Apparatus for optical inspection of wafers during polishing

• US 6,045,433 A
• Filed: 06/29/1995
• Issued: 04/04/2000
• Est. Priority Date: 05/23/1995
• Status: Expired due to Term

• Current Assignee: Nova Measuring Instruments Limited (Honeywell International Inc.)
• Original Assignee: Nova Measuring Instruments Limited (Honeywell International Inc.)
• Inventors: Haimovich, Eli, Dvir, Eran, Shulman, Benjamin
• Primary Examiner(s): Morgan, Eileen P.
• Application Number:
  US08/497,382
• Time in Patent Office: 1,741 Days
• Field of Search: 451/41, 451/285, 451/287, 451/288, 451/6
• US Class Current: 451/6
• CPC Class Codes: B24B 37/005 Control means for lapping machines or devices
• CPC Class Codes: B24B 37/013 Devices or means for detecting lapping completion
• CPC Class Codes: B24B 49/12 involving optical means
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring
• CPC Class Codes: H01L 21/6838 with gripping and holding devices using a vacuum; Bernoulli devices
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14
• CPC Class Codes: H01L 22/20 Sequence of activities consisting of a plurality of measurements, corrections, marking or sorting steps

Abstract

An optical system is disclosed for the inspection of wafers during polishing which also includes a measurement system for measuring the thickness of the wafer'"'"'s top layer. The optical system views the wafer through a window and includes a gripping system, which places the wafer in a predetermined viewing location while maintaining the patterned surface completely under water. The optical system also includes a pull-down unit for pulling the measurement system slightly below the horizontal prior to the measurement and returns the measuring system to the horizontal afterwards.

Claims

1. A thickness measuring unit for mounting on a water track of a polisher for measuring the thickness of a top layer of a wafer, said thickness measuring unit comprising:

a. a curved gate having a radius of curvature generally similar to that of said wafer, said curved gate being located at a gripping position;

b. a window mounted in a bottom surface of said water track;

c. a gripper for moving said wafer from said gripping position to a measuring position above a layer of water located above said window, said gripper including a gripping pad, having a planar surface wherein said planar surface of said gripping pad is at an angle to a horizontal plane; and

d. an optical system, mounted underneath said window, for measuring said thickness of said top layer through said window and said layer of water.

2. A thickness measuring unit for mounting on a water bath for measuring the thickness of a top layer of a wafer, said thickness measuring unit comprising:

a. a window mounted in a bottom surface of said water bath;

b. a gripper for moving said wafer from a gripping position above said water bath to a measuring position above a layer of water located above said window, said gripper including a gripping pad having a planar surface, wherein said planar surface of said gripping pad is at an angle to a horizontal plane; and

c. an optical system, mounted underneath said window, for measuring said thickness of said top layer through said window and said layer of water.

3. A method of measuring the thickness of a polished top layer of a wafer before removing said wafer from a polishing machine, said method comprising the steps of:

a. picking said wafer up from a gripping position;

b. moving said wafer from said gripping position to a measuring position;

c. immersing said wafer within a bath of water over said measuring position such that a plane defined by the circumference of said wafer is at an angle to a surface of said water;

d. placing said wafer in said measuring position underneath a surface of said water and above a window but with a thin layer of said water between said wafer and said window; and

e. measuring said thickness of said top layer through said window and said thin layer of water.

4. A method according to claim 3 wherein said water is held within a water bath and wherein said step of moving comprises the step of rotating the plane of a lower surface of said water bath from a relatively horizontal plane to one which causes said water to move towards said measuring position.