Method and apparatus for target support in electron projection systems

For use in an electron image projection system, apparatus for supporting a target wafer in an electron-accelerating electric field between a cathode and an anode without significant distortion of the field, said apparatus comprising:

• pedestal means affixed to the anode and having a flat surface against which the wafer is to be secured;
• a relatively thin sheet of dielectric material covering said pedestal means and insulating the wafer from said pedestal means;
• and
• means for applying a bias voltage between the wafer and said pedestal means, and for thereby charging the wafer to such a potential as to maintain a relatively uniform and undistorted voltage gradient from the cathode to the anode, and electrostatically attracting and flattening the wafer to said pedestal surface.

For use in an electron image projection system having an electron-emitting cathode, apparatus for supporting a target wafer in an electron-accelerating electric field without significantly distorting the field, said apparatus comprising:

• a wafer-supporting anode structure;
• an anode pedestal having a flat surface elevated from said anode structure;
• a relatively thin sheet of dielectric material covering said anode pedestal surface;
• retaining means having an opening sized to fit snugly over said pedestal covered with said sheet, to retain said sheet in position;
• electrical contact means including resilient means for obtaining reliable electrical contact with the wafer;
• means for applying a bias voltage between said electrical contact means and said pedestal, to charge the wafer to such a potential as to maintain a substantially uniform and undistorted voltage gradient in the electron-accelerating field between the cathode and said anode pedestal, and to attract and flatten the wafer electrostatically to said pedestal surface.

For use in an electron projection system, apparatus for supporting a target wafer in an electron-accelerating electric field with minimal distortion to the field, said apparatus comprising:

• wafer support means including a lip extending over the edges of the wafer, the wafer being secured by pressure urging it against said lip, said lip including
• an outer portion against which the wafer is held,
• an inner portion extending significantly across but spaced from the wafer,
• a dielectric sheet substantially covering said lip except for said outer portion, and
• a conductive coating substantially covering said dielectric sheet;
• and
• means for applying a bias voltage between said conductive coating and the wafer, whereby the bias voltage tends to maintain uniformity in the electron-accelerating field, which would otherwise be distorted by the presence of said lip.

A method of supporting a target wafer with minimal electric field distortion due to the presence of a target support in an electron-accelerating field between a cathode and an anode of an electron image projection system, said method comprising the steps of:

• supporting a target wafer on the target support;
• interposing in the electric field an insulating layer positioned on the target support;
• and
• applying a bias voltage across the thickness of the insulating layer, thereby to maintain substantial uniformity of the electric field between the cathode and anode.