Apparatus and methods for detecting overlay errors using scatterometry

Abstract

Embodiments of the invention include a scatterometry target for use in determining the alignment between substrate layers. A target arrangement is formed on a substrate and comprises a plurality of target cells. Each cell has two layers of periodic features constructed such that an upper layer is arranged above a lower layer and configured so that the periodic features of the upper layer have an offset and/or different pitch than periodic features of the lower layer. The pitches are arranged to generate a periodic signal when the target is exposed to an illumination source. The target also includes disambiguation features arranged between the cells and configured to resolve ambiguities caused by the periodic signals generated by the cells when exposed to the illumination source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description will be more readily understood in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates the relative distribution of designed overlay offsets X_a, X_b, X_c, and X_d for corresponding interlayer patterns (overlay targets) A, B, C, and D according to an embodiment of the present invention.

FIG. 2( a) is a side view illustration of a patterned top layer L2 being offset by an amount +F from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( b) is a side view illustration of a patterned top layer L2 being offset by an amount −F from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( c) is a side view illustration of a patterned top layer L2 being offset by an amount +F+f₀ from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( d) is a side view illustration of a patterned top layer L2 being offset by an amount −F+f₀ from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( e) is a side view illustration of a patterned top layer L2 being offset by an amount +F+f₀+E from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( f) is a side view illustration of a patterned top layer L2 being offset by an amount −F+f₀+E from a patterned bottom layer L1 in accordance with one embodiment of the present invention.

FIG. 2( g) is a simplified flow diagram illustrating an embodiment of determining overlay error in accordance with the present invention.

FIG. 2( h) is a set of simplified side view illustrations showing an example offset and the pitch differentials between a first and second layer of periodic features of a target cell constructed in accordance with the principles of the present invention.

FIGS. 3( a) & 3(b) are simplified plan view depictions of SCOL targets constructed in accordance with the principles of the invention.

FIG. 4 is a simplified schematic side section view of a portion of the target depicted in FIG. 4 and constructed in accordance with the principles of the invention.

FIG. 5 is a simplified plan view depiction of a SCOL target constructed in accordance with the principles of the invention and showing ROI's.

FIG. 6 is a simplified plan view depiction of another SCOL target embodiment constructed in accordance with the principles of the invention.

FIG. 7 depicts a SCOL target such as embodied in FIG. 6 depicting ROI's as used in accordance with the principles of the invention.

FIG. 8 is another simplified plan view depiction of a SCOL target embodiment constructed in accordance with the principles of the invention.

Claims

1. A target arrangement for determining overlay alignment on a substrate, the target arrangement comprising: a substrate having at least two layers formed thereon;a target arrangement formed on the substrate, the target arrangement comprising two sets of target cells, a first set of target cells configured in two layers and arranged to provide alignment information in a first axis, anda second set of target cells configured in two layers and arranged to provide alignment information in a second axis wherein the second axis is perpendicular to the first axis.

2. The target arrangement of claim 1 wherein the first set of cells includes at least a first layer having a first set of periodically arranged features arranged above a second layer that a second set of periodically arranged features and said first and second sets of periodically arranged features are offset relative to each other and configured to generate a periodic signal when illuminated; andthe second set of cells includes at least a third layer having a third set of periodically arranged features arranged above a fourth layer such that the third set of periodically arranged features and said fourth set of periodically arranged features are offset relative to each other and configured to generate a periodic signal when illuminated.

3. The target arrangement of claim 2 wherein the first set of periodic features has the same pitch as the second set of periodic features, andthe third set of periodic features has the same pitch as the fourth set of periodic features.

4. The target arrangement of claim 2 wherein the first set of periodic features has a different pitch than the second set of periodic features, andthe third set of periodic features has a different pitch than the fourth set of periodic features.

5. The target arrangement of claim 2 wherein the first layer of the first set of cells is the same as the third layer of the second set of cells; andthe second layer of the first set of cells is the same as the fourth layer of the second set of cells.

6. The target arrangement of claim 2 wherein the first set of cells includes four cells, andthe second set of cells includes four cells.

7. The target arrangement of claim 6 wherein each cell defines a spatial periodicity having a value (p) associated with a greatest common denominator for the pitches associated with each cell; andthe offset of each cell is associated with the value (p) of the cell and a free parameter (f0).

8. The target arrangement of claim 6 wherein the four cells of each set of cells has an offset characterized by the value (p) and the free parameter (f0) in accordance with following relation:in a first cell in the first set of cells the first layer is offset relative to the second layer by a value of +p/4+f0,in a second cell in the first set of cells the first layer is offset relative to the second layer by a value of +p/4−f0,in a third cell in the first set of cells the first layer is offset relative to the second layer by a value of −p/4+f0,in a fourth cell in the first set of cells the first layer is offset relative to the second layer by a value of −p/4−f0; andin a first cell in the second set of cells the third layer is offset relative to the fourth layer by a value of +p/4+f0,in a second cell in the second set of cells the third layer is offset relative to the fourth layer by a value of +p/4−f0,in a third cell in the second set of cells the third layer is offset relative to the fourth layer by a value of −p/4+f0,in a fourth cell in the second set of cells the third layer is offset relative to the fourth layer by a value of −p/4−f0;and wherein the free parameter is defined by a value greater than zero and less than p/4.

9. The target arrangement of claim 2 wherein the first set of cells includes six cells, andthe second set of cells includes six cells.

10. The target arrangement of claim 9 wherein each cell defines a spatial periodicity having a value (p) associated with a greatest common denominator for the pitches associated with each cell;the offset of each cell is associated with the value (p) of the cell; andwherein the six cells of each set of cells has an offset characterized by the value (p) in accordance with following relation:in a first cell in the first set of cells the first layer is offset relative to the second layer by a value of +p·( 1/12),in a second cell in the first set of cells the first layer is offset relative to the second layer by a value of +p·( 3/12),in a third cell in the first set of cells the first layer is offset relative to the second layer by a value of +p·( 5/12),in a fourth cell in the first set of cells the first layer is offset relative to the second layer by a value of −p·( 1/12),in a fifth cell in the first set of cells the first layer is offset relative to the second layer by a value of −p·( 3/12),in a sixth cell in the first set of cells the first layer is offset relative to the second layer by a value of −p·( 5/12); andin a first cell in the second set of cells the third layer is offset relative to the fourth layer by a value of +p( 1/12),in a second cell in the second set of cells the third layer is offset relative to the fourth layer by a value of +p·( 3/12),in a third cell in the second set of cells the third layer is offset relative to the fourth layer by a value of +p·( 5/12),in a fourth cell in the second set of cells the third layer is offset relative to the fourth layer by a value of −p·( 1/12),in a fifth cell in the second set of cells the third layer is offset relative to the fourth layer by a value of −p·( 3/12),in a sixth cell in the second set of cells the third layer is offset relative to the fourth layer by a value of −p·( 5/12).

11. The target arrangement of claim 2 wherein the target arrangement includes disambiguation features suitable for resolving ambiguities caused by signals produced by illuminating the cells.

12. A target arrangement for determining overlay alignment on a substrate, the target arrangement comprising: a substrate having at least two layers formed thereon; anda target arrangement formed on the substrate, the target arrangement comprising a plurality of periodic target cells configured such that each cell has a top layer arranged above a bottom layer and configured such that the top layer has periodic features and the bottom layer has periodic features and such that there is a predetermined offset between the periodic features of the top layer and the periodic features of the bottom layer of the cell.

13. The target arrangement recited in claim 12 wherein the target cells are configured so that the periodic features of the top layer have a different pitch than the periodic features of the bottom layer wherein the relationship between the pitches is arranged to generate a periodic signal for the target when the target cell is exposed to an illumination source.

14. The target arrangement recited in claim 12 wherein the target cells are configured so that the periodic features of the top layer have the same pitch as the periodic features of the bottom layer.

15. The target arrangement recited in claim 12 further including a set of disambiguation features configured to resolve alignment ambiguities in the periodic signal generated by the illuminated target cell.

16. The target arrangement of claim 15 wherein each disambiguation feature has two at least two perpendicular edges.

17. The target arrangement of claim 12 wherein the plurality of periodic target cells include a first set of periodic target cells arranged so that the periodic features of the top and bottom layers of the first set of periodic target cells are oriented in a first direction.

18. The target arrangement of claim 17 wherein the first set of periodic target cells arranged so that the periodic features enable the targeting arrangement to determine overlay error in first direction.

19. The target arrangement of claim 17 further including disambiguation features arranged between the target cells, the disambiguation features configured to resolve signal ambiguities caused by the generation of the periodic signal when the target arrangement is exposed to the illumination source.

20. The target arrangement of claim 17 wherein the periodic features of the top layer of the target cells have a first pitch p1 and an associated value n1 and the periodic features of the bottom layer have a second pitch p2 and an associated value n2 wherein the relationship between the pitches is defined by the relationship n1p1=n2p2, and wherein a spatial periodicity (P) is defined for the target cell in accordance with the relation n1p1=n2p2=P and wherein the pitches are selected so that the fraction p1/p2 is a rational number.

21. The target arrangement of claim 20 wherein the predetermined offset between the periodic features of the bottom layer and the periodic features of the top layer is associated with the greatest common divisor of the values for p1 and p2.

22. The target arrangement of claim 20 wherein the target cells have a size dimension of at least fifteen times the spatial periodicity (P) for the cell.

23. The target arrangement of claim 17 wherein the target arrangement further includes a second set of periodic target cells having a second plurality of target cells configured such that each cell of the second set has two layers of periodic features, a top layer arranged above a bottom layer, both arranged with periodic features oriented in a second direction and configured so that the periodic features of the top layer and bottom layers of the second set have different pitches from each other and wherein the relationship between the pitches is arranged to generate a signal when the second set is exposed to the illumination source.

24. The target arrangement of claim 23 wherein the second set of periodic target cells arranged so that the periodic features enable the targeting arrangement to determine overlay error in a second direction perpendicular to the first direction.

25. The target arrangement of claim 23 further including at least two disambiguation features arranged between the periodic target cells and configured to resolve signal ambiguities caused by the generation of signal when the target arrangement is exposed to the illumination source.

26. The target arrangement of claim 25 wherein the target arrangement has a center of symmetry and the at least two disambiguation features are such configured such that the disambiguation features are capable of being symmetrically rotated 180 degrees about axis of symmetry.

27. The target arrangement of claim 26 wherein, the first set of periodic target cells of the target arrangement are arranged on the substrate in a two by two arrangement of four target cells; andthe second set of periodic target cells of the target arrangement are arranged on the substrate and positioned adjacent to the first set in another two by two arrangement of four target cells; andthe at least two disambiguation features are arranged so that, a first disambiguation feature comprises a cross-shaped feature arranged between the four target cells of the first set of periodic features and constructed so that it resides in one of the top or bottom layers;a second disambiguation feature comprises a cross-shaped feature arranged between the four target cells of the second set of periodic features and constructed so that it resides in same layer as the first disambiguation feature; anda third disambiguation feature constructed so that it resides in the other of the top or bottom layers, and that includes an outer section that extends around four sides of the target arrangement encompassing the first and second disambiguation features and that includes an inner section that passes between the first and second sets of disambiguation features.

28. The target arrangement of claim 26 wherein each disambiguation feature has two at least two perpendicular edges.

29. The target arrangement of claim 28 wherein each disambiguation feature is positioned in its entirety in a space between two adjacent target cells.

30. The target arrangement of claim 29 wherein each disambiguation feature is rectangular in shape.

31. The target arrangement of claim 12 wherein the plurality of periodic target cells includes, a first set of periodic target cells arranged so that the periodic features of the top and bottom layers of the first set of periodic target cells are oriented in a first configuration and arranged to enable the targeting arrangement to determine overlay error in a first direction;a second set of periodic target cells arranged so that the periodic features of the top and bottom layers of the second set of periodic target cells are oriented in a second configuration that is perpendicular to the first configuration and arranged to enable the targeting arrangement to determine overlay error in a second direction that is perpendicular to the first direction; anddisambiguation features arranged between the periodic target cells, the disambiguation features configured to resolve signal ambiguities caused by the generation of the periodic signal when the target arrangement is exposed to the illumination source.

32. The target arrangement of claim 31 wherein, the first set of periodic target cells includes six target cells; andthe second set of periodic target cells includes six target cells.

33. The target arrangement of claim 31 wherein, the first set of periodic target cells includes four target cells; andthe second set of periodic target cells includes four target cells.

34. A method for determining an overlay error between layers of a sample, the method comprising: providing a substrate having a target arrangement formed thereon, the target arrangement comprising a plurality of target cells constructed such that each cell has a first and a second layer, each layer with a set of periodic features configured such that the periodic features of the first layer have an offset relative to the periodic features of the second layer;providing an illumination source capable of illuminating the target arrangement to produce a periodic signal;navigating the substrate to an appropriate location so that portions of the target arrangement can be illuminated by the illumination source;illuminating the target cells with the illumination source to obtain a signal for each of the target cells; anddetermining any overlay error between the first and second layers using information obtained from the signal obtained for each of the target cells.

35. The method of claim 34, wherein the providing of the substrate having a target arrangement includes providing a target arrangement constructed such that the periodic features of the first layer have a different pitch than the periodic features of the second layer.

36. The method of claim 34, wherein, providing the targeting arrangement further includes providing a targeting arrangement having a first set of target cells having periodic features oriented in a first direction and a second set of target cells having periodic features oriented in a second direction and wherein the periodic features of both sets of target cells are configured so that said first and second layers each have a different pitch, wherein the relationship between the pitches is arranged to generate a periodic signal the target cells are exposed to an illumination source.

37. The method of claim 34 wherein, providing the targeting arrangement further includes providing a targeting arrangement having disambiguation features arranged between the target cells, the disambiguation features configured to enable signal ambiguities caused by the generation of the periodic signal to be resolved;illuminating disambiguation features with the illumination source to obtain a signal associated with the disambiguation features; andresolving an ambiguity in the determination of the overlay error by using information obtained from the signal associated with the disambiguation features.