We present a tunable flipflop-based frequency divider and a fully differential push-push VCO designed in a 200GHz f T SiGe BiCMOS technology. A new technique for tuning the sensitivity of the divider in the frequency range of interest is presented. The chip works from 60GHz up to 113GHz. The VCO is based on a new topology which allows generating differential push-push outputs. The VCO shows a tuning range larger than 7GHz. The phase noise is 75dBc/Hz at 100kHz offset. The chip shows a frequency drift of 12.3MHz/C. The fundamental signal suppression is larger than 50dB. The output power is 2×5dBm. At a 3.3V supply, the circuits consume 35mA and 65mA, respectively.
Etching silicon with the standard HNOJHF/H=O solution in the low HF regime is investigated using a single-wafer spray-etching machine. The single-crystal silicon and undoped polysilicon etch rate is measured for different percentages of HF between 0.13 and 0.18% (by weight). The polysilieon etched about five times faster than single-crystal silicon. Spray-etching damaged n silicon out of isolation trench structures is examined at spin speeds of i0 and i000 rpm by scanning electron microscopy (SEM) photographs. The etch rates are measured from the photographs and compared to the etching Of undoped polysilieon at the same spin speeds. Both of these have a linear etch rate. The damaged silicon etch rate varies between one-half and one-third of the poly etch rate depending on the spin speed. The spray-etching at I000 rpm yields the best uniformity for both the polysilicon and the damaged silicon in the trench. Furthermore, the etch rate of the silicon in the n § buried layer in the trench is measured and compared with the etch rate on the n-silicon in the trench. The results show a clear etch-rate dependence on doping. The etch rate of the n § silicon is about three times as fast as the etch rate of the n-silicon in the trench.The HNO3/HF/H20 silicon etch system is a much discussed topic. Many papers have been published that deal with anisotropic etching along crystal planes. ~4 But many papers on this subject deal with only a solution that has a high percentage of HF. 48 Some attention has also been given to the low HF regime. 9 The growing application of these low HF solutions is etching damaged silicon from isolation trenches in integrated circuits. ~~ This paper is to investigate spray-etching of damaged silicon from the trenches with respect to %HF, spin speed, and background doping of the silicon.The basic reaction that takes place during the etching of silicon is shown in the equation below ~ Si + HNO3 + 6HF -~ H2SiF~ + HNO2 + H2 + H20 Basically, the nitric acid oxidizes the silicon and the HF then etches away the oxide. To attain a constant, steadystate reaction, however, a catalyst must be added to the reaction in sufficient amount. Oxides of nitrogen are this catalyst. ~ The addition of this catalyst to the reaction is known as the activation process. Without this activation, the etch rate of silicon is lower than the etch rate with the catalyst, and the etch uniformity across the wafer is poor. This activation can be accomplished by etching bare silicon wafers in the etch for a certain period of time. Oxides of nitrogen emitted by the etching reaction are dissolved into the etchant and build up to the necessary level during activation.
ExperimentThe first step in the experiment was to characterize the etch rate of silicon as a function of %HF in the low HF regime. Four different solutions of HF were mixed using 70% assay HNO~ and 49 % assay HF to yield solutions in the range of 0.13 to 0.18 %HF by weight. These four solutions then were analyzed by ion chromatography on a Dionex Series 4500i and were 0.133,...
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