Method for monitoring film thickness using heterodyne reflectometry and grating interferometry
First Claim
1. A method for measuring a thickness parameter comprising:
- directing an optical light source for producing a split frequency, dual polarized beam toward a target at a predetermined angle of incidence, said split frequency, dual polarized beam having a first polarized beam component oscillating at a first frequency and a second polarized beam component oscillating at a second frequency, the first frequency being unique from the second frequency, said target comprising a surface and a body;
generating a reference signal by heterodyning the first polarized beam component oscillating at the first frequency and the second polarized beam component oscillating at the second frequency;
receiving a reflected split frequency, dual polarized beam from the target;
diffracting the reflected split frequency, dual polarized beam as a zeroth-order beam and a first-order beam, said zeroth-order beam comprises a first zeroth-order polarized beam component and a second zeroth-order polarized beam component, and said first-order beam comprises a first first-order polarized beam component and a second first-order polarized beam component;
receiving the zeroth-order beam;
generating a measurement signal by heterodyning the first zeroth-order polarized beam component and the second zeroth-order polarized beam component;
detecting a measurement phase shift between said measurement and reference signals;
receiving the first-order beam;
generating a grating signal by heterodyning the first first-order polarized beam component and the second first-order polarized beam component;
detecting a grating induced phase shift between said grating and measurement signals; and
calculating a thickness of the target body from the grating induced phase shift and the measurement phase shift.
1 Assignment
0 Petitions
Accused Products
Abstract
A linearly polarized light comprised of two linearly polarized components, orthogonal to each other and with split optical frequencies, is directed toward a film. A detector receives the beam prior to incidence on the film layer and generates a reference signal. The reflected beam is diffracted into zeroth- and first-order bands, which are then detected by separate detectors; a measurement signal is generated from the zeroth-order beam and a grating signal from the first-order beam. The zeroth-order beam'"'"'s measurement signal and reference signal are analyzed by a phase detector for a heterodyne phase shift, and an accurate film thickness calculated from this phase shift by knowing a refractive index for the film. Additionally, the zeroth-order beam measurement signal is analyzed with the grating signal by a phase detector for detecting a grating phase shift induced by the grating. The refractive index for the film can then be calculated directly from grating phase shift and the heterodyne phase shift for the grating pitch, and the beam'"'"'s wavelength and incidence angle on the film of the measurement apparatus. Using the refractive index and heterodyne phase shift, the film'"'"'s thickness is determined for the apparatus. Conversely, the thickness of the film can be calculated independent of the refractive index, and without knowing the film'"'"'s refractive index, directly from the grating phase shift and the heterodyne phase shift for the apparatus.
21 Citations
21 Claims
-
1. A method for measuring a thickness parameter comprising:
-
directing an optical light source for producing a split frequency, dual polarized beam toward a target at a predetermined angle of incidence, said split frequency, dual polarized beam having a first polarized beam component oscillating at a first frequency and a second polarized beam component oscillating at a second frequency, the first frequency being unique from the second frequency, said target comprising a surface and a body;
generating a reference signal by heterodyning the first polarized beam component oscillating at the first frequency and the second polarized beam component oscillating at the second frequency;
receiving a reflected split frequency, dual polarized beam from the target;
diffracting the reflected split frequency, dual polarized beam as a zeroth-order beam and a first-order beam, said zeroth-order beam comprises a first zeroth-order polarized beam component and a second zeroth-order polarized beam component, and said first-order beam comprises a first first-order polarized beam component and a second first-order polarized beam component;
receiving the zeroth-order beam;
generating a measurement signal by heterodyning the first zeroth-order polarized beam component and the second zeroth-order polarized beam component;
detecting a measurement phase shift between said measurement and reference signals;
receiving the first-order beam;
generating a grating signal by heterodyning the first first-order polarized beam component and the second first-order polarized beam component;
detecting a grating induced phase shift between said grating and measurement signals; and
calculating a thickness of the target body from the grating induced phase shift and the measurement phase shift. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
-
Specification