Eliminating yield impact of stochastics in lithography
Methods and apparatuses for performing cycles of aspect ratio dependent deposition and aspect ratio independent etching on lithographically patterned substrates are described herein. Methods are suitable for reducing variation of feature depths and/or aspect ratios between features formed and partially formed by lithography, some partially formed features being partially formed due to stochastic effects. Methods and apparatuses are suitable for processing a substrate having a photoresist after extreme ultraviolet lithography. Some methods involve cycles of deposition by plasma enhanced chemical vapor deposition and directional etching by atomic layer etching.
1. A method of processing semiconductor substrates, the method comprising:
providing a substrate having a first feature and a second feature formed by lithography in a first hard mask material,
wherein the first feature is partially formed by the lithography and comprises a bottom, and the first hard mask material comprises a field region between feature openings of the first feature and the second feature;
depositing a second hard mask material over the first hard mask material for a duration sufficient to preferentially form second hard mask material on the field region to a thickness greater than thickness of the second hard mask material in the first feature; and
directionally etching the second hard mask material to remove material at the bottom of the first feature by exposing the second hard mask material to an etching species to form a modified surface and igniting a plasma in an inert gas environment without the etching species while applying a bias to remove the modified surface, the material at the bottom of the first feature is the first hard mask material or the second hard mask material.
2. The method of claim 1 , wherein the directionally etching is performed to etch through the second hard mask material and expose a third hard mask material under the first hard mask material at the bottom of the first feature.
3. The method of claim 2 , wherein a bottom of the second feature comprises third hard mask material under the first hard mask material.
4. The method of claim 1 , wherein an amount of the second hard mask material deposited into the first and second features depends on aspect ratio of the first feature and aspect ratio of the second feature.
5. The method of claim 1 , wherein directionally etching is performed independent of aspect ratios of the first and second features.
6. The method of claim 1 , wherein at least one of aspect ratio or depth of the first feature is different from aspect ratio or depth of the second feature.
7. The method of claim 1 , wherein the first feature is underexposed during lithography.
8. The method of claim 1 , wherein critical dimension of the first feature after the depositing and the directionally etching is within about 0.5% to about 1% of critical dimension of the second feature prior to the depositing and the directionally etching.
9. The method of claim 1 , wherein aspect ratio of the first feature after the depositing and the directionally etching is within about 1% to about 10% of aspect ratio of the second feature prior to the depositing and the directionally etching.
10. The method of claim 1 , wherein variation in critical dimension across the first and second features on the substrate after the depositing and the directionally etching is less than variation of critical dimension across the first and second features after being lithographically defined.
11. The method of claim 1 , further comprising repeating depositing of the second hard mask material and directionally etching the second hard mask material in sufficient cycles to remove the first hard mask material at the bottom of the first feature, wherein the directionally etching in each cycle removes first hard mask material at the bottom of the first feature such that difference between depth of the first feature and depth of the second feature approaches 0.
12. The method of claim 1 , wherein the second hard mask material is selected from the group consisting of carbon-containing material, silicon-containing material, and tin-containing material.
13. The method of claim 1 , wherein the second hard mask material has a composition or lattice structure different from that of the first hard mask material.
14. The method of claim 2 , wherein the second hard mask material has etch selectivity relative to the third hard mask material such that etch rate of the second hard mask material is at least 3 times greater than the third hard mask material.
15. The method of claim 1 , wherein the depositing of the second hard mask material and the directionally etching are performed without breaking vacuum.
16. The method of claim 1 , wherein the first and second features are formed by a technique selected from the group consisting of extreme ultraviolet lithography and immersion lithography.