Metrology Method and Apparatus, Lithographic System and Device Manufacturing Method

• US 20130258310A1
• Filed: 03/13/2013
• Published: 10/03/2013
• Est. Priority Date: 03/27/2012
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: SMILDE, Hendrik Jan Hidde, Adam, Omer Abubaker Omer
• Granted Patent: US 9,134,256 B2
• Time in Patent Office: Days
• US Class Current: 355/77
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• CPC Class Codes: G03F 7/70683 Mark designs
• CPC Class Codes: G03F 9/7019 Calibration
• CPC Class Codes: Y10T 428/24802 Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]

Abstract

A lithographic process is used to form a plurality of target structures (T) on a substrate (W). Each target structure comprises overlaid gratings each having a specific overlay bias. Asymmetry (A) of each grating, measured by scatterometry, includes contributions due to (i) the overlay bias, (ii) an overlay error (OV) in the lithographic process and (iii) bottom grating asymmetry within the overlaid gratings. Asymmetry measurements are obtained for three or more target structures having three or more different values of overlay bias (e.g., −d, 0, +d). Knowing the three different overlay bias values and a theoretical curve relationship between overlay error and asymmetry, overlay error (OV) can be calculated while correcting the effect of bottom grating asymmetry. Bias schemes with three and four different biases are disclosed as examples. Gratings with different directions and biases can be interleaved in a composite target structure.

Claims

1. A method comprising:

using a lithographic process to form a plurality of target structures on a substrate, each target structure comprising overlaid periodic structures and each having a specific overlay bias;

illuminating the target structures and detecting radiation scattered by each target structure to obtain for that target structure a measurement representing an overall asymmetry that includes contributions due to (i) the overlay bias, (ii) an overlay error in the lithographic process and (iii) feature asymmetry within one or more of the periodic structures;

using the overall asymmetry measurements for three or more target structures having three or more different values of overlay bias to calculate a measurement of overlay error, the calculation being performed using knowledge of the three different overlay bias values and an assumed non-linear relationship between overlay error and target asymmetry, thereby to exclude the contribution due to feature asymmetry.

2. The method of claim 1, wherein the assumed non-linear relationship is a sinusoidal function or a combination of sinusoidal functions related harmonically to one another.

3. The method of claim 1, wherein the calculation is performed with the assumption that the contribution due to feature asymmetry is constant for all values of overlay.

4. The method of claim 1, wherein asymmetry measurements for target structures having three different overlay bias values are used in the calculation of overlay error.

5. The method of claim 1, wherein asymmetry measurements for target structures having four different overlay bias values are used in the calculation of overlay error.

6. The method of claim 1, wherein the different overlay bias values span a range greater than about 5% or 10%, greater than about 15% or 20%, of a pitch of the periodic structures.

7. The method of claim 1, wherein in the illuminating, asymmetry measurements for the three or more target structures are performed in parallel by capturing radiation scattered from the different target structures on different portions of an image sensor.

8. The method of claim 1, wherein:

a first plurality of target structures having three or more different values of overlay bias are provided with periodicity in a first direction and a second plurality of target structures having three or more different values of overlay bias are provided with periodicity in a second direction,

the method is performed using both the first and second pluralities of target structures to calculate overlay error separately in the first and second directions; and

the first and second pluralities of target structures are arranged together in a composite target structure in an alternating pattern so that the structures having periodicity in the first direction are separated by structures having periodicity in the second direction.

9. An inspection apparatus comprising:

a support configured for a substrate having a plurality of target structures thereon, each target structure comprising overlaid periodic structures and each having a specific overlay bias;

an optical system configured to illuminate the target structures and detect radiation scattered by each target structure to obtain for that target structure a measurement representing an overall asymmetry that includes contributions due to (i) the overlay bias, (ii) an overlay error in the lithographic process and (iii) feature asymmetry within one or more of the periodic structures;

a processor configured to use the overall asymmetry measurements for three or more target structures having three or more different values of overlay bias to calculate a measurement of overlay error, the calculation being performed using knowledge of the three different overlay bias values and an assumed non-linear relationship between overlay error and target asymmetry, thereby to exclude the contribution due to feature asymmetry.

10. The apparatus of claim 9, wherein the assumed non-linear relationship is a sinusoidal function or a combination of sinusoidal functions related harmonically to one another.

11. The apparatus of claim 9, wherein the processor is arranged to perform the calculation with the assumption that the contribution due to feature asymmetry is constant for all values of overlay.

12. The apparatus of claim 9, wherein the processor is arranged to use asymmetry measurements for target structures having three different overlay bias values in the calculation of overlay error.

13. The apparatus of claim 9, wherein the processor is arranged to use asymmetry measurements for target structures having four different overlay bias values in the calculation of overlay error.

14. The apparatus of claim 9, wherein the optical system includes an image sensor and is configured to capture radiation scattered from the different target structures substantially simultaneously on different portions of the image sensor.

15. A substrate comprising:

a plurality of target structures formed thereon by a lithographic process, each target structure comprising overlaid periodic structures and each having a specific overlay bias,

wherein some of the target structures have periodicity in a first direction having three or more different values of overlay bias and

wherein some of the target structures have periodicity in a second direction having three or more different values of overlay bias, and

wherein the target structures are arranged in a composite target structure in an alternating pattern so that the structures having periodicity in the first direction are separated by structures having periodicity in the second direction.

16. The substrate of claim 15, wherein six rectangular target structures having three different biases in each of two different directions are arranged in a 2×

3 array to form the composite target structure.

17. The substrate of claim 15, wherein eight rectangular target structures having four different biases in each of two different directions are arranged in a 2×

4 array to form the composite target structure.

18. A substrate comprising:

a plurality of target structures formed thereon by a lithographic process,

wherein each target structure comprises overlaid periodic structures and each having a specific overlay bias, including target structures having three or more different values of overlay bias, and

wherein the overlay bias values span a range greater than about 10%, greater than about 15% or 20%, of a pitch of the periodic structures.

19. A non-transitory computer readable medium having stored thereon computer-executable instructions that, in response to execution by a computing device, cause the computing device to perform operations comprising:

using a lithographic process to form a plurality of target structures on a substrate, each target structure comprising overlaid periodic structures and each having a specific overlay bias;

illuminating the target structures and detecting radiation scattered by each target structure to obtain for that target structure a measurement representing an overall asymmetry that includes contributions due to (i) the overlay bias, (ii) an overlay error in the lithographic process and (iii) feature asymmetry within one or more of the periodic structures;

using the overall asymmetry measurements for three or more target structures having three or more different values of overlay bias to calculate a measurement of overlay error, the calculation being performed using knowledge of the three different overlay bias values and an assumed non-linear relationship between overlay error and target asymmetry, thereby to exclude the contribution due to feature asymmetry.

20. A lithographic system comprising:

a lithographic apparatus comprising;

an illumination optical system arranged to illuminate a pattern;

a projection optical system arranged to project an image of the pattern onto a substrate; and

a support configured for a substrate having a plurality of target structures thereon, each target structure comprising overlaid periodic structures and each having a specific overlay bias; and

an inspection apparatus comprising;

an optical system configured to illuminate the target structures and detect radiation scattered by each target structure to obtain for that target structure a measurement representing an overall asymmetry that includes contributions due to (i) the overlay bias, (ii) an overlay error in the lithographic process and (iii) feature asymmetry within one or more of the periodic structures; and

a processor configured to use the overall asymmetry measurements for three or more target structures having three or more different values of overlay bias to calculate a measurement of overlay error, the calculation being performed using knowledge of the three different overlay bias values and an assumed non-linear relationship between overlay error and target asymmetry, thereby to exclude the contribution due to feature asymmetry,

wherein the lithographic apparatus is arranged to use the measurement results from the inspection apparatus in applying the pattern to further substrates.

21. A method comprising:

inspecting at least one periodic structure formed as part of or beside the device pattern on at least one of the substrates;

using a lithographic process to form a plurality of target structures on a substrate, each target structure comprising overlaid periodic structures and each having a specific overlay bias;

illuminating the target structures and detecting radiation scattered by each target structure to obtain for that target structure a measurement representing an overall asymmetry that includes contributions due to (i) the overlay bias, (ii) an overlay error in the lithographic process and (iii) feature asymmetry within one or more of the periodic structures;

using the overall asymmetry measurements for three or more target structures having three or more different values of overlay bias to calculate a measurement of overlay error, the calculation being performed using knowledge of the three different overlay bias values and an assumed non-linear relationship between overlay error and target asymmetry, thereby to exclude the contribution due to feature asymmetry; and

controlling the lithographic process for later substrates in accordance with the result of the inspection method.