Yukihiro Kiyota

A 0.2-/spl mu/m 180-GHz-f/sub max/ 6.7-ps-ECL SOI/HRS self aligned SEG SiGe HBT/CMOS technology for microwave and high-speed digital applications

A technology for combining 0.2-/spl mu/m self-aligned selective-epitaxial-growth (SEG) SiGe heterojunction bipolar transistors (HBTs) with CMOS transistors and high-quality passive elements has been developed for use in microwave wireless and optical communication systems. The technology has been applied to fabricate devices on a 200-mm SOI wafer based on a high-resistivity substrate (SOI/HRS). The fabrication process is almost completely compatible with the existing 0.2-/spl mu/m bipolar-CMOS process because of the essential similarity of the two processes. SiGe HBTs with shallow-trench isolations (STIs) and deep-trench isolations (DTIs) and Ti-salicide electrodes exhibited high-frequency and high-speed capabilities with an f/sub max/ of 180 GHz and an ECL-gate delay of 6.7 ps, along with good controllability and reliability and high yield. A high-breakdown-voltage HBT that could produce large output swings for the interface circuit was successfully added. CMOS devices (with gate lengths of 0.25 /spl mu/m for nMOS and 0.3 /spl mu/m for pMOS) exhibited excellent subthreshold slopes. Poly-Si resistors with a quasi-layer-by-layer structure had a low temperature coefficient. Varactors were constructed from the collector-base junctions of the SiGe HBTs. MIM capacitors were formed between the first and second metal layers by using plasma SiO/sub 2/ as an insulator. High-Q octagonal spiral inductors were fabricated by using a 3-/spl mu/m thick fourth metal layer.

0.1 mu m CMOS devices using low-impurity-channel transistors (LICT)

Summary form only given. It was found that LICTs are very effective for providing low threshold voltages with good turn-offs in 0.1 mu m CMOS devices. Attention is given to device fabrication criteria, key process technologies used, and the features achieved using LICTs.<<ETX>>

Design and performance of 0.1- mu m CMOS devices using low-impurity-channel transistors (LICT's)

0.1- mu m CMOS devices using low-impurity-channel transistors (LICTs) with dual-polysilicon gates have been fabricated by nondoped epitaxial growth technology, high-pressure oxidation of field oxide, and electron-beam lithography. These devices, with gate lengths of 0.135 mu m, achieved normal transistor operation at both 300 and 77 K using 1.5-V supply voltage. Maximum transconductances are 203 mS/mm for nMOS transistors and 124 mS/mm for pMOS transistors at 300 K. Low-impurity channels grown on highly doped wells provide low threshold voltages of about 0.35 V for nMOS transistors and about -0.15 V for pMOS transistors at 77 K, and preserve good turn-offs with subthreshold swings of 25 mV/decade at 77 K. LICTs suppress short-channel effects more effectively, compared with conventional devices with nearly uniform dopings.<<ETX>>

Ultra-thin-base Si bipolar transistor using rapid vapor-phase direct doping (RVD)

A novel doping method called rapid vapor-phase direct doping (RVD) is developed to form ultra-shallow junctions. The base region of a conventional bipolar transistor is formed by this method, and in ultra-narrow 25-nm base is obtained. The Gummel plot of this device shows almost ideal characteristics. This result suggests that this method does not induce any defects which cause a leakage current. RVD is a thermal diffusion method using hydrogen as a carrier gas and B/sub 2/H/sub 6/ as a source gas. In this method, the impurity atoms directly diffuse from the vapor phase into silicon by a rapid thermal process without a boron-glass layer or metallic boron layer. By varying the source gas flow rate, doping time, and temperature, ultra-shallow junctions below 40 nm with controlled surface concentrations are successfully formed. An ultra-shallow 20-nm junction with surface boron concentration of 4*10/sup 18/ cm/sup -3/ is obtained at 800 degrees C for 5 min with B/sub 2/H/sub 6/ flow rate of 30 ml/min. >

Formation of ultrashallow p+ layers in silicon by thermal diffusion of boron and by subsequent rapid thermal annealing

Boron atoms are incorporated into (100)Si wafers by heating the substrates at 800 °C for 30 min in a (B2H6+H2) atmosphere and by subsequent rapid thermal annealing above 900 °C. Atomic and carrier‐concentration profiles of boron‐doped layers have been examined by a secondary‐ion mass spectrometry and by differential Hall measurements, respectively. Experimental results have clearly shown that ultrashallow p+ layers, 300 A thick, with a surface carrier concentration of 7.26×1019/cm3 can be formed by diffusion of boron at 800 °C and by subsequent RTA at 100 °C.

Role of hydrogen during rapid vapor-phase doping analyzed by x-ray photoelectron spectroscopy and Fourier-transform infrared-attenuated total reflection

The surface of boron-doped layers formed by rapid vapor-phase doping was analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR), to determine the role of the hydrogen carrier gas. Boron doping was carried out with a B2H6 source gas and a hydrogen carrier gas at 800 and 900 °C. A nitrogen carrier gas was also used for comparison. Using hydrogen carrier gas, no evidence of boron segregation was observed in the XPS spectra. FTIR-ATR analysis confirmed that the hydrogen termination of the surface was maintained during doping. Using nitrogen carrier gas, layers that included segregated boron and silicon nitride were produced on the surface, which led to poor controllability of the boron concentration. When a hydrogen carrier gas is used, the hydrogen termination should promote the surface migration of adsorbed species. The hydrogen carrier gas plays an important role in terminating the silicon dangling bonds, thus preventing excessive chemisorption of boron.The surface of boron-doped layers formed by rapid vapor-phase doping was analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR), to determine the role of the hydrogen carrier gas. Boron doping was carried out with a B2H6 source gas and a hydrogen carrier gas at 800 and 900 °C. A nitrogen carrier gas was also used for comparison. Using hydrogen carrier gas, no evidence of boron segregation was observed in the XPS spectra. FTIR-ATR analysis confirmed that the hydrogen termination of the surface was maintained during doping. Using nitrogen carrier gas, layers that included segregated boron and silicon nitride were produced on the surface, which led to poor controllability of the boron concentration. When a hydrogen carrier gas is used, the hydrogen termination should promote the surface migration of adsorbed species. The hydrogen carrier gas plays an important role in terminating the silicon dangling bonds, thus preventing excessive chemisorpt...

H 2 Cleaning of Silicon Wafers before Low‐Temperature Epitaxial Growth by Ultrahigh Vacuum/Chemical Vapor Deposition

High-pressure H 2 cleaning is proposed for precleaning wafers used in low-temperature silicon epitaxial growth to remove such contaminants as oxygen and carbon at the interface between the epitaxial layer and the substrate in ultrahigh-vacuum/chemical vapor deposition. Increasing the H 2 partial pressure up to 1300 Pa during H 2 cleaning at 850°C was found to produce a smooth surface with the contaminants perfectly removed. To investigate the effects of roughness and contaminants in the wafer surface on the crystallinity of the epitaxial layer, p-n diodes were fabricated in the epitaxial layer and their characteristics were measured. Annealing at an H 2 partial pressure of 120 Pa produced roughness and contaminants in the wafer surface causing a leakage current. Annealing at 1300 Pa produced smooth clean surfaces and no leakage current was observed. These results suggest that the electronic properties of epitaxial layers are influenced by contaminants and roughness in the wafer surface. High pressure H 2 cleaning reduces roughness and removes contaminants in the surface, resulting in good electronic properties in the epitaxial layer.

Recent progress of heterostructure technologies for novel silicon devices

The recent progress in Si heterostructure technologies is reviewed from physical and engineering viewpoints. Advanced methods to fabricate ultrashallow p-n junctions and high quality heterojunctions (SiGe/Si, μc-Si/SiC/Si) are developed to make a breakthrough in pushing back the limitation of Si-ULSI. Band engineering technology based on superstructures is also established by developing atomic hydrogen assisted molecular beam epitaxy. This opens up new expectations for Si-based optoelectronic integrated circuits. In addition, self-organized processing for nano-structure fabrication is being developed to realize new-concept quantum functional devices.

Very-high-speed silicon bipolar transistors with in-situ doped polysilicon emitter and rapid vapor-phase doping base

We present a detailed study of the performance of very-high-speed silicon bipolar transistors with ultra-shallow junctions formed by thermal diffusion. Devices are fabricated with double-polysilicon self-aligned bipolar technology with U-groove isolation on directly bonded SOI wafers to reduce the parasitic capacitances. Very thin and low resistivity bases are obtained by rapid vapor-phase doping (RVD), which is a vapor diffusion technique using a source gas of B/sub 2/H/sub 6/. Very shallow emitters are formed by in-situ phosphorus doped polysilicon (IDP) emitter technology with rapid thermal annealing (RTA). In IDP emitter technology, the emitters are formed by diffusion from the in-situ phosphorus doped amorphous silicon layer. Fabricated transistors are found to have ideal I-V characteristics, large current gain and low emitter resistance for a small emitter. Furthermore, a minimum ECL gate delay time of 15 ps is achieved using these key techniques. Analyses of the high performance using circuit and device simulations indicate that the most effective delay components of an ECL gate are cut-off frequency and base resistance. A high cut-off frequency is achieved by reducing the base width and active collector region. In this study, RVD is used to achieve both high cut-off frequency and low base resistance at the same time. >

Characteristics of Shallow Boron‐Doped Layers in Si by Rapid Vapor‐Phase Direct Doping

Characteristics are shown for shallow boron-doped layers formed by a new doping method called rapid vapor-phase direct doping which is suitable for making shallow junctions of less than 50 nm. An atmospheric pressure CVD system is used for the experiments and, in this process, boron atoms are doped into Si from the vapor phase after the native oxide is removed in hydrogen. From the results obtained for time dependence of doping characteristics, the surface boron concentration increases almost proportionally to the doping time. This result means that the surface boron concentration is determined by the amount of supplied boron atoms. This unique characteristic is the reason why shallow junctions can be formed as confirmed by the simulation