A PIN-type back-incident germanium-silicon photodiode based on emotional peaking

Abstract

The application discloses a PIN type back incidence germanium-silicon photodiode based on inductance peaking, and the photodiode structure sequentially comprises a back incidence area, an absorption area and a collection area from top to bottom; the back incidence area comprises a silicon substrate and silicon microlenses formed by etching on the back surface of the silicon substrate; the absorption area comprises a doped area and a germanium absorption layer, the built-in electric field is formed by P-type and N-type doping of the doped area, and the germanium absorption layer is used for absorbing incident photons and generating photo-generated carriers; the collection area comprises a self-alignment resistance layer, an interlayer dielectric layer, a coplanar waveguide electrode and a metal bump, and the geometric parameters of the coplanar waveguide electrode are optimized to introduce a compensation inductance L p The inductance peaking is realized, so that the bandwidth of the photodiode is optimized; the metal bump is arranged on the surface of the coplanar waveguide electrode to realize flip-chip bonding of the photodiode and an external circuit. p The bandwidth of the device can be significantly improved under the premise of ensuring high responsivity and low dark current.

Description

Technical Field

[0001] This invention belongs to the field of photodetector technology, and specifically relates to a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking. Background Technology

[0002] Photodiodes are key devices in optical communication used to receive optical signals, and their performance directly affects the speed, sensitivity, and power consumption of the entire optical communication link. Based on their material system, photodiodes can be divided into III-V compound type and germanium-silicon type. Germanium-silicon type photodiodes have a relatively simple structure design and are compatible with existing complementary metal-oxide-semiconductor (CMOS) circuit processes. They have significant advantages in the technology path towards co-package optics (CPO) and have become key devices for high-speed, short-range optical interconnects in data center optical networks, making them one of the key research areas currently being focused on by various research institutions.

[0003] The PIN-type germanium-silicon photodiode employs a PIN structure, which is realized on a silicon substrate using CMOS-compatible technology. The P-region and N-region are formed by doping silicon with trivalent and pentavalent elements, respectively, while the intrinsic I-region is composed of germanium material, which exhibits high absorption efficiency in the near-infrared band. Under reverse bias conditions, incident photons generate photogenerated carriers in the intrinsic I-region. These carriers are rapidly collected to the electrodes through drift, forming a photocurrent.

[0004] To meet the ultra-high-speed transmission demands of modern data centers (400G, 800G, and even future 1.6T+), traditional solutions primarily increase the bandwidth of photodiodes by reducing the thickness of the intrinsic I-region to shorten carrier drift time. However, reducing the thickness of the intrinsic I-region directly leads to a decrease in the photodiode's responsivity and an increase in junction capacitance, limiting the upper limit of bandwidth improvement. Therefore, improving the bandwidth of PIN-type germanium-silicon (Si) photodiodes without sacrificing responsivity is considered a key technical challenge in the development of this type of device. Summary of the Invention

[0005] To address the existing problem of bandwidth and responsivity being mutually constrained, this invention provides a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking. By rationally designing the coplanar waveguide electrode of the photodiode and introducing a compensating inductor to achieve inductive peaking, the bandwidth of the device can be significantly improved while ensuring high responsivity and low dark current. At the same time, the geometric parameters of the coplanar waveguide electrode are optimized so that the parasitic capacitance of the photodiode is not significantly degraded or improved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A PIN-type back-incidence germanium-silicon photodiode based on inductive peaking, wherein the photodiode structure consists of a back-incidence region, an absorption region, and a collection region from top to bottom;

[0008] The back incident region includes a silicon substrate and a silicon microlens etched on its back side for efficiently focusing incident light onto the absorption region.

[0009] The absorption region includes a doped region and a germanium absorption layer. The doped region forms a built-in electric field through P-type and N-type doping, and the germanium absorption layer is used to absorb incident photons and generate photogenerated carriers.

[0010] The collection region includes a self-aligned impedance layer, an interlayer dielectric layer, coplanar waveguide electrodes, and metal bumps. The self-aligned impedance layer provides good ohmic contact, the interlayer dielectric layer provides insulation and support, and the optimized geometric parameters of the coplanar waveguide electrodes introduce a compensating inductance L. p Inductive peaking is achieved to optimize the bandwidth of the photodiode; metal bumps are provided on the surface of the coplanar waveguide electrode to achieve flip-chip bonding between the photodiode and the external circuit.

[0011] A further preferred embodiment of the technical solution of the present invention is that the structure of the coplanar waveguide electrode is ground I-signal-ground II, and the geometric parameters include the length of the main transmission section of the electrode. Length of the extension near the active region The parameters are electrode width t, pad spacing w, and pad area s. The pad spacing w is determined by the back-end chip, and the pad area s is proportional to the square of the pad radius r. k is a coefficient dependent on the pad geometry. The coplanar waveguide electrode itself is used as a peaking inductor to design the geometric parameters of the aluminum Al coplanar waveguide electrode, introducing a compensating inductor L. p At a given dielectric constant Below, the geometric parameters of the coplanar waveguide electrodes are related to the parasitic capacitance C. p The relationship between them satisfies the relation (1), where As a correction factor, satisfying ,represent For C p The contribution is relatively small, thus achieving optimal bandwidth for the photodiode:

[0012] (1)

[0013] In a further preferred embodiment of the technical solution of the present invention, when the pads of the coplanar waveguide electrodes are circular, k is... When the shape is square, k is 4.

[0014] A further preferred embodiment of the technical solution of the present invention is that the silicon microlens has an axisymmetric arcuate profile surface;

[0015] The absorption region includes a silicon layer, a germanium absorption layer and a polycrystalline silicon layer arranged sequentially. A P-type heavily doped region is formed in the silicon layer, the germanium absorption layer is located below the silicon layer, and an N-type heavily doped region is formed in the polycrystalline silicon layer located below the germanium absorption layer.

[0016] The collection region includes a self-aligned impedance layer, an interlayer dielectric layer, an N-type coplanar waveguide electrode, a P-type coplanar waveguide electrode, metal bump I, and metal bump II. The N-type and P-type coplanar waveguide electrodes are located on the same plane as a source of peaking inductance to compensate for the attenuation of the photodiode at high frequencies. The P-type heavily doped region and the N-type heavily doped region form ohmic contacts with the N-type and P-type coplanar waveguide electrodes, respectively, through the self-aligned impedance layer. The interlayer dielectric layer is located between the self-aligned impedance layer and the coplanar waveguide electrodes, and metal bump I and metal bump II are respectively disposed on the surfaces of the two coplanar waveguide electrodes.

[0017] In a further preferred embodiment of the technical solution of the present invention, the silicon microlens has a near-spherical convex structure with a radius of curvature of 90 μm to 120 μm.

[0018] In a further preferred embodiment of the technical solution of the present invention, the silicon microlens is located directly below the back incidence window region.

[0019] In a further preferred embodiment of the technical solution of the present invention, the germanium absorber layer is formed by selective epitaxial growth, and the thickness of the germanium absorber layer is 700 μm to 900 nm.

[0020] In a further preferred embodiment of the technical solution of the present invention, both the N-type coplanar waveguide electrode and the P-type coplanar waveguide electrode are aluminum coplanar waveguide electrodes, and the shape of the pad is circular.

[0021] In a further preferred embodiment of the technical solution of the present invention, both metal bump I and metal bump II are made of gold.

[0022] The advantages of this invention compared to the prior art are as follows:

[0023] 1. This invention provides a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking, which introduces a compensating inductor L based on inductive peaking technology. p This can significantly improve the bandwidth of the device while ensuring high responsivity and low dark current.

[0024] 2. This invention provides a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking, which optimizes the geometric parameters of the coplanar waveguide electrodes to reduce the parasitic capacitance C. p Without significant degradation or improvement, the upper limit of the device bandwidth increase is raised.

[0025] 3. The present invention provides a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking. The fabrication process of the coplanar waveguide electrode is highly compatible with the CMOS integration process. The connection method of flip-chip bonding with external circuits is easy to realize optoelectronic co-packaging. It has the advantages of fast iteration speed and low fabrication cost. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the PIN-type back-incidence germanium-silicon photodiode based on inductive peaking of the present invention;

[0027] Figure 2 This is a schematic diagram of a coplanar waveguide electrode according to the present invention;

[0028] Figure 3 This is a schematic diagram of the equivalent circuit model considering inductive peaking in the implementation of this invention;

[0029] Figure 4 This is a schematic diagram of another coplanar waveguide electrode of the present invention;

[0030] Figure 5 These are the S21 simulation results from the equivalent circuit model analysis;

[0031] Among them, 1. Silicon microlens, 2. Silicon substrate, 3. Silicon layer, 4. P-type heavily doped region, 5. Germanium absorber layer, 6. Polycrystalline silicon layer, 7. N-type heavily doped region, 8. Self-aligned impedance layer, 9. Interlayer dielectric layer, 10. N-type coplanar waveguide electrode, 11. Metal bump I, 12. P-type coplanar waveguide electrode, 13. Metal bump II, 14. Ground I, 15. Signal, 16. Ground II. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1 -Appendix Figure 5 The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. 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.

[0033] like Figure 1 As shown, this embodiment is a PIN-type back-incidence germanium-silicon photodiode based on inductive peaking, and its structure from top to bottom consists of: a back-incidence region, an absorption region, and a collection region.

[0034] The back incident region is etched on the silicon substrate 2. The silicon microlens 1 is the back side of the device. The near-spherical protrusion structure is photolithographically etched on the back side of the silicon substrate 2. The radius of curvature is 90um to 120um. It has an axisymmetric arc-shaped profile. The silicon microlens 1 is located directly below the back incident window region and can effectively focus the incident light to the absorption region.

[0035] The absorption region consists of a silicon layer 3, a germanium absorption layer 5, and a polycrystalline silicon layer 6. P-type light doping and then P-type heavy doping are sequentially performed in the silicon layer 3, forming a heavily doped P-type region 4 in a specific area. The germanium absorption layer 5, located below the silicon layer 3, is formed using selective epitaxial growth and has a thickness of 700 μm to 900 nm, used for efficient absorption in the near-infrared band. The polycrystalline silicon layer 6 below the germanium absorption layer 5 undergoes N-type heavy doping implantation to form a heavily doped N-type region 7 in a specific area. Under reverse bias, incident light is absorbed in the germanium absorption layer 5, generating photogenerated carriers. These photogenerated carriers are transported to the collection region by drift motion under the influence of the built-in electric field.

[0036] The collection region includes a self-aligned impedance layer 8, an interlayer dielectric layer 9, an N-type coplanar waveguide electrode 10, a P-type coplanar waveguide electrode 12, metal bump I 11, and metal bump II 13. The self-aligned impedance layer 8 is formed by depositing cobalt (Co) in the contact window regions of the heavily doped N-type region 7 and the heavily doped P-type region 4, to form good ohmic contacts with the N-type and P-type coplanar waveguide electrodes 10 and 12. Silicon dioxide and silicon nitride are deposited to form the interlayer dielectric layer 9, providing insulation and support for the coplanar waveguide electrodes. The N-type and P-type coplanar waveguide electrodes 10 and 12 are used to introduce compensating inductance to achieve inductive peaking and improve the device bandwidth. Metal bumps I 11 and II 13 are designed and formed on the surface of the coplanar waveguide electrodes to achieve flip-chip bonding between the photodiode and the external circuit. The current after photoelectric conversion is ultimately transmitted to the external circuit through the metal bumps.

[0037] like Figure 2 As shown, the structure of the coplanar waveguide electrode is Ground I 14-Signal 15-Ground II 16. With proper design of its geometric parameters, the coplanar waveguide electrode can itself serve as a source of peaking inductance, compensating for the attenuation of the photodiode at high frequencies and enhancing the 3dB bandwidth of the photodiode without reducing its responsivity. Therefore, the compensation inductance L... p By designing the geometric parameters of the coplanar waveguide electrodes, the geometric parameters of the coplanar waveguide electrodes include the length of the main transmission section of the electrode. The length of the extension near the active region The electrode width t, pad spacing w, and pad area s are given. The pad area s is proportional to the square of the pad radius r, i.e. k is a coefficient that depends on the geometry of the pads.

[0038] Peaking is introduced by changing the geometric parameters of the coplanar waveguide electrodes, specifically: the length of the main transmission section of the electrode. The extension of the electrode and the reduction of the electrode width t can increase the compensation inductance L. p However, according to formula (1), the parasitic capacitance C p Also follow Increase, therefore, consider and against C p Smaller contribution Synergistic extension; pad spacing w and pad area s mainly affect parasitic capacitance C p According to formula (1), the larger the pad spacing w, the greater the parasitic capacitance C. p The smaller the value, the larger the pad area s, and the greater the parasitic capacitance C. p The larger the value, the better. Therefore, by adjusting the geometric parameters of the coplanar waveguide electrodes, a suitable compensating inductance L can be introduced. p At the same time, avoid parasitic capacitance C p The deterioration of the photodiode increases the upper limit of its inductive peaking, thereby improving the bandwidth.

[0039] like Figure 3 As shown, the compensating inductor L of the coplanar waveguide electrode is... p and parasitic capacitance C p Extracted through electromagnetic simulation and substituted. Figure 3 Bandwidth analysis is performed using the equivalent circuit model shown. The equivalent circuit model is known to those skilled in the art, and includes the photocurrent source I of the photodiode. ph Junction resistance R j Junction capacitance C j Series resistor R s Parasitic capacitance C p Internal inductor L1 and compensation inductor L p In this equivalent circuit model, the total 3dB bandwidth of the photodiode is determined by the transit bandwidth of the photogenerated carrier transit process and the RLC bandwidth of the resistor-inductor-capacitor circuit. The transit bandwidth is determined by the photogenerated current source I... ph The response bandwidth is determined by the junction resistance R. j Junction capacitance C j Series resistor R s Parasitic capacitance C p Internal inductor L1 and compensation inductor L p The thickness of the germanium absorption layer 5 in the photodiode of this embodiment remains constant, therefore the transit bandwidth is considered constant; thus, by reducing the parasitic capacitance C... p And introduce a compensating inductor L pThe high-frequency attenuation of the photodiode is compensated, which can improve the RLC bandwidth and thus improve the 3dB bandwidth of the photodiode.

[0040] like Figure 3 As shown, based on the bandwidth results of the equivalent circuit model, feedback optimization is performed on the geometric parameters of the coplanar waveguide electrodes to achieve the optimization of the compensation inductor L. p and parasitic capacitance C p Coordinated regulation. Compensating inductor L p and parasitic capacitance C p The bandwidth characteristics are determined based on the application's desired characteristics. Specifically, the structure of the coplanar waveguide electrodes is Ground I 14 - Signal 15 - Ground II 16, and the geometric parameters include the length of the main transmission section of the electrodes. The length of the extension near the active region The parameters are electrode width t, pad spacing w, and pad area s, where the pad spacing w is 125 μm and is determined by the back-end electrical chip. The pad area s is proportional to the square of the pad radius r. k is a coefficient that depends on the pad geometry; the coplanar waveguide electrode itself serves as a source of peaking inductance, and the geometric parameters of the coplanar waveguide electrode are designed to introduce a compensating inductance L. p This ensures that the geometric parameters of the coplanar waveguide electrodes are related to the parasitic capacitance C. p The relationship between them satisfies equation (1), thus achieving the optimal bandwidth of the photodiode.

[0041] (1)

[0042] like Figure 4 As shown, this embodiment first extends the length of the main transmission section of the coplanar waveguide electrode. Then increase the length of the extension near the active region. , The extended section has a narrower cross-section, which reduces the parasitic capacitance C. p The contribution is relatively small. Meanwhile, reducing the metal width t of the coplanar waveguide electrode and changing the pads of the coplanar waveguide electrode from square to circular with a reduced radius r to decrease the pad area s effectively increases the compensating inductance L. p At the same time, the parasitic capacitance C is not degraded. p Electromagnetic simulation results show that, Increase by 10um Under the condition of geometric parameter optimization (increasing by 30µm, reducing electrode width t by 5µm, and reducing pad radius r by 14µm), the compensation inductance L p It significantly increased by 40 pH, while the parasitic capacitance C p Only an increase of 0.5fF. Finally, the equivalent circuit model analysis results are as follows: Figure 5 As shown, the 3dB bandwidth can be increased to 57GHz.

[0043] Those skilled in the art will readily understand that the above description is merely 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 scope of protection of the present invention.

Claims

1. A PIN-type back-incidence germanium-silicon photodiode based on inductive peaking, characterized in that, The structure of a photodiode, from top to bottom, consists of a back incidence region, an absorption region, and a collection region. The back incident region includes a silicon substrate (2) and a silicon microlens (1) etched on its back side for efficiently focusing incident light into the absorption region; The absorption region includes a doped region and a germanium absorption layer (5). The doped region forms a built-in electric field through P-type and N-type doping, and the germanium absorption layer (5) is used to absorb incident photons and generate photogenerated carriers. The collection area includes a self-aligned impedance layer (8), an interlayer dielectric layer (9), coplanar waveguide electrodes, and metal bumps. The self-aligned impedance layer (8) provides good ohmic contact, the interlayer dielectric layer (9) provides insulation and support, and the optimized geometric parameters of the coplanar waveguide electrodes introduce a compensating inductance L. p Inductive peaking is achieved to compensate for the attenuation of the photodiode at high frequencies, thereby enhancing the 3dB bandwidth of the photodiode without reducing the responsivity. Metal bumps are provided on the surface of the coplanar waveguide electrode to achieve flip-chip bonding between the photodiode and the external circuit.

2. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 1, characterized in that: The structure of the coplanar waveguide electrode is ground I (14) - signal (15) - ground II (16), and the geometric parameters include the length of the main transmission section of the electrode. Length of the extension near the active region The parameters are electrode width t, pad spacing w, and pad area s. The pad spacing w is determined by the back-end chip, and the pad area s is proportional to the square of the pad radius r. k is a coefficient dependent on the pad geometry. The coplanar waveguide electrode itself is used as a peaking inductor to design the geometric parameters of the aluminum Al coplanar waveguide electrode, introducing a compensating inductor L. p At a given dielectric constant Below, the geometric parameters of the coplanar waveguide electrodes are related to the parasitic capacitance C. p The relationship between them satisfies the relation (1), where As a correction factor, satisfying ,represent For C p The contribution is small, but it compensates for the attenuation of the photodiode at high frequencies, enhancing the 3dB bandwidth of the photodiode without reducing the responsivity. （1）。 3. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 2, characterized in that: When the pads of the coplanar waveguide electrodes are circular, k is When the shape is square, k is 4.

4. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 1, characterized in that: The silicon microlens (1) has an axisymmetric arcuate profile surface; The absorption region includes a silicon layer (3), a germanium absorption layer (5) and a polycrystalline silicon layer (6) arranged sequentially. A P-type heavily doped region (4) is formed in the silicon layer (3). The germanium absorption layer (5) is located below the silicon layer (3). An N-type heavily doped region (7) is formed in the polycrystalline silicon layer (6) located below the germanium absorption layer (5). The collection area includes a self-aligned impedance layer (8), an interlayer dielectric layer (9), an N-type coplanar waveguide electrode (10), a P-type coplanar waveguide electrode (12), a metal bump I (11), and a metal bump II (13). The N-type coplanar waveguide electrode (10) and the P-type coplanar waveguide electrode (12) are located on the same plane as a source of peaking inductance to compensate for the attenuation of the photodiode at high frequencies. The P-type heavily doped region (4) and the N-type heavily doped region (7) form ohmic contacts with the N-type coplanar waveguide electrode (10) and the P-type coplanar waveguide electrode (12) respectively through the self-aligned impedance layer (8). The interlayer dielectric layer (9) is located between the self-aligned impedance layer (8) and the coplanar waveguide electrode. The metal bump I (11) and the metal bump II (13) are respectively disposed on the surfaces of the two coplanar waveguide electrodes.

5. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 1 or 4, characterized in that: The silicon microlens (1) is a near-spherical convex structure with a radius of curvature of 90um to 120um.

6. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 5, characterized in that: The silicon microlens (1) is located directly below the back incidence window region.

7. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 1 or 4, characterized in that: The germanium absorption layer (5) is formed by selective epitaxial growth and has a thickness of 700 μm to 900 nm.

8. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 1 or 4, characterized in that: Both the N-type coplanar waveguide electrode (10) and the P-type coplanar waveguide electrode (12) are aluminum coplanar waveguide electrodes, and the pads are circular.

9. The PIN-type back-incidence germanium-silicon photodiode based on inductive peaking according to claim 4, characterized in that: Both metal bump I (11) and metal bump II (13) are made of gold.

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