Mask-to-wafer alignment system

A device for mask-to-wafer alignment that comprises:

• a source of electromagnetic radiation for alignment;
• optics means for delivering radiation from the source of radiation to a reflective mask;
• a camera to image an alignment pattern on the reflective mask through a beam splitter to a wafer plane wherein the beam splitter comprises a substrate having a first surface facing the camera and a second surface that is reflective of said electromagnetic radiation, wherein the substrate includes a number of apertures with at least a majority of the apertures defining a hole pattern about a central point of the substrate, and wherein the pattern defines a plurality of holes that defines a hole pattern about the central point of the substrate such that each hole with its corresponding aperture through to the second surface of the substrate at a defined distance from the central point has a corresponding area located the same distance on the other side of the central point that defines a reflective solid surface;
• means for projecting electromagnetic radiation containing a roughly centered image of the mask alignment pattern toward the first surface of the substrate;
• a wafer having a complementary alignment pattern on its surface wherein the wafer is positioned downstream from the beam splitter substrate so that electromagnetic radiation that passes through the at least one hole of the substrate is reflected from the wafer to produce reflected electromagnetic radiation containing superimposed images of the mask pattern and of the wafer pattern toward the reflective second surface of the substrate;
• and
• means for detecting the superimposed images reflected from the second surface.

A method for mask-to-wafer alignment that comprises the steps of:

• providing a mask that has an alignment pattern on its surface;
• providing a wafer that has a complementary alignment pattern on its surface;
• providing a source of electromagnetic radiation and delivering radiation from the source to the mask;
• providing a camera that images the alignment pattern on the mask through the beam splitter and onto the wafer;
• providing a beam splitter that comprises a substrate having a first surface facing the source of electromagnetic radiation and second surface that is reflective of said electromagnetic radiation, wherein the substrate includes a number of apertures with at least a majority of the apertures defining a hole pattern about a central point of the substrate, and wherein the pattern defines a plurality of holes that defines a hole pattern about the central point of the substrate such that each hole with its corresponding aperture in the second surface of the substrate at a defined distance from the central point has a corresponding area located the same distance on the other side of the central point that defines a reflective solid surface;
• projecting electromagnetic radiation from the source of electromagnetic radiation containing an image of the mask pattern through the beam splitter whereby electromagnetic radiation that traverses through at least one hole that is formed through the substrate is reflected off the wafer surface to form a reflected electromagnetic radiation containing superimposed images of the mask alignment pattern and of the complementary wafer alignment pattern that is directed toward the reflective second surface of the substrate;
• reflecting a combined signal off the second surface of the beam splitter;
• and
• detecting the superimposed images.