Lithographic apparatus, device manufacturing method and device manufactured thereby

Abstract

A device manufacturing method using lithographic apparatus, in which method a patterned beam of radiation is projected on to a target portion of a substrate. Prior to exposing the substrate to the patterned beam of radiation a beam of compensating radiation is irradiated on to a predetermined area of the substrate, the beam of compensating radiation having an intensity which varies across said predetermined area. In the described embodiment the beam of compensating radiation is applied to an annular edge region of the substrate and has an intensity which is tilted across the cross-section of the beam so as to increase or decrease in intensity towards the edge of the substrate. This is done to improve the critical dimension (CD) uniformity across the substrate.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a lithographic apparatus, a device manufacturing method and a device manufactured thereby. In particular the invention concerns critical dimension (CD) profile correction in lithography. [0003] 2. Background to the Invention [0004] A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., comprising part of, one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist) on it. In general, a single substrate will contain a network of adjac...

AI Technical Summary

Benefits of technology

[0015] Irradiating the annular edge region of the substrate with the beam of compensating radiation, prior to projecting the patterned beam of radiation on to the substrate, means that a layer of photoresist present on the whole exposed surface of the substrate has extra energy applied to it in this edge region, compared with the rest of the substrate which is only irradiated with the subsequently projected patterned beam. Where the pattern projected on to the edge region of the substrate comprises a set of lines of uniform width, this results in a set of lines of non-uniform width on the substrate once the layer of resist on the substrate has been developed, but following a subsequent etch step to etch these developed lines in the substrate the etched lines are found to be more uniform in width. By selecting an appropriate level of intensity, and tilt in the intensity level across the physical span of the compensating beam, substantially uniform linewidth can be achieved in the etched lines in the edge region of the substrate.

[0016] Unlike in the prior art systems in which individual die on the substrate are irradiated each with a uniform offset energy level when the pattern to be written on those die is exposed on to those die, in the present invention the rotationally symmetrical nature of the CD variation at the edge region of the wafer (as seen in FIG. 1) is compensated in a complementary rotationally symmetric manner by pre-exposing the annular edge region of the substrate using a compensating beam of radiation which itself has a tilted (or otherwise appropriately shaped) intensity level, the tilt being such that the intensity increases (or decreases) towards the edge of the substrate. This results in better correction of the variation in critical dimension (CD) across the substrate.

Problems solved by technology

One problem encountered in lithography is that the critical dimension (CD), namely the width of a patterned line that can be printed (on the wafer) within design tolerances, varies across the wafer.

This results in a decrease in yield (i.e., less useable chips from each printed wafer) for the chip manufacturer.

However this has the disadvantage that the whole field has an offset applied to it.

This results in an over-correction on one side of the field and under-correction on the other side.

Another problem issue is that in some cases the CD profile may in some cases be relatively flat across the wafer, but one or more device performance characteristics may vary in a plurality of devices formed at different positions across the wafer (where the plurality of devices were all designed to have the same said device performance characteristics).

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