photographic sensor

Abstract

Embodiments of the present disclosure relate to a photography sensor. A semiconductor substrate includes a matrix of photosites. Each photosite is bounded by an isolation trench that includes polysilicon. A peripheral region extends directly around the matrix of photosites. The peripheral region includes dummy photosites that are bounded by isolation trenches that include polysilicon. A density of the polysilicon in the peripheral region is between a density of the polysilicon at an edge of the matrix of photosites and a density of the polysilicon around the peripheral region.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims the priority benefit of French Patent Application No. 2104163, filed on April 21, 2021, the contents of which are incorporated herein by reference in their entirety to the maximum extent legally permissible. TECHNICAL FIELD

[0003] Embodiments relate to a photographic sensor, and in particular to a stacked image sensor. BACKGROUND

[0004] A photographic sensor comprises a matrix of photosites. A photosite allows the conversion of an electromagnetic radiation (UV, visible or IR) into an analog electrical signal.

[0005] The photosites are arranged in a matrix in a manner of rows and columns. The photosites of the matrix are usually separated from each other by a capacitive isolation trench, also called a capacitive deep trench isolation (CDTI) trench in the art.

[0006] The photosite matrix is subjected to mechanical stresses during its manufacturing process. In particular, during the manufacturing process of the photosite matrix, the CDTI trenches are filled by depositing a material made of amorphous silicon. This material made of amorphous silicon is transformed into polycrystalline silicon during a high-temperature annealing process. This transformation induces a material shrinkage which translates into a tensile mechanical stress.

[0007] These mechanical stresses can cause the photosite matrix to deform. In particular, the mechanical stresses to which the photosite matrix is subjected can cause it to bend, thereby forming a concave on the surface of the photosite matrix.

[0008] Therefore, the surface of the photosite matrix is curved, and not flat. As a result, performing a method for mechanical-chemical polishing on the concave surface of the photosite matrix leaves residues on the surface of the photosite matrix. These residues can cause the photosites of the photosite matrix to short-circuit.

[0009] Moreover, a particular photographic sensor is arranged on several superimposed layers. A first layer, having a free face, comprises the photosite matrix. A second layer, arranged under the first layer, i.e. opposite the free face of the first layer, comprises the electrical circuit for processing the signals generated by the photosite matrix. The photographic sensor can comprise other layers under the second layer.

[0010] The first layer can be assembled to the second layer by a method of direct bonding (without adhesive), which is a method of thermal annealing after molecular bonding to solidify the oxide-oxide bonding interface.

[0011] In particular, the face of the first layer opposite to its free face is assembled to the second layer. This face of the first layer opposite to its free face can have recesses at the photonic point matrix.

[0012] When the photonic point matrix is recessed, the assembly between the first layer and the second layer can have a lower performance.

[0013] In particular, the assembly between the first layer and the second layer can have bonding voids at the photonic point matrix. These bonding voids can cause the assembly to break during a thinning method after bonding the two layers, or after an electrical interruption between the two layers.

[0014] In particular, these bonding voids are caused by the photonic point matrix curvature at the photonic point matrix edges. The greater the photonic point matrix curvature, the greater the bonding voids.

[0015] It has been noticed that the photonic point matrix curvature is caused by a sudden change in silicon density between the photonic point matrix and the semiconductor substrate surrounding it.

[0016] Therefore, for such a photonic point matrix, the topology of the first layer is not suitable to obtain a satisfactory assembly between the first layer and the second layer.

[0017] Therefore, there is a need to propose a solution allowing to reduce the photonic point matrix curvature. SUMMARY

[0018] According to one aspect, a sensor is proposed, comprising a semiconductor plate comprising a semiconductor substrate, the semiconductor substrate comprising: a photonic point matrix, each photonic point being delimited by an isolation trench; and a peripheral zone extending directly around the photonic point matrix, the peripheral zone having a polysilicon density that is between a polysilicon density at edges of the photonic point matrix and a polysilicon density surrounding the peripheral zone.

[0019] The peripheral zone allows to gradually reduce the polysilicon density from the photonic point matrix.

[0020] Therefore, the mechanical stress is gradually decreased from the photonic point matrix.

[0021] Therefore, the peripheral zone allows to reduce the curvature at the edges of the photonic point matrix.

[0022] Such a semiconductor plate can form a layer of a back-illuminated multi-layer photographic sensor. In particular, the semiconductor plate can thus be bonded to another plate of the semiconductor substrate.

[0023] In an advantageous implementation, the peripheral zone comprises isolation trenches surrounding the photonic point matrix, the isolation trenches of the peripheral zone being separated from the photonic point matrix by a distance greater than the photonic point width.

[0024] Such a peripheral zone allows to gradually reduce the polysilicon density surrounding the photonic point matrix.

[0025] Advantageously, the peripheral zone comprises a set of dummy photosites formed in the substrate and delimited from each other by isolation trenches. Thus, the dummy photosites have a width greater than the width of the photosites in the matrix of photosites.

[0026] Preferentially, the peripheral zone comprises a series of isolation trenches extending around the matrix, the distance between two successive isolation trenches of the series of isolation trenches being greater than the width of the photosites, this distance between the isolation trenches increasing from the trench closest to the matrix of photosites.

[0027] Alternatively, the peripheral zone comprises an isolation trench around the matrix of photosites, the isolation trench of the peripheral zone extending at a depth less than the depth of the isolation trench delimiting the photosites.

[0028] Such a peripheral zone also allows to gradually decrease the polysilicon density around the matrix of photosites.

[0029] Advantageously, the peripheral zone comprises a set of dummy photosites formed in the substrate and delimited from each other by isolation trenches. Thus, the isolation trenches of the peripheral zone extend at a depth less than the depth of the isolation trenches delimiting the photosites of the matrix of photosites.

[0030] Preferentially, the peripheral zone comprises a series of isolation trenches extending around the matrix, the depth of these isolation trenches and the width of these isolation trenches decreasing from the isolation trench closest to the matrix of photosites.

[0031] Advantageously, the isolation trenches of the peripheral zone have a depth comprised between one third and two thirds of the depth of the isolation trenches of the photosites delimiting the matrix of photosites.

[0032] Preferentially, the peripheral zone has a width comprised between 20 pm and 400 pm.

[0033] According to another aspect, a method for manufacturing a sensor is proposed, comprising: obtaining a semiconductor plate comprising a semiconductor substrate; forming a matrix of photosites in the semiconductor substrate, each photosite being delimited by an isolation trench; and forming a peripheral zone in the semiconductor substrate, the peripheral zone having a polysilicon density comprised between the polysilicon density at the edge of the matrix of photosites and the polysilicon density around the peripheral zone.

[0034] In an advantageous embodiment, the forming of the peripheral zone comprises forming an isolation trench around the matrix of photosites, the isolation trench of the peripheral zone being separated from the matrix of photosites by a distance greater than the width of the photosites.

[0035] Preferentially, the forming of the peripheral zone comprises forming a series of isolation trenches extending around the matrix, the distance between two successive isolation trenches of the series of isolation trenches being greater than the width of the photosites, this distance between the isolation trenches increasing from the trench closest to the matrix of photosites.

[0036] Alternatively, forming the peripheral zone comprises forming isolation trenches surrounding the matrix of photosites, the isolation trenches of the peripheral zone extending at a depth less than the depth of the isolation trenches delimiting the photosites.

[0037] Preferably, forming the peripheral zone comprises forming a series of isolation trenches extending around the matrix, the depth of these isolation trenches and the width of these isolation trenches decreasing from the isolation trenches closest to the matrix of photosites.

[0038] Advantageously, the isolation trenches making up the peripheral zone are such that they have a depth comprised between one third and two thirds of the depth of the isolation trenches delimiting the photosites of the matrix of photosites.

[0039] Preferably, the peripheral zone has a width comprised between 20 pm and 400 pm. BRIEF DESCRIPTION OF DRAWINGS

[0040] Other advantages and features of the application will become apparent from review of the detailed description of the embodiments and implementations, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the application.

[0041] Figure 1 A top view of a semiconductor plate of a sensor is shown;

[0042] Figure 2 A cross-sectional view of the semiconductor plate shown in Figure 1 is shown;

[0043] Figure 3 A cross-sectional view of a second embodiment of a semiconductor plate is shown; and

[0044] Figure 4 An embodiment of a method for manufacturing a sensor is shown. DETAILED DESCRIPTION

[0045] Figure 1 A top view of a semiconductor plate PS1 of a sensor CPT according to an embodiment is shown. Figure 2 A cross-sectional view of this semiconductor plate PS1 is shown.

[0046] The semiconductor plate PS1 comprises a semiconductor substrate SUB1 comprising a matrix MPH1 of photosites PH1. The photosites PH1 of the matrix MPH1 are arranged in rows and columns.

[0047] The photosensitive points PH1 of the matrix MPH1 are isolated from each other by isolation trenches PHT1, which are preferably capacitive isolation trenches (also called capacitive deep trench isolation (CDTI) trenches in the art). The profile of the matrix MPH1 thus comprises the isolation trenches PHT1. The isolation trenches PHT1 extend in the semiconductor substrate SUB1 along a depth from the free face FL1 of the semiconductor substrate SUB1. For example, the isolation trenches PHT1 extend over a depth comprised between 3 pm and 10 pm.

[0048] The photosensitive points PH1 have a width L 10 comprised between 0.5 pm and 5 pm. The width of a photosensitive point is defined by the distance between two opposite isolation trenches PHT1 delimiting the photosensitive point PH1.

[0049] The matrix of photosensitive points MPH1 has a given pitch. This pitch is defined by the sum of the width of a photosensitive point PH1 and the width of the isolation trenches PHT1 delimiting this photosensitive point PH1.

[0050] The semiconductor plate PS1 further comprises a peripheral zone ZP1 surrounding the matrix of photosensitive points. The peripheral zone ZP1 is thus formed in the semiconductor substrate SUB1. The extent of the semiconductor substrate SUB1 further surrounds the peripheral zone ZP1.

[0051] In particular, in Figure 1 the peripheral zone ZP1 comprises two annular zones ZA11, ZA12.

[0052] The peripheral zone ZP1 has a width L1 comprised between 20 pm and 400 pm.

[0053] The first annular zone ZA11 comprises two (peripheral) isolation trenches TI11, TI12. The first annular zone can comprise a dummy photosensitive point PHF11 located between the two isolation trenches TI11, TI12 and the isolation trench TI11 and the matrix of photosensitive points. In this text, a “dummy photosensitive point” can for example have the same composition, configuration and general layout as a photosensitive point PH1, except that the dummy photosensitive point does not establish electrical connections. Or, a “dummy photosensitive point” can for example only comprise a portion of the substrate delimited by the (peripheral) isolation trenches.

[0054] The first isolation trench TI11 extends around the matrix of photosensitive points MPH1.

[0055] The second isolation trench TI12 extends around the first isolation trench TI11.

[0056] The first isolation trench TI11 is located at a distance L 11 from the matrix of photosensitive points MPH1, which distance is greater than the width L 10 of a photosensitive point PH1.

[0057] Likewise, the second isolation trench T112 is located at a distance greater than the width of the photosensitive point PHi. This distance is equal to the distance between the first isolation trench T111 and the photosensitive point matrix MPH1. These distances are for example between 1 pm and 10 pm.

[0058] The isolation trenches T111, T112 of the first annular zone are deep isolation trenches. The isolation trenches T111, T112 extend from the free face of the substrate SUB1 at the same depth as the depth of the isolation trench PHT1 delimiting the photosensitive point PHi. The isolation trenches T111, T112 can be CDTI trenches. The isolation trenches T111, T112 are thus formed of a dielectric coating material such as silicon dioxide and filled with silicon. Alternatively, the isolation trenches T111, T112 can be Deep Trench Isolation - DTI. The isolation trenches T111, T112 are thus filled only with a dielectric coating material such as silicon dioxide.

[0059] The isolation trenches T111, T112 of the first annular zone ZA11 have the same width. The width of the isolation trenches T111, T112 of the first annular zone ZA11 is the same as the width of the isolation trench PHT1 of the photosensitive point matrix MPH1.

[0060] Preferably, the first annular zone ZA11 has a pitch that is twice greater than the pitch of the photosensitive point matrix MPH1. The pitch of the first annular zone ZA11 is defined by the sum of the width of the isolation trenches T111, T112 and the distance between two isolation trenches T111, T112.

[0061] The second annular zone ZA12 extends around the first annular zone ZA11. The second annular zone ZA12 comprises an isolation trench T113. This isolation trench T113 extends around the first annular zone ZA11. The second annular zone can comprise a dummy photosensitive point PHF12 formed in the substrate between the isolation trench T113 and the isolation trench T112.

[0062] The isolation trench T113 of the second annular zone ZA12 is located at a distance L 12 from the first annular zone ZA11, this distance being greater than the distance L 11 between two isolation trenches T111, T112 from the first annular zone ZA11. This distance is for example between 2 pm and 20 pm.

[0063] The isolation trench TI13 is a deep isolation trench. The isolation trench TI13 extends from the free face of the substrate at the same depth as the depth of the isolation trench PHT1 that delimits the photosensitive point PH1. The isolation trench TI13 can be a CDTI trench. The isolation trench TI13 is thus formed of a dielectric coating material such as silicon dioxide and filled with silicon. Alternatively, the isolation trench T113 can be a Deep Trench Isolation. The isolation trench TI13 is thus filled only with a dielectric coating material such as silicon dioxide.

[0064] The width of the isolation trench TI13 of the second annular zone ZA12 is the same as the width of the isolation trench PHT1 of the photosensitive point matrix MPH1.

[0065] Preferably, the second annular zone ZA12 has a pitch that is four times greater than the pitch of the photosensitive point matrix MPH1. The pitch of the second annular zone ZA12 is defined by the sum of the width of the isolation trench TI13 and the distance between the isolation trench TI13 and the first annular zone ZA11.

[0066] The pitch of each annular zone ZA11, ZA12 of the peripheral zone ZP1 is thus greater than the pitch of the photosensitive point matrix MPH1 and increases starting from the annular zone ZA11 closest to the photosensitive point matrix MPH1.

[0067] This allows the polysilicon density to be gradually reduced starting from the photosensitive point matrix MPH1. In particular, the greater the pitch, the lower the polysilicon density.

[0068] The first annular zone ZA11 thus has a polysilicon density dl. The second annular zone ZA12 has a polysilicon density d2. The polysilicon density dl of the first annular zone ZA11 is between the polysilicon density do on the edge of the photosensitive point matrix and the polysilicon density d2 of the second annular zone ZA12. The polysilicon density d2 of the second annular zone ZA12 is greater than the polysilicon density d3 in the extent of the semiconductor substrate surrounding the peripheral zone ZP1.

[0069] The mechanical stress thus gradually decreases starting from the photosensitive point matrix MPH1.

[0070] The peripheral zone ZP1 thus allows the curvature at the edge of the photosensitive point matrix to be reduced.

[0071] This semiconductor plate PS1 can form a layer of a multi-layer photographic sensor. The semiconductor plate PS1 can thus be bonded to another plate of the semiconductor substrate.

[0072] Of course, this first embodiment can be subjected to various substitutions and modifications that will be obvious to those skilled in the art.

[0073] Specifically, the second annular region ZA12 may include a plurality of isolation trenches arranged according to the spacing of the second annular region ZA12. Therefore, these isolation trenches extend at the same depth as the isolation trench T113.

[0074] Similarly, the first annular region ZA11 may include two or more isolation trenches arranged according to the spacing of the first annular region ZA11. The first annular region ZA11 may also include a single isolation trench.

[0075] Furthermore, the peripheral region ZP1 may include two or more annular regions surrounding the photosensitive dot matrix. In this case, the annular region includes at least one isolation trench with a width equal to the width of the isolation trench defining the photosensitive dots. The annular regions have a spacing that increases from the beginning of the photosensitive dot matrix.

[0076] Figure 3 A cross-sectional view of a second embodiment of the semiconductor board PS2 is shown.

[0077] The semiconductor board PS2 includes a semiconductor substrate SUB2, which includes a photosensitive dot matrix MPH2. The photosensitive dots PH2 of the matrix MPH2 are arranged in rows and columns.

[0078] and Figure 1 Similarly, the photosensitive points PH2 of the matrix MPH2 are isolated from each other by isolation trenches PHT2, preferably capacitive isolation trenches (also known as capacitive deep trench isolation (CDTI) trenches). Therefore, the outline of the matrix MPH2 includes the isolation trenches PHT2. The isolation trenches PHT2 extend along the depth in the semiconductor substrate SUB2 from the free surface FL2 of the substrate SUB2. For example, the isolation trenches PHT2 have a depth PF between 3 μm and 10 μm. 20 Extending upwards. Furthermore, the width of the isolation trench PHT2 is, for example, between 0.2 μm and 0.6 μm.

[0079] and Figure 1 Similarly, the photosensitive spot PH2 has a width L 20 It is between 0.5μm and 5μm. The width of the photosensitive spot PH2 is defined by the distance between the two opposing isolation grooves PHT2 that define the photosensitive spot PH2.

[0080] The semiconductor substrate PS2 also includes a peripheral region ZP2 surrounding the photosensitive dot matrix MPH2. Therefore, the peripheral region ZP2 is formed in the semiconductor substrate SUB2.

[0081] Specifically, the outer perimeter ZP2 includes two annular regions ZA21 and ZA22.

[0082] The width L2 of the outer region ZP2 is between 20 μm and 400 μm.

[0083] The first annular zone ZA21 comprises two isolation trenches TI21, TI22. The isolation trenches TI21, TI22 can be CDTI trenches. Thus the isolation trenches TI21, TI22 are formed of a dielectric coating material such as silicon dioxide and filled with silicon. Alternatively, the isolation trenches TI21, TI22 can be Deep Trench Isolation. Thus the isolation trenches TI21, TI22 are filled only with a dielectric coating material such as silicon dioxide.

[0084] The first isolation trench TI21 extends around the matrix of photosensitive points MPH2.

[0085] The second isolation trench TI22 extends around the first isolation trench TI21.

[0086] The distance L between the first isolation trench TI21 and the second isolation trench TI22 is equal to the width L of the photosensitive point PH2. 21 20 Likewise, the distance between the first isolation trench TI21 and the matrix of photosensitive points MPH2 is equal to the width of the photosensitive point PH2.

[0087] The first annular zone ZA21 can comprise a dummy photosensitive point PHF21 formed in the substrate between the (peripheral) isolation trench TI22 and the (peripheral) isolation trench TI21, and between the isolation trench TI21 and the matrix of photosensitive points.

[0088] The isolation trenches TI21, TI22 of the first annular zone ZA21 have a width LT 21 which is less than the width LT of the isolation trench PHT2 delimiting the photosensitive point PH2. 20 For example, the isolation trenches TI21, TI22 of the first annular zone ZA21 have a width L 21 which is between 0.1 pm and 0.3 pm.

[0089] Furthermore, the isolation trenches TI21, TI22 of the first annular zone ZA21 extend shallower than the isolation trench PHT2 delimiting the photosensitive point PH2. For example, the isolation trenches TI21, TI22 of the first annular zone ZA21 extend from the free face FL2 of the substrate SUB2 to a depth PF 21 which is between one half and two thirds of the depth of the isolation trench delimiting the photosensitive point of the matrix of photosensitive points.

[0090] ​The second annular zone ZA22 comprises two isolation trenches TI23, TI24. These isolation trenches TI23, TI24 extend around the first annular zone ZA21. The isolation trenches TI23, TI24 can be CDTI trenches. Thus the isolation trenches TI23, TI24 are formed of a dielectric coating material such as silicon dioxide and filled with silicon. Alternatively, the isolation trenches TI23, TI24 can be Deep Trench Isolation. Thus the isolation trenches TI23, TI24 are filled only with a dielectric coating material such as silicon dioxide.

[0091] The distance L between the two isolation trenches TI23, TI24 of the second annular zone ZA22 22 is equal to the width L of the photosensitive points PH2 of the matrix of photosensitive points MPH2 20 . Likewise, the first isolation trench TI23 of the second annular zone ZA22 is located at a distance from the first annular zone ZA21 which is equal to the width L of the photosensitive points PH2 of the matrix of photosensitive points MPH2 20 .

[0092] The second annular zone ZA22 can comprise a dummy photosensitive point PHF22 formed in the substrate between the isolation trench TI24 and the isolation trench TI23, and between the isolation trench TI23 and the isolation trench TI22.

[0093] The isolation trenches TI23, TI24 of the second annular zone ZA22 have a width LT 22 which is less than the width LT of the isolation trenches TI21, TI22 of the first annular zone ZA21 21 . For example, the isolation trenches TI23, TI24 of the second annular zone ZA22 have a width L 22 which is between 0.05 pm and 0.15 pm.

[0094] Furthermore, the isolation trenches TI23, TI24 of the second annular zone ZA22 extend less deeply than the isolation trenches TI21, TI22 of the first annular zone ZA22. For example, the isolation trenches TI23, TI24 of the second annular zone ZA22 extend from the free face FL2 of the substrate to a depth PF 22 which is between one third and one half of the depth of the isolation trenches delimiting the photosensitive points of the matrix of photosensitive points.

[0095] Therefore, the width and depth of the isolation trenches TI21, TI22, TI23, TI24 of each annular zone ZA21, ZA22 of the peripheral zone ZP2 are smaller than the width of the isolation trench PHT2 of the photosensitive point matrix MPH2. Moreover, the width and depth of the isolation trenches TI21, TI22, TI23, TI24 decrease from the annular zone ZA21 closest to the photosensitive point matrix MPH2.

[0096] This peripheral zone ZP2 also allows a gradual decrease in the polysilicon density from the photosensitive point matrix MPH2. In particular, the smaller the depth of the isolation trenches, the lower the polysilicon density.

[0097] Therefore, the mechanical stress decreases gradually from the photosensitive point matrix MPH2.

[0098] Therefore, the peripheral zone ZP2 allows a decrease in the curvature at the edge of the photosensitive point matrix MPH2.

[0099] This semiconductor plate PS2 can also form a layer of a multi-layer photographic sensor. Therefore, the semiconductor plate can be bonded to another plate of the semiconductor substrate.

[0100] Of course, this second embodiment can be subjected to various substitutions and modifications apparent to those skilled in the art.

[0101] In particular, the first annular zone ZA21 can comprise two or more isolation trenches having the same width and extending at the same depth. The first annular zone can also comprise a single isolation trench.

[0102] Likewise, the second annular zone ZA22 can comprise two or more isolation trenches having the same width and extending at the same depth. The second annular zone ZA22 can also comprise a single isolation trench.

[0103] Moreover, the peripheral zone ZP2 can comprise two or more annular zones surrounding the photosensitive point matrix, or a single annular zone. In this case, the annular zones comprise at least one isolation trench. Therefore, the width and depth of the isolation trenches decrease between the annular zones from the photosensitive point matrix. Moreover, the distance between the isolation trenches of each annular zone remains the same as the photosensitive point width of the photosensitive point matrix.

[0104] The first embodiment of the semiconductor plate exemplarily shown in Figure 1 and Figure 2 can also be combined with the second embodiment shown in Figure 3 . In this case, the annular zones of the peripheral zone have an increasing pitch from the annular zone closest to the photosensitive point matrix, and the isolation trenches of the annular zones of the peripheral zone have a decreasing width and depth from the annular zone closest to the photosensitive point matrix.

[0105] Figure 4 An embodiment of a method for manufacturing a sensor according to an embodiment of the application is shown.

[0106] The method comprises an acquisition step 40, wherein a semiconductor plate comprising a semiconductor substrate is acquired. Such a semiconductor plate can be acquired by methods known to the person skilled in the art.

[0107] The method further comprises a step 41 of forming a matrix of photosensitive points, wherein the matrix of photosensitive points is formed in the semiconductor substrate of the semiconductor plate. The matrix of photosensitive points can be formed by methods known to the person skilled in the art. In particular, the matrix of photosensitive points is formed so as to acquire a number of photosensitive points arranged in rows and columns, each photosensitive point being separated by an isolation trench, in particular a capacitive isolation trench.

[0108] The method further comprises a step 42 of forming a peripheral zone. In this step, the peripheral zone is formed around the matrix of photosensitive points.

[0109] In particular, forming the peripheral zone comprises forming at least one annular zone comprising at least one isolation trench.

[0110] For example, forming the peripheral zone can comprise forming the annular zone shown in Figure 1 and Figure 2 or the annular zone shown in Figure 3 .

[0111] The isolation trench of the annular zone can be acquired by methods known to the person skilled in the art. For example, the isolation trench of the annular zone can be acquired by depositing a dielectric material such as silicon dioxide after etching.

Claims

1. A sensor, comprising: a semiconductor substrate; a matrix of photosites in the semiconductor substrate, each photosite of the matrix defined by an isolation trench comprising polysilicon; and a peripheral region of the semiconductor substrate extending directly around the matrix of photosites, the peripheral region comprising dummy photosites defined by isolation trenches containing polysilicon; wherein the density of polysilicon in the peripheral region is lower than the density of polysilicon at an outer edge of the matrix of photosites, and greater than the density of polysilicon in a range of the semiconductor substrate around the peripheral region.

2. The sensor of claim 1, wherein the peripheral region comprises a peripheral isolation trench around the matrix of photosites, the peripheral isolation trench of the peripheral region separated from the outer edge of the matrix of photosites by a distance greater than a width of the photosites in the matrix.

3. The sensor of claim 1, wherein the peripheral region comprises a series of peripheral isolation trenches extending around the matrix of photosites, wherein a distance between two consecutive peripheral isolation trenches of the series of peripheral isolation trenches is greater than a width of the photosites in the matrix, and wherein the distance between the two consecutive peripheral isolation trenches increases from the peripheral isolation trench closest to the outer edge of the matrix of photosites.

4. The sensor of claim 1, wherein the peripheral region comprises a peripheral isolation trench around the matrix of photosites, the peripheral isolation trench of the peripheral region extending at a depth less than a depth of the isolation trenches defining the photosites of the matrix.

5. The sensor of claim 1, wherein the peripheral region comprises a series of peripheral isolation trenches extending around the matrix of photosites, wherein a depth of the peripheral isolation trenches and a width of the peripheral isolation trenches decreases from the peripheral isolation trench closest to the matrix of photosites.

6. The sensor of claim 5, wherein the peripheral isolation trench of the peripheral region has the depth between one-third and two-thirds of a depth of the isolation trenches defining the photosites of the matrix.

7. The sensor of claim 1, wherein the peripheral region has a width between 20 pm and 400 pm.

8. A method for manufacturing a sensor, comprising: forming a matrix of photosites in a semiconductor substrate, each photosite defined by an isolation trench comprising polysilicon; and forming a peripheral region in the semiconductor substrate extending directly around the matrix of photosites, the peripheral region comprising dummy photosites defined by isolation trenches containing polysilicon; wherein the density of polysilicon in the peripheral region is lower than the density of polysilicon at an outer edge of the matrix of photosites, and higher than the density of polysilicon in a range of the semiconductor substrate around the peripheral region.

9. The method of claim 8, wherein forming the peripheral region comprises: forming a peripheral isolation trench around the matrix of photosites, the peripheral isolation trench of the peripheral region separated from the matrix of photosites by a distance greater than a width of the photosites.

10. The method of claim 8 wherein forming the peripheral region comprises: forming a series of peripheral isolation trenches extending around the matrix, wherein a distance between two consecutive peripheral isolation trenches of the series of peripheral isolation trenches is greater than a width of the photosensitive dot, wherein the distance between the peripheral isolation trenches increases starting from the peripheral isolation trench of the matrix closest to the photosensitive dot.

11. The method of claim 8 wherein forming the peripheral region comprises: forming a peripheral isolation trench around the matrix of photosensitive dots, the peripheral isolation trench of the peripheral region extending at a depth less than a depth of the isolation trench defining the photosensitive dot.

12. The method of claim 8 wherein forming the peripheral region comprises: forming a series of peripheral isolation trenches extending around the matrix, wherein a depth of the peripheral isolation trenches and a width of the peripheral isolation trenches decreases starting from the peripheral isolation trench of the matrix closest to the photosensitive dot.

13. The method of claim 12, wherein the peripheral isolation trench of the peripheral region is made so that the peripheral isolation trench has the depth between one third and two thirds of a depth of the isolation trench defining the photosensitive dot of the matrix.

14. The method of claim 8, wherein the peripheral region has a width between 20 pm and 400 pm.

15. A sensor comprising: a semiconductor substrate; a matrix of photosensitive dots in the semiconductor substrate, defined by a first isolation trench comprising polysilicon; and a first peripheral region of the semiconductor substrate around the matrix of photosensitive dots, the first peripheral region comprising a first dummy photosensitive dot defined by a second isolation trench comprising polysilicon; wherein a polysilicon density in the second isolation trench of the first peripheral region is lower than a polysilicon density in the first isolation trench for the matrix of photosensitive dots.

16. The sensor of claim 15, further comprising: a second peripheral region of the semiconductor substrate around the first peripheral region of the semiconductor substrate, the second peripheral region comprising a second dummy photosensitive dot defined by a third isolation trench comprising polysilicon; wherein a polysilicon density in the third isolation trench of the second peripheral region is less than the polysilicon density in the second isolation trench of the first peripheral region.

17. The sensor of claim 16, wherein the matrix of photosensitive dots is arranged at a first pitch, the first dummy photosensitive dot is arranged at a second pitch greater than the first pitch, and the second dummy photosensitive dot is arranged at a third pitch greater than the second pitch.

18. The sensor of claim 17, wherein the second pitch is twice the first pitch, and the third pitch is four times the first pitch.

19. The sensor of claim 16, wherein a depth of the second isolation trench is less than a depth of the first isolation trench, and wherein a depth of the third isolation trench is less than a depth of the second isolation trench.

20. The sensor of claim 15, wherein the matrix of photosensitive dots is arranged at a first pitch, and the first dummy photosensitive dot is arranged at a second pitch greater than the first pitch.

21. The sensor of claim 20, wherein the second pitch is twice the first pitch.

22. The sensor of claim 15, wherein a depth of the second isolation trench is less than a depth of the first isolation trench.

Images