Double-Sided Alignment Keys for Microdevice Substrate Precision

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Solution Overview

Problem

Conventional microfabrication processes face challenges in achieving high alignment accuracy between device structures on opposing sides of a substrate, such as semiconductor wafers, due to indirect alignment methods which may not provide sufficient precision for advanced applications.

Innovation Solution

The method involves selectively etching alignment keys through the substrate from one surface to the opposing surface, allowing for direct photolithographic alignment and pattern formation on the second surface using these keys, which can include forming an electrically insulating layer and semiconductor handling layer, and optionally bonding a capping layer or thermally oxidizing to expose the keys for precise alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If indirect alignment process is used based on captured image, then alignment process can be performed, but alignment accuracy is insufficient for high precision applications

Engineering Contradiction:

Improvealignment accuracyVSAvoidalignment precision between device structures

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent introduces alignment keys as intermediary physical features etched through the substrate that serve as direct reference markers for photolithographic alignment. These keys act as a mediator between the first and second device structures, enabling precise optical alignment without relying on indirect image capture and processing methods.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the indirect mechanical/image-based alignment system with a direct optical alignment system using photolithography. By etching alignment keys that extend through the substrate and using them as direct references for photolithographic mask alignment, the method substitutes complex mechanical alignment procedures with simpler, more accurate optical alignment.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If alignment keys extend through substrate to second surface, then direct photolithographic alignment is enabled, but additional etching steps are required

Engineering Contradiction:

Improvealignment accuracyVSAvoidprocess complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the alignment key formation process with the device structure fabrication process. By etching alignment keys through the substrate during the same manufacturing sequence used to create device structures, the method combines multiple functions into a unified process flow, reducing overall process complexity despite the through-substrate etching requirement.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent performs preliminary etching of alignment keys through the substrate before final device structure formation. By preparing the alignment reference features in advance, the method enables subsequent direct photolithographic alignment without adding significant complexity to the overall process, as the keys are already in place to guide subsequent fabrication steps.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If conventional indirect alignment is used, then process steps are simpler, but alignment precision between opposing surfaces is insufficient

Engineering Contradiction:

Improvealignment precisionVSAvoidfabrication simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The alignment keys serve as intermediary physical reference features that simplify the alignment process by providing direct, visible markers for photolithographic mask alignment. Instead of complex indirect image processing, the keys act as straightforward reference points that enhance manufacturing precision while maintaining relative ease of fabrication through standard photolithographic techniques.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 enhances alignment accuracy and precision in forming two-sided microstructures, enabling the creation of complex patterns and microelectromechanical resonators with improved structural integrity and alignment.

Implementation Method 1

A direct photolithographic alignment step is then performed on a second surface of the substrate by aligning a photolithography mask to the plurality of alignment keys at the second surface

Methodology Applied

Scientific EffectPhotolithographic alignment: Photography

Implementation Method 2

selectively etching a first surface of the substrate to define a plurality of alignment keys therein that extend through the substrate to a second surface

Methodology Applied

Scientific EffectSelective etching:

Data Source

PatentUS8283256B1Methods of forming microdevice substrates using double-sided alignment techniques

Publication Date: 2012.10.09 RENESAS ELECTRONICS AMERICA INC

AI summary

Methods of forming substrates having two-sided microstructures therein include selectively etching a first surface of the substrate to define a plurality of alignment keys therein that extend through the substrate to a second surface thereof. A direct photolithographic alignment step is then performed on a second surface of the substrate by aligning a photolithography mask to the plurality of alignment keys at the second surface. This direct alignment step is performed during steps to photolithographically define patterns in the second surface.