Apparatus and a method for high numerical aperture microscopic examination of materials

Apparatus for aiding in the internal inspection of a semiconductor wafer, said wafer having a front surface and a back surface and having an index of refraction greater than unity for light in a predetermined band of frequencies, said apparatus comprising:

• an optical device made from a material having an index of refraction which approximates the index of refraction of the semiconductor wafer and having a flat face, the optical device including a lens system having an adjustable focal length including:
• a plano-convex lens coupled to the optical coupling means;
• and
• a variable focus lens adjustably configured with respect to the plano-convex lens to selectively change the focal position of the optical device;
• optical coupling means for coupling the flat face of said optical device to the back surface of said semiconductor wafer in a manner that allows light rays, from inside the object, which have an angle of incidence greater than a critical angle defined for the back surface of the semiconductor wafer, to propagate into said optical device;
• and
• wafer chuck means for coupling to the back surface of the semiconductor wafer to hold the wafer in a substantially fixed position, said wafer chuck means being configured to leave at least a portion of the back surface of the semiconductor wafer exposed, wherein said optical device is coupled to the exposed portion of the wafer by said optical coupling means.

A high-numerical aperture microscope useful in examining semiconductor wafers having a front surface which includes features and a substantially featureless back surface and having an index of refraction greater than unity, said microscope comprising:

• a plano-convex lens having an index of refraction approximately equal to the index of refraction of the semiconductor wafer, said plano-convex lens having a spherical surface and a flat surface wherein the geometrical center of the spherical surface is beyond the flat surface;
• means for optically coupling the plano-convex lens to the back surface of the semiconductor wafer;
• illuminating means for applying light energy to the wafer from the back side wherein a portion of applied light energy is reflected by the features on the front surface of the wafer;
• and
• imaging means, responsive to the reflected light which is coupled through the plano-convex lens for forming an image of the features on the front surface of the wafer.

A high-numerical aperture microscope useful in examining semiconductor wafers having a front surface which includes features and a substantially featureless back surface and having an index of refraction greater than unity, said microscope comprising:

• a plano-convex lens having an index of refraction approximately equal to the index of refraction of the semiconductor wafer;
• means for optically coupling the plano-convex lens to the back surface of the semiconductor wafer;
• illuminating means for applying light energy to the wafer through the plano-convex lens wherein substantially all of the applied light energy is totally internally reflected in the semiconductor wafer;
• and
• imaging means, positioned outside of the front surface of the semiconductor wafer and responsive to light energy converted to propagating light energy by the features on the front surface of the semiconductor wafer, for generating a dark-field image of the features on the front surface of the semiconductor wafer.

A method of developing an image of the interior of a semiconductor wafer having a front surface and a flat back surface and having an index of refraction greater than unity comprising the steps of:

• a) optically coupling an optical device having a flat surface and an index of refraction which approximates the index of refraction of the semiconductor wafer to the back surface of the semiconductor wafer wherein light rays inside the semiconductor wafer having an angle of incidence with respect to the back surface of the semiconductor wafer that are greater than a critical angle are coupled through the optical device;
• b) illuminating the semiconductor wafer;
• and
• c) generating an image of the interior of the semiconductor wafer using the rays propagating from the inside of the semiconductor wafer and through the optical device.