Optics: measuring and testing – By polarized light examination – With birefringent element
Patent
1991-06-07
1993-04-13
Turner, Samuel A.
Optics: measuring and testing
By polarized light examination
With birefringent element
356 72, 356363, G01B 902
Patent
active
052027481
ABSTRACT:
The in situ process control system includes a full aperture sensor for observing the wafer through the optical train. A reference laser is provided and directed through the optical train to the wafer which partially reflects the reference beam back to an interferometer, with interference fringes being detected by the full aperture sensor. The interferometer provides a map of optical path difference before and during exposure which is then used by the control processor to monitor and control wafer warpage, aberration and distortions due to thermal effects and prior process steps. The reference laser may have multiple wavelengths to differentiate between the photoresist and the underlying layer on the wafer. Backscattered light from the wafer back through the optical train and the mask or mask plane is used to monitor exposure realtime. This monitor collects data on the actual delivered irradiance and stores it in the control processor, the data being used to determine resist characteristics, focus characterization, pattern definition, registration and alignment. The control processor receives information from the interferometers and other sensors and, using a library of algorithms, adapts the stepper to the desired characteristics by causing changes in focus, mask manipulation, wafer chuck manipulation, etc.
REFERENCES:
patent: 4669866 (1987-06-01), Phillips
patent: 4682025 (1987-07-01), Livingston et al.
Hunter, Jr. Robert O.
MacDonald Bruce G.
Smith Adlai H.
Litel Instruments
Turner Samuel A.
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