# SLIDE 1: Fabrication of Polycrystalline Silicon Thin Films by a Two-Step Growth Method

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Fabrication of Polycrystalline Silicon Thin Films by a Two-Step Growth Method – Structural Control and Properties through Surface Reaction Control – (Tokyo Institute of Technology) ○Toshio Kamiya, Koichi Nakahata, Atsushi Mitsuida, Hwa-Kyung Lu, C. M. Fortmann, Isamu Shimizu

Outline:
*   Background
*   Two-Step Growth Method
*   Experimental Results
    *   Interface Structure (Ellipsometry)
    *   Influence of Seed Crystal
*   Summary

Substrate
Seed crystal
poly-Si grain
Substrate

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# SLIDE 2: Background

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Fabrication of Polycrystalline Silicon Thin Films by PE-CVD Method Using SiF4 Source Gas
*   Highly crystalline poly-Si at low temperatures (200~350C)
*   High deposition rate (~10Å/s)
*   High orientation (e.g., (022) growth on glass substrates)

Need to reduce amorphous layer at initial deposition stage
*   Layer-By-Layer Method
*   Two-Step Growth Method
Background

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# SLIDE 3: Two-Step Growth Method

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Two-Step Growth Method
Growth Process
Substrate
Epitaxial-like growth
Low-temperature deposition (200~350C)
Fast deposition rate
poly-Si

Seed Crystal Process
Substrate
Seed crystal
~100nm
High orientation
High crystallinity
High-temperature deposition Ts (> 360C)
Layer-By-Layer Method

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# SLIDE 4: Evolution of <e2> during Deposition

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0510152002000400060008000
on P-doped poly-Si
SiF4 50 sccm
SiF4 40 sccm
SiF4 30 sccm
<e2>
Time (sec)

## Figure

![Figure 1 of Slide 4](images\slide4_image1.png)
![Figure 2 of Slide 4](images\slide4_image2.png)
![Figure 3 of Slide 4](images\slide4_image3.png)
![Figure 4 of Slide 4](images\slide4_image4.png)
![Figure 5 of Slide 4](images\slide4_image5.png)
![Figure 6 of Slide 4](images\slide4_image6.png)
![Figure 7 of Slide 4](images\slide4_image7.png)
![Figure 8 of Slide 4](images\slide4_image8.png)
![Figure 9 of Slide 4](images\slide4_image9.png)
![Figure 10 of Slide 4](images\slide4_image10.png)
![Figure 11 of Slide 4](images\slide4_image11.png)
![Figure 12 of Slide 4](images\slide4_image12.png)
![Figure 13 of Slide 4](images\slide4_image13.png)
![Figure 14 of Slide 4](images\slide4_image14.png)
![Figure 15 of Slide 4](images\slide4_image15.x-wmf)
![Figure 16 of Slide 4](images\slide4_image16.x-wmf)

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# SLIDE 5: Objective

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Objective
1. Achieve an epitaxial-like interface between the seed crystal and the grown polycrystalline thin film using the two-step growth method.
2. Investigate the influence of the seed crystal's crystallinity on the properties of the grown polycrystalline thin film.

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# SLIDE 6: Experimental Setup

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Experimental Setup
Modulator
Susceptor
MBP
Auto Vacuum Controller
Ar/H2
SiF4
Shutter
in-situ Spectroscopic Ellipsometer
Substrate
Light source
Controlled by Sequencer
Layer-By-Layer Method
H2
SiF4
Process time
Gas flow
0
Deposition
Atomic Hydrogen Treatment
Crystallinity enhancement
Detector
Microwave Magnet

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# SLIDE 7: Experimental Methods

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Experimental Methods
Structural evaluation:
Spectroscopic Ellipsometer (SE)
X-ray Diffraction (XRD)

Observation of deposition process:
Ellipsometry (<e2> at 4.15eV)

Typical deposition conditions

## Figure

![Figure 1 of Slide 7](images\slide7_image1.x-emf)
![Figure 2 of Slide 7](images\slide7_image2.x-emf)

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# SLIDE 8: Evolution of <e2> during the Growth Process

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Evolution of <e2> during the Growth Process
(SiF4/H2: Same for seed crystal process and growth process)
(Seed: 50/5/30, 380C - poly-Si: 50/5/30)

## Figure

![Figure 1 of Slide 8](images\slide8_image1.x-emf)

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# SLIDE 9: Evolution of <e2> during the Growth Process

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Evolution of <e2> during the Growth Process
(SiF4/H2: Increased SiF4 flow rate in seed crystal process)
(Seed: 50/5/60, 380C - poly-Si: 50/5/30)

## Figure

![Figure 1 of Slide 9](images\slide9_image1.x-wmf)

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# SLIDE 10: Evolution of <e2> during the Growth Process

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Evolution of <e2> during the Growth Process
(SiF4/H2: Further increased H2 flow rate in growth process)
(Seed: 60/5/60, 380C - poly-Si: 60/10/30)

## Figure

![Figure 1 of Slide 10](images\slide10_image1.x-wmf)

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# SLIDE 11: Influence of Seed Crystal on the Structure of Thin Films Fabricated by the Two-Step Growth Method

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Influence of Seed Crystal on the Structure of Thin Films Fabricated by the Two-Step Growth Method

## Figure

![Figure 1 of Slide 11](images\slide11_image1.x-wmf)

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# SLIDE 12: Seed Crystal Dependence of <e2> Evolution during the Growth Process

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Seed Crystal Dependence of <e2> Evolution during the Growth Process
Seed: 60/5/60
Seed: 60/10/60
(poly-Si: 60/10/60)

## Figure

![Figure 1 of Slide 12](images\slide12_image1.x-wmf)
![Figure 2 of Slide 12](images\slide12_image2.x-wmf)

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# SLIDE 13: Influence of Seed Crystal on the Structure of Thin Films Fabricated by the Two-Step Growth Method

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Influence of Seed Crystal on the Structure of Thin Films Fabricated by the Two-Step Growth Method
Seed: 60/5/60
Seed: 60/10/60
Diffraction intensity / counts
<e2>
(poly-Si: 60/10/60)

## Figure

![Figure 1 of Slide 13](images\slide13_image1.x-wmf)
![Figure 2 of Slide 13](images\slide13_image2.x-wmf)
![Figure 3 of Slide 13](images\slide13_image3.x-wmf)
![Figure 4 of Slide 13](images\slide13_image4.x-wmf)

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# SLIDE 14: Summary

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Summary
*   The interface structure was improved by controlling gas flow rates in both the seed crystal process and the growth process.
*   The structure of the seed crystal significantly influences the final film structure.