FR3111015A1 - Optoelectronic device - Google Patents

Abstract

Optoelectronic device The present description relates to an optoelectronic device (10) comprising a stack: - a first stage (14) comprising first photodiodes configured to operate in a first range of wavelengths; and - a second stage (16) comprising second photodiodes configured to operate in a second range of wavelengths, the first stage being located between radiations (12) adapted to be received by the device and the second stage (16 ), the portions of the first stage located between the second stage and the radiation being made of materials transparent at wavelengths of the first range of wavelengths. Figure for the abstract: Fig. 1

Description

Optoelectronic device

The present description generally relates to optoelectronic devices and more particularly to optoelectronic devices comprising photodiodes.

Optoelectronic devices include an optical part and an electronic part. An optoelectronic device is, for example, a device making it possible to generate digital images of a scene, for example a camera or video camera.

In many devices, it is desirable to obtain images in several distinct wavelength ranges, for example in the visible and infrared range.

One embodiment overcomes all or part of the drawbacks of known optoelectronic devices.

One embodiment provides an optoelectronic device comprising a stack:
- a first stage comprising first photodiodes configured to operate in a first range of wavelengths;
- a second stage comprising second photodiodes configured to operate in a second range of wavelengths, the first stage being located between radiation adapted to be received by the device and the second stage,
the portions of the first stage located between the second stage and the radiation being made of materials transparent to the wavelengths of the first range of wavelengths.

Another embodiment provides a method of manufacturing an optoelectronic device comprising:
a) the formation of a first stage of a stack comprising first photodiodes configured to operate in a first range of wavelengths;
b) the formation of a second stage of the stack comprising second photodiodes configured to operate in a second range of wavelengths, the first stage being located between radiation adapted to be received by the device and the second stage,
the portions of the first stage located between the second stage and the radiation being made of materials transparent to the wavelengths of the first range.

According to one embodiment, the device comprises a third stage, in contact with a face of the second stage opposite a face in contact with the first stage.

According to one embodiment, the third stage comprises a circuit for reading the first and second photodiodes.

According to one embodiment, the third stage has a thickness greater than 70 μm.

According to one embodiment, the first range of wavelengths corresponds to the visible range and the second range of wavelengths corresponds to the infrared range.

According to one embodiment, the first photodiodes are formed in a first silicon or indium phosphide substrate.

According to one embodiment, the second photodiodes are formed in a second substrate made of a type III-V alloy.

According to one embodiment, step b) comprises:
b1) attaching a substrate to the first stage; And
b2) the formation of the second photodiodes in said substrate.

According to one embodiment, step b) comprises the formation of transistors in and on the substrate.

According to one embodiment, the method comprises, after steps a) and b), the formation of the third stage.

According to one embodiment, the third stage is fixed to the second stage by hybrid bonding.

These characteristics and advantages, as well as others, will be set out in detail in the following description of particular embodiments given on a non-limiting basis in relation to the attached figures, among which:

FIG. 1 represents an embodiment of an optoelectronic device;

FIG. 2 represents two embodiments of an optoelectronic device;

FIG. 3 represents a manufacturing step of a variant of the embodiment of FIG. 1;

FIG. 4 represents another manufacturing step of a variant of the embodiment of FIG. 1;

FIG. 5 represents another manufacturing step of a variant of the embodiment of FIG. 1;

FIG. 6 represents another manufacturing step of a variant of the embodiment of FIG. 1;

FIG. 7 represents another manufacturing step of a variant of the embodiment of FIG. 1;

FIG. 8 represents a manufacturing step of another variant of the embodiment of FIG. 1;

FIG. 9 represents another manufacturing step of another variant of the embodiment of FIG. 1;

FIG. 10 represents another manufacturing step of another variant of the embodiment of FIG. 1; And

Figure 11 shows another manufacturing step of another variant of the embodiment of Figure 1.

The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the various embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed.

Unless otherwise specified, when reference is made to two elements connected together, this means directly connected without intermediate elements other than conductors, and when reference is made to two elements connected (in English "coupled") between them, this means that these two elements can be connected or be linked through one or more other elements.

In the following description, when referring to absolute position qualifiers, such as "front", "rear", "up", "down", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to qualifiers of orientation, such as the terms "horizontal", "vertical", etc., it reference is made unless otherwise specified to the orientation of the figures.

Unless specified otherwise, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably within 5%.

FIG. 1 represents an embodiment of an optoelectronic device 10. Device 10 is a device comprising photodiodes forming pixels and is configured to generate images from radiation 12 received by the device.

Device 10 includes first and second stages 14 and 16. Each of stages 14 and 16 includes a plurality of photodiodes. Each of the stages 14 and 16 is configured to generate, by its photodiodes, an image. Stages 14 and 16 of device 10 can therefore generate two distinct and different images from the same radiation source 12.

Stages 14 and 16 are stacked on top of each other. More specifically, the first stage 14 is closest to the radiation source 12. The second stage 16 is located on the first stage 14, i.e. the first stage is located between the second stage and the source of radiation. The first stage therefore receives the radiation 12 on a first face 14a, for example via lenses 20. The lenses 20 are located on the first face 14a of the first stage 14. Preferably, a lens is located opposite each first and second stage photodiode.

Preferably, the photodiodes of the first and second stages are located one above the other. Preferably, no metal track is located between the photodiodes and the radiation 12.

A second face 14b of the first stage 14, opposite the first face 14a, is located on the side of the second stage, preferably in contact with the second stage 16, more precisely in contact with a first face 16a of the second stage. The rays 12 therefore pass through the first stage 14, and possibly the lenses 20, before reaching the second stage 16.

The first stage 14, and more particularly the photodiodes of the first stage, is preferably configured to absorb a range of wavelengths corresponding to the visible, that is to say for example the range of wavelengths ranging from 400 nm to 800 nm. The image generated by the first stage 14 is therefore an image representing the visible.

The second stage 16, and more particularly the photodiodes of the second stage, is preferably configured to absorb a range of wavelengths corresponding to the infrared, that is to say for example the range of wavelengths from from 900 nm to 1700 nm. The image generated by the second stage 16 is therefore an image representing infrared.

The second stage photodiodes 16 are configured to absorb radiation having wavelengths in the infrared range. The photodiodes of the second stage are therefore formed in a material, preferably in a substrate in a semiconductor material, absorbing wavelengths in the infrared range. This material is for example an alloy of type III-V, that is to say an alloy comprising at least one element from group III and at least one element from group V. Group III comprises the following elements: Boron (B ), Aluminum (Al), Gallium (Ga), Indium (In) and Thallium (Tl). Group V includes the following elements: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi). The material of the photodiodes of the second stage is therefore for example: InGaAs, GaSb or InGaSb.

Each of the photodiodes of the second stage therefore preferably has an active zone, that is to say the zone in which the radiation is transformed into electrical charges, in an alloy of the III-V type.

The first stage photodiodes 14 are configured to absorb radiation having wavelengths in the visible range. The photodiodes of the first stage are therefore formed in a material, preferably in a substrate in a semiconductor material, absorbing wavelengths in the visible range. Each of the photodiodes of the first stage therefore preferably has an active zone, that is to say the zone in which the radiation is transformed into electrical charges, in this material.

In addition, the materials of the first stage located between the radiation 12 and the photodiodes of the second stage are transparent to the operating wavelengths of the photodiodes of the second stage, for example the wavelengths corresponding to the infrared, for example the range from 900 nm to 1700 nm. It is for example silicon (Si). It can also be indium phosphide (InP). Thus, radiation having wavelengths in the operating range of the photodiodes of the second stage passes through the first stage so as to reach the second stage.

Preferably, the first and second stage photodiodes are located on top of each other. Thus, the materials of the first stage photodiodes are transparent to these wavelengths, for example silicon (Si) or indium phosphide (InP).

Preferably, the first stage substrate is silicon and the first stage photodiodes are silicon and doped silicon. Indeed, silicon is particularly suitable for the formation of photodiodes operating in the visible range and is transparent to infrared wavelengths. Furthermore, the dark current generated by silicon for radiation in the visible range is low compared to other materials.

It would have been possible to form, instead of the first and second stages, a single stage comprising photodiodes made of a material absorbing the two ranges of wavelengths. For example, the InGaAs alloy is suitable for absorbing both wavelength ranges. However, this material does not have the same performance and in particular does not provide as good a yield for visible wavelengths as silicon photodiodes. In particular, in the absence of radiation, the InGaAs alloy has a stronger dark current than silicon, which degrades the quality of the image at low level of illumination.

In the embodiment described, radiation having wavelengths in the visible range is absorbed in the first stage so as to form a visible image. Radiation having wavelengths in the visible range therefore does not pass through the first stage and does not reach the second stage. Radiation with wavelengths in the visible range therefore does not cause a parasitic visible signal in the material of the second stage, i.e. does not cause an increase in noise on the infrared signal.

Radiation having wavelengths in the infrared range passes through the first stage without being absorbed and reaches the second stage. Radiation having wavelengths in the infrared range is absorbed in the photodiodes of the second stage so as to form an infrared image.

The two images are formed, for example, simultaneously, i.e. in parallel.

The device preferably comprises a third stage 18. The third stage is located on the side of the second stage opposite the first stage. A second face 16b of the second floor opposite the first face 16a, is in contact with a first face 18a of the third floor.

Thus, the stack of the device 10 comprises, in this order from the side receiving the radiation 12, the first stage 14, the second stage 16 and the third stage 18. The third stage comprises for example a circuit for reading the photodiodes. The read circuit is for example configured to process the signals generated by the photodiodes of the first and second stages, preferably in parallel. The two stages are connected to the third stage so as to be able to supply these signals to the read circuit.

According to one embodiment, the first and second stages do not include any components other than the photodiodes and connection elements. Components, for example transistors, are located in the third stage.

As a variant, each of the three stages can comprise other components, for example transistors, capacitors etc. These components are then arranged so as not to be located between the rays and the photodiodes.

The first stage preferably has a thickness comprised between 5 μm and 10 μm. The second stage preferably has a thickness of between 0.5 μm and 5 μm. The third stage preferably has a thickness greater than 70 μm, preferably between 70 μm and 200 μm. The third stage thus makes it possible to ensure mechanical reinforcement of the device and to ensure the strength of the stack of the first, second and third stages.

FIG. 2 represents two embodiments of an optoelectronic device. More precisely, FIG. 2 comprises views A and B, each representing a more precise example of implementation of the embodiment of FIG. 1. In particular, views A and B represent examples of assembly of the various stages. Thus, the devices of views A and B each include the elements of the embodiment of Figure 1.

The device 10a of view A thus comprises the first, second and third stages 14, 16 and 18 described previously, as well as the lenses 20.

Similarly, device 10b of view B includes the first, second and third stages 14, 16 and 18 previously described, as well as lenses 20.

In the case of the variant of view A, the second stage is formed directly on the first stage. Thus, the substrate of the second stage is formed, or fixed, on the first stage, more precisely on the second face of the first stage. The substrate of the second stage has for example undergone only doping steps, for example part of the doping steps making it possible to form the photodiodes of the second stage. Preferably, no components have been formed in the second stage substrate before the second stage is attached to the first stage. Thus, if the second stage includes components other than the photodiodes, these components are formed in the second stage substrate when the second stage substrate is stacked on the first stage.

In the variant of view A, the third stage is formed independently of the first and second stages. That is, at least some of the components of the third stage, preferably all of the components, are formed before the third stage is attached to the second stage. The third stage is for example fixed to the second stage, more precisely to the second face of the second stage, by fixing, or bonding, hybrid, that is to say by molecular bonding. In other words, the second floor comprises, on the side of its second face, that is to say the face in contact with the third floor, metallic elements 24 flush with the level of the second face. Metallic elements 22 are, moreover, located at the level of the first face of the third floor, that is to say the face in contact with the second floor, and are flush with said first face. The metallic elements 22 and 24 of the second and third stages have dimensions and locations such that each metallic element 24 of the second stage is in contact with a metallic element 22 of the third stage.

In the example of view B, the second and third stages are fixed by hybrid bonding as described in relation to view A. In addition, the first and second stages are also connected by hybrid bonding. Thus, the first floor comprises metallic elements 28 flush with the side of its second face, that is to say the face in contact with the second floor and the second floor comprises metallic elements 26 flush with its first face, that is i.e. the face in contact with the first floor. These metallic elements 26 and 28 are, like the metallic elements 22 and 24 of view A, located in such a way that each metallic element 26 or 28 of one of the two stages is in contact with a metallic element 28 or 26 of the other floor.

Alternatively, the third stage can be formed on the stack comprising the first and second stages in the same way that the second stage is fixed on the first stage in the case of view A. In other words, the substrate of the third stage, having for example been spot-doped, is fixed on the second stage and the components of the third stage are subsequently formed.

Figures 3 to 7 illustrate successive manufacturing steps of a variant of the embodiment of Figure 1. The variant of the embodiment of Figure 1 corresponding to the method of Figures 3 to 7 is the variant in which the first stage 14 comprises, in addition to the photodiodes, transistors, and in which the second stage comprises photodiodes but no transistor.

FIG. 3 represents a manufacturing step of a variant of the embodiment of FIG. 1. More specifically, FIG. 3 comprises views A and B each representing the result of a manufacturing step of a variant of the embodiment of embodiment of Figure 1. The steps of views A and B can be performed simultaneously or successively.

View A represents the result of the step of forming the first stage 14. This step comprises:
- the formation, in a substrate 30, of photodiodes 32;
- the formation of transistors 34 in and on the substrate 30;
- the formation of other components not shown;
- The formation of insulating trenches 36, for example between transistors 34;
- the formation of metal tracks and conductive vias 40 making it possible to connect the components and the photodiodes to one another and/or with elements external to the first stage; And
- The formation of an insulating layer 42 on the substrate 30, the transistors, the photodiodes, the metal tracks and the conductive vias.

The metal tracks and the conductive vias are arranged so as not to be located facing the photodiodes.

The first face 14a of the first stage is the lower face in FIG. 3, that is to say the face of the substrate 30 not covered by the layer 42. The second face 14b of the first stage is the upper face in FIG. 3, c ie the face of the layer 42 not in contact with the substrate.

As described above, the substrate 30 is made of a material making it possible to ensure that the photodiodes 32 absorb radiation having wavelengths in the visible range and making it possible to ensure that the radiation having wavelengths in the infrared pass through the substrate. Thus, the photodiodes 32 and the substrate 30 are preferably made of silicon.

The various elements, here the photodiodes and the layer 42, which will be located facing the second stage photodiodes are made of materials transparent to the wavelengths of the range absorbed by the second stage photodiodes. Thus, in the case of FIG. 3, the insulating layer 42 is made of a material transparent to wavelengths in the infrared range.

View B shows a step in the formation of the substrate 44 of the second stage 16. The substrate 44 is made of a material allowing the formation of photodiodes of the second stage absorbing radiation in the infrared range. The substrate is preferably made of a type III-V alloy, preferably of InGaAs.

Substrate 44 comprises a first face corresponding to face 16a of FIG. 1, and a second face 45. The stage of view B comprises the formation of doped layers 46 and 48.

Layer 46 is located at face 16a. Thus, face 16a is a face of layer 46. Layer 48 is a buried doped layer. Layer 48 is thus located in substrate 44, for example separated from layer 46 by a layer 50, preferably undoped, of the material of the substrate. Layers 46 and 48 are doped so as to be able to form photodiodes. Thus, layer 46 is preferably P-type doped and layer 48 is preferably N-type doped.

The substrate 44 preferably has a thickness comprised between 100 μm and 150 μm.

Figure 4 shows another manufacturing step of a variant of the embodiment of Figure 1.

During this step, the substrate 44 of view B of FIG. 3 is fixed, preferably by molecular bonding, to the first stage, represented in view A of FIG. 3. The substrate 44 is arranged in such a way that the face 16a is in contact with the face 14b of the first floor.

Figure 5 shows another manufacturing step of a variant of the embodiment of Figure 1.

During this step, the substrate 44 is thinned by the face 45, that is to say the face not being in contact with the first stage. The substrate is preferably thinned down to layer 48.

Thus, the structure resulting from this step comprises a stack of semiconductor layers 52 fixed on the face 14b of the first stage. The stack 52 comprises, starting from the face 14b, the layer 46, the layer 50, and the layer 48.

The stack 52 is located at least at the places where it is desired to form second-stage photodiodes. The stack 52 preferably covers the entire first floor, that is to say the entire face 14b.

Figure 6 shows another manufacturing step of a variant of the embodiment of Figure 1.

During this step, the layers 48 and 50 of the structure of FIG. 5 are partially etched so as to retain only the portions of layers 48 and 50 located at the places where the photodiodes of the second stage will be located, preferably opposite photodiodes 32 of the first stage.

Figure 7 shows another manufacturing step of a variant of the embodiment of Figure 1.

During this step, layer 46 is etched so as to retain portions 46a of layer 46 located under portions of layers 48 and 50 and portions 46b, extending from portions 46a and not being located between the layer portions 50 and the first floor.

During this step, an insulating layer 56 is formed on the face 14b of the first stage and on the portions of layers 46, 48 and 50. In addition, conductive vias 58 are formed through the layer 56 so as to reach the layers 46 and 48. Optionally, other conductive vias can be formed, for example vias passing through layers 56 and 42 so as to reach the metal tracks of the first stage.

Figures 8 to 11 show steps, preferably successive, of manufacturing another variant of the embodiment of Figure 1.

FIG. 8 represents a manufacturing step of another variant of the embodiment of FIG. 1. More precisely, FIG. 8 comprises views A and B each representing the result of a manufacturing step of a variant of the embodiment. embodiment of Figure 1. The steps of views A and B can be performed simultaneously or successively.

View A of Figure 8 is identical to view A of Figure 3. First stage 14 is preferably formed in the same manner as first stage 14 of view A of Figure 3.

View B shows a step for forming the substrate 60 of the second stage 16. The substrate 60 is made of a material allowing the formation of photodiodes of the second stage absorbing radiation in the infrared range. Substrate 60 is preferably made of a type III-V alloy, preferably InGaAs. The substrate 60 includes a face 62 and a face 63, opposite the face 62.

The step of view B includes the formation of a layer 64 on the substrate 60. The layer 64 includes a face in contact with the face 63 of the substrate 60. Another face of the layer 64, opposite to the face in contact with the substrate 60, corresponds to the face 16a.

Layer 64 is made of a material which makes it possible to form a layer of second-stage photodiodes. Layer 64 is for example made of indium phosphide.

Figure 9 shows another manufacturing step of another variant of the embodiment of Figure 1.

During this step, the substrate 60 of view B of FIG. 8 is fixed, preferably by molecular bonding, to the first stage, represented in view A of FIG. 8. The substrate 60 is arranged in such a way that the face 16a is in contact with the face 14b of the first stage.

During this step, the substrate 60 is thinned by the face 62, that is to say the face not being in contact with the first stage. The substrate 60 is preferably thinned down to a thickness corresponding substantially to the desired thickness of the photodiodes.

Figure 10 shows another manufacturing step of another variant of the embodiment of Figure 1.

During this step, the substrate 60 of the structure of FIG. 9 is partially etched so as to keep only the portions of the substrate 60 located at the places where the photodiodes of the second stage will be located, preferably facing the photodiodes 32 of the first stage, and where the second stage transistors will be located.

During this step, layer 64 is etched so as to retain:
- Portions 64a of layer 64 located under the portions of substrate 60 at the locations of the transistors;
- Portions 64b of layer 64 located under the portions of substrate 60 at the locations of the photodiodes; And
- Portions 64c of layer 64 extending from portions 64b and not being located between the portions of substrate 60 and the first stage.

During this step, gates 68 of the transistors are formed on the portions of the substrate 60 located at the locations of the transistors.

Figure 11 shows another manufacturing step of another variant of the embodiment of Figure 1.

During this step, the portions of substrate 60 located at the locations of the photodiodes are doped so as to form a layer 70, separated from layer 64 by a layer 72 of substrate 60. The photodiodes of the second stage therefore comprise a stack, in this order from face 14b, layers 64, 72 and 70.

During this step, portions of the substrate 60 located at the locations of the transistors are doped so as to form the source and drain areas 74 of the transistors.

During this step, an insulating layer 76 is formed on face 14b of the first stage, on the photodiodes and on the transistors. Additionally, conductive vias 78 are formed through layer 76 to reach layers 64 and 70, drain and source areas 74, and gates 68 of the transistors. Optionally, other conductive vias, not shown, can be formed, for example vias passing through the layers 76 and 42 so as to reach the metal tracks of the first stage.

The steps of views A of FIGS. 3 and 8 can be replaced by other steps for forming the first stage. For example, the steps of views A of FIGS. 3 and 8 can be replaced by steps of forming a first stage not comprising a transistor, comprising for example only photodiodes and connection elements.

Various embodiments and variants have been described. The person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to the person skilled in the art.

Finally, the practical implementation of the embodiments and variants described is within the abilities of those skilled in the art based on the functional indications given above.

Claims (13)

Optoelectronic device (10) comprising a stack:
- a first stage (14) comprising first photodiodes configured to operate in a first range of wavelengths; And
- a second stage (16) comprising second photodiodes configured to operate in a second range of wavelengths, the first stage being located between radiation (12) adapted to be received by the device and the second stage (16 ),
the portions of the first stage located between the second stage and the radiation being made of materials transparent to the wavelengths of the first range of wavelengths. Device according to Claim 1, in which the device comprises a third stage (18), in contact with a face of the second stage (16) opposite a face in contact with the first stage (14). Device according to Claim 2, in which the third stage (18) comprises a circuit for reading the first and second photodiodes. Device according to Claim 2 or 3, in which the third stage (18) has a thickness greater than 70 µm. Device according to any one of Claims 1 to 4, in which the first range of wavelengths corresponds to the visible range and the second range of wavelengths corresponds to the infrared range. A device according to any of claims 1 to 5, wherein the first photodiodes are formed in a first silicon or indium phosphide substrate. Device according to any one of claims 1 to 6, in which the second photodiodes are formed in a second substrate of a type III-V alloy. Method of manufacturing an optoelectronic device comprising:
a) forming a first stage (14) of a stack comprising first photodiodes configured to operate in a first wavelength range; And
b) the formation of a second stage (16) of the stack comprising second photodiodes configured to operate in a second range of wavelengths, the first stage being located between radiation adapted to be received by the device and the second floor,
the portions of the first stage located between the second stage and the radiation being made of materials transparent to the wavelengths of the first range. Process according to Claim 8 applied to the manufacture of a device according to any one of Claims 1 to 7. A method as claimed in claim 8 or 9, wherein step b) comprises:
b1) attaching a substrate to the first stage; And
b2) the formation of the second photodiodes in said substrate. A method according to claim 10, wherein step b) comprises forming transistors in and on the substrate. Process according to Claim 9 or 10 when appended to Claim 3, comprising, after steps a) and b), the formation of the third stage. A method according to claim 12, wherein the third tier is bonded to the second tier by hybrid bonding.