Ultra-shallow junction silicon nanowire vector hydrophone and preparation method thereof

Abstract

This invention relates to an ultra-shallow junction silicon nanowire vector hydrophone and its fabrication method, belonging to the field of MEMS sensor technology. The vector hydrophone comprises an SOI substrate and micropillars. The SOI substrate consists of a four-beam structure, a central mass block, and an outer frame. Each beam has an ultra-shallow junction silicon nanowire piezoresistive sensing unit distributed at both ends, and these sensing units are connected by metal leads to form a Wheatstone bridge. This invention addresses the problem of low underwater acoustic detection sensitivity in existing hydrophones by proposing a piezoresistive MEMS vector hydrophone based on the giant piezoresistive effect. This vector hydrophone transmits underwater acoustic signals with torque through the micropillars and the four-beam structure, and achieves high-sensitivity detection through the Wheatstone bridge composed of ultra-shallow junction silicon nanowire piezoresistive sensing units. This vector hydrophone is suitable for highly sensitive detection of weak underwater sound signals.

Description

Technical Field

[0001] This invention belongs to the field of MEMS sensor technology, and specifically relates to a piezoresistive vector hydrophone, specifically an ultra-shallow junction silicon nanowire vector hydrophone and its fabrication method. Background Technology

[0002] Hydrophones play a vital role in marine fisheries, seabed resource exploration, maritime search and rescue, and anti-submarine warfare. MEMS vector hydrophones, benefiting from their vectoring capabilities and miniaturization, have seen widespread application. However, traditional MEMS vector hydrophones are based on the bulk silicon piezoresistive effect, relying on stress to modulate carrier mobility and thus change the piezoresistive resistance value for underwater acoustic signal detection. This sensitivity method has relatively low sensitivity and is gradually failing to meet the requirements of modern industries. Therefore, there is an urgent need to invent a MEMS vector hydrophone based on novel sensing elements and sensing methods to achieve highly sensitive underwater acoustic detection. Summary of the Invention

[0003] The purpose of this invention is to address the low sensitivity of existing vector hydrophones by providing a vector hydrophone based on silicon nanowires formed by ultra-shallow junction implantation as the sensing unit. This vector hydrophone transmits underwater acoustic signals with torque through a micro-pillar and four-beam structure. Based on the giant piezoresistive effect, it achieves high-sensitivity detection of underwater acoustic signals by using a Wheatstone bridge composed of ultra-shallow junction silicon nanowire piezoresistive sensing units formed by ultra-shallow junction implantation of boron impurities and MEMS etching.

[0004] This invention is achieved through the following technical solution:

[0005] An ultra-shallow junction silicon nanowire vector hydrophone includes an SOI substrate and micropillars. A four-beam structure, a central mass block, and an outer frame of the SOI substrate are etched onto the SOI substrate. The four-beam structure consists of four rectangular beams. The central mass block is integrally connected to the center of the four-beam structure, and the central mass block and the four-beam structure are located in the same plane. The four ends of the four-beam structure are integrally connected to the outer frame of the SOI substrate. The micropillars are vertically fixed at the center of the upper surface of the central mass block. Each rectangular beam in the four-beam structure has an ultra-shallow junction silicon nanowire piezoresistive sensing unit at both its inner and outer ends. The ultra-shallow junction silicon nanowire piezoresistive sensing unit is cuboid in shape, and its length direction is consistent with the length direction of the rectangular beam. The upper surface of the ultra-shallow junction silicon nanowire piezoresistive sensing unit is made of silicon oxide. The upper surface is a "P-type silicon" interface, and the lower surface is an "N-type silicon-P-type silicon" interface. The depletion regions formed at the two interfaces on the upper and lower surfaces partially overlap. Both side surfaces of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are "silicon oxide-P-type silicon" interfaces, and the depletion regions formed at the two interfaces on the two side surfaces partially overlap. The two ends of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are connected by ohmic contacts with metal leads. The four ultra-shallow junction silicon nanowire piezoresistive sensing units on the left and right rectangular beams are connected by metal leads to form a Wheatstone bridge for detecting underwater acoustic signals in the X direction in the Cartesian coordinate system. The four ultra-shallow junction silicon nanowire piezoresistive sensing units on the front and rear rectangular beams are connected by metal leads to form a Wheatstone bridge for detecting underwater acoustic signals in the Y direction in the Cartesian coordinate system.

[0006] As a preferred technical solution, the SOI substrate has a side length of 4000um and a thickness of 450um; the micro-pillar has a height of 5000um and a radius of 175um; each rectangular beam in the four-beam structure has a length of 1000um, a width of 160um, and a thickness of 20um; the central mass block has a side length of 600um and a thickness of 20um; and the outer frame of the substrate has a width of 700um.

[0007] Another object of the present invention is to provide a method for fabricating the above-mentioned ultra-shallow junction silicon nanowire vector hydrophone, specifically including the following steps:

[0008] S1: An SOI wafer is selected as the substrate, with a device layer at the top, a buried oxide layer in the middle, and a substrate layer at the bottom. The device layer is N-type with a crystal orientation of [missing information]. <100> Its resistivity is 10~20Ω·cm.

[0009] S2: Low doses of boron impurities are injected into the device layer under low energy conditions to form a 100-nanometer-scale P-type ultra-shallow junction.

[0010] S3: Etch the device layer on the front side to form silicon nanowires.

[0011] S4: A layer of silicon oxide is deposited on the front side, and the silicon oxide at both ends of the silicon nanowire is etched to form a concentrated boron ion implantation hole, and the silicon oxide at the center position is etched to form a micro-pillar mounting hole.

[0012] S5: High-energy injection of concentrated boron impurities through the injection hole forms a heavily doped region at the injection hole, followed by rapid annealing.

[0013] S6: Metal is sputtered onto the front side and patterned to form metal leads. Alloy annealing is then performed to form ohmic contacts. At this point, the fabrication of the ultra-shallow junction silicon nanowire piezoresistive sensing unit is complete.

[0014] S7: The front side is etched with silicon oxide and device layers to form a four-beam structure and a central mass block.

[0015] S8: Deep silicon etching of the substrate and buried oxide layer on the back side to release the four-beam structure and central mass block.

[0016] S9: The micro-pillars are vertically bonded and fixed in the mounting holes using UV adhesive. Finally, the ultra-shallow junction silicon nanowire vector hydrophone is fabricated.

[0017] As a preferred technical solution, in step S1, the thickness of the device layer is 20 μm, the thickness of the buried oxide layer is 2 μm, and the thickness of the substrate layer is 450 μm.

[0018] As a preferred technical solution, in step S2, the injected energy is 10keV and the dose is 4×10⁻⁶. 13 cm -2 The depth of the P-type shallow junction is 150 nm.

[0019] As a preferred technical solution, in step S3, the silicon nanowires formed by etching have a length of 10 μm and a width of 200 nm.

[0020] As a preferred technical solution, in step S4, the thickness of the deposited silicon oxide layer is 1 μm.

[0021] As a preferred technical solution, in step S5, the injected energy is 100keV and the dose is 10. 16 cm -2 .

[0022] This invention addresses the problem of low sensitivity in underwater acoustic detection in existing hydrophones by proposing a piezoresistive MEMS vector hydrophone based on the giant piezoresistive effect. This vector hydrophone transmits the underwater acoustic signal through a miniature column and a four-beam structure, and achieves high-sensitivity detection through a Wheatstone bridge composed of ultra-shallow junction silicon nanowire piezoresistive sensitive units. This vector hydrophone is suitable for high-sensitivity detection of weak underwater sound signals. Attached Figure Description

[0023] The accompanying drawings, which are provided to further illustrate the invention and form part of this application, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention.

[0024] Figure 1 This is a three-dimensional structural diagram of the hydrophone of the present invention.

[0025] Figure 2 This is a top view of the hydrophone of the present invention.

[0026] Figures 3 to 12 This is a schematic diagram of the manufacturing process of the hydrophone of the present invention and the corresponding layout.

[0027] Figure 13 This is a schematic diagram of the upper and lower interfaces of the ultra-shallow junction silicon nanowire piezoresistive sensing unit in the hydrophone of this invention.

[0028] Figure 14 This is a schematic diagram of the interfaces on both sides of the ultra-shallow junction silicon nanowire piezoresistive sensing unit in the hydrophone of this invention.

[0029] In the figure: 1-SOI substrate, 2-micro pillar, 3-four-beam structure, 4-central mass block, 5-SOI substrate outer frame, 6-ultra-shallow junction silicon nanowire piezoresistive sensing unit, 7-mounting hole, 8-device layer, 9-buried oxide layer, 10-substrate layer, 11-P-type ultra-shallow junction, 12-silicon nanowire, 13-silicon oxide, 14-implantation hole, 15-heavily doped region, 16-metal lead, 17-ohmic contact, 18-"silicon oxide-P-type silicon" interface, 19-"N-type silicon-P-type silicon" interface, 20-depletion region, 21-partial overlap;

[0030] X1 - First ultra-shallow junction silicon nanowire piezoresistive sensing unit, X2 - Second ultra-shallow junction silicon nanowire piezoresistive sensing unit, Y1 - Third ultra-shallow junction silicon nanowire piezoresistive sensing unit, Y2 - Fourth ultra-shallow junction silicon nanowire piezoresistive sensing unit, X3 - Fifth ultra-shallow junction silicon nanowire piezoresistive sensing unit, X4 - Sixth ultra-shallow junction silicon nanowire piezoresistive sensing unit, Y3 - Seventh ultra-shallow junction silicon nanowire piezoresistive sensing unit, Y4 - Eighth ultra-shallow junction silicon nanowire piezoresistive sensing unit;

[0031] B1 - Left rectangular beam, B2 - Front rectangular beam, B3 - Right rectangular beam, B4 - Rear rectangular beam. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the present invention will be further described clearly and completely below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] In the description of this invention, if directional descriptions are involved, such as "upper", "lower", "outer" or other indications of directional or positional relationships based on the directional or positional relationships shown in the accompanying drawings, it is only for the convenience of describing this invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0034] In the description of this embodiment, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. 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 an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] An ultra-shallow junction silicon nanowire vector hydrophone, such as Figure 1 and Figure 2 As shown, it includes an SOI substrate 1 and micropillars 2; a four-beam structure 3, a central mass block 4, and an outer frame 5 of the SOI substrate are etched on the SOI substrate. The four-beam structure 3 consists of four rectangular beams. The central mass block 4 is integrally connected to the center of the four-beam structure 3. The central mass block 4 and the four-beam structure 3 are located on the same plane. The four ends of the four-beam structure 3 are integrally connected to the outer frame 5 of the SOI substrate. The micropillars 2 are vertically fixed at the center of the upper surface of the central mass block 4. Each rectangular beam in the four-beam structure 3 has an ultra-shallow junction silicon nanowire piezoresistive sensing unit 6 at its inner and outer ends. Specifically, the four-beam structure 3 includes a left rectangular beam B1, a front rectangular beam B2, and a rear rectangular beam B3. B2, right rectangular beam B3, and rear rectangular beam B4; the outer end of the left rectangular beam B1 is provided with a first ultra-shallow junction silicon nanowire piezoresistive sensing unit X1, and the inner end is provided with a second ultra-shallow junction silicon nanowire piezoresistive sensing unit X2; the outer end of the front rectangular beam B2 is provided with a third ultra-shallow junction silicon nanowire piezoresistive sensing unit Y1, and the inner end is provided with a fourth ultra-shallow junction silicon nanowire piezoresistive sensing unit Y2; the inner end of the right rectangular beam B3 is provided with a fifth ultra-shallow junction silicon nanowire piezoresistive sensing unit X3, and the outer end is provided with a sixth ultra-shallow junction silicon nanowire piezoresistive sensing unit X4; the inner end of the rear rectangular beam B4 is provided with a seventh ultra-shallow junction silicon nanowire piezoresistive sensing unit Y3, and the outer end is provided with an eighth ultra-shallow junction silicon nanowire piezoresistive sensing unit Y4. The ultra-shallow junction silicon nanowire piezoresistive sensing unit 6 is rectangular, with its length direction aligned with that of the rectangular beam. The upper surface of the ultra-shallow junction silicon nanowire piezoresistive sensing unit 6 is a silicon oxide-P-type silicon interface 18, and the lower surface is an N-type silicon-P-type silicon interface 19. The depletion regions 20 formed at the two interfaces on the upper and lower surfaces partially overlap 21. Figure 13As shown, this figure is in the main view direction; both side surfaces of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are "silicon oxide-P-type silicon" interfaces 18, and the depletion regions 20 formed at the two interfaces of the two side surfaces partially overlap 21, as shown. Figure 14 As shown in the figure, this is a top view; the two ends of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are connected to metal leads 16 by ohmic contacts 17 respectively. The first ultra-shallow junction silicon nanowire piezoresistive sensing unit X1, the second ultra-shallow junction silicon nanowire piezoresistive sensing unit X2, the fifth ultra-shallow junction silicon nanowire piezoresistive sensing unit X3 and the sixth ultra-shallow junction silicon nanowire piezoresistive sensing unit X4 are connected by metal leads 16 to form a Wheatstone bridge for detecting underwater acoustic signals in the X direction in the Cartesian coordinate system; the third ultra-shallow junction silicon nanowire piezoresistive sensing unit Y1, the fourth ultra-shallow junction silicon nanowire piezoresistive sensing unit Y2, the seventh ultra-shallow junction silicon nanowire piezoresistive sensing unit Y3 and the eighth ultra-shallow junction silicon nanowire piezoresistive sensing unit Y4 are connected by metal leads 16 to form a Wheatstone bridge for detecting underwater acoustic signals in the Y direction in the Cartesian coordinate system.

[0036] This embodiment also provides a method for fabricating the aforementioned ultrashallow junction silicon nanowire vector hydrophone, the fabrication flowchart of which is shown below. Figures 3 to 12 As shown, it should be noted that Figures 3 to 12 Based on Figure 2 The HH profile line is used to display the data. The specific preparation method includes the following steps:

[0037] S1: An SOI wafer is selected as the substrate, with the top layer being the device layer 8, the middle layer being the buried oxide layer 9, and the bottom layer being the substrate layer 10. Figure 3 As shown; where device layer 8 has a thickness of 20 μm, is of type N, and has a crystal orientation of <100> The resistivity is 10~20Ω·cm; the thickness of the buried oxide layer 9 is 2um; and the thickness of the substrate layer 10 is 450um.

[0038] S2: Low-dose boron impurities are implanted into device layer 8 under low-energy conditions. The implantation energy is 10 keV and the dose is 4 × 10⁻⁶. 13 cm -2 Doping forms a 150nm-deep P-type ultrashallow junction 11, such as... Figure 4 As shown.

[0039] S3: Etch device layer 8 on the front side to form silicon nanowires 12 with a length of 10 μm and a width of 200 nm, such as Figure 5 As shown.

[0040] S4: A 1µm thick layer of silicon oxide 13 is deposited on the front side, and the silicon oxide 13 at both ends of the silicon nanowire 12 is etched to form concentrated boron ion implantation holes 14. The silicon oxide 13 at the center is etched to form mounting holes 7 for the micropillar 2, such as... Figure 6 As shown.

[0041] S5: High-energy injection of concentrated boron impurities is performed through injection port 14 at an injection energy of 100 keV and a dose of 10. 16 cm -2 A heavily doped region 15 is formed at the injection hole 14 and subjected to rapid annealing, such as Figure 7 As shown.

[0042] S6: Front-side metal sputtering and patterning to form metal leads 16, alloy annealing to form ohmic contacts 17, such as Figure 8 As shown; the ultra-shallow junction silicon nanowire piezoresistive sensing unit 6 has now been fabricated.

[0043] S7: The front side is etched with silicon oxide 13 and device layer 8 to form a four-beam structure 3 and a central mass block 4, such as Figure 9 As shown.

[0044] S8: Backside deep silicon etched substrate layer 10 and buried oxide layer 9, releasing the four-beam structure 3, central mass block 4 and SOI substrate outer frame 5, as shown. Figure 10 and Figure 11 As shown.

[0045] S9: Vertically bond and fix the miniature column 2 into the mounting hole 7 using UV adhesive, such as... Figure 12 As shown; finally, the ultra-shallow junction silicon nanowire vector hydrophone was successfully fabricated.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A shallow-junction silicon nanowire vector hydrophone, comprising an SOI substrate (1) and a micro-pillar (2); a four-beam structure (3), a central mass block (4), and an outer frame (5) of the SOI substrate are etched on the SOI substrate, the four-beam structure (3) being four rectangular beams, the central mass block (4) being integrally connected to the center of the four-beam structure (3), the central mass block (4) and the four-beam structure (3) being located on the same plane, the four ends of the four-beam structure (3) being integrally connected to the outer frame (5) of the SOI substrate, and the micro-pillar (2) being vertically fixed at the center of the upper surface of the central mass block (4); characterized in that: In the four-beam structure (3), each rectangular beam has an ultra-shallow junction silicon nanowire piezoresistive sensitive unit set at both its inner and outer ends. The ultra-shallow junction silicon nanowire piezoresistive sensitive unit is cuboid in shape, and its length direction is consistent with the length direction of the rectangular beam. The upper surface of the ultra-shallow junction silicon nanowire piezoresistive sensing unit is a "silicon oxide-P-type silicon" interface (18), and the lower surface is an "N-type silicon-P-type silicon" interface (19). The depletion regions (19) formed at the two interfaces of the upper and lower surfaces partially overlap (20). Both side surfaces of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are "silicon oxide-P-type silicon" interfaces (18). The depletion regions (19) formed at the two interfaces of the two side surfaces partially overlap (20). The two ends of the ultra-shallow junction silicon nanowire piezoresistive sensing unit are connected by ohmic contacts (17) to metal leads (16). The four ultra-shallow junction silicon nanowire piezoresistive sensing units on the left and right rectangular beams are connected by metal leads to form a Wheatstone bridge for detecting underwater acoustic signals in the X direction in the Cartesian coordinate system. The four ultra-shallow junction silicon nanowire piezoresistive sensing units on the front and rear rectangular beams are connected by metal leads to form a Wheatstone bridge for detecting underwater acoustic signals in the Y direction in the Cartesian coordinate system.

2. The ultra-shallow junction silicon nanowire vector hydrophone according to claim 1, characterized in that: The SOI substrate (1) has a side length of 4000um and a thickness of 450um; the micro-pillar (2) has a height of 5000um and a radius of 175um; each rectangular beam in the four-beam structure (3) has a length of 1000um, a width of 160um, and a thickness of 20um; the central mass block (4) has a side length of 600um and a thickness of 20um; and the outer frame (5) of the substrate has a width of 700um.

3. The method for fabricating the ultrashallow junction silicon nanowire vector hydrophone as described in claim 1, characterized in that, Includes the following steps: S1: An SOI wafer is selected as the substrate, with a device layer (8) at the top, a buried oxide layer (9) in the middle, and a substrate layer (10) at the bottom. The device layer (8) is of type N and has a crystal orientation of [missing information]. <100> Its resistivity is 10~20 Ω·cm; S2: Low dose of boron impurities are injected into the device layer (8) under low energy conditions to form a layer of P-type ultra-shallow junction (11) at the scale of hundreds of nanometers. S3: Etch the device layer (8) on the front side to form silicon nanowires (12). S4: A layer of silicon oxide (13) is deposited on the front side, and the silicon oxide (13) at both ends of the silicon nanowire (12) is etched to form a concentrated boron ion implantation hole (14-1), and the silicon oxide (13) at the center position is etched to form a micro-pillar (2) mounting hole (14-2). S5: High-energy injection of concentrated boron impurities through injection hole (14-1) forms a heavily doped region (15) at injection hole (14-1) and is subjected to rapid annealing. S6: Sputter metal on the front side and pattern it to form metal leads (16), then anneal the alloy to form ohmic contacts (17). At this point, the preparation of the ultra-shallow junction silicon nanowire piezoresistive sensitive unit is completed. S7: The front side is etched with silicon oxide (13) and device layer (8) to form a four-beam structure (3) and a central mass block (4); S8: Deep silicon etching of the substrate layer (10) and buried oxide layer (9) on the back side to release the four-beam structure (3) and the central mass block (4); S9: The micro-pillar (2) is vertically bonded and fixed in the mounting hole (14-2) with UV glue. Finally, the ultra-shallow junction silicon nanowire vector hydrophone is prepared.

4. The method for fabricating the ultrashallow junction silicon nanowire vector hydrophone according to claim 3, characterized in that: In step S1, the thickness of the device layer (8) is 20 μm, the thickness of the buried oxide layer (9) is 2 μm, and the thickness of the substrate layer (10) is 450 μm.

5. The method for fabricating the ultrashallow junction silicon nanowire vector hydrophone according to claim 3, characterized in that: In step S2, the injected energy is 10 keV and the dose is 4 × 10⁻⁶. 13 cm -2 The depth of the P-type shallow junction is 150 nm.

6. The method for fabricating an ultrashallow junction silicon nanowire vector hydrophone according to claim 3, characterized in that: In step S3, the silicon nanowires formed by etching have a length of 10 μm and a width of 200 nm.

7. The method for fabricating an ultrashallow junction silicon nanowire vector hydrophone according to claim 3, characterized in that: In step S4, the thickness of the deposited silicon oxide (13) layer is 1 μm.

8. The method for fabricating an ultrashallow junction silicon nanowire vector hydrophone according to claim 3, characterized in that: In step S5, the injected energy is 100 keV and the dose is 10. 16 cm -2 .

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