Photodiode with integrated light focusing element

Abstract

The present disclosure relates to semiconductor structures, and more particularly to photodiodes with integrated light focusing elements and methods of manufacturing the same. The structure includes: a trench photodiode including a dome structure; and a doped material on the dome structure, the doped material having a concave lower side surface.

Description

Technical Field

[0001] The present disclosure relates to semiconductor structures, and more particularly to photodiodes with integrated light focusing elements and methods of fabrication. Background Art

[0002] A photodiode is a semiconductor device that converts light into an electric current. A photodiode may contain an optical filter, a built-in lens, and may have a larger or smaller surface area depending on the specific application. Photodiodes can be used in many different optical applications. For example, germanium (Ge) photodiodes can be used in state-of-the-art LIDAR applications because of their higher absorptivity than silicon (Si). In this way, smaller pixel sizes and active areas can be achieved. In such an embodiment, the signal-to-noise ratio (S / N) is reduced due to insufficient coupling with the absorber, and crosstalk increases as the spacing decreases.

[0003] Microlenses can be used to focus light into the photodiode material. However, the microlenses are separated from the absorber by a non-absorbing optical path (e.g., polymer microlenses in a back-end-of-line (BEOL) stack). This can result in loss or degradation of light, in addition to requiring additional manufacturing steps that increase the overall cost of the structure. Summary of the invention

[0004] In one aspect of the present disclosure, a structure includes: a trench photodiode including a domed structure; and a doped material on the domed structure, the doped material having a concave lower side surface.

[0005] In one aspect of the present disclosure, a structure includes: a trench photodiode that extends into a well region of a semiconductor substrate and includes a dome structure at its upper end; a doped material located on the dome structure that extends to one side of the trench photodiode; a first contact that is electrically in contact with the doped material; and a second contact that is electrically in contact with the well region of the semiconductor substrate.

[0006] In one aspect of the present disclosure, a method includes: forming a trench photodiode in a trench structure, the trench photodiode including an integrated dome structure; forming an impurity material on the integrated dome structure extending to one side of the trench photodiode, the impurity material having a concave lower side surface; and forming a contact that electrically contacts the impurity material on the one side of the trench photodiode. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In the following detailed description, the present disclosure is described by way of non-limiting examples of exemplary embodiments of the present disclosure with reference to the several accompanying drawings mentioned.

[0008] Figure 1A substrate having a shallow trench isolation structure and a corresponding manufacturing process according to some aspects of the present disclosure, among other features, are shown.

[0009] Figure 2 A trench formed in a substrate and a corresponding fabrication process are shown, among other features, in accordance with some aspects of the present disclosure.

[0010] Figure 3 Trench photodiodes, each having a dome structure, and corresponding fabrication processes are shown, among other features, in accordance with some aspects of the present disclosure.

[0011] Figure 4 Materials with concave features on a dome structure and corresponding manufacturing processes are shown, among other features, in accordance with some aspects of the present disclosure.

[0012] Figure 5 Contacts to a photodiode and corresponding fabrication processes are shown, among other features, in accordance with some aspects of the present disclosure.

[0013] Figures 6 to 8 Alternative photodiode structures are shown in accordance with further aspects of the present disclosure. DETAILED DESCRIPTION

[0014] The present disclosure relates to semiconductor structures, and more particularly to photodiodes with integrated light focusing elements and methods of manufacturing. More particularly, the present disclosure relates to deep trench photodiodes with aligned light focusing elements. In an embodiment, the deep trench photodiode is a deep trench Ge photodiode, and the light focusing element is aligned with the deep trench photodiode. The light focusing element includes a dome structure that is fully integrated with the deep trench photodiode and uses the same material as the deep trench photodiode. Advantageously, the integrated focusing element enables a smaller active area pixel array with improved signal-to-noise ratio (S / N) and isolation.

[0015] In an embodiment, the photodiode is a trench photodiode having a dome structure (e.g., convex) that is fully integrated with and aligned with the photodiode itself. The dome structure is covered by a doped polysilicon material and an optional dielectric material (e.g., SiN) to form a concave stacked structure above the dome structure. The combination of the dome structure and the concave material results in a focusing element that is aligned with the trench photodiode or pixel element. That is, the focusing element includes a combination of polysilicon material, dielectric material, and dome structure, wherein the dielectric and polysilicon material have concave lower side surfaces, and the dome-shaped material has a convex upper surface.

[0016] In an embodiment, the trench photodiode and the dome structure include a Ge-based material. Moreover, the photodiode is disposed in a doped well region formed in a bulk Si material. The polysilicon material may be doped with a polarity opposite to that of the doped well region of the bulk Si material; however, as described below, other doping arrangements may also be conceived. The polysilicon material extends to one side of the photodiode to form a contact to the photodiode. In this way, the contact will not be located directly above the photodiode and therefore will not block light from entering the photodiode. However, in alternative embodiments, the contact may be located directly above the dome structure. In further embodiments, the dome structure may be surrounded by a shallow trench isolation material above the doped well region. An array of focusing elements may also be provided.

[0017] The photodiode structures of the present disclosure can be manufactured in a variety of ways using a variety of different tools. However, in general, these methods and tools are used to form structures with dimensions in the micrometer and nanometer range. The methods (i.e., techniques) for manufacturing the photodiode structures of the present disclosure have been adopted from integrated circuit (IC) technology. For example, these structures are built on a wafer and implemented in a film of material patterned by performing a photolithography process on top of the wafer. In particular, the manufacture of these photodiode structures uses three basic building blocks: (i) depositing a thin film of material on a substrate, (ii) applying a patterned mask on top of the film by photolithographic imaging, and (iii) selectively etching the film to the mask.

[0018] Figure 1 A substrate having a shallow trench isolation structure and a corresponding manufacturing process according to some aspects of the present disclosure, among other features, are shown. More specifically, Figure 1 The structure 10 includes a semiconductor substrate 12 having a shallow trench isolation structure 14. In an embodiment, the semiconductor substrate 12 is a substrate composed of a bulk semiconductor material. The bulk semiconductor substrate 12 can be a high resistivity substrate composed of a Si material, but other bulk materials used in photodiode embodiments are contemplated herein.

[0019] The shallow trench isolation structure 14 can be formed by conventional photolithography, etching and deposition methods known to those skilled in the art. For example, a resist formed on the semiconductor substrate 12 is exposed to energy (light) to form a pattern (opening). An etching process with selective chemical action (e.g., reactive ion etching (RIE)) is used to form one or more trenches in the semiconductor substrate 12 through the openings of the resist. After the resist is removed by a conventional oxygen ashing process or other known stripping agent, an insulator material, such as SiO2, can be deposited in the trench by any conventional deposition process, such as a chemical vapor deposition (CVD) process. Any residual insulator material on the surface of the semiconductor substrate 12 can be removed by a conventional chemical mechanical polishing (CMP) process.

[0020] Still refer to Figure 1 , an ion implantation process is performed on the semiconductor substrate 12 to form a doped well region 16. In an embodiment, the well region 16 may be doped with the same dopant type and polarity as the bulk semiconductor substrate 12 to reduce its resistivity. For example, the P-well is doped with a p-type dopant, such as boron (B), and the N-well is doped with an n-type dopant, such as arsenic (As), phosphorus (P), and Sb, among other suitable examples.

[0021] To perform the ion implantation process, a patterned implantation mask is used to define selected areas exposed for implantation. The implantation mask may include a layer of photosensitive material, such as an organic photoresist layer, applied by a spin coating process, then pre-baked, exposed to light projected through a photomask, baked after exposure, and developed using a chemical developer. The implantation mask has a thickness and stopping power sufficient to prevent the masked area from receiving a certain dose of implanted ions. After implantation, the implantation mask used to select the exposed area for forming the well region 16 is stripped.

[0022] exist Figure 2 In the embodiment of the present invention, a silicidation process is performed on the exposed areas (e.g., well regions 16) of the semiconductor substrate 12 between the shallow trench isolation structures 14. It should be understood by those skilled in the art that the silicidation process begins by depositing a thin transition metal layer, such as nickel, cobalt, or titanium, over the exposed well regions 16. After the material is deposited, the structure is heated to cause the transition metal to react with the exposed silicon (or other semiconductor materials described herein) to form a low resistance transition metal silicide. After the reaction, any remaining transition metal is removed by chemical etching, leaving the silicide contacts 18.

[0023] Still refer to Figure 2 After the silicidation process, a deep trench 20 is formed in the semiconductor substrate 12. Figure 2 In the structure shown, the deep trench 20 extends into the well region 16; however, it should be understood by those skilled in the art that the deep trench 20 can extend into the undoped region of the semiconductor substrate 12. For example, the deep trench 20 can have a depth of 0.3 μm to 10.0 μm and a depth outside this range. In an embodiment, the deep trench 20 can be formed by conventional photolithography and etching processes as described herein. From a top view, the deep trench 20 can have different cross-sectional shapes, such as circular, square, rectangular, elliptical, diamond, etc.

[0024] Figure 3A trench photodiode and a corresponding manufacturing process are shown, each having a dome structure, among other features. More specifically, the trench photodiode is formed from an epitaxial semiconductor material 22 using an epitaxial growth process within the deep trench 20. In an embodiment, the epitaxial growth process will grow the epitaxial semiconductor material 22 on the exposed surface of the semiconductor substrate 12 within the deep trench 20. From a top view, the epitaxial semiconductor material 22 can take the shape of the deep trench 20, such as a circle, square, rectangle, ellipse, diamond, etc.

[0025] In an embodiment, the epitaxial growth process can be modulated to include a dome structure 24 of the epitaxial semiconductor material 22. In an embodiment, the dome structure 24 is convex and is fully integrated and aligned with the trench photodiode (e.g., the epitaxial semiconductor material 22), as shown by the dashed lines. The alignment can be the result of growing the dome structure 24 and the epitaxial semiconductor material 22 of the trench photodiode within the same deep trench, for example, both extending to the same sidewall of the deep trench, as shown by the dashed lines. When the dome structure 24 is epitaxially grown with material from the epitaxial semiconductor material 22, the dome structure aligns itself with the sidewalls of the trench and is fully integrated with the epitaxial semiconductor material 22 in the deep trench.

[0026] Similar to the epitaxial semiconductor material 22, the dome structure 24 can present the shape of the deep trench 20 from a top view, such as a circle, square, rectangle, ellipse, diamond, etc. The epitaxial semiconductor material 22 and the integrated dome structure 24 can be Ge material; however, other highly light-absorbing material compounds are also contemplated herein. For example, other materials include, but are not limited to, SiGe, SiGeSn, or GeSn. In other embodiments, the epitaxial semiconductor material 22 and the integrated dome structure 24 can be doped with boron (or in other embodiments, with any p-type or n-type dopant) in an in-situ process.

[0027] The dome structure 24 will be used to form a fully integrated focusing element aligned with the photodiode material 22. Moreover, by growing the dome structure 24 of epitaxial semiconductor material directly on the photodiode material 22, the dome structure 24 will be self-aligned with the photodiode material 22 and is therefore a fully integrated self-aligned focusing element. The dome structure 24 can be optimized by adjusting the relationship between the pressure, growth time and pixel size and / or temperature parameters by means of the epitaxial growth process. For example, the pressure is in the range of 1μT to 760T and the temperature is in the range of 100°C to 900°C. This pressure and temperature range covers the full range of the entire series of UHVCVD, RP-CVD and molecular beam epitaxy (MBE) growth processes known in the art. In other embodiments, the epitaxial growth process can result in the dome structure 24 being located at, below or above the surface of the shallow trench isolation structure 14. Alternatively, the dome structure 24 can be provided by a crystallographic etching process after the epitaxial growth process.

[0028] Figure 4 A material having concave features located on the dome structure 24, among other features, is shown. After the epitaxial process, a DHF cleaning process can be used to remove the native oxide formed on the Ge photodiode material. Alternatively, if the Ge epitaxial process includes an in-situ deposited Si cap, the DHF cleaning process removes the native oxide formed on the Si cap. After the DHF cleaning process, in this example, a polysilicon material 26 is formed (e.g., deposited) over the dome structure and other exposed surfaces. The polysilicon material 26 is a doped polysilicon material having a polarity opposite to that of the well region 16. For example, the well region 16 can have a p-type dopant; and the polysilicon material 26 has an n-type dopant. However, in alternative embodiments, the dopant polarity of the well region 16 and the polysilicon material 26 can be the same.

[0029] The polysilicon material 26 may be deposited to a thickness of from about 50 nm to 2 microns by a CVD process or a plasma vapor deposition (PVD) process (both of which may include in-situ doping), although other dimensions are contemplated herein. The deposition of the polysilicon material 26 over the dome structure 24 results in a concave lower side surface 26 a that is located directly over and in contact with the dome structure 24.

[0030] After the deposition process, a patterning process is performed on the polysilicon material 26 by conventional photolithography and an etching process with selective chemistry. The patterning process causes the polysilicon material 26 to extend on one side of the photodiode material 22. The polysilicon material 26 extending to one side of the photodiode material 22 can have a planar surface for forming a contact to the photodiode material 22. In this way, the contact can be located on one side of the photodiode without interfering with or blocking light from entering the photodiode.

[0031] Still refer to Figure 4 , an optional dielectric material 28, such as SiN or other anti-reflective material, is deposited over the polysilicon material 26, which also extends over the silicide contact 18. Similar to the polysilicon material 26, the dielectric material 28 can be deposited by a CVD process or a PVD process, which also results in a concave underside surface 28a. In this embodiment, the combination of the dome structure 24, the concave polysilicon material 26a, and the concave dielectric material 28a forms an aligned focusing element that is fully integrated with the photodiode (e.g., material 22). In an alternative embodiment, in the absence of the dielectric material 28, the combination of the dome structure 24 and the concave polysilicon material 26a forms a self-aligned focusing element that is fully integrated with the deep photodiode (e.g., material 22).

[0032] Figure 5 A contact 38 is shown that contacts the photodiode structure. More specifically, as shown in FIG. Figure 5 As shown, contact 38 lands on silicide contact 18 and polysilicon material 26 on one side of photodiode material 22. Those skilled in the art will appreciate that contact 38 may be formed by conventional lithography, etching, and deposition methods used to fabricate back-end-of-line (BEOL) stacks.

[0033] For example, after the dielectric materials 30, 32, 34, 36 are deposited, trenches are formed in these materials by photolithography and etching processes. Those skilled in the art will appreciate that the dielectric materials 30, 32, 34, 36 can be any anti-reflective material, such as a combination of SiO2 and SiN3 used in various orders and sequences in the BEOL stack. The first dielectric material 30 (e.g., SiO2) can also have a concave lower side surface and a planar top surface. The remaining layers 32, 34, 36 can have planar surfaces. A conductive material (e.g., aluminum or tungsten) can be deposited within the trenches to form contacts 38. Any excess conductive material can be removed by a CMP process.

[0034] Figures 6 to 8 Alternative photodiode structures according to other aspects of the present disclosure are shown. For example, Figure 6 Structure 10a shows a photodiode structure without optional material 28. Figure 7 In structure 10b, the photodiode structure has a contact 38 that is located directly above a fully integrated focusing element, such as above the dome structure 24. Figure 8In structure 10c of FIG. 1 , the photodiode structure has a contact 38 located directly above a self-aligned fully integrated focusing element, such as above dome structure 24, but without optional material 28. For example, the remaining features of each of these structures are similar to those of reference Figure 5 Same as described.

[0035] Photodiodes with focusing structures can be utilized in system-on-chip (SoC) technology. It will be understood by those skilled in the art that SoC is an integrated circuit (also referred to as a "chip") that integrates all components of an electronic system on a single chip or substrate. Because the components are integrated on a single substrate, SoC consumes much less power and occupies much less area than multi-chip designs with equivalent functionality. As a result, SoC is becoming a dominant force in the mobile computing (e.g., smartphones) and edge computing markets. SoC is also commonly used in embedded systems and the Internet of Things.

[0036] The above method is used for the manufacture of integrated circuit chips. The resulting integrated circuit chips can be distributed by the manufacturer in raw wafer form (i.e., as a single wafer with multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in the form of a single chip package (e.g., a plastic carrier whose leads are fixed to a motherboard or other higher-level carrier) or a multi-chip package (e.g., a ceramic carrier with surface interconnects and / or buried interconnects). In any case, the chip is then integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of (a) an intermediate product (e.g., a motherboard) or (b) a final product. The final product can be any product that includes an integrated circuit chip, ranging from toys and other low-end applications to advanced computer products with displays, keyboards or other input devices, and central processing units.

[0037] The description of various embodiments of the present disclosure has been given for the purpose of illustration, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the various embodiments, practical applications, or technical improvements to technologies found in the marketplace, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A semiconductor structure comprising: a substrate including a doped well region; A shallow trench isolation structure located above the doped well region; a trench photodiode extending into the doped well region of the substrate and comprising a domed structure and an upper surface extending above a top surface of the shallow trench isolation structure, wherein a sidewall of the trench photodiode contacts the doped well region; as well as A doping material is located on the dome structure, wherein the doping material has a concave lower side surface.

2. The structure of claim 1, wherein the dome structure is aligned with and fully integrated with the trench photodiode, the dome structure and the trench photodiode both comprising the same light absorbing material.

3. The structure of claim 2, wherein the light absorbing material comprises a Ge-based material.

4. The structure of claim 2, wherein the dome structure comprises a convex surface. The structure of claim 4 , wherein the doped material and the doped well region have opposite polarities.

6. The structure of claim 1, wherein the doped material comprises polysilicon material extending to a side of the trench photodiode, and a contact is placed on the polysilicon material on the side of the trench photodiode.

7. The structure of claim 1 further comprising a first contact electrically contacting the dopant material and a second contact electrically connected to the well region.

8. The structure of claim 1 further comprising a non-reflective dielectric material on the doped material, the non-reflective dielectric material comprising a lower side surface having a concave surface.

9. The structure of claim 8 wherein the domed structure in combination with the doped material and the non-reflective dielectric material comprises a focusing element aligned with and integrated with the trench photodiode.

10. The structure of claim 1, wherein the dome structure comprises a cross-sectional shape corresponding to a shape of a trench of the trench photodiode.

11. The structure of claim 1 wherein the trench photodiode and the dome structure are surrounded by the shallow trench isolation structure.

12. A semiconductor structure comprising: A shallow trench isolation structure located on a well region of a semiconductor substrate; a trench photodiode extending into the well region of the semiconductor substrate and including a dome structure at an upper end thereof and an upper surface extending above a top surface of the shallow trench isolation structure; a doped material on the dome structure extending to one side of the trench photodiode; a first contact in electrical contact with the dopant material; as well as A second contact is in electrical contact with the well region of the semiconductor substrate.

13. The structure of claim 12, wherein the dome structure is aligned with and integral with the trench photodiode, the dome structure and the trench photodiode both comprising the same light absorbing material.

14. The structure of claim 13, wherein the light absorbing material comprises a Ge-based material.

15. The structure of claim 12 wherein the dome structure comprises a convex surface and the doped material comprises a concave underside surface.

16. The structure of claim 12 wherein the doping material and the well region have opposite polarities.

17. The structure of claim 12 wherein the doped material comprises a polysilicon material having a polarity opposite to that of the well region.

18. The structure of claim 17, further comprising a non-reflective dielectric material on the polysilicon material, wherein the non-reflective dielectric material comprises an underside concave surface.

19. The structure of claim 18 wherein the dome structure, the non-reflective dielectric material, and the polysilicon material are configured to form a light focusing element for the trench photodiode.

20. A method of forming a semiconductor structure, comprising: forming a shallow trench isolation structure on a well region of a semiconductor substrate; forming a trench photodiode in a trench structure formed in the well region of the semiconductor substrate, the trench photodiode comprising an integrated dome structure and an upper surface extending above a top surface of the shallow trench isolation structure; forming a doping material on the integrated dome structure extending to one side of the trench photodiode, the doping material having a concave lower side surface; as well as A contact is formed in electrical contact with the doped material on the one side of the trench photodiode.

Images