CN211529954U - TOF sensor having highly light-transmissive electrode structure and imaging apparatus - Google Patents

Abstract

The application provides TOF sensor and imaging device with high printing opacity electrode structure, it includes: a semiconductor substrate; an array of photodiodes formed within the semiconductor substrate; a stacked electrode structure disposed on a light incident side of the photodiode array, including a multilayer electrode and a multilayer insulating film, and a transparent region aligned with the photodiode and allowing infrared light to pass therethrough; and a micro lens array arranged at the light incidence side of the incident light through hole; at least one layer of the electrodes of the superposed electrodes extends and bends towards the substrate at the edge of the through hole to guide light to enter the photodiode. The structure of this application can prevent effectively that light from getting into horizontal crosstalk and the light energy loss that causes between the multilayer electrode.

Description

TOF sensor having highly light-transmissive electrode structure and imaging apparatus

Technical Field

The present application relates to the field of images, and more particularly to TOF sensors and imaging devices having highly transparent electrode structures.

Background

In the prior art, TOF is time of flight, an abbreviation for time of flight. The working principle of the TOF sensor is that the transmitting module actively transmits near-infrared light, the TOF sensor receives reflected or scattered light when encountering an object to transmit or scatter in the transmission process, and the TOF sensor calculates the phase difference or time difference between the transmitted light and the received light to obtain the distance information of the object to be measured.

Referring to fig. 1, the structure of the TOF sensor includes: by a Microlens (ML), a Multilayer Electrode (ME), a photodiode (PPD), a photo charge storage region (FD), a Deep Trench Isolation (DTI), and the like. The main workflow of the TOF sensor is as follows:

first, the micro lens converges the light reflected and scattered by the object to be measured, the light is transmitted through the empty area in the middle of the multilayer electrode, the light is projected to the photodiode, and at the moment, the optical signal is converted into an electrical signal. And finally, the input signals are subjected to subtraction by a subsequent circuit to obtain analog values representing corresponding optical signals, the analog values are converted into digital values by a subsequent ADC, and the digital values are processed to obtain the required image.

Before the light reflected or scattered by the object to be measured is projected onto the micro-lens, a lens or a lens group is generally used to converge the light once, and the imaging optics has a certain field angle to ensure a certain field range. As shown in fig. 2, the CRA (chief ray angle) represents the maximum angle of a ray that can be focused on a pixel. Thus, the light rays reach the microlenses at an angle to the microlenses.

Referring to fig. 3, when light is projected onto the microlens at a certain angle, a part of the light cannot be projected onto the photosensitive surface, since most of the electrode materials are metal layers and the reflectivity of metal is high, such a part of the light can propagate among the multi-layer electrode structures, and the spacing between the electrode layers is small, since the light of the TOF sensor is generally a single wavelength of near infrared, the interference phenomenon between the metal layers is significant. When light rays propagate along the metal layer to adjacent pixel cells, lateral cross-talk is large, and in severe cases, the normal operation of the TOF sensor is disturbed.

To correct the position of the light projected onto the photosurface, translation of the position of the microlens is typically used. This reduces lateral crosstalk to some extent, but the ability to correct the light by translating the microlens position is limited, and the light will not be incident perfectly parallel, some of which will always cause interference effects and lateral crosstalk due to multiple reflections.

Disclosure of Invention

The application provides a TOF sensor and imaging device with high printing opacity electrode structure can make partial light can't project the interference phenomenon between the metal more serious and light along the metal level spread adjacent pixel unit and cause the problem of transverse cross talk and influence TOF sensor's detection performance when solving present light and projecting TOF sensor because the angle problem.

According to a first aspect of the present application, there is provided a TOF sensor having a highly light transmissive electrode structure, comprising: a substrate; a photodiode formed in a central region within a substrate; at least two layers of electrodes disposed over the substrate; and a microlens disposed above the electrode corresponding to the photodiode; one end of the electrode at the topmost layer in at least one layer of electrodes extends towards the center direction of the substrate and is bent or bent to prevent incident light from entering between the electrodes.

Preferably, one end of the topmost electrode among the electrodes extends toward the center of the substrate and is bent or bent downward.

Preferably, one end of the electrode at the lowermost layer among the electrodes extends toward the center of the substrate and is bent or curved upward.

Preferably, one end of the electrode at the topmost layer among the electrodes extends toward the center of the substrate and is bent or curved downward, and one end of the electrode at the bottommost layer among the electrodes extends toward the center of the substrate and is bent or curved downward.

Preferably, the TOF sensor includes two or more layers of electrodes, and one end of the electrodes of the other layers of the electrodes except for the topmost or bottommost layer extends toward the center of the substrate and is bent or curved downward, and/or one end of the electrodes of the other layers of the electrodes except for the topmost or bottommost layer extends toward the center of the substrate and is bent or curved upward.

Preferably, the TOF sensor further comprises a shield disposed around the electrode to block incident light illumination.

Preferably, the TOF sensor further comprises an antireflection film disposed above, below the microlens or inside the pixel of the TOF sensor, wherein the thickness of the antireflection film is a uniform preset thickness.

Preferably, the preset thickness is obtained by pixels in the TOF sensor according to the following formula:

wherein e is a preset thickness, is a main light angle of an edge pixel area of the TOF sensor, is a single near-infrared light wavelength, n is a medium refractive index, and k can be 0 or a positive integer.

Preferably, the TOF sensor further comprises: a first photo-charge storage region disposed at one side of the photodiode; a second photo-charge storage region symmetrically arranged at the other side of the photodiode; the first deep groove isolation region is arranged on one side, far away from the photodiode, of the first photo-charge storage region; and the second deep trench isolation region is arranged on one side of the second photoelectric charge storage region far away from the photodiode in symmetry with the first deep trench isolation region.

According to a second aspect of the present application, there is provided an imaging apparatus comprising a TOF sensor as described above.

The beneficial effect of this application lies in: under the condition of not changing the original structure of TOF sensor, adopt closed electrode structure, through the bent part of electrode, make oblique incidence and because multiple reflection or scattering to the inboard light of electrode can't transversely conduct between the electrode interval, greatly reduced the interference effect of the light of single wavelength between multilayer electrode, eliminated because the transverse cross talk that multilayer electrode structure caused, improved the anti transverse cross talk ability of this sensor greatly, improved the performance of this TOF sensor, make TOF sensor's measurement more accurate.

Drawings

FIG. 1 is a schematic diagram of a conventional TOF sensor;

FIG. 2 is a schematic view of a depth sensor imaging;

FIG. 3 is a schematic diagram of oblique incidence of light rays onto a TOF sensor;

FIG. 4 is a schematic diagram of a TOF sensor of the present application having a first closed electrode configuration;

FIG. 5 is a schematic diagram of a TOF sensor of the present application having a first closed electrode configuration; and

FIG. 6 is a schematic diagram of a TOF sensor of the present application having a first closed electrode configuration.

Description of reference numerals: the photodiode array PPD overlaps the electrode set ME microlens array ML first photo-charge storage region FD1 second photo-charge storage region FD2 first deep trench isolation region DTI1 second deep trench isolation region DTI 2.

Detailed Description

The present application will be described in further detail below with reference to the accompanying drawings by way of specific embodiments.

In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Referring to fig. 1 to 6, the present application provides a TOF sensor having a high light-transmitting electrode structure, which includes: a semiconductor substrate, a photodiode array PPD, a superimposed electrode set ME, and a microlens array ML.

The photodiode array PPD has photoelectric response to infrared light and is formed in the semiconductor substrate; a superimposed electrode group ME provided on the light incident side of the photodiode array PPD and including a multilayer electrode, a multilayer insulating film, and a transparent region through which infrared light is transmitted aligned with the photodiode; a microlens array ML aligned with the transparent region and disposed at a light incident side of the transparent region; at least one electrode in the stacked electrode set ME extends toward the center of the transparent region and is bent toward the substrate to guide light into the photodiode array PPD.

Semiconductor substrates, including silicon substrates, silicon germanium substrates, silicon carbide substrates, Silicon On Insulator (SOI) substrates, Germanium On Insulator (GOI) substrates, glass substrates, or III-V compound substrates (e.g., silicon nitride or gallium arsenide, etc.), are used to form device structures or chip circuits. The substrate may also be a bulk base, i.e., a silicon substrate, a silicon germanium substrate, or a silicon carbide substrate. In other embodiments, the substrate can also be a silicon-on-insulator substrate or a germanium-on-insulator substrate. In other embodiments, the substrate can further include a semiconductor base and an epitaxial layer formed on a surface of the semiconductor base through an epitaxial process.

The photodiode array PPD is disposed in the substrate, is formed through an ion implantation process, and can control the depth and implantation range of ion implantation by controlling the energy and concentration of the ion implantation, thereby controlling the depth and thickness of the photodiode array PPD.

In this embodiment, the photodiode array PPD includes a clamp photodiode. The clamping photodiode is doped with N-type ions, and the N-type ions comprise phosphorus ions, arsenic ions or antimony ions.

Furthermore, the photodiode can be additionally provided with a thin P + layer relative to the surface layer of the traditional photodiode, the N buried layer of the charge collection layer is separated from the top surface of the Si/SiO2 through the top P + layer, so that traps causing the main cause of dark current are covered, the photodiode has smaller dark current relative to the traditional photodiode on one hand, and a completely depleted accumulation region can be formed on the other hand, and the problem of output image lag is solved.

This application reduces the interference effect between the electrode structure through setting up the structure of adjusting stack electrode group ME, reduces because the horizontal crosstalk that the multiple reflection of light between multilayer electrode structure caused.

The specific structure of the superposed electrode group ME comprises the following structures:

referring to fig. 4, the first method is: the electrode closest to the microlens array ML side of the superimposed electrode group ME extends toward the center of the transparent region and is bent toward the substrate.

Referring to fig. 5, the second method is: the electrode closest to the microlens array ML in the superposed electrode group ME extends to the center of the transparent region and bends towards the substrate, the electrode closest to the semiconductor substrate in the superposed electrode group ME extends to the center of the transparent region and bends towards the microlens array ML, and the two layers of electrodes cover the electrode in the middle layer at the same time, so that the incident light can be blocked.

Referring to fig. 6, the third is: the electrodes of the superimposed electrode group ME excluding the electrode closest to the side of the microlens array ML or the electrodes of the other layers closest to the side of the semiconductor substrate extend toward the center of the transparent region and are bent toward the microlens array ML and/or the semiconductor substrate.

Here, the material of the stacked electrode group ME is a metal material containing more than 90% of copper, and the stacked electrode group ME is manufactured to have a curved structure by a special manufacturing process. Since the sharp-angle bending or right-angle bending structure is easy to form bending point discharge at the bending part and is easy to accumulate impurities in the region, the metal layer is easy to structurally break after long-time work, and the extra parasitic capacitance at the corner can also influence the signal transmission. In order to avoid the above negative effects, the curved structure is generally bent at an obtuse angle or bent at an arc.

In this embodiment, the angle at which the electrode is bent toward the semiconductor substrate or the microlens array ML is 30 degrees or more. The bending angle can be set according to practical situations, and is not limited herein.

Further, the light transmission aperture formed by the electrode in the transparent area is smaller than that formed by any other electrode in the superposed electrode layer.

Further, at least one electrode of the set of superimposed electrodes ME is transparent to infrared light and extends to a transparent area covering more than 90% of the area of the transparent area.

In this embodiment, the electrode that is transparent to infrared light is the electrode closest to the semiconductor substrate in the stacked electrode group ME.

In this embodiment, the electrode transparent to infrared rays is made of a polysilicon thin film.

In other embodiments, the infrared transparent electrode is made of an alloy material mainly comprising ITO (indium tin oxide).

The transparent electrode may be used to apply a gate control voltage to control the performance of a charge well, or may be used as a patch to connect electrodes, the function of the transparent electrode is not limited herein.

The working principle of the TOF sensor with a highly transparent electrode structure of the present application is explained below.

Since the outer lens group can converge the light, the light necessarily makes an angle with the microlens array ML when it reaches the microlens array ML on the TOF sensor except when the light is normally incident on the outer lens. When light rays are obliquely incident on the surface of the micro lens array ML at the angle, the micro lens array ML has the capability of converging and correcting the light rays, but is limited by the volume, the material and the manufacturing process of the micro lens array ML, the converging capability of the micro lens array ML to the light rays is limited, so the correction capability of the obliquely incident light rays is limited, most of the light rays can be incident on the photosensitive surface of the TOF sensor, the depth information measurement and calculation of the TOF sensor are completed through the conversion from optical signals to electric signals, but a part of the light rays can be obliquely incident on the side surface of the multi-layer overlapping electrode group ME structure, especially when the pixels are positioned at the edge of the whole pixel array, the angle of the obliquely incident light rays to the micro lens array ML is larger, and more light rays cannot be incident on the detection photosensitive surface of. In addition, due to the randomness of the light, multiple catadioptric scattering before reaching the ME structure of the stacked electrode set, and the like, part of the light is inevitably incident on the side surface of the ME structure of the stacked electrode set.

If the structure of the overlapping electrode group ME is a conventional open overlapping electrode group ME structure, part of light will propagate transversely along the opening of the multi-layer overlapping electrode group ME, the detection light used by the TOF sensor is generally active near-infrared wavelength, multiple reflections of a single wavelength between the layers of the multi-layer overlapping electrode group ME may cause significant interference effects, which may seriously affect the normal operation of the sensor, and the light will be transmitted to the adjacent pixels along the structure of the open overlapping electrode group ME, and thus captured by the photosensitive surface. Since the TOF sensor obtains depth information of the object to be measured by measuring a phase difference or a time difference between the emitted light and the received light, the TOF sensor may obtain incorrect depth information.

However, when the structure of the overlapping electrode group ME of the present application is adopted, when light propagates to the side face of the structure of the overlapping electrode group ME, the light cannot enter between the multiple layers of the overlapping electrode groups ME due to the blocking of the electrodes, the reflected light can be captured by the corresponding photosensitive surface through a small number of reflections, even if the light enters between the structures of the overlapping electrode groups ME due to various effects, because the adjacent pixels also adopt a closed structure, the light cannot enter into the adjacent pixels, and thus the normal measurement of the TOF sensor is ensured.

Therefore, when a closed type overlapping electrode group ME structure is adopted, the closed overlapping electrode group ME structure can be reasonably designed on the function of ensuring that the original structure is not changed, the interference effect between the multilayer overlapping electrode group ME structures is reduced as much as possible, the transverse crosstalk caused by multiple reflections of light rays between the multilayer overlapping electrode group ME structures is reduced as much as possible, the accurate depth information detection of the TOF sensor is realized, and the detection performance of the TOF sensor is improved.

The present application also proposes an imaging device comprising a TOF sensor with a highly light-transmissive electrode structure as described above.

The beneficial effect of this application lies in: under the condition of not changing the original structure of TOF sensor, adopt closed electrode structure, through the bent part of electrode, make oblique incidence and because multiple reflection or scattering to the inboard light of electrode can't transversely conduct between the electrode interval, greatly reduced the interference effect of the light of single wavelength between multilayer electrode, eliminated because the transverse cross talk that multilayer electrode structure caused, improved the anti transverse cross talk ability of this sensor greatly, improved the performance of this TOF sensor, make TOF sensor's measurement more accurate.

Those skilled in the art will appreciate that all or part of the steps of the various methods in the above embodiments may be implemented by instructions associated with hardware via a program, which may be stored in a computer-readable storage medium, and the storage medium may include: read-only memory, random access memory, magnetic or optical disk, and the like.

The foregoing is a more detailed description of the present application in connection with specific embodiments thereof, and it is not intended that the present application be limited to the specific embodiments thereof. It will be apparent to those skilled in the art from this disclosure that many more simple derivations or substitutions can be made without departing from the inventive concepts herein.

Claims (9)

1. A TOF sensor having a highly light transmissive electrode structure, comprising:

a semiconductor substrate;

a photodiode array having a photoelectric response to infrared light, formed in the semiconductor substrate;

a superimposed electrode group provided on a light incident side of the photodiode array and including a plurality of layers of electrodes, a plurality of layers of insulating films, and a transparent region through which infrared light is transmitted, aligned with the photodiodes; and

a micro lens array aligned with the transparent region and disposed at a light incident side of the transparent region;

at least one layer of the electrodes in the superposed electrode group extends towards the center of the transparent area and bends towards the substrate to guide light into the photodiode array.

2. The TOF sensor of claim 1, wherein an electrode of the set of superimposed electrodes that is closest to a side of the microlens array extends toward a center of the transparent region and curves toward a substrate.

3. The TOF sensor of claim 1, wherein the angle of bending of the electrode toward the semiconductor substrate is 30 degrees or greater.

4. The TOF sensor of claim 1, wherein the electrodes form a smaller clear aperture in the transparent region than any other electrode in the superimposed electrode layer.

5. The TOF sensor of claim 1, wherein at least one electrode of the superimposed set of electrodes is transparent to infrared light and extends to an area where said transparent region covers more than 90% of the area of said transparent region.

6. The TOF sensor of claim 5, wherein the infrared transparent electrode is formed by an electrode of the stacked set of electrodes that is closest to the semiconductor substrate.

7. The TOF sensor of claim 5, wherein the infrared transparent electrode is made of polysilicon film.

8. The TOF sensor of claim 5, wherein the infrared transparent electrode is made of an alloy material consisting essentially of ITO.

9. An imaging apparatus, characterized in that it comprises a TOF sensor with a highly light-transmissive electrode structure according to any of claims 1 to 8.

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