In-situ backgrind wafer thickness monitor

• US 6,198,294 B1
• Filed: 05/17/1999
• Issued: 03/06/2001
• Est. Priority Date: 05/17/1999
• Status: Expired due to Term

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: VLSI Technology, Inc. (Koninklijke Philips N.V.)
• Inventors: Black, Andrew J.
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US09/312,776
• Time in Patent Office: 659 Days
• Field of Search: 324/663, 324/671
• US Class Current: 324/671
• CPC Class Codes: G01B 7/08 using capacitive means

Abstract

Thickness of a wafer is monitored during grinding. A conductive plate is located below the wafer during grinding. One or more capacitive sensors are located above the wafer during grinding. A monitoring device monitors capacitance of the conductive plate and the capacitive sensor.

Claims

1. A system for monitoring thickness of a wafer during grinding, the system comprising;

a conductive plate located below the wafer during grinding;

a capacitive sensor located above the wafer during grinding; and

,

a monitoring device which monitors capacitance of the conductive plate and the capacitive sensor, wherein the conductive plate and the capacitive sensor act as electrodes of a capacitor of which capacitance is monitored.

2. A system as in claim 1 wherein the conductive plate is embedded within a chuck onto which the wafer is placed during grinding.

3. A system as in claim 1 wherein the capacitive sensor is one of a plurality of capacitive sensors mounted over the wafer during grinding, the capacitive sensors allowing capacitance to be measured in several locations across a radius of the wafer.

4. A system as in claim 1 wherein the capacitive sensor is mounted within a rod suspended over the wafer during grinding.

5. A method for monitoring thickness of a wafer during grinding, the method comprising the following steps;

(a) locating a conductive plate below the wafer during grinding;

(b) locating a capacitive sensor above the wafer during grinding; and

,

(c) monitoring capacitance of the conductive plate and the capacitive sensor, wherein the conductive plate and the capacitive sensor act as electrodes of a capacitor of which capacitance is monitored.

6. A method as in claim 5 wherein step (a) includes embedding the conductive plate within a chuck onto which the wafer is placed during grinding.

7. A method as in claim 5 wherein in step (b) the capacitive sensor is mounted with a plurality of capacitive sensors, so as to allow capacitance to be measured in several locations across a radius of the wafer.

8. A method as in claim 5 wherein in step (b) the capacitive sensor is mounted within a rod suspended over the wafer during grinding.