Silicon Crystallization Mask for Void-Free Polysilicon

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Solution Overview

Problem

The existing PECVD process for forming silicon thin films in TFTs results in amorphous silicon layers with high hydrogen content, which requires additional dehydrogenation steps and increased process time due to explosive out-gassing during laser crystallization, complicating the production of LTPS.

Innovation Solution

A silicon crystallization mask with alternating complete and incomplete light transmission regions, allowing for gradual energy increase during laser irradiation to simultaneously dehydrogenate and crystallize the amorphous silicon layer, preventing explosive out-gassing and void formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If amorphous silicon layer is formed by PECVD process, then deposition speed and uniformity are improved, but hydrogen content increases causing explosive out-gassing during laser crystallization

Engineering Contradiction:

Improvedeposition speedVSAvoidhydrogen out-gassing

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing dehydrogenation treatment before laser crystallization. The amorphous silicon layer undergoes a first laser irradiation process at lower energy density to remove hydrogen content, followed by a second laser irradiation at higher energy density for complete crystallization. This preliminary dehydrogenation step prevents explosive out-gassing during the main crystallization process.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If dehydrogenation process is performed separately before crystallization, then explosive out-gassing is prevented, but process time and equipment requirements increase

Engineering Contradiction:

Improveprevention of explosive out-gassingVSAvoidprocess time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent merges the dehydrogenation process and crystallization process into a single laser irradiation step with spatially varying energy density. By designing the laser system to provide a gradient energy distribution across the substrate, the patent simultaneously achieves hydrogen removal and crystallization without requiring separate processing steps or additional equipment.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the energy density parameter of laser irradiation across different regions of the substrate. The energy density is set to be lower in regions requiring dehydrogenation and higher in regions requiring crystallization, allowing both processes to occur simultaneously during a single laser treatment step.

Inventive Principle:

Principle #35Parameter changes

3Speed

If high energy laser irradiation is applied directly to amorphous silicon layer, then crystallization is achieved rapidly, but hydrogen vaporizes explosively creating voids

Engineering Contradiction:

Improvecrystallization speedVSAvoidvoid formation

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent applies local quality by creating different energy density zones within the laser irradiation field. Different regions of the amorphous silicon layer receive different energy densities - lower energy for dehydrogenation and higher energy for rapid crystallization. This spatial variation in energy quality prevents explosive out-gassing in regions where it would cause voids while maintaining rapid crystallization in appropriate zones.

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

This method stabilizes the dehydrogenation process, preventing hydrogen outgassing during polycrystallization, resulting in an excellent polysilicon layer without voids and simplifying the production process for LTPS.

Implementation Method 1

irradiating a laser beam onto the deposited amorphous silicon layer

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

crystallized into polysilicon by a laser

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 3

irradiating the amorphous silicon layer with an intensity sufficient to melt the amorphous silicon layer

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS8052790B2Mask for silicon crystallization, method of forming poly-silicon thin film, and manufacturing method of thin film transistor

Publication Date: 2011.11.08 SAMSUNG DISPLAY CO LTD

AI summary

A silicon crystallization mask of the present invention includes; a main exposure portion including a plurality of complete light transmission regions which completely transmit light therethrough, and a preliminary exposure portion including a plurality of incomplete light transmission regions, which each partially transmit light therethrough, wherein at least two of the incomplete light transmission regions have different magnitudes of light transmittance from each other.