INTEGRATED OPTICAL SENSOR OF THE SINGLE-PHOTON AVALANCHE PHOTODIODE TYPE, AND MANUFACTURING METHOD

Abstract

An integrated optical sensor includes a photon-detection module of a single-photon avalanche photodiode type. The detection module includes a semiconductive active zone in a substrate. The semiconductive active zone includes a region that contains germanium with a percentage between 3% and 10%. This percentage range is advantageous because it makes it possible to obtain a material firstly containing germanium (which in particular increases the efficiency of the sensor in the infrared or near infrared domain) and secondly having no or very few dislocations (which facilitates the implementation of a functional sensor in integrated form).

Claims

1. An integrated optical sensor, comprising: at least one photon-detection module of a single-photon avalanche photodiode type; wherein said at least one photon-detection module comprises: a substrate; and a semiconducting active zone in the substrate containing germanium, wherein the semiconducting active zone comprises a region containing silicon and germanium; and wherein the region contains a stack of alternating layers of silicon and layers of a silicon germanium alloy.

2. The sensor according to claim 1, wherein the substrate comprises a p-type doped layer overlying the stack of alternating layers.

3. The sensor according to claim 1, wherein the substrate comprises an n-type doped layer, and wherein the stack of alternating layers overlies the n-type doped layer.

4. The sensor according to claim 3, wherein the substrate further comprises a P-type doped layer overlying the stack of alternating layers.

5. The sensor according to claim 1, wherein the substrate comprises a top face and a top of said region of the semiconducting active zone is located at a distance from said top face.

6. The sensor according to claim 5, further comprising a layer of silicon located between said top face and the top of said region.

7. The sensor according to claim 1, wherein the layers of silicon and the layers of the silicon germanium alloy in the stack of alternating layers are undoped.

8. The sensor according to claim 1, wherein the sensor includes a plurality of photon-detection modules.

9. The sensor according to claim 1, wherein the sensor is a component of an imaging system.

10. The sensor according to claim 9, wherein the imaging system is a component of an electronic apparatus selected from a group consisting of a tablet or a cellular mobile telephone.

11. The sensor according to claim 1, wherein an atomic percentage of germanium in said region of the semiconducting active zone is between 3% and 10%.

12. The sensor according to claim 1, wherein the layers of silicon and the layers of the silicon germanium alloy in the stack of alternating layers are epitaxial layers.

13. The sensor according to claim 1, wherein the stack alternating layers includes at least three layers of silicon and three layers of the silicon germanium alloy.

14. An integrated optical sensor, comprising: at least one photon-detection module of a single-photon avalanche photodiode type; wherein said at least one photon-detection module comprises: a substrate; and a semiconducting active zone in the substrate containing germanium, wherein the semiconducting active zone comprises a region containing silicon and germanium; and wherein an atomic percentage of germanium in said semiconducting active zone exhibits a concentration gradient over a thickness of said semiconducting active zone.

15. The sensor according to claim 14, wherein the region contains a silicon germanium alloy.

16. The sensor according to claim 14, wherein the substrate comprises a p-type doped layer overlying the semiconducting active zone with the concentration gradient.

17. The sensor according to claim 14, wherein the semiconducting active zone comprises an n-type doped region formed of a silicon-germanium alloy and an undoped region also formed of the silicon-germanium alloy overlying the n-type doped region, with said concentration gradient extending over both the n-type doped region and the undoped region.

18. The sensor according to claim 17, wherein the substrate further comprises a p-type doped layer overlying the undoped region.

19. The sensor according to claim 14, wherein the substrate comprises a top face and a top of said region of the semiconducting active zone is located at a distance from said top face.

20. The sensor according to claim 19, further comprising a layer of silicon located between said top face and the top of said region.

21. The sensor according to claim 14, wherein the sensor includes a plurality of photon-detection modules.

22. The sensor according to claim 14, wherein the sensor is a component of an imaging system.

23. The sensor according to claim 22, wherein the imaging system is a component of an electronic apparatus selected from a group consisting of a tablet or a cellular mobile telephone.

24. The sensor according to claim 14, wherein an atomic percentage of germanium in said region of the semiconducting active zone is between 3% and 10%.

25. The sensor according to claim 14, wherein the concentration gradient changes from an atomic percentage of germanium of about 3% at a location closer to a bottom of the semiconducting active zone to an atomic percentage of germanium of about 10% at a location closer to a top of the semiconducting active zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Other advantages and features of the invention will emerge from an examination of the detailed description of embodiments and implementation, and the accompanying drawings, on which:

[0051] FIG. 1 is a cross-section of a photon detection module of the single-photon avalanche photodiode (SPAD) type;

[0052] FIG. 2 is a cross section of the SPAD implemented using an alternation of layers of silicon and layers of silicon-germanium;

[0053] FIG. 3 illustrates an embodiment of a method for manufacturing the active zone of the module in FIG. 1;

[0054] FIG. 4 illustrates an embodiment of a method for manufacturing the active zone of the module in FIG. 2;

[0055] FIG. 5 shows an integrated optical sensor comprising a plurality of detection modules arranged for example in rows or in a matrix;

[0056] FIG. 6 shows a sensor incorporated in an imaging system CM;

[0057] FIG. 7 shows an electronic apparatus that uses the sensor;

[0058] FIG. 8 is a cross-section of a photon detection module of the SPAD type which utilizes a concentration gradient.

DETAILED DESCRIPTION

[0059] In FIG. 1, the reference MD designates overall a photon detection module of the single-photon avalanche photodiode (SPAD) type.

[0060] This detection module MD comprises, in a substrate SB1, a semiconductive active zone 1 containing germanium.

[0061] More precisely, in this embodiment, the active zone 1 comprises a region 100 containing silicon and germanium, the volume percentage of germanium in said region being comprised between 3 and 10%.

[0062] In FIG. 1, the various contacts and other elements of the SPAD detection module, which are conventional and known per se, have intentionally not been depicted, for reasons of simplification.

[0063] In the active zone 1, a deep N-doped layer 11, forming the N electrode of the photodiode, is located above a P-type support substrate SB.

[0064] The thickness of this layer 11 is, for example, around 1 micrometer and the concentration of dopants is, for example, around 2×10.sup.18 atoms of dopants (N-type) per cm.sup.3.

[0065] A very weakly P doped thick layer 10 is located above the N-doped layer 100.

[0066] This layer, referenced overall 10, comprises a bottom part 10a and a top part 10b.

[0067] The layer 10 forms the P electrode of the photodiode.

[0068] The region 100 of silicon-germanium incorporates the N-doped layer 11 as well as also incorporates the part 10a of the layer 10.

[0069] The thickness of the region 100, containing germanium, is around 1 micrometer, for example, and the atomic percentage of germanium is around 4.

[0070] The concentration of dopants (P type) in the part 10a of the layer 10 is, for example, zero (not intentionally doped) or around 10.sup.15 or 2×10.sup.15 at/cm.sup.3 or even less, while the concentration of dopants (P type) in the part 10b of the layer 10, located above the part 10a, is around 10.sup.18 to 4×10.sup.18 at/cm.sup.3.

[0071] The layer 10 is surmounted by a P+ doped top layer 12, with a concentration of dopants of around 10.sup.18 to 5×10.sup.18 at/cm.sup.3, for example.

[0072] In this example, the region 100 containing germanium is located deep and at a distance d from the top face FS of the substrate SB1.

[0073] On an indicative basis, this distance d may be around 0.5 μm for a region 100 having a thickness of around 1 μm.

[0074] In a variant shown in FIG. 8, the region 100 may include silicon and germanium with a concentration gradient GR1 extending over a thickness of the region 100. The concentration gradient GR1 is a positive gradient in that the atomic percentage of germanium in the region 100 gradually (and preferably monotonically) increases with proximity to the overlying layer 10b. For example, the atomic percentage may increase from about X % (where, for example, X=0 to 3, more preferably closer to or equal to 0) at or near the substrate SB to Y % (where, for example, Y=6 to 10, more preferably closer to or equal to 10) at or near the layer 10b.

[0075] Whereas in the embodiment in FIG. 1, the region 100 is formed by a homogeneous alloy of silicon-germanium, FIG. 2 instead shows an embodiment where the region is formed by an alternation of layers of silicon 110 and layers of silicon-germanium 111.

[0076] The volume percentage of germanium for each of these silicon-germanium layers 111 is chosen so that the mean final volume percentage of germanium in the region 100 is comprised between 3 and 10%. The concentration of dopants (P type) in the alternating layers 110, 110 is, for example, zero (not intentionally doped) or around 10.sup.15 or 2×10.sup.15 at/cm.sup.3 or even less. The concentration of dopants (P type) in the layer 10, located above the alternating layers 110, 111, is around 10.sup.18 to 4×10.sup.18 at/cm.sup.3.

[0077] This stack forming the region 100 is located above the N-doped buried layer 11 and under the P-doped silicon layer 10.

[0078] In this embodiment, the region 100 is also located at a distance d from the top face FS of the substrate SB1.

[0079] Reference is now made more particularly to FIG. 3 in order to illustrate an embodiment of a method for manufacturing the active zone 1 of the module in FIG. 1.

[0080] On the substrate SB, an epitaxy 30 is performed so as to form the region 100 consisting of 96% silicon in atomic percentage and 4% germanium in atomic percentage.

[0081] A silicon-germanium epitaxy is a step well known to persons skilled in the art.

[0082] By way of example, the SiGe epitaxy may be performed by chemical vapor deposition (acronym CVD) using a dichlorosilane+germanium+hydrogen chemistry at 900°-950° C. and at low pressure (10-60 Torr).

[0083] The epitaxy 30 is then followed by another epitaxy 31, this time solely of silicon, conventional and known per se, so as to form the top part 10b of the layer 10.

[0084] This epitaxy is preferentially P-doped (10.sup.15 to 10.sup.16 at/cm.sup.3) and the P-type doping (10.sup.18 at/cm.sup.3) is then obtained in a localized fashion by ion implantation.

[0085] By way of example, the conditions of this epitaxy are substantially the same as those used for the SiGe epitaxy, optionally with a temperature increased from 50° to 100° C. It should be noted that these two epitaxies, often performed at the same step, may be performed in the same epitaxy operation, and therefore in the same epitaxy reactor and with the same recipe, and therefore often without cooling of the wafer between the two types of deposition.

[0086] After implantation of dopants in the upper epitaxed region, the layer 12 is obtained. As for the layer 11, it can be obtained, for example, by an implantation of N-type dopants prior to the SiGe epitaxy.

[0087] Reference is now made more particularly to FIG. 4, which illustrates an example of implementation of a method for obtaining the active zone 1 of the module illustrated in FIG. 2.

[0088] On the support substrate SB, an epitaxy 40 of silicon is this time performed so as to form the layer 11 (N-type electrode) and then successive alternating epitaxies of silicon and silicon-germanium, referenced 41, so as to obtain the stack of layers 110 and 111.

[0089] The volume percentage of germanium for each of these epitaxies is chosen so that the mean final volume percentage of germanium is comprised between 3 and 10%.

[0090] In a variant, the layer 11 (N-type electrode) may be obtained, for example, by an implantation of N-type dopants prior to the successive epitaxies of silicon and silicon-germanium.

[0091] After the production of the stack of layers 110 and 111, an epitaxy and then an implantation 42 are once again performed so as to form the layers 10 and 12.

[0092] As illustrated in FIG. 5, an integrated optical sensor SNS may comprise a plurality of detection modules MD1-MDn arranged for example in rows or in a matrix.

[0093] As illustrated in FIG. 6, the sensor SNS may be incorporated in an imaging system CM, for example a camera that can itself be incorporated in an electronic apparatus APP (FIG. 7), for example of the tablet or cellular mobile telephone type.

[0094] The invention is not limited to the embodiments and implementations described above but embraces all variants.

[0095] Thus the following implementation is possible, starting from a bulk substrate: [0096] epitaxy of silicon (boron doping at 10.sup.15 at/cm.sup.3) over a few micrometers; [0097] localized implantation with an N-type dopant in order to form the bottom electrode of the sensor; [0098] epitaxy of silicon-germanium or epitaxies of silicon/silicon-germanium in alternation, with potentially a “sublayer” of silicon) over a thickness of approximately 1 micrometer with an intentionally zero or very low doping (below 10.sup.15 at/cm.sup.3); [0099] epitaxy of a layer of silicon over a thickness of approximately 0.5 micrometers with an intentionally zero or very low doping (below 10.sup.15 at/cm.sup.3), with often the same recipe as the previous epitaxy; [0100] localized implantation of a P-type dopant in order to form the top electrode of the sensor, optionally followed by an implantation annealing; [0101] superficial localized implantation of a P-type dopant with a high dose optionally followed by an implantation annealing, in order to form the contact zone.

[0102] It should be noted that these annealings may be mutualized and may be or are advantageously common with the other annealings used in the technology in question for manufacturing other components of the integrated circuit.

[0103] Thus, for example, the second annealing may correspond to the annealing for activation of the source/drain regions of MOS transistors.

[0104] The substrate may advantageously be formed by a wafer (P+ wafer (2×10.sup.18-2×10.sup.19 at/cm.sup.3)) covered with a P− epitaxy typically 10.sup.15-10.sup.16 at/cm.sup.3. This P+ substrate thus makes it possible to protect the sensor from metallic contaminations (getter effect) and forms a better ground plane (reduction in electronic noise).

[0105] Whereas the above description relates to the use of an N-type bottom electrode and a P-type top electrode, often advantageous for managing the ground and electrical voltages, it would also be possible to use an SPAD sensor with a P-type bottom electrode and an N-type top electrode.