Multi-surface optical inspector

• US 8,830,457 B1
• Filed: 04/12/2013
• Issued: 09/09/2014
• Est. Priority Date: 04/12/2013
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation (KLA Corporation)
• Original Assignee: Zeta Instruments, Inc. (KLA Corporation)
• Inventors: Meeks, Steven W., Kudinar, Rusmin, Nguyen, Hung P.
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): Rahman, Md
• Application Number:
  US13/861,378
• Time in Patent Office: 515 Days
• Field of Search: 356/237.4
• US Class Current: 356/237.4
• CPC Class Codes: G01N 2021/8967 Discriminating defects on opposite sides or at different depths of sheet or rod
• CPC Class Codes: G01N 21/958 Inspecting transparent materials or objects, e.g. windscreens for conveyed flat sheet or rod G01N21/896

Abstract

An optical inspector includes a radiating source, a time varying beam reflector, a telecentric scan lens, a first waveplate, a second waveplate, a polarizing beam splitter, and a detector. The radiating source irradiates the first waveplate with a linearly polarized source beam generating a circularly polarized source beam, which irradiates a first position of on the time varying beam reflector. The time varying beam reflector directs the source beam to the telecentric scan lens, which in turn directs the source beam to a transparent sample. The reflected radiation from the transparent sample is directed via the telecentric lens and the time varying beam reflector to the second waveplate, which converts circularly polarized reflected radiation to linearly polarized reflected radiation including radiation that is vertically polarized and radiation that is horizontally polarized. The polarizing beam splitter redirects vertically polarized reflected radiation to the detector while horizontally polarized reflected radiation passes through.

Claims

1. A method, comprising:

(a) generating a linearly polarized source beam;

(b) converting the linearly polarized source beam to a circularly polarized source beam, wherein the generating of (a) is performed by a laser, wherein the converting of (b) is performed by a first waveplate;

(c) irradiating a first position on a time varying beam reflector with the circularly polarized source beam, wherein the time varying beam reflector is a rotating polygon;

(d) directing the circularly polarized source radiation beam from the time varying beam reflector to a telecentric scan lens thereby directing a circularly polarized scanning beam onto a sample;

(e) directing a reflected polarized scanning beam onto the time varying beam reflector to produce a stationary polarized reflected beam;

(f) converting the stationary polarized reflected beam to a stationary linearly polarized reflected beam;

(g) directing a first portion of the stationary linearly polarized reflected beam onto a first detector, wherein the converting of (f) is performed by a second waveplate, and wherein the directing of (g) is performed by a polarizing beam splitter;

(h) directing a second portion of the stationary linearly polarized reflected beam onto a second detector, wherein the first portion of the stationary linearly polarized reflected beam is polarized in a first manner, and wherein the second portion of the stationary linearly polarized reflected beam is polarized in a second manner;

(i) processing output signals of the first detector to determine the surface slope and the specular reflectivity of a first surface of the sample; and

(j) processing output signals of the second detector to determine the surface slope and the specular reflectivity of a second surface of the sample, wherein the processing of (i) and (j) is performed by a processor.

2. An apparatus, comprising:

a time varying beam reflector, wherein the time varying beam reflector is a rotating polygon;

a radiating source that irradiates the time varying beam reflector with source radiation, wherein the radiating source is a laser;

a first waveplate, wherein the first waveplate is positioned along the source radiation path between the radiating source and the time varying beam reflector;

a second waveplate, and wherein the second waveplate is positioned along the reflected radiation path between the time varying beam reflector and the polarizing beam splitter;

a telecentric scan lens that directs the source radiation from the time varying beam reflector onto a sample;

a polarizing beam splitter that receives reflected radiation from the sample;

a first detector that receives a portion of the reflected radiation from the polarizing beam splitter;

a second detector that receives a second portion of the reflected radiation from the polarizing beam splitter; and

a processor, wherein the processor communicates with the first detector, wherein the first portion of the reflected beam is polarized in a first manner, and wherein the second portion of the reflected beam is polarized in a second manner, wherein the reflected radiation includes;

(i) reflected radiation from a first surface of the sample, and (ii) reflected radiation from a second surface of the sample, wherein the polarizing beam splitter redirects a majority of the reflected radiation from the first surface of the sample, and wherein the polarizing beam splitter does not redirect a majority of the reflected radiation from the second surface of the sample; and

a separation mirror that directs a third portion of the reflected radiation from the polarizing beam splitter to a third detector, wherein the first portion of the reflected radiation is not directed by the separation mirror and is received by the first detector.

wherein the third portion of the reflected radiation is primarily near specular scattered radiation, and wherein the third detector is a photomultiplier tube that generates a signal indicating the intensity of the third portion of the reflected radiation.

3. The apparatus of claim 2, wherein the sample is transparent, and wherein the first detector is a photodiode bi-cell.

4. The apparatus of claim 2, wherein the source radiation emitted by the radiating source is linearly polarized, wherein the first waveplate converts the linearly polarized source radiation to circularly polarized radiation, and wherein the second waveplate converts the reflected polarized radiation to linearly polarized radiation.

5. The apparatus of claim 2, wherein the first surface of the sample faces the telecentric scan lens, and wherein the second surface of the sample does not face the telecentric scan lens.

6. The apparatus of claim 2, further comprising:

wherein the portion of the reflected radiation received by the first detector is a first portion of the reflected radiation, and wherein the first and second portions of the reflected radiation are primarily specular reflection.

7. The apparatus of claim 2, further comprising:

a separation mirror that directs the first portion of the reflected radiation from the polarizing beam splitter to the first detector, wherein a third portion of the reflected radiation is not directed by the separation mirror and is received by a third detector.

8. The apparatus of claim 2, wherein the radiating source irradiates the time varying beam reflector at a first position with source radiation, and wherein the telecentric scan lens directs the reflected radiation from the sample to the time varying beam reflector at a second position symmetrically opposite the first position about a central axis of the telecentric scan lens.

9. The apparatus of claim 2, wherein the first portion of the reflected radiation is reflected by a first surface of the sample, and wherein the second portion of the reflected radiation is reflected by a second surface of the sample.

10. The apparatus of claim 2, wherein the radiating source irradiates the time varying beam reflector at a first position with source radiation, wherein the source radiation directed by the time varying beam reflector and the telecentric scan lens produces a moving irradiated spot on the sample, and wherein the reflected radiation directed onto the second position on the time varying beam reflector by the telecentric scan lens produces a stationary reflected beam.

11. The apparatus of claim 2, wherein the first detector is a multi-cell photo detector, and wherein the multi-cell photo detector generates a sum signal indicating the total reflectivity of the sample and a difference signal indicating the surface slope of the sample.

12. The apparatus of claim 2, wherein the processor determines:

(i) the surface slope of the sample, and (ii) the specular reflectivity of a first surface the sample.

13. The apparatus of claim 2, wherein the processor communicates with the second detector, and wherein the processor determines:

(i) the surface slope of the sample, and (ii) the specular reflectivity of a second surface the sample.