Low-Temperature PVD Cavity Sealing with Germanium or Silicon

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Solution Overview

Problem

Existing methods for sealing micro- or nano-devices under vacuum face challenges such as high production costs, temperature limitations, and unsuitability for applications requiring low-pressure and low-temperature processes, particularly in fields like uncooled infrared detectors where thermal insulation and infrared transparency are crucial.

Innovation Solution

The method involves physical vapour deposition of germanium (Ge) or silicon (Si) using standard equipment at low pressures and temperatures below 100°C, without intentional heating of the substrate, allowing for efficient sealing of cavities while maintaining transparency to infrared radiation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If CVD techniques are used for cavity sealing, then good conformity of the deposit is achieved, but high temperature (>400°C) is required which precludes certain applications

Engineering Contradiction:

Improveconformity of the depositVSAvoiddeposition temperature

Core Design Contradiction:

Manufacturing precisionVSTemperature

Solution Approach 1:

The invention changes the fundamental parameter of deposition temperature from high (>400°C in CVD) to low (<100°C in PVD) while maintaining deposit quality through a different physical mechanism (physical vapor deposition instead of chemical vapor deposition). This parameter change enables applications with low thermal budgets such as micro-bolometers and integrated circuits.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the chemical mechanism of CVD (chemical reactions of precursor gases) with a physical mechanism (PVD through evaporation or sputtering). This substitution eliminates the need for high temperatures and chemical precursors, reducing thermal budget and organic waste while achieving conformal deposits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If wafer bonding methods are used for cavity sealing, then sealing is achieved, but the process is complicated and requires temperature rise that may be critical for certain devices

Engineering Contradiction:

Improvesealing effectivenessVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention extracts the sealing function from the complex wafer bonding process and implements it through a simpler PVD deposition step. By depositing material directly onto the wafer surface to form the seal, the process eliminates the need for separate bonding operations, temperature cycling, and alignment procedures required by wafer bonding methods.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention merges the sealing function with the existing PVD deposition process used for other wafer treatments. The same PVD equipment and process conditions used for depositing functional layers are utilized to create the seal, consolidating multiple functions into a single process step and reducing overall process complexity.

Inventive Principle:

Principle #5Merging (Combining)

3Temperature

If PVD methods are used for cavity sealing, then low temperature process is achieved, but substrate heating is typically required to densify deposits and improve adhesion

Engineering Contradiction:

Improveprocess temperatureVSAvoiddeposit density and adhesion

Core Design Contradiction:

TemperatureVSManufacturing precision

Solution Approach 1:

The invention changes the deposition parameters (flux rate, substrate distance, vacuum level) to optimize low-temperature PVD performance. By controlling these parameters, high-quality deposits with good adhesion and density are achieved without substrate heating, enabling low-thermal-budget applications.

Inventive Principle:

Principle #35Parameter changes

4Reliability

If standard packaging methods are used for cavity sealing, then sealing is achieved, but production cost remains very high

Engineering Contradiction:

Improvesealing effectivenessVSAvoidproduction cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention makes the PVD deposition process multi-functional by using it both for depositing functional layers and for creating seals. This universal application of the PVD process eliminates the need for separate sealing operations and enables collective treatment of multiple wafers simultaneously, significantly reducing production costs while maintaining seal quality.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 significantly reduces production costs, avoids temperature-related issues, and achieves effective sealing of cavities with high infrared transparency, suitable for sensitive materials like glasses and polymers, and micro-bolometers, while maintaining a low thermal budget.

Implementation Method 1

The method involves physical vapour deposition of germanium (Ge) or silicon (Si) using standard equipment at low pressures and temperatures below 100°C

Methodology Applied

Scientific EffectPhysical vapour deposition: Physical Vapour Deposition