Isao Suzumura

High-speed scaled-down self-aligned SEG SiGe HBTs

A scaled-down self-aligned selective-epitaxial-growth (SEG) SiGe HBT, structurally optimized for an emitter scaled down toward 100 nm, was developed. This SiGe HBT features a funnel-shaped emitter electrode and a narrow separation between the emitter and base electrodes. The first feature is effective for suppressing the increase of the emitter resistance, while the second one reduces the base resistance of the scaled-down emitter. The good current-voltage performance - a current gain of 500 for the SiGe HBT with an emitter area of 0.11 /spl times/ 0.34 /spl mu/m and V/sub BE/ standard deviation of less than 0.8 mV for emitter width down to about 0.13 /spl mu/m - demonstrates the applicability of this SiGe HBT with a narrow emitter. This SiGe HBT demonstrated high-speed operation: an emitter-coupled logic (ECL) gate delay of 4.8 ps and a maximum operating frequency of 81 GHz for a static frequency divider.

Suppression of B Outdiffusion by C Incorporation in Ultra-High-Speed SiGeC HBTs

The effect of incorporated C on preventing the diffusion of B in selectively grown Si1-x-yGexCy layers has been studied. The diffusivity of B was significantly decreased by increasing the C content, even when the concentrations of B were high. Furthermore, self-aligned SiGeC heterojunction bipolar transistors (HBTs) were fabricated, and the effects of incorporating C in the base layer on device performance were evaluated. A shallower base with a higher concentration of B was produced by suppression the B outdiffusion. Consequently, low values for base resistance and a high cutoff frequency of 168 GHz were achieved with a 4-nm-thick p-Si1-x-yGexCy layer where the C content was 0.2% and the B concentration was 1×1020 cm-3.

Hydrogen Effects on Heteroepitaxial Growth of Ge Films on Si(111) Surfaces by Solid Phase Epitaxy

The influences of hydrogen atoms on Ge heteroepitaxial growth on Si(111) surfaces using solid phase epitaxy (SPE) have been investigated by scanning tunneling microscopy (STM). In the SPE growth of Ge films on H-terminated Si(111) surfaces, the formation of 3-dimensional (3D) Ge islands are suppressed. With the desorption of H atoms, the 3D islands appear on the Ge surface, which are considered to be formed by the agglomeration of Ge atoms. The density of the islands is decreased and the size of the islands is increased by the existence of Si-H bonding at the Ge/Si interface. These phenomena are considered to be caused by the release of the stress in the Ge film and the weakening of the interaction between the Ge film and the Si substrate by Si–H bonding. In addition, the activation energy of the migration of Ge atoms during the agglomeration is determined to be 0.3 eV.

Properties of SiGe Films Fabricated by Reactive Thermal Chemical Vapor Deposition Using Lamp Heating

The structural and electrical properties of SiGe films deposited by reactive thermal chemical vapor deposition using a lamp heating system with a source gas mixture of GeF4 and Si2H6 were investigated. In the SiGe film depositions with respective GeF4 and Si2H6 flow rates of 0.06 and 3 sccm, the film structure changed from crystalline to amorphous during the film growth. The results of secondary ion mass spectroscopy analysis and high-temperature deposition suggest that the gas phase reactions cause the structural change. To suppress the gas phase reactions, low-pressure depositions are investigated. The SiGe film deposited at a relatively low pressure of 400 Pa shows good crystallinity. The thin-film transistor with this SiGe film also reveals a high p-channel mobility of about 10 cm2V-1s-1.

High On/Off-Current Ratio in Bottom-Gated Microcrystalline-Silicon Thin-Film Transistors With Vertical-Offset Structure

The high on/off-current ratio of microcrystalline-silicon thin-film transistors (TFTs) with vertical offset was demonstrated. These TFTs have a bottom-gate structure and offset regions formed along the side surfaces of the thick interlayer films. Due to a decrease of maximum electric-field intensity and a narrow distribution of high electric field, the on/off current ratio of vertical-offset TFTs is about three orders of magnitude higher than that of conventional TFTs.

Study on SiGe Film Properties Fabricated using a Reactive Thermal CVD Method

1 Materials Research Laboratory, Hitachi, Ltd. Hitachi-shi, 319-1292 Japan Phone: +81-294-52-7555, Fax: +81-294-52-7615, e-mail: masatoshi.wakagi.vd@hitachi.com 2 Central Research Laboratory, Hitachi, Ltd. Kokubunji-shi, 185-8601 Japan 3 Mechanical Engineering Research Laboratory, Hitachi, Ltd. Hitachinaka-shi,312-0034 Japan 4 Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama-shi, 226-8530 Japan