Uniform density charge deposit source

• US 5,644,223 A
• Filed: 05/12/1995
• Issued: 07/01/1997
• Est. Priority Date: 05/12/1995
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Verkuil, Roger Leonard
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US08/440,502
• Time in Patent Office: 781 Days
• Field of Search: 324/158.1, 324/455, 324/500, 324/501, 250/288, 250/281
• US Class Current: 324/754.21
• CPC Class Codes: G01B 7/06 for measuring thickness measuring during the manufacture of coatings C23C14/54
• CPC Class Codes: G01N 27/60 by investigating electrostatic variables , e.g. electrographic flaw testing G01N27/007 takes precedence
• 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: 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 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A method for measuring the thickness of very thin oxide layers on a silicon substrate. A corona discharge source repetitively deposits a calibrated fixed charge density on the surface of the oxide. The resultant change in oxide surface potential for each charge deposition is measured. By choosing a starting value for an assumed oxide thickness, the approximate change in silicon bandbending per corona discharge step is determined. The cumulative changes in bandbending versus oxide surface potential yields an experimental bandbending versus bias characteristic. A theoretical bandbending versus bias characteristic is established. The experimental and theoretical characteristics are matched at the predetermined points thereof and then the assumed oxide thickness is iterated until both characteristics superimpose in the silicon accumulation region. The iterated oxide thickness that allows both characteristics to superimpose is the oxide thickness value being sought. The finally evolved experimental characteristic also is used to determine the interface states density of the oxide. Specially designed corona discharge guns are described for use with the oxide thickness and interface states density measurement techniques.

Claims

1. A device including a corona discharge gun having a longitudinal, vertical axis and a transverse axis intersecting said longitudinal axis, said gun comprising at least one transversely oriented, biased needle-shaped electrode providing a source of ions of a given polarity at the tip of each said at least one needle-shaped electrode,

a biased focusing ring electrode, and

a biased masking electrode, said masking electrode comprising a centrally apertured disk,

said electrodes being insulated from each other and supported so that said ring electrode and said apertured disk are mutually coaxial with said vertical axis,

said ring electrode being positioned intermediate to each said tip and said masking electrode.

2. The device described in claim 1 wherein said ring and said masking electrodes are biased with a voltage having the same polarity as the polarity of said ions.

5. The device described in claim 1 wherein said disk is thin.

6. The device described in claim 2 wherein said disk is thin.

3. A device including a corona discharge gun adapted for interacting with a work piece positioned at a work piece location, said gun including a first transverse axis and a second, vertical axis, said first axis and said second axis being substantially perpendicular to each other,

a biased focusing ring, beam-shaping electrode having beam shaping walls,

said gun comprising two biased co-axial needle-shaped electrodes spaced apart, and aligned along said first transverse axis, the tips of said needle-shaped electrodes facing each other and facing said beam-shaping walls and providing a source of ions of a given polarity,

said biased, focusing ring, beam-shaping electrode having said second, vertical axis as the axis thereof perpendicular to the plane of said ring, a space defined within said beam-shaping electrode, said tips of said needle-shaped electrodes extending within said space within said beam-shaping electrode, and

a biased masking electrode, said masking electrode comprising a centrally apertured disk located between said needle shaped electrodes and said work piece location,

said electrodes being insulated from each other, and said electrodes being supported, so that said focusing ring, beam-shaping electrode and said apertured disk of said masking electrode are coaxial along said second, vertical axis,

said ring and said masking electrodes being biased with a voltage having the same polarity as the polarity of said ions,

said first axis and said second axis being perpendicular relative to each other and said first axis intersecting said second axis centrally between said facing tips of said needle-shaped electrodes so ions generated at the tip of said needle-shaped electrodes are first directed at said beam-shaping walls of said beam shaping electrode before travelling down to the surface of said work piece, and

said ring electrode being positioned intermediate said facing tips and said masking electrode.

7. The device described in claim 3 wherein said disk is thin.

4. A device including a corona discharge gun adapted for interacting with a work piece positioned at a wafer,

said gun including a first transverse axis and a second, vertical axis, said first axis and said second axis being substantially perpendicular to each other,

a biased, beam-shaping electrode having beam-shaping walls defining a beam-shaping space,

said gun comprising two biased co-axial needle-shaped electrodes spaced apart, and aligned along said first transverse axis, the tips of said needle-shaped electrodes facing each other and facing said beam-shaping walls and providing a source of ions of a given polarity,

said beam-shaping electrode having said second, vertical axis as the axis thereof perpendicular to the plane of said ring,

said tips of said needle-shaped electrodes extending within said beam-shaping space within said beam-shaping walls of said beam-shaping electrode, and

a biased masking electrode, said masking electrode comprising a thin, centrally apertured disk located between said needle shaped electrodes and said wafer,

said electrodes being insulated from each other, and said electrodes being supported, so that said beam-shaping electrode and said apertured disk of said masking electrode are coaxial along said second, vertical axis,

said ring and said masking electrodes being biased with a voltage having the same polarity as the polarity of said ions,

said first axis and said second axis being perpendicular relative to each other and said first axis intersecting said second axis centrally between said facing tips of said needle-shaped electrodes so ions generated at the tip of said needle-shaped electrodes are first directed at said beam-shaping walls of said beam-shaping electrode before travelling down to the surface of said wafer, and

said ring electrode being positioned intermediate said facing tips and said masking electrode,

whereby ions are directed from said beam-shaping electrode towards said wafer through said masking electrode.

8. The device described in claim 4 wherein said thin disk of said masking electrode comprises a round flat plate with a central aperture.