A micro atomic gas chamber with inner wall protective layer and preparation method thereof

Abstract

The present invention discloses a micro-atomic gas chamber with an inner wall protective layer and a preparation method thereof: the structure of the micro-atomic gas chamber comprises: a second glass layer, a silicon substrate with a through-hole structure, and a first glass layer arranged in sequence from top to bottom; the through-hole structure, the first glass layer, and the second glass layer constitute a micro-atomic gas chamber; the inner surface of the micro-atomic gas chamber is completely covered by the protective layer, and the alkali metal is encapsulated in the micro-atomic gas chamber by the protective layer. Among them, in the micro-atomic gas chamber provided by the present invention, the protective layer only exists on the inner wall of the atomic gas chamber, and there is no interface between the glass and the silicon substrate, which will not affect the atomic gas chamber bonding process interface, and is conducive to achieving high strength and high airtightness of the micro-atomic gas chamber; and the alkali metal is encapsulated in the atomic gas chamber by the protective layer, preventing the alkali metal atoms from diffusing into the inner wall or chemically reacting with the inner wall material, thereby improving the life of the micro-atomic gas chamber.

Description

Technical Field

[0001] The present invention relates to the field of vacuum electronics technology, and more particularly to a micro atomic gas chamber with an inner wall protective layer and a preparation method thereof. Background Art

[0002] Currently, the preparation of miniaturized atomic gas chambers generally adopts the standard micro-electromechanical system (MEMS) process: photolithography, wet or dry etching are used to form a silicon wafer cavity structure, which is filled with alkali metal atoms, and then anodic bonding is used to achieve glass-silicon cavity-glass packaging. A major technical challenge for the practical application of MEMS technology to prepare alkali metal atomic gas chambers is to maintain a sufficient amount of alkali metal vapor inside the atomic gas chamber during its working life. Due to the overall reduction in volume, the alkali metal filling amount of MEMS micro gas chambers is also greatly reduced compared to traditional atomic gas chambers, and these alkali metals will continue to be consumed as the device works. Once the gradually consumed alkali metal is insufficient to maintain the saturated vapor pressure inside the gas chamber, it will significantly affect the working performance of the atomic gas chamber or may cause the device to fail. Research shows that there are two reasons for the gradual decrease of alkali metals in micro-machined atomic gas chambers: one is the direct diffusion and escape of atoms into the inner wall layer of the gas chamber; the other is the consumption of alkali metals by chemical reactions with the inner wall material of the gas chamber. Specifically, the anodic bonding technology for preparing atomic gas chambers requires the use of borosilicate glass and silicon wafers rich in sodium ions as the wall materials. In addition to diffusing and disappearing into the glass, alkali metals can also easily undergo substitution reactions with sodium oxide in the borosilicate glass, resulting in a reduction in their number.

[0003] Applying a protective layer to the inner wall of the atomic chamber, physically isolating the alkali metal from the chamber material, is an effective means of preventing alkali metal depletion within the chamber. In theory, oxides are well suited for forming dense thin films, and many oxides have Gibbs free energies greater than those of alkali metal oxides, making them less reactive with alkali metals and therefore suitable for use as protective layer materials.

[0004] Existing literature discloses methods that use MEMS technology to create a protective layer on the inner wall of an atomic gas chamber, effectively increasing the resistance of the gas chamber wall to alkali metal atoms by 100 times, which is expected to significantly increase the lifespan of the alkali metal atomic gas chamber. However, these literature methods for preparing protective layers have two major drawbacks that hinder further improvement in the quality and lifespan of the atomic gas chamber. First, the use of atomic layer and molecular layer deposition methods requires matching suitable material precursors, which greatly limits the types of protective layer materials that can be used. Second, this method does not, and is not suitable for, patterning the protective layer, which will result in the presence of a protective layer between the upper glass and silicon substrate bonding interface. This intermediate protective layer seriously affects the effect of anodic bonding, eliminating many potential protective layer materials (the presence of this material at the anodic bonding interface will cause bonding failure). As a result, the protective layer of the existing literature methods can only use aluminum oxide materials, and the resulting atomic gas chamber, due to the presence of the aluminum oxide intermediate layer, has doubts about the bonding strength and airtightness, which will still affect the long-term application of the device.

[0005] Therefore, whether from the perspective of scientific research or practical application, there is an urgent need for a practical and reliable micro-atomic gas chamber preparation process to achieve high-strength bonding and high-quality airtight performance of the atomic gas chamber. Summary of the Invention

[0006] In light of the above-mentioned problems, one object of the present invention is to provide a method for fabricating a micro-atomic gas cell with an inner wall protective layer. This method can be used with a variety of protective layer materials, and the protective layer can be patterned. The inner wall protective layer of the resulting micro-atomic gas cell exists only on the inner surface of the gas cell, effectively preventing contact between alkali metals and the gas cell wall while not affecting the gas cell's bonding interface.

[0007] Another object of the present invention is to provide a micro atomic gas chamber with an inner wall protective layer.

[0008] To achieve the first objective, the present invention provides a method for preparing a micro atomic gas chamber structure having an inner wall protective layer, comprising the following steps:

[0009] 1) Providing a silicon substrate with a through-hole structure;

[0010] 2) performing anodic bonding on the lower surface of the silicon substrate and the first glass layer, so that the through-hole structure and the first glass layer form a bearing cavity;

[0011] 3) depositing a sacrificial layer on the upper surface of the silicon substrate and on the upper edge of the sidewall of the through-hole structure; then depositing a protective layer on the surface of the sacrificial layer and on the inner surface of the bearing cavity; wherein the height of the upper edge of the sidewall does not exceed the thickness of the protective layer;

[0012] 4) removing the sacrificial layer and the protective layer on the surface of the sacrificial layer by etching;

[0013] 5) filling the carrying cavity including the protective layer with an alkali metal;

[0014] 6) forming a patterned protective layer on the surface of the second glass layer so that the patterned protective layer corresponds to the lower surface of the bearing cavity;

[0015] 7) Anodically bonding the upper surface of the silicon substrate and the second glass layer so that the protective layer and the patterned protective layer completely cover the inner wall surface of the atomic chamber.

[0016] Preferably, the primary anodic bonding is performed in a vacuum environment under the conditions of a bonding voltage of 200V-1200V, a bonding temperature of 200°C-500°C, and a bonding pressure of 1000N-1500N.

[0017] Preferably, the secondary anodic bonding is performed in a vacuum environment at a bonding voltage of 200V-800V, a bonding temperature of 200°C-300°C, and a bonding pressure of 1500N-2000N.

[0018] Preferably, the first glass layer and the second glass layer are made of borosilicate glass, preferably Corning Pyrex7740 glass or Schott BF33 glass.

[0019] Preferably, the thickness of the first glass layer or the second glass layer is in the range of 200 μm to 500 μm.

[0020] Preferably, the silicon substrate is a double-sided polished P-type doped silicon wafer.

[0021] Preferably, the thickness of the silicon substrate is in the range of 1 mm to 5 mm.

[0022] Preferably, the protective layer and the patterned protective layer are made of the same material, which is selected from one of boron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, calcium oxide, and silicon nitride.

[0023] Preferably, the protective layer and the patterned protective layer are the same, and have a thickness in the range of 10 nm to 20 nm.

[0024] Preferably, the filling amount of the alkali metal is in the range of 1 μg-50 μg.

[0025] To achieve the above-mentioned second purpose, the present invention provides a micro-atomic gas chamber with an inner wall protective layer, whose structure includes: a second glass layer, a silicon substrate with a through-hole structure, and a second glass layer arranged in sequence from top to bottom; the through-hole structure, the first glass layer, and the second glass layer constitute a micro-atomic gas chamber; the inner surface of the micro-atomic gas chamber is completely covered by the protective layer, and the alkali metal is isolated inside the micro-atomic gas chamber by the protective layer.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The preparation method provided by the present invention is universal and applicable to a variety of protective layer materials. Moreover, the preparation method is fully compatible with MEMS and microelectronic processes, can reliably realize the batch production of atomic gas chambers, and the process flow is simple, easy to implement, and highly operable.

[0028] 2. The inner wall protective layer of the micro atomic gas chamber provided by the present invention can avoid direct contact between alkali metals and the inner wall of the atomic gas chamber, preventing the number of alkali metal atoms from being reduced due to diffusion into the inner wall or chemical reaction with the inner wall material, thereby improving the life of the atomic gas chamber.

[0029] 3. The protective layer of the micro atomic gas chamber provided by the present invention can be patterned and only exists on the inner surface of the gas chamber, which does not affect the atomic gas chamber bonding process interface and is conducive to achieving a high-strength and high-airtightness atomic gas chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] Figure 1 The present invention provides a micro atomic gas chamber structure with an inner wall protection layer.

[0032] Figures 2a to 2h The present invention provides a preparation flow chart of a micro atomic gas chamber with an inner wall protection layer.

[0033] Figure 3 A micrograph of the surface of the aluminum oxide protective layer prepared in Example 1 of the present invention is shown.

[0034] Figure 4 The micro atomic gas cell array prepared in Example 1 of the present invention is shown.

[0035] Figure 5 A single micro atomic gas chamber prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0036] In order to explain the present invention more clearly, the present invention will be further described below with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and values ​​described in these embodiments do not limit the scope of the present invention.

[0037] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0038] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

[0039] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0040] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0041] In view of the limited materials that can be matched with the protective layer of the micro atomic gas chamber in the prior art, the existence of the atomic gas chamber bonding surface in the protective layer, which affects the bonding quality and leads to low bonding strength and poor airtightness, the main purpose of the present invention is to provide a method for preparing a micro atomic gas chamber with an inner wall protective layer, wherein the micro atomic gas chamber is as follows Figure 1 As shown, the preparation method specifically comprises the following steps:

[0042] 1) Providing a silicon substrate 11 having a through-hole structure 12;

[0043] 2) performing anodic bonding on the lower surface of the silicon substrate and the first glass layer 13, so that the through-hole structure 12 and the first glass layer 13 form a bearing cavity;

[0044] 3) depositing a sacrificial layer 14 on the upper surface of the silicon substrate and on the upper edge of the sidewall of the through-hole structure 12; then depositing a protective layer 15 on the surface of the sacrificial layer 14 and the inner surface of the bearing cavity; wherein the height of the upper edge of the sidewall does not exceed the thickness of the protective layer;

[0045] 4) etching and removing the sacrificial layer 14 and the protective layer on the surface of the sacrificial layer;

[0046] 5) filling the carrier cavity including the protective layer with an alkali metal 17;

[0047] 6) forming a patterned protective layer 19 on the surface of the second glass layer 18 so that the patterned protective layer corresponds to the lower surface of the bearing cavity;

[0048] 7) Anodically bonding the upper surface of the silicon substrate to the second glass layer 18 so that the protective layer 15 and the patterned protective layer 19 completely cover the inner wall surface of the atomic chamber.

[0049] In the present invention, protective layer 15 and protective layer 19 are integrated, completely covering the inner wall of the micro-atomic chamber. Furthermore, the protective layer is absent from the interface between the second glass layer 18 and the silicon substrate 11, or the interface between the first glass layer 13 and the silicon substrate 11. This means that there is no excess material at the bonding surface between the silicon wafer and the glass, resulting in a micro-atomic chamber with superior bonding strength and airtightness.

[0050] It should be noted that the requirements for the protective layer 15 and the protective layer 19 are, first, that they are easy to form a uniform and dense thin film; second, that the protective layer itself does not react with the alkali metal 17, that is, the Gibbs free energy value of the protective layer material must be greater than that of the alkali metal 17 oxide. The alkali metal 17 includes, but is not limited to, metals such as cesium and rubidium commonly used in atomic gas chambers. In a preferred embodiment, the alkali metal 17 oxide is cesium oxide, which has a Gibbs free energy value of 326.4 kJ / mol. The materials for the protective layer 15 and the protective layer 19 include, but are not limited to, boron oxide (1181.1 kJ / mol), aluminum oxide (1576.5 kJ / mol), titanium oxide (889.1 kJ / mol), magnesium oxide (559.4 kJ / mol), zirconium oxide (1094.0 kJ / mol), calcium oxide (604.2 kJ / mol), silicon nitride (642.6 kJ / mol), etc.

[0051] The thickness of the protective layer 15 and the protective layer 19 is selected based on two principles: a certain lower thickness limit must be maintained to form a continuous thin film; and a certain upper thickness limit is set to ensure the light transmittance of the glass layer. In the present invention, a conventional vacuum coating method is used to obtain a continuous thin film, and its lower thickness limit is close to 10nm. The light transmittance of the film is related to the material properties and the thickness of the film layer. As shown in a preferred example, a surface-attached aluminum oxide film with a thickness of 22nm has almost no effect on the light transmittance of borosilicate glass, while a titanium oxide layer with a thickness of 20nm slightly reduces the light transmittance of borosilicate glass from 93% to 87%. Taking the above factors into consideration, in a preferred embodiment of the present invention, the thickness of the protective layer 15 and the protective layer 19 is in the range of 10-20nm.

[0052] The filling amount of the alkali metal 17 is selected based on 100,000 times the amount of alkali metal required to reach the saturated vapor pressure at the atomic chamber operating temperature. In a preferred embodiment, for an atomic chamber with a volume of 2 mm × 2 mm × 1 mm, the required amount of alkali metal cesium operating at 80°C is calculated based on the ideal gas state equation. Taking into account the atomic chamber volume and the type of alkali metal in this embodiment, the filling amount of the alkali metal 17 is preferably within the range of 1-50 μg.

[0053] The thickness of the first or second glass layer is selected based on two considerations: sufficient thickness to ensure mechanical support for the atomic vapor chamber and prevent breakage during the bonding process; and thinness to reduce power consumption due to thermal dissipation during operation. Taking all these factors into consideration, the preferred thickness is between 200 and 500 μm. The first and second glass layers can be of equal or different thicknesses, but are preferably identical.

[0054] Furthermore, the present invention is now combined with Figures 2a-2h To elaborate on the above steps:

[0055] In step 1), the through-hole structure 12 is obtained by photolithography and etching process on the silicon substrate 11, such as Figure 2a shown.

[0056] Silicon wafer through-hole etching is a standard semiconductor micromachining technique, achieved through photolithography and silicon etching. Silicon etching can be performed using two methods: a potassium hydroxide solution wet etching process and a deep reactive ion dry etching process. In one example, a 20% potassium hydroxide solution was used to etch the silicon substrate at 85°C, using silicon nitride as a masking layer. To minimize the impact of sidewall tilt, a double-sided etching method was employed. In another example, sulfur hexafluoride and octafluorocyclobutane were used as the etching and shielding gases, respectively, for dry etching of the silicon substrate, using a commercial AZ4620 positive photoresist as a masking layer.

[0057] The silicon substrate is preferably a double-sided polished P-type doped silicon wafer. The carriers in the P-type doped silicon wafer are mostly holes rather than electrons, which is more conducive to forming electrostatic force between the depletion layer. The requirement for double-sided polishing is that the upper and lower surfaces of the silicon substrate need to be bonded to the first glass layer and the second glass layer respectively, and the polished surface is very necessary for the bonding process.

[0058] The thickness of the silicon substrate determines the height of the silicon substrate through-hole structure, and the height value of the through-hole structure basically determines the longitudinal length of the atomic gas chamber. According to the longitudinal length range of the corresponding micro atomic gas chamber required in different application scenarios, the thickness of the silicon substrate is preferably in the range of 1-5mm.

[0059] The shape of the through-hole structure determines the shape of the micro atomic gas chamber, and the actual atomic gas chamber basically requires an axisymmetric structure, with no special requirements for the specific shape. Combined with the convenience of conventional silicon wafer through-hole micromachining technology, the shape of the silicon substrate through-hole structure can be selected from a circle, a square, and other regular polygons. According to the requirements of the corresponding atomic gas chamber volume in different application scenarios and the height of the through-hole structure, the diameter, side length, and diagonal length of the through-hole structure are preferably within the range of 1-5 mm.

[0060] In step 2), the silicon substrate 11 with the through-hole structure 12 and the first glass layer 13 are bonded by anodic bonding, and the through-hole structure 12 and the first glass layer 13 form a bearing cavity structure, such as Figure 2b shown.

[0061] Among them, the anodic bonding process is one of the most important modern MEMS packaging technologies. It can realize micro-air chambers with high strength and high airtightness packaging. Its main applicable materials are borosilicate glass and silicon wafers. It mainly uses high pressure, high temperature and electric field to cause the sodium ions in the glass to migrate and move, generating electrostatic force and chemical bonds at the interface between the glass and silicon wafer. In one example, the anodic bonding equipment uses the SUSS SB6 bonder. The first glass layer uses Schott BF33 glass. In a vacuum environment, the bonding voltage range is 200-1200V, the bonding temperature range is 200-500℃, and the bonding pressure range is 1000-1500N.

[0062] In step 3), a sacrificial layer 14 is deposited only on the upper surface of the silicon substrate 11 and the upper edge of the through-hole structure 12 by using a surface low-angle vacuum coating method. Figure 2c At the same time, a large-angle vacuum coating method is used to form a protective layer 15 and a redundant protective layer 16 on the inner surface of the bearing cavity and the surface of the sacrificial layer 14, as shown. Figure 2d shown.

[0063] The purpose of making the sacrificial layer is to pattern the protective layer material formed subsequently by a sacrificial layer peeling technique, so that the protective layer remains only on the surface of the bearing cavity formed by the through-hole structure and the first glass layer.

[0064] To deposit a sacrificial layer on the edge of the through-hole structure, the silicon substrate and first glass layer can be rotated perpendicular to the normal direction, while simultaneously depositing the film with a parallel beam at a very small angle on the surface, using the "line of sight" deposition principle. In one example, the parallel beam is generated by an electron beam evaporation source, with the angle controlled between 0 and 5 degrees depending on the size of the silicon via. The thickness of the sacrificial layer ranges from 20 to 50 nm, and the height of the sacrificial layer covering the silicon via generally does not exceed the thickness of the protective layer formed later.

[0065] Furthermore, to achieve a fully covered protective layer on the inner surface of the cavity, vacuum coating utilizes a "line-of-sight" deposition principle by rotating the substrate while maintaining a parallel coating beam incident at an oblique angle. In one example, the protective layer material is aluminum oxide, and the parallel beam is generated using an electron beam evaporation source. The inclination angle is adjusted based on the height and lateral dimensions of the through-hole structure, and a control range of 30-60 degrees produces a uniform film layer. The thickness of the cavity protective layer and redundant protective layer ranges from 10-20nm.

[0066] In step 4), the sacrificial layer 14 is removed by etching, and the redundant protective layer 16 on the surface of the sacrificial layer 14 is removed, leaving only the protective layer 15 in the bearing cavity. Figure 2e shown.

[0067] The purpose of this step is to pattern the formed protective layer, leaving a protective layer in the carrier cavity to isolate the alkali metal filled subsequently; at the same time, a clean upper surface of the silicon substrate is obtained, which can be subsequently bonded with the second glass layer with high quality.

[0068] It is understood that the materials of the sacrificial layer, the silicon substrate, the first glass layer, the second glass layer, and the protective layer all need to be corrosion-resistant to prevent damage to the air chamber structure during the corrosion and stripping process. In one example, the sacrificial layer is made of metal materials compatible with micromachining technology, including but not limited to aluminum and copper. In another specific example, the sacrificial layer is made of metallic aluminum with a thickness of 40nm; the protective layer is made of aluminum oxide with a thickness of 20nm; and the etching solution is 20% HCl. This etching solution can effectively dissolve the sacrificial layer and strip the redundant protective layer without damaging the bearing cavity structure or the internal protective layer.

[0069] In step 5), the alkali metal 17 is filled in the bearing cavity including the protective layer 15, such as Figure 2f shown.

[0070] Methods for filling the atomic gas chamber with alkali metals include direct filling with liquid alkali metals and filling with liquid alkali metals via chemical reaction. In one example, a pipette is used to directly transfer metallic cesium droplets into the gas chamber's carrier cavity. In another example, the carrier cavity is filled with cesium azide particles, and after the gas chamber is sealed, the entire chamber is heated to 300°C to decompose the cesium azide into metallic cesium and nitrogen.

[0071] In step 6), a patterned protective layer 19 is formed on the surface of the second glass layer 18 by photolithography, vacuum coating and stripping processes, such as Figure 2g shown.

[0072] It can be understood that the length of the long side of the patterned protection layer should be consistent with the length of the long side of the inner surface of the bearing cavity.

[0073] Furthermore, the stripping process, which uses photoresist as a sacrificial layer, is a standard process in modern micromachining. It can easily pattern many thin film materials without requiring specialized etching solutions. In one example, the photoresist used was commercial Shipley 1813 photoresist with a thickness of 1.4μm. The developer and stripper used were MF319 and N-methylpyrrolidone (NMP), respectively. The upper cover plate protective layer 19 was made of aluminum oxide with a thickness of 20nm. The height difference between the photoresist and the protective layer makes the stripping process relatively simple.

[0074] In step 7), the combination of the second glass layer 18, the silicon substrate 11 and the first glass layer 13 is aligned and integrated by anodic bonding to obtain an atomic gas chamber with an inner wall protective layer, such as Figure 2h shown.

[0075] The alignment required in this step is essentially to strictly align the patterned protective layer and the through-hole structure, so that the patterned protective layer will not affect the anodic bonding process of the second glass layer and the silicon substrate; and after bonding, the patterned plate protective layer and the protective layer in the carrier cavity together form a complete atomic gas chamber inner wall protective layer inside the carrier cavity.

[0076] In addition, since the alkali metal 17 that is not resistant to high temperatures already exists in the carrier cavity in this step, and the atomic gas chamber requires the sealing of a buffer gas at a certain pressure, the bonding process needs to be changed accordingly. The general principle is to use a lower bonding temperature, a lower bonding voltage, and a higher bonding pressure. In one example, the anode bonding equipment uses the SUSS SB6 bonding machine, the upper glass 18 uses Schott BF33 glass, the bonding voltage range is 200-800V, the bonding temperature range is 200-300°C, and the bonding pressure range is 1500-2000N. In addition, since the silicon substrate has been covered by the first glass layer during bonding and cannot directly contact the bonding electrode, it is necessary to lead out an electrical lead from the side of the silicon substrate to connect to the electrode plate of the bonding equipment.

[0077] Another object of the present invention is to provide a micro atomic gas chamber structure having an inner wall protective layer obtained by the above method, such as Figure 1 As shown, its structure includes: a second glass layer 18, a silicon substrate 11 with a through-hole structure 12, and a first glass layer 13 arranged in sequence from top to bottom, wherein the through-hole structure 12, the first glass layer 13 and the second glass layer 18 constitute a micro-atomic gas chamber; the inner surface of the micro-atomic gas chamber is completely covered by a protective layer, and the alkali metal 17 is isolated inside the micro-atomic gas chamber by the protective layer.

[0078] It can be understood that the inner surface of the micro atomic chamber is completely covered by the protective layer (including the protective layer 15 and the protective layer 19 ), and the alkali metal 17 is placed inside the atomic chamber and does not contact the second glass layer 18 , the first glass layer 13 and the silicon substrate 11 .

[0079] The following is explained with reference to specific embodiments:

[0080] Example 1

[0081] A micro atomic gas chamber with an inner wall protective layer, the structure of which is as follows Figure 1 As shown, its structure includes a second glass layer 18, a silicon substrate 11 and a first glass layer 13 arranged in sequence from top to bottom, wherein the silicon substrate 11 contains a through-hole structure 12, the through-hole structure 12 and the first glass 13 constitute a bearing cavity, and the bearing cavity and the second glass 18 constitute an atomic gas chamber; the inner surface of the micro atomic gas chamber is completely covered by a protective layer (protective layer 15 and protective layer 19), and the alkali metal is isolated inside the micro atomic gas chamber by the protective layer.

[0082] The preparation method thereof comprises the following steps:

[0083] 1. A 4-inch diameter, 1mm thick, P-type doped, double-sided polished silicon wafer was selected as the silicon substrate 11. Shipley 1813 was used as the photoresist, chemical vapor deposited silicon nitride was used as the masking layer, and potassium hydroxide solution was used as the silicon-based etching solution. Through-silicon vias 12 were formed through standard photolithography and wet etching processes. The potassium hydroxide etching solution concentration was 20%, the etching temperature was 85°C, and both sides were etched simultaneously for 6 hours to complete the 1mm thick through-holes. A dense array of square through-hole structures 12 was obtained on the 4-inch silicon wafer, with a side length of 2mm and a center-to-center spacing of 10mm. Figure 2a shown.

[0084] 2. Anodic bonding is performed on the silicon substrate 11 with the through-hole structure 12 and the first glass layer 13. The first glass layer 13 is made of Schott BF33 glass with a diameter of 4 inches and a thickness of 0.5 mm. The anodic bonding equipment is a SUSS SB6 bonding machine. -3 Under the vacuum environment of Pa, the bonding voltage range is 800V, the bonding temperature is 350℃, and the bonding pressure is 1000N. After the anodic bonding is completed, the silicon substrate 11 and the first glass layer 13 are combined into one to form a bearing cavity structure, such as Figure 2b shown.

[0085] 3. Rotate the silicon substrate 11 and the first glass layer 13 obtained in step 2 at a rate of 30 RPM along the surface normal direction. Simultaneously, vacuum-deposit aluminum onto the surface of the composite using parallel electron beam evaporation at a plane angle of 2 degrees. Using an electron gun power of 2kW, the deposition process lasts for 10 minutes, forming a sacrificial aluminum layer 14 approximately 40nm thick. Due to the "line of sight" angle, the sacrificial layer 14 only exists on the upper surface of the silicon substrate 11 and the upper edge of the through-hole structure 12, as shown in FIG. Figure 2c shown.

[0086] 4. Continue rotating the structure obtained in step 3 at a speed of 30 RPM. Simultaneously, vacuum-deposit aluminum oxide onto the surface of the structure using parallel electron beam evaporation at a 45-degree angle. Use a 3kW electron gun for 2 minutes. Aluminum oxide is deposited on the surface of the sacrificial layer 14, forming a redundant protective layer 16 with a thickness of 20 nm. Simultaneously, due to the "line of sight" angle, aluminum oxide also enters the bearing cavity formed by the through-silicon via 12 and the first glass layer 13, and is deposited on the inner wall surface to form a protective layer 15 with a thickness of 20 nm. Figure 2d shown.

[0087] 5. Use 20% HCl to etch and remove the sacrificial layer 14. After the sacrificial layer 14 is dissolved, the redundant protective layer 16 attached to the sacrificial layer 14 is peeled off, exposing the clean upper surface of the silicon substrate 11. The 20% HCl etching solution will not affect all other structures made of materials other than the sacrificial layer 14, including the silicon substrate 11, the first glass layer 13 and the protective layer 15 in the carrier cavity. Figure 2e shown.

[0088] 6. In a glove box with a water oxygen value lower than 0.01 ppm, use a micropipette to drop 5 μg of liquid cesium metal-alkali metal 17 directly into the carrier cavity. Due to the presence of the carrier cavity protective layer 15, the alkali metal cesium does not come into contact with the silicon substrate 11 and the first glass layer 13 constituting the carrier cavity. Figure 2f shown.

[0089] 7. Using standard photolithography, electron beam vacuum coating, and photoresist stripping techniques, a patterned upper cover plate protective layer 19 is formed on the surface of the upper glass 18 using 1.4 μm thick Shipley 1813 photoresist as a sacrificial layer, MF319 as a developer, and NMP as a debonding agent. The second glass layer 18 is made of Schott BF33 glass with a diameter of 4 inches and a thickness of 0.5 mm. The protective layer 19 is also a 20 nm thick aluminum oxide film, patterned into a square array densely distributed on the 4-inch glass sheet. The squares have a side length of 2 mm and a center spacing of 10 mm. The position and size of the pattern strictly correspond to the array pattern of the through-silicon via structure 12 on the silicon substrate 11, as shown in FIG. Figure 2g shown.

[0090] 8. Align the second glass layer 18 including the protective layer 19 with the combination of the silicon substrate 11 and the first glass layer 13, that is, after the protective layer 19 and the silicon through-hole 12 are strictly aligned, use the anodic bonding technology to bond the two together. The anodic bonding equipment used in this step is a SUSS SB6 bonding machine with a base vacuum of 10 -3 Pa, filled with 10kPa buffer nitrogen and then bonded, bonding voltage 800V, bonding temperature 250℃, bonding pressure 2000N. After bonding, the entire atomic gas chamber with inner wall protection layer is prepared, such as Figure 2h shown.

[0091] Figure 3 A surface photograph of the aluminum oxide protective layer prepared in Example 1 observed by a Hitachi S4800 scanning electron microscope is shown. The figure shows that the film layer is fine and uniform. Measurements using a BRUKER Dimension Icon atomic force microscope show that its smoothness is better than 2 nm.

[0092] The 4-inch substrate obtained in Example 1 is densely covered with atomic gas cells, and its bonding yield is close to 100%. Figure 4 As shown in the figure, the outer dimensions of the cut single atomic gas chamber are 10mm×10mm×2mm, and the gas chamber dimensions are 2mm×2mm×1mm. Figure 5 The bonding quality was tested as shown in the figure. The Royce 650 shear force tester showed that the bonding force between the second glass layer, the silicon substrate, and the first glass layer was greater than 21 kg (the instrument limit), which is consistent with the bonding force of the micro atomic chamber sample without a protective layer. The PHOENIXL 300 helium mass spectrometer leak detector showed that the atomic chamber had a leakage rate of better than 1.0×10 -13 Pa·m 3 / s (instrument limit), which is much better than the minimum value of 1.0×10 -11 Pa·m 3 / s.

[0093] Example 2

[0094] A micro atomic gas chamber with an inner wall protective layer, the structure of which is as follows Figure 1 As shown, its structure includes a second glass layer 18, a silicon substrate 11, and a first glass layer 13 arranged in sequence from top to bottom, wherein the silicon substrate 11 includes a through-hole structure 12, the through-hole structure 12 and the first glass layer 13 constitute a bearing cavity, and the bearing cavity and the upper glass 18 constitute an atomic gas chamber; the inner surface of the micro atomic gas chamber is completely covered by a protective layer (protective layer 15 and protective layer 19), and the alkali metal is encapsulated in the micro atomic gas chamber by the protective layer. The manufacturing method thereof comprises repeating Example 1, with the following differences:

[0095] In step 1, a through-hole structure 12 is formed by deep reactive ion etching technology in silicon, and the etching equipment is LPXASE of STS company. TM Using commercial AZ4620 positive photoresist as a masking layer, sulfur hexafluoride as an etching gas, and octafluorocyclobutane as a shielding gas, a standard Bosch etching process was used to obtain a circular through-hole structure array with a diameter of 2 mm and a center-to-center spacing of 10 mm on a silicon substrate 11.

[0096] In step 3, copper is vacuum-deposited onto the surface of the combined body. The electron gun power is 2.5 kW, and the deposition time is 10 minutes, forming a copper sacrificial layer 14 with a thickness of about 40 nm.

[0097] In step 4, titanium oxide is vacuum-deposited onto the surface of the structure. The electron gun power is 3 kW and the deposition time is 2 minutes. The titanium oxide is deposited on the surface of the sacrificial layer 14 to form a redundant protective layer 16 with a thickness of 20 nm.

[0098] In step 5, a copper etching solution (Cr2O3:H2SO4:H2O=1g:5ml:37.5mL) is used to remove the sacrificial layer 14, and then the redundant protective layer 16 is peeled off to expose the clean upper surface of the silicon substrate 11.

[0099] In step 6, 10 μg of cesium azide particles are filled into the carrying cavity in an atmospheric environment.

[0100] In step 7, a titanium oxide thin film with a thickness of 20 nm is used as the protective layer 19 .

[0101] In step 8, after the anodic bonding is completed, the atomic gas chamber is heated to 300° C. to decompose the cesium azide into metallic cesium and nitrogen.

[0102] The bonding quality and the gas leakage rate of the micro atomic gas chamber were tested according to the method of Example 1, and the results were basically consistent with those of Example 1.

[0103] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a micro atomic gas chamber with an inner wall protective layer, characterized in that: The steps include: 1) Providing a silicon substrate with a through-hole structure; 2) performing a primary anodic bonding on the lower surface of the silicon substrate and the first glass layer, so that the through-hole structure and the first glass layer form a bearing cavity; 3) depositing a sacrificial layer on the upper surface of the silicon substrate and on the upper edge of the sidewall of the through-hole structure; then depositing a protective layer on the surface of the sacrificial layer and on the inner surface of the bearing cavity; wherein the height of the upper edge of the sidewall does not exceed the thickness of the protective layer; 4) removing the sacrificial layer and the protective layer on the surface of the sacrificial layer by etching; 5) filling the carrier cavity including the protective layer with an alkali metal; 6) forming a patterned protective layer on the surface of the second glass layer so that the patterned protective layer corresponds to the lower surface of the bearing cavity; 7) Performing secondary anodic bonding on the upper surface of the silicon substrate and the second glass layer, so that the protective layer and the patterned protective layer completely cover the inner wall surface of the atomic gas chamber.

2. The preparation method according to claim 1, characterized in that The primary anodic bonding is performed in a vacuum environment under the conditions of a bonding voltage of 200V-1200V, a bonding temperature of 200°C-500°C, and a bonding pressure of 1000N-1500N; The secondary anodic bonding is performed in a vacuum environment under the conditions of a bonding voltage of 200V-800V, a bonding temperature of 200°C-300°C, and a bonding pressure of 1500N-2000N.

3. The preparation method according to claim 1, characterized in that The first glass layer and the second glass layer are made of borosilicate glass.

4. The preparation method according to claim 3, characterized in that The borosilicate glass is Corning Pyrex7740 glass or Schott BF33 glass.

5. The preparation method according to claim 1, characterized in that The thickness of the first glass layer or the second glass layer is in the range of 200 μm to 500 μm.

6. The preparation method according to claim 1, characterized in that The silicon substrate is a double-sided polished P-type doped silicon wafer.

7. The preparation method according to claim 1, characterized in that The thickness of the silicon substrate is in the range of 1 mm to 5 mm.

8. The preparation method according to claim 1, characterized in that The protective layer and the patterned protective layer are made of the same material, which is selected from one of boron oxide, aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, calcium oxide, and silicon nitride.

9. The preparation method according to claim 1, characterized in that The protective layer and the patterned protective layer have the same thickness, which is within the range of 10 nm to 20 nm.

10. The preparation method according to claim 1, characterized in that The filling amount of the alkali metal is in the range of 1 μg to 50 μg.

11. A micro atomic gas chamber with an inner wall protective layer prepared by the preparation method according to any one of claims 1 to 10, characterized in that: Its structure includes: a second glass layer, a silicon substrate with a through-hole structure, and a first glass layer arranged in sequence from top to bottom; the through-hole structure, the first glass layer, and the second glass layer constitute a micro-atomic gas chamber; the inner surface of the micro-atomic gas chamber is completely covered by a protective layer, and the alkali metal is isolated inside the micro-atomic gas chamber by the protective layer.

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