A method for manufacturing a gallium nitride ultraviolet sensor

Abstract

The application discloses a preparation method of a gallium nitride ultraviolet sensor and relates to the technical field of gallium nitride ultraviolet sensor processing. The application comprises the following steps: step a: obtaining an epitaxial wafer, the epitaxial wafer comprises a silicon substrate, a buffer layer, a semiconductor layer and a barrier layer from bottom to top; step b: etching the barrier layer and part of the semiconductor layer by using an inductively coupled plasma etching process; and step c: depositing ohmic contact metal on both ends of the barrier layer to form ohmic contact electrodes. The application effectively overcomes the limitations of traditional silicon-based ultraviolet sensors in sensitivity, power consumption and temperature drift by introducing gallium nitride material and its unique wide band gap characteristics. Compared with traditional silicon, zinc oxide and other materials, the GaN material has high temperature stability, low power consumption and low dark current characteristics. In particular, by optimizing the device structure design and material parameters, the photoelectric conversion efficiency is improved, and the sensor has ultrahigh sensitivity in weak ultraviolet signal detection.

Description

A method for fabricating a gallium nitride ultraviolet sensor Technical Field

[0001] This invention relates to the field of gallium nitride ultraviolet sensor fabrication technology, and in particular to a method for fabricating a gallium nitride ultraviolet sensor. Background Technology

[0002] GaN ultraviolet sensors are currently widely used in flame detection, high-energy environment monitoring, ultraviolet imaging, and space exploration due to their excellent thermal stability, high breakdown voltage, and wide bandgap characteristics. However, in practical applications, the output signal strength of the sensor is usually weak, making it difficult to accurately extract ultraviolet intensity information in a high-noise background. The traditional approach is to use an off-chip signal amplifier to perform secondary processing on the output signal, but this approach introduces additional noise, increases system power consumption, and is not conducive to chip-level integration.

[0003] Furthermore, to improve the signal-to-noise ratio, a Wheatstone bridge structure is often used to integrate four identical sensors and perform differential processing. Two of these sensors serve as photosensitive devices, while the other two are shielded and act as reference devices (Ref). However, current mainstream shielding methods, such as metal covers and electrode extension shielding, cause significant disturbances to the two-dimensional electron gas (2DEG) distribution in the AlGaN / GaN heterojunction. This disrupts the resistance symmetry of the bridge, leading to increased device offset voltage, severely reducing signal stability and linearity, and affecting sensor sensitivity and temperature drift characteristics. Additionally, a single device without a Wheatstone bridge structure, consisting only of the sensor end, can still detect ultraviolet light, but its resistance to temperature drift and other interferences is weak, failing to effectively suppress common-mode noise. The output signal drifts severely with temperature changes, making high-precision ultraviolet detection difficult. Constructing a Wheatstone bridge on a PCB using a single device requires matching devices with similar parameters, greatly increasing process complexity and leading to parameter inconsistencies between devices, resulting in inherent misalignment and affecting measurement accuracy.

[0004] On the other hand, to enhance the sensor's coupling capability to ultraviolet light, traditional methods require the introduction of additional lens structures or packaging cavities. This not only increases the complexity of the process but may also create bottlenecks in miniaturization and mass production. If traditional planar packaging is used, it is easily corroded by environmental factors such as moisture and oxygen, affecting the device's lifespan and performance stability. Therefore, existing GaN ultraviolet sensors have significant shortcomings in signal amplification methods, bridge structure matching, and packaging integration. In particular, they are unable to meet the requirements of high-end applications in key performance indicators such as high-sensitivity detection, low temperature drift characteristics, and low offset voltage.

[0005] To address these issues, we provide a method for fabricating a gallium nitride ultraviolet sensor. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating a gallium nitride ultraviolet sensor. By using an AlGaN / GaN heterojunction structure to fabricate a highly consistent sensing unit, integrating it into a Wheatstone bridge to achieve in-situ differential amplification, and combining it with non-contact light-shielding treatment and COB packaging with integrated optical structures, this method solves the problems in the prior art, such as weak sensor output signals requiring external amplification circuits, the symmetry of bridge resistance values ​​being easily damaged by light-shielding processes, and the complexity and unfavorable nature of traditional packaging methods for optical integration.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0008] This invention relates to a method for fabricating a gallium nitride ultraviolet sensor, comprising the following steps:

[0009] Step a: Obtain an epitaxial wafer, which comprises, from bottom to top, a silicon substrate, a buffer layer, a semiconductor layer, and a barrier layer;

[0010] Step b: Etch the barrier layer and part of the semiconductor layer using inductively coupled plasma etching (ICP-C) process;

[0011] Step c: Deposit ohmic contact metal at both ends of the barrier layer to form ohmic contact electrodes;

[0012] Step d: A first passivation layer is grown on the barrier layer, the semiconductor layer and the ohmic contact metal, and an opening is made above the ohmic contact metal using an ICP etching process;

[0013] Step e: Fabricate a metal lead on the first passivation layer, the metal lead being connected to the ohmic contact metal through the opening;

[0014] Step f: A second passivation layer is grown on the metal lead and the ohmic contact metal, and the metal pad openings on the metal lead are opened using an ICP etching process;

[0015] Step g: The light-transmitting window of the gate region is opened on the second passivation layer using ICP etching process, and a passivation layer with a thickness of 5~20nm is retained at the light-transmitting window. This fabrication method is based on AlGaN / GaN heterojunction structure. The fabricated sensor unit has the high temperature stability, low power consumption and low dark current characteristics of gallium nitride material, effectively overcoming the limitations of traditional silicon-based sensors in terms of sensitivity and temperature drift, and providing a core device foundation for building high-performance ultraviolet sensing modules.

[0016] The present invention is further configured such that the material of the buffer layer in step a is AlN, the material of the semiconductor layer is GaN, and the material of the barrier layer is AlGaN, adopting an AlGaN / GaN heterojunction structure, which makes full use of the wide bandgap characteristics of gallium nitride-based materials, enabling the sensor to have excellent thermal stability and high breakdown voltage, and is suitable for extreme environments and high temperature conditions such as flame detection and space exploration.

[0017] The present invention is further configured such that the ohmic contact metal in step c includes one or more of Ti, Al, Ni, Au and Cr. Using the metal combination can form a good ohmic contact electrode, ensuring the stability and reliability of the electrical performance of the sensor unit, which is a prerequisite for realizing a high-matching bridge structure.

[0018] The present invention is further configured such that the materials of the first passivation layer and the second passivation layer in steps d and e are each independently selected from one of SiNx, SiO2 and Al2O3. The growth of the passivation layer and the retention of a window passivation layer of a specific thickness can effectively prevent the oxidation of the device channel region by water vapor or oxygen, protect and stabilize the two-dimensional electron gas (2DEG) characteristics, and at the same time ensure the effective transmission of ultraviolet light.

[0019] The present invention is further configured such that the metal lead fabrication method in step e is magnetron sputtering or electron beam evaporation, and the material of the metal lead is selected from one of Au, Al, Cu, Ti, Ni and Cr. The metal interconnect fabrication using the aforementioned process and materials ensures the reliability and low resistance of the lead, providing a guarantee for the subsequent integration of Wheatstone bridges and the realization of stable signal transmission.

[0020] The present invention is further configured such that, after step g, four sensor units fabricated using the same process are electrically connected in a Wheatstone bridge structure, wherein two sensor units serve as photosensitive devices and the other two sensor units serve as reference devices. By integrating four highly consistent sensor units into a Wheatstone bridge, common-mode noise such as temperature drift can be directly suppressed using the differential principle. In-situ differential amplification of the signal can be achieved without external operational amplifiers, thereby improving the signal-to-noise ratio and system integration.

[0021] The present invention is further configured such that the reference device is shielded by inkjet printing carbonized material to cover the light-transmitting window of its gate region. The non-contact inkjet printing or dispensing shielding method avoids the disturbance caused by the traditional metal shielding layer to the two-dimensional electron gas distribution in the AlGaN / GaN heterojunction, ensuring the initial matching accuracy of the four-arm resistors of the bridge, thereby improving the stability and linearity of the differential signal.

[0022] The present invention is further configured such that the chip integrated as a Wheatstone bridge is subjected to on-board chip packaging. During packaging, a high UV transmittance encapsulating adhesive is applied above the light-transmitting window of the photosensitive device. The on-board chip (COB) packaging and UV transmittance adhesive are applied. This structure has good airtightness, can effectively isolate moisture, oxygen and other environmental corrosion, improve the long-term reliability and environmental stability of the device, and at the same time provide a foundation for subsequent optical integration.

[0023] The present invention is further configured such that the high ultraviolet transmittance encapsulant is a colloid with high transmittance to ultraviolet light in the wavelength range of 200 nanometers to 400 nanometers. By using an encapsulant with high transmittance in a specific wavelength band, it is possible to achieve environmental protection while ensuring efficient incident ultraviolet light and initially filtering stray light of non-target wavelengths, thereby improving detection accuracy.

[0024] The present invention is further configured such that a UV-based fused silica convex mirror is bonded above the photosensitive device encapsulating adhesive. The convex mirror and the encapsulating adhesive together form a microlens structure. By integrating the fused silica convex mirror to form a microlens structure, ultraviolet light can be effectively focused, the incident angle can be expanded, and the optical coupling efficiency and responsivity of the sensor can be improved. At the same time, the complexity of additional assembly of discrete lenses is avoided, which is conducive to the miniaturization and mass production of the module.

[0025] The present invention has the following beneficial effects:

[0026] 1. This invention effectively overcomes the limitations of traditional silicon-based ultraviolet sensors in terms of sensitivity, power consumption, and temperature drift by introducing gallium nitride (GaN) material and its unique wide bandgap characteristics. Compared with traditional silicon, zinc oxide, and other materials, GaN material has high-temperature stability, low power consumption, and low dark current characteristics, and exhibits excellent performance, especially in extreme environments and high-temperature conditions. In particular, by optimizing the device structure design and material parameters, the photoelectric conversion efficiency is improved, enabling the sensor to have ultra-high sensitivity in the detection of weak ultraviolet signals. At the same time, the intrinsic material properties endow the device with excellent temperature stability.

[0027] 2. This invention further proposes using a Wheatstone bridge structure with high resistance as the first-stage analog front-end amplifier circuit, which improves the amplification factor of the ultraviolet response and effectively suppresses common-mode noise such as temperature drift through the differential bridge principle. Using high-resistance sensor units in the bridge arms ensures low-power operation while enhancing the differential-mode output signal, thereby achieving accurate reading of weak ultraviolet signals. Compared with traditional gallium nitride ultraviolet sensors + operational amplifier circuits, the amplification factor of this design increases proportionally with the increase of resistance, while the stability of the device's operating point is enhanced. This in-situ differential amplification structure not only significantly improves the sensor's signal-to-noise ratio and sensitivity but also effectively offsets signal drift caused by temperature changes through common-mode rejection ratio (CMRR), enabling the system to maintain a stable zero-point output over a wide temperature range and reducing the temperature drift coefficient.

[0028] 3. To ensure the matching of the four arms of the bridge resistors, this invention employs inkjet printing of carbonized material or black encapsulating adhesive to shield the two reference branches in the device. This avoids the two-dimensional electron gas mismatch problem caused by the metal shielding layer, improving the matching accuracy and signal differential characteristics of the bridge. This non-contact shielding method preserves the integrity and consistency of the device structure, preventing inconsistencies caused by stress or charge introduction. This innovative shielding process gives the four sensing units highly consistent electrical characteristics, fundamentally reducing the initial offset voltage of the bridge. Combined with the differential structure design, this allows the sensor to maintain extremely low output offset under long-term operation and temperature variations, providing a foundation for high-precision measurement.

[0029] 4. This invention employs a COB (Chip-on-Board) packaging structure, and a 200–400 nm light-transmitting window material, such as fused silica or UV-grade optical epoxy, is drop-coated onto the top of the sensor. This packaging method not only possesses excellent hermeticity and environmental stability, but also allows for the formation of a micro-lens structure by controlling the colloid morphology, effectively expanding the UV light incident angle and improving incident efficiency. It also possesses composite functions such as filtering, imaging, and focusing, providing a new integrated packaging solution for high-performance UV sensors. The synergistic effect of this packaging structure and microlens design significantly improves optical coupling efficiency, further enhancing detection sensitivity, while providing excellent environmental isolation performance to prevent device parameter drift caused by moisture, contaminants, etc., effectively ensuring long-term operational stability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0031] Figure 1 shows the process flow of a gallium nitride ultraviolet sensor fabrication method.

[0032] Figure 2 shows the process flow of a gallium nitride ultraviolet sensor fabrication method.

[0033] Figure 3 is a partial drawing of a gallium nitride ultraviolet sensor fabrication method.

[0034] Figure 4 shows a gallium nitride ultraviolet sensor fabrication method with a gallium nitride ultraviolet sensor (a) concave gate and (b) pGaN gate sensor scheme.

[0035] Figure 5 shows a gallium nitride ultraviolet sensor fabrication method and its principle diagram.

[0036] Figure 6 is a schematic diagram illustrating the packaging principle of a gallium nitride ultraviolet sensor, which is a method for fabricating a gallium nitride ultraviolet sensor.

[0037] In the attached figures: 1-1, silicon substrate; 1-2, buffer layer; 1-3, semiconductor layer; 1-4, barrier layer; 1-5, ohmic contact metal; 1-6, first passivation layer; 1-7, metal lead; 1-8, second passivation layer. Detailed Implementation

[0038] The technical solutions of the present invention will be described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] Please refer to Figures 1-6. This invention discloses a method for fabricating a gallium nitride ultraviolet sensor, comprising the following steps:

[0040] Step a: Obtain an epitaxial wafer, which from bottom to top includes a silicon substrate 1-1, a buffer layer 1-2, a semiconductor layer 1-3, and a barrier layer 1-4;

[0041] Step b: Etch barrier layers 1-4 and part of semiconductor layers 1-3 using inductively coupled plasma etching (ICP-E).

[0042] Step c: Deposit ohmic contact metals 1-5 at both ends of the barrier layer 1-4 to form ohmic contact electrodes;

[0043] Step d: A first passivation layer 1-6 is grown on the barrier layer 1-4, the semiconductor layer 1-3 and the ohmic contact metal 1-5, and an opening is made above the ohmic contact metal 1-5 using an ICP etching process.

[0044] Step e: Prepare metal leads 1-7 on the first passivation layer 1-6, and connect the metal leads 1-7 to the ohmic contact metal 1-5 through openings;

[0045] Step f: A second passivation layer 1-8 is grown on the metal lead 1-7 and the ohmic contact metal 1-5, and the metal pad opening on the metal lead 1-7 is opened using the ICP etching process.

[0046] Step g: Use ICP etching process to open the light transmission window of the gate region on the second passivation layer 1-8, and retain a passivation layer with a thickness of 5~20nm at the light transmission window.

[0047] Specifically, this fabrication method is based on an AlGaN / GaN heterojunction structure. The fabricated sensor unit has the high-temperature stability, low power consumption, and low dark current characteristics of gallium nitride materials, effectively overcoming the limitations of traditional silicon-based sensors in terms of sensitivity and temperature drift, and providing a core device foundation for building high-performance ultraviolet sensing modules.

[0048] Specifically, this invention first utilizes an AlGaN / GaN heterojunction structure to improve the device amplification factor through a high-resistance method (using a concave gate or pGaN). By using such high-resistance devices to form a Wheatstone bridge, the response slope of the output voltage to minute changes in illumination can be improved, achieving in-situ signal amplification.

[0049] The output voltage of the Wheatstone bridge is:

[0050] ;

[0051] Ideally, in the absence of light , at this time ;

[0052] After exposure to sunlight, and As a sensor resistor, its resistance decreases when exposed to ultraviolet light. That is, it becomes At this time, the output voltage is:

[0053] ;

[0054] Further analysis revealed:

[0055] ;

[0056] Or equivalent to:

[0057] ;

[0058] In a high-resistivity state, the electron concentration of the device is low. Photoelectric conversion after ultraviolet irradiation provides a large number of charge carriers, which will... The rate of change increases, while the denominator... Correspondingly, the resistance can be reduced, and the sensitivity of the device can also be linearly improved by increasing the area of ​​the sensing region. Therefore, under the premise of ensuring stable operation in the linear region, a high-resistance structure can increase the amplification factor and improve the detection sensitivity to changes in micro-light.

[0059] Furthermore, in the high-resistance operating range, since the thermal noise voltage is proportional to the square root of the resistance, but the differential circuit can effectively filter out the common-mode temperature drift, this structure has better stability and low temperature drift performance under high-temperature conditions.

[0060] In step a, the buffer layer 1-2 is made of AlN, the semiconductor layer 1-3 is made of GaN, and the barrier layer 1-4 is made of AlGaN. In step c, the ohmic contact metal 1-5 includes one or more combinations of Ti, Al, Ni, Au, and Cr. In steps d and e, the first passivation layer 1-6 and the second passivation layer 1-8 are each independently selected from SiNx, SiO2, and Al2O3. In step e, the metal leads 1-7 are prepared by magnetron sputtering or electron beam evaporation, and the metal leads 1-7 are selected from Au, Al, Cu, Ti, Ni, and Cr. After step g, four sensors prepared using the same process are... The device unit is electrically connected using a Wheatstone bridge structure. Two sensor units serve as photosensitive devices, and the other two serve as reference devices. The reference devices are shielded by inkjet-printed carbon material to cover the light-transmitting window of their gate region. The chip integrated as a Wheatstone bridge is then packaged on-board. During packaging, a high UV transmittance encapsulant is applied above the light-transmitting window of the photosensitive device. The high UV transmittance encapsulant is a colloid with high transmittance for UV light in the wavelength range of 200 nm to 400 nm. A UV-based fused silica convex mirror is bonded on top of the photosensitive device encapsulant. The convex mirror and the encapsulant together form a microlens structure.

[0061] Specifically: The AlGaN / GaN heterojunction structure fully utilizes the wide bandgap characteristics of gallium nitride-based materials, giving the sensor excellent thermal stability and high breakdown voltage. This makes it suitable for extreme environments and high-temperature conditions such as flame detection and space exploration. The use of metal combinations forms excellent ohmic contact electrodes, ensuring the stability and reliability of the sensor unit's electrical performance, a prerequisite for achieving a highly matched bridge structure. Growing a passivation layer and retaining a window passivation layer of a specific thickness effectively prevents oxidation of the device channel region by moisture or oxygen, protecting and stabilizing the 2DEG (two-dimensional electron gas) characteristics while ensuring effective ultraviolet light transmission. The fabrication of metal interconnects using specific processes and materials ensures the reliability and low resistance of the leads, providing a guarantee for subsequent integration of a Wheatstone bridge and stable signal transmission. By integrating four highly consistent sensor units into a Wheatstone bridge, the differential principle can directly suppress common-mode noise such as temperature drift, achieving in-situ differential signal amplification without the need for external operational amplifiers, thus improving signal strength. To improve noise ratio and system integration, non-contact inkjet printing or dispensing for light shielding is employed, avoiding the disturbances caused by traditional metal shielding layers to the two-dimensional electron gas distribution in the AlGaN / GaN heterojunction. This ensures the initial matching accuracy of the four-arm resistors of the bridge, thereby improving the stability and linearity of the differential signal. On-board chip-on-board COB packaging with UV-transmitting adhesive is used. This structure has good airtightness, effectively isolating the device from environmental corrosion such as moisture and oxygen, improving the long-term reliability and environmental stability of the device, and providing a foundation for subsequent optical integration. Using high-transmittance encapsulating adhesive of specific wavelengths can ensure efficient UV light incidence while achieving environmental protection, and initially filter stray light of non-target wavelengths, improving detection accuracy. By integrating fused silica convex mirrors to form a microlens structure, UV light can be effectively focused, the incident angle can be expanded, and the optical coupling efficiency and responsivity of the sensor can be improved. At the same time, the complexity of additional assembly of discrete lenses is avoided, which is conducive to the miniaturization and mass production of the module.

[0062] Please refer to Figures 4 and 5. This embodiment provides a method for fabricating a gallium nitride ultraviolet sensor with high resistance and high sensitivity by reducing the concentration of two-dimensional electron gas (2DEG) through a concave gate structure.

[0063] The specific steps are as follows:

[0064] a. Obtain an epitaxial wafer whose structure from bottom to top includes: silicon substrate 1-1, buffer layer 1-2, semiconductor layer 1-3, and barrier layer 1-4, wherein the buffer layer 1-2 is AlN, the semiconductor layer 1-3 is GaN, and the barrier layer 1-4 is AlGaN.

[0065] b. Inductively coupled plasma (ICP) etching process is used to etch barrier layers 1-4 and part of semiconductor layers 1-3 for preliminary device isolation.

[0066] c. Using ICP etching process, the gate region of barrier layer 1-4 after step b is further etched to retain a thickness of 4~15nm to form a concave gate structure. This step can effectively reduce the concentration of two-dimensional electron gas 2DEG in AlGaN / GaN heterojunction in this region, thereby improving the initial resistance of the device.

[0067] d. At both ends of the barrier layer 1-4 after the concave gate structure is formed, ohmic contact metal 1-5 is deposited to form ohmic contact electrodes. The ohmic contact metal can be a material system such as Ti, Al, Ni, Au, Cr, etc.

[0068] e. A first passivation layer 1-6 is grown on the barrier layer 1-4, the semiconductor layer 1-3 and the ohmic contact metal 1-5. Then, the opening above the ohmic contact metal 1-5 is opened using the ICP etching process. The passivation layer material can be selected from SiNx, SiO2, Al2O3, etc.

[0069] f. Using magnetron sputtering or electron beam evaporation technology, metal leads 1-7 are grown on the first passivation layer 1-6, and connected to the ohmic contact metal 1-5 through openings. The metal lead material can be Au, Al, Cu, Ti, Ni, Cr, etc.

[0070] g. A second passivation layer 1-8 is grown on the metal leads 1-7 and the ohmic contact metal 1-5. Then, the metal pad openings on the metal leads 1-7 are opened using ICP etching. The passivation layer material can be selected from SiNx, SiO2, Al2O3, etc.

[0071] h. Using ICP etching, a light-transmitting window is opened on the second passivation layer 1-8 corresponding to the area of ​​the device recessed gate, and the etching depth is precisely controlled to retain a passivation layer with a thickness of 5~20nm. This retained thin passivation layer can effectively protect the channel from environmental influences without affecting ultraviolet light transmission.

[0072] Please refer to Figures 4 and 5. This embodiment provides a method for fabricating a gallium nitride ultraviolet sensor with high resistance and high responsivity by introducing a p-type GaN layer.

[0073] The specific steps are as follows:

[0074] a. Obtain an epitaxial wafer whose structure from bottom to top includes: silicon substrate 1-1, buffer layer 1-2, semiconductor layer 1-3, barrier layer 1-4, and p-type GaN layer, wherein the buffer layer 1-2 is AlN, the semiconductor layer 1-3 is GaN, and the barrier layer 1-4 is AlGaN.

[0075] b. The p-type GaN layer, barrier layers 1-4 and part of the semiconductor layers 1-3 are etched using inductively coupled plasma (ICP) etching process to isolate and pattern the device.

[0076] c. Using ICP etching process, the p-type GaN layer outside the gate region is selectively etched away, and the p-type GaN structure is retained only at predetermined positions. This p-type GaN layer can effectively deplete the two-dimensional electron gas 2DEG in the AlGaN / GaN heterojunction below it, thereby significantly improving the initial resistance of the device.

[0077] d. At both ends of the barrier layers 1-4, i.e., in the regions not covered by p-type GaN, deposit ohmic contact metals 1-5 to form ohmic contact electrodes. The ohmic contact metals can be made of materials such as Ti, Al, Ni, Au, and Cr.

[0078] e. A first passivation layer 1-6 is grown on the barrier layer 1-4, the semiconductor layer 1-3, the p-type GaN layer and the ohmic contact metal 1-5. Then, the opening above the ohmic contact metal 1-5 is opened using the ICP etching process. The passivation layer material can be selected from SiNx, SiO2, Al2O3, etc.

[0079] f. Using magnetron sputtering or electron beam evaporation technology, metal leads 1-7 are grown on the first passivation layer 1-6, and connected to the ohmic contact metal 1-5 through openings. The metal lead material can be Au, Al, Cu, Ti, Ni, Cr, etc.

[0080] g. A second passivation layer 1-8 is grown on the metal leads 1-7 and the ohmic contact metal 1-5. Then, the metal pad openings on the metal leads 1-7 are opened using ICP etching. The passivation layer material can be selected from SiNx, SiO2, Al2O3, etc.

[0081] h. Using ICP etching, a light-transmitting window is opened on the second passivation layer 1-8 in the region corresponding to the retained p-type GaN layer, and the etching depth is precisely controlled to retain a passivation layer with a thickness of 5~20nm. This window is used for ultraviolet light incident, while the retained thin passivation layer plays a protective role.

[0082] Please refer to Figures 1-5. This embodiment provides a method for fabricating a high-resistance, high-stability ultraviolet sensor by using silicon carbide semiconductor material to replace gallium nitride.

[0083] The specific steps are as follows:

[0084] a. Obtain an epitaxial wafer whose structure from bottom to top includes: a high-resistivity silicon carbide substrate, a buffer layer, a p-type silicon carbide (p-SiC) semiconductor layer, and an n-type barrier layer;

[0085] b. An inductively coupled plasma (ICP) etching process is used to etch the barrier layer and part of the p-SiC semiconductor layer to form the device isolation mesa;

[0086] c. Ohmic contact metal is deposited at both ends of the barrier layer to form ohmic contact electrodes. The ohmic contact metal can be made of materials such as Ni, Ti, and Al and then subjected to high-temperature annealing.

[0087] d. A first passivation layer is grown on the barrier layer, semiconductor layer and ohmic contact metal, and then the opening above the ohmic contact metal is opened using ICP etching process. The passivation layer material can be selected from SiO2, Al2O3, etc.

[0088] e. Using magnetron sputtering technology, metal leads are grown on the first passivation layer and connected to the ohmic contact metal through openings. The metal lead material can be Al, Ti, Au, etc.

[0089] f. A second passivation layer is grown on the metal lead and the ohmic contact metal, and then the metal pad opening on the metal lead is opened using the ICP etching process.

[0090] g. Using ICP etching, a light-transmitting window for the gate region is opened on the second passivation layer; subsequently, the surface of the p-SiC semiconductor layer can be nanotextured or an ultrathin SiO2 passivation layer can be grown to enhance its ultraviolet light absorption and stability.

[0091] Please refer to Figures 1-6. This embodiment provides a method for fabricating a gallium nitride ultraviolet sensor with high responsivity by introducing a floating gate structure to replace the concave gate or p-GaN layer and controlling the photogenerated charge.

[0092] The specific steps are as follows:

[0093] a. Obtain an epitaxial wafer whose structure from bottom to top includes: a silicon substrate, an AlN buffer layer, a GaN semiconductor layer, and an AlGaN barrier layer;

[0094] b. ICP etching process is used to etch the AlGaN barrier layer and part of the GaN layer to isolate the device;

[0095] c. Deposit ohmic contact metal at both ends of the barrier layer to form ohmic contact electrodes;

[0096] d. Deposit a first dielectric layer (such as Al2O3 or SiNx) as a tunneling layer across the entire structure surface;

[0097] e. On the first dielectric layer, a polysilicon floating gate layer is formed by chemical vapor deposition (CVD) and then patterned and etched.

[0098] f. Deposit a second dielectric layer (such as SiO2) on the floating gate layer as a barrier layer to complete the encapsulation and insulation of the floating gate;

[0099] g. Grow a passivation layer covering the dielectric layer and use ICP etching to open the openings connected to the ohmic contact metal;

[0100] h. Prepare metal leads and connect them to the ohmic contact metal through openings;

[0101] i. A light-transmitting window is opened directly above the floating grating, which serves as the photosensitive area. Ultraviolet light passes through the window, generating photogenerated charges that are captured by the floating grating, thereby modulating the concentration of the channel two-dimensional electron gas (2DEG).

[0102] Please refer to Figures 1-5. This embodiment provides a method for preparing an ultraviolet sensing module that uses a differential amplifier circuit to replace the Wheatstone bridge to achieve signal amplification and temperature drift compensation.

[0103] The specific steps are as follows:

[0104] a. Two AlGaN / GaN ultraviolet sensor chips with highly matched performance parameters were fabricated using conventional processes;

[0105] b. The photosensitive area of ​​one of the sensor chips is shielded as a reference device; the shielding method can be achieved by spin-coating a layer of ultraviolet-absorbing polymer coating and then curing it in a patterned manner;

[0106] c. Mount the photosensitive device and the reference device side by side on the designated pads of the same PCB substrate or ceramic substrate;

[0107] d. Mount a differential amplifier chip (such as a low-noise operational amplifier) ​​on the substrate between AlGaN and GaN;

[0108] e. Perform wire bonding: Connect the output electrode of the photosensitive device to the non-inverting input (+) of the differential amplifier, and connect the output electrode of the reference device to the inverting input (-) of the differential amplifier.

[0109] f. Use a casing with a UV-transmitting window for encapsulation, or directly apply a high UV-transmittance encapsulating adhesive over the device to form a protective layer.

[0110] Please refer to Figures 1-6. This embodiment provides a method for fabricating a highly reliable ultraviolet sensor by using a ceramic tube shell and an inorganic optical window for hermetically sealed packaging, replacing COB dispensing encapsulation.

[0111] The specific steps are as follows:

[0112] a. Complete the fabrication, testing, and dicing of a gallium nitride ultraviolet sensor chip containing a Wheatstone bridge structure;

[0113] b. Fix the chip to the central cavity of a ceramic socket (such as Al2O3 or AlN) by gold-tin eutectic bonding or conductive silver paste;

[0114] c. Gold wire bonding is used to connect the chip's electrodes to the metallized pins around the ceramic socket;

[0115] d. Place a polished magnesium fluoride (MgF2) optical window of a specific thickness onto the window ring of the ceramic tube holder.

[0116] e. Using a parallel seam welding machine, the metallized edge of the optical window is melt-sealed with the window ring of the ceramic tube seat to form a completely airtight inner cavity filled with inert gas;

[0117] f. Before or after packaging, a light-shielding metal film (such as chromium) is deposited on the inner surface of the optical window corresponding to the photosensitive area of ​​the reference device on the chip using a vacuum deposition process to complete the light shielding of the reference device.

[0118] Please refer to Figures 1-6. This embodiment provides a method for preparing a polymer light-shielding layer using spin coating and photolithography processes, replacing inkjet printing or dot coating of black glue, to achieve high-precision patterned light shielding.

[0119] The specific steps are as follows:

[0120] a. Perform standard surface cleaning and dehydration baking on the sensor wafer that has completed the front-end process and opened the light-transmitting window;

[0121] b. Fix the wafer on a spin coater and drop a negative polyimide (PI) photoresist solution that strongly absorbs ultraviolet light onto the center of the wafer;

[0122] c. Start the spin coater, first rotate at low speed to spread the adhesive, then rotate at high speed to form a uniform film, and control the film thickness by rotating for a period of time;

[0123] d. Place the spin-coated wafer on a hot plate for pre-baking to allow some of the solvent to evaporate and form a solid film;

[0124] e. Use a custom photomask to cover the wafer, and expose the areas that need to be shielded with ultraviolet light. The polymer in the exposed areas undergoes a cross-linking reaction.

[0125] f. Use a dedicated developer to spray and develop the wafer, completely dissolving and removing the polyimide in the unexposed areas, leaving only a precisely patterned polymer light-shielding pattern on the window of the reference device;

[0126] g. Finally, the wafer is placed in a high-temperature oven for imidization curing to harden the light-shielding pattern and form a strong, dense, and UV-blocking permanent light-shielding layer.

[0127] The preferred embodiments of the present invention disclosed above are only for the purpose of illustrating the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation described herein. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can better understand and utilize the present invention.

Claims

1. A method for fabricating a gallium nitride ultraviolet sensor, characterized in that: Including the following Steps: Step a: Obtain an epitaxial wafer, which from bottom to top includes a silicon substrate (1-1), a buffer layer (1-2), a semiconductor layer (1-3), and a barrier layer (1-4); Step b: Etch the barrier layer (1-4) and a portion of the semiconductor layer (1-3) using inductively coupled plasma etching (ICP); Step c: Deposit ohmic contact metals (1-5) at both ends of the barrier layer (1-4) to form ohmic contact electrodes; Step d: Grow a first passivation layer (1-6) on the barrier layer (1-4), the semiconductor layer (1-3), and the ohmic contact metal (1-5), and open an opening above the ohmic contact metal (1-5) using ICP etching; Step e: Fabricate metal leads (1-7) on the first passivation layer (1-6), wherein the metal leads (1- 7) Connect to the ohmic contact metal (1-5) through the opening; Step f: Grow a second passivation layer (1-8) on the metal lead (1-7) and the ohmic contact metal (1-5), and open the metal pad opening on the metal lead (1-7) using ICP etching process; Step g: Open the light-transmitting window of the gate region on the second passivation layer (1-8) using ICP etching process, and retain a passivation layer with a thickness of 5~20nm at the light-transmitting window. Then, connect four sensor units prepared by the same process to each other in a Wheatstone bridge structure. Two sensor units are used as photosensitive devices, and the other two sensor units are used as reference devices. The reference devices are shielded by inkjet printing carbon material to cover the light-transmitting window of their gate region.

2. The method for fabricating a gallium nitride ultraviolet sensor according to claim 1, characterized in that: In step a, the material of the buffer layer (1-2) is AlN, the material of the semiconductor layer (1-3) is GaN, and the material of the barrier layer (1-4) is AlGaN.

3. The method for fabricating a gallium nitride ultraviolet sensor according to claim 1, characterized in that: The ohmic contact metal (1-5) in step c includes one of Ti, Al, Ni, Au and Cr.

4. The method for fabricating a gallium nitride ultraviolet sensor according to claim 1, characterized in that: In steps d and e, the materials of the first passivation layer (1-6) and the second passivation layer (1-8) are each independently selected from one of SiNx, SiO2 and Al2O3.

5. The method for fabricating a gallium nitride ultraviolet sensor according to claim 1, characterized in that: The metal leads (1-7) in step e are prepared by one of magnetron sputtering and electron beam evaporation, and the material of the metal leads (1-7) is selected from Au, Al, Cu, Ti, Ni and Cr.

6. The method for fabricating a gallium nitride ultraviolet sensor according to claim 1, characterized in that: The chip integrated as a Wheatstone bridge is packaged on the board. During the packaging process, a high UV transmittance encapsulating adhesive is applied above the light-transmitting window of the photosensitive device.

7. The method for fabricating a gallium nitride ultraviolet sensor according to claim 6, characterized in that: The high UV transmittance encapsulant is a colloid with high transmittance to ultraviolet light in the wavelength range of 200 nm to 400 nm.

8. The method for fabricating a gallium nitride ultraviolet sensor according to claim 6, characterized in that: A UV-based fused silica convex mirror is bonded to the top of the photosensitive device encapsulation adhesive, and the convex mirror and the encapsulation adhesive together form a microlens structure.

Images