Method of imaging using lithographic projection apparatus

A method of compensating for effects of flare due to stray radiation in use of a projection system of lithographic apparatus to project a radiation beam patterned by a patterning device to produce a pattern image in an image plane, the method comprising:

• monitoring the stray radiation as a function of time;
• establishing parameters determining a power spectral density (PSD) indicative of a spatial frequency of the stray radiation produced as a function of time;
• establishing a trend in the parameters as a function of time;
• and
• using the parameters to determine adjustments to be made to the patterning device to compensate for the effect of flare.

A device manufacturing method comprising using a projection system of a lithographic apparatus to project a radiation beam patterned by a patterned by a patterning device to produce a pattern image in an image plane, the method including compensating for the effect of flare due to stray radiation by:

• establishing a power spectral density (PSD) indicative of a spatial frequency of the stray radiation produced by the projection system;
• determining, from the PSD, a modulation transfer function (MTF) relating the PSD to the pattern applied by the patterning device based at least in part on an effect of flare on the pattern image;
• using the MTF to determine the effect of flare on a critical dimension (CD) of the pattern image;
• and
• establishing a relationship between a change in the CD of the pattern image and a change in the CD of the pattern.

A method of compensating for the effect of flare due to stray radiation in use of a projection system of lithographic apparatus to project a radiation beam patterned by a patterning device to produce a pattern image in an image plane, the method comprising:

• monitoring the stray radiation as a function of time;
• estimating the stray radiation likely to be produced at a predetermined end of lifetime;
• determining the likely effect of flare on a critical dimension (CD) of the pattern image at the end of lifetime;
• setting the design of the patterning device in such a way as to at least partially offset the likely effect of flare on the CD of the pattern image at the end of lifetime;
• establishing a power spectral density (PSD) indicative of the spatial frequency of the stray radiation produced;
• establishing the effect of flare on the CD of the pattern image for the current level of stray radiation;
• and
• applying an amount of moving standard deviation MSDxy indicative of the the effect of vibration in the image plane such that the sum of the projected change in CD due to changing MSDxy at the end of lifetime and the projected change in CD due to flare at the end of lifetime is substantially constant over the likely lifetime.