Method and apparatus for measurement of mobile charges with a corona screen gun

• US 5,767,693 A
• Filed: 09/04/1996
• Issued: 06/16/1998
• Est. Priority Date: 09/04/1996
• Status: Expired due to Term

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Smithley Instruments Incorporated
• Inventors: Verkuil, Roger L.
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): PHUNG, ANH K
• Application Number:
  US08/706,459
• Time in Patent Office: 650 Days
• Field of Search: 324/767, 324/765-769, 324/501, 324/455, 324/750, 250/492.2
• US Class Current: 324/762.05
• CPC Class Codes: G01R 29/24 Arrangements for measuring quantities of charge
• CPC Class Codes: G01R 31/2648 Characterising semiconductor materials testing of materials or semi-finished products G01R31/2831; testing during manufacture H01L22/00
• CPC Class Codes: G01R 31/265 Contactless testing of circuits, also in wafer-form G01R31/302
• CPC Class Codes: G01R 31/2831 Testing of materials or semi-finished products, e.g. semiconductor wafers or substrates G01R31/318511 takes precedence; testing during manufacture H01L22/00
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

The surface of a wafer is charged with corona passing through a screen. The screen is part of a feedback loop that forces a constant corona current. This results in the potential of the wafer surface following the potential of the screen. This allows contemporaneous measurement of the surface charge and potential that are used to measure mobile charge in an oxide layer on the wafer.

Claims

1. A method for measuring mobile charge in a dielectric layer on a heated semiconductor wafer, said method comprising:

applying corona charges having a first polarity to a surface of said layer until said surface has a potential at least as much as a first potential value;

applying corona charges having an opposite polarity to said first polarity to said surface while contemporaneously repeatedly measuring a first parameter indicative of the quantity of said opposite polarity charges and contemporaneously measuring a second parameter indicative of said surface potential until said surface has a potential at least as much as a second potential value;

applying corona charges having said first polarity to said surface while contemporaneously repeatedly measuring a third parameter indicative of the quantity of said first polarity charges and contemporaneously measuring a fourth parameter indicative of said surface potential until said surface has a potential at least as much as a third potential value; and

determining said mobile charge from said measured parameters.

2. A method according to claim 1, wherein said first and third parameters are the time differential of the potential of said surface and said second and fourth parameters are the relative potential of said surface.