Method and apparatus for mechanical planarization and endpoint detection of a semiconductor wafer

A process for polishing a thin flat semiconductor wafer having an oxide surface comprising:

• a. holding the semiconductor wafer in a rotatable polishing head mounted for movement across and over a peripheral edge of a polishing platen;
• b. rotating the wafer in a polishing slurry across the polishing platen;
• c. overhanging a portion of the wafer across a peripheral edge of the polishing platen to expose a surface of the wafer;
• and
• d. detecting a thickness of the oxide coating of the wafer utilizing a laser detection apparatus having a detecting laser beam enclosed in a column of water and directed at an unpatterned die on the wafer surface.

A process for polishing a thin flat generally circular shaped semiconductor wafer having an oxide coating and for detecting the thickness of the oxide coating, comprising:

• a. holding the semiconductor wafer in a rotatable polishing head;
• b. rotating the semiconductor wafer over a rotating polishing platen under pressure from the polishing head in a polishing slurry;
• c. overhanging a portion of a surface of the semiconductor wafer over the polishing platen to expose the surface for endpoint detection of an oxide on the semiconductor wafer;
• d. directing a laser beam enclosed in a column of liquid at an unpatterned die on the wafer, for detecting using laser interferometry a thickness of an oxide coating on the wafer;
• and
• e. moving the wafer across the peripheral edge of the polishing platen for overhanging the wafer and for compensating for velocity differentials on different potions of the generally circular shaped wafer.

Apparatus for mechanically planarizing a thin flat wafer comprising:

• a. polishing means including a polishing platen and an abrasive slurry;
• b. a polishing head for holding the wafer and mounted for rotating and for moving the wafer across the polishing platen and past a peripheral edge of the polishing platen under a controlled pressure;
• and
• c. endpoint detection means including a laser interferometer with a laser beam contained in a column of liquid for detecting an endpoint on an exposed surface of the wafer.

Apparatus for mechanically planarizing a thin flat semiconductor wafer comprising:

• a. polishing means including a rotating generally circular shaped polishing platen and an abrasive slurry;
• b. a polishing head for holding the semiconductor wafer and mounted for rotation and for moving the wafer across a peripheral circumferential edge of the polishing platen under a controlled pressure to expose a surface of the wafer;
• and
• c. endpoint detection means including a laser interferometer measuring device having a laser light beam directed at an unpatterned die on the surface of the wafer and including a control unit, a light return conduit, and a liquid conduit circumjacent to the laser light beam for directing a liquid at the wafer surface to clean the surface and provide a reference medium for the laser light beam.