High-Resolution Integrated X-Ray CMOS Image Sensor

• US 20090181491A1
• Filed: 02/20/2009
• Published: 07/16/2009
• Est. Priority Date: 11/24/2006
• Status: Active Grant

• Current Assignee: Tower Semiconductor Limited
• Original Assignee: Tower Semiconductor Limited
• Inventors: Strum, Avi, Pardess, Doron, Fenigstein, Amos, Roizin, Yakov, Heiman, Alexey
• Granted Patent: US 8,501,573 B2
• Time in Patent Office: Days
• US Class Current: 438/72
• CPC Class Codes: G01T 1/20183 Arrangements for preventing or correcting crosstalk, e.g. optical or electrical arrangements for correcting crosstalk
• CPC Class Codes: G01T 1/20187 Position of the scintillator with respect to the photodiode, e.g. photodiode surrounding the crystal, the crystal surrounding the photodiode, shape or size of the scintillator

Abstract

An X-ray image sensor having scintillating material embedded into wave-guide structures fabricated in a CMOS image sensor (CIS). After the CIS has been fabricated, openings (deep pores) are formed in the back side of the CIS wafer. These openings terminate at a distance of about 1 to 5 microns below the upper silicon surface of the wafer. The depth of these openings can be controlled by stopping on a buried insulating layer, or by stopping on an epitaxial silicon layer having a distinctive doping concentration. The openings are aligned with corresponding photodiodes of the CIS. The openings may have a shape that narrows as approaching the photodiodes. A thin layer of a reflective material may be formed on the sidewalls of the openings, thereby improving the efficiency of the resulting waveguide structures. Scintillating material (e.g., CsI(Tl)) is introduced into the openings using a ForceFill™ technology or by mechanical pressing.

Claims

1. A method of fabricating an integrated X-ray image sensor comprising:

reducing a thickness of a semiconductor image sensor by removing material from a back side of the semiconductor image sensor;

then

forming a plurality of openings in the back side of the semiconductor image sensor;

then

forming a layer of scintillating material over the back side of the semiconductor image sensor; and

then

applying a force to the layer of scintillating material, such that scintillating material is forced into the openings.

2. The method of claim 1, wherein the step of reducing the thickness of the semiconductor image sensor comprises grinding the back side of a semiconductor wafer.

3. The method of claim 2, wherein the step of reducing the thickness of the semiconductor image sensor is stopped when the back side of the semiconductor wafer has a thickness in the range of 50 to 250 microns.

4. The method of claim 1, wherein the step of forming a plurality of openings in the back side of the semiconductor image sensor comprises performing a deep reactive ion etch.

5. The method of claim 4, further comprising stopping the deep reactive ion etch on a buried insulating layer in the semiconductor image sensor.

6. The method of claim 4, further comprises performing a wet etch after the deep reactive ion etch has been stopped, and stopping the wet etch on an epitaxial silicon layer in the semiconductor image sensor.

7. The method of claim 6, further comprising thermally oxidizing portions of the epitaxial silicon layer exposed by the wet etch.

8. The method of claim 6, further comprising implanting an impurity into portions of the epitaxial silicon layer exposed by the wet etch.

9. The method of claim 1, further comprising forming a layer of reflective material on sidewalls of the openings prior to forming the layer of scintillating material.

10. The method of claim 9, further comprising forming the layer of reflective material by forming silicon oxide on the sidewalls of the openings.

11. The method of claim 9, further comprising forming the layer of reflective material by forming a metal on the sidewalls of the openings.

12. The method of claim 1, wherein the steps of forming the layer of scintillating material and applying a force to the layer of scintillating material are performed at temperatures that do not exceed 500°

C.

13. The method of claim 1, wherein the step of applying a force to the scintillating material comprises introducing a pressure of at least about 10 MPa to the layer of scintillating material.

14. The method of claim 1, wherein the step of applying a force to the scintillating material comprises mechanically pressing the layer of scintillating material.

15. The method of claim 1, further comprising depositing a layer of reflective material over the back side of the semiconductor image sensor after scintillating material has been forced into the openings.

16. The method of claim 1, wherein the step of forming the openings is performed such that the openings have a conical shape.