TECHNICAL FIELD

The present invention relates to the technical field of plasma gas detection, and in particular to a device for measuring gas temperature in plasmas.

BACKGROUND

Low-pressure radio-frequency (RF) capacitively-coupled plasma (CCP) sources have been widely used in the fields of material processing, such as dielectric etching and thin film deposition due to their advantages of simple structure, and good uniformity. A plasma is mainly composed of neutral gas molecules (atoms), electrons, ions, and active reactive species. The neutral gas molecules (atoms) account for more than 99%, and the gas temperature is critical for various parameters of the plasma, which in turn greatly affects the material processing. For example, the temperature distribution of the neutral gas will significantly affect the plasma density distribution and the flow distribution in the plasma, which in turn affects the uniformity of material processing. The temperature of the neutral gas will also affect the energy distribution function of the electrons, which in turn will affect the efficiency of material processing. Therefore, the gas temperature of the low-pressure RF-CCP is of important scientific interest and of great significance in industrial application.

However, due to the complex electromagnetic environment of the low-pressure RF plasma, there are few methods for the determination of gas temperature in plasmas. For example, a thermocouple sensor is widely used for gas temperature measurement. However, this method is susceptible to various electromagnetic fields, and the thermocouple itself will also interfere with the plasma; therefore, this method is not suitable to measure the temperature of the neutral gas in the low-pressure RF plasma.

At present, traditional neutral gas temperature measurement methods are mainly based on spectroscopic diagnostics, such as optical emission spectroscopy, absorption spectroscopy, laser-induced fluorescence. Such diagnostic methods are often based on some assumptions, for example, that the rotational temperature and the translational temperature of a gas are equal. Under atmospheric pressure, this assumption is true, so the measurement results are relatively accurate. However, under low pressure conditions (less than 100 Pa), the temperature value measured by spectroscopic diagnostics is very different from the real temperature of the neutral gas, and no satisfactory measurement result can be obtained. In addition, traditional spectroscopy diagnostic methods have some limitations, such as long response time, expensive equipment, complicated calculation process, poor spatial resolution. Therefore, the temperature measurement of the neutral gas in a low-pressure RF-CCP has always been a problem.

SUMMARY

In view of this, an objective of the present invention is to provide a device for measuring gas temperature in plasmas. One scientific application example is that the gas temperature measurement is capable of characterizing the electromagnetic effect in the very high frequency (VHF) large-area CCP by using the measured temperature of the neutral gas with fast response and accurate detection.

To achieve the above objective, the present invention provides the following solutions:

A device for measuring gas temperature in plasmas includes a vacuum chamber, a fiber optic temperature sensor, a quartz tube, a circulator, a spectrometer, a broadband light source and a computer, where

one end of the quartz tube is inserted into the vacuum chamber;

the fiber optic temperature sensor is located in the plasma of the vacuum chamber and fixed to the quartz tube;

the fiber optic temperature sensor is connected to the circulator by means of an optical fiber passing through the quartz tube;

the circulator is connected to the broadband light source and the spectrometer through optical fibers, respectively; and

the spectrometer is electrically connected to the computer which is configured to read and record spectra collected by the spectrometer;

Optionally, the device further includes a two-dimensional driving system, where

the two-dimensional driving system is configured to move the quartz tube horizontally and vertically; and

one end of the quartz tube is inserted into the vacuum chamber through the two-dimensional driving system.

Optionally, an inner diameter of the quartz tube gradually decreases from the end inserted into the vacuum chamber to the other end.

Optionally, the inner diameter of the quartz tube gradually decreases from 0.1 cm to 0.02 cm.

Optionally, an end of the quartz tube that has the smallest inner diameter is sealed with the vacuum cement.

Optionally, the device further includes a packaging system which retains the quartz tube in the two-dimensional driving system.

Optionally, the vacuum sealing system includes a first rubber sealing ring, a first flange joint, a second rubber sealing ring, a second flange joint and a baffle, where

the first rubber sealing ring sleeves the first flange joint;

the first flange joint and the second rubber sealing ring successively sleeve the quartz tube in a direction from the end, having the largest inner diameter, of the quartz tube to the end, having the smallest inner diameter, of the quartz tube;

the second flange joint and the first flange joint are symmetrically disposed about the central position of the second rubber sealing ring, and the two ends of the second rubber sealing ring are clamped in the first flange joint and the second flange joint, respectively;

the baffle sleeves the second flange joint; a screw hole is formed in the baffle; and

the first flange joint is connected to a flange port in the two-dimensional driving system, and the baffle is fixed to the two-dimensional driving system by means of a screw.

Optionally, each of the optical fibers used has an outer diameter of 0.0125 cm.

According to the specific examples provided by the present invention, the present invention discloses the following technical effects: in the device for measuring gas temperature in a plasma provided by the present invention, the broadband light source emits a beam of broadband light to the head of the fiber optic temperature sensor via the circulator and the optical fiber. A beam of reflected light then returns along the original path due to the periodic structure of the fiber optic temperature sensor, and its spectral line is split by the spectrometer, and read and recorded by the computer. When the temperature of the neutral gas in a plasma in the vacuum chamber rises or falls, the central wavelength value of the reflected light will rapidly increase or decrease instantly. Then, the change in the temperature of the neutral gas in a plasma can be obtained according to the change of the measured central wavelength value of the reflected light. In addition, an optical signal, rather than an electrical signal, is used as a carrier for the fiber optic temperature sensor in the device, which avoids the interference of the electromagnetic fields of the plasma and allows to improve the detection accuracy.

