Giant-grain silicon (GGS) and its application to stable thin-film transistor

doi:10.1016/j.displa.2005.04.001

Displays

Volume 26, Issue 3, June 2005, Pages 137-142

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Abstract

We developed a giant-grain silicon (GGS) by Ni-mediated crystallization of amorphous silicon (a-Si) with a silicon-nitride (SiN_x) cap layer. Ni particles were sputtered onto the SiN_x/a-Si layer and then it was annealed at around 600 °C. The Ni diffuses through a SiN_x cap and then forms NiSi₂ crystallites in a-Si, which is able to induce crystallization. The grain size can be controlled from a few to 100 μm. The grain size can be increased with increasing the cap layer thickness or by decreasing the Ni density on the SiN_x. The p-channel GGS poly-Si TFT exhibited a field-effect mobility of 101 cm²/Vs and a threshold voltage of −3.6 V and is very stable under gate or hot carrier bias-stress. These superior performances may be due to the smooth surface of GGS poly-Si and solid-phase crystallization of a-Si.

Introduction

Low-temperature polycrystalline silicon (LTPS) on glass is of increasing interest for large-area electronics such as active-matrix liquid-crystal displays (AMLCDs) [1], active-matrix organic light emitting diodes (AMOLEDs) [2] and system-on-glass (SOG) [3] because of its high field-effect mobility compared to amorphous silicon (a-Si).

To improve the quality of the poly-Si on insulator, several approaches have been conducted on the crystallization of a-Si including a capping layer on it. For example, in zone-melting recrystallization of Si with a strip-heater, an encapsulation layer is necessary and appears to play three major roles: to achieve a smooth surface, to prevent agglomeration, and to induce preferred (100) orientation [4]. To control the lateral growth of ELA (excimer laser annealing) poly-Si through lateral thermal gradients, three different patterned capping layers have been used: anti-reflective (SiO₂), heat-sink (Silicon nitride) and reflective (metal) capping layers [5]. On the other hand, Ni mediated crystallization using various Ni solutions [6], [7] and ultra thin Ni layer of ∼10¹³ cm⁻² has been studied [8], [9].

Amorphous dielectric thin films of silicon oxide and nitride are widely used in ultra-large scale integrated (ULSI) structures and in thin-film transistor addressed flat panel displays. But, it is known that the transition-metals such as Ti, Al and Cu diffuse into SiO₂ during the heat treatments in the fabrication process. H. Miyazaki et al. found that the Cu could be diffused into the silicon nitride, probably through the micro-defects in the PECVD (plasma enhanced chemical vapor deposition) SiN_x films. The prevention of metal diffusion into the insulator is an important issue [10].

Ni mediated lateral crystallization of a-Si was studied a lot because of its simple and low temperature process for poly-Si [11], [12]. However, in conventional MIC (metal induced crystallization) or MILC (metal induced lateral crystallization), the metal layer for inducing crystallization was deposited at least on a portion of a-Si surface. In this case, the Ni-contacted region on the a-Si for metal-induced crystallization can be contaminated by Ni.

To achieve a GGS with clean and smooth surface, we developed a technique to make poly-Si with large grain by thermal annealing of a thin Ni layer on a SiN_x/a-Si:H, where the capping layer (SiN_x) is a filter for metal diffusion [13], [14]. The a-Si is crystallized by the elapse of the NiSi₂ crystallites, and then the crystallization proceeds form these nuclei. The crystallization is carried out with a disk shaped from a nucleus. The grain size can be controlled from a few μm to 100 μm, and thus the crystallized material can be called a giant-grain silicon (GGS).

Section snippets

Experimental

We deposited an hydrogenated amorphous silicon (a-Si:H) film onto SiO₂ (100 nm)/glass. After its dehydrogenation at 430 °C for 2 h, the SiN_x cap was deposited onto an a-Si/SiO₂/glass by PECVD with a RF power density of 0.27 W/cm² at the substrate temperature of 270 °C using a mixture of SiH₄ and NH₃. The thicknesses of a-Si:H and SiN_x were 50–100 and 50–400 nm, respectively. The Ni area density was 10¹³–10¹⁵ atoms/cm², and then the RF power for the deposition of Ni particles by sputtering was 0.27 W/cm²

Results and discussion

Fig. 1 shows the schematic diagram of the conventional silicide-mediated crystallization (SMC) (a) and crystallization with a cap layer for GGS (b). Ni was deposited on a-Si for SMC. The metal-contacted region on the a-Si for SMC can be contaminated by metal impurities. On the other hand, in the case of GGS, metal particles were deposited onto the SiN_x/a-Si:H. The role of capping layer is the passivation layer for clean and smooth surface of the crystallized poly-Si as well as the reduction of

Conclusion

We developed GGS by the Ni-mediated crystallization of a-Si with a SiN_x cap layer. The poly-Si TFT exhibited a field-effect mobility of higher than 100 cm²/Vs and stable operation under hot carrier bias-stress or gate bias stress. The Ni on a SiN_x cap was diffused through the cap into the a-Si and then NiSi₂ crystallites are formed in a-Si. These can be the seeds for lateral giant-grain growth. The lateral crystallization takes place until the neighboring grains collides. Therefore, the grain

Acknowledgements

This work was supported by the National Research Lab Program of Korea.

References (20)

Y.M. Ha
SID Digest
(2000)
M. Stewart et al.
IEEE Trans. Electron Device
(2001)
H. Sakamoto et al.
SID Digest
(2000)
M.W. Geis et al.
J. Electrochem. Soc.
(1982)
L. Mariucci et al.
Thin Solid Films
(1999)
J.H. Ahn et al.
J. Electrochem. Soc.
(2001)
S.Y. Yoon et al.
Jpn. J. Appl. Phys.
(1998)
Y.J. Choi et al.
SID'99 Digest
(1999)
J.H. Choi et al.
Thin Solid Films
(2003)
H. Miyazaki et al.
J. Appl. Phys.
(1997)

There are more references available in the full text version of this article.

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Giant-grain silicon (GGS) and its application to stable thin-film transistor

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgements

SID Digest

IEEE Trans. Electron Device

SID Digest

J. Electrochem. Soc.

Thin Solid Films

J. Electrochem. Soc.

Jpn. J. Appl. Phys.

SID'99 Digest

Thin Solid Films

J. Appl. Phys.