Semiconductor structure and forming method thereof

Abstract

The invention relates to a semiconductor structure and a forming method thereof, the semiconductor structure comprises a first substrate, the first substrate comprises a plurality of mutually discrete photosensitive areas and isolation areas located between the adjacent photosensitive areas, the first substrate comprises a first surface and a second surface which are opposite, and the second surface is used as a light incident surface; the deep trenches are located in the isolation regions, the deep trenches penetrate through the first substrate in the normal direction of the surface of the first substrate, each deep trench comprises a first trench region and a second trench region, the distance from the first trench region to the first surface is smaller than the distance from the second trench region to the first surface, the first trench region has a first projection on the surface of the first substrate, and the second trench region has a second projection on the surface of the second substrate; the second groove region has a second projection on the surface of the first substrate, and the second projection is located in the range of the first projection; the isolation structures are located in the deep trenches, each isolation structure comprises a light reflection layer, the utilization rate of incident photons is improved, light transmission and reflection losses are reduced, and then the photon detection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and in particular to a semiconductor structure and a forming method thereof. Background Art

[0002] Direct Time of Flight (dToF) technology is widely used in scenarios with high requirements for ranging accuracy and long-distance ranging because of its characteristics of accurate measurement, fast response, low power consumption and accurate synchronous detection of multiple objects. Its optical components are mainly composed of vertical cavity surface emitting laser (Vertical-Cavity Surface-EmittingLaser, VCSEL), single photon avalanche diode (SPAD) and time digital converter (TDC). Among them, the SPAD device is a photoelectric detection avalanche diode with single photon detection capability working in Geiger mode. It is a semiconductor device that converts light signals into current. In Geiger mode, when photons are absorbed by SPAD, photons collide with the lattice to generate electron-hole pairs. Electron-hole pairs will undergo an avalanche multiplication effect under the action of a strong electric field, forming an avalanche current. After quenching and resetting, the avalanche current forms pulses, achieving the purpose of detecting a single photon with high sensitivity.

[0003] In order to obtain better spatial resolution and signal-to-noise ratio (SNR), SPAD devices usually exist in the form of arrays. As the pixel array expands, the problems of optical / electrical crosstalk and low photon detection efficiency become increasingly prominent, which will not only cause erroneous counting of corresponding pixel units and affect the accuracy of photon detection, but also require the addition of more isolation structures, thereby sacrificing the fill factor and reducing the photon detection sensitivity.

[0004] Therefore, the performance of existing SPAD devices needs to be further improved. Summary of the invention

[0005] The technical problem solved by the present invention is to provide a semiconductor structure and a method for forming the same, so as to improve the performance of the formed SPAD device.

[0006] In order to solve the above technical problems, the technical solution of the present invention provides a semiconductor structure, including: a first substrate, the first substrate including a plurality of discrete photosensitive areas and an isolation area located between adjacent photosensitive areas, the first substrate including a first surface and a second surface opposite to each other, the second surface being used as an incident surface for light; a deep trench located in each isolation area, the deep trench penetrating the first substrate along a normal direction of the surface of the first substrate, the deep trench including a first trench area and a second trench area, the distance from the first trench area to the first surface is smaller than the distance from the second trench area to the first surface, and the first trench area has a first projection on the surface of the first substrate, the second trench area has a second projection on the surface of the first substrate, and the second projection is located within the range of the first projection; an isolation structure located in each deep trench, the isolation structure including a reflective layer.

[0007] Optionally, the isolation structure also includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure; the material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon carbon oxide, silicon nitride oxide, aluminum oxide, aluminum nitride, silicon carbide nitride and silicon carbon nitride oxide.

[0008] Optionally, the medium structure includes a first medium layer and a second medium layer located on the surface of the first medium layer; the first medium layer has a first refractive index, the second medium layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index.

[0009] Optionally, the material of the reflective layer includes metal, and the metal includes aluminum.

[0010] Optionally, it also includes: a plurality of openings arranged in an array in each photosensitive area, the plurality of openings are recessed from the second surface toward the first surface, the top width of each opening is greater than the bottom width, and the side wall of each opening is an obtuse angle relative to the second surface.

[0011] Optionally, it also includes: a second substrate located on the first surface, and a logic circuit is provided in the second substrate.

[0012] Optionally, a diode region is provided in the photosensitive region, and the diode region extends from the first surface to the second surface.

[0013] Optionally, it also includes: a first doping region and a second doping region that are located in contact with each other in each isolation region, the first side exposes the surface of the first doping region, the second side exposes the surface of the second doping region, and the doping ion concentration in the first doping region is greater than the doping ion concentration in the second doping region; the first trench region runs through the first doping region, and the second trench region runs through the second doping region; the conductivity type of the first doping region and the second doping region is the same as the conductivity type of the first substrate; taking the doping ion concentration in the first substrate as a reference value, the doping ion concentration in the first doping region and the second doping region are both greater than 100 times the reference value and lower than 1E13atom / cm3 .

[0014] Correspondingly, the technical solution of the present invention also provides a method for forming a semiconductor structure, including: providing a first substrate, the first substrate including a plurality of discrete photosensitive areas and an isolation area located between adjacent photosensitive areas, the first substrate including a first surface and a second surface relative to each other; forming a deep groove in each isolation area, the deep groove penetrating the first substrate along a normal direction of the surface of the first substrate, the deep groove including a first groove area and a second groove area, the distance from the first groove area to the first surface is smaller than the distance from the second groove area to the first surface, and the first groove area has a first projection on the surface of the first substrate, the second groove area has a second projection on the surface of the first substrate, and the second projection is located within the range of the first projection; forming an isolation structure in each deep groove, the isolation structure including a reflective layer.

[0015] Optionally, the method for forming a deep trench includes: injecting doping ions into the isolation region from the second surface to form a first doping region and a second doping region in contact with the first doping region in the isolation region, the first surface exposes the surface of the first doping region, the second surface exposes the surface of the second doping region, and the doping ion concentration of the first doping region is greater than the doping ion concentration of the second doping region; etching the isolation region, and making the etching rate of the second doping region less than the etching rate of the first doping region to form a deep trench, the first trench region is located in the first doping region, and the second trench region is located in the second doping region.

[0016] Optionally, before forming the deep trench, the method further includes: providing a second substrate having a logic circuit therein; forming a bonding layer on a surface of the second substrate; and bonding the first substrate to the second substrate with the first surface facing the surface of the bonding layer.

[0017] Optionally, the method of etching the isolation region further includes: etching the isolation region from the second surface until the surface of the bonding layer is exposed.

[0018] Optionally, the conductivity type of the doped ions is the same as the conductivity type of the first substrate; taking the doped ion concentration in the first substrate as a reference value, the concentration of the doped ions is greater than 100 times the reference value and less than 1E13atom / cm 3 .

[0019] Optionally, the method for forming the deep trench includes: etching the isolation region from the first surface to form a first trench region; etching the isolation region from the second surface until it is connected to the first trench region to form a second trench region.

[0020] Optionally, before forming the deep trench, it also includes: providing a second substrate, the second substrate having a logic circuit; forming a bonding layer on the surface of the second substrate; facing the first surface toward the surface of the bonding layer to bond the first substrate and the second substrate; the first trench area is formed before the bonding process, and the second trench area is formed after the bonding process.

[0021] Optionally, the method for forming the isolation structure includes: forming a reflective material layer on the surface of the second surface and in a plurality of deep grooves, wherein the reflective material layer fills the deep grooves; and planarizing the reflective material layer until the surface of the second surface is exposed.

[0022] Optionally, the isolation structure also includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure; the material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon carbon oxide, silicon nitride oxide, aluminum oxide, aluminum nitride, silicon carbonitride and silicon carbonitride oxide; the material of the reflective layer includes a metal, and the metal includes aluminum.

[0023] Optionally, the medium structure includes a first medium layer and a second medium layer located on the surface of the first medium layer; the first medium layer has a first refractive index, the second medium layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index.

[0024] Optionally, the method for forming the isolation structure includes: forming a dielectric structure in a plurality of deep grooves before the reflective material layer; and forming a reflective material layer on the surface of the dielectric structure.

[0025] Optionally, the photosensitive area has a diode region, which extends from the first surface to the second surface; the first groove region has a first depth value, and the edge of the doped region in the diode region has a second depth value from the first surface, and the first depth value is less than the second depth value.

[0026] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0027] In the semiconductor structure provided by the technical solution of the present invention, the first substrate includes a plurality of mutually discrete photosensitive areas and an isolation area located between adjacent photosensitive areas, each isolation area has a deep groove, and each deep groove has an isolation structure, the isolation structure includes a reflective layer, the deep groove includes a first groove area and a second groove area, the projection of the second groove area on the surface of the first substrate is located within the projection range of the first groove area on the surface of the first substrate, so that the isolation structure is "inverted T-shaped", the isolation structure in the first groove area is wider than the isolation structure in the second groove area, the reflection area is increased, so that part of the light incident into the first substrate is reflected to the effective photosensitive area through the isolation structure in the second groove area, the number of refractions of light in the photosensitive area is increased, and the full absorption of incident photons is improved, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0028] Furthermore, the material of the reflective layer includes metal, and the metal includes aluminum. The aluminum material presents an "aluminum mirror" structure in the deep groove, which improves the light reflection capability of the isolation structure and helps to reduce the optical crosstalk caused by photons generated by carrier radiation recombination in the photodiode to adjacent pixel units.

[0029] Furthermore, the isolation structure also includes a dielectric structure, the dielectric structure includes a first dielectric layer and a second dielectric layer located on the surface of the first dielectric layer, and the first dielectric layer has a first refractive index, the second dielectric layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index. Since the third refractive index is greater than the first refractive index and the first refractive index is greater than the second refractive index, the photosensitive area forms a planar dielectric optical waveguide structure, which is conducive to achieving total internal reflection of photons in a single pixel area (photosensitive area), thereby improving the photon detection efficiency.

[0030] In the method for forming a semiconductor structure provided by the technical solution of the present invention, the first substrate includes a plurality of mutually discrete photosensitive areas and an isolation area located between adjacent photosensitive areas, a deep groove is formed in each isolation area, an isolation structure is formed in each deep groove, the isolation structure includes a reflective layer, the deep groove includes a first groove area and a second groove area, the projection of the second groove area on the surface of the first substrate is located within the projection range of the first groove area on the surface of the first substrate, so that the isolation structure is "inverted T-shaped", the isolation structure in the first groove area is wider than the isolation structure in the second groove area, the reflection area is increased, so that part of the light incident into the first substrate is reflected to the effective photosensitive area through the isolation structure in the second groove area, the number of refractions of light in the photosensitive area is increased, and the full absorption of incident photons is improved, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0031] Furthermore, by forming doping regions with different doping concentrations at different depths in the isolation region (i.e., the doping ion concentration of the first doping region is greater than the doping ion concentration of the second doping region), and then etching the isolation region to form a deep groove, a suitable etching process is selected so that the etching rate of the second doping region is less than the etching rate of the first doping region, thereby forming a deep groove, which is conducive to forming a better deep trench morphology, thereby improving the quality of the isolation structure.

[0032] Furthermore, before the bonding process, the isolation area is etched from the first side to form a first trench area; after the bonding process, the isolation area is etched from the second side until it is connected with the first trench area to form a second trench area. The first trench area and the second trench area are deep trenches, and the deep trenches are formed twice, thereby reducing the etching morphology problems caused by the large depth-width ratio of the trench, and facilitating the formation of a better deep trench morphology, thereby improving the quality of the isolation structure.

[0033] Furthermore, the material of the reflective layer includes aluminum. Metal aluminum has a high filling capacity and forms an "aluminum mirror" in the deep groove, which improves the light reflectivity of the isolation structure and helps reduce the optical crosstalk caused by photons generated by carrier radiation recombination in the photodiode to adjacent pixel units.

[0034] Furthermore, the isolation structure also includes a dielectric structure, the dielectric structure includes a first dielectric layer and a second dielectric layer located on the surface of the first dielectric layer, and the first dielectric layer has a first refractive index, the second dielectric layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index. Since the third refractive index is greater than the first refractive index and the first refractive index is greater than the second refractive index, the photosensitive area forms a planar dielectric optical waveguide structure, which is conducive to achieving total internal reflection of photons in a single pixel area (photosensitive area), thereby improving the photon detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figures 1 to 3 It is a structural schematic diagram of each step of a method for forming a semiconductor structure;

[0036] Figures 4 to 9 is a structural schematic diagram of each step of a method for forming a semiconductor structure according to an embodiment of the present invention;

[0037] Figures 10 to 13 It is a structural schematic diagram of each step of a method for forming a semiconductor structure according to another embodiment of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the terms “surface” and “on” in this specification are used to describe relative positional relationships in space and are not limited to direct contact.

[0039] As described in the background art, the performance of existing SPAD devices needs to be further improved. Now, an explanation and analysis will be given in conjunction with a semiconductor structure.

[0040] Figures 1 to 3 The present invention is a structural schematic diagram of each step of a method for forming a semiconductor structure.

[0041] Please refer to Figure 1 , providing a first substrate 101 and a second substrate 102 bonded to each other through a bonding layer 100, the first substrate 101 having a logic circuit (not shown in the figure), the second substrate 102 including a first surface 102a and a second surface 102b opposite to each other, the first surface 102a being in contact with the bonding layer 100, the second substrate 102 having a plurality of diode regions 103, the diode regions 103 extending from the first surface 102a to the second surface 102b.

[0042] Please refer to Figure 2The second substrate 102 is etched from the second surface 102 b until the bonding layer 100 is exposed, thereby forming a deep trench 104 penetrating the second substrate 102 . The deep trench 104 is located between adjacent diode regions 103 .

[0043] Please refer to Figure 3 , an isolation structure 105 is formed in the deep trench 104 .

[0044] In the SPAD device formed by the above method, the material of the isolation structure 105 is usually SiO2 and polysilicon. The isolation structure 105 has a good electrical isolation function, but has high light transmittance and cannot solve the optical crosstalk problem between adjacent pixels.

[0045] In order to solve the above problems, the present invention provides a semiconductor structure and a formation method, so that the isolation structure is in an "inverted T-shape", and the isolation structure in the first groove area is wider than the isolation structure in the second groove area, thereby increasing the reflection area, so that part of the light incident into the first substrate is reflected to the effective photosensitive area through the isolation structure in the second groove area, thereby increasing the number of refractions of light in the photosensitive area, and improving the full absorption of incident photons, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0046] In order to make the above-mentioned objects, features and beneficial effects of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0047] Figures 4 to 9 It is a schematic cross-sectional structure diagram of each step of a method for forming a semiconductor structure according to an embodiment of the present invention.

[0048] Please refer to Figure 4 , providing a first substrate 202, the first substrate 202 includes a plurality of mutually discrete photosensitive regions I and an isolation region II located between adjacent photosensitive regions I, and the first substrate 202 includes a first surface 202a and a second surface 202b opposite to each other.

[0049] The conductivity type of the first substrate 202 includes N type or P type.

[0050] In this embodiment, when the SPAD device is in operation, light is incident from the second surface 202 b .

[0051] In this embodiment, the photosensitive region I has a diode region 203, and the diode region 203 extends from the first surface 202a to the second surface 202b.

[0052] Subsequently, a deep trench is formed in each isolation region II, and the deep trench penetrates the first substrate 202 along the normal direction of the surface of the first substrate 202. The deep trench includes a first trench region and a second trench region. The distance from the first trench region to the first surface 202a is smaller than the distance from the second trench region to the first surface 202a, and the first trench region has a first projection on the surface of the first substrate 202, and the second trench region has a second projection on the surface of the first substrate 202, and the second projection is located within the range of the first projection.

[0053] In this embodiment, before forming the deep trench, a second substrate 201 is provided, and a logic circuit (not shown in the figure) is provided in the second substrate 201; a bonding layer 200 is formed on the surface of the second substrate 201; the first surface 202a is directed toward the surface of the bonding layer 200, so that the first substrate 202 and the second substrate 201 are bonded. This embodiment is used to form a back side illumination (BSI) structure, and in other embodiments, it can be used to form a front side illumination (FSI) structure.

[0054] In this embodiment, the method for forming the deep trench is as follows. Figure 5 to Figure 6 .

[0055] Please refer to Figure 5 , doping ions are injected into the isolation region II from the second surface 202b to form a first doping region 204a and a second doping region 204b in contact with the first doping region 204a in the isolation region II, the first surface 202a exposes the surface of the first doping region 204a, and the second surface 202b exposes the surface of the second doping region 204b, and the doping ion concentration of the first doping region 204a is greater than the doping ion concentration of the second doping region 204b.

[0056] In this embodiment, the conductivity type of the doped ions is the same as the conductivity type of the first substrate 202; taking the doped ion concentration in the first substrate 202 as a reference value, the concentration of the doped ions is greater than 100 times the reference value and is lower than 1E13atom / cm 3 .

[0057] Please refer to Figure 6 , the isolation region II is etched, and the etching rate of the second doping region 204b is made lower than the etching rate of the first doping region 204a, so as to form a deep trench, the first trench region 205a is located in the first doping region 204a, and the second trench region 205b is located in the second doping region 204b.

[0058] Here, doping regions with different doping concentrations are formed at different depths in the isolation region II (i.e., the doping ion concentration of the first doping region 204a is greater than the doping ion concentration of the second doping region 204b), and then a deep groove is formed by etching the isolation region II. A suitable etching process is selected so that the etching rate of the second doping region 204b is less than the etching rate of the first doping region 204a, thereby forming a deep groove, which is conducive to forming a better deep trench morphology, thereby improving the quality of the isolation structure.

[0059] In this embodiment, the method for etching the isolation region II further includes: etching the isolation region II from the second surface 202 b until the surface of the bonding layer 200 is exposed.

[0060] It should be noted that the first trench region 205a has a first depth, that is, the isolation structure subsequently formed in the first trench region 205a has a first depth, and the PN junction depletion region in the diode region 203 has a second depth from the first surface 202a. Making the first depth smaller than the second depth can improve the absorption of incident photons.

[0061] In this embodiment, before forming the deep grooves, a plurality of photosensitive regions I are etched from the second surface 202b toward the first surface 202a, and a plurality of openings 206 arranged in an array are formed in each photosensitive region I. The plurality of openings 206 are recessed from the second surface 202b toward the first surface 202a, the top width of each opening 206 is greater than the bottom width, and the angle between the sidewall of each opening 206 and the second surface 202b is an obtuse angle. The plurality of openings 206 are used to increase the optical path of light in the photosensitive region I, increase the probability of capturing photons, and help improve the quantum effect of the device.

[0062] Subsequently, an isolation structure is formed in each deep trench, wherein the isolation structure includes a reflective layer.

[0063] An isolation structure is formed in each deep groove. Since the projection of the second groove area 205b on the surface of the first substrate 202 is located within the projection range of the first groove area 205a on the surface of the first substrate 202, the isolation structure is in an "inverted T shape". The isolation structure in the first groove area 205a is wider than the isolation structure in the second groove area 205b, which increases the reflection area, so that part of the light incident into the first substrate 202 is reflected to the effective photosensitive area I through the isolation structure in the second groove area 205b, increasing the number of refractions of light in the photosensitive area I, and improving the full absorption of incident photons, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0064] The method for forming the isolation structure includes: forming a reflective material layer on the surface of the second surface 202b and in a plurality of deep grooves, wherein the reflective material layer fills the deep grooves; and flattening the reflective material layer until the surface of the second surface is exposed.

[0065] In this embodiment, the isolation structure further includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure.

[0066] In this embodiment, the method for forming the isolation structure is shown in Figures 7 and 8 .

[0067] Please refer to Figure 7 Before the reflective material layer, a dielectric structure is formed in a plurality of deep grooves, and the dielectric structure includes a first dielectric layer 207 and a second dielectric layer 208 located on the surface of the first dielectric layer 207 .

[0068] In this embodiment, the dielectric structure is also located on the surface of the second surface 202b and the opening 206 (eg Figure 6 shown).

[0069] The material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon oxycarbon, silicon nitride oxide, aluminum oxide, aluminum nitride, silicon carbonitride, and silicon carbonitride oxide. In this embodiment, the material of the first dielectric layer 207 is silicon oxide, and the material of the second dielectric layer 208 is silicon oxynitride. The refractive index of silicon oxide is about 1.6, and a silicon oxynitride material with a suitable refractive index can be obtained by controlling the nitrogen content.

[0070] In this embodiment, the first dielectric layer 207 has a first refractive index, the second dielectric layer 208 has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive region I has a third refractive index, and the third refractive index is greater than the first refractive index. Since the third refractive index is greater than the first refractive index, and the first refractive index is greater than the second refractive index, the photosensitive region forms a planar dielectric optical waveguide structure, which is conducive to achieving total internal reflection of photons in a single pixel region (photosensitive region I), thereby improving the photon detection efficiency.

[0071] Please refer to Figure 8 , a reflective material layer 209 is formed on the surface of the dielectric structure.

[0072] In this embodiment, the material of the reflective material layer 209 includes metal, and the metal includes aluminum. Metal aluminum has a high filling capacity, and forms an "aluminum mirror" in the deep groove, which improves the light reflection ability of the isolation structure and helps to reduce the optical crosstalk caused by photons generated by carrier radiation recombination in the photodiode to adjacent pixel units.

[0073] Please refer to Fig. 9 , the reflective material layer 209 is planarized until the surface of the second surface 202 b is exposed to form a reflective layer 210 .

[0074] Specifically, the reflective material layer 209 is planarized until the dielectric structure surface on the second surface 202 b is exposed.

[0075] In this embodiment, the material of the reflective layer 210 includes metal, and the metal includes aluminum.

[0076] Accordingly, the embodiment of the present invention further provides a semiconductor structure formed by the above method, please continue to refer to Fig. 9 , comprising: a first substrate 202, the first substrate 202 comprising a plurality of mutually discrete photosensitive regions I and an isolation region II located between adjacent photosensitive regions I, the first substrate 202 comprising a first surface 202a and a second surface 202b opposite to each other, the second surface 202b being used as an incident surface for light; a deep groove located in each isolation region II, the deep groove penetrating the first substrate 202 along a surface normal direction of the first substrate 202, the deep groove comprising a first groove region 205a (such as Figure 6 as shown) and the second trench region 205b (as shown Figure 6 As shown), the distance from the first groove area 205a to the first surface 202a is smaller than the distance from the second groove area 205b to the first surface 202a, and the first groove area 205a has a first projection on the surface of the first substrate 202, and the second groove area 205b has a second projection on the surface of the first substrate 202, and the second projection is located within the range of the first projection; an isolation structure is located in each deep groove, and the isolation structure includes a reflective layer 210.

[0077] At this point, since the projection of the second groove area 205b on the surface of the first substrate 202 is located within the projection range of the first groove area 205a on the surface of the first substrate 202, the isolation structure is in an "inverted T shape", and the isolation structure in the first groove area 205a is wider than the isolation structure in the second groove area 205b, thereby increasing the reflection area, so that part of the light incident into the first substrate 202 is reflected to the effective photosensitive area I through the isolation structure in the second groove area 205b, increasing the number of refractions of light in the photosensitive area I, and improving the full absorption of incident photons, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0078] In this embodiment, the material of the reflective layer 210 includes metal, and the metal includes aluminum. The aluminum material presents an "aluminum mirror" structure in the deep groove, which improves the light reflection capability of the isolation structure and helps to reduce the optical crosstalk caused by photons generated by carrier radiation recombination in the photodiode to adjacent pixel units.

[0079] In this embodiment, the isolation structure further includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure.

[0080] The material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon oxycarbon, silicon nitride oxide, aluminum oxide, aluminum nitride, silicon carbonitride, and silicon carbonitride oxide. In this embodiment, the material of the first dielectric layer 207 is silicon oxide, and the material of the second dielectric layer 208 is silicon oxynitride. The refractive index of silicon oxide is about 1.6, and a silicon oxynitride material with a suitable refractive index can be obtained by controlling the nitrogen content.

[0081] In this embodiment, the dielectric structure includes a first dielectric layer 207 and a second dielectric layer 208 located on the surface of the first dielectric layer 207 .

[0082] In this embodiment, the first dielectric layer 207 has a first refractive index, the second dielectric layer 208 has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive region I has a third refractive index, and the third refractive index is greater than the first refractive index. Since the third refractive index is greater than the first refractive index, and the first refractive index is greater than the second refractive index, the photosensitive region forms a planar dielectric optical waveguide structure, which is conducive to achieving total internal reflection of photons in a single pixel region (photosensitive region), thereby improving the photon detection efficiency.

[0083] In this embodiment, the semiconductor structure further includes: a plurality of openings 206 arranged in an array in each photosensitive region I (eg Figure 6 As shown in FIG. 2 , a plurality of openings 206 are recessed from the second surface 202b to the first surface 202a, the top width of each opening 206 is greater than the bottom width, and the sidewall of each opening 206 is at an obtuse angle relative to the second surface 202b. The plurality of openings 206 are used to increase the optical path of light in the photosensitive area I, increase the probability of capturing photons, and help improve the quantum effect of the device.

[0084] In this embodiment, the semiconductor structure further includes: a second substrate 201 located on the first surface 202a, and a logic circuit is provided in the second substrate 201. Specifically, the first substrate 202 and the second substrate 201 are bonded to each other via a bonding layer 200.

[0085] In this embodiment, the photosensitive region I has a diode region 203, and the diode region 203 extends from the first surface 202a to the second surface 202b.

[0086] It should be noted that the isolation structure in the first trench region 205a has a first depth, and the PN junction depletion region in the diode region 203 has a second depth from the first surface 202a. The first depth is smaller than the second depth, which can improve the absorption of incident photons.

[0087] In this embodiment, the semiconductor structure also includes: a first doping region 204a and a second doping region 204b located in each isolation region II and in contact with each other, the first surface 202a exposes the surface of the first doping region 204a, the second surface 202b exposes the surface of the second doping region 204b, and the doping ion concentration in the first doping region 204a is greater than the doping ion concentration in the second doping region 204b; the first trench region 205a penetrates the first doping region 204a, and the second trench region 205b penetrates the second doping region 204b.

[0088] In this embodiment, the conductivity type of the first doping region 204a and the second doping region 204b is the same as the conductivity type of the first substrate 202; taking the doping ion concentration in the first substrate 202 as a reference value, the doping ion concentration in the first doping region 204a and the second doping region 204b is greater than 100 times the reference value and less than 1E13atom / cm 3

[0089] Figures 10 to 13 It is a structural schematic diagram of each step of a method for forming a semiconductor structure according to another embodiment of the present invention.

[0090] The main difference between this embodiment and the previous embodiment is that the deep trench is formed in a different method. For the method of forming the semiconductor structure of this embodiment, please refer to Figures 10 to 13 .

[0091] Please refer to Fig.10 , providing a first substrate 302, the first substrate 302 includes a plurality of mutually discrete photosensitive regions i and isolation regions ii located between adjacent photosensitive regions i, and the first substrate 302 includes a first surface 302a and a second surface 302b opposite to each other.

[0092] In this embodiment, when the SPAD device is in operation, light is incident from the second surface 302 b .

[0093] In this embodiment, a diode region 303 is provided in the photosensitive region I, and the diode region 303 extends from the first surface 302a to the second surface 302b.

[0094] Subsequently, a deep trench is formed in each isolation region II, and the deep trench penetrates the first substrate 302 along the normal direction of the surface of the first substrate 302. The deep trench includes a first trench region and a second trench region. The distance from the first trench region to the first surface 302a is smaller than the distance from the second trench region to the first surface 302a, and the first trench region has a first projection on the surface of the first substrate 302, and the second trench region has a second projection on the surface of the first substrate 302, and the second projection is located within the range of the first projection.

[0095] In this embodiment, the method for forming the deep trench is as follows. Figure 11 to Figure 12 .

[0096] Please refer to Fig.11 , the isolation region ii is etched from the first surface 302a to form a first trench region 304a.

[0097] In this embodiment, before forming the deep trench, a second substrate 301 is provided, and the second substrate 301 has a logic circuit (not shown in the figure); a bonding layer 300 is formed on the surface of the second substrate 301; the first surface 302a is facing the surface of the bonding layer 300, so that the first substrate 302 and the second substrate 301 are bonded.

[0098] In this embodiment, the first trench region 304 a is formed before the bonding process.

[0099] Please refer to Fig.12 , the isolation region ii is etched from the second surface 302b until it is connected with the first trench region 304a, thereby forming a second trench region 304b.

[0100] Here, the first trench region 304a and the second trench region 304b are deep trenches, and the deep trenches are formed twice, which reduces the etching morphology problem caused by the large trench depth-width ratio, is conducive to forming a better deep trench morphology, and thus improves the quality of the isolation structure.

[0101] In this embodiment, the second trench region 304 b is formed after the bonding process.

[0102] In this embodiment, before forming the deep groove, a plurality of photosensitive regions i are etched from the second surface 302b toward the first surface 302a, and a plurality of openings 305 arranged in an array are formed in each photosensitive region i. The plurality of openings 305 are recessed from the second surface 302b toward the first surface 302a, the top width of each opening 305 is greater than the bottom width, and the angle between the sidewall of each opening 305 and the second surface 302b is an obtuse angle. Specifically, after the bonding process and before forming the second groove region 304b, the plurality of openings 305 are formed.

[0103] Please refer to Fig.13 , an isolation structure is formed in each deep trench, and the isolation structure includes a reflective layer 306.

[0104] At this point, since the projection of the second groove area 304b on the surface of the first substrate 302 is located within the projection range of the first groove area 304a on the surface of the first substrate 302, the isolation structure is in an "inverted T shape", and the isolation structure in the first groove area 304a is wider than the isolation structure in the second groove area 304b, thereby increasing the reflection area, so that part of the light incident into the first substrate 302 is reflected to the effective photosensitive area i through the isolation structure in the second groove area 304b, increasing the number of refractions of light in the photosensitive area i, and improving the full absorption of incident photons, thereby improving the utilization rate of incident photons, reducing light transmission and reflection losses, and further improving photon detection efficiency.

[0105] In this embodiment, the material of the reflective layer 306 includes metal, and the metal includes aluminum. Metal aluminum has a high filling capacity, and forms an "aluminum mirror" in the deep groove, which improves the light reflection ability of the isolation structure and helps to reduce the optical crosstalk caused by photons generated by carrier radiation recombination in the photodiode to adjacent pixel units.

[0106] In this embodiment, the isolation structure further includes a dielectric structure, and the reflective layer 306 is located on the surface of the dielectric structure.

[0107] In this embodiment, the dielectric structure includes a first dielectric layer 307 and a second dielectric layer 308 located on the surface of the first dielectric layer 307 .

[0108] In this embodiment, the first dielectric layer 307 and the second dielectric layer 308 are also located on the surface of the second surface 302b and the opening 305 (eg Fig.12 shown).

[0109] In this embodiment, the first dielectric layer 307 has a first refractive index, the second dielectric layer 308 has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive region i has a third refractive index, and the third refractive index is greater than the first refractive index. Since the third refractive index is greater than the first refractive index, and the first refractive index is greater than the second refractive index, the photosensitive region forms a planar dielectric optical waveguide structure, which is conducive to achieving total internal reflection of photons in a single pixel region (photosensitive region i), thereby improving the photon detection efficiency.

[0110] The material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon oxycarbon, silicon nitride oxide, aluminum oxide, aluminum nitride, silicon carbide nitride, and silicon oxycarbon nitride. In this embodiment, the material of the first dielectric layer 307 is silicon oxide, and the material of the second dielectric layer 308 is silicon oxynitride. The refractive index of silicon oxide is about 1.6, and a silicon oxynitride material with a suitable refractive index can be obtained by controlling the nitrogen content.

[0111] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A semiconductor structure, characterized in that: include: A first substrate, the first substrate comprising a plurality of mutually discrete photosensitive regions and an isolation region between adjacent photosensitive regions, the first substrate comprising a first surface and a second surface opposite to each other, the second surface being used as an incident surface for light; a deep trench located in each of the isolation regions, the deep trench penetrating the first substrate along a normal direction of the first substrate surface, the deep trench comprising a first trench region and a second trench region, the distance between the first trench region and the first surface is smaller than the distance between the second trench region and the first surface, the first trench region has a first projection on the first substrate surface, the second trench region has a second projection on the first substrate surface, and the second projection is within the range of the first projection; An isolation structure is located in each of the deep trenches, and the isolation structure includes a reflective layer.

2. The semiconductor structure according to claim 1, wherein: The isolation structure also includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure; the material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon oxycarbide, silicon oxynitride, aluminum oxide, aluminum nitride, silicon carbide nitride and silicon oxycarbon nitride.

3. The semiconductor structure according to claim 2, wherein: The medium structure includes a first medium layer and a second medium layer located on the surface of the first medium layer; the first medium layer has a first refractive index, the second medium layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index.

4. The semiconductor structure according to claim 1, wherein: The material of the light reflecting layer includes metal, and the metal includes aluminum.

5. The semiconductor structure according to claim 1, wherein: Also includes: A plurality of openings arranged in an array are located in each of the photosensitive areas, and the plurality of openings are recessed from the second surface toward the first surface. The top width of each opening is greater than the bottom width, and the side wall of each opening forms an obtuse angle relative to the second surface.

6. The semiconductor structure according to claim 1, wherein: Also includes: A second substrate is located on the first surface, and a logic circuit is provided in the second substrate.

7. The semiconductor structure according to claim 1, wherein: A diode region is defined in the photosensitive region, and the diode region extends from the first surface to the second surface.

8. The semiconductor structure according to claim 1, wherein: Also includes: A first doping region and a second doping region contacting each other in each of the isolation regions, the first surface exposes the surface of the first doping region, the second surface exposes the surface of the second doping region, and the doping ion concentration in the first doping region is greater than the doping ion concentration in the second doping region; the first trench region runs through the first doping region, and the second trench region runs through the second doping region; the conductivity type of the first doping region and the second doping region is the same as the conductivity type of the first substrate; taking the doping ion concentration in the first substrate as a reference value, the doping ion concentrations in the first doping region and the second doping region are both greater than 100 times the reference value and lower than 1E13atom / cm 3 .

9. A method for forming a semiconductor structure, characterized in that: include: Providing a first substrate, the first substrate comprising a plurality of mutually discrete photosensitive regions and an isolation region located between adjacent photosensitive regions, the first substrate comprising a first surface and a second surface opposite to each other; A deep trench is formed in each of the isolation regions, wherein the deep trench penetrates the first substrate along a normal direction of the surface of the first substrate, the deep trench comprises a first trench region and a second trench region, the distance between the first trench region and the first surface is smaller than the distance between the second trench region and the first surface, and the first trench region has a first projection on the surface of the first substrate, and the second trench region has a second projection on the surface of the first substrate, and the second projection is located within the range of the first projection; An isolation structure is formed in each of the deep trenches, wherein the isolation structure comprises a light reflecting layer.

10. The method for forming a semiconductor structure according to claim 9, wherein: The method for forming the deep trench comprises: injecting doping ions into the isolation region from the second surface to form a first doping region and a second doping region in contact with the first doping region in the isolation region, the first surface exposes the surface of the first doping region, the second surface exposes the surface of the second doping region, and the doping ion concentration of the first doping region is greater than the doping ion concentration of the second doping region; etching the isolation region and making the etching rate of the second doping region lower than the etching rate of the first doping region to form the deep trench, the first trench region is located in the first doping region, and the second trench region is located in the second doping region.

11. The method for forming a semiconductor structure according to claim 10, wherein: Before forming the deep trench, the method further includes: providing a second substrate having a logic circuit therein; forming a bonding layer on a surface of the second substrate; and bonding the first substrate to the second substrate by facing the first surface toward a surface of the bonding layer.

12. The method for forming a semiconductor structure according to claim 11, wherein: The method of etching the isolation region further includes: etching the isolation region from the second surface until the surface of the bonding layer is exposed.

13. The method for forming a semiconductor structure according to claim 10, wherein: The conductivity type of the doped ions is the same as the conductivity type of the first substrate; taking the doped ion concentration in the first substrate as a reference value, the concentration of the doped ions is greater than 100 times the reference value and is lower than 1E13atom / cm 3 .

14. The method for forming a semiconductor structure according to claim 9, wherein: The method for forming the deep trench comprises: etching the isolation region from the first surface to form the first trench region; etching the isolation region from the second surface until it is connected with the first trench region to form the second trench region.

15. The method for forming a semiconductor structure according to claim 14, wherein: Before forming the deep trench, it also includes: providing a second substrate, wherein the second substrate has a logic circuit; forming a bonding layer on the surface of the second substrate; facing the first surface toward the surface of the bonding layer to bond the first substrate and the second substrate; the first trench area is formed before the bonding process, and the second trench area is formed after the bonding process.

16. The method for forming a semiconductor structure according to claim 9, wherein: The method for forming the isolation structure comprises: forming a reflective material layer on the surface of the second surface and in the plurality of deep grooves, wherein the reflective material layer fills the deep grooves; and planarizing the reflective material layer until the surface of the second surface is exposed.

17. The method for forming a semiconductor structure according to claim 16, wherein: The isolation structure also includes a dielectric structure, and the reflective layer is located on the surface of the dielectric structure; the material of the dielectric structure includes a dielectric material, and the dielectric material includes a combination of one or more of silicon oxide, silicon nitride, silicon carbide, silicon oxycarbide, silicon oxynitride, aluminum oxide, aluminum nitride, silicon carbide nitride and silicon oxycarbon nitride; the material of the reflective layer includes a metal, and the metal includes aluminum.

18. The method for forming a semiconductor structure according to claim 17, wherein: The medium structure includes a first medium layer and a second medium layer located on the surface of the first medium layer; the first medium layer has a first refractive index, the second medium layer has a second refractive index, and the first refractive index is greater than the second refractive index; the photosensitive area has a third refractive index, and the third refractive index is greater than the first refractive index.

19. The method for forming a semiconductor structure according to claim 18, wherein: The method for forming the isolation structure comprises: forming the dielectric structure in a plurality of the deep grooves before the reflective material layer; and forming the reflective material layer on the surface of the dielectric structure.

20. The method for forming a semiconductor structure according to claim 9, wherein: The photosensitive area has a diode region, and the diode region extends from the first surface to the second surface; the first groove region has a first depth value, and the edge of the doped region in the diode region has a second depth value from the first surface, and the first depth value is smaller than the second depth value.

Images