Takeshi Ichikawa

Formation of device-grade epitaxial silicon films at extremely low temperatures by low-energy bias sputtering

Device‐grade epitaxial single silicon layers have been formed at extremely low temperatures of about 300 °C by low‐energy bias sputtering in conjunction with in situ substrate surface cleaning and an ultraclean processing environment. Dopant impurities in the target material are fully incorporated into the sputter‐deposited silicon film and these impurities are 100% electrically activated without any additional heat cycles. An epitaxial silicon film having a resistivity as low as 0.0014 Ω cm has been obtained using a heavily arsenic‐doped silicon block as a target material. A p‐n junction diode formed by directly depositing a phosphorus‐doped n‐type epilayer on a p‐type substrate indicates a reverse current level as low as 1.88×10−9 A/cm2 at a reverse bias voltage of 5 V, thus verifying that the in situ substrate surface cleaning by low‐energy Ar ion bombardment is very effective and damage free. The electrical characteristics of a grown film have shown a good correlation to the crystal structure of the f...

In situ substrate‐surface cleaning for very low temperature silicon epitaxy by low‐kinetic‐energy particle bombardment

A very low temperature in situ substrate‐surface cleaning process utilizing low‐kinetic‐energy particle bombardment has been developed. Dramatic improvements have been achieved in the crystallinity of epitaxial silicon films grown by the newly developed low‐kinetic‐energy particle process, in which argon ions having precisely controlled energies are continuously bombarding the film surface during the entire growth operation. With the optimized substrate‐surface cleaning conditions, in which the contaminants on the surface of silicon substrates are removed without introducing any damages to the substrates, the epitaxial silicon layer with a perfect crystallinity has been obtained at such very low temperatures below 350 °C.

Low‐temperature silicon epitaxy by low‐energy bias sputtering

Bias sputtering at low energies, i.e., comparable to typical crystal interatomic binding energies, has been utilized to control the kinetics of thin‐film growth. It was found that the crystallographic structures of sputter‐deposited silicon films are drastically changed by the energy of ions incident at the substrate. As a result, formation of high quality epitaxial silicon films on (100) silicon substrates has been realized at such low temperatures as 320–350 °C. At the same time, low‐temperature impurity doping of the epitaxial layer has been also demonstrated. Furthermore, the low‐energy bias sputtering process has made it possible to perform very effective substrate surface cleaning at extremely low temperatures without introducing any damage to the substrate.

Electrical characterization of epitaxial silicon films formed by a low kinetic energy particle process

Electrical properties of epitaxial silicon layers formed at very low temperatures of 320–350 °C by a low kinetic energy particle process are presented. Dopant impurities in the target material are substitutionally incorporated into the epitaxially grown layer, thus being electrically activated without any additional heat cycles. An epitaxial silicon layer having a resistivity as low as 0.0018 Ω cm has been obtained using a heavily arsenic‐doped silicon target. A p‐n junction diode formed by directly depositing an n‐type epilayer on a p‐type substrate exhibits a reverse current level as low as 1.88×10−9 A/cm2 at a reverse‐bias voltage of 5 V. The electrical properties of the grown film have shown a good correlation to the crystallinity of the film, which changes depending upon the ion bombardment energy.

Crystal structure analysis of epitaxial silicon films formed by a low kinetic energy particle process

Formation of high quality epitaxial silicon films at 350 °C by a low kinetic energy particle process has been verified by a series of crystal structure analyses performed on these films. It was found that the crystallinity of a grown film is drastically changed by the energy of Ar ions concurrently bombarding the growing silicon film surface. The epitaxially grown film with an optimum ion bombardment energy is defect‐free both at the interface and in the bulk of the film as revealed by high‐resolution transmission electron microscopy.

Very-Low-Temperature Epitaxial Silicon Growth By Low-Kinetic-Energy Particle Bombardment

Low-kinetic-energy Ar ions have been utilized to control the kinetics of thin film growth as well as to perform very effective predeposition substrate surface cleaning. As a result, epitaxial silicon layers with a perfect crystallinity are grown on silicon substrates at a temperature as low as 350°C. The resistivity of an as-grown epitaxial silicon film as low as 0.0018 Ωcm has been obtained, showing the impurity activation without any heat treatment. A p-n junction formed by growing an n-type epitaxial silicon layer directly on a p-type substrate at 350°C exhibited a low reverse current of 1.88×10-9 A/cm2 at a reverse bias of 5 V.

Chaotic Oscillation in a Single-Mode Class A He–Ne Laser (6328 Å) II

Chaotic oscillation in a single-mode He-Ne laser (6328 A), which belongs to a class A laser, is investigated through experiments I which were reported in our previous paper [F. Kuwashima, I. Kitazima and H. Iwasawa: Jpn. J. Appl. Phys. 37 (1998) L325.], and the improved experiments II. The results of experiments II, which were conducted using a neutral density (ND) filter instead of the tilted mirror used in experiments I, demonstrate the effect of the tilted mirror and a pumping parameter on the chaotic behavior of this laser. We also confirm and discuss the threshold value for chaos vs control parameters from the estimated Lyapunov exponents. The route to chaos in this laser is also discussed. Lastly, the laser equation of the class A laser with delayed feedback is introduced and numerical results which reveal chaotic oscillations are reported.