Optical sensor

An optical sensor is provided. The optical sensor includes a substrate, a transistor, a dielectric layer, a first electrode, a photodiode, a second electrode and a gap. The transistor is disposed over the substrate. The dielectric layer is disposed over the transistor. The first electrode is disposed over the dielectric layer and includes a U-shaped portion electrically connected to the transistor. The second electrode is disposed over the first electrode, and the photodiode is disposed between the first electrode and the second electrode. The gap is surrounded by the U-shaped portion of the first electrode and is sealed by the first electrode or the second electrode.

TECHNICAL FIELD

The present disclosure is related to a semiconductor structure, especially a structure of an optical sensor.

BACKGROUND

A touchscreen is an input and output device usually layered on the top of an electronic visual display. A user can enter input or control an information processing system by touching the screen with one or more fingers, a stylus or a special pen to substitute for (or use instead of) a mouse or a remote control. The touchscreen enables the user to interact directly with what is displayed, rather than using a mouse, a keyboard, or other such devices (other than a stylus, which is optional for most modern touchscreens). With easily-marketed features of easy portability, use and control, which is especially important for elder users and children, the touchscreen provides high convenience and has become a main product in the consumer display market.

SUMMARY

One aspect of the present disclosure provides an optical sensor. The optical sensor includes a substrate, a transistor, a dielectric layer, a first electrode, a photodiode, a second electrode and a gap. The transistor is disposed over the substrate. The dielectric layer is disposed over the transistor. The first electrode is disposed over the dielectric layer and includes a U-shaped portion electrically connected to the transistor. The second electrode is disposed over the first electrode, and the photodiode is disposed between the first electrode and the second electrode. The gap is surrounded by the U-shaped portion of the first electrode and sealed by the first electrode or the second electrode.

In an embodiment of the present disclosure, the photodiode and a portion of the second electrode line the U shaped portion of the first electrode, and the gap is sealed by the second electrode.

In an embodiment of the present disclosure, the second electrode includes a first portion, lining the photodiode and the U-shaped portion of the first electrode; and a second portion, covering the first portion to seal the gap.

In an embodiment of the present disclosure, a thickness of the second portion of the second electrode is greater than a thickness of the first portion of the second electrode.

In an embodiment of the present disclosure, the second portion of the second electrode comprises a first convex portion disposed over the gap and protruding opposite to the gap.

In an embodiment of the present disclosure, the optical sensor further includes an anti-reflective layer, disposed over the first convex portion of the second electrode.

In an embodiment of the present disclosure, the second portion of the second electrode comprises a second convex portion over the gap, adjacent to the first convex portion and protruding toward the gap.

In an embodiment of the present disclosure, a thickness of the second electrode is greater than a thickness of the first electrode.

In an embodiment of the present disclosure, the first electrode further comprises a cap portion covering the U-shaped portion, and the gap is sealed by the cap portion and the U-shaped portion of the first electrode.

In an embodiment of the present disclosure, a thickness of the cap portion is greater than a thickness of the U-shaped portion of the first electrode.

In an embodiment of the present disclosure, the cap portion of the first electrode comprises a concave portion disposed over the gap and facing the gap.

In an embodiment of the present disclosure, the cap portion of the first electrode comprises a convex portion disposed over the gap and protruding away from the gap.

In an embodiment of the present disclosure, the photodiode lines the first electrode and comprises a convex portion over the convex portion of the first electrode.

In an embodiment of the present disclosure, the second electrode lines the photodiode and comprises a convex portion corresponding to the convex portion of the photodiode.

In an embodiment of the present disclosure, the optical sensor further includes an anti-reflective layer, lining the photodiode and comprising a convex portion over the convex portion of the photodiode.

In an embodiment of the present disclosure, a thickness of the first electrode is greater than a thickness of the second electrode.

In an embodiment of the present disclosure, the first electrode or the second electrode sealing the gap comprises a top surface facing away from the gap, and the top surface has a recessed portion overlapping the gap.

In an embodiment of the present disclosure, the transistor is a thin-film transistor, and the first electrode is electrically connected to a source/drain region of the transistor.

In an embodiment of the present disclosure, the optical sensor further includes a reflective layer disposed between the dielectric layer and the first electrode.

In an embodiment of the present disclosure, the substrate comprises a flexible substrate.

From another aspect of the present disclosure, an optical sensor is provided. The optical sensor includes: a substrate, a transistor, a dielectric layer, a first electrode, a photodiode, a second electrode, an anti-reflective layer and a gap. The transistor is disposed over the substrate. The dielectric layer is disposed over the transistor. The first electrode is disposed over the dielectric layer and includes a U-shaped portion electrically connected to the transistor. The second electrode is conformally disposed over the first electrode, and the photodiode is disposed between the first electrode and the second electrode. The gap is surrounded by the U-shaped portion of the first electrode and disposed between the second electrode and at least a portion of the anti-reflective layer.

In an embodiment of the present disclosure, the gap is sealed in the anti-reflective layer.

In an embodiment of the present disclosure, the gap is defined by the second electrode and the anti-reflective layer.

DETAILED DESCRIPTION

FIG. 1shows a cross-sectional diagram of an optical sensor10in accordance with some embodiments of the present disclosure. A substrate110is provided in the optical sensor10. The substrate110is a transparent substrate, or at least a portion of the substrate110is transparent. In some embodiments, the substrate110is an inflexible substrate, and a material of the substrate110may include glass, quartz, or other suitable material. In some embodiments, the substrate110is a flexible substrate, and a material of the substrate110may include transparent epoxy resin, polyimide, polyvinyl chloride, methyl methacrylate, or other suitable material. A dielectric layer120is optionally disposed over the substrate110as shown inFIG. 1. In some embodiments, the dielectric layer120may include silicon oxide, silicon nitride, silicon oxynitride, or other suitable materials.

A circuit or several circuits are disposed over the substrate110. The circuit may have several transistors210and several capacitors220adjacent to the transistors, wherein the transistors210and the capacitors220are formed over the dielectric layer120. In some embodiments, the transistors are thin-film transistors (TFT). Each transistor210includes source/drain regions212(including at least a source region and a drain region), a channel region213between the source/drain regions212, a gate electrode214over the channel region213, and a gate insulator215between the channel region213and the gate electrode214. The gate electrode214can be made with conductive material such as metal, silicide, or metal alloy. In some embodiments, the gate electrode214can be a composite structure including several different layers and the different layers may be distinguishable after applying etchant and observed under microscope. In some embodiments, the gate electrode214is formed concurrently with a first metal layer of an inter-layer dielectric structure230. The inter-layer dielectric structure230is disposed over the circuit or the transistors210. The inter-layer dielectric structure230may include several layers of metal wiring and dielectric material for electrical connection and isolation. The channel region213of the transistor210may be made with semiconductive material such as silicon, or other element selected from group IV, or groups III and V.

In some embodiments, the gate insulator215covers the channel region213and the source/drain regions212of the transistor210, and the gate insulator215is disposed between the adjacent capacitor220and the dielectric layer120. In some embodiments, the gate insulator215is formed after formation of the source/drain regions212and the channel region213over the dielectric layer120. The source/drain regions212are disposed on opposite sides of the channel region213to provide carriers. In some embodiments, the capacitors220are disposed between the transistors210. Each capacitor220includes a bottom electrode221, a top electrode222, and an insulating layer223between the top electrode222and the bottom electrode221. In some embodiments, the bottom electrode221is formed concurrently with a first metal layer of the inter-layer dielectric structure230over the dielectric layer120. In some embodiments, the insulating layer223is formed over the transistors210after formation of the first metal layer. In some embodiments, the insulating layer223is disposed on and conformal to the bottom electrode221and also the transistors210. The top electrode222is disposed over the insulating layer223in the inter-dielectric structure230. The top electrode222may include titanium, aluminum, copper, titanium nitride, a combination thereof, or other suitable materials. In some embodiments, the top electrode222is formed concurrently with a second metal layer of the inter-layer dielectric structure230. In some embodiments, the top electrode222and the second metal layer are formed after formation of the insulating layer223.

A connecting structure240is formed to electrically connect the transistor210to the capacitor220. The connecting structure240includes a plurality of connecting vias and a plurality of connecting lines. The connecting vias may connect to the source/drain regions212of the transistor210, the gate electrode214of the transistor210, and the bottom and/or top electrodes221and222of the capacitors220to the connecting line and to form an integrated circuit over the substrate110. The connecting structure240may include some connecting vias241, which connect to the drain region212of the transistor210at one end. The connecting structure240may include some connecting vias242, which connect to the source region212of the transistor210at one end. The connecting structure240may include some connecting vias243, which connect to the bottom electrode221of the capacitor220at one end. The connecting structure240may include some connecting lines244, which connect to the connecting vias241at one end, respectively. The connecting structure240may include some connecting lines, which only connect to the connecting vias242at one end, respectively (not shown). The connecting structure240may further include some connecting lines245, which connect to the connecting vias242and also the connecting vias243at one end. In some embodiments, the connecting lines are formed concurrently with one of the metal layers (e.g., a third metal layer) of the inter-layer dielectric structure230.

A data line (not shown) is disposed over the connecting lines of the connecting structure240to electrically connect to the source/drain regions212. A dielectric layer310is disposed over the data line, the inter-layer dielectric structure230and the connecting structure240. In some embodiments, the dielectric layer310is formed by a conformal deposition. The dielectric layer310can be conformal to a configuration of the underlying structure. A planar layer320is disposed over the dielectric layer310. In some embodiments, the planar layer320includes dielectric or insulating materials. In some embodiments, the planar layer320is formed by a blanket deposition, wherein a bottom surface of the planar layer320is conformal to a configuration of the underlying structure, and a top surface of the planar layer320is substantially planar. In some embodiments, the planar layer320and the dielectric layer310include a through hole (or an opening) over the connecting line245, wherein the connecting line245is exposed through the dielectric layer310and the planar layer320via the through hole.

In the optical sensor10, a first electrode410is disposed over the planar layer320, wherein a portion of the first electrode410has a planar surface as the planar layer432, and a portion of the first electrode410penetrates through the planar layer320and the dielectric layer310to electrically connect to the connecting line245. The first electrode410includes a U-shaped portion411disposed in the through hole from a cross-sectional perspective, and the U-shaped portion411of the first electrode410is surrounded by the planar layer320and the dielectric layer310. The first electrode410electrically connects to the transistor210and/or the capacitor220through the U-shaped portion411and the connecting structure240(including the connecting vias242,243and the connecting line245). In some embodiments, the U-shaped portion411of the first electrode410electrically connects to the transistor210through a conductive material or an electrical component. In some embodiments, a bottom of the U-shaped portion411of the first electrode410physically contacts the connecting line245. In some embodiments, the bottom of the U-shaped portion411of the first electrode410completely overlaps the connecting line245.

In some embodiments, the optical sensor10further includes a reflective layer330disposed between the planar layer320and the first electrode410, and between the connecting line245and the first electrode410. The reflective layer330is conformal to the through hole and the planar layer320. The reflective layer330includes a U-shaped configuration conformal to the U-shaped portion411of the first electrode410. The reflective layer330may be made of one or more metal materials. In some embodiments, the reflective layer330includes aluminum. In some embodiments, the reflective layer330physically contacts the connecting line245, and the first electrode410electrically connects to the transistor210and/or the capacitor220through the reflective layer330.

In the optical sensor10, a photodiode420is disposed over and conformal to the first electrode410, wherein a portion of the photodiode420is disposed over the planar layer320and thus has a planar surface as the planar layer320, and a portion of the photodiode420is also in a U-shaped configuration corresponding to the U-shaped portion of the first electrode410from a cross-sectional perspective. The photodiode420can be a PIN photo-sensor including an N-type doping layer421, an intrinsic layer422, and a P-type doping layer423stacked in sequence over the first electrode410. In some embodiments, the N-type doping layer421, the intrinsic layer422, and the P-type doping layer423are α-silicon layers. In some embodiments, a portion, having the U-shaped configuration, of the photodiode420is between (or surrounded by) the planar layer320. In some embodiments, the portion having the U-shaped configuration of the photodiode420penetrates through the planar layer320. In some embodiments, a bottom of the photodiode420is between (or surrounded by) the dielectric layer310.

In the optical sensor10, a second electrode430is disposed over the photodiode420, and a gap440is sealed by the second electrode430. The photodiode420is disposed between the first electrode410and the second electrode430. A portion of the second electrode430is disposed over the planar layer320and thus has a planar surface as the planar layer320. Further, the second electrode430includes a first portion431and a second portion432. The first portion431lines the photodiode420corresponding to the U-shaped portion411of the first electrode410. The first portion431of the second electrode430also has a U-shaped configuration corresponding to the U-shaped configuration of the photodiode420and the U-shaped portion411of the first electrode410. In some embodiments, the first portion431includes a convex portion4311at the bottom of the U-shaped configuration. The convex portion4311is adjacent to the gap440and protrudes toward the gap440. The second portion432is disposed over the first portion431to form the gap440in the second electrode430at a position corresponding to the U-shaped portion411of the first electrode410. The gap440is surrounded, in sequence toward the gap440, by the U-shaped portion411of the first electrode, the portion having the U-shaped configuration of the photodiode420, and the first portion431of the second electrode430from a cross-sectional perspective. In some embodiments, in order to seal the gap440inside the second electrode430, a thickness D430of the second electrode430is greater than a thickness D410of the first electrode410. In addition, due to formation of the second electrode430(details of forming the gap440within the second electrode430are illustrated in the following description), in some embodiments, the second portion432of the second electrode430includes convex portions4321and4323over the gap440and protruding away from the gap440from a cross-sectional perspective as shown inFIG. 1. In some embodiments, the second portion432includes only one convex portion (not shown) over the gap440and protruding away from the gap440. In some embodiments, the second electrode430has a top surface T430with a recessed portion between the convex portions4321and4323from the cross-sectional perspective. The recessed portion of the top surface T430of the second electrode430overlaps the gap440. In some embodiments, the recessed portion of the top surface T430is directly over the gap440. In some embodiments, the second portion432of the second electrode430further includes a convex portion4322over the gap440and protruding toward the gap440. In some embodiments having the gap440sealed in the second electrode430, the second electrode430is a multi-layer structure. In some embodiments, average grain sizes of the first portion431and the second portion432are different. In some embodiments, an interface or a boundary between the first portion431and the second portion432of the second electrode430can be observed under microscope.

A pixel defining layer (PDL)450is disposed at the same elevation as the photodiode420and separated from the gap440and adjacent to the U-shaped portion411of the first electrode410. In some embodiments, the PDL450is configured to separate luminous regions of different pixel units of the optical sensor10. In some embodiments, the PDL450encircles the gap440, the photodiode420, the transistor210and the capacitor220from a top view perspective (not shown; the cross-sectional diagrams ofFIGS. 1 and 2show only a portion of the PDL450). In some embodiments, the PDL450is covered by the second electrode430.

An anti-reflective layer510is disposed over the second electrode430. The anti-reflective layer510includes a convex portion5101at a position corresponding to the convex portions4321and4323of the second electrode430. Further, the convex portion5101is formed over the gap. In some embodiments, due to a small value of a depth D432rof the recessed portion of the top surface T430of the second electrode430, the anti-reflective layer510includes only one convex portion5101covering the convex portions4321and4323as shown inFIG. 1. In some embodiments, the anti-reflective layer510may include two convex portions5101(not shown) corresponding to the convex portions4321and4323of the second electrode430. The anti-reflective layer510of the present disclosure is made of transparent materials. In some embodiments, the anti-reflective layer510includes silicon oxynitride.

The U-shaped configuration of the photodiode420can increase an area of light absorption and thus enhance signal detection of the optical sensor10. Signals can be enhanced especially under a low light environment, e.g., when using a finger or a stylus to control a touch panel. Incident light may enter the optical sensor10from outside the anti-reflective layer510. The convex portion5101of the anti-reflective layer510can function as a micron lens to change direction of incident light toward the photodiode420in the gap440. Therefore, the incident light from different directions is concentrated and redirected toward the gap440. In some embodiments, a height H440of the gap440is in a range of 10 to 5000 nm. In some embodiments, for a better concentration result, an aspect ratio (the height H440to a top width W440) of the gap440is in a range of 2 to 30.

In some embodiments, incident lights LS is concentrated and focused in the gap440as shown inFIG. 17. In some embodiments, the focus of the concentrated incident light LS is in the gap440and proximal to the convex portion4311of the second electrode430. In some embodiments, the focus of the concentrated incident light LS is at a surface of the convex portion4311of the second electrode430. By concentrating the incident lights LS, signals strength can be increased. In some embodiments, the anti-reflective layer510functions to increase light absorption, and a layer of a micron lens array is not formed over the anti-reflective layer510. In some embodiments, the layer of the micron lens array is formed over the anti-reflective layer510to further increase light absorption. The anti-reflective layer510can be similar to a conventional anti-reflection coating layer used in semiconductor manufacturing.

The incident light passing through the gap440is concentrated due to different reflective indexes of the second electrode430and the gap440. In some embodiments, the gap440is formed in a low-pressure environment. In some embodiments, the gap440is a substantially vacuum environment. A reflective index of the second electrode430is greater than a reflective index of the gap440, and the incident light is concentrated when entering the gap440from the second electrode430. The use of the reflective layer330has an advantage of reflecting incident light back into the photodiode420. Light signals can be enhanced by the presence of the gap440of the present disclosure, and further enhanced by the presence of the reflective layer330. Moreover, formation of the gap440can be integrated with formation of electrical connection between a photodiode and a transistor in a conventional manufacturing process. Formation of the optical sensor10can be highly integrated with a manufacturing process of a conventional optical sensor.

In order to further illustrate concepts of the present disclosure, various embodiments are provided below. However, it is not intended to limit the present disclosure to specific embodiments. In addition, conditions or parameters illustrated in different embodiments can be combined or modified to form different combinations of embodiments as long as the parameters or conditions used are not conflicted. For ease of illustration, reference numerals with similar or same functions and properties are repeatedly used in different embodiments and figures, but such repetition is not intended to limit the present disclosure to specific embodiments.

FIG. 2shows a cross-sectional diagram of an optical sensor20in accordance with some embodiments of the present disclosure. The optical sensor20is similar to the optical sensor10. In the following description, only features of the optical sensor20that are different from those of the optical sensor10are mentioned for the purpose of brevity, but are not intended to limit the present disclosure.

In the optical sensor20, a gap440is disposed within a first electrode410. The gap440of the optical sensor20is surrounded by a U-shaped portion411of the first electrode410. The first electrode410of the optical sensor20further includes a cap portion412covering the U-shaped portion411, wherein the gap440is sealed by the cap portion412and the U-shaped portion411of the first electrode410. A thickness D412of the cap portion412is greater than a thickness D411of the U-shaped portion411. The cap portion412of the first electrode410of the optical sensor20is similar to the second portion432of the second electrode430of the optical sensor10. Due to formation of the first electrode410(details of forming the gap440within the first electrode410are illustrated in the following description), in some embodiments, the cap portion412of the first electrode410includes convex portions4121and4123over the gap440and protruding away from the gap440. In some embodiments, the cap portion412of the first electrode410includes only one convex portion (not shown) over the gap440and protruding away from the gap440. In some embodiments, the first electrode410has a top surface T410with a recessed portion between the convex portions4121and4123from a cross-sectional perspective. The recessed portion of the top surface T410of the first electrode410overlaps the gap440. In some embodiments, the recessed portion of the top surface T410is directly over the gap440. In some embodiments, the cap portion412of the first electrode410further includes a concave portion4124over the gap440and facing the gap440. In some embodiments having the gap440sealed in the first electrode410, the first electrode410is a multi-layer structure. In some embodiments, average grain sizes of the U-shaped portion411and the cap portion412are different. In some embodiments, an interface or a boundary between the U-shaped portion411and the cap portion412of the second electrode430can be observed under microscope.

A photodiode420, which includes an N-type doping layer421, an intrinsic layer422, and a P-type doping layer423stacked in sequence, is disposed over the first electrode410. The photodiode420includes one or more convex portions4201at a position corresponding to the convex portions4121and4123. In some embodiments, due to a small value of a depth D412rof the recessed portion of the top surface T410of the first electrode410, the photodiode420includes only one convex portion4201covering the convex portions4121and4123as shown inFIG. 2. A second electrode430is disposed over the photodiode420. The second electrode430includes a convex portion4301over the convex portion4201of the photodiode420. A configuration of the convex portion4301of the second electrode430corresponds to a configuration of the convex portion4201of the photodiode420. An anti-reflective layer510is disposed over the second electrode430. The anti-reflective layer510includes a convex portion5101at a position corresponding to the convex portion4301of the second electrode430. A configuration of the convex portion5101of the anti-reflective layer510is in accordance with the configuration of the convex portion4301of the second electrode430. In some embodiments having the gap in the first electrode410, a thickness D430of the second electrode510is less than the thickness D410of the first electrode410. In some embodiments, the thickness D430of the second electrode510is in a range of 10 to 100 nanometers. In some embodiments, the thickness D410of the first electrode410is in a range of 300 to 750 nanometers.

The convex portion5101of the anti-reflective layer510can function as a micron lens to change direction of incident light toward the photodiode420. A layer of a micron lens array disposed over the anti-reflective layer510of the optical sensor20is optional. Incident light passing through the gap440is concentrated due to different reflective indexes of the first electrode410and the gap440. Light signals can be further enhanced by the presence of the gap440of the present disclosure. In addition, formation of the gap440in the first electrode410can be integrated with formation of electrical connection between a photodiode and a transistor in a conventional manufacturing process. Formation of the optical sensor20can be highly integrated with a manufacturing process of a conventional optical sensor.

In order to further illustrate the present disclosure,FIG. 3is a flowchart of a method M10for forming an optical sensor in accordance with some embodiments. The method M10for forming an optical sensor similar to the optical sensor10or20includes following operations: (O11) receiving a semiconductor substrate having a connecting structure exposed through an opening; (O12) forming a first electrode over the semiconductor substrate, wherein at least a portion of the first electrode lines the opening; (O13) forming a photodiode over the first electrode; (O14) forming a second electrode over the photodiode; and (O15) forming an gap within the first electrode or the second electrode. It should be noted that the flowchart shown inFIG. 3is for a purpose of illustration but is not intended to limit the operations into a specific order. A sequence of the operations (O11) to (O15) can be arranged in accordance with different embodiments.

Referring toFIGS. 4 to 5in accordance with the operation (O11), a semiconductor substrate is received. The semiconductor substrate includes a substrate110, a dielectric layer120, several transistors210, several capacitors220, an inter-layer dielectric structure230, several connecting structures240, a dielectric layer310and a planar layer320, which are similar to those illustrated in relation to the optical sensor10, and repeated description is omitted herein. A portion of the dielectric layer310and a portion of the planar layer320directly over a connecting line245of the connecting structure240are removed to form an opening H10to expose the connecting line245. In some embodiments, a diameter W10of the opening H10(measured at the bottom of the opening H10on the connecting line245) is in a range of 1.8 to 2.2 micrometers. In some embodiments, the opening H10has a tapered configuration with a narrower bottom and a wider top.

Referring toFIG. 6, in accordance with the operation (O12), a first electrode410is formed over the semiconductor substrate and conformal to the opening H10. A U-shaped portion411of the first electrode410lines the opening H10. In some embodiments, a reflective layer330is formed prior to formation of the first electrode410. At least a portion of the reflective layer330lines the opening H10. In some embodiments, the reflective layer330and the first electrode410are formed by conformal depositions. In some embodiments, a reflectance of the reflective layer330is greater than a reflectance of the first electrode410, and thus incident light passing through the first electrode410can be reflected back toward a photodiode420to be formed over the first electrode410. Light absorption by the photodiode420can be enhanced. In some embodiments, a thickness of the reflective layer330is in a range of 30 to 200 nanometers. In some embodiments, the first electrode410includes indium tin oxide (ITO). In some embodiments, a thickness D410of the first electrode410is in a range of 10 to 100 nanometers. In some embodiments, the thickness of the reflective layer330is greater than the thickness D410of the first electrode410.

Referring toFIG. 7, in accordance with the operation (O13), the photodiode420, which includes an N-type doping layer421, an intrinsic layer422, and a P-type doping layer423stacked in sequence, is formed over and conformal to the first electrode410. In order to form an optical sensor similar to the optical sensor10, the photodiode420is formed directly over the intermediate structure as shown inFIG. 6. A portion of the photodiode420has a U-shaped configuration lining the opening H10over the U-shaped portion411of the first electrode410, thereby forming an opening H420defined by the portion of the photodiode420having the U-shaped configuration. The U-shaped configuration of the portion of the photodiode420corresponds to the U-shaped portion411of the first electrode410. In some embodiments, a thickness of the N-type doping layer421is in a range of 10 to 50 nanometers. In some embodiments, a thickness of the intrinsic layer422is in a range of 300 to 500 nanometers. In some embodiments, a thickness of the P-type doping layer423is in a range of 5 to 20 nanometers. In some embodiments, the thickness of the N-type doping layer421is greater than the thickness of the P-type doping layer423. The thicknesses of different layers of the photodiode420can be adjusted in order to receive light with different wavelength ranges in accordance with different embodiments.

Referring toFIGS. 8 to 9, in accordance with the operations (O14) to (O15), a second electrode430and a gap440are formed by multiple depositions. A first deposition is performed as shown inFIG. 8to form a first layer431′ including a first portion431of the first electrode430lines the photodiode420and disposed in the opening H420of the photodiode420, thereby forming an opening H431defined by the first portion431of the first layer431′. A configuration of the first portion431of the first layer431′ corresponds to the U-shaped configuration of the photodiode420and the U-shaped portion411of the first electrode410. A convex portion4311of the first portion431is formed at a bottom of the first portion431due to limited space for deposition at the bottom of the opening H420, and due to properties of the deposition technique by which more material of the first layer431′ may be deposited at the bottom of the opening H420.

A second deposition is performed as shown inFIG. 9to form a second layer432′ including a second portion432of the second electrode430over the first layer431′, wherein a deposition rate of the second deposition is greater than a deposition rate of the first deposition. Due to the higher deposition rate of the second deposition, the second portion432is not able to line the opening H431but instead forms a cap over the opening H431. Thus, the gap440is formed in and sealed by the second electrode430. Convex portions4321and4323are formed over the gap440corresponding to top edges E431of the opening H431due to properties of deposition technique. A recessed portion of a top surface T430of the second electrode430is thereby formed between the convex portions4321and4323. A convex portion4322is also formed over the gap440protruding toward the gap440during the second deposition. The deposition rate of the second deposition is adjusted according to a size of the opening H431, and is not limited herein. A thickness D430of the second electrode430is greater than the thickness of the D410of the first electrode410due to extra deposition.

In some embodiments, the thickness D430of the second electrode430is in a range of 200 to 400 nanometers. In some embodiments, a thickness D432of the second portion432covering the gap440is in a range of 300 to 400 nanometers. The first layer431′ and the second layer432′ together form the second electrode430. In some embodiments, the second electrode430includes indium tin oxide (ITO). In some embodiments having the gap440sealed in the second electrode430, the second electrode430is a multi-layer structure. In some embodiments, average grand sizes of the first layer431′ and the second layer432′ are different due to different deposition rate. In some embodiments, the average grain size of the first layer431′ is smaller than the average grand size of the second layer432′ of the second electrode430due to the lower deposition rate. In some embodiments, an interface or a boundary between the first layer431′ and the second layer432′ of the second electrode430can be observed under microscope.

In some embodiments, a PDL450is formed prior to formation of the second electrode430. In some embodiments, the PDL450is formed during the forming of the photodiode420.

Referring toFIG. 10, an anti-reflective layer510is formed over the second electrode430, and an optical sensor11similar to the optical sensor10is formed. The anti-reflective layer510includes a convex portion5101at a position corresponding to the convex portions4321and4323of the second electrode430. The convex portion5101can function as a micron lens. In some embodiments, a thickness D510of the anti-reflective layer510is in a range of 150 to 270 nanometers. In some embodiments, a width W5101of the convex portion5101over the gap440is in a range of 160 to 300 micrometers. In some embodiments, the convex portion5101has a circular shape from a top view perspective (not shown), wherein the width W5101is the diameter of the convex portion5101. In some embodiments, the anti-reflective layer510includes two convex portions5101conformal to the two convex portions4321and4323of the second electrode430depending on a deposition rate for forming the anti-reflective layer510. In some embodiments, a layer of a micron lens array is formed over the anti-reflective layer510(not shown).

In accordance with other embodiments of the present disclosure, in order to form an optical sensor similar to the optical sensor20, the operation (O15) is performed during formation of the first electrode410of the operation (O12). Referring toFIGS. 11 to 12in accordance with some embodiments and the operations (O12) and (O15), a first deposition is performed to form a first layer411′ including a U-shaped portion411of the first electrode410. The intermediate structure as shown inFIG. 11is similar to the intermediate structure as shown inFIG. 6, and repeated description is omitted herein. In the embodiments shown inFIG. 11, a thickness of a reflective layer330is in a range of 30 to 200 nanometers.

A second deposition is performed to form a second layer412′ over the first layer411′, thereby forming the first electrode410and an gap440within the first electrode410, wherein a deposition rate of the second deposition is greater than a deposition rate of the first deposition. The second layer412′ includes a cap portion412formed over the gap440and the U-shaped portion411. The formation of the first electrode410as shown inFIGS. 11 to 12is similar to the formation of the second electrode430as shown inFIGS. 8 to 9. However, in the embodiments shown inFIGS. 11 to 12, the cap portion412of the second layer412′ includes a concave portion4124over the gap440and facing the gap440. Since the opening H411′ shown inFIG. 11is wider than the opening H431shown inFIG. 8, the recessed portion4124is formed instead of a convex portion, and the recessed portion4124may be similar to the convex portion4322of the optical sensor10.

In some embodiments having the gap440sealed in the first electrode410, the first electrode410is a multi-layer structure. In some embodiments, average grand sizes of the first layer411′ and the second layer412′ are different due to different deposition rate. In some embodiments, the average grain size of the first layer411′ is smaller than the average grand size of the second layer412′ of the first electrode410due to the lower deposition rate. In some embodiments, an interface or a boundary between the first layer411′ and the second layer412′ of the first electrode410can be observed under microscope.

Referring toFIG. 13, a photodiode420, a second electrode430and an anti-reflective layer510are subsequently formed over the first electrode410. The photodiode420, the second electrode430and the anti-reflective layer510are similar to those illustrated inFIG. 2, and repeated description is omitted herein. An optical sensor21similar to the optical sensor20is formed. In some embodiments, the optical sensor21further includes a layer of a micron lens array (not shown) formed over the anti-reflective layer510to further enhance light absorption.

Under the same concepts, some embodiments of the present disclosure provide an optical sensor includes a gap between a second electrode and at least a portion of an anti-reflective layer. In some embodiments, an optical sensor30includes a gap440defined by a second electrode430and an anti-reflective layer510is provided as shown inFIG. 14. The gap is defined by the U-shaped first portion431of the second electrode430and the anti-reflective layer510. As shown inFIG. 14, a deposition operation is performed to form anti-reflective layer510, wherein the deposition operation has a high deposition rate, after the first deposition of the second electrode as illustrated inFIG. 8and relevant paragraphs. One or more convex portions5121, protruding away from the gap440, are formed over the gap440. In some embodiments, depending on the deposition rate, multiple convex portions5121are formed as shown inFIG. 14at positions corresponding to the top edges E431of the second electrode430as shown inFIG. 8. In some embodiments, one convex portion5121is formed directly over the gap440(not show). In order to form a micro lens structure of the anti-reflective layer510, in some embodiments, a thickness D510of the anti-reflective layer510is greater than or equal to 1000 nanometers. In some embodiments, the thickness D510of the anti-reflective layer510is in a range of 1000 to 5000 nanometers.

Depending on the deposition rate for forming the anti-reflective layer510, the anti-reflective layer510may include a concave portion5122facing the gap440as shown inFIG. 14of the optical sensor30, or the anti-reflective layer510may include a convex portion5123protruding toward the gap440as shown inFIG. 15of an optical sensor31.

Referring toFIG. 16, in accordance with some embodiments of the present disclosure, an optical sensor32having a gap440sealed in an anti-reflective layer510is provided. Similar to the first deposition and second deposition of forming the second electrode430as illustrated inFIGS. 8 to 9and relevant paragraphs, a first deposition with low deposition rate is performed to form a first portion511conformal to a second electrode430, wherein the first portion511includes a U-shaped portion lining a U-shaped portion431of the second electrode430and a planar portion over a planar layer320. A second deposition with high deposition rate is performed to form a second portion512capping the U-shaped portion of the first portion511. The second portion512includes a planar portion over the planar portion of the first portion511, and a cap portion including a convex portion5121and a convex portion5123. In some embodiments, a concave portion5122is formed over the U-shaped portion of the first portion511of the anti-reflective layer510instead of the convex portion5123depending on the deposition rate. In some embodiments, a portion of the first portion511is adjacent to the gap440and conformal to a convex portion4311of the second electrode430.

In some embodiments having the gap440sealed in the anti-reflective layer510, the anti-reflective layer510is a multi-layer structure. In some embodiments, average grand sizes of the first portion511and the second portion512are different due to different deposition rate. In some embodiments, the average grain size of the first portion511is smaller than the average grand size of the second portion512of the anti-reflective layer510due to the lower deposition rate. In some embodiments, an interface or a boundary between the first portion511and the second portion512of the anti-reflective layer510can be observed under microscope.

Therefore, from an aspect of the present disclosure, an optical sensor is provided. The optical sensor includes a substrate, a transistor, a dielectric layer, a first electrode, a photodiode, a second electrode and a gap. The transistor is disposed over the substrate. The dielectric layer is disposed over the transistor. The first electrode is disposed over the dielectric layer and includes a U-shaped portion electrically connected to the transistor. The second electrode is disposed over the first electrode, and the photodiode is disposed between the first electrode and the second electrode. The gap is surrounded by the U-shaped portion of the first electrode and sealed by the first electrode or the second electrode.

From another aspect of the present disclosure, a method for forming an optical sensor is provided. The method includes following operations: (O11) receiving a semiconductor substrate having a connecting structure exposed through an opening; (O12) forming a first electrode over the semiconductor substrate, wherein at least a portion of the first electrode lines the opening; (O13) forming a photodiode over the first electrode; (O14) forming a second electrode over the photodiode; and (O15) forming an gap within the first electrode or the second electrode. The operation (O15) can be performed during the formation of the first electrode of the operation (O12), or during the formation of the second electrode of the operation (O14).

From another aspect of the present disclosure, an optical sensor is provided. The optical sensor includes: a substrate, a transistor, a dielectric layer, a first electrode, a photodiode, a second electrode, an anti-reflective layer and a gap. The transistor is disposed over the substrate. The dielectric layer is disposed over the transistor. The first electrode is disposed over the dielectric layer and includes a U-shaped portion electrically connected to the transistor. The second electrode is conformally disposed over the first electrode, and the photodiode is disposed between the first electrode and the second electrode. The gap is surrounded by the U-shaped portion of the first electrode and disposed between the second electrode and at least a portion of the anti-reflective layer.