US20190088705A1 - Backside illuminated image sensor with self-aligned metal pad structures - Google Patents
Backside illuminated image sensor with self-aligned metal pad structures Download PDFInfo
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- US20190088705A1 US20190088705A1 US15/707,940 US201715707940A US2019088705A1 US 20190088705 A1 US20190088705 A1 US 20190088705A1 US 201715707940 A US201715707940 A US 201715707940A US 2019088705 A1 US2019088705 A1 US 2019088705A1
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- H—ELECTRICITY
- 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
- H01L27/14601—Structural or functional details thereof
- H01L27/14636—Interconnect structures
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- H—ELECTRICITY
- 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
- H01L27/14601—Structural or functional details thereof
- H01L27/1463—Pixel isolation structures
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- H—ELECTRICITY
- 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
- H01L27/14601—Structural or functional details thereof
- H01L27/1464—Back illuminated imager structures
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- H—ELECTRICITY
- 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
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- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
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- H—ELECTRICITY
- 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
- H01L27/14687—Wafer level processing
Definitions
- Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as medical, automobile, and other applications.
- the device architecture of image sensors has continued to advance at a great pace due to increasing demands for higher resolution, lower power consumption, increased dynamic range, etc. These demands have also encouraged the further miniaturization and integration of image sensors into these devices.
- FIG. 1A - FIG. 1D are cross sectional illustrations of an example image sensor, wherein each of the figures represents the example image sensor after a series of critical process steps are finished during fabrication of the example image sensor with a standard metal pad structure in FIG. 1D , in accordance with the teachings of the present invention.
- FIG. 3 is a block diagram schematically illustrating one example of an imaging system with self-aligned metal pad structures, in accordance with the teachings of the present invention.
- FIG. 4 illustrates one example process flow for fabricating an example image sensor with a self-aligned metal pad structure, in accordance with the teachings of the present invention.
- pixel array 305 is a two-dimensional (2D) array of photodiodes, or image sensor pixels (e.g., pixels P 1 , P 2 . . . , Pn).
- photodiodes are arranged into rows (e.g., rows R 1 to Ry) and columns (e.g., column C 1 to Cx) to acquire image data of a person, place, object, etc., which can then be used to render a 2D image of the person, place, object, etc.
- rows R 1 to Ry rows
- columns e.g., column C 1 to Cx
- the photodiodes do not have to be arranged into rows and columns and may take other configurations.
- readout circuitry 311 may include amplification circuitry, analog-to-digital conversion (ADC) circuitry, or otherwise.
- Function logic 315 may simply store the image data or even manipulate the image data by applying post image effects (e.g., crop, rotate, remove red eye, adjust brightness, adjust contrast, or otherwise).
- readout circuitry 311 may readout a row of image data at a time along readout column lines (illustrated) or may readout the image data using a variety of other techniques (not illustrated), such as a serial readout or a full parallel readout of all pixels simultaneously.
- control circuitry 321 is coupled to pixel array 305 to control operation of the plurality of photodiodes in pixel array 312 .
- control circuitry 321 may generate a shutter signal for controlling image acquisition.
- the shutter signal is a global shutter signal for simultaneously enabling all pixels within pixel array 312 to simultaneously capture their respective image data during a single acquisition window.
- the shutter signal is a rolling shutter signal such that each row, column, or group of pixels is sequentially enabled during consecutive acquisition windows.
- image acquisition is synchronized with lighting effects such as a flash.
- imaging system 300 may be included in a digital camera, cell phone, laptop computer, automobile or the like. Additionally, imaging system 300 may be coupled to other pieces of hardware such as a processor (general purpose or otherwise), memory elements, output (USB port, wireless transmitter, HDMI port, etc.), lighting/flash, electrical input (keyboard, touch display, track pad, mouse, microphone, etc.), and/or display. Other pieces of hardware may deliver instructions to imaging system 300 , extract image data from imaging system 300 , or manipulate image data supplied by imaging system 300 .
- a processor general purpose or otherwise
- memory elements such as a processor (general purpose or otherwise), memory elements, output (USB port, wireless transmitter, HDMI port, etc.), lighting/flash, electrical input (keyboard, touch display, track pad, mouse, microphone, etc.), and/or display.
- Other pieces of hardware may deliver instructions to imaging system 300 , extract image data from imaging system 300 , or manipulate image data supplied by imaging system 300 .
- FIG. 1A - FIG. 1D are cross sectional illustrations of an example image sensor 100 , wherein each of the figures represents the example image sensor 100 after a series of critical process steps are finished during fabrication of the example image sensor 100 with a standard metal pad structure in FIG. 1D , in accordance with the teachings of the present invention.
- FIG. 1A - FIG. 1D are cross sectional illustrations of an example image sensor 100 , wherein each of the figures represents the example image sensor 100 after a series of critical process steps are finished during fabrication of the example image sensor 100 with a standard metal pad structure in FIG. 1D , in accordance with the teachings of the present invention.
- the same structure is defined with the same number in FIG. 1A - FIG. 1D .
- FIG. 1A illustrates a cross sectional view of the example image sensor 100 comprising a semiconductor material 102 having a front side 111 and a back side 109 opposite the font side 111 .
- a shallow trench isolation (STI) structure 103 which extends from the front side 111 of the semiconductor material 102 into the semiconductor material 102 .
- the STI structure 103 is used to electrically separate adjacent image sensors.
- the STI structure 103 is filled by at least one of dielectric materials such as silicon oxide or silicon nitride.
- the STI structure 103 may also comprise a negative charged material liner at an interface between the filled dielectric materials and the semiconductor material 102 (not illustrated in the figures).
- the negative charged material liner is used to form a P+ pinning layer at the interface between the filled dielectric materials and the semiconductor material 102 in order to reduce the dark current and white pixels.
- On the front side 111 of the semiconductor material 102 there are also a thin dielectric layer 104 , an interlayer dielectric material 105 and an inter-metal layer 106 .
- the thin dielectric layer 104 may be the gate oxide of the pixel transistors.
- the interlayer dielectric material 105 is disposed between the thin dielectric layer 104 and the inter-metal layer 106 .
- the metal interconnect 107 is made of at least one of metals comprising Cu and TiN.
- the interlayer dielectric material 105 , the dielectric layer 104 and the inter-metal layer 106 are made of at least one of dielectric materials comprising silicon oxide and silicon nitride. In one example, they are made of same dielectric materials. In another example, they are made of different dielectric materials.
- a buffer layer 101 is disposed on the back side 109 of the semiconductor material 102 in order to protect the back side 109 of the semiconductor material 102 .
- the buffer layer 101 comprises at least one of dielectric materials such as silicon oxide or silicon nitride.
- FIG. 1B illustrates a cross sectional view of the example image sensor 100 after a contact pad trench 108 is formed in the example image sensor 100 of FIG. 1A .
- the contact pad trench 108 extends from the back side 109 of the semiconductor material 102 into the semiconductor material 102 until lands on a first side 118 of the STI structure 103 , wherein the contact pad trench 108 is enclosed with the STI structure 103 .
- the contact pad trench 108 is formed by a first patterning process which comprises at least a first photolithography process followed by a first etch processes comprising at least one of a first anisotropic plasma etch and a first selective wet etch process.
- the first etch processes have significantly higher etch rate for the semiconductor material 102 compared to the dielectric materials in the STI structure 103 . Therefore, the first etch processes stop on the first side 118 of the STI structure 103 .
- the contact pad trench 108 extends from the buffer layer 101 into the semiconductor material 102 , wherein the buffer layer 101 is also selectively etched during the first patterning process to form the contact pad trench 108 .
- FIG. 1C illustrates a cross sectional view of the example image sensor 100 after a plurality of contact plugs 110 are formed in the example image sensor 100 of FIG. 1B .
- Each of the plurality of contact plugs 110 extends from the first side 118 of the STI structure 103 through the dielectric layer 104 , the interlayer dielectric material 105 and lands on the metal interconnect 107 at the interface 114 between the interlayer dielectric material 105 and the metal interconnect 107 .
- each of the plurality of contact plugs 110 is formed by a second patterning process which comprises at least a second photolithography process followed by at least one of a second anisotropic plasma dry etch and a second selective wet etch process.
- the second etch rates for the dielectric materials in the STI structures 103 , the interlayer dielectric material 105 and the dielectric layer 104 are significantly higher than the second etch rates for the conductive materials in the metal interconnect 107 . Therefore, the second etch processes stop at the interface 114 between the interlayer dielectric material 105 and the metal interconnect 107 . As a result, each of the plurality of contact plugs 110 lands on the metal interconnect 107 .
- FIG. 1D illustrates a cross sectional view of the example image sensor 100 after a contact pad 112 is formed in the example image sensor 100 of FIG. 1C .
- the contact pad 112 is disposed on the first side 118 of the STI structure 103 and coupled with the metal interconnect 107 by the plurality of contact plugs 110 .
- each of the plurality of the contact plugs 110 is filled by at least one of conductive materials comprising Al, W, Cu, and TiN, and the contact pad is made of the same conductive materials as ones in each of the plurality of the contact plugs 110 .
- the contact pad is made of different conductive materials from ones in each of the plurality of the contact plugs 110 .
- the conductive materials comprise at least one of Al, Cu, W, and TiN.
- the contact pad 112 and the air gap 113 are formed by a third patterning process which comprises at least a third photolithography process followed by at least one of a third anisotropic plasma dry etch and a third selective wet etch process.
- the third etch rates for the conductive materials in the contact pad 112 is significantly higher than the third etch rates for the dielectric materials in the STI structures 103 and the semiconductor material 102 . Therefore, the third etch processes stop at the first side 118 of the STI structure 103 and there is no undercut on sidewalls of the contact pad trench 108 .
- FIG. 2A - FIG. 2F are cross sectional illustrations of an example image sensor 200 , wherein each of the figures represents the example image sensor 200 after a series of critical process steps are finished during fabrication of the example image sensor 200 with a self-aligned metal pad structure in FIG. 2F , in accordance with the teachings of the present invention.
- FIG. 4 illustrates an example method 400 for forming the example image sensors with a self-aligned metal pad in FIG. 2A-2F , wherein each of the process blocks in FIG. 4 corresponds to one of the figures in FIG. 2A - FIG. 2F as described in the next paragraphs.
- method 400 should not be deemed limited. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of method 400 may be executed in a variety of orders not illustrated, or even in parallel. Furthermore, method 400 may omit certain process blocks in order to avoid obscuring certain aspects. Alternatively, method 400 may include additional process blocks that may not be necessary in some embodiments or examples of the disclosure.
- FIG. 2A illustrates a cross sectional view of the example image sensor 200 comprising a semiconductor material 102 after the corresponding process block 401 and partial process block 402 in FIG. 4 has been done.
- the semiconductor material 102 is provided, which has a front side 111 and a back side 109 opposite the front side 111 , wherein a plurality of first shallow trench isolation (STI) structures 201 a and a plurality of second STI structures 201 b are formed extending from the front side 111 of the semiconductor material 102 into the semiconductor material 102 , wherein each of the plurality of first STI structures 201 a is fully surrounded by adjacent first 201 a and second 201 b STI structures and each of the plurality of second STI structures 201 b is partially surrounded by adjacent first 201 a and second 201 b STI structures.
- STI shallow trench isolation
- the plurality of first STI structures 201 a and second STI structures 201 b are used to electrically separate adjacent image sensors.
- each of the plurality of first STI structures 201 a and second STI structures 201 b is filled by at least one of dielectric materials such as silicon oxide or silicon nitride.
- each of the plurality of first STI structures 201 a and second STI structures 201 b may also comprise a negative charged material liner at an interface between the filled dielectric materials in each of the plurality of first 201 a and second 201 b STI structures and the semiconductor material 102 (not illustrated in the figures).
- the negative charged material liner is used to form a P+ pinning layer at the interface so as to reduce the dark current and white pixels.
- a dielectric layer 104 may be disposed on the front side 111 of the semiconductor material 102 at the same process step as disposing the gate oxide of the pixel and periphery transistors.
- a poly layer 202 may also be disposed on the thin dielectric layer 104 at the same process step as disposing the poly gate of pixel and periphery transistors.
- a buffer layer 101 is disposed on the back side 109 of the semiconductor material 102 in order to protect the back side 109 of the semiconductor material 102 .
- the buffer layer 101 comprises at least one of dielectric materials such as silicon oxide or silicon nitride.
- FIG. 2B illustrates a cross sectional view of the example image sensor 200 after a plurality of open slots 203 are formed in the poly layer 202 in the example image sensor 200 of FIG. 2A .
- the corresponding process block is 402 in FIG. 4 .
- Each of the plurality of open slots 203 extends from a first side 220 of the poly layer 202 to the interface of the poly layer 202 and the dielectric layer 104 , wherein each of the plurality of open slots 203 aligns up with each of the plurality of first STI structures 201 a and has same two dimensional lateral dimensions as the aligned first STI structure 201 a .
- the plurality of open slots 203 and the poly gates of the pixel and periphery transistors are formed at the same time with the same patterning process and photo mask. Therefore, compared to the fabrication processes of the standard metal pad structure in FIG. 1A-1D , it does not require an additional patterning process step to form the plurality of open slots 203 .
- FIG. 2C illustrates a cross sectional view of the example image sensor 200 after an interlayer dielectric material 105 and an inter-metal layer 106 are disposed on the example image sensor 200 of FIG. 2B .
- the corresponding process block is 403 in FIG. 4 .
- the interlayer dielectric material 105 is disposed between the dielectric layer 104 and the inter-metal layer 106 .
- the dielectric layer 104 and the poly layer 202 are covered by the interlayer dielectric material 105 , wherein the plurality of open slots 203 are filled with the interlayer dielectric material 105 .
- the inter-metal layer 106 there is a metal interconnect 107 wherein the metal interconnect 107 is made of at least one of metals comprising Cu and TiN.
- the interlayer dielectric material 105 , the dielectric layer 104 and the inter-metal layer 106 are made of at least one of dielectric materials comprising silicon oxide and silicon nitride. In one example, they are made of same dielectric materials. In another example, they are made of different dielectric materials.
- FIG. 2D illustrates a cross sectional view of the example image sensor 200 after a contact pad trench 204 is formed in the example image sensor 200 of FIG. 2C .
- the corresponding process block is 404 in FIG. 4 .
- the contact pad trench 204 extends from the back side 109 of the semiconductor material 102 into the semiconductor material 102 until lands on a first side 218 of the plurality of first STI structure 201 a and second STI structure 201 b , wherein the sidewalls of the contact pad trench 204 land on the plurality of the second STI structures 201 b .
- the contact pad trench 204 is formed by a fourth patterning process which comprises at least a fourth photolithography process followed by at least one of a fourth anisotropic plasma etch and a fourth selective wet etch process.
- the fourth etch processes have significantly higher etch rate for the semiconductor material 102 compared to the dielectric materials in the plurality of the first STI structures 201 a and the second STI structures 201 b .
- the etch time is preciously monitored and controlled during the plasma dry etch and the selective wet etch processes in order to avoid over etch and under etch. As a result, the fourth etch processes stop on the first side 218 of the first STI structures 201 a and the second STI structures 201 b .
- the contact pad trench 204 extends from the buffer layer 101 into the semiconductor material 102 , wherein the buffer layer 101 is also selectively etched during the fourth patterning process to form the contact pad trench 204 .
- FIG. 2E illustrates a cross sectional view of the example image sensor 200 after a plurality of contact plugs 205 and at least one air gap 208 a are formed in the example image sensor 200 of FIG. 2D .
- the corresponding process block is 405 in FIG. 4 .
- Each of the plurality of contact plugs 205 extends from the first side 218 of the first 201 a and second 201 b STI structure through the dielectric layer 104 , the interlayer dielectric material 105 and lands on the metal interconnect 107 at the interface 114 between the interlayer dielectric material 105 and the metal interconnect 107 .
- the portion of the dielectric layer 104 and the portion of the interlayer dielectric material 105 are self-aligned with the STI structures, wherein the portions 206 of the semiconductor material 102 are used as a hard mask during the selective etch processes.
- the selective plasma dry etch and the selective wet etch processes have significantly higher etch rates for the dielectric materials in the STI structures 201 a and 201 b , the dielectric layer 104 and the interlayer dielectric material 105 , than the etch rates for the conductive materials in the metal interconnect 107 and the semiconductor materials in the portions 206 of the semiconductor material 102 and the poly layer 202 .
- the selective etch processes automatically slow down greatly at the interface 114 between the interlayer dielectric material 105 and the metal interconnect 107 so as to form the plurality of contact plugs 205 , wherein each of the plurality of contact plugs 205 lands on the metal interconnect 107 .
- the selective etch processes also automatically slow down greatly at the interface between the poly layer 202 and the dielectric layer 104 , so as to form at least one air gap 208 a , wherein each of the air gaps lands on the poly layer 202 .
- there are a portion of the dielectric materials remained in each of the plurality of the second STI structures 201 b between the air gaps and the semiconductor material 102 .
- FIG. 2F illustrates a cross sectional view of the example image sensor 200 after a contact pad 207 and at least one air gap 208 b are formed in the example image sensor 200 of FIG. 2E .
- the corresponding process block is 406 in FIG. 4 .
- the contact pad 207 is disposed on the first side 218 of the plurality of first STI structures 201 a and second STI structures 201 b .
- the contact pad 207 is coupled with the metal interconnect 107 by the plurality of contact plugs 205 .
- each of the plurality of the contact plugs 205 is filled by at least one of conductive materials comprising Al, and the contact pad 207 is made of the same conductive materials as the conductive materials in each of the plurality of the contact plugs 205 .
- the contact pad 207 is made of different conductive materials than the conductive materials in each of the plurality of the contact plugs 205 .
- the conductive materials comprise at least one of Al, Cu, W, and TiN.
- the contact pad 207 and the air gap 208 a and 208 b are formed by a sixth patterning process which comprises at least a sixth photolithography process followed by at least one of a sixth anisotropic plasma dry etch and a sixth selective wet etch process.
- the sixth etch rates for the conductive materials in the contact pad 207 and the contact plugs 205 are significantly higher than the sixth etch rates for the dielectric materials in the STI structures ( 201 a and 201 b ) and the semiconductor material 102 and 206 . Therefore, the sixth etch processes stop on the first side 218 of the STI structures ( 201 a and 201 b ) and there is no undercut on sidewalls of the contact pad trench 204 .
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Abstract
Description
- This disclosure relates generally to semiconductor image sensors, and in particular but not exclusively, relates to backside illuminated semiconductor image sensors.
- Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as medical, automobile, and other applications. The device architecture of image sensors has continued to advance at a great pace due to increasing demands for higher resolution, lower power consumption, increased dynamic range, etc. These demands have also encouraged the further miniaturization and integration of image sensors into these devices.
- The typical image sensor operates as follows. Image light from an external scene is incident on the image sensor. The image sensor includes a plurality of photosensitive elements such that each photosensitive element absorbs a portion of incident image light. Photosensitive elements included in the image sensor, such as photodiodes, each generate image charge upon absorption of the image light. The amount of image charge generated is proportional to the intensity of the image light. The generated image charge may be used to produce an image representing the external scene.
- While there are a variety of ways to make image sensors, reducing the number of steps with fewer photo masks in semiconductor processing applications is always important. Since every fabrication step adds cost and time on the assembly line, new techniques to enhance image senor throughput are needed.
- Non-limiting and non-exhaustive examples of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
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FIG. 1A -FIG. 1D are cross sectional illustrations of an example image sensor, wherein each of the figures represents the example image sensor after a series of critical process steps are finished during fabrication of the example image sensor with a standard metal pad structure inFIG. 1D , in accordance with the teachings of the present invention. -
FIG. 2A -FIG. 2F are cross sectional illustrations of an example image sensor, wherein each of the figures represents the example image sensor after a series of critical process steps are finished during fabrication of the example image sensor with a self-aligned metal pad structure inFIG. 2F , in accordance with the teachings of the present invention. -
FIG. 3 is a block diagram schematically illustrating one example of an imaging system with self-aligned metal pad structures, in accordance with the teachings of the present invention. -
FIG. 4 illustrates one example process flow for fabricating an example image sensor with a self-aligned metal pad structure, in accordance with the teachings of the present invention. - Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.
- Examples of an apparatus and method for an image sensor with simplified process are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the examples. One skilled in the relevant art will recognize; however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
- Reference throughout this specification to “one example” or “one embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases “in one example” or “in one embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more examples.
- Throughout this specification, several terms of art are used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise. It should be noted that element names and symbols may be used interchangeably through this document (e.g., Si vs. silicon); however, both have identical meaning.
-
FIG. 3 is a block diagram schematically illustrating one example of animaging system 300 with self-aligned metal pad structures, in accordance with the teachings of the present invention.Imaging system 300 includespixel array 312,control circuitry 321,readout circuitry 311, andfunction logic 315.Readout circuitry 311 andcontrol circuitry 321 may be at least partially disposed ininter-metal layer 106 ofFIGS. 2A-2F . For example, ametal interconnect 107 may be included in at least one of readout circuitry and control circuitry. - Referring back to
FIG. 3 , in one example, pixel array 305 is a two-dimensional (2D) array of photodiodes, or image sensor pixels (e.g., pixels P1, P2 . . . , Pn). As illustrated, photodiodes are arranged into rows (e.g., rows R1 to Ry) and columns (e.g., column C1 to Cx) to acquire image data of a person, place, object, etc., which can then be used to render a 2D image of the person, place, object, etc. However, in other examples, it is appreciated that the photodiodes do not have to be arranged into rows and columns and may take other configurations. - In one example, after the image sensor photodiode/pixel in
pixel array 312 has acquired its image data or image charge, the image data is readout byreadout circuitry 311 and then transferred tofunction logic 315. In various examples,readout circuitry 311 may include amplification circuitry, analog-to-digital conversion (ADC) circuitry, or otherwise.Function logic 315 may simply store the image data or even manipulate the image data by applying post image effects (e.g., crop, rotate, remove red eye, adjust brightness, adjust contrast, or otherwise). In one example,readout circuitry 311 may readout a row of image data at a time along readout column lines (illustrated) or may readout the image data using a variety of other techniques (not illustrated), such as a serial readout or a full parallel readout of all pixels simultaneously. - In one example,
control circuitry 321 is coupled to pixel array 305 to control operation of the plurality of photodiodes inpixel array 312. For example,control circuitry 321 may generate a shutter signal for controlling image acquisition. In one example, the shutter signal is a global shutter signal for simultaneously enabling all pixels withinpixel array 312 to simultaneously capture their respective image data during a single acquisition window. In another example, the shutter signal is a rolling shutter signal such that each row, column, or group of pixels is sequentially enabled during consecutive acquisition windows. In another example, image acquisition is synchronized with lighting effects such as a flash. - In one example,
imaging system 300 may be included in a digital camera, cell phone, laptop computer, automobile or the like. Additionally,imaging system 300 may be coupled to other pieces of hardware such as a processor (general purpose or otherwise), memory elements, output (USB port, wireless transmitter, HDMI port, etc.), lighting/flash, electrical input (keyboard, touch display, track pad, mouse, microphone, etc.), and/or display. Other pieces of hardware may deliver instructions toimaging system 300, extract image data fromimaging system 300, or manipulate image data supplied byimaging system 300. -
FIG. 1A -FIG. 1D are cross sectional illustrations of anexample image sensor 100, wherein each of the figures represents theexample image sensor 100 after a series of critical process steps are finished during fabrication of theexample image sensor 100 with a standard metal pad structure inFIG. 1D , in accordance with the teachings of the present invention. In order to keep the description consistent and simple, the same structure is defined with the same number inFIG. 1A -FIG. 1D . -
FIG. 1A illustrates a cross sectional view of theexample image sensor 100 comprising asemiconductor material 102 having afront side 111 and aback side 109 opposite thefont side 111. In thesemiconductor material 102, there is a shallow trench isolation (STI)structure 103 which extends from thefront side 111 of thesemiconductor material 102 into thesemiconductor material 102. TheSTI structure 103 is used to electrically separate adjacent image sensors. In one example, theSTI structure 103 is filled by at least one of dielectric materials such as silicon oxide or silicon nitride. In another example, theSTI structure 103 may also comprise a negative charged material liner at an interface between the filled dielectric materials and the semiconductor material 102 (not illustrated in the figures). The negative charged material liner is used to form a P+ pinning layer at the interface between the filled dielectric materials and thesemiconductor material 102 in order to reduce the dark current and white pixels. On thefront side 111 of thesemiconductor material 102, there are also athin dielectric layer 104, aninterlayer dielectric material 105 and aninter-metal layer 106. Thethin dielectric layer 104 may be the gate oxide of the pixel transistors. Theinterlayer dielectric material 105 is disposed between thethin dielectric layer 104 and theinter-metal layer 106. In theinter-metal layer 106, there is ametal interconnect 107 wherein themetal interconnect 107 is made of at least one of metals comprising Cu and TiN. Theinterlayer dielectric material 105, thedielectric layer 104 and theinter-metal layer 106 are made of at least one of dielectric materials comprising silicon oxide and silicon nitride. In one example, they are made of same dielectric materials. In another example, they are made of different dielectric materials. In one example, abuffer layer 101 is disposed on theback side 109 of thesemiconductor material 102 in order to protect theback side 109 of thesemiconductor material 102. Thebuffer layer 101 comprises at least one of dielectric materials such as silicon oxide or silicon nitride. -
FIG. 1B illustrates a cross sectional view of theexample image sensor 100 after acontact pad trench 108 is formed in theexample image sensor 100 ofFIG. 1A . In one example, thecontact pad trench 108 extends from theback side 109 of thesemiconductor material 102 into thesemiconductor material 102 until lands on afirst side 118 of theSTI structure 103, wherein thecontact pad trench 108 is enclosed with theSTI structure 103. In one example, thecontact pad trench 108 is formed by a first patterning process which comprises at least a first photolithography process followed by a first etch processes comprising at least one of a first anisotropic plasma etch and a first selective wet etch process. The first etch processes have significantly higher etch rate for thesemiconductor material 102 compared to the dielectric materials in theSTI structure 103. Therefore, the first etch processes stop on thefirst side 118 of theSTI structure 103. In another example, thecontact pad trench 108 extends from thebuffer layer 101 into thesemiconductor material 102, wherein thebuffer layer 101 is also selectively etched during the first patterning process to form thecontact pad trench 108. -
FIG. 1C illustrates a cross sectional view of theexample image sensor 100 after a plurality of contact plugs 110 are formed in theexample image sensor 100 ofFIG. 1B . Each of the plurality of contact plugs 110 extends from thefirst side 118 of theSTI structure 103 through thedielectric layer 104, theinterlayer dielectric material 105 and lands on themetal interconnect 107 at theinterface 114 between the interlayerdielectric material 105 and themetal interconnect 107. In one example, each of the plurality of contact plugs 110 is formed by a second patterning process which comprises at least a second photolithography process followed by at least one of a second anisotropic plasma dry etch and a second selective wet etch process. In the second etch processes, the second etch rates for the dielectric materials in theSTI structures 103, theinterlayer dielectric material 105 and thedielectric layer 104 are significantly higher than the second etch rates for the conductive materials in themetal interconnect 107. Therefore, the second etch processes stop at theinterface 114 between the interlayerdielectric material 105 and themetal interconnect 107. As a result, each of the plurality of contact plugs 110 lands on themetal interconnect 107. -
FIG. 1D illustrates a cross sectional view of theexample image sensor 100 after acontact pad 112 is formed in theexample image sensor 100 ofFIG. 1C . In thecontact pad trench 108, thecontact pad 112 is disposed on thefirst side 118 of theSTI structure 103 and coupled with themetal interconnect 107 by the plurality of contact plugs 110. In one example, each of the plurality of the contact plugs 110 is filled by at least one of conductive materials comprising Al, W, Cu, and TiN, and the contact pad is made of the same conductive materials as ones in each of the plurality of the contact plugs 110. In another example, the contact pad is made of different conductive materials from ones in each of the plurality of the contact plugs 110. The conductive materials comprise at least one of Al, Cu, W, and TiN. There is at least oneair gap 113 between thecontact pad 112 and sidewalls of thecontact pad trench 108, wherein the air gaps isolate thecontact pad 112 from thesemiconductor material 102. In one example, thecontact pad 112 and theair gap 113 are formed by a third patterning process which comprises at least a third photolithography process followed by at least one of a third anisotropic plasma dry etch and a third selective wet etch process. In the third etch processes, the third etch rates for the conductive materials in thecontact pad 112 is significantly higher than the third etch rates for the dielectric materials in theSTI structures 103 and thesemiconductor material 102. Therefore, the third etch processes stop at thefirst side 118 of theSTI structure 103 and there is no undercut on sidewalls of thecontact pad trench 108. -
FIG. 2A -FIG. 2F are cross sectional illustrations of anexample image sensor 200, wherein each of the figures represents theexample image sensor 200 after a series of critical process steps are finished during fabrication of theexample image sensor 200 with a self-aligned metal pad structure inFIG. 2F , in accordance with the teachings of the present invention. In order to keep the description consistent and simple, the same structure is defined with the same number inFIG. 1A-1D andFIG. 2A-2F .FIG. 4 illustrates anexample method 400 for forming the example image sensors with a self-aligned metal pad inFIG. 2A-2F , wherein each of the process blocks inFIG. 4 corresponds to one of the figures inFIG. 2A -FIG. 2F as described in the next paragraphs. The order in which some or all process blocks appear inmethod 400 should not be deemed limited. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some ofmethod 400 may be executed in a variety of orders not illustrated, or even in parallel. Furthermore,method 400 may omit certain process blocks in order to avoid obscuring certain aspects. Alternatively,method 400 may include additional process blocks that may not be necessary in some embodiments or examples of the disclosure. -
FIG. 2A illustrates a cross sectional view of theexample image sensor 200 comprising asemiconductor material 102 after thecorresponding process block 401 andpartial process block 402 inFIG. 4 has been done. In theprocess block 401, thesemiconductor material 102 is provided, which has afront side 111 and aback side 109 opposite thefront side 111, wherein a plurality of first shallow trench isolation (STI)structures 201 a and a plurality ofsecond STI structures 201 b are formed extending from thefront side 111 of thesemiconductor material 102 into thesemiconductor material 102, wherein each of the plurality offirst STI structures 201 a is fully surrounded by adjacent first 201 a and second 201 b STI structures and each of the plurality ofsecond STI structures 201 b is partially surrounded by adjacent first 201 a and second 201 b STI structures. The plurality offirst STI structures 201 a andsecond STI structures 201 b are used to electrically separate adjacent image sensors. In one example, each of the plurality offirst STI structures 201 a andsecond STI structures 201 b is filled by at least one of dielectric materials such as silicon oxide or silicon nitride. In another example, each of the plurality offirst STI structures 201 a andsecond STI structures 201 b may also comprise a negative charged material liner at an interface between the filled dielectric materials in each of the plurality of first 201 a and second 201 b STI structures and the semiconductor material 102 (not illustrated in the figures). The negative charged material liner is used to form a P+ pinning layer at the interface so as to reduce the dark current and white pixels. - As illustrated in
FIG. 2A and described in theprocess block 402 inFIG. 4 , adielectric layer 104 may be disposed on thefront side 111 of thesemiconductor material 102 at the same process step as disposing the gate oxide of the pixel and periphery transistors. Moreover, apoly layer 202 may also be disposed on thethin dielectric layer 104 at the same process step as disposing the poly gate of pixel and periphery transistors. In one example, abuffer layer 101 is disposed on theback side 109 of thesemiconductor material 102 in order to protect theback side 109 of thesemiconductor material 102. Thebuffer layer 101 comprises at least one of dielectric materials such as silicon oxide or silicon nitride. -
FIG. 2B illustrates a cross sectional view of theexample image sensor 200 after a plurality ofopen slots 203 are formed in thepoly layer 202 in theexample image sensor 200 ofFIG. 2A . The corresponding process block is 402 inFIG. 4 . Each of the plurality ofopen slots 203 extends from afirst side 220 of thepoly layer 202 to the interface of thepoly layer 202 and thedielectric layer 104, wherein each of the plurality ofopen slots 203 aligns up with each of the plurality offirst STI structures 201 a and has same two dimensional lateral dimensions as the alignedfirst STI structure 201 a. In one example, the plurality ofopen slots 203 and the poly gates of the pixel and periphery transistors are formed at the same time with the same patterning process and photo mask. Therefore, compared to the fabrication processes of the standard metal pad structure inFIG. 1A-1D , it does not require an additional patterning process step to form the plurality ofopen slots 203. -
FIG. 2C illustrates a cross sectional view of theexample image sensor 200 after aninterlayer dielectric material 105 and aninter-metal layer 106 are disposed on theexample image sensor 200 ofFIG. 2B . The corresponding process block is 403 inFIG. 4 . Theinterlayer dielectric material 105 is disposed between thedielectric layer 104 and theinter-metal layer 106. Thedielectric layer 104 and thepoly layer 202 are covered by theinterlayer dielectric material 105, wherein the plurality ofopen slots 203 are filled with theinterlayer dielectric material 105. In theinter-metal layer 106, there is ametal interconnect 107 wherein themetal interconnect 107 is made of at least one of metals comprising Cu and TiN. Theinterlayer dielectric material 105, thedielectric layer 104 and theinter-metal layer 106 are made of at least one of dielectric materials comprising silicon oxide and silicon nitride. In one example, they are made of same dielectric materials. In another example, they are made of different dielectric materials. -
FIG. 2D illustrates a cross sectional view of theexample image sensor 200 after acontact pad trench 204 is formed in theexample image sensor 200 ofFIG. 2C . The corresponding process block is 404 inFIG. 4 . In one example, thecontact pad trench 204 extends from theback side 109 of thesemiconductor material 102 into thesemiconductor material 102 until lands on afirst side 218 of the plurality offirst STI structure 201 a andsecond STI structure 201 b, wherein the sidewalls of thecontact pad trench 204 land on the plurality of thesecond STI structures 201 b. In one example, thecontact pad trench 204 is formed by a fourth patterning process which comprises at least a fourth photolithography process followed by at least one of a fourth anisotropic plasma etch and a fourth selective wet etch process. The fourth etch processes have significantly higher etch rate for thesemiconductor material 102 compared to the dielectric materials in the plurality of thefirst STI structures 201 a and thesecond STI structures 201 b. Moreover, the etch time is preciously monitored and controlled during the plasma dry etch and the selective wet etch processes in order to avoid over etch and under etch. As a result, the fourth etch processes stop on thefirst side 218 of thefirst STI structures 201 a and thesecond STI structures 201 b. There areportions 206 of thesemiconductor material 102 remained between adjacent first 201 a and second 201 b STI structures, which will be used as a hard mask in the following self-aligned patterning process steps. In another example, thecontact pad trench 204 extends from thebuffer layer 101 into thesemiconductor material 102, wherein thebuffer layer 101 is also selectively etched during the fourth patterning process to form thecontact pad trench 204. -
FIG. 2E illustrates a cross sectional view of theexample image sensor 200 after a plurality of contact plugs 205 and at least oneair gap 208 a are formed in theexample image sensor 200 ofFIG. 2D . The corresponding process block is 405 inFIG. 4 . Each of the plurality of contact plugs 205 extends from thefirst side 218 of the first 201 a and second 201 b STI structure through thedielectric layer 104, theinterlayer dielectric material 105 and lands on themetal interconnect 107 at theinterface 114 between the interlayerdielectric material 105 and themetal interconnect 107. - In one example, each of the plurality of contact plugs 205 is formed by a self-aligned patterning process, wherein the
portions 206 of thesemiconductor material 102 are used as a hard mask to define the plurality of the contact plugs 205 and theair gaps 208 a. Therefore, the self-aligned patterning process comprises only a fifth selective etch process without a fifth photolithography process, which may help to reduce the fabrication cost and simplify the fabrication process by minimizing the number of photolithography steps. - During the fifth selective etch process, the dielectric materials defined by the
portions 206 of thesemiconductor material 102 are selectively removed by at least one of selective anisotropic plasma dry etch and a selective wet etch processes. The removed dielectric materials include the dielectric materials in each of the plurality of thefirst STI structure 201 a and a partialsecond STI structure 201 b, the dielectric materials in each of the plurality ofopen slots 203 in thepoly layer 202, a portion of thedielectric layer 104, and a portion of theinterlayer dielectric material 105. The portion of thedielectric layer 104 and the portion of theinterlayer dielectric material 105 are self-aligned with the STI structures, wherein theportions 206 of thesemiconductor material 102 are used as a hard mask during the selective etch processes. The selective plasma dry etch and the selective wet etch processes have significantly higher etch rates for the dielectric materials in theSTI structures dielectric layer 104 and theinterlayer dielectric material 105, than the etch rates for the conductive materials in themetal interconnect 107 and the semiconductor materials in theportions 206 of thesemiconductor material 102 and thepoly layer 202. As a result, the selective etch processes automatically slow down greatly at theinterface 114 between the interlayerdielectric material 105 and themetal interconnect 107 so as to form the plurality of contact plugs 205, wherein each of the plurality of contact plugs 205 lands on themetal interconnect 107. Moreover, the selective etch processes also automatically slow down greatly at the interface between thepoly layer 202 and thedielectric layer 104, so as to form at least oneair gap 208 a, wherein each of the air gaps lands on thepoly layer 202. In one example, after the selective anisotropic etch processes are finished, there are a portion of the dielectric materials remained in each of the plurality of thesecond STI structures 201 b between the air gaps and thesemiconductor material 102. -
FIG. 2F illustrates a cross sectional view of theexample image sensor 200 after acontact pad 207 and at least oneair gap 208 b are formed in theexample image sensor 200 ofFIG. 2E . The corresponding process block is 406 inFIG. 4 . In thecontact pad trench 204, thecontact pad 207 is disposed on thefirst side 218 of the plurality offirst STI structures 201 a andsecond STI structures 201 b. Thecontact pad 207 is coupled with themetal interconnect 107 by the plurality of contact plugs 205. In one example, each of the plurality of the contact plugs 205 is filled by at least one of conductive materials comprising Al, and thecontact pad 207 is made of the same conductive materials as the conductive materials in each of the plurality of the contact plugs 205. In another example, thecontact pad 207 is made of different conductive materials than the conductive materials in each of the plurality of the contact plugs 205. The conductive materials comprise at least one of Al, Cu, W, and TiN. There is at least oneair gap 208 a and at least oneair gap 208 b between thecontact pad 207 and sidewalls of thecontact pad trench 204, wherein the air gaps isolate thecontact pad 207 from thesemiconductor material 102. - In one example, the
contact pad 207 and theair gap contact pad 207 and the contact plugs 205 are significantly higher than the sixth etch rates for the dielectric materials in the STI structures (201 a and 201 b) and thesemiconductor material first side 218 of the STI structures (201 a and 201 b) and there is no undercut on sidewalls of thecontact pad trench 204. - The above description of illustrated examples of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific examples of the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
- These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific examples disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
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US20100244173A1 (en) * | 2009-03-30 | 2010-09-30 | Taiwan Semiconductor Manufacturing Company, Ltd. | Image sensor and method of fabricating same |
US20140124889A1 (en) * | 2012-11-05 | 2014-05-08 | Omnivision Technologies, Inc. | Die seal ring for integrated circuit system with stacked device wafers |
US20170186802A1 (en) * | 2015-12-29 | 2017-06-29 | Taiwan Semiconductor Manufacturing Co., Ltd. | Via support structure under pad areas for bsi bondability improvement |
US20170229494A1 (en) * | 2016-02-05 | 2017-08-10 | Taiwan Semiconductor Manufacturing Co., Ltd. | Voltage biased metal shielding and deep trench isolation for backside illuminated (bsi) image sensors |
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US20100244173A1 (en) * | 2009-03-30 | 2010-09-30 | Taiwan Semiconductor Manufacturing Company, Ltd. | Image sensor and method of fabricating same |
US20140124889A1 (en) * | 2012-11-05 | 2014-05-08 | Omnivision Technologies, Inc. | Die seal ring for integrated circuit system with stacked device wafers |
US20170186802A1 (en) * | 2015-12-29 | 2017-06-29 | Taiwan Semiconductor Manufacturing Co., Ltd. | Via support structure under pad areas for bsi bondability improvement |
US20170229494A1 (en) * | 2016-02-05 | 2017-08-10 | Taiwan Semiconductor Manufacturing Co., Ltd. | Voltage biased metal shielding and deep trench isolation for backside illuminated (bsi) image sensors |
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