A method for manufacturing a photosensitive diode and a photosensitive diode

Abstract

The application relates to a preparation method of a photosensitive diode and the photosensitive diode, which comprises the following steps: epitaxially growing a buffer layer, an absorption layer and a cap layer on a substrate to form an epitaxial structure; depositing a medium film on the surface of the epitaxial structure, and forming honeycomb-shaped diffusion mask windows on the medium film; diffusing impurities to the cap layer and the absorption layer through the honeycomb-shaped diffusion mask windows, so that the top of diffusion areas formed by each diffusion mask window is connected in series, and the bottom is arranged to be spaced from each other; and removing the medium film provided with the honeycomb-shaped diffusion mask windows. Since the diffusion mask windows are used to diffuse the diffusion areas in a honeycomb shape, the top of the diffusion areas is connected in series, and the bottom is arranged to be spaced from each other, the effective junction area is reduced, the junction capacitance is reduced, the response capability of the photosensitive diode to high-frequency signals is improved, the medium film provided with the honeycomb-shaped diffusion mask windows is removed subsequently, and the original photosensitive surface appearance can be restored, therefore, the epitaxial structure does not need to be changed, and the working voltage is not increased.

Description

Technical Field

[0001] This invention relates to the field of photodiode technology, and particularly to a method for fabricating a photodiode and the photodiode itself. Background Technology

[0002] Currently, PIN photodiodes are widely used in various security, communication, and low-light detection applications. In recent years, with the rapid development of the high-speed optical communication industry, increasingly higher requirements have been placed on the high-frequency response capability of PIN photodiodes.

[0003] Due to the change in charge stored in the PN junction region, the photodiode exhibits a junction capacitance C related to the voltage junction in the external circuit. j The amplitude of the response signal to incident light decreases as the frequency increases, with a high-frequency cutoff frequency of [missing value]. The junction capacitance C can be seen from this equation. j The high-frequency response capability of a PIN photodiode is directly determined by its junction capacitance Cj. Reducing the junction capacitance Cj is the key to improving the high-frequency response capability of a PIN photodiode.

[0004] To reduce the junction capacitance, related technologies typically employ methods that increase the depletion layer thickness. However, this approach has drawbacks, including increased epitaxial growth costs and higher operating voltage.

[0005] Therefore, it is necessary to design a new method for fabricating photodiodes to overcome the above problems. Summary of the Invention

[0006] This invention provides a method for fabricating a photodiode and a photodiode in order to solve the problem that increasing the thickness of the depletion layer in related technologies would increase the cost of epitaxial growth and the operating voltage.

[0007] In a first aspect, a method for fabricating a photodiode is provided, comprising the following steps: epitaxially growing a buffer layer, an absorber layer, and a cap layer on a substrate to form an epitaxial structure; depositing a dielectric film on the surface of the epitaxial structure and forming a honeycomb-shaped diffusion mask window on the dielectric film; diffusing impurities through the honeycomb-shaped diffusion mask window to the cap layer and the absorber layer, such that the tops of the diffusion regions formed by the diffusion through each diffusion mask window are connected in series and the bottoms are spaced apart from each other; and removing the dielectric film with the honeycomb-shaped diffusion mask window.

[0008] In some embodiments, forming a honeycomb-shaped diffusion mask window on the dielectric film includes forming the honeycomb-shaped diffusion mask window on the dielectric film by photolithography and etching processes.

[0009] In some embodiments, the edge spacing between two adjacent diffusion mask windows is less than the depth value of the diffusion region.

[0010] In some embodiments, the edge spacing between two adjacent diffusion mask windows is less than half the depth value of the diffusion region.

[0011] In some embodiments, after removing the dielectric film with the honeycomb-shaped diffusion mask window, the method further includes: fabricating a front electrode on the front side of the epitaxial structure; and fabricating a back electrode on the back side of the epitaxial structure.

[0012] In some embodiments, the substrate is further thinned and polished before a back electrode is fabricated on the back side of the epitaxial structure.

[0013] In some embodiments, removing the dielectric film with the honeycomb-shaped diffusion mask window includes removing the dielectric film with the honeycomb-shaped diffusion mask window by photolithography and etching processes.

[0014] In some embodiments, the deposition of a dielectric film on the surface of the epitaxial structure includes: depositing a dielectric film on the surface of the cap layer using plasma-enhanced chemistry vapor deposition.

[0015] Secondly, a photodiode prepared by the above-described photodiode preparation method is provided, which includes a substrate, an absorption layer and a cap layer from bottom to top; impurities diffuse into the cap layer to form multiple diffusion regions, each diffusion region diffuses downward to the absorption layer, and the tops of the multiple diffusion regions are connected in series and the bottoms are spaced apart from each other.

[0016] In some embodiments, the diffusion region is P-doped and the substrate is N-doped.

[0017] The beneficial effects of the technical solution provided by this invention include:

[0018] This invention provides a method for fabricating a photodiode and a photodiode in general. By using a honeycomb-shaped diffusion mask window to diffuse impurities and form a diffusion region, and by connecting the tops of the diffusion regions in series and spacing them apart at the bottom, the junction area is reduced, thereby reducing the junction capacitance and improving the photodiode's response to high-frequency signals. Furthermore, by removing the dielectric film with the honeycomb-shaped diffusion mask window, the original photosensitive surface morphology can be restored. Therefore, there is no need to change the epitaxial structure or increase the operating voltage. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0020] Figure 1 A flowchart illustrating a method for fabricating a photodiode according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the epitaxial structure provided in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the structure of the honeycomb diffusion mask window provided in an embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the structure of a conventional diffusion window photosensitive surface;

[0024] Figure 5 This is a schematic diagram of the structure of the honeycomb diffusion mask window forming the diffusion region provided in an embodiment of the present invention;

[0025] Figure 6 This is a schematic diagram of the structure of an existing ordinary diffusion region;

[0026] Figure 7 for Figure 5 A schematic diagram of the structure after removing the honeycomb diffusion mask window;

[0027] Figure 8 This is a schematic diagram of the structure of a photodiode provided in an embodiment of the present invention.

[0028] In the picture:

[0029] 1. Substrate; 2. Buffer layer; 3. Absorber layer; 4. Cap layer; 5. Dielectric film; 6. Diffusion mask window; 7. Diffusion region; 8. Front electrode; 9. Back electrode. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Junction capacitance is an important parameter of PIN photodiodes. The size of the junction capacitance determines the high-frequency response capability of the PIN photodiode. In order to reduce the junction capacitance, the mainstream fabrication process is to reduce the photosensitive surface area and increase the thickness of the intrinsic layer. However, the drawback of this method is that it requires changes to the application scenario of the PIN photodiode and the structure of the epitaxial material.

[0032] This invention provides a method for fabricating a photodiode, which solves the problem in related technologies that increasing the thickness of the depletion layer increases the cost of epitaxial growth and the operating voltage.

[0033] This invention does not change any material structure or pattern design. It forms a honeycomb pattern on the original photosensitive surface using processes such as coating, photolithography, and RIE. After forming a PN junction using a diffusion method, the honeycomb pattern is removed and the original photosensitive surface is restored using processes such as photolithography and RIE. This method reduces the PN junction area, thereby reducing the junction capacitance.

[0034] See Figure 1 As shown, this invention provides a method for fabricating a photodiode, which may include the following steps:

[0035] S1: Buffer layer 2, absorber layer 3, and cap layer 4 are epitaxially grown on substrate 1 to form an epitaxial structure (see...). Figure 2 (As shown). Among them, the cap layer 4 can be the top layer of the epitaxial structure, the absorption layer 3 is the middle layer and is the undoped absorption region, the buffer layer 2 is low-doped and has the same doping type as the substrate, and the substrate 1 is a high-doped substrate 1, preferably N-doped.

[0036] S2: A dielectric film 5 is deposited on the surface of the epitaxial structure, and a honeycomb-shaped diffusion mask window 6 is formed on the dielectric film 5. That is, a plurality of diffusion mask windows 6 are arranged on the dielectric film 5, the plurality of diffusion mask windows 6 are spaced apart, and the plurality of diffusion mask windows 6 are arranged to form a honeycomb pattern.

[0037] S3: Impurities are diffused into the cap layer 4 and the absorption layer 3 through the honeycomb-shaped diffusion mask window 6, so that the tops of the diffusion regions 7 formed by the diffusion through each diffusion mask window 6 are connected together, and the bottoms are spaced apart. By using the honeycomb-shaped diffusion mask window 6, impurities are diffused into the material bulk through a diffusion method, thereby achieving material modification.

[0038] S4: Remove the dielectric film 5 with the honeycomb-shaped diffusion mask window 6 to restore the original photosensitive surface morphology. At this point, the photosensitive surface is completely identical to the photosensitive surface prepared by ordinary methods. See [link to documentation]. Figure 7 As shown.

[0039] In this embodiment, the PN junction capacitance

[0040] Here, Q refers to the total charge generated by the depletion layer, and V refers to the applied bias voltage.

[0041]

[0042] Where q refers to the amount of charge, and N DN A These refer to the surface charge density of the n-region and p-region, respectively; S refers to the junction area; and W refers to the surface charge density of the n-region and p-region, respectively. n W p These refer to the barrier widths of the n-region and p-region, respectively; z is the coordinate axis constructed along the direction of the barrier width.

[0043] Substituting formula ② into formula ①, we get:

[0044]

[0045] Additionally, the built-in potential V formed by the PN junction bi The following relationship exists between the applied bias voltage V and the bias voltage V:

[0046]

[0047] Here, ε refers to the dielectric constant.

[0048] From formulas ③ and ④, we can obtain:

[0049]

[0050] In formula ⑤ above:

[0051]

[0052] Substituting formula ⑤ into formula ③, we get:

[0053]

[0054] in

[0055]

[0056] For a photosensitive surface device with a fixed junction area S, S p =S n = constant value, then C s -1 =0.

[0057] Because this invention uses a honeycomb-shaped diffusion mask window 6 to diffuse impurities and form diffusion regions 7, and the tops of the diffusion regions 7 are connected in series while the bottoms are spaced apart, the junction area is reduced relative to the photosensitive surface area. Therefore, in formula ⑦, C s -1 >0, and C p -1 and C n -1The junction area also increases as the junction area shrinks, which can reduce the junction capacitance and thus improve the photodiode's response to high-frequency signals. After removing the dielectric film 5 with the honeycomb diffusion mask window 6, the original photosensitive surface morphology can be restored. Therefore, there is no need to change the epitaxial structure or increase the operating voltage.

[0058] See Figure 3 As shown, in some embodiments, in step S2, forming a honeycomb-shaped diffusion mask window 6 on the dielectric film 5 may include: forming the honeycomb-shaped diffusion mask window 6 on the dielectric film 5 through photolithography and etching processes. The etching may employ a RIE etching process to design the shape of the diffusion mask window 6 as a honeycomb.

[0059] Furthermore, in step S2, the edge spacing between two adjacent diffusion mask windows 6 can be less than the depth of the diffusion region 7. Since impurities typically diffuse isotropically within a material, meaning the lateral diffusion length and longitudinal diffusion depth are essentially the same, in this embodiment, the edge spacing between two adjacent diffusion mask windows 6 is set to be less than the depth of the diffusion region 7. This ensures that when the impurities diffuse to the designed depth, the diffusion regions 7 corresponding to the two adjacent diffusion mask windows 6 will inevitably connect in the lateral direction, guaranteeing that the tops of the diffusion regions 7 are connected in series, while their bottoms are spaced apart.

[0060] Of course, in other embodiments, other methods can be adopted to connect the tops of the diffusion regions 7 formed by the diffusion of each diffusion mask window 6 together, while the bottoms are spaced apart from each other.

[0061] Preferred, see Figure 8 As shown, the edge spacing between two adjacent diffusion mask windows 6 is less than half the depth of the diffusion region 7, so that the two adjacent diffusion regions 7 are connected for a considerable depth. Typically, to reduce the dark current of the PIN photodiode, the depth of the diffusion region 7 will exceed the thickness of the cap layer 4 and reach the top of the material absorption layer 3. Therefore, the edge spacing of the honeycomb diffusion mask window 6 is usually designed to be less than half the thickness of the cap layer 4 to ensure that the diffusion impurities through the honeycomb diffusion mask window 6 are connected in series through lateral diffusion. Furthermore, while ensuring that the edge spacing of the honeycomb diffusion mask window 6 is consistent, by reducing the size of the honeycomb window area, the duty cycle of the window can be reduced, which can further reduce the junction capacitance.

[0062] See Figure 5 and Figure 6 As shown, the morphology of the diffusion region 7 in this embodiment is as follows: Figure 5 As shown, the tops of the diffusion regions 7 formed by the honeycomb diffusion mask window 6 are connected in series through lateral diffusion, while the bottoms are independent. Figure 6The morphology of the diffusion region 7 formed by the ordinary diffusion window is significantly different between the upper and lower parts of the same area.

[0063] Furthermore, after removing the dielectric film 5 with the honeycomb-shaped diffusion mask window 6, the process may further include: fabricating a front electrode 8 on the front side of the epitaxial structure; and fabricating a back electrode 9 on the back side of the epitaxial structure. In this embodiment, the front electrode 8 is fabricated on the surface of the cap layer 4, and the back electrode 9 is fabricated on the bottom surface of the substrate 1.

[0064] Furthermore, before fabricating the back electrode 9 on the back side of the epitaxial structure, the substrate 1 may be thinned and polished.

[0065] In some embodiments, removing the dielectric film 5 with the honeycomb-shaped diffusion mask window 6 may include removing the dielectric film 5 with the honeycomb-shaped diffusion mask window 6 by photolithography and etching processes. The etching may employ a refractive indexing (RIE) etching process to remove the dielectric film 5. Before removing the dielectric film 5, due to the light-blocking effect of the honeycomb-shaped dielectric film 5, the area of ​​the photosensitive surface is much smaller than that of a normal photosensitive surface. Subsequently, the honeycomb-shaped dielectric film 5 window is removed using photolithography and RIE methods, such as... Figure 7 As shown, the area of ​​the photosensitive surface at this time is basically the same as that of the photosensitive surface prepared by the ordinary method. Figure 4 This is a schematic diagram of the structure of a conventional diffusion window photosensitive surface.

[0066] In some optional embodiments, the deposition of the dielectric film 5 on the surface of the epitaxial structure may include: depositing a dielectric film 5 on the surface of the cap layer 4 using plasma-enhanced chemical vapor deposition. That is, depositing a dielectric film 5 on the material surface using processes such as PECVD to serve as a diffusion mask.

[0067] This invention, without altering the photosensitive surface area and epitaxial layer thickness of a PIN photodiode, rationally designs a honeycomb diffusion mask window 6 on the photosensitive surface using photolithography, deposition, and etching processes. The honeycomb diffusion mask window 6 then diffuses impurities into the material bulk via diffusion, achieving material modification. Utilizing the isotropic diffusion of impurities within the material, the impurities entering the material bulk through the honeycomb diffusion mask window 6 are connected in series via lateral diffusion. The photosensitive surface area is not reduced due to the isolation provided by the honeycomb diffusion mask window 6, thus lowering the junction capacitance. This significantly reduces the junction capacitance of the PIN photodiode without altering its original pattern design or epitaxial material structure, thereby improving the PIN photodiode's response to high-frequency signals.

[0068] See Figure 8As shown, this embodiment of the invention also provides a photodiode fabricated using the above-described photodiode fabrication method. From bottom to top, it comprises a substrate 1, a buffer layer 2, an absorption layer 3, and a cap layer 4, forming an epitaxial structure. The cap layer 4 can be the top of the epitaxial structure, the absorption layer 3 is an intermediate layer and is an undoped absorption region, the buffer layer 2 is lightly doped, and the substrate 1 is heavily doped. Impurities diffuse within the cap layer 4 to form multiple diffusion regions 7. Each diffusion region 7 diffuses downwards to the absorption layer 3, and the tops of the multiple diffusion regions 7 are connected in series, while their bottoms are spaced apart.

[0069] Preferably, the diffusion region 7 is P-doped and the substrate 1 is N-doped.

[0070] The photodiode provided in this embodiment of the invention improves C in formula ⑨ by changing the effective junction area. s -1 C p -1 and C n -1 The size is adjusted to ultimately reduce the junction capacitance Cj, thereby improving the PIN photodiode's response to high-frequency signals.

[0071] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "manufactured," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0072] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0073] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for fabricating a photodiode, characterized in that, It includes the following steps: A buffer layer (2), an absorption layer (3), and a cap layer (4) are epitaxially grown on a substrate (1) to form an epitaxial structure; A dielectric film (5) is deposited on the surface of the epitaxial structure, and a honeycomb diffusion mask window (6) is formed on the dielectric film (5). Impurities are diffused into the cap layer (4) and the absorption layer (3) through the honeycomb-shaped diffusion mask window (6), so that the tops of the diffusion areas (7) formed by each diffusion mask window (6) are connected together, the bottoms are spaced apart, and the bottoms of the multiple diffusion areas (7) are arranged in a honeycomb pattern. The edge spacing between two adjacent diffusion mask windows (6) is less than half the depth value of the diffusion area (7). Remove the dielectric film (5) with the honeycomb diffusion mask window (6).

2. The method for fabricating a photodiode as described in claim 1, characterized in that, The formation of the honeycomb diffusion mask window (6) on the dielectric film (5) includes: A honeycomb-shaped diffusion mask window (6) is formed on the dielectric film (5) by photolithography and etching processes.

3. The method for fabricating a photodiode as described in claim 1, characterized in that, After removing the dielectric film (5) with the honeycomb diffusion mask window (6), the process further includes: A front electrode (8) is formed on the front side of the epitaxial structure; a back electrode (9) is formed on the back side of the epitaxial structure.

4. The method for fabricating a photodiode as described in claim 3, characterized in that: Before fabricating the back electrode (9) on the back side of the epitaxial structure, the substrate (1) is thinned and polished.

5. The method for fabricating a photodiode as described in claim 1, characterized in that, The removal of the dielectric film (5) with the honeycomb diffusion mask window (6) includes: The dielectric film (5) with the honeycomb diffusion mask window (6) is removed by photolithography and etching processes.

6. The method for fabricating a photodiode as described in claim 1, characterized in that, The deposition of a dielectric film (5) on the surface of the epitaxial structure includes: A dielectric film (5) is deposited on the surface of the cap layer (4) using plasma-enhanced chemical vapor deposition.

7. A photodiode fabricated using the method described in claim 1, characterized in that, From bottom to top, it includes a substrate (1), a buffer layer (2), an absorption layer (3), and a cap layer (4); Impurities diffuse within the cap layer (4) form multiple diffusion zones (7), each diffusion zone (7) diffuses downwards to the absorption layer (3), and the tops of the multiple diffusion zones (7) are connected in series, while their bottoms are spaced apart from each other.

8. The photodiode as described in claim 7, characterized in that: The diffusion region (7) is P-doped, and the substrate (1) is N-doped.

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