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-9427776-B2
Application number	US-201213688714-A
Country	US
Kind code	B2
Filing date	Nov 29, 2012
Priority date	Aug 23, 2012
Publication date	Aug 30, 2016
Grant date	Aug 30, 2016

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 at least one recessed region and a dividing region on either side of the at least one recessed region;
positioning a first shadow mask having at least one opening therein over the planar side of the cap wafer, the at least one opening dimensioned to extend beyond the at least one recessed region on the cap wafer;
aligning the first shadow mask such that the at least one opening is positioned opposite the at least one recessed region; and
depositing at least one layer of an anti-reflective coating material through the first shadow mask onto the planar side of the cap wafer to provide a discontinuous coating on the planar side, the discontinuous coating dimensioned and configured such that a wafer bow induced by the anti-reflective coating is less than 30 microns for an 8 inch diameter cap wafer.

2. The method of claim 1 , wherein the wafer bow is less than 20 microns.

3. The method of claim 1 , wherein the at least one recessed region corresponds to the location of at least one micro-electromechanical system (MEMS) device on a corresponding device wafer.

4. The method of claim 1 , wherein the discontinuous coating corresponds to saw streets on the cap wafer.

5. The method of claim 1 , further comprising positioning a second shadow mask having at least one opening therein over the cavity side of the cap wafer and aligning the second shadow mask such that the at least one opening is positioned over the at least one recessed region.

6. The method of claim 5 , further comprising depositing at least one layer of an anti-reflective coating material through the at least one opening in the second shadow mask onto the cavity side of the cap wafer to provide a discontinuous coating on the cavity side.

7. The method of claim 6 , wherein the discontinuous coating on the planar side is dimensioned and configured such that a wafer bow induced by the anti-reflective coating is in balance with a wafer bow induced by the anti-reflective coating on the cavity side.

8. The method of claim 7 , further comprising providing a device wafer onto which at least one MEMS device is formed.

9. The method of claim 8 , 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.

10. The method of claim 9 , further comprising inspecting the bonding structures through inspection regions provided by the discontinuous coating on the planar side of the cap wafer.

11. The method of claim 10 , wherein the inspection is performed using a charge-coupled device (CCD).

Assignees

• Raytheon Co

Inventors

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

Classifications

• B05D5/061 Primary

  Special surface effect · CPC title

• B81B7/0067

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

• B81B2201/0207

  Bolometers · CPC title

• B81C2203/0118

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

• B81C1/00325 Primary

  for reducing stress inside of the package structure · CPC title