David Angell

Self-aligned SiGe NPN transistors with 285 GHz f/sub MAX/ and 207 GHz f/sub T/ in a manufacturable technology

This paper reports on SiGe NPN HBTs with unity gain cutoff frequency (f/sub T/) of 207 GHz and an f/sub MAX/ extrapolated from Masons unilateral gain of 285 GHz. f/sub MAX/ extrapolated from maximum available gain is 194 GHz. Transistors sized 0.12/spl times/2.5 /spl mu/m/sup 2/ have these characteristics at a linear current of 1.0 mA//spl mu/m (8.3 mA//spl mu/m/sup 2/). Smaller transistors (0.12/spl times/0.5 /spl mu/m/sup 2/) have an f/sub T/ of 180 GHz at 800 /spl mu/A current. The devices have a pinched base sheet resistance of 2.5 k/spl Omega//sq. and an open-base breakdown voltage BV/sub CEO/ of 1.7 V. The improved performance is a result of a new self-aligned device structure that minimizes parasitic resistance and capacitance without affecting f/sub T/ at small lateral dimensions.

SiGe HBTs with cut-off frequency of 350 GHz

This work reports on SiGe HBTs with f/sub T/ of 350 GHz. This is the highest reported f/sub T/ for any Si-based transistor as well as any bipolar transistor. Associated f/sub max/ is 170 GHz, and BV/sub CEO/ and BV/sub CBO/ are measured to be 1.4 V and 5.0 V, respectively. Also achieved was the simultaneous optimization of f/sub T/ and f/sub max/ resulting in 270 GHz and 260 GHz, with BV/sub CEO/ and BV/sub CBO/ of 1.6 V and 5.5 V, respectively. The dependence of device performance on bias condition and device dimension has been investigated. Considerations regarding the extraction of such high f/sub T/ and f/sub max/ values are also discussed.

Principal Component Analysis of Optical Emission Spectroscopy and Mass Spectrometry: Application to Reactive Ion Etch Process Parameter Estimation Using Neural Networks

We report on a simple technique that characterizes the effect of process parameters (i.e., pressure, RF power, and gas mixture) on the optical emission and mass spectra of CHFJO2 plasma. This technique is sensitive to changes in chamber contamination levels (e.g., formation of Teflon-like thin-film), and appears to be a promising tool for real-time monitoring and control of reactive ion etching. Through principal component analysis, we observe that 99% of the variance in the more than 1100 optical and mass spectra channels are accounted for by the first four principal components of each sensor. Projection of the mass spectrum on its principal components suggests a strong linear relationship with respect to chamber pressure. This representation also shows that the effect of changes in thin-film levels, gas mixture, and RF power on the mass spectrum is complicated, but predictable. To model the nonlinear relationship between these process parameters and the principal component projections, a feedforward, multi-layered neural network is trained and is shown to be able to predict all process parameters from either the mass or the optical spectrum. The projections of the optical emission spectrum on its principal components suggest that optical emission spectroscopy is much more sensitive to changes in RF power than the mass spectrum, as measured by the residual gas analyzer. Model performance can be significantly improved if both the optical and mass spectrum projections are used (so called sensor fusion). Our analysis indicates that accurate estimates of process parameters and chamber conditions can be made with relatively simple neural network models which fuse the principal components of the measured optical emission and mass spectra. In the reactive ion etching (RIE) process, plasma characteristics depend on many parameters; some of these parameter values are set by the tool operator, e.g., chamber pressure, RF power, and gas flow, while others are internal to the condition of the chamber, e.g., thin-film thickness on the chamber walls, or the amount of material etched. Plasma characteristics can be observed using in situ measurements, e.g., via optical emission spectroscopy (OES) or residual gas analysis (RGA). How these measurements can be used to estimate the process parameters is the question

Cryogenic reactive ion etching of silicon in SF6

Reactive ion etching of Si and SiO2 in SF6 plasmas in which the samples are mounted on a liquid‐nitrogen‐cooled electrode has been studied. At this temperature SF6 condenses on the electrode surface, but it is possible to maintain a plasma. Si etch anisotropy has been demonstrated at low temperature, in agreement with previous studies. Mass spectrometry and optical emission spectroscopy indicate that fluorine is the dominant species in the plasma because SF6 and SFx species are removed from the gas phase by condensation.

Grazing angle optical emission interferometry for end‐point detection

Light emitted from a plasma during reactive ion etching and reflected by the wafer surface at a grazing angle is utilized to determine the remaining film thickness with an accuracy of ±30 A. This promises a more flexible etching approach, e.g., tailoring the final stage of etching to minimize lattice damage.

Process variability analysis of a Si/SiGe HBT technology with greater than 200 GHz performance

A process tolerance analysis of a SiGe NPN HBT with >200 GHz f/sub T/ and >250 GHz f/sub MAX/ is presented. AC and DC device results on 200 mm wafers demonstrate a wide process window resulting in a highly manufacturable HBT technology.

Etch tailoring through flexible end-point detection

Accurate measurement in-situ and in real-time of film thickness during Reactive Ion Etching (THE) can lead to new levels of process control. The two techniques described are used to stop an etch close to an interface less than 5Onm and have an accuracy of 3nm and 8nm respectively. The long term goal etch tailoring depends on pin-pointing in real-time the film remaining to be etched. With etch tailoring process parameters can be changed to improve product quality.