Particle-optical projection system

Abstract

In a particle-optical projection system (32) a pattern (B) is imaged onto a target (tp) by means of energetic electrically charged particles. The pattern is represented in a patterned beam (pb) of said charged particles emerging from the object plane through at least one cross-over (c); it is imaged into an image (S) with a given size and distortion. To compensate for the Z-deviation of the image (S) position from the actual positioning of the target (tp) (Z denotes an axial coordinate substantially parallel to the optical axis cx), without changing the size of the image (S), the system comprises a position detection means (ZD) for measuring the Z-position of several locations of the target (tp), a control means (33) for calculating modifications (cr) of selected lens parameters of the final particle-optical lens (L2) and controlling said lens parameters according to said modifications.

Description

FIELD OF THE INVENTION AND DESCRIPTION OF PRIOR ART [0001] The invention relates to the field of particle-optical projection systems and, in particular, to the adjustment of the image field position along the optical axis with the actual position of the target in a particle-optical projection system without a change of magnification or image quality. More in detail, the invention relates to the improvement of a particle-optical projection system for imaging a pattern onto a target by means of energetic electrically charged particles in a particle-beam exposure apparatus, adapted to produce, from the pattern positioned at an object plane and represented in a patterned beam of said charged particles emerging from the object plane through at least one cross-over, an image at the position of the target, with said image having a given size and distortion. [0002] In systems of this kind, the Z-position of the image plane, i.e. the position as measured along the direction of the particle b...

AI Technical Summary

Benefits of technology

[0010] It is a goal of the present invention to provide a way to arbitrarily change image position and magnification, so as to compensate for deviations between the image position and the target position with respect to the axial direction (Z-direction), which may be due, in particular, to the individual geometrical properties of the target and the space charge effect of the current through each momentary pattern, taking into account the dependence of these imaging characteristics caused by the pattern distribution and the total illumination current density. A primary task to be solved is to move the optical image plane as required, i.e. to “refocus”, but to keep the value of the demagnification constant in order to comply with the requirements (typically to ΔM / M=1×10−5). Furthermore, the image distortion shall be minimized, also in connection with varying space charge effect.

[0012] This solution allows for a simple way to deal with issues of Z-positioning of the target, which also will allow to compensate for the geometry fast. Thus, the invention makes a high throughput possible, in contrast to prior-art arrangements where an insufficient Z-positioning could severely obstruct the performance of a product line. For most applications one lens parameter will be sufficient to effect the desired modification; if appropriate, more lens parameters of the lens, or lens parameters of several lenses, can be modified.

[0019] at least one deflector array means separate from the aperture array means, with said deflector array means having a plurality of openings surrounding the beamlets, wherein for each opening or group of openings are provided at least two deflecting electrodes to which different electrostatic potentials are applicable, thus correcting the path of the beamlet(s) passing through the respective opening according to a desired path through the device, wherein at least one of said deflector array means is adapted to adjust the angles of the beamlets passing the apertures to minimize the aberration of the crossover.

[0022] It is further advantageous when the deflector array means is adapted to produce a virtual object different from the object as defined by the apertures of the aperture array means. This enables to correct for various defects that may occur, in particular deviations of the transfer function and distortion of the projection optical system.

[0024] a first deflector array means which is adapted to adjust the angles of the beamlets passing the apertures to minimize the aberration of the crossover,

Problems solved by technology

An uncertainty in the position of the stage to which the wafer is mounted does also lead to deviating target positions.

Without correction or compensation, the space charge effect will vary at the same rate, with the result that not only the image position, but also the magnification and distortion will continuously change, thereby increasing the image blur as well as the image distortion.

These approaches are, however, not appropriate in projection optical imaging systems, as the magnification is affected by a variation of the focal length as well.

Moreover, the space charge effect will also cause different current density distributions within the particle beam to lead to different image distortions.

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