Discontinuous Anti-Reflective Coating for Wafer Bow Reduction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The application of anti-reflective coatings on both sides of a cap wafer in MEMS devices induces internal stress, causing wafer bow, which interferes with processing steps and hermetic sealing in vacuum packaging.

Innovation Solution

A discontinuous anti-reflective coating is applied to the planar side of the cap wafer, with selective coating in recessed regions on the cavity side, using a shadow mask to reduce internal stress and minimize wafer bow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If anti-reflective coatings are applied on both sides of the cap wafer, then optical performance is improved, but internal stress increases causing wafer bow

Engineering Contradiction:

Improveoptical performanceVSAvoidwafer bow

Core Design Contradiction:

Illumination intensityVSShape

Solution Approach 1:

The patent applies anti-reflective coatings selectively only in the recessed regions of the cap wafer rather than uniformly across the entire surface. This localized coating approach maintains the optical performance benefits where needed (in the recesses) while minimizing the total coated area, thereby reducing internal stress and preventing wafer bow.

Inventive Principle:

Principle #3Local quality

2Area of stationary object

If continuous anti-reflective coating is applied, then optical coverage is improved, but manufacturing complexity increases due to wafer bow interference

Engineering Contradiction:

Improvecoating coverageVSAvoidprocessing difficulty

Core Design Contradiction:

Area of stationary objectVSEase of manufacture

Solution Approach 1:

The patent segments the anti-reflective coating into discrete regions corresponding to the recessed areas of the cap wafer. Instead of applying a continuous coating across the entire wafer surface, the coating is applied only in segmented recessed regions, which eliminates wafer bow and simplifies subsequent processing steps while still providing adequate optical coverage in the critical areas.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The method effectively reduces wafer bow to less than 30 microns, ensuring proper alignment, uniform polishing, and enhanced thermal contact, thereby improving the reliability of the hermetic sealing process.

Implementation Method 1

A discontinuous anti-reflective coating is applied to the planar side of the cap wafer, with selective coating in recessed regions on the cavity side, using a shadow mask to reduce internal stress

Methodology Applied

Scientific EffectShadow mask blocking: Shadow

Data Source

PatentEP2888196B1Method of stress relief in Anti-reflective coated cap wafers for wafer level packaged infrared focal plane arrays

Publication Date: 2020.03.18 RAYTHEON CO

Figure 1
Figure 2A
Figure 2B

AI summary

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.