The work in this thesis has been focused on processintegration issues for high-performance bipolar technologyincluding experimental work on self-aligned silicides,ion-implanted andin situdoped polysilicon emitters, strained silicongermanium for heterojunction bipolar transistors and physicalprocess and device simulation.
Key issues for the self-aligned silicidation of small devicefeatures such as the influence of dopants, silicon morphologyand line width on titanium disilicide formation, phasetransformation and temperature stability, have been addressed.Pre-amorphization and ion beam mixing by arsenic implantationprior to the suicide formation was shown to extend the use oftitanium silicide into the sub-micron line width range, wheretransformation to the low-resistive phase is otherwise impeded.The temperature stability of cobalt disilicide has also beenstudied.
An epitaxial silicon germanium base was integrated into adeep trench isolated double polysilicon high-frequency bipolarprocess. The integrity of the boron and germanium profiles inthe silicon germanium base was investigated for processrelevant furnace and rapid thermal annealings. It was shownthat the outdiffusion of boron and germanium can besignificantly lowered by the use ofin situdoping of the polysilicon emitter compared tothe conventional ion implantation.
Physical process and device simulation was utilized as apowerful tool for device design and the development of a shortturn-around time high-frequency bipolar transistor researchprocess. Simulations were used both for prediction andanalysis. Analysis by simulation revealed that the non-linearforward common emitter current gain, observed for the firsttransistors fabricated in the research process, originated froma high interface charge carrier recombination velocity belowthe emitter oxide spacers. Measurements on fabricated devices,with different ratios between the emitter interface area andoxide spacer area, verified the simulation results. It wasshown that passivation with hydrogen could improve thelinearity and peak value of the forward common emitter currentgain as well as the maximum transition frequency.
The workhas been carried out within the high-frequencybipolar project at the Department of Electronics at KTH.
Keywords:process integration, bipolar technology,silicon, silicon germanium, titanium silicide, phasetransformation, pre-amorphization,in situdoping, physical process simulation, physicaldevice simulation.
Institutionen för elektronisk systemkonstruktion , 1997. , 65 p.