Reticle alignment technique

• US 20060285113A1
• Filed: 06/21/2005
• Published: 12/21/2006
• Est. Priority Date: 06/21/2005
• Status: Active Grant

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Sadjadi, S.M. Reza
• Granted Patent: US 7,629,259 B2
• Time in Patent Office: Days
• US Class Current: 356/401
• 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 9/7011 Pre-exposure scan; original with original holder alignment; Prealignment, i.e. workpiece with workpiece holder
• CPC Class Codes: G03F 9/7019 Calibration
• CPC Class Codes: G03F 9/7046 Strategy, e.g. mark, sensor or wavelength selection
• CPC Class Codes: Y10S 438/975 Substrate or mask aligning feature

Abstract

A method for aligning a reticle is provided. A first patterned layer with a first alignment grid is formed. Sidewall layers are formed over the first patterned layer to perform a first shrink. The first alignment grid after shrink is etched into an etch layer to form an etched first alignment grid. The patterned layer is removed. An optical pattern of a second alignment grid aligned over the etched first alignment grid is measured. The optical pattern is used to determine whether the second alignment grid is aligned over the etched first alignment grid.

Claims

1. A method, comprising:

forming a first patterned layer with a first alignment grid;

forming sidewall layers over the first patterned layer to perform a first shrink;

etching the first alignment grid after shrink into an etch layer to form an etched first alignment grid;

removing the patterned layer;

measuring an optical pattern of a second alignment grid aligned over the etched first alignment grid; and

using the optical pattern to determine whether the second alignment grid is aligned over the etched first alignment grid.

2. The method, as recited in claim 1, further comprising correcting the alignment until the optical pattern of the second alignment grid is aligned over the etched first alignment grid.

3. The method, as recited in claim 2, further comprising:

creating a theoretical model of optical pattern for the etched first alignment grid in the first pattern layer after the first shrink;

measuring optical pattern from the etched first alignment grid;

comparing the measured optical pattern from the etched first alignment grid with the theoretical model of the optical pattern for the etched first alignment grid;

identifying sources of any differences due to critical dimensions being off target; and

creating a theoretical model of the optical pattern of the second alignment grid aligned over the etched first alignment grid using the identified sources of any differences.

4. The method as recited in claim 3, wherein the using the optical pattern to determine whether the second alignment grid is aligned over the etched first alignment grid, comprises determining if measured optical pattern of the second alignment grid aligned over the etched first alignment grid matches with the theoretical model of the optical pattern of the second alignment grid aligned over the etched first alignment grid.

5. The method, as recited in claim 4, wherein the etched first alignment grid comprises:

a first line with a length and a width, wherein the length is at least four times greater than the width;

a second line substantially parallel to and spaced apart from the first line to form a first space between the first line and the second line;

a third line with a length and width, wherein the length is at least four times greater than the width, and wherein the second line is perpendicular to the first line; and

a fourth line substantially parallel to and spaced apart from the third line.

6. The method, as recited in claim 5, wherein the first space between the first line and the second line is less than a CD for a lithographic device used to form the first alignment grid.

7. The method, as recited in claim 5, further comprising:

adding a photoresist layer after the removing the patterned layer;

exposing the photoresist layer after the second alignment grid is aligned over the etched first alignment grid;

forming the exposed photoresist layer into a patterned photoresist layer; and

etching features into the etch layer through the patterned photoresist layer.

8. The method, as recited in claim 7, further comprising forming a sidewall layer over the patterned photoresist layer before etching features into the etch layer through the patterned photoresist layer.

9. The method, as recited in claim 5, wherein the optical process uses the entire alignment grid instead of edges of the alignment grid.

10. The method, as recited in claim 1, wherein the etched first alignment grid comprises:

a first line with a length and a width, wherein the length is at least four times greater than the width;

a second line parallel to and spaced apart from the first line to form a first space between the first line and the second line;

a third line with a length and width, wherein the length is at least four times greater than the width, and wherein the second line is perpendicular to the first line; and

a fourth line parallel to and spaced apart from the third line.

11. The method, as recited in claim 10, wherein the first space between the first line and the second line is less than a CD for a lithographic device used to form the first alignment grid.

12. The method, as recited in claim 1, further comprising:

adding a photoresist layer after the removing the patterned layer;

exposing the photoresist layer after the second alignment grid is aligned over the etched first alignment grid;

forming the exposed photoresist layer into a patterned photoresist layer; and

etching features into the etch layer through the patterned photoresist layer.

13. The method, as recited in claim 12, further comprising forming a sidewall layer over the patterned photoresist layer before etching features into the etch layer through the patterned photoresist layer.

14. The method, as recited in claim 1, wherein the optical process uses the entire alignment grid instead of edges of the alignment grid.

15. A method for forming devices on a wafer using a plurality of masks, comprising:

a) forming a first patterned layer for a plurality of dice on a wafer, wherein each die of the plurality of dice has a first alignment grid;

b) forming sidewall layers over the first patterned layer to perform a first shrink;

c) etching the features formed by the first pattern layer and first alignment grid after shrink into an etch layer to form an etched first alignment grid for each dye of the plurality of dice;

d) removing the mask from the patterned layer;

e) forming a photoresist layer over the wafer;

f) placing the wafer in a photolithographic tool;

g) stepping a reticle to a die of the plurality of dice;

h) measuring an optical pattern of a second alignment grid of the reticle aligned over an etched first alignment grid of the stepped to die;

i) using the optical pattern to determine whether the second alignment grid is aligned over the etched first alignment grid of the stepped to die;

j) adjusting the photolithographic tool until the optical pattern of the second alignment grid is aligned over the etched first alignment grid after of the stepped to die;

k) exposing the photoresist above the stepped to die;

j) stepping to another die and returning to step h, until all of the dice of the plurality of dice are stepped to.

16. The method, as recited in claim 15, wherein a deviation from a nominal alignment is fed back to the photolithography tool to correct for any misalignments.

17. The method, as recited in claim 15, further comprising developing the photoresist layer to form a patterned photoresist layer.

18. The method, as recited in claim 17, further comprising forming a sidewall layer over the patterned photoresist layer.

19. The method, as recited in claim 18, further comprising etching features through the sidewall layer into the etch layer.

20. The method, as recited in claim 15, wherein the optical process uses the entire alignment grid instead of edges of the alignment grid.