Polysilicon Mask for Grain Boundary Orientation Control

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Solution Overview

Problem

Conventional polysilicon layer fabrication methods using sequential lateral solidification (SLS) laser crystallization result in polysilicon thin-film transistors (TFTs) with varying electrical properties due to inconsistent grain boundary orientations, affecting carrier mobility and device performance.

Innovation Solution

A mask with a primary opaque pattern and clusters of secondary opaque patterns is used, where the secondary opaque patterns are positioned within transparent slits to create included angles not equal to 90°, ensuring consistent electrical properties of polysilicon TFTs by controlling grain boundary orientations during the SLS laser crystallization process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional masks with straight opaque patterns are used, then the manufacturing process is simple, but the electrical properties of polysilicon TFTs vary due to inconsistent grain boundary orientations

Engineering Contradiction:

Improveelectrical properties consistencyVSAvoidmask pattern complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies asymmetry by designing mask opaque patterns with non-perpendicular angles (e.g., 45 degrees) instead of conventional perpendicular orientations. This asymmetric angular configuration controls grain boundary formation to achieve consistent electrical properties across polysilicon TFTs, resolving the contradiction between electrical consistency and mask complexity.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent implements local quality by varying the angular orientations of opaque patterns in different regions of the mask. Specific angular configurations (e.g., 45 degrees) are applied locally to control grain boundary orientations in corresponding TFT channel regions, ensuring consistent electrical properties while maintaining manufacturing feasibility.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If perpendicular grain boundaries are formed, then the mask pattern is simple and easy to manufacture, but carrier mobility is reduced due to inconsistent grain boundary orientations

Engineering Contradiction:

Improvegrain boundary orientation controlVSAvoidmask fabrication difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent changes the angular parameter of mask opaque patterns from conventional perpendicular (90 degrees) to non-perpendicular angles (e.g., 45 degrees). This parameter modification enables precise control of grain boundary orientations to improve manufacturing precision while the angular configuration remains manufacturable using standard photolithography processes.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the mask uses complex angular patterns, then grain boundary orientation can be controlled for better electrical properties, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvedevice performance consistencyVSAvoidmask pattern design complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the mask opaque patterns into multiple angular configurations (e.g., different 45-degree oriented segments) that can be independently designed and manufactured. This segmentation allows control of grain boundary orientations for consistent device performance while enabling modular mask fabrication processes.

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 approach results in polysilicon TFTs with consistent electrical properties, enhancing carrier mobility and device performance by aligning grain boundaries at non-perpendicular angles, thus improving the reliability of polysilicon TFTs in electronic devices.

Implementation Method 1

a laser beam 140 passing through a mask 112 is patterned, and the laser beam 140 irradiates the amorphous silicon layer on the substrate 130 through a projection lens 114

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

The amorphous silicon layer irradiated by the laser beam 140 is transformed to be silicon which is 'melted state'

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 3

The melted silicon is laterally grown with use of the amorphous silicon layer as a nucleus, such that the amorphous silicon layer in the irradiated region becomes a polysilicon layer

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Data Source

PatentUS7871907B2Mask and method of fabricating a polysilicon layer using the same

Publication Date: 2011.01.18 AU OPTRONICS CORP

AI summary

A mask includes a primary opaque pattern and a number of clusters of secondary opaque patterns. The primary opaque pattern defines a number of strip transparent slits whose extending directions are substantially the same. The clusters of the secondary opaque patterns are connected to the primary opaque pattern, and each of the clusters of the secondary opaque patterns is disposed in one of the transparent slits, respectively. Each of the clusters of the secondary opaque patterns includes a number of secondary opaque patterns, and extending directions of at least a portion of the secondary opaque patterns and the extending directions of the transparent slits together form included angles that are not equal to about 90°.