Takashi Fukada

Design of Single-Wafer Furnace and Its Rapid Thermal Processing Applications

A resistively heated, vacuum- and atmospheric-pressure-compatible, single-wafer furnace (SWF) system is designed to improve the operational flexibility of conventional furnaces and the productivity of single-wafer rapid thermal processing (RTP) systems. The heat source design and system operation concepts are described. The temperature measurement/control techniques and thermal characteristics of the heat source are described. The heat transfer mechanism between the heat source and Si wafer is discussed. Temperature and process uniformity in SWF were demonstrated in TiSi formation, implant annealing and thin-oxide formation. The defect-generation phenomenon in Si wafers during atmospheric pressure RTP in a SWF system is investigated as a function of temperature, process time, wafer handling method and speed. Highly repeatable slip-free RTP results were achieved in 200-mm-diameter Si wafers processed at 1100°C for 60 s (up to 5 times) through the optimization of the wafer handling method and speed.

Laser irradiation during MBE growth of ZnSxSe1−x: A new growth parameter

Abstract The effects of light irradiation of a He-Cd laser (441.6 nm) on MBE growth of ZnS x Se 1− x ( x =0−0.13) were studied. The growth rates of the epilayers were reduced and the photo-desorption rate constanSts of Zn, Se and S were obtained. In the photoluminescence spectra at 11 K, the intensities of the free exciton emission increased, and thus the crystallinity of the epilayers was found to be improved. The behavior of surface adatoms on the growing surface under laser irradiation is discussed.

Thermal Behavior of Large-Diameter Silicon Wafers during High-Temperature Rapid Thermal Processing in Single Wafer Furnace

Thermal behavior of 200-mm- and 300-mm-diameter Si (100) wafers during high-temperature rapid thermal processing (RTP) in a single wafer furnace (SWF) is investigated as a function of temperature, pressure, process time, wafer handling method and speed. Significant elastic wafer shape deformation was observed during wafer temperature ramp-up. Slip generation was frequently observed in wafers processed above 1050°C. Size, shape and spatial distribution of crystal defects generated during RTP were characterized using an optical microscope and X-ray topography. The wafer handling method and speed are found to be very important in reducing defect generation during RTP at the given process conditions. Highly reproducible, slip-free RTP results were achieved in 200-mm- and 300-mm-diameter Si (100) wafers processed at 1100°C by optimizing the wafer handling method and speed.

Photo-assisted MBE growth of ZnSe on GaAs substrates

ZnSe epilayers have been grown by photo-assisted MBE on GaAs substrates at various substrates temperatures and under various molecular beam intensity ratios of group VI to group III element. A He-Cd laser with 441.6 mm wavelength was used as a light source. From the temperature dependence of the photo-desorption rate constants, the activation energies of photo-desorption of Zn and Se adatoms from the physical adsorption state (EPZn, EPSs) and from the chemical adsorption state (EC) are obtained, that is, EPZn=7.8 kcal/mol, EPSe=6.7 kcal/mol and EC=16.1 kcal/mol. Thus, the photo-desorption observed is photo-enhanced “thermal” desorption. ZnSe epilayers have been successfully grown at a temperature as low as 150°C. A sharp and strong free-excition emission is observed in photoluminescence spectra at 11 K in the low-temperature grown samples, which shows that the crystallinity is almost comparable with that of the unirradiated epilayer grown at 340°C (the optimum growth temperature without irradiation).

Molecular Beam Epitaxial Growth of ZnSSe with Hg-Xe Lamp Irradiation

ZnSSe epilayers were grown by MBE with light irradiation using a Hg-Xe lamp. The free-exciton-emission intensities increased in the photoluminescence spectra of the light-irradiated epilayers, and the sulfur composition also increased. However, the surface morphologies were rough. The irradiated-photon-energy dependence of the above irradiation effects was investigated for the first time, and it turned out that the photons of energy larger than the band-gap energy of the epilayer were responsible for the light-irradiation effects.

Low-Temperature Growth of ZnSe by Photoassisted Molecular Beam Epitaxy

ZnSe epilayers have been successfully grown at a low temperature of 150°C for the first time by photoassisted molecular beam epitaxy. A He-Cd laser (441.6 nm) with an intensity of about 300 mW/cm2 was used as a light source. The free-exciton line in photoluminescence spectra at 11 K was sharp and strong, comparable with that of unirradiated epilayers grown at 340°C which is the optimum growth temperature without irradiation.

Single Wafer Furnace and Its Thermal Processing Applications

A resistively heated, vacuum and atmospheric pressure compatible, single wafer furnace (SWF) system is proposed to improve operational flexibility of conventional furnaces and productivity of single wafer rapid thermal processing (RTP) systems. The design concept and hardware configuration of the SWF system are described. The temperature measurement/control techniques and thermal characteristics of the SWF system are described. Typical process results in TiSi formation, implant anneal and thin oxide formation using the SWF system are reported. Due to the vertically stacked, dual chamber configuration and steady state temperature control, very flexible operation with a high throughput at a minimal power consumption (<3.5 kW per process chamber at 1150°C) was realized. Many thermal processes used in furnaces and RTP systems can easily be converted to SWF processes without decreasing cost performance and/or deteriorating process results by using the SWF system.

Redistribution of Boron and Fluorine Atoms in BF2 Implanted Silicon Wafers during Rapid Thermal Annealing

Rapid thermal annealing (RTA) of 49BF2+ (70 keV, 1×1015 cm-2) implanted Si wafers (200 mm in diameter) was carried out using a single wafer furnace-type system and a lamp-based system. Sheet resistance and the uniformity of implanted wafers were measured after annealing under various annealing conditions. Boron and fluorine depth profiles were investigated using secondary ion mass spectroscopy (SIMS) after annealing. Boron atoms diffuse into bulk crystal as annealing progresses, while fluorine atoms move towards the surface and form two peculiar peaks around 65 nm and 105 nm from the surface, regardless of annealing conditions. A significant increase in sheet resistance due to boron clustering near the F peaks was observed in wafers annealed at 1100°C using a lamp-based system. The effects of annealing method, temperature and time on dopant redistribution were discussed.

Slip-Free Rapid Thermal Processing in Single Wafer Furnace.

Defect generation phenomena in Si wafers during atmospheric pressure rapid thermal processing (RTP) in a single wafer furnace (SWF) are investigated as a function of temperature, process time, wafer handling method and speed. The size, shape and spatial distribution of crystal defects generated during RTP were characterized using an optical microscope and X-ray topography. The wafer handling method and speed are found to be very important in controlling defect generation during RTP under given process conditions. Highly reproducible slip-free RTP results were achieved in 200-mm-diameter Si wafers processed at 1100 ‐ C for 60 s (up to 5 times) by optimizing the wafer handling method and speed.

Study on the behavior of surface adatoms during photoassisted MBE of ZnSe and improvement of surface morphology

Abstract We have found for the first time that the total photodesorption of adatoms from physical- and chemical-adsorption state reduces when a DC electric field is applied normal to the surface. Considering this result and other irradiation effects on MBE growth, a model of the behavior of surface adatoms is proposed. In this model the important role of both photogenerated electrons and holes is emphasized. Moreover, we have succeeded in improving the surface morphologies of light-irradiated epilayers using misoriented (100)GaAs substrates toward the [0 1 1] direction. This improvement is explained taking into account the atomic steps on this surface.