Dry etch process
A method for conformal dry etch of a liner material in a high aspect ratio trench is achieved by depositing or forming an inhomogeneous passivation layer which is thicker near the opening of a trench but thinner deep within the trench. The method described herein use a selective etch following formation of the inhomogeneous passivation layer. The selective etch etches liner material faster than the passivation material. The inhomogeneous passivation layer suppresses the etch rate of the selective etch near the top of the trench (where it would otherwise be fastest) and gives the etch a head start deeper in the trench (where is would otherwise be slowest). This method may also find utility in removing bulk material uniformly from within a trench.
1. A method of etching material from a high aspect ratio trench on a patterned substrate, the method comprising the sequential steps of:
providing a patterned substrate having a conformal liner layer on walls of the high aspect ratio trench;
forming an inhomogeneous passivation layer over the conformal liner layer in the high aspect ratio trench, wherein the inhomogeneous passivation layer has an outer passivation thickness near the opening of the high aspect ratio trench and an inner passivation thickness deep within the high aspect ratio trench, and wherein the outer passivation thickness is greater than the inner passivation thickness;
gas phase etching the conformal liner layer, wherein the gas phase etching process selectively removes material from the conformal liner layer faster than material from the inhomogeneous passivation layer;
removing the remainder of the inhomogeneous passivation layer to leave a remainder of the conformal liner layer, wherein the remainder of the conformal liner layer has an outer remaining conformal liner thickness near the opening of the high aspect ratio trench and an inner remaining conformal liner thickness deep within the high aspect ratio trench, and wherein the outer remaining conformal liner thickness is greater than the inner remaining conformal liner thickness;
gas phase etching the remainder of the conformal liner layer to leave nearly vertical walls on the sides of the high aspect ratio trench.
2. The method of claim 1 wherein an aspect ratio of the high aspect ratio trench may be greater than 10:1.
3. The method of claim 1 wherein the inner passivation thickness is less than or about 20% of the outer passivation thickness.
4. The method of claim 1 wherein the inner remaining conformal liner thickness is less than or about 20% of the outer remaining conformal liner thickness.
5. The method of claim 1 wherein the inner remaining conformal liner thickness is measured within the bottom 20% of the high aspect ratio trench.
6. The method of claim 1 wherein the inner passivation thickness is measured within the bottom 20% of the high aspect ratio trench.
7. The method of claim 1 wherein the outer remaining conformal liner thickness is measured within the top 20% of the high aspect ratio trench.
8. The method of claim 1 wherein the outer passivation thickness is measured within the top 20% of the high aspect ratio trench.
9. The method of claim 1 wherein the inhomogeneous passivation layer is formed by consuming some material from the conformal liner layer such that the conformal liner layer is thinner near the opening of the trench and thicker deep within the trench.
10. The method of claim 1 wherein the conformal liner layer is single crystal silicon, polysilicon or amorphous silicon.
11. The method of claim 1 wherein the inhomogeneous passivation layer is silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycarbide or silicon carbon nitride.
12. The method of claim 1 wherein the conformal liner layer is silicon oxide and the inhomogeneous passivation layer is silicon nitride or silicon.
13. The method of claim 1 wherein the conformal liner layer is silicon nitride and the inhomogeneous passivation layer is silicon oxide or silicon.
14. The method of claim 1 wherein the conformal liner layer is tungsten and the inhomogeneous passivation layer is tungsten oxide or tungsten nitride.
15. The method of claim 1 wherein the conformal liner layer is titanium and the inhomogeneous passivation layer is titanium oxide or titanium nitride.
16. The method of claim 1 wherein the conformal liner layer is an outer portion of a bulk material within walls of the high aspect ratio trench.
17. The method of claim 1 wherein the high aspect ratio trench has a depth greater than 0.5 μm.