Two-dimensional beam deflector

Abstract

A two dimensional beam deflector is disclosed which deflects beams from multiple optical assemblies. The input of beams of the multiple optical assemblies follow parallel optical paths until deflection to a wafer. An ellipsometer using a two-dimensional beam deflector is also disclosed.

Description

FIELD OF THE INVENTIONThe present invention relates to systems and methods for non-destructive quality control in general and to optical systems and methods for measuring the thickness and an index of refraction of thin films, in particular.BACKGROUND OF THE INVENTIONOptical measuring instruments are typically utilized in the microelectronic industry for non-contact, non destructive measurement of the thickness of thin films. Two main systems are utilized, spectrophotometers (or reflectometers) and ellipsometers. The following U.S. patents represent the prior art: For ellipsometers: U.S. Pat. Nos. 5,166,752, 5,061,072, 5,042,951, 4,957,368, 4,681,450, 4,653,924, 4,647,207 and 4,516,855. For spectrophotometers: U.S. Pat. Nos. 5,181.080, 5,159,412, 5,125,966, 4,999,014 and 4,585,348.The two prior art systems are illustrated in FIGS. 1A and 1B, respectively, to which reference is now made. The spectrophotometer utilizes the fact that light beams reflected off thin film boundaries, will...

AI Technical Summary

Problems solved by technology

The spectrophotometer utilizes the fact that light beams reflected off thin film boundaries, will interfere one with another.

The spectrophotometers have difficulty measuring structures with very small reflectance, such as thin films of glass substrates, because the relatively low brightness of traditional white light sources does not provide a sufficient signal-to-noise ration (SNR).

Spectrophotometers also have difficulty measuring films with unknown or unrepeatable dispersions of optical constants, such as amorphous silicon.

Because ellipsometers measure two polarization parameters (amplitude and phase), both of which are independent of the light intensity, they are quite accurate and can also measure ultra thin films of the size of 0-100 .ANG.. However, since ellipsometers require oblique illumination as well as a highly collimated light beam, their use for high spatial resolution measurements in dense patterned structures is rather difficult.

This limits the speed with which a thickness mapping can occur, especially during inspection of large size substrates such as 8.DELTA.

They cannot be utilized for in-process control, since wafer handling and other mechanical movements are not allowed within a vacuum chamber.

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