Patent ID: 7968418

Claim:
A method of forming an isolation trench structure comprising: forming a first trench in a substrate and in a stack of layers over the substrate, wherein the first trench comprises a top portion that is wider within the stack and a bottom portion that is narrower within the substrate, and wherein the top portion of the first trench has more angled sides within the stack and the bottom portion of the first trench has less angled sides within the substrate; depositing one or more first materials in the first trench; forming a second trench in the substrate and the stack, wherein forming the second trench comprises performing a two-step etch process, wherein a first etch step non-selectively removes exposed portions of the stack down to the substrate and removes the one or more deposited first materials in the top portion of the first trench, wherein a second etch step selectively removes exposed portions of the substrate while leaving the remaining one or more first materials in the bottom portion of the first trench substantially intact, wherein the second trench completely encircles an upper section of the bottom portion of the first trench, and wherein the second trench is more shallow than the first trench; and depositing one or more second materials in the second trench, wherein the one or more second materials completely encircle the upper section of the bottom portion of the first trench.