SLS Mask Parallelizing Repeat Patterns for Multi-Directional Grain Growth

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Solution Overview

Problem

Existing Sequential Lateral Solidification (SLS) processes for crystallizing amorphous silicon into polycrystalline silicon are limited by the need for grain growth direction, which restricts TFT channel design and circuit pattern variety, as grain boundaries are typically perpendicular to the growth direction.

Innovation Solution

A mask with parallelizing repeat patterns, comprising symmetrical units of light transmitting and absorption portions, allows for crystallization with multiple grain growing directions by reversing the pattern after initial irradiation, enabling dual gate TFTs with uniform and improved electrical performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a conventional SLS mask with simple slit patterns is used, then the manufacturing process is simple, but the grain growth direction is restricted to a single direction which limits circuit pattern design variety

Engineering Contradiction:

Improvecircuit pattern design varietyVSAvoidmask structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The mask is divided into multiple light transmitting portions and light absorption portions arranged in specific patterns. Each portion can control grain growth in different directions, allowing the mask to create multi-directional grain structures in polycrystalline silicon while maintaining a manageable segmented structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mask employs asymmetric arrangements of light transmitting and absorption portions relative to the laser beam scanning direction. This asymmetry enables grain growth in multiple directions perpendicular to the scanning direction, breaking the single-direction growth limitation of conventional symmetric slit masks

Inventive Principle:

Principle #4Asymmetry

2Reliability

If the laser beam scans in a fixed back-and-forth pattern, then the manufacturing process is simple, but the grain boundaries are perpendicular to the growing direction which reduces electrical performance

Engineering Contradiction:

Improveelectrical performanceVSAvoidcrystallization process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The mask uses periodic patterns of light transmitting and absorption portions that correspond to the periodic back-and-forth scanning motion of the laser beam. This periodic structure ensures that grain growth occurs in controlled directions during each scan cycle, creating favorable grain boundary orientations for electrical performance

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

Instead of trying to change the fixed scanning direction to achieve desired grain orientation, the invention inverts the approach by using a complex mask pattern that works with the fixed scanning direction to produce multi-directional grain growth and favorable grain boundary orientations

Inventive Principle:

Principle #13The other way round (Inversion)

3Adaptability or versatility

If a mask with complex patterns is used to achieve multi-directional grain growth, then circuit design flexibility is improved, but the manufacturing precision required for the mask increases

Engineering Contradiction:

Improvegrain growth direction controlVSAvoidmask pattern precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

Different regions of the mask have different local patterns of light transmitting and absorption portions, each optimized to control grain growth in specific directions for different areas of the substrate. This local quality approach allows multi-directional grain growth control without requiring the entire mask to achieve maximum precision

Inventive Principle:

Principle #3Local quality

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 solution enables the generation of polycrystalline silicon films with at least two grain boundary directions, enhancing electrical performance and circuit design flexibility by controlling grain structure through mirror symmetry and portion sizes on the mask.

Implementation Method 1

the laser beam irradiates on an amorphous silicon film, the amorphous silicon film absorbs energy of the laser beam and is transformed into a polycrystalline silicon film

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

melt the amorphous silicon, such that the melted silicon can grow laterally silicon grains in recrystallization

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 3

silicon grains tend to grow laterally from the boundary of the liquid silicon and the solid silicon

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 4

a sequential lateral solidification (SLS), which using a technique of Excimer laser annealing

Methodology Applied

Scientific EffectSequential lateral solidification:

Data Source

PatentUS7649206B2Sequential lateral solidification mask

Publication Date: 2010.01.19 AU OPTRONICS CORP

AI summary

A sequential lateral solidification (SLS) mask comprises a plurality of parallelizing repeat patterns. Each of the patterns further comprises a major symmetrical axis and a short axis, and each of the patterns is also composed of first units and second units, in which both the first unit and the second unit comprise respectively a plurality of light transmitting portions and light absorption portions. The first units are positioned in mirror symmetry to the second units via the major symmetrical axis.