Control of amplitude and phase of diffraction orders using polarizing targets and polarized illumination
Metrology scatterometry targets, optical systems and corresponding metrology tools and measurement methods are provided. Targets and/or optical systems are designed to enhance first order diffraction signals with respect to a zeroth order diffraction signal from the scatterometry target by creating a phase shift of 180° between zeroth order diffraction signals upon illumination of the scatterometry targets. For example, the targets may be designed to respond to polarized illumination by producing a first phase shift between zeroth order diffraction signals upon illumination thereof and optical systems may be designed to illuminate the target by polarized illumination and to analyze a resulting diffraction signal to yield a second phase shift between zeroth order diffraction signals upon illumination thereof. The phase shifts add up to 180° to cancel out the zeroth order diffraction signals, with either phase shift being between 0 and 180°.
1. A method comprising:
enhancing first order diffraction signals with respect to a zeroth order diffraction signal from a scatterometry target having a coarse pitch, by designing the scatterometry target and/or by configuring a metrology tool's optical system to yield a phase shift of 180° between zeroth order diffraction signals upon illumination of the scatterometry target; and
configuring the metrology tool's optical system to illuminate the scatterometry target by two perpendicularly-polarized illumination components and analyzing the diffraction signal at two perpendicular polarization directions that complement the two perpendicularly-polarized illumination components to cancel out the zeroth order diffraction signals.
2. The method of claim 1 , further comprising designing the scatterometry target to have polarizers at half the coarse pitch to yield the 180° phase shift, wherein the polarizers are configured to be perpendicularly polarizing.
3. The method of claim 1 , further comprising combining a first phase shift by target design with a second phase shift by optical system configuration, wherein a sum of the first and second phase shifts is 180°.
4. The method of claim 1 , further comprising designing the scatterometry target, having non-polarizing structures, to have at least one additional target layer having at least one polarizing structure configured to yield the phase shift of 180°.
5. The method of claim 4 , wherein the at least one additional target layer is above the non-polarizing structures.
6. The method of claim 4 , wherein the at least one additional target layer is below the non-polarizing structures.
7. A scatterometry metrology target having a coarse pitch and configured to yield a phase shift of 180° between zeroth order diffraction signals upon illumination thereof, wherein a first part of an area with the coarse pitch is segmented in one direction and a second part of the area with the coarse pitch is segmented in a perpendicular direction to that of the first area, and wherein the target has initial non-polarizing structures, and at least one additional target layer having at least one polarizing structure configured to yield the phase shift of 180°.
8. The scatterometry metrology target of claim 7 , designed to have polarizers at half the coarse pitch to yield the 180° phase shift, wherein the polarizers are configured to be perpendicularly polarizing.
9. The scatterometry metrology target of claim 8 , wherein the polarizers are segmented at a fine pitch.
10. The scatterometry metrology target of claim 7 , wherein the at least one polarizing structure is segmented at a fine unresolved pitch.
11. The scatterometry metrology target of claim 10 , wherein the at least one polarizing structure is segmented along a direction that is perpendicular to a segmentation direction of the initial non-polarizing structures.
12. The scatterometry metrology target of claim 7 , wherein the additional target layer is above the non-polarizing structures.
13. The scatterometry metrology target of claim 7 , wherein the additional target layer is below the non-polarizing structures.
14. A metrology tool having an optical system configured to illuminate a non-polarizing scatterometry target by two perpendicularly-polarized illumination components and to analyze a resulting diffraction signal at two perpendicular polarization directions that complement the two perpendicularly-polarized illumination components to cancel out the zeroth order diffraction signals by configuring the illumination and the analysis to yield a phase shift of 180° between identical zeroth order diffraction signals from the scatterometry target.
15. The metrology tool of claim 14 , wherein the optical system comprises, for controlling a polarization of the illumination and the diffraction signals, at least one of: a polarizer and an analyzer, at least one wave plate, at least one polarizing beam splitter and at least one neutral density filter.
16. A metrology system, comprising:
a scatterometry metrology target having a coarse pitch and configured to yield a first phase shift between zeroth order diffraction signals upon illumination thereof, and
a metrology tool having an optical system configured to illuminate the target by two perpendicularly-polarized illumination components and to analyze a resulting diffraction signal at two perpendicular polarization directions that complement the two perpendicularly-polarized illumination components to yield a second phase shift between zeroth order diffraction signals upon illumination thereof,
wherein a sum of the first and second phase shifts is 180° to cancel out the zeroth order diffraction signals.
17. The metrology system of claim 16 , wherein the optical system comprises, for controlling a polarization of the illumination and the diffraction signals, at least one of: a polarizer and an analyzer, at least one wave plate, at least one polarizing beam splitter and at least one neutral density filter.
18. The metrology system of claim 16 , wherein the first phase shift is 180° and the second phase shift is zero.
19. The metrology system of claim 18 , wherein the scatterometry metrology target is configured to yield a phase shift of 180° between zeroth order diffraction signals upon illumination thereof.
20. The metrology system of claim 19 , designed to have polarizers at half a coarse pitch of the target to yield the 180° phase shift, wherein the polarizers are configured to be perpendicularly polarizing.
21. The metrology system of claim 16 , wherein the target has initial non-polarizing structures, and at least one additional target layer having at least one polarizing structure configured to yield the first phase shift.
22. A scatterometry metrology target having a coarse pitch and configured to yield a phase shift of 180° between zeroth order diffraction signals upon illumination thereof, wherein a first part of an area with the coarse pitch is segmented in one direction and a second part of the area with the coarse pitch is segmented in a perpendicular direction to that of the first area, wherein the scatterometry metrology target is designed to have polarizers at half the coarse pitch to yield the 180° phase shift, and wherein the polarizers are configured to be perpendicularly polarizing.
23. The scatterometry metrology target of claim 22 , wherein the polarizers are segmented at a fine pitch.