BACKGROUND

Technical Field

The disclosure relates to an optical element, and more particularly to an optical sensor and a method for forming the same.

Description of the Related Art

An optical sensor (e.g. image sensor) is used to convert an optical image focused on the image sensor into an electrical signal. The image sensor usually includes several groups of light-detecting elements, such as photodiodes, and a light-detecting element is configured to produce an electrical signal corresponding to the intensity of light incident to the light-detecting element. The electrical signal thus produced may be further processed by a signal-processing circuit to display a corresponding image on a monitor or provide information about the optical image.

Optical sensors are widely used in digital still cameras, security cameras, medical, automobile, and other applications. Currently, the technology used to manufacture image sensors (e.g. complementary metal-oxide-semiconductor (CMOS) image sensors (CIS)) and image quality, have continued to advance at a great pace.

While existing optical sensors have been generally adequate for their intended purposes, they have not been satisfactory in all respects. There is a particular need for further improvements in the light sensitivity of optical sensors.

SUMMARY

In one embodiment of the present disclosure, an optical sensor is provided, wherein the optical sensor includes a substrate, a first well, a second well, a third well, a deep trench isolation structure, and a passivation layer. The substrate has a first conductivity type and includes a sensing region. The first well is disposed in the sensing region, wherein the first well has a second conductivity type that is different from the first conductivity type and a first depth. The second well is disposed in the sensing region, wherein the second well has the second conductivity type and a second depth. The third well is disposed in the sensing region, wherein the third well has the first conductivity type and a third depth. The deep trench isolation structure is disposed in the substrate and surrounding the sensing region, wherein a depth of the deep trench isolation structure is greater than the first depth, the first depth is greater than the second depth, and the second depth is greater than the third depth. The passivation layer is disposed over the substrate, wherein the passivation layer includes a plurality of protruding portions disposed directly above the sensing region.

In one embodiment of the present disclosure, a method for forming an optical sensor is provided, wherein the method includes: providing a substrate having a first conductivity type, wherein the substrate comprises a sensing region; forming a first well in the sensing region, wherein the first well has a second conductivity type that is different from the first conductivity type and a first depth; forming a second well in the sensing region, wherein the second well has the second conductivity type and a second depth; forming a third well in the sensing region, wherein the third well has the first conductivity type and a third depth; forming a deep trench isolation structure in the substrate and surrounding the sensing region, wherein a depth of the deep trench isolation structure is greater than the first depth, the first depth is greater than the second depth, and the second depth is greater than the third depth; and forming a passivation layer over the substrate, wherein the passivation layer comprises a plurality of protruding portions disposed directly above the sensing region.

