Low Temperature Polysilicon TFT Low Doped Drain Fabrication

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Solution Overview

Problem

The existing methods for forming low temperature polysilicon thin film transistors with a low doped drain structure require an additional photo mask, leading to increased costs and complexity, as well as inaccuracies in the fabrication process that result in shifting of the low doped drain structure, limiting yield.

Innovation Solution

A method that forms a low temperature polysilicon thin film transistor without an added photo mask by using a metal layer and cap layer sequence, where the metal layer acts as a mask for both high and low concentration ion-doping, eliminating the need for additional photo-etching steps and aligning inaccuracies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If an additional photo mask is used to define the low doped drain structure, then the doping regions can be formed with proper definition, but the fabrication cost increases and the process becomes more complicated

Engineering Contradiction:

Improvedefinition of doping regionsVSAvoidfabrication process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent introduces a metal layer as an intermediary mask layer between the photo-resist patterned layer and the polysilicon island. This metal layer serves as a reusable mask for both high concentration and low concentration ion-doping processes, eliminating the need for a second photo mask while maintaining precise definition of doping regions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The metal layer is designed to perform multiple functions: it acts as a mask for high concentration ion-doping to form heavily doped regions, and subsequently serves as a mask for low concentration ion-doping to form low doped drain regions. This multi-functionality eliminates the need for additional photo masks and reduces process complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Manufacturing precision

If an additional photo mask is used to form the low doped drain structure, then the doping regions can be properly defined, but the fabrication cost increases

Engineering Contradiction:

Improvedefinition of doping regionsVSAvoidfabrication cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The metal layer is retained and reused as a mask for the low concentration ion-doping process after serving as a mask for high concentration doping. This recovery and reuse of the metal layer mask eliminates the need to discard it after the first doping step, thereby reducing material costs and process steps.

Inventive Principle:

Principle #34Discarding and recovering

3Manufacturing precision

If photo etching process is used to form the photo-resist patterned layer, then the low doped drain structure can be defined, but aligning inaccuracy results in shifting of the structure

Engineering Contradiction:

Improvepositioning of low doped drain structureVSAvoidalignment accuracy

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The metal layer serves as an intermediary mask that is formed with high precision using sputtering deposition. This metal layer mask provides a stable and precise reference for subsequent ion-doping steps, eliminating the alignment errors that occur when using photo-resist patterns that are sensitive to photo-etching alignment inaccuracies.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the photo-etching process (which relies on optical alignment) with a sputtering deposition process for forming the metal layer mask. Sputtering provides superior alignment precision and eliminates the alignment inaccuracies inherent in photo-etching, thereby preventing shifting of the low doped drain structure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 reduces fabrication costs, simplifies the process, and improves the accuracy of the low doped drain structure formation, enhancing the overall efficiency and reliability of the thin film transistor production.

Implementation Method 1

performing a high concentration ion-doping using the metal layer as a mask to form a heavily doped region in the portion of the polysilicon island uncovered by the metal layer

Methodology Applied

Scientific EffectPhysical barrier masking:

Implementation Method 2

performing a high concentration ion-doping using the metal layer as a mask to form a heavily doped region in the portion of the polysilicon island uncovered by the metal layer

Methodology Applied

Scientific EffectIon implantation: Ion Implantation

Data Source

PatentUS7638404B2Method for forming low temperature polysilicon thin film transistor with low doped drain structure

Publication Date: 2009.12.29 AU OPTRONICS CORP

AI summary

A method for forming a low temperature polysilicon thin film transistor with a low doped drain structure comprises: a) forming a polysilicon island on a substrate; b) forming a dielectric layer, a metal layer and a cap layer in sequence cover to the polysilicon island; c) forming a photo-resist patterened layer on the cap layer; d) removing the portion of the metal layer and the portion of the cap layer which are uncovered by the photo-resist patterned layer, and the remaining metal layer is uncovered by the remaining cap layer with a predetermined distance at the same side; e) performing a high concentration ion-doping using the metal layer as a mask; f) removing the portion of the metal layer uncovered by the remaining cap layer; and g) performing a low concentration ion-doping using the metal layer as a mask.