Infrared Window Wafer AR Gratings on Planar Handle Silicon

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Solution Overview

Problem

Existing methods for fabricating infrared transparent window wafers with integrated anti-reflection grating structures face challenges in using sub-micron lithography and etching due to the nonplanarity of surfaces after cavity formation in silicon on insulator (SOI) structures.

Innovation Solution

The method involves etching high spatial frequency anti-reflection (AR) grating structures into the first surface of an infrared transparent silicon handle wafer before bonding it with a silicon device wafer to form a silicon on insulator (SOI) structure, allowing for the use of sub-micron lithography and etching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If AR grating structures are formed after cavity formation in SOI structure, then the cavity structure is achieved, but sub-micron lithography and etching cannot be used due to nonplanarity

Engineering Contradiction:

ImproveAR grating structure precisionVSAvoidFabrication process complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by forming the AR grating structures on the handle wafer before bonding it to the device wafer to create the SOI structure. This sequence allows sub-micron lithography and etching to be performed on a planar surface, achieving high manufacturing precision for the AR gratings while avoiding the nonplanarity problem that would occur if the same processes were attempted after cavity formation.

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If sub-micron lithography and etching are used, then fine AR grating structures are achieved, but nonplanar surfaces prevent this approach after cavity formation

Engineering Contradiction:

ImproveAR grating structure precisionVSAvoidSurface planarity

Core Design Contradiction:

Manufacturing precisionVSShape

Solution Approach 1:

The patent performs the sub-micron lithography and etching operations before the bonding step that creates the nonplanar SOI structure. By executing these precision processes on the flat handle wafer surface prior to assembly, the method achieves fine AR grating structures with high manufacturing precision while avoiding the surface nonplanarity that would otherwise prevent such operations.

Inventive Principle:

Principle #10Preliminary action

3Shape

If AR gratings are formed on nonplanar surfaces, then cavity structure is maintained, but lithography and etching precision deteriorates

Engineering Contradiction:

ImproveCavity structureVSAvoidLithography and etching precision

Core Design Contradiction:

ShapeVSManufacturing precision

Solution Approach 1:

The patent resolves this contradiction by performing all lithography and etching operations to form the AR gratings before the bonding step that creates the cavity structure. This timing ensures that the lithography and etching processes occur on a planar surface, maintaining high precision, while the subsequent bonding step establishes the required cavity structure without compromising the already-formed AR gratings.

Inventive Principle:

Principle #10Preliminary action

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

This approach enables the fabrication of fine AR grating structures with desired optical properties, enhancing the transmittance and reducing reflectance of infrared radiation across the 7.5-13.5 μm spectral band, thus improving the performance of infrared transparent window wafers in wafer-level vacuum packaging.

Implementation Method 1

forming anti-reflection (AR) grating structures in a first portion of the first surface of the handle wafer

Methodology Applied

Scientific EffectAnti-reflection: Anti-Reflective Coating

Implementation Method 2

enhancing the transmittance and reducing reflectance of infrared radiation across the 7.5-13.5 μm spectral band

Methodology Applied

Scientific EffectOptical interference: Interference

Implementation Method 3

etching a recess in the planar side of the single crystal silicon layer to remove the oxide layer, form a plurality of recess walls, and expose the AR grating structures

Methodology Applied

Scientific EffectEtching: Ablation

Implementation Method 4

bonding the bonding side of the oxide layer to the first surface of the handle wafer

Methodology Applied

Scientific EffectBonding: Adhesive

Data Source

PatentUS20250185393A1Methods and systems for fabrication of infrared transparent window wafer with integrated Anti-reflection grating structures

Publication Date: 2025.06.05 DRS NETWORK & IMAGING SYSTEMS LLC

AI summary

A method of fabricating an IR transparent window wafer with integrated AR grating structures includes providing a handle wafer having a first surface and a second surface opposite the first surface, providing a device wafer including a single crystal silicon layer disposed on an oxide layer, the single crystal silicon layer having a planar side and the oxide layer having a bonding side that is opposite the planar side, forming AR grating structures in a first portion of the first surface of the handle wafer, bonding the bonding side of the oxide layer to the first surface of the handle wafer, and etching a recess in the planar side of the single crystal silicon layer to: remove the buried oxide layer, form a plurality of recess walls, and expose the AR grating structures in the first portion of the first surface of the handle wafer.