Patent Description:
In order to increase the light path in the silicon of a photodetector of a pixel, for example of the SPAD type ("Single Photon Avalanche Diode"), it is known to add structuration on a face of the pixel which is intended to receive light. The document <CIT> is a relevant prior art.

<FIG> shows an example of a face <NUM> of a silicon photodetector of a pixel Pix1, the face <NUM> being intended to receive light and being provided with such structurations. More particularly, <FIG> is a top view of this structured face <NUM>. The <FIG> is a simplified reproduction of <FIG> of the <CIT> and the <CIT>.

The face <NUM> has two opposite sides <NUM> and <NUM> parallel to each other and to a direction Y, and two opposite sides <NUM> and <NUM> parallel to each other and to a direction X. The direction X is perpendicular to the direction Y. The face <NUM> has a square shape in a top view of the pixel Pix1.

The face <NUM> is one face of a silicon portion forming a photodetector of the pixel Pix1. The photodetector of pixel Pix1 is, for example, laterally delimited by insulation structure <NUM>. The structure <NUM> are, for example, capacitive deep trench insulation (CDTI).

The pixel Pix1 comprises a plurality of trenches <NUM> extending in length in the direction X, and a plurality of trenches <NUM> extending in length in the direction Y. In <FIG>, only few of the trenches <NUM> and <NUM> are referenced to not overload the Figure. In <FIG>, the trenches <NUM> and <NUM> are hatched.

A first part of trenches <NUM> extends from the side <NUM> toward the side <NUM>, and a second part of trenches <NUM> extends from the side <NUM> toward the side <NUM>. Similarly, a first part of trenches <NUM> extends from the side <NUM> toward the side <NUM>, and a second part of trenches <NUM> extends from the side <NUM> toward the side <NUM>. The trenches <NUM> of the first part of trenches <NUM> do not join the trenches <NUM> of the second part of trenches <NUM>. Similarly, the trenches <NUM> of the first part of trenches <NUM> do not join the trenches <NUM> of the second part of trenches <NUM>. Further, the trenches <NUM> do not cross the trenches <NUM>.

The above-mentioned French patent and US patent application disclose other examples of a face of a silicon photodetector of a pixel provided with first and second trenches, where the first trenches are perpendicular to the second trenches and the first trenches do not cross the second trenches.

These first and second trenches allow to increase the light path in the silicon of the photodetector, thus increasing the quantum efficiency of the pixel. For example, increasing the light path is particularly important when the light received and sensed by the pixel is infra-red light having wavelengths, for example, comprised between <NUM> and <NUM>, for example a wavelength equal to approximately <NUM>, preferably equal to <NUM>.

Other examples of pixel having a photodetector in silicon where a face of the silicon portion corresponding to the photodetector is provided with first trenches and second trenches perpendicular to the first trenches are known.

There is a need to increase the light path in the silicon of a photodetector of pixel with respect to the known pixels provided with first and second trenches has described above.

One embodiment addresses all or some of the drawbacks of known pixels provided with first and second trenches has described above.

One embodiment provides a pixel comprising:.

According to one embodiment, the first face has two first sides parallel to the first direction and two second sides parallel to the second direction.

According to one embodiment, the first face comprises:.

According to one embodiment, the first and second trenches are devoid of notch outside the central region.

According to one embodiment, at least one V-shaped pattern made of one first trench and one second trench is arranged in each corner of the first face, outside the central region.

According to one embodiment, in each corner of the first face, said at least one V-shaped pattern arranged in said corner is symmetrical with respect to a diagonal of the first face extending from said corner, and has its apex turned toward the center of the first face.

According to one embodiment, for each corner of the first face:.

According to one embodiment, in the central region, the first trenches are aligned on first lines of a grid pattern and the second trenches are aligned on second lines of a grid pattern, the first notches being aligned on the second lines of the grid pattern and the second notches being aligned with the first lines.

According to one embodiment, in the first direction, the central region has a length comprised between <NUM> and <NUM>% of the length of each first side, and, in the second direction, the central region has a length comprised between <NUM> and <NUM>% of the length of each first side.

According to one embodiment, in the central region, the first and second trenches together with the first and second notches form a pattern similar to a grid pattern.

According to one embodiment, the first and second trenches together with the first and second notches form a pattern having a <NUM>° rotational symmetry with respect to the center of the first face.

According to one embodiment, the first trenches are disposed with a first pitch in the second direction and the second trenches are disposed with a second pitch in the first direction, the first and second pitches being equal to each other and, for example, comprised between <NUM> and <NUM>, preferably equal to approximately <NUM>.

According to one embodiment, the length of the first notches in the second direction and the length of the second notches in the first direction are comprised between <NUM> and <NUM>% of the first and second pitches.

According to one embodiment, a width of the first trenches is equal to a width of the second trenches, the width of the first and second trenches being comprised between <NUM> and <NUM>, for example equal to approximatively <NUM>.

One embodiment provides a method of fabricating the pixel described above, the method comprising :.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the implementation of the described pixels in a light sensor, for example a time of flight sensor, comprising at least one of the described pixels, for example a matrix of pixels identical to one of the described pixels, has not been described, the implementation of such a sensor being in the abilities of those skilled in the art.

Unless specified otherwise, the expressions "around", "approximately", "substantially" and "in the order of" signify within <NUM>%, and preferably within <NUM>%.

In the following disclosure, a pixel configured to operate with one or several wavelengths in the near infrared, that is to say in the range from <NUM> to <NUM>, for example a pixel configured to operate with a wavelength equal to substantially <NUM>, is considered as an example. The photodiode of the pixel is further considered to be made of silicon, which has a poor light absorption for these wavelengths. It is further considered, as an example, that the pixel is configured so that its photodiode operates in a single photon avalanche mode, or, say in other words, that the pixel comprises a single photon avalanche diode or SPAD.

The inventors here propose to increase the quantum efficiency of a photodiode of a pixel by providing a structure for dispersing, out of the normal incident angle, the light which reaches the photodiode. As a result, the light pathlength in the photodiode is increased, which lead to an increase of the quantum efficiency.

<FIG> is a schematic top view of an ideal embodiment of a face <NUM> of a silicon photodetector of a pixel Pix2.

The face <NUM> is intended to receive light and is provided with structurations made by trenches <NUM> and trenches <NUM>.

The face <NUM> has two opposite sides <NUM> and <NUM> parallel to each other and to a direction Y, and two opposite sides <NUM> and <NUM> parallel to each other and to a direction X. The direction X is perpendicular to the direction Y. The face <NUM> has, preferably, a square shape.

The face <NUM> is one face of a silicon portion forming a photodetector of the pixel Pix2. The photodetector of pixel Pix2 is, for example, laterally delimited by insulation structure <NUM>. The structure <NUM> are, for example, capacitive deep trench insulation (CDTI). In an alternative example, the structure <NUM> are deep trench insulation (DTI).

The trenches <NUM> extend in length in the direction Y, and the trenches <NUM> extend in length in the direction X. In <FIG>, only few of the trenches <NUM> and <NUM> are referenced to not overload the Figure. In <FIG>, the trenches <NUM> and <NUM> are hatched.

The trenches <NUM> are regularly spaced in the X direction. Said otherwise, the trenches <NUM> are arranged with a pitch P1. Similarly, the trenches <NUM> are regularly spaced in the Y direction. Said otherwise, the trenches <NUM> are arranged with a pitch P2. The pitch P1 is equal to the pitch P2.

For example, for a received light in the infra-red, the pitches P1 and P2 are comprised between <NUM> and <NUM>, for example equal to approximately <NUM>, preferably equal to <NUM>.

For example, the width of the trenches <NUM> (measured in the direction X) is equal to the width of the trenches <NUM> (measured in the direction Y). For example, for a received light in the infra-red, the width of the trenches <NUM> and <NUM> is comprised between <NUM> and <NUM>, for example equal to approximately to <NUM>.

Although this is not visible in the view of the <FIG>, the trenches <NUM> and <NUM> penetrate into the silicon of the photodetector from the face <NUM>. For example, for a received light in the infra-red, the trenches <NUM> and <NUM> penetrate into the silicon on a depth comprised between <NUM> and <NUM>, for example a depth equal to approximatively <NUM>.

The face <NUM> comprises a central region <NUM>, delimited in dotted lines in <FIG>. The region <NUM> for example has a length, measured in the direction X, which is comprised between <NUM> and <NUM>% of the length of the sides <NUM> and <NUM>, a length, measured in the direction Y, which is comprised between <NUM> and <NUM>% of the length of the sides <NUM> and <NUM>. Preferably, the central region <NUM> are a square shape.

In the ideal embodiment of <FIG>, the trenches <NUM> cross the trenches <NUM> in the central region <NUM>, in order to form a grid pattern in the whole central region <NUM>. Said otherwise, in the central region <NUM>, the trenches <NUM> are aligned on first lines of a grid pattern and the trenches <NUM> are aligned on second lines of a grid pattern, the first lines being orthogonal to the second lines and being parallel to the direction Y.

In the ideal embodiment of <FIG>, the pixel Pix2 comprises a region which extends from the side <NUM> toward, preferably until, the central region <NUM> and which comprises only trenches <NUM>, or said otherwise, which is devoid of trenches <NUM>. The pixel Pix2 further comprises a region which extends from the side <NUM> toward, preferably until, the central region <NUM> and which comprises only trenches <NUM>, or said otherwise, which is devoid of trenches <NUM>. The pixel Pix2 comprises a region which extends from the side <NUM> toward, preferably until, the central region <NUM> and which comprises only trenches <NUM>, or said otherwise, which is devoid of trenches <NUM>. The pixel Pix2 further comprises a region which extends from the side <NUM> toward, preferably until, the central region <NUM> and which comprises only trenches <NUM>, or said otherwise, which is devoid of trenches <NUM>.

In the ideal embodiment of <FIG>, the pixel Pix2 comprises, in each corner of the face <NUM>, a V-shaped pattern made of one trench <NUM> and one trench <NUM>. In each corner, this V-shaped pattern has its apex turned toward the center O of the face <NUM>. Preferably, in each corner of the face <NUM>, the V-shaped pattern arranged in this corner is symmetrical with respect to a diagonal of the face <NUM> which extends from this corner.

It has been found by simulation that the pixel Pix2 of <FIG> has an optimized pattern made of trenches <NUM> and <NUM> for improving the light absorption in the photodetector of the Pix2 with respect to a pixel having a similar photodetector but with trenches <NUM> and <NUM> of the type described in relation with <FIG>.

However, in view of the dimension of the trenches <NUM> and <NUM> and of their pitch P1 and P2, the pixel Pix2 may be not manufacturable with the usual microelectronic fabrication processes. For example, when using a mask made of a photoresist patterned with openings at the location of the trenches <NUM> and <NUM>, the portions of the photoresist left in place between these opening may not adhere sufficiently and be stripped out, which lead to defect in the pattern of the trenches <NUM> and <NUM> compared to the one described in relation with <FIG>. This is, for example, more particularly the case when the dimensions of the trenches <NUM> and <NUM> and their pitches P1 and P2 are chosen, or optimized, for a received light in the infra-red.

Thus, rather than providing trenches <NUM> and <NUM> which form a grid pattern in the central region <NUM> of the pixel Pix2, it is here proposed a pixel Pix3 similar to pixel Pix2 but in which the trenches <NUM> and <NUM> are replaced by similar trenches respectively <NUM> and <NUM> which comprise, in a central region <NUM> of the pixel Pix3, notches <NUM> and <NUM>.

More particularly, the trenches <NUM> are parallel to the direction Y and the trenches <NUM> are parallel to the direction <NUM>. Further, the trenches <NUM> comprise, in the central region <NUM>, notches <NUM> which each extends in the direction X from a corresponding trench <NUM> toward a neighboring trench <NUM> but without reaching this neighboring trench <NUM>, the notch <NUM> being aligned with a trench <NUM>. Similarly, the trenches <NUM> comprise, in the central region <NUM>, notches <NUM> which each extends in the direction Y from a corresponding trench <NUM> toward a neighboring trench <NUM> but without reaching this neighboring trench <NUM>, the notch <NUM> being aligned with a trench <NUM>.

Thus, in the central region <NUM>, the pattern formed by the trenches <NUM> and <NUM> and the notches <NUM> and <NUM> is similar to a grid pattern but is not identical to a grid pattern. This allows to improve the absorption in the photodetector of the pixel Pix3 in a manner similar to the grid pattern of the pixel Pix2, and, in the same time, this allows for the pixel Pix3 to be manufactured using usual steps of the microelectronic fabrication processes.

<FIG> illustrate an embodiment of the pixel Pix3. More particularly, the <FIG> is a schematic top view of an embodiment of a face <NUM> of a silicon photodetector of the pixel Pix3.

The face <NUM> is one face of a silicon portion forming a photodetector of the pixel Pix3. The photodetector of pixel Pix3 is, for example, laterally delimited by insulation structure <NUM>. The structure <NUM> are, for example, capacitive deep trench insulation (CDTI). In an alternative example, the structure <NUM> are deep trench insulation (DTI).

The trenches <NUM>, respectively <NUM>, are similar to the trenches <NUM>, respectively <NUM>, previously described, at the difference that the trenches <NUM> and <NUM> do not form a complete grid pattern in the central region <NUM> of the pixel Pix3. Thus, unless specified otherwise, all that have been indicated for the trenches <NUM> and <NUM> applies to the trenches respectively <NUM> and <NUM>. Furthermore, in the pixel Pix3, the central region <NUM> of the face <NUM> (delimited by dotted lines in <FIG>) is similar to the central region <NUM> of the face <NUM> of the pixel Pix2. Thus, unless indicated otherwise, all that have been described for the region <NUM> applies to the central region <NUM>. In particular, the dimensions of the region <NUM> with respect to the sides <NUM>, <NUM>, <NUM> and <NUM> are identical to the dimensions of the region <NUM> with respect to the sides <NUM>, <NUM>, <NUM> and <NUM> respectively.

As indicated before and shown on <FIG>, in the central region <NUM>, the trenches <NUM> comprise notches <NUM> and the trenches <NUM> comprise notches <NUM>. Only few of the notches <NUM> and <NUM> are referenced in <FIG> in order to not overload the Figure. Thus, in the central region, the trenches <NUM> and the notches <NUM> are aligned on first lines of a grid pattern, the trenches <NUM> and the notches <NUM> are aligned on second lines of the grid pattern, the first lines being parallel to the direction Y and the second lines being aligned with the direction X. Preferably, there is no notch <NUM> which is not aligned with a corresponding trench <NUM>, and there is no notch <NUM> which is not aligned with a corresponding trench <NUM>.

The notches <NUM> and <NUM> penetrate into the silicon of the pixel Pix3 from the face <NUM>. Preferably, the notches <NUM> and <NUM> penetrate the silicon of the photodetector of the pixel Pix3 on the same depth as the trenches <NUM> and <NUM>.

Preferably, the width of the notches <NUM> (measured in the direction X) is equal to the width of the trenches <NUM>, and the width of the notches <NUM> (measured in the direction Y) is equal to the width of the trenches <NUM>.

Preferably, the length of the notches <NUM> (measured in the direction Y) and the length of the notches <NUM> (measured in the direction X) are comprised between <NUM> and <NUM>% of respectively the pitch P2 of the trenches <NUM> and the pitch P1 of the trenches <NUM>, the pitches P1 and P2 being preferably equal to each other.

Preferably, the pixel Pix3 comprises, similarly to pixel Pix2:.

Preferably, as in the pixel Pix2 the grid pattern is located only on the central region <NUM> of the face <NUM>, and as the notches <NUM> and <NUM> help to mimic the pattern shown on <FIG>, the trenches <NUM> and <NUM> are devoid of notches <NUM> and <NUM> in the first, second, third and fourth regions defined above.

As for the pixel Pix2, preferably, the pixel Pix3 comprises, in each corner of the face <NUM>, one or a plurality of V-shaped patterns each made of one trench <NUM> and one trench <NUM>. In each corner, each V-shaped pattern arranged in the corner has its apex turned toward the center O of the face <NUM>. Preferably, in each corner of the face <NUM>, each V-shaped pattern arranged in this corner is symmetrical with respect to a diagonal of the face <NUM> which extends from this corner.

In the example of <FIG>, the pixel Pix3 comprises only one V-shaped pattern in each corner.

Preferably, as in the pixel Pix2 the grid pattern is located only on the central region <NUM> of the face <NUM>, and as the notches <NUM> and <NUM> help to mimic the pattern shown on <FIG>, the trenches <NUM> and <NUM> of the V-shaped pattern disposed in the corners of the face <NUM> which are outside of the central region, and are devoid of notches <NUM> and <NUM>.

Preferably, the trenches <NUM> comprise notches <NUM> only in the central region <NUM> and the trenches <NUM> comprise notches <NUM> only in the central region <NUM>.

Preferably, as it is the case in the embodiment of <FIG>, for each corner of the face <NUM>:.

Preferably, as it is the case in the embodiment of <FIG>, independently from the fact that the trenches <NUM> and <NUM> are arranged in V-shaped patterns, in the central region <NUM>, for each trench <NUM>, the notches <NUM> are arranged along the trench <NUM> with the pitch P2 of the trenches <NUM>, and, for each trench <NUM>, the notches <NUM> are arranged along the trench <NUM> with the pitch P1 of the trenches <NUM>.

Preferably, as it is the case in the embodiment of <FIG>, independently from the fact that the notches <NUM> are arranged with the pitch P2 and the notches <NUM> are arranged with the pitch P1, and independently from the fact that the trenches <NUM> and <NUM> are arranged in V-shaped patterns, for each trench <NUM>, the notches <NUM> of this trench <NUM> are all disposed on a same side of the trench <NUM>, and, for each trench <NUM>, the notches <NUM> of this trench <NUM> are all disposed on the same side of the trench <NUM>.

In the embodiment of <FIG>, preferably, each trench <NUM> and each trench <NUM> belong to one corresponding V-shaped pattern. Said in other words, there is no trench <NUM> or <NUM> which does not belong to a V-shaped pattern. In particular there is no pair of a trench <NUM> and a trench <NUM> in which the trenches <NUM> and <NUM> cross each other and form a X-shaped pattern.

Preferably, as it is the case in the embodiment of <FIG>, independently from the fact that the trenches <NUM> and <NUM> are arranged in V-shaped patterns and of the pitches of the notches <NUM> and <NUM>, the pattern made by the trenches <NUM> and <NUM> has a rotational symmetry by a rotation of <NUM>° with respect to the center O of the face <NUM>. Thank to this rotational symmetry, the pixel Pix3 is insensitive to the polarization of this incident light.

According to an embodiment, the process of fabricating the pixel Pix3 comprises the following successive steps:.

With the above process, it may be impossible to fabricate the pixel Pix2 of <FIG> as most of the portion of the photoresist mask left in place between the first openings between etching the hard mask have small dimensions in the directions X and Y and each form a small square. On the contrary, the above process may be used for fabricating the pixel Pix3 because, the portion of the photoresist mask left in place before the etching of the hard mask have bigger dimensions in the directions X and Y, and, for example, each forms a strip. Thus, this portion of the photoresist mask adhere better to the hard mask.

<FIG> is a schematic top view of another embodiment of the face <NUM> of the silicon photodetector of the pixel Pix3.

Pixels Pix3 of <FIG> have a lot of element in common, and only the differences between these two pixels will be detailed. In particular, unless indicated otherwise, all that have been indicated for the pixel Pix3 of <FIG> applies to the pixel Pix3 of <FIG>.

In particular, compared to the pixel Pix3 of <FIG>, in the pixel Pix3 of <FIG>, the trenches <NUM> and <NUM> are not only arranged in V-shaped patterns, but also in at least one square-shaped pattern, the at least one square-shaped pattern being preferably arranged in the central region <NUM>.

For example, as shown in the example of <FIG>, a first trench <NUM> and a second trench <NUM> spaced from each other by a distance D taken in the X direction each crosses a first trench <NUM> and a second trench <NUM> spaced from each other by the same distance D. Preferably, the distance D is at least twice the pitches P1 and P2.

Preferably, the square-shaped pattern formed by the crossing of these four trenches <NUM> and <NUM> is centered on the center O of the face <NUM>.

Although, in the example of <FIG>, there is only one square-shaped pattern formed by two trenches <NUM> and two trenches <NUM>, in other examples where the pixel Pix3 comprises more than one squared pattern, preferably the side of each square-shaped pattern is longer than the pitches P1 and P2 and/or each of the square-shaped pattern is centered on the center O of the face <NUM>.

Compared with the pixel Pix3 of <FIG>, the pixel Pix3 does not have any rotational symmetry with respect to the center O of the pixel Pix3.

Pixels Pix3 of <FIG> and <FIG> have a lot of element in common, and only the differences between these two pixels will be detailed. In particular, unless indicated otherwise, all that have been indicated for the pixel Pix3 of <FIG> applies to the pixel Pix3 of <FIG>.

In particular, compared to the pixel Pix3 of <FIG>, in the pixel Pix3 of <FIG>, there is more than one square-shaped pattern formed by two trenches <NUM> and two trenches <NUM>. For example, in the <FIG>, there are two square-shaped patterns, each of which being formed by two trenches <NUM> and two trenches <NUM>.

For example, as it is the case in the example of <FIG>, the pixel Pix3 does not comprise, in the central region <NUM>, any V-shaped pattern made of one trench <NUM> and one trench <NUM>. Said in other words, the pixel Pix3 does not comprise, in the example of <FIG>, any V-shaped pattern formed by one trench <NUM> and on trench <NUM> in which the trench <NUM> comprises notches <NUM> and the trench <NUM> comprises notches <NUM>.

For example, as it is the case in the example of <FIG>, the Pix3 comprises, in each corner, outside of the central region <NUM>, more than one V-shaped pattern formed by one trench <NUM> and one trench <NUM>, these patterns being devoid of notches <NUM> and <NUM> as there are arranged outside of the central region. Further, each of these V-shaped patterns has its apex turned toward the center O of the face <NUM>. Further, in each corner of the face <NUM>, the V-shaped patterns arranged in the corner are successively and regularly arranged from this corner toward the center O of the face <NUM>. Further, in each corner of the face <NUM>, each of the V-shaped patterns arranged in the corner is symmetrical with respect to the diagonal of the face <NUM> which extends from this corner.

In the example of the <FIG>, in each corner of the face <NUM>, the pixel Pix3 comprises two successive V-shaped patterns devoid of notches <NUM> and <NUM>.

Further, as it is the case in the example of <FIG>, in the central region <NUM>, at least some of trenches <NUM>, preferably all the trenches <NUM>, each comprises notches <NUM> on both sides (taken along the length of the trench <NUM>) of the trench <NUM>, and, similarly, at least some of trenches <NUM>, preferably all the trenches <NUM>, each comprises notches <NUM> on both sides (taken along the length of the trench <NUM>) of the trench <NUM>. Although not illustrated, in other example, each trench <NUM> comprises, in the central region <NUM>, notches <NUM> on only one side of the trench <NUM>, and/or each trench <NUM> comprises, in the central region <NUM>, notches <NUM> on only one side of the trench <NUM>.

In particular, compared to the pixel Pix3 of <FIG>, in the pixel Pix3 of <FIG>, the central region <NUM> of the pixel Pix3 is smaller.

Further, and independently from the fact the region <NUM> is smaller, there is no V-shaped pattern whose trenches <NUM> and <NUM> comprise notches <NUM> and <NUM> respectively.

Further, and independently from the fact the region <NUM> is smaller and from the fact that there is no no V-shaped pattern whose trenches <NUM> and <NUM> comprise notches <NUM> and <NUM> respectively, in the pixel Pix3 of <FIG>, in the central region <NUM>, the trenches <NUM> comprise notches <NUM> but the trenches <NUM> are devoid of notch <NUM> in the central region. Although not illustrated, the contrary is also possible, meaning that in other examples, in the central region <NUM>, the trenches <NUM> comprise notches <NUM> but the trenches <NUM> are devoid of notch <NUM>.

Simulations have shown that, for a received light in the infra-red and for a photodetector having a portion of epitaxial silicon with a thickness of <NUM>, the pixel Pix3 of <FIG> exhibit an improvement of <NUM>% of the absorption with respect to a similar pixel Pix1, the pixel Pix3 of <FIG> exhibit an improvement of <NUM>% of the absorption with respect to a similar pixel Pix1, the pixel Pix3 of <FIG> exhibit an improvement of <NUM>% of the absorption with respect to a similar pixel Pix1, and the pixel Pix3 of <FIG> exhibit an improvement of <NUM>% of the absorption with respect to a similar pixel Pix1.

Preferably, in the pixel Pix3, as illustrated in all the embodiments previously described in relation with <FIG>, <FIG>, there is no square-shaped pattern formed by the intersection of two tranches <NUM> with two corresponding trenches <NUM> whose sides length is equal to the pitches P1 and P2. Said in other words, there is no square-shaped pattern formed by the intersection of two successive (or neighboring) trenches <NUM> with two successive (or neighboring) trenches <NUM>.

Preferably, in the pixel Pix3, as illustrated in all the embodiments previously described in relation with <FIG>, <FIG>, outside of the central region <NUM>, the trenches <NUM> and <NUM> do not comprise any notch respectively <NUM> and <NUM>.

Although it has not been explicitly indicated previously, in the pixel Pix3 each trench <NUM> which comprises a portion outside the region <NUM> and a portion inside the region <NUM> is devoid of notch <NUM> on its portion outside the region <NUM> and may comprises notches <NUM> on its portion inside the region <NUM>. Similarly, in the pixel Pix3 each trench <NUM> which comprises a portion outside the region <NUM> and a portion inside the region <NUM> is devoid of notch <NUM> on its portion outside the region <NUM> and may comprises notches <NUM> on its portion inside the region <NUM>.

Claim 1:
A pixel (Pix3) comprising:
a silicon portion having a first face (<NUM>) configured to received light, for example infra-red light;
first trenches (<NUM>) parallel to a first direction (Y) and regularly spaced in a second direction (X) perpendicular to the first direction (Y), the first trenches (<NUM>) penetrating into the silicon portion from the first face (<NUM>); and
second trenches (<NUM>) parallel to the second direction (X) and regularly spaced in the first direction (Y), the second trenches (<NUM>) penetrating into the silicon portion from the first face (<NUM>),
wherein:
in a central region (<NUM>) of the first face (<NUM>), the first trenches (<NUM>) comprise first notches (<NUM>) each penetrating into the silicon from the first face, extending from a first trench (<NUM>) comprising said notch (<NUM>) toward a neighboring first trench (<NUM>) without reaching said neighboring first trench (<NUM>), and being aligned with a corresponding second trench (<NUM>), and/or
in the central region (<NUM>), the second trenches (<NUM>) comprise second notches (<NUM>) each penetrating into the silicon form the first face (<NUM>), extending from a second trench (<NUM>) comprising said notch (<NUM>) toward a neighboring second trench (<NUM>) without reaching said neighboring second trench (<NUM>), and being aligned with a corresponding first trench (<NUM>).