Mobile charge measurement using corona charge and ultraviolet light

• US 5,834,941 A
• Filed: 08/11/1997
• Issued: 11/10/1998
• Est. Priority Date: 08/11/1997
• Status: Expired due to Term

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Keithley Instruments, Inc.
• Inventors: Verkuil, Roger L.
• Primary Examiner(s): BROWN, GLENN WARNER
• Application Number:
  US08/909,176
• Time in Patent Office: 456 Days
• Field of Search: 324/452, 324/455, 324/457, 324/72, 324/109, 324/501, 324/750, 324/753, 324/766
• US Class Current: 324/455
• 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 31/2831 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: G01R 31/311 of integrated circuits G01R31/31728 takes precedence
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

Corona charge is applied to an oxide layer on a semiconductor wafer. Then ultraviolet light is used to erase a grid pattern of the corona charge. Opposite polarity corona charge is then applied to the layer, resulting in a grid of field-induced PN junctions. The surface photovoltage of the junctions is measured over time to provide a measure of the mobile charge in the oxide layer.

Claims

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

applying a first polarity corona charge to said layer;

illuminating said layer in a grid-like pattern with light;

applying a second polarity corona charge to said layer; and

measuring a surface photovoltage characteristic for said layer, said characteristic being indicative of said mobile charge.

2. A method according to 1, further including providing a relative humidity of below 10 percent during said applying steps and said illuminating step.

3. A method according to 1, further including providing a relative humidity of above 10 percent during said measuring step.

4. A method according to 1, wherein said light is in the ultraviolet range.

5. A method for measuring mobile charge in an insulator layer on a semiconductor wafer, said method comprising:

placing said wafer on a vacuum chuck;

depositing corona charge of a first polarity on said layer with a corona gun;

illuminating said layer with ultraviolet light transmitted through a grid-like mask;

depositing corona charge of a second polarity on said layer with said corona gun;

measuring a surface photovoltage characteristic for said layer, said characteristic being indicative of said mobile charge.

6. A method according to 5, further including providing a relative humidity of below 10 percent during said depositing steps and said illuminating step.

7. A method according to 5, further including providing a relative humidity of above 10 percent during said measuring step.