We have proposed that germanium-tin (GeSn) particles with high substitutional Sn concentrations can be synthesized by pulsed laser deposition (PLD) in ambient Ar at low pressure (~100 Pa). In this method, a Ge<sub>0.9</sub>Sn<sub>0.1</sub> target is ablated by KrF excimer laser irradiation. At low Ar pressure (~100 Pa), the agglomeration of Ge and Sn atoms occurs easily in ambient Ar, and the agglomerated particles are rapidly cooled by collision with Ar atoms. An Si-receiving substrate was placed in front of the target. Various GeSn particles from several 100 nm to approximately 20 μm with spherical, disk, and irregular shapes were deposited on the Si-receiving substrate. In Raman spectra, the Ge-Ge vibration peaks of all the particles were shifted to lower wavenumbers compared with those of the Ge(100) crystal. The Raman peak position reportedly shifts to lower wavenumbers with increased substitutional Sn concentration in crystalline Ge. Thus, GeSn crystal particles with over 10% substituted Sn atoms can be synthesized by low-pressure PLD.
The electrical properties of poly-Si thin films doped using KrF excimer laser irradiation with a phosphoric-acid coating were investigated. After laser doping, the mobility, carrier concentration, activation ratio, and contact resistivity of the poly-Si were found to be 61 cm<sup>2</sup> /Vs, 1.5×10<sup>18</sup> cm<sup>-3</sup> , 18.1 %, and 8.5 × 10<sup>−5 </sup>Ω⋅cm<sup>2</sup> , respectively. Additionally, the operation of a bottom gate transistor fabricated using laser doping was realized and is described herein.
Ultra-large scale integrated circuits (ULSIs) have been continually scaled down according to Moore’s law. This can improve their power consumption and operation frequency but not the RC delay of their interconnections; to this end, super low dielectric constant films are required. We propose a novel method to fabricate porous SiO<sub>2</sub> films with a super low dielectric constant by F<sub>2</sub> laser deposition. In this method, a quartz target is evaporated by F<sub>2</sub> laser ablation in vacuum-chamber-controlled Ar partial pressure. The evaporated SiO<sub>2 </sub>molecules are agglomerated in the vacuum, and the size of the SiO<sup>2</sup> nanoparticles are controlled by the Ar partial pressure. Porous SiO<sub>2</sub> films are formed on a Si-receiving substrate, which is placed in front of the quartz target. The pulse duration of the F<sub>2</sub> laser was approximately 20 ns, and the repetition rate of laser shots was 100 Hz. The base pressure of the vacuum chamber was 5 × 10<sup>−3</sup> Pa. Then, Ar gas was introduced into the vacuum chamber through a mass flow controller to control the Ar partial pressure. The dominant size of the SiO<sub>2</sub> nanoparticles decreased from 1.5–2.0 nm to 1.0–1.5 nm with the Ar partial pressure decreasing from 20 Pa to 4.5 Pa. In addition, the relative dielectric constant k of the porous SiO<sub>2</sub> film formed at an Ar partial pressure of 4.5 Pa was 2.8, which is lower than that of thermal SiO<sub>2</sub> (k = 4.0). In addition, the leakage current of the nanoporous SiO<sub>2</sub> film was almost equal to that of the thermal SiO<sub>2</sub> film. From these results, we conclude that nanoporous SiO<sub>2 </sub>films with a super low dielectric constant can be formed by F<sub>2</sub> laser deposition.
We propose low-temperature and high-concentration doping of 4H-silicon carbide (4H-SiC)(0001) by KrF excimer laser irradiation of source films on a 4H-SiC substrate, in which a dopant atom is included. In n-type doping, a SiN<sub>x</sub> film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. A gas supply nozzle for ambient environment control was installed to prevent oxidation of the SiC surface. High-concentration nitrogen doping (~1 × 10<sup>21</sup>/cm<sup>3</sup> at the surface) was achieved by laser ablation of the SiN<sub>x</sub> film. Al/Ti electrodes were formed on the doped area at a room temperature, and a contact resistance of 2.2 × 10<sup>-5</sup> Ω･cm<sup>2</sup> was obtained, which is sufficiently small for the backside contact resistance of Schottky barrier diodes. In p-type doping, an Al film with a thickness of 240 nm was deposited on a 4H-SiC substrate by sputtering deposition. After laser irradiation of the Al film in ambient Ar, high-concentration Al doping (~1 × 10<sup>21</sup>/cm<sup>3</sup> at the surface) was achieved. Al/Ti electrodes were formed on the doped area at a low temperature of 600 °C, and a contact resistance 1.9 × 10<sup>-4</sup> Ω･cm<sup>2</sup> was obtained. We conclude that low-temperature and high-concentration doping of 4H-SiC for low contact resistance can be achieved by laser ablation of the source films on the 4H-SiC substrate.