Flip photodiode and manufacturing method thereof

Abstract

The invention relates to the technical field of chip manufacturing, in particular to a flip photodiode and a manufacturing method thereof.The flip photodiode comprises an epitaxial wafer, a reflecting layer and a lens layer, and a P electrode and an N electrode are arranged on the epitaxial wafer; the lens layer receives an optical signal from the laser, the epitaxial wafer absorbs the optical signal to generate an electric signal, and the electric signal is transmitted through the P electrode and the N electrode; the reflecting layer reflects the optical signal, so that the epitaxial wafer repeatedly absorbs the optical signal; a lens layer is corroded on the back surface of an epitaxial wafer, so that an optical signal enters from the back surface of the photodiode, and the coupling problem of the photodiode with light entering from the back surface and a laser is solved; and on the other hand, the reflecting layer is arranged on the front surface of the photodiode, so that after the optical signal transmitted from the lens layer is absorbed by the epitaxial wafer, the remaining optical signal can be reflected back by the reflecting layer to be continuously absorbed, the thickness of the absorbing layer in the epitaxial wafer is reduced, and the response speed is improved under the condition that the responsivity of the photodiode is not influenced.

Description

Technical Field

[0001] This invention relates to the field of chip manufacturing technology, and in particular to a flip-chip photodiode and its fabrication method. Background Technology

[0002] Currently, dispersion loss and chirp have become important factors restricting technological development in long-distance optical fiber communication. Therefore, electro-absorption modulated lasers (EMLs) are receiving increasing attention. Their packaging differs from traditional TOs. The photodiode for backlight detection must be horizontally mounted with the EML. Therefore, side-ported ESPDs are currently mainly used to monitor the EML.

[0003] With the development of 400G, 800G and higher speeds, photomultiplier tubes (EMLs) using lithium niobate as the photoelectric material have rapidly developed. Side-lit ESPDs are no longer suitable for monitoring this type of EML. Currently, front-lit monitor photodiodes (MPDs) are used to monitor this type of EML. To maintain the responsivity R, the MPD has a thicker absorption layer and a larger photosensitive surface. Due to the perpendicular incidence of light and the inconsistent optical path, f... 3db With speeds of only around 500MHz, it's difficult to achieve speeds of 1-2GHz. Therefore, existing photodiodes can no longer meet the requirements for monitoring the optical path of high-speed modulated lasers.

[0004] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to solve the problem of low responsivity of existing front-facing photodiodes.

[0006] The present invention adopts the following technical solution:

[0007] In a first aspect, a flip-chip photodiode is provided, comprising: an epitaxial wafer 1, a reflective layer 2, and a lens layer 3, wherein the reflective layer 2 is disposed above the epitaxial wafer 1, and the lens layer 3 is disposed at the bottom of the epitaxial wafer 1; a P electrode and an N electrode are disposed on the epitaxial wafer 1.

[0008] The lens layer 3 is used for coupling with the laser and for receiving optical signals from the laser. The epitaxial wafer 1 is used for absorbing the optical signals to generate electrical signals and transmitting the electrical signals through the P and N electrodes. The reflective layer 2 is used for reflecting the optical signals so that the epitaxial wafer 1 can repeatedly absorb the optical signals.

[0009] Preferably, the epitaxial wafer 1 includes a substrate layer 10, a buffer layer 11, an absorption layer 12, a cap layer 13 and a contact layer 14 stacked sequentially, wherein the contact layer 14 covers a portion of the cap layer 13;

[0010] An insulating layer 4 is also provided on the cap layer 13; the lens layer 3 is disposed at the bottom of the substrate layer 10, a part of the reflective layer 2 is disposed on the insulating layer 4, and another part of the reflective layer 2 is disposed on the cap layer 13.

[0011] Preferably, a first opening is formed on the insulating layer 4, and a portion of the cap layer 13, a portion of the absorbent layer 12, and a portion of the buffer layer 11 are sequentially etched through the first opening to obtain an etching hole 5. The insulating layer 4 is disposed around the outer ring of the etching hole 5 and on the surface of the cap layer 13; wherein, the etching hole 5 terminates at the buffer layer 11.

[0012] An N metal contact layer 6 is provided on the corrosion hole 5, and the N metal contact layer 6 and the corrosion hole 5 form an ohmic contact to obtain the N electrode.

[0013] Preferably, a second opening is formed on the insulating layer 4, and the contact layer 14 is disposed on the cap layer 13 corresponding to the second opening; a diffusion material is diffused from the second opening to a portion of the cap layer 13 to form a diffusion hole 7;

[0014] A P-metal contact layer 8 is also provided on the contact layer 14. The P-metal contact layer 8, the contact layer 14, and the diffusion hole 7 constitute an ohmic contact to obtain the P electrode.

[0015] Preferably, the contact layer 14 is a contact ring, and another part of the reflective layer 2 is disposed in the inner ring of the contact layer 14 and is in the same plane as the contact ring.

[0016] Preferably, the materials of the P electrode and the N electrode are one or more of Ti, Pt and Au.

[0017] Secondly, a method for fabricating a flip-chip photodiode is provided, the method being used to fabricate the flip-chip photodiode as described in the first aspect, comprising:

[0018] An epitaxial wafer 1 is fabricated, and a reflective layer 2 is fabricated on top of the epitaxial wafer 1, and a lens layer 3 is fabricated on the bottom of the epitaxial wafer 1;

[0019] P-electrodes and N-electrodes are fabricated on the epitaxial wafer 1;

[0020] The lens layer 3 is used for coupling with the laser and for receiving optical signals from the laser. The epitaxial wafer 1 is used for absorbing the optical signals to generate electrical signals and transmitting the electrical signals through the P and N electrodes. The reflective layer 2 is used for reflecting the optical signals so that the epitaxial wafer 1 can repeatedly absorb the optical signals.

[0021] Preferably, the fabrication of the epitaxial wafer 1, the fabrication of a reflective layer 2 on top of the epitaxial wafer 1, and the fabrication of a lens layer 3 on the bottom of the epitaxial wafer 1 include:

[0022] A buffer layer 11, an absorption layer 12, a cap layer 13, and a contact layer 14 are sequentially grown on a substrate layer 10 to obtain the epitaxial wafer 1;

[0023] An insulating layer 4 is formed on the cap layer 13, and the reflective layer 2 is disposed on the insulating layer 4;

[0024] A lens is etched into the bottom of the substrate layer 10 to obtain the lens layer 3.

[0025] Preferably, the fabrication of the P-electrode and N-electrode on the epitaxial wafer 1 includes:

[0026] A first opening is formed on the insulating layer 4. Through the first opening, a portion of the cap layer 13, a portion of the absorbent layer 12 and a portion of the buffer layer 11 are etched to obtain an corrosion hole 5, so as to form an N-type contact layer.

[0027] A second opening is formed on the insulating layer 4, and the diffusion material is diffused from the second opening to a portion of the cap layer 13 to form a diffusion hole 7, thereby forming a P-type contact layer;

[0028] A reflective layer 2 is deposited on the insulating layer 4, the area corresponding to the first opening and the second opening;

[0029] Remove the reflective layer 2 at the first opening to expose the N-type contact layer; remove part of the reflective layer 2 at the second opening to expose the P-type contact layer;

[0030] An N-metal contact layer 6 is formed in the region corresponding to the first opening, and a P-metal contact layer 8 is formed in the region corresponding to the second opening, so as to obtain the P electrode and the N electrode respectively.

[0031] Preferably, fabricating P-electrodes and N-electrodes on the epitaxial wafer 1 further includes:

[0032] A second opening is formed on the insulating layer 4, and the diffusion material is diffused from the second opening to a portion of the cap layer 13 to form a diffusion hole 7, thereby forming a P-type contact layer;

[0033] A reflective layer 2 is deposited on the insulating layer 4 and the area corresponding to the second opening;

[0034] Remove part of the reflective layer 2 at the second opening to expose the P-type contact layer;

[0035] A P-metal contact layer 8 is formed in the region corresponding to the second opening to obtain the P electrode;

[0036] An N metal contact layer 6 is disposed at the bottom of the substrate layer 10, away from the lens layer 3, to obtain the N electrode.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] This invention provides a flip-chip MPD photodiode, comprising: an epitaxial wafer 1, a reflective layer 2, and a lens layer 3. A P-electrode and an N-electrode are disposed on the epitaxial wafer 1. The lens layer 3 receives an optical signal from a laser, and the epitaxial wafer 1 absorbs the optical signal to generate an electrical signal, which is then transmitted through the P-electrode and N-electrode. The reflective layer 2 reflects the optical signal, allowing the epitaxial wafer 1 to repeatedly absorb the optical signal. This invention employs a back-light-entry photodiode, meaning that by etching the lens layer 3 on the back side of the epitaxial wafer 1, the optical signal can enter from the back side of the photodiode, solving the coupling problem between the back-light-entry photodiode and the laser. Furthermore, by providing the reflective layer 2 on the front side of the photodiode, after the optical signal from the lens layer 3 is absorbed by the epitaxial wafer 1, the remaining optical signal can be reflected back by the reflective layer 2 for further absorption. This reduces the thickness of the absorption layer 12 in the epitaxial wafer 1, thereby improving the response speed without affecting the photodiode's responsivity. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the structure of a flip-chip photodiode provided in an embodiment of the present invention;

[0041] Figure 2This is a schematic diagram of another flip-chip photodiode provided in an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram of the epitaxial wafer structure of a flip-chip photodiode provided in an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram of the insulating layer and reflective layer of a flip-chip photodiode provided in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram of the etched holes and diffusion holes of a flip-chip photodiode provided in an embodiment of the present invention;

[0045] Figure 6 This is a top view schematic diagram of a flip-chip photodiode provided in an embodiment of the present invention;

[0046] Figure 7 This is a schematic flowchart of a method for fabricating a flip-chip photodiode according to an embodiment of the present invention;

[0047] Figure 8 This is a schematic flowchart of another method for manufacturing a flip-chip photodiode provided in an embodiment of the present invention;

[0048] Figure 9 This is a schematic diagram of another structure of an epitaxial wafer for a flip-chip photodiode provided in an embodiment of the present invention;

[0049] Figure 10 This is a schematic diagram of the fabrication stage structure of a flip-chip photodiode provided in an embodiment of the present invention;

[0050] Figure 11 This is a top view structural diagram of the fabrication stage of a flip-chip photodiode provided in an embodiment of the present invention;

[0051] Figure 12 This is a schematic diagram of the lens layer structure of a flip-chip photodiode provided in an embodiment of the present invention;

[0052] Figure 13 This is a schematic diagram of the photosensitive surface of a flip-chip photodiode provided in an embodiment of the present invention;

[0053] Figure 14 This is a schematic diagram of the structure of a P-electrode provided in an embodiment of the present invention;

[0054] Figure 15 This is a schematic diagram of the structure of a P electrode and an N electrode provided in an embodiment of the present invention.

[0055] In all the accompanying drawings, the same reference numerals denote the same structure, wherein:

[0056] Epitaxial wafer 1, substrate layer 10, buffer layer 11, absorption layer 12, cap layer 13, contact layer 14, reflective layer 2, lens layer 3, insulating layer 4, etched hole 5, N metal contact layer 6, diffusion hole 7, P metal contact layer 8, photosensitive surface 9. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0058] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0059] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, for example, the description may use the prefix "A" or "B" to describe the same type of nouns as two independent entities. In this case, the corresponding features defined with "A" and "B" are used only to distinguish between similar entities and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0060] In describing some embodiments, the terms "coupled," "coupled," and "connected," and their derivative expressions, may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. Similarly, the term "coupled" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the terms "connected" or "coupled" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other, such as "optical coupling," "wireless connection," etc. The embodiments disclosed herein are not necessarily limited to the scope of this invention.

[0061] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0062] Example 1:

[0063] EML is a type of laser used in fiber optic communication, which modulates the laser output through an electro-absorption modulation mechanism. It typically features high modulation speed and low power consumption, making it highly useful in high-speed communication systems. ESPD is a side-aperture photodiode suitable for monitoring high-speed modulated lasers. However, with the development of 400G, 800G, and even higher speeds, electro-absorption modulators using lithium niobate as the optoelectronic material have rapidly developed. These employ waveguide transmission, necessitating the use of front-aperture MPDs to monitor the laser output.

[0064] To maintain a high responsivity R, traditional front-facing MPDs typically have a thicker absorption layer and a larger photosensitive area. Under high-speed modulation, the thicker absorption layer may prolong the signal response time, thus affecting the accuracy of monitoring. Furthermore, because traditional MPDs are front-facing, the light needs to be incident perpendicularly onto the absorption layer. In high-speed modulated lasers, the optical path between the laser and the photodiode may experience slight offsets due to packaging structure, thermal expansion, and mechanical vibrations. This leads to optical path inconsistency, resulting in f... 3db (The third-order cutoff frequency of a photodiode describes the upper limit of its response frequency when receiving optical signals.) It is only about 500M, which is difficult to achieve speeds of 1-2G and can no longer meet the monitoring optical path requirements of high-speed modulators.

[0065] To address the aforementioned problems, Embodiment 1 of the present invention provides a flip-chip photodiode, such as... Figure 1As shown, the system includes: an epitaxial wafer 1, a reflective layer 2, and a lens layer 3. The reflective layer 2 is disposed above the epitaxial wafer 1, and the lens layer 3 is disposed at the bottom of the epitaxial wafer 1. A P electrode (represented by P in the figure) and an N electrode (represented by N in the figure) are disposed on the epitaxial wafer 1. The lens layer 3 is used for coupling with a laser and for receiving optical signals from the laser. The epitaxial wafer 1 is used for absorbing the optical signals to generate electrical signals and transmitting the electrical signals through the P electrode and the N electrode. The reflective layer 2 is used for reflecting the optical signals so that the epitaxial wafer 1 can repeatedly absorb the optical signals.

[0066] For ease of description, directional terms such as "above" and "bottom" are limited to use in [specific contexts]. Figure 1 The vertical position of the device in the text does not represent the actual vertical position of the device during use. This will be consistent in the following text and will not be explained further in this embodiment.

[0067] The epitaxial wafer 1 is the core component of the photodiode, typically made of multilayer semiconductor materials. The epitaxial wafer 1 contains P-layers, I-layers, and N-layers. The I-layer is an absorption layer that absorbs light signals and generates electrical signals. The P-layer is composed of P-type semiconductors, and the N-layer is composed of N-type semiconductors. N-type semiconductors contain excess electrons, and P-type semiconductors contain excess holes. Photons (particles of light) interact with electrons in the semiconductor materials. If the energy of the photons is high enough (greater than or equal to the band gap energy of the material), they can excite electrons to transition from the valence band to the conduction band, generating electron-hole pairs. These electron-hole pairs are separated under the electric field of the PN junction; electrons are pushed towards the N-type region, and holes are pushed towards the P-type region, thus creating a potential difference across the PN junction, i.e., the photocurrent.

[0068] The reflective layer 2 is located above the epitaxial wafer 1. Its function is to reflect the light signal that has not been absorbed by the epitaxial wafer 1, allowing it to shine back onto the epitaxial wafer 1, thereby increasing the absorption probability of photons in the light signal and improving the photoelectric conversion efficiency. The lens layer 3 is located at the bottom of the epitaxial wafer 1 and is usually made of a high refractive index material, such as silicone or polymer. The function of the lens layer 3 is to collect the light signal emitted from the laser and focus it onto the absorption layer in the epitaxial wafer 1, thereby improving the intensity of the light signal and the photoelectric conversion efficiency.

[0069] In one embodiment, such as Figure 2 As shown, a photosensitive surface 9 is also provided on the back side of the lens layer 3. The photosensitive surface 9 is used to couple with the laser to improve the absorption efficiency of the optical signal. The photosensitive layer is made of a silicon-nitrogen compound, such as a SiNx antireflection film.

[0070] The P electrode and the N electrode are respectively connected to the P layer and N layer regions of the epitaxial wafer 1, and are used to collect the electrical signal generated by the optical signal and transmit it to an external circuit. In one embodiment, the materials of the P electrode and the N electrode can be one or more of Ti, Pt, and Au. For example, the P electrode and the N electrode are made of... Ti、 Pt and Au was obtained by alternating growth.

[0071] The working principle of the photodiode is as follows:

[0072] The lens layer 3 acts as an optical focuser, directing the light signal from the laser onto the absorption layer of the epitaxial wafer 1, thus increasing the intensity of the light signal. The lens layer 3 converges the received light signal and transmits it to the epitaxial wafer 1. Photons in the light signal are absorbed by the semiconductor material. Under the influence of the photon energy, the covalent bonds within the semiconductor are ionized, generating electron-hole pairs. At the PN junction in the epitaxial wafer 1, due to the built-in electric field of the PN junction, electrons are pushed towards the N-region, and holes are pushed towards the P-region, thereby achieving electron-hole pair separation. Under reverse bias, photogenerated electrons and holes drift in the N-region and P-region of the PN junction, respectively, forming a photocurrent. This process is known as the photoconductivity effect. The reflective layer 2 reflects the light signal that has not been absorbed by the epitaxial wafer 1 back into the semiconductor material, increasing the number of absorption cycles and thus improving the photoelectric conversion efficiency. The photocurrent is transmitted to the P and N electrodes and output through an external circuit, ultimately forming a detectable electrical signal.

[0073] The photodiode with a flip-chip structure proposed in this embodiment effectively improves the absorption of optical signals and the output efficiency of electrical signals by integrating the reflective layer 2 and the lens layer 3 onto the epitaxial wafer 1, thereby effectively improving the responsivity of the photodiode.

[0074] The structure of the photodiode will now be described in detail. In one embodiment, such as... Figure 3 and Figure 4 As shown, the epitaxial wafer 1 includes a substrate layer 10, a buffer layer 11, an absorption layer 12, a cap layer 13, and a contact layer 14 stacked sequentially, wherein the contact layer 14 covers a portion of the cap layer 13; an insulating layer 4 is also disposed on the cap layer 13; the lens layer 3 is disposed at the bottom of the substrate layer 10, a portion of the reflective layer 2 is disposed on the insulating layer 4, and another portion of the reflective layer 2 is disposed on the cap layer 13.

[0075] The substrate layer 10 is typically a stable semiconductor material, providing support for the entire structure. The buffer layer 11 is located above the substrate layer 10, and the buffer layer 11 can be an N-type InP buffer layer with a doping concentration of 1e17cm⁻¹. -3 -1.5e17cm -3 The thickness is 1.0µm-2.0µm. The doping concentration of the N-type InP buffer layer can be 1e17cm. -3 It can also be 1.5e17cm -3 It can also be 1e17cm -3 -1.5e17cm -3 For any doping concentration between 1.0µm and 2.0µm, the thickness of the N-type InP buffer layer can be 1.0µm or 2.0µm, or any thickness value between 1.0µm and 2.0µm. This rule applies to the following text and will not be elaborated further in this embodiment.

[0076] The absorption layer 12 is the key light absorption region of the photodiode, typically having a small band gap to effectively absorb light signals. It is usually composed of heavily doped semiconductor materials to improve light absorption efficiency. The absorption layer 12 can be a type I InGaAs absorption layer with a doping concentration of 1e13cm⁻¹. -3 -1e15cm -3 The thickness is 1.0um-3.5um.

[0077] The cap layer 13 is located above the absorption layer 12. Its function is to protect the absorption layer 12 from environmental factors and also to provide passivation, reducing surface defects. The cap layer 13 can be a P-type InP cap layer with a doping concentration of 1e17cm⁻¹. -3 -1e18cm -3 The thickness is 0.5-1.5um.

[0078] The contact layer 14 is located above the cap layer 13 and is used to provide electrical contact with external circuits. The contact layer 14 can be a P+ type InGaAs contact layer with a doping concentration greater than 1e19cm. -3 The thickness is 0.1um-0.2um.

[0079] The insulating layer 4 is located above the cap layer 13, and a portion of the reflective layer 2 is disposed on the insulating layer 4. The function of the insulating layer 4 is to isolate the semiconductor material and the reflective layer 2, prevent charge injection, and maintain the electrical insulation of the reflective layer 2.

[0080] The structural design of the epitaxial wafer 1 maximizes light absorption efficiency and enhances the focusing and repetitive absorption of light signals through the reflective layer 2 and lens layer 3, thereby improving the photoelectric conversion efficiency of the photodiode. Simultaneously, by precisely controlling the doping concentration level and materials of each layer, the overall electrical performance of the photodiode can be optimized.

[0081] To obtain the N electrode, in one embodiment, such as Figure 5 and Figure 6 As shown, a first opening is formed in the insulating layer 4. Through this first opening, a portion of the cap layer 13, a portion of the absorber layer 12, and a portion of the buffer layer 11 are sequentially etched to obtain an etching hole 5. The insulating layer 4 is disposed around the outer ring of the etching hole 5 and on the surface of the cap layer 13. The etching hole 5 terminates at the buffer layer 11. An N-metal contact layer 6 is disposed on the etching hole 5, and the N-metal contact layer 6 and the etching hole 5 form an ohmic contact to obtain the N-electrode. First, an opening is formed in the insulating layer 4 to obtain the first opening. Through this first opening, a portion of the cap layer 13, a portion of the absorber layer 12, and a portion of the buffer layer 11 are sequentially etched to obtain the etching hole 5. The purpose of the etching hole 5 is to expose the buffer layer 11 and the absorber layer 12 to facilitate the formation of the N-electrode in subsequent steps. Compared to the etching area of ​​current MPD methods, the etching area of ​​the etching hole 5 in this embodiment is increased by 10µm x 10µm, which ensures good metal contact and reduces the positive voltage. Depositing the N metal contact layer 6 on the corrosion pit 5 is typically achieved through methods such as physical vapor deposition or chemical vapor deposition. In one embodiment, the material of the N metal contact layer 6 can be... Ti、 Pt and Au was obtained by alternating growth.

[0082] The N-metal contact layer 6 and the etched hole 5 form an ohmic contact. An ohmic contact is a contact between a metal and a semiconductor, characterized by low resistivity that is almost independent of the work function difference between the two. This contact method ensures good conductivity and stability. Through the above steps, an ohmic contact is formed between the N-metal contact layer 6 on the etched hole 5 and the semiconductor material, thus obtaining the N-electrode. The N-electrode is used to collect electrons generated by photogenerated carriers in the absorption layer 12.

[0083] like Figure 6As shown, the photodiode can be frustum-shaped, or in one embodiment, square or other shapes; no specific limitation is made in this embodiment. The entire process requires precise control of the etching depth and the thickness of the metal deposition to ensure a good ohmic contact between the N electrode and the semiconductor material, while the insulating layer 4 effectively isolates the semiconductor material between the N electrode and the cap layer 13. This structural design helps improve the performance of the photodiode, including reducing contact resistance and preventing leakage.

[0084] In one embodiment, the P electrode and the N electrode can be disposed on the same side (i.e., the front side of the photodiode) or on opposite sides (i.e., the P electrode is disposed on the front side of the photodiode, and the N electrode is disposed on the back side of the photodiode). When the P electrode and the N electrode are disposed on the same side, the N electrode is disposed as described in the steps above. When the P electrode and the N electrode are disposed on opposite sides, the N electrode is directly disposed on the back side of the photodiode (i.e., the N metal contact layer is directly fabricated on the substrate layer, avoiding the position of the lens layer 3, to obtain the corresponding N electrode). For specific fabrication methods, please refer to the following embodiments.

[0085] To obtain the P electrode, in one embodiment, as follows: Figure 5 and Figure 6 As shown, a second opening is formed on the insulating layer 4, and the contact layer 14 is disposed on the cap layer 13 corresponding to the second opening; the diffusion material diffuses from the second opening to a portion of the cap layer 13 to form a diffusion hole 7; a P metal contact layer 8 is also disposed on the contact layer 14, and the P metal contact layer 8, the contact layer 14 and the diffusion hole 7 constitute an ohmic contact to obtain the P electrode.

[0086] The diffusion hole 7 is designed to form an intermediate region within the cap layer 13, which can serve as the contact area for the P electrode. An insulating layer 4 is disposed around the outer ring of the diffusion hole 7, located on the surface of the cap layer 13. The insulating layer 4 isolates the semiconductor material between the P electrode and the cap layer 13, preventing charge injection and short circuits.

[0087] The P-metal contact layer 8 is disposed on the contact layer 14, typically achieved by methods such as physical vapor deposition or chemical vapor deposition. In one embodiment, the material of the P-metal contact layer 8 can be... Ti、 Pt and The P-metal contact layer 8, contact layer 14, and diffusion hole 7 are alternately grown to form an ohmic contact. This contact method is also to ensure good conductivity and stability. Through the above steps, an ohmic contact is formed between the P-metal contact layer 8 on the diffusion hole 7 and the semiconductor material, thus obtaining the P-electrode. The P-electrode is used to collect holes generated by photogenerated carriers in the absorption layer 12.

[0088] It is worth noting that when the optical signal is reflected and transmitted in the epitaxial wafer 1, at the openings corresponding to the etched holes 5 and the diffusion holes 7, the optical signal can be reflected by the P metal contact layer 8 and the N metal contact layer 6. That is, through the P metal contact layer 8, the N metal contact layer 6 and the corresponding reflective layer 2, all the optical signals from the lens layer 3 can be reflected, thereby improving the absorption efficiency of the optical signal and the responsivity of the photodiode.

[0089] In one embodiment, refer to Figure 6 The contact layer 14 is a contact ring, and another portion of the reflective layer 2 is disposed within the inner ring of the contact layer 14 and is coplanar with the contact ring. Specifically, the contact layer 14 is designed as a P+ type InGaAs contact ring. InGaAs is a III-V group semiconductor material, an alloy of indium (In) and gallium (Ga), commonly used in optoelectronic and photodetector applications. P+ indicates that the doping level in the material is sufficient to generate free holes, which can act as charge carriers to transmit signals in a photodiode. The contact ring design allows light to enter the photodiode and be absorbed by the absorption layer 12, while providing a region to contact the P-electrode to collect the electrical signal generated by photogenerated charge carriers (electrons and holes). The presence of the P+ type InGaAs contact ring ensures efficient hole collection, thereby achieving efficient photoelectric conversion.

[0090] A portion of the reflective layer 2 is disposed within the inner ring of the contact layer 14. The presence of this portion of the reflective layer 2 is also intended to enhance the multiple reflections of light within the absorption layer 12, thereby improving the light absorption efficiency. The reflective layer 2 and the contact ring are on the same plane, which helps maintain the planarity of the device structure and reduces the propagation path of the optical signal within the device, thus reducing light loss.

[0091] It is worth noting that the formation of the N-electrode and P-electrode is a critical step in the actual manufacturing process of photodiodes, determining the charge injection and separation efficiency of the device. The accurate formation of the etched holes 5 and diffusion holes 7, as well as the precise deposition of the metal contact layer 14, are essential for achieving high-performance photodiodes. Furthermore, the insulating layer 4 is provided to ensure isolation between the electrodes and the semiconductor material, preventing short circuits and leakage, thereby improving the overall performance of the device.

[0092] This embodiment provides a flip-chip MPD photodiode, comprising: an epitaxial wafer 1, a reflective layer 2, and a lens layer 3. P-electrodes and N-electrodes are disposed on the epitaxial wafer 1. The lens layer 3 receives optical signals from a laser, and the epitaxial wafer 1 absorbs the optical signals to generate electrical signals, which are then transmitted through the P-electrodes and N-electrodes. The reflective layer 2 reflects the optical signals, allowing the epitaxial wafer 1 to repeatedly absorb the optical signals. This invention employs a back-light-entry photodiode, meaning that by etching the lens layer 3 on the back side of the epitaxial wafer 1, the optical signals can enter from the back side of the photodiode, solving the coupling problem between the back-light-entry photodiode and the laser. Furthermore, by providing the reflective layer 2 on the front side of the photodiode, after the optical signals from the lens layer 3 are absorbed by the epitaxial wafer 1, the remaining optical signals can be reflected back by the reflective layer 2 for further absorption. This reduces the thickness of the absorption layer 12 in the epitaxial wafer 1, thereby improving the response speed without affecting the photodiode's responsivity.

[0093] Example 2:

[0094] After providing a flip-chip photodiode as described in Embodiment 1, this invention will further provide a method for manufacturing a flip-chip photodiode, in order to elaborate on the implementation method of the corresponding structure in Embodiment 1 from an angle perspective, and to further analyze its design principle in depth.

[0095] In one embodiment, such as Figure 7 As shown, the manufacturing method includes:

[0096] Step 101: Fabricate an epitaxial wafer 1, and fabricate a reflective layer 2 on top of the epitaxial wafer 1, and fabricate a lens layer 3 on the bottom of the epitaxial wafer 1.

[0097] In one embodiment, such as Figure 8 As shown, step 101 specifically includes:

[0098] Step 1011: A buffer layer 11, an absorption layer 12, a cap layer 13 and a contact layer 14 are sequentially grown on the substrate layer 10 to obtain the epitaxial wafer 1.

[0099] like Figure 3 and Figure 9 As shown, a P+ type InGaAs contact layer was fabricated using photolithography and chemical etching processes.

[0100] Step 1012: An insulating layer 4 is formed on the cap layer 13, and the reflective layer 2 is disposed on the insulating layer 4.

[0101] Among them, such as Figure 10 and Figure 11As shown, an insulating dielectric film material is deposited using PECVD, and part of the insulating dielectric film material is removed by photolithography and dry etching processes to form diffusion holes 7 and etching holes 5 for diffusion. The insulating dielectric film material is generally a composite film of silicon nitride and silicon oxide used as a mask to obtain the insulating layer 4.

[0102] Step 1013: Etch a lens at the bottom of the substrate layer 10 to obtain the lens layer 3.

[0103] In one embodiment, such as Figure 12 and Figure 13 As shown, a lens layer 3 is etched on the back side of the substrate layer 10 using back-side photolithography and wet etching processes, and an antireflection film is grown using PECVD. A photosensitive surface 9 is then fabricated at the bottom of the lens layer 3 using photolithography and dry etching.

[0104] Step 102: Fabricate P-electrodes and N-electrodes on the epitaxial wafer 1.

[0105] In one embodiment, the P electrode and the N electrode can be disposed on the same side (i.e., the front side of the photodiode) or on opposite sides (i.e., the P electrode is disposed on the front side of the photodiode, and the N electrode is disposed on the back side of the photodiode). When the P electrode and the N electrode are disposed on the same side, such as... Figure 5 and Figure 6 As shown, a first opening is formed on the insulating layer 4. Through the first opening, a portion of the cap layer 13, a portion of the absorber layer 12, and a portion of the buffer layer 11 are sequentially etched to obtain an etching hole 5, thereby forming an N-type contact layer. A second opening is formed on the insulating layer 4. Diffusion material is diffused from the second opening to a portion of the cap layer 13 to form a diffusion hole 7, thereby forming a P-type contact layer. A reflective layer 2 is deposited on the insulating layer 4, the area corresponding to the first opening, and the area corresponding to the second opening. The reflective layer 2 at the first opening is removed to expose the N-type contact layer. A portion of the reflective layer 2 at the second opening is removed to expose the P-type contact layer. An N-metal contact layer 6 is formed on the area corresponding to the first opening, and a P-metal contact layer 8 is formed on the area corresponding to the second opening, thereby obtaining the P electrode and the N electrode, respectively.

[0106] The N-type contact layer refers to the region layer where the N-type InP buffer layer is located in the etched hole 5; the P-type contact layer refers to the region layer where the P-type InP cap layer is located. Through photolithography, electron beam evaporation, and lift-off processes, a P-metal contact layer 8 and an N-metal contact layer 6 are formed at the openings in the insulating layer 4 to obtain the P electrode and the N electrode.

[0107] In one embodiment, when the P electrode and the N electrode are positioned on opposite sides, such as Figure 14and Figure 15 As shown, a second opening is formed on the insulating layer 4, and a diffusion material is diffused from the second opening to a portion of the cap layer 13 to form a diffusion hole 7, thereby forming a P-type contact layer; a reflective layer 2 is deposited on the insulating layer 4 and the area corresponding to the second opening; a portion of the reflective layer 2 at the second opening is removed to expose the P-type contact layer; a P-metal contact layer 8 is formed in the area corresponding to the second opening to obtain the P electrode; an N-metal contact layer 6 is disposed at the bottom of the substrate layer 10, away from the lens layer 3, to obtain the N electrode.

[0108] After obtaining the P and N electrodes, the epitaxial wafer 1 is thinned and polished to 180±20um using a chemical mechanical polishing (CMP) process.

[0109] In one embodiment, in the photodiode obtained according to the above steps, the lens layer 3 is used to couple with a laser, the lens layer 3 is used to receive optical signals from the laser, the epitaxial wafer 1 is used to absorb the optical signals to generate electrical signals, and transmit the electrical signals through the P electrode and N electrode; the reflective layer 2 is used to reflect the optical signals so that the epitaxial wafer 1 repeatedly absorbs the optical signals.

[0110] For the specific structure and implementation principle of the flip-chip photodiode, please refer to Example 1, which will not be repeated in this example.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flip-chip photodiode, characterized in that, include: An epitaxial wafer (1), a reflective layer (2), and a lens layer (3) are provided. The reflective layer (2) is disposed above the epitaxial wafer (1), and the lens layer (3) is disposed at the bottom of the epitaxial wafer (1). A P electrode and an N electrode are disposed on the epitaxial wafer (1). The lens layer (3) is used to couple with the laser and to receive the optical signal from the laser. The epitaxial wafer (1) is used to absorb the optical signal to generate an electrical signal and to transmit the electrical signal through the P electrode and the N electrode. The reflective layer (2) is used to reflect the optical signal so that the epitaxial wafer (1) can repeatedly absorb the optical signal.

2. The flip-chip photodiode according to claim 1, characterized in that, The epitaxial wafer (1) includes a substrate layer (10), a buffer layer (11), an absorption layer (12), a cap layer (13), and a contact layer (14) stacked sequentially, wherein the contact layer (14) covers a portion of the cap layer (13); An insulating layer (4) is also provided on the cap layer (13); the lens layer (3) is disposed at the bottom of the substrate layer (10); a part of the reflective layer (2) is disposed on the insulating layer (4); and another part of the reflective layer (2) is disposed on the cap layer (13).

3. The flip-chip photodiode according to claim 2, characterized in that, A first opening is formed on the insulating layer (4), and a portion of the cap layer (13), a portion of the absorbent layer (12), and a portion of the buffer layer (11) are sequentially etched through the first opening to obtain an etch hole (5). The insulating layer (4) is disposed around the outer ring of the etch hole (5) and on the surface of the cap layer (13); wherein the etch hole (5) ends at the buffer layer (11). An N metal contact layer (6) is provided on the corrosion hole (5), and the N metal contact layer (6) and the corrosion hole (5) form an ohmic contact to obtain the N electrode.

4. The flip-chip photodiode according to claim 2, characterized in that, A second opening is formed on the insulating layer (4), and the contact layer (14) is disposed on the cap layer (13) corresponding to the second opening; the diffusion material diffuses from the second opening to a portion of the cap layer (13) to form a diffusion hole (7); A P-metal contact layer (8) is also provided on the contact layer (14). The P-metal contact layer (8), the contact layer (14), and the diffusion hole (7) constitute an ohmic contact to obtain the P electrode.

5. The flip-chip photodiode according to claim 2, characterized in that, The contact layer (14) is a contact ring, and another part of the reflective layer (2) is disposed in the inner ring of the contact layer (14) and is in the same plane as the contact ring.

6. The flip-chip photodiode according to claim 1, characterized in that, The materials of the P electrode and the N electrode are one or more of Ti, Pt and Au.

7. A method for fabricating a flip-chip photodiode, characterized in that, The manufacturing method is used to manufacture the flip-chip photodiode as described in any one of claims 1-6, comprising: An epitaxial wafer (1) is fabricated, and a reflective layer (2) is fabricated on top of the epitaxial wafer (1), and a lens layer (3) is fabricated on the bottom of the epitaxial wafer (1). P-electrodes and N-electrodes are fabricated on the epitaxial wafer (1); The lens layer (3) is used to couple with the laser and to receive the optical signal from the laser. The epitaxial wafer (1) is used to absorb the optical signal to generate an electrical signal and to transmit the electrical signal through the P electrode and the N electrode. The reflective layer (2) is used to reflect the optical signal so that the epitaxial wafer (1) can repeatedly absorb the optical signal.

8. The method for fabricating a flip-chip photodiode according to claim 7, characterized in that, The process of fabricating an epitaxial wafer (1), fabricating a reflective layer (2) on top of the epitaxial wafer (1), and fabricating a lens layer (3) at the bottom of the epitaxial wafer (1) includes: A buffer layer (11), an absorption layer (12), a cap layer (13) and a contact layer (14) are sequentially grown on a substrate layer (10) to obtain the epitaxial wafer (1); An insulating layer (4) is formed on the cap layer (13), and a reflective layer (2) is formed on the insulating layer (4); A lens is etched into the bottom of the substrate layer (10) to obtain the lens layer (3).

9. The method for fabricating a flip-chip photodiode according to claim 8, characterized in that, The fabrication of P and N electrodes on the epitaxial wafer (1) includes: A first opening is formed on the insulating layer (4), and a portion of the cap layer (13), a portion of the absorbent layer (12) and a portion of the buffer layer (11) are etched through the first opening to obtain an corrosion hole (5) to form an N-type contact layer; A second opening is formed on the insulating layer (4), and the diffusion material is diffused from the second opening to a portion of the cap layer (13) to form a diffusion hole (7) to form a P-type contact layer; A reflective layer (2) is deposited on the insulating layer (4), the area corresponding to the first opening and the second opening; Remove the reflective layer (2) at the first opening to expose the N-type contact layer; remove part of the reflective layer (2) at the second opening to expose the P-type contact layer; An N metal contact layer (6) is formed in the region corresponding to the first opening, and a P metal contact layer (8) is formed in the region corresponding to the second opening, so as to obtain the P electrode and the N electrode respectively.

10. The method for fabricating a flip-chip photodiode according to claim 8, characterized in that, Fabricating P and N electrodes on the epitaxial wafer (1) further includes: A second opening is formed on the insulating layer (4), and the diffusion material is diffused from the second opening to a portion of the cap layer (13) to form a diffusion hole (7) to form a P-type contact layer; A reflective layer (2) is deposited on the region corresponding to the insulating layer (4) and the second opening; Remove part of the reflective layer (2) at the second opening to expose the P-type contact layer; A P-metal contact layer (8) is formed in the region corresponding to the second opening to obtain the P electrode; An N metal contact layer (6) is disposed at the bottom of the substrate layer (10) away from the lens layer (3) to obtain the N electrode.

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