Development of inward plasma

抄録

Inward plasma is a very unique plasma processing technique capable of performing etching by irradiating local plasma near the capillary inlet against the flow of gas while sucking the etching gas [1]. Fig. 1(a) shows the basic schematic diagram of the inward plasma. By arbitrarily adjusting the pressure and the gap in the capillary tube (the distance between the sample and the end face of the capillary tube) to supply gas from the sample surface and high frequency power to RF electrodes surrounding the capillary, localized plasmas equivalent to the inner diameter of the capillary tube are generated against the gas flow in the aforementioned gap area. As the superiority of the inward plasma, by performing etching while sucking gas from the sample surface side, and that the processed surface is clean, the temperature rise of the sample during etching as compared with the general down-flow type plasma [2], it is possible to greatly change the flux ratio of the charged particles and radicals and the like. From these features, the inward plasma has been used for wiring exposure of semiconductor devices as preprocessing in failure analysis until now. Recently, the application to the semiconductor front-end processing device manufacturing is also expected. When it is used in the manufacturing process of semiconductor devices, contamination and damage caused by the manufacturing process become a problem, so it is necessary to grasp the damage caused to the device by each process. However, the plasma density, ion energy, and so on, which are factors of stress [3], have not been quantitatively evaluated. The reason is that the Langmuir probe method [4] using a single probe is known as a measurement method of plasma density and ion energy, but in the inward plasma, the plasma emission region from the tip of the capillary to the sample stage is only in the order of several hundred um. Therefore, in addition to the difficulty of placing the probe collector itself, it also affects the plasma itself. Therefore, we prepared an electrostatic type ion energy analyzer (IEA) shown in Fig. 1 (b), and decided to measure the ion energy. By placing a negatively biased (V_G) grid-electrode on the sample stage, we can obtain the ion current I_c by catching the positive ions back into the collector. In this study, RF frequency 13.56 MHz, RF power 20 W, the chamber pressure 7 Pa and the inner diameter of the capillary were set to 4 mm, V_G = -20 V and Ar gases were localized plasmas in the ceramic made capillary tubes. In this plasma configuration, the potential of the plasma can be controlled by applying a bias-voltage V_a to the electrodes inserted into the capillary tube. Fig. 1(c) shows the voltage/current properties obtained when Fig. 1(d) is V_a = 0 V in the case of V_a = 120 V. As for the high-energy component of ions, since V_c appears from 0 V or higher, the change in | I_c | due to the high-energy component was compared by drawing a tangent to V_c = 50 ~ 150 V section where I_c is the smallest and taking the leak current into account. We could observe that the largest value of the ion energy is larger in Fig. 1(c) where the plasma-potential is larger. Further, from Fig. 1 (d), the ion saturation current was found to be approximately 10 uA, when estimating the plasma density through Bohm flux, the plasma density becomes about 4.2×10¹⁴ m^-3, the smallest maximal ion energy depending on V_a became about 20 eV. By using IEA, quantitative results were obtained for the first time on the stressors of the inward plasma. In this lecture, we report on IEA of the inward plasma.

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