Study Of The Langmuir Probe Diagnostic Circuit For The Low-Temperature Plasma

Low-temperature plasma has been widely applied to various fields of industry, such as material, microelectronics, chemical engineering, machine, and environment protection. Film deposition and etching, which using the chemical activity of plasma, are the essential process in advanced electronic equipment manufacture. For instance, plasma chemical vapor deposition technique is used for researching kinds of polymer film, diamond-like film and carbon nanometer tube, etc. And reactive ion etching has been the necessary process in the fine processing of very large-scale integration. So it becomes more important to acquire plasma characters and mechanism of the processing through diagnosing plasma. It can afford useful information for further study of the plasma mechanism and searching the best processing parameters.Langmuir probe possesses lots of advantages in plasma diagnostic, such as simple equipment and easy manufacture, high space resolving power, and flexible etc. It has been widely applied in plasma equipment as a normal diagnostic technique. From the probe V/I curves we can acquire plasma electron temperature, electron density, ion density, and space potential etc. Other plasma diagnostic techniques, like spectrum analysis technique and microwave transmission technique, are complex and can acquire less plasma parameter.According to the structure and principle of Langmuir probe, a high frequency supply is necessary. Meanwhile, sampling frequency of probe current and scanning voltage must be sufficient. So as to reduce the influence of Langmuir probe on plasma, also to get better diagnostic results. From the papers reported, common Langmuir probe diagnostic system usually can't satisfy the above requests, and can't exactly reflect plasma parameter.In this paper, we give a new Langmuir probe scheme, including Langmuir probe, probe supply, and data sampling module. The probe supply with MAX038 can generate alterable sawtooth-wave range from 1Hz to 1MHz. Then, Power amplifier PA88 amplifies the scanning voltage up to±100V as Langmuir probe supply. Data acquisition module adopts PCL-818HG data acquisition card to connect with computer. In addition, chocks are designed to reduce radio frequency interference based on RF compensation theory, and self-made Langmuir probe is installed on RF-500 vacuum filming machine. In the experiment of plasma diagnostic with Langmuir probe, probe voltage and current under 10Hz and 100Hz scanning frequency are recorded. Experiment results and analysis show that, the self-made Langmuir probe diagnostic circuits possess certain precision, and can afford useful information for diagnosing plasma.