Method of stress relief in anti-reflective coated cap wafers for wafer level packaged infrared focal plane arrays

Patent metadata

Field	Value
Publication number	US-10315918-B2
Application number	US-201615227181-A
Country	US
Kind code	B2
Filing date	Aug 3, 2016
Priority date	Aug 23, 2012
Publication date	Jun 11, 2019
Grant date	Jun 11, 2019

Abstract

Methods for reducing wafer bow induced by an anti-reflective coating of a cap wafer are provided. The method may utilize a shadow mask having at least one opening therein that is positioned opposite recessed regions in a cap wafer. The method may further include depositing at least one layer of an anti-reflective coating material through the shadow mask onto a planar side of a cap wafer to provide a discontinuous coating on the planar side.

First claim

What is claimed is:

1. A method of reducing wafer bow induced by an anti-reflective coating on a cap wafer, the method comprising:
providing the cap wafer having a planar side and an opposing cavity side, the cavity side including a plurality of recessed regions and a dividing region on either side of the each of the plurality of recessed regions;
depositing a first discontinuous layer of an anti-reflective coating material onto the cavity side of the cap wafer; and
depositing a second layer of an anti-reflective coating material onto the planar side of the cap wafer to provide a discontinuous coating on the planar side such that the second discontinuous layer of the anti-reflective coating material is dimensioned and configured to partially overlap the dividing region and such that a wafer bow induced by the second discontinuous layer of the anti-reflective coating material is less than 30 microns.

2. The method of claim 1 , wherein depositing the first discontinuous layer of the anti-reflective coating material onto the cavity side of the cap wafer includes depositing the first discontinuous layer of the anti-reflective coating material in the recessed regions on the cavity side of the cap wafer.

3. The method of claim 2 , wherein the first and second discontinuous layers of the anti-reflective coating material are dimensioned and configured such that the wafer bow induced by the second discontinuous layer of the anti-reflective coating material is in balance with a wafer bow induced by the first discontinuous layer of the anti-reflective coating material.

4. The method of claim 2 , further comprising providing a device wafer onto which at least one MEMS device is formed.

5. The method of claim 4 , further comprising:
positioning the cap wafer over the device wafer such that the cavity side of the cap wafer is facing the at least one MEMS device;
aligning the cap wafer to the device wafer such that the at least one recessed region is positioned over the at least one MEMS device; and
bonding the cap wafer to the device wafer to create bonding structures.

6. The method of claim 5 , further comprising inspecting the bonding structures through inspection regions provided by the second discontinuous layer of the anti-reflective coating material.

7. The method of claim 6 , wherein the inspection is performed using a charge-coupled device (CCD).

8. A method of reducing wafer bow induced by an anti-reflective coating on a cap wafer, the method comprising:
providing the cap wafer having a planar side and an opposing cavity side;
depositing a first discontinuous layer of anti-reflective coating material onto the cavity side of the cap wafer; and
depositing a second discontinuous layer of anti-reflective coating material onto the planar side of the cap wafer such that the second discontinuous coating is dimensioned and configured such that a wafer bow induced by the second discontinuous layer of anti-reflective coating is less than 30 microns.

9. A cap wafer, comprising:
a planar side and an opposing cavity side;
a first discontinuous layer of anti-reflective coating material disposed on the cavity side; and
a second discontinuous layer of anti-reflective coating material disposed on the planar side, the second discontinuous layer of anti-reflective coating material being dimensioned and configured such that a wafer bow induced by the second discontinuous layer of anti-reflective coating is less than 30 microns.

10. The cap wafer of claim 9 , wherein the cavity side of the cap wafer includes a plurality of recessed regions and the first discontinuous layer of anti-reflective coating is disposed in the plurality of recessed regions.

11. The cap wafer of claim 9 , wherein the dimensions of the second discontinuous layer of anti-reflective coating material are larger than the dimensions of the first discontinuous layer of anti-reflective coating material.

12. The cap wafer of claim 9 , wherein the second discontinuous layer of anti-reflective coating corresponds to saw streets on the cap wafer such that the dimensions of the anti-reflective coating material extend to the saw streets.

13. The cap wafer of claim 10 , wherein the second discontinuous layer of anti-reflective coating material is dimensioned and configured to extend beyond each recessed region of the plurality of recessed regions.

14. The cap wafer of claim 13 , wherein the cavity side of the cap wafer includes a dividing region on each side of each recessed region, and the second discontinuous layer of anti-reflective coating material is dimensioned and configured to partially overlap each dividing region.

15. The cap wafer of claim 9 , wherein the first discontinuous layer of anti-reflective coating material and the second discontinuous layer of anti-reflective coating material are dimensioned and configured such that the wafer bow induced by the second discontinuous layer is in balance with a wafer bow induced by the first discontinuous layer of anti-reflective coating material.

16. The cap wafer of claim 9 , wherein the wafer bow induced by the second discontinuous layer of anti-reflective coating is less than 20 microns.

17. The cap wafer of claim 9 , wherein the second discontinuous layer of anti-reflective coating material is dimensioned and configured to correspond to saw streets on the cap wafer.

18. The cap wafer of claim 9 , wherein the cap wafer is constructed from a material that is optically transmissive in both the visible and the infrared electromagnetic spectrum.

Assignees

• Raytheon Co

Inventors

• Gooch Roland W
• Diep Buu Q
• Black Stephen H
• Kocian Thomas A
• Kennedy Adam M

Classifications

• B81C2203/0118

  Bonding a wafer on the substrate, i.e. where the cap consists of another wafer · CPC title

• B81B2201/0207

  Bolometers · CPC title

• B81C1/00325 Primary

  for reducing stress inside of the package structure · CPC title

• B05D5/061

  Special surface effect · CPC title

• B81B7/0067

  for controlling the passage of optical signals through the package · CPC title