Automation of a Mass Flow Controller for Application in Time‐Multiplex SF₆+CH₄ Plasma Etching of Silicon

Abstract

In this work is proposed the automation of a gas injection (mass flow) system in order to generate timemultiplex SF 6/CH4 radiofrequency plasma applied for silicon (Si) etching process. The control of the gas injection system is important in order to better control the process anisotropy, i.e., the high-aspect-ratio of mask pattern transfer to substrate surface. In other words, this control allows the attainment of deep Si etching process. Here, the automation of the gas injection system was realized through the interface between a computer and a data acquisition board. The automation software developed allows controlling the gas flow rate switching it on and off during whole process through the use of a square waveform routine, intermittent flow, beyond the conventional condition of a fixed value for gas flow rate, continuous flow. In order to investigate the timemultiplex SF6/CH4 plasma etching of Si, the residual gas analysis was performed. The investigations were made keeping the following process parameters: flow of SF6: 10 sccm, flow of CH4: 6 sccm, 100 W rf power, wave period: 20 sec. It were monitored the partial pressure of SF + 5 (parent neutral specie: SF6), CH + 4 (CH4) and SiF + 3 (SiF4) species as a function of time for different gas flow switching and duty cycle. The results showed that with the generation of plasma occurs a drastic change in behavior of partial pressures of SF + 5 and CH + 4 species. Moreover, it is evidenced that the interactions between the SF6 and CH4 fragments promotes a high production rate of HF molecule and consequently a decrease of atomic fluorine, mainly when plasma is on. Finally, the behavior of partial pressure of SiF + 3 specie for alternatively intermittent SF6 and CH4 flow operation shows us that both the etching processes and the deposition of a polymer passivation layer are occurring alternatively, a desirable feature for multi-step etching process.