Optical system used for focusing and leveling

Abstract

The invention discloses an optical system for focusing and leveling, which comprises an illumination unit, a marking plate, an oblique imaging unit, a projection imaging unit, an accept imaging unit, a correction imaging unit and a detector, wherein the illumination unit provides broadband light for uniform illumination and illuminates the marking plate; the marking plate forms an oblique mark image through the oblique imaging unit; the oblique mark image is imaged on a silicon slice surface by the projection imaging unit and reflected by the silicon slice surface, and forms an accept mark through the accept imaging unit; and the accept mark is transmitted to the detector through the correction imaging unit. The novel proposal for the focusing and leveling system provided on the basis of Scheimpflug condition comprises that: a vertical plane is changed into an oblique plane in an imaging mode so as to reduce reflection loss and design difficulty. Simultaneously, the aim of reducing the focal length and increasing the operating distance is achieved by adoption of a telephoto structure on a near measuring plane of a telecentric optical system.

Description

technical field [0001] The invention relates to an automatic focusing control system of projection exposure equipment, in particular to an optical system for focusing and leveling. Background technique [0002] A projection lithography machine is a device that projects a pattern on a mask onto a silicon wafer through an objective lens. In the projection exposure equipment, there must be an automatic focus control system to accurately bring the silicon wafer to the designated exposure position, and there are many different technical solutions for realizing this system. At present, the non-contact photoelectric measurement technology is more commonly used, among which the focusing technology of NIKON, CANON, and ASML is the most representative. The schemes of the above companies have their own characteristics. What they have in common is that the optical part of the measurement system adopts an optical structure that satisfies the Scheimpflug condition (that is, the condition...

AI Technical Summary

Problems solved by technology

Because the aperture and numerical aperture of the objective lens in the lithography machine are both large and its working distance is very small, this leads to a large projection angle of the focusing subsystem, that is, the incident angle of each object image plane is very large, and the angle on each oblique mark The reflection loss is very large, which reduces the sensitivity of the system; at the same time, the focal length requirements of the ordinary double-telecentric system are also increased, which increases the size of key components (such as scanning mirrors)

In order to reduce the reflection loss, the main method used in the NIKON patent of US Patent No. US5602399 is to use the prism correction mechanism, but with the increase of the incident angle, the aberration (especially astigmatism and chromatic aberration) brought by the correction prism becomes uncontrollable, very difficult to design, and the effect of correction is not obvious

In the patent of CANON company with US Patent No. US5414515, the compensation scheme of setting a lens for each point is mainly used. This scheme has a huge and complex structure, and the structural design is very difficult.

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