Method for forming multi-level contacts using a h-containing

Abstract

A method for forming multi-level contact holes in a semiconductor structure is disclosed. The semiconductor structure includes a dielectric layer overlying a silicon substrate, a silicon nitride layer within the dielectric layer, the silicon nitride layer overlying a first conductive layer, a silicon oxynitride layer within the dielectric layer, the silicon oxynitride layer overlying a second conductive layer, and a plate poly layer. The method comprises: using a first etching step to etch through the dielectric layer to reach the silicon nitride layer as well as reach the silicon oxynitride layer, the first etching step using a combination of a first gas mixture and a first gas, the first gas mixture comprising a combination of N.sub.2, CO and Ar. The first gas includes C.sub.4 F.sub.8, CH.sub.3 F and O.sub.2, the flow rate ratio of the first gas C.sub.4 F.sub.8 /CH.sub.3 F/O.sub.2 is about 6:1:3. The flow rate of each component of the first gas mixture is that, the flow rate of N.sub.2 is about 0-20 sccm, the flow rate of CO is about 0-200 sccm, and the flow rate of Ar is about 100-600 sccm. In addition, the flow rate of each component of the first gas is that, the flow rate of C.sub.4 F.sub.8 is about 8-40 sccm, the flow rate of CH.sub.3 F is about 1-7 sccm, and the flow rate of O.sub.2 is about 0-20 sccm. Then using a second etching step to etch through the silicon nitride layer to reach the first conductive layer, the second etching step also etching through the silicon oxynitride layer to reach the second conductive layer. The second etching step uses a combination of the first gas mixture and a second gas, the second gas comprising CH.sub.3 F of the flow rate of about 3-14 sccm.