While plasmas using mixtures of SF6, C4F8, and Ar are widely used in deep silicon etching, very few studies have linked the discharge parameters to etching results. The authors form such linkages in this report. The authors measured the optical emission intensities of lines from Ar, F, S, SFx, CF2, C2, C3, and CS as a function of the percentage C4F8 in the gas flow, the total gas flow rate, and the bias power. In addition, the ion current density and electron temperature were measured using a floating Langmuir probe. For comparison, trenches were etched of various widths and the trench profiles (etch depth, undercut) were measured. The addition of C4F8 to an SF6/Ar plasma acts to reduce the availability of F as well as increase the deposition of passivation film. Sulfur combines with carbon in the plasma efficiently to create a large optical emission of CS and suppress optical emissions from C2 and C3. At low fractional flows of C4F8, the etch process appears to be controlled by the ion flux more so than by the F density. At large C4F8 fractional flows, the etch process appears to be controlled more by the F density than by the ion flux or deposition rate of passivation film. CF2 and C2 do not appear to cause deposition from the plasma, but CS and other carbon containing molecules as well as ions do.
Attempts have been made by several investigators to measure the effects of tobacco smoking upon systolic and diastolic pressure. In such investigations, the number of measurements are usually too small to give reliable results, in some cases a single determination of systolic pressure being made before smoking, and a single determination after smoking. Consideration of the various causes which operate in establishing and varying blood pressure indicates that such investigations are unreliable, and that although the conclusions might in some cases be true, the evidence does not warrant them.'As has been already pointed out by Carver, 2 the method of investigation of blood pressure changes developed by Dunlap and Bagby, and subsequently used in the physiological branch of the Air Medical Service, is quite applicable to problems such as those of tobacco smoking. This method consists in making a reading, with a clinical sphygmomanometer, every two or three minutes, over a prolonged interval. A well trained examiner may readily make sufficiently accurate readings of both systolic and diastolic pressure every two minutes, and in the intervening periods, may make counts of heart rate. In this procedure, a blood-pressure reading is commenced on the first, third, fifth and so on, minutes. The systolic and diastolic pressures are determined in from thirty to forty seconds, and the arm bandage
Articles you may be interested inDependence of selectivity on plasma conditions in selective etching in submicrometer pitch grating on InP surface by CH4/H2 reactive ion etching J. Appl. Phys. 109, 073516 (2011); 10.1063/1.3573536 Model for aspect ratio dependent etch modulated processing J. Vac. Sci. Technol. A 28, 334 (2010); 10.1116/1.3305716Aspect ratio dependent etching lag reduction in deep silicon etch processes Maximum achievable aspect ratio in deep reactive ion etching of silicon due to aspect ratio dependent transport and the microloading effect Kinetics and crystal orientation dependence in high aspect ratio silicon dry etchingThe etch rate of deep features in silicon, such as trenches and vias, can vary significantly with the feature aspect ratio (AR). Small AR features generally etch faster than large AR features. The reasons for this AR dependence include a slowing of the etch rate with increasing AR due to the necessary transport of molecules into and out of the features as well as ion flux reductions at feature bottom due to the angular spread of the ion flux and ion deflection caused by differential charging of the microstructures. Finding ways to reduce, eliminate, or reverse this AR dependence is both an active subject of research and difficult. In this work, instead of focusing on methods to reduce or prevent AR dependence in an etch process, the authors focus on methods to correct it after the fact. The authors show that an inhibitor film deposition step can be used under some circumstances to allow feature depth disparities to be corrected. This process can be used to correct feature depth disparities whenever the AR dependence of the inhibitor film deposition step is worse (larger) than the AR dependence of the following inhibitor etch step. To test the theory, a plasma process through SF 6 /C 4 F 8 /Ar mixtures was used to both produce trenches of various ARs having significant depth disparities and correct those disparities. The etch depth of small AR features can be held essentially constant while that of larger AR features is increased to match or even exceed.
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