Method for fabricating image sensor with uniform photosensitizing sensitivity

• US 8,431,425 B2
• Filed: 05/11/2012
• Issued: 04/30/2013
• Est. Priority Date: 08/27/2009
• Status: Active Grant

• Current Assignee: United Microelectronics Corporation
• Original Assignee: United Microelectronics Corporation
• Inventors: Hsieh, Cheng-Yu
• Primary Examiner(s): Pert, Evan
• Assistant Examiner(s): Laurenzi, Mark A
• Application Number:
  US13/469,369
• Publication Number:
  US 20120225516A1
• Time in Patent Office: 354 Days
• Field of Search: 257/98, 257/184, 257431-432, 257/E21.211, 438 69- 70, 438/75, 438/151, 438/321, 359/652, 359/665, 359/741, 359/796, 359/666
• US Class Current: 438/29
• CPC Class Codes: H01L 27/14627 Microlenses
• CPC Class Codes: H01L 27/14685 Process for coatings or optical elements

Abstract

A method for fabricating an image sensor is provided. A substrate is provided, and then a plurality of photoresist patterns is formed on the substrate. The photoresist patterns are arranged in a first array and defined by a plurality of photomask patterns arranged as a photomask pattern array, wherein a top view of each photoresist pattern has a substantially square shape and a distance between two neighboring photoresist patterns decreases from a center of the first array toward an edge of the first array. Besides, each photomask pattern includes a transparent portion and an opaque portion, wherein an area proportion of the transparent portion included in a photomask pattern increases from the center toward the edge of the photomask pattern array. Then, a thermal reflow step is performed to convert the photoresist patterns into a plurality of microlenses arranged in a second array.

Claims

1. A method of fabricating an image sensor, comprising:

providing a substrate of the image sensor;

defining on the substrate a plurality of photoresist patterns arranged in a first array by a plurality of photomask patterns arranged as a photomask pattern array, wherein a top view of each photoresist pattern has a substantially square shape and a distance between two neighboring photoresist patterns decreases from a center of the first array toward an edge of the first array, and each photomask pattern includes a transparent portion and an opaque portion, wherein an area proportion of the transparent portion included in the photomask pattern increases from the center of the photomask pattern array toward the edge of the photomask pattern array; and

performing a thermal reflow step to convert the photoresist patterns into a plurality of microlenses arranged in a second array.

2. The method of claim 1, wherein a height of the photoresist pattern decreases from the center of the first array toward an edge of the first array.

3. The method of claim 1, wherein the transparent portion includes a plurality of transparent line regions.

4. The method of claim 1, wherein the transparent portion includes a plurality of transparent dot regions.

5. The method of claim 1, wherein the image sensor is a CMOS image sensor or a CCD image sensor.

6. The method of claim 1, wherein curvature of the microlens decreases from a center of the second array toward an edge of the second array.

7. The method of claim 1, wherein area of the photoresist pattern increases from the center of the first array toward the edge of the first array.