1. A method of forming shallow trenches in a substrate comprising:
(a) providing a substrate;
(b) forming a layer stack comprising a top photosensitive layer, a middle hardmask layer and a bottom silicon nitride layer on said substrate;
(c) patterning said photosensitive layer to form trenches;
(d) transferring said pattern through said hardmask;
(e) trimming said hardmask and said photosensitive layer; and
(f) transferring said pattern through the silicon nitride layer and into the substrate with a plasma etch.
2. The method of claim 1 wherein said hard mask is comprised of silicon oxynitride.
3. The method of claim 1 further comprising an ARC between the photoresist and hardmask layers.
4. The method of claim 3 wherein the ARC is an organic or inorganic material having a thickness of about 300 to 1000 Angstroms.
5. The method of claim 1 wherein said photoresist has a thickness between about 1500 and 4000 Angstroms.
6. The method of claim 1 wherein the minimum distance between adjacent trenches is less than 300 nm.
7. The method of claim 1 wherein said hardmask etch is preferably performed with conditions comprising a CF4 flow rate of 50 to 200 sccm, an argon flow rate of 5 to 300 seem, a chamber pressure of about 5 to 20 mTorr, a chamber temperature of about 50\xb0 C. to 70\xb0 C. and a RF power of between 200 and 600 Watts.
8. The method of claim 1 wherein said hardmask trim etch is performed with conditions comprising a CXFY gas flow rate of about 50 to 200 sccm, a H2 flow rate of about 5 to 200 sccm, a chamber pressure of about 5 to 20 mTorr, a chamber temperature of about 50\xb0 C. to 70\xb0 C., and a RF power between about 300 and 1000 Watts.
9. The method of claim 8 further comprising an oxygen flow rate of about 5 to 50 sccm.
10. The method of claim 8 wherein said CXFY gas is selected from a group including CF4, C3F6, C4F6, C4F8, and C5F8.
11. The method of claim 3 wherein said photoresist and ARC are removed before the substrate etch.
12. The method of claim 1 wherein the amount of trimming between said trenches ranges from 0 to about 20 run per trench end for a total trench lengthening of 0 to about 40 nm.
13. The method of claim 1 wherein a majority of the photosensitive layer thickness is retained after said hardmask etch and hardmask trim steps.
14. The method of claim 1 wherein said hardmask etch and hardmask trim are performed in the same etch chamber.
15. The method of claim 1 further comprising removing said photosensitive layer, hardmask and nitride layers and filling said trenches with a dielectric material to form STI features in said substrate.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method for supplying an entrained-flow gasification reactor with carbonaceous fuel for producing a gas that contains CO, H2, and flue ash under pressure and at a temperature above the melting point of the ash, the method comprising steps of:
providing an entrained-flow gasification reactor;
supplying the entrained-flow gasification reactor with carbonaceous fuel;
producing via the entrained-flow gasification reactor and the carbonaceous fuel in the entrained-flow gasification reactor the gas that contains CO, H2, and flue ash;
subjecting the gas to a plurality of treatment stages to form a waste gas;
mixing the waste gas with CO2 to form a mixed gas;
compressing the mixed gas to form a recirculation gas; and
conveying the carbonaceous fuel pneumatically into the entrained-flow gasification reactor using the recirculation gas;
wherein said plurality of treatment stages comprises at least one synthesis stage, a CO conversion stage, a gas purification stage, a first synthesis stage, and a second synthesis stage; and
wherein the recirculation gas contains at least 1 vol.-% of hydrocarbons andor 1 vol.-% of hydrogen.
2. The method according to claim 1, wherein a further gas obtained during the plurality of treatment stages contains predominantly CO2 and at least 10 ppm H2S andor CO and is mixed into the recirculation gas.
3. The method according to claim 1, wherein the recirculation gas is used at least in part for conveying the carbonaceous fuel in a feed container, for building up pressure in the feed container andor for fluidization of the carbonaceous fuel in the feed container.