US-12628442-B2 - Lens structure configured to increase quantum efficiency of image sensor

Abstract

Various embodiments of the present disclosure are directed towards a method for forming an image sensor, the method includes forming a photodetector within a substrate. The substrate is etched to define a plurality of first protrusions over the photodetector. A first dielectric layer is deposited on the substrate. A second dielectric layer is deposited on the first dielectric layer. An etching process is performed on the first and second dielectric layers such that the first dielectric layer comprises a plurality of second protrusions different from the plurality of first protrusions. The first dielectric layer is etched more quickly than the second dielectric layer during the etching process.

Inventors

• Jiech-Fun Lu
• Chun-Tsung Kuo

Assignees

• TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.

Dates

Publication Date

20260512

Application Date

20220503

Claims (20)

1. 1 . A method for forming an image sensor, the method comprising: forming a photodetector within a substrate; etching the substrate to define a plurality of first protrusions over the photodetector; depositing a first dielectric layer on the substrate; depositing a second dielectric layer on the first dielectric layer; and performing an etching process on the first and second dielectric layers, wherein the etching process forms a plurality of second protrusions in the first dielectric layer different from the plurality of first protrusions, wherein the first dielectric layer is etched more quickly than the second dielectric layer during the etching process.
2. 2 . The method of claim 1 , wherein the first dielectric layer is formed to a first thickness and the second dielectric layer is formed to a second thickness greater than the first thickness.
3. 3 . The method of claim 1 , wherein the first dielectric layer comprises a first material and the second dielectric layer comprises a second material different from the first material.
4. 4 . The method of claim 1 , wherein the etching process completely removes the second dielectric layer from over the substrate.
5. 5 . The method of claim 1 , wherein the etching process includes performing a first etch to reduce a thickness of the second dielectric layer and a second etch to define the plurality of second protrusions in the first dielectric layer.
6. 6 . The method of claim 5 , wherein the first etch is different from the second etch.
7. 7 . The method of claim 1 , further comprising: forming a light filter on the plurality of second protrusions; and forming an upper lens over the light filter, wherein the upper lens and the second protrusions respectively comprise a curved upper surface.
8. 8 . The method of claim 1 , wherein a height of the plurality of first protrusions is greater than a height of the plurality of second protrusions.
9. 9 . The method of claim 1 , wherein the second dielectric layer is deposited such that an upper surface of the second dielectric layer comprises a plurality of upper protrusions that conform to a shape of the plurality of first protrusions, wherein the upper protrusions are removed by the etching process.
10. 10 . A method for forming an image sensor, the method comprising: forming a photodetector within a substrate; etching the substrate to define a plurality of first protrusions over the photodetector; depositing a first dielectric layer on the substrate, wherein the first dielectric layer is disposed laterally between and contacts an adjacent pair of protrusions in the plurality of first protrusions; depositing a second dielectric layer on the first dielectric layer; and performing an etching process on the first and second dielectric layers, wherein the etching process forms a plurality of second protrusions in the first dielectric layer different from the plurality of first protrusions, wherein the first dielectric layer is etched more quickly than the second dielectric layer during the etching process, wherein the second protrusions respectively comprise a convex upper surface.
11. 11 . The method of claim 10 , wherein an index of refraction of the substrate is greater than an index of refraction of the first dielectric layer.
12. 12 . The method of claim 10 , wherein the substrate comprises silicon and the first dielectric layer comprises silicon dioxide.
13. 13 . The method of claim 10 , further comprising: forming an isolation structure extending into a front-side surface of the substrate, wherein the photodetector is spaced between sidewalls of the isolation structure, and wherein the first protrusions are disposed along a back-side surface of the substrate opposite the front-side surface.
14. 14 . The method of claim 10 , wherein the adjacent pair of protrusions are separated from one another by a lateral distance that is greater than a height of the plurality of second protrusions.
15. 15 . The method of claim 10 , wherein the etching process comprises flowing one or more first etchants to reduce a thickness of the second dielectric layer and flowing one or more second etchants to form the plurality of second protrusions, wherein the one or more first etchants are different from the one or more second etchants.
16. 16 . A method for forming an image sensor, the method comprising: forming a photodetector within a substrate; etching the substrate to define a plurality of first protrusions over the photodetector; depositing a first dielectric layer on the substrate, wherein the first dielectric layer comprises a first material; depositing a second dielectric layer on the first dielectric layer, wherein the second dielectric layer comprises a second material different from the first material; and performing an etching process on the first and second dielectric layers, wherein the etching process forms a plurality of second protrusions in the first dielectric layer different from the plurality of first protrusions, wherein the first dielectric layer is etched more quickly than the second dielectric layer during the etching process, wherein the etching process comprises performing a first etch to reduce a thickness of the second dielectric layer and a second etch to define the plurality of second protrusions in the first dielectric layer.
17. 17 . The method of claim 16 , wherein the second etch comprises a blanket dry etch.
18. 18 . The method of claim 16 , further comprising: forming a light filter on the first dielectric layer and directly contacting the plurality of second protrusions.
19. 19 . The method of claim 16 , further comprising: forming a lens structure over the first dielectric layer, wherein the lens structure comprises a curved upper surface having a length greater than a length of a convex upper surface of an individual protrusion in the plurality of second protrusions.
20. 20 . The method of claim 16 , wherein the second etch comprises exposing the first and second dielectric layers to octafluorocyclobutane and/or trifluoromethane.

Description

REFERENCE TO RELATED APPLICATIONS This application is a Divisional of U.S. application Ser. No. 16/804,208, filed on Feb. 28, 2020, which claims the benefit of U.S. Provisional Application No. 62/928,559, filed on Oct. 31, 2019. The contents of the above-referenced patent applications are hereby incorporated by reference in their entirety. BACKGROUND Many modern day electronic devices (e.g., digital cameras, optical imaging devices, etc.) comprise image sensors. Image sensors convert optical images to digital data that may be represented as digital images. An image sensor includes an array of pixel sensors, which are unit devices for the conversion of an optical image into digital data. Some types of pixel sensors include charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors (CIS). Compared to CCD pixel sensors, CIS are favored due to low power consumption, small size, fast data processing, a direct output of data, and low manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. FIG. 1 illustrates a cross-sectional view of some embodiments of an image sensor including a substrate with a plurality of protrusions, and a plurality of micro-lenses disposed over and spaced laterally between the protrusions. FIG. 2 illustrates a cross-sectional view of some alternative embodiments of the image sensor of FIG. 1, in which a plurality of semiconductor devices are disposed on a front-side surface of the substrate. FIGS. 3A-B illustrate cross-sectional views of some alternative embodiments of the image sensor of FIG. 2, in which light filters overlie the plurality of micro-lenses. FIGS. 4-9 illustrate cross-sectional views of some embodiments of a method of forming an image sensor that includes a substrate with a plurality of protrusions, and a plurality of micro-lenses disposed over and spaced laterally between the protrusions. FIG. 10 illustrates a method in flow chart format that illustrates some embodiments of forming an image sensor that includes a substrate with a plurality of protrusions, and a plurality of micro-lenses disposed over and spaced laterally between the protrusions. DETAILED DESCRIPTION The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. CMOS image sensors (CIS) typically comprise an array of pixel regions, which respectively have a photodetector arranged within a semiconductor substrate. Light filters (e.g., color filters, infrared (IR) filters, etc.) are arranged over the photodetectors and are configured to filter incident light provided to different photodetectors within the CIS. Upon receiving light, the photodetectors are configured to generate electric signals corresponding to the received light. The electric signals from the photodetectors can be processed by a signal processing unit to determine an image captured by the CIS. Quantum efficiency (QE) is a ratio of the numbers of photons that contribute to an electric signal generated by a photodetector within a pixel region to the number of photons incident on the pixel region. It has been appreciated that the QE of a CIS can be impro