Suppression of Arsenic Autodoping with Rapid Thermal Epitaxy for Low Power Bipolar Complementary Metal Oxide Semiconductor

Abstract

Scaled bipolar transistors for bipolar complementary metal oxide semiconductor (BiCMOS) integrated circuits require low collector-substrate capacitance in order to minimize power consumption. The unintentional incorporation of dopant into a growing epitaxial layer, known as autodoping, can affect the ultimate lower limit of the collector-substrate capacitance. In this work, we studied the effects of epitaxial layer growth rate, arsenic-buried layer implant dose, and pre-epitaxia] bake temperature on autodoping using rapid thermal epitaxy (RTE). To begin, we experimented with the buried layer implant dose to check its affect on lateral autodoping. The amount of autodoping increased when the buried layer implant dose increased, confirming the source of the arsenic autodoping as the buried layer. Also, in contrast to data from conventional reactors, we found the peak interface concentration and integrated dose in regions adjacent to the buried layer to be linearly dependent on the growth rate (i.e., low growth rates trap less arsenic at the substrate/epi layer interface) for all growth rates studied. Next, by adjusting the prebake temperature over a range from 800 to I050~ without changing the growth conditions, we first observed a rise in autodoping with temperature to 950~ at which point the incorporated autodoping dose and peak concentration began to fall. Through simulation of the evaporated arsenic from the buried layer and data for arsenic desorption from the silicon surface, we explain this behavior. Finally, using the data gathered on the autodoping characteristics of RTE, we show a process using two growth rate steps and a low temperature prebake step which completely eliminates the lateral autodoping peak. Using this new growth process, epitaxial silicon films over arsenic-doped buried layers for low power BiCMOS are possible.

A brief review of co-doping

“…The formation of these Eu-O complexes appears to be more beneficial to the crystal quality and stability than either defect is on its own [232]. Actually, during the growth of nitrides and oxides, unintentional As and B impurities were also observed [233][234][235].…”

Control of Arsenic Doping during Low Temperature CVD Epitaxy of Silicon (100)

“…Agnello et al 5 have shown that when low temperature AP-CVD is used with DCS as the Si source, it is possible to incorporate a very high As concentration of 2 ϫ 10 21 cm Ϫ3 . Moreover, the growth rate is enhanced in a manner similar to that of P. J. H. Comfort et al 3 have also grown epi layers with a high As concentration (7 ϫ 10 19 cm Ϫ3 ) by using silane based plasma-enhanced CVD. With this technology, a higher growth rate can be achieved than with DCS, but generally, it has a higher defect density.…”

“…This undesirable effect is generally referred to as autodoping. [1][2][3] With low temperature, atmospheric pressure CVD (AP-CVD) using SiCl 2 H 2 (DCS) as the Si source, Sedgwick et al 4 have shown that highly phosphorus-doped Si layers with a low defect density can be grown. By growing very sharp P profiles, they demonstrated that the P concentration in the epi layer can be controlled directly by adjusting the phosphine concentration in the H 2 carrier gas.…”

“…Previously reported autodoping-suppression schemes use a high temperature (T Ն 1000ЊC) to remove the As from the Si surface. 3,9 The high temperature causes strong solid-state diffusion, thus impeding the fabrication of a sharp As profile. The desorption kinetics 6 suggest that a kinetic limitation of the desorption process is probably not present at such a high temperature, which has motivated us to develop an autodoping-suppression scheme at a lower temperature.…”

Controlled Growth of Non-Uniform Arsenic Profiles in Silicon Reduced-Pressure Chemical Vapor Deposition Epitaxial Layers

“…5 The effect of the surface segregation is to hamper any abrupt transition to another doping level, and, in the case of an abrupt drop in doping, the undesired lingering of the higher As doping is referred to as autodoping. Previous experimental investigations have focused on exploring the optimal conditions for achieving goals such as suppressing lateral autodoping, 6 determining the impact on the growth rate, 7 growing highly-doped layers of poly-Si, 8 or Ge x Si 1Àx alloys. 9 By the analysis of the mechanism governing the doping from the As segregated layer, good results were in the past achieved and applied to the growth of high-doped abrupt As peaks.…”