Production of semiconductor regions in an electronic chip
A method can be used for fabricating first and second semiconductor regions separated by isolating trenches. A semiconductor substrate is covered with silicon nitride. The silicon nitride situated above the first region is doped by ion implantation. Trenches are etched through the silicon nitride and the doped silicon nitride is partially etching in an isotropic manner. The trenches are filled with an insulator to a level situated above that of the first region. The silicon nitride is removed resulting in the edges of the first region only being covered with an insulator annulus.
1. A method for fabricating a semiconductor device, the method comprising:
forming a silicon nitride layer over a semiconductor substrate;
doping the silicon nitride layer above a first region of the semiconductor substrate thereby forming a doped portion of the silicon nitride layer, the doping performed by ion implantation, wherein portions of the silicon nitride layer over a second region remain undoped;
etching trenches through the silicon nitride layer that is disposed above both the first and second regions, the trenches etched into the semiconductor substrate so that the first region is isolated from the second region;
partially isotropically etching the doped portion of the silicon nitride layer;
filling the trenches with an insulator to a level higher than a level of an upper surface of the first and second regions of the semiconductor substrate; and
removing remaining portions of the doped portion of the silicon nitride layer from over the first region of the semiconductor substrate, edges of the first region of the semiconductor substrate being covered with an insulator annulus after removing the doped silicon nitride layer.
2. The method according to claim 1 , wherein the silicon nitride layer has a thickness of between 80 and 200 nm and wherein the ion implantation is carried out with an energy of greater than 60 keV.
3. The method according to claim 1 , wherein doping the silicon nitride layer comprises doping the silicon nitride layer with argon or phosphorus.
4. The method according to claim 1 , wherein partially isotropically etching the doped portion of the silicon nitride layer comprises removing a thickness of silicon nitride of between 2 and 15 nm, and the trenches are filled to a level that is between 1 and 10 nm above the level of the upper surface of the first and second regions of the semiconductor substrate.
5. The method according to claim 1 , wherein partially isotropically etching the doped portion of the silicon nitride layer comprises etching using a solution comprising phosphoric acid.
6. The method according to claim 1 , wherein the semiconductor substrate is an upper semiconductor layer of an SOI structure.
7. The method according to claim 1 , wherein the semiconductor substrate is a bulk semiconductor substrate.
8. A method for fabricating a semiconductor device, the method comprising:
forming a silicon nitride layer over a semiconductor substrate that includes a p-doped first region and an n-doped second region;
doping the silicon nitride layer over the first region by ion implantation, the silicon nitride layer over the second region not being doped;
etching trenches through the silicon nitride layer above both the first and second regions and into the semiconductor substrate so that the first region is isolated from the second region;
partially isotropically etching the doped silicon nitride layer over the first region;
filling the trenches with an insulator to a level higher than a level of an upper surface of the semiconductor substrate; and
removing remaining portions of the doped silicon nitride layer from over the first region of the semiconductor substrate, edges of the first region of the semiconductor substrate being covered with an insulator annulus after removing the remaining portions of the doped silicon nitride layer over the first region.
9. The method according to claim 8 , wherein pits are formed on a surface of the insulator around the second region after removing the remaining portions of the silicon nitride layer that are not doped.
10. The method according to claim 8 , further comprising forming an n-channel transistor at the first region and forming a p-channel transistor at the second region.
11. The method according to claim 8 , wherein
the silicon nitride layer has a thickness of between 80 and 200 nm when formed;
the ion implantation is carried out with an energy of greater than 60 keV;
wherein partially isotropically etching the doped silicon nitride layer comprises removing a thickness of silicon nitride of between 2 and 15 nm; and
the trenches are filled to a level that is between 1 and 10 nm above the level of the upper surface of the semiconductor substrate.
12. The method according to claim 8 , wherein doping the silicon nitride layer comprises doping the silicon nitride layer with argon or phosphorus.
13. The method according to claim 8 , wherein partially isotropically etching the doped silicon nitride layer comprises etching using a solution comprising phosphoric acid.
14. A method for fabricating a semiconductor device, the method comprising:
forming a p-well region in a first region of a semiconductor substrate and a n-well region in a second region of the semiconductor substrate;
forming a silicon nitride layer over the first region and the second region;
forming a mask over the second region with a resist mask layer;
implanting into a first portion of the silicon nitride layer disposed over the first region while the resist mask layer blocks ions from the implanting in reaching a second portion of the silicon nitride layer disposed over the second region thereby forming doped and undoped portions of the silicon nitride layer;
etching a trench through the silicon nitride layer disposed above both the first and second regions and into the semiconductor substrate so that the first region is isolated from the second region;
etching the doped and undoped portions of the silicon nitride layer so that the doped portion of the silicon nitride layer etches faster than the undoped portion of the silicon nitride layer;
forming a shallow trench isolation by filling the trench with an insulator to a level higher than a level of an upper surface of the semiconductor substrate; and
forming a n-channel transistor in the first region and a p-channel transistor in the second region, the shallow trench isolation separating the n-channel transistor from the p-channel transistor.
15. The method according to claim 14 , wherein the implanting comprises implanting argon or phosphorus.
16. The method according to claim 14 , wherein etching the silicon nitride layer disposed above both the first and second regions, comprises etching using a solution comprising phosphoric acid.
17. The method according to claim 14 , wherein the first portion of the doped silicon nitride layer is etched 10 to 100 times faster than the second portion of the undoped portion of the silicon nitride layer.
18. The method according to claim 14 , further comprising removing the resist mask layer after the implanting.
19. The method according to claim 14 , further comprising removing the silicon nitride layer disposed above both the first and second regions after filling the trench, wherein edges of the first region remain surrounded with a portion of the insulator after removing the doped portion of the silicon nitride layer.
20. The method according to claim 14 , further comprising forming a divot in the insulator over the second region while edges of the first region remain surrounded with a portion of the insulator.
21. The method according to claim 1 , further comprising emoving remaining portions of the undoped portion of the silicon nitride layer from over the second region of the semiconductor substrate, wherein pits are formed at edges of the second region of the semiconductor substrate after removing the undoped portion of the silicon nitride layer.