PHOTODIOD WITH INTEGRATED, SELF-ALIGNED, LIGHT-FOCUSING ELEMENT AND METHOD

Abstract

Structure (10) comprising: a semiconductor substrate (12) comprising a doped well region (16); a trench photodiode extending into the doped well region (16) of the semiconductor substrate (12) and comprising a dome-shaped structure (24), wherein side walls of the trench photodiode contact the doped well region (16); and a doped material (26) on the dome-shaped structure (24), wherein the doped material (26) has a concave underside surface (26a).

Description

AREA OF INVENTION

[0001] The present disclosure relates to semiconductor structures and in particular a photodiode with integrated light-focusing elements and manufacturing methods. BACKGROUND

[0002] A photodiode is a semiconductor device that converts light into an electric current. Photodiodes can contain optical filters and built-in lenses, and can have large or small surface areas depending on the specific application. Photodiodes can be used in many different optical applications. For example, germanium (Ge) photodiodes, due to their high absorption compared to silicon (Si), can be used for LiDAR applications according to the state of the art. This allows for smaller pixel sizes and active areas. In such implementations, the signal-to-noise (S / N) ratio is reduced by inefficient coupling with the absorber, and crosstalk increases with smaller pitch.

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

[0004] In one aspect of the disclosure, a structure comprises: a trench photodiode comprising a dome-shaped structure; and a doped material on the dome-shaped structure, the doped material having a concave underside surface.

[0005] In one aspect of the disclosure, a structure comprises: a trench photodiode extending into a well region of a semiconductor substrate and including a dome-shaped structure at its upper end; a doped material on the dome-shaped structure extending to one side of the trench photodiode; a first contact in electrical contact with the doped material; and a second contact in electrical contact with the well region of the semiconductor substrate.

[0006] In one aspect of the disclosure, a method comprises: forming a trench photodiode in a trench structure, wherein the trench photodiode comprises an integrated dome-shaped structure; forming a doped material on the integrated dome-shaped structure and extending to one side of the trench photodiode, wherein the doped material has a concave underside surface; and forming a contact in electrical contact with the doped material on the side of the trench photodiode. List of characters

[0007] The present disclosure is described in the following detailed description with reference to the aforementioned multitude of drawings, using non-limiting examples of exemplary embodiments of the present disclosure. Fig. Figure 1 shows a substrate with shallow trench isolation structures, among other features, and a respective fabrication process according to aspects of the present disclosure. Fig. Figure 2 shows trenches formed in the substrate, among other features, and a respective manufacturing process according to aspects of the present disclosure. Fig. Figure 3 shows trench photodiodes, each with a dome-shaped structure, among other features, and a respective fabrication process according to aspects of the present disclosure. Fig. Figure 4 shows material with concave features on the dome-shaped structure, among other features, and a respective manufacturing process according to aspects of the present disclosure. Fig. Figure 5 shows contacts to the photodiode structure, among other features, and a respective fabrication process according to aspects of the present disclosure. Fig. Figures 6-8 show alternative photodiode structures according to additional aspects of the present disclosure. DETAILED DESCRIPTION

[0008] The present disclosure relates to semiconductor structures and, in particular, a photodiode with integrated light-focusing elements and a fabrication method. Specifically, the present disclosure relates to deep-trench photodiodes with aligned light-focusing elements. In embodiments, the deep-trench photodiode is a deep-trench germanium photodiode, and the light-focusing element is aligned with the deep-trench photodiode. The light-focusing element comprises a dome-shaped structure that is fully integrated with and uses the same material as the deep-trench photodiode. Advantageously, the integrated focusing element enables pixel arrays with a small active area, improved signal-to-noise (S / N) ratio, and isolation.

[0009] In embodiments, the photodiode is a trench photodiode with a dome-shaped structure (e.g., convex) that is fully integrated and aligned with the photodiode itself. The dome-shaped structure is covered by a doped polysilicon material and an optional dielectric material, e.g., SiN, resulting in a concave layered structure over the dome-shaped structure. The combination of the dome-shaped structure and the concave material(s) results in a focusing element that is aligned with the trench photodiode or pixel element. That is, the focusing element comprises a combination of polysilicon material, dielectric material, and the dome-shaped structure, wherein the dielectric and polysilicon materials have a concave underside surface and the dome-shaped material has a convex upper surface.

[0010] In embodiments, the trench photodiode and the dome-shaped structure comprise Ge-based material. The photodiode is also provided within a doped well region formed in bulk silicon material. The polysilicon material can be doped with a polarity opposite to that of the doped well region of the bulk silicon material; although other doping arrangements are also considered, as described below. The polysilicon material extends to one side of the photodiode to form a contact with it. In this way, the contact is not directly above the photodiode and thus does not impede light from entering it. In alternative implementations, however, the contact can be located directly on the dome-shaped structure. In further embodiments, the dome-shaped structure can be surrounded by shallow trench insulating material over the doped well region.An array of focusing elements can also be provided.

[0011] The photodiode structures of this disclosure can be fabricated in several ways using various tools. Generally, however, the methodologies and tools used are for forming structures with dimensions on the micrometer and nanometer scale. The methodologies, i.e., technologies, employed to fabricate the photodiode structures of this disclosure were derived from integrated circuit (IC) technology. For example, the structures are fabricated on wafers and realized in material films that are patterned on the top surface of a wafer by photolithographic processes.In particular, the fabrication of the photodiode structures uses three basic building blocks: (i) deposition of thin material films onto a substrate, (ii) application of a structured mask to the top of the films by photolithographic imaging, and (iii) etching the film selectively with respect to the mask.

[0012] Fig. Figure 1 shows a substrate with shallow trench insulation structures, among other features, and a respective fabrication process according to aspects of the present disclosure. In particular, structure 10 comprises Fig. 1 a semiconductor substrate 12 with flat-trench insulation structures 14. In embodiments, 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 Si material; although other bulk materials used in photodiode implementations are considered herein.

[0013] The shallow trench insulation structures 14 can be formed by conventional lithography, etching, and deposition processes known to those skilled in the art. For example, a resist formed over the semiconductor substrate 12 is exposed to energy (light) to form a structure (opening). An etching process using selective chemistry, 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. Following resist removal by a conventional oxygen ashing process or other known stripping agents, an insulating material, e.g., SiO2, can be deposited in the trenches by any conventional deposition process, e.g., chemical vapor deposition (CVD).Any remaining insulating material on the surface of the semiconductor substrate 12 can be removed by conventional chemical mechanical polishing (CMP) processes.

[0014] Referring further to Fig. 1. The semiconductor substrate 12 is subjected to an ion implantation process to form a doped well region 16. In embodiments, the well region 16 can be doped with a dopant of the same type and polarity as the bulk semiconductor substrate 12 to reduce its resistivity. For example, among other examples, a P-well is doped with p-type dopants, e.g., boron (B), and an N-well is doped with n-type dopants, e.g., arsenic (As), phosphorus (P), and Sb.

[0015] To perform the ion implantation process, a structured implantation mask is used to define selected areas exposed for implantation. The implantation mask may consist of a layer of a photosensitive material, such as an organic photoresist, applied by a spin-coating process, pre-baked, exposed to light projected through a photomask, baked after exposure, and developed with a chemical developer. The implantation masks possess a thickness and stopping power sufficient to block masked areas from receiving a dose of the implanted ions. The implantation mask used to select the exposed area for forming well region 16 is stripped after implantation.

[0016] In Fig. 2. An exposed region of the semiconductor substrate 12, e.g., well region 16, between the shallow trench insulation structures 14, is subjected to a silicide process. As should be clear to those skilled in the art, the silicide process begins with the deposition of a thin transition metal layer, e.g., nickel, cobalt, or titanium, over the exposed well region 16. After deposition of the material, the structure is heated, which allows the transition metal to react with exposed silicon (or another semiconductor material as described herein), forming a low-resistance transition metal silicide. Following the reaction, any remaining transition metal is removed by chemical etching, leaving the silicide contact 18.

[0017] Referring further to Fig. 2, deep trenches 20 are formed in the semiconductor substrate 12 following the silicide process. In the Fig. In the structure shown in Figure 2, the grooves 20 extend within the well region 16; however, it should be clear to those skilled in the art that the grooves 20 can extend within the undoped region of the semiconductor substrate 12. For example, the grooves 20 can have a depth of 0.3 µm to 10.0 µm and beyond. In embodiments, the grooves 20 can be formed by conventional lithography and etching processes, as already described herein. The grooves 20, viewed from above, can have different cross-sectional shapes, such as circular, square, rectangular, oval, rhomboid, etc.

[0018] Fig. Figure 3 shows trench photodiodes, each with a dome-shaped structure, among other features, and a respective manufacturing process. In particular, the trench photodiodes are formed from an epitaxial semiconductor material 22 using an epitaxial growth process within the trenches 20. In embodiments, the epitaxial growth process grows the epitaxial semiconductor material 22 on the exposed surfaces of the semiconductor substrate 12 within the trenches 20. In a top-down view, the epitaxial semiconductor material 22 can assume the shape of the trenches 20, e.g., circular, square, rectangular, oval, rhomboid, etc.

[0019] In embodiments, the epitaxial growth process can be modulated to include a dome-shaped structure 24 of the epitaxial semiconductor material 22. In embodiments, the dome-shaped structure 24 is convex and fully integrated and aligned with the trench photodiodes, e.g., epitaxial semiconductor material 22, as shown by the dashed lines. The alignment can result from the growth of the dome-shaped structure 24 and the epitaxial semiconductor material 22 of the trench photodiodes within the same trench, e.g., both extending from them to the same side walls of the trench, as shown by the dashed lines.Since the dome-shaped structure 24 is epitaxially grown with the material of the epitaxial semiconductor material 22, the dome-shaped structure aligns itself with the side walls of the trench and is fully integrated with the epitaxial semiconductor material 22 in the deep trench.

[0020] Similar to the epitaxial semiconductor material 22, the dome-shaped structure 24, viewed from above, can assume the shape of the deep trenches 20, e.g., circular, square, rectangular, oval, rhomboid, etc. The epitaxial semiconductor material 22 and the integrated dome-shaped structure 24 can be a Ge material; however, other highly light-absorbing material compounds are also considered. For example, other materials include, but are not limited to, SiGe, SiGeSn, or GeSn. In further embodiments, the epitaxial semiconductor material 22 and the integrated dome-shaped structure 24 can be doped with boron (or, in further embodiments, with any p- or n-type dopant) in an in-situ process.

[0021] The dome-shaped structure 24 is used to form a fully integrated, focusing element that aligns with the photodiode material 22. By growing the dome-shaped structure 24 of epitaxial semiconductor material directly onto the photodiode material 22, the dome-shaped structure 24 self-aligns with the photodiode material 22, thus forming a fully integrated, self-aligned focusing element. The dome-shaped structure 24 can be optimized during the epitaxial growth process by modulating the pressure, the relationship between growth time and pixel dimensions, and / or temperature parameters. For example, pressures in the range of 1µT to 760T and temperatures in the range of 100°C to 900°C. This pressure and temperature range accommodates a full range of UHVCVD, RP-CVD and molecular-beam epitaxy (MBE) growth processes as known in the industry.In further embodiments, the epitaxial growth process can result in the dome-shaped structure 24 being located on, below, or above a surface of the shallow trench isolation structures 14. Alternatively, the dome-shaped structure 24 can be provided by a crystallographic etching process following the epitaxial growth process.

[0022] Fig. Figure 4 shows material with concave features on the dome-shaped structure 24, among other features. Following 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. Subsequent to the DHF cleaning process, in this example, a polysilicon material 26 is formed, e.g., deposited, over the dome-shaped structure and other exposed surfaces. The polysilicon material 26 is a doped polysilicon material that includes a polarity opposite to that of the well region 16. For example, the well region 16 may contain a p-type dopant; whereas the polysilicon material 26 contains an n-type dopant.In alternative embodiments, however, the polarity of the dopant can be the same for the well region 16 and the polysilicon material 26.

[0023] The polysilicon material 26 can be deposited by a CVD or plasma vapor deposition (PVD) process (both of which may include in-situ doping) to a thickness of approximately 50 nm to 2 micrometers, although other dimensions are considered here. The deposition of the polysilicon material 26 over the dome-shaped structure 24 results in a concave underside surface 26a, directly above and in contact with the dome-shaped structure 24.

[0024] Following the deposition process, the polysilicon material 26 undergoes a structuring process using a conventional lithography and etching process with selective chemistry. The structuring process leaves polysilicon material 26 extending onto one side of the photodiode material 22. The polysilicon material 26 extending onto the side of the photodiode material 22 can have a planar surface, which is used to form contacts with the photodiode material 22. In this way, a contact can be established on the side of the photodiode without interfering with or blocking light entering the photodiode.

[0025] Referring further to Fig. 4, an optional dielectric material 28, e.g., SiN or another anti-reflective material, is deposited over the polysilicon material 26, extending also over the silicide contact 18. Similar to the polysilicon material 26, the dielectric material 28 can be deposited by a CVD or PVD process, which also results in a concave underside surface 28a. In this embodiment, the combination of the dome-shaped 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 optional embodiments without the dielectric material 28, the combination of the dome-shaped structure 24 and the concave polysilicon material 26a forms the self-aligned focusing element, which is fully integrated with the deep photodiode, e.g. material 22.

[0026] Fig. Figure 5 shows contacts 38 that contact the photodiode structure. In particular, as shown in Fig. As shown in Figure 5, the contacts 38 are located on the silicide contact 18 and the polysilicon material 26 on the side of the photodiode material 22. The contacts 38 can be formed by conventional lithography, etching and deposition processes used to manufacture back-end-of-line (BEOL) stacks, as should be clear to those skilled in the art.

[0027] For example, after deposition of the dielectric materials 30, 32, 34, 36 by lithography and etching processes, a trench is formed in these materials. The dielectric materials 30, 32, 34, 36 can be any anti-reflective materials, such as a combination of SiO2 and SiN3 in various sequences and orders used in BEOL stacks, as should be known to those skilled in the art. The first dielectric material 30, e.g., SiO2, can also have a concave underside surface with a planar upper 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 the contacts 38. Any excess material can be removed by a CMP process.

[0028] Fig. Figures 6-8 show alternative photodiode structures according to additional aspects of the present disclosure. For example, structure 10a of Fig. 6 the photodiode structure without the optional material 28. In structure 10b of Fig. In Figure 7, the photodiode structure has the contact 38 directly above the fully integrated focusing element, e.g., above the dome-shaped structure 24. In structure 10c of Fig. Figure 8 shows the photodiode structure with contact 38 directly above the self-aligned, fully integrated focusing element, e.g., above the dome-shaped structure 24, but without the optional material 28. The remaining features of each of these structures are the same as, for example, with reference to Fig. 5 described.

[0029] The photodiode with focusing structures can be used in system-on-chip (SoC) technology. It should be clear to those in the know that an SoC is an integrated circuit (also known as a "chip") that integrates all the components of an electronic system onto a single chip or substrate. Because the components are integrated onto a single substrate, SoCs consume far less power and occupy much less space than multi-chip designs with equivalent functionality. For this reason, SoCs are becoming the dominant force in the mobile computing (such as in smartphones) and edge computing markets. SoCs are also commonly used in embedded systems and the Internet of Things (IoT).

[0030] The process(s) described above is / are used in the fabrication of integrated circuit chips. The resulting integrated circuit chips may be distributed by the manufacturer in raw wafer form (that is, as a single wafer containing multiple unpackaged chips), as bare die chips, or in a packaged form. In the latter case, the chip is mounted in a single-chip assembly (such as a plastic substrate with conductors attached to a motherboard or other higher-level support) or in a multi-chip assembly (such as a ceramic substrate having one or both surface interconnects or buried interconnects). In each case, the chip is then integrated with other chips, discrete switching elements, and / or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) a final product.The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products that feature a display, a keyboard or other input device, and a central processor.

[0031] The descriptions of the various embodiments of the present disclosure are presented for illustrative purposes only and are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations are obvious to the ordinary person skilled in the art without altering the scope and concept of the described embodiments. The terminology used herein has been chosen to best explain the principles of the embodiments, their practical application or technical improvement over commercially available technologies, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

[1] Structure comprising: a trench photodiode comprising a dome-shaped structure; and a doped material on the dome-shaped structure, wherein the doped material has a concave bottom surface. [2] The structure of claim 1, wherein the dome-shaped structure is aligned and fully integrated with the trench photodiode, both of which comprise a 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 or 3, wherein the trench photodiode is within a well region of a substrate, and the dome-shaped structure comprises a convex surface. [5] The structure of claim 4, wherein the doped material and the well region have opposite polarities. [6] The structure of any one of claims 1 to 5, wherein the doped material comprises a polysilicon material extending to one side of the trench photodiode, and a contact on the polysilicon material lands on the side of the deep photodiode. [7] The structure of any one of claims 1 to 6, further comprising a first contact in electrical contact with the doped material and a second contact having an electrical connection with a well region. [8] The structure of any one of claims 1 to 7, further comprising a non-reflective dielectric material on the doped material, comprising a bottom surface having a concave surface. [9] The structure of claim 8, wherein the dome-shaped structure in combination with the doped material and the non-reflective dielectric material comprises a focusing element aligned and integrated with the trench photodiode. [10] The structure according to any one of claims 1 to 9, wherein the dome-shaped structure comprises a cross-sectional shape corresponding to a shape of a trench of the trench photodiode. [11] The structure of any one of claims 1 to 10, wherein the trench photodiode and the dome-shaped structure are surrounded by shallow trench isolation regions. [12] Structure comprising: a trench photodiode extending into a well region of a semiconductor substrate and including a dome-shaped structure at its upper end; a doped material on the dome-shaped structure extending to one side of the trench photodiode; a first contact in electrical contact with the doped material; and a second contact in electrical contact with the well region of the semiconductor substrate. [13] The structure of claim 12, wherein the dome-shaped structure is aligned and integrated with the trench photodiode, both of which comprise a same light absorbing material. [14] The structure of claim 13, wherein the light absorbing material comprises a Ge-based material. [15] The structure of any one of claims 12 to 14, wherein the dome-shaped structure comprises a convex surface and the doped material comprises a concave bottom surface. [16] The structure of any one of claims 12 to 15, wherein the doped material and the well region have opposite polarities. [17] The structure of any one of claims 12 to 16, wherein the doped material comprises 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, the non-reflective dielectric material comprising a bottom concave surface. [19] The structure of claim 18, wherein the dome-shaped structure, the non-reflective dielectric material, and the polysilicon material are configured to form a light-focusing element for the trench photodiode. [20] Procedure comprising: Forming a trench photodiode in a trench structure, the trench photodiode comprising an integrated dome-shaped structure; Forming a doped material on the integrated dome-shaped structure and extending to one side of the trench photodiode, the doped material having a concave bottom surface; Forming a contact in electrical contact with the doped material on the trench photodiode side.

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