielectric layer SiN film with a thickness of 120nm prepared by a CVD process. Then, a VOx film with a thickness of 80nm and a square resistance of 170kΩ / port was prepared by a reactive magnetron sputtering process, with Ar and O2 as reaction gases and an oxygen-argon ratio of 3:100. Then, a second dielectric layer SiN and an ion implantation mask layer were deposited. The mask layer was patterned by a photolithography process and the energy was 450eV and the beam density was 3mA / cm 2 The mask layer and the second dielectric layer were etched by an Ar ion beam to expose the VOx electrode area; ions were implanted into the VOx electrode area with an implantation energy of 150 keV and an implantation dose of 3×10 15 The implanted element is W. After the W element is implanted, the same implant energy of 150 keV and implant dose of 3×10 15The same area is injected with Ti element to achieve W and Ti co-doping; then the ion implantation mask layer is stripped off; and then a metal Ti layer is prepared by DC magnetron sputtering process as an electrode directly in contact with VOx. The post-implantation annealing is vacuum annealing, with an annealing temperature of 275℃, a heating rate of 10℃ / min, a holding time of 30min, and a vacuum degree better than 1×10 -3 After the array was vacuum packaged, the performance was tested at an operating temperature of 25°C with a bias pulse of 5μs and 200μA. The NETD of the focal plane array device was 45mk.

[0046] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the contact between vanadium oxide and titanium electrodes in a microbolometer, It is characterized in that The method is ion implantation, and the implantation area is the contact area between vanadium oxide and titanium electrode in the microbolometer structure; The implanted elements are one or two of Ti, W, Mo, V, and Ta, with a mass ratio of 50% to 75%; the implanted dose is 6×10 15 ~9×10 16 The implantation depth is 10nm~20nm; after implantation, the structure is subjected to pulse current rapid annealing, and the vacuum degree is specified to be better than 1×10 -3 Pa, the pulse frequency is 10~100Hz, and the required current density is (4~7)×10 3 A / mm2, pulse width is 5~50μs, annealing temperature is 250~400℃, and heating time is 0.1~15s.

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