Fabrication method of ultra-wideband high-saturation photodetector integrated with terahertz amplifier

Abstract

This invention discloses a method for fabricating an ultra-wideband high-saturation photodetector integrating a terahertz amplifier, belonging to the technical field of basic electrical components. The fabrication method mainly includes: fabricating a terahertz amplifier active device on an InP HBT epitaxial wafer; growing a UTC-type photodetector epitaxial layer on an InP semi-insulating substrate; transferring the detector epitaxial wafer to the terahertz amplifier wafer via metal bonding; removing the detector epitaxial wafer substrate through mechanical polishing and chemical etching; fabricating an InP UTC-type photodetector; fabricating a passive terahertz amplifier device; and completing the electrical signal connection between the detector and the terahertz amplifier through vertical electrical interconnection. This method not only enables monolithic integration of an ultra-wideband high-saturation photodetector and a terahertz amplifier, but the introduction of the metal bonding layer also improves the detector's responsivity and heat dissipation, thereby enhancing the overall chip performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor devices, specifically disclosing a method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier, belonging to the technical field of basic electrical components. Background Technology

[0002] Optical mixing is an important technique for generating terahertz waves by combining optical methods with radio frequency technology. Terahertz sources generated using optical mixing technology have advantages such as wide bandwidth, continuous tunability, and ease of miniaturization. Ultra-wideband, high-saturation uni-traveling carrier (UTC) photodetectors are a typical type of terahertz optical mixing device. Compared to PIN photodetectors, electrons are the primary carriers involved in the transport process in UTC photodetectors, thus enabling them to achieve greater bandwidth and higher saturation output power.

[0003] Currently, the main drawback of ultra-wideband (UTC) photodetectors generating terahertz waves is their insufficient terahertz output power. Since terahertz amplifiers across various frequency bands have been gradually realized, monolithically integrating an UTC photodetector with a terahertz amplifier is an effective way to increase saturated output power. However, a suitable integration fabrication method is currently lacking, resulting in the absence of a solution that can effectively improve the saturated output power of UTC photodetectors.

[0004] In summary, the present invention aims to propose a method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier to overcome the shortcomings of existing ultra-wideband UTC photodetectors. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier. By integrating the terahertz amplifier with an ultra-wideband UTC photodetector through metal bonding technology, the output power of the terahertz wave generated by optical mixing technology is improved. This achieves the invention's objective of improving the responsivity performance of the ultra-wideband UTC photodetector while simultaneously increasing the saturation output power, thus solving the technical problem that the saturation output power of existing ultra-wideband UTC photodetectors needs to be improved.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0007] A method for fabricating an ultrawideband high-saturation photodetector integrated with a terahertz amplifier includes the following steps:

[0008] Step 1: Fabricate active devices based on InP HBT terahertz amplifiers on InP HBT epitaxial wafers;

[0009] Step 2: Grow a UTC type photodetector epitaxial layer on an InP semi-insulating substrate to form a UTC type photodetector epitaxial wafer;

[0010] Step 3: Transfer the UTC type photodetector epitaxial wafer onto the InP HBT epitaxial wafer via metal bonding;

[0011] Step 4: Remove the epitaxial substrate of the UTC photodetector by mechanical grinding and chemical etching;

[0012] Step 5: Fabrication of InP UTC type photodetector;

[0013] Step 6: Fabricate a passive device based on an InP HBT terahertz amplifier, and complete the electrical signal connection between the UTC photodetector and the terahertz amplifier through vertical electrical interconnection.

[0014] Further, the specific method for fabricating the active device based on the InP HBT terahertz amplifier on the InP HBT epitaxial wafer in step 1 is as follows: the emitter region, base region, and collector region of the InP HBT are prepared on the InP HBT epitaxial wafer using a wet etching process, and then the emitter metal, base metal, and collector metal are fabricated in sequence.

[0015] Further, the specific method for growing the epitaxial layer of the UTC type photodetector on the InP semi-insulating substrate in step 2 is as follows: growing the InP buffer layer, i-InGaAs etch stop layer, N-InP contact layer, N-InP drift layer, i-InGaAsP bandgap smoothing layer, i-InGaAs absorption layer, P-InGaAs absorption layer, P-InGaAsP bandgap smoothing layer, P-InP blocking layer and P-InGaAs contact layer sequentially on the InP semi-insulating substrate.

[0016] Further, the specific method for transferring the UTC-type photodetector epitaxial wafer to the InP HBT epitaxial wafer via metal bonding in step 3 is as follows: Pd, Ti, Pd, and Au are sequentially evaporated on the P-InGaAs contact layer of the UTC-type photodetector epitaxial wafer to form a P-type contact metal; Ti and Au are sequentially evaporated at the bonding positions on the InP HBT epitaxial wafer to form the bonding metal on the InP HBT epitaxial wafer; the UTC-type photodetector epitaxial wafer is inverted, and the UTC-type photodetector epitaxial wafer is transferred to the terahertz amplifier wafer via gold-gold bonding. The bonding temperature is set to 250℃, the bonding pressure is 4000mbar, and the time is 2h.

[0017] Furthermore, the specific method for removing the epitaxial substrate of the UTC photodetector in step 4 is as follows: most of the InP semi-insulating substrate of the UTC photodetector epitaxial wafer is removed by mechanical grinding, the remaining InP semi-insulating substrate and InP buffer layer are removed by wet etching, and then the i-InGaAs etching stop layer is removed by wet etching.

[0018] Further, the specific method for fabricating the InP UTC type photodetector in step 5 is as follows: An N-type contact metal is fabricated on the epitaxial wafer of the UTC type photodetector where the substrate was removed in step 4. The N-type contact metal is then annealed to form PD mesa, and the bonding metal layer is etched. During the etching of the bonding metal layer, potassium cyanide solution is used to remove Pd and Au metals, and dilute HF solution is used to remove Ti metal.

[0019] Further, the specific method for fabricating the passive device based on the InP HBT terahertz amplifier in step 6 is as follows: a styrene-cyclobutene solution is spin-coated onto the InP HBT epitaxial wafer, and the styrene-cyclobutene solution is cured at high temperature to form a first styrene-cyclobutene film. The three electrodes of the InP HBT are exposed by a dry etching process, completing the fabrication of the first wiring metal. Silicon nitride dielectric is deposited on the metal formed after the first metal wiring in the HBT collector region, and a MIM capacitor is fabricated using the silicon nitride dielectric. A styrene-cyclobutene solution is spin-coated onto the InP HBT epitaxial wafer after the MIM capacitor is fabricated, and the styrene-cyclobutene solution is cured at high temperature to form a second styrene-cyclobutene film, completing the fabrication of the second wiring metal.

[0020] Furthermore, step 6, which completes the electrical signal connection between the UTC photodetector and the terahertz amplifier through vertical electrical interconnection, specifically involves etching BCB at the corresponding positions of the second metal wiring of the terahertz amplifier and the electrodes of the UTC photodetector to form dielectric holes; and filling the dielectric holes with electroplated metal Au to achieve electrical interconnection between the UTC photodetector and the terahertz amplifier.

[0021] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0022] (1) This invention integrates a UTC type photodetector onto a terahertz amplifier epitaxial wafer using metal bonding technology. This integrated fabrication scheme allows for flexible and independent design of the epitaxial structure of the InP detector and the InP HBT, enabling both the detector and the terahertz amplifier to achieve their respective optimal performance. This provides a monolithic integration scheme that effectively increases the saturated output power of the ultra-wideband UTC type photodetector.

[0023] (2) The present invention forms a P-type contact metal by evaporating Pd, Ti, Pd and Au in sequence, which can reduce the P-type contact resistance. Since the light reflectivity of metal Pd is very high, compared with the traditional method of evaporating Ti, Pt and Au in sequence to form the detector P-type contact metal, the detector P-type contact metal prepared by the present invention has a greater light reflectivity, which enables the detector using Pd / Ti / Pd / Au as the P-type contact metal to absorb more reflected light again, thereby improving the light responsivity of the UTC type photodetector. Experimental results show that for an InGaAs light absorption layer with a thickness of 250nm, the light responsivity of the photodetector using Pd / Ti / Pd / Au as the P-type contact metal is about 18% higher than that of the detector using Ti / Pt / Au as the P-type contact metal.

[0024] (3) The present invention utilizes the advantage of high thermal conductivity of metal bonding layer to enable high bandwidth saturated photodetector to effectively dissipate heat under high power operation, thereby improving the saturated output power of detector and thus improving the output power of the entire integrated chip. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the fabrication process of an ultra-wideband high-saturation photodetector integrating a terahertz amplifier in a specific embodiment of the present invention.

[0026] Figure 2 This is a cross-sectional schematic diagram of the InP HBT-based terahertz amplifier completed in step 1 of this invention.

[0027] Figure 3 This is a diagram of the epitaxial layer structure of the InP UTC type photodetector grown in step 2 of this invention.

[0028] Figure 4 This is a schematic cross-sectional view of the detector epitaxial wafer and the terahertz amplifier wafer after metal bonding in step 3 of the present invention.

[0029] Figure 5 This is a schematic cross-sectional view of the integrated chip after step 5 of the present invention, which completes the fabrication of the InP UTC type photodetector.

[0030] Figure 6 This is a cross-sectional schematic diagram of the ultra-wideband high-saturation photodetector integrated with a terahertz amplifier, completed in step 6 of the present invention.

[0031] The labels in the diagram are as follows: 1. InP HBT epitaxial substrate, 2. InP HBT emitter region, 3. InP HBT base region, 4. InPHBT collector region, 5. Bonding metal of InP HBT epitaxial wafer, 6. P-type contact metal, 7. Detector epitaxial layer, 8. Detector substrate, 9. PD mesa, 10. First BCB film, 11. First wiring metal, 12. MIM capacitor, 13. Second BCB film, 14. Second wiring metal, 15. Third BCB film, 16. Third wiring metal. Detailed Implementation

[0032] The technical solution of the invention will now be described in detail with reference to the accompanying drawings.

[0033] The technical solutions of the present invention will now be described in detail with reference to the accompanying drawings.

[0034] This embodiment provides a method for fabricating an ultra-wideband high-saturation photodetector integrated with a terahertz amplifier. The flowchart of this fabrication method is shown below. Figure 1 As shown, it specifically includes the following 6 steps.

[0035] Step 1: Fabricate an active device based on an InP HBT terahertz amplifier on the InP HBT epitaxial wafer 1. The specific method is as follows: Using a wet etching process, etch the three mesa areas of the InP HBT emitter region 2, InP HBT base region 3, and InP HBT collector region 4 on the InP HBT epitaxial substrate 1. This sequentially fabricates the emitter metal, base metal, and collector metal, resulting in the InP HBT-based terahertz amplifier. Figure 2 As shown.

[0036] Step 2: Grow an InP UTC type photodetector epitaxial layer on an InP semi-insulating substrate. The structure of the grown epitaxial layer material is as follows: Figure 3As shown, from bottom to top, the layers are: a 0.5 μm InP buffer layer (i.e., indium phosphide buffer layer), a 0.4 μm i-InGaAs etch stop layer (i.e., intrinsic indium gallium arsenide etch stop layer), a 0.4 μm N-InP contact layer (i.e., N-type indium phosphide contact layer), a 0.2 μm N-InP drift layer (i.e., N-type indium phosphide drift layer), a 0.01 μm i-InGaAsP bandgap smoothing layer (i.e., intrinsic indium gallium arsenide phosphide bandgap smoothing layer), and a 0.1 μm i-InGaAs absorber layer (i.e., ... The structure consists of an intrinsic indium gallium arsenide (IGaAs) absorber layer, a 0.15 μm P-InGaAs absorber layer (i.e., a P-type IGaAs absorber layer), a 0.01 μm P-InGaAsP bandgap smoothing layer (i.e., a P-type IGaAs phosphide bandgap smoothing layer), a 0.1 μm P-InP blocking layer (i.e., a P-type indium phosphide blocking layer), and a 0.1 μm P-InGaAs contact layer (i.e., a P-type IGaAs contact layer). The center wavelengths of the I-InGaAsP bandgap smoothing layer and the P-InGaAsP bandgap smoothing layer are both 1.2 μm.

[0037] Step 3: Evaporate P-type contact metal 6 on the P-InGaAs contact layer of the InP UTC photodetector epitaxial wafer. The P-type contact metal 6 is prepared by sequentially evaporating Pd, Ti, Pd, and Au. Evaporate bonding metal 5 of the InP HBT epitaxial wafer on the terahertz amplifier wafer. The bonding metal 5 of the InP HBT epitaxial wafer is prepared by sequentially evaporating Ti and Au. Invert the InP UTC photodetector epitaxial wafer and transfer it to the terahertz amplifier wafer via gold-gold bonding. The bonding temperature is set to 250℃, the bonding pressure to 4000 mbar, and the bonding time to 2 hours. Figure 4 This is a schematic diagram of the cross-section of the detector epitaxial wafer and the terahertz amplifier wafer after metal bonding. The bonded detector epitaxial layer 7 is located above the P-type contact metal 6, and the detector substrate 8 is located above the detector epitaxial layer 7.

[0038] Step 4: Remove the detector substrate 8 by mechanical polishing and chemical etching. The specific methods are as follows: remove most of the InP semi-insulating substrate by mechanical polishing; remove the remaining InP semi-insulating substrate and InP buffer layer by wet etching. The etching solution used is a mixed solution of phosphoric acid and hydrochloric acid, which can etch InP relatively quickly, but reacts slowly with InGaAs; then remove the i-InGaAs etching stop layer by wet etching. The etching solution used is a mixed solution of phosphoric acid, hydrogen peroxide and water, which can etch InGaAs relatively quickly, but reacts slowly with InP.

[0039] Step 5: The specific method for fabricating the InP UTC type photodetector is as follows: An N-type contact metal, AuGeNi / Au, is fabricated on the N-InP contact layer; the N-type contact metal is annealed at 405℃ for 50s; using photoresist as a mask, the N-InP contact layer, N-InP drift layer, i-InGaAsP bandgap smoothing layer, i-InGaAs absorption layer, P-InGaAs absorption layer, P-InGaAsP bandgap smoothing layer, P-InP blocking layer, and P-InGaAs contact layer are etched sequentially to form the PD mesa 9. The etching solution for InP is a mixture of hydrochloric acid and phosphoric acid, and the etching solutions for InGaAsP and InGaAs are a mixture of phosphoric acid, hydrogen peroxide, and water; using photoresist as a mask, potassium cyanide solution is used to remove Pd and Au metals from the etched bonding metal layer, and dilute HF solution is used to remove Ti metals from the etched bonding metal layer. Figure 5 This is a schematic diagram of the cross-section of the integrated chip after the fabrication of the InP UTC type ultrawideband high saturation photodetector is completed.

[0040] Step 6: Fabricate passive devices based on the InP HBT terahertz amplifier, and complete the electrical signal connection between the detector and the terahertz amplifier through vertical electrical interconnection. First, the passive devices in the terahertz amplifier are fabricated. The specific steps are as follows: spin-coating a styrene-cyclobutene solution onto the terahertz amplifier wafer and curing it at high temperature to achieve planarization of the first BCB film 10. Then, the three electrodes of the InP HBT device are exposed by a dry etching process to complete the fabrication of the first wiring metal 11. After that, SiN dielectric is deposited to fabricate the MIM capacitor 12, BCB is spin-coated and cured at high temperature to achieve planarization of the second BCB film 13, and finally, the second wiring metal 14 is fabricated. After the passive part of the terahertz amplifier is prepared, BCB solution is spin-coated to achieve the planarization of the third BCB film 15. BCB is etched in the vertical space where the second wiring metal 14 of the terahertz amplifier and the electrode metal of the InP UTC type photodetector are located to form dielectric holes. The dielectric holes are filled by electroplating metal Au to complete the fabrication of the third wiring metal 16 and realize the electrical interconnection between the detector and the terahertz amplifier. Figure 6 This is a schematic cross-sectional view of a completed ultrawideband high-saturation photodetector with an integrated terahertz amplifier.

[0041] The above embodiments are merely illustrative examples of the present invention and do not limit its scope of protection. Those skilled in the art can make local modifications. For example, a metal with low contact resistance and high light emissivity can be selected as the bonding metal. This can effectively improve the photoresponsivity and saturated output power of the detector while integrating the terahertz amplifier and the ultra-wideband UTC photodetector. The preparation method of the present invention can also be used for ultra-wideband UTC photodetectors and terahertz amplifiers with specific structures as described in this embodiment, and any equivalent substitutions that conform to the spirit of the invention fall within the scope of protection of the present invention.

Claims

1. A method for fabricating an ultra-broadband high-saturation photodetector integrated with a terahertz amplifier, characterized in that, Includes the following steps: Step 1: Fabricate an active device based on an indium phosphide heterojunction transistor terahertz amplifier on an indium phosphide heterojunction transistor epitaxial wafer; Step 2: Grow a UTC-type photodetector epitaxial layer on an indium phosphide semi-insulating substrate to form a UTC-type photodetector epitaxial wafer. The specific method for growing the UTC-type photodetector epitaxial layer on the indium phosphide semi-insulating substrate is as follows: sequentially grow an indium phosphide buffer layer, an intrinsic indium gallium arsenide etch stop layer, an N-type indium phosphide contact layer, an N-type indium phosphide drift layer, an intrinsic indium gallium arsenide phosphide bandgap smoothing layer, an intrinsic indium gallium arsenide absorbing layer, a P-type indium gallium arsenide absorbing layer, a P-type indium gallium arsenide phosphide bandgap smoothing layer, a P-type indium phosphide blocking layer, and a P-type indium gallium arsenide contact layer on the indium phosphide semi-insulating substrate. Step 3: The UTC-type photodetector epitaxial wafer is transferred to the indium phosphide heterojunction transistor epitaxial wafer using metal bonding technology. The specific method is as follows: Palladium, titanium, palladium, and gold are sequentially evaporated onto the P-type indium gallium arsenide contact layer of the UTC-type photodetector epitaxial wafer to form the P-type contact metal of the UTC-type photodetector epitaxial wafer. Titanium and gold are evaporated on the epitaxial wafer of the indium phosphide heterojunction transistor to form the bonding metal of the epitaxial wafer. The UTC photodetector epitaxial wafer forming the P-type contact metal is inverted, and the P-type contact metal is bonded to the bonding metal of the indium phosphide heterojunction transistor epitaxial wafer to form a bonding metal layer. The UTC photodetector epitaxial wafer is then transferred onto the indium phosphide heterojunction transistor epitaxial wafer. Step 4: Remove the epitaxial substrate of the UTC type photodetector; Step 5: Fabrication of indium phosphide UTC photodetector; Step 6: Fabricate a passive device based on an indium phosphide heterojunction transistor terahertz amplifier, and complete the electrical signal connection between the indium phosphide UTC photodetector and the indium phosphide heterojunction transistor terahertz amplifier through vertical electrical interconnection.

2. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 1, characterized in that, The specific method for removing the UTC type photodetector epitaxial wafer substrate in step 4 is as follows: remove the indium phosphide semi-insulating substrate of the UTC type photodetector epitaxial wafer by mechanical grinding, remove the remaining indium phosphide semi-insulating substrate and indium phosphide buffer layer by wet etching, and then remove the intrinsic indium gallium arsenide etching stop layer by wet etching.

3. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 2, characterized in that, The etching solution used to remove the remaining indium phosphide semi-insulating substrate and indium phosphide buffer layer by wet etching is a mixed solution of phosphoric acid and hydrochloric acid. The etching solution used to remove the intrinsic indium gallium arsenide etching stop layer by wet etching is a mixed solution of phosphoric acid, hydrogen peroxide and water.

4. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 2, characterized in that, The specific method for preparing the indium phosphide UTC type photodetector in step 5 is as follows: In step 4, after removing the substrate, an N-type contact metal is prepared on the epitaxial wafer of the UTC type photodetector, and the N-type contact metal is annealed. Using photoresist as a mask, the N-type indium phosphide contact layer, N-type indium phosphide drift layer, intrinsic indium gallium arsenide phosphide bandgap smoothing layer, intrinsic indium gallium arsenide absorption layer, P-type indium gallium arsenide absorption layer, P-type indium gallium arsenide phosphide bandgap smoothing layer, P-type indium phosphide barrier layer and P-type indium gallium arsenide contact layer are etched sequentially to form a PD mesa. Corrosion of bonded metal layers.

5. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 4, characterized in that, During the process of etching the bonded metal layer, potassium cyanide solution is used to remove palladium and gold, and dilute HF solution is used to remove titanium.

6. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 4, characterized in that, The specific method for fabricating the passive device based on the indium phosphide heterojunction transistor terahertz amplifier in step 6 is as follows: After fabricating an indium phosphide UTC photodetector, a styrene solution was spin-coated onto the epitaxial wafer of an indium phosphide heterojunction transistor. The styrene solution was then cured at high temperature to form a first styrene film. The three electrodes of the indium phosphide heterojunction transistor were exposed by a dry etching process, thus completing the fabrication of the first wiring metal. Silicon nitride dielectric is deposited on the metal formed after the first metal wiring in the collector region of the heterojunction transistor, and MIM capacitors are fabricated using silicon nitride dielectric. A styrene solution was spin-coated onto the epitaxial wafer of an indium phosphide heterojunction transistor after the fabrication of the MIM capacitor. The styrene solution was then cured at high temperature to form a second styrene film, thus completing the fabrication of the second wiring metal.

7. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to claim 6, characterized in that, The specific method for completing the electrical signal connection between the indium phosphide UTC photodetector and the indium phosphide heterojunction transistor-based terahertz amplifier in step 6 via vertical electrical interconnection is as follows: After the second wiring metal fabrication was completed, a styrene solution was spin-coated onto the epitaxial wafer of the indium phosphide heterojunction transistor, and the styrene solution was cured at high temperature to form a third styrene film. A styrene-cyclobutene film is etched in the vertical space where the second wiring metal and the electrode metal of the indium phosphide UTC photodetector are located to form a dielectric hole; the dielectric hole is filled by electroplating gold; and the electrical interconnection between the indium phosphide UTC photodetector and the indium phosphide heterojunction transistor terahertz amplifier is completed by fabricating the third wiring metal.

8. The method for fabricating an ultra-wideband high-saturation photodetector with an integrated terahertz amplifier according to any one of claims 1 to 7, characterized in that, The specific method for fabricating an active device based on an indium phosphide heterojunction transistor terahertz amplifier on an indium phosphide heterojunction transistor epitaxial wafer in step 1 is as follows: the emitter region, base region, and collector region of the indium phosphide heterojunction transistor are prepared on the indium phosphide heterojunction transistor epitaxial wafer using a wet etching process, and then the emitter metal, base metal, and collector metal are fabricated sequentially.

Images