Method for making backside illuminated image sensor

• US 6,168,965 B1
• Filed: 08/12/1999
• Issued: 01/02/2001
• Est. Priority Date: 08/12/1999
• Status: Expired due to Term

• Current Assignee: Alidouble Inc.
• Original Assignee: Tower Semiconductor Limited
• Inventors: Malinovich, Yacov, Koltin, Ephie
• Primary Examiner(s): Pham, Long
• Application Number:
  US09/372,863
• Time in Patent Office: 509 Days
• Field of Search: 438/641, 438/66, 438/68, 148/DIG.12, 148/DIG.135, 257/258, 257/447
• US Class Current: 438/66
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14632 Wafer-level processed structures
• CPC Class Codes: H01L 27/14634 Assemblies, i.e. Hybrid structures
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14687 Wafer level processing
• CPC Class Codes: Y10S 148/012 Bonding, e.g. electrostatic for strain gauges
• CPC Class Codes: Y10S 148/135 Removal of substrate

Abstract

A method for producing a back-illuminated CMOS image sensor including a matrix of pixels (e.g., CMOS APS cells) that are fabricated on a semiconductor substrate. The semiconductor substrate is secured to a protective substrate by an adhesive such that the processed (frontside) surface of the semiconductor substrate faces the protective substrate. With the protective substrate providing structural support, the exposed backside surface of the semiconductor substrate is then subjected to grinding and/or chemical etching, followed by optional chemical/mechanical processing, to thin the semiconductor substrate to a range of 10 to 15 microns. A transparent substrate (e.g., glass) is then secured to the backside surface of the semiconductor substrate, thereby sandwiching the semiconductor substrate between the transparent substrate and the protective substrate.

Claims

1. A method of producing backside illuminated image sensors comprising the steps of:

producing a plurality of image sensor circuits on a wafer having first and second surfaces each of the image sensor circuits being formed on the first surface and including a matrix of light-sensitive pixel regions extending into the wafer from the first surface;

securing the wafer onto a protective substrate such that the first surface faces the protective substrate;

removing material from the second surface of the wafer until the light-sensitive pixel regions of each image sensor circuit are effectively exposed through the second surface;

securing a transparent substrate onto the second surface of the wafer, thereby producing a waferwise sandwich; and

slicing the waferwise sandwich, thereby defining a plurality of backside illuminated image sensors.

2. The method according to claim 1, wherein the step of securing the protective substrate onto the first surface comprises depositing an adhesive onto the protective substrate, and then placing the wafer onto the protective substrate such that the first surface contacts the deposited adhesive.

3. The method according to claim 1, wherein the step of removing material from the wafer comprises:

grinding the second surface until a thickness of each image sensor circuit is in the range of 120 to 140 microns; and

etching the second surface until a thickness of each image sensor circuit is in the range of 10 to 15 microns.

4. The method according to claim 3, wherein the step of etching comprises:

scribing the second surface along predetermined dice lines located between the plurality of image sensor circuits; and

applying an etching solution to the second surface to expose metal contact pads located on the first surface of the wafer.

5. The method according to claim 1, wherein the step of removing material from the wafer comprises:

performing a first etching process on the second surface, and

performing a second etching process on the second surface to separate the image sensor circuits from each other so as to define edges thereof.

6. The method according to claim 5, wherein the step of performing the second etching process comprises:

scribing the second surface along predetermined dice lines located between the plurality of image sensor circuits; and

applying an etching solution to the second surface to expose metal contact pads located on the first surface of the wafer.

7. The method according to claim 1, wherein the step of securing a transparent substrate onto the second surface comprises depositing an adhesive onto the second surface, and then placing the transparent substrate onto the deposited adhesive.

8. The method according to claim 7,

wherein the step of removing material includes separating each of the plurality of image sensor circuits;

and

wherein the step of depositing the adhesive onto the second surface further comprises depositing adhesive into interstices located between the plurality of image sensor circuits, thereby protecting the image sensor circuits.

9. The method according to claim 1, further comprising the step of forming metal leads on the protective substrate after the step of securing the transparent substrate, wherein the metal leads are connected to metal contact pads located on the first surface of the wafer.

10. The method according to claim 1, wherein the step of securing the wafer onto a protective substrate further comprises:

forming a passivation layer on the first surface of the wafer;

forming openings in the passivation layer; and

securing the protective substrate onto the passivation layer.

11. The method according to claim 1, further comprising, after the step of securing the transparent substrate, grinding the protective substrate until the protective substrate has a thickness of 50 microns.