Method for forming multiple gate oxide thickness utilizing ashing and cleaning
View Patent ↗Embodiments of the present invention relate to semiconductor structures having multiple gate dielectric structures. One embodiment forms semiconductor devices in multiple regions having different dielectric thicknesses where the interface between the gate dielectric and the semiconductor substrate is protected to result in an improved (e.g. less rough) interface. One embodiment includes forming a dielectric layer overlying a substrate, partially etching the dielectric layer in at least one of the multiple regions, and ashing the dielectric layer. The remaining portion of the dielectric layer (due to the partial etch) may then help protect the underlying substrate from damage during a subsequent preclean. Afterwards, in one embodiment, the gate dielectric layer is grown to achieve a target gate dielectric thickness in at least one of the regions. This may also help further densify the gate dielectric layer. Processing may then be continued to form semiconductor devices in each of the multiple regions.
1. A method for forming a multigate dielectric structure for a semiconductor device, said method comprising:
providing a substrate, the substrate having a surface with a first surface roughness;
providing a dielectric layer overlying the substrate and forming a dielectric/substrate interface between the dielectric layer and the substrate at the surface of the substrate, the dielectric layer having an initial thickness;
forming a patterned photoresist overlying the dielectric layer and the substrate, the patterned photoresist defining a region for formation of a gate dielectric of a desired target thickness;
etching the region so that a portion of the dielectric layer remains within the region, wherein the portion of remaining dielectric layer within the region has a first intermediate thickness, the first intermediate thickness being less than the initial thickness and being less than approximately ten Angstroms;
ashing the portion of remaining dielectric layer within the region, wherein ashing causes an increase in thickness of the dielectric layer remaining within the region from the first intermediate thickness to a second intermediate thickness, the second intermediate thickness being in a range of approximately 15 to 20 Angstroms;
cleaning the portion of the dielectric layer remaining within the region, wherein cleaning causes a decrease in thickness of the dielectric layer remaining within the region from the second intermediate thickness to a third intermediate thickness; and
thermally oxidizing the dielectric layer, wherein thermally oxidizing causes the portion of remaining dielectric layer within the region to have a desired target thickness, and further wherein the thermal oxidation increases a density of the portion of remaining dielectric layer.
2. The method of claim 1 , wherein the substrate includes one of a bulk substrate and an SOI substrate.
3. The method of claim 1 , wherein the dielectric layer includes a silicon dioxide layer.
4. The method of claim 1 , wherein the region includes a high performance device region.
5. The method of claim 1 , wherein the portion of the dielectric layer remaining within the region further prevents the dielectric/substrate interface from subsequently being breached by an etchant.
6. The method of claim 1 , wherein ashing further includes ashing the patterned photoresist for removing the patterned photoresist.
7. The method of claim 1 , wherein the second intermediate thickness is on the order of eighteen (18) Angstroms.
8. The method of claim 1 , wherein ashing includes exposing the portion of remaining dielectric layer to an oxygen plasma.
9. The method of claim 1 , further comprising subsequent to ashing, performing a post-ashing clean.
10. The method of claim 9 , wherein the post-ashing clean includes use of a sulfuric acid peroxide mixture (SPM).
11. The method of claim 1 , wherein cleaning includes a preclean.
12. The method of claim 11 , wherein a duration of the preclean is selected such that the preclean does not affect the first surface roughness of the substrate layer within the region.
13. The method of claim 11 , wherein the preclean is maintained for a given duration without affecting a surface roughness of the dielectric/substrate interface.
14. The method of claim 11 , wherein the preclean includes a piranha clean, followed by an ammonium peroxide mixture (APM) clean and a hydrochloric acid peroxide mixture (HPM) clean.
15. The method of claim 14 , further wherein the APM clean is of a limited time duration, the limited time duration being determined as a function of a beginning thickness and a desired target ending thickness.
16. The method of claim 14 , wherein the piranha clean includes use of a sulfuric acid peroxide mixture (SPM).
17. The method of claim 1 , wherein the third intermediate thickness is in on the order of eleven (11) to fifteen (15) Angstroms.
18. The method of claim 1 , wherein the dielectric layer includes a first thermal oxide, and wherein thermal oxidation of the dielectric layer forms a second thermal oxide at the dielectric/substrate interface, wherein the portion of the dielectric layer remaining within the region includes a composite of the first thermal oxide, a plasma oxide, and the second thermal oxide, and wherein thermal oxidation further densifies the first thermal oxide and the plasma oxide of the composite remaining within the region.
19. The method of claim 1 , further wherein a surface roughness of the dielectric/substrate interface is substantially preserved.
20. The method of claim 19 , wherein the substantially preserved dielectric/substrate surface roughness is a resultant surface roughness of the dielectric/substrate interface within the region that is substantially similar to the initial surface roughness of the dielectric/substrate interface.
21. The method of claim 1 , wherein the portion of remaining dielectric layer is devoid of chemical oxide incorporation at the dielectric/substrate interface.
22. The method of claim 1 , wherein the method includes one of a dual gate oxide (DGO) process and a triple gate oxide (TGO) process.
23. The method of claim 1 , further comprising forming a semiconductor device structure using a portion of the portion of remaining dielectric layer within the region as a gate dielectric and forming another semiconductor device structure using a portion of the dielectric layer outside the region as a gate dielectric.