Metrology marks for unidirectional grating superposition patterning processes
Cut spacer reference marks, targets having such cut spacer reference marks, and methods of making the same by forming spacer gratings around grating lines on a first layer, and fabricating an angled template mask that extends across and resides at an angle with respect to such spacer gratings. Angled, cut spacer gratings are etched into a second layer using the angled template mask to superimpose at least a portion of the spacer gratings of the first layer into the second layer.
1. A method of fabricating reference marks for lithography comprising:
providing grating lines on a first layer;
forming spacer gratings around said grating lines;
forming an angled template mask extending across and residing at an angle with respect to said spacer gratings;
etching a second layer using said angled template mask to superimpose at least a portion of said spacer gratings of said first layer into said second layer, thereby forming angled cut spacer gratings in said second layer;
forming one or more additional angled template masks extending across and at an angle with respect to one or more additional spacer gratings of one or more additional layers; and
etching other cut spacer gratings in still further other layers by using said one or more additional angled template masks to superimpose at least a portion of said one or more additional spacer gratings into said still further other layers.
2. The method of claim 1 wherein the angled template mask comprises an angled unidirectional mask residing in an x,y plane.
3. The method of claim 2 wherein the angled unidirectional mask comprises a positive tone mask.
4. The method of claim 2 wherein the angled unidirectional mask comprises a negative tone mask.
5. The method of claim 2 wherein the angled unidirectional mask resides at an angle ranging from about 30°-60° with respect to the spacer gratings.
6. The method of claim 2 wherein the angled unidirectional mask resides at an angle of about 45° with respect to the spacer gratings.
7. The method of claim 1 wherein the angled template mask comprises an angled bi-directional mask residing in an x, y plane.
8. The method of claim 7 wherein the angled bi-directional mask comprises a positive tone mask.
9. The method of claim 7 wherein the angled bi-directional mask comprises a negative tone mask.
10. The method of claim 7 wherein the angled bi-directional mask resides at an angle ranging from about 30°-60° with respect to the spacer gratings.
11. The method of claim 7 wherein the angled bi-directional mask resides at an angle of about 45° with respect to the spacer gratings.
12. The method of claim 1 further including covering the first layer with one or more films, the upper most film comprising a resist layer, the resist layer having said angled template mask.
13. A method of determining positioning error between lithographically produced integrated circuit fields comprising:
providing grating lines on a first layer;
forming spacer gratings around said grating lines;
forming an angled template mask extending across and residing at an angle with respect to said spacer gratings;
etching a second layer using said angled template mask to superimpose at least a portion of said spacer gratings of said first layer into said second layer, thereby forming angled cut spacer gratings in said second layer;
measuring a position of the angled cut spacer gratings in said second layer relative to the grating lines on the first layer to determine any alignment error; and
aligning a third layer to said cut spacer gratings in said second layer to form third layer spacer gratings, and further determining alignment error between said third layer spacer gratings and said cut spacer gratings in said second layer.
14. The method of claim 13 further including using any detected alignment error for processing subsequent layers.
15. The method of claim 13 further including the steps:
providing other grating lines on the third layer;
forming other spacer gratings around said other grating lines;
forming a second angled template mask extending across and residing at an angle with respect to said other spacer gratings on said third layer; and
etching a fourth layer using said second angled template mask to superimpose at least a portion of said other spacer gratings of said third layer into said fourth layer, thereby forming other angled cut spacer gratings in said fourth.
16. The method of claim 15 further including the step of measuring positioning of the other angled cut spacer gratings in said fourth layer relative to the grating lines on the first layer to determine any alignment error.
17. The method of claim 15 further including the step of measuring positioning of the other angled cut spacer gratings in said fourth layer relative to the other grating lines on the third layer to determine any alignment error.