System for detecting a film layer on an object

• US 4,972,072 A
• Filed: 01/17/1990
• Issued: 11/20/1990
• Est. Priority Date: 10/03/1988
• Status: Expired due to Fees

• Current Assignee: Tritec Industries Incorporated
• Original Assignee: Tritec Industries Incorporated
• Inventors: Monahan, Kevin M., Hauser, Hugo
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Messinger, Michael
• Application Number:
  US07/467,314
• Time in Patent Office: 307 Days
• Field of Search: 250/225, 250/560, 250/226, 356/369, 356/367, 356/355, 356/357, 356/381, 356/382, 356/626, 430/329
• US Class Current: 250/225
• CPC Class Codes: G01B 11/0683 measurement during deposition or removal of the layer
• CPC Class Codes: G03F 7/3028 characterised by means for on-wafer monitoring of the processing

Abstract

Circularly polarized light is used to detect an end point of a thin film layer. Collimated light is passed through a polarizing filter and a polarizing beam splitter resulting in light which is almost entirely linearly polarized in a first direction. This first direction polarized light is passed through a quarter wave retarder and is converted to circularly polarized light. The circularly polarized light is reflected off of a surface having a thin film layer and passes back through the quarter wave retarder. This reflected circularly polarized light is converted by the quarterwave retarder into linearly polarized light having a second direction. This second direction polarized light is easily isolated by passing it back through the beam splitter. The light may then be analyzed by end-point detection circuitry and the end-point of the film layer detected.

Claims

1. A system for detecting a film layer comprising:

a circularly polarizing means for producing circularly polarized light and reflecting said circularly polarized light off of a first and second surface of said film layer;

filter means in optical communication with said surface, for receiving and isolating said circularly polarized light and producing a linear polarized light;

detection means in optical communication with the filter means, for receiving said linear polarized light, said detection means having a plurality of frequency bandwidth detectors for isolating a selected bandwidth of said linearly polarized light, an analog-to-digital converter connected to said detectors for providing a digital intensity signal, and a processing means connected to said converter for analyzing said digital intensity signal with respect to time and determining when said film layer is no longer present on said surface.

2. A system for detecting a film layer comprising:

a housing having a first longitudinal chamber located along a first axis and a second longitudinal chamber located along a second axis and intersecting said first chamber;

a light source located at a first end of said first chamber;

a polarizing beam splitter located where said first and second chambers intersect;

a linear polarizing filter located in said first chamber between the light source and the polarizing beam splitter;

a collimating lens located in said first chamber between the lens polarizing filter and the beam splitter and having a focus point located at said light source;

a light aperture located at a second end of said first chamber for allowing light to pass outside the housing;

a detection means located at a first end of said second chamber for analyzing a light source, said detection means comprising a plurality of frequency bandwidth detectors for isolating a selected bandwidth of said light signal, an analog-to-digital converter connected to said detectors for producing a digital intensity signal, a processing means connected to said converter for analyzing said digital intensity signal, and a processing means connected to said converter for analyzing said digital intensity signal with respect to time and determining when said film layer is no longer present on said surface; and

a focusing lens located in said second chamber between the beam splitter and the detection means and having a focus point located at an input point of the detection means.

3. The system of claim 2 further including,

a beam dump located in a second end of said second chamber for receiving and absorbing a light beam from the beam splitter, said beam dump comprising a blade stack of Delrin material.

4. The system of claim 2 further including,

a frequency filter located in said first chamber between the light source and the collimating lens.

5. The system of claim 2 further including,

adjustment means connected to the light source for moving said light source relative to said focus point of said collimating lens.

6. The system of claim 3 wherein,

said input point of said detection means comprises a fiber optic coupling;

and

the device further comprises adjustment means connected to said fiber optic coupling for moving said fiber optic coupling relative to said focus point of said focusing lens.