Vacuum microcavity interferometer chip, manufacturing method and ultra-high precision optical pressure sensor

Abstract

The present application relates to a vacuum microcavity interferometer chip, a manufacturing method and an ultra-high precision optical pressure sensor, comprising a first substrate having a concave cavity formed by etching the lower surface thereof, wherein when the first substrate and the second substrate are bonded, the concave cavity is formed into an F-P interference cavity, a first reflecting surface is arranged on the surface of the first substrate in the F-P interference cavity, a second reflecting surface is arranged on the surface of the second substrate in the F-P interference cavity, an annular cavity is formed on the upper surface of the third substrate, the getter film is deposited on at least one surface in the annular cavity, at least one vent is arranged on the second substrate, the vent connects the F-P interference cavity and the annular cavity; the projections of the annular cavity and the F-P interference cavity on the horizontal plane at least partially overlap.

Description

Technical Field

[0001] The present invention relates to sensors in the field of optoelectronic technology, and specifically to a wide-range vacuum microcavity interferometer chip, a manufacturing method and an ultra-high precision optical pressure sensor based on the principle of a vacuum microcavity multi-beam interferometer. The sensor is mainly used to measure the pressure of fluid media such as gas and liquid, and can also be used to measure and control flow, flow velocity, density, liquid level, altitude, contact force between objects, etc. Background Art

[0002] Pressure sensor refers to a device or apparatus that can sense the pressure signal of fluid media such as gas and liquid, and can convert the pressure signal into a usable output electrical signal or optical signal according to certain rules. Pressure sensor is the most commonly used sensor in industrial practice. It is widely used in various industrial automatic control environments such as water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military industry, petrochemical, oil wells, electricity, ships, machine tools, pipelines, etc., and is also increasingly widely used in consumer electronics fields such as medical equipment, robots and automotive electronics, smart phones, smart home appliances and wearable electronic products.

[0003] The price of pressure sensor products mainly depends on the applicable use conditions and the measurement accuracy that can be maintained for a long time. The price of industrial-grade pressure sensors with an accuracy of 0.01% in the working temperature range of -55℃ to 85℃ and pressure sensors with a temperature resistance of more than 200℃ and an accuracy of 0.1% in the whole temperature range are several thousand yuan or even tens of thousands of yuan. Pressure sensors with wide temperature range, high accuracy and high reliability have huge application demands in many fields such as nuclear power, aerospace, rail transportation, semiconductor equipment and process industry. Pressure sensors can be classified according to the detection method, such as electrical detection and optical detection pressure sensors. At present, among the electrical detection pressure sensors, resonant pressure sensors have a series of advantages such as high temperature stability, high long-term stability and high comprehensive accuracy and are widely recognized by the market. However, their use in high temperature, or radiation, electromagnetic interference and other occasions will be restricted, while optical fiber pressure sensors can meet the use requirements of the above occasions. Optical fiber sensing technology is a new technology that has developed rapidly in the late 1970s. It is the application of fiber optics in non-communication fields. Fiber optic sensing technology can measure more than one hundred physical quantities. Its advantages are: wide range of applications, high sensitivity, anti-electromagnetic interference, good insulation, corrosion resistance, flexibility, small size, low cost, and good compatibility with fiber optic transmission lines, etc.

[0004] The fiber FP (Fabry-Perot) pressure sensor is a type of fiber optic pressure sensor. It usually consists of a Fabry-Perot micro-resonant cavity formed by the fiber end face and the diaphragm end face. When pressure acts on the pressure sensitive membrane, it deforms, causing the length of the Fabry-Perot cavity to change, thereby realizing sensing measurement. The fiber optic Fabry-Perot pressure sensor has a simple structure and is relatively easy to implement. It is currently the most commonly used interference fiber optic pressure sensor. The pressure sensitive membrane of some sensors is made using the micro-electromechanical (MEMS) bulk silicon process and the surface sacrificial layer process; the pressure sensitive membrane of some sensors is made using the fiber optic corrosion fusion process. MEMS fiber optic pressure sensors combine the advantages of miniaturization, high reliability and high consistency of MEMS technology with the advantages of fiber optic signal readout technology, greatly expanding the scope of use of high-precision pressure sensors. High-precision MEMS fiber optic sensors usually use wavelength demodulation, especially the FP optical interference cavity (Fabry-Perot) interference type. Its working principle is to integrate the pressure sensitive film with the optical FP optical interference cavity. The external pressure causes the pressure sensitive film to bend, and the cavity length of the FP optical interference cavity changes synchronously, and its interference wavelength also changes. The change in wavelength is read out through the optical fiber, thereby measuring the external pressure. For details, please refer to the Chinese patent application CN201410728291.6 in the prior art, which discloses the use of the FP optical interference cavity to measure pressure. The sensor has a membrane island structure arranged in the FP optical interference cavity. The membrane island structure arranged inward increases the volume of the FP optical interference cavity, further increasing the layout area of ​​the required getter film. At the same time, the membrane island structure arranged inward is limited in height due to the limitation of the FP optical interference cavity, resulting in the optical anti-reflection film arranged thereon needing to have a high transmittance, which increases the cost of the sensitive chip; in addition, the membrane island structure arranged inward cannot be further processed after the sensitive chip is bonded and connected, and the parameters of the sensitive chip cannot be adjusted.

[0005] Since the dynamic detection resolution of the cavity length of the multi-beam FP interferometer can reach 1pm to 10pm, while the dynamic detection resolution of the cavity length of the dual-beam FP interferometer can only reach the order of 100pm to 1nm, the sensitivity of the pressure sensor can be greatly improved by constructing a multi-beam FP interferometer inside the pressure sensitive chip. However, the construction of the multi-beam FP interferometer requires the deposition of optical films to improve the optical reflectivity of the two reflection surfaces of the FP interferometer, and there are very high requirements for the parallelism and cleanliness of the two reflection surfaces in order to maintain the laser signal incident into the cavity to form hundreds of reflections between the two reflection surfaces to meet the basic conditions of multi-wavelength interference. Limited by the temperature resistance range of 500℃~600℃ of the optical film, only the silicon-glass bonding process with a temperature range of 300℃~400℃ can ensure that the optical film on the reflective surface of the multi-beam FP interferometer inside the MEMS chip remains intact. However, the gas released by the silicon-glass bonding will cause the vacuum degree of the interference cavity inside the multi-beam FP interferometer to decrease and form an unstable refractive index, which affects the low-pressure measurement range and zero-point stability of the MEMS pressure-sensitive chip, and will also increase the temperature coefficient and reduce the measurement repeatability. In order to perform high-precision pressure measurements, this type of sensor usually needs to evacuate the inside of the FP optical interference cavity, and its vacuum degree needs to be kept stable. Usually, some residual gas will remain in the cavity during the manufacturing process. Therefore, it is necessary to seal a getter in the vacuum cavity, and activate the getter during the sensor manufacturing process to absorb the residual gas in the FP optical interference cavity to achieve a high vacuum inside the pressure sensor. Chinese patent application CN20121017590.0 discloses a MEMS chip packaging structure. Usually, the getter is deposited inside the FP optical interference cavity by PVD (physical vapor deposition). To ensure that the residual gas is absorbed cleanly, the getter usually occupies a large area. Therefore, when the sensor range is increased by reducing the area of ​​the pressure sensitive membrane, it will be limited by the getter area; on the other hand, the getter is a porous structure with poor density. The getter will produce particles when heated or vibrated by the outside world, polluting the FP optical interference cavity, potentially causing spectral degradation, and having a great impact on the measurement of optical sensors, especially, and causing device failure in severe cases; the getter film arranged radially in the sensor is not conducive to the smaller radial size of the sensor, and in some specific application scenarios, a sensor chip with a smaller radial size is required so that it can be arranged in a smaller aperture.Chinese patent application CN201410264998.6 relates to a hybrid wafer-level vacuum packaging method, in which a getter cavity is provided on the side of the chip packaging cavity and is connected through a vent hole. After the getter is fixed in the getter cavity, a cover plate is fixed. This structure and method also have the potential possibility of the getter contaminating the FP optical interference cavity. In this method, the getter cavity and the getter are superimposed after the chip is formed, and the manufacturing process is complicated; and there is a certain possibility that the getter particles enter the working cavity through the vent hole channel. The getter particles have a certain insulation property, and have little effect on electrical detection sensors.

[0006] In addition, after the MEMS pressure sensitive chip and the optical fiber coupling package form a MEMS optical pressure module, it is usually necessary to perform secondary packaging and fix it on the pressure sensor housing to achieve isolation and protection from sealing pressure taking, module measurement to lead-out cable, so as to become a MEMS optical pressure sensor that can be installed and used independently. The sensitive chip structure recorded in CN201410728291.6 has the problem that during the secondary packaging process, whether the external mechanical force on the housing is transmitted to the MEMS pressure sensitive chip or to the welding and packaging part between the MEMS pressure sensitive chip and the optical fiber, the multi-beam FP interferometer will be subjected to uneven stress, causing the interference spectrum to deteriorate and causing abnormal changes in the measured value. Summary of the invention

[0007] In order to overcome the technical deficiencies of optical fiber pressure sensors in the prior art, the present invention proposes a vacuum microcavity interferometer chip, a manufacturing method and an ultra-high precision optical pressure sensor. The vacuum microcavity interferometer chip includes a first substrate, a second substrate and a third substrate. Preferably, the first substrate and the third substrate are silicon wafer substrates or silicon nitride silicon wafers or other substrates with similar functions, and the second substrate is a glass wafer or a sapphire wafer or other substrates with similar functions and high light transmittance. The three substrates are fixed by silicon-glass-silicon bonding or by bonding with corresponding dielectric layers such as BCB glue, gold layer or glass slurry. The lower surface of the first substrate is etched to form a concave cavity. When the After the first substrate and the second substrate are bonded, the concave cavity is formed into a FP interference cavity, a first reflection surface is arranged on the surface of the first substrate in the FP interference cavity, a second reflection surface is arranged on the surface of the second substrate in the FP interference cavity, an annular cavity is formed on the upper surface of the third substrate, the getter film is deposited on at least one surface in the annular cavity, at least one vent is arranged on the second substrate, the vent connects the FP interference cavity and the annular cavity; the projections of the annular cavity and the FP interference cavity on the horizontal plane at least partially overlap; the center of the third substrate is arranged with a mounting hole for the optical fiber collimator. Through the above structure, the annular cavity and the FP interference cavity are connected through the vent hole, so that the annular cavity with the getter film deposited is set separately, which ensures that the annular cavity has enough surface area to absorb the residual gas in the FP optical interference cavity; in addition, since the annular cavity and the FP interference cavity are not set on the same substrate, the projections of the annular cavity and the FP interference cavity in the structure on the horizontal plane at least partially overlap, which reduces the radial size of the vacuum microcavity interferometer chip and meets the installation requirements of special application scenarios; it also ensures that the area of ​​the pressure sensitive film in the chip with the same radial size is large enough during pressure measurement, eliminates the gas in the FP optical interference cavity, improves the accuracy of the sensor during pressure measurement, and meets the requirements of ultra-high precision pressure measurement.

[0008] Preferably, the width of the annular cavity is greater than the diameter of the vent hole, so that a small amount of particulate matter will be generated when the getter film is heated or vibrated by the outside world, and the second substrate is used to block the particulate matter to prevent the particulate matter from entering the FP interference cavity through the vent hole and contaminating the FP optical interference cavity, potentially causing spectral degradation, and having a great impact on the measurement of optical sensors, especially, and causing device failure in severe cases.

[0009] Preferably, a first accommodating space is provided in the annular cavity at a position corresponding to the vent hole. The first accommodating space is a sedimentation groove arranged at the bottom of the annular cavity, which is used to accommodate a small amount of particulate matter formed by the getter film. The depth of the first accommodating space is greater than the depth of the annular cavity, further preventing particulate matter from entering the FP interference cavity through the vent hole.

[0010] Preferably, the opening of the annular cavity is provided with a sink groove having a circular ring structure, and the sink groove and the bottom surface of the first substrate cooperate to form a second accommodating space. When the vacuum microcavity interferometer chip is in use and is subjected to vibration and / or tilt, since the diameter of the air hole is smaller than the width of the annular cavity, the particles move toward the air hole along the side wall of the first accommodating space, and are blocked by the bottom surface of the second substrate from entering the second accommodating space, thereby further preventing the particles from entering the FP interference cavity through the air hole, affecting the light beam of the FP interference cavity and causing inaccurate measurement.

[0011] Preferably, the annular cavity includes two peripheral walls and a bottom wall, and at least one peripheral wall of the annular cavity is inclined. The inclined peripheral wall makes the bottom width of the annular cavity smaller than the opening width of the annular cavity. The inclined peripheral wall increases the difference between the diameter of the vent hole and the opening width of the annular cavity, which can not only better prevent particles from entering the vent hole from the annular cavity, but also better guide the particles into the second containing space.

[0012] Preferably, the side wall of the first containing space and the two peripheral walls of the annular cavity are formed smoothly and continuously, and the smooth and continuous side wall and peripheral wall enable the particles to be directly guided to the second containing space.

[0013] Preferably, a step portion is provided on the second substrate, the diameter of the step portion is larger than the diameter of the vent hole, and the step portion is provided between the vent hole and the annular cavity. By utilizing the change in the diameter of the step portion and the vent hole, trace particles received by the first accommodating space and the second accommodating space are blocked, thereby further preventing the particles from entering the FP interference cavity.

[0014] Preferably, a film island structure is formed on the upper surface of the first substrate, the film island structure includes a protrusion formed by a countersunk hole and a pressure-sensitive film surrounding the protrusion, a first optical anti-reflection film is deposited on the surface of the protrusion, and the first optical anti-reflection film, the protrusion, the pressure-sensitive film, the first reflection surface and the second reflection surface have the same center. The upper surface of the first substrate is the pressure-facing side, and through the film island structure facing the pressure-facing side, the thickness of the protrusion can be increased, and the high refractive index of silicon in the protrusion can be used to increase the optical path, and the light passing through the first reflection surface can be attenuated, thereby reducing the process difficulty of depositing the optical anti-reflection film on the surface of the protrusion and the transmittance requirement of the optical anti-reflection film, better eliminating the interference effect of multi-interface reflected light on the FP interference cavity, so that the multi-beam FP interference cavity has more excellent spectral characteristics, and reduces the pressure monitoring noise of the vacuum microcavity interferometer chip; when using the semi-reflection demodulation method, the reflectivity of the first reflection surface is set to be non-total reflection, with a reflectivity of less than 50%, and more than 50% of the light will be reflected from the first reflection surface. The incident light is transmitted into the protrusion. When the thickness of the protrusion is small, the attenuation of the transmitted light is small. Therefore, it is necessary to set a first optical anti-reflection film with a higher transmittance, or even a first optical anti-reflection film with a transmittance of more than 99%. The process and cost of the first optical anti-reflection film are high. At the same time, the membrane island structure facing the pressure side is not only conducive to reducing the cavity volume of the FP interference cavity, thereby reducing the air therein and reducing the area of ​​the getter film; after the three-layer substrate is completed by silicon-glass-silicon bonding, the geometric dimensions of the protrusion of the membrane island structure, the pressure sensitive film and the frame located outside the pressure sensitive film can be selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip.

[0015] Preferably, the protrusion is a cylindrical structure, and the pressure-sensitive film has a circular area. This structure is conducive to achieving uniform force in fluid media such as gas and liquid, improving the chip's ability to withstand high pressure, and improving the interference spectrum stability between the two reflecting surfaces of the FP interference cavity inside the vacuum microcavity interferometer chip under pressure.

[0016] Preferably, the first substrate and the third substrate have the same diameter, and the first substrate and the third substrate have the same thickness, and the same thickness and diameter form a roughly symmetrical structure about the second substrate. Since the first substrate and the third substrate are both silicon wafers and have the same temperature coefficient, the three-layer substrate has good stress matching characteristics, which can achieve an extremely low temperature coefficient for the vacuum microcavity interferometer chip as a whole, reduce the bending deformation of the center of the vacuum microcavity interferometer chip, ensure that the two reflection surfaces of the FP optical interference cavity remain relatively parallel under the full-scale pressure, and are conducive to achieving high stability of the zero-point output of the vacuum microcavity interferometer chip through good stress matching.

[0017] Preferably, the size of the second substrate is larger than that of the first substrate and the third substrate, and the size may be the diameter or side length of the substrate, depending on the shape of the second substrate. Therefore, when the vacuum microcavity interferometer chip is used to make a sensor, the second substrate is larger than the first substrate and the third substrate to form an exposed surface for bonding or welding to the sensor housing, so that the first substrate and the third substrate and the optical fiber collimator are not in contact with the sensor housing; stress isolation is achieved between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate. Since the first substrate and the third substrate are arranged on both sides of the second substrate and have a roughly symmetrical structure, the first substrate and the third substrate will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator on the third substrate, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when impacted by external force.

[0018] The present application also relates to an ultra-high precision optical pressure sensor, comprising a sensor housing and a chip mounting seat arranged in the sensor housing, wherein the vacuum microcavity interferometer chip is fixed in contact with the chip mounting seat only through the second substrate. This structure can achieve stress isolation between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate and the sensor housing. When the sensor housing is subjected to force or vibration, it will be directly transmitted to the second substrate. Since the first substrate and the third substrate are arranged on both sides of the second substrate and have a roughly symmetrical structure, the first substrate and the third substrate will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator on the third substrate, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when subjected to external force impact.

[0019] The present application also relates to a method for manufacturing a vacuum microcavity interferometer chip, wherein the first substrate is selected to be an SOI silicon wafer (a three-layer structure of top silicon-buried oxide layer-bottom silicon); S1. A cavity is formed on one surface of the first substrate by etching and / or KOH etching process, and a first reflection surface is arranged on the surface of the first substrate of the cavity; the membrane island structure is formed by etching and / or KOH etching on another surface of the first substrate, the surface of the protruding portion is an original polished surface, having the same thickness as the frame, and a first optical anti-reflection film is deposited on the protruding portion; the formation of the membrane island structure in this step is not a necessary step, and since the membrane island structure is arranged on the upper surface of the first substrate, it can also be placed in the last step to form the membrane island structure; S2. The second substrate is a double-sided polished glass sheet, and a ventilation hole is formed by etching through the second substrate, and a second reflection surface is deposited on the surface of the second substrate at a position corresponding to the first reflection surface; a second optical anti-reflection film is deposited on the other surface of the second substrate at a position corresponding to the mounting hole; S3 . The third substrate is selected as an ultra-flat double-polished silicon wafer, on which a mounting hole for installing the optical fiber collimator is made; a countersunk hole and an annular cavity are arranged on the surface of the third substrate facing the second substrate, the area of ​​the countersunk hole is larger than the area of ​​the second optical anti-reflection film, so as to prevent the second optical anti-reflection film from affecting the bonding quality of the second substrate and the third substrate; a sink groove is formed by etching at the opening of the annular cavity; a getter film is deposited on the surface of the annular cavity; S4. The first substrate, the second substrate and the third substrate are bonded by silicon-glass-silicon three-layer bonding or dielectric layer bonding technology, and the bonding temperature is 300℃-400℃. Since thermal activation is usually required after the getter is deposited, and the activation temperature is usually above 300℃, the getter film can be activated at the same time as bonding, and there is no need to activate the getter film after the device is manufactured; the bonding temperature of silicon-glass-silicon is usually lower than 400℃, which can ensure that the optical film with a temperature resistance of more than 500℃ made by optical dielectric material deposition inside the chip is not affected.

[0020] Preferably, the method further comprises step S5, wherein after the three-layer substrate is bonded by silicon-glass-silicon, the thickness of the single crystal silicon of the protruding portion of the membrane island structure and the pressure sensitive film is measured in real time and selectively processed. The geometric dimensions of the protruding portion of the membrane island structure, the pressure sensitive film and the frame outside the pressure sensitive film are selectively processed, thereby flexibly adjusting the sensitivity of the pressure sensitive chip.

[0021] Preferably, the method further comprises step S6, after step S5, depositing a first optical anti-reflection film on the protrusion. After the size of the membrane island structure is selectively processed, the first optical anti-reflection film is deposited to reduce the influence of multi-interface reflected stray light on the FP interference cavity.

[0022] The present invention aims to provide a high-precision vacuum microcavity interferometer chip based on the principle of vacuum microcavity multi-beam interferometer, a manufacturing method and a sensor thereof. By separating a multi-beam FP interference cavity for pressure sensitivity and detection from a getter cavity in a sensitive chip and connecting the two through a vent hole, the structure can independently adjust the pressure sensitive film area and the getter area according to demand; the projections of the annular cavity and the FP interference cavity on the horizontal plane are arranged to at least partially overlap, thereby reducing the radial size of the vacuum microcavity interferometer chip, ensuring that the area of ​​the pressure sensitive film in the chip with the same radial size is large enough during pressure measurement, eliminating the gas in the FP optical interference cavity, improving the accuracy of the sensor during pressure measurement, and meeting the requirements of ultra-high precision pressure measurement; and preventing activated getter particles from entering the FP interference cavity through a corresponding structure to affect the measurement reliability of the vacuum microcavity interferometer chip; the outer dimensions of the second substrate of the MEMS vacuum microcavity interferometer chip are larger than the exposed surface formed by the first substrate and the third substrate or through the glass The protective tube is bonded or welded to the sensor housing, and the first substrate, the third substrate, and the optical fiber collimator are not connected to the sensor housing with solder or adhesive, so that stress isolation is achieved between the sensitive structure of the MEMS vacuum microcavity interferometer chip, the packaging part of the optical fiber collimator and the chip, and the pressure sensor housing; the chip adopts a three-layer bonding structure, and various structures and materials such as the pressure sensitive film, the optical FP optical interference cavity and the getter are integrated and miniaturized. The getter film is activated during the bonding process, which simplifies the manufacturing process of the sensor and does not need to consume energy to activate the getter film separately; the membrane island structure facing the pressure side is not only conducive to reducing the volume in the FP interference cavity, thereby reducing its volume and the air in it, and reducing the area of ​​the getter film; after the three-layer substrate is bonded by silicon-glass-silicon, the geometric dimensions of the raised part of the membrane island structure, the pressure sensitive film and the frame located outside the pressure sensitive film can be selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of the vacuum microcavity interferometer chip of this application;

[0024] Figure 2 This is a second structural schematic diagram of the vacuum microcavity interferometer chip of the present application;

[0025] Figure 3 This is a third structural schematic diagram of the vacuum microcavity interferometer chip of the present application;

[0026] Figure 4 A top view of the second substrate of the present application;

[0027] Figure 5 A bottom view of the second substrate of the present application;

[0028] Figure 6 A top view of the third substrate of the present application;

[0029] Figure 7 This is a schematic diagram of the structure of the ultra-high precision optical pressure sensor of this application;

[0030] Figure 8 This is a schematic diagram of the partial structure of the ultra-high precision optical pressure sensor of this application.

[0031] Description of reference numerals:

[0032] 1-first substrate; 11-FP interference cavity; 12-first reflection surface; 13-second reflection surface; 14-pressure sensitive film; 15-first optical anti-reflection film; 2-second substrate; 21-vent; 22-step portion; 23-second optical anti-reflection film; 3-third substrate; 31-annular cavity; 32-adsorbent film; 33-first accommodating space; 34-second accommodating space; 41-sensor housing; 42-chip mounting seat. DETAILED DESCRIPTION

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0035] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0036] In this document, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In order to overcome the technical deficiencies of optical fiber pressure sensors in the prior art, the present invention proposes a vacuum microcavity interferometer chip, a manufacturing method and an ultra-high precision optical pressure sensor, wherein the vacuum microcavity interferometer chip comprises a first substrate 1, a second substrate 2 and a third substrate 3, wherein the first substrate 1 and the third substrate 3 are preferably silicon wafer substrates or silicon nitride silicon wafers or other substrates with similar functions, and the second substrate 2 is a glass sheet or a sapphire sheet or other substrates with similar functions and high light transmittance, and the three substrates are fixed by silicon-glass-silicon bonding or by bonding through corresponding dielectric layers such as BCB glue, gold layer or glass slurry, etc., for specific reference Figure 1 A concave cavity is formed by etching the lower surface of the first substrate 1. When the first substrate 1 and the second substrate 2 are bonded, the concave cavity is formed into a FP interference cavity 11. A first reflection surface 12 is arranged on the surface of the first substrate 1 in the FP interference cavity 11, and a second reflection surface 13 is arranged on the surface of the second substrate 2 in the FP interference cavity 11. An annular cavity 31 is formed on the upper surface of the third substrate 3. The getter film 32 is deposited on at least one surface of the annular cavity 31. At least one vent hole 21 is arranged on the second substrate 2, and the vent hole 21 connects the FP interference cavity 11 and the annular cavity 31; the projections of the annular cavity 31 and the FP interference cavity 11 on the horizontal plane at least partially overlap; the center of the third substrate 3 is provided with a mounting hole for the optical fiber collimator. Through the above structure, the annular cavity 31 is connected to the FP interference cavity 11 through the vent hole 21, so that the annular cavity 31 deposited with the getter film 32 is set separately, which ensures that the annular cavity 31 has sufficient surface area to absorb the residual gas in the FP optical interference cavity; in addition, since the annular cavity 31 and the FP interference cavity 11 are not set on the same substrate, the projections of the annular cavity 31 and the FP interference cavity 11 in the structure on the horizontal plane at least partially overlap, which reduces the radial size of the vacuum microcavity interferometer chip and meets the installation requirements of special application scenarios; it also ensures that the area of ​​the pressure sensitive film 14 in the chip with the same radial size is large enough during pressure measurement, eliminates the gas in the FP optical interference cavity, improves the accuracy of the sensor during pressure measurement, and meets the ultra-high precision pressure measurement requirements.

[0038] In a further preferred embodiment, the width of the annular cavity 31 is greater than the diameter of the vent hole 21, so that a small amount of particulate matter will be generated when the getter film 32 is heated or vibrated by the outside world, and the second substrate 2 is used to block the particulate matter to prevent the particulate matter from entering the FP interference cavity 11 through the vent hole 21 and contaminating the FP optical interference cavity, potentially causing spectral degradation, and having a great impact on the measurement of optical sensors, especially, and even causing device failure in severe cases.

[0039] In a further preferred embodiment, the annular cavity 31 is provided with a first accommodation space 33 at a position corresponding to the vent hole 21. Figure 2 As shown in the figure, the first accommodation space 33 is a sedimentation groove arranged at the bottom of the annular cavity 31, which is used to accommodate a small amount of particles formed by the getter film 32. The depth of the first accommodation space 33 is greater than the depth of the annular cavity 31, further preventing particles from entering the FP interference cavity 11 through the vent hole 21. It can be understood that the first accommodation space 33 is a groove structure arranged on the bottom wall of the annular cavity.

[0040] In a further preferred embodiment, the opening of the annular cavity 31 is provided with a sink groove, and the sink groove has a circular ring structure. The circular ring structure can be a sink groove that only surrounds the first accommodating space 33, that is, the sink groove and the first accommodating space 33 have the same center. Figure 2 or preferably the annular structure of the sink groove may be a sink groove along the circumferential direction of the annular cavity 31 opening, such as Figure 3 , as shown in FIG6 , that is, the sink and the annular cavity 31 have a center; the latter sink has a better accommodating space, and since the getter film is arranged in a circular distribution in the annular cavity, the particles generated by it are roughly distributed in a circular distribution, which can better accommodate and collect the particles along the circumferential direction of the getter film, thereby reducing the movement of free particles; the sink and the bottom surface of the second substrate 2 cooperate to form a second accommodating space 34. When the vacuum microcavity interferometer chip is in use and is subjected to vibration and / or tilt, since the diameter of the vent 21 is smaller than the width of the annular cavity 31, the particles move toward the vent 21 along the side wall of the first accommodating space 33, and are blocked by the bottom surface of the second substrate 2 from entering the second accommodating space 34, thereby further preventing the particles from entering the FP interference cavity 11 through the vent 21, thereby contaminating the optical film of the FP interference cavity 11 and causing device failure.

[0041] In a further preferred embodiment, the annular cavity 31 includes two peripheral walls and a bottom wall, and at least one peripheral wall of the annular cavity 31 is inclined. The inclined peripheral wall makes the bottom width of the annular cavity 31 smaller than the opening width of the annular cavity 31. The inclined peripheral wall increases the difference between the diameter of the vent 21 and the opening width of the annular cavity 31, which can not only better prevent particles from entering the vent 21 from the annular cavity 31, but also better guide the particles into the second containing space 34.

[0042] In a further preferred embodiment, the side wall of the first accommodating space 33 and the two peripheral walls of the annular cavity 31 are smoothly and continuously formed, and the smooth and continuous side wall and peripheral wall enable the particles to be directly guided to the second accommodating space 34 .

[0043] In a further preferred embodiment, a step portion 22 is provided on the second substrate, and the diameter of the step portion 22 is larger than the diameter of the vent hole 21. Figure 4-5 As shown in the figure, it is arranged between the vent 21 and the annular cavity 31, and the step portion 22 and the diameter change of the vent 21 are utilized to block the trace particles received by the first accommodating space and the second accommodating space, thereby further preventing the particles from entering the FP interference cavity.

[0044] In a further preferred embodiment, a film island structure is formed on the upper surface of the first substrate 1, and the film island structure includes a protrusion formed by a countersunk hole and a pressure-sensitive film 14 surrounding the protrusion, and a first optical anti-reflection film 15 is deposited on the surface of the protrusion, and the first optical anti-reflection film 15, the protrusion, the pressure-sensitive film 14, the first reflective surface 12 and the second reflective surface 13 have the same center. The upper surface of the first substrate 1 is the pressure-facing side. Through the membrane island structure facing the pressure-facing side, the thickness of the protrusion can be increased, and the high refractive index of silicon in the protrusion can be used to increase the optical path, so that the light passing through the first reflecting surface 12 is attenuated, thereby reducing the process difficulty of depositing the optical anti-reflection film on the surface of the protrusion and the transmittance of the optical anti-reflection film, and better eliminating the interference effect of multi-interface reflected light on the FP interference cavity 11, so that the multi-beam FP interference cavity 11 has more excellent spectral characteristics, and reduces the pressure monitoring interference of the vacuum microcavity interferometer chip; when using a semi-reflection demodulation method, the reflectivity of the first reflecting surface 12 is set to be non-total reflection, with a reflectivity of less than 50%, and more than 50% of the light will be reflected from the first reflecting surface 1 2 is transmitted into the protrusion. When the thickness of the protrusion is small, the attenuation of the transmitted light is small. Therefore, it is necessary to set a first optical anti-reflection film 15 with a higher transmittance, or even a first optical anti-reflection film 15 with a transmittance of 99%. The process and cost requirements of the first optical anti-reflection film 15 are high. At the same time, the membrane island structure facing the pressure side is not only conducive to reducing the volume in the FP interference cavity 11, thereby reducing the air therein and reducing the area of ​​the getter film 32; after the three-layer substrate is completed by silicon-glass-silicon bonding, the geometric dimensions of the protrusion of the membrane island structure, the pressure sensitive film 14 and the frame located outside the pressure sensitive film 14 can be selectively processed, so as to flexibly adjust the sensitivity of the vacuum microcavity interferometer chip.

[0045] In a preferred embodiment, the protrusion is a cylindrical structure, and the pressure sensitive film 14 has a circular area. This structure is conducive to achieving uniform force in fluid media such as gas and liquid, thereby improving the chip's ability to withstand high pressure and improving the interference spectrum stability between the two reflecting surfaces of the FP interference cavity 11 inside the vacuum microcavity interferometer chip under pressure.

[0046] In a preferred embodiment, the first substrate 1 and the third substrate 3 have the same diameter, and the first substrate 1 and the third substrate 3 have the same thickness, and the same thickness and diameter form a substantially symmetrical structure with respect to the second substrate 2, with specific reference to Figure 3As shown in the figure, since the first substrate 1 and the third substrate 3 are both silicon wafers with the same temperature coefficient, the three-layer substrate has good stress matching characteristics, which can achieve an extremely low temperature coefficient for the vacuum microcavity interferometer chip as a whole, reduce the bending deformation of the center of the vacuum microcavity interferometer chip, and ensure that the two reflection surfaces of the FP optical interference cavity remain relatively parallel under the full-scale pressure, which is conducive to achieving high stability of the zero-point output of the vacuum microcavity interferometer chip through good stress matching.

[0047] In a preferred embodiment, the size of the second substrate 2 is larger than the first substrate 1 and the third substrate 3. Therefore, when the vacuum microcavity interferometer chip is used to make a sensor, the second substrate 2 is larger than the first substrate 1 and the third substrate 3 to form an exposed surface to be bonded or welded to the sensor housing 41, so that the first substrate 1 and the third substrate 3 and the optical fiber collimator are not in contact with the sensor housing 41; stress isolation is achieved between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate 3 and the sensor housing 41. When the sensor housing 41 is subjected to force or vibration, it will be directly transmitted to the second substrate 2. Since the first substrate 1 and the third substrate 3 are arranged on both sides of the second substrate 2 with a roughly symmetrical structure, the first substrate 1 and the third substrate 3 will vibrate as a whole, and no stress will be applied to the membrane island structure and the optical fiber collimator on the third substrate 3, thereby ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when subjected to external force impact.

[0048] The present application also relates to an ultra-high precision optical pressure sensor, comprising a sensor housing 41 and a chip mounting seat 42 disposed in the sensor housing 41. Figure 7-8 As shown in , the vacuum microcavity interferometer chip is fixed in contact with the chip mounting seat 42 only through the second substrate 2. This structure can achieve stress isolation between the membrane island structure of the vacuum microcavity interferometer chip, the optical fiber collimator on the third substrate 3 and the sensor housing 41. When the sensor housing 41 is subjected to force or vibration, it will be directly transmitted to the second substrate 2. Since the first substrate 1 and the third substrate 3 are arranged on both sides of the second substrate 2 and have a roughly symmetrical structure, the first substrate 1 and the third substrate 3 will vibrate as a whole, and will not apply stress to the membrane island structure and the optical fiber collimator on the third substrate 3, ensuring that the zero-point output of the vacuum microcavity interferometer chip does not change before and after mechanical fastening and installation on site or when impacted by external force.

[0049] The present application also relates to a method for manufacturing a vacuum microcavity interferometer chip, wherein the first substrate 1 is selected to be an SOI silicon wafer (a three-layer structure of top silicon-buried oxide layer-bottom silicon); S1. A cavity is formed on one surface of the first substrate 1 by etching and / or KOH etching process, and a first reflection surface 12 is arranged on the surface of the first substrate 1 of the cavity; the membrane island structure is formed by etching and / or KOH etching on another surface of the first substrate 1, the surface of the protruding portion is an original polished surface, having the same thickness as the frame, and a first optical anti-reflection film 15 is deposited on the protruding portion; the formation of the membrane island structure in this step is not a necessary step, and since the membrane island structure is arranged on the upper surface of the first substrate 1, it can also be placed in the last step to form the membrane island structure; S2. The second substrate 2 is a double-sided polished glass sheet, and a vent hole 21 is formed by etching through the second substrate 2, and a second reflection surface 13 is deposited on the surface of the second substrate 2 at a position corresponding to the first reflection surface 12; a second optical anti-reflection film 23 is deposited on the other surface of the second substrate 2 at a position corresponding to the mounting hole; S3. The third substrate 3 is selected to be an ultra-flat double-polished silicon A sheet is formed on which a mounting hole for mounting the optical fiber collimator is made; a countersunk hole and an annular cavity 31 are arranged on the surface of the third substrate 3 facing the second substrate 2, and the area of ​​the countersunk hole is larger than the area of ​​the second optical anti-reflection film 23 to prevent the second optical anti-reflection film 23 from affecting the bonding quality of the second substrate 2 and the third substrate 3; a sink groove is formed by etching the opening of the annular cavity 31; a getter film 32 is deposited on the surface of the annular cavity 31; it can be understood that steps S1-S3 have no sequential relationship; S4. Through the silicon-glass-silicon three-layer bonding technology The first substrate 1, the second substrate 2, and the third substrate 3 are bonded at a bonding temperature of 300°C-400°C. Since the getter usually needs to be thermally activated after deposition, and the activation temperature is usually above 300°C, the activation of the getter film 32 can be completed at the same time as bonding, and there is no need to activate the getter film 32 after the device is manufactured. The bonding temperature of silicon-glass-silicon or the bonding using a dielectric layer is usually lower than 400°C, which can ensure that the optical film with a temperature resistance of more than 500°C made by depositing optical dielectric materials inside the chip is not affected.

[0050] A further preferred embodiment further includes step S5, after the three-layer substrate bonding is completed, the thickness of the single crystal silicon of the protruding portion of the membrane island structure and the pressure sensitive film 14 is measured in real time and selectively processed and controlled. The geometric dimensions of the protruding portion of the membrane island structure, the pressure sensitive film 14 and the frame located outside the pressure sensitive film 14 are selectively processed, so as to flexibly adjust the sensitivity of the pressure sensitive chip.

[0051] Preferably, the method further comprises step S6, after step S5, depositing a first optical anti-reflection film on the protrusion. After the size of the membrane island structure is selectively processed, the first optical anti-reflection film is deposited to reduce the influence of multi-interface reflected stray light on the FP interference cavity.

Claims

1. A vacuum microcavity interferometer chip, comprising a first substrate, a second substrate and a third substrate, wherein the three substrates are bonded and fixed; characterized in that: A film island structure is formed on the upper surface of the first substrate, a concave cavity is formed by etching the lower surface of the first substrate, when the first substrate and the second substrate are bonded, the concave cavity forms an FP interference cavity, a first reflection surface is arranged on the surface of the first substrate in the FP interference cavity, a second reflection surface is arranged on the surface of the second substrate in the FP interference cavity, an annular cavity is formed on the third substrate, a getter film is deposited on at least one surface in the annular cavity, at least one vent hole is arranged on the second substrate, the vent hole connects the FP interference cavity and the annular cavity; the projections of the annular cavity and the FP interference cavity on the horizontal plane at least partially overlap; The center of the third substrate is provided with a mounting hole for the optical fiber collimator; the second substrate is provided with a step portion, the diameter of the step portion is larger than the diameter of the vent hole, and the step portion is provided between the vent hole and the annular cavity.

2. The vacuum microcavity interferometer chip according to claim 1, characterized in that: The width of the annular cavity is greater than the diameter of the vent hole.

3. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The annular cavity is provided with a first accommodating space at a position corresponding to the vent hole. The first accommodating space is a sedimentation groove arranged at the bottom of the annular cavity for accommodating particles formed by the getter film. The depth of the first accommodating space is greater than the depth of the annular cavity.

4. The vacuum microcavity interferometer chip according to claim 2, characterized in that: The opening of the annular cavity is provided with a sinking groove having a circular ring structure, and the sinking groove cooperates with the bottom surface of the first base to form a second accommodating space.

5. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The annular cavity includes two peripheral walls and a bottom wall. At least one peripheral wall of the annular cavity is inclined. The inclined peripheral wall makes the bottom width of the annular cavity smaller than the opening width of the annular cavity. The inclined peripheral wall increases the difference between the diameter of the vent hole and the opening width of the annular cavity.

6. The vacuum microcavity interferometer chip according to claim 5, characterized in that: It also includes a second accommodating space arranged on the third base, and a first accommodating space is arranged at the position of the annular cavity corresponding to the vent hole, and the side wall of the first accommodating space and the two peripheral walls of the annular cavity are smoothly and continuously formed, and the smooth and continuous side wall and peripheral wall allow the particles to be directly guided to the second accommodating space.

7. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: A membrane island structure is formed on the upper surface of the first substrate, and the membrane island structure includes a protrusion formed by a countersunk hole and a pressure-sensitive film surrounding the protrusion, and a first optical anti-reflection film is deposited on the surface of the protrusion, and the first optical anti-reflection film, the protrusion, the pressure-sensitive film, the first reflective surface and the second reflective surface have the same center.

8. The vacuum microcavity interferometer chip according to claim 7, characterized in that: The protrusion is a cylindrical structure, and the pressure sensitive film has a circular area.

9. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The first substrate and the third substrate have the same diameter, and the first substrate and the third substrate have the same thickness.

10. The vacuum microcavity interferometer chip according to claim 1 or 2, characterized in that: The second substrate has a size larger than that of the first substrate and the third substrate.

11. An ultra-high precision optical pressure sensor comprising a vacuum microcavity interferometer chip according to any one of claims 1 to 10, characterized in that: The invention comprises a sensor housing and a chip mounting seat arranged in the sensor housing, wherein the vacuum microcavity interferometer chip is contacted and fixed with the chip mounting seat only through the second substrate.

12. A method for manufacturing a vacuum microcavity interferometer chip according to any one of claims 1 to 10, comprising: S1. A concave cavity is formed on a surface of a first substrate by etching and / or KOH etching process, and a first reflective surface is provided on the surface of the first substrate of the concave cavity; Etching and / or KOH etching on another surface of the first substrate to form the membrane island structure, wherein the membrane island structure includes a protrusion formed by a countersink and a pressure-sensitive film surrounding the protrusion; S2. A vent hole is formed by etching through the second substrate, and a second reflective surface is deposited at a position on the surface of the second substrate corresponding to the first reflective surface; a second optical anti-reflection film is deposited at a position on the other surface of the second substrate corresponding to the mounting hole; S3. A mounting hole for mounting the optical fiber collimator is made on the third substrate; an annular cavity is provided on the surface of the third substrate facing the second substrate, and a sink groove is formed by etching at the opening of the annular cavity; a getter film is deposited on the surface of the annular cavity; S4. Bonding the first substrate, the second substrate, and the third substrate by three-layer bonding at a bonding temperature of 300° C.-400° C.

13. The manufacturing method according to claim 12, characterized in that: The method further comprises step S5, wherein after the three-layer substrate bonding is completed, the thickness of the protruding portion of the membrane island structure and the pressure sensitive film are measured in real time and selectively processed and controlled.

14. The manufacturing method according to claim 13, characterized in that: The method further comprises step S6, after completing step S5, depositing a first optical anti-reflection film on the protruding portion.

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