Method and apparatus for nondestructively measuring micro defects in materials

• US 5,032,734 A
• Filed: 10/15/1990
• Issued: 07/16/1991
• Est. Priority Date: 10/15/1990
• Status: Expired due to Term

• Current Assignee: VTI Incorporated
• Original Assignee: VTI Incorporated
• Inventors: Orazio, Fred D. Jr., Silva, deceased, Robert M., Sledge, Robert B. Jr.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): ALLEN, STEPHONE B
• Application Number:
  US07/597,857
• Time in Patent Office: 274 Days
• Field of Search: 250/562, 250/563, 250/572, 250/225, 356/338, 356/340, 356/341, 356/368, 356/369, 356/370, 356/429-431, 356/445-449
• US Class Current: 250/559.46
• CPC Class Codes: G01N 2021/1782 In-depth resolution
• CPC Class Codes: G01N 2021/8845 Multiple wavelengths of illumination or detection
• CPC Class Codes: G01N 2021/8864 Mapping zones of defects
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/9505 Wafer internal defects, e.g. microcracks

Abstract

A method and apparatus are disclosed for nondestructively measuring the density and orientation of crystalline and other micro defects on and directly below the surface of a properly prepared material such as a semiconductor wafer. The material surface is illuminated with a probe beam of electromagnetic radiation which is limited to a nondestructive power level or levels. Polarization and wavelength or wavelengths of the electromagnetic radiation are selected according to certain characteristics of the material so that penetration depth is controlled. Specific orientation of the material with respect to the probe beam and the detector is required to detect that portion of the probe beam scattered from the defects of interest, surface or subsurface, without interference from other scatter sources and to identify the orientation of the defects. Maps of scatter intensity versus position are made according to the density of the defects encountered.

Claims

1. A method of simultaneously measuring the distribution of surface and subsurface micro defects on a predetermined area of a material, comprising the steps of:

(a) generating a beam of electromagnetic radiation with substantially equal S and P polarized components;

(b) directing the beam towards the surface at a predetermined fixed angle of incidence and focusing the beam to expose a small portion of the material to the electromagnetic radiation;

(c) directing the lines of sight of two detectors toward the surface of the material to the point where the beam intercepts the surface, one line of sight and detector for only P polarized electromagnetic radiation and the other line of sight and detector for only S polarized electromagnetic radiation;

(d) limiting the extent of the scattered electromagnetic radiation entering each detector in order to detect the scatter coming from a small solid angle around the line of sight of each detector, for detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal proportional to the detected intensity from each detector;

(e) producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational positions of selected scatter signature for that point;

(f) producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) repeating above steps (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) mapping the selected scatter intensity versus the coordinate position of each point of measurement for the predetermined area, the scatter intensity sensed at the P polarization detector being related to the subsurface defects and the scatter intensity sensed at the S polarization detector being related to the surface defects and the rotational positions being related to the defect orientations.

2. A method of simultaneously measuring the distribution of surface and subsurface micro defects on a predetermined area of a material, comprising the steps of:

(a) generating a beam of electromagnetic radiation with elliptical polarization;

(b) directing the beam towards the surface at a predetermined fixed angle of incidence and focusing the beam to expose a small portion of the material to the electromagnetic radiation;

(c) directing the lines of sight of two detectors toward the surface of the material to the point where the beam intercepts the surface, one line of sight and detector for only P polarized electromagnetic radiation and the other line of sight and detector for only S polarized electromagnetic radiation;

(d) limiting the extent of the scattered electromagnetic radiation entering each detector in order to detect the scatter coming from a small solid angle around the line of sight of each detector, for detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal proportional to the detected intensity from each detector;

(e) producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational positions of selected scatter signature for that point;

(f) producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) repeating above steps (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) mapping the selected scatter intensity versus the coordinate position of each point of measurement for the predetermined area, the scatter intensity sensed at the P polarization detector being related to the subsurface defects and the scatter intensity sensed at the S polarization detector being related to the surface defects and the rotational positions being related to the defect orientations.

3. A method of measuring the distribution of subsurface micro defects caused by random processes such as ion implantation, on a predetermined area of a material, comprising the steps of:

(a) generating a beam of electromagnetic radiation;

(b) directing the beam towards the surface at a predetermined fixed angle of incidence and focusing the beam to expose a small portion of the material to the electromagnetic radiation;

(c) directing the line of sight of the detector toward the surface of the material to the point where the beam intercepts the surface;

(d) limiting the extent of the scattered electromagnetic radiation entering the detector in order to detect the scatter coming from a small solid angle around the line of sight, for detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal proportional to the detected intensity;

(e) producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational position of the selected minimum scatter for that point;

(f) producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) repeating above steps (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) mapping the selected minimum scatter intensity versus the coordinate position of each point of measurement for the predetermined area.

4. Apparatus for simultaneously measuring the distribution of surface and subsurface micro defects on a predetermined area of a material, comprising the steps of:

(a) means for generating a beam of electromagnetic radiation with substantially equal S and P polarized components;

(b) means for directing the beam towards the surface at a predetermined fixed angle of incidence and focusing the beam to expose a small portion of the material to the electromagnetic radiation;

(c) means for directing the lines of sight of two detectors toward the surface of the material to the point where the beam intercepts the surface, one line of sight and detector for only P polarized electromagnetic radiation and the other line of sight and detector for only S polarized electromagnetic radiation;

(d) means for limiting the extent of the scattered electromagnetic radiation entering each detector in order to detect the scatter coming from a small solid angle around the line of sight of each detector, for detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal proportional to the detected intensity from each detector;

(e) means for producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational positions of selected scatter signature for that point;

(f) means for producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) means for repeatably engaging means (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) mean for mapping the selected scatter intensity versus the coordinate position of each point of measurement for the predetermined area, the scatter intensity sensed at the P polarization detector being related to the subsurface defects and the scatter intensity sensed at the S polarization detector being related to the surface defects and the rotational positions being related to the defect orientations.

5. A method of measuring the distribution of micro defects on a predetermined area of a material, comprising the steps of:

(a) generating a beam of electromagnetic radiation;

(b) directing the beam towards the surface at a predetermined fixed angle of incidence;

(c) directing a detector'"'"'s line of sight toward the surface of the material to the point where the beam intercepts the surface;

(d) detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal related to the detected intensity;

(e) producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational position of selected scatter for that point;

(f) producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) repeating above steps (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) mapping the selected scatter intensity versus the coordinate position of each point of measurement for the predetermined area.

6. Apparatus for measuring the distribution of micro defects on a predetermined area of a material, comprising the steps of:

(a) means for generating a beam of electromagnetic radiation;

(b) means for directing the beam towards the surface at a predetermined fixed angle of incidence;

(c) means for directing a detector'"'"'s line of sight toward the surface of the material to the point where the beam intercepts the surface;

(d) means for detecting a portion of the scattered electromagnetic radiation and converting it to an electrical signal related to the detected intensity;

(e) means for producing relative rotation between the beam and the material about an axis substantially perpendicular to the surface and at the point where the beam intercepts the surface and determining the rotational position of selected scatter for that point;

(f) means for producing relative lateral movement between the beam and the material to expose an adjacent portion of the material to the electromagnetic radiation;

(g) means for repeatably engaging means (e) and (f) for each portion of the material exposed until the predetermined area is covered in a contiguous manner; and

(h) means for mapping the selected scatter intensity versus the coordinate position of each point of measurement for the predetermined area.