CN109192741B - Method for forming back side illumination type image sensor - Google Patents
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- CN109192741B CN109192741B CN201810965371.1A CN201810965371A CN109192741B CN 109192741 B CN109192741 B CN 109192741B CN 201810965371 A CN201810965371 A CN 201810965371A CN 109192741 B CN109192741 B CN 109192741B
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- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
- H01L27/14689—MOS based technologies
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Abstract
A method of forming a backside illuminated image sensor, comprising: the semiconductor substrate comprises a first side and a second side opposite to the first side; etching the semiconductor substrate on the first side, and forming a plurality of grooves in the semiconductor substrate on the first side; forming a boron-containing silicon glass layer in the groove, wherein the surface of the boron-containing silicon glass layer is lower than the surface of the semiconductor substrate on the first side; annealing process is carried out, so that boron ions in the boron-containing silicon glass layer are diffused into the semiconductor substrate between the adjacent grooves to form a doping stop layer; filling an isolation material in the trench to form a deep trench isolation structure; forming a pixel of an image sensor on a semiconductor substrate of a first side, the pixel sensing light incident from a second side; thinning the semiconductor substrate from the second side of the semiconductor substrate by taking the doped stop layer and the boron-containing silicon glass layer as stop layers; and removing the doping stop layer and the boron-containing silicate glass layer by wet etching. The method has simple process.
Description
Technical Field
The present invention relates to an image sensor, and more particularly, to a method of forming a backside illuminated image sensor.
Background
Semiconductor image sensors are used to sense radiation such as light. Complementary Metal Oxide Semiconductor (CMOS) image sensors (CIS) and Charge Coupled Device (CCD) sensors are widely used in still digital cameras, camera phones, digital video cameras, medical image pickup devices (e.g., gastroscopes), and vehicle image pickup devices. These devices utilize an array of pixels (which may include photodiodes (photosensitive regions) and transistors) in the substrate to absorb radiation directed toward the substrate and convert the sensed radiation into electrical signals.
A backside illuminated (BSI) image sensing device is one type of image sensing device. Backside illuminated (BSI) image sensing devices may be used to detect light from the backside of a substrate. BSI image sensing devices have better performance, especially in low light conditions, than front-illuminated (FSI) image sensing devices. However, the conventional manufacturing process of a backside illuminated (BSI) image sensor device includes: forming an epitaxial silicon layer on a semiconductor substrate; then manufacturing a photosensitive area in the epitaxial silicon layer; manufacturing an interconnection structure on a semiconductor substrate; then thinning the semiconductor substrate to expose the epitaxial layer; and forming a filter layer and a micro lens on the back of the epitaxial layer.
The conventional back-illuminated image sensing device needs to be additionally provided with an epitaxial silicon layer, so that the manufacturing cost of the back-illuminated image sensing device is high, and the process is complex.
Disclosure of Invention
The invention solves the problem of reducing the manufacturing cost of the back-illuminated image sensing device and simplifying the process.
To solve the above problems, the present invention provides a method of forming a backside illuminated image sensor, comprising:
providing a semiconductor substrate, wherein the semiconductor substrate comprises a first side and a second side opposite to the first side;
etching the semiconductor substrate on the first side, and forming a plurality of grooves in the semiconductor substrate on the first side;
forming a boron-containing silicon glass layer in the groove, wherein the boron-containing silicon glass layer covers part of the side wall of the groove, and the surface of the boron-containing silicon glass layer is lower than the surface of the semiconductor substrate on the first side;
annealing process is carried out, so that boron ions in the boron-containing silicon glass layer are diffused into the semiconductor substrate between the adjacent grooves to form a doping stop layer;
filling an isolation material in the trench to form a deep trench isolation structure;
forming pixels of an image sensor on the semiconductor substrate at the first side between the deep trench isolation structures, the pixels sensing light incident from the second side;
thinning the semiconductor substrate from the second side of the semiconductor substrate by taking the doped stop layer and the boron-containing silicon glass layer as stop layers;
and removing the doping stop layer and the boron-containing silicate glass layer by wet etching.
Optionally, the forming process of the boron-containing silicon glass layer is as follows: filling a boron-containing silicon glass material layer in the groove; and etching to remove part of the boron-containing silicate glass material layer in part of the thickness, and forming a boron-containing silicate glass layer in the groove, wherein the boron-containing silicate glass layer covers part of the side wall of the groove, and the surface of the boron-containing silicate glass layer is lower than the surface of the semiconductor substrate on the first side.
Optionally, the annealing temperature is 800-.
Optionally, the process of thinning the semiconductor substrate from the second side of the semiconductor substrate includes: removing the semiconductor substrate with the thickness of the second side part by adopting a chemical mechanical polishing process; and continuously etching the semiconductor substrate after the chemical mechanical grinding process by adopting a wet etching process, and taking the doped stop layer and the boron-containing silicon glass layer as etching stop layers.
Optionally, HNO is used as the etching solution when the wet etching process is used to continuously etch the semiconductor substrate after the chemical mechanical polishing process3And a mixed solution of HF.
Optionally, the etching solution used for removing the doping stop layer and the boron-containing silicate glass layer by wet etching is HF and HNO3、CH3Mixed solution of COOH.
Optionally, the depth of the trench is 4-6 microns, and the distance between the surface of the boron-containing silicon glass layer and the surface of the semiconductor substrate on the first side is 2-4 microns.
Optionally, the pixel includes a photosensitive region in the semiconductor substrate between the deep trench isolation structures, the photosensitive region being formed by ion implantation.
Optionally, the method further includes: after forming the photosensitive area, forming a dielectric layer and an interconnection structure positioned in the dielectric layer on the surface of the semiconductor substrate on the first side; bonding a support substrate on the surface of the dielectric layer; thinning the semiconductor substrate from the second side of the semiconductor substrate after forming the support substrate; and after removing the doping stop layer and the boron-containing silicate glass layer by wet etching, forming a color filter layer on the surface of the semiconductor substrate on the second side.
Compared with the prior art, the technical scheme of the invention has the following advantages:
in the process of forming the back-illuminated image sensor, an epitaxial silicon layer does not need to be additionally formed, so that the manufacturing cost of the back-illuminated image sensor is reduced;
in addition, by forming the doping stop layer, the thinning stop position can be accurately controlled in the process of thinning the semiconductor substrate, and a device (photosensitive area) formed in the semiconductor substrate cannot be damaged;
in addition, according to the scheme of the invention, the grooves are formed firstly, then the boron-containing silicon glass layer is formed at the bottom of the grooves, and then boron ions in the boron-containing silicon glass layer are diffused into the semiconductor substrate between the adjacent grooves through the annealing process to form the doping stop layer, so that the scheme of the doping stop layer is compatible with the process for forming the deep groove isolation structure, the semiconductor substrate is not damaged when the doping stop layer is formed, the position precision of the formed doping stop layer is higher, and the concentration distribution of impurity ions is more uniform.
Drawings
Fig. 1-11 are schematic structural views illustrating a process of forming a backside illuminated image sensor according to an embodiment of the present invention.
Detailed Description
As background art, backside illuminated (BSI) image sensors are expensive and complex to fabricate.
Therefore, the invention provides a method for forming a back-illuminated image sensor, which does not need to additionally form an epitaxial silicon layer in the process of forming the back-illuminated image sensor and reduces the manufacturing cost of the back-illuminated image sensor.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In describing the embodiments of the present invention in detail, the drawings are not to be considered as being enlarged partially in accordance with the general scale, and the drawings are only examples, which should not be construed as limiting the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
Fig. 1-11 are schematic structural views illustrating a process of forming a backside illuminated image sensor according to an embodiment of the present invention.
Referring to fig. 1, a semiconductor substrate 201 is provided, the semiconductor substrate 201 comprising a first side 21 and a second side 22 opposite the first side 21.
The semiconductor substrate 201 material can be silicon (Si), germanium (Ge), or silicon germanium (GeSi), silicon carbide (SiC); or silicon-on-insulator (SOI), germanium-on-insulator (GOI); or may be other materials such as group iii-v compounds such as gallium arsenide. In this embodiment, the material of the semiconductor substrate 201 is silicon (Si).
A photosensitive region of a back-illuminated image sensor is subsequently formed in the semiconductor substrate 201 of the first side 201.
Referring to fig. 2, the semiconductor substrate 201 of the first side 21 is etched, and a number of trenches 202 are formed in the semiconductor substrate 201 of the first side 21.
Before etching the semiconductor substrate 201, a patterned mask layer (not shown in the figure) is formed on the semiconductor substrate 201 on the first side 21, the patterned mask layer is used as a mask when etching the semiconductor substrate 201 on the first side 21, the patterned mask layer has a plurality of openings exposing the surface of the semiconductor substrate 201 on the first side 21, and the positions and the number of the openings correspond to the number and the positions of the subsequently formed trenches 202.
The patterned mask layer may be a single-layer or multi-layer stacked structure, and the material of the patterned mask layer is one or more of a hard mask material (such as silicon nitride, silicon oxide), a metal nitride (such as titanium nitride or tantalum nitride), or a photoresist material.
A deep trench isolation structure is subsequently formed in the trench 202 to isolate adjacent photosensitive regions, and the trench 202 serves as a window for subsequently forming a doping stop layer, so as to control the formation position of the doping stop layer and reduce the process difficulty of the doping stop layer, thereby facilitating the formation of the doping stop layer.
The trench 202 is formed by an etching process, which may be a plasma etching process or a bosch etching process, and the etching process uses HBr and Cl as gases2、O2、SF6One or more of them.
In this embodiment, the depth of the formed trench 202 is 4 to 6 μm.
Referring to fig. 3 and 4, a boron-containing silicon glass layer 204 is formed in the trench 202 (refer to fig. 2), the boron-containing silicon glass layer 204 covers a portion of the sidewall of the trench 202 and the surface of the boron-containing silicon glass 204 is lower than the surface of the semiconductor substrate 201 of the first side 21.
The forming process of the boron-containing silicon glass layer 204 is as follows: filling the trench 202 (refer to fig. 2) with a boron-containing silicon glass material layer 203; and etching to remove part of the thickness of the boron-containing silicate glass material layer 203, and forming a boron-containing silicate glass layer 204 in the trench 202, wherein the boron-containing silicate glass layer 204 covers part of the side wall of the trench 202, and the surface of the boron-containing silicate glass layer 204 is lower than the surface of the semiconductor substrate 201 on the first side 21.
In an embodiment, the forming process of the boron-containing silicate glass material layer 203 is a spin coating process, and it should be noted that the boron-containing silicate glass material layer 203 covers the surface of the semiconductor substrate on the first side 21 in addition to filling the trench 202.
The etching process for removing a part of the thickness of the boron-containing silicate glass material layer 203 may be a dry etching process or a wet etching process, in this embodiment, a plasma etching process is used to etch and remove a part of the thickness of the boron-containing silicate glass material layer 203, and the etching gas used in the plasma etching process includes CF4。
In this embodiment, the distance between the surface of the boron-containing silicate glass layer 204 and the surface of the substrate on the first side is 2 to 4 μm, so that during subsequent annealing, it can be ensured that a sufficient thickness of the semiconductor substrate is provided above the formed doping stop layer to form a photosensitive region of the image sensor.
The purpose of forming the boron-containing silicon glass layer 204 in this application is that upon subsequent annealing, boron ions in the boron-containing silicon glass layer 204 can diffuse into the semiconductor substrate 201 in contact with the boron-containing silicon glass layer 204, thereby forming a diffusion stop layer in the semiconductor substrate 201 adjacent to the trench 202.
Referring to fig. 5, an annealing process is performed to diffuse boron ions in the boron-containing silicon glass layer 204 into the semiconductor substrate 201 between adjacent trenches 202 to form a doping stop layer 205.
When annealing is performed, boron ions in the boron-containing silicon glass layer 204 laterally diffuse into the semiconductor substrate 201 between adjacent trenches 202, forming a doping stop layer 205 having a continuous boron ion distribution in the semiconductor substrate 201.
In this embodiment, the distance between the surface of the formed doping stop layer 205 and the surface of the semiconductor substrate on the first side is 2 to 4 micrometers.
According to the scheme of the invention, the trenches 202 are formed first, then the boron-containing silicon glass layer 204 is formed at the bottoms of the trenches 202, and then boron ions in the boron-containing silicon glass layer 204 are diffused into the semiconductor substrate 201 between the adjacent trenches 202 through the annealing process to form the doping stop layer 205, so that the scheme of the doping stop layer 205 is compatible with the process for forming the deep trench isolation structure 206 (refer to the subsequent figure 6), the semiconductor substrate 201 is not damaged when the doping stop layer 205 is formed, the position precision of the formed doping stop layer 205 is high, and the concentration distribution of impurity ions is uniform.
In one embodiment, the annealing process is furnace annealing at 800-.
Referring to fig. 6, the trench 202 (see fig. 5) is filled with an isolation material to form a deep trench isolation structure 206.
The deep trench isolation structures 206 are used for isolation between active regions, and the semiconductor substrate 201 between adjacent deep trench isolation structures 206 is used as an active region and is subsequently used for forming a pixel structure of the back-illuminated image sensor.
The material of the deep trench isolation structure 206 can be nitride, oxide, oxynitride or other suitable material, and the deep trench isolation structure 206 can be a single-layer or multi-layer stacked structure (e.g., a double-layer stacked structure). In one embodiment, the method of forming the deep trench isolation structure 206 includes: forming an isolation material layer filling the trench 202 and covering the surface of the semiconductor substrate 201 on the first side 21; the layer of isolation material is planarized until the surface of the semiconductor substrate 201 on the first side is exposed, forming a deep trench isolation structure 206 in the trench 202.
After forming the deep trench isolation structures 206, well regions may be formed in the semiconductor substrate 201 above the doping stop layer 205 between the deep trench isolation structures 206, the well regions being formed by ion implantation.
Referring to fig. 7, pixels of the image sensor are formed on the semiconductor substrate 201 of the first side 21 between the deep trench isolation structures 206, the pixels sensing light incident from the second side 22.
The pixel at least comprises a photosensitive area 207 which is positioned in the semiconductor substrate 201 between the deep trench isolation structures 206, the photosensitive area 207 senses light incident from the second side 22 to generate photo-generated carriers, the photosensitive area 207 is formed by ion implantation, the doping type of the photosensitive area 207 is opposite to that of the semiconductor substrate 201, a PN structure is formed between the photosensitive area 207 and the semiconductor substrate 201 to form a photodiode, for example, when the semiconductor substrate 201 is doped with P-type impurity ions, the photosensitive area 207 is doped with N-type impurity ions, or when the semiconductor substrate 201 is doped with N-type impurity ions, the photosensitive area 207 is doped with P-type impurity ions. The number of the photosensitive regions 207 is several, and the plurality of photosensitive regions 207 are arranged in rows and columns, and only three photosensitive regions 207 are illustrated as an example in fig. 1.
In one embodiment, a pixel typically includes one photodiode and 3 or 4 MOS transistors, referred to as 3T-type or 4T-type. Most of the CMOS image sensors on the market today are of the 4T type, and the 4T type image sensor includes: 4 MOS transistors and 1 photodiode PD, the said 4 MOS transistors are reset transistor, amplifying transistor, selection transistor and transmission transistor respectively. The working principle of the pixel unit of the 4T-type image sensor is as follows: firstly, before receiving illumination, a reset transistor and a transmission transistor are conducted, other transistors are turned off, and a floating diffusion region and a photodiode are reset; then, all transistors are turned off, and the photodiode receives illumination and performs photoelectric conversion to form a photogenerated carrier; then the transmission transistor is switched on, other transistors are switched off, and the photon-generated carriers are transferred to the floating diffusion region from the photodiode; and then, the amplifying transistor and the selecting transistor are conducted, and photo-generated carriers are sequentially output from the floating diffusion region through the amplifying transistor and the selecting transistor, so that the collection and transmission of optical signals are completed. In fig. 7, only the gate structure 220 of the transfer transistor is shown as an illustration, the gate structure 220 includes a gate dielectric layer on the surface of the semiconductor substrate on the first side 21 and a gate electrode on the gate dielectric layer, and in an embodiment, the gate structure 220 may be formed on the surface of the semiconductor substrate on the first side through deposition and etching processes (gates of the reset transistor, the amplifying transistor and the select transistor may also be formed simultaneously), then the photosensitive region 207 is formed on one side of the gate structure 220, and a floating diffusion region is formed on the other side of the gate structure 220 (not shown in the figure, source and drain regions corresponding to the reset transistor, the amplifying transistor and the select transistor may also be formed simultaneously).
With continued reference to fig. 7, a dielectric layer 208 may also be formed on the surface of the semiconductor substrate 201 on the first side, and an interconnect structure 209 is formed in the dielectric layer 208. The dielectric layer 208 may be a single-layer or multi-layer stacked structure, the material of the dielectric layer 208 may be silicon oxide, a low-k or ultra-low-k dielectric material, the interconnect structure 209 is used to connect devices formed on the semiconductor substrate 201 on the first side, such as a gate of a select transistor, a floating diffusion region, a reset transistor, an amplifying transistor, a gate of a select transistor, a source drain region, and the like, and the interconnect structure 209 may include a plug, a metal interconnect line, or a damascene structure.
A supporting substrate 210 is further bonded to the surface of the dielectric layer 208, and the supporting substrate 210 is suitable for protecting devices and structures formed on the first side of the semiconductor substrate 201 and is used as a support when devices are manufactured on the second side of the semiconductor substrate 201.
After the support substrate 210 is formed, the second side of the semiconductor substrate 201 is thinned, and the semiconductor substrate is removed by a part of the thickness.
Referring to fig. 8 and 9, the semiconductor substrate is thinned from the second side 22 of the semiconductor substrate 201 with the doped stop layer 205 and the boron-containing silicon glass layer 204 as stop layers.
The process of thinning the semiconductor substrate from the second side 22 of the semiconductor substrate 201 comprises: removing the semiconductor substrate 201 with the partial thickness of the second side 22 by adopting a chemical mechanical polishing process; and continuously etching the semiconductor substrate 201 after the chemical mechanical polishing process by adopting a wet etching process, wherein the doped stop layer 205 and the boron-containing silicate glass layer 204 are used as etching stop layers.
The HNO solution is used as the etching solution when the wet etching process is adopted to continuously etch the semiconductor substrate 201 after the chemical mechanical polishing process3And HF mixed solution, due to the existence of the doping stop layer 205 and the boron-containing silicate glass layer 204, when wet etching is carried out by adopting the mixed solution, the semiconductor substrate material has high etching selectivity ratio relative to the doping stop layer 205 and the boron-containing silicate glass layer 204, so that the etching stop position can be accurately controlled during etching, and the etching can be accurately stopped when the doping is stoppedA stop layer 205 and a boron-containing silicon glass layer 204.
Referring to fig. 9 and 10, the doped stop layer 205 and the boron-containing silicon glass layer 204 are removed by wet etching.
The etching solution adopted for removing the doping stop layer 205 and the boron-containing silicate glass layer 204 by wet etching is HF and HNO3、CH3When the mixed solution of COOH is used for wet etching, since the doping stop layer 205 and the boron-containing silicate glass layer 204 have a high etching selectivity relative to the semiconductor substrate material at the bottom, the etching stop position can be precisely controlled when the doping stop layer 205 and the boron-containing silicate glass layer 204 are removed, and thus, etching damage to a photosensitive region and the like formed in the semiconductor substrate at the bottom is avoided.
Referring to fig. 11, after the doping stop layer 205 and the boron-containing silicate glass layer 204 (refer to fig. 9) are removed by wet etching, a color filter layer 212 is formed on the surface of the semiconductor substrate 201 of the second side 22.
A color filter layer 212 is correspondingly formed above each photosensitive area 207, and the color filter layer 212 may be one of a red color filter layer, a green color filter layer, and a blue color filter layer. Before forming the color filter layer 212, an isolation dielectric layer 211 may also be formed on the surface of the semiconductor substrate 201 on the second side 22.
After the color filter layer 212 is formed, the microlenses 213 are formed on the color filter layer 212.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A method of forming a backside illuminated image sensor, comprising:
providing a semiconductor substrate, wherein the semiconductor substrate comprises a first side and a second side opposite to the first side;
etching the semiconductor substrate on the first side, and forming a plurality of grooves in the semiconductor substrate on the first side;
forming a boron-containing silicon glass layer in the groove, wherein the boron-containing silicon glass layer covers part of the side wall of the groove, and the surface of the boron-containing silicon glass layer is lower than the surface of the semiconductor substrate on the first side;
annealing process is carried out, so that boron ions in the boron-containing silicon glass layer are diffused into the semiconductor substrate between the adjacent grooves to form a doping stop layer;
filling an isolation material in the trench to form a deep trench isolation structure;
forming pixels of an image sensor on the semiconductor substrate at the first side between the deep trench isolation structures, the pixels sensing light incident from the second side;
thinning the semiconductor substrate from the second side of the semiconductor substrate by taking the doped stop layer and the boron-containing silicon glass layer as stop layers;
and removing the doping stop layer and the boron-containing silicate glass layer by wet etching.
2. The method of forming a backside illuminated image sensor of claim 1, wherein the boron-containing silicon glass layer is formed by: filling a boron-containing silicon glass material layer in the groove; and etching to remove part of the boron-containing silicate glass material layer in part of the thickness, and forming a boron-containing silicate glass layer in the groove, wherein the boron-containing silicate glass layer covers part of the side wall of the groove, and the surface of the boron-containing silicate glass layer is lower than the surface of the semiconductor substrate on the first side.
3. The method as claimed in claim 1, wherein the annealing temperature in the annealing process is 800-950 ℃ for 0.5-2 hours.
4. The method of forming a back-illuminated image sensor as claimed in claim 1, wherein the process of thinning the semiconductor substrate from the second side of the semiconductor substrate comprises: removing the semiconductor substrate with the thickness of the second side part by adopting a chemical mechanical polishing process; and continuously etching the semiconductor substrate after the chemical mechanical grinding process by adopting a wet etching process, and taking the doped stop layer and the boron-containing silicon glass layer as etching stop layers.
5. The method of claim 4, wherein the HNO is used as an etching solution in the step of continuously etching the semiconductor substrate after the CMP process by using a wet etching process3And a mixed solution of HF.
6. The method of claim 1, wherein the etching solution used for wet etching to remove the doped stop layer and the boron-containing silicate glass layer is HF, HNO3、CH3Mixed solution of COOH.
7. The method of claim 1, wherein the trench has a depth of 4 to 6 microns and the distance between the surface of the boron-containing silicon glass layer and the surface of the first side semiconductor substrate is 2 to 4 microns.
8. The method of forming a back-illuminated image sensor of claim 1, wherein the pixel comprises a photosensitive region in the semiconductor substrate between the deep trench isolation structures, the photosensitive region formed by ion implantation.
9. The method of forming a back-illuminated image sensor of claim 8, further comprising: after forming the photosensitive area, forming a dielectric layer and an interconnection structure positioned in the dielectric layer on the surface of the semiconductor substrate on the first side; bonding a support substrate on the surface of the dielectric layer; thinning the semiconductor substrate from the second side of the semiconductor substrate after forming the support substrate; and after removing the doping stop layer and the boron-containing silicate glass layer by wet etching, forming a color filter layer on the surface of the semiconductor substrate on the second side.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810965371.1A CN109192741B (en) | 2018-08-23 | 2018-08-23 | Method for forming back side illumination type image sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201810965371.1A CN109192741B (en) | 2018-08-23 | 2018-08-23 | Method for forming back side illumination type image sensor |
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