A PLASMA REACTOR FOR SOLID SURFACE MODIFICATION

Abstract
A general purpose plasma reactor has been designed and built to be used in various fields such as metallurgy, and microelectronics. The important aspects of the system design are : (a) the chamber can be evacuated to a base pressure of approximately 5 x 10^-7 Torr ; (b) capabilities for thermal bake out at 150°C, and nitrogen pre-burn at a pressure of about 3 x 10^-3 Torr ; (c) substrate holder which is capable of heating the substrate up to 400°C, and it is able to move the target so that plasma-surface reactions can be done anywhere inside the chamber ; (d) provision for inductively exciting a gas or a mixture of gases using 1.0 KW of r.f. power at a frequency of 13.56 MHz ; (e) capabilities for controlling gas flow rates, and mixing them outside the chamber, so that the deposited layer composition can be controlled by varying the ratio of the gases. Also another gas can be supplied to the chamber outside the r.f. region near the substrate. This is an important design consideration if a reactant gas is to be excited and mixed with a neutral gas outside the r.f. region. (f) A capability for axially confining the plasma using a magnetic field. In this way the plasma density at the target inside the plasma is enhanced. We have characterized nitrogen plasma in our system by measuring the plasma density and electron temperature with respect to distance from the middle of the plasma chamber towards the target in the reactor chamber. The results show electron temperature and plasma density in the range of 4-40 ev and 10¹¹ - 10⁸ cm^-3 respectively.