Method for processing a substrate to form a structure
View Patent ↗A method for processing a substrate to produce a structure, for example an insulating trench, uses a lithographic mask exposure process. Conventionally, the optical resolution limit prescribes the minimum width for any structure that can be produced. The method produces structures having a width less than the optical resolution limit on raised regions of the semiconductor substrate. Use is made of spacer technology, before the application of which the method first involves the local level ratios on the semiconductor substrate being reversed by trench etching, trench filling and subsequent back-etching of the trench interspace. The method allows insulating trenches of any narrow width between zero and the respective optical resolution limit to be produced on locally raised surface regions of the substrate.
1. A method for processing a substrate to form a structure using a lithographic mask exposure, which comprises the steps of:
providing the substrate;
etching two trenches disposed at a distance from one another, the distance corresponding to an optical resolution limit of the lithographic mask exposure;
filling the trenches with a trench filling resulting in filled trenches, wherein filling the trenches includes forming word lines in the two trenches;
back-etching a material other than a material of the trench filling in an interspace between the filled trenches at a level of the trench filling resulting in a depression;
producing spacers in the depression on opposite sidewalls of the depression, the spacers being at a distance from one another which is less than the optical resolution limit for the lithographic mask exposure; and
etching in a region of the depression for forming an insulating trench disposed between the spacers, a width of the insulating trench being less than the optical resolution limit for the lithographic mask exposure.
2. The method according to claim 1 , further comprising the step of filling the insulating trench with an electrical insulator.
3. The method according to claim 1 , which comprises producing the spacers by depositing a conformal layer onto the substrate after the depression has been formed and back-etching the conformal layer in a direction perpendicular to a surface of the substrate using an anisotropic etching process.
4. The method according to claim 3 , which comprises forming the conformal layer from silicon dioxide deposited on the substrate for producing the spacers.
5. The method according to claim 1 , further comprising the steps of:
depositing a sacrificial layer before the two trenches are etched; and
back-etching the sacrificial layer in the interspace between the trenches, the sacrificial layer being the material in the interspace.
6. The method according to claim 5 , further comprising forming the sacrificial layer from nitride.
7. The method according to claim 1 , further comprising the steps of depositing a first insulating layer, a dielectric layer and a second insulating layer onto internal walls of the trenches between the steps of etching the two trenches and the filling of the trenches.
8. The method according to claim 1 , further comprising the step of providing a preprocessed semiconductor substrate having an oxide layer as the substrate.
9. The method according to claim 6 , which comprises using a silicon nitride as the nitride.