Crystallization of Si 1- x Ge x Multilayer by Soft X-ray Irradiation

ECS J. Solid State Sci. Technol.

Hamada

2019

Thin-film transistors (TFTs) utilizing low-temperature polycrystalline-Si (LTPS) are critical for system-on-panel applications. The requirements for LTPS are a high quality, a large grain size and position control of the nucleation. Many promising crystallization methods have been developed to satisfy these requirements. Herein, two scientific discoveries related to the low-temperature crystallization and high-performance TFT structure using the tunnel effect are introduced. Hydrogens in an amorphous (a-Si) film greatly accelerate the crystal velocity and improved the crystallinity of the excimer-laser annealing (ELA) poly-Si film, thereby providing a high-quality, a large-grained film referred to as secondary-grain film, under the solid-phase condition. In addition, a soft X-ray crystallization (SXC) method was developed. It reduces the threshold temperature of crystallization for a-Si, SiXGe1-X and Ge films by 100°C–140°C in comparison to that for films prepared by conventional thermal crystallization. The SXC method is expected to become the critical low-temperature crystallization method in the era of the flexible electronics. On the other hand, although high-performance TFTs that utilize large single-crystalline grains have been intensively researched, such research has not been successful from the viewpoint of mass production. A novel device structure – tunneling dielectric TFT (TDTFT)–has been developed. The TDTFT reduces the gate-off current to less than 1/10 of that with a conventional TFT. In addition, the TDTFT improved the hump effect. We conclude that the triple-gate (Fin) TDTFT will be a promising candidate for next-generation poly-Si TFT structures.

Section: Resultsmentioning

confidence: 99%

Review—Technology Trends of Poly-Si TFTs from the Viewpoints of Crystallization and Device Performance

ECS J. Solid State Sci. Technol.

Hamada

2019

“…The crystallization mechanism of a-Si irradiated with soft X-rays is explained as follows. 15,20) During soft X-ray irradiation, the electrons in the Si core levels are excited to the vacuum level and the ionization of Si atoms occurs. In this case, the atomic movement of Si is enhanced by the composition of local lattice vibrations and Coulomb force between Si atoms.…”

Section: Resultsmentioning

confidence: 99%

“…The authors have developed a novel semiconductor fabrication process using high-brightness soft X-rays. [14][15][16][17][18][19][20][21] The effects of electron excitation and atomic migration upon soft X-ray irradiation from a 2.28 m undulator at the synchrotron radiation facility NewSUBARU 22) and a laser plasma X-ray (LPX) source on the crystallization of amorphous semiconductor films were investigated. The LPX system is compact in size compared with the synchrotron radiation facility and is expected to be used in industry.…”

Section: Introductionmentioning

confidence: 99%

Formation of nanocrystalline silicon in SiO_xby soft X-ray irradiation at low temperature

Kusakabe

et al. 2017

Jpn. J. Appl. Phys.

Self Cite

The low-temperature formation of nanocrystalline Si (nc-Si) in SiOx film is one of the key technologies in the realization of Si-based photonics and memories. We proposed a low-temperature nc-Si formation method with soft X-ray irradiation. The nc-Si formation depended on the Si/O atomic ratio in the pristine SiOx film. The Si-rich regions in SiOx films with Si/O ratios higher than 0.67 were crystallized by atomic migration via electron excitation with soft X-ray irradiation at a photon energy near the core level of Si 2p. nc-Si with a mean size of 20 nm was formed by soft X-ray irradiation at a low temperature of 660 °C.

“…Therefore, we have proposed a Si 1¹x Ge x multilayer film with controlled Ge concentration for light absorption and crystallization. 17) This method is known to be influenced by the Ge concentration and photon flux density. The Ge atom is a trigger for crystallization because the migration of Ge atoms is enhanced by soft X-ray irradiation.…”

Section: Introductionmentioning

confidence: 99%

“…The present crystallization technique is expected to be applied to the fabrication of solar cells with high conversion efficiency. 17) However, the details of the relationship between the photon energy of soft X-rays and the crystallization of Si 1¹x Ge x films are not clear. In this paper, we report detailed studies on the photon energy dependence of Si 1¹x Ge x films crystallized by soft X-ray irradiation to understand the crystallization mechanism.…”

Section: Introductionmentioning

confidence: 99%

Photon energy dependence of crystallization of Si₁₋_xGe_xfilms by soft X-ray irradiation

Kanda

2014

Jpn. J. Appl. Phys.

Self Cite

Amorphous silicon germanium (a-Si1−xGex) films were crystallized by irradiation with soft X-rays of various photon energies. The crystallization upon soft X-ray irradiation is related to Ge concentration, photon energy, and photon flux density. The Ge atom was the trigger for the crystallization of the SiGe film because the atomic migration of Ge atoms was enhanced by electron excitation during soft X-ray irradiation, compared with Si atoms. As the photon energy decreased from 130 to 50 eV, the crystalline fraction increased. In the Si0.5Ge0.5 film, the ratio of peaks attributable to the crystal phases to those attributable to the amorphous phases of Si–Si, Si–Ge, and Ge–Ge bonds changed with irradiated photon energy. This is explained by the relationship between the orbital energies of Si 2p and Ge 3d and the photon energy of irradiated soft X-rays, because the electron excitation probability was determined by this relationship. Therefore, it is considered that soft X-ray irradiation crystallization occurred via the exitation of electrons from the core level.