Mercury probe apparatus with improved safety

An apparatus for measuring electrical properties of a semiconductor wafer, said apparatus comprising:

• a wafer holder;
• a mercury probe for contacting the top surface of said wafer with a mercury column, said mercury probe including a capillary tube for containing said mercury column;
• a pneumatic control means for applying a partial vacuum or pressure above said mercury column within said capillary tube;
• a probe arm having said mercury probe affixed thereto;
• a positioning means for controlling the position of said capillary tube relative to the upper surface of said wafer;
• a measurement means for causing an electrical current to flow through said wafer and for measuring electrical properties of said wafer;
• a first electrical contact electrically connected to said mercury column and to said measurement means;
• a second electrical contact electrically connected to said wafer holder and said measurement means;
• a clean mercury container;
• and
• a control unit in operating connection with the pneumatic control means, the positioning means and the measurement means,
• wherein said mercury probe has at least one measurement position and a first mercury change position, the capillary tube is separated from the clean mercury container in said at least one measurement position, and the capillary tube is in fluid communication with the clean mercury container in said first mercury change position.