What is claimed is:
1. A method for fabricating a trench Schottky barrier semiconductor device, comprising the steps of: forming a nitride layer directly on a face of a silicon substrate having a first conductivity type; patterning the nitride layer to define spaced windows and then etching through the windows to form spaced trenches extending downward from the face into the silicon substrate; and lining the interior walls of the trenches with a final oxide layer without forming and etching a sacrificial oxide layer to prevent formation of bird beaks at tops of the interior walls of the trenches.
2. The method defined in claim 1, further comprising filling the trenches with a conductive material of a second conductivity type; forming a Schottky metal layer atop and in contact with the face; and forming anode and cathode electrodes across and in contact with the Schottky metal layer and an opposite face of the silicon substrate, respectively, wherein the windows are opened by etching through the nitride layer and through spaced regions of the silicon substrate juxtaposed with the windows to form alternating trenches and mesas.
3. The method defined in claim 1, wherein the step of filling the trenches with the conductive material of the second conductivity includes depositing a continuous layer of un-doped polisilicon over the patterned nitride layer and implanting second type conductivity impurities into the un-doped polysilicon layer filling the trenches.
4. The method defined in claim 2, further comprising stripping the nitride layer overlaying the mesas to expose spaced portions the silicon substrate, the stripping being performed by wet etching in phosphoric acid at 150 C. after lining the interior walls of the spaced trenches with the final oxide layer.
5. The method defined in claim 4, wherein the Schottky metal layer is applied over the exposed portions the silicon substrate atop the mesas and atop the trenches to form a Schottky barrier.
6. The method defined in claim 1, wherein the silicon substrate has a thickness of 2.5-4 um and a resistively of 0.3 to 0.5 ohm cm.
7. The method defined in claim 2, wherein the final oxide layer is grown to a thickness of at most 500 .
8. The method defined in claim 3, wherein the un-doped layer is deposited to a thickness of approximately 7500 .
9. The method defined in claim 3, wherein implanting of impurities includes applying boron ions to the un-doped silicon layer filling the trenches at concentration of 31016 per cm2, and driving the boron ions into the trenches at 1050 C. for 1 hour to form P-conductivity regions and to provide the semiconductor device with a plurality of p-n junctions between the neighboring mesas and trenches.
10. The method defined in claim 3, further comprising the step of blanket etching of the un-doped polysilicon layer by a plasma etch for a period of time exceeding the end point of the etching for 5 seconds.
11. The method defined in claim 5, wherein the Schottky metal is one of titanium or titanium-tungsten sputtered to a thickness of at most 600 .
12. The method defined in claim 11, further comprising the steps of annealing the Schottky barrier layer at 625 C. for a 30 sec interval and selectively etching the annealed Schottky barrier layer.
13. The method defined in claim 1, wherein the silicon substrate has an N-epitaxial layer extending from the one face and terminating below the trenches and an N substrate layer extending between the N-epitaxial layer and the opposite face of the semiconductor substrate.
14. A method of forming a trench Schottky barrier device, the method comprising the steps of:
forming a nitride layer on one of the opposite faces of a semiconductor substrate having a first conductivity;
patterning the nitride layer to define spaced windows on the nitride layer;
opening windows in said nitride layer by etching through said windows and through regions of the one face of the semiconductor substrate opposing the windows to form alternating trenches and mesas in the semiconductor substrate;
forming an oxide layer on a bottom surface and sidewalls of the trenches without forming a sacrificial oxide layer to avoid bird beak formations at spaced interfaces between the nitride layer and the semiconductor substrate along the mesa;
depositing a continuous layer of un-doped polysilicon over the nitride layer to fill the trenches with the un-doped polysilicon layer;
implanting a second type conductivity impurities into the non-doped polysilicon layer to provide the polysilicon layer with the second type conductivity;
stripping the nitride layer overlaying the mesas to expose the semiconductor substrate;
applying a continuous barrier layer over the one face to form a Schottky between the exposed portion of the semiconductor substrate of the mesas and the barrier layer; and
applying metal on the opposite faces of the semiconductor substrate to form anode and cathode electrodes of the semiconductor device.
15. The process of claim 1, wherein a termination trench is formed simultaneously with the formation of the spaced trenches; the Schottky metal layer being at least partly excluded from said termination trench.
16. A trench Schottky barrier semiconductor device comprising a silicon substrate; the silicon substrate having opposite faces; one of the opposite faces having a plurality of spaced trenches and a removable nitride layer provided directly on the one face between the trenches; each of the trenches having an interior wall lined with a final oxide layer, which is grown directly on the interior wall without preliminary lining the interior walls with a sacrificial oxide layer, so that when the nitride layer is stripped from the one surface of the silicon substrate, no rounded oxides are formed at tops of the interior walls of the spaced trenches.
17. The device of claim 16, wherein a termination trench is formed simultaneously with the formation of the spaced trenches; the Schottky metal layer being excluded from said termination trench.
18. The device of claim 17, wherein a thin silicon dioxide layer is formed over the bottom surface of said termination and is interposed between said trench bottom and an overlapping portion of said Schottky metal layer.
19. The device of claim 18, which further includes a TEOS barrier layer interposed between said silicon dioxide layer and sais overlapping portion of said Schottky metal layer.
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 of screening for a cocrystal of a hydrochloric acid salt of an active agent, comprising the steps of:
selecting a carboxylic acid having at least 4 carbons to coordinate via hydrogen bonding with the chloride anion of the hydrochloric acid salt of the active agent,
preparing a solution, melt, or physical mixture of the hydrochloric acid salt of the active agent and the carboxylic acid,
subjecting the solution or melt to a crystallization process, or the physical mixture to grinding, and
determining whether a cocrystal of the hydrochloric acid salt of the active agent and the carboxylic acid has formed.
2. The method of claim 1 wherein the carboxylic acid having at least 4 carbons is selected from benzoic acid, succinic acid, and fumaric acid.
3. The method of claim 1 wherein the active agent is an active pharmaceutical ingredient.
4. The method of claim 1 wherein the active agent is a nitrogen containing base.
5. The method of claim 4 wherein the nitrogen containing base is a tertiary amine.
6. The method of claim 4 wherein the nitrogen containing base is a secondary amine.
7. The method of claim 4 wherein the nitrogen containing base is a primary amine.
8. The method of claim 1 wherein x-ray diffraction is used to determine whether a cocrystal of the hydrochloric acid salt of the active agent and the carboxylic acid has formed.
9. The method of claim 1 wherein the preparing step comprises preparing a solution of the hydrochloric acid salt of the active agent and the carboxylic acid.
10. The method of claim 1 wherein the preparing step comprises preparing a melt of the hydrochloric acid salt of the active agent and the carboxylic acid.
11. The method of claim 1 wherein the preparing step comprises preparing a physical mixture of the hydrochloric acid salt of the active agent and the carboxylic acid.