Apparatus for elimination of low temperature ammonia salts in TiCl.sub.4 NH.sub.3 CVD reaction

An apparatus for processing semiconductor wafers comprising:

• a CVD reaction chamber bounded by a sealable cold wall and having a wafer supporting susceptor contained therein, a heater positioned to heat a wafer supported on the susceptor to a primary reaction temperature, a reaction gas inlet, and a gas outlet, the susceptor, inlet and outlet being positioned such that reaction gases from the inlet flow in a path from the inlet, against the susceptor, and downstream to the outlet;
• a surface liner on the cold wall partially thermally insulated therefrom, along the path downstream from the susceptor, on internal surfaces of the chamber where undesirable particulate contaminants tend to form when unspent reaction gases contact the cold reactor wall;
• a secondary electrode in the path downstream of the susceptor;
• an electrical potential source, connected to the secondary electrode, sufficient to form a low energy plasma in gas between the secondary electrode and at least a portion of the reactor surfaces that are in contact with gases flowing downstream of the susceptor to raise the temperature of gas downstream of the susceptor to a temperature above that at which undesirable contaminants will form but below the primary reaction temperature.