Kaicheng Li

Reactive ion etching of Si1-xGex alloy with hydrogen bromide

Abstract In this paper, the reactive ion etching (RIE) of Si 1− x Ge x alloys using hydrogen bromide (HBr) plasma is reported. In order to obtain a more precise process control, the Ge content-dependence of HBr-based RIE etch rates has been studied. The experimental results showed that the RIE etch rate of SiGe increased monotonically with increasing the Ge-content in SiGe. The higher the Ge-content, the higher is the ratio of SiGe etch rate to Si etch rate. For instance, when x =0.1, the ratio is 1.12, but, when x =0.23, the ratio is 1.8. The HBr-based RIE process has been applied to the device fabrication of SiGe-heterojunction bipolar transistors (HBTs). Expected DC and high-frequency characteristics of processed SiGe HBTs have been obtained.

Research for SiGe HBT

In this paper, a SiGe HBT was described, which was based on a unique process technology. To characterize the SiGe HBT, HP8510C network analyzer, HP83650A synthetic signal sources, HP8517b S parameter measuring systems etc. have been used for radio frequency performances. The measurements showed the satisfactory results. The SiGe HBT cutoff frequency f/sub T/ is 108GHz, and the maximum oscillation frequency f/sub Max/ is 157GHz.

Growth and quality control of MBE-based SiGe-HBT for amplifier applications

This study aims at getting precise growth and doping control of the well-designed multiple SiGe heterostructure layers for amplifier applications using MBE. Large efforts have been made in calibrating the deposition rates of Si and Ge, and the doping concentrations, in order to ensure the high quality growth. The measured cutoff frequency was 5.1 GHz, which is not high but in an agreement with the simulated value (5.6 GHz) made by Medici for such a large size device without using device isolation. Finally, the development of test amplifiers, using the developed SiGe HBT technology, is underway. The broad-band low-noise amplifier with the certain functions has been obtained.

Growth and quality control of MBE SiGe-HBT structures for analog IC applications

MBE-based SiGe/Si heterostructures prepared by molecular beam epitaxy (MBE) are described in this study with an aim at manufacturing SiGe heterojunction bipolar transistors (HBTs) for the applications in analog ICs. Based on the simulations made by Medici, MBE-based SiGe/Si heterostructures have been designed and grown. The quality of the MBE layered heterostructures has been characterized by reflection high-energy electron diffraction, X-ray diffraction, secondary ion mass spectrometry and spreading resistance. Furthermore, SiGe-HBTs have been fabricated using the 3 /spl mu/m process technology. The experimental results indicate that both the direct current (DC) characteristics and the cutoff frequency of SiGe HBTs are satisfactory. The current gain /spl beta/ of HBT devices is 50, when the collector voltage V/sub C/=2 V and the collector current I/sub C/=5 mA. The cutoff frequency f/sub T/=5.1 GHz. And the uniformity of the cutoff frequency of HBT is quite good. The Gummel plot of an MBE-grown SiGe HBT with the common-emitter configuration shows the excellent performance.

Comparison between MBE-based SiGe/Si HBT and Si-based bipolar transistor technologies

In the paper, the comparison between MBE-based SiGe/Si heterojunction bipolar transistors (HBT) technologies and Si bipolar transistors technologies is made. The SiGe/Si film used in the present work was grown by solid source molecular beam epitaxy (MBE) system. 3 /spl mu/m process technology was used to develop SiGe HBT devices. The experimental results indicate that both the direct current (DC) characteristics and the cutoff frequency of SiGe HBT are satisfactory. The current gain /spl beta/ of HBT devices is 50, when the collector voltage V/sub C/=2 V and the collector current I/sub C/=5 mA. The cutoff frequency f/sub T/=5.1 GHz, and the uniformity of the cutoff frequency of HBT is quite good. With the same layout, 3 /spl mu/m process technology was used to develop Si bipolar transistor devices. The measured results show that the cutoff frequency f/sub T/ of the Si devices is 1.5 GHz.

MBE-based SiGe/Si heterojunction multilayer structures

In this paper, SiGe/Si multilayer heterostructures prepared by molecular beam epitaxy (MBE) are described with the aim of manufacturing SiGe heterojunction bipolar transistors (HBTs). Based on the simulations made by Medici, device structures have been designed and grown. The quality of the MBE layered structures has been characterized by reflection high-energy electron diffraction, X-ray diffraction, secondary ion mass spectrometry and spreading resistance. Furthermore, SiGe-HBTs have been fabricated. Promising DC and RF results of processed HBT devices have been obtained.

A novel p+ Poly-SiGe Gate CMOS device

In order to improve the matching performance of the nMOSFET and pMOSFET threshold voltages in CMOS circuit, a novel p+ Poly-SiGe gate CMOS device is described in this paper. With the change in work function and bandgap, the device effectively reduces the threshold voltage Vth of pMOSFET while the performance of nMOSFET is maintained. Moreover, the threshold voltage Vth of pMOSFET can be continuously adjusted with the change in Ge composition. Thus the performance of pMOSFET is made closer to that of nMOSFET, which is of great importance to further improving the performance of CMOS circuit.

Design of monolithic BiCMOS open-loop detection circuit for MEMS capacitance accelerometer

A novel monolithic BiCMOS open-loop detection circuit for capacitive MEMS accelerometers was presented. It has been developed in 2 ¿m CMOS process. The tested results were as follows. Noise was 1 mg/¿Hz, power was smaller than 10 mW, supply voltage was as low as 5 V, and there is a 2-pole filter on chip.

Self-Aligned SiGe HBT Based on Combined Dry and Wet Etching

In this paper, a self-aligned SiGe/Si HBT was fabricated based on dry & wet etching, in which Si and SiGe materials were etched by KOH (potassium hydroxide) solution and SF6 (sulfur hexafluoride). The measured results are: cutoff frequency fT=103.3GHz, maximum oscillation frequency fmax=124.2GHz. 1. Mechanism of chemical reactions for etch The main chemical composition of etch solution is KOH which reacts with silicon as follows [1][2]: Si +2KOH+H2O=K2SiO3 +H2↑ (1) Germanium is not as active as silicon, and doesn’t react with KOH solution at room temperature. When SiGe is etched in the etching solution, germanium plays an obstructive role in etching, decreasing the etch rate greatly. The hydrolysis in water of H2GeO3 formed by reaction of Ge and etch solution is pasty deposit. The reaction is as follows. Ge + 4OH=GeO2.2H2O (2) Adsorptive power of the substrate is so high that SiGe alloy surface is protected. Therefore, KOH contributes little to etching SiGe alloy. Roughly speaking, KOH doesn’t etch SiGe alloy as an etch endpoint. Silicon was etched by SF6 and oxygen. At RF power, SF6 is dissociated into F groups that have high chemical activity and reacts easily with silicon, germanium, etc. The chemistry is as follows.

Development of high f/sub MAX/ SiGe HBT with air-bridge

In this paper. a SiGe HBT was described, which was based on a unique process technology. To characterize the SiGe HBT, HP85 10C network analyzer, HP83650A synthetic signal sources, HP8517b S parameter measuring systems etc. have been used for measuring radiofrequency performance of SiGe HBT. The measurements showed satisfactory results. The SiGe HBT cutoff frequency f/sub T/ is 108 GHz, and the maximum oscillation frequency is 157 GHz.