Atmospheric Pressure RF-Plasma System And Its Application In Photoresist Stripping

Photoresist stripping plays a very important role in microelectronics industry. It occupies about 30-35% of the semiconductor manufacturing procedures, and will directly affect the yield and the cost of IC product.Recently, more attention has been paid to a novel photoresist stripping technology based on atmospheric pressure plasma. This method can overcome the disadvantages of the wet chemical method: the reactions cannot be controlled accurately, the photoresist cannot be stripped completely, the environment can be polluted, and the photoresist after high temperature processes cannot be stripped easily. The damage caused by the ion bombing with high energy can also be avoided by using this method. Therefore, the study of photoresist stripping by using atmospheric pressure plasma is very important in the research and the practical application.Atmospheric pressure RF-plasma was generated by capacitor couple. The experiments, in which helium and argon was used as carrier gas, respectively, showed the stripping rate by Ar/O2 plasma was similar with that by He/O2 plasma. It was the first time that argon replaced expensive helium as carrier gas that was generally used.An immersion plasma apparatus with a diameter of 150mm, a plate with the largest discharge area in the reported works, was developed in this work. Discharge and temperature characteristics have been studied in detail. A uniform stable plasma has been generated by controlling the input power, the gas composition, and the distance between the electrodes. The temperature distribution showed that the plasma temperature was below 150℃ which would not cause damage. All these results showed this atmospheric pressureplasma could be applied to photoresist stripping.The photoresists S9912 and kapton have been stripped using the immersion plasma. The results indicated that stripping rate was dependent on the input power, the mixed ratio of O2/ Ar, and the substrate temperature. The stripping rate increased with the increasing input power and the increasing substrate temperature. Under a constant input power and substrate temperature, the stripping rate reached the largest when the 1% O2 was added. The stripping rate was 500nm/min at the condition of input power 300W, Ar gas flow rate 5L/min and 1% O2. This has been qualified for application in the industry which requires a stripping rate of several hundred of nanometer every minute. The SEM pictures showed that the photoresist has been completedly removed and no residues remained.